gms | German Medical Science

Objectives: It is unclear whether Femoral Retrotorsion acts as an independent cause of extra-articular or anterior intra-articular femoroacetabular impingement.

Therefore, we evaluated symptomatic hips with Femoral Retrotorsion, with and without cam and pincer FAI, using CT-based virtual 3D range of motion (ROM) and impingement simulation and questioned:

(1)What is the osseous range of motion?

(2)Where are the osseous femoral and acetabular impingement zones located?

(3)Is impingement extra- or intra-articular?

and we compared this group to symptomatic FAI patients with normal Femoral Torsion (FT).

Methods: We performed a retrospective comparative analysis of 37 hips in 24 symptomatic FAI patients with Femoral Retrotorsion. These hips were compared to 21 hips of 18 symptomatic patients with anterior FAI with normal FT (10-25°) and 26 asymptomatic hips with no FAI morphology on the AP radiograph and normal FT. This resulted in a total of 84 hips in 68 patients.

All FAI patients were symptomatic and presented with anterior hip pain, a positive anterior impingement test during clinical examination. All patients with FAI underwent CT scans to measure FT according to Murphy et al. Femoral Retrotorsion was defined as FT < 5°. CT-based Impingement Simulation was performed for 84 hips according to a validated method.

Results: (1) Hips with FAI combined with Femoral Retrotorsion have a significantly lower mean flexion (114 ± 8° vs 125 ± 13°, p<0.001) and internal rotation at 90° of flexion (18 ± 6° vs 32 ± 9°, p<0.001) compared to the asymptomatic control group. the anterior impingement test was positive in significantly less (p<0.001) internal rotation in 90 to 120° of flexion for hips with Femoral Retrotorsion compared to the asymptomatic control group.

(2) The maximal acetabular impingement zone for hips with Femoral Retrotorsion was located at the 2 o'clock position and ranged from 1 to 3 o'clock. The anterior femoral impingement zones were located more anteriorly compared to the control group (p<0.001).

(3) In hips with Femoral Retrotorsion, 95% of the impingement locations were located intra-articular and 32% were extra-articular subspine FAI for the anterior impingement test in 90° of flexion and in 0° of adduction. In addition to anterior intra-articular FAI, a concomitant subspine FAI between the tuberculum tertius and the anterior inferior iliac spine (AIIS) was detected in 68% (25/37 hips) and in 84% (31/37 hips) of the hips with Femoral Retrotorsion in the anterior impingement test.

Conclusion: Hips with FAI and Femoral Retrotorsion demonstrate less flexion and internal rotation in 90° of flexion compared to the asymptomatic control group. The vast majority of hip impingement due to Femoral Retrotorsion is intraarticular combined with subspine FAI, and it is located more anteriorly than standard FAI. Hips with anterior hip impingement can be caused by decreased FV even in the absence of cam or pincer type morphologies.