The relationship between bone mineral density and biomechanics in patients with osteoporosis and scoliosis

Bone density in postmenopausal women with scoliosis is associated with markers of degenerative joint disease

PURPOSE

Bone mineral density (BMD) measured with dual x-ray absorptiometry (DXA) is the clinical standard for the diagnosis of osteoporosis and prediction of bone fracture risk. In the aging skeleton, osteoporosis is often concomitantly present with degenerative joint disease (DJD).

METHODS

In this study, we evaluated tissue-level changes in the differentially loaded concave (CC) and convex (CV) sides of the lumbar spine in a sample of postmenopausal women with scoliosis. We used a cumulative degeneration score to assess osteophyte formation, the severity of sclerotic morphology, and marrow changes as markers of DJD in the lumbar spine and examined the correlation between markers of DJD and BMD.

RESULTS

More severe osteophyte growth and sclerosis were present on the CC side of the spine. The degenerative score (DS) was higher on the CC side of the lumbar spine compared with the CV side. While CC BMD was positively correlated with CC DS and marrow, CV DS was not correlated with CV BMD. Marrow changes were correlated with DS on the CC lumbar spine.

CONCLUSION

These results highlight the importance of mechanoadaptive as well as broader inflammatory processes in the manifestation of degenerative changes and local mineral deposition at the lumbar spine. DXA-based BMD measurement of osteoporosis need to be contextualized within the biomechanical and degenerative conditions of a joint rather than using a strict threshold cutoff.

Studying trabecular bone samples demonstrates a power law relation between deteriorated structure and mechanical properties - a study combining 3D printing with the finite element method

Introduction

The bone volume fraction (BV/TV) significantly contributes to the mechanical properties of trabecular bone. However, when studies compare normal trabeculae against osteoporotic trabeculae (in terms of BV/TV decrease), only an "average" mechanical result has been determined because of the limitation that no two trabecular structures are the same and that each unique trabecular structure can be mechanically tested only once. The mathematic relation between individual structural deterioration and mechanical properties during aging or the osteoporosis process has yet to be further clarified. Three-dimensional (3D) printing and micro-CT-based finite element method (μFEM) can assist in overcoming this issue.

Methods

In this study, we 3D printed structural-identical but BV/TV value-attenuated trabecular bones (scaled up ×20) from the distal femur of healthy and ovariectomized rats and performed compression mechanical tests. Corresponding μFEM models were also established for simulations. The tissue modulus and strength of 3D printed trabecular bones as well as the effective tissue modulus (denoted as Ez) derived from μFEM models were finally corrected by the side-artifact correction factor.

Results

The results showed that the tissue modulus _corrected, strength _corrected and Ez _corrected exhibited a significant power law function of BV/TV in structural-identical but BV/TV value-attenuated trabecular samples.

Discussion

Using 3D printed bones, this study confirms the long-known relationship measured in trabecular tissue with varying volume fractions. In the future, 3D printing may help us attain better bone strength evaluations and even personal fracture risk assessments for patients who suffer from osteoporosis.

Prevalence of osteoporosis in spinal surgery patients older than 50 years: A systematic review and meta-analysis

INTRODUCTION

In spine surgery, poor bone condition is associated with several complications like adjacent segment fractures, proximal junctional kyphosis, and screw loosening. Our study explored the prevalence of osteoporosis in spinal surgery patients older than 50 years through a systematic review and meta-analysis.

METHODS

This systematic review and meta-analysis were conducted according to the PRISMA criteria. Three electronic databases, including PubMed, EMBASE, and Web of Science, were searched from inception to August 2022. We used the random-effects model to calculate the overall estimates, and the heterogeneity was measured using Cochran's Q and I2 tests. Meta-regression and subgroup analyses were used to determine the source of the heterogeneity.

RESULTS

Based on the inclusion and criteria, we chose ten studies with 2958 individuals for our analysis. The prevalence of osteoporosis, osteopenia, and osteoporosis/osteopenia in the spinal surgery patients was 34.2% (95%CI: 24.5%-44.6%), 43.5% (95%CI: 39.8%-47.2%), and 78.7% (95%CI: 69.0%-87.0%), respectively. Regarding different diagnoses, the prevalence was highest in patients with lumbar scoliosis (55.8%; 95%CI: 46.8%-64.7%) and the lowest in patients with cervical disc herniation (12.9%; 95%CI: 8.1%-18.7%). In age groups 50-59, 50-69,70-79, the prevalence was 27.8%, 60.4%, 75.4% in females, and 18.9%, 17.4%, 26.1% in males.

CONCLUSIONS

This study showed a high prevalence of osteoporosis in patients undergoing spine surgery, especially in females, people of older age, and patients who received degenerative scoliosis and compression fractures. Current osteoporosis screening standards for patients undergoing spine surgery may not be adequate. Orthopedic specialists should make more efforts regarding preoperative osteoporosis screening and treatment.

Efficacy of percutaneous kyphoplasty on vertebral compression fractures with different bone mineral densities: a retrospective study

BACKGROUND

This study was performed to investigate the clinical efficacy of percutaneous kyphoplasty (PKP) for vertebral compression fractures with different bone mineral densities (BMD).

METHODS

We performed a retrospective analysis of 232 patients with single-segment vertebral compression fractures who underwent PKP. Patients were divided into the normal BMD, osteopenia, and osteoporosis groups according to their average lumbar BMD before surgery. The visual analog scale (VAS) was used to compare differences in pain relief before and after surgery in each group. Corrections of the wedge angle and kyphotic angle before and after surgery were observed using anteroposterior and lateral radiographs and compared among the groups, as was the incidence of bone cement leakage.

RESULTS

Patients were followed up for 6-12 months, with an average follow-up time of 9.12 ± 1.68 months. The VAS score, wedge angle, and kyphotic angle of the three groups of patients decreased significantly at the end of the follow-up (P < 0.05). The changes in VAS score and wedge angle correction in the osteoporosis group were significantly larger than those in the normal BMD and osteopenia groups (P < 0.05). There were no significant differences among the three groups in terms of kyphotic angle correction or bone cement leakage rates (P > 0.05).

CONCLUSIONS

PKP has a positive effect on vertebral compression fractures with different BMD, and is especially suitable for osteoporotic vertebral compression fractures.

Analysis of stress and stabilization in adolescent with osteoporotic idiopathic scoliosis: finite element method

Objective: To explore the effect of osteoporosis on the stress, stability, and lumbar intervertebral disc of AIS lumbar vertebrae by finite element method. Better understand the biomechanical characteristics of osteoporotic scoliosis.Methods: Based on the CT images of normal lumbar vertebrae and lumbar vertebrae with AIS, the finite element models were established to simulate the estimated osteoporosis by changing the Young's modulus of cortical bone, cancellous bone, and endplate. Four finite element models of normal lumbar, osteoporotic lumbar, normal AIS lumbar and osteoporotic AIS lumbar were established, and the same load and boundary conditions were applied respectively. The displacement, stress, and intervertebral disc strain of the four models were compared to explore the effect of osteoporosis on the stability and injury risk of AIS.Results: After suffering from osteoporosis, under the same load, the displacement of lumbar spine increases, the stability decreases, and the stability of AIS lumbar spine decrease more obviously, especially under extension load. Suffering from osteoporosis will increase the stress of lumbar spine, AIS lumbar spine increases more obviously, and the stress is more concentrated, Osteoporotic lumbar spine only affects the strain of intervertebral disc when AIS lumbar spine bends on the concave side, resulting in greater strain behind the concave side of intervertebral disc.Conclusions: AIS patients with OP have lower lumbar stability, a higher risk of fracture of lumbar vertebrae, and spinal nerves are more likely to be compressed by intervertebral discs. OP can aggravate the scoliosis of lumbar vertebrae.

New Horizons for Hydroxyapatite Supported by DXA Assessment-A Preliminary Study

Dual Energy X-ray Absorptiometry (DXA) is a tool that allows the assessment of bone density. It was first presented by Cameron and Sorenson in 1963 and was approved by the Food and Drug Administration. Misplacing the femoral neck box, placing a trochanteric line below the midland and improper placement of boundary lines are the most common errors made during a DXA diagnostic test made by auto analysis. Hydroxyapatite is the most important inorganic component of teeth and bone tissue. It is estimated to constitute up to 70% of human bone weight and up to 50% of its volume. Calcium phosphate comes in many forms; however, studies have shown that only tricalcium phosphate and hydroxyapatite have the characteristics that allow their use as bone-substituted materials. The purpose of this study is aimed at analyzing the results of hip densitometry and hydorxyapatite distribution in order to better assess the structure and mineral density of the femoral neck. However, a detailed analysis of the individual density curves shows some qualitative differences that may be important in assessing bone strength in the area under study. To draw more specific conclusions on the therapy applied for individual patients, we need to determine the correct orientation of the bone from the resulting density and document the trends in the density distribution change. The average results presented with the DXA method are insufficient.

Adult Degenerative Scoliosis

Populational aging increases the incidence of musculoskeletal degenerative processes, such as adult scoliosis (AS). Adult scoliosis is defined as a spinal deformity in the coronal plane with a Cobb angle > 10°. Adult scoliosis may be iatrogenic or result from a degenerative process (scoliosis de novo ) or a pre-existing scoliosis.

Adult scoliosis is a potentially limiting condition that affects a heterogeneous group of patients. Clinical treatment proved to be ineffective and surgery is often indicated. The present paper reviews AS pathophysiology, clinical presentation and diagnosis, in addition to surgical indications and the main techniques currently used.

Evaluation of vertebral bone mineral density in scoliosis by using quantitative computed tomography

Purpose

Scoliosis is described as a lateral curvature of the spine. We aimed to evaluate bone mineral density (BMD) in patients with scoliosis by using quantitative computed tomography (QCT) and compare the BMD of idiopathic and congenital scoliosis patients.

Material and methods

Forty-three patients aged 1 to 40 years with idiopathic, congenital, or neuromuscular scoliosis and 41 matched controls of the same sex and approximate age were included in the study. Measurements of BMD were performed by QCT analysis for each vertebral body from T12 to L5, and mean BMD was calculated for each case.

Results

Twenty-two of the patients with scoliosis were idiopathic, 15 were congenital, four were neuromuscular, and two were neurofibromatosis. The mean BMD values of patients with scoliosis were significantly lower compared with the control group (106.8 ± 33.4 mg/cm³ vs. 124.9 ± 29.1 mg/cm³, p = 0.009). No significant difference in BMD values was found between idiopathic and congenital scoliosis patients (p > 0.05).

Conclusions

This study illustrated that the vertebral body BMD values of the patients with scoliosis were significantly lower than those seen in the control group.

Transient peak-strain matching partially recovers the age-impaired mechanoadaptive cortical bone response

Mechanoadaptation maintains bone mass and architecture; its failure underlies age-related decline in bone strength. It is unclear whether this is due to failure of osteocytes to sense strain, osteoblasts to form bone or insufficient mechanical stimulus. Mechanoadaptation can be restored to aged bone by surgical neurectomy, suggesting that changes in loading history can rescue mechanoadaptation. We use non-biased, whole-bone tibial analyses, along with characterisation of surface strains and ensuing mechanoadaptive responses in mice at a range of ages, to explore whether sufficient load magnitude can activate mechanoadaptation in aged bone. We find that younger mice adapt when imposed strains are lower than in mature and aged bone. Intriguingly, imposition of short-term, high magnitude loading effectively primes cortical but not trabecular bone of aged mice to respond. This response was regionally-matched to highest strains measured by digital image correlation and to osteocytic mechanoactivation. These data indicate that aged bone’s loading response can be partially recovered, non-invasively by transient, focal high strain regions. Our results indicate that old murine bone does respond to load when the loading is of sufficient magnitude, and bones’ age-related adaptation failure may be due to insufficient mechanical stimulus to trigger mechanoadaptation.

Degenerative Scoliosis

PURPOSE OF REVIEW

The purpose of this review is to provide an updated review of adult degenerative scoliosis (ADS). Epidemiology, classification, pathophysiology, and natural history are discussed along with a summary of commonly used outcome measures. Operative vs non-operative outcomes and new surgical techniques are discussed.

RECENT FINDINGS

The SRS-Schwab classification (2012) combines clinical and radiographic evaluation including overall global alignment. Current evidence regarding risk factors and efficacy of non-surgical modalities are discussed. Recent studies have reported surgical management to provide superior outcomes to non-operative modalities. New surgical techniques provide promising early data in regard to decreasing perioperative morbidity. ADS is a potentially debilitating condition that occurs with asymmetric spinal degeneration. This can produce global sagittal malalignment and central and foraminal stenosis and can lead to significant impairment often necessitating surgery. The surgeon must be aware of the perioperative risks in this population and implement appropriate age-specific alignment goals to achieve the best outcome for patients.

Anterior and posterior variations in mechanical properties of human vertebrae measured by nanoindentation

Osteoporotic spinal fractures are a significant global public health issue affecting more than 200 million people. Local degradation of the mechanical properties of bone and changes in global spine curvature increase fracture risk. However, a gap in knowledge exists relating material properties of trabecular bone in different regions of the spine. The purpose of our project was to measure the intrinsic mechanical properties of the anterior and posterior regions of human vertebral bodies in the thoracic and lumbar spine. Nanoindentation was used to evaluate Young's modulus (E) and hardness (H) of anterior and posterior trabecular bone regions from each vertebra (T7, T8 and L4). One-way ANOVA and the Turkey-Kramer test were used to analyze significance between vertebrae and t-test was used to test for significance within vertebrae. There was no difference in (E) and (H) within vertebrae. Young's modulus in the anterior regions of T7 (19.8±1.3) and T8 (19.6±1.4) were statistically greater than that in L4 (17.6±0.5). There was no difference between the posterior regions of all the vertebrae. There was a statistical significant difference in hardness between the anterior regions of T7 and T8 compared to L4, while the posterior regions demonstrated no difference. The results presented in this study, for the first time, reveal the differences in bone properties between the kyphotic thoracic spine and lordotic lumbar spine regions. This information will be helpful in understanding vertebral body remodeling and adaption in different regions of the spine which may be associated with spinal curvature and loading conditions.

Longitudinal changes in lumbar bone mineral density distribution may increase the risk of wedge fractures

BACKGROUND

Trabecular bone strength diminishes as a result of osteoporosis and altered biomechanical loading at the vertebral and spinal levels. The spine consists of the anterior, middle and posterior columns and the load supported by the anterior and middle columns will differ across different regions of the spine. Stress shielding of the anterior column can contribute to bone loss and increase the risk of wedge fracture. There is a lack of quantitative data related to regional spinal bone mineral density distribution over time. We hypothesize that there is an increase in the posterior-to-anterior vertebral body bone mineral density ratio and a decrease in whole-body bone mineral density over time.

METHODS

Bone mineral density was measured in 33 subjects using quantitative computed tomography scans for L1-L3 vertebrae, region (anterior and posterior vertebral body), and time (baseline and 6 years after).

FINDINGS

Lumbar bone mineral density decreased significantly (Δ: ~15%) from baseline to the 6th year visit. Individual vertebra differences over time (L1: ~14%, L2: ~14%, L3: ~17%) showed statistical significance. Anterior bone mineral density change was significantly greater than in the posterior vertebral body region (Δ anterior: ~18%; Δ posterior: ~13%). Posterior-to-anterior bone mineral density ratio was significantly greater in the 6th year compared to baseline values (mean (SD), 1.33 (0.2) vs. 1.23 (0.1)).

INTERPRETATION

This study provides longitudinal quantitative measurement of bone mineral density in vertebrae as well as regional changes in the anterior and posterior regions. Understanding bone mineral density distribution over time may help to decrease the risk of wedge fractures if interventions can be developed to bring spine loading to its normal state.

Characterization of osteopenia/osteoporosis in adult scoliosis: does bone density affect surgical outcome?

STUDY DESIGN

Retrospective study.

OBJECTIVE

The aim of this study is to validate the prevalence of low bone mineral density (BMD) in woman patients with adult scoliosis and to relate that to surgical treatment outcome. Despite reports of the high prevalence of low BMD among female with adolescent idiopathic, these findings have not been substantiated in any comprehensive review of adult scoliosis patients undergoing surgical treatment.

SUMMARY OF BACKGROUND DATA

It has been suggested that scoliosis may predispose to osteoporosis and that degenerative scoliosis could falsely elevate spinal BMD measurements with dual energy radiograph absorptiometry (DXA). The discordance between hip and spine BMD measurement using DXA has also been shown in previous cross-sectional study for adult population.

METHODS

A retrospective review of 176 women treated surgically for scoliosis. BMD of the lumbar spine and femoral neck were determined by DXA. Patients were categorized as follows: concordance (osteoporosis, osteopenia, or normal BMD on both sites), minor discordance (osteoporosis in one site and osteopenia in the other site), and major discordance (osteoporosis in one site and normal the other site). Body mass index (BMI), preoperative Cobb angle, fusion ratio, and complication were recorded. Statistical analysis included the Student t test, χ(2) test, regression coefficient test, and simple linear regression. P value was set at P < 0.05.

RESULTS

The mean age was 51 ± 12 years (26-82 years). The mean T score of the hip was -1.23 ± 0.89 and of the spine was -0.52 ± 1.57. Major discordance in BMD 7 (4%) points, minor discordance 68 (39%) points, and concordance was 101 (57%) points. There was moderate correlation between T score of hip and spine (R = 0.55P < 0.01). T score of the hip and of the spine showed 10.8% and 10.2% of the patients were osteoporotic. The mean Z score of the hip and of the spine showed comparable age and sex matched values. No correlation was observed between BMD and Cobb angle (R = 0.05, P = 0.464). The fusion rate was 93% and surgical complication rate was 14.9%. No significant correlation was observed between BMD and fusion (P = 0.80) complication (P = 0.13).

CONCLUSION

Comparable bone density exists among adult scoliosis patients with no correlation between BMD and curve magnitude, fusion and complication rates. The difference in BMD of the hip and of spine cannot be fully explained in the review. These results will guide in surgical planning, patient selection on the treatment options.

Lateral bone density variations in the scoliotic spine

Adolescent Idiopathic Scoliosis (AIS) is the most common deformity of the spine, affecting 2-4% of the population. Previous studies have shown that the vertebrae in scoliotic spines undergo abnormal shape changes, however there has been little exploration of how scoliosis affects bone density distribution within the vertebrae. In this study, existing CT scans of 53 female idiopathic scoliosis patients with right-sided main thoracic curves were used to measure the lateral (right to left) bone density profile at mid-height through each vertebral body. Five key bone density profile measures were identified from each normalized bone density distribution, and multiple regression analysis was performed to explore the relationship between bone density distribution and patient demographics (age, height, weight, body mass index (BMI), skeletal maturity, time since Menarche, vertebral level, and scoliosis curve severity). Results showed a marked convex/concave asymmetry in bone density for vertebral levels at or near the apex of the scoliotic curve. At the apical vertebra, mean bone density at the left side (concave) cortical shell was 23.5% higher than for the right (convex) cortical shell, and cancellous bone density along the central 60% of the lateral path from convex to concave increased by 13.8%. The centre of mass of the bone density profile at the thoracic curve apex was located 53.8% of the distance along the lateral path, indicating a shift of nearly 4% toward the concavity of the deformity. These lateral bone density gradients tapered off when moving away from the apical vertebra. Multi-linear regressions showed that the right cortical shell peak bone density is significantly correlated with skeletal maturity, with each Risser increment corresponding to an increase in mineral equivalent bone density of 4-5%. There were also statistically significant relationships between patient height, weight and BMI, and the gradient of cancellous bone density along the central 60% of the lateral path. Bone density gradient is positively correlated with weight, and negatively correlated with height and BMI, such that at the apical vertebra, a unit decrease in BMI corresponds to an almost 100% increase in bone density gradient.

The effects of anti-resorptive therapies and estrogen withdrawal in adult scoliosis measured by sub-segmental vertebral BMD analysis

The sub-segmental analysis of dual energy X-ray absorptiometry (DXA) scans from scoliotic vertebrae has established that there are differences in bone mass between the concave and convex sides of the vertebrae. Furthermore, these differences persisted in patients with low bone mass and were related to the geometry and applied loads, suggesting that this is a good model of bone adaptation in response to external stimuli. The goal of this study was to characterize the response of the human scoliotic spine to anti-resorptive treatments and estrogen withdrawal on the concave and convex sides of the spine. A total of 576 vertebrae (199 no treatment, 214 bisphosphonate, 69 estrogen and 94 estrogen withdrawal) were analyzed from 167 postmenopausal, Caucasian women. An analysis of variance (ANOVA) was used in conjunction with post-hoc Tukey tests to examine the effects of concavity, treatment group, and age. We found that the average change in BMD per year was greater than zero on the concave and convex sides with the exception of the estrogen withdrawal group. Discontinuing estrogen therapy caused patients to maintain bone mass on the concave side, but lose substantial bone density on the convex side. A differential response was also observed with respect to age. Patients younger than 60 exhibited a decrease in total BMD per year concomitant with a small degree of straightening, while those who were 60 or over demonstrated an increase in bone mass and a slight increase in the deformity. Based on these data, it is clear that the differences in BMD between the concave and convex sides of the vertebrae are not simply a result of the deformity, but more likely due to bone accretion. Further study is needed to elucidate the relationship between biomechanical forces and the adaptive response in the spine as a function of time.

Bone mineral density deficits in pediatric patients treated for sarcoma

BACKGROUND

Children treated for sarcoma are at risk of treatment-associated deficits in bone mineral density (BMD). We investigated the severity of risk factors for BMD deficits in this patient population.

PROCEDURE

Using signed-rank test and logistic regression analysis, we retrospectively analyzed the relation of treatment variables and other potential risk factors to BMD (using quantitative computed tomography (QCT)) of 99 patients treated for pediatric sarcoma who had completed therapy at least 1 year previously.

RESULTS

The study group (38% rhabdomyosarcoma (RMS), 25% osteosarcoma (OS), 24% Ewing-family tumors, and 12% non-rhabdomyosarcoma soft-tissue sarcoma (NRSTS)) represented 22% of the sarcoma survivors treated between 1982 and 2003 who remained in follow-up at St. Jude. These patients underwent QCT between July 1, 1997 and February 5, 2003. Their median age was 8.7 years (range, 0.2-21.3 years) at diagnosis and 17.4 years (range, 3.3-30.2 years) at the time of BMD measurement; 58% were male and 82% Caucasian. Median BMD Z-score was -0.75 (range, -3.33-3.02), and median BMD was 168.0 mg/cc (range, 89.2-264.8 mg/cc). Risk of BMD deficit increased significantly with younger age at diagnosis (P = 0.044) and higher cumulative cyclophosphamide dose (P = 0.007). Patients with lower extremity primary disease had a significantly lower risk of BMD deficits than others. We found no association between BMD and body habitus, primary disease, lifestyle factors, or endocrinopathy.

CONCLUSION

A significant subset of sarcoma survivors are at risk of BMD deficits warranting prospective study of BMD to verify our results and refine risk factors contributing to BMD deficits.

Modeling the mechanical consequences of vibratory loading in the vertebral body: microscale effects

Osteoporosis affects nearly 10 million individuals in the United States. Conventional treatments include anti-resorptive drug therapies, but recently, it has been demonstrated that delivering a low magnitude, dynamic stimulus via whole body vibration can have an osteogenic effect without the need for large magnitude strain stimulus. Vibration of the vertebral body induces a range of stimuli that may account for the anabolic response including low magnitude strains, interfacial shear stress due to marrow movement, and blood transport. In order to evaluate the relative importance of these stimuli, we integrated a microstructural model of vertebral cancellous bone with a mixture theory model of the vertebral body. The predicted shear stresses on the surfaces of the trabeculae during vibratory loading are in the range of values considered to be stimulatory and increase with increasing solid volume fraction. Peak volumetric blood flow rates also varied with strain amplitude and frequency, but exhibited little dependence on solid volume fraction. These results suggest that fluid shear stress governs the response of the vertebrae to whole body vibration and that the marrow viscosity is a critical parameter which modulates the shear stress.