Background: Breech position subjects the fetal hip to abnormal mechanical forces. However, unlike genetic or tissue factors linked to developmental dysplasia of the hip (DDH), the causative effect of the breech position ends when the infant is born. The purpose of this study was to evaluate the rate of spontaneous stabilization in mildly unstable hips of breech-presenting infants compared with similarly lax hips in infants with a genetic or tissue-related cause of DDH.
Methods: We studied a consecutive series of infants presenting to our institution at 8 weeks of age or younger with DDH from January 2008 to January 2012. Infants with increased hip laxity on dynamic ultrasound examination but without frank instability on clinical provocation maneuvers and no history of prior treatment were evaluated. The endpoint was spontaneous stabilization of ultrasound-detected instability, or intervention due to persistent instability on follow-up dynamic ultrasound. A logistic regression model using backward likelihood ratio method was used to analyze predictors of spontaneous stabilization.
Results: We identified 122 hips in 79 infants with instability on dynamic ultrasound evaluation but with stable clinical examinations. Spontaneous stabilization of sonographic instability occurred in 90 hips (74%) at a mean age of 9 weeks (range, 4 to 18 wk). Breech hips more frequently spontaneously stabilized compared with nonbreech hips (80% vs. 66%). Regression analysis determined that breech presentation was a strong independent predictor for spontaneous hip stabilization (odds ratio, 3.72; 95% confidence interval, 1.45-9.60; P=0.006). Sex, family history, intrauterine positioning syndromes, side involved, bilateralism, and grade of sonographic hip instability were not independently predictive of spontaneous hip stabilization.
Conclusions: DDH infants with a history of breech presentation are 3.72 times more likely to experience spontaneous resolution of mild hip instability compared with nonbreech infants. Awareness that breech presentation is a strong independent predictor of spontaneous laxity resolution can guide parental counseling and early care of DDH.
Level of evidence: Level II, prognostic retrospective study.