A2 Pulley Injury

The pulley apparatus functions to secure the flexor tendon onto the adjacent phalanx. During forceful gripping activities, significant forces are exerted on the pulley as it maintains the tendon's close proximity to the bone against the distracting force exerted by the tendon's line of pull. When this force exceeds the static restraint capacity of the pulley, it fails.

The most common pathology is the disruption of the A2 pulley (the second annular pulley that originates from the level of the proximal phalanx), but injuries may also occur at the A3, A4, and rarely the A5 pulleys. The loss of integrity of the pulley leads to bowstringing of the tendon and its sheath away from the phalanx during active flexion activities. This alteration in the line of pull results in an inefficient gripping mechanism, leading to weakness and pain. Conservative and potentially surgical management of these injuries are crucial for re-establishing the correct biomechanical positioning.

Identifying the "lift-off" of the flexor tendon from the bone is the initial and easiest way to detect a pulley injury. Resisted flexion may further highlight this bowstringing effect. Rotating the probe in a short axis to the tendon and identifying the pulley can also aid in diagnosing this pathology. Subsequently, rotating the probe around the digit to align it parallel to the origin of the pulley will allow identification of which arm has been injured.