Assessment of ulnar nerve tension directed towards understanding cubital tunnel syndrome

Background: Ulnar nerve compression at the elbow is the second most common compressive neuropathy of the upper extremity. We hypothesize that tension on the ulnar nerve produced by elbow flexion and distraction contributes to this condition. We measured ulnar nerve tension generated during elbow flexion and proportional distraction to evaluate locations of soft tissue constraints to nerve translation. Methods: Eight fresh-frozen upper limb specimens were tested. Each specimen included the proximal humeral shaft to the wrist. The ulnar nerve was dissected proximally and clamped to the humerus 8 cm proximal to the medial epicondyle. At 8 cm distal to the medial epicondyle, the ulnar nerve was dissected and clamped distally to a load cell that was mounted on a laboratory stand. A stage on the stand could be translated distally to apply load. Soft tissue was removed distal to the load cell clamp; all soft tissue from the load cell to the proximal humeral clamp was left intact.We measured the tension generated on the nerve throughout the full arc of elbow flexion with additional distal distractions of 0%, 2.5% and 5% of nerve length applied by distal translation of the stage on the lab stand. We then repeated these steps with the nerve unclamped proximally. We then excised 1 cm of soft tissue distally, clamped the nerve 7 cm distal to the medial epicondyle, and repeated the measurements. We continued this sequential dissection and testing until the nerve was clamped to the load cell 1 cm distal to the medial epicondyle. Results: Flexion, distraction, and proximal clamping each increased nerve tension. Tension was greatest at 4, 5, and 6 cm distal to the medial epicondyle (p < 0.01). Conclusion: Flexion, distraction, and proximal clamping each increased ulnar nerve tension. The greatest ulnar nerve tension was recorded between 4 and 6 cm distal to the medial epicondyle.