Hip Displacement After Triradiate Cartilage Closure in Nonambulatory Cerebral Palsy: Who Needs Continued Radiographic Surveillance?

BACKGROUND: Recommendations with regard to the need for continued hip surveillance after skeletal maturity are based on expert opinion rather than evidence. This study aimed to determine the prevalence of and risk factors associated with progressive hip displacement in cerebral palsy (CP) after triradiate cartilage (TRC) closure.

METHODS: Patients who had spastic nonambulatory CP (Gross Motor Function Classification System IV to V) and hypertonic (spastic or mixed-type) motor type and follow-up of at least 2 years after TRC closure were included. The primary outcome variable was the hip migration percentage (MP). The secondary outcome variables included patient age at the time of TRC closure, prior preventative or reconstructive surgery, a prior intrathecal baclofen pump, history of scoliosis, history of epilepsy, a prior gastrostomy tube, a previous tracheostomy, and gender. An unsuccessful hip outcome was defined as a hip with an MP of ≥40% and/or requiring a reconstructive surgical procedure after TRC closure.

RESULTS: In this study, 163 patients met the inclusion criteria, with a mean follow-up of 4.8 years (95% confidence interval [CI], 4.4 to 5.1 years) after TRC closure at a mean patient age of 14.0 years (95% CI, 13.7 to 14.3 years). Of these hips, 22.1% (36 of 163) had an unsuccessful hip outcome. In multivariate analysis, the first MP at TRC closure (hazard ratio [HR] per degree, 1.04; p < 0.001) and pelvic obliquity (HR per degree, 1.06; p = 0.003) were independent risk factors for an unsuccessful hip outcome, but gender was not found to be significant (HR for male gender, 1.7 [95% CI, 0.8 to 3.58; p = 0.16]; female gender was the reference). However, the mean survival time for progression to an unsuccessful hip outcome was longer for female patients at 9.2 years [95% CI, 8.1 to 10.2 years]) compared with 6.2 years (95% CI, 5.6 to 6.9 years) for male patients (p = 0.02). There was also a significant improvement in survivorship for prior reconstructive surgical procedures (p = 0.002). The survivorship in patients who underwent reconstructive surgery performed at a patient age of ≥6 years was significantly higher compared with those who underwent surgery performed at <6 years of age (p < 0.05). A first MP at TRC closure of ≥35% was associated with an unsuccessful hip outcome, as determined by receiver operating characteristic (ROC) curve analysis (p < 0.001; area under the ROC curve of 0.891, sensitivity of 81%, and specificity of 94%).

CONCLUSIONS: The risk factors for the progression of hip displacement after TRC closure in patients with CP included a higher MP and increased pelvic obliquity; there was decreased survivorship for male patients and patients with no prior reconstructive surgery. Patients with these risk factors and/or an MP of ≥35% at TRC closure should have continued radiographic surveillance to detect late hip displacement.

LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.