Posterior Extra-articular Ischiofemoral Hip Impingement Caused by Increased Femoral Torsion and Acetabular Version Is a Novel Cause for FAI

Purpose: Femoroacetabular impingement (FAI) can be caused by cam or pincer deformities. Abnormal femoral torsion (FT) could be a new cause for FAI. Hips with increased FT can be combined with valgus deformity and can present clinically with a lack of external rotation and extension and a positive posterior impingement test. We asked whether (1) the range of motion (ROM); (2) the location of posterior osseous impingement zones; and (3) the prevalence of posterior extra-articular impingement differ between hips with isolated increased FT, hips with combined increased FT and increased acetabular version (AV), and valgus hips with increased FT and increased AV.

Methods and Materials: A three-dimensional (3D) impingement simulation study involving 52 hips and approved by the institutional review board was performed. Three-dimensional models of the pelvis and the femur based on 3D computed tomography scans of 52 hips with symptomatic posterior FAI were reconstructed using AMIRA software. These included 21 hips with isolated increased FT (FT > 25 degrees), 22 hips with combined increased FT and AV (> 25 degrees), and 9 valgus hips with increased FT and AV. Previously validated 3D collision detection software was used to quantify the simulated ROM and the location of acetabular and femoral impingement. The collision detection software is based on the equidistant method.

Results: (1) Valgus hips with combined increased FT and AV showed decreased flexion (p < 0.001) and external rotation in 90 degrees of flexion (p = 0.011), whereas internal rotation in 0 degrees of flexion was increased (p = 0.003) compared with hips with increased FT and AV. (2) Acetabular and femoral location of posterior impingement zones differed significantly (p < 0.001) between hips with increased FT and AV and hips with valgus and increased FT and AV. (3) Most (90%) of acetabular and femoral impingement zones were located posterior extra-articular in hips with increased FT and AV. This was significantly (p < 0.001) increased compared with 60% of valgus hips with increased FT and AV. Posterior extra-articular ischiofemoral impingement was located between the lesser trochanter and the ischial tuberosity.

Conclusion: Hips with combined increased FT and AV and hips with isolated increased FT seem to be a novel cause for posterior extra-articular FAI. This was mostly located between the ischium and the lesser trochanter. Treatment with derotational femoral osteotomy and hip arthroscopy or open FAI surgery should be evaluated for these hips. Isolated increased FT seems to be a novel cause for posterior extra-articular ischiofemoral hip impingement and potential anterior hip instability in young and athletic patients.

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Artikel online veröffentlicht:
17. Dezember 2020