Gamekeeper’s thumb: Injuries of the ulnar collateral ligament (UCL) of the thumb are encountered frequently. The most common mechanism is excessive radial deviation of the proximal phalanx, either acutely or through chronic repetitive microtrauma. Rupture of the ligament most often occurs at the ligament’s distal insertion on the base of the proximal phalanx. Failure has been reported in the mid-substance, proximal attachment, with an avulsed fragment of bone, and as attritional failure (a thinning of the ligament resulting in laxity) [4].

Stener lesion: Stener described a complication of the UCL injury of the thumb in which the adductor pollicis longus aponeurosis was interpositioned between the distally avulsed ligament and its insertion. Due to the lack of contact between torn ligament and enthesis, he predicted instability would ensue. He further deduced that such lesions represented a surgical repair indication [5].

Collateral ligament injury: While less common that UCL injuries, RCL injuries of the thumb are relatively common. The RCL is important for pinch movements and depression, such as pushing button. The mechanism of injury is forced and sudden adduction of the MCP. Grading systems have incorporated clinical and structural elements: Grade I partial tear with pain but no instability, Grade 2 partial tear with pain and asymmetric laxity, Grade 3 full thickness tear with pain and instability [6].

Injuries to the collateral ligaments of the MCP joints in the fingers are less common than in the thumb. Most reports have described lesions in the RCL of the index finger. The imaging diagnosis can be challenging due to some degree of preexisting “normal” laxity in the joints [7]. The PIP joints are the most common injured articulation in the hand [8]. Grades I and II volar plate and collateral ligament sprains represent the vast majority of PIP joint injuries. The primary indications for surgical treatment include irreducible dislocation or subluxation, or association with a large fracture fragment [9]. Collateral ligament injuries result in instability in the coronal plane, whereas volar plate injuries result in instability in the sagittal plane.

Injury to the flexor tendon is not as common as injuries to the extensor mechanism. Lesions are broadly categorized as open or closed injuries. In the flexor tendons, pulley lesions are also included.

Flexor tendon lacerations are more common than closed injury. Tendon failure can be partial or complete. Lesions are characterized by zone for identification of point of failure as well as prognostication. The zones are as follows: Zone I from distal FDP to distal FDS insertion, Zone II (no man’s land) from distal FDS to distal palmar fold, Zone III from proximal part of A1 pulley (MCP) to distal flexor retinaculum, Zone IV at carpal tunnel, and Zone V forearm proximal to flexor retinaculum. Zone II lesions are the most frequent with the most severe prognosis [10]. Trauma to the four proximal zones implies involvement of both the FDS and FDP and would affect both the PIP and DIP.

In closed injury, avulsion of the FDP is the most common type of failure. It is caused by sudden hyperextension in a flexed finger, and referred to as ‘sweater’ or ‘jersey’ finger [11]. These lesions are characterized by degree of retraction and presence of bone fragment.

Pulley lesion: Pulley lesions were recognized with increasing frequency as rock climbing gained popularity as a sport. Flexion of the fingers with MCP joint extension, PIP joint flexion and DIP joint extension results in extensive force at the A2 and A3 pulley, the former being the most common. Injury is reported to begin at eth distal part of the pulley [12]. This injury can be complicated by fibrous scarring and flexion contracture at the PIP.