Description
OBJECTIVES: Shelf acetabuloplasty (SA) has been described as a surgical treatment for developmental dysplasia of the hip. Although favorable outcomes have been reported after endoscopic SA, the biomechanical effect of SA remains a topic of controversy due to the lack of evidence. The purpose of this study was to evaluate the stabilizing effect of SA in the setting of hip dysplasia (HD).
METHODS: Ten cadaveric hips dissected down to the capsule were mounted to a 6-degrees of freedom robotic arm. Each specimen underwent biomechanical testing in 4 states: 1) Intact, 2) Capsular repair (CR), 3) HD model and 4) SA. For the CR state, the capsule was detached 7 cm from its acetabular rim. The hip capsule was then repaired with four No.2 high-strength sutures passed through the 8 transosseous tunnels created through the ilium. The CR state was tested because the capsule needed to be opened to create the HD model. For the HD model, the labrum was detached from the acetabulum, then the acetabular rim was resected to achieve lateral center-edge angle (LCEA) of 15-20 degrees confirmed by a fluoroscope. The labrum was then re-attached with three suture anchors. The hip capsule was then closed. For the SA, a bone graft was introduced into the slot created above the capsule using press-fit fixation to achieve LCEA of 35-40 degrees. Biomechanical evaluation consisted of 4 robotic tests: 1) 5-Nm abduction, 2) 5-Nm internal rotation (IR) 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. The effect of specimen state was determined using ANOVA followed by Tukey’s method to adjust for multiple comparisons.
RESULTS SECTION: The CR showed no significant differences compared to native in any test. The HD 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 SA restored native abduction and IR at 75° flexion, but reduced hip flexion (-1.7° p=0.003).
CONCLUSION: This study demonstrated that SA restored hip stability in terms of abduction and internal rotation to a level similar to that of native hips. Notably, lateral translation of the hip remained consistent between native and surgically altered states. This study provides the first evidence that SA can enhance hip instability in a HD model, evident through range of motion testing utilizing human hip cadavers.
