Clinical Use of Opportunistic Computed Tomography Screening for Osteoporosis

CT- and MRI-based endplate osteoporosis status assessment for predicting adjacent vertebral fractures after thoracolumbar percutaneous kyphoplasty: a matched comparison study

PURPOSE

This study aimed to investigate the predictive value of adjacent vertebral endplate osteoporotic status for adjacent vertebral fracture (AVF) after percutaneous kyphoplasty (PKP) for treating osteoporotic vertebral compression fracture (OVCF) and compared it with vertebral cancellous bone.

METHODS

This study retrospectively analyzed consecutive patients with OVCF who underwent PKP. Participants were categorized into the study group (49 patients with AVF) and the control group (49 matched patients without AVF). The vertebral Hounsfield units (VHU), endplate HU (EHU), vertebral bone quality (VBQ), and endplate bone quality (EBQ) scores were calculated using preoperative CT and MRI. To identify the predictive ability of the HU and EBQ scores, multivariable logistic regression and receiver operating characteristic (ROC) curve analyses were conducted.

RESULTS

VHU (p = 0.006), EHU proximal to the fracture segment (pEHU) (p = 0.001), average level of EHUs (aEHU) (p = 0.001), and EBQ score proximal to the fracture segment (pEBQ score) (p = 0.034) of the adjacent fractured vertebrae (AFV) in the study group were significantly different from the control study. The lower VHU (OR = 0.981, p = 0.007), pEHU (OR = 0.984, p < 0.001), lower aEHU (OR = 0.986, p = 0.002), and higher pEBQ score (OR = 1.002, p = 0.050) of the AFV were determined as the independent predictors for AVF. The ROC curve analysis revealed that the adjusted area under the curve (AUC) for the pEHU was 0.756 and the most suitable threshold was 254.87 (sensitivity: 69.4% and specificity: 77.6%), indicating that the predictive performance of pEHU was relatively higher. Further, the adjusted AUCs for the VHU, aEHU, and pEBQ scores were 0.703, 0.699, and 0.666, respectively.

CONCLUSION

This study revealed that the endplate osteoporosis status predicted AVF better than the vertebral cancellous bone and the predictive performance of pEHU was relatively higher.

Lee's TRIAD-osteoporosis, fragility fracture, and bone health optimization

Osteoporosis, fragility fractures, and bone health optimization share the same pathophysiology, diagnostic tools, risk assessment, and treatments. Grouping them into "Lee's TRIAD" allows surgeons and physicians to collaborate more efficiently, using unified principles and strategies for managing these conditions.

PURPOSE

The primary goal of osteoporosis management is to prevent fragility fractures, which occur from falls from standing height or less in individuals over fifty. However, the management of bone health optimization is often neglected in patients undergoing elective surgeries, such as arthroplasty and spinal surgeries. The objective of this article is to link all these three conditions into a TRIAD so that surgeons and physicians can collaborate more effectively, utilizing similar principles and strategies for better management.

METHODOLOGY

Clinical approaches based on country-specific guidelines are commonly used to manage osteoporosis. However, skeletal assessments are rarely conducted before or after elective procedures, leading to overlooked conditions such as osteoporosis, osteopenia, and fragility fracture risk factors. These three conditions are illustrated from the patient case study shown, to highlight the importance of not neglecting bone health optimization in high risk individuals undergoing elective surgery, with underlying osteopenia and multiple risk factors who sustained fragility fracture intraoperatively.

RESULT

Patients undergoing elective surgeries often have their bone health neglected, leading to a higher incidence of complications such as aseptic loosening and peri-prosthetic fractures due to poor bone quality and density. Bone health assessment and optimization therefore is essential in patients with osteoporosis, osteopenia with clinical risk factors, and patients with history of fragility fracture, to ensure implants sit on bone with good density and quality to minimize the complications.

CONCLUSION

By combining osteoporosis, fragility fractures, and bone health optimization into a TRIAD, "Lee's TRIAD," surgeons and physicians can collaborate more effectively, utilizing similar principles and strategies for better management.

Opportunistic Screening for Low Bone Mineral Density in Routine Computed Tomography Scans: A Brazilian Validation Study

INTRODUCTION/BACKGROUND

Osteoporotic fractures are a major health concern worldwide due to high mortality rates, deterioration in quality of life, and elevated healthcare costs related to hospital treatment. However, most patients who sustain an osteoporotic fracture have never been formally screened for osteoporosis. Opportunistic screening of osteoporosis through conventional computed tomography (CT) scans performed for unrelated reasons could help identify patients with low bone mass. There are currently no studies validating the opportunistic screening of low bone mass through CT in South America. The aim of our study is to assess whether conventional CT scans could be used for the opportunistic screening of osteopenia and osteoporosis in Brazilian patients.

METHODOLOGY

Patients who underwent unenhanced CT and dual-energy X-ray absorptiometry (DXA) scans within a six-month interval were assessed retrospectively. Mean CT attenuation was measured in the first lumbar vertebra (L1) in axial, coronal, and sagittal planes and compared to their respective DXA T-scores; vertebral fractures were assessed in the sagittal plane. Potential thresholds suggestive of low bone mass density (BMD) were established using receiver operating characteristics analysis.

RESULTS

491 patients were included (93.2 % female; mean age of 64.1 ± 9.8 years; mean interval of 63.5 days between scans). Mean L1 CT attenuation was significantly lower in osteopenic and osteoporotic patients in all CT planes (p < 0.001). Positive linear correlations were found between DXA T-scores and the average L1 attenuations in all CT planes (p < 0.001). An average L1 attenuation equal or below 100 Hounsfield Units (HU) in the sagittal plane identified low BMD (osteopenia or osteoporosis) with a specificity of 96.3 % and a positive predictive value of 96 %. In contrast, an average L1 attenuation above 180 HU demonstrated a sensitivity of 97.6 % and a negative predictive value of 94.9 % for detecting osteoporosis. Patients with L1 sagittal attenuation at or below 100 HU exhibited a significantly higher prevalence of vertebral fractures (prevalence ratio: 8.67; p < 0.001). An online calculator based on the results of this study is freely available at www.osteotc.com.br.

CONCLUSIONS

Routine CT scans can identify probable low bone density (osteopenia or osteoporosis) in Brazilian patients without additional costs or radiation exposure. Opportunistic CT screening does not substitute formal bone mineral density assessment; instead, it assists in identifying patients who may benefit from it.

Enhancing the Opportunistic Bone Status Assessment Using Radiomics Based on Dual-Energy Spectral CT Material Decomposition Images

The dual-energy spectral CT (DEsCT) employs material decomposition (MD) technology, opening up novel avenues for the opportunistic assessment of bone status. Radiomics, a powerful tool for elucidating the structural and textural characteristics of bone, aids in the detection of mineral loss. Therefore, this study aims to compare the efficacy of bone status assessment using both bone density measurements and radiomics models derived from MD images and to further explore the clinical value of radiomics models.

METHODS

Retrospective data were collected from 307 patients who underwent both quantitative computed tomography (QCT) and full-abdomen DEsCT scans at our institution. Based on QCT measurements, patients were divided into three categories: normal bone mineral density (BMD), osteopenia, and osteoporosis. Using the abdominal DEsCT data, six types of MD images were reconstructed, including HAP (Water), HAP (Fat), Ca (Water), Ca (Fat), Fat (Ca), and Fat (HAP). Patients were randomly divided into a training cohort (n = 214) and a validation cohort (n = 93) at a ratio of 7:3. Focusing on the L1 to L3 vertebrae, density values from the six MD images were measured. Six density value models and six radiomics models were constructed using a random forest (RF) classifier. The performance of these models in assessing bone status was evaluated using the receiver operating characteristic (ROC) curves, and the DeLong test was employed to compare performance differences between the models.

RESULTS

The macro-area under the curve (AUC) values for the density value models based on HAP (Water), HAP (Fat), Ca (Water), and Ca (Fat) MD images were 0.870, 0.870, 0.847, and 0.765, respectively, which outperformed those of Fat (Ca) (AUC = 0.623) and Fat (HAP) (AUC = 0.618) density value models. In the comparison of radiomics models, the trends of model performance were consistent with the density value models across the six MD images. However, the models based on HAP (Water), Ca (Water), HAP (Fat), Ca (Fat), Fat (Ca), and Fat (HAP) images exhibited superior performance than those of the density value models with the corresponding MD images, with values of 0.946, 0.941, 0.934, 0.926, 0.831, and 0.824, respectively.

CONCLUSIONS

Bone status assessment can be accurately conducted using density values from HAP (Water), HAP (Fat), Ca (Water), and Ca (Fat) MD images. However, radiomics models derived from MD images surpass traditional density measurement methods in evaluating bone status, highlighting their superior diagnostic potential.

Osteoporosis screening using QCT-based cutoff value of Hounsfield units in patients with degenerative lumbar diseases

PURPOSE

In patients with degenerative lumbar diseases, we aimed to establish the cutoff value of Hounsfield units (HU) for osteoporosis screening on the basis of the relationship between computed tomography (CT) HU value and volume bone mineral density (BMD) measured by quantitative computed tomography (QCT).

METHODS

A total of 136 patients aged ≥ 50 years with degenerative lumbar diseases were retrospectively included. Their QCT-BMD of L1-2 were recorded, and the CT values of L1-2 were measured with the same CT images of QCT. The degree of bone loss was evaluated with the criteria based on QCT-BMD: cutoff value of 80 mg/cm3 for osteoporosis and cutoff value of 120 mg/cm3 for osteopenia. The cutoff of CT value was acquired according to the linear regression equation between CT value and QCT-BMD.

RESULTS

The rate of osteoporosis, osteopenia, normal BMD was 33.8% (46/136), 51.5% (70/136), and 14.7% (20/136), respectively. The Pearson correlation coefficients between CT value and QCT-BMD were over 0.9 (P < 0.05). The cutoff of average CT value of L1-2 was calculated and adjusted to 110HU for osteoporosis and 160HU for osteopenia according the equation: average QCT-BMD of L1-2 = 0.76 ✕ average CT value of L1-2-0.46 (R2 = 0.931, P < 0.001). Cutoff value of 110HU was 91.2% (42/46) sensitive and 88.9% (80/90) specific for identifying osteoporosis. The cutoff value of 160HU was 95.0% (19/20) sensitive and 96.6% (112/116) specific for distinguishing normal BMD from abnormal BMD (osteoporosis and osteopenia).

CONCLUSION

The CT value is effective in osteoporosis screening, and the QCT-based cutoff value is 110 HU for osteoporosis and 160 HU for osteopenia in the patients with degenerative lumbar disease.

Multi-site phantomless bone mineral density from clinical quantitative computed tomography in males

Volumetric bone mineral density (vBMD) is commonly assessed using QCT. Although standard vBMD calculation methods require phantom rods that may not be available, internal-reference phantomless (IPL) and direct measurements of Hounsfield units (HU) can be used to calculate vBMD in their absence. Yet, neither approach has been systemically assessed across skeletal sites, and HU need further validation as a vBMD proxy. This study evaluated the accuracy of phantomless methods, including IPL and regression-based phantomless (RPL) calibration using HU to calculate vBMD, compared to phantom-based (PB) methods. vBMD from QCT scans of 100 male post-mortem human subjects (PMHS) was calculated using site-specific PB calibration at multiple skeletal sites throughout the body. A development sample of 50/100 PMHS was used to determine site-specific reference material density for IPL calibration and RPL equations. Reference densities and equations from the development sample were used to calculate IPL and RPL vBMD on the remaining 50/100 PMHS for method validation. PB and IPL/RPL vBMD were not significantly different (p > .05). Univariate regressions between PB and IPL/RPL vBMD were universally significant (p < 0.05), except for IPL Rad-30 (p = 0.078), with a percent difference across all sites of 6.97% ± 5.95% and 5.22% ± 4.59% between PB and IPL/RPL vBMD, respectively. As vBMD increased, there were weaker relationships and larger differences between PB vBMD and IPL/RPL vBMD. IPL and RPL vBMD had strong relationships with PB vBMD across sites (R2 = 97.99, R2 = 99.17%, respectively), but larger residual differences were found for IPL vBMD. As the accuracy of IPL/RPL vBMD varied between sites, phantomless methods should be site-specific to provide values more comparable to PB vBMD. Overall, this study suggests that RPL calibration may better represent PB vBMD compared to IPL calibration, increases the utility of opportunistic QCT, and provides insight into bone quality and fracture risk.

Do Hounsfield Units From Intraoperative CT Scans Correlate With Preoperative Values?

BACKGROUND

There is increasing interest in forecasting postoperative complications using bone density metrics. Vertebral Hounsfield unit measurements obtained from CT scans performed for surgical planning or other purposes, known as opportunistic CTs, have shown promise for their ease of measurement and the ability to target density measurement to a particular region of interest. Concomitant with the rising interest in prognostic bone density measurement use has been the increasing adoption of intraoperative advanced imaging techniques. Despite the interest in both outcome prognostication and intraoperative advanced imaging, there is little information regarding the use of CT-based intraoperative imaging as a means to measure bone density.

QUESTIONS/PURPOSES

(1) Can vertebral Hounsfield units be reliably measured by physician reviewers from CT scans obtained intraoperatively? (2) Do Hounsfield units measured from intraoperative studies correlate with values measured from preoperative CT scans?

METHODS

To be eligible for this retrospective study, patients had to have been treated with the use of an intraoperative CT scan for instrumented spinal fusion for either degenerative conditions or traumatic injuries between January 2015 and December 2022. Importantly, patients without a preoperative CT scan of the fused levels within 180 days before surgery or who were indicated for surgery because of infection, metastatic disease, or who were having revision surgery after prior instrumentation were excluded from the query. Of the 285 patients meeting these inclusion criteria, 53% (151) were initially excluded for the following reasons: 36% (102) had intraoperative CT scans obtained after placement of instrumentation, 16% (47) had undergone intraoperative CT scans but the studies were not accessible for Hounsfield unit measurement, and 0.7% (2) had prior kyphoplasty wherein the cement prevented Hounsfield unit measurement. Finally, an additional 19% (53) of patients were excluded because the preoperative CT and intraoperative CT were obtained at different peak voltages, which can influence Hounsfield unit measurement. This yielded a final population of 81 patients from whom 276 preoperative and 276 intraoperative vertebral Hounsfield unit measurements were taken. Hounsfield unit data were abstracted from the same vertebra(e) from both preoperative and intraoperative studies by two physician reviewers (one PGY3 and one PGY5 orthopaedic surgery resident, both pursuing spine surgery fellowships). For a small, representative subset of patients, measurements were taken by both reviewers. The feasibility and reliability of Hounsfield unit measurement were then assessed with interrater reliability of values measured from the same vertebra by the two different reviewers. To compare Hounsfield unit values from intraoperative CT scans with preoperative CT studies, an intraclass correlation using a two-way random effects, absolute agreement testing technique was employed. Because the data were formatted as multiple measurements from the same vertebra at different times, a repeated measures correlation was used to assess the relationship between preoperative and intraoperative Hounsfield unit values. Finally, a linear mixed model with patients handled as a random effect was used to control for different patient and clinical factors (age, BMI, use of bone density modifying agents, American Society of Anesthesiologists [ASA] classification, smoking status, and total Charlson comorbidity index [CCI] score).

RESULTS

We found that Hounsfield units can be reliably measured from intraoperative CT scans by human raters with good concordance. Hounsfield unit measurements of 31 vertebrae from a representative sample of 10 patients, measured by both reviewers, demonstrated a correlation value of 0.82 (95% CI 0.66 to 0.91), indicating good correlation. With regard to the relationship between preoperative and intraoperative measurements of the same vertebra, repeated measures correlation testing demonstrated no correlation between preoperative and intraoperative measurements (r = 0.01 [95% CI -0.13 to 0.15]; p = 0.84). When controlling for patient and clinical factors, we continued to observe no relationship between preoperative and intraoperative Hounsfield unit measurements.

CONCLUSION

As intraoperative CT and measurement of vertebral Hounsfield units both become increasingly popular, it would be a natural extension for spine surgeons to try to extract Hounsfield unit data from intraoperative CTs. However, we found that although it is feasible to measure Hounsfield data from intraoperative CT scans, the obtained values do not have any predictable relationship with values obtained from preoperative studies, and thus, these values should not be used interchangeably. With this knowledge, future studies should explore the prognostic value of intraoperative Hounsfield unit measurements as a distinct entity from preoperative measurements.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Intraoperative Surgeon Assessment of Bone: Correlation to Bone Mineral Density, CT Hounsfield Units, and Vertebral Bone Quality

STUDY DESIGN

Retrospective observational study of consecutive patients.

OBJECTIVE

The purpose of the study is to determine if a surgeon's qualitative assessment of bone intraoperatively correlates with radiologic parameters of bone strength.

SUMMARY OF BACKGROUND DATA

Preoperative radiologic assessment of bone can include modalities such as computed tomography (CT) Hounsfield units (HUs), dual-energy x-ray absorptiometry (DXA) bone mineral density with trabecular bone score (TBS) and magnetic resonance imaging vertebral bone quality (VBQ). Quantitative analysis of bone with screw insertional torque and pull-out strength measurement has been performed in cadaveric models and has been correlated to these radiologic parameters. However, these quantitative measurements are not routinely available for use in surgery. Surgeons anecdotally judge bone strength, but the fidelity of the intraoperative judgment has not been investigated.

METHODS

All adult patients undergoing instrumented posterior thoracolumbar spine fusion by one of seven surgeons at a single center over a 3-month period were included. Surgeons evaluated the strength of bone based on intraoperative feedback and graded each patient's bone on a 5-point Likert scale. Two independent reviewers measured preoperative CT HUs and magnetic resonance imaging VBQ. Bone mineral density, lowest T-score, and TBS were extracted from DXA within 2 years of surgery.

RESULTS

Eighty-nine patients were enrolled and 16, 28, 31, 13, and 1 patients had Likert grade 1 (strongest bone), 2, 3, 4, and 5 (weakest bone), respectively. The surgeon assessment of bone correlated with VBQ (τ=0.15, P =0.07), CT HU (τ=-0.31, P <0.01), lowest DXA T-score (τ=-0.47, P <0.01), and TBS (τ=-0.23, P =0.06).

CONCLUSION

Spine surgeons' qualitative intraoperative assessment of bone correlates with preoperative radiologic parameters, particularly in posterior thoracolumbar surgeries. This information is valuable to surgeons as this supports the idea that decisions based on feel in surgery have a statistical foundation.

Correlations among MRI-based cervical and thoracic vertebral bone quality score, CT-based Hounsfield Unit score, and DEXA t-score in assessment of bone mineral density

BACKGROUND

Further optimization of the validated vertebral bone quality (VBQ) score using magnetic resonance imaging (MRI) may expand its clinical utility for bone mineral density (BMD) assessment. This study evaluated the correlations among cervical and thoracic VBQ scores, the validated Hounsfield Unit (HU) measured on computed tomography (CT), and dual-energy x-ray absorptiometry (DEXA) values.

METHODS

We retrieved the medical and radiographic records of 165 patients who underwent synchronous MRI of the cervical and thoracic spine, as well as DEXA and CT imaging of the spine obtained within 1 year of each other between 2015 and 2022. Radiographic data consisted of the MRI-based cervical and thoracic VBQ scores, CT-based HU, and DEXA T-scores of the spine and hip. Patient age, sex, body mass index (BMI), and ethnicity were also obtained.

RESULTS

Mean cervical and thoracic VBQ scores were 3.99 ± 1.68 and 3.82 ± 2.11, respectively. Mean HU and DEXA T-scores of the spine and hip were 135.75 ± 60.36, -1.01 ± 1.15, and -0.47 ± 2.27. All correlations among VBQ, HU, and DEXA were insignificant except for weak correlations between cervical and thoracic VBQ, and cervical VBQ and HU. No correlations were observed between radiographic scores and patient age or BMI. No differences based on ethnicity or sex were observed with respect to cervical or thoracic VBQ, HU, or DEXA.

CONCLUSION

Cervical and thoracic VBQ scores are distinct from Hounsfield Unit and DEXA values. VBQ scoring in the cervical and thoracic spine is not influenced by patient age, ethnicity, sex, or BMI.

Preoperative low Hounsfield units in the lumbar spine are associated with postoperative mechanical complications in adult spinal deformity

PURPOSE

To determine the most valid bone health parameter to predict mechanical complications (MCs) following surgery for adult spinal deformity (ASD).

METHODS

This multicenter study retrospectively examined the records of patients who had undergone fusion of three or more motion segments, including the pelvis, with a minimum two-year follow-up period. Patients with moderate and severe global alignment and proportion scores were included in the study and divided into two groups: those who developed MCs and those who did not. Bone mineral density (BMD) of the lumbar spine and femoral neck was measured using dual-energy X-ray absorptiometry, and Hounsfield units (HUs) were measured in the lumbar spine on computed tomography. Radiographic parameters were evaluated preoperatively, immediately after surgery, and at final follow-up.

RESULTS

Of 108 patients, 30 (27.8%) developed MCs, including 26 cases of proximal junctional kyphosis/failure, 2 of distal junctional failure, 6 of rod fracture, and 11 reoperations. HUs were significantly lower in patients who experienced MCs (113.7 ± 41.1) than in those who did not (137.0 ± 46.8; P = 0.02). BMD did not differ significantly between the two groups. The preoperative and two-year postoperative global tilt, as well as the immediately postoperative sagittal vertical axis, were significantly greater in patients who developed MCs than in those who did not (P = 0.02, P < 0.01, and P = 0.01, respectively).

CONCLUSION

Patients who experienced MCs following surgery for ASD had lower HUs than those who did not. HUs may therefore be more useful than BMD for predicting MCs following surgery for ASD.

Biomechanical Comparison of Unilateral and Bilateral Pedicle Screw Fixation after Multilevel Lumbar Lateral Interbody Fusion

STUDY DESIGN

Human Cadaveric Biomechanical Study.

OBJECTIVES

Lumbar Lateral Interbody Fusion (LLIF) utilizing a wide cage has been reported as having favorable biomechanical characteristics. We examine the biomechanical stability of unilateral pedicle screw and rod fixation after multilevel LLIF utilizing 26 mm wide cages compared to bilateral fixation.

METHODS

Eight human cadaveric specimens of L1-L5 were included. Specimens were attached to a universal testing machine (MTS 30/G). Three-dimensional specimen range of motion (ROM) was recorded using an optical motion-tracking device. Specimens were tested in 3 conditions: 1) intact, 2) L1-L5 LLIF (4 levels) with unilateral rod, 3) L1-L5 LLIF with bilateral rods.

RESULTS

From the intact condition, LLIF with unilateral rod decreased flexion-extension by 77%, lateral bending by 53%, and axial rotation by 26%. In LLIF with bilateral rods, flexion-extension decreased by 83%, lateral bending by 64%, and axial rotation by 34%. Comparing unilateral and bilateral fixation, LLIF with bilateral rods reduced ROM by a further 23% in flexion-extension, 25% in lateral bending, and 11% in axial rotation. The difference was statistically significant in flexion-extension and lateral bending (P < .005).

CONCLUSIONS

Considerable decreases in ROM were observed after multilevel (4-level) LLIF utilizing 26 mm cages supplemented with both unilateral and bilateral pedicle screws and rods. The addition of bilateral fixation provides a 10-25% additional decrease in ROM. These results can inform surgeons of the incremental biomechanical benefit when considering unilateral or bilateral posterior fixation after multilevel LLIF.

Medial Calcar Density Measured via Opportunistic Computed Tomography Is Well Represented by the Dorr C Classification

Introduction The canal-to-calcar isthmus (CC) ratio has been previously correlated with proximal femur osteology, but its relationship with bone density is not well established. Our purpose was to assess the relationship between femoral bone density, measured on opportunistic quantitative CT in Hounsfield units (HU), and CC ratio. Methods A total of 148 THA patients were included. The CC ratio was measured on anteroposterior hip radiographs. Using perioperative CT scans, a 1 cm diameter area was identified on a single mid-coronal slice in the medial calcar just proximal to the intertrochanteric ridge. The mean HU was calculated in this region to represent calcar bone density. Results Twenty-four percent (n = 35) of patients were classified as Dorr A (average CC ratio 0.47 [0.45; 0.48]), 67% (n = 96) as Dorr B (0.62 [0.55; 0.68]), and 11% (n = 17) as Dorr C (0.78 [0.77; 0.80]). There was a significant difference between Dorr A and Dorr C femurs (769 (144) vs. 588 (154) HU) as well as between B and C femurs (718 (166) vs. 588 (154) HU). The CC ratio was correlated with calcar bone density on CT (-0.370). Conclusion CC ratio is correlated with bone density determined by HU measurements on an opportunistic quantitative computed tomography scan, and bone density HU values were able to accurately differentiate bone density in Dorr A and B from Dorr C femurs. These findings suggest that the CC ratio is a reliable measurement to predict bone density in Dorr C femurs. Therefore, arthroplasty surgeons can confidently use the Dorr classification for patients with Dorr C femurs when preoperatively planning for THA.

Bone loss over time and risk of osteoporosis in advanced pancreatic cancer

BACKGROUND

Pancreatic cancer has a high risk of developing osteoporosis. However, the impact of osteoporosis has not been well-studied. This study aimed to evaluate bone loss over time and risk of osteoporosis in patients with advanced pancreatic cancer.

METHODS

We retrospectively examined consecutive patients with unresectable pancreatic cancer who had evaluable computed tomography before treatment and at 1-year follow-up. Bone mineral density at the first lumbar vertebra was measured on computed tomography, and osteoporosis was defined as bone mineral density < 135 Hounsfield units. The prevalence and risk factors for osteoporosis, changes in bone mineral density over time and incidence of bone fractures were analyzed.

RESULTS

Three hundred eighty patients were included. Osteoporosis was associated with older age, female sex, low body mass index and poor performance status at baseline. A consistent decrease in bone mineral density was observed over time regardless of age, sex or disease status, resulting in an increase in the prevalence of osteoporosis over time (47% at baseline, 79% at 1 year, 88% at 2 years, 89% at 3 years, 95% at 4 years and 100% at 5 years). Changes in bone mineral density from baseline were greater in patients with locally-advanced pancreatic cancer, in those who received modified FOLFIRINOX or S-IROX for more than 3 months, and in those who received radiation therapy. Incident fractures developed in 45 patients (12%) during follow-up.

CONCLUSIONS

Osteoporosis and osteoporotic fractures were highly prevalent in patients with advanced pancreatic cancer. This study highlights the importance of screening for osteoporosis in such patients.

Reduced Bone Density Based on Hounsfield Units After Long-Segment Spinal Fusion with Harrington Rods

BACKGROUND

Long-segment instrumentation, such as Harrington rods, offloads vertebrae within the construct, which may result in significant stress shielding of the fused segments. The present study aimed to determine the effects of spinal fusion on bone density by measuring Hounsfield units (HUs) throughout the spine in patients with a history of Harrington rod fusion.

METHODS

Patients with a history of Harrington rod fusion treated at a single academic institution were identified. Mean HUs were calculated at 5 spinal segments for each patient: cranial adjacent mobile segment, cranial fused segment, midconstruct fused segment, caudal fused segment, and caudal adjacent mobile segment. Mean HUs for each level were compared using a paired-sample t test, with statistical significance defined by P < 0.05. Hierarchic multiple regression, including age, gender, body mass index, and time since original fusion, was used to determine predictors of midfused segment HUs.

RESULTS

One hundred patients were included (mean age, 55 ± 12 years; 62% female). Mean HUs for the midconstruct fused segment (110; 95% confidence interval [CI], 100-121) were significantly lower than both the cranial and caudal fused segments (150 and 118, respectively; both P < 0.05), as well as both the cranial and caudal adjacent mobile segments (210 and 130, respectively; both P < 0.001). Multivariable regression showed midconstruct HUs were predicted only by patient age (-2.6 HU/year; 95% CI, -3.4 to -1.9; P < 0.001) and time since original surgery (-1.4 HU/year; 95% CI, -2.6 to -0.2; P = 0.02).

CONCLUSIONS

HUs were significantly decreased in the middle of previous long-segment fusion constructs, suggesting that multilevel fusion constructs lead to vertebral bone density loss within the construct, potentially from stress shielding.

Sagittal Section Hounsfield Units of the Upper Instrumented Vertebrae as a Predictor of Proximal Junctional Vertebral Fractures Following Adult Spinal Deformity Surgery

STUDY DESIGN

A retrospective observational study.

PURPOSE

This study aimed to determine an accurate and convenient screening method for predicting proximal junctional fractures (PJFr) following surgery for adult spinal deformity (ASD) using computed tomography (CT)-based measurement of Hounsfield units (HUs).

OVERVIEW OF LITERATURE

CT-based measurement of HUs is an alternative tool for assessing bone mineral density. However, the optimal method for predicting adjacent vertebral fractures following spinal fusion using HUs remains unclear.

METHODS

This retrospective observational study included 42 patients who underwent reconstructive surgery for ASD. Elliptical regions of interest (ROIs) on the axial section and rectangular ROIs on the sagittal section were placed at the upper instrumented vertebrae (UIV), UIV+1, and UIV+2. In addition, the HU value of the L2 vertebra was used as the representative.

RESULTS

PJFr occurred in 28.6% of patients within 2 years following surgery. The HU values obtained from the axial sections of L2, UIV, UIV+1, and UIV+2 were not significantly associated with the incidence of PJFr within 2 years, except for the ROI set in the lower region of the L2 vertebra. However, the HU value of the anterior third of the UIV in the sagittal section was significantly lower in the PJFr group than in the nonPJFr group (87.0 vs. 160.3, p =0.001). A UIV HU value of <100 was associated with a higher incidence of PJFr than an HU vaue of >100 (p <0.05).

CONCLUSIONS

Measurements of HU in the anterior one-third of the UIV in the sagittal section demonstrated predictive ability for PJFr following ASD surgery. A UIV HU value of <100 emerged as a risk factor for PJFr.

Significant Reduction in Bone Density as Measured by Hounsfield Units in Patients with Ankylosing Spondylitis or Diffuse Idiopathic Skeletal Hyperostosis

Background: Multisegmental pathologic autofusion occurs in patients with ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH). It may lead to reduced vertebral bone density due to stress shielding. Methods: This study aimed to determine the effects of autofusion on bone density by measuring Hounsfield units (HU) in the mobile and immobile spinal segments of patients with AS and DISH treated at a tertiary care center. The mean HU was calculated for five distinct regions-cranial adjacent mobile segment, cranial fused segment, mid-construct fused segment, caudal fused segment, and caudal adjacent mobile segment. Means for each region were compared using paired-sample t-tests. Multivariable regression was used to determine independent predictors of mid-fused segment HUs. Results: One hundred patients were included (mean age 76 ± 11 years, 74% male). The mean HU for the mid-construct fused segment (100, 95% CI [86, 113]) was significantly lower than both cranial and caudal fused segments (174 and 108, respectively; both p < 0.001), and cranial and caudal adjacent mobile segments (195 and 115, respectively; both p < 0.001). Multivariable regression showed the mid-construct HUs were predicted by history of smoking (-30 HU, p = 0.009). Conclusions: HUs were significantly reduced in the middle of long-segment autofusion, which was consistent with stress shielding. Such shielding may contribute to the diminution of vertebral bone integrity in AS/DISH patients and potentially increased fracture risk.

Correlations among Cervical, Thoracic, and lumbar Hounsfield Unit measurements for assessment of bone mineral density

OBJECTIVE

Bone mineral density assessment using Hounsfield Unit (HU) currently depends upon the availability of computed tomography (CT) of the lumbar spine. The primary aim of this study was to evaluate the associations among HU measurements of the cervical (CHU), thoracic (THU), and lumbar (LHU) spine. The secondary aim of this study was to analyze the influence of patient demographic and anthropometric characteristics on HU measurements.

METHODS

Radiographic records of 165 patients who underwent CT of the cervical, thoracic, and lumbar spine were retrieved. The CHU, THU, and LHU were calculated by obtaining the mean signal intensity from the medullary portions of C3-C7, T8-T12, and L1-L4 vertebral bodies.

RESULTS

Mean CHU, THU, and LHU values were 266.26 ± 88.69, 165.57 ± 55.06, and 166.45 ± 51.38. Significant differences of 100.69, 99.81, and 0.88 were observed between CHU and THU (p <.001), CHU and LHU (p <.001), and THU and LHU (p =.023). Correlations of 0.574, 0.488, and 0.686 were observed between CHU and THU (p <.001), CHU and LHU (p <.001), and THU and LHU (p <.001). No differences in HU based on sex, age, height, weight, or ethnicity were observed. Multivariate regression models demonstrated R2 values of 0.770 - 0.790 (p <.001) in prediction of LHU.

CONCLUSIONS

Hounsfield Unit measurements derived from the cervical and thoracic spine correlate with the validated lumbar Hounsfield Unit. Hounsfield Unit measurements do not vary based on sex, ethnicity, age, height, or weight.

Risk Factors for Distal Junctional Problems Following Long Instrumented Fusion for Degenerative Lumbar Scoliosis: Are they Related to the Paraspinal Muscles

PURPOSE

Although the incidence of distal junctional problems (DJPs) following long construct-based treatment for degenerative lumbar scoliosis (DLS) is lower, affected patients are more likely to require revision surgery when they occur. So the aim of this study is to identify risk factors associated with DJPs to avoid its occurrence by at least 1-year follow-up.

METHODS

A total of 182 DLS patients undergoing long instrumented fusion surgery (≥4 levels) between February 2011 and March 2022 were retrospectively analyzed. Patients were placed into the DJP group if a DJP occurred at the final follow-up; patients without mechanical complications were matched 1:2 according to age, sex and BMI as the control group. Patient characteristics, surgical variables, radiographic parameters, lumbar muscularity and fatty degeneration were analyzed statistically. The statistical differences in the results between the two groups (p values <0.05) and other variables selected by experts were entered into a multivariate logistic regression model, and the forwards likelihood ratio method was used to analyze the independent risk factors for DJPs.

RESULTS

Twenty-four (13.2%) patients suffered a DJP in the postoperative period and the reoperation rate was 8.8%. On univariate analysis, the lowest instrumented vertebra (LIV) CT value (p = 0.042); instrumented levels (p = 0.030); preoperative coronal vertical axis (CVA) (p = 0.046), thoracolumbar kyphosis (TLK) (p = 0.006), L4-S1 lordosis (p = 0.013), sacral slop (SS) (p = 0.030), pelvic tilt (PT) classification (p = 0.004), and sagittal vertical axis (SVA) (p = 0.021); TLK correction (p = 0.049); post-operative CVA (p = 0.029); Overall, There was no significant difference in the paraspinal muscle parameters between the two groups. On multivariate analysis, instrumented levels (OR = 1.595; p = 0.035), preoperative SVA (OR = 1.016; p = 0.022) and preoperative PT (OR = 0.873; p = 0.001) were identified as significant independent risk factors for DJP.

CONCLUSION

Longer instrumented levels, a greater preoperative SVA and a smaller PT were found to be strongly associated with the presence of DJPs in patients treated for DLS. The degeneration of the paraspinal muscles may not be related to the occurrence of DJPs. For DLS patients, the occurrence of DJP can be reduced by selecting reasonable fusion segments and evaluating the patient's sagittal balance and spino-pelvic parameters before operation.

Generalizability of Deep Learning Classification of Spinal Osteoporotic Compression Fractures on Radiographs Using an Adaptation of the Modified-2 Algorithm-Based Qualitative Criteria

RATIONALE AND OBJECTIVES

Spinal osteoporotic compression fractures (OCFs) can be an early biomarker for osteoporosis but are often subtle, incidental, and underreported. To ensure early diagnosis and treatment of osteoporosis, we aimed to build a deep learning vertebral body classifier for OCFs as a critical component of our future automated opportunistic screening tool.

MATERIALS AND METHODS

We retrospectively assembled a local dataset, including 1790 subjects and 15,050 vertebral bodies (thoracic and lumbar). Each vertebral body was annotated using an adaption of the modified-2 algorithm-based qualitative criteria. The Osteoporotic Fractures in Men (MrOS) Study dataset provided thoracic and lumbar spine radiographs of 5994 men from six clinical centers. Using both datasets, five deep learning algorithms were trained to classify each individual vertebral body of the spine radiographs. Classification performance was compared for these models using multiple metrics, including the area under the receiver operating characteristic curve (AUC-ROC), sensitivity, specificity, and positive predictive value (PPV).

RESULTS

Our best model, built with ensemble averaging, achieved an AUC-ROC of 0.948 and 0.936 on the local dataset's test set and the MrOS dataset's test set, respectively. After setting the cutoff threshold to prioritize PPV, this model achieved a sensitivity of 54.5% and 47.8%, a specificity of 99.7% and 99.6%, and a PPV of 89.8% and 94.8%.

CONCLUSION

Our model achieved an AUC-ROC>0.90 on both datasets. This testing shows some generalizability to real-world clinical datasets and a suitable performance for a future opportunistic osteoporosis screening tool.

The impact of osteosarcopenia in patients with unresectable or recurrent biliary tract cancer receiving palliative chemotherapy

BACKGROUND

Osteosarcopenia is a newly described syndrome that has been reported to be associated with worse outcomes in various types of cancer. However, its impact on survival in biliary tract cancer remains unclear. This study evaluated the impact of osteosarcopenia on survival in patients with unresectable or recurrent biliary tract cancer.

METHODS

A total of 306 patients with unresectable or recurrent biliary tract cancer who initiated chemotherapy at our institution between 2015 and 2021 were retrospectively investigated. Skeletal muscle index and bone mineral density were measured using pretreatment cross-sectional computed tomography images. Baseline characteristics and survival outcomes were compared between patients with osteosarcopenia and those without. The Cox proportional hazards regression model was used to identify factors associated with survival.

RESULTS

Osteosarcopenia was present in 66 patients (22%) and was associated with older age (74 vs. 69 years, P < 0.001) and female sex (58 vs. 37%, P = 0.003). Patients with osteosarcopenia tended to have worse performance status (P = 0.098), higher modified Glasgow prognostic score (P = 0.082), higher neutrophil to lymphocyte ratio (P = 0.058) and were significantly less likely to receive combination chemotherapy (68 vs. 80%, P = 0.044) than those without. Osteosarcopenia was associated with reduced survival (8.9 vs. 14.0 months, P < 0.001) and was identified as an independent factor predicting shorter survival in multivariate analysis.

CONCLUSIONS

Osteosarcopenia was associated with poor survival in unresectable or recurrent biliary tract cancer treated with chemotherapy. This study highlights the potential importance of screening for osteosarcopenia in patients with biliary tract cancer.

Addressing Challenges of Opportunistic Computed Tomography Bone Mineral Density Analysis

Computed tomography (CT) offers advanced biomedical imaging of the body and is broadly utilized for clinical diagnosis. Traditionally, clinical CT scans have not been used for volumetric bone mineral density (vBMD) assessment; however, computational advances can now leverage clinically obtained CT data for the secondary analysis of bone, known as opportunistic CT analysis. Initial applications focused on using clinically acquired CT scans for secondary osteoporosis screening, but opportunistic CT analysis can also be applied to answer research questions related to vBMD changes in response to various disease states. There are several considerations for opportunistic CT analysis, including scan acquisition, contrast enhancement, the internal calibration technique, and bone segmentation, but there remains no consensus on applying these methods. These factors may influence vBMD measures and therefore the robustness of the opportunistic CT analysis. Further research and standardization efforts are needed to establish a consensus and optimize the application of opportunistic CT analysis for accurate and reliable assessment of vBMD in clinical and research settings. This review summarizes the current state of opportunistic CT analysis, highlighting its potential and addressing the associated challenges.

Chance Fracture Pattern Presenting in Proximal Junctional Failure

INTRODUCTION

We present a case series of proximal junctional failure due to a Chance-type fracture.

METHODS

This is a retrospective review of patients who developed proximal junctional kyphosis because of Chance-type proximal junctional failure after spinal fusion for adult spinal deformity.

RESULTS

Fifteen patients were identified (4M:11F). The average age was 61.4 years (range, 39 to 77). The mean time to fracture identification was 25.4 days (range, 3 to 65). The average number of levels instrumented was 6.7 (range, 2 to 17). No patients had antecedent trauma before fracture onset. In 67% of cases with a lumbar upper instrumented vertebra (UIV), there was overcorrection of lumbar lordosis (LL) and/or lower LL. The five cases with a lower thoracic UIV had undergone notable correction of preoperative thoracolumbar junction kyphosis. 14 of 15 patients were treated with extension of fusion. Pedicle screws at the fracture level were salvaged by changing to an anatomic trajectory.

CONCLUSION

Continued pain at 6 to 12 weeks with radiographs showing an increased proximal junctional angle and cephalocaudal pedicle widening at the UIV should raise suspicion for this unique fracture pattern. A CT scan is recommended. Low bone density, LL and/or lower LL overcorrection, and selection of lower thoracic UIV in the setting of notable thoracolumbar junction correction may contribute to fracture risk.

Characteristics of MRI‑based vertebral bone quality scores in elderly patients with vertebral fragility fractures

OBJECTIVE

To explore the characteristics of vertebral bone quality (VBQ) scores in patients with vertebral fragility fractures, including VBQ score and single-level VBQ score, and evaluate their effectiveness as predictors.

METHODS

The VBQ scores were measured using T1-weighted MRI images. VBQ scores were compared in patients with different times of previous fragility fractures. In addition, patients with fractures were matched for age and sex with patients without fractures, and VBQ scores were compared between the two groups. Finally, the predictive efficiency of VBQ scores for vertebral fragility fractures was analyzed by the receiver-operator curve (ROC).

RESULTS

The average VBQ score and single-level VBQ score in patients with fractures were 3.48 ± 0.56 and 3.60 ± 0.60 and no difference among patients with different times of previous fractures. As for the age- and sex-matched patients, fracture patients had higher VBQ scores (VBQ score: 3.48 ± 0.56 vs. 2.88 ± 0.40, p < 0.001; single-level VBQ score: 3.60 ± 0.60 vs. 2.95 ± 0.44, p < 0.001). The AUCs using the VBQ score and single-level VBQ score to predict fragility fractures were 0.815 and 0.817, respectively. The optimal thresholds of the VBQ score and single-level VBQ score for predicting fragility fractures were 3.22 and 3.16, respectively.

CONCLUSION

MRI‑based VBQ scores are important predictors of vertebral fragility fracture but have no predictive value for the recurrence of fractures in patients with a history of fragility fractures. The VBQ score of 3.22 and single-level VBQ score of 3.16 are optimal thresholds that can be used when using lumbar MRI scans to identify individuals at high risk for fragility fractures.

Bone quality in total shoulder arthroplasty: a prospective study correlating computed tomography Hounsfield units with thumb test and fracture risk assessment tool score

Background

To evaluate if Hounsfield units (HU) measured on preoperative computed tomography (CT) scans at the anatomic neck of the proximal humerus correlates with intraoperative findings of the "thumb test" in assessment of bone quality in shoulder arthroplasty patients.

Methods

Primary anatomic total shoulder and reverse total shoulder arthroplasty patients from 2019-2022 with an available preoperative CT scan of the operative shoulder were prospectively enrolled at a single center with 3 surgeons who perform shoulder arthroplasty. The "thumb test" was performed intraoperatively; a positive test signified "good bone." Demographic information, including prior dual x-ray absorptiometry scans, was extracted from the medical record. HU at the cut surface of the proximal humerus were calculated, as was cortical bone thickness on preoperative CT. Fracture risk assessment tool (FRAX) scores were calculated for 10-year risk of osteoporotic fracture.

Results

A total of 149 patients were enrolled. Mean age was 67.6 ± 8.5 years with 69 (46.3%) being males. Patients with a negative thumb test were significantly older (72.3 ± 6.6 vs. 66.5 ± 8.6 years; P < .001) than those with a positive thumb test. Males were more likely to have a positive thumb test than females (P = .014). Patients with a negative thumb test had significantly lower HUs on preoperative CT (16.3 ± 29.7 vs. 51.9 ± 35.2; P < .001). Patients with a negative thumb test had a higher mean FRAX score (14.1 ± 7.9 vs. 8.0 ± 4.8; P < .001). Receiver operator curve analysis was performed to identify a cut-off value for CT HU of 36.67, above which the thumb test is likely to be positive. Furthermore, receiver operator curve analysis also identified optimal cut-off values for 10-year risk of fracture by FRAX score of 7.75 HU, below which the thumb test is likely to be positive. Fifty patients were at high risk based on FRAX and HU; surgeons classified 21 (42%) as having "poor bone" quality through a negative thumb test. High-risk patients had a negative thumb test 33.8% (23/68) and 37.1% (26/71) of the time for HU and FRAX, respectively.

Conclusions

Surgeons are poor at identifying suboptimal bone quality at the anatomic neck of the proximal humerus based on intraoperative thumb test when referencing against CT HU and FRAX scores. The objective measures of CT HU and FRAX scoring may be useful metrics to incorporate into surgeons' preoperative plans for humeral stem fixation using readily available imaging and demographic data.

Biomechanical Comparison of Multilevel Stand-Alone Lumbar Lateral Interbody Fusion With Posterior Pedicle Screws: An In Vitro Study

OBJECTIVE

Lumbar lateral interbody fusion (LLIF) allows placement of large interbody cages while preserving ligamentous structures important for stability. Multiple clinical and biomechanical studies have demonstrated the feasibility of stand-alone LLIF in single-level fusion. We sought to compare the stability of 4-level stand-alone LLIF utilizing wide (26 mm) cages with bilateral pedicle screw and rod fixation.

METHODS

Eight human cadaveric specimens of L1-5 were included. Specimens were attached to a universal testing machine (MTS 30/G). Flexion, extension, and lateral bending were attained by applying a 200 N load at a rate of 2 mm/sec. Axial rotation of ± 8° of the specimen was performed at 2°/sec. Three-dimensional specimen motion was recorded using an optical motion-tracking device. Specimens were tested in 4 conditions: (1) intact, (2) bilateral pedicle screws and rods, (3) 26-mm stand-alone LLIF, (4) 26-mm LLIF with bilateral pedicle screws and rods.

RESULTS

Compared to the stand-alone LLIF, bilateral pedicle screws and rods had 47% less range of motion in flexion-extension (p < 0.001), 21% less in lateral bending (p < 0.05), and 20% less in axial rotation (p = 0.1). The addition of bilateral posterior instrumentation to the stand-alone LLIF resulted in decreases of all 3 planes of motion: 61% in flexion-extension ( p < 0.001), 57% in lateral bending (p < 0.001), 22% in axial rotation (p = 0.002).

CONCLUSION

Despite the biomechanical advantages associated with the lateral approach and 26 mm wide cages, stand-alone LLIF for 4-level fusion is not equivalent to pedicle screws and rods.

Prognostic impact of osteosarcopenia in patients with advanced pancreatic cancer receiving gemcitabine plus nab-paclitaxel

BACKGROUND

Osteosarcopenia, defined as the combination of osteoporosis and sarcopenia, has recently gained attention as a novel prognostic factor for survival in patients with cancer. This study aimed to evaluate the prognostic impact of osteosarcopenia in metastatic pancreatic cancer (PC).

METHODS

We retrospectively investigated consecutive metastatic PC patients receiving first-line gemcitabine plus nab-paclitaxel (GnP). Skeletal muscle index at the third lumbar vertebra and bone mineral density at the first lumbar vertebra were measured using pretreatment computed tomography. Treatment outcomes of osteosarcopenia and non-osteosarcopenia groups were compared and analyzed. Multivariate analysis was performed to identify variables associated with survival.

RESULTS

Among 313 patients, osteosarcopenia was present in 59 patients (19%). The osteosarcopenia group was associated with older age, higher proportion of females, worse performance status, and higher modified Glasgow prognostic scores (mGPS). Response rates to chemotherapy, progression-free survival (3.5 months vs. 6.4 months, p < 0.001), and overall survival (5.6 months vs. 13.0 months, p < 0.001) were significantly better in the non-osteosarcopenia group. Osteosarcopenia, performance status of 1-2, mGPS score of 1-2, carcinoembryonic antigen ≥10 ng/mL, and carbohydrate antigen 19-9 ≥ 1000 IU/mL were identified as independent factors predicting shorter survival. Grade 3 or higher anemia and febrile neutropenia occurred more frequently in the osteosarcopenia group.

CONCLUSIONS

Osteosarcopenia was associated with poor survival in metastatic PC treated with first-line GnP. Screening for osteosarcopenia may be helpful for better management of metastatic PC.

Discrepancy between DXA and CT-based assessment of spine bone mineral density

PURPOSE

Adequate bone mineral density (BMD) is necessary for success in spine surgery. Dual-energy X-ray absorptiometry (DXA) is the gold standard in determining BMD but may give spuriously high values. Hounsfield units (HU) from computed tomography (CT) may provide a more accurate depiction of the focal BMD encountered during spine surgery. Our objective is to determine the discrepancy rate between DXA and CT BMD determinations and how often DXA overestimates BMD compared to CT.

METHODS

We retrospectively reviewed 93 patients with both DXA and CT within 6 months. DXA lumbar spine and overall T scores were classified as osteoporotic (T Score  ≤ - 2.5) or non-osteoporotic (T Score > -2.5). L1 vertebral body HU were classified as osteoporotic or non-osteoporotic using cutoff thresholds of either ≤ 135 HU or ≤ 110 HU. Corresponding DXA and HU classifications were compared to determine disagreement and overestimation rates.

RESULTS

Using lumbar T scores, the CT vs DXA disagreement rate was 40-54% depending on the HU threshold. DXA overestimated BMD 97-100% of the time compared to CT. Using overall DXA T scores, the disagreement rate was 33-47% with DXA greater than CT 74-87% of the time. In the sub-cohort of 10 patients with very low HU (HU < 80), DXA overestimated BMD compared to CT in every instance.

CONCLUSIONS

There is a large discrepancy between DXA and CT BMD determinations. DXA frequently overestimates regional BMD encountered during spine surgery compared with CT. While DXA remains the gold standard in determining BMD, CT may play an important role in defining the focal BMD pertinent to spine surgery.

Evaluation of femoral head bone quality by Hounsfield units: A predictor of implant failure for intertrochanteric fractures after intramedullary nail fixation

Purpose

The aim of present study is to evaluate the femoral head bone quality by Hounsfield units and its relationship to the occurrence of implant failure for intertrochanteric fractures after intramedullary nail fixation.

Methods

This retrospective study assessed 160 intertrochanteric fractures treated with intramedullary fixation. Patients with and without implant failure were divided into failure and control groups, respectively. The demographic information, femoral head Hounsfield unit (HU) value, the reduction quality, status of posteromedial support and position of the screw/blade were collected and compared. The logistic regression analyses were performed to evaluate risk factors of implant failure in intertrochanteric fractures after intramedullary nail fixation.

Results

Of the patients, 15 (9.38%) suffered from implant failure after intramedullary fixation. The mean HU value of femoral head was much lower in the failure group than the control group (133.25 ± 34.10 vs. 166.12 ± 42.68, p = 0.004). And the univariate analyses showed that A3 fracture and poor reduction quality were associated with implant failure (p < 0.05). After adjustment for confounding variables, the multivariable logistic regression analyzes showed that femoral head HU value (odds ratio [OR], 0.972; 95% CI, 0.952-0.993; p = 0.008) and poor reduction quality (OR, 7.614; 95% CI, 1.390-41.717; p = 0.019) were independent influencing factors for implant failure.

Conclusion

The femoral head HU value was significantly correlated with the incidence of implant failure and can be used as an independent factor to predict implant failure for intertrochanteric fractures after intramedullary fixation.

Deep Learning Classification of Spinal Osteoporotic Compression Fractures on Radiographs using an Adaptation of the Genant Semiquantitative Criteria

RATIONALE AND OBJECTIVES

Osteoporosis affects 9% of individuals over 50 in the United States and 200 million women globally. Spinal osteoporotic compression fractures (OCFs), an osteoporosis biomarker, are often incidental and under-reported. Accurate automated opportunistic OCF screening can increase the diagnosis rate and ensure adequate treatment. We aimed to develop a deep learning classifier for OCFs, a critical component of our future automated opportunistic screening tool.

MATERIALS AND METHODS

The dataset from the Osteoporotic Fractures in Men Study comprised 4461 subjects and 15,524 spine radiographs. This dataset was split by subject: 76.5% training, 8.5% validation, and 15% testing. From the radiographs, 100,409 vertebral bodies were extracted, each assigned one of two labels adapted from the Genant semiquantitative system: moderate to severe fracture vs. normal/trace/mild fracture. GoogLeNet, a deep learning model, was trained to classify the vertebral bodies. The classification threshold on the predicted probability of OCF outputted by GoogLeNet was set to prioritize the positive predictive value (PPV) while balancing it with the sensitivity. Vertebral bodies with the top 0.75% predicted probabilities were classified as moderate to severe fracture.

RESULTS

Our model yielded a sensitivity of 59.8%, a PPV of 91.2%, and an F1 score of 0.72. The areas under the receiver operating characteristic curve (AUC-ROC) and the precision-recall curve were 0.99 and 0.82, respectively.

CONCLUSION

Our model classified vertebral bodies with an AUC-ROC of 0.99, providing a critical component for our future automated opportunistic screening tool. This could lead to earlier detection and treatment of OCFs.

Osteoporosis as a Risk Factor for Intraoperative Complications and Long-term Instrumentation Failure in Patients With Scoliotic Spinal Deformity

STUDY DESIGN

A retrospective review study.

OBJECTIVE

This study aims to determine the effect of osteoporosis on spine instrumentation.

SUMMARY OF BACKGROUND DATA

Osteoporosis is a common skeletal pathology that affects systemic cortical bone maintenance and remodeling. This disease accelerates the degeneration of the spine, often necessitating spinal surgery for progressive vertebral deformity, pathologic fracture, bony canal stenosis, and/or neural element decompression. There is a paucity of literature describing the role of osteoporosis as it relates to both perioperative complications and outcomes after spine fusion surgery.

MATERIALS AND METHODS

A retrospective review was conducted of a prospectively maintained database for patients undergoing spine surgery between January 1, 2006 and October 3, 2017. Inclusion criteria included age 18 years and above and surgery performed for the correction of thoracolumbar scoliosis. Data collected included various demographic, clinical, and operative variables.

RESULTS

A total of 532 patients met inclusion criteria, including 144 (27%) patients with a diagnosis of osteoporosis. Osteoporosis was significantly associated with increased blood volume loss (P=0.003). Postoperatively, osteoporosis was associated with increased rates of instrumentation failure (19% vs. 10%; P=0.008) and the need for revision surgery (33% vs. 16%; P<0.001). Multivariate analysis confirmed osteoporosis to be an independent risk factor for increased mean number of spinal segments fused (P<0.05), mean blood volume loss (P<0.05), rate of postoperative deep venous thrombosis/pulmonary embolism (P<0.05), rate of instrumentation failure (P<0.05), and need for revision surgery (P<0.05).

CONCLUSION

Osteoporosis is a significant risk factor for instrumentation failure and need for revision surgery following arthrodesis for scoliosis correction. Furthermore, patients with osteoporosis have a significantly higher risk of intraoperative blood volume loss and postoperative thromboembolic events.

Hounsfield unit for assessing asymmetrical loss of vertebral bone mineral density and its correlation with curve severity in adolescent idiopathic scoliosis

Background

Low bone mass concomitantly occurs in patients with adolescent idiopathic scoliosis (AIS) and can persist until skeletal maturity. The purpose of this study was to assess the asymmetrical loss of vertebral bone mineral density (vBMD) and its correlation with curve severity in patients with AIS using Hounsfield unit (HU) values measured from computed tomography scans.

Methods

A total of 93 AIS patients were retrospectively recruited. The HU values of the vertebral body (VB-HU) and pedicle screw trajectory (PST-HU) were measured from four vertebrae above (Apex − 4) to four below (Apex + 4) the apical vertebra (Apex) of the major curve. The VB-HU and PST-HU at the upper end vertebra, Apex, and lower end vertebra within the concave and convex sides of the major and minor curves and stable vertebrae were obtained.

Results

A significant correlation was found between the Cobb angle and VB-HU at the periapical levels of the major curve. VB-HU and PST-HU at periapical levels were significantly greater within the concavity than the convexity of both major and minor curves. The asymmetric ratios of VB-HU and PST-HU were significantly correlated with the major curve Cobb angle, peaked at the apex, and gradually diminished from the apex to the end vertebrae. The asymmetrical loss of vBMD aggravated with the progression of curve severity, presenting as VB-HU, significantly decreased within the convexity and insignificantly decreased within the concavity of the major curve.

Conclusion

The asymmetrical loss of vBMD was associated with the progression of curve severity in AIS. For patients with severe AIS, the distraction of the pedicle screws at the concave side should be a priority in correcting the major curve, and supplemental anchors and larger-sized screws should be placed within the convex side around the apex of the major curve to reduce the risk of screw loosening after surgery.

Rethinking the 10% strain rule in fracture healing: A distal femur fracture case series

Since the 1970s, the 2%-10% rule has been used to describe the range of interfragmentary gap closure strains that are conducive for secondary bone healing. Interpreting the available evidence for the association between strain and bone healing remains challenging because interfragmentary strain is impossible to directly measure in vivo. The question of how much strain occurs within and around the fracture gap is also difficult to resolve using bench tests with osteotomy models because these do not reflect the complexity of injury patterns seen in the clinic. To account for these challenges, we used finite element modeling to assess the three-dimensional interfragmentary strain in a case series of naturally occurring distal femur fractures treated with lateral plating under load conditions representative of the early postoperative period. Preoperative computed tomography scans were used to construct patient-specific finite element models and plate fixation constructs to match the operative management of each patient. The simulations showed that gap strains were within 2%-10% only for the lowest load application level, 20% static body weight (BW). Moderate loading of 60% static BW and above caused gap strains that far exceeded 10%, but in all cases, strains in the periosteal region external to the fracture line remained low. Comparing these findings with postoperative radiographs suggests that in vivo secondary healing of distal femur fractures may be robust to early gap strains much greater than 10% because formation of new bone is initiated outside the gap where strains are lower, followed by later consolidation within the gap.

Effect of degeneration on bone mineral density, trabecular bone score and CT Hounsfield unit measurements in a spine surgery patient population

This study investigated the impact of spinal degeneration on bone mineral density (BMD), trabecular bone score (TBS), and CT Hounsfield units in an at-risk population. We found that BMD was increased by degeneration, whereas TBS and HU were unaffected. These findings support that TBS is not adversely affected by spinal degeneration.

INTRODUCTION

This study evaluated the impact of spinal degeneration on BMD and TBS measured by dual-energy x-ray absorptiometry (DXA) and on CT HU in a spine surgery patient population.

METHODS

A retrospective study of 63 patients referred for consideration of spine surgery or with history of spine surgery was performed. Patients were included if a DXA scan and a CT containing the lumbar spine were obtained within 18 months of each other. DXA data were collected and analyzed by vertebral level. Individual vertebrae were assessed for degenerative changes by qualitative evaluation of the anterior and posterior elements using CT. Degeneration scores were compared to BMD T-scores, TBS and CT HU at individual vertebral levels L1-4, and after applying International Society for Clinical Densitometry (ISCD) criteria for excluding vertebrae from diagnostic consideration.

RESULTS

Mean patient age and BMI were 67.2 years and 27.8 kg/m², respectively; 79.4% were female. Mean (SD) lowest T-scores of the hip, spine, and lowest overall T-score were - 1.3 (1.4), - 1.7 (0.9), and - 1.9 (1.0), respectively. Osteoporosis was present by T-score in 38% and osteopenia in 52%; 10% had a history of osteoporotic fracture. The mean degeneration score of individual vertebrae was 4.1 on a 0-6 scale. T-score correlated moderately with degeneration score (Spearman's rho 0.484, p < 0.001), whereas TBS and HU were unrelated. ISCD excluded vertebrae had a higher degeneration score than included vertebrae (p =  < 0.001).

CONCLUSIONS

In a spine surgery population, TBS and CT HU values are unrelated to degeneration score and thus appear unaffected by lumbar vertebral degenerative changes. Additionally, these data support the ISCD criteria for vertebral exclusion.

A Pilot Study to Assess Opportunistic Use of CT-Scan for Osteoporosis Screening in Chronic Pancreatitis

Objectives: CT scans are commonly performed in patients with chronic pancreatitis (CP). Osteopathy and fractures are recognized in CP but no osteoporosis screening guidelines are recommended. "Opportunistic" CT scan-derived bone density thresholds are assessed for identifying osteoporosis in CP. Methods: Retrospective pilot cohort study. CP subjects who had CT scans and dual-energy x-ray absorptiometry (DXA) within 1 year were included. CT-derived bone density was measured at the L1 level. Pearson's correlation was performed between age and CT-derived bone density in Hounsfield unit (HU). Univariate analysis using HU to identify osteoporosis was performed at various thresholds of bone density. The discriminatory ability of the model was evaluated with the area under the receiver operating characteristic (ROC) curve (AUC). Several HU thresholds were tested. Results: Twenty-seven CP subjects were included, of whom 11 had normal bone density, 12 osteopenia, and four osteoporosis on DXA. The mean age was 59.9 years (SD 13.0). There was a negative correlation of age with HU (r = -0.519, p = 0.006). CT-derived bone density predicted DXA-based osteoporosis in the univariable analysis (Odds Ratio (OR) = 0.97 95% Confidence Interval (CI) 0.94-1.00, p = 0.03). HU thresholds were tested. A threshold of 106 HU maximized the accuracy (AUC of 0.870). Conclusions: CT scan may be repurposed for "opportunistic" screening to rule out osteoporosis in CP. A larger study is warranted to confirm these results.

Low Hounsfield units on computed tomography are associated with cage subsidence following oblique lumbar interbody fusion (OLIF)

BACKGROUND CONTEXT

Cage subsidence is one of the most common complications following lumbar interbody fusion surgery. Low bone mineral density (BMD) is an important risk factor that contributes to cage subsidence. Hounsfield units (HU) obtained from clinical computed tomography (CT) scans provided a reliable method for determining regional BMD. The association between HU and cage subsidence following oblique lumbar interbody fusion (OLIF) remains unclear.

PURPOSE

The objective of this study is to evaluate the association between vertebral HU value and cage subsidence following OLIF.

STUDY DESIGN/SETTING

A retrospective study.

PATIENT SAMPLE

Adults with degenerative spinal conditions underwent single-level OLIF at our institution from October 2017 and August 2020 OUTCOME MEASURES: Cage subsidence, disc height, vertebral body global HU value, upper and lower instrumented vertebrae HU value, endplate HU value, fusion rate.

METHODS

This retrospective study was conducted on patients who underwent single-level OLIF at one institution between October 2017 and August 2020. Cage subsidence was measured using the CT scan postoperatively based on the cage protrusion through the vertebral endplates. The HU values were measured from preoperative CT according to previously reported methods.

RESULTS

A total of 70 patients with a mean follow-up of 15.4 months were included in the analysis. The subsidence rate was 25.7% (n=18/70). The average cage subsidence was 2.2 mm, with a range of 0-7.7 mm. No significant difference was found in age, sex, or body mass index (BMI) between the two groups. The mean global HU value of the lumbar vertebral body (L1-5) was 142.7±30.1 in nonsubsidence and 103.7±11.5 in subsidence (p=.004). The upper instrumented vertebrae (UIV) HU value was 141.4±29.7 in the nonsubsidence and 101.1±10.2 in subsidence, (p=.005). The lower instrumented vertebrae (LIV) HU value was 147.4±34.9 in nonsubsidence and 108.1±13.7 in subsidence, (p<.001). The AUC of the UIV HU value was 0.917 (95% CI: 0.853-0.981), and the most appropriate threshold of the HU value was 115 (sensitivity: 84.6%, specificity: 100%). The AUC of the LIV HU value was 0.893 (95%CI: 0.819-0.966), and the most appropriate threshold of the HU value was 125 (sensitivity: 76.9%, specificity: 100%). The mean upper endplate HU value was 235.4±50.9, and the mean lower endplate HU value was 193.4±40.3. No significant difference (upper endplate p=.314, lower endplate p=.189) was observed between the two groups.

CONSLUSIONS

Lower preoperative vertebral body HU values were associated with cage subsidence after single-level OLIF. However, the endplate HU values were not associated with cage subsidence. Preoperative HU measurement is useful in the prediction of the cage subsidence.

Paraspinal muscle characteristics on MRI in degenerative lumbar spine with normal bone density, osteopenia and osteoporosis: a case-control study

Background

To investigate the difference of paraspinal muscles in patients with normal bone density, osteopenia and osteoporosis.

Methods

Patients undergoing surgery for lumbar spinal stenosis were included. Thirty-eight patients with osteoporosis were matched to patients with osteopenia and patients with normal bone density in a 1:1 manner according to WHO criteria. Dual-energy X-ray absorptiometry (DXA) scans and lumbar CT were performed preoperatively to measure the BMD of lumbar, femur and hip and HU values of L1-L4 respectively. The relative total cross-sectional area (rTCSA) and fat infiltration (FI) of multifidus (MF) and erector spinae (ES), and the relative functional CSA (rFCSA) of psoas major (PS) were measured at L4–5 and L5-S level on preoperative MRI.

Results

Osteoporotic patients showed lower BMI, higher MF FI and higher ES FI when compared with normal bone density group (25.57 ± 3.71 vs 27.46 ± 3.11; 0.38 ± 0.1 vs 0.32 ± 0.08; 0.33 ± 0.1 vs 0.28 ± 0.08; all adjusted p < 0.05). Both the MF FI and ES FI were significantly correlated with lumbar T-score (r = − 0.223, p < 0.05; r = − 0.208, p < 0.05) and the averaged lumbar HU value (r = − 0.305, p < 0.01; r = − 0.239, p < 0.05).

Conclusions

Osteoporosis and paraspinal muscle degeneration might interact with each other and coexist in patients with degenerative lumbar diseases. It is recommended that the paraspinal muscle degeneration should be considered simultaneously when finding a patient with low bone mass before surgery.

Does Total Hip Arthroplasty Influence the Development and Localization of Sacral Insufficiency Fractures?

BACKGROUND

Sacral insufficiency fractures (SIFs) are fractures related to reduced bone strength. In a previous study, we noticed that many patients with SIF had undergone total hip arthroplasty (THA). Therefore, the purpose of the present study was to research the localization of clinically apparent SIFs in relation to unilateral THA as well as the influence of unilateral THA on bone mineral density changes in the sacrum.

METHODS

In this retrospective study, 171 patients with SIFs were screened for unilateral THA. In the group of patients with SIF and THA, the rate of SIF ipsilateral and contralateral to the side of the THA was determined. In a second cohort of 39 THA patients with healthy bone, changes in bone mineral density at the sacral alae ipsilateral and contralateral to the THA were analyzed by use of computed tomography immediately postoperatively and at the 1-year follow-up.

RESULTS

Of the 171 patients with SIF, 50 (40 female; mean age, 79 years; range, 54 to 101 years) were previously treated with THA. Of the 50, 31 patients were treated with unilateral THA. The proportion of patients with an SIF contralateral to the THA was 42% (13 of 31) and ipsilateral to the THA was 19% (6 of 31). Twelve patients had bilateral SIFs. The mean age of the THA group without SIF was 62 years (range, 49 to 79 years); 17 were female. The median bone mineral density decreased significantly (p = 0.023), from 35.0 to 13.0 HU, at the sacral ala contralateral to the THA, whereas the decrease of ipsilateral bone mineral density, from 24.0 to 17.0 HU, was not significant (p = 0.361).

CONCLUSIONS

The proportion of patients with an SIF contralateral to a THA was twice as high as that of patients with an SIF ipsilateral to a THA. These findings are supported by the second cohort's decrease in bone mineral density at the sacral ala contralateral to the THA at 1 year after surgery. We conclude that THA can lead to spatially different remodeling of the sacrum, possibly affecting the development of SIFs.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Age estimation based on computed tomography exploration: a combined method

Despite an extensive number of existing methods, age estimation of human remains is still an unsolved matter in the field of forensic anthropology, especially when it comes to mature adults. The specific aim of this work was to propose a combined method for age estimation, for forensic purposes, by coupling the Suchey-Brooks method and the measure of the pubic bone density. For this purpose, we used an independent test sample comprising 339 CT scans of living individuals aged 15 to 99 years old. Measurement of bone density and staging according to the Suchey-Brooks phases were performed, followed by estimation of ages based on a combined method and an existing virtual reference sample. Results highlighted a significant negative correlation between bone density and age. Good accuracy was obtained for the measurement of pubic bone density for age estimation of men and women, especially concerning mature adults, with an absolute error ranging from 9 to 16 years for all individuals. The authors propose a practical combined method consisting of, first, allocating phases according to the scannographic approach of the Suchey-Brooks method. For phases I to IV, the age estimation is given using the Suchey-Brooks method. For phases V to VI, the pubic bone density measurement is used. Further study will be needed to assess the reproducibility of these results on cadavers and dry bones, as the post-mortem process could interfere with the measurement of mineral bone density.

Lower Hounsfield Units at the Upper Instrumented Vertebrae are Significantly Associated With Proximal Junctional Kyphosis and Failure Near the Thoracolumbar Junction

BACKGROUND

Low bone mineral density (BMD) on dual energy x-ray absorptiometry (DXA) is likely a risk factor for proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). However, prior instrumentation and degenerative changes can preclude a lumbar BMD measurement. Hounsfield units (HU) represent an alternative method to estimate BMD via targeted measurements at the intended operative levels.

OBJECTIVE

To determine if patients with lower HU at the upper instrumented vertebrae (UIV) and vertebral body superior to the UIV (UIV + 1) are at greater risk for PJK and PJF.

METHODS

A retrospective chart review identified patients at least 50 yr of age who underwent instrumented lumbar fusion with pelvic fixation, a UIV from T10 to L2, and a preoperative computed tomography (CT) encompassing the UIV. HU were measured at the UIV, UIV + 1, and the L3-L4 vertebral bodies.

RESULTS

A total of 150 patients (80 women and 70 men) were included with an average age of 66 yr and average follow-up of 32 mo. Multivariable logistic regression analysis with an area under the curve (AUC) of 0.89 demonstrated HU at the UIV/UIV + 1 as the only independent predictor of PJK/PJF with an odds ratio of 0.94 (P-value = .031) for a change in a single HU. Patients with HU at UIV/UIV + 1 of <110 (n = 35), 110 to 160 (n = 73), and >160 (n = 42) had a rate of PJK/PJF of 63%, 27%, and 12%, respectively (P-value < .001).

CONCLUSION

Patients with lower HU at the UIV and UIV + 1 were significantly associated with PJK and PJF, with an optimal cutoff of 122 HU that maximizes sensitivity and specificity.

Assessment of Skeletal Strength: Bone Density Testing and Beyond

A bone fractures when a force applied to it exceeds its strength. Assessment of bone strength is an important component in determining the risk of fracture and guiding treatment decisions. Dual-energy X-ray absorptiometry is used to diagnosis osteoporosis, estimate fracture risk, and monitor changes in bone density. Fracture risk algorithms provide enhanced fracture risk predictability. Advanced technologies with computed tomography (CT) and MRI can measure parameters of bone microarchitecture. Mathematical modeling using CT data can evaluate the behavior of bone structures in response to external loading. Microindentation techniques directly measure the strength of outer bone cortex.

High resolution 3D structures of mineralized tissues in health and disease

A thorough knowledge of the structures of healthy mineralized tissues, such as bone or cartilage, is key to understanding the pathological changes occurring during disease. Such knowledge enables the underlying mechanisms that are responsible for pathology to be pinpointed. One high-resolution 3D method in particular - focused ion beam-scanning electron microscopy (FIB-SEM) - has fundamentally changed our understanding of healthy vertebrate mineralized tissues. FIB-SEM can be used to study demineralized matrix, the hydrated components of tissue (including cells) using cryo-fixation and even untreated mineralized tissue. The latter requires minimal sample preparation, making it possible to study enough samples to carry out studies capable of detecting statistically significant differences - a pre-requisite for the study of pathological tissues. Here, we present an imaging and characterization strategy for tissue structures at different length scales, describe new insights obtained on healthy mineralized tissues using FIB-SEM, and suggest future research directions for both healthy and diseased mineralized tissues.

Opportunistic use of dual-energy X-ray absorptiometry to evaluate lumbar scoliosis

Low bone mineral density is associated with spinal deformity. Dual-energy X-ray absorptiometry (DXA), a modality that assesses bone density, portends a theoretical means to also assess spinal deformity. We found that DXA can reliably assess spine alignment. DXA may permit surveillance of spine alignment, i.e., scoliosis in the clinical setting.

PURPOSE

Osteoporosis and scoliosis are interrelated disease processes. Dual-energy X-ray absorptiometry (DXA), used to assess bone density, can also be used to evaluate spinal deformity since it captures a posteroanterior (PA) image of the lumbar spine. We assessed the use of DXA to evaluate lumbar spine alignment.

METHODS

A lumbar spine DXA phantom was used to assess the effects of axial and sagittal plane rotation on lumbar bone mineral content (BMC), density (BMD), and L1-L4 Cobb angle measurements. Using two subject cohorts, intra- and inter-observer reliability and validity of using DXA for L1-L4 Cobb angle measurements in the coronal and sagittal planes were assessed.

RESULTS

Axial and sagittal plane rotation greater than 15° and 10°, respectively, significantly reduced measured BMD and BMC; there was minimal effect on Cobb angle measurement reliability. In human subjects, excellent intra- and inter-observer reliability was observed using lumbar PA DXA images for Cobb angle measurements. Agreement between Cobb angles derived from lumbar PA DXA images and AP lumbar radiographs ranged from good to excellent. The mean difference in Cobb angles between supine lumbar PA DXA images and upright AP lumbar radiographs was 2.8° in all subjects and 5.8° in those with scoliosis.

CONCLUSIONS

Lumbar spine rotation does not significantly affect BMD and BMC within 15° and 10° of axial and sagittal plane rotation, respectively, and minimally affects Cobb angle measurement. Spine alignment in the coronal plane can be reliably assessed using lumbar PA DXA images.

Preoperative Hounsfield Units at the Planned Upper Instrumented Vertebrae May Predict Proximal Junctional Kyphosis in Adult Spinal Deformity

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate the association between Hounsfield units (HU) measured at the planned upper instrumented vertebra (UIV) and UIV+1 and proximal junctional kyphosis (PJK) in patients with adult spinal deformity (ASD).

SUMMARY OF BACKGROUND DATA

PJK is a common complication following surgery for ASD and poor bone quality is noted to be one of the risk factors. HUs from standard computed tomography (CT) scans can be used for evaluating regional bone quality.

METHODS

Sixty-three patients were included from a single institution. The demographic characteristics and radiographic parameters were recorded. Local vertebral HUs at the planned UIV and UIV+ 1 were measured using preoperative CT scans. The patients were divided into three groups: no PJK, non-bony PJK, and bony PJK. The risk factors between the three groups and the correlation between the mean HU and increase in the PJK angle were analyzed.

RESULTS

The incidence of PJK was 36.5%. The mean HU was significantly lower in the bony PJK group (HU: 109.0) than in the no PJK group (HU: 168.7, P = 0.038), and the mean HU in the non-bony PJK group (HU: 141.7) was not different compared to the other two groups. There was a significant negative correlation between the mean HU values and the increase in the PJK angles (r = -0.475, P < 0.01). The cutoff value for the mean HU used to predict bony PJK was 120 and a HU value less than 120 was a significant risk factor for bony PJK (OR: 5.74, 95% CI [1.01-32.54], P = 0.04).

CONCLUSIONS

We noted a significant inverse relationship between the mean HUs at the UIV and UIV+ 1 and increase in the PJK angles postoperatively. In ASD patients, the HUs may be used preoperatively to identify patients with a higher risk of bony PJK.Level of Evidence: 3.

Computed Tomography Evaluation of Forearm and Hand Muscles in Patients With Distal Radius Fracture

INTRODUCTION

Computed tomography (CT) can be used to assess bone status with measurement of Hounsfield unit (HU). The objective of this study was to evaluate whether HU of muscle might be associated with parameters of bone and muscle status.

METHODS

We reviewed 71 women aged over 50 yr of age who had distal radius fracture and underwent CT evaluation of affected wrist. We assessed HUs of forearm flexor muscles (flexor digitorum superficialis) and thenar muscles and bone HUs at the capitate and the ulnar head. Other parameters included femur neck and lumbar bone mineral density (BMD), upper extremity lean mass, hand grip strength, and muscle fiber cross-sectional area. We performed correlation analyses to determine associations between variables.

RESULTS

Thenar and forearm muscle HUs were significantly correlated with each other, but not with other parameters. HUs of the capitate and ulnar head were positively correlated with femur neck and lumbar BMDs and inversely correlated with age. Ulnar head HU was positively correlated hand grip strength.

CONCLUSIONS

HUs of forearm and thenar muscles did not show significant correlations with bone or muscle parameters, although bone HUs correlated well with bone mineral densities. These results support the opportunistic use of CT for evaluating bone fragility. Clinical usefulness of muscle HU measurement needs further studies.

Association between forearm cortical bone properties and handgrip strength in women with distal radius fractures: A cross-sectional study

OBJECTIVES

Mechanical and biochemical bone properties are influenced by muscles. However, the muscle-bone interaction has not been fully elucidated regarding the upper extremities. The objective of the present study was to evaluate the mechanical muscle-bone interaction at the forearm by evaluating the relationship between the properties of three-dimensional (3D) forearm cortical bone models derived from conventional computed tomography (CT) images and handgrip strength (HGS).

METHODS

A total of 108 women (mean age, 75.2 ± 9.4 years; range, 62-101 years) with a distal radius fracture who took conventional CT scans for the assessment of the fracture were included in this study. Distal radius 3D models were reconstructed and the average cortical bone density (Cd) and thickness (Ct) of the region of interest (ROI), which might be affected by the forearm flexor muscles, were calculated using a 3D modeling software. Clinical parameters including HGS, lumbar and hip bone mineral densities (BMDs), and other demographic factors were also obtained. A multivariate linear regression analysis was performed to identify relevant factors associated with HGS.

RESULTS

HGS was found to be independently associated with height and Cd, but no significant difference was found between HGS and Ct, age, weight, as well as lumber and hip BMDs.

CONCLUSIONS

Cortical bone density might be associated with HGS, which is generated by the forearm flexor muscles. Hence, the mechanical muscle-bone interaction in the upper extremities could be supported by the present study.

Association of Perioperative Computed Tomography Hounsfield Units and Failure of Femoral Neck Fracture Fixation

OBJECTIVES

To determine whether Hounsfield units (HUs) measured on perioperative computed tomographic scans are associated with radiographic outcomes and reoperations after femoral neck fracture fixation.

DESIGN

Retrospective cohort study.

SETTING

Level I trauma center.

PATIENTS

One hundred fourteen patients age ≥18 years, who presented to a Level I trauma center, and who underwent surgical fixation of intracapsular femoral neck fracture and had perioperative computed tomographic scans and adequate follow-up.

INTERVENTION

None.

MAIN OUTCOME MEASUREMENTS

Screw penetration, femoral neck shortening >5 mm, and revision surgery.

RESULTS

A median follow-up was 23 months. An HU measurement of the femoral head was significantly associated with screw penetration and femoral neck shortening but not revision surgery. Patients with middle femoral head HU measurements <146 had 17 times (95% confidence interval: 4.32-78.9, P < 0.001) increased odds of screw penetration. Greater than 5 mm shortening was seen in patients with HUs <212.5 in the low head section by an odds ratio of 7.8 (95% confidence interval: 2.15-33.0, P = 0.014).

CONCLUSION

Outcome differences regarding screw penetration and femoral neck shortening related to the HU or densities of femoral head and neck at the time of fracture are significant. These findings can help the clinician with developing a treatment plan for either arthroplasty or fixation of a femoral neck fracture based on objective bone quality measurements rather than relying on an arbitrary age recommendation.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Ten-year fracture risk predicted by proximal femur Hounsfield units

Colon cancer screening occurs at younger ages than osteoporosis screening. Bone density measurements using virtual colonoscopy performed for colon cancer screening can provide an early warning sign of patients at potential risk for osteoporosis-related fractures. Earlier identification may improve treatment and potentially fracture prevention.

INTRODUCTION

Opportunistic osteoporosis screening with computed tomography colonography (CTC) offers an opportunity to capitalize on earlier colorectal cancer screening to identify patients at risk of future fractures. The purpose of this study is to evaluate 10-year fracture and specifically hip fracture risk based on Hounsfield units (HU) obtained from CTC.

METHODS

We identified all CTC scans between 2004 and 2007 of patients 40 years and older with 10 years minimum follow-up. Hounsfield units were measured within the proximal femur and fractures identified via worldwide military records. Patients were stratified into two cohorts based on the presence or lack of a fracture in the wrist, spine, hip, or proximal humerus. Hounsfield unit measurements were compared between groups using Student's t test and the HU threshold was calculated that best approximated an 80% sensitivity to optimally screen patients for fracture risk. The odds ratio, negative predictive value, 10-year incidence of fracture, and survival curves were calculated.

RESULTS

We identified 3711 patients with 183 fractures over 10 years. The HU threshold that corresponded with an 80% sensitivity to identify fractures was 112 HU. The negative predictive value (NPV) for overall fractures and hip fractures was over 97%. The 10-year fracture incidence was higher in patients below 112 HU compared to those above for both overall fractures (6.3% vs 1.7%) and hip fractures (2.7% vs 0.07%). The 112 HU threshold corresponds with an odds ratio for overall fracture and hip fractures of 2.5 (95% confidence interval (CI), 1.7-3.6) and 24.5 (95% CI, 3.3-175.5), respectively.

CONCLUSION

In the 10 years following CTC, patients who experienced a fracture had lower hip HU. Decreasing HU on CTC may be an early warning sign of fracture potential.

Using opportunistic screening with abdominal CT to identify osteoporosis and osteopenia in patients with diabetes

Opportunistic osteoporosis screening involves measuring the attenuation of L1 vertebrae on abdominal computed tomography (CT), which correlates with DXA T-score. We found that this approach is useful for detecting low bone mass in patients with diabetes and propose L1 attenuation ≤ 135 Hounsfield units (HU) as a threshold for which DXA should be strongly considered.

INTRODUCTION

Attenuation of the L1 vertebrae on computer tomography (CT) images done for other reasons ("Opportunistic Osteoporosis Screening") has been found to correlate well with DXA-derived T-score. However, the method and the thresholds have never been tested specifically in those with diabetes mellitus (DM), in whom the fracture risk is greater than explained by BMD.

METHODS

In a retrospective study of subjects with DM who had both abdominal CT and DXA within 6 months of each other, we compared L1 attenuation and DXA T-score to define the sensitivity and specificity of thresholds previously established in the general population.

RESULTS

There were 313 subjects among whom 18 (5.8%) had prior major osteoporotic fracture (MOF). Subjects with MOF had lower T-scores (- 2.3 ± 1.4 vs. - 0.9 ± 1.4, p < 0.001) and L1 attenuation (104 HU ± 46 vs. 149 HU ± 47, p < 0.001) than non-fracture subjects. L1 attenuation ≤ 160 HU was 91% sensitive for osteoporosis, while ≤ 110 HU was 80% specific. For a higher T-score of ≤ - 1.5, L1 attenuation ≤ 135 HU showed balanced sensitivity and specificity (65% and 69%, respectively).

CONCLUSION

Opportunistic osteoporosis screening with abdominal CT is useful in determining the need for DXA screening in subjects with diabetes. We propose L1 attenuation ≤ 135 HU as a reasonable threshold for detecting the T-score of ≤ - 1.5, which is likely associated with increased fragility in DM.

Opportunistic Computed Tomography and Spine Surgery: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVE

This article seeks to provide a narrative review regarding the ability of opportunistic information available from computed tomography (CT) scans to guide decisions in spine surgery related to patient bone quality.

METHODS

A review of the literature (limited to human and English language) was performed via PubMed and Google Scholar using the search terms; "osteoporosis" AND "opportunistic" AND "computed tomography" AND "spine surgery." The titles and then abstracts of all identified citations were reviewed for inclusion by 2 of the authors (MS, BAF). Relevant articles were then studied in full text.

RESULTS

A review of the literature found 25 articles that were selected for inclusion in this narrative review. These articles were broadly divided into 4 subcategories: (1) opportunistic CT (oCT) and osteoporosis detection, (2) oCT data and the quality of screw fixation, (3) utilization of Hounsfield units to assess clinical and/or radiographic outcomes following spine fusion, and (4) virtual stress testing in spine surgery.

CONCLUSION

The literature on oCT, as well as associated virtual stress-testing techniques, demonstrate the potential to enhance spine surgery outcomes by preoperatively identifying at-risk patients in need of bone health optimization and informing best techniques for performing spinal fusion surgery on patients with diminished bone quality. While our narrative summary of the limited literature to date suggests a promising future for oCT data, significant additional research and/or radiographic workflow standardization is needed to validate these methods for clinical use.