We identified patients with a poor outcome by examining cases where nerve conduction studies had been repeated after surgery. 168 patients were identified in whom two sets of tests had been performed. 28 were excluded as either they had no pre-operative studies or had insufficient clinical information. Our study group was 140 patients (174 hands) in whom NCS had been performed before and after surgery, with adequate clinical information. Information on the clinical outcome was obtained from postal questionnaires and from hospital records. A proportion of the hands in which two tests had been performed turned out to have been retested because of presentation with symptoms in the other hand, after a satisfactory outcome from surgery on the first side. This accounted for 44 of the 174 hands, and these were used as control group. 130 hands in 92 patients were identified as having a poor outcome from surgery. Of these, 39 underwent a further operation; two went on to a third procedure. Logistic Regression Analysis was used to analyze the data (Stastica).

There was a trend for the poor results to be more common in the elderly, but age was not a statistically significant factor, (p< 0.36). The good results were found mainly in grades 2 to 5 and this was statistically significant, (p< 0.01). A poorer outcome was seen grouped in grades 0, 1, 2 and 6 and this was statistically significant. (p< 0.01). The NCS have been validated, are reproducible and cost about £15 per study. In the group with good outcome, the grade of severity of NCS improved or remained unchanged in the majority. Of the 39 re-explorations, 17 were found to have incomplete division of the ligament. Of these, 10 showed clinical improvement after re-operation. Of the 22 with no evidence of incomplete division, 7 were improved, 10 had persistent symptoms and 5 were worse after revision surgery.

We believe that pre-operative NCS are helpful for two reasons: Firstly, they provide as a baseline for comparison if the patient has unsatisfactory result following decompression. Secondly, we have shown that they are of prognostic value.