DISLOCATION, FINGER CARPOMETACARPAL (CMC) JOINT

Isolated carpometacarpal (CMC) joint dislocations without associated fracture are rare and only represent <1% of all hand-related injuries.¹  The exact mechanism of injury is not clearly defined, but it is generally agreed that high-energy trauma is needed, which can result from a direct blow, fall from a height, or a rotational force.²The ring and little CMC joints are involved in these injuries far more frequently than the index and long CMC joints.  The very stable index and long CMC joints are rarely dislocated.^3,4  Many CMC dislocations are missed or misdiagnosed in the emergency department because other, more pressing injuries may require attention after high-energy accidents.  In addition, CMC dislocations can easily be missed on AP x-rays of the hand or wrist.  Even on lateral x-rays these dislocations or subluxations can be missed because of the overlapping bones. This highlights the need for elevated clinical suspicion when evaluating wrist injuries.⁴  Although the optimal treatment approach is still debated, it appears that a few CMC dislocations remain stable after closed reduction.  Therefore, most CMC dislocations require a closed reduction with percutaneous pinning and splinting to maintain the reduction while the ligaments heal.^4-6

Definitions

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

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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

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D – Direction of displacement

• The primary description and characterization of CMC joint dislocations are done by noting the direction of the displacement of the metacarpal relative to the distal carpal. The three possible directions of displacement are dorsal, lateral, and volar.⁷Dorsal dislocations are the most common, accounting for ~85% of all CMC dislocations.⁸  The reason dorsal dislocations are most common is that stronger static (dorsal ligaments) and dynamic (wrist extensors) restraints may cause the failure of bony ligament insertions dorsally, with the subsequent rupture of the volar ligaments.³  These 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 carpal in an extended position, and the rare bayonet subtype, where the metacarpal base is displaced on top of the distal carpal in a position parallel to the longitudinal axis of the distal carpal.

• The degree of displacement of the metacarpal further characterizes CMC dislocations. In a true complete dislocation, the articular surface of the metacarpal is no longer in contact with the articular cartilage of the distal carpal. If there is partial contact of the cartilaginous surfaces, then this is not a true dislocation but rather a joint subluxation.⁷  Many of these injuries are actually subluxations.

O – Open vs closed

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

C – Complex vs simple

• Most 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 metacarpal and carpal joint surfaces.²
• Complex (irreducible) CMC joint dislocations are rare, but do occur on some occasions.  Of the soft tissue structures that may be interposed in the joint, the extensor carpi radialis brevis (ECRB) tendon is the most commonly involved, but the extensor carpi radialis longus (ECRL) tendon may also be responsible for an irreducible CMC dislocation.^2,9

S – Stability

• A stable CMC joint dislocation can be reduced and then put through an active range of motion (ROM) test of the wrist under a local anesthetic block without redislocating.
• Furthermore, a stable CMC joint dislocation is stable to stress testing of the collateral ligaments in the radial/ulnar plane after reduction.  Note, radial or ulnar instability is extremely rare except for ulnar displacement of the fifth metacarpal.

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Related anatomy^3,6,9

• Extensor tendons – ECRB, ECRL, and extensor carpi ulnaris (ECU)
• Flexor tendons – flexor carpi ulnaris (FCU) and flexor carpi radialis (FCR)
• CMC ligaments
• Interosseous ligaments
• Deep capsular ligaments
• Superficial ligaments
• Osteology of the metacarpal base and distal carpal(s) bones
• The CMC joints are usually stable because of strong transverse dorsal ligaments and longitudinal volar ligaments.⁴
• The ligamentous and skeletal anatomy of the CMC joints other than the thumb have not been well described in the literature.⁵

Overall incidence

• The literature on CMC dislocations is scarce, with only small case series and case reports having been published, but it appears that they represent <1% of all hand injuries.^1,10
• CMC dislocations often associated with fracture(s) of the metacarpals or carpals are more frequent than pure dislocations.⁶
• Most CMC dislocations occur in young adults and usually involve the little or ring metacarpal, while dislocations of the index and long CMC joints are extremely rare.^3,4
• Complex CMC joint dislocations are very uncommon.

Related Injuries/Conditions

• Fractures of the metacarpal
• Fractures of the carpal
• CMC ligament injuries
• Interosseous ligament injuries
• Deep capsular/superficial ligament injuries
• Extensor tendon ruptures
• Flexor tendon ruptures

The typical patient is a 23-year-old right-handed female who was recently in a car accident. The woman was driving at ~60 MPH and going through a traffic light when a car coming from the road perpendicular to her ran a red light. She slammed on the breaks but was unable to avoid T-boning the passing car. With her hands on the steering wheel, the impact hyperextended both of her hands.  She dislocated the fifth CMC joint of her left hand. Immediate pain and swelling followed, but the woman had more serious injuries that required tending to first.  Once her other injuries were stabilized, her CMC joint dislocation was reduced with a closed reduction and then percutaneously pinned.

• Many patients with closed CMC joint dislocations that are reduced early can potentially exercise the wrist on their own after pins are removed and the cast is discontinued.
• However, patients with marked swelling and pain will need hand therapy to help reduce swelling and improve ROM and strength.
• Surgically repaired complex CMC dislocations, repaired ligaments, and unstable CMC dislocations will definitely need hand therapy, custom splinting, and dynamic extension splints.

• When treated acutely, the risk of complications in CMC dislocations is low.^5,4
• Stiffness
• Pain and/or residual deformity
• Weakened grip
• Impaired ROM
• Carpal tunnel syndrome
• Neurovascular damage
• Chronic CMC instability
• Osteoarthritis
• Carpal regional pain syndrome

• The majority of simple CMC joint dislocations that are treated early and appropriately have excellent outcomes without residual pain or functional impairments. This has been found to be the case regardless of whether reduction is achieved through open or closed means.^12,13
• It is not possible to establish the best management strategies for CMC dislocations because there are no studies with an adequate number of patients to reach strong conclusions.  Most authors who have performed K-wire fixation report positive outcomes.²
• All patients with CMC joint dislocations should be warned that the CMC joint on the injured side will likely remain slightly larger than the opposite CMC joint because the stretched ligaments are likely to heal with a little extra bulk (collagen).

• Simple stable closed CMC joint dislocations can be mobilized early and should get a good outcome with minimal loss of ROM and residual deformity.
• Unstable CMC joint dislocations require closed reduction, pinning, and splinting with continuous monitoring by hand therapy for splint adjustment, etc.
• Open and complex CMC joint dislocations require urgent surgical treatment.
• Diagnosing CMC dislocations may be difficult due to edema that can mask the deformity or it may be overlooked initially after an accident if more severe injuries are present. Clinical vigilance is therefore required in the emergency department to properly identify CMC dislocations.^3,6
• Although dislocations of the thumb and little CMC joints are well researched, there is a shortage of published literature on those involving the other CMC joints.¹¹
• Deformity:  Dorsal dislocations typically present with a depression in the palm and a characteristic “dinner-fork” deformity, while volar dislocations present with a depression on the dorsum of the hand and may present with a “spade type” deformity.¹¹
• Delayed and missed diagnoses are common in CMC dislocations due to their low incidence and subtle radiographic findings, so clinical suspicion must be high.⁵
• X-ray:  On the anteroposterior (AP) view, overlapping of joint surfaces, loss of parallelism, and asymmetry at the CMC may suggest the possibility of a subtle CMC injury.⁴  Also, lateral and oblique views are important for recognizing the extent of the injury, with the true lateral view often being regarded as the most helpful in the diagnosis.⁵
• CT scan:  May be needed for better visualization of the injury and any associated lesions undetected on standard radiographs.¹⁰

New and Cited Articles

1. Dobyns, JH, Linscheid, RL and Cooney, WP, 3rd. Fractures and dislocations of the wrist and hand, then and now. J Hand Surg Am 1983;8(5 Pt 2):687-90. PMID: 6630950
2. Cardozo, DF, Plata, GV, Casas, JA, et al. Acute Dislocation of the Metacarpal-Trapezoid Joint. Clin Orthop Surg 2016;8(2):223-7. PMID: 27247751
3. Hani, R, Jeddi, I and Berrada, MS. Divergent dislocation of the carpometacarpal joints: a case report. J Med Case Rep 2018;12(1):157. PMID: 29875012
4. Jumeau, H, Lechien, P and Dupriez, F. Conservative Treatment of Carpometacarpal Dislocation of the Three Last Fingers. Case Rep Emerg Med 2016;2016.PMID: 27703817
5. Ardente, PDF, Biayna, JC, Sarrias, JS, et al. Volar Dislocation of Second, Third and Fourth Carpometacarpal Joints in Association with a Bennet's Fracture of the Thumb Carpo-Metacarpal Dislocation: A Case Report. Open Orthop J 2017;11:1035-1040.PMID: 28979606
6. Anjum, R, Roy, A, Farooque, K, et al. An Isolated Pure Dislocation of Fifth Carpometacarpal Joint: Case Report and Review of Literature. J Orthop Case Rep 2017;7(2):14-16.PMID: 28819593
7. 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.
8. Mito, K, Nakamura, T, Sato, K, et al. Dorsal dislocations of the second to fifth carpometacarpal joints: a case report. Hand Surg 2008;13(2):129-32. PMID: 19054847
9. Ho, PK, Choban, SJ, Eshman, SJ, et al. Complex dorsal dislocation of the second carpometacarpal joint. J Hand Surg Am 1987;12(6):1074-6. PMID: 3693840
10. Silk, G, Vetharajan, N and Nagata, H. Volar dislocation of the second and third carpometacarpal joints - the Lisfranc injury of the hand? Hand Surg Rehabil 2018. [Epub] PMID: 30170770
11. Schaefer, N, Elliott, D and Loveridge, J. Volar dislocation of the index, middle, and ring carpometacarpal joints: a review. Plast Reconstr Surg Glob Open 2015;3(3):e330.PMID: 25878941
12. Henderson, JJ and Arafa, MA. Carpometacarpal dislocation. An easily missed diagnosis. J Bone Joint Surg Br 1987;69(2):212-4. PMID: 3818751
13. Mueller, JJ. Carpometacarpal dislocations: report of five cases and review of the literature. J Hand Surg Am 1986;11(2):184-8. PMID: 3958446

Reviews

1. Schaefer, N, Elliott, D and Loveridge, J. Volar dislocation of the index, middle, and ring carpometacarpal joints: a review. Plast Reconstr Surg Glob Open 2015;3(3):e330.PMID: 25878941
2. Anjum, R, Roy, A, Farooque, K, et al. An Isolated Pure Dislocation of Fifth Carpometacarpal Joint: Case Report and Review of Literature. J Orthop Case Rep 2017;7(2):14-16.PMID: 28819593

Classics

1. Whitson RO. Carpometacarpal dislocation; a case report. Clin Orthop1955;6:189-95. PMID: 13270437
2. Eskey CW, Jones DT. Carpometacarpal dislocation; a case report. Clin Orthop1956;8:244-8. PMID: 13374918