Osteophytes and progression of knee osteoarthritis

Biomechanical considerations in the pathogenesis of osteoarthritis of the knee

Osteoarthritis is the most common joint disease and a major cause of disability. The knee is the large joint most affected. While chronological age is the single most important risk factor of osteoarthritis, the pathogenesis of knee osteoarthritis in the young patient is predominantly related to an unfavorable biomechanical environment at the joint. This results in mechanical demand that exceeds the ability of a joint to repair and maintain itself, predisposing the articular cartilage to premature degeneration. This review examines the available basic science, preclinical and clinical evidence regarding several such unfavorable biomechanical conditions about the knee: malalignment, loss of meniscal tissue, cartilage defects and joint instability or laxity. Level of evidence IV.

Definition of osteoarthritis on MRI: results of a Delphi exercise

OBJECTIVE

Despite a growing body of Magnetic Resonance Imaging (MRI) literature in osteoarthritis (OA), there is little uniformity in its diagnostic application. We envisage in the first instance the definition requiring further validation and testing in the research setting before considering implementation/feasibility testing in the clinical setting. The objective of our research was to develop an MRI definition of structural OA.

METHODS

We undertook a multistage process consisting of a number of different steps. The intent was to develop testable definitions of OA (knee, hip and/or hand) on MRI. This was an evidence driven approach with results of a systematic review provided to the group prior to a Delphi exercise. Each participant of the steering group was allowed to submit independently up to five propositions related to key aspects in MRI diagnosis of knee OA. The steering group then participated in a Delphi exercise to reach consensus on which propositions we would recommend for a definition of structural OA on MRI. For each round of voting, ≥60% votes led to include and ≤20% votes led to exclude a proposition. After developing the proposition one of the definitions developed was tested for its validity against radiographic OA in an extant database.

RESULTS

For the systematic review we identified 25 studies which met all of our inclusion criteria and contained relevant diagnostic measure and performance data. At the completion of the Delphi voting exercise 11 propositions were accepted for definition of structural OA on MRI. We assessed the diagnostic performance of the tibiofemoral MRI definition against a radiographic reference standard. The diagnostic performance for individual features was: osteophyte C statistic=0.61, for cartilage loss C statistic=0.73, for bone marrow lesions C statistic=0.72 and for meniscus tear in any region C statistic=0.78. The overall composite model for these four features was a C statistic=0.59. We detected good specificity (1) but less optimal sensitivity (0.46) likely due to detection of disease earlier on MRI.

CONCLUSION

We have developed MRI definition of knee OA that requires further formal testing with regards their diagnostic performance (especially in datasets of persons with early disease), before they are more widely used. Our current analysis suggests that further testing should focus on comparisons other than the radiograph, that may capture later stage disease and thus nullify the potential for detecting early disease that MRI may afford. The propositions are not to detract from, nor to discourage the use of traditional means of diagnosing OA.

Varus-valgus alignment: reduced risk of subsequent cartilage loss in the less loaded compartment

OBJECTIVE

Varus-valgus alignment has been linked to subsequent progression of osteoarthritis (OA) within the mechanically stressed (medial for varus, lateral for valgus) tibiofemoral compartment. Cartilage data from the off-loaded compartment are sparse. The purpose of this study was to examine our hypotheses that neutral and valgus (versus varus) knees each have reduced odds of cartilage loss in the medial subregions and that neutral and varus (versus valgus) knees each have reduced odds of cartilage loss in the lateral subregions.

METHODS

Patients with knee OA underwent knee magnetic resonance imaging at baseline and 2 years. The mean cartilage thickness was quantified within 5 tibial and 3 femoral subregions. We used logistic regression with generalized estimating equations to analyze the relationship between baseline alignment and subregional cartilage loss at 2 years, adjusting for age, sex, body mass index, and disease severity.

RESULTS

A reduced risk of cartilage loss in the medial subregions was associated with neutral (versus varus) alignment (external tibial, central femoral, external femoral) and with valgus (versus varus) alignment (central tibial, external tibial, central femoral, external femoral). A reduced risk of cartilage loss in the lateral subregions was associated with neutral (versus valgus) alignment (central tibial, internal tibial, posterior tibial) and with varus (versus valgus) alignment (central tibial, external tibial, posterior tibial, external femoral).

CONCLUSION

Neutral and valgus alignment were each associated with a reduction in the risk of subsequent cartilage loss in certain medial subregions and neutral and varus alignment with a reduction in the risk of cartilage loss in certain lateral subregions. These results support load redistribution as an in vivo mechanism of the long-term alignment effects on cartilage loss in knee OA.

Magnetic resonance imaging of the knee: clinical significance of common findings

Magnetic resonance imaging (MRI) of the knee is a widely used study that accurately depicts internal derangement. However, the relevance of the findings on knee MRI to the patient's symptoms and clinical course may often be uncertain. This article discusses the clinical significance and natural history of several common findings on knee MRI examinations.

MR imaging of knee osteoarthritis and correlation of findings with reported patient pain

To evaluate lesion detection of MRI in knee joint osteoarthritis in patients with symptoms of pain, the correlation between MRI findings and varying degrees of reported pain was assessed. Twenty-eight patients (31 knees) with osteoarthritis were recruited for this study. The degree of knee pain was assessed by VRS scores. The knees were evaluated by plain film radiograph utilizing Kellgren-Lawrence scores. Multiple MR sequences were performed on a 1.5T MR-system, including sagittal and coronal dual fast spin echo (TR/TE 3660/11/120 ms, slice thickness 5 mm), coronal spin echo T1-weighted (TR/TE 360/9 ms, slice thickness 5 mm), sagittal fat saturated 3D-spoiled gradient-recalled echo (TR/TE 50/6 ms; slice thickness 1.5 mm; flip angle 40 degrees ), and 3D steady-state free precession (TR/TE 6/2.2 ms; slice thickness 1.6 mm; flip angle 30 degrees ) pulse sequences for the purpose of detecting abnormities of cartilage, menisci, the anterior cruciate ligaments, bone marrow edema-like lesions, osteophytes, synovitis, and joint effusions. MR findings were compared with the degree of pain using Fisher exact test with P values less than 0.05 indicating a statistically significant difference. The results showed that, of the 31 knees evaluated, mild pain was reported in 11 and severe pain in the remainder. Kellgren-Lawrence scores of all 31 evaluated OA knees were as follows: grade 1 lesions (n=6), grade 2 lesions (n=14), grade 3 lesions (n=8), and grade 4 lesions (n=3). Articular cartilaginous defects were found in 37.1% of knees. Abnormalities of the menisci and anterior cruciate ligaments, bone marrow edema-like lesions, osteophytes, synovitis, and joint effusions were detected in 32.3%, 38.7%, 45.2%, 100%, 15.1% and 67.7% of knees, respectively. Of these variables, only the differences in prevalence of joint effusions were significantly different in the mild and severe pain groups (P=0.004). It is concluded that MRI evaluates the entire joint structure of the osteoarthritic knee, demonstrating abnormalities of the cartilage, menisci, and anterior cruciate ligaments as well as bone marrow edema-like lesions, osteophytes, synovitis, and joint effusions. The difference in pain grading between OA patients reporting mild and severe degrees of pain is related to the presence of joint effusion.

Does cartilage volume or thickness distinguish knees with and without mild radiographic osteoarthritis? The Framingham Study

OBJECTIVES

To examine whether the quantity of cartilage or semiquantitative scores actually differ in knees with mild radiographic osteoarthritis compared with knees without osteoarthritis.

METHODS

Framingham Osteoarthritis Study participants had knee tibiofemoral magnetic resonance imaging-based measurements of cartilage. Using three-dimensional FLASH-water excitation sequences, cartilage volume, thickness and subregional cartilage thickness were measured and cartilage scored semiquantitatively (using the whole-organ magnetic resonance imaging score; WORMS). Using weight-bearing radiographs, mild osteoarthritis was defined as Kellgren/Lawrence (K/L) grade 2 and non-osteoarthritis as K/L grade 0. Differences between osteoarthritis and non-osteoarthritis knees in median cartilage measurements were tested using the Wilcoxon rank sum test.

RESULTS

Among 948 participants (one knee each), neither cartilage volume nor regional thickness were different in mild versus non-osteoarthritis knees. In mild osteoarthritis, cartilage erosions in focal areas were missed when cartilage was quantified over large regions such as the medial tibia. For some but not all subregions of cartilage, especially among men, cartilage thickness was lower (p<0.05) in mild osteoarthritis than non-osteoarthritis knees. Because semiquantitative scores captured focal erosions, median WORMS scores were higher in mild osteoarthritis than non-osteoarthritis (all p<0.05). In moderate/severe osteoarthritis (K/L grades 3 or 4), osteoarthritis knees had much lower cartilage thickness and higher WORMS scores than knees without osteoarthritis.

CONCLUSIONS

In mild osteoarthritis, the focal loss of cartilage is missed by quantitative measures of cartilage volume or thickness over broad areas. Regional cartilage volume and thickness (eg, medial tibia) are not different in mild osteoarthritis versus non-osteoarthritis. Subregional thickness may be decreased in mild osteoarthritis. Semiquantitative scoring that assesses focal cartilage damage differentiates mild osteoarthritis from non-osteoarthritis.

Magnetic resonance imaging-based cartilage loss in painful contralateral knees with and without radiographic joint space narrowing: Data from the Osteoarthritis Initiative

OBJECTIVE

To determine by magnetic resonance imaging (MRI), whether knees with advanced radiographic disease (medial joint space narrowing [mJSN]) encounter greater longitudinal cartilage loss than contralateral knees with earlier disease (no or less mJSN).

METHODS

Participants were selected from 2,678 cases in the Osteoarthritis Initiative, based on exhibition of bilateral pain, body mass index >25 (kg/m(2)), mJSN in 1 knee, no or less mJSN in the contralateral knee, and no lateral JSN in both knees. Eighty participants (mean +/- SD age 60.6 +/- 9.1 years) fulfilled these criteria. Medial tibial and femoral cartilage morphology was analyzed from the baseline and the 1-year followup MRI (sagittal double echo at steady state by 3.0T) of both knees by experienced readers blinded to the time point and mJSN status.

RESULTS

Knees with more radiographic mJSN displayed greater medial cartilage loss (-80 mum) assessed by MRI than contralateral knees with less mJSN (-57 mum). The difference reached statistical significance in participants with an mJSN grade of 2 or 3 (P = 0.005-0.08), but not in participants with an mJSN grade of 1 (P = 0.28-0.98). In knees with more mJSN, cartilage loss increased with higher grades of mJSN (P = 0.003 in the medial femur). Knees with an mJSN grade of 2 or 3 displayed greater cartilage loss in the weight-bearing medial femur than in the posterior femur or in the medial tibia (P = 0.048).

CONCLUSION

Knees with advanced mJSN displayed greater cartilage loss than contralateral knees with less mJSN. These data suggest that radiography can be used to stratify fast structural progressors, and that MRI cartilage thickness loss is more pronounced at advanced radiographic disease stage.

Transcription factor Nfat1 deficiency causes osteoarthritis through dysfunction of adult articular chondrocytes

Osteoarthritis (OA) is the most common form of joint disease in middle-aged and older individuals. Previous studies have shown that over-expression of matrix-degrading proteinases and proinflammatory cytokines is associated with osteoarthritic cartilage degradation. However, it remains unclear which transcription factors regulate the expression of these cartilage-degrading molecules in articular chondrocytes. This study demonstrated that mice lacking Nfat1, a member of the nuclear factor of activated T cells (NFAT) transcription factors, exhibited normal skeletal development but displayed loss of type II collagen (collagen-2) and aggrecan with over-expression of specific matrix-degrading proteinases and proinflammatory cytokines in young adult articular cartilage of load-bearing joints. These initial changes are followed by articular chondrocyte proliferation/clustering, progressive articular surface destruction, periarticular chondro-osteophyte formation and exposure of thickened subchondral bone, all of which resemble human OA. Forced expression of Nfat1 delivered with lentiviral vectors in cultured 3 month-old primary Nfat1 knockout (Nfat1(-/-)) articular chondrocytes partially or completely rescued the abnormal catabolic and anabolic activities of Nfat1(-/-) articular chondrocytes. These new findings revealed a previously unrecognized critical role of Nfat1 in maintaining the physiological function of differentiated adult articular chondrocytes through regulating the expression of specific matrix-degrading proteinases and proinflammatory cytokines. Nfat1 deficiency causes OA due to an imbalance between the catabolic and anabolic activities of adult articular chondrocytes, leading to articular cartilage degradation and failed repair activities in and around articular cartilage. These results may provide new insights into the aetiology, pathogenesis and potential therapeutic strategies for osteoarthritis.

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.

Imaging of knee osteoarthritis

New imaging modalities are broadening the possibilities in osteoarthritis (OA) research, and are offering new insights to help better understand the pathogenesis of this disease. Although knee radiographs are widely employed in epidemiological and clinical studies to assess structural pathology, joint radiographs provide limited outcome measures in knee OA, and other more valid, reliable and sensitive imaging modalities are now available. In particular, magnetic resonance imaging can directly visualize articular cartilage and other joint structures, such as bone and soft tissue, that are now recognized as part of the disease process. This chapter will examine imaging modalities in the assessment of knee OA, and the impact of these on our understanding of the pathogenesis of this disease.

Osteoblasts derived from osteophytes produce interleukin-6, interleukin-8, and matrix metalloproteinase-13 in osteoarthritis

To clarify the significance of the osteophytes that appear during the progression of osteoarthritis (OA), we investigated the expression of inflammatory cytokines and proteases in osteoblasts from osteophytes. We also examined the influence of mechanical stress loading on osteoblasts on the expression of inflammatory cytokines and proteases. Osteoblasts were isolated from osteophytes in 19 patients diagnosed with knee OA and from subchondral bone in 4 patients diagnosed with femoral neck fracture. Messenger RNA expression and protein production of inflammatory cytokines and proteases were analyzed using real-time RT-PCR and ELISA, respectively. To examine the effects of mechanical loading, continuous hydrostatic pressure was applied to the osteoblasts. We determined the mRNA expression and protein production of IL-6, IL-8, and MMP-13, which are involved in the progression of OA, were increased in the osteophytes. Additionally, when OA pathological conditions were simulated by applying a nonphysiological mechanical stress load, the gene expression of IL-6 and IL-8 increased. Our results suggested that nonphysiological mechanical stress may induce the expression of biological factors in the osteophytes and is involved in OA progression. By controlling the expression of these genes in the osteophytes, the progression of cartilage degeneration in OA may be reduced, suggesting a new treatment strategy for OA.

Osteophytosis, subchondral bone sclerosis, joint effusion and soft tissue thickening in canine experimental stifle osteoarthritis: comparison between 1.5 T magnetic resonance imaging and computed radiography

OBJECTIVE

To compare use of 1.5 T magnetic resonance imaging (MRI) and computed radiography (CR) for morphologic and temporal evaluation of osteophytosis, subchondral sclerosis, joint effusion, and synovial thickening in experimentally induced canine stifle osteoarthritis (OA).

STUDY DESIGN

Prospective study.

ANIMALS

Dogs (n=8).

METHODS

CR (mediolateral and caudocranial projections) and MRI (dorsal 3D T1-weighted gradient echo, sagittal 3D SPGR and T2-weighted fast spin echo with fat saturation) were performed at baseline (n=8) and at week 4 (n=5), week 8 (n=8), and week 26 (n=5) after cranial cruciate ligament transection. Osteophytosis, subchondral bone sclerosis, and joint effusion were scored on CR and MRI, and synovial thickening on MRI.

RESULTS

MRI was more sensitive than CR for detection of osteophytosis and could better discriminate joint effusion from soft tissue thickening, although scores for these variables strongly correlated between modalities (rho=0.94 [osteophytosis] and 0.80 [effusion]; P<.001). Scores for subchondral bone sclerosis also correlated (rho=0.54, P<.004), although this variable may have been over interpreted on CR. Joint effusion and synovial thickening peaked at week 8, before partially regressing at week 26. Conversely, osteophytosis and sclerosis progressed semi-linearly over 26 weeks.

CONCLUSION

MRI is more sensitive than radiography in assessing onset and progression of osteophytosis in canine experimental stifle OA and provides enhanced discrimination between joint effusion and synovial thickening.

CLINICAL RELEVANCE

MRI is as a more powerful imaging modality that should be increasingly used in animals to assess the joint related effects of disease-modifying OA drugs.

Effect of medial tibial plateau alignment on serial radiographs on the capacity to predict progression of knee osteoarthritis

OBJECTIVE

To evaluate the effect of medial tibial plateau (MTP) alignment of serial radiographs on the capacity to detect associations between baseline characteristics and progression of joint space narrowing (JSN) in knee osteoarthritis (OA).

METHODS

Standardised posteroanterior weight-bearing knee radiographs of 83 knee OA patients were obtained at baseline and after 24 months using the non-fluoroscopic fixed-flexion protocol. Minimum joint space width (JSW) of the medial tibiofemoral joint spaces was measured manually in paired radiographs. Progression of JSN was defined by a change in JSW larger than the smallest detectable difference (0.4mm). Satisfactory MTP alignment was present if the distance between the anterior and posterior margins of the MTP was < or = 1mm. Standardised questionnaires were used to record age, sex and body mass index. Medial tibiofemoral JSN and osteophyte severity at baseline were graded with the Osteoarthritis Research Society International (OARSI) atlas.

RESULTS

Progression of JSN was observed in 31 (28.4%) of 109 OA knees. In the sub sample of 48 (44%) OA knees with satisfactory MTP alignment on baseline and 24-month radiographs, 18 (37.5%) knees progressed. Stronger (statistically significant) associations were found between sex, generalised OA, JSN and osteophyte severity at baseline and progression of JSN in the sub sample of radiographs with serial satisfactorily MTP alignment than in all radiographs together.

CONCLUSION

Insufficient quality of MTP alignment on serial radiographs could prevent detection of associations between baseline characteristics and progression of JSN in knee OA. These findings may have implications for longitudinal knee OA studies using the fixed-flexion protocol.

Static knee alignment is associated with the risk of unicompartmental knee cartilage defects

Although knee malalignment is a risk factor for the progression of unicompartmental knee osteoarthritis (OA), it is unclear how this relationship is mediated. Cartilage defects are known to predate cartilage loss and the onset of knee OA, and it may be that knee malalignment increases the risk of unicompartmental knee cartilage defects. Knee radiographs and MRI were performed on a total of 202 subjects, 36.6% of whom had radiographic knee OA, to determine the relationship between static knee alignment and knee cartilage defects. Analyses were performed for the entire cohort, as well as for healthy and OA subgroups. For every 1 degrees increase in a valgus direction, there was an associated reduced risk of the presence of cartilage defects in the medial compartment of subjects with knee OA (p = 0.02), healthy subjects (p = 0.002), and the combined (p < 0.001) group. Moreover, for every 1 degrees increase in a valgus direction, there was an associated increased risk of the presence of lateral cartilage defects in the OA group (p = 0.006), although the relationship between change toward genu valgum and lateral compartment cartilage defects did not persist for the healthy group (p = 0.16). This cross-sectional study has demonstrated that knee alignment is associated with the risk for compartment specific knee cartilage defects in both healthy and arthritic people. Given that the natural history of cartilage volume reduction appears to be predated by the presence of cartilage defects, whether knee alignment affects the longitudinal progression from cartilage defects to cartilage loss requires further examination.

Interleukin-1 and transforming growth factor-beta 1 as crucial factors in osteoarthritic cartilage metabolism

In osteoarthritis (OA), interleukin-1 (IL-1) stimulates the expression of metalloproteinases and aggrecanases, which induce cartilage degradation. IL-1 is also capable of reducing the production of cartilage-specific macromolecules, including type II collagen, through modulation of the transcription factors Sp1 and Sp3. Conversely, Transforming growth factor-beta (TGF-beta) counteracts with most of the IL-1 deleterious effects and contributes to cartilage homeostasis. However, OA chondrocytes progressively loose the expression of TGF-beta type II receptor and become insensitive to the factor. This downregulation is also driven by IL-1. This review provides insights into the molecular mechanisms that underly the interplay between IL-1 and TGF-beta in OA cartilage metabolism and enlightens the central role of Sp1 and Sp3 transcription factors in the matrix pathological alterations.

Effect of physical activity on articular knee joint structures in community-based adults

OBJECTIVE

It is unclear whether physical activity that is beneficial for the cardiovascular system is detrimental to knee structures. We examined the association between intensity, frequency, and duration of physical activity and knee structures in a community-based population.

METHODS

A total of 297 healthy adults ages 50-79 years with no history of knee injury or disease were recruited from an existing study on healthy aging. Each subject underwent knee magnetic resonance imaging (MRI) to measure tibial cartilage volume, tibiofemoral cartilage defects, and bone marrow lesions. Physical activity and anthropometric data were obtained via questionnaire during 1990-1994 and 2003-2004.

RESULTS

Tibial cartilage volume increased with frequency (P = 0.01) and duration (P = 0.001) of vigorous activity (activity leading to diaphoresis or dyspnea) reported 10 years previously, as well as recent vigorous activity in the 7 days prior to MRI (P = 0.05). Recent weight-bearing vigorous activity increased with tibial cartilage volume (P = 0.02) and was inversely associated with cartilage defects (P = 0.02). A reduced risk of bone marrow lesions was associated with regular walking (P = 0.04).

CONCLUSION

Vigorous physical activity appears to have a beneficial effect on knee articular cartilage in healthy, community-based adults with no history of knee injury or disease. Regular walking reduces the risk of bone marrow lesions in the knee. This study provides further support for a beneficial effect of physical activity for diseases associated with aging and suggests that exercise that is good for the heart is also good for the knees.

Effects of long-term estrogen replacement therapy on the prevalence and area of periarticular tibial osteophytes in surgically postmenopausal cynomolgus monkeys

Osteoarthritis (OA) occurs naturally in cynomolgus macaques. The purposes of the present study were to: 1) develop histological measurement schemes to measure the cross-sectional area of axial and abaxial osteophytes in the proximal tibia; 2) determine the effects of long-term estrogen replacement therapy (ERT) on osteophyte prevalence and area; and 3) assess relationships between osteophyte size and risk factors of OA (age and body weight) and concurrent bone and cartilage lesions. Adult female cynomolgus macaques (n=180) were bilaterally ovariectomized (OVX) and were treated for 3 years with ERT, soy phytoestrogens (SPE), or no hormones (OVX controls). At necropsy, the prevalence and cross-sectional area of periarticular tibial osteophytes were evaluated histologically. Treatment effects on osteophyte prevalence and area were evaluated using Chi-square analyses and Kruskal-Wallis test, respectively; other comparisons were evaluated using regression analyses. The prevalence of abaxial osteophytes in the medial tibial plateau was not significantly affected by treatment group; however, the prevalence of abaxial osteophytes in the lateral tibial plateau was significantly lower in ERT group than SPE group (p<0.01). The total number of abaxial osteophytes (sum of lateral and medial) was significantly lower in ERT group compared to OVX and SPE groups. Neither the prevalence of axial osteophytes nor the sum of lateral and medial axial osteophytes was significantly affected by treatment in either tibial plateau. There were no significant treatment effects on axial or abaxial osteophyte cross-sectional area in either tibial plateau. There was a significant positive correlation between abaxial osteophyte area and SCB thickness in the medial tibial plateau (p=0.048); however, there were no significant correlations between abaxial osteophyte area (medial or lateral) and age or body weight. In this model of naturally occurring OA, long-term ERT does not consistently reduce the prevalence, and has no significant effects on cross-sectional area, of periarticular tibial osteophytes.

Static knee alignment and its association with radiographic knee osteoarthritis

OBJECTIVES

Although knee alignment is associated with the progression of knee osteoarthritis (OA), it is unclear which features that characterize radiographic OA are related to alignment. The aim of this study was to examine the relationship between static knee joint alignment (measured as a continuous variable) and the radiographic features of knee OA (joint space narrowing and osteophytes).

METHODS

One hundred and twenty one adults with symptomatic knee OA were recruited using a combined strategy including referral from specialist centres, arthritis support groups and media advertising. X-rays were performed to classify the severity of disease and to determine static knee alignment.

RESULTS

Increasing varus knee alignment was associated with increasing risk of medial compartment joint space narrowing (P < 0.001) and osteophytes (P = 0.005). Increasing valgus knee alignment was associated with an increased risk for lateral compartment joint space narrowing (P < 0.001) and osteophytes (P = 0.002).

CONCLUSION

This study has demonstrated that the static knee angle, measured as a continuous variable, is an important determinant of the compartment-specific features of radiographic knee OA. Further work is required to determine whether interventions aimed at correcting these relatively minor levels of varus and valgus angulation will have an effect on the risk of tibiofemoral OA.

Musculoskeletal disorders associated with obesity: a biomechanical perspective

Despite the multifactorial nature of musculoskeletal disease, obesity consistently emerges as a key and potentially modifiable risk factor in the onset and progression of musculoskeletal conditions of the hip, knee, ankle, foot and shoulder. To date, the majority of research has focused on the impact of obesity on bone and joint disorders, such as the risk of fracture and osteoarthritis. However, emerging evidence indicates that obesity may also have a profound effect on soft-tissue structures, such as tendon, fascia and cartilage. Although the mechanism remains unclear, the functional and structural limitations imposed by the additional loading of the locomotor system in obesity have been almost universally accepted to produce aberrant mechanics during locomotor tasks, thereby unduly raising stress within connective-tissue structures and the potential for musculoskeletal injury. While such mechanical theories abound, there is surprisingly little scientific evidence directly linking musculoskeletal injury to altered biomechanics in the obese. For the most part, even the biomechanical effects of obesity on the locomotor system remain unknown. Given the global increase in obesity and the rapid rise in musculoskeletal disorders, there is a need to determine the physical consequences of continued repetitive loading of major structures of the locomotor system in the obese and to establish how obesity may interact with other factors to potentially increase the risk of musculoskeletal disease.

Low vitamin K status is associated with osteoarthritis in the hand and knee

OBJECTIVE

Poor intake of vitamin K is common. Insufficient vitamin K can result in abnormal cartilage and bone mineralization. Furthermore, osteophyte growth, seen in osteoarthritis (OA), may be a vitamin K-dependent process. We undertook this study to determine whether vitamin K deficiency is associated with radiographic features of OA.

METHODS

We conducted an analysis among 672 participants (mean age 65.6 years, 358 women) in the Framingham Offspring Study, a population-based prospective observational cohort. Levels of plasma phylloquinone (the primary form of vitamin K) had previously been measured in these participants, for whom we also had bilateral hand and knee radiographs. The main outcomes were 1) prevalence ratios (PRs) of OA, osteophytes, and joint space narrowing (JSN) per quartile of plasma phylloquinone level for each joint, adjusting for correlated joints using generalized estimating equations, and 2) adjusted mean number of joints with each feature per quartile of plasma phylloquinone level. Analyses were conducted in hands and knees separately and adjusted for age, sex, body mass index, total energy intake, plasma vitamin D, and femoral neck bone mineral density.

RESULTS

The PRs for OA, osteophytes, and JSN and adjusted mean number of joints with all 3 features in the hand decreased significantly with increasing plasma phylloquinone levels (P<or=0.03 for all). For example, as plasma phylloquinone levels rose, the PR for hand OA decreased from 1.0 to 0.7 (P=0.005). For the knee, only the PR for osteophytes and the adjusted mean number of knee joints with osteophytes decreased significantly with increasing plasma phylloquinone levels (PR decreased from 1.0 to 0.6, P=0.01).

CONCLUSION

These observational data support the hypothesis of an association between low plasma levels of vitamin K and increased prevalence of OA manifestations in the hand and knee.

MRI and non-cartilaginous structures in knee osteoarthritis

Magnetic resonance imaging (MRI) provides a sensitive tool for examining all the structures involved in the osteoarthritis (OA) process. While much of the MRI literature previously focussed on cartilage, there is increasing research on whole-organ evaluation and including features such as synovitis, bone marrow edema, and meniscal and ligamentous pathology. The aim of this session at the Outcome Measures in Rheumatology Clinical Trials (OMERACT)-Osteoarthritis Research Society International (OARSI) Workshop for Consensus in Osteoarthritis Imaging was to describe the current MRI methods for identifying and quantifying non-cartilaginous structures and review their associations with both OA symptoms and structural progression. Although there is much experience in measuring synovitis (derived from the rheumatoid arthritis literature), only one study has reported an association of MRI-detected synovitis and effusions with OA pain. Bone marrow edema lesions, which may represent areas of trabecular remodelling, have been associated with pain and compartment-specific structural deterioration. MRI studies have confirmed the frequency and importance of meniscal damage in progressive cartilage loss, but not related such damage to symptoms. Osteophytes have been associated with cartilage loss and malalignment to the side of the osteophyte. Ligament damage, including anterior cruciate ligament tears, has been found more commonly than expected in painful OA knees. Improvements in quantitative and semi-quantitative assessments of non-cartilage features will greatly assist understanding of the OA process and its response to therapy.