We report a case of extensor pollicis longus (EPL) tendon rupture caused by repetitive motions and awkward posture on hand and wrist joints.

A 47-year-old right-handed man who worked for 15 years in an assembly line at an automotive manufacturing company has been diagnosed with a complete tear of right EPL tendon. We investigated the patient's occupational history in detail and evaluated the tasks ergonomically through musculoskeletal risk factors survey and job strain index (JSI) using the 22 task-related videos recorded by the patient. Three out of the 12 tasks (25%) were identified as high-risk work on the hand and wrist in the musculoskeletal risk factors survey in 2016. Among the 22 tasks analyzed by JSI, 11 tasks (50%) were evaluated as probably hazardous. In addition, he used localized vibration tools in 19 (86.4%) out of 22 tasks.

We concluded the patient's disease was probably caused by repetitive motion and improper posture of the hand and wrist, and the hand-arm vibration is a possible cause as well.