THE EFFECT OF ALTERED WORK-REST RATIOS ON PORCINE STIFLES

Abstract

Background: Knee osteoarthritis (OA) is a prevalent disease that contributes to lower limb immobility and pain resulting in lost productivity in the work place. Repetitive loading of the knee joint, particularly in occupational settings, significantly increases OA risk. However, rest may promote tissue recovery and increase tissue tolerance to load. Therefore rest should be examined as a mechanism to prevent the development of knee OA. Purpose: The primary objective was to determine if rest can mitigate mechanical deformation of the stifle (knee) joint and articular cartilage damage during loading compared to an unloaded control in an intact porcine stifle model. Methods: A randomized controlled trial was conducted. Among 18 pairs of porcine hind limbs, one limb in each pair was randomly assigned to receive a loading intervention; while the matched pair served as control. Stifles in both groups were dissected, mounted into the loading apparatus, and pre-loaded. Intervention joints were then randomized into one of three loading protocols: no rest, 3:2 work:rest, and 1:1 work:rest; all of these protocols exposed joints to the same amount of cumulative load. Following loading, all joints were dissected to expose the cartilage. Cartilage damage was scored on a categorical scale. Deformation and energy dissipation were calculated for intervention limbs from data obtained from the loading apparatus. Results: Rest did not mitigate displacement or energy dissipation in the stifles exposed to loading. Rest was associated with reduced cartilage damage scores in the lateral femur in the 1:1 condition. Conclusion: Rest had little impact on joint mechanics and cartilage damage in this model. The small sample size may explain these results. Future investigations involving larger samples should assess if longer periods of rest are need to minimize joint damage as a result of loading.