Ultrasound imaging of the ulnar nerve: correlation of preoperative and intraoperative dimensions.

OBJECTIVES: Recently, ultrasonography of the ulnar nerve has been introduced to confirm the diagnosis of ulnar neuropathy at the elbow. The reported diameters appear to be small when compared to those known from surgery (=actual diameter). The actual diameter is compared with the diameter on ultrasonography.

PATIENTS AND METHODS: Nine patients that were scheduled for decompression of the ulnar nerve at the elbow underwent an ultrasonographic examination preoperatively and intraoperatively. Longitudinal and transversal sonographical scans were made. The maximal diameters of the ulnar nerve at ultrasound were compared with the maximal diameter of the ulnar nerve intraoperatively.

RESULTS: Pre- and intraoperatively on the longitudinal scans, the maximal diameter is smaller than the actual maximal diameter of the ulnar nerve. The difference was 3.7+/-1.0 mm (p<0.001) 3.0+/-1.1 mm (p<0.001), respectively. The same was true on the transverse scans: 1.5+/-1.3 mm (p=0.008) versus 1.1+/-0.6 mm (p=0.001).

CONCLUSION: The diameter of the ulnar nerve as determined sonographically suggesting ulnar neuropathy does not correspond with the anatomically determined actual diameter. The maximal diameter can be best estimated with transverse scans.