Anatomical Parameters Associated with the Shortening Decision in Crowe Type 4 Dysplastic Hip Osteoarthritis: A Case–Control Study

Background: Muscle and bone morphometry may be potent indicators for predicting femoral subtrochanteric shortening osteotomy (FSSO). We aimed to investigate muscular and bony factors that may be predictive of FSSO. Methods: Patients with unilateral Crowe type 4 developmental dysplasia of the hip (DDH) who underwent unilateral total hip arthroplasty (THA) without (Group 1, 31 patients) and with FSSO (Group 2, 39 patients) were included. Sixty healthy hips (Group 3) were selected as the control group. Several muscular and bony parameters were measured on the operative (O) and non-operative (NO) hips on radiographs and computed tomography (CT) images. Results: The mean NO gluteus medius cross-sectional area (CSA) index (NO-GMed CI), NO tensor fasia lata (TFL) CI, NO iliopsoas (IP) CI, and NO gluteus maximus (GMax) CI for the control group were lower than those for both Crowe type IV DDH with and without FSSO. The mean NO gluteus minimus CI (NO-GMin CI) for the control group were higher than those for both Crowe type IV DDH with and without FSSO. There was significant difference between Groups 1 and 2 regarding axial position of neo-acetabulum (APNA) (− 0.03 ± 8.5 vs. 5.27 ± 6.33, p = 0.004), coronal position of neo-acetabulum (CPNA) (33.39 ± 10.65 vs. 53.70 ± 12.27, p = 0.000), operative leg length discrepancy (O-LLD) (14.18 ± 15.14 vs. 24.44 ± 15.80, p = 0.001), O-gluteus minimus (GMin) length (155.34 ± 157.73 vs. 106.79 ± 20, p = < 0.01), and O-GMin CI (57.28 ± 58.59 vs. 29.95 ± 12.13, p = < 0.01). The cutoff values determined by the receiving operating curve analyses were as follows: 13.7 mm, 2.5 mm, and 41.4 mm for O-LLD, APNA, and CPNA, respectively. Conclusion: FSSO is associated with APNA, CPNA, O-LLD, O-GMin length, and O-GMin CI. By using cutoff values of APNA, CPNA, and O-LLD, predicting FSSO preoperatively is possible. Owing to these parameters, it may be possible to lower the technically demanding level of surgery.