Effect of femoral greater trochanter compression on chair-sitting difficulty due to sacroiliac joint disorder: A clinical and numerical study.

Background: Sacroiliac joint disorder commonly causes low back pain, aggravated by sitting, thereby affecting daily activities. Although clinical observations suggest that compression of the greater trochanter may improve sacroiliac joint pain while sitting, the biomechanical effects remain unknown. We investigated their clinical effects and validated them through in silico analysis.

Methods: We included five patients with sacroiliac joint disorder and one with discogenic pain, all of whom experienced severe pain while sitting. A handmade seating orthosis was used to compress the greater trochanters. We investigated the maximum sitting time with and without the orthosis and the patients' daily activities. Additionally, we visualized pelvic stress distribution under greater trochanter compression using finite element analysis.

Findings: Sitting time improved from a mean of 12.0 ± 5.7 min to 46.3 ± 11.1 with the use of the orthosis (p = 0.0054). Daily activity function also improved. Mean equivalent and minimum principal stresses on the sacroiliac joint surface during sitting increased under compression parallel to the long axis of the femoral neck and decreased with horizontal compression. Ligament loads under each loading condition were consistent across all scenarios, with a decrease in the load on the sacrotuberous, sacrospinous, anterior sacroiliac, and pubic ligaments.

Interpretation: This study demonstrated the clinical efficacy of the seating orthosis and showed that biomechanical effects on the sacroiliac joint surface varied with the direction of applied pressure to the greater trochanter during sitting, based on in silico analysis. These findings may help classify the mechanisms underlying sitting-related sacroiliac joint pain and inform more targeted treatment strategies.