Commentary

Physical activity and knee osteoarthritis

Dietary fiber reduces body weight and inflammation in clinical trials. It is unclear whether body mass index (BMI) and inflammation might explain the observed association between higher fiber intake and the lower risk of symptomatic knee osteoarthritis (SXKOA).

We quantified the extent to which BMI and inflammation influenced the relation between dietary fiber and SXKOA.

We used longitudinal data from the Osteoarthritis Initiative (OAI) and the Framingham Offspring Osteoarthritis Study. At baseline of each study, men and women (mean age: 61 y) with or at risk of knee osteoarthritis were followed for 48 mo in the OAI. Adults (mean age: 53 y) were followed for 9.5 y in the Framingham study. Dietary fiber intake was estimated using a validated food-frequency questionnaire. Measured weight and height were used to calculate BMI. Serum high-sensitivity C-reactive protein (CRP) was measured in the Framingham study only. Incident SXKOA was defined as new onset of a combination of knee pain and radiographic osteoarthritis. We applied marginal structural models to quantify the mediation through BMI in the OAI and the sequential mediation through BMI and CRP in the Framingham study.

Incident SXKOA occurred in 861 knees among 2876 persons in the OAI and in 143 knees among 971 persons in the Framingham study. In persons whose fiber intake was ≥21 g/d compared with those with intakes <21 g/d, the OR (95% CI) was 0.70 (0.53, 0.91) for the overall association with SXKOA and was 0.93 (0.92, 0.95) for the mediation via BMI (per kg/m²) in the OAI. In the Framingham study, the overall association was 0.57 (0.30, 1.09), the mediation through BMI (via BMI and the influence of BMI on CRP) was 0.94 (0.85, 1.02), and the mediation through CRP (per milligram per liter) was 0.99 (0.84, 1.19).

Our findings suggest that the inverse association of fiber intake and the risk of incident symptomatic knee osteoarthritis is partially mediated by BMI.

Systematic reviews agree that knee osteoarthritis (OA) is related to occupational activities, but have not quantified the overall risks.

Systematic review of observational studies of knee OA and occupation. Job titles, elite sport, heavy work, kneeling, and other activities were included. Relative risk estimate and 95% confidence interval (CI) compared to sedentary work were retrieved or calculated for meta-analysis. Publication bias was examined with Egger tests and heterogeneity was determined with I² values and Q tests. Subgroup analysis was performed to examine causes of heterogeneity. A random effects model was performed to combine the data.

Studies of knee OA (n = 51), persistent knee pain (n = 12) and knee OA progression (n = 3) were retrieved. Occupational risks for knee OA were examined in a total of 526,343 subjects in 8 cohort/prospective/longitudinal studies, 25 cross-sectional studies and 18 case control studies. The overall odds ratio (OR) was 1.61 (95% CI 1.45–1.78) with significant heterogeneity (I² = 83.6%). Study designs showed a positive association between knee OA and occupational activities; cohort (OR 1.38, 95% CI 1.10–1.74), cross-sectional (OR 1.57, 95% CI 1.37–1.81) and case control (OR 1.80, 95% CI 1.48–2.19). Overall there was evidence of publication bias (P < 0.0001) which was apparent in the cross-sectional and case control studies (P < 0.0001 and P = 0.0247 respectively).

Some occupational activities increase the risk of knee OA, although the influences of publication bias and heterogeneity are important limitations of this study. Prospective studies would greatly improve the evidence base.

Objective To investigate the incidence and severity of osteoarthritis (OA) and the effects of voluntary wheel running in normal mice and mice carrying either a targeted inactivation of one allele, heterozygous ‘knockout’, of Col2a1 gene or both alleles, homozygous ‘knockout’, of Col11a2 gene.

Methods Mice lived until 15 months of age in individual cages. Running activity was recorded around the clock. OA changes were evaluated from serial knee joint sections by light microscopy.

Results Heterozygous inactivation of Col2a1 gene coding for type II procollagen made the cartilage more susceptible to OA. At 15 months of age, OA prevalence was 60–90% in knockouts and 20–45% in normal controls (P< 0.01–0.001). Unexpectedly, a reduction of OA due to wheel running was observed in both knockout strains (P< 0.05–0.01). This effect was most evident in the femoral condyles. Incidence of OA in runners was approximately 50–85% of that in sedentary littermates. OA prevalence was higher in normal control and runner mice with high body weight. Running did not affect OA development in normal mice.

Conclusion Heterozygous knockout of Col2a1 gene increased the OA prevalence in mice. Lifelong voluntary wheel running had a protective effect against OA in both knockout mice lines. The reason for this remains unknown. Reduction of OA may result from the reorganization and strengthening of the articular cartilage collagen network and/or adjacent muscles due to running, or lower body weight. Increased compliance of the articular cartilage and bones of the knockout mice may also contribute to the reduction of OA in exercised animals.

Objectifs : Faire la revue des connaissances actuelles sur les rapports entre lˈactivité physique, la biologie du cartilage et lˈarthrose ainsi que les déductions pour la rééducation.

Méthode : Les bases de données PubMed, Ovid, Cochrane Data Base ont été interrogées sur la période 1966–2000. Mots clés : chondrocyte, cartilage, osteoarthritis, mechanical stimulation, exercises, physical therapy, rehabilitation. Ont été revus : la mécanobiologie du chondrocyte et du cartilage, la mécanotransduction et la réponse métabolique des chondrocytes, les effets de lˈactivité physique et de lˈimmobilisation sur le cartilage dans des modèles animaux, les principales études épidémiologiques dans lˈarthrose des membres et les essais thérapeutiques évaluant lˈeffet de la rééducation.

Résultats : In vitro, certaines molécules permettent la transduction du signal mécanique en signal biologique intracellulaire avec modulation de la balance synthèse/dégradation de la matrice extracellulaire du chondrocyte. Les stimulations cycliques appliquées au cartilage ou aux chondrocytes ont probablement un effet anabolique sur la matrice extracellulaire contrairement aux stimulations statiques. In vivo et chez lˈanimal, l’activité physique intense ou au contraire l’immobilité ont plutôt des effets nocifs pour le cartilage. Chez l’homme l’activité physique intense prolongée et certains sports « à risque » favorisent l’arthrose des membres inférieurs. Les exercices et la mobilisation passive continue semblent avoir une efficacité thérapeutique. Toutefois, les études fondamentales et cliniques ne permettent pas aujourdˈhui de proposer pour une articulation donnée, des protocoles précis de rééducation dans un but de chondromodulation. L’utilisation de la mobilisation passive est une voie de recherche prometteuse tant en terme dˈefficacité clinique que de compréhension de la relation biomécanique-trophicité du cartilage chez lˈhomme.

Conclusion : La prise en charge de lˈarthrose des membres paraît bénéficier de la rééducation. Les protocoles doivent cependant être évalués dans des études contrôlées.

Objectives: To review the current knowledge about the relationship between physical activities, cartilage biology, osteoarthritis and rehabilitation.

Method: PubMed, Ovid, Cochrane Data base were interrogated for the period 1966-2000. Key words were: chondrocyte, cartilage, osteoarthritis, mechanical stimulation, exercises, physical therapy, rehabilitation. Were reviewed: the mechanical biology of the chondrocytes and the cartilage, the mechanisms of transduction, the metabolic response of the chondrocytes to mechanical stresses; the effects of physical activity and immobilization on the cartilage in animal models, the main studies on the epidemiology of limbs osteoarthritis and clinical trials on rehabilitation.

Results: In vitro studies have demonstrated that some molecules are involved in the transduction of mechanical stress into intracellular biological event. Chondrocytes and cartilage are sensitive to mechanical stress and cartilage extracellular matrix synthesis and degradation can be modulated by mechanical events. Applications of cyclic loads usually lead to an enhanced matrix synthesis while static loads usually decrease matrix production. In animal models, intensive physical activity or immobilization lead to cartilage alteration mimicking osteoarthritis. In human, intensive and prolonged physical activities are probably associated with hip and knee osteoarthritis. However, there is evidence that exercise therapy and continuous passive motion have beneficial effects on patients with knee or hip osteoarthritis. Fundamental and clinical studies are still needed to determine if exercise programs could have an effect on chondromodulation. Continuous passive motion could help, in the future, to better understand the relationship between mechanical stimulation and cartilage homeostasis.

Conclusion: Rehabilitation could be beneficial in the therapeutic management of limbs osteoarthritis. The protocols of rehabilitation should however be more evaluated in controlled trials.