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Shelf acetabuloplasty restores native rotational motion in a cadaveric acetabular dysplasia model
Haruki Nishimura1, Kohei Yamaura1, Justin Brown1
1Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, CO, USA.
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.
