Trigger finger is a common condition, and the usual cause is stenosing tenosynovitis. Trigger finger caused by trauma is extremely rare. We examined a patient in whom an apparently trivial laceration caused partial laceration of the flexor tendon, leading to trigger finger. In this case, ultrasonography was useful in establishing the presurgical diagnosis. Removal of the impinging tag cured the trigger finger. We also review nine previously reported cases. When triggering occurs after an injury near the base of a finger, partial laceration of the flexor tendon should be kept in mind as the cause. Ultrasonography may be valuable for the diagnosis.