Summary

Shelf acetabuloplasty restored hip stability in terms of abduction and internal rotation to a level similar to that of native hips.

Abstract

Background

Shelf acetabuloplasty has been described as a surgical treatment for developmental dysplasia of the hip (DDH) and has been gaining attention as a less invasive procedure compared to peri-acetabular osteotomy. Although favorable outcomes have been reported after endoscopic shelf acetabuloplasty, the biomechanical effect of shelf acetabuloplasty remains a topic of controversy due to the lack of evidence from previous biomechanics studies.

Objectives: To evaluate the stabilizing effect of shelf acetabuloplasty in the setting of hip dysplasia using cadaveric hips.

Methods

Ten fresh-frozen cadaveric hips were dissected down to the hip capsule and mounted to a 6-degrees of freedom robotic arm. Each specimen underwent biomechanical testing in 4 states: 1) Intact, 2) Capsular repair, 3) Hip dysplasia model and 4) Shelf acetabuloplasty. The capsule repair state was introduced to serve as a control, because the capsule needed to be opened to create hip dysplasia model. After the native state was test, the hip capsule was detached from its acetabular rim. Eight transosseous tunnels through the ilium were created and the hip capsule was then repaired with four No.2 high-strength sutures passed through those tunnels. For the hip dysplasia model, the repaired capsule was detached, and the labrum was taken down from the acetabulum. The acetabular rim was then resected with a bone saw to achieve lateral center-edge angle (LCEA) of 15-20 degrees confirmed by a fluoroscope. After that, the labrum was re-fixated with three suture anchors. The hip capsule was then reattached using the same method used for the capsular repair state. For Shelf acetabuloplasty, a tricortical bone graft (5 mm in height x 30 mm in width x 35 mm in length) was harvested from the iliac crest. The slot (5 mm in height x 25 mm in width x at least 20 mm in depth) was created above the hip capsule. The bone graft was introduced into the slot to achieve LCEA of 35 - 40 degree. Biomechanical evaluation consisted of 4 robotic tests: 1) 5-Nm abduction, 2) 5-Nm internal rotation at 75° flexion, 3) 5-Nm flexion 4) 88-N Lateral Drawer. Primary outcomes were range of motion in degrees for the rotation tests and lateral displacement in mm for the lateral drawer test. Statistical analysis was performed using ANOVA and Tukey's method.

Results

The capsule repair showed no significant differences compared to native in any test. The Hip dysplasia model showed increased abduction (+2.3° p=0.003), and IR at 75° flexion (+0.9°, p=0.017), compared to native, and showed no increase in flexion or lateral translation. The shelf acetabuloplasty restored native abduction and IR at 75° flexion, but reduced hip flexion (-1.7° p=0.003).

Conclusion

This study demonstrated that shelf acetabuloplasty restored hip stability in terms of abduction and internal rotation to a level similar to that of native hips. This study provides the first evidence that shelf acetabuloplasty can enhance hip instability in a hip dysplasia model utilizing human hip cadavers.