Shin-ichi izumi 7,8 , eiichi Murakami 2 , Hiroshi ozawa 9 & toshiro ohashi 10 the sacroiliac joint (SiJ) is burdened with variant loads. However, no methods have allowed to measure objectively how the SiJ deforms during bipedal walking. in this study, in-vivo walking conditions were replicated in a kinematic model combining the finite element method with 3D walking analysis data divided into five phases in order to visualize the load transition on the SIJ and clarify the role of the SiJ. Both models with and without inclusion of the SiJ were investigated. in models with bilateral SIJs, the displacement differed greatly between the sacrum and both hip bones on the SIJ as the boundary. the movements of the sacrum involved a nutation movement in the stance phase and a counter-nutation in the swing phase relative to the ilium. in models without SiJs, the displacement of the pelvis and loads of pelvic ligaments decreased, and the equivalent stress of the SiJs increased compared to the model with SiJs. the walking loads cause distortion of the entire pelvis, and stress concentration at the SiJ are seen due to the morphology of the pelvic ring. However, the SiJs help dissipate the resulting stresses, and the surrounding ligaments are likewise involved in load transmission.
BACKGROUND: Pain related to the sacroiliac joint (SIJ) accounts for low back pain in 15%–30% of patients. One of the most common treatment options is the use of pelvic belts. Various types of pelvic belts exist; however, the mechanisms underlying treatment and their effectiveness remain unclear to date. OBJECTIVE: To analyze stress distribution in the pelvis when a pelvic rubber belt or a padded pelvic belt is applied, to assess the effectiveness of treatment from a numerical biomechanical perspective. METHODS: The pressure distribution at the pelvic belts was measured using a device and subsequently modeled with the finite element method of a pelvis with soft tissues. The stress environment when wearing a pelvic belt in a double-leg stance was simulated. RESULTS: With the application of pelvic belts, the innominate bone rotated outward, which was termed an out-flare. This caused the SIJ to compress and cause reduction in sacrotuberous, sacrospinous, interosseous, and posterior sacroiliac ligament loading. Padded pelvic belts decreased the SIJ displacement to a greater extent than in pelvic rubber belts. CONCLUSION: Pelvic belts aid in compressing the SIJ and reduce its mobility.
In acetabular dysplasia, the cartilaginous roof on the acetabular side does not fully cover the femoral head, which may lead to abnormal stress distribution in both the femoral head and pelvis. These stress changes may have implications to the adjacent sacroiliac joint (SIJ). The SIJ has a minimal range of motion and is closely coupled to the adjacent spine and pelvis. In consequence, the SIJ may react sensitively to changes in stress distribution at the acetabulum, with hypermobility-induced pain. The purpose of this study was to investigate the stress distribution of the SIJ in acetabular dysplasia, and to gain insight into the cause and mechanisms of hypermobility-induced pain at the SIJ. Finite element models of pre- and postoperative pelves of four patients with acetabular dysplasia were created and analyzed in double leg standing positions. The preoperative models were relatively inflare, the sacral nutation movement, SIJ cartilage equivalent stress, and the load on the surrounding ligaments decreased with increased posterior acetabular coverage. Acetabular morphology was shown to affect the SIJ, and improvement of the posterior acetabular coverage may help normalize load transmission of the pelvis and thus improve the stress environment of the SIJ in acetabular dysplasia.
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