Symptomatic sacroiliac joint disease and radiographic evidence of femoroacetabular impingement

Symptomatic sacroiliac (SI) joint disease is poorly understood. The literature provides no clear aetiology for SI joint pathology, making evaluation and diagnosis challenging. We hypothesised that patients with documented sacroiliac pain might provide insight into the aetiology of these symptoms. Specifically, we questioned whether SI joint symptoms might be associated with abnormal hip radiographs. We reviewed the pelvic and hip radiographs of a prospectively collected cohort of 30 consecutive patients with SI joint pathology. This database included 33 hips from 30 patients. Radiographic analysis included measurements of the lateral centre edge angle, Tönnis angle, and the triangular index, of the ipsilateral hip. Evidence for retrotorsion of the hemipelvis was recorded. Hips were graded on the Tönnis grading system for hip arthrosis. In this cohort 14/33 (42%) of hips had evidence of significant osteoarthrosis indicated by Tönnis grade 2 or greater and 15/33 (45%) displayed subchondral cyst formation around the hip or head neck junction. In assessing acetabular anatomy, 21% (7/33) had retroversion, 12% (4/33) had a lateral centre edge angle >40° with 3% (1/33) >45°. Tönnis angle was <0° in 27% (9/33). Coxa profunda and acetabuli protrusio were present in 47% (17/33) and 3% (1/33), respectively. When femoral head morphology was assessed, 33% (11/33) showed evidence of cam impingement. Overall, 76% (25/33) had at least one abnormality on their hip radiograph. A significant number of patients meeting strict diagnostic criteria for SI joint pain had radiographic evidence of femoroacetabular impingement (FAI) and hip arthrosis. The clinician should maintain FAI in the differential diagnosis when investigating patients with buttock pain.