Neuromonitoring Changes During Hip Arthroscopy in the Pediatric Population

OBJECTIVES: The objectives of this study were to determine the prevalence, pattern, and predisposing factors for sciatic, femoral, obturator, and pudendal nerve injury during hip arthroscopy in the pediatric population. METHODS: We retrospectively reviewed charts of all pediatric patients who underwent hip arthroscopy with neuromonitoring from 2013 until May 2018. Neuromonitoring included when traction was applied and removed, and somatosensory evoked potentials (SSEP) in the peroneal and posterior tibial nerves and electromyography (EMG) signal for the obturator, femoral, and peroneal and posterior tibial branch of the sciatic nerves. Each report was reviewed for total traction time, EMG changes, SSEP changes more than 50% after traction application, and the time for SSEPs to return to baseline. Demographic data and postoperative notes were reviewed for any signs of clinical nerve injury and if/when recovery occurred. We determined the rate of SSEP and EMG changes, time from traction onset to SSEP and EMG changes, time after traction released until SSEP returns to baseline, and rate of neuropraxia and any potential risk factors. RESULTS: We identified 78 patients who underwent hip arthroscopy (16±2 years of age; 54 females). Reasons for hip arthroscopy included femoral acetabular impingement (37%), hip dysplasia with labral tear (27%), slipped capital femoral epiphysis (23%), labral tear (5%), snapping hip (3%), diagnostic scope (3%), Perthes with labral tear (1%), and trauma (1%). Average traction time was 64±30 min. SSEPs decreases of less than 50% occurred in 76% of patients in the peroneal nerve, and 69% of patients in the posterior tibial nerve. In the contralateral limb, there was a 50% drop in SSEPs in the peroneal nerve in 13% of patients and in the posterior tibial nerve in 8% of patients. For the peroneal nerve, this drop in signal occurred 23±11 min after traction was applied and returned intraoperatively at a rate of 74% 29±23 min after traction removal. For the posterior tibial nerve, this drop in signal occurred 22±12 min after traction was applied and returned intraoperatively at a rate of 83% 24±15 min. after traction removal. EMG activity was observed after traction application in 10% of patients in the obturator nerve at 36±34 min., 9% of patients in the femoral nerve at 22 ± 15 min., 14% of patients in the peroneal nerve at 19±27 min, and 5% of patients in the posterior tibial nerve at 42±42 min. The rate of pudendal nerve neuropraxia was 0%. The rate of clinical neuropraxia postoperatively was 18%. Those who sustained a neuropraxia had on average a 54 min. longer surgery (p=0.005) and a trend towards a 14 min. longer traction time (p=0.096). Diagnosis had no statistical effect on the rate of clinical diagnosis. CONCLUSION: Hip arthroscopy is increasingly utilized to treat several unique diagnoses in the pediatric population. As such, it is important to understand the potential risks of treating different diagnosis in this population. The important findings of this study are that neuromonitoring changes occur in more than 70% of patients and 18% will have some decreased sensation in either their peroneal nerve or posterior tibial nerve that resolves within 1-2 days after surgery. There is also a low risk of neuropraxia if there are no neuromonitoring changes during surgery. Diagnosis (Hip dysplasia/SCFE/FAI) did not change incidence of neuropraxia. Longer surgery and traction time appear to be the only risk factors for neuropraxia in hip arthroscopy in pediatric patients.