Objective
To investigate the anatomy of the ulnar nerve according to the degree of elbow flexion and to obtain optimal elbow position for ulnar nerve conduction study.

Methods
Eleven elbows in nine cadavers were dissected. We estimated the 10 cm elbow segment to be the distance between 2 points, 4 cm distal and 6 cm proximal to the center of the cubital tunnel, which was determined to be the halfway point between the medial epicondyle and olecranon with elbow position in extension and 45^o, 90^o, 135^o flexion. Anatomical measurements of the actual length of ulnar nerve, distance between medial epicondyle and ulnar nerve, and distance between medial epicondyle and olecranon were obtained in each position. The actual length of the ulnar nerve was measured between two points of the ulnar nerve closest to the landmarks of the estimated 10 cm with flexible ligature.

Results
The actual lengths of ulnar nerve were 10.23 cm, 10.00 cm, 9.44 cm, and 9.08 cm in elbow extension, and 45^o, 90^o, 135^o flexion, respectively. The difference between actual length and estimated lengths were least in 45^o elbow flexion (p=0.0001). The distance between medial epicondyle and olecranon increased with increasing elbow flexion (p=0.0001). However, there was no difference in the distance between medial epicondyle and ulnar regardless of the elbow position. As a result, the ulnar nerve seemed to have migrated anteriorly in the cubital tunnel with increasing elbow flexion.

Conclusion
This study suggest that the optimal angle in ulnar nerve conduction study would be 45^o flexion, under the condition that the distance measurement is through the halfway point between the medial epicondyle and olecranon.