Femoroacetabular Impingement Patients With Decreased Femoral Version Have Different Impingement Locations and Intra- and Extraarticular Anterior Subspine FAI on 3D-CT–Based Impingement Simulation: Implications for Hip Arthroscopy
Authors: Lerch Till D. , Boschung Adam , Todorski Inga A.S. , Steppacher Simon D. , Schmaranzer Florian , Zheng Guoyan , Ryan Michael K. , Siebenrock Klaus A. , Tannast Moritz 
Published: September 2019

Background: It remains unclear whether decreased femoral version (FV) causes anterior intra- or extra-articular femoroacetabular impingement (FAI). Therefore, we evaluated symptomatic hips with decreased FV, with and without cam and pincer FAI, by using computed tomography (CT)–based virtual 3-dimensional (3D) impingement simulation and compared this group with patients with normal FV and with asymptomatic hips. Purpose: To investigate (1) the osseous range of motion, (2) the osseous femoral and acetabular impingement zones, and (3) whether hip impingement is extra- or intra-articular in symptomatic hips with FAI. Study Design: Cross-sectional study; Level of evidence, 3. Methods: An institutional review board–approved, retrospective comparative analysis was performed on a total of 84 hips in 68 participants. Of these, 37 hips in 24 symptomatic patients with FAI had decreased FV. These hips were compared with 21 hips of 18 symptomatic patients with anterior FAI with normal FV (10°-25°) and 26 asymptomatic hips with no FAI and normal FV. All patients with FAI were symptomatic and had anterior hip pain and a positive anterior impingement test. They underwent pelvic CT scans to measure FV. Decreased FV was defined as FV less than 5°. The 37 hips with decreased FV presented both with and without cam and pincer FAI. All 84 hips were evaluated by use of CT-based 3D models and a validated 3D range of motion and impingement simulation. Asymptomatic hips were contralateral normal hips imaged in patients undergoing total hip arthroplasty. Results: Hips with FAI combined with decreased FV had a significantly ( P < .001) lower mean flexion (114°± 8° vs 125°± 13°) and internal rotation (IR) at 90° of flexion (18°± 6° vs 32°± 9°, P < .001) compared with the asymptomatic control group. Symptomatic patients with FAI and normal FV had flexion of 120°± 16° and IR at 90° of flexion of 23°± 15°. In a subgroup analysis, we found a significantly ( P < .001) lower IR in 90° of flexion in hips with FV less than 5° combined with mixed-type FAI compared with hips with FV less than 5° without a cam- or pincer-type deformity. The maximal acetabular impingement zone for hips with decreased FV was located at the 2-o’clock position and ranged from 1 to 3 o’clock. In hips with decreased FV, most of the impingement locations were intra-articular but 32% of hips had combined intra- and extra-articular FAI in internal rotation in 90° of flexion. During the flexion-adduction-IR test performed in 10° and 20° of adduction, extra-articular subspine FAI had significantly ( P < .001) higher prevalence (68% and 84%) in hips with decreased FV compared with normal hips. Conclusion: Hips with FAI and decreased FV had less flexion and internal rotation in 90° of flexion compared with the asymptomatic control group. The majority of hip impingement due to low FV was intra-articular, but one-third of samples had combined intra- and extra-articular subspine FAI. Anterior extra- and intra-articular hip impingement can be present in patients who have FAI with decreased FV. This could be important for patients undergoing hip arthroscopy.