Osteoporosis-Induced Biomechanical Alterations in the Sacroiliac Joint.

Osteoporosis is a prevalent systemic disease primarily affecting the skeletal system, with the spine being one of the most commonly affected areas. Numerous studies have demonstrated detrimental biomechanical effects of osteoporosis on the lumbar spine. However, its influence on adjacent SIJ remains poorly understood. This study aimed to determine how osteoporosis alters SIJ biomechanics under physiological and vibrational load. A validated, 3D finite element model of the normal lumbopelvic segment (L1-pelvis) was modified to simulate osteoporosis by decreasing bone mechanical properties. Biomechanical responses within the SIJs to both static loading (flexion, extension, lateral bending, rotation) and vibration loading (cyclic axial compression) were analyzed and compared between the normal and osteoporotic conditions. Static analysis revealed that osteoporosis significantly increased SIJ range of motion (ROM) by 20.6%-52.7% and elevated maximum von Mises stress by 30.8%-90.3% compared to the normal condition. Also, forced vibration analysis revealed a 35%-36% increase in stress amplitudes in the osteoporotic model. These alterations correlated with reduced bone stiffness, suggesting compromised joint stability. These findings demonstrate that osteoporosis adversely affects SIJ biomechanics by increasing motion and internal stress, thereby potentially elevating the risks of SIJ instability, degeneration, and subsequent joint dysfunction and pain. This study provides novel insights into the overlooked role of SIJ pathology in osteoporotic patients, emphasizing the need for targeted diagnostic and therapeutic strategies.