The effect of arthroscopic capsulotomy and repair on native resting hip joint forces using a non-destructive extra-articular method

Previous methods for measuring intra-articular forces require significant soft tissue dissection and intra-articular insertion of sensory instruments. This study demonstrates a minimally invasive method of measuring native resting hip joint force without disrupting the soft tissue envelope. This method is then utilized to determine the effect of capsulotomy and repair on these forces. Twenty fresh-frozen human cadaver hemipelves were percutaneously instrumented with an iliac crest locking plate and retrograde femoral nail to allow for testing using a distracting force. Force–displacement curves were generated in the native state, and after joint venting, an anterior hip approach, capsulotomy, capsular repair and soft tissue dissections. Mean native resting hip joint force was 110.5 N (SD 54.3 N). Capsular venting resulted in a significant decrease in hip joint force compared with the native state (100.2 N, SD 45.2 N, P = 0.026). A further decrease in hip joint force was observed with a T-capsulotomy (79.9 N, SD 40.1 N, P < 0.001 compared with anterior hip approach), with restoration of these forces after capsular repair (84.8 N, SD 40.5, P = 0.014 versus T-capsulotomy and P = 0.67 versus anterior hip approach). Soft tissue dissection resulted in a large decrease in hip joint force compared with the hip’s native state (59.7 N, SD 28.4 N, P = 0.002). Taken together, the findings suggest that this method is effective in measuring hip joint force and may be more accurate than those requiring significant soft tissue dissection. Furthermore, the data suggest that capsular repair likely plays an important role in the restoration of biomechanical forces in the hip after capsulotomy.