[Hounsfield units as a measure of bone density-applications in spine surgery]

Rod persuading reduces primary construct stability in lumbar interbody fusion in the osteoporotic spine - A biomechanical in-vitro study

BACKGROUND

With the introduction of the pedicle screw-rod system and intervertebral cages, posterior spinal fusion has increasingly become a standard procedure in the treatment of degenerative spinal conditions. The aim of this study is to investigate the influence of rod persuading in lumbar spinal fusion constructs on the pullout strength of pedicle screws, considering different bone qualities.

METHODS

Ten fresh-frozen lumbar spines (L1-5) from 10 cadaveric donors were initially included. All specimens were examined at the beginning of the study both macroscopically and by computed tomography scans (HR-CT, Siemens) to ensure specimen integrity, and the mineral bone density by using Hounsfield units. One specimen had to be excluded prior to biomechanical testing due to a vertebral fracture extending into the pedicle, leaving a total of 9 specimens available for the study.

FINDINGS

The displacement of the screws during the pullout test was significantly greater in the osteoporotic specimens after rod persuader use (Group 2), compared to the non-osteoporotic specimens (3.7 ± 0.7 mm vs. 5.5 ± 0.4 mm, p = 0.0486). This difference was not observed in the non-rod persuader group. Overall, rod persuading decreased the displacement distance until tensile load to screw failure by 29 %.

INTERPRETATION

The use of the rod persuader reduces the pedicle screw pullout strength, thereby compromising the construct stability. This reduction is particularly significant in osteoporotic vertebral bodies, highlighting the need for careful consideration of rod persuader use in this patient population.

[Diagnostics and classification of fractures of the thoracic and lumbar spine in adults : Approach depending on the bone structure]

BACKGROUND

The epidemiology, treatment and prognosis of thoracolumbar vertebral fractures are fundamentally influenced by the bone quality of the patient. In individuals with healthy bone structure, a high-energy trauma is typically required to cause a fracture. In contrast, osteoporosis can cause fractures and also be present as a comorbid pathology in traumatic fractures. Comprehensive diagnostics and a precise classification are essential for appropriate treatment.

MATERIAL AND METHOD

This narrative review outlines the diagnostic approach and classification of thoracolumbar vertebral fractures depending on the bone quality as the basis of treatment.

RESULTS

In addition to a physical examination, conventional radiographs with the patient in a standing position and computed tomography (CT) scans of the affected region serve as the foundation for fracture classification. Supplementary magnetic resonance imaging (MRI) primarily assesses discoligamentous and neurological structures of the spine as well as the age of the fracture. In suspected cases of osteoporotic fractures, a short-tau inversion recovery (STIR) sequence of the entire thoracic and lumbar spine is recommended for reliable detection of bone marrow edema. For patients with healthy bone structure, the AO Spine classification is used, whereas the osteoporotic fracture (OF) classification and the OF score are applied in cases of osteoporosis.

Opportunistic Osteoporosis Assessment and Fracture Risk Determination Using Cancellous Density Measurement in Hounsfield Units of Native Lumbar Computed Tomography Images-A Comparative Study with Conventional Bone Density Evaluation

Background/Objectives: Osteoporosis is a global problem that will increase as the population increases and ages, requiring prevention, early detection, and appropriate treatment. An increasing loss in bone mineral density (BMD) is the hallmark of osteoporosis, leading to an increased risk for insufficiency fractures. We aimed to investigate and analyze the applicability of native lumbar spine computed tomography (CT) scans for the evaluation of bone density compared with standard bone density measurements with quantitative computed tomography (QCT) and computed tomography X-ray absorptiometry of the hip (CTXA). Methods: Patients who were referred to our institution for diagnostic investigations and underwent CT imaging of the lumbar spine, as well as standard osteoporosis assessments including QCT and CTXA, were included in the study, resulting in a total of 240 patients (mean age: 65.9 years, range: 24-91). An ANOVA test was used to compare patient groups without a fracture, with one fracture, with more than one fracture, and with additional sacral fractures. An ROC analysis was performed to assess the predictive power of fracture risk estimation considering HU, QCT, and CTXA values. Results: At least one fracture was detected in 42.9% of these patients. For the lumbar spine, the median HU was 89.9 (range 67.9-126.9) and the median BMD was 73.7 (range 57.1-104.2) mg/cm3. With a correlation coefficient of 0.98 (p < 0.001), the HU values obtained from native lumbar CT scans can be calculated using the following formula: BMDspine = 0.84 + (0.81 × HU). With HU values < 80 and a BMD of the lumbar spine < 66 mg/cm3, a significantly increased number of osteoporotic vertebral fractures were found in the mid-thoracic, thoracolumbar, and sacral regions with an effect size of 0.89. In 32 patients (13.3%), additional sacral fractures were found; these patients showed the lowest density values with a median HU value of 31.8 (12.7-58.2). An ROC analysis of HU revealed a 93% sensitivity for the coincidence of a vertebral fracture. There was no significant difference compared with the AUC of QCT (p = 0.395) for concomitant vertebral body fractures. CTXA values also allowed for risk assessment but showed a significantly lower AUC. We found a negative correlation of BMD with age and a positive correlation of BMD with body mass index. Conclusions: Cancellous density measurements in HU values can be effectively converted into quantitative BMD values in mg/cm3, enabling a reliable assessment of osteoporosis severity and fracture risk prediction. Further quantitative density evaluation of the hip does not add value to fracture risk assessment for the axial skeleton. Based on this study's findings, using HU values in native CT of the lumbar spine alone offers a viable, opportunistic approach towards fracture risk evaluation of the spine.

Evaluation of Cancellous Bone Density from C3 to L5 in 11 Body Donors: CT Versus Micro-CT Measurements

Introduction: Comparative studies on Hounsfield units (HU) and bone volume fraction (BVF%) for the demonstration of cancellous bone density in the entire spine and in the various intravertebral regions are rare. The aim of the present study was to determine HU in various segments and sectional planes (sagittal, axial, coronary) of the spine and their description in the context of bone density measurement on micro-CT, as well as the significance of the values for bone loss and fracture risk. Materials/Methods: The spines of 11 body donors were analyzed by means of high-resolution spiral CT and micro-CT. Vertebral deformities were identified on sagittal reformations and classified. Cancellous bone density in the individual vertebrae from C3 to L5, expressed in HU, was measured on CT images (in all 242 vertebral bodies). For this purpose, a manually positioned ROI was established in mid-vertebral cancellous bone in the axial, sagittal, and coronary planes. Using a Jamshidi® needle, we obtained 726 specimens from prepared vertebrae extracted from three quadrants (QI: right-sided edge, QII: central, QIII: left-sided edge) and analyzed these on a micro-CT device (SKYSCAN 1172, RJL Micro & Analytic GmbH, Germany). The study design with multiple measurements was reflected by a General Linear Model Repeated Measures. The model was adjusted to the bone density values of both procedures (HU, BVF%) in the viewed sectional planes and quadrants for 22 vertebrae, with the predictors gender and fracture status, controlled for age and body mass index (BMI). Analysis of variance provided estimations of density values and comparisons of several subgroups. Results: All spines were osteoporotic. Both procedures revealed a significant reduction in cancellous bone density from C3 to L5 (p ≤ 0.018). Gender (p = 0.002) and fracture status (p = 0.001) have an impact on bone density: men have higher bone density values than women; cases with fewer fractures also have higher bone density values. CT revealed both effects (p = 0.002 for each) with greater clarity. HU on CT measurements in the axial plane showed higher density values than in the sagittal or coronary planes. CT measurement profiles along the spine as well as along the individual profiles of the 11 body donors were independent of the measured quadrants, but the micro-CT measurements were not. Discussion: The craniocaudal reduction in bone density was demonstrated in different degrees of clarity by the two procedures. Likewise, the procedure-related visualization of differences in cancellous bone density between genders, fracture groups, sectional planes, and quadrants indicates the need for a better understanding of the advantages of each procedure for patient-oriented approaches to the diagnosis of osteoporosis. Future research should be focused on the determination of standard values and their clinical application for the prevention and treatment of osteoporosis.

The stent-screw assisted internal fixation (SAIF) technique: A treatment option for OF5, the three-column unstable osteoporotic vertebral fractures - A case series

PURPOSE

The OF5 type of vertebral osteoporotic fracture (AO Spine-DGOU classification) represents a three-column lesion and as such is considered as highly unstable. These lesions, however, tend to affect elderly, frail patients, in whom invasive management options are limited. The stent-screw-assisted internal fixation (SAIF) technique has previously been reported as a minimally invasive treatment for osteoporotic and neoplastic vertebral fractures. Here, we sought to assess the safety and efficacy of the SAIF technique in a retrospective series of patients with thoracic OF5-fractures.

METHODS

Retrospective identification, in a prospectively maintained database, of patients with OF5-fractures treated with SAIF. Intra- and post-operative complications were reported. Clinical outcome using NRS pain scale and Patient's Global Impression of Change (PGIC) and radiological outcome, with local kyphotic angle (LKA) and VB height (VBH) correction were analyzed.

RESULTS

N = 22 consecutive patients were identified. All fractures were located in the thoracic spine. No intra-procedural complications occurred, although hospitalization-related complications did occur in 2 patients (9 %). There was a statistically significant pain reduction on follow-up. VBH restoration range was 0-12 mm (mean 5.5 mm). The mean postoperative LKA correction was 7.5°, which was maintained at last follow-up.

CONCLUSION

The SAIF technique appears to be a viable alternative in the management of OF5-fractures. Although it does not address all elements of OF5 instability, it appears that the stabilisation of the anterior and middle vertebral columns, coupled with the stabilising effect of the ribcage in the hypomobile thoracic spine, are biomechanically sufficient to treat OF5-fractures in this section of the spine.

Does Baseline Hounsfield Unit Predict Patients' Outcomes Following Surgical Management of Unstable Osteoporotic Thoracolumbar Fractures?

Background and Objectives: Osteoporotic fractures in the thoracic/lumbar spine pose significant challenges in surgical management, with high risks of complications. This study investigates the role of preoperative CT scans and Hounsfield Units (HUs) in predicting postoperative outcomes. Materials and Methods: A retrospective study was conducted from November 2015 to January 2018. Sixty-one patients over 60 years of age with unstable osteoporotic thoracolumbar spine fractures (OF: 3-4) were included. Preoperative CT scans were performed to measure HU values. Postoperative standing X-rays were taken at 3-12 months to assess signs of loosening, adjacent fractures, or screw dislodgement. HU was divided into quartiles: Q1 (<56.24), Q2 (56.24-72.63), Q3 (72.63-87.59), and Q4 (>87.59). Results: Out of the 61 patients, 14 (23%) exhibited signs of screw loosening, adjacent fractures, or screw dislodgement within 3 to 12 months postoperatively. The mean HU value measured was 65.21, with a range from 21.43 to 140.7. Notably, all patients with observed loosening or dislodgement had HU values below 68. HU significantly predicted mortality, with the second quartile showing a markedly increased risk (adjusted odds ratio [aOR] = 8.12; p = 0.044). However, HU quartiles were not significant predictors of other outcomes. Other factors (fracture level and ASA classification) also influenced clinical outcomes, particularly mortality. Conclusions: HU values from preoperative CT scans are crucial in predicting the risk of screw loosening, dislodgement, and adjacent fractures in osteoporotic spinal fractures. Integrating HU assessment into clinical practice can improve preoperative planning, allowing for more targeted surgical interventions and better clinical outcomes.

[Comparative evaluation of trabecular bone density in Hounsfield units in the lumbar native CT cross-section for osteoporosis diagnosis and fracture risk determination by different examiners]

BACKGROUND

An increasing loss of bone mineral density (BMD) in the axial skeleton leads to osteoporosis and fractures, with an increase found in the thoracic and thoracolumbar regions.

RESEARCH QUESTION

The extent to which an examiner-independent assessment of the extent of osteoporosis and fracture risk determination is possible by determining the trabecular density in Hounsfield units (HU) in the spine should be examined. The next question was whether quantitative BMD values can be calculated from the HU values.

PATIENTS AND METHODS

225 patients (pt.) with an average age of 64.9 ± 13.1 years and a body-mass-index (BMI) of 26.8 ± 6.8 kg/m2, of which 37 were men and 188 were women, were examined to determine whether they had osteoporosis. The BMD was determined in mg/cm3 using quantitative computed tomography (QCT) in the lumbar region. After anonymization by three experienced radiologists, an additional measurement of the trabecular bone density in HU, was carried out in the same vertebral bodies (a total of 675 vertebral bodies), each using a region of interest (ROI) positioned in the midvertebral cancellous space in the sagittal reformed CT image. In additional lateral X‑rays of the thoracic and lumbar spine, vertebral fractures were detected and graded. Sacral insufficiency fractures that occurred at the same time were also recorded.

RESULTS

The median BMD was 73.2 (57.05-104.17) mg/cm3 and the median HU was 89.93 (67.90-126.95). With a correlation of 0.988 (p < 0.001), quantitative values in mg/cm3 can be calculated using the following formula: Xq = 12.1 + 0.68 × HU. With HU values less than 69.84 and a BMD of the lumbar spine below 59.54 mg/cm3, there was a significantly increased number of OVF. At least one OVF was found in 137/225 pt. In 17/137 pt., sacral fractures were also found; these patients showed the significantly lowest values with a median BMD of 41.81 (16.2-53.7) mg/cm3. Comparable HU values were determined independently of the examiners (p > 0.05).

DISCUSSION

The trabecular density measurements in HU values can be converted into quantitative BMD values in mg/cm3, which enables a good assessment of osteoporosis and fracture risk. Taking the results obtained into account, an opportunistic evaluation using HU values in native CT alone seems quite possible. Experienced examiners have arrived at comparable results.

Tips and tricks for using cement augmentation of pedicle screws and vertebral body replacements-A literature review supported by two case reports

BACKGROUND

The prevalence of osteoporosis is escalating alongside an aging global population, increasing the demand for spinal surgeries, including those necessitating cement augmentation for enhanced construct stability.

OBJECTIVE

This article delves into the nuanced application of cement augmentation techniques for pedicle screws and vertebral body replacements (VBR), aimed at optimizing surgical outcomes in osteoporotic spines.

METHOD

Drawing from a comprehensive literature review according to important clinical and biomechanical studies and the authors' clinical experiences, we elucidate strategies to mitigate complications and improve surgical efficacy.

RESULTS

Cement augmentation has shown promise in managing vertebral fractures and in securing pedicle screws within osteoporotic vertebrae, with the advent of polymethylmethacrylate (PMMA) bone cement marking a pivotal advancement in spinal surgery. We highlight intraoperative measures like the choice between pre-injecting cement and utilizing cannulated or fenestrated screws, emphasizing the importance of controlling cement viscosity to prevent leakage and embolism. Through two case reports, we demonstrate the practical application of endplate cementation following VBR.

CONCLUSION

While the use of cement augmentation poses certain risks, its judicious application-supported by evidence-based guidelines and surgical expertise-can substantially enhance the stability of spinal constructs in osteoporotic patients. This allows a reduction in instrumentation length by enhancing biomechanical stability concerning pullout, bending, and rotational forces. Furthermore, the incidence of endplate sintering following VBF can be significantly reduced. Future research, particularly on antibiotic-loaded PMMA, may further expand its utility and optimize its safety profile.

The accuracy of the Hounsfield unit in pulmonary embolism diagnostics

OBJECTIVE

Pulmonary embolism (PE) is a vascular disease that is most frequently diagnosed using the radiological imaging technique computed tomography pulmonary angiography (CTPA). In this study, we aimed to demonstrate the diagnostic accuracy of the Hounsfield unit (HU) for PE based on the hypothesis that acute thrombosis causes an increase in HU value on CT.

METHODS

This research was a single-center, retrospective study. Patients presenting to the emergency department diagnosed with PE on CTPA were enrolled as the study group. Patients admitted to the same emergency department who were not diagnosed with PE and had noncontrast CT scans were included as the control group. A receiver operating curve was produced to determine the diagnostic accuracy of HU values in predicting PE.

RESULTS

The study population (n=74) consisted of a study group (n=46) and a control group (n=28). The sensitivity and specificity of the HU value for predicting PE on thoracic CT were as follows: for the right main pulmonary artery, 61.5% and 96.4% at a value of 54.8 (area under the curve [AUC], 0.690); for the left main pulmonary artery, 65.0% and 96.4% at a value of 55.9 (AUC, 0.736); for the right interlobar artery, 44.4% and 96.4% at a value of 62.7 (AUC, 0.615); and for the left interlobar artery, 60.0% and 92.9% at a value of 56.7 (AUC, 0.736).

CONCLUSION

HU may exhibit high diagnostic specificity on CT for thrombi up to the interlobar level. An HU value exceeding 54.8 up to the interlobar level may raise suspicion of the presence of PE.

Tips and tricks for using cement augmentation of pedicle screws and vertebral body replacements-A literature review supported by two case reports

BACKGROUND

The prevalence of osteoporosis is escalating alongside an aging global population, increasing the demand for spinal surgeries, including those necessitating cement augmentation for enhanced construct stability.

OBJECTIVE

This article delves into the nuanced application of cement augmentation techniques for pedicle screws and vertebral body replacements (VBR), aimed at optimizing surgical outcomes in osteoporotic spines.

METHOD

Drawing from a comprehensive literature review according to important clinical and biomechanical studies and the authors' clinical experiences, we elucidate strategies to mitigate complications and improve surgical efficacy.

RESULTS

Cement augmentation has shown promise in managing vertebral fractures and in securing pedicle screws within osteoporotic vertebrae, with the advent of polymethylmethacrylate (PMMA) bone cement marking a pivotal advancement in spinal surgery. We highlight intraoperative measures like the choice between pre-injecting cement and utilizing cannulated or fenestrated screws, emphasizing the importance of controlling cement viscosity to prevent leakage and embolism. Through two case reports, we demonstrate the practical application of endplate cementation following VBR.

CONCLUSION

While the use of cement augmentation poses certain risks, its judicious application-supported by evidence-based guidelines and surgical expertise-can substantially enhance the stability of spinal constructs in osteoporotic patients. This allows a reduction in instrumentation length by enhancing biomechanical stability concerning pullout, bending, and rotational forces. Furthermore, the incidence of endplate sintering following VBF can be significantly reduced. Future research, particularly on antibiotic-loaded PMMA, may further expand its utility and optimize its safety profile.

Paraspinal muscle parameters' predictive value for new vertebral compression fractures post-vertebral augmentation: Nomogram development and validation

Objective

Prior research underscores the significance of paraspinal muscles in maintaining spinal stability. This study aims to investigate the predictive value of paraspinal muscle parameters for the occurrence of new vertebral compression fractures (NVCF) following percutaneous vertebroplasty (PVP) or percutaneous kyphoplasty (PKP) in patients with osteoporotic vertebral compression fractures (OVCF).

Methods

Retrospectively collected data from October 2019 to February 2021 (internal validation, n = 235) and March 2021 to November 2021 (external validation, n = 105) for patients with OVCF treated with PVP/PKP at our institution. They were randomly divided into training (188 cases) and validation groups (47 cases) at an 8:2 ratio. Lasso regression and multivariable logistic regression identified independent risk factors in the training set, and a Nomogram model was developed. Accuracy was assessed using receiver operating characteristic curves (ROC), calibration was evaluated with calibration curves and the Hosmer-Lemeshow test, and clinical utility was analyzed using decision curve analysis (DCA) and clinical impact curve (CIC).

Results

Surgical approach, spinal computed tomography (CT) values, and multifidus skeletal muscle index (SMI) are independent predictors of postoperative NVCF in OVCF patients. A Nomogram model, based on the identified predictors, was developed and uploaded online. Internal validation results showed area under the curve (AUC) values of 0.801, 0.664, and 0.832 for the training set, validation set, and external validation, respectively. Hosmer-Lemeshow goodness-of-fit tests (χ2 = 7.311-14.474, p = 0.070-0.504) and calibration curves indicated good consistency between observed and predicted values. DCA and CIC demonstrated clinical net benefit within risk thresholds of 0.06-0.84, 0.12-0.23, and 0.01-0.27. At specificity 1.00-0.80, the partial AUC (0.106) exceeded that at sensitivity 1.00-0.80 (0.062).

Conclusion

Compared to the spinal CT value, the multifidus SMI has certain potential in predicting the occurrence of NVCF. Additionally, the Nomogram model of this study has a greater negative predictive value.

Interobserver variability in the determination of bone mineral density in Hounsfield units from differently configured fields of measurement in the cancellous bone of vertebral bodies from elderly body donors

Background

Due to the absence of suitable diagnostic procedures, osteoporosis (OP) is frequently detected late or not at all. Many elderly persons undergo computed tomographies (CT). The routine determination of Hounsfield units (HU) in bone as a part of these examinations could close a gap here.

Methods

Spines were extracted from 22 body donors, fixed in a PVC water phantom, and subjected to a high-resolution CT investigation. Cancellous bone was examined and its bone mineral density measured in HU from cervical vertebra 3 to lumbar vertebra 5 (484 vertebral bodies). On sagittal sections, a circular and a rectangular region of interest (ROI) were defined in mid-vertebral cancellous bone, positioned manually, and the measurements were performed by three experienced radiologists. Bone mineral density (BMD), measured in mg/cm3, was used to determine the presence of OP.

Results

All of the spines were osteoporotic. In the presence of a BMD below 60 mg/cm3 and HU values below 63.36 in lumbar vertebrae, there were significantly more vertebral body fractures in the thoracic and thoracolumbar spine. No difference was observed between the manually positioned circular and rectangular regions of interest (ROI) on the sagittal CT section (p > 0.05). Similar HU counts were obtained by the individual examiners (p > 0.05). The following formula was used to determine QCT values on a non-contrasted CT of the spine: QCT = 0.6 × HU + 13.7.

Conclusions

Measurement of the density of cancellous bone in HU can be used to determine BMD for estimating demineralization. Quantitative BMD values in mg/cm3, which can be calculated from the HU data, concur well with QCT values.

Treatment and Outcome of Osteoporotic Thoracolumbar Vertebral Fractures With Anterior or Posterior Tension Band Failure (OF 5): Short-Term Results From the Prospective EOFTT Multicenter Study

STUDY DESIGN

Subgroup analysis of a multicenter prospective cohort study.

OBJECTIVE

To analyse surgical strategies applied to osteoporotic thoracolumbar osteoporotic fracture (OF) 5 injuries with anterior or posterior tension band failure and to assess related complications and clinical outcome.

METHODS

A multicenter prospective cohort study (EOFTT) was conducted at 17 spine centers including 518 consecutive patients who were treated for an osteoporotic vertebral fracture (OVF). For the present study, only patients with OF 5 fractures were analysed. Outcome parameters were complications, Visual Analogue Scale (VAS), Oswestry Disability Questionnaire (ODI), Timed Up & Go test (TUG), EQ-5D 5L, and Barthel Index.

RESULTS

In total, 19 patients (78 ± 7 years, 13 female) were analysed. Operative treatment consisted of long-segment posterior instrumentation in 9 cases and short-segment posterior instrumentation in 10 cases. Pedicle screws were augmented in 68 %, augmentation of the fractured vertebra was performed in 42%, and additional anterior reconstruction was done in 21 %. Two patients (11 %) received short-segment posterior instrumentation without either anterior reconstruction or cement-augmentation of the fractured vertebra. No surgical or major complications occurred, but general postoperative complications were observed in 45%. At a follow-up of mean 20 ± 10 weeks (range, 12 to 48 weeks), patients showed significant improvements in all functional outcome parameters.

CONCLUSIONS

In this analysis of patients with type OF 5 fractures, surgical stabilization was the treatment of choice and lead to significant short-term improvement in terms of functional outcome and quality of life despite a high general complication rate.

Avoiding Spinal Implant Failures in Osteoporotic Patients: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVES

With an aging population, the prevalence of osteoporosis is continuously rising. As osseous integrity is crucial for bony fusion and implant stability, previous studies have shown osteoporosis to be associated with an increased risk for implant failure and higher reoperation rates after spine surgery. Thus, our review's purpose was to provide an update of evidence-based solutions in the surgical treatment of osteoporosis patients.

METHODS

We summarize the existing literature regarding changes associated with decreased bone mineral density (BMD) and resulting biomechanical implications for the spine as well as multidisciplinary treatment strategies to avoid implant failures in osteoporotic patients.

RESULTS

Osteoporosis is caused by an uncoupling of the bone remodeling cycle based on an unbalancing of bone resorption and formation and resulting reduced BMD. The reduction in trabecular structure, increased porosity of cancellous bone and decreased cross-linking between trabeculae cause a higher risk of complications after spinal implant-based surgeries. Thus, patients with osteoporosis require special planning considerations, including adequate preoperative evaluation and optimization. Surgical strategies aim towards maximizing screw pull-out strength, toggle resistance, as well as primary and secondary construct stability.

CONCLUSIONS

As osteoporosis plays a crucial role in the fate of patients undergoing spine surgery, surgeons need to be aware of the specific implications of low BMD. While there still is no consensus on the best course of treatment, multidisciplinary preoperative assessment and adherence to specific surgical principles help reduce the rate of implant-related complications.

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.

Assessment of Bone Mineral Density in the Distal Tibia Using Quantitative Hounsfield Samples From Computer Tomography

The distal tibia bone quality is of paramount importance for ankle fractures, total ankle implants, ankle fusions, and osteotomy procedures. Despite this fact relatively little is known regarding the overall bone quality for this section of the tibia. Previous literature suggest that there is a statistically significant decrease in bone mineral density within the distal 5% to 10% segment of the tibia medullary canal. This segment of medullary bone is considerable in size and thus valuable for fixation constructs as it is oftentimes utilized for medial malleolar fractures, distal tibia fractures, total ankle replacements, ankle fusions, and other procedures. This study assessed bone attenuation between the distal 5% and 10% mark of the tibia in 1% slices via Hounsfield unit measurements on CT scans based on previously established correlation between Hounsfield units and bone mineral density found on DEXA scans. One hundred five distal tibia segments were assessed with an average interval in percentile slices of 3.8 mm. As expected there was a gradual decrease in bone attenuation noted with each proximal percentile segment. There exists a statistically significant difference in bone attenuation among males versus females as well as those older than 60 years versus younger than 60 years. The findings suggest fixation constructs in the tibia medullary canal may find limited benefit proximal from 7% segment in females ≥60, or 26.1 mm from tibial plafond. Fixation constructs in tibia medullary canal may find limited benefit proximal from 8% segment in males <60, or 32.3 mm from tibial plafond.

OF spine classification of osteoporotic thoracolumbar vertebral body fractures by MRI and conventional radiographs only leads to high inter-observer agreement rates-an additional CT adds limited information for the of classification and the OF score

OBJECTIVES

The purpose of this study was to investigate whether the addition of computed tomography (CT) to magnetic resonance imaging (MRI) improves the accuracy of classifying osteoporotic vertebral body fractures (OVBF).

METHODS

A retrospective analysis of a prospective single-center database has been performed. All consecutive patients who had suffered an acute thoracolumbar OVBF in one level II spine center between 2017 and 2019 were analyzed. Thereby, fractures of type OF 1 and OF 5 were excluded. All fractures were initially classified by 5 board-certified orthopaedic surgeons based on MRI and conventional radiographs. Afterwards a reclassification including CT scans were performed. Differences in OF classification and OF score values between both measurements were analyzed.

RESULTS

A total of 61 patients were analyzed with a mean age 75.8 years (SD: 8.8 years). In 82.9% of the cases, there was no difference in OF classification comparing classification based only on MRI versus MRI + CT. A difference of more than two OF types was observed in less than 1% of all ratings. The inter-rater reliabilities of the OF classification based on CT + MRI and MRI alone were 0.63 and 0.49, respectively. In 97.5% of the cases there was no therapy-relevant difference of the treatment recommendation with respect of a surgical or nonoperative treatment recommendation based on the OF score.

CONCLUSION

In terms of the OF classification and the OF score, the addition of CT add limited value compared to conventional radiographs and MRI only. Additionally, there is only a minor rate of disagreement in treatment recommendations when adding a CT.

Insuffizienzfrakturen der Wirbelsäule in Abhängigkeit von der spongiösen Knochendichte

Hintergrund

Das Risiko für osteoporotische Insuffizienzfrakturen (Fx) am Achsenskelett steigt mit zunehmender Abnahme der Knochendichte, wobei sich thorakal und thorakolumbal eine Häufung findet. Um die unterschiedliche Verteilung von Fx entlang der Wirbelsäule (WS) besser zu verstehen, wurden morphologische und osteodensitometrische Untersuchungen mittels Computertomographie (CT) in den verschiedenen WS-Abschnitten durchgeführt. Zudem war zu klären, ob die bei CT-Untersuchungen aus anderen Indikationen gefunden Hounsfield-Einheiten (HE) mit der Knochendichte korrelieren und Anlass für eine osteologische Diagnostik sein könnten.

Material und Methoden

Von 26 Körperspenden wurden die gesamten WS in einem Plexiglas-Wasser-Phantom fixiert und mittels hochauflösende Spiral-CT analysiert. Zusätzlich erfolgte die Messung der CT-morphologischen Spongiosadichte in HE von C3 bis S2 (624 Wirbelkörper). Der Knochenmineralgehalt (KMG, mg/ml) wurde ermittelt und zur Abschätzung einer Osteoporose (OPO) herangezogen.

Ergebnisse

Bei allen WS lag eine OPO vor. Bei einem KMG unterhalb von 60 mg/ml fanden sich signifikant vermehrte Sinterungsfrakturen im thorakalen und thorakolumbalen Bereich. Osteoporotische Insuffizienzfrakturen im HWS-Bereich fanden sich insgesamt nicht. Die Spongiosadichte war signifikant höher in den zervikalen (Median 188,6 HE) als in den lumbalen (Median 63,6 HE) und sakralen (Median 25,5 HE) Wirbelkörpern aller untersuchten WS.

Schlussfolgerung

Ein KMG-Verlust der Wirbelkörperspongiosa führt zu einem erhöhten Fx-Risiko, welches sich auch bei den verwendeten WS findet. Jedoch wird im zervikalen Bereich ein scheinbarer Schwellenwert für das Auftreten von Sinterungsfrakturen nicht unterschritten. Einen Schwellenwert für HE zu finden, wäre für die klinische Praxis relevant.

Low-dose CT hounsfield units: a reliable methodology for assessing vertebral bone density in radiographic axial spondyloarthritis

Objective

Studying vertebral bone loss in radiographic axial spondyloarthritis (r-axSpA) has been challenging due to ectopic bone formation. We cross-sectionally analysed low-dose CT (ldCT) trabecular bone density Hounsfield units (HU) measurements and calculated inter-reader reliability at the vertebral level in patients with r-axSpA.

Methods

LdCT scans of 50 patients with r-axSpA from the sensitive imaging in ankylosing spondylitis study, a multicentre 2-year prospective cohort were included. Trabecular bone HU taken from a region of interest at the centre of each vertebra (C3-L5) were independently assessed by two trained readers. HU mean (SD), and range were provided at the vertebral level, for each reader and centre separately. Inter-reader reliability and agreement were assessed using intraclass correlation coefficients (ICC; single measurements, absolute agreement, two-way mixed effects models); smallest detectable difference and Bland-Altman plots.

Results

Overall, 1100 vertebrae were assessed by each reader. HU values decreased from cranial to caudal vertebrae. For readers 1 and 2 respectively, the highest mean (SD) HU value was obtained at C3 (354(106) and 355(108)), and the lowest at L3 (153(65) and 150 (65)). Inter-reader reliability was excellent (ICC(2,1):0.89 to 1.00). SDD varied from 4 to 8. For most vertebrae, reader 1 scored somewhat higher than reader 2 (mean difference of scores ranging from −0.6 to 2.9 HU). Bland-Altman plots showed homoscedasticity.

Conclusion

LdCT measurement of HU is a feasible method to assess vertebral bone density in r-axSpA with excellent inter-reader reliability from C3 to L5. These results warrant further validation and longitudinal assessment of reliability.

Impact of Multifidus Muscle Atrophy on the Occurrence of Secondary Symptomatic Adjacent Osteoporotic Vertebral Compression Fractures

To assess the potential influence of multifidus atrophy and fatty degeneration on the incidence of adjacent vertebral compression fractures within one year after the index fracture. In a retrospective cohort study, patients who underwent surgery for an OVCF were identified and baseline characteristics, fracture patterns and the occurrence of secondary adjacent fractures within one year were obtained by chart review. Multifidus muscle atrophy and fatty degeneration were determined on preoperative MRI or CT scans. In this analysis of 191 patients (mean age 77 years, SD 8, 116 female), OF type 3 was the most common type of OVCF (49.2%). Symptomatic adjacent OVCFs within one year after index fracture were observed in 23/191 patients (12%) at mean 12, SD 12 weeks (range 1-42 weeks) postoperatively. The mean multifidus muscle area was 264, SD 53 mm² in patients with an adjacent vertebral fracture and 271, SD 92 mm² in patients without a secondary fracture (p = 0.755). Mean multifidus fatty infiltration was graded Goutallier 2.2, SD 0.6 in patients with an adjacent fracture and Goutallier 2.2, SD 0.7 in patients without an adjacent fracture (p = 0.694). Pre-existing medication with corticosteroids was associated with the occurrence of an adjacent fracture (p = 0.006). Multifidus area and multifidus fatty infiltration had no significant effect on the occurrence of adjacent vertebral fractures within one year after the index fracture. Patients with a pre-existing medication with corticosteroids were more likely to sustain an adjacent fracture.

The influence of bone quality on radiological outcome in 50 consecutive acetabular fractures treated with a pre-contoured anatomic suprapectineal plate

PURPOSE

To investigate the range of indications of an anatomical-preshaped three-dimensional suprapectineal plate and to assess the impact of the bone mass density on radiologic outcomes in different types of acetabular fractures.

PATIENTS AND METHODS

A consecutive case series of 50 acetabular fractures (patient age 69 ± 23 years) treated with suprapectineal anatomic plates were analyzed in a retrospective study. The analysis included: Mechanism of injury, fracture pattern, surgical approach, need for additional total hip arthroplasty, intra- or postoperative complications, as well as bone mass density and radiological outcome on postoperative computed tomography.

RESULTS

Most frequently, anterior column fracture patterns with and without hemitransverse components as well as associated two column fractures were encountered. The anterior intrapelvic approach (AIP) was used in 98% (49/50) of the cases as primary approach with additional utilization of the first window of the ilioinguinal approach in 13/50 cases (26%). Determination of bone density revealed impaired bone quality in 70% (31/44). Postoperative steps and gaps were significantly greater in this subgroup (p < 0.05). Fracture reduction quality for postoperative steps revealed anatomic results in 92% if the bone quality was normal and in 46% if impaired (p < 0.05). In seven cases (14%), the plate was utilized in combination with acute primary arthroplasty.

CONCLUSION

A preshaped suprapectineal plate provides good radiological outcomes in a variety of indications in a predominantly geriatric cohort. Impaired bone quality has a significantly higher risk of poor reduction results. In cases with extensive joint destruction, the combination with total hip arthroplasty was a valuable option.

How relevant is lumbar bone mineral density for the stability of symphyseal implants? A biomechanical cadaver study

PURPOSE

Osteoporotic bone tissue appears to be an important risk factor for implant loosening, compromising the stability of surgical implants. However, it is unclear whether lumbar measured bone mineral density (BMD) is of any predictive value for stability of surgical implants at the pubic symphysis. This study examines the fixation strength of cortical screws in human cadaver specimens with different BMDs.

METHODS

The lumbar BMD of ten human specimens was measured using quantitative computed tomography (qCT). A cut-off BMD was set at 120 mg Ca-Ha/mL, dividing the specimens into two groups. One cortical screw was drilled into each superior pubic ramus. The screw was withdrawn in an axial direction with a steady speed and considered failed when a force decrease was detected. Required force (N) and pull-out distance (mm) were constantly tracked.

RESULTS

The median peak force of group 1 was 231.88 N and 228.08 N in group 2. While BMD values differed significantly (p < 0.01), a comparison of peak forces between both groups showed no significant difference (p = 0.481).

CONCLUSION

Higher lumbar BMD did not result in significantly higher pull-out forces at the symphysis. The high proportion of cortical bone near the symphyseal joint allows an increased contact of pubic screws and could explain sufficient fixation. This condition is not reflected by a compromised lumbar BMD in a qCT scan. Therefore, site-specific BMD measurement could improve individual fracture management.

Possible Correlation Between Kyphosis of Lumbar Osteoporosis Fractures and the Spinal Signal Intensity Ratio (SSIR)

BACKGROUND

The aim of this study was to examine the correlation between the risk of increasing kyphosis as well as collapse of the osteoporotic vertebral body fractures and the intensity of the bone edema in magnetic resonance imaging (MRI) scans. Inclusion criteria included the following: age >18 years and osteoporotic vertebral body fracture grade I-IV according to OF classification. Exclusion criteria included the following: other pathological fractures due to primary tumors or metastasis, OF grade V fractures, and AO type B or C fractures.

METHODS

This was a retrospective study from pseudonymized data of a tertiary spine center. No additional imaging were performed. Measurements of bisegmental kyphosis angle of the fracture for involvement of both endplates and monosegmental angle for involvement of 1 endplate, as well as vertebral body height loss in initial radiographs and at follow-ups after 3 and 6 months have been performed. Also, the initial signal intensity of the vertebral body edema was measured using integrated tool of the DICOM viewer (Impax V6.5 Agfa, Brentford, UK) in addition to the signal intensity of the cerebrospinal fluid (CSF) as reference for T1, T2, and separate target illumination radar (STIR) sequences of the MRI scans. A quotient from the signal intensity of the vertebral body edema and the reference (CSF) has been generated. Patients have been divided to 4 groups according to the ratio (<1, 1-2, 2-3, >3) and compared in regards to the results of the degree of kyphosis and vertebral collapse at follow-ups and final examination. The statistical analysis was performed using linear regression using statistic software SPSS version 26.

RESULTS AND CONCLUSIONS

Forty-four patients have been included: 9 males and 35 females with an average age of 71.5 years. The analysis showed a significant correlation between the increasing kyphosis at follow-ups and the quotient of the signal intensity for STIR and T2 weighing with P = .002 (SD ±2.664) for STIR and P = .001 (SD ±1.616) for T2 sequences. Furthermore, there was only a correlation between the intensity ratio and kyphosis for STIR weighting at last examination (P = .017; SD ±1.360). There was no correlation between the height loss and the signal intensity.

LEVEL OF EVIDENCE

Level 2.

Differentiation of Traumatic Osteoporotic and Non-Osteoporotic Vertebral AO A3 Fractures by Analyzing the Posterior Edge Morphology-A Retrospective Feasibility Study

BACKGROUND

Differentiation between traumatic osteoporotic and non-osteoporotic vertebral fractures is crucial for optimal therapy planning. We postulated that the morphology of the posterior edge of the cranial fragment of A3 vertebral fractures is different in these entities. Therefore, the purpose of this study is to develop and validate a simple method to differentiate between osteoporotic and non-osteoporotic A3 vertebral fractures by morphological analysis.

METHODS

A total of 86 computer tomography scans of AO Type A3 (cranial burst) vertebral body fractures (52 non-osteoporotic, 34 osteoporotic) were included in this retrospective study. Posterior edge morphology was analyzed using the sagittal paramedian slice with the most prominent shaped bulging. Later, the degree of bulging of the posterior edge fragment was quantified using a geometric approach. Additionally, the Hounsfield units of the broken vertebral body, the vertebra above, and the vertebra below the fracture were measured.

RESULTS

We found significant differences in the extent of bulging comparing osteoporotic and non-osteoporotic fractures in our cohort. Using the presented method, sensitivity was 100%, specificity was 96%. The positive predictive value (PPV) was 94%. In contrast, by evaluating the Hounsfield units, sensitivity was 94%, specificity 94% and the PPV was 91%.

CONCLUSIONS

Our method of analysis of the bulging of the dorsal edge fragment in traumatic cranial burst fractures cases allows, in our cases, a simple and valid differentiation between osteoporotic and non-osteoporotic fractures. Further validation in a larger sample, including dual-energy X-ray absorptiometry (DXA) measurements, is necessary.

[Minimally invasive stabilization of thoracolumbar osteoporotic fractures]

BACKGROUND

Minimally invasive stabilization of thoracolumbar osteoporotic fractures (OF) in neurologically intact patients is well established. Various posterior and anterior surgical techniques are available. The OF classification and OF score are helpful for defining the indications and choice of operative technique.

OBJECTIVE

This article gives an overview of the minimally invasive stabilization techniques, typical complications and outcome.

MATERIAL AND METHODS

Selective literature search and description of surgical techniques and outcome.

RESULTS

Vertebral body augmentation alone can be indicated in painful but stable fractures of types OF 1 and OF 2 and to some extent for type OF 3. Kyphoplasty has proven to be an effective and safe procedure with a favorable clinical outcome. Unstable fractures and kyphotic deformities (types OF 3-5) should be percutaneously stabilized from posterior. The length of the pedicle screw construct depends on the extent of instability and deformity. Bone cement augmentation of the pedicle screws is indicated in severe osteoporosis but increases the complication rate. Restoration of stability of the anterior column can be achieved through additional vertebral body augmentation or rarely by anterior stabilization. Clinical and radiological short and mid-term results of the stabilization techniques are promising; however, the more invasive the surgery, the more complications occur.

CONCLUSION

Minimally invasive stabilization techniques are safe and effective. The specific indications for the individual procedures are guided by the OF classification and the individual clinical situation of the patient.

Modified therapy concepts for fragility fractures of the pelvis after additional MRI

BACKGROUND

Fractures of the pelvic ring in elderly patients have increased in frequency over time. These injuries are associated with a high morbidity and have a socio-economic impact. The diagnostic procedures and their influence of therapy decisions are still controversial.

METHODS

In a retrospective study, we investigate the value of additional MRI examination on therapy decision of fragility fractures of the pelvis. The evaluation of all patients with pelvic fractures without adequate trauma and with performed CT and MRI was conducted at three large German hospitals. The imaging procedure took place within a maximum interval of 4 weeks. After evaluation of the imaging, the resulting therapeutic consequences either based on CT alone or on CT and MRI were reviewed by experienced pelvic surgeons.

RESULTS

Of 754 patients with pelvic injuries, 67 (age 80 +/- 9.7 years, f: m 54:13) could be included. The detection of vertical fractures in CT (n = 40 unilateral, n = 11 bilateral) could be increased by the additional MRI (n = 44 unilateral, n = 23 bilateral). A horizontal fracture component was identified in CT in 9.0% (n = 6) vs. MRI in 25.4% (n = 17) of the cases. An anterior pelvic ring injury was detected in 71.6% (n = 44; 4x bilateral) in CT, in 80.6% in MRI (n = 50, 4 bilateral). Additive MRI imaging increased the decision rate for surgical therapy from 20.9% (n = 14) to 31.3% (n = 21).

CONCLUSIONS

The results of this study further support the value of bone marrow edema detection by MRI diagnostics (or dual source CT which showed promising initial results) for the detection of pelvic ring fractures. For the first time, the study identifies an additional therapeutic consequence by an increased rate of surgical procedures.