Assessment of the Femoro-Epiphyseal Acetabular Roof (FEAR) Index as a Predictor of Long-Term Outcomes in Developmental Dysplasia of the Hip

Abstract

Purpose: Periacetabular osteotomy (PAO) is an alternative to arthroplasty in patients with developmental dysplasia of the hip (DDH). PAO, a joint preserving surgery, is a desirable option as arthroplasty in young patients may be associated with prosthetic failure and activity restrictions.1 The Femoro-Epiphyseal Acetabular Roof (FEAR) index has been shown to be a useful and reliable marker in determining clinical instability in patients with borderline hip dysplasia.2 The primary aim of this study to is to assess if there is an association between preoperative/postoperative FEAR index and long-term failure in DDH patients treated with PAO. Methods: This study is a retrospective review of long-term outcomes (>20 years) for approximately 135 patients undergoing PAO from August 1991 to September 1998 at Boston Children’s Hospital. The preoperative and postoperative FEAR indices were assessed on AP pelvis radiographs. Preoperative and postoperative FEAR indices were analyzed to assess whether preoperative index or degree of postoperative correction was predictive of PAO failure. Results: 135 patient records were included in the initial study. 19 (19.8%) hips failed by WOMAC Score or conversion to THA with mean of 96 months ± 14 months to failure. 77 (80.2%) of hips were preserved. Mean FEAR index improved from 13.66o preoperatively to -4.47o postoperatively. Mean lateral center edge angle (LCEA) improved from 5.41o preoperatively to 31.75o postoperatively. Mean preoperative Tönnis angle improved from 25.69o to 7.74o postoperatively. Mean anterior center edge angle (ACEA) improved from 6.1o to 27.41o postoperatively. Preoperative Tönnis grade 2-3 (OR: 3.613, 95% CI 1.21-10.01, p= 0.042), postoperative Tönnis grade 2-3 (OR: 15.5, 95% CI 2.12-11.35, p= 0.007) and postoperative minimum joint space width < 2 mm (OR: 9.046, 95% CI 1.43-6.54, p= 0.031.) were found to be significantly associated with PAO failure Conclusions: This retrospective review suggests that there is no association between preoperative/postoperative FEAR index measurement and long term PAO outcomes.