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DISLOCATION, THUMB CARPOMETACARPAL (CMC) JOINT

Introduction

Isolated thumb carpometacarpal (CMC) dislocations without any other concomitant injury are rare and account for <1% of all hand injuries.1These are high-energy injuries most commonly seen in young, active individuals, and the mechanism responsible is believed to be either a longitudinally-directed force along the axis of the thumb metacarpal with the CMC joint in full flexion, or a force driven into the first web space.2,3Thumb CMC dislocations in the dorsal direction are more common than volar dislocations, and because the volar ligaments are very strong, there may also be an avulsion of the thumb metacarpal base producing a Bennett's fracture.4  As with many other hand and wrist dislocations, these injuries are frequently missed or misdiagnosed upon initial presentation, which is why clinical suspicion must remain high. Although the optimal treatment approach for thumb CMC dislocations is still debated, it appears that closed reduction is indicated as the initial intervention for most acute cases that are closed and reducible. After reduction, thumb CMC joint stability is the main determining factor in whether to continue with conservative treatment or progress to surgical treatment.5,6
 

Definitions

  • A thumb CMC joint dislocation occurs when the articular surface of the base of the thumb metacarpal is displaced off the articular surface of the distal end of the trapezium.

Hand Surgery Resource’s Dislocation Description and Characterization Acronym

D O C S

D – Direction of displacement

O – Open vs closed dislocation

C – Complex vs simple

S – Stability post reduction

D – Direction of displacement

  • The primary description and characterization of thumb CMC joint dislocations are done by noting the direction of the displacement of the thumb metacarpal relative to the trapezium. The three possible directions of displacement are dorsal, lateral, and volar.7 Dorsal dislocations are the most common, while only a few cases of volar dislocations have been reported.5,6
    • Dorsal dislocations are further divided into two subtypes: the hyperextension subtype, where the volar base of the metacarpal catches on the dorsal edge of the trapezium in an extended position, and the bayonet subtype, where the metacarpal base is displaced on top of the distal trapezium in a position parallel to its longitudinal axis.
  • The degree of displacement of the thumb metacarpal further characterizes thumb CMC dislocations. In a true complete dislocation, the articular surface of the thumb metacarpal is no longer in contact with the articular cartilage of the distal trapezium. If there is partial contact of the cartilaginous surfaces, then this is not a true dislocation but rather a joint subluxation.7

O – Open vs closed

  • The majority of thumb CMC joint dislocations are closed; the skin is intact, and there is no route for bacteria to contaminate the joint space.
  • Open thumb CMC dislocations are extremely rare, but when present, require urgent irrigation, debridement, open reduction, pinning and ligament repair.

C – Complex vs simple

  • Most thumb CMC joint dislocations are simple, meaning that reduction is easily achieved under digital anesthetic block and is not blocked by soft tissue being interposed in the joint between the thumb metacarpal and trapezium joint surfaces. 
  • Complex (irreducible) thumb CMC joint dislocations are rare, but do occur on some occasions. These cases are clear indications for open surgical repair.5,7

S – Stability

  • A stable thumb CMC joint dislocation can be reduced and then put through an active range of motion (ROM) test under a local anesthetic block without redislocating.
  • Furthermore, a stable thumb CMC joint dislocation is stable to stress testing of associated ligaments after reduction.

Related anatomy2,5

  • Extensor pollicis longus
  • Extensor pollicis brevis
  • Flexor pollicis longus
  • Flexor pollicis brevis
  • Dorsal radial sensory nerve
  • Abductor pollicis longus 
  • Opponens pollicis 
  • Anterior oblique ligament
  • Intermetacarpal ligament 
  • Dorsoradial capsular ligament 
  • Posterior oblique ligament
  • Osteology of the thumb metacarpal base and trapezium saddle joint
  • The thumb CMC joint is supported by a thickened joint capsule composed of 16 ligaments, but its stability is primarily provided by 4 ligaments: the deep anterior oblique, intermetacarpal, dorsoradial capsular ligament, and posterior oblique ligaments. Dislocation may disrupt at least one of these ligaments.2,8

Overall incidence

  • Isolated thumb CMC joint dislocations only account for <1% of all hand injuries.1As of 2014, fewer than 50 cases had been published in the literature.8,9
    • Thumb CMC dislocations are more likely to occur with other concomitant injuries, like thumb metacarpophalangeal (MP) dislocation or fractures of the trapezium or distal radius.3,5
    • Dislocations of the thumb CMC joint also appear to be less common than those occurring in the other CMC joints.10,11
  • Complex thumb CMC joint dislocations are very uncommon.

Related Injuries/Conditions

  • Fractures of the thumb metacarpal
  • Fractures of the trapezium
  • Dorsal ligament complex injuries
  • Extensor tendon ruptures
  • Flexor tendon ruptures
  • Abductor pollicis longus tendon rupture
  • Opponens pollicis tendon rupture
ICD-10 Codes

  • DISLOCATION, THUMB CARPOMETACARPAL (CMC) JOINT

    Diagnostic Guide Name

    DISLOCATION, THUMB CARPOMETACARPAL (CMC) JOINT

    ICD 10 Diagnosis, Single Code, Left Code, Right Code and Bilateral Code

    DIAGNOSISSINGLE CODE ONLYLEFTRIGHTBILATERAL (If Available)
    DISLOCATION THUMB: CMC Joint S63.045_S63.044_ 

    Instructions (ICD 10 CM 2020, U.S. Version)

    THE APPROPRIATE SEVENTH CHARACTER IS TO BE ADDED TO EACH CODE FROM CATEGORY S63, S64, S65 AND S69
    A - Initial Encounter
    D - Subsequent Routine Healing
    S - Sequela

    ICD-10 Reference

    Reproduced from the International statistical classification of diseases and related health problems, 10th revision, Fifth edition, 2016. Geneva, World Health Organization, 2016 https://apps.who.int/iris/handle/10665/246208

Clinical Presentation Photos and Related Diagrams
Thumb CMC Dislocation
  • Left thumb CMC dislocation (arrow)
    Left thumb CMC dislocation (arrow)
Symptoms
History of trauma to the thumb and radial wrist
Pain, swelling and deformity at the thumb CMC joint
Typical History

The typical patient is a 21-year-old right-handed male who is an amateur motocross rider, which entails racing a motorized dirt bike on a course with obstacles. During a recent tournament, the man was racing at a fast speed and coming around a sharp turn when another competitor cut him off. Without much time to react, he veered off the course and hit a barrier while still gripping the handlebars. The force of this impact was driven into the first web space of his right hand and dislocated the thumb CMC joint, causing pain and swelling in its wake. The patient was splinted and taken to an emergency room where a closed reduction was performed under local anesthesia.  The CMC joint remained subluxed after reduction so the patient was splinted and referred to a hand surgeon for an urgent evaluation of his injury.

Positive Tests, Exams or Signs
Work-up Options
Treatment Options
Treatment Goals
  • Reduce the dislocation
  • Analyze the thumb CMC joint’s stability
  • Rehab the thumb to regain ROM and normal thumb and hand function
Conservative
  • The optimal treatment method for thumb CMC dislocations has not yet been established, but it appears that conservative treatment is indicated for acute injuries that are recognized early. In these cases, closed reduction under local anesthesia with a thumb or wrist block. This anesthesia should allow a gentle reduction with minimal pain.5,6,8. After reduction, the wrist should be immobilized in a plaster cast with the thumb in slight abduction, extension and open first web. If the joint remains congruent with no signs of instability on radiography, immobilization should be continued for 4-6 weeks. If the joint is unstable, surgery is needed.5,6
Operative
  • Surgical treatment is typically indicated when closed reduction fails, in chronic cases, and for open, complex (irreducible), and/or unstable thumb CMC dislocations.2,5,6
  • Surgical options include closed reduction and percutaneous pinning (CRPP), open reduction and internal fixation (ORIF), capsulorrhaphy, trapeziectomy, trapeziometacarpal arthrodesis, and ligament reconstruction.5,6
    • If a dislocation remains unstable or incongruent after initial closed reduction, CRPP with K-wire fixation should be attempted next, but ORIF with capsulorrhaphy and/or ligament reconstruction may also be needed to obtain an absolute anatomic and stable reduction.6
    • In cases of neglected injury or secondary dislocation, open reduction, K-wire fixation, capsulorrhaphy, and/or ligament reconstruction with a plaster cast are mandatory.6
  • Trapeziectomy with ligament reconstruction or trapeziometacarpal arthrodesis are potential salvage options when the dislocation is irreducible, associated with a fracture or severe osteoarthritis in the CMC thumb joint.  Arthrodesis is sometimes indicated for young, active individuals, while trapeziectomy is more suitable for older, low-demand individuals in which pain relief is the primary goal.6
Treatment Photos and Diagrams
Thumb CMC Dislocation Treatment
  • Thumb CMC Dislocation without fracture treated with closed reduction . After cast removed at 6 weeks severe CMC subluxation. Reduction, pinning and cast may have prevent symptomatic subluxation.
    Thumb CMC Dislocation without fracture treated with closed reduction . After cast removed at 6 weeks severe CMC subluxation. Reduction, pinning and cast may have prevent symptomatic subluxation.
Hand Therapy
  • Many patients with closed thumb CMC joint dislocations that are reduced early can potentially exercise their thumb on their own after an appropriate period of immobilization.
  • However, patients with marked swelling and pain will need hand therapy to help reduce swelling and improve ROM and strength after casting.
  • Surgically repaired complex thumb CMC dislocations, repaired ligaments, and unstable thumb CMC dislocations will definitely need hand therapy, custom splinting, and dynamic extension splints after casting.12
Complications
  • Stiffness
  • Pain
  • Residual deformity
  • Weakened grip
  • Impaired ROM
  • Recurrent instability
  • Osteoarthritis of the thumb CMC joint
  • Infection after open surgical treatment
Outcomes
  • Most simple thumb CMC joint dislocations that are treated early and appropriately have excellent outcomes. 
  • However, all patients with thumb CMC joint dislocations should be warned that the thumb CMC joint on the injured side will likely remain slightly larger than the opposite thumb CMC joint because the damaged ligaments are likely to heal with a little extra bulk (collagen).
  • In one study of 12 patients with thumb CMC dislocations, 9 were treated with closed reduction and cast immobilization alone, and 3 with CRPP.  At the final follow-up, outcomes were positive with stable joints no symptoms for all but 3 patients (2 treated conservatively and 1 surgically). These patients experienced instability and other symptoms, and all presented to treatment in a delayed fashion.13
  • In another series of 17 patients, 8 were treated with CRPP and 9 underwent early ligament reconstruction and percutaneous pinning.  At the long-term follow-up, 4 of the 8 patients treated with CRPP had residual instability that required ligament reconstruction, while all 9 of those initially treated with ligament reconstruction had normal grip strength and ROM.14
Key Educational Points
  • Thumb CMC dislocation can predispose the CMC joint to early arthritis.  The thumb CMC joint is the most common wrist joint to develop osteoarthritis.12
  • Simple closed thumb CMC joint dislocations can be mobilized early and should get a good outcome with minimal loss of ROM and residual deformity unfortunately a stable CMC joint after a closed reduction is uncommon.
  • Unstable thumb CMC joint dislocations require prolonged extension block splinting with continuous monitoring by hand therapy for splint adjustment, etc.
  • Open and complex thumb CMC joint dislocations usually require urgent surgical treatment.
  • Many thumb CMC dislocations are missed or misdiagnosed because the injuries are uncommon and standard views of the hand and the wrist typically do not provide orthogonal views of the CMC joint. Clinical suspicion therefore must remain high and any indication of a thumb CMC dislocation followed by a careful detailed physical examination.6
  • X-ray:  In addition to routine posteroanterior (PA), lateral, and oblique views, a hyperpronated thumb view is recommended for any thumb injury.3,6
  • CT scan and or MRI may be needed when dislocation is suspected for better visualization of the injury and any associated lesions undetected on standard radiographs.3,8
  • How long the thumb CMC joint remains reducible following dislocation, whether by closed or open means, remains unclear.6
  • It is currently unclear if there is any superior management strategy for cases of residual instability after initial closed reduction. It appears that neither CRPP nor ORIF can always guarantee an optimum result, and ligament reconstruction should therefore be considered a viable option in these cases.6,9
  • The osteology of the thumb metacarpal/trapezial saddle joint provides a significant inherent degree of CMC joint stability.
  • The screw home torque mechanism associated with power pinch also dynamically augments the thumb CMC joint stability.
  • Strauch et al have demonstrated that the dorsal radial capsular ligament is the major stabilizer that resists dorsal thumb CMC dislocation.4
  • Clinical experience shows that the thumb CMC dislocation is often easy to reduce but very difficult to hold in a reduced position in a splint or cast.
References

New and Cited Articles
 

Mueller, JJ. Carpometacarpal dislocations: report of five cases and review of the literature. J Hand Surg Am 1986;11(2):184-8. PMID: 3958446

  1. Jeong, C, Kim, HM, Lee, SU, et al. Bilateral carpometacarpal joint dislocations of the thumb. Clin Orthop Surg 2012;4(3):246-8. PMID: 22949958
  2. Kraus, CK and Weaver, KR. Traumatic dislocation of the first carpometacarpal joint. Am J Emerg Med 2014;32(12):1561 e1-2. PMID: 24993682
  3. Bosmans, B, Verhofstad, MH and Gosens, T. Traumatic thumb carpometacarpal joint dislocations. J Hand Surg Am 2008;33(3):438-41. PMID: 18343304
  4. Suresh, SS, Zaki, H and Ahmed, A. Isolated Carpo-Metacarpal Dislocation of the Thumb. J Orthop Case Rep 2012;2(1):15-7. PMID: 27298846
  5. McCarley, M and Foreman, M. Chronic Carpometacarpal Dislocation of the Thumb: A Case Report and Review of the Literature. JBJS Case Connect 2018. [Epub] PMID: 29995663
  6. Merrell G, Slade JF. Dislocations and ligament injuries in the digits. In: Wolfe, SW, Hotchkiss RN, Pederson WC, Kozin SH (eds): Green’s Operative Hand Surgery.  Philadelphia 2011: Elsevier Churchill Livingstone, pp. 291-332.
  7. Pizon, AF and Wang, HE. Carpometacarpal dislocation of the thumb. J Emerg Med 2010;38(3):376-7.PMID: 18554842
  8. Fotiadis, E, Svarnas, T, Lyrtzis, C, et al. Isolated thumb carpometacarpal joint dislocation: a case report and review of the literature. J Orthop Surg Res 2010;5:16.PMID: 20219137
  9. Horneff, JG, 3rd, Park, MJ and Steinberg, DR. Acute closed dislocation of the second through fourth carpometacarpal joints: satisfactory treatment with closed reduction and immobilization. Hand (N Y) 2013;8(2):227-31. PMID: 24426924
  10. Chick, JF, Mandell, JC, de Souza, DA, et al. Hand pain after fall. Dislocation of the fifth carpometacarpal. Ann Emerg Med 2013;62(1):13, 27. PMID: 23842050
  11. Wollstein, R, Michael, D and Harel, H. Postoperative Therapy for Chronic Thumb Carpometacarpal (CMC) Joint Dislocation. Am J Occup Ther 2016;70(1):1-4.PMID: 26709434
  12. Watt, N and Hooper, G. Dislocation of the trapezio-metacarpal joint. J Hand Surg Br1987;12(2):242-5. PMID: 3624988
  13. Simonian, PT and Trumble, TE. Traumatic dislocation of the thumb carpometacarpal joint: early ligamentous reconstruction versus closed reduction and pinning. J Hand Surg Am 1996;21(5):802-6. PMID: 8891977

Reviews

  1. Annappa R, Kotian P, P JA, Mudiganty S. Ligamentous Reconstruction of Traumatic Dislocation of Thumb Carpometacarpal Joint: Case Report and Review of Literature. J Orthop Case Rep2015;5(4):79-81. PMID: 27299108
  2. Lahiji F, Zandi R, Maleki A. First Carpometacarpal Joint Dislocation and Review of Literatures. Arch Bone Jt Surg2015;3(4):300-3. PMID: 2655059

Classics

  1. Shah J, Patel M. Dislocation of the carpometacarpal joint of the thumb. A report of four cases. Clin Orthop Relat Res1983;(175):166-9. PMID: 6839582
  2. Chen VT. Dislocation of the carpometacarpal joint of the thumb. J Hand Surg Br1987;12(2):246-51. PMID: 3624989
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