Subchondral tibial bone mineral density predicts future joint space narrowing at the medial femoro-tibial compartment in patients with knee osteoarthritis

Quantitative CT of the knee in the IMI-APPROACH osteoarthritis cohort: Association of bone mineral density with radiographic disease severity, meniscal coverage and meniscal extrusion

OBJECTIVE

Osteoarthritis (OA) is a highly prevalent chronic condition. The subchondral bone plays an important role in onset and progression of OA making it a potential treatment target for disease-modifying therapeutic approaches. However, little is known about changes of periarticular bone mineral density (BMD) in OA and its relation to meniscal coverage and meniscal extrusion at the knee. Thus, the aim of this study was to describe periarticular BMD in the Applied Public-Private Research enabling OsteoArthritis Clinical Headway (APPROACH) cohort at the knee and to analyze the association with structural disease severity, meniscal coverage and meniscal extrusion.

DESIGN

Quantitative CT (QCT), MRI and radiographic examinations were acquired in 275 patients with knee osteoarthritis (OA). QCT was used to assess BMD at the femur and tibia, at the cortical bone plate (Cort) and at the epiphysis at three locations: subchondral (Sub), mid-epiphysis (Mid) and adjacent to the physis (Juxta). BMD was evaluated for the medial and lateral compartment separately and for subregions covered and not covered by the meniscus. Radiographs were used to determine the femorotibial angle and were evaluated according to the Kellgren and Lawrence (KL) system. Meniscal extrusion was assessed from 0 to 3.

RESULTS

Mean BMD differed significantly between each anatomic location at both the femur and tibia (p < 0.001) in patients with KL0. Tibial regions assumed to be covered with meniscus in patients with KL0 showed lower BMD at Sub (p < 0.001), equivalent BMD at Mid (p = 0.07) and higher BMD at Juxta (p < 0.001) subregions compared to regions not covered with meniscus. Knees with KL2-4 showed lower Sub (p = 0.03), Mid (p = 0.01) and Juxta (p < 0.05) BMD at the medial femur compared to KL0/1. Meniscal extrusion grade 2 and 3 was associated with greater BMD at the tibial Cort (p < 0.001, p = 0.007). Varus malalignment is associated with significant greater BMD at the medial femur and at the medial tibia at all anatomic locations.

CONCLUSION

BMD within the epiphyses of the tibia and femur decreases with increasing distance from the articular surface. Knees with structural OA (KL2-4) exhibit greater cortical BMD values at the tibia and lower BMD at the femur at the subchondral level and levels beneath compared to KL0/1. BMD at the tibial cortical bone plate is greater in patients with meniscal extrusion grade 2/3.

Mapping knowledge landscapes and emerging trends of the links between osteoarthritis and osteoporosis: A bibliometric analysis

Background

Osteoarthritis has the characteristics of degenerative changes in articular cartilage and secondary osteoporosis, and it is a common chronic irreversible joint disease. In addition to affecting articular cartilage, subchondral bone, joint capsule and synovial membrane also undergo pathological changes during the development of the disease. Multiple studies have revealed that patients with osteoarthritis were found to have a significantly increased risk of osteoporosis, which also contributes to the progression of osteoarthritis. However, in the current existing studies, we found that no scholars have used bibliometric analysis in the study of the relationship between osteoarthritis and osteoporosis. From the perspective of bibliometrics, this study summarizes in detail the degree of cooperation between countries, research institutions, authors, and related journals in the field of osteoarthritis and osteoporosis research and their respective influence. In this way, the evolution of knowledge structure, the change of research focus and the hot topics with research potential in the future can be further visualized and analyzed.

Methods

Search the Web of Science core collection in Science Citation Index Expanded for articles and reviews of research on osteoarthritis and osteoporosis from 1998 to 2021. Bibliometric tools such as VOSviewer, CiteSpace, were be frequently used in our study. They are mainly used to analyze collaborations between countries, research institutions, and publication authors. Meantime, co-citation analysis of journals, co-occurrence analysis of keywords and subject categories will also be reflected in the study.

Results

According to the search strategy, 1,078 publications were included during the period 1998-2021. And the number of annual publications on the relationship between osteoarthritis and osteoporosis is on the rise. The United States has achieved the most and contributed the most in this field and the Boston University was the most prolific institution. For the statistical analysis of published publications, Reginster JY had the highest number of publications, while Felson DT had the highest co-citation frequency. Respectively, Osteoarthritis And Cartilage was the most productive journal in this area of research. The keywords "inflammation," "expression," and "mesenchymal stem cells" may also be the development trend and research hotspot of the future research direction in this field.

Conclusions

In our study, the relationship between osteoarthritis and osteoporosis was analyzed by using literature measurement. These analysis results can lead researchers to learn more directly about the trend in this area and provide guidance for determining popular research directions.

The role of bone mineral density and cartilage volume to predict knee cartilage degeneration

Knee Osteoarthritis (OA) is a highly prevalent condition affecting knee joint that causes loss of physical function and pain. Clinical treatments are mainly focused on pain relief and limitation of disabilities; therefore, it is crucial to find new paradigms assessing cartilage conditions for detecting and monitoring the progression of OA. The goal of this paper is to highlight the predictive power of several features, such as cartilage density, volume and surface. These features were extracted from the 3D reconstruction of knee joint of forty-seven different patients, subdivided into two categories: degenerative and non-degenerative. The most influent parameters for the degeneration of the knee cartilage were determined using two machine learning classification algorithms (logistic regression and support vector machine); later, box plots, which depicted differences between the classes by gender, were presented to analyze several of the key features’ trend. This work is part of a strategy that aims to find a new solution to assess cartilage condition based on new-investigated features.

Hemodynamic stress shapes subchondral bone in osteoarthritis: An emerging hypothesis

Osteoarthritis (OA) is no longer regarded as a simple wear-and-tear problem of articular cartilage. Instead, OA is a whole joint disorder involving both cartilaginous and non-cartilaginous tissues such as subchondral bone and synovium. Among them, subchondral bone undergoes constant remodeling in response to the changes of mechanical environment. Current understanding of subchondral bone disturbance in OA is limited to its link with an altered local mechanical loading as a result of ligament or meniscus injury. Very recently, hypertension, the most common vascular morbidity, has been emerged as an independent risk factor of OA. It might suggest a plausible role of systemic hemodynamic mechanical stress in subchondral bone remodeling and the pathogenesis of OA. However, their relationship remains not fully understood. Based on our preliminary clinical observation on the association of hemodynamic parameters with subchondral bone mass and microstructure in late-stage knee OA patients, we formulate a vascular etiology hypothesis of OA from a mechanobiology perspective. Noteworthily, hemodynamic stress associated with subchondral bone mineral density; yet compressive mechanical loading does not. Furthermore, hemodynamic parameters positively correlated with subchondral plate-like trabecular bone volume but negatively associated with rod-like trabecular bone volume. In contrast, compressive mechanical loading tends to increase both plate-like and rod-like trabecular bone volume. Taken together, it warrants further investigations into the distinct role of hemodynamic or compressive stress in shaping subchondral bone in the pathophysiology of OA.

The Translational potential of this article

This work provides a new insight, from the angle of biomechanics, into the emerging role of vascular pathologies, such as hypertension, in the pathogenesis of OA. It might open up a new avenue for the development of a mechanism-based discovery of novel diagnostics and therapeutics.

Osteoarthritis: Insights Offered by the Study of Bone Mass Genetics

PURPOSE OF REVIEW

This paper reviews how bone genetics has contributed to our understanding of the pathogenesis of osteoarthritis. As well as identifying specific genetic mechanisms involved in osteoporosis which also contribute to osteoarthritis, we review whether bone mineral density (BMD) plays a causal role in OA development.

RECENT FINDINGS

We examined whether those genetically predisposed to elevated BMD are at increased risk of developing OA, using our high bone mass (HBM) cohort. HBM individuals were found to have a greater prevalence of OA compared with family controls and greater development of radiographic features of OA over 8 years, with predominantly osteophytic OA. Initial Mendelian randomisation analysis provided additional support for a causal effect of increased BMD on increased OA risk. In contrast, more recent investigation estimates this relationship to be bi-directional. However, both these findings could be explained instead by shared biological pathways. Pathways which contribute to BMD appear to play an important role in OA development, likely reflecting shared common mechanisms as opposed to a causal effect of raised BMD on OA. Studies in HBM individuals suggest this reflects an important role of mechanisms involved in bone formation in OA development; however further work is required to establish whether the same applies to more common forms of OA within the general population.

Underestimation and undertreatment of osteoporosis in patients awaiting primary total knee arthroplasty

INTRODUCTION

Osteoporosis is generally regarded as a risk factor for periprosthetic fracture during or after primary total knee arthroplasty (TKA). Despite this, little is known about osteoporosis in patients undergoing elective primary TKA Therefore, we sought to investigate the prevalence of osteoporosis and rates of pharmacologic osteoporosis treatment prior to primary TKA. We hypothesized that preoperative osteoporosis is underestimated and undertreated in the primary TKA population.

MATERIALS AND METHODS

This retrospective study included consecutive 1972 patients scheduled for elective primary TKA at a single tertiary hospital (age, 50-89 years). Charts were reviewed for patient demographics, prior pharmacologic osteoporosis treatment and Knee Society (KS) scoring system and WOMAC score. Dual energy X-ray absorptiometry (DEXA) measurement of the lumbar vertebrae and proximal femur was performed in all patients on the day before surgery. The associations of BMD with age, sex, body mass index (BMI), and clinical outcome were analyzed.

RESULTS

The prevalence of osteoporosis was 50.0% (53.4% in women and 7.0% in men). Among patients with osteoporosis, only 15.1% (149/986) of patients (15.0% in women and 30.0% in men) had pharmacological osteoporosis treatment prior to primary TKA. Age, sex and WOMAC stiffness showed association with osteoporosis. Sex (odds ratio (OR): 20.83, p < 0.001) was the most significant factor associated with osteoporosis.

CONCLUSION

Osteoporosis was highly prevalent in patients awaiting TKA, but the rates of diagnosis and pharmacologic osteoporosis treatment were low. Therefore, more attention needs to estimate and treat osteoporosis in patients awaiting primary TKA, especially in female patients.

Impact of meniscal coverage on subchondral bone mineral density of the proximal tibia in female subjects - A cross-sectional in vivo study using QCT

OBJECTIVE

To verify earlier data in cadavers that in female subjects with OA meniscal coverage is associated with lowered bone mineral density of the underlying subchondral bone in the proximal tibia by investigating the local bone mineral density (BMD) distribution within the epiphysis.

METHODS

BMD of the subchondral bone of the tibia was measured by QCT in 67 elderly females diagnosed with OA (Kellgren-Lawrence grades 2-3). The epiphysis was subdivided along the axis of the tibia into a subchondral-epiphyseal VOI covering the first 5-6 mm below the subchondral bone plate, a mid-epiphyseal VOI covering the adjacent 7-8 and a juxtaphyseal VOI of another 7-8 mm that bordered the growth plate. These VIOs were further divided into lateral and medial and then into anterior, mid and posterior sub-VOIs. Finally, all subVOIs were divided in one subVOI covered by the menisci (CM) and another not covered by the menisci (nCM). BMD ratios of these two subVOIs were compared.

RESULTS

In the subchondral epiphysis BMD was significantly lower (Medial: mean BMD_diff = 125 mg/cm³, p<0.001; Lateral: mean BMD_diff = 56 mg/cm³p < 0.001) in subVOIs covered by the meniscus compared to subVOIs not covered by the meniscus. The BMD difference was no longer significant in the mid epiphysis (Medial: mean BMD_diff = 10 mg/cm³, p>0.82; Lateral: mean BMD_diff = 7 mg/cm³, p=0.99) and was reversed in the juxtaphysis. With a few exceptions these BMD differences were independent of the lateral-medial and the anterior-mid-posterior position. BMD significantly (p<0.05) decreased with age independent on whether the location was covered or uncovered by the meniscus, however the BMD ratio of the corresponding nCM and CM subVOIs did not significantly (p>0.1) change with age.

CONCLUSION

In-vivo QCT measurements of the BMD distribution in the proximal tibia indicate a protective effect of the menisci in the subchondral bone close to the joint. This protective effect is age independent despite the overall age-related decrease of BMD.

The association of subchondral and systemic bone mineral density with osteoarthritis-related joint replacements in older adults

OBJECTIVE

To describe the association of subchondral and systemic bone mineral density (BMD) with knee and hip replacements (KR and HR, respectively) due to osteoarthritis.

DESIGN

1,095 participants (mean age 63 years, 51% female) were included. At baseline, subchondral BMD of the medial and lateral tibia in three regions of interest (ROI) for the right knee, and systemic BMD of the lumbar spine, femoral neck, total hip and whole-body, were measured using dual-energy X-ray absorptiometry. Subchondral BMD of the hip was not measured. Competing risk regression models were used to estimate sub-distribution hazard ratios (SHRs) of KR/HR per one standard deviation (SD) higher in BMD measures, with adjustment of potential confounders.

RESULTS

Over 12.2 years, 79 (7.2%) participants underwent a KR and 56 (5.1%) an HR due to osteoarthritis. For the right side, medial subchondral BMD in ROI-3 was associated with an increased risk of KR (SHR 1.95 per SD; 95% Confidence Interval [CI], 1.57 to 2.43). In contrast, systemic BMD was not associated with the risk of KR, but higher BMD at the lumbar spine (1.42, 1.07 to 1.88) and whole-body (1.29, 1.00 to 1.66) were associated with an increased risk of HR at both sides.

CONCLUSIONS

Subchondral BMD is positively associated with an increased risk of KR and systemic BMD with an increased risk of HR, suggesting a role of BMD in the progression of osteoarthritis.

Relationships between cartilage thickness and subchondral bone mineral density in non-osteoarthritic and severely osteoarthritic knees: In vivo concomitant 3D analysis using CT arthrography

OBJECTIVE

To test whether subchondral bone mineral density (sBMD) and cartilage thickness (CTh) of femoral condyles are correlated in knees without and with severe medial femorotibial osteoarthritis (OA), using a subregional analysis with computerized tomography (CT) arthrography.

METHODS

CT arthrograms of 50 non-OA (18 males, 58.7 (interquartile range (IQR) = 6.6 years)) and 50 severe medial OA (24 males, 60.5 (IQR = 10.7) years) knees, were retrospectively analyzed. Bone and cartilage were segmented using custom-designed software, leading to 3D models on which each point of the subchondral surface is given a CTh and sBMD value. The average sBMD and CTh were then calculated for the entire weight-bearing regions as well as specific subregions of interest. Linear bivariate and multivariable analyses were performed to test for relationships between sBMD and CTh (regional and subregional measures, or medial-to-lateral ratios), with confounders of age, gender, femoral bone size and femorotibial angle.

RESULTS

In non-OA knees, the sBMD and CTh medial-to-lateral ratios were positively correlated for the total region and the external and internal subregions (r ≥ 0.341, P ≤ 0.015). In OA knees, sBMD and CTh medial-to-lateral ratios were negatively correlated for the total region and the external and central subregions (r ≤ -0.538, P < 0.001). Additional positive/negative relationships in the non-OA/OA knees were observed between sBMD and CTh measures in the medial compartment.

CONCLUSIONS

The positive correlation between sBMD and CTh in non-OA knees, and the negative one in OA knees, bring support to the theory of a subchondral bone/cartilage functional unit, which could help to better understand the pathophysiology of OA.

Two-year follow-up of bone mineral density changes in the knee after meniscal allograft transplantation: Results of an explorative study

BACKGROUND

The potential chondroprotective effect of meniscal allograft transplantation (MAT) is unclear. Subchondral bone mineral density (BMD) and subchondral bone remodeling play important roles in osteoarthritis development. Evaluation of subchondral BMD after MAT might give more insight into the potential chondroprotective effect. The purpose of this study was to determine early BMD changes in the knee after MAT.

METHODS

Twenty-six consecutive patients underwent MAT during 2010-2013. The BMD was measured using dual-energy x-ray absorptiometry (DXA) scan preoperatively, and six months, one and two years postoperatively. Bone mineral density was measured in six regions of interest (ROIs) in the tibia and femur (medial, central, lateral) in both treated and healthy contralateral knees.

RESULTS

The BMD levels of MAT knees did not significantly change during two years of follow-up in almost all ROIs. Bone mineral density was significant higher in nearly all ROIs in MAT knees at almost all follow-ups compared to healthy contralateral knees. In the healthy contralateral knees, BMD slightly, but not statistically, decreased in the first postoperative year, where it normalized to baseline values at two-year follow-up. The BMD levels in all ROIs did not significantly differ between the patients with or without chondropathy at baseline and two-year follow-up.

CONCLUSION

Based on the findings, MAT did not show a significant influence on BMD in the first two postoperative years. Longer follow-up is necessary to prove the potential chondroprotective effect of MAT using BMD measurements.

Subchondral tibial bone texture predicts the incidence of radiographic knee osteoarthritis: data from the Osteoarthritis Initiative

OBJECTIVES

To evaluate whether trabecular bone texture (TBT) parameters measured on computed radiographs (CR) could predict the onset of radiographic knee osteoarthritis (OA).

MATERIALS AND METHODS

Subjects from the Osteoarthritis Initiative (OAI) with no sign of radiographic OA at baseline were included. Cases that developed either a global radiographic OA defined by the Kellgren-Lawrence (KL) scale, a joint space narrowing (JSN) or tibial osteophytes (TOS) were compared with the controls with no changes after 48 months of follow-up. Baseline bilateral fixed flexion CR were analyzed using a fractal method to characterize the local variations. The prediction was explored using logistic regression models evaluated by the area under the receiver operating characteristic curves (AUC).

RESULTS

From the 344 knees, 79 (23%) developed radiographic OA after 48 months, 44 (13%) developed progressive JSN and 59 (17%) developed osteophytes. Neither age, gender and BMI, nor their combination predicted poorer KL (AUC 0.57), JSN or TOS (AUC 0.59) scores. The inclusion of the TBT parameters in the models improved the global prediction results for KL (AUC 0.69), JSN (AUC 0.73) and TOS (AUC 0.71) scores.

CONCLUSIONS

Several differences were found between the models predictive of three different outcomes (KL, JSN and TOS), indicating different underlying mechanisms. These results suggest that TBT parameters assessed when radiographic signs are not yet apparent on radiographs may be useful in predicting the onset of radiological tibiofemoral OA as well as identifying at-risk patients for future clinical trials.

Quantitative regional and sub-regional analysis of femoral and tibial subchondral bone mineral density (sBMD) using computed tomography (CT): comparison of non-osteoarthritic (OA) and severe OA knees

OBJECTIVE

This study aimed to compare subchondral bone mineral density (sBMD) between non-radiographic osteoarthritic (OA) and medial femorotibial OA knees, using computed tomography (CT).

DESIGN

CT exams from 16 non-radiographic OA (KL grade < 2) and 16 severe medial OA (KL grade ≥ 3) knees (average age of 61.7 ± 3 and 62.2 ± 5 years old respectively, 50% male in each group), were retrospectively analyzed. CT exams were segmented and 3D maps of sBMD based on the CT number in the most superficial 3 mm of femoral and tibial subchondral bone were computed. Average sBMD and medial-to-lateral sBMD ratios were calculated for total load-bearing regions and for sub-regions of interest in the femur and tibia.

RESULTS

The analysis of total load-bearing regions did not reveal any significant difference between groups, except for the lateral tibia, where OA knees had lower sBMD. Sub-regional analysis unveiled differences with some sub-regions of the femur and tibia presenting significantly lower (in the lateral compartment) or higher (in the medial compartment) sBMD in OA knees compared to non-OA knees. The M/L sBMD ratios were significantly higher for OA knees compared to non-OA knees for all regions and sub-regions, except for the internal sub-regions.

CONCLUSIONS

sBMD locally differs between non-OA and OA knees, in agreement with prior knowledge on biomechanics. CT proved to be a valuable tool for 3D analysis of femoral and tibial sBMD, which can be used in future studies to describe the chronology of sBMD alterations and improve our understanding of the role of subchondral bone in knee OA.

Associations between systemic bone mineral density, knee cartilage defects and bone marrow lesions in patients with knee osteoarthritis

AIM

The relationship between bone mineral density (BMD) and osteoarthritis (OA) remains controversial. This study aimed to explore the cross-sectional associations between BMD at the total body, hip and spine and joint structural abnormalities including cartilage defects and bone marrow lesions (BMLs) in patients with knee OA.

METHOD

One hundred and eight-five subjects with symptomatic knee OA were included in this study. T2-weighted fast spin echo magnetic resonance imaging was used to assess knee cartilage defects and BMLs. Total body, hip and spine BMD were measured using dual-energy X-ray absorptiometry.

RESULTS

After adjustment for potential confounders, total hip BMD was negatively associated with medial tibial cartilage defects, lateral femoral cartilage defects, medial tibial BMLs and lateral tibial BMLs. Spine and total body BMD were negatively associated with lateral femoral cartilage defects, but not with BMLs.

CONCLUSION

We concluded that BMD particularly at the hip was negatively associated with knee cartilage defects and BMLs.

Relation between phalangeal bone mineral density and radiographic knee osteoarthritis: a cross-sectional study

Background

Major reports have suggested that bone mineral density (BMD) is higher in patients with osteoarthritis (OA), while other studies do not agree. Our aim was to examine the cross-sectional association between phalangeal BMD and radiographic knee OA.

Methods

A total of 2855 participants were included in this study. Radiographic knee OA was defined as Kellgren-Lawrence (K-L) Grade ≥ 2 in at least one leg. BMD scans of the middle phalanges of the second, third and fourth digits of the nondominant hand were performed with a compact radiographic absorptiometry system (Alara MetriScan®). A multivariable logistic analysis model was applied to test the relation between phalangeal BMD with radiographic knee OA, the presence of knee osteophytes (OSTs), and knee joint space narrowing (JSN) after adjusting for a number of potential confounding factors.

Results

The multivariable-adjusted odds ratios with 95 % confidence intervals [ORs (95 % CI)] of radiographic knee OA across phalangeal BMDs were 1.08 (95 % CI 0.89–1.32) and 0.62 (95 % CI 0.45–0.86), respectively. The P for trend was 0.09. For the female population, the multivariable-adjusted ORs (95 % CI) of radiographic knee OA across phalangeal BMD were 1.01 (95 % CI 0.73–1.37) and 0.58 (95 % CI 0.38 − 0.87), respectively. The P for trend was 0.02. This positive finding, however, did not exist in the male subgroup. There was a significantly lower prevalence of OST in the osteoporosis (OP) group than in the normal group (OR = 0.59, 95 % CI 0.40–0.88; P for trend was 0.01). In contrast, the prevalence of JSN was significantly higher in the osteopenia group (OR = 1.22, 95 % CI 1.00–1.48) and the OP group (OR = 1.35, 95 % CI 1.00–1.84) than in the normal group. The P for trend was 0.02.

Conclusions

This study observed lower odds for the presence of radiographic knee OA and OST in OP patients than in normal subjects. The prevalence of JSN was higher in the osteopenia and OP groups than in normal subjects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-0918-x) contains supplementary material, which is available to authorized users.

Elevated marrow inflammatory cells and osteoclasts in subchondral osteosclerosis in human knee osteoarthritis

Subchondral osteosclerosis, characterized by an increase of hypomineralized bone material, is a pathological hallmark of osteoarthritis. The cellular components in the subchondral marrow compartment that participate in this aberrant bone remodeling process remain to be elucidated. This study assessed the presence of marrow inflammatory cells and their relative abundance between nonsclerotic and sclerotic tissues in knee osteoarthritis. Bone samples from osteoarthritic knee tibial plateaus were stratified for histological analyses using computed tomography osteoabsorptiometry. Immunohistological analysis revealed the presence of CD20 (B-lymphocyte) and CD68 (macrophage), but not CD3 (T-lymphocyte) immunoreactive mononuclear cells in subchondral marrow tissues and their relative abundance was significantly increased in sclerotic compared with nonsclerotic bone samples. Multinucleated osteoclasts that stained positive for CD68 and tartrate-resistant acid phosphatase, predominantly associated with CD34-positive blood vessels and their abundance was strongly increased in sclerotic samples. Bone-specific alkaline phosphatase activity in outgrowth osteoblasts was induced by conditioned medium from nonsclerotic, but not sclerotic, bone pieces. These results suggest that an interaction between bone-resident cells and marrow inflammatory cells might play a role in aberrant bone remodeling leading to subchondral osteosclerosis. Elevated osteoclast activity in sclerotic bone suggests that bone formation and resorption activities are increased, yet uncoupled, in human knee osteoarthritis.

MRI texture analysis of subchondral bone at the tibial plateau

OBJECTIVES

To determine the feasibility of MRI texture analysis as a method of quantifying subchondral bone architecture in knee osteoarthritis (OA).

METHODS

Asymptomatic subjects aged 20-30 (group 1, n = 10), symptomatic patients aged 40-50 (group 2, n = 10) and patients scheduled for knee replacement aged 55-85 (group 3, n = 10) underwent high spatial resolution T1-weighted coronal 3T knee MRI. Regions of interest were created in the medial (MT) and lateral (LT) tibial subchondral bone from which 20 texture parameters were calculated. T2 mapping of the tibial cartilage was performed in groups 1 and 2. Mean parameter values were compared between groups using ANOVA. Linear discriminant analysis (LDA) was used to evaluate the ability of texture analysis to classify subjects correctly.

RESULTS

Significant differences in 18/20 and 12/20 subchondral bone texture parameters were demonstrated between groups at the MT and LT respectively. There was no significant difference in mean MT or LT cartilage T2 values between group 1 and group 2. LDA demonstrated subject classification accuracy of 97 % (95 % CI 91-100 %).

CONCLUSION

MRI texture analysis of tibial subchondral bone may allow detection of alteration in subchondral bone architecture in OA. This has potential applications in understanding OA pathogenesis and assessing response to treatment.

KEY POINTS

• Improved techniques to monitor OA disease progression and treatment response are desirable • Subchondral bone (SB) may play significant role in the development of OA • MRI texture analysis is a method of quantifying changes in SB architecture • Pilot study showed that this technique is feasible and reliable • Significant differences in SB texture were demonstrated between individuals with/without OA.

Cartilage Degeneration and Alignment in Severe Varus Knee Osteoarthritis

OBJECTIVES

The aim of this study was to examine the relationship between cartilage, ligament, and meniscus degeneration and radiographic alignment in severe varus knee osteoarthritis in order to understand the development of varus knee osteoarthritis.

DESIGN

Fifty-three patients (71 knees) with primary varus knee osteoarthritis and who underwent total knee arthroplasty were selected for this study. There were 6 men and 47 women, with 40 right knees and 31 left knees studied; their mean age at operation was 73.5 years. The ligament, meniscus, degeneration of joint cartilage, and radiographic alignments were examined visually.

RESULTS

The tibial plateau-tibial shaft angle was larger if the condition of the cartilage in the lateral femoral condyle was worse. The femorotibial angle and tibial plateau-tibial shaft angle were larger if the conditions of the lateral meniscus or the cartilage in the lateral tibial plateau were worse.

CONCLUSION

Based on the results of this study, progression of varus knee osteoarthritis may occur in the following manner: medial knee osteoarthritis starts in the central portion of the medial tibial plateau, and accompanied by medial meniscal extrusion and anterior cruciate ligament rupture, cartilage degeneration expands from the anterior to the posterior in the medial tibial plateau. Bone attrition occurs in the medial tibial plateau, and the femoro-tibial angle and tibial plateau-tibial shaft angle increase. Therefore, the lateral intercondylar eminence injures the cartilage of the lateral femoral condyle in the longitudinal fissure type. Thereafter, the cartilage degeneration expands in the whole of the knee joints.

Cartilage Degeneration, Subchondral Mineral and Meniscal Mineral Densities in Hartley and Strain 13 Guinea Pigs

Osteoarthritis is a joint disease involved in articular cartilage, subchondral bone, meniscus and synovial membrane. This study sought to examine cartilage degeneration, subchondral bone mineral density (BMD) and meniscal mineral density (MD) in male Hartley, female Hartley and female strain 13 guinea pigs to determine the association of cartilage degeneration with subchondral BMD and meniscal MD. Cartilage degeneration, subchondral BMD and meniscal MD in 12 months old guinea pigs were examined with histochemistry, X-ray densitometry and calcium analysis. We found that male Hartley guinea pigs had more severe cartilage degeneration, subchondral BMD and meniscal MD than female Hartley guinea pigs, but not female strain 13 guinea pigs. Female strain 13 guinea pigs had more severe cartilage degeneration and higher subchondral BMD, but not meniscal MD, than female Hartley guinea pigs. These findings indicate that higher subchondral BMD, not meniscal MD, is associated with more severe cartilage degeneration in the guinea pigs and suggest that abnormal subchondral BMD may be a therapeutic target for OA treatment. These findings also indicate that the pathogenesis of OA in the male guinea pigs and female guinea pigs are different. Female strain 13 guinea pig may be used to study female gender-specific pathogenesis of OA.

Wolff's law in action: a mechanism for early knee osteoarthritis

There is growing interest in the role of bone in knee osteoarthritis. Bone is a dynamic organ, tightly regulated by a multitude of homeostatic controls, including genetic and environmental factors. One such key environmental regulator of periarticular bone is mechanical stimulation, which, according to Wolff’s law, is a key determinant of bone properties. Wolff’s law theorizes that repetitive loading of bone will cause adaptive responses enabling the bone to better cope with these loads. Despite being an adaptive response of bone, the remodeling process may inadvertently trigger maladaptive responses in other articular structures. Accumulating evidence at the knee suggests that expanding articular bone surface area is driven by mechanical stimulation and is a strong predictor of articular cartilage loss. Similarly, fractal analysis of bone architecture provides further clues that bone adaptation may have untoward consequences for joint health. This review hypothesizes that adaptations of periarticular bone in response to mechanical stimulation cause maladaptive responses in other articular structures that mediate the development of knee osteoarthritis. A potential disease paradigm to account for such a hypothesis is also proposed, and novel therapeutic targets that may have a bone-modifying effect, and therefore potentially a disease-modifying effect, are also explored.

A systematic review of the relationship between subchondral bone features, pain and structural pathology in peripheral joint osteoarthritis

INTRODUCTION

Bone is an integral part of the osteoarthritis (OA) process. We conducted a systematic literature review in order to understand the relationship between non-conventional radiographic imaging of subchondral bone, pain, structural pathology and joint replacement in peripheral joint OA.

METHODS

A search of the Medline, EMBASE and Cochrane library databases was performed for original articles reporting association between non-conventional radiographic imaging-assessed subchondral bone pathologies and joint replacement, pain or structural progression in knee, hip, hand, ankle and foot OA. Each association was qualitatively characterised by a synthesis of the data from each analysis based upon study design, adequacy of covariate adjustment and quality scoring.

RESULTS

In total 2456 abstracts were screened and 139 papers were included (70 cross-sectional, 71 longitudinal analyses; 116 knee, 15 hip, six hand, two ankle and involved 113 MRI, eight DXA, four CT, eight scintigraphic and eight 2D shape analyses). BMLs, osteophytes and bone shape were independently associated with structural progression or joint replacement. BMLs and bone shape were independently associated with longitudinal change in pain and incident frequent knee pain respectively.

CONCLUSION

Subchondral bone features have independent associations with structural progression, pain and joint replacement in peripheral OA in the hip and hand but especially in the knee. For peripheral OA sites other than the knee, there are fewer associations and independent associations of bone pathologies with these important OA outcomes which may reflect fewer studies; for example the foot and ankle were poorly studied. Subchondral OA bone appears to be a relevant therapeutic target.

SYSTEMATIC REVIEW

PROSPERO registration number: CRD 42013005009.

DXA in the assessment of subchondral bone mineral density in knee osteoarthritis--A semi-standardized protocol after systematic review

INTRODUCTION

Subchondral bone mineral density (sBMD) contributes to the initiation and progression of knee osteoarthritis (OA). Reliable methods to assess sBMD status may predict the response of specific OA phenotypes to targeted therapies. While dual-energy X-ray absorptiometry (DXA) of the knee can determine sBMD, no consensus exists regarding its methodology.

OBJECTIVE

Construct a semi-standardized protocol for knee DXA to measure sBMD in patients with OA of the knee by evaluating the varying methodologies present in existing literature.

METHODS

We performed a systematic review of original papers published in PubMed and Web of Science from their inception to July 2014 using the following search terms: subchondral bone, osteoarthritis, and bone mineral density.

RESULTS

DXA of the knee can be performed with similar reproducibility values to those proposed by the International Society for Clinical Densitometry for the hip and spine. We identified acquisition view, hip rotation, knee positioning and stabilization, ROI location and definition, and the type of analysis software as important sources of variation. A proposed knee DXA protocol was constructed taking into consideration the results of the review.

CONCLUSIONS

DXA of the knee can be reliably performed in patients with knee OA. Nevertheless, we found substantial methodological variation across previous studies. Methodological standardization may provide a foundation from which to establish DXA of the knee as a valid tool for identification of SB changes and as an outcome measure in clinical trials of disease modifying osteoarthritic drugs.

Age dependent changes in cartilage matrix, subchondral bone mass, and estradiol levels in blood serum, in naturally occurring osteoarthritis in Guinea pigs

The Dunkin Hartley (DH) guinea pig is a widely used naturally occurring osteoarthritis model. The aim of this study was to provide detailed evidence of age-related changes in articular cartilage, subchondral bone mineral density, and estradiol levels. We studied the female Dunkin Hartley guinea pigs at 1, 3, 6, 9, and 12 months of age (eight animals in each group). Histological analysis were used to identify degenerative cartilage and electron microscopy was performed to further observe the ultrastructure. Estradiol expression levels in serum were assessed, and matrix metalloproteinase 3 and glycosaminoglycan expression in cartilage was performed by immunohistochemistry. Bone mineral density of the tibia subchondral bone was measured using dual X-ray absorptiometry. Histological analysis showed that the degeneration of articular cartilage grew more severe with increasing age starting at 3 months, coupled with the loss of normal cells and an increase in degenerated cells. Serum estradiol levels increased with age from 1 to 6 months and thereafter remained stable from 6 to 12 months. Matrix metalloproteinase 3 expression in cartilage increased with age, but no significant difference was found in glycosaminoglycan expression between 1- and 3-month old animals. The bone mineral density of the tibia subchondral bone increased with age before reaching a stable value at 9 months of age. Age-related articular cartilage degeneration occurred in Dunkin Hartley guinea pigs beginning at 3 months of age, while no directly positive or negative correlation between osteoarthritis progression and estradiol serum level or subchondral bone mineral density was discovered.

The relationship between subchondral sclerosis detected with MRI and cartilage loss in a cohort of subjects with knee pain: the knee osteoarthritis progression (KOAP) study

PURPOSE

To assess the association between subchondral sclerosis detected at baseline with MRI and cartilage loss over time in the same region of the knee in a cohort of subjects with knee pain.

METHODS

163 subjects with knee pain participated in a longitudinal study to assess knee osteoarthritis progression (KOAP). Subjects received baseline knee radiographs as well as baseline and 3-year follow-up MRI examinations. Baseline subchondral sclerosis and bone marrow lesions (BMLs) were scored semiquantitatively on MRI in each region from 0 to 3. Cartilage morphology at baseline and follow-up was scored semiquantitatively from 0 to 4. The association between baseline subchondral sclerosis and cartilage loss in the same region of the knee was evaluated using logistic regression, adjusting the results for age, gender, body mass index, and the presence of concomitant BMLs.

RESULTS

The prevalence of subchondral sclerosis detected by MRI in the regions of the knee varied between 1.6% (trochlea) and 17% (medial tibia). The occurrence of cartilage loss over time in regions varied between 6% (lateral tibia) and 13.1% (medial femur). The prevalence of radiographically-detected subchondral sclerosis in compartments varied from 2.9% (patellofemoral) to 14.2% (medial tibiofemoral). In logistic regression models, there were no significant associations between baseline subchondral sclerosis detected by MRI and cartilage loss in the same region of the knee.

CONCLUSION

Baseline subchondral sclerosis as detected by MRI did not increase the risk of cartilage loss over time.

Bone mineral density changes in the knee following anterior cruciate ligament rupture

OBJECTIVE

The pathophysiology of anterior cruciate ligament (ACL) rupture leading to knee osteoarthritis (OA) remains largely unknown. It seems that bone loss occurs after ACL rupture. The purpose of our study was to determine bone mineral density (BMD) changes in the knee after ACL rupture during 2-year follow-up period and to compare BMD changes between the injured and healthy contralateral knee.

DESIGN

Patients were included in an observational prospective follow-up study within 6 months after ACL trauma and evaluated for 2 years. Patients were treated operatively or non-operatively. At baseline and at the one- and 2-year follow-ups, BMD was measured in six regions of the tibia and femur for both knees (medial, central, lateral) using a Dual-energy X-ray Absorptiometry (DXA) scanner.

RESULTS

One hundred forty-one patients were included, with the following characteristics: 66% were male, median age at baseline was 25.3 (inter-quartile range 11.3) years, and 63% were treated operatively. After 1 year, BMD was significantly lower in all regions of the injured knee of the operatively treated patients compared to baseline. After 2 years, BMD was significantly increased, but remained lower than the baseline levels. In all regions for all measurements, the mean BMD was significantly lower in the injured knee than in the healthy contralateral knee.

CONCLUSIONS

During a 2-year follow-up period after ACL rupture, the BMD level in the injured knee was found to be lower than in the healthy contralateral knee. In operatively treated patients, the BMD decreased in the first year and increased in the second follow-up year.

Tibial subchondral bone mineral density: sources of variability and reproducibility

OBJECTIVES

It has been shown that subchondral bone mineral density (sBMD) measurement may be a relevant parameter of osteoarthritis (OA) progression. However, factors implicating the reproducibility and contributing to the variability of the measurement have not been fully described. Thus, the aim of this study was to explore the reproducibility of sBMD by Dual energy X-ray Absorptiometry (DXA) and to further examine its sources of variability.

METHODS

In this study, short-term, intra and inter-observer reproducibility of sBMD was examined on knee images obtained on DXA scans. The influence of software (lumbar spine and forearm modes), knee positioning (flexion or extension), site and size of regions of interest (ROI) and use of rice, on both lateral and medial tibial sBMD, were assessed. Root mean square coefficient of variation (RMS CV) and least significant changes (LSC) were calculated.

RESULTS

The short-term precision of sBMD ranged between 2.24% and 5.12% for RMS CV and between 0.053 and 0.135 g/cm(2) for LSC. Good intra-observer precision was found for knee flexion conditions whatever the software used (RMS CV ranging from 0.43 to 1.41%). The reproducibility was dependant from the ROI size (the ROI including joint space exhibiting better precision results than ROI including solely the subchondral plate). For a constant size of the ROI, the precision results were site-dependant. Inter-observer RMS CV results ranged from 0.59 to 5.01% according to ROI and software used. For the specific task of monitoring medial sBMD in the ROI including solely subchondral plate, forearm flexion condition produced the highest intra-observer and short-term precision (respectively RMS CV: 0.45% and 2.77%; LSC: 0.013 and 0.080 g/cm(2)).

CONCLUSION

Taking account into the excellent precision of the sBMD measurements expressed as RMS CV with the protocol proposed in the present study, clinical application of these measurements might be envisaged.

An OA phenotype may obtain major benefit from bone-acting agents

BACKGROUND

Osteoarthritis (OA) joints display relevant microstructure alterations associated to an increase in remodeling at subchondral bone, which supports its crucial role in OA pathogenesis. Despite this, the treatment of knee OA patients with antiresorptive drugs has given discordant results, suggesting the existence of a particular patient subset with good response to halting high subchondral remodeling.

OBJECTIVE

To identify an OA phenotype that may obtain major benefit from therapy with bone-acting agents.

METHODS

A systematic review of the literature was performed by searching the Medline and PubMed databases from 1990 to April 2013 using the following keywords: subchondral bone, articular cartilage, and osteoarthritis in various combinations with bone agents, bone mineral density, and scintigraphy.

RESULTS

Early animal and human studies provided the rationale for the beneficial use of bone agents on OA cartilage damage. Several bone-acting agents have reduced low back pain and likely spondylosis progression. Recently, strontium ranelate has been reported to exert both structural and clinical benefits in knee OA patients with radiological progression. However, other antiresorptives have shown divergent results. Human studies suggest that these contradictory results may be due to the lack of well-defined OA phenotypes and an accurate methodology to recruit and follow up these patients.

CONCLUSIONS

A particular subset of postmenopausal patients with high remodeling and/or low subchondral bone density may benefit from the treatment with bone-acting agents hindering OA progression. This OA population could be identified with the simultaneous use of subchondral bone dual-energy X-ray absorptiometry and scintigraphy.

Cross-sectional and longitudinal associations between systemic, subchondral bone mineral density and knee cartilage thickness in older adults with or without radiographic osteoarthritis

OBJECTIVES

To investigate cross-sectional and longitudinal associations between systemic bone mineral density (BMD), subchondral BMD (sBMD) and knee cartilage thickness in older adults with or without radiographic osteoarthritis (ROA).

METHODS

A prospective cohort of 158 randomly selected subjects (mean 63 years, 48% women) including 69 non-ROA and 89 ROA subjects were studied at baseline and 2.7 years later. Knee cartilage thickness was semi-automatically determined from T1-weighted fat-suppressed MRI. Knee cartilage volume was measured from MRI. Systemic BMD and sBMD were measured by dual-energy X-ray absorptiometry (DXA).

RESULTS

Cross-sectionally, total body, total hip, spine BMD and/or lateral tibial sBMD were significantly and positively associated with femoral, lateral tibial and/or patellar cartilage thickness in subjects with ROA after adjustment for potential confounders. Longitudinally, a high total body BMD was associated with an increase in femoral cartilage thickness (β: 0.33 mm/g/cm(2), 95% CI 0.13 to 0.53); a high spine BMD was associated with increases in femoral and lateral tibial cartilage thickness (β: 0.25 mm/g/cm(2), 95% CI 0.10 to 0.41; and β: 0.18 mm/g/cm(2), 95% CI: 0.01 to 0.34, respectively) and a high medial tibial sBMD was associated with an increase in medial tibial cartilage thickness (β: 0.45 mm/g/cm(2), 95% CI 0.02 to 0.89) in subjects with ROA. In contrast, there were no significant associations between baseline systemic BMD, sBMD and cartilage volume loss, nor were there associations between BMD and cartilage thickness in subjects without ROA.

CONCLUSIONS

Both systemic and subchondral BMD are positively associated with increased cartilage thickness in subjects with ROA, suggesting BMD may play a protective role against cartilage loss in knee OA.

Examination of osteoarthritis and subchondral bone alterations within the stifle joint of an ovariectomised ovine model

The exact relationship between osteoporosis and osteoarthritis is still a matter for debate for many. The ovariectomised ewe is frequently used as a model for osteoporosis, resulting in significant alterations in bone morphometry and turnover in both trabecular and subchondral bone after 1 year. This study examines whether ovariectomy has any impact on development of osteoarthritis within the ovine stifle joint at the same time point. In addition, we investigate whether there are any significant correlations present between articular cartilage degeneration and alterations in microstructural parameters or turnover rates in the underlying bone. Twenty-two sheep were examined in this study; 10 of the sheep underwent ovariectomy and 12 were kept as controls. Five distinctive fluorochrome dyes were administered intravenously at 12-week intervals to both groups, to label sites of bone turnover. All animals were then sacrificed 12 months postoperatively. Although most specimens showed some evidence of osteoarthritis, no measurable difference between the two study groups was detected. Osteoarthritis was associated with a thinning of the subchondral plate, specifically the subchondral cortical bone; however, whereas previous studies have suggested a link between trabecular thinning and osteoarthritis, this was not confirmed. No correlation was found between osteoarthritis and bone turnover rates of either the subchondral trabecular bone or bone plate. In conclusion, despite the fact that ovariectomy results in marked morphological and structural changes in the ovine stifle joint at 1-year postoperatively, no evidence was found to suggest that it plays a direct role in the aetiology of osteoarthritis.

Effect of bisphosphonate use in patients with symptomatic and radiographic knee osteoarthritis: data from the Osteoarthritis Initiative

OBJECTIVES

Bisphosphonates have some reported beneficial effects in treating osteoarthritis (OA). This study examined the effects of bisphosphonate use on symptoms and structural progression of knee OA in participants from the NIH Osteoarthritis Initiative cohort.

METHODS

People with typical OA trial entry criteria (KL2/3, minimum joint space width 2.5-5.0 mm and pain ≥4 on a numeric rating scale) were classified as bisphosphonate users (≥3 of the 5 years; n=55) or non-users (no use in the preceding 5 years or during follow-up; n=268). Annual data over 4 years were analysed using linear mixed modelling and generalised estimating equations.

RESULTS

Bisphosphonate compliance was 85% at year 1, reducing to 76% by year 4. Numeric rating scale pain scores were significantly reduced among bisphosphonate users at years 2 and 3 (year 3, -0.9 vs -2.2, p=0.004), though not year 4, after adjustment for baseline pain and analgesic use. Differences in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and disability scores did not reach statistical significance at any time point. There was a trend to less joint space narrowing in bisphosphonate users over time (year 4, 0.51 vs 0.29 mm; p=0.06).

CONCLUSIONS

Significant reduction in numeric rating scale pain was observed in the first 3 years with bisphosphonate use; diminution of effects by year 4 may reflect reduced compliance. Differences in results obtained using numeric rating scale and WOMAC may reflect different constructs measured by these tools. The beneficial trend on structural progression should be considered in terms of the sample size.

Periprosthetic bone mineral density changes after unicondylar knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has received renewed interest in the last decade. UKA involves minor injury to soft tissues, limited removal of bone and delicate preservation of knee anatomy and geometry. In theory, UKA provides an opportunity to restore post-surgical knee kinematics to near normal.

HYPOTHESIS

UKA leaves patellofemoral joint free to meet high mechanical forces with no stress-shielding and therefore might preserve bone mineral density (BMD).

PATIENTS AND METHODS

We studied 21 patients with osteoarthritis (OA), who had received medial compartment UKA at Kuopio University Hospital between October 1997 and September 2000. BMD was measured by dual-energy X-ray absorptiometry (DEXA), at baseline (within a week after surgery) and at intervals until 7 years.

RESULTS

DEXA results were reproducible. The highest rate of periprosthetic bone loss occurred during the first 3 months after UKA. The average loss in BMD was 4.4% (p = 0.039) in the femoral diaphysis and it ranged from 11.2% (p < 0.001) to 11.9% (p = 0.002) in the distal femoral metaphysis; however, BMD changes in these regions, from 2 years to 7 years, were nonsignificant. At the 1-year follow-up, the BMD of the medial tibial metaphysis had increased by 8.9% (p = 0.02), whereas those in the lateral tibial metaphysial (-2.4%) and diaphysial regions (-2.0%) did not change significantly.

INTERPRETATIONS

UKA did not preserve periprosthetic BMD in the distal femoral metaphysis, whereas BMD changes in the tibial metaphysis were minor, consistent with a mechanical balance between the medial and lateral tibial compartments. LEVEL OF EVIDENCE 2B: Prospective case control study.

Assessment of bone mineral density and radiographic texture analysis at the tibial subchondral bone

Microstructural changes of subchondral bone constitute one of the figures characterising osteoarthritis on a structural level. Subchondral bone mineral density may reflect the complex relationship between bone and cartilage submitted to movement and loading. In this review, the authors discussed the interest of tibial subchondral bone mineral density assessment in the perspective of its diagnostic, etiopathogenic and prognostic value in osteoarthritis. In addition, the sources of variability linked to the measurement of tibial subchondral bone mineral density are precised. Trabecular bone structure characterisation by radiographic texture analyses may also represent a new promising tool to evaluate the microarchitectural changes that occur with initiation and progression of osteoarthritis. In this paper, the authors also highlighted the interest of different radiographic texture analyses and their clinical relevance in the field of osteoarthritis.

Serum xylosyltransferase 1 level increases during early posttraumatic osteoarthritis in mice with high bone forming potential

Increased proteoglycan (PG) synthesis is essential for the stimulation of cartilage repair processes that take place during the reversible phase of osteoarthritis (OA). In articular cartilage, xylosyltransferase 1 (Xylt1) is the key enzyme that initiates glycosaminoglycan (GAG) chain synthesis by transferring the first sugar residue to the PG core protein. Biological activity of PGs is closely linked to GAG biosynthesis since their polyanionic nature directly contributes to the proper hydration and elastic properties of the cartilage tissue present at the articular interface. The aim of this study was to investigate whether variations in the level of Xylt1 present in serum can be used to predict OA disease progression. The influence of bone forming activity on the systemic release of this enzyme was addressed by experimentally-inducing OA in mice of two different genetic backgrounds that were previously characterized for their distinct bone metabolism: C57BL/6J (B6, high bone remodelers) or C3H/HeJ (C3H, high bone formers). Serum was collected after medial meniscectomy or sham surgeries in young adult mice of these two strains over a period of 3.5months at which point knee histopathology was assessed. A significant increase in serum Xylt1 levels observed shortly after meniscectomy positively correlated with severe cartilage damage evaluated by histological assessment at later time points in mice of the C3H background. In contrast, no temporal regulation of Xylt1 level was found between meniscectomies and control surgeries in B6 mice, which developed OA at a slower rate. Additionally, longitudinal evaluation of the serum levels of other markers of cartilage/bone metabolism (C1,2C, osteocalcin) did not reveal any association with late knee damages. Our results strongly support the idea that serum Xylt1 has a clinical value for monitoring risk of OA progression in young adults with high bone forming potential. Ultimately, the understanding of posttraumatic mechanisms regulating PG synthesis and their modification by GAG will be essential so that interventions that stimulate cartilage regrowth can be undertaken prior to irreversible destruction of the joint tissue. This article is part of a Special Issue entitled "Osteoarthritis".

Cross-sectional DXA and MR measures of tibial periarticular bone associate with radiographic knee osteoarthritis severity

OBJECTIVE

We evaluated the relationship of medial proximal tibial periarticular areal bone mineral density (paBMD) and trabecular morphometry and determined whether these bone measures differed across radiographic medial joint space narrowing (JSN) scores.

METHODS

482 participants of the Osteoarthritis Initiative (OAI) Bone Ancillary Study had knee dual X-ray absorptiometry (DXA) and trabecular bone 3T magnetic resonance imaging (MRI) exams assessed at the same visit. Medial proximal tibial paBMD was measured on DXA and apparent trabecular bone volume fraction (aBV/TV), thickness (aTb.Th), number (aTb.N), and spacing (aTb.Sp) were determined from MR images. Radiographs were assessed for medial JSN scores (0-3). We evaluated associations between medial paBMD and trabecular morphometry. Whisker plots with notches of these measures versus medial JSN scores were generated and presented.

RESULTS

Mean age was 63.9 (9.2) years, BMI 29.6 (4.8) kg/m(2), and 53% were male. The Spearman correlation coefficients between DXA-measured medial paBMD and aBV/TV was 0.61 [95% confidence interval (CI) 0.55-0.66]; between paBMD and aTb.Th was 0.38 (95%CI 0.30-0.46); paBMD and aTb.N was 0.65 (95%CI 0.60-0.70); paBMD and aTb.Sp was -0.65 (95%CI -0.70 to -0.59). paBMD and the trabecular metrics were associated with medial JSN scores.

CONCLUSION

The moderate associations between periarticular trabecular bone density and morphometry and their relationship with greater severity of knee OA support hypotheses of remodeling and/or microscopic compression fractures in the natural history of OA. Longitudinal studies are needed to assess whether knee DXA will be a predictor of OA progression. Further characterization of the periarticular bone in OA utilizing complementary imaging modalities will help clarify OA pathophysiology.

Bone mineral density is cross sectionally associated with cartilage volume in healthy, asymptomatic adult females: Geelong Osteoporosis Study

INTRODUCTION

The association between osteoporosis and osteoarthritis (OA) is controversial. Although previous studies have shown total body, lower limb, spinal and knee BMD and knee cartilage volume to be positively associated, the relationship between other distant site-specific measures of BMD and other knee structures is unknown. The aim of this study was to determine the associations between BMD at eight skeletal sites, and knee structure in asymptomatic young to middle-aged females without any clinical signs of OA.

METHODS

One hundred and sixty healthy, asymptomatic females (29-50 yr) underwent magnetic resonance imaging of the knee. BMD was measured at the spine, hip, total body and forearm by dual energy X-ray absorptiometry, and at the calcaneus by quantitative ultrasound. BMD was tested for an association with cartilage volume, defects, and bone marrow lesions (BMLs).

RESULTS

Medial cartilage volume was positively associated with BMD at the spine, total body, femoral neck, and Ward's triangle (all p<0.05), with non-significant associations in the same direction at the trochanter (p=0.07). Findings in the lateral compartment were similar. The presence of medial cartilage knee defects were also associated with BMD at the spine; defects in the lateral compartment were associated with BMD at the forearm (both p=0.05). BMD was not associated with the presence of BMLs. No associations were observed with calcaneus BMD.

CONCLUSIONS

Site-specific BMD is associated with cartilage volume at the knee in asymptomatic young to middle-aged adults, with the direction and effects trending in the same direction. The magnitude of changes correlates with clinically relevant changes. QUS defined calcaneus BMD, showed no associations with knee structure. Although systemic factors may underlie the association between knee cartilage volume and axial/lower limb BMD, these data suggest that common local, possibly biomechanical factors may also play a role.

Regulation of osteoarthritis by omega-3 (n-3) polyunsaturated fatty acids in a naturally occurring model of disease

OBJECTIVE

To examine effects of high omega-3 (n-3) polyunsaturated fatty acid (PUFA) diets on development of osteoarthritis (OA) in a spontaneous guinea pig model, and to further characterise pathogenesis in this model. Modern diets low in n-3 PUFAs have been linked with increases in inflammatory disorders, possibly including OA. However, n-3 is also thought to increases bone density, which is a possible contributing factor in OA. Therefore we aim to determine the net influence of n-3 in disease development.

METHOD

OA-prone Dunkin-Hartley (DH) Guinea pigs were compared with OA-resistant Bristol Strain-2s (BS2) each fed a standard or an n-3 diet from 10 to 30 weeks (10/group). We examined cartilage and subchondral bone pathology by histology, and biochemistry, including collagen cross-links, matrix metalloproteinases (MMPs), alkaline phosphatase, glycosaminoglycan (GAG), and denatured type II collagen.

RESULTS

Dietary n-3 reduced disease in OA-prone animals. Most cartilage parameters were modified by n-3 diet towards those seen in the non-pathological BS2 strain - significantly active MMP-2, lysyl-pyridinoline and total collagen cross-links - the only exception being pro MMP-9 which was lower in the BS2, yet increased with n-3. GAG content was higher and denatured type II lower in the n-3 group. Subchondral bone parameters in the DH n-3 group also changed towards those seen in the non-pathological strain, significantly calcium:phosphate ratios and epiphyseal bone density.

CONCLUSION

Dietary n-3 PUFA reduced OA in the prone strain, and most disease markers were modified towards those of the non-OA strain, though not all significantly so. Omega-3 did not increase markers of pathology in either strain.

A comparison of conventional maximum intensity projection with a new depth-specific topographic mapping technique in the CT analysis of proximal tibial subchondral bone density

OBJECTIVE

The objective was to identify subchondral bone density differences between normal and osteoarthritic (OA) proximal tibiae using computed tomography osteoabsorptiometry (CT-OAM) and computed tomography topographic mapping of subchondral density (CT-TOMASD).

MATERIALS AND METHODS

Sixteen intact cadaver knees from ten donors (8 male:2 female; mean age:77.8, SD:7.4 years) were categorized as normal (n = 10) or OA (n = 6) based upon CT reconstructions. CT-OAM assessed maximum subchondral bone mineral density (BMD). CT-TOMASD assessed average subchondral BMD across three layers (0-2.5, 2.5-5 and 5-10 mm) measured in relation to depth from the subchondral surface. Regional analyses of CT-OAM and CT-TOMASD included: medial BMD, lateral BMD, and average BMD of a 10-mm diameter area that searched each medial and lateral plateau for the highest "focal" density present within each knee.

RESULTS

Compared with normal knees, both CT-OAM and CT-TOMASD demonstrated an average of 17% greater whole medial compartment density in OA knees (p < 0.016). CT-OAM did not distinguish focal density differences between OA and normal knees (p > 0.05). CT-TOMASD focal region analyses revealed an average of 24% greater density in the 0- to 2.5-mm layer (p = 0.003) and 36% greater density in the 2.5- to 5-mm layer (p = 0.034) in OA knees.

CONCLUSIONS

Both CT-OAM and TOMASD identified higher medial compartment density in OA tibiae compared with normal tibiae. In addition, CT-TOMASD indicated greater focal density differences between normal and OA knees with increased depth from the subchondral surface. Depth-specific density analyses may help identify and quantify small changes in subchondral BMD associated with OA disease onset and progression.

Tibial subchondral trabecular volumetric bone density in medial knee joint osteoarthritis using peripheral quantitative computed tomography technology

OBJECTIVE

Knee osteoarthritis (OA) is an organ-level failure of the joint involving pathologic changes in articular cartilage and bone. This cross-sectional study compared apparent volumetric bone mineral density (vBMD) of proximal tibial subchondral trabecular bone in people with and without knee OA, using peripheral quantitative computed tomography (pQCT).

METHODS

Seventy-five individuals with mild or moderate medial compartment knee OA and 41 asymptomatic controls were recruited. Peripheral QCT was used to measure vBMD of trabecular bone beneath medial and lateral tibiofemoral compartments at levels of 2% and 4% of tibial length, distal to the tibial plateau.

RESULTS

There was no significant difference in vBMD beneath the overall medial and lateral compartments between the 3 groups. However, in the affected medial compartment of those with moderate OA, lower vBMD was seen in the 2 posterior subregions compared with controls and those with mild knee OA, while higher vBMD was seen in the anteromedial subregion. Beneath the unaffected or lesser affected lateral compartment, significantly lower vBMD was seen at the 2% level in the anterior and lateral subregions of those with moderate disease. Volumetric BMD ratios showed relatively higher vBMD in the medial compartment compared with the lateral compartment, but these ratios were not influenced by disease status.

CONCLUSION

Subregional vBMD changes were evident beneath the medial and lateral compartments of those with moderate medial knee OA. Of import, the posterior subchondral trabecular regions of the medial tibial plateau have markedly lower vBMD.

Prevention of bone loss during 56 days of strict bed rest by side-alternating resistive vibration exercise

Bed rest is a recognized model for muscle atrophy and bone loss in space flight and in clinical medicine. We hypothesized that whole body vibration in combination with resistive exercise (RVE) would be an effective countermeasure. Twenty healthy male volunteers underwent horizontal bed rest for 56 days and were randomly assigned either to a group that performed RVE 11 times per week or to a group that underwent bed rest only (Ctrl). Bone mineral content (BMC) was assessed by peripheral quantitative computed tomography (pQCT) in the tibia and the radius and by dual x-ray absorptiometry (DXA) in the hip and lumbar spine at baseline and at regular intervals during bed rest and a 12-month follow-up. RVE appeared to protect muscle size and function, and it also prevented bone loss (p-values between <0.001 and 0.01). Bone losses were largest in the distal tibia epiphysis, where BMC declined from 421.8 mg/mm (SD 51.3) to 406.6 mg/mm (SD 52.7) in Ctrl, but only from 411.1 mg/mm (SD 56.6) to 409.6 mg/mm (SD 66.7) in RVE. Most of the BMC losses were recovered by 12-month follow-up. Analyses showed that the epiphyseal cortex, rather than spongiosa, depicted the most pronounced changes during bed rest and recovery. These results suggest that the combined countermeasure applied in this study is effective to prevent bone losses from the tibia. This underlines the importance of mechanical usage for the maintenance of the human skeleton.

Quantitative analysis of subchondral sclerosis of the tibia by bone texture parameters in knee radiographs: site-specific relationships with joint space width

OBJECTIVES

To determine the ability of radiographic bone texture (BTX) parameters to quantify subchondral tibia sclerosis and to examine clinical relevance for assessing osteoarthritis (OA) progression. We examined the relationship between BTX parameters and each of (1) location-specific joint space width (JSW) [JSW(x)] and minimum JSW (mJSW) of the affected compartment, and (2) knee alignment (KA) angle in knee radiographs of participants undergoing total knee arthroplasty (TKA).

DESIGN

Digitized fixed-flexion knee radiographs were analyzed for run-length and topological BTX parameters in a subchondral region using an algorithm. Medial JSW(x) was computed at x=0.200, 0.225, 0.250 and 0.275 according to a coordinate system defined by anatomic landmarks. mJSW was determined for medial and lateral compartment lesions. KA angles were determined from radiographs using an anatomic landmark-guided algorithm. JSW measures and the magnitude of knee malalignment were each correlated with BTX parameters. Reproducibility of BTX parameters was measured by root-mean square coefficients of variation (RMSCV%).

RESULTS

Run-length BTX parameters were highly reproducible (RMSCV%<1%) while topological parameters showed poorer reproducibility (>5%). In TKA participants (17 women, 13 men; age: 66+/-9 years; body mass index (BMI): 31+/-6 kg m(-2); WOMAC: 41.5+/-16.1; Kellgren-Lawrence score mode: 4), reduced trabecular spacing (Tb.Sp) and increased free ends (FE) were correlated with decreased JSW after accounting for BMI, gender and knee malalignment. These relationships were dependent on site of JSW measurement.

CONCLUSION

High reproducibility in quantifying bone sclerosis using Tb.Sp and its significant relationship with JSW demonstrated potential for assessing OA progression. Increased trabecular FE and reduced porosity observed with smaller JSW suggest collapsing subchondral bone or trabecular plate perforation in advanced knee OA.

Computed tomography topographic mapping of subchondral density (CT-TOMASD) in osteoarthritic and normal knees: methodological development and preliminary findings

OBJECTIVES

To develop a precise imaging tool which measures three-dimensional (3D) subchondral bone mineral density (BMD), and investigate its ability to distinguish subchondral bone properties in osteoarthritic and normal cadaveric tibiae.

METHODS

We developed a novel imaging tool [Computed tomography topographic mapping of subchondral density (CT-TOMASD)], which employs a surface projection image processing technique to map 3D subchondral BMD measured in relation to depth from the joint surface. Sixteen intact cadaver knees from 10 donors (8M:2F; age: 77.8+/-7.4) were scanned using quantitative computed tomography (QCT). Projections of average BMD to normalized depths of 2.5mm and 5.0mm were acquired, with regional analyses including: (1) medial and lateral BMD, (2) anterior/central/posterior compartmental BMD, (3) max BMD contained within a 10mm diameter 'core', and (4) medial:lateral BMD ratio. Precision was assessed using coefficients of variation (CV%). Osteoarthritis (OA) severity was assessed by examination of computed tomography (CT) and fluoroscopic radiographic images, and categorized using modified Kellgren-Lawrence (mKL) scoring.

RESULTS

Precision errors for CT-TOMASD BMD measures were focused around 1.5%, reaching a maximum CV% of 3.5%. OA was identified in eight compartments of six knees. Substantial qualitative and quantitative differences were observed between the OA and normal knees, with the medial:lateral BMD ratio and peak core regional analyses demonstrating differences greater than 4.7 standard deviations (SDs) when compared with normals. Preliminary results revealed effect sizes ranging from 1.6 to 4.3 between OA and normal knees.

CONCLUSIONS

CT-TOMASD offers precise 3D measures of subchondral BMD. Preliminary results demonstrate large qualitative and quantitative differences and large effect sizes between OA and normal knees. This method has the potential to identify and quantify changes in subchondral BMD associated with OA disease progression.

Osteoarthritis associated with estrogen deficiency

Osteoarthritis (OA) affects all articular tissues and finally leads to joint failure. Although articular tissues have long been considered unresponsive to estrogens or their deficiency, there is now increasing evidence that estrogens influence the activity of joint tissues through complex molecular pathways that act at multiple levels. Indeed, we are only just beginning to understand the effects of estrogen deficiency on articular tissues during OA development and progression, as well as on the association between OA and osteoporosis. Estrogen replacement therapy and current selective estrogen receptor modulators have mixed effectiveness in preserving and/or restoring joint tissue in OA. Thus, a better understanding of how estrogen acts on joints and other tissues in OA will aid the development of specific and safe estrogen ligands as novel therapeutic agents targeting the OA joint as a whole organ.

Relationship of compartment-specific structural knee status at baseline with change in cartilage morphology: a prospective observational study using data from the osteoarthritis initiative

INTRODUCTION

The aim was to investigate the relationship of cartilage loss (change in medial femorotibial cartilage thickness measured with magnetic resonance imaging (MRI)) with compartment-specific baseline radiographic findings and MRI cartilage morphometry features, and to identify which baseline features can be used for stratification of fast progressors.

METHODS

An age and gender stratified subsample of the osteoarthritis (OA) initiative progression subcohort (79 women; 77 men; age 60.9 +/- 9.9 years; body mass index (BMI) 30.3 +/- 4.7) with symptomatic, radiographic OA in at least one knee was studied. Baseline fixed flexion radiographs were read centrally and adjudicated, and cartilage morphometry was performed at baseline and at one year follow-up from coronal FLASH 3 Tesla MR images of the right knee.

RESULTS

Osteophyte status at baseline was not associated with medial cartilage loss. Knees with medial joint space narrowing tended to show higher rates of change than those without, but the relationship was not statistically significant. Knees with medial femoral subchondral bone sclerosis (radiography), medial denuded subchondral bone areas (MRI), and low cartilage thickness (MRI) at baseline displayed significantly higher cartilage loss than those without, both with and without adjusting for age, sex, and BMI. Participants with denuded subchondral bone showed a standardized response mean of up to -0.64 versus -0.33 for the entire subcohort.

CONCLUSIONS

The results indicate that radiographic and MRI cartilage morphometry features suggestive of advanced disease appear to be associated with greater cartilage loss. These features may be suited for selecting patients with a higher likelihood of fast progression in studies that attempt to demonstrate the cartilage-preserving effect of disease-modifying osteoarthritis drugs.

Bone loss in the lower leg during 35 days of bed rest is predominantly from the cortical compartment

Immobilization-induced bone loss is usually greater in the epiphyses than in the diaphyses. The larger fraction of trabecular bone in the epiphyses than in the diaphyses offers an intuitive explanation to account for this phenomenon. However, recent evidence contradicts this notion and suggests that immobilization-induced bone loss from the distal tibia epiphysis is mainly from the cortical compartment. The aim of this study was to establish whether this pattern of bone loss was a general rule during immobilization. We monitored various skeletal sites with different tissue composition during 5 weeks of immobilization. Ten healthy male volunteers with mean age of 24.3 years (SD 2.6 years) underwent strict horizontal bed rest. Bone scans were obtained during baseline data collection, at the end of bed rest and after 14 days of recovery by peripheral Quantitative Computed Tomography (pQCT). Sectional images were obtained from the distal tibia epiphysis (at 4% of the tibia's length), from the diaphysis (at 38%), from the proximal metaphysis (at 93%) and from the proximal epiphysis (at 98%), as well as from the distal femur epiphysis (at 4% of the femur's length) and from the patella. Relative bone losses were largest at the patella, where they amounted to -3.2% (SD 1.8%, p<0.001) of the baseline values, and smallest at the tibia diaphysis, where they amounted to -0.7% (SD 1.0%, p=0.019). The relative losses were generally larger from cortical than from trabecular compartments (p=0.004), and whilst all skeletal sites depicted such cortical losses, substantial trabecular losses were found only from the proximal tibia epiphysis. Results confirm that the differential losses from the various skeletal sites cannot be explained on the basis of trabecular vs. cortical tissue composition differences, but that endocortical circumference can account for the different amounts of bone loss in the tibia. The present study therefore supports the suggestion of the subendocortical layer as a transitional zone, which can readily be transformed into trabecular bone in response to immobilization. The latter will lead to cortical thinning, a factor that has been associated with the risk of fracture and with osteoarthritis.

Use of routine clinical multimodality imaging in a rabbit model of osteoarthritis--part II: bone mineral density assessment

OBJECTIVE

To assess bone mineral density (BMD) at different depths from the articular surface in vivo and temporally in a rabbit model of osteoarthritis (OA) using clinical computed tomography (CT) equipment.

METHODS

The knee joints of rabbits (N=10 with Anterior cruciate ligament transection (ACLT) and contralateral sham joints, and N=6 unoperated controls) were scanned in a transverse image plane with a single-slice helical CT scanner. BMD was calculated at defined depths from the articular surface to the growth plate in the lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibial plateau (LTP) and medial tibial plateau (MTP). Baseline BMD was measured at 2 weeks before surgery, and then repeated at weeks 2, 4 and 8 post-surgery in all 10 operated rabbits, and again at week 12 in five of the operated rabbits and at weeks -2 and 8 in the six control rabbits.

RESULTS

In the control joints, BMD decreased with increasing distance into the epiphysis and remained stable over time within each depth. A significant reduction in BMD was observed at week 2 post-operatively in three compartments (LFC, MFC and MTP) in the ACLT joints and persisted to week 12. A modest reduction in BMD occurred in the LTP and MTP of the sham joints at week 12 alone.

CONCLUSION

Clinical CT equipment permitted rapid, repeated, in vivo, non-invasive BMD assessment in a rabbit model of OA. A marked BMD reduction was measured with progression of OA until the end point at 12 weeks.

A pilot study of the reproducibility and validity of measuring knee subchondral bone density in the tibia

OBJECTIVE

To describe the reproducibility and validity of six different measurement techniques for knee subchondral bone mineral density (sBMD).

METHODS

A consecutive sample of 50 male and female participants from a population-based longitudinal study had sBMD assessed using dual energy X-ray absorptiometry scans. Anthropometric, knee pain, cartilage and bone measures by magnetic resonance imaging and radiographic osteoarthritis (OA) were assessed. The six methods were defined as: (1) the midpoint of one intercondylar spine, across the tibial surface and descending 10mm; from the midpoint of the two intercondylar spines (2) the top of the spine descending 20mm, (3) 10-20mm beneath the top of the spine; from the tibial surface descending, (4) 10mm, (5) 15 mm, and (6) 20mm.

RESULTS

All six methods had excellent reproducibility (intra-class correlation coefficient 0.98-1.00). sBMD was higher in males (methods 2-4) and higher in those with medial tibial osteophytes (methods 1, 3 and 4). Medial tibial cartilage defects and overall cartilage defects correlated with sBMD (methods 3 and 4). Method 2, which includes the intercondylar spine, correlated with medial tibial bone size. Measuring sBMD using methods 3 and 4 produced the greatest number of associations with joint features of OA.

CONCLUSIONS

These preliminary results need confirmation in larger longitudinal samples but suggest that sBMD can be accurately measured and plays a role in knee OA. Methods 3 and 4 had the best concurrent validity; however, method 2 adds additional information on tibial bone size, suggesting that two measures are necessary in clinical studies.

Bone mineral density of the proximal tibia relates to axial torsion in the lower limb

This study sought to determine the relationship between bone mineral density distribution in the proximal tibia and tibial and femoral torsions, hip-knee-ankle angle, hip rotation index (internal-external rotation), knee abduction moments, and the foot progression angle. Simple linear regression found that the hip rotation index (r=-0.59, p<0.001), tibial torsion (r=-0.41, p=0.004), and knee abduction moments (r=0.39, p=0.005) were significantly related to medial-lateral BMD ratio for all subjects. The three variables were then studied together to determine their relationship to the bone mineral distribution in the proximal tibia using multiple linear regression (r=0.80, p<0.001). These findings suggest that higher medial knee joint loads, loss of internal rotation of the hip, and internal tibial torsion may lead to increased medial versus lateral BMD of the proximal tibia of healthy knees. Similar bone distribution patterns are found in knees with osteoarthritis; therefore, we suggest these may be risk factors.

The effects of glucosamine hydrochloride on subchondral bone changes in an animal model of osteoarthritis

OBJECTIVE

To quantify periarticular subchondral bone changes in a rabbit model of experimental osteoarthritis (OA), and to determine the effects of continuous administration of a clinically relevant dose of glucosamine HCl on subchondral bone changes in this model.

METHODS

Anterior cruciate ligament transection (ACLT) was performed on the left femorotibial joints of 16 rabbits to induce OA. Ten rabbits that did not undergo ACLT served as unoperated controls. Eight rabbits that underwent ACLT and 6 control rabbits were treated with 100 mg of glucosamine daily, and the others were given a placebo. The articular cartilage was evaluated macroscopically and graded at the time of necropsy, 8 weeks after ACLT. Bone mineral density (BMD) was measured using dual-energy x-ray absorptiometry on the dissected distal femur and proximal tibia. Subchondral trabecular bone turnover, architecture, and connectivity, as well as subchondral plate thickness and mineralization were studied on the undecalcified tibia sections from each animal.

RESULTS

Eight weeks after ACLT, most of the operated joints had various degrees of cartilage damage and fibrillation. Compared with the control group, the ACLT group had significantly increased subchondral bone turnover and lower BMD, bone volume, connectivity, and bone mineralization. The high bone turnover was significantly reduced in glucosamine-treated animals that underwent ACLT. In fact, there were no significant differences between the ACLT/glucosamine group and the control/glucosamine group in most of the bone parameters studied.

CONCLUSION

This study shows that subchondral bone turnover, structure, and mineralization are significantly altered in the early stages of experimental OA, and that these changes are attenuated by glucosamine treatment.

Bone mineral density in the proximal tibia varies as a function of static alignment and knee adduction angular momentum in individuals with medial knee osteoarthritis

Based on the premise that bone mass and bone geometry are related to load history and that subchondral bone may play a role in osteoarthritis (OA), we sought to determine if static and dynamic markers of knee joint loads explain variance in the medial-to-lateral ratio of proximal tibial bone mineral density (BMD) in subjects with mild and moderate medial knee OA. We utilized two surrogate markers of dynamic load, the peak knee adduction moment and the knee adduction angular momentum, the latter being the time integral of the frontal plane knee joint moment. BMD for medial and lateral regions of the proximal tibial plateau and one distal region in the tibial shaft was measured in 84 symptomatic subjects with Kellgren and Lawrence radiographic OA grades of 2 or 3. Utilizing gait analysis, the peak knee adduction moment (the external adduction moment of greatest magnitude) and the time integral of the frontal plane knee joint moment (the angular momentum) over the entire stance phase as well as for each of the four subdivisions of stance were calculated. The BMD ratio was not significantly different in grade 2 (1.32 +/- 0.27) and grade 3 knees (1.47 +/- 0.40) (P = 0.215). BMD of the tibial shaft was not correlated with any loading parameter or static alignment. Of all the surrogate gait markers of dynamic load, the knee adduction angular momentum in terminal stance explained the most variance (20%) in the medial-to-lateral BMD ratio (adjusted r(2) = 0.196, P < 0.001). The knee adduction angular momentum for the entire stance phase explained 18% of the variance in the BMD ratio (adjusted r(2) = 0.178, P < 0.001), 10% more variance than explained by the overall peak knee adduction moment (adjusted r(2) = 0.081, P < 0.001). 18% of the variance in the BMD ratio was also explained by the knee alignment angle (adjusted r(2) = 0.183, P < 0.001), and the total explanatory power was increased to 22% when the knee adduction angular momentum in terminal stance was added (change in r(2) = 0.041, P < 0.05, total adjusted r(2) = 0.215, P < 0.001). The BMD ratio and its relationship to dynamic and static markers of loading were independent of height, weight, and the body mass index, demonstrating that both dynamic markers of knee loading as well as knee alignment explained variance in the tibial BMD ratio independent of body size.