A minimum of 16° of rotation of transcervical femoral neck fractures leads to arterial collapse: an anatomical cadaveric study.

PURPOSE: Avascular necrosis (AVN) of the femoral head is a significant complication following femoral neck fractures. Rotational deformity has been proposed as a mechanism of vascular compromise, yet the degree of rotation required to interrupt intracapsular blood flow remains undefined. This cadaveric study quantified the degree of external rotation required to produce angiographic occlusion of the femoral circumflex arteries. METHODS: Twelve cadaveric hips underwent catheterization of the deep femoral artery with radiocontrast injection under fluoroscopy to visualize the medial and lateral femoral circumflex arteries and their retinacular branches. A transcervical (AO/OTA 31B2) osteotomy was created while preserving capsular vessels. Controlled external rotation was applied using Schanz pins, and rotational angles were measured using a validated digital protractor. The angles of individual vessel occlusion and complete circumflex flow cessation were recorded. Paired analysis compared lateral femoral circumflex artery (LFCA) occlusion to complete circumflex occlusion. RESULTS: Complete circumflex flow cessation occurred at a mean of 16.83° (SD 3.11; range 10–21°). In all specimens, the LFCA occluded prior to the medial femoral circumflex artery (MFCA). In paired analysis (n = 11), LFCA occlusion occurred at significantly lower rotational angles than complete circumflex occlusion (mean difference 4.24°, 95% CI 3.11°–5.37°, p < 0.001). No differences were observed based on age or gender. CONCLUSION: Controlled external rotation across a transcervical femoral neck osteotomy resulted in sequential angiographic flow cessation at modest degrees of rotation. Intracapsular vessels appear highly vulnerable to torsional strain. Surgeons should minimize rotational deformity during femoral neck fracture management given the susceptibility of circumflex and retinacular vessels to mechanical rotation.