Objectives To evaluate the development of median nerve affection in relation to hand-intensive seasonal work. We hypothesised that at end-season, median nerve conduction would be impaired and then recover within weeks.
Methods Using nerve conduction studies (NCS), we examined median nerve affection before, during, and after engaging in 22 days of mink skinning. We used technical measurements (goniometry and surface electromyography) to characterise occupational mechanical exposures and obtained questionnaire information on symptoms, disability, and lifestyle factors.
Results 11 male mink skinners without median nerve affection at pre-season were included (mean age: 35.7, mean number of seasons with skinning: 8.9). Mink skinning was characterised by a median angle of wrist flexion/extension of 16° extension, a median velocity of wrist flexion/extension of 22 °/s, and force exertions of 11% of maximal voluntary electrical activity. At end-season, mean distal motor latency (DML) had increased 0.41 ms (p<0.001), mean sensory nerve conduction velocity (SNCV) digit 2 had decreased 6.3 m/s (p=0.004), and mean SNCV digit 3 had decreased 6.2 m/s (p=0.01); 9 had decreases in nerve conduction, 5 fulfilled electrodiagnostic criteria, and 4 fulfilled electrodiagnostic and clinical criteria (a positive Katz hand diagram) for carpal tunnel syndrome (CTS). Three to six weeks post-season, the changes had reverted to normal. Symptom and disability scores showed corresponding changes.
Conclusions In this natural experiment, impaired median nerve conduction developed during 22 days of repetitive industrial work with moderate wrist postures and limited force exertion. Recovery occurred within 3–6 weeks post-season.
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