Image Interpretation: In non-diseased states, the A4 pulley is normally quite difficult to distinguish in long axis, however it is intact if there is minimal distance between the flexor tendons and phalanx as seen in the non-injured left 3rd middle phalanx. Literature has stated tendon-to-bone distances at least 2mm is usually a sensitive threshold to diagnose A2 and A4 pulley ruptures. This is clearly observed for the injured Left 4th middle phalanx with the hypoechoic gap of 2.8mm.
Teaching Pearl: In rock climbing, finger flexor pulley system injuries are the most common overuse injuries and almost rarely occur outside of this activity given unique biomechanical demands. The mechanism for such injuries is usually from crimp grip, a technique utilizing PIP flexion and DIP hyperextension, which is used commonly by rock climbers to maximize contact of the fingertips on rock climbing holds with small surface areas. Specifically, it is the sudden opening of the hand described as the eccentric portion where injury is the most prone given that the pulleys are not muscular in nature. Although the flexor pulleys, particularly A2 and A4, can withstand large amounts of forces relative to other pulleys, repetitive loading can lead to overuse injuries. Ultrasound is highly sensitive and specific for diagnosis and is the initial imaging of choice.