The relationship between specific tissue lesions and pain severity in persons with knee osteoarthritis

Imaging the painful osteoarthritic knee joint: what have we learned?

Pain in the peripheral joints is an increasingly common problem, resulting in significant patient disability and health-care expenditure. Osteoarthritis (OA), a syndrome of joint pain with associated structural changes, is the most prevalent joint disease, yet the etiology of pain in OA is not entirely clear. Traditional assessment of the structure-pain relationship in knee OA has relied on conventional radiography, which has several limitations, not least the discrepancy between symptoms and radiographic findings. MRI has the capability to visualize all the structures within the knee joint, and there is a growing body of work using MRI to examine the correlation between structural findings and symptoms. In large cohort studies, synovial hypertrophy, synovial effusions, and abnormalities in the subchondral bone have been associated with knee pain. Advances in our understanding of the etiology of pain in OA will assist in the identification of further targets for treatment of this common and painful disease.

The natural history of bone marrow lesions in community-based adults with no clinical knee osteoarthritis

OBJECTIVE

Although bone marrow lesions (BML) have been implicated in the pathogenesis of osteoarthritis, their natural history in a healthy population is unknown. This study in a healthy, pain-free population aimed to examine the natural history of BML; factors associated with incidence and progression of BML over 2 years and whether incident BML are associated with the development of pain.

METHODS

271 subjects with no clinical knee osteoarthritis, being pain free at baseline, underwent magnetic resonance imaging of their dominant knee at baseline and 2 years later. The presence of BML was assessed.

RESULTS

In knees initially free of BML, incident BML developed in 14% of people over the study period. Increased body mass index (BMI; odds ratio (OR) 1.15, 95% CI 1.06 to 1.2, p = 0.001) was associated with incident BML. Those who developed a BML were more likely to develop knee pain compared with those in whom no BML developed (OR 4.2, 95% CI 1.2 to 15.1, p = 0.03). Among those in whom BML were present at baseline, 46% completely resolved. There was no association between age, gender and BMI and persistence of BML over 2 years.

CONCLUSION

In this healthy population, the rate of incident BML is lower than previously described in a population with osteoarthritis. Incident BML are associated with increased BMI and the development of pain. Approximately half the BML present at baseline resolved. These data suggest that in pain-free people with no clinical knee osteoarthritis, BML are reversible and may provide a target for interventions aimed at the prevention of knee osteoarthritis.

Developments in the clinical understanding of osteoarthritis

With the recognition that osteoarthritis is a disease of the whole joint, attention has focused increasingly on features in the joint environment which cause ongoing joint damage and are likely sources of pain. This article reviews current ways of assessing osteoarthritis progression and what factors potentiate it, structural abnormalities that probably produce pain, new understandings of the genetics of osteoarthritis, and evaluations of new and old treatments.

The symptoms of osteoarthritis and the genesis of pain

This article delineates the characteristic symptoms and signs associated with OA and how they can be used to make the clinical diagnosis. The predominant symptom in most patients is pain. The remainder of the article focuses on what we know causes pain in OA and contributes to its severity. Much has been learned over recent years; however, for the budding researcher much of this puzzle remains unexplored or inadequately understood.

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.

The symptoms of osteoarthritis and the genesis of pain

Symptomatic osteoarthritis (OA) causes substantial physical and psychosocial disability. This article delineates the characteristic symptoms and signs associated with OA and how they can be used to make the clinical diagnosis. The predominant symptom in most patients is pain. The remainder of the article focuses on what is known about the causes of pain in OA and factors that contribute to its severity. Much has been learned during recent years, but much of this puzzle remains unexplored or inadequately understood.

Surgical suturing of articular cartilage induces osteoarthritis-like changes

INTRODUCTION

In clinical tissue-engineering-based approaches to articular cartilage repair, various types of flap are frequently used to retain an implanted construct within the defect, and they are usually affixed by suturing. We hypothesize that the suturing of articular cartilage is associated with a loss of chondrocytes from, and osteoarthritis-like changes within, the perisutural area.

MATERIALS AND METHODS

We established a large, partial-thickness defect model in the femoral groove of adult goats. The defects were filled with bovine fibrinogen to support a devitalized flap of autologous synovial tissue, which was sutured to the surrounding articular cartilage with single, interrupted stitches. The perisutural and control regions were analyzed histologically, histochemically and histomorphometrically shortly after surgery and 3 weeks later.

RESULTS

Compared to control regions, chondrocytes were lost from the perisutural area even during the first few hours of surgery. During the ensuing 3 weeks, the numerical density of cells in the perisutural area decreased significantly. The cell losses were associated with a loss of proteoglycans from the extracellular matrix. Shortly after surgery, fissures were observed within the walls of the suture channels. By the third week, their surface density had increased significantly and they were filled with avascular mesenchymal tissue.

CONCLUSIONS

The suturing of articular cartilage induces severe local damage, which is progressive and reminiscent of that associated with the early stages of osteoarthritis. This damage could be most readily circumvented by adopting an alternative mode of flap affixation, such as gluing with a biological adhesive.

Mechanical factors relate to pain in knee osteoarthritis

BACKGROUND

Pain experienced by people with knee osteoarthritis is related to psychosocial factors and damage to articular tissues and/or the pain pathway itself. Mechanical factors have been speculated to trigger this pain experience; yet mechanics have not been identified as a source of pain in this population. The purpose of this study was to identify whether mechanics could explain variance in pain intensity in people with knee osteoarthritis.

METHODS

Data from 53 participants with physician-diagnosed knee osteoarthritis (mean age=68.5 years; standard deviation=8.6 years) were analyzed. Pain intensity was reported on the Western Ontario and McMaster Universities Osteoarthritis Index. Mechanical measures included weight-bearing varus-valgus alignment, body mass index and isokinetic quadriceps torque. Gait analysis captured the range of adduction-abduction angle, range of flexion-extension angle and external knee adduction moment during level walking.

FINDINGS

Pain intensity was significantly related to the dynamic range of flexion-extension during gait and body mass index. A total of 29% of the variance in pain intensity was explained by mechanical variables. The range of flexion-extension explained 18% of variance in pain intensity. Body mass index added 11% to the model. The knee adduction moment was unrelated to pain intensity.

INTERPRETATION

The findings support that mechanical factors are related to knee osteoarthritis pain. Because limitations in flexion-extension range of motion and body size are modifiable factors, future research could examine whether interventions targeting these mechanics would facilitate pain management.

Correlation between bone lesion changes and cartilage volume loss in patients with osteoarthritis of the knee as assessed by quantitative magnetic resonance imaging over a 24-month period

OBJECTIVE

To evaluate in patients with knee osteoarthritis (OA) the size changes in bone oedema and cysts over 24 months, and to contrast these changes with cartilage volume loss using quantitative magnetic resonance imaging.

METHODS

107 patients with knee OA, selected from a large trial evaluating the effect of a bisphosphonate, were analysed by magnetic resonance imaging at baseline and 24 months. Assessments of subchondral bone oedema and cysts, and cartilage volume were done.

RESULTS

At baseline, 86 patients showed the presence of at least one type of bone lesion: 71 oedema, 61 cysts and 51 both. At 24 months, although not statistically significant, the oedema total size change increased by 2.09 (SD 15.03) mm, and the cyst by 1.09 (8.13) mm; mean size change for the oedema was +0.38 (2.18) mm and -0.10 (4.36) mm for the cyst. When analysed according to subregions, an increase was found for the cyst size in the trochlea (+0.67 (2.74) mm, p = 0.02) and in the lateral tibial plateau (+0.15 (0.83) mm, p = 0.09), and for the oedema size in the medial tibial plateau (+1.73 (8.11) mm, p = 0.05). At 24 months, significant correlations were seen between the loss of cartilage volume and oedema size change in the medial condyle (-0.40, p = 0.0001) and the medial tibial plateau (-0.23, p = 0.03), and the changes in cyst size in the medial condyle (-0.29, p = 0.01). A multivariate analysis showed that the oedema size change was strongly and independently associated with medial cartilage volume loss (-0.31, p = 0.0004).

CONCLUSION

These data demonstrate that bone lesions are prevalent in knee OA. The correlation of the oedema and cyst size increase in the medial compartment over time with a greater loss of cartilage volume in this area underlines the importance of subchondral bone lesions in OA pathophysiology.

Risk factors associated with the loss of cartilage volume on weight-bearing areas in knee osteoarthritis patients assessed by quantitative magnetic resonance imaging: a longitudinal study

The objective of this study was to identify, on a symptomatic knee osteoarthritis (OA) cohort, the risk factors associated with the progression of the disease. More specifically, we investigated the correlation between knee cartilage volume loss from subregions over the span of 24 months by means of quantitative magnetic resonance imaging (qMRI) with demographic, clinical, radiological, and MRI structural changes.

A cohort of 107 patients with knee OA selected from a large trial evaluating the effect of a bisphosphonate underwent x-rays and MRI of the knee at baseline and 24 months. Joint space width (JSW) and joint space narrowing (JSN) and cartilage volume loss over time in subregions of the tibial plateaus and femoral condyles were quantitated. Structural changes in the subchondral bone (hypersignal) and in the menisci (tear and extrusion) were also evaluated.

The greatest cartilage volume loss was found in the medial compartment, and risk factors included female gender, JSW, meniscal lesions, and bone changes at baseline. Subregion analysis revealed that the greatest cartilage volume loss at 24 months was found in the central area of the medial tibial plateau (15%; p < 0.0001) and of the medial femoral condyle (12%; p < 0.0001). These findings were associated with the presence at baseline of meniscal extrusion, particularly severe meniscal extrusion, medial and severe meniscal tear, bone hypersignal, high body mass index (BMI), smaller JSW, increases in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and patient global scores over time, and greater JSN. Parameters predicting medial central femoral condyle cartilage volume loss at 24 months were lateral meniscal tear, SF-36 and BMI at baseline, and JSN. At the medial central tibial plateau, the parameters were severe meniscal extrusion, severe lateral meniscal tear, and bone hypersignal in the lateral compartment at baseline, and WOMAC pain change.

Meniscal damage and bone changes are the features most closely associated with the greatest subregional cartilage volume loss. Interestingly, for the first time, JSN was strongly associated with cartilage loss in the central areas of plateaus and condyles. This study also further confirms the correlation between cartilage volume loss and JSN and symptomatic changes at 24 months.

Central bone marrow lesions in symptomatic knee osteoarthritis and their relationship to anterior cruciate ligament tears and cartilage loss

OBJECTIVE

Medial and lateral compartment bone marrow lesions (BMLs) have been tied to cartilage loss. We undertook this study to assess 2 types of BMLs in the central region of the knee (type 1 BMLs, which are related anatomically to anterior cruciate ligament [ACL]/posterior cruciate ligament [PCL] insertions, and type 2 BMLs, which encompass both the central region and either the medial or the lateral compartment) and determine their relationship to cartilage loss and ACL tears.

METHODS

Magnetic resonance imaging (MRI) of the knee was performed at baseline and at followup (15 and/or 30 months) in 258 subjects with symptomatic osteoarthritis (OA). At baseline, we assessed ACL tears and central BMLs located at or between the tibial spines or adjacent to the femoral notch. Cartilage loss was present if the score in any region of the tibiofemoral joint increased by >or= 1 units at the last available followup, using a modified Whole-Organ MRI Score. We used logistic regression adjusted for alignment, body mass index, Kellgren/Lawrence score, sex, and age.

RESULTS

One hundred thirty-nine knees (53.8%) had central BMLs, of which 129 had type 1 BMLs (96 abutted the ACL and had no coexistent type 2 features) and 25 had type 2 BMLs (often overlapped with type 1). Type 1 lesions were associated with ACL tears (odds ratio [OR] 5.9, 95% confidence interval [95% CI] 2.2-16.2) but not with cartilage loss (OR 1.6, 95% CI 0.8-3.1), while medial type 2 BMLs were related to medial cartilage loss (OR 6.1, 95% CI 1.0-35.2).

CONCLUSION

Central BMLs that abutted the ACL were highly prevalent and strongly related to ACL pathology, suggesting a role of enthesopathy in OA. Only BMLs with medial extension were related to ipsilateral cartilage loss.

The association of bone attrition with knee pain and other MRI features of osteoarthritis

OBJECTIVE

To determine whether bone attrition (flattening or depression of the subchondral bone) was associated with the presence and severity of knee pain and to evaluate the coexistence of attrition and other MRI features likely associated with pain.

METHODS

Participants in the Framingham Osteoarthritis Study, a community cohort unselected for OA, answered questions about knee pain and underwent knee x rays and MRI. Attrition, bone marrow lesions (BMLs) and effusions were scored on MRI using the WORMS scale. We assessed attrition in knees with and without pain, and using logistic regression examined its association with pain adjusting for age, gender, Kellgren-Lawrence (K-L)grade, BMI, BML and effusion. We also explored the relation between attrition, pain severity and nocturnal pain.

RESULTS

Attrition (Grade >2) was present in 28% (167/592) of painful knees and in 10% (106/1035) of nonpainful knees (adjusted OR 1.6 (95% CI 1.1 to 2.2)). Of knees with OA (n=368), 74% had pain if attrition was present and 58% if it was absent (adjusted OR 1.2 (95%CI 0.7 to 2.0)). Of knees without OA (n=1222), pain was reported in 39% of knees with attrition and in 27%without it (adjusted OR 2.1 (95% CI 1.1 to 4.0)). We found no association between either attrition/pain severity or attrition/nocturnal pain. Attrition often co-occurred with other OA features associated with pain such as BMLs and effusions.

CONCLUSIONS

Attrition was associated independently with knee pain. Unlike knees without OA, the association was lost in OA knees where other pathological features that may cause pain also coexisted.

Imaging of knee osteoarthritis: data beyond the beauty

PURPOSE OF REVIEW

MRI has revolutionized osteoarthritis research by providing semi-quantitative and quantitative imaging endpoints on most articular tissues. With the first image data of the Osteoarthritis Initiative now becoming publicly available, this article reviews recent developments in quantitative imaging of osteoarthritis.

RECENT FINDINGS

Although radiography remains the standard for regulatory studies on disease modifying osteoarthritis drugs, there is no consensus on the optimal positioning and acquisition protocol. With MRI, semi-quantitative scoring systems for evaluation of multiple articular tissue changes have been developed and are currently investigated in the context of correlation with symptoms and of predicting structural progression of osteoarthritis. Most efforts on quantitative measurement of imaging endpoints have focused on cartilage morphology and composition, with higher field strength (3T), newer sequences, and new measurement endpoints being a driver of current innovation.

SUMMARY

The semi-quantitative and quantitative tools for analysis of articular structure are now available and permit comprehensive analysis of morphological and compositional tissue changes in osteoarthritis. These changes will need to be related to clinical outcomes (e.g. how a patient feels or functions) with current epidemiological studies, such as the Osteoarthritis Initiatives, providing the opportunity for clinical validation of these imaging biomarkers.

Elevated high-sensitivity C-reactive protein levels are associated with local inflammatory findings in patients with osteoarthritis

OBJECTIVE

C-reactive protein (CRP) has been associated with disease progression in patients with osteoarthritis (OA), but the reasons for this remain unclear. We hypothesized that higher CRP would be related to local inflammatory findings in the joints of patients with OA.

METHODS

Plasma and synovial membrane specimens from 54 OA patients undergoing total hip or knee arthroplasty or arthroscopy were obtained. Synovial fluid was obtained from 25 of these patients. Hematoxylin and eosin stained synovial membrane sections were scored for degree of inflammatory cell infiltration. Plasma high-sensitivity CRP (hsCRP) levels, and serum and synovial fluid interleukin (IL)-6 and IL-1beta levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Fifty-seven percent of patients with idiopathic OA had inflammatory infiltrates within the synovial membrane. The mean hsCRP level in patients with inflammatory infiltrates was significantly higher than those without inflammation (4.7 +/- 5.0 mg/L vs 1.7 +/- 3.6 mg/L, P = 0.003). There were significant correlations between hsCRP levels and synovial fluid IL-6 (r = 0.64, P = 0.0006), degree of synovial inflammatory infiltration (r = 0.43, P = 0.002), and body mass index (r = 0.31, P = 0.02). Multivariate analysis indicated that only degree of inflammatory infiltrate was significantly associated with hsCRP level (P = 0.026).

CONCLUSION

These results suggest that systemic hsCRP levels reflect synovial inflammation in OA patients, perhaps by means of synovial IL-6 production. Future studies are needed to clarify how these infiltrates and their products may contribute to disease pathogenesis.

Tibial subchondral bone size and knee cartilage defects: relevance to knee osteoarthritis

Unlike knee plain radiography which can only detect joint space narrowing and osteophytes, magnetic resonance imaging can directly visualize and analyse the whole knee structure, including bone size, cartilage defects and loss of cartilage volume. Tibial subchondral bone area expansion may be primary and is associated with risk factors such as age, body mass index (BMI), genetics and/or limb malalignment. It can lead to the development of knee defects, which may also be caused by demographic, anthropometric and environmental factors such as age, female sex, BMI and smoking as well as structural changes such as osteophytes, bone marrow lesions, meniscal tears, meniscal extrusion and ligament abnormalities. Once knee cartilage defects develop, they have a variable natural history but are associated with subsequent cartilage loss in a dose-response manner. Both tibial subchondral bone area and knee cartilage defects are quantitatively related to the severity of knee osteoarthritis (OA), and predictive of the need for knee joint replacement in subjects with knee OA independent of radiographic change. Taken as a whole, these studies suggest that tibial subchondral bone expansion and cartilage defect development represent important targets for the prevention of cartilage loss and joint replacement.