Optimal nerve release range and transposition distance in anterior ulnar nerve transposition for cubital tunnel syndrome: an anatomical study

Background: Cubital tunnel syndrome, the second most common entrapment neuropathy, results from ulnar nerve compression at the medial epicondyle (ME). Conservative treatment often fails, requiring surgery. Transposition is an effective but invasive procedure, necessitating precise anatomical guidelines. We aimed to investigate the optimal anatomical measurements for ulnar nerve transposition to facilitate standardization of the technique. Methods: We examined 12 upper limbs from 6 fresh-frozen cadavers with elbows flexed at 60° and forearms supinated. The optimal transposition distance was defined as the distance from the ME to where the ulnar and median nerves run parallel. We measured this distance; pivot points A and B (where the ulnar nerve's course changes after transposition); crossing points over the medial intermuscular septum and flexors (A′, B′); and ulnar nerve branch positions from the inferior border of the ME. Results: After excluding 3 outliers using the interquartile range method, 10 limbs were analyzed. The transposition distance was 16.6 ± 3.3 mm. Pivot points A and B were 53.8 ± 6.5 mm and 50.2 ± 9.1 mm from the ME. Crossing points A′ and B′ were 39.6 ± 7.9 mm and 40.2 ± 6.7 mm. Nerve branches were 21.1 ± 6.0 mm, 32.4 ± 14.8 mm, and 50.9 ± 24.6 mm from the inferior border of the ME. Conclusion: Anterior transposition shifts the ulnar nerve 17 mm anterior to the ME. To prevent kinking, dissection should extend 54 mm proximally and 50 mm distally, totaling approximately 105 mm. These measurements can guide intraoperative planning and emphasize the need for direct visualization to ensure safe and effective anterior transposition.