Establishing Normal Values of the Proximal Median Motor Nerve−A Study of the Pronator Teres and Flexor Carpi Radialis in Healthy Volunteers

Abstract

The importance of normative peripheral nerve data is increasing due to advances in medical implantation, microsurgical suturing, and tubulization repair techniques. Because the median nerve is often affected, its normal values must be reliable. Although the distal portion of the median nerve has been well studied using electrodiagnostic methods, the proximal forearm segment has not. This study establishes a normative database for median nerve conduction to the pronator teres (PT) and to the flexor carpi radialis (FCR). Two hundred-eight asymptomatic subjects were studied using proximal median motor stimulation at 10 cm. Latencies, amplitudes, areas, and durations were recorded. To the pronator teres: The upper limit for normal (ULN) motor latency was 3.5 ms (2.9 +/- 0.3 ms). The side-to-side latency difference was </= 0.5 ms. Overall, the lower limit of normal (LLN) amplitude was 2.2 mV. However, this decreased to 1.5 mV in the over-50 age group. To the flexor carpi radialis: The ULN motor latency was 3.6 ms (2.8 +/- 0.4 ms). The side-to-side latency difference was </= 0.7 ms. Overall, the LLN amplitude was 2.3 mV. However, this decreased to 1.7 mV in the over-50 group. This study produced a large database of normal results for the median motor nerve conduction to the pronator teres and to the flexor carpi radialis. The 10-cm techniques are easily reproducible and helpful when evaluating this portion of the median nerve.