Cross-Table Lateral Radiographs for Screening of Anterior Femoral Head-Neck Offset in Patients with Femoro-Acetabular Impingement

One theory for the aetiology of osteoarthrosis of the hip is the impingement of the anterior femoral neck against the acetabulum in flexion. The reduced femoral head-neck offset not visible on AP-radiography is implicated in this impingement. The anterior part of the head-neck region is well visualised on cross table lateral radiographs. A retrospective analysis of the offset using cross table lateral radiographs was therefore performed on twelve symptomatic and ten asymptomatic hips. The anterior offset (AOS) was defined as the difference in radius between the anterior femoral head and the anterior femoral neck. The offset ratio (OSR) was defined as the AOS divided by the femoral head diameter. The AOS was 11.6 ± 0.7 mm in the asymptomatic group and 7.2 ± 0.7 mm in the symptomatic group, which was statistically significantly different (p=0.0006). The OSR was 0.21 ± 0.03 in the asymptomatic group and 0.13 ± 0.05 in the symptomatic group, which was also statistically significantly different (p=0.0004). Cross-table lateral radiographs of the hip are useful for screening patients complaining of anterior femoro-acetabular impingement symptoms, as their anterior femoral head-neck offset may be smaller.