Carpal tunnel syndrome: correlation between median nerve relative constriction in the carpal tunnel and distal motor latency

Abstract

This study analyses the correlation between the constriction in the substance of the median nerve in the carpal tunnel and distal motor latency, gender and age of patients with a carpal tunnel syndrome. In 82 patients (59 women and 23 men with an average age of 66.6 (41-89) years) with an electrophysiologically verified carpal tunnel syndrome undergoing open carpal tunnel release, the diameter of the median nerve was measured at the narrowest point of the nerve at the level of the constriction and the widest point of the nerve proximal to the constriction. The grade of nerve constriction was the ratio between the diameter at the level of the constriction and the widest diameter proximal to the constriction. Additionally, the distance from the distal wrist crease to the beginning of the constriction was measured. The grade of constriction was correlated with the patients' distal motor latency, gender and age. The diameter of the median nerve at the narrowest point of the constriction averaged 6.0 (SD 1.1) mm; the diameter at the widest point proximal to the constriction was 7.6 (SD 1.5) mm. The distance from the distal wrist crease to the beginning of the constriction averaged 17.6 (SD 3.7) mm. Grade of nerve constriction did not correlate with distal motor latency. However, there was a correlation between patient age and distal motor latency. The grade of nerve constriction cannot be estimated based on the severity of prolongation of distal motor latency. There is a positive correlation between the age of patients with a carpal tunnel syndrome and distal motor latency.