Assessment of Biomechanical Changes After Sacroiliac Joint Fusion by Application of the 3-Dimensional Motion Analysis Technique

BACKGROUND: Sacroiliac (SI) joint motion is complex and is poorly understood overall. In this study we evaluated a new biomechanical method developed to provide more insight into SI joint movement and to elucidate biomechanical changes after SI joint fusion surgery in a one-leg standing model. METHODS: Eight lumbosacral cadaver specimens (L5-pelvis specimens, age 28-57 years, 6 female and 2 male) were used in this experiment. We analyzed the changes in range of motion (ROM) in single-plane motion and mobility in 3 groups of patients: intact, unilateral fusion, and bilateral fusion groups. For statistical analysis, we used repeated-measures analysis of variance to compare SI joint ROM among the 3 groups. iFuse implants were prepared using the standard posterior placement technique. Pure-moment multidirectional bending tests were performed in each direction (nutation and counternutation, axial rotation, and lateral bending). RESULTS: Average ROM in single-plane motion and mobility of the intact SI joint were 4.5 +/- 3.3 degrees and 4.8 +/- 3.4 degrees, respectively in nutation-counternutation; 2.9 +/- 2.1 degrees and 3.3 +/- 2.3 degrees, respectively, in axial rotation; and 1.5 +/- 1.5 degrees and 2.8 +/- 2.5 degrees, respectively, in lateral bending. We observed statistically significantly (P = 0.05) greater mobility in lateral moment testing than in single motion testing. Comparisons among the intact, unilateral fusion, and bilateral fusion groups showed statistically significant differences in the lateral moment test. CONCLUSIONS: This study suggests that our new biomechanical method for SI joint evaluation may provide improved insight into SI joint movement and biomechanical changes after SI joint fusion surgery in a one-leg standing model.