Do the Changes in Hip Lateralization Up to One-Year Post-reduction in Developmental Dysplasia of the Hip Affect Those Observed at the Age of Four?

Background Treatment outcomes of developmental dysplasia of the hip (DDH) are evaluated by various factors. Although it is reported that centripetality is important for the development of the acetabulum in DDH, only a limited number of studies have examined the changes in lateralization following reduction. This study aimed to determine whether variations in hip lateralization within one year after reduction with the Pavlik harness (PH) in DDH influence the degree of lateralization observed at a mean age of four. Methodology This study included DDH patients who were successfully treated exclusively with the PH between 2014 and 2020, and who were able to be followed up for more than three years. For the evaluation of lateralization, the center head distance discrepancy (CHDD) was utilized. Measurements of CHDD were collected at four key time points: before the application of the PH (CHDD-before), immediately following its removal (CHDD-just after), one year post-reduction (CHDD-1y), and at a mean age of four (CHDD-4y). Results In total, 23 patients (one boy and 22 girls) were included in this study. The mean ages at the time of each CHDD measurement were 4.2 months (range = 1.4-6.2 months), 7.2 months (range = 4.4-9.2), 1.7 years (range = 1.3-2.4), and 4.9 years (range = 3.1-8.2). The average CHDD values were 18.5% (CHDD-before), 5.3% (CHDD-just after), 3.2% (CHDD-1y), and 2.5% (CHDD-4y). Only ΔCHDD (from one year to four years) showed a significant correlation with CHDD-4y (Pearson's correlation coefficient, r = 0.56, p < 0.01). Conclusions Some cases that showed improvement within the first year after reduction later deteriorated, while others that initially worsened within the first year subsequently improved. Changes in CHDD that occurred more than one year after reduction were found to influence the outcomes at a mean age of four years. Therefore, we suggest a follow-up period of at least four years is necessary for an adequate assessment.