Dynamic changes in the contact area of the sacroiliac joint

Thirty adult dry-bone ilium specimens were used in conjunction with computer analysis to determine the average articular contact area between the sacrum and ilium at the sacroiliac joint. Simulating an unstable pelvic injury, the sacroiliac joint was displaced in three directions by moving the ilium posteriorly, superiorly, and posterosuperiorly. After each displacement, the contact area between the sacrum and ilium at the sacroiliac joint was calculated. The data showed that the average articular surface area of the male sacroiliac joint (1138.3 mm2) was approximately 12.8% greater than the average surface area of the female sacroiliac joint (992.5 mm2). The average articular contact area between the sacrum and ilium at the sacroiliac joint was lowest with the ilium displaced posterosuperiorly compared to equal displacements superiorly or posteriorly. This study quantitatively illustrated the loss of contact surface area between the sacrum and ilium during various displacements of the ilium, thus indicating the clinical cross-section area available for open reduction and internal fixation or fusion.