How Often Does Femoroacetabular Impingement Occur After an Innominate Osteotomy for Acetabular Dysplasia?

BACKGROUND: Femoroacetabular impingement is increasingly recognized as a cause of hip pain but its incidence after an innominate osteotomy for the correction of acetabular dysplasia has not been determined. This information would be essential for the orthopaedic surgeon because it has the potential to produce a poor outcome in the long term when trying to balance acetabular instability and overcorrection. QUESTIONS/PURPOSES: The purposes of our study were (1) to determine the frequency with which clinically relevant femoroacetabular impingement (FAI) occurs after an innominate osteotomy for the treatment of acetabular dysplasia; (2) to determine risk factors for the development of FAI; and (3) to compare postoperative radiographic and clinical outcomes in patients having undergone an innominate osteotomy for the correction of acetabular dysplasia both with and without FAI.
METHODS: This was a retrospective review of 154 hips (132 patients) that had undergone an innominate osteotomy for acetabular dysplasia and were evaluated at a minimum followup of 10 years (mean = 12 years). Mean age at the time of surgery was 3 years, 114 hips had a concomitant open reduction, and 54 hips also had femoral shortening. One hundred eight hips had a Salter osteotomy and 46 had a Pemberton osteotomy. Radiographs were analyzed to determine the lateral center-edge angle (CE angle) and the presence of a crossover sign. The diagnosis of FAI was established when the CE angle was greater than 40°, there was a positive crossover sign, and the patient had groin pain when flexing the hip less than 90°. Comparisons between nonparametric variables were performed with a Mann-Whitney's U test. Categorical variables were compared with a chi-square test. Change in acetabular index (correction) was dichotomized considering 20° of correction as the cutoff point. Association is presented as odds ratio (95% confidence interval), and logistic regression was performed.
RESULTS: According to our criteria, 18 of 154 hips had FAI (12%). Of the 18 patients with FAI, 10 had undergone a Pemberton osteotomy (10 of 46 [22%]) and eight a Salter osteotomy (eight of 108 [7%]). A change in the postoperative acetabular index greater than 20° was associated with a greater likelihood of developing FAI. The mean postoperative acetabular index was lower for the group with FAI, for whom it was 20°, compared with the group without FAI, for whom it was 27° (p = 0.04). The mean Iowa Hip Score for the group with FAI was 85, whereas for those without FAI, it was 93 (p = 0.03).
CONCLUSIONS: FAI is not common after an innominate osteotomy for the treatment of acetabular dysplasia; however, overcorrection is related to a higher incidence. When FAI is present, it can affect the outcome. Overcorrection should be avoided when performing an innominate osteotomy for the treatment of acetabular dysplasia because it can create iatrogenic FAI and have an adverse effect on outcome. LEVEL OF EVIDENCE: Level III, therapeutic study.