O2145: Identifying Factors that Predict Early Lateralization of the Hip After Open Reduction and Spica Casting for DDH

Background: In addition to immediate or early re-dislocation that occurs after open reduction (OR), we have observed cases with hip lateralization (subluxation) within 6 months of cast removal. Our aim was to identify risk factors for hip lateralization after OR and casting for DDH and to determine the outcomes of these hips.

Methods: This is a retrospective review of patients treated with OR for DDH from 1981 to 2021. Patient data included sex, age at OR, concomitant osteotomies, and DDH severity based on IHDI classification. IHDI grade and acetabular index (AI) were collected pre-op, within 6 months after cast removal, and from 2- and 4-year post-cast X-rays. Patients missing X-rays at these timepoints and syndromic dislocations were excluded.

Results: Of 151 hips treated with OR, 56 (37%) lateralized (IHDI II-IV) within 6 months post-cast. The lateralized hips were in younger patients (14±11mo vs 20±14mo, p=0.009), were less likely to have had a concomitant pelvic osteotomy (5% vs 21%, p< 0.01) and/or a concomitant femoral osteotomy (11% vs 24%, p=0.04), and had a shorter cast duration than non-lateralized (post-cast IHDI I) hips (2.5±0.6 vs 2.9±0.9 months, p=0.006). Two multivariate models using subgroups < 24 months and ≥24 months at surgery showed decreasing cast duration as a significant predictor < 24 months (p=0.004), and absence of a concomitant pelvic and/or femoral osteotomy as a significant predictor ≥24 months (p=0.03). There was no difference in sex (p=0.69), preop IHDI grade (p=0.22), or preop AI (p=0.24). 51 (91%) previously lateralized hips returned to IHDI I by 2 years (p=0.03), however 35 hips normalized on their own and 16 hips required additional surgery < 2 years. Mean AI was higher in lateralized hips compared to non-lateralized hips at 2 years (31±7° vs 27±6°, p=0.002) and 4 years (27±8° vs 22±6°, p=0.001). At 4 years, lateralized hips were about 4 times more likely to have undergone secondary surgery than non-lateralized hips (52% vs 14%, p< 0.001). Of 42 hips that underwent secondary procedures, 29 were lateralized hips (9 redo OR < 2 years, 20 pelvic and/or femoral osteotomies), and 13 were non-lateralized hips (13 pelvic osteotomies). This left 27 lateralized hips and 82 non-lateralized hips without secondary surgical intervention, and group comparison showed mean AI was higher in the lateralized group at 2 years (32±6° vs 27±6°, p< 0.001) and 4 years (26±8° vs 22±6°, p=0.014).

Conclusion: Younger age at OR, no concomitant pelvic/femoral osteotomy, and shorter cast duration were significantly associated with post-cast lateralization. The rate of secondary surgery was about 4 times greater in lateralized hips. Our study provides new insight into the risk factors for hip lateralization after OR and reveals the need to improve the outcomes of these patients and decrease the rate of secondary surgery.