Shelf acetabuloplasty restores native rotational motion in a cadaveric acetabular dysplasia model.

INTRODUCTION/

OBJECTIVES

Developmental dysplasia of the hip is associated with inferior clinical outcomes when treating concomitant intra-articular pathologies. Shelf acetabuloplasty has been proposed as a less invasive alternative to periacetabular osteotomy for developmental dysplasia of the hip; however, there is a lack of biomechanical studies regarding its efficacy. We hypothesized that a cadaveric dysplasia model would cause increased range of motion and lateral femoral head translation compared to native, and that shelf acetabuloplasty would restore native biomechanics.

METHODS

Ten cadaveric hips were dissected down to the capsule and mounted to a six-degree-of-freedom robotic arm. Each specimen was tested sequentially in 4 states: 1) Native, 2) Capsular repair, 3) Acetabular dysplasia model created by acetabular rim resection to achieve a lateral center-edge angle (LCEA) of 15-20° under fluoroscopic guidance, and 4) Shelf acetabuloplasty restoring LCEA of 35-40° utilizing a bone graft harvested from the iliac crest. Robotic testing included: 1) 5- Newton Meter (Nm) abduction, 2) 5-Nm internal rotation (IR) at 75° flexion, 3) 5-Nm flexion, and 4) 88-N lateral drawer. Range of motion under standardized torque was used as a surrogate measure of rotational stability. The effect of specimen state was determined using analysis of variance, and post hoc pairwise comparisons were made using Tukey's method.

RESULTS

Capsular repair did not statistically significantly differ from the native state. Compared to native, the acetabular dysplasia model showed increased abduction (+2.3°, p = 0.004) and IR at 75° flexion (+0.9°, p = 0.017) without statistically significant changes in flexion or lateral translation. Shelf acetabuloplasty restored native abduction and IR at 75° flexion but reduced hip flexion (-1.7°, p = 0.003).

CONCLUSION

This study demonstrated that acetabular rim resection increased rotational motion under applied torque, while shelf acetabuloplasty restored rotational motion to native levels. However, shelf acetabuloplasty resulted in a statistically significant reduction in hip flexion (-1.7°, p = 0.003), suggesting potential over-constraint depending on graft positioning.

LEVEL OF EVIDENCE: Not Applicable, Controlled Laboratory Study.