Distance measure error induced by displacement of the ulnar nerve when the elbow is flexed.
OBJECTIVE
To determine the presence of ulnar nerve displacement at the elbow when it is flexed and to determine its effect on distance measurements using the conventional measurement method for nerve conduction studies (NCSs).


METHODS
Comparing the ultrasonography-assisted distance measurement method with the conventional measurement method.


METHODS
An electrodiagnostic laboratory at a university hospital.


METHODS
Seventy-eight elbows of 39 healthy volunteers.


METHODS
We used high-resolution ultrasonography in real time. Based on sonographic searching, we marked 3 points on the skin through the course of the displaced ulnar nerve when the elbow is flexed: (1) point A, 7 cm above the elbow (from the midpoint between the medial epicondyle tip and olecranon in the postcondylar groove [point M]); (2) point B, 3 cm below the elbow; and (3) point C, the point closest to the medial epicondyle tip.


METHODS
Distance measurements between points A, B, and C were taken. These values were compared with measurements obtained through conventional measurement methods.


RESULTS
Ulnar nerve displacement occurred in 24.3% (19/78) of the elbows; approximately 20.5% (16/78) were subluxation, and 3.8% (3/78) were dislocation. In the ulnar nerve displacement group, the distance between points A and C was 5.84+/-0.33 cm (range, 5.10-6.30 cm), and the distance between points B and C in the flexed position was 3.35+/-0.19 cm (range, 3.10-3.70 cm). When the conventional distance measurement was used, the ulnar nerve conduction velocity across the elbow was overestimated by approximately 5.33+/-2.29 m/s in the ulnar nerve displacement group.


CONCLUSIONS
This distance measurement error may be responsible for the decreased sensitivity found in NCSs that test for ulnar neuropathy at the elbow. If the NCS results are normal in patients who have clear symptoms of ulnar neuropathy, the possibility of ulnar nerve displacement at the elbow should be considered, and further investigation with ultrasonography would be beneficial.
Kim
Byung-Jo
BJ
Division of Physical Medicine & Rehabilitation, Stanford University School of Medicine, CA, USA.
Date
Elaine S
ES
Lee
Sang-Heon
SH
Yoon
Joon Shik
JS
Hur
Soo Yeun
SY
Kim
Sei Ju
SJ
D000328:Adult; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000294:innervation*; D004568:Electrodiagnosis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction; D014459:Ulnar Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D020424:Ulnar Neuropathies / Q000175:diagnosis*; D014463:Ultrasonography