Dorsoradial Instability of the Thumb Metacarpophalangeal Joint: A Biomechanical Investigation

Radial Collateral Ligament Injuries of the Thumb Metacarpophalangeal Joint

PURPOSE OF REVIEW

Injuries to the radial collateral ligament (RCL) of the thumb are thought to be relatively uncommon, especially when compared to the ulnar collateral ligament. However, the radial collateral ligament is increasingly recognized as critical for the overall stability of the thumb metacarpophalangeal joint. This article sets out to provide a comprehensive review of RCL injuries of the thumb MCP joint, including epidemiology, biomechanics, diagnosis, and treatment.

RECENT FINDINGS

Although traditionally thought to respond well to conservative management, especially when compared to injuries to the ulnar collateral ligament, there is mounting evidence that chronic RCL injury leads to thumb metacarpophalangeal joint instability and can accelerate post-traumatic joint degeneration. Thus, much of the recent literature details surgical treatment options for radial collateral ligament injury, including repair and reconstruction. While incomplete tears of the thumb RCL respond well to immobilization, complete tears should generally be treated with operative management, either direct repair or anatomic reconstruction, depending on tissue quality. Even subacute and chronic injuries may be amenable to direct repair, with good to excellent outcomes, including in high-demand patient populations, such as professional athletes.

Biomechanical Analysis of Thumb Ulnar Collateral Ligament Tear Kinematics

Background: Thumb ulnar collateral ligament (UCL) injuries are common, but the kinematics of these injuries have not been comprehensively described, especially regarding kinematic changes with progressive UCL injury. Methods: Eleven cadaveric thumbs underwent kinematic testing under 4 conditions: intact, partial tear (50%) of the proper UCL, full tear of the proper UCL, and complete tear of both the proper and accessory UCL. Kinematic testing parameters included varus/valgus stress, pronation/supination, and volar/dorsal translation at -10 degree, 0 degree, 15 degree, and 30 degree of metacarpophalangeal flexion. Results: Partial tear of the proper UCL did not result in significant increases in laxity in any direction compared with intact (P ≥ .132). Full tear of the proper UCL resulted in a significant increase in valgus angulation (18.8° ± 1.7° vs 11.5° ± 1.5°; P = .024) and pronation (15.4° ± 2.5° vs 12.6° ± 2.3°; P = .034) at 30 degree of flexion relative to intact. Complete tear of both the proper and accessory collateral ligaments resulted in increased valgus angulation at all degrees of flexion (P < .001). Complete tear also resulted in a significant volar translation at 0 degree, 15 degree, and 30 degree of flexion (P ≤ .016). Conclusion: Partial tear of the proper UCL does not significantly affect the stability of the joint, but full tear of the proper UCL increases valgus instability at 30 degree of flexion. Complete tear of the UCL is necessary for increased varus/valgus instability at all degrees of flexion and results in significant increases in pronation/supination and volar translation.

An anatomical study on the Stener-type lesion of the radial collateral ligament of the metacarpophalangeal joint of the thumb

The Stener-type lesion of the radial collateral ligament is rare. The insertion of the abductor pollicis brevis is believed to preclude its occurrence. The aim of this study was to determine whether this lesion can be induced mechanically. Four specimens were tested in neutral rotation and 20° of supination, in 45° and 30° of flexion, and in the neutral position. The angle of ulnar adduction to form a Stener-type lesion was measured. The lesion occurred only in 45° flexion in all specimens. A lesser angle of flexion decreased the rate of ligament displacement. In the neutral position no ligament displacement was found. A Stener-type lesion of the radial collateral ligament can occur in ulnar adduction and flexion of the metacarpophalangeal joint. Supination of the joint increases the likelihood of ligament displacement. As distal ruptures of the radial collateral ligament are uncommon, a high index of suspicion is required for diagnosis.

Thumb Metacarpophalangeal Joint Arthritis

Arthritis of the thumb metacarpophalangeal joint can be debilitating whether in isolation or in conjunction with degenerative disease at the adjacent joints. Despite its crucial role in fluid and dexterous motion of the thumb axis, little is known about the isolated incidence of pathology at this joint. Etiologies include primary, posttraumatic, and inflammatory arthritis. For early, isolated degenerative disease, arthroscopic synovectomy has been shown to yield satisfactory results. For more advanced disease, fusion is the benchmark. The literature suggests that increased flexion angles may mitigate development of trapeziometacarpal arthritis. In case of advanced arthropathy of the entire thumb axis, arthroplasty is a viable option to reduce pain, preserve motion, and thus limit progression of adjacent joint disease. Special considerations should be given to the rheumatoid thumb because a select combination of treatments for each deformity is thought to best address the unique pathomechanics.

Additional Dorsal Fibrocartilage Repair in a Combined Radial Collateral Ligament and Dorsal Fibrocartilage Injury of the Thumb Metacarpophalangeal Joint

The purpose of this study was to evaluate the necessity of an additional dorsal fibrocartilage (DFC) repair in combined radial collateral ligament (RCL) and DFC injuries of the thumb metacarpophalangeal joint (MPJ). Eight cadaveric thumbs were used. Ulnar/radial deviation, prosupination, and volar/dorsal laxity were measured. Serial sectioning was performed of the RCL and the DFC. The RCL followed by the DFC were then reattached sequentially. Measurements were performed for intact, RCL cut, RCL+DFC cut, RCL repair alone, and RCL+DFC repair. The neutral position shifted ulnarly, pronated, and subluxed volarly after RCL+DFC cut. Volar subluxation was reduced with RCL+DFC repair compared with RCL repair alone. With external loading, ulnar deviation, pronation, and volar laxity increased significantly after RCL+DFC cut. Ulnar deviation reduced significantly with RCL+DFC repair (12.4°, 10.8°, and 10.9°) compared with RCL repair alone (14.4°, 14.3°, and 18.9°) at 0°, 30°, and 60°, respectively. Pronation reduced significantly with RCL+DFC repair (7.1° and 9.4°) compared with RCL repair alone (10.2° and 12.6°) at 0° and 30°, respectively. Volar subluxation reduced significantly with RCL+DFC repair (0.9 mm and 1.2 mm) compared with RCL repair alone (2.1 mm and 1.8 mm) at 30°and 60°, respectively. Radial collateral ligament repair alone does not restore anatomic dorsoradial stability of the thumb MPJ in a combined RCL and DFC injury. Combined repair of the RCL and the DFC is recommended to reduce the MPJ to its native position and minimize postoperative laxity. [Orthopedics. 2019; 42(2):e268-e272.].