Abstract| Volume 20, SUPPLEMENT 1, S105-S106, April 2012

Is increased joint loading detrimental to knee osteoarthritis in obese patients? a secondary data analysis from a randomized trial

      Purpose: Weight loss is recommended as a treatment of knee osteoarthritis (OA) with the mechanisms of efficacy mainly thought to be through reduced knee loads. Successful outcomes can reduce pain and improve ambulatory function. Yet the improved ambulatory function raises concern of the risk of increased knee joint loading during walking that is thought to be detrimental to knee OA and accelerate structural changes. The results of our recent weight loss study offered the opportunity to address the concern of increase ambulatory loads following weight loss since approximately 1/3 of the participants responded to a significant weight loss by improving ambulatory function in a manner that increased loading at the knee during walking. The purpose of this study was to investigate whether increased loading of the knee joint following weight loss caused accelerated structural disease progression and fewer changes in symptoms over 1 year in an overweight/obese population with knee OA.
      Methods: Data from the biomechanics sub-cohort in a prospective randomized weight loss trial (the CAROT study) were used. The CAROT study is designed with an initial 16 week weight loss period with a subsequent 1-year weight maintenance period. The biomechanics sub-cohort consisted of participants with complete pre- and post weight loss records of biomechanical gait analysis. Based on the changes in ambulatory knee joint loadings after the weight loss, the participants were divided into ‘Unloaders’ (participants that reduced the joint loads) and ‘Loaders’ (participants that increased the joint loads). According to this study design both participants and outcome assessors were concealed to the “group allocation”. The primary structural outcome was changes in tibiofemoral cartilage volume measured from automatic segmentation of MRI from baseline (after weight loss) to 52 weeks (weight maintenance period). The primary symptomatic outcome was changes in average knee symptoms measured as the mean of 4 out of the 5 KOOS subscales (excluding sports and recreation subscale) over 52 weeks. Changes from baseline to 1 year were compared between groups using analysis of covariance adjusting for baseline values, age, gender, BMI and other potential confounding factors.
      Results: 157 participants (82% of the CAROT cohort) were included in the biomechanics sub-cohort. Of these 100 were classified as Unloaders and 57 as Loaders based on gait changes from baseline to after the weight loss: The Unloaders on average reduced the peak knee compression force during walking by -509N (18%) and the Loaders increased the peak compression force by 425N (19%). There were no baseline differences between the groups except that the Loaders walked with significantly higher (11%) knee loads. Both groups showed the same significant reduction in cartilage volume and symptoms at one year yet there were no statistically significant difference in the change in tibiofemoral cartilage volumes or average symptoms (table) between Loaders and Unloaders.
      Conclusions: For obese patients undergoing a significant weight loss, increased knee joint loading (Loaders) for 1 year did not accelerate disease progression (as assessed by changes in tibiofemoral cartilage volume and worsening of symptoms) relative to a similar weight loss group (Unloaders) that had reduced ambulatory knee joint loads.
      This is the first study to assess consequences of increased knee joint loading on OA progression and the results support the application of interventions that improve function and potentially increase ambulatory load in obese subjects since there does not appear to be detrimental effects of increased load in this group.
      Trial registration: {NCT00655941}
      Tabled 1ANCOVA results for primary outcomes of cartilage volumes (mm3) and average symptoms pain (KOOS)
      BaselineFollow-upChange (Follow-up - Baseline)Difference†
      UnloadersMean (SD)LoadersMean (SD)UnloadersMean (SD)LoadersMean (SD)UnloadersMean (SE)LoadersMean (SE)Mean Difference (95% CI)P
      Cartilage volume2,603(734)2,554 (454)2,269(72.5)2,315(86.3)-316 (72.5)-270(86.3)-46.3

      Average symptoms66.6 (16.4)64.3(17.1)63.4 (1.6)64.2(1.9)-2.4


      †Adjusted for baseline value age, gender, BMI and other potential confounding factors.