Features of the Ulnar Nerve Predicting Postoperative Prognosis in Idiopathic Cubital Tunnel Syndrome

PURPOSE: This retrospective case-control study was performed to determine the relationships between features of the ulnar nerve and postoperative outcomes following in situ decompression in idiopathic cubital tunnel syndrome (CuTS). METHODS: The study population consisted of 86 patients who had undergone surgery for CuTS. We evaluated demographic factors, hand dominance, symptom onset time, time from diagnosis to surgery, findings of electrodiagnosis (nerve conduction velocity/electromyography), and preoperative clinical status. Intraoperatively, the ulnar nerve was defined as a definitively compressed, abnormally enlarged, or inflammatory lesion. Clinical improvements were evaluated at least 2 years after surgery. RESULTS: Fifty-four patients showed improvement after surgery in terms of the modified McGowan grade and were designated as group 1. Meanwhile, 32 patients with unchanged or aggravated status were classified as group 2. Preoperative status, as determined by the modified McGowan grade, Boston Symptom Severity Scale score, severity of electrodiagnosis, and predominant symptoms were similar between the groups (all, P > 0.05). On regression analysis, only the classification of nerve lesions and the time from diagnosis to surgery had an impact on postoperative outcome (all, P < 0.05). Especially, enlarged ulnar lesion predicted poor prognosis (P = 0.003). CONCLUSIONS: Ulnar nerve enlargement, grossly detected intraoperatively, and long interval between diagnosis and surgery were independently associated with poor prognosis of CuTS. Among the anatomic structures involved in the generation of CuTS, the medial epicondyle showed a strong association with enlarged nerve lesions.