Surgical treatment options in patients with impaired bone quality

Toward Fully Automated Personalized Orthopedic Treatments: Innovations and Interdisciplinary Gaps

Personalized orthopedic devices are increasingly favored for their potential to enhance long-term treatment success. Despite significant advancements across various disciplines, the seamless integration and full automation of personalized orthopedic treatments remain elusive. This paper identifies key interdisciplinary gaps in integrating and automating advanced technologies for personalized orthopedic treatment. It begins by outlining the standard clinical practices in orthopedic treatments and the extent of personalization achievable. The paper then explores recent innovations in artificial intelligence, biomaterials, genomic and proteomic analyses, lab-on-a-chip, medical imaging, image-based biomechanical finite element modeling, biomimicry, 3D printing and bioprinting, and implantable sensors, emphasizing their contributions to personalized treatments. Tentative strategies or solutions are proposed to address the interdisciplinary gaps by utilizing innovative technologies. The key findings highlight the need for the non-invasive quantitative assessment of bone quality, patient-specific biocompatibility, and device designs that address individual biological and mechanical conditions. This comprehensive review underscores the transformative potential of these technologies and the importance of multidisciplinary collaboration to integrate and automate them into a cohesive, intelligent system for personalized orthopedic treatments.

Bone quality in patients with osteoporosis undergoing lumbar fusion surgery: analysis of the MRI-based vertebral bone quality score and the bone microstructure derived from microcomputed tomography

BACKGROUND CONTEXT

Osteoporosis is a risk factor for instrumentation failure in spine surgery. Bone strength is commonly assessed by bone mineral density (BMD) as a surrogate marker. However, BMD represents only a portion of bone strength and does not capture the qualitative dimensions of bone. Recently, the magnetic resonance imaging (MRI)-based vertebral bone quality (VBQ) score was introduced as a novel marker of bone quality. However, it is still unclear if the VBQ score correlates with in-vivo bone microstructure.

PURPOSE

The aims of the study were (1) to demonstrate differences in MRI-based (VBQ) and in-vivo (microcomputed tomography; μCT) bone quality between osteopenic/osteoporotic and normal bone, (2) to show the correlation between VBQ, bone microstructure and volumetric BMD (vBMD), and (3) to determine the predictive value of the VBQ score for the prevalence of osteopenia/osteoporosis.

STUDY DESIGN/SETTING

Retrospective cross-sectional study.

PATIENT SAMPLE

267 patients who underwent posterior lumbar fusion surgery from 2014 to 2021 at a single academic institution. Bone biopsies were harvested intraoperatively in 118 patients.

OUTCOME MEASURES

VBMD, VBQ score, and bone microstructure parameters derived from μCT.

METHODS

Quantitative computed tomography (QCT) measurements were performed at the lumbar spine and the L1/L2 average was used to categorize patients with a vBMD ≤120mg/cm³ as osteopenic/osteoporotic. The VBQ score was determined by dividing the median signal intensity of the L1-L4 vertebrae by the signal intensity of the cerebrospinal fluid using sagittal T1-weighted MRI scans. Intraoperative bone biopsies from the posterior superior iliac spine were obtained and evaluated with μCT. VBQ scores and μCT parameters were compared between the normal and the osteopenic/osteoporotic group. Correlations between VBQ score, μCT parameters and vBMD were assessed with Spearman's correlation (ρ). Receiver operating characteristic (ROC) analysis was performed to determine the VBQ score as a predictor for osteopenia/osteoporosis. Multiple linear regression analysis with vBMD L1/L2 as outcome was used to identify independent predictors from VBQ, μCT parameters and demographics.

RESULTS

267 patients (55.8% female, age 63.3 years, BMI 29.7 kg/m²; n=118 with bone biopsy) with a prevalence of osteopenia/osteoporosis of 65.2% were analyzed. In the osteopenic/osteoporotic group the VBQ score, structured model index (SMI), and trabecular separation (Tb.Sp) were significantly higher, whereas bone volume fraction (BV/TV), connectivity density (Conn.D) and trabecular number (Tb.N) were significantly lower. There were significant correlations between VBQ and μCT parameters ranging from ρ=-.387 to ρ=0.314 as well as between vBMD and μCT parameters ranging from ρ=-.425 to ρ=.421, and vBMD and VBQ (ρ=-.300, p<.001). ROC analysis discriminated osteopenia/osteoporosis with a sensitivity of 84.7% and a specificity of 40.6% at a VBQ score threshold value of 2.18. Age, BV/TV and trabecular thickness (Tb.Th), but not VBQ, were significant independent predictors for vBMD (corrected R²=0.434).

CONCLUSIONS

This study demonstrated for the first time that the VBQ score is associated with trabecular microstructure determined by μCT. The bone microstructure and VBQ score were significantly different in patients with impaired vBMD. However, the ability to predict osteopenia/osteoporosis with the VBQ score was moderate. The VBQ score appears to reflect additional bone quality characteristics and might have a complementary role to vBMD. This enhances our understanding of the biological background of the radiographic VBQ score and might be a take-off point to evaluate the clinical utility of it as non-invasive screening tool for bone quality.

Intraoperative use of impact microindentation to assess distal radius bone quality

Impact microindentation is a new technique that measures the resistance of a patient's bone to micro-indentation but has not yet been implemented in an intraoperative setting. To assess the technique's safety and utility, we acquired microindentation measurements of bone material strength index (BMSi) using the OsteoProbe prior to distal radius fixation with a volar locking plate. Subsequently, the patients received a dual-energy x-ray absorptiometry scan to measure the areal bone mineral density of the proximal femur, lumbar spine, and contralateral distal radius. By assigning the patients to low-energy, fragility fracture (n = 17) and high-energy fracture (n = 11) groups based on clinical history, we investigated whether intraoperative BMSi was sensitive to osteoporosis. Impact microindentation added a maximum of 10 min of operative time and did not result in any intraoperative or postoperative complications. There were, however, no significant differences in BMSi at the radius between these two groups. This study demonstrates the feasibility of performing intraoperative impact microindentation to directly assess a patient's bone quality, but additional research is necessary to establish whether intraoperative microindentation can identify patients with inferior bone matrix quality.

Dual-energy X-ray Absorptiometry Does Not Represent Bone Structure in Patients with Osteoporosis: A Comparison of Lumbar Dual-Energy X-Ray Absorptiometry with Vertebral Biopsies

STUDY DESIGN

Prospective cross-sectional exploratory study.

OBJECTIVE

To evaluate the correlation between in vivo lumbar dual-energy x-ray absorptiometry (DXA) and parameters of bone architecture in micro-computed tomography (micro-CT) in patients with osteoporosis.

SUMMARY OF BACKGROUND DATA

DXA is the current diagnostic standard for evaluating osteoporosis. However, there are various concerns regarding its validity, especially in the spine. No study has so far investigated whether in vivo DXA correlates with the actual lumbar bone architecture.

METHODS

Lumbar DXA scans were compared with micro-CT analysis of vertebral biopsies in patients with osteoporotic vertebral fractures (fracture group) and those without (control group). Preoperatively, all patients underwent a DXA scan (L1-L4). Intraoperative biopsies from nonfractured vertebrae (preferably L3) were analyzed by micro-CT regarding bone quantity and quality. The groups were compared regarding differences in DXA and micro-CT results. In each group, a correlation analysis was performed between DXA and micro-CT.

RESULTS

The study included 66 patients (33 per group). Preoperative DXA results were worse in the fracture group than the control group (areal bone mineral density [aBMD] 0.95 vs. 1.31, T-score -1.97 vs. 0.92, each P < 0.001). Micro-CT analysis confirmed differences regarding quantitative parameters (bone/total volume: 0.09 vs. 0.12, P < 0.001) and qualitative parameters (connectivity index: 15.73 vs. 26.67, P < 0.001; structure model index: 2.66 vs. 2.27, P < 0.001; trabecular number: 2.11 vs. 2.28, P = 0.014) of bone architecture between both groups. The DXA results did not correlate with micro-CT parameters in the fracture group. In the control group, correlations were found for some parameters (bone/total volume vs. aBMD: r = 0.51, P = 0.005; trabecular number vs. aBMD: r = 0.56, P = 0.001).

CONCLUSION

These data constitute the first comparison of DXA measurements with microstructural analysis of vertebral biopsies in patients with osteoporosis. Our results indicate that lumbar DXA neither qualitatively nor quantitatively represents microstructural bone architecture and is therefore not a reliable tool for the evaluation of bone quality in the spine.Level of Evidence: 3.

Bone structure determined by HR-MDCT does not correlate with micro-CT of lumbar vertebral biopsies: a prospective cross-sectional human in vivo study

Background

Osteoporosis is characterized by a deterioration of bone structure and quantity that leads to an increased risk of fractures. The primary diagnostic tool for the assessment of the bone quality is currently the dual-energy X-ray absorptiometry (DXA), which however only measures bone quantity. High-resolution multidetector computed tomography (HR-MDCT) offers an alternative approach to assess bone structure, but still lacks evidence for its validity in vivo. The objective of this study was to assess the validity of HR-MDCT for the evaluation of bone architecture in the lumbar spine.

Methods

We conducted a prospective cross-sectional study to compare the results of preoperative lumbar HR-MDCT scans with those from microcomputed tomography (μCT) analysis of transpedicular vertebral body biopsies. For this purpose, we included patients undergoing spinal surgery in our orthopedic department. Each patient underwent preoperative HR-MDCT scanning (L1-L4). Intraoperatively, transpedicular biopsies were obtained from intact vertebrae. Micro-CT analysis of these biopsies was used as a reference method to assess the actual bone architecture. HR-MDCT results were statistically analyzed regarding the correlation with results from μCT.

Results

Thirty-four patients with a mean age of 69.09 years (± 10.07) were included in the study. There was no significant correlation for any of the parameters (bone volume/total volume, trabecular separation, trabecular thickness) between μCT and HR-MDCT (bone volume/total volume: r = − 0.026 and p = 0.872; trabecular thickness: r = 0.074 and r = 6.42; and trabecular separation: r = − 0.18 and p = 0.254).

Conclusion

To our knowledge, this is the first study comparing in vivo HR-MDCT with μCT analysis of vertebral biopsies in human patients. Our findings suggest that lumbar HR-MDCT is not valid for the in vivo evaluation of bone architecture in the lumbar spine. New diagnostic tools for the evaluation of osteoporosis and preoperative orthopedic planning are urgently needed.

Bone density of the calcaneus correlates with radiologic and clinical outcomes after calcaneal fracture fixation

BACKGROUND

This study aimed to determine whether bone density correlates with radiologic and clinical outcomes after screw fixation of displaced intra-articular calcaneal fractures (DIACF) with the sinus tarsi approach.

MATERIALS AND METHODS

We retrospectively evaluated 43 consecutive cases of unilateral DIACF between March 2015 and December 2017. Radiologic evaluations were performed using preoperative, postoperative, and last follow-up calcaneal lateral and axial radiographs. In all patients, preoperative CT scanning of both injured and uninjured calcaneus were performed at one scanning and dual x-ray absorptiometry (DXA) scans were obtained. Hounsfield unit (HU) measurement values were determined by placing an elliptical region of interest confined to the cancellous region of the uninjured calcaneus. Clinical outcomes were assessed at a minimum of 12 months postoperatively using Foot and Ankle Outcome Scores (FAOS).

RESULTS

Mean HU values of the uninjured calcaneus significantly correlated with bone mineral density scores obtained from DXA scans of the lumbar and femur (Spearman ρ = 0.656 - 0.748; p < 0.001 for both). Decreased HU values of the uninjured calcaneus significantly correlated with decreased Böhler's angle and widening of calcaneal width from postoperative to last follow-up. (Pearson r = 0.348, p = 0.022; Pearson r = -0.582, p < 0.001, respectively). Increased HU values of the uninjured calcaneus significantly correlated with improved clinical outcomes in three of five FAOS domains, including activities of daily living, sports, and quality of life (beta = 0.283 - 0.322; p < 0.05 for all).

CONCLUSION

Decreased preoperative bone density significantly correlated with decreased Böhler's angle, widening of calcaneal width, and inferior short-term clinical outcomes after screw fixation of DIACF. By quantifying bone density using HU value in area where DXA cannot be performed, such foot bones, determining whether different fixation methods or systemic treatments can be tailored to bone density could help in optimizing clinical outcomes.

LEVEL OF EVIDENCE

Level III, Retrospective case series.

Bone Mineral Density Around the Knee Joint: Correlation With Central Bone Mineral Density and Associated Factors

INTRODUCTION

The aims of this study were to (1) assess the bone mineral density (BMD) around the knee joint, (2) determine the correlation between central and knee BMDs, and (3) investigate the factors associated with BMD around the knee joint in patients with knee osteoarthritis (OA).

METHODOLOGY

This cross-sectional study included 122 patients who underwent total knee arthroplasty. Central and knee dual-energy X-ray absorptiometry was performed preoperatively. BMD at 6 regions of interest (ROIs) around the knee joint were measured, and their correlations with central BMD were determined using Spearman's correlation analysis. Lower limb alignment, severity of OA, body mass index (BMI), preoperative functional and pain scores were assessed to elucidate the factors associated with knee BMD using linear regression analysis.

RESULTS

Around the knee joint, BMD was the lowest at the distal femoral metaphysis and lateral tibial condyle. Knee BMD was significantly correlated with central BMD. However, the correlation coefficients varied by the ROI. Additionally, multivariate analysis revealed different associations with respect to the regions around the knee joint. Varus alignment of the lower limb was associated with increased BMD of the medial condyles and decreased BMD of lateral condyles. High grade OA was a protective factor; it was associated with increased BMD at the lateral condyles of the femur and tibia. Higher BMI was an independent protective factor in all ROIs around the knee joint except the lateral femoral condyles. Lower functional level was not associated with decreased BMD, whereas a higher pain score was significantly associated with lower BMD at the proximal tibial metaphysis.

CONCLUSIONS

Knee BMD was significantly correlated with central BMD. However, the correlations varied with the regions around the knee joint probably due to their independent association with the alignment of the lower limb, severity of OA, BMI, and preoperative pain level.

Bench-to-bedside strategies for osteoporotic fracture: From osteoimmunology to mechanosensation

Osteoporosis is characterized by a decrease in bone mass and strength, rendering people prone to osteoporotic fractures caused by low-energy forces. The primary treatment strategy for osteoporotic fractures is surgery; however, the compromised and comminuted bones in osteoporotic fracture sites are not conducive to optimum reduction and rigid fixation. In addition, these patients always exhibit accompanying aging-related disorders, including high inflammatory status, decreased mechanical loading and abnormal skeletal metabolism, which are disadvantages for fracture healing around sites that have undergone orthopedic procedures. Since the incidence of osteoporosis is expected to increase worldwide, orthopedic surgeons should pay more attention to comprehensive strategies for improving the poor prognosis of osteoporotic fractures. Herein, we highlight the molecular basis of osteoimmunology and bone mechanosensation in different healing phases of elderly osteoporotic fractures, guiding perioperative management to alleviate the unfavorable effects of insufficient mechanical loading, high inflammatory levels and pathogen infection. The well-informed pharmacologic and surgical intervention, including treatment with anti-inflammatory drugs and sufficient application of antibiotics, as well as bench-to-bedside strategies for bone augmentation and hardware selection, should be made according to a comprehensive understanding of bone biomechanical properties in addition to the remodeling status of osteoporotic bones, which is necessary for creating proper biological and mechanical environments for bone union and remodeling. Multidisciplinary collaboration will facilitate the improvement of overall osteoporotic care and reduction of secondary fracture incidence.

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties

The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients. Techniques that can potentially be applied in vivo to measure bone stiffness, including computed tomography (CT), bulk wave ultrasound (BWUS) and indentation, were compared against in vitro techniques, including compression testing, density measurements and resonant ultrasound spectroscopy. Porosity, as measured by micro-CT, correlated with femoral neck cortical bone's elastic modulus and ultimate compressive strength at the millimetre length scale. Large-tip spherical indentation also correlated with bone mechanical properties at this length scale but to a lesser extent. As the elastic mechanical properties of cortical bone correlated with porosity, we would recommend further development of technologies that can safely measure cortical porosity in vivo.

Supination External Rotational Ankle Fracture Injury Pattern Correlation With Regional Bone Density

BACKGROUND:

Rotational ankle fractures can present with an array of possible osseous and ligamentous injury combinations in reliable anatomic locations. What accounts for these different injury patterns and whether specific patient and injury factors underlie the different injury patterns is unclear. The purpose of this study was to determine whether causative factors exist that could account for the various injury patterns seen with rotational ankle fractures.

METHODS:

A registry of operatively treated supination external rotation stage IV (SER IV) ankle fractures was used to identify patients. Computed tomography imaging was used to calculate regional bone density by using average Hounsfield unit measurements on axial images from the distal tibia and fibula. Patients were grouped into those with no posterior or medial malleolar fracture (equivalent group), those with either a posterior or medial malleolus fracture (bimalleolar group), and those with both posterior and medial malleolar fractures (trimalleolar group). Sixty-seven patients met inclusion criteria.

RESULTS:

Regional bone density at the ankle, as measured with Hounsfield units, was significantly higher in the equivalent group (371) than in the bimalleolar group (271, P < .0001) and trimalleolar group (228, P < .0001). Logistic regression analyses identified regional bone density as a significant predictor of a medial malleolus fracture ( P = .002) and of a posterior malleolus fracture ( P = .005).

CONCLUSION:

In our cohort of SER IV ankle fractures, regional bone density at the ankle significantly correlated with the presence and number of malleolar fractures compared with ligamentous ruptures. Treating surgeons can use this information to anticipate bone quality during operative fixation based on ankle fracture injury pattern. In addition, the presence of a trimalleolar ankle fracture was a significant indicator of poor bone quality and may represent the first clinical sign of abnormal bone metabolism in many patients.

LEVEL OF EVIDENCE:

Level III, prognostic retrospective cohort study.

Bone density correlates with clinical outcomes after ankle fracture fixation

INTRODUCTION

Osteoporosis and decreased bone density are known to increase fracture incidence and severity. Although much is known regarding the effects of bone density on fracture risk and the treatment options for prevention of fragility fractures, whether bone quality alters clinical outcomes after fracture fixation is unknown. The purpose of this study was to determine whether bone quality correlates with clinical outcomes after fracture fixation.

MATERIALS AND METHODS

A prospective database of all operatively treated ankle fractures by a single surgeon from 2003 to 2013 was used to identify patients. All patients included in the study had preoperative computed tomography (CT) imaging of the injured ankle and postoperative CT imaging of the contralateral ankle. Hounsfield unit (HU) measurement values were determined by placing an elliptical region of interest confined to the cancellous metaphyseal region of the distal tibia and fibula. The primary and secondary clinical outcomes included Foot and Ankle Outcome Scores (FAOS) and ankle range of motion (ROM). Included patients had at least 12 months of clinical outcome data.

RESULTS

Sixty-four patients met the inclusion criteria. Comparison of HU values from the injured and contralateral side demonstrated almost perfect agreement (ICC(2,1) = 0.938), suggesting that HU values can be accurately measured in the setting of a fracture. Increased HU values of the injured distal tibia and fibula significantly correlated with improved outcomes in four of five FAOS domains, including pain, activities of daily living, sports, and quality of life (beta = 0.285-0.344; P ≤ 0.05 for all). Range of motion outcomes did not significantly correlate with HU values.

CONCLUSIONS

Our results suggest that decreased bone quality, as measured using preoperative CT, significantly correlates with inferior short-term clinical outcomes. These results have significant implications for integrating bone quality into treatment algorithms for fracture patients.

Segmental bone replacement via patient-specific, three-dimensional printed bioresorbable graft substitutes and their use as templates for the culture of mesenchymal stem cells under mechanical stimulation at various frequencies

The treatment of large segmental bone defects remains a challenge as infection, delayed union, and nonunion are common postoperative complications. A three-dimensional printed bioresorbable and physiologically load-sustaining graft substitute was developed to mimic native bone tissue for segmental bone repair. Fabricated from polylactic acid, this graft substitute is novel as it is readily customizable to accommodate the particular size and location of the segmental bone of the patient to be replaced. Inspired by the structure of the native bone tissue, the graft substitute exhibits a gradient in porosity and pore size in the radial direction and exhibit mechanical properties similar to those of the native bone tissue. The graft substitute can serve as a template for tissue constructs via seeding with stem cells. The biocompatibility of such templates was tested under in vitro conditions using a dynamic culture of human mesenchymal stem cells. The effects of the mechanical loading of cell-seeded templates under in vitro conditions were assessed via subjecting the tissue constructs to 28 days of daily mechanical stimulation. The frequency of loading was found to have a significant effect on the rate of mineralization, as the alkaline phosphatase activity and calcium deposition were determined to be particularly high at the typical walking frequency of 2 Hz, suggesting that mechanical stimulation plays a significant role in facilitating the healing process of bone defects. Utilization of such patient-specific and biocompatible graft substitutes, coupled with patient's bone marrow cells seeded and exposed to mechanical stimulation of 2 Hz have the potential of reducing significant volumes of cadaveric tissue required, improving long-term graft stability and incorporation, and alleviating financial burdens associated with delayed or failed fusions of long bone defects.

The association of inflammatory bowel disease and immediate postoperative outcomes following lumbar fusion

BACKGROUND CONTEXT

The United States Centers for Disease Control and Prevention estimates the prevalence of inflammatory bowel disease (IBD) at more than 3.1 million people. As diagnostic techniques and treatment options for IBD improve, the prevalence of IBD is expected to increase. For spine surgeons, patients with IBD have a unique complication profile because patients with IBD may present with poor nutritional status and because the medications used to manage IBD have been associated with poor vertebral bone mineralization and immunosuppression. Presently, there are very limited data regarding perioperative outcomes among patients with IBD who undergo spinal surgery. The present study begins to address this knowledge gap by describing trends in patients with IBD undergoing lumbar fusion and by quantifying the association between IBD and immediate postoperative outcomes using a large, national database.

PURPOSE

To advance our understanding of the potential pitfalls and risks associated with lumbar fusion surgery in patients with IBD.

DESIGN/SETTING

Retrospective cross-sectional analysis.

PATIENT SAMPLE

The Nationwide Inpatient Sample (NIS) database was queried from 1998 to 2011 to identify adult patients (18+) who underwent primary lumbar fusion operations using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) coding.

OUTCOME MEASURES

Incidence of lumbar fusion procedures, prevalence of IBD, complication rates, length of stay, and total hospital charges.

METHODS

The annual number of primary lumbar fusion operations performed between 1998 and 2011 was obtained from the NIS database. Patients younger than 18 years of age were excluded. The prevalence of IBD in this population (both Crohn disease and ulcerative colitis) was determined using ICD-9-CM codes. Logistic regression models were estimated to determine the association between IBD and the odds of postoperative medical and surgical complications, while controlling for patient demographics, comorbidity burden, and hospital characteristics. The complex survey design of the NIS was taken into account by clustering on hospitals and assuming an exchangeable working correlation using the discharge weights supplied by the NIS. We accounted for multiple comparisons using the Bonferroni correction and an alpha level for statistical significance of . 0028.

RESULTS

The prevalence of IBD is increasing among patients undergoing lumbar fusion, from 0.21% of all patients undergoing lumbar fusion in 1998 to 0.48% of all patients undergoing lumbar fusion in 2011 (p<.001). The odds of experiencing a postoperative medical or surgical complication were not significantly different when comparing patients with IBD with control patients without IBD after controlling for patient demographics, comorbidity burden, and hospital characteristics (adjusted odds ratio=1.1, 95% confidence interval [CI] 0.99-1.3, p=.08). On multivariable analysis, the presence of IBD in patients undergoing lumbar fusion surgery was associated with longer length of stay and greater hospitalization charges.

CONCLUSIONS

Among patients who underwent lumbar fusion, IBD is a rare comorbidity that is becoming increasingly more common. Importantly, patients with IBD were not at increased risk of postoperative complications. Spine surgeons should be prepared to treat more patients with IBD and should incorporate the present findings into preoperative risk counseling and patient selection.

Insufficient stability of pedicle screws in osteoporotic vertebrae: biomechanical correlation of bone mineral density and pedicle screw fixation strength

PURPOSE

Loosening of pedicle screws is one major complication of posterior spinal stabilisation, especially in the patients with osteoporosis. Augmentation of pedicle screws with cement or lengthening of the instrumentation is widely used to improve implant stability in these patients. However, it is still unclear from which value of bone mineral density (BMD) the stability of pedicle screws is insufficient and an additional stabilisation should be performed. The aim of this study was to investigate the correlation of bone mineral density and pedicle screw fatigue strength as well as to define a threshold value for BMD below which an additional stabilisation is recommended.

METHODS

Twenty-one human T12 vertebral bodies were collected from donors between 19 and 96 years of age and the BMD was measured using quantitative computed tomography. Each vertebral body was instrumented with one pedicle screw and mounted in a servo-hydraulic testing machine. Fatigue testing was performed by implementing a cranio-caudal sinusoidal, cyclic (0.5 Hz) load with stepwise increasing peak force.

RESULTS

A significant correlation between BMD and cycles to failure (r = 0.862, r ² = 0.743, p < 0.001) as well as for the linearly related fatigue load was found. Specimens with BMD below 80 mg/cm³ only reached 45% of the cycles to failure and only 60% of the fatigue load compared to the specimens with adequate bone quality (BMD > 120 mg/cm³).

CONCLUSIONS

There is a close correlation between BMD and pedicle screw stability. If the BMD of the thoracolumbar spine is less than 80 mg/cm³, stability of pedicle screws might be insufficient and an additional stabilisation should be considered.

Fracture repair: general aspects and influence of osteoporosis and anti-osteoporosis treatment

Bone differs from other tissues in its capacity to self-repair after a fracture. The low bone mass and structural deterioration of bone associated with osteoporosis increases the risk of fragility fracture compared with healthy individuals. The intention of this article is to review the complex process of fracture repair and essential requirements for a successful fracture healing response summarized as the "diamond concept" in terms of aging and osteoporosis. The current preclinical and clinical evidence for a beneficial or harmful influence of anti-osteoporosis medications such as bisphosphonates, parathyroid hormone (PTH), strontium ranelate and antibodies of Wnt-inhibiting signaling proteins on bone healing is presented and discussed. Literature suggests that there are no detrimental consequences of such therapeutics on fracture repair processes. Following a fragility fracture, it seems that early start of preventive anti-osteoporotic treatment right after surgery does not delay the union of the fracture, except perhaps in the case of very rigidly fixed fracture requiring direct bone healing. There is some promising experimental and clinical evidence for possible enhancement of the bone repair process via administration of systemic agents. Further well designed studies in humans are necessary to accumulate more evidence on the positive effects and to translate this knowledge into valid therapeutic applications.

A comparison of conventional compression plates and locking compression plates using cantilever bending in an ilial fracture model

OBJECTIVES

The purpose of this study was to compare the stiffness, yield load, ultimate load at failure, displacement at failure, and mode of failure in cantilever bending of locking compression plates (LCP) and dynamic compression plates (DCP) in an acute failure ilial fracture model. Our hypothesis was that the LCP would be superior to the DCP for all of these biomechanical properties.

METHODS

Ten pelves were harvested from healthy dogs euthanatized for reasons unrelated to this study and divided into two groups. A transverse osteotomy was performed and stabilized with either a 6-hole DCP applied in compression or a 6-hole LCP. Pelves were tested in cantilever bending at 20 mm/min to failure and construct stiffness, yield load, ultimate load at failure, displacement at failure, and mode of failure were compared.

RESULTS

The mean stiffness of DCP constructs (193 N/mm [95% CI 121 - 264]) and of LCP constructs (224 N/mm [95% CI 152 - 295]) was not significantly different. Mean yield load of DCP constructs (900 N [95% CI 649 -1151]) and of LCP constructs (984 N [95% CI 733 -1235]) was not significantly different. No significant differences were found between the DCP and LCP constructs with respect to mode of failure, displacement at failure, or ultimate load at failure.

CLINICAL SIGNIFICANCE

Our study did not demonstrate any differences between DCP and LCP construct performance in acute failure testing in vitro.

Bone structural and mechanical indices in Adolescent Idiopathic Scoliosis evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT)

Adolescent Idiopathic Scoliosis (AIS) is associated with systemic low bone mass. It could persist into adulthood and was shown to be an important prognostic factor for curve progression in AIS. Previous studies were confined to areal bone mineral density (aBMD) measured by Dual-energy X-ray Absorptiometry (DXA) which was a two-dimensional measurement for a three-dimensional structure. This conventional measurement was inadequate to evaluate volumetric bone density and bone quality which are important determinants for bone strength and bone health status as defined in the 2000 NIH consensus statement. High-resolution peripheral quantitative computed tomography (HR-pQCT) was therefore used in this study for three-dimensional evaluation of volumetric bone mineral density and bone micro-architecture as well as estimation of bone strength. In this study, 214 newly diagnosed AIS girls and 187 age and gender-matched normal control aged between 11 and 13years old were recruited for HR-pQCT evaluations on bone geometry, trabecular bone micro-architecture and volumetric BMD (vBMD) at the non-dominant distal radius. We demonstrated that AIS was associated with lower Cortical Bone Area, Cortical Bone vBMD, Trabecular Number and greater Trabecular Separation. With multivariate linear regression analysis and after adjustment for age, dietary calcium intake and physical activity level, the association of AIS with lower Cortical Bone vBMD, lower Trabecular Number and greater Trabecular Separation remained statistically significant. The findings of this study indicated that AIS was associated with an abnormal bone quality profile suggestive of alteration in endocortical modeling, derangement in trabecular bone structure and disturbance in bone mineralization. The cause for these changes and how they are related to the etiopathogenesis of AIS warrant further studies.

The osteoporotic acetabular fracture

Fractures of the acetabulum are some of the most challenging fractures that face orthopedic surgeons. In geriatric patients, these challenges are enhanced by the complexity of fracture patterns, the poor biomechanical characteristics of osteoporotic bone, and the comorbidities present in this population. Nonsurgical management is preferable when the fracture is stable enough to allow mobilization, and healing in a functional position can be expected. When significant displacement and/or hip instability are present, operative management is preferred in most patients, which may include open reduction and internal fixation with or without total hip arthroplasty.