The optimal measurement of across elbow segment in ulnar motor conduction study

There is room for considerable error in the measurement of across-elbow conduction velocity due to the different possible positions of the elbow and the difficulty in accurately measuring distance. A standardized method should be used for clinical measurement. Many advocate a fully flexed elbow position with the arm abducted at 90 degrees. When the elbow is fully flexed, skin measurement across the bent elbow is difficult with respect to defining the path, which most accurately follows the nerve. However, studies on measurement technique for across-elbow segment have not been performed to date. We have proposed a standardized technique for the measurement of conduction velocity through the elbow segment. We assumed "ideal" across-elbow segmental conduction velocity is the mean of the forearm and arm segmental conduction velocities, and established an optimal deflection point at the elbow, which best reflects the ideal conduction velocity. The optimal deflection point was located medially two thirds distance between the epicondyle and the olecranon in an arm abducted 90 degrees, fully flexed elbow position. Our data suggests that an across-elbow segment velocity lower than 57.8 m/sec, or a difference of more than 7.7 m/sec between the across-elbow and forearm segments is to be considered abnormal. The lower limit values expressed as mean-2 S.D. for absolute across-elbow segmental conduction velocity and relative velocity difference between the across-elbow segment and forearm segments at other possible deflection points of the elbow were also calculated.