gms | German Medical Science

Objectives: The cubical tunnel syndrome is the second most common compression neuropathy in the upper limb with surgical options such as endoscopic or in situ decompression, medial epicondylectomy or transposition of the ulnar nerve. In situ endoscopic decompression has the advantage of less soft tissue morbidity. However, the problem of predicting a secondary nerve instability after long distance in situ decompression remains unsolved. Predictive values forecasting instability of the ulnar nerve do not exist. The purpose of this study is to define possible anatomical variations of the ulnar groove predicting a possible nerve instability using radiographs (cubital tunnel view, CTV) and ultrasonography (US).

Method: 33 elbows (11 women, 48 (31-73) years; 21 men, 50 (21-79) years) were examined with CTV and US. 23 of all participants suffer from ulnar nerve compression symptoms and 9 of them present a clinical instability of the ulnar nerve proven by ultrasonography.

For the CTV, the humerus was put on the collector of the image intensifier, the elbow flexed 100° and a tangential x-ray beam generated the tunnel view of the cubital tunnel. With US the identical skyline view was used placing the transducer on the medial elbow in order to picture the most prominent point of the olecranon and the medial epicondyle at the cubital tunnel. A tangential line between these most prominent points indicated the width of the tunnel. A perpendicular line from the tangential line (depth) to the deepest point of the cubital tunnel groove indicated the depth. The quotient of the depth and width lines (Q=depth/width) was calculated.

Results: In the CTV, a significant difference of the quotient was found for ulnar nerve instability (mean: 0.183 [SD 0.024] vs. 0.257 [SD 0.047], p <0.001). 6 of the 9 elbows with clinical ulnar nerve instability showed a quotient < 0.2, whereas the elbows without nerve instability had a quotient > 0.205.

However, the same quotient measured by US showed no significant difference. Furthermore, no differences of quotient with CTV or US could be found in ulnar nerve compression neuropathy. The depth of the cubital tunnel alone did not indicate a higher risk for instability.

Conclusion: Taking the small sample size into account, only CTV not US quotient indicated a possible ulnar nerve instability. A quotient less than 0.2 in CTV may indicate a higher risk of instability of the ulnar nerve.

Further investigation is required to confirm these measurements.