Intraoperative Measurement of Pressure Adjacent to the Ulnar Nerve in Patients with Cubital Tunnel Syndrome

Abstract

As hand therapists, we commonly treat cubital tunnel syndrome in patients both conservatively and postoperatively. It is interesting to learn that questions still arise regarding the cause of this nerve entrapment. Is it due to compression of the cubital tunnel wall, stretching of the nerve itself, or a combination of these factors? Previous studies have examined interstitial pressure within the cubital tunnel and have shown increased pressure with increased elbow flexion. However, these studies have all been performed in the cadaver lab. In this present study from Japan, pressure around the ulnar nerve was measured during surgery and a link was found to the duration of the disease and the severity of the neuropathy. Method: The study looked at eight patients undergoing decompression of the cubital tunnel. All of the patients complained of pain, numbness and parathesias of the ulnar hand, and loss of strength. The patients also demonstrated a positive Tinel's sign at the elbow, atrophy of the intrinsic muscles, decreased motor nerve conduction velocity, and symptom reproduction with elbow flexion. All eight patients demonstrated severe symptoms of cubital tunnel syndrome warranting surgical decompression. The Akahori classification system was used to grade the severity of the cubital tunnel syndrome. The surgical technique used is described. Pressures in each elbow were recorded at three locations: 1 cm, 2 cm, and 3 cm distal to the proximal edge of the cubital tunnel retinaculum. Measurements at each location were performed with the elbow flexed to 130° and in full extension. The measurements were taken three times and an average of the three was recorded. Statistical Analysis: The Student's t-test was used to evaluate the difference in pressures between elbow flexion and elbow extension and the differences in pressure between elbow flexion and the stages of ulnar nerve palsy. The Pearson's correlation analysis was used to study the relationship between age and pressure, motor nerve conduction velocity and pressure, and disease duration and pressure. Results: The statistical analysis indicates a statistically significant difference in the measurement of extraneural pressure with elbow flexion over elbow extension and increased pressure more proximally to the cubital tunnel than distally. Results of the statistical analysis also show a positive correlation between extraneural pressure with elbow flexion and the severity of the disease at each location in the cubital tunnel. The pressures also correlated positively with motor nerve conduction velocity. Conclusions: Previous studies on pressure around the ulnar nerve in cubital tunnel have been performed in the cadaver lab. This study measures pressure around the ulnar nerve during surgery and finds correlations with the amount of pressure and the severity of the nerve entrapment. A transducer-tipped fiberoptic probe is used to for intraoperative pressure measurement. This device was created for intracranial pressure monitoring. It is simple to use and has a rapid response to pressure changes. Reviewer's Commentary: This study makes no statement regarding the causative factors leading to cubital tunnel syndrome. However, the authors suggest that external compression plays a significant role in the development of ulnar nerve entrapment. They conclude that simple decompression of the ulnar nerve is insufficient and selected anterior transposition of the ulnar nerve as the surgical technique in all eight patients.