WHAT NEUROMONITORING CHANGES CAN BE EXPECTED DURING HIP ARTHROSCOPY IN THE PEDIATRIC POPULATION?
Authors: Shelton Trevor J. , Patel Akash R. , Agatstein Lauren , Haus Brian 
Published: March 2019

Background: Hip arthroscopy continues to evolve for treating hip pathologies disorders. With this evolution, comes an awareness of its associated complications. One potential side effect is damage to the nerves about the hip, usually affecting the pudendal or sciatic nerve. In one study of 60 adults, 58% of the patients had intraoperative nerve dysfunction and 7% sustained a clinical nerve injury. It has been reported that the rate of pediatric pudendal nerve palsy ranges from < 1% to 6% following hip arthroscopy. However, the rate of sciatic nerve injury during hip arthroscopy in the pediatric population is unknown. As such, the objectives of this study were to determine the 1) prevalence, pattern, and predisposing factors for sciatic, femoral, and obturator nerve injury during hip arthroscopy in the pediatric population, and 2) were there any risk factors associated with 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, rate of neuropraxia and any potential risk factors, and the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of SSEP changes in predicting neuropraxia. Risk factors for neuropraxia were assessed using a Wilcoxon Rank Sums test between those who sustained a neuropraxia and those who did not. Results: We identified 78 patients who underwent hip arthroscopy (16±2 years of age; 24 males, 54 females; BMI 26 ± 6 kg/m2). Reasons for hip arthroscopy included femoral acetabular impingement (37%, N=29), hip dysplasia with labral tear (27%, N=21), slipped capital femoral epiphysis (23%, N=18), labral tear (5%, N=4), snapping hip (3%, N=2), diagnostic scope (3%, N=2), Perthes with labral tear (1%, N=1), and trauma (1%, N=1). Average traction time was 64±30 min. SSEPs decreases of less than 50% occurred in 76% of patients (N=59) in the peroneal branch of the sciatic nerve, and 69% of patients (N=54) in the posterior tibial branch of the sciatic nerve. In the contralateral limb, there was a 50% drop in SSEPs in the peroneal branch of the sciatic nerve in 13% of patients (N=10) and in the posterior tibial branch of the sciatic nerve in 8% of patients (N=6). 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 clinical neuropraxia postoperatively was 18% (N=14), manifesting as sensory disruption in the peroneal nerve in 11 patients, sensory and motor disruption of the peroneal nerve in 2 patients, sensory disruption in the posterior tibial nerve in 1 patient, and 1 patient with combined sensory peroneal and posterior tibial nerve disruption. Thus, the drop in SSEPs in predicting a postoperative clinical neuropraxia of the peroneal nerve yields a sensitivity of 64%, a specificity of 28%, a PPV of 20%, and a NPV value of 95%. For the posterior tibial nerve, the sensitivity is 100%, specificity is 21%, PPV is 4%, and NPV is 100%. In all cases, the neuropraxia resolved before the first postoperative visit. Those who sustained a neuropraxia had on average a 54 min. longer surgery (p = 0.0053) and a trend towards a 14 min. longer traction time (p = 0.0955). Conclusion: Hip arthroscopy continues to have more uses in the pediatric population. As such, it is important to understand the potential risks with this surgery. The important findings of this study are that neuromonitoring changes occur in more than 70% of patients and nearly 20% of patients will have some decreased sensation in either their peroneal nerve or posterior tibial nerve that resolves within 1-2 days after surgery. Another important finding is that there is a low risk of neuropraxia if there are no neuromonitoring changes during surgery. Finally, longer surgery and traction time appear to be the only risk factors for neuropraxia in hip arthroscopy in pediatric patients.