A Vessel Preserving Posterior Surgical Hip Dislocation Through the Posterolateral Approach: A Cadaveric Vascularity Study Using Gadolinium-Enhanced MRI

Introduction: A surgical hip dislocation provides circumferential access to the femoral head and is essential in the treatment pediatric and adult hip disease. Iatrogenic injury to the femoral head blood supply during a surgical may result in the osteonecrosis of the femoral head. In order to reduce vessel injury and incidence of AVN, the Greater Trochanteric Osteotomy (GTO) was developed and popularized by Ganz. The downside of this approach is the increased morbidity associated with the GTO including non-union in 8% and painful hardware requiring removal in 20% of patients. (reference) Recent studies performed at our institution have mapped the extra-osseous course of the medial femoral circumflex artery and provide surgical guidelines for a vessel preserving posterolateral approach. In this cadaveric model using Gadolinium enhanced MRI, we investigate whether standardized alterations in the postero-lateral surgical approach may reliably preserve femoral head vascularity during a posterior surgical hip dislocation Methods: In 8 cadaveric specimens the senior author (ES) performed a surgical hip dislocation through the posterolateral approach with surgical modifications designed to protect the superior and inferior retinacular arteries. In every specimen the same surgical alterations were made using a ruler: the Quadratus Femoris myotomy occurred 2.5 cm off its trochanteric insertion, the piriformis tenotomy occurred at its insertion and extended obliquely leaving a 2 cm cuff of conjoin tendon (inferior gemellus), and the Obturator Externus (OE) was myotomized 2 cm off its trochanteric insertion. (Figure 1) For the capsulotomy, the incision started on the posterior femoral neck directly beneath the cut obturator externus tendon and extending posteriorly to the acetabulum. Superior and inferior extensions of the capsulotomy ran parallel to the acetabular rim creating a T-shaped capsulotomy. After the surgical dislocation was complete, the medial femoral circumflex artery (MFCA) was cannulated and Gadolinium-enhanced MRI performed in order to assess intra-osseous femoral head perfusion and compared to the gadolinium femoral head perfusion of the contra-lateral hip as a non-operative control. Gross-dissection after polyurethane latex injection in the cannulated MFCA was performed to validate MRI findings and to assess for vessel integrity after the surgical dislocation. Results: In 8 cadaveric specimens MRI quantification of femoral head perfusion was 94.3% and femoral head-neck junction perfusion was 93.5% compared to the non-operative control. (Figure 2) Gross dissection after latex injection into the MFCA demonstrated intact superior and inferior retinacular arteries in all 8 specimens. (Figure 3) Discussion and Conclusions: In this study, perfusion to the femoral head and head-neck junction is preserved following posterior surgical dislocation through the postero-lateral approach. These preliminary findings suggest that specific surgical modifications can protect and reliably maintain vascularity to the femoral head after surgical hip dislocation. This approach may benefit hip resurfacing and potentially decease risk of femoral neck fracture secondary to osteonecrosis. In addition this may allow a vascular preserving surgical hip dislocation to be performed without the need for a GTO.