SPRAIN, THUMB CMC JOINT

The thumb carpometacarpal (CMC) joint features a strong, complex ligamentous system to provide it with stability and protect it from the significant axial loads that occur with pinch and grip. Consequently, injuries involving the thumb CMC joint, ranging from mild sprains to complete ligament ruptures and joint dislocations, are  rare. In most cases, these injuries result from an axial load that causes hyperextension and/or hyperabduction of the thumb, which can occur secondary to a fall from a height or in certain ball-handling sports. Despite the infrequency of ligamentous thumb CMC joint injuries, an accurate diagnosis and appropriate treatment regimen are necessary to prevent long-term complications like chronic stiffness or laxity.^1-3

Pathophysiology

• Due to its position and functional role, relatively large demands are routinely placed on the thumb CMC joint. As a result, the combination of large compression and shear forces can create a potentially stressful environment at the joint and lead to ligamentous injuries.²
• The mechanism of injury is usually an axial load that causes hyperextension and/or hyperabduction of the thumb CMC joint, such as from a fall on an outstretched hand (FOOSH) or in ball-handling sports like football and basketball. Thumb CMC joint injuries may be complete or partial, with partial injuries being far more common and often resulting in varying degrees of joint subluxation.  Complete injuries with thumb CMC joint dislocation are relatively rare and occur when a flexed metacarpal is loaded axially. These dislocations are typically dorsal and result in ruptures of the dorsal radial and volar oblique ligaments.^1,3 The reader should also see Thumb CMC Dislocations Diagnostic Guide.

Related Anatomy^4,5

• Ulnar collateral ligament (UCL): proper and accessory
• Radial collateral ligament (RCL): proper and accessory
• Dorsal capsule
• Anterior oblique ligament
• Dorsal radial ligament
• Dorsal central ligament
• Posterior oblique ligament
• First intermetacarpal ligament
• The thumb CMC joint is a double saddle joint that is concave in one direction and convex on the other, and it moves in flexion/extension, abduction/adduction, and pronation/supination planes.³
• The thumb CMC joint is stabilized by its joint capsule and the palmar oblique, first intermetacarpal, dorsal radial, and posterior oblique ligaments. Many researchers consider the anterior oblique ligament to be the primary stabilizer of the joint and that dislocation results in injury to this structure.^1,3
• Ligamentous injuries of the thumb CMC joint are typically classified using the following system:
  • Grade 1: involves asymmetric swelling and tenderness over the injured ligament without instability on the lateral stress test
  • Grade 2: involves complete disruption of the injured ligament, but other stabilizing restraints remain intact. There is some instability, but stress testing reveals a definite soft tissue endpoint indicating that the ligament is not completely torn.
  • Grade 3: involves total ligament disruption, with clinical examination depicting evidence of subluxation or dislocation on active extension.^6,7 Stress testing reveals no soft tissue endpoint indicating that the ligament is completely torn.

Incidence and Related Conditions

• One study found that finger injuries accounted for 38% of 3.5 million upper extremity injuries in the U.S. About 16% of these injuries were sprains and strains, while dislocations only accounted for ~5%.⁸
• The incidence of finger sprains is 37.3 per 100,000 person/years, and the proximal interphalangeal (PIP) joint is the most commonly injured joint of the hand, followed by the thumb metacarpophalangeal (MP) joint and MP joint of the fingers. Due to their infrequency, statistics are lacking on the specific occurrence rates of sprains involving the thumb CMC joint, distal interphalangeal (DIP) joint of the fingers, and thumb interphalangeal (IP) joint.⁸

Differential Diagnosis

• UCL tear
• RCL tear
• Thumb CMC joint dislocation or significant subluxation
• Trapezoid fracture
• Anterior oblique ligament tear
• Dorsal radial ligament tear
• Dorsal central ligament tear
• Posterior oblique ligament tear
• First intermetacarpal ligament tear
• Thumb metacarpal base fracture a Bennett's fracture
• Trapezoid fracture

A typical patient is a 35-year-old, right-handed, amateur male rock climber. The man was bouldering without a harness or rope.  He was climbing a difficult rock outcrop 6-8 feet off the ground with a significant overhang when he lost his grip and slipped. He placed his hands out to break his fall and jammed his thumb against the rock as he slid down the side of the boulder.  This hyperextended and hyperabducted the thumb CMC joint and causing severe pain at the base of the thumb. The area surrounding the joint immediately swelled and became tender to the slightest touch.  His increasing pain prompted him to seek out medical attention at a nearby ER where the thumb sprain was diagnosed and treated with a splint.

Infection

• Stiffness
• Thumb CMC flexion deformity
• Osteoarthritis
• Thumb CMC joint contracture
• Thumb CMC joint instability
• Impaired grip/pinch strength
• According to some authors, most complications are due to over-treatment—such as extended periods of immobilization—rather than the absence of treatment.¹⁵
• Failure to initially repair a completely torn ligament of the CMC joint may result in chronic pain, instability, deformity, weakness, and/or osteoarthritis. Late ligament repair or reconstruction may be needed to resolve these cases.¹⁰

• When treated early and appropriately, ligamentous injuries to the thumb CMC joint typically have a good to excellent prognosis, and most patients will eventually regain thumb ROM and grip and pinch strength.^13,16  One of the primary predictors of success is the promptness of treatment, as injuries managed early are typically associated with more positive outcomes.¹⁶

• Many patients present several weeks or months after injury, at which point they still experience pain, swelling, and stiffness. This can lead some patients to protect the thumb excessively, which results in additional stiffness and hinders their recovery.¹⁷
• Patients, athletic trainers, and coaches often overlook thumb CMC joint injuries, and delayed or improper treatment often occurs as a result, which can lead to permanent deformities of the affected digit.⁷
• Over the past 10 years, there have been many advances in the understanding of the anatomy, physiology, and biomechanics of the ligamentous joint capsule of the finger and thumb joints, which may help to better deliver effective treatments to patients in the future.⁶
• The thumb is undoubtedly the most important digit of the hand, and the CMC joint is commonly regarded as the most important joint of the thumb when it comes to functionality.²
• Routine X-rays - appropriate radiographs should supplement the clinical examination in order to properly evaluate thumb CMC joint injuries.¹  Standard posteroanterior (PA) and true lateral views are helpful for identifying associated fractures, but the best evaluation of the thumb CMC joint is obtained with a Robert’s view.³  Some experts recommend taking radiographs before stress testing.¹⁰
• Ultrasound has become increasingly effective at imaging the articular surface and associated soft tissues of the digits, in part because it allows for dynamic evaluation.¹¹  Findings indicative of ligamentous injuries include frank ligament discontinuity or detachment, ligament thickening, and extracapsular leakage of joint fluid.¹¹
• MRI may be helpful for diagnosing the degree of ligamentous injury and for differentiating between partial tears and avulsions.  When patients are treated conservatively, MRI can also be used to monitor healing and to evaluate ligament quality and joint stability before returning to normal activity.¹
• MR arthrography (MRa) has been found to be more useful than an MRI and ultrasound for demonstrating the UCL, which is the most difficult ligament of the thumb CMC joint to visualize.⁹

New and Cited Articles

1. Connell, DA, Pike, J, Koulouris, G, et al. MR imaging of thumb carpometacarpal joint ligament injuries. J Hand Surg Br 2004;29(1):46-54. PMID: 14734072
2. Neumann, DA and Bielefeld, T. The carpometacarpal joint of the thumb: stability, deformity, and therapeutic intervention. J Orthop Sports Phys Ther 2003;33(7):386-99. PMID: 12918864
3. Owings, FP, Calandruccio, JH and Mauck, BM. Thumb Ligament Injuries in the Athlete. Orthop Clin North Am 2016;47(4):799-807.PMID: 27637666
4. Bowers, WH, Wolf, JW, Jr., Nehil, JL, et al. The proximal interphalangeal joint volar plate. I. An anatomical and biomechanical study. J Hand Surg Am 1980;5(1):79-88. PMID: 7365222
5. Bowers, WH. The proximal interphalangeal joint volar plate. II: a clinical study of hyperextension injury. J Hand Surg Am 1981;6(1):77-81.PMID: 7204922
6. Rozmaryn, LM. The Collateral Ligament of the Digits of the Hand: Anatomy, Physiology, Biomechanics, Injury, and Treatment. J Hand Surg Am 2017;42(11):904-915. PMID: 29101974
7. Kamnerdnakta, S, Huetteman, HE and Chung, KC. Complications of Proximal Interphalangeal Joint Injuries: Prevention and Treatment. Hand Clin 2018;34(2):267-288. PMID: 29625645
8. Ootes, D, Lambers, KT and Ring, DC. The epidemiology of upper extremity injuries presenting to the emergency department in the United States. Hand (N Y) 2012;7(1):18-22. PMID: 23449400
9. Rawat, U, Pierce, JL, Evans, S, et al. High-Resolution MR Imaging and US Anatomy of the Thumb. Radiographics 2016;36(6):1701-1716.PMID: 27726751
10. Lourie, GM, Gaston, RG and Freeland, AE. Collateral ligament injuries of the metacarpophalangeal joints of the fingers. Hand Clin 2006;22(3):357-64. PMID: 16843801
11. Prucz, RB and Friedrich, JB. Finger joint injuries. Clin Sports Med 2015;34(1):99-116. PMID: 25455398
12. Joyce, KM, Joyce, CW, Conroy, F, et al. Proximal interphalangeal joint dislocations and treatment: an evolutionary process. Arch Plast Surg 2014;41(4):394-7. PMID: 25075363
13. Avery, DM, 3rd, Caggiano, NM and Matullo, KS. Ulnar collateral ligament injuries of the thumb: a comprehensive review. Orthop Clin North Am 2015;46(2):281-92. PMID: 25771322
14. Folk, B. Traumatic thumb injury management using mobilization with movement. Man Ther 2001;6(3):178-82. PMID: 11527458
15. Adi, M, Hidalgo Diaz, JJ, Salazar Botero, S, et al. Results of conservative treatment of volar plate sprains of the proximal interphalangeal joint with and without avulsion fracture. Hand Surg Rehabil 2017;36(1):44-47.PMID: 28137442
16. Draghi, F, Gitto, S and Bianchi, S. Injuries to the Collateral Ligaments of the Metacarpophalangeal and Interphalangeal Joints: Sonographic Appearance. J Ultrasound Med 2018;37(9):2117-2133. PMID: 29480577
17. Bot, AG, Bekkers, S, Herndon, JH, et al. Determinants of disability after proximal interphalangeal joint sprain or dislocation. Psychosomatics 2014;55(6):595-601. PMID: 25034813

Reviews

1. Avery, DM, 3rd, Caggiano, NM and Matullo, KS. Ulnar collateral ligament injuries of the thumb: a comprehensive review. Orthop Clin North Am 2015;46(2):281-92. PMID: 25771322
2. Gluck, JS, Balutis, EC and Glickel, SZ. Thumb ligament injuries. J Hand Surg Am 2015;40(4):835-42. PMID: 25813924

Classic

1. Frank WE, Dobyns J. Surgical pathology of collateral ligamentous injuries of the thumb. Clin Orthop Relat Res1972;83:102-14. PMID: 5014798