65 Thumb Metacarpophalangeal Joint Collateral Ligament Reconstruction
Abstract
Thumb metacarpophalangeal joint (MCPJ) ulnar collateral ligament (UCL) reconstruction is indicated in patients with symptomatic chronic instability without degenerative changes or subluxation. The native origin and insertion site of the UCL may be less clear during the operative intervention for chronic instability. Recent anatomical studies provide valuable details that can be used for anatomic reconstruction of the thumb UCL. We believe that anatomic reconstruction is essential to restore MCPJ stability, as previous biomechanical studies have shown that even a small deviation from the native origin and insertion sites significantly increase the MCPJ laxity.
65.1 Description
Acute injuries to the ulnar collateral ligament (UCL) of the metacarpophalangeal joint (MCPJ) of the thumb are common among skiers and frequently referred to as “skier’s thumb.” “Gamekeeper’s thumb” refers to chronic attritional attenuation of the UCL due to the repetitive trauma to the ulnar side of the thumb. Scottish gamekeepers fractured the necks of rabbits between their thumbs and index fingers. The repetitive radial deviation of the thumb proximal phalanx at the MCPJ resulted in progressive stretching and attenuation of the UCL. In addition to attritional attenuation, chronic instability may be due to an untreated acute tear.
65.2 Relevant Anatomy
A combination of static and dynamic structures provide stability to the thumb MCPJ. The static stabilizers of thumb MCPJ include bony congruity, dorsal capsule, volar plate, proper, and accessory UCLs and radial collateral ligaments (RCLs). 1 There are intrinsic and extrinsic muscles that act as dynamic stabilizers of the thumb MCPJ. The extrinsic muscles include the extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and flexor pollicis longus (FPL). The intrinsic muscular stabilizers include the abductor pollicis brevis (APB), flexor pollicis brevis (FPB), and adductor pollicis. 2
Although the origin and insertion sites of the collateral ligaments can usually be identified without much difficulty in the acute setting, these attachment sites may be less clear during operative interventions for chronic instability. Thus, understanding the anatomy of the UCL is crucial for its reconstruction. Carlson et al showed that the mean center of the metacarpal origin of UCL was 4.2 mm (± 0.8 mm) or 38% (± 8%) from the dorsal edge of the metacarpal head and 5.3 mm from the articular surface. 3 They also showed that the mean center of the phalangeal insertion was 2.8 mm (± 0.7 mm) or 24% (± 7%) from the volar surface of the proximal phalanx and 3.4 mm from the articular surface. 3
A Stener lesion is when the proximal stump of ruptured UCL is displaced proximal and superficial to the adductor aponeurosis. The interposed adductor aponeurosis prevents reapproximation and thus healing of the avulsed UCL to its anatomic insertion site.
65.3 Clinical Presentation
65.3.1 History
Patients with chronic UCL instability usually present with pain, weakness, and functional disability. The pain is localized to the MCPJ and they experience difficulty performing activities requiring forceful pinch or grasp, for example, pencil grip, turning keys, and unscrewing a jar lid.
65.3.2 Physical Examination
Clinical evaluation of patients with chronic UCL instability begins with inspection. The resting posture of the thumb should be assessed for the presence of any radial deviation or volar subluxation at the MCPJ. The MCPJ should then be palpated for tenderness. A palpable thickening on the ulnar aspect of the metacarpal neck may suggest a Stener lesion. Finally, the stability of the MCPJ should be assessed with stress testing of the ligaments in extension and in 30° of flexion. The proper collateral ligaments are taut in flexion; whereas, the accessory collateral ligaments are taut in extension. A complete rupture of both the proper and accessory collateralligamentsresultinlaxityinbothpositions.
Patients with chronic instability generally present with gross instability with no endpoint on MCPJ stress testing. As with acute injuries, however, there is no consensus in the literature regarding the criteria to define an abnormal stress test. Most publications have considered the test abnormal if there is more than 30 to 45° of radial deviation of the MCPJ or more than 10 to 20° of radial laxity compared to the contralateral side. 4 Malik and colleagues showed, however, that there is a large variation in comparative MCPJ laxity between the thumbs even in normal individuals with 34% having at least 10° of variation and 12% having at least 15° of variation. 4
65.3.3 Radiographic Evaluation
Thumb radiographs should be obtained and assessed for radial and/or volar subluxation of the MCPJ as well as any evidence of degenerative changes.
65.4 Indications
Thumb MCPJ UCL reconstruction is indicated in patients with chronic UCL instability who experience significant pain or functional limitations.
Various techniques of UCL reconstruction have been described. The authors prefer an anatomic reconstruction of UCL based on a modification of the Glickel procedure for thumb UCL reconstruction. 5 , 6 In an in vitro cadaveric study, Bean and col-leagues showed that even a 2 mm palmar displacement of UCL metacarpal origin or a 2 mm dorsal displacement of UCL phalangeal insertion significantly increases the radial deviation of the MCPJ. 7 Thus, the authors advocate a more anatomic reconstruction of the thumb UCL based on the native origin and insertion sites.
65.5 Contraindications
Thumb MCPJ UCL reconstruction is contraindicated in the setting of MCPJ degenerative changes or severe chondromalacia, multidirectional instability, or a chronically fixed subluxation of the MCPJ. 6 In these cases, MCPJ arthrodesis may be considered.
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