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DISLOCATION, THUMB METACARPOPHALANGEAL (MP) JOINT

Introduction

Metacarpophalangeal (MP) joint dislocations are rare injuries, which is primarily due to the strong connective tissue surrounding these joints and their basal location in the hand.1The index MP joint is most commonly affected, with the thumb MP joint ranking second in incidence.2,3 Thumb MP dislocations usually occur in young, active individuals and the mechanism of injury in most cases is a fall on an outstretched hand (FOOSH) that causes forcible hyperextension of the MP joint.4,5 Most thumb MP dislocations are simple, meaning there is no soft tissue within the joint and the injury can usually be reduced by closed reduction.6 Complex dislocations occur less frequently but are more likely when the dislocation is in the volar direction, often from hyperflexion or a direct blow to the dorsum of the proximal phalanx. Volar, complex, and open thumb MP dislocations are all indications for surgery.7
 

Definitions

  • A thumb MP joint dislocation occurs when the articular surface of the base of the thumb proximal phalanx is displaced off the articular surface of the head of the thumb metacarpal.

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 MP joint dislocations are done by noting the direction of the displacement of the thumb proximal phalanx relative to the head of the thumb metacarpal. The three possible directions of displacement are dorsal (most common)9, lateral, and volar.8 
    • Dorsal dislocations of the thumb MP joint are further divided into two subtypes: 
      • the hyperextension subtype (most common) where the volar base of the proximal phalanx catches on the dorsal edge of the metacarpal condyles in an extended position
      • the bayonet subtype, where the base of the proximal phalanx is displaced on top of the neck of the metacarpal in a position parallel to the longitudinal axis of the metacarpal neck.5
    • Volar dislocations are far less common than dorsal dislocations. These injuries are typically complex (irreducible) and caused by hyperflexion of the thumb MP joint or a force to the thumb proximal phalanx in flexion.7,10
  • The degree of displacement of the proximal phalanx further characterizes thumb MP dislocations. In a true complete dislocation, the articular surface of the thumb proximal phalanx is no longer in contact with the articular cartilage of the thumb metacarpal head. If there is partial contact of the cartilaginous surfaces, then this is not a true dislocation but rather a joint subluxation.8

O – Open vs closed

  • The majority of thumb MP dislocations are closed; the skin is intact, and there is no route for bacteria to contaminate the joint space.
  • Open thumb MP dislocations are rare and have only been found to account for 8% of these injuries. When present, urgent irrigation, debridement, open reduction, and ligament repair are required.11

C – Complex vs simple

  • Dorsal thumb MP dislocations may be classified with respect to their ease of reduction into 3 categories: incomplete, simple complete, and complex.12
  • Most thumb MP 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 proximal phalanx and metacarpal joint surfaces.6
  • Complex MP joint dislocations are complete, irreducible dislocations that require a surgical approach for reduction and proper alignment. They are rarely seen in the thumb but do occur, and the majority are dorsal dislocations.
    • The volar plate is the most commonly interposed structure in dorsal thumb MP dislocations, but other possible obstacles include the flexor and adductor tendons, the extensor expansion, the collateral ligaments, the joint capsule, and the sesamoid bones.5

S – Stability

  • A stable thumb MP 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 MP joint dislocation is stable to stress testing of the collateral ligaments in the radial/ulnar plane after reduction.

Thumb MP dislocation with special and complex features other than fractures

Anchor

Complex (irreducible) thumb MP dislocation

  • Complex thumb MP joint dislocations are very rare. The majority of these injuries are dorsal MP dislocations, while volar dislocations are even less common.13
  • The mechanism of injury typically involves forced MP joint hyperextension and torsional stresses that draw the volar plate or another soft-tissue structure into the thumb MP joint. The volar plate usually ruptures from its weakest proximal attachments to the metacarpal bone, remains attached to the base of the proximal phalanx, and then resides within the joint space trapped between the base of the proximal phalanx and the head of the metacarpal.12
    • Other structures that may be interposed include the flexor and adductor tendons, the extensor expansion, the collateral ligaments, the joint capsule, and the sesamoid bones.5,6
  • Physical characteristics of a complex MP dislocation include a palpable metacarpal head, slight hyperextension of the proximal phalanx base, dimpling of the volar skin near the dislocated joint, and slight ulnar deviation of the affected digit.14

Imaging

  • X-ray
    • In simple dislocations, the MP joint usually hyperextends to ~90°, while in complex dislocations, the metacarpal and proximal phalanx usually lie more parallel to each other. 5
    • In complex dislocations, radiographs typically show the MP joint to be hyperextended with the proximal phalanx dorsal and sometimes lying in a "bayonet" apposition to the metacarpal. There may be increased space between the metacarpal head and proximal phalanx suggestive of interposed soft tissue.
      • Interposition of the sesamoids between the metacarpal head and proximal phalanx is strong evidence of a complex irreducible dislocation.3
  • MRI

Treatment

  • Early diagnosis of complex thumb MP joint dislocations is very important.
  • Ideally, this is followed by open reduction and surgical anatomic repair of the interposed soft-tissue structure(s), as the likelihood of success for closed reduction in these cases is low.5,12
    • Whether a dorsal or volar approach should be used is a matter of debate, and the choice is usually based on surgeon preference.
    • Advantages of the dorsal approach include lower risk of injury to the neurovascular bundles, full visualization of a dorsally entrapped volar plate, and if present, a better management of associated osteochondral fractures; however, it requires vertical splitting of the volar plate to reduce it and the metacarpal head, which may impair long-term MP joint stability.5,12
    • A percutaneous approach is another viable option that may avoid the risks associated with an open approach.5
    • If there is still instability post reduction, consider direct ligament repair, pull out suture or bone anchor repair or K-wires to stabilize the joint preferably in approximately 25 degrees of flexion.3,12
  • Postoperatively, early motion with a dynamic extension splint helps improve the post-injury function, but there is also no consensus regarding the duration of immobilization: some authors recommend an early mobilization protocol, while others prefer immobilization for 3-4 weeks postoperatively.5,12

Complications

  • Stiffness
  • MP joint pain
  • Persistent deformity
  • Impaired ROM
  • Digital nerve damage
  • Osteoarthritis

Outcome

  • Early diagnosis, surgical repair, and therapy will usually give a positive functional outcome, but some limited ROM is to be expected.

Related anatomy6

  • Extensor tendons – central slip and lateral bands
  • Flexor tendons
  • Dorsal capsule
  • Proper collateral ligament
  • Accessory collateral ligament
  • Volar plate
  • Neurovascular bundle
  • Abductor pollicis brevis tendon
  • Opponens pollicis tendon
  • Transverse metacarpal ligament
  • Osteology of the head of the thumb metacarpal and base of the thumb proximal phalanx
  • The thumb MP joint is similar to the MP joints of the other fingers, but due to unique articular surfaces, it is more hingelike than multiaxial. The sesamoids lie anterior to the metacarpal head and articulate with it because they are embedded in the volar plate.6

Overall incidence

  • Thumb MP dislocations rank second to index MP dislocations in incidence amongst the digits. Dislocations of the little MP joint rank third, while dislocations of the long and ring MP joints are extremely rare.2,3
  • Complex thumb MP joint dislocations are very uncommon.
  • According to one study, only 8% of all MP joint dislocations are open injuries.11
  • Dorsal dislocations of the thumb MP joint are most commonly seen in young, active individuals.5
  • As of 2017, only 26 cases of volar dislocations of the thumb MP joint have been reported in the English literature.9

Related Injuries/Conditions

  • Fractures of the thumb proximal phalanx
  • Fractures of the thumb metacarpal
  • Collateral ligament injuries
  • Volar plate injuries
  • Central slip ruptures
ICD-10 Codes

  • DISLOCATION, THUMB METACARPOPHALANGEAL (MP) JOINT

    Diagnostic Guide Name

    DISLOCATION, THUMB METACARPOPHALANGEAL (MP) JOINT

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

    DIAGNOSISSINGLE CODE ONLYLEFTRIGHTBILATERAL (If Available)
    DISLOCATION THUMB: MCP Joint S63.115_S63.114_ 

    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

Symptoms
History of trauma
Thumb pain, swelling and deformity localized at the thumb MP joint
Typical History

The typical patient is a 21-year-old right-handed collegiate female tennis player. During a recent match, she dove to hit a lobbed ball, but subsequently landed with her hand gripping the racquet. This forced the thumb of her right hand into hyperextension and resulted in a closed, simple, dorsal dislocation of the thumb MP joint. Immediate pain and swelling surrounding this joint followed, and she was taken out of the match for treatment. 

Positive Tests, Exams or Signs
Work-up Options
Treatment Options
Treatment Goals
  • Reduce the dislocation
  • Analyze the thumb MP joint’s stability
  • Rehab the thumb to regain ROM and normal thumb and hand function
Conservative
  • The majority of simple, dorsal thumb MP joint dislocations can be effectively treated with early closed reduction under local anesthesia, while complex and volar dislocations typically require surgery. Anesthesia allows for a gentle reduction with minimal pain and should be applied with a radial and median nerve block at the wrist.5,6,12
    • The preferred reduction technique is hyperextension of the MP joint with direct pressure on the dorsal base of the proximal phalanx to push it gently over the metacarpal head.3
    • If necessary, flexing the interphalangeal (IP) joint and wrist will further relax an entrapped flexor pollicis longus (FPL) tendon if it is blocking reduction.
    • It is imperative not to pull and distract the proximal phalanx when attempting reduction. This opens up the MP joint space and affords the opportunity for the volar plate to flip over the metacarpal head and become trapped, converting a simple dislocation into a complex one.12
  • After reduction, performing an active ROM test and stress testing of the collateral ligaments is very important. This should be done before splinting. If the patient can actively extend and flex the thumb almost normally without it redislocating, and if the collateral ligaments are stable to stress testing, then splinting the thumb in mild flexion for comfort is indicated. The splint should be removed after ~3 weeks.4
Operative
  • Operative treatment is indicated when closed reduction fails and for open thumb MP joint dislocations, complex (irreducible) dislocations, and lateral dislocations in young individuals with a completely torn collateral ligament that is unstable.4,5,11,12
    • Surgery is also indicated for most volar dislocations of the thumb MP joint, as the rate of recurrent dislocation has been found to be high in these injuries, even with pinning.7,16
  • Surgical treatment options open reduction with or without internal fixation (ORIF).
    • Whether a dorsal or volar approach should be used is still a matter of debate.
      • The dorsal approach enables access to the dorsal capsule, the osteochondral injury on the metacarpal head, and the volar plate, and carries an extremely low risk for neurovascular injury.6,12,13
      • The volar approach involves a higher risk of digital nerve injury, but careful dissection allows for excellent visualization of involved structures. Unlike the dorsal approach, it does not require vertical splitting of the volar plate, which has been found to reduce long-term stability of the thumb MP joint.6,12
      • The dorsal approach appears to be preferable in most cases, but a volar approach may be superior in patients that present late.6,9
      • If the joint does not stay reduced except in positions of flexion, repair of the collateral ligaments should be considered. Also consider pull out suture or bone anchor repair or K-wires to stabilize the joint preferably in approximately 25 degrees of flexion.3,12
Hand Therapy

Post-treatment Management

  • Many patients with closed thumb MP joint dislocations that are reduced early can potentially exercise the thumb on their own.
  • However, patients with marked swelling and pain will need hand therapy to help reduce swelling and improve ROM and strength.
  • Surgically repaired complex thumb MP dislocations, repaired collateral ligaments, and unstable dislocations will definitely need hand therapy, custom splinting, and dynamic extension splints.
  • There is no consensus regarding the duration of immobilization after surgery: some authors recommend an early mobilization protocol, while others prefer immobilization for 3-4 weeks postoperatively.
    • One way to determine which is appropriate is to stress test the thumb MP joint after surgery to assess the degree of joint stability. If it feels stable, earlier mobilization is indicated. If it is unstable, splinting and/or K-wires are usually required to stabilize the joint.12
    • Isolated dorsal dislocations should not be immobilized for >2 weeks.5
Complications
  • Stiffness
  • Pain
  • Residual deformity
  • Weak grip
  • Neurovascular bundle damage
  • Impaired ROM
  • Reduced grip/pinch strength
  • Joint contracture
Outcomes
  • Simple thumb MP dislocations that are treated early typically have an excellent outcome, and closed reduction is more likely to be successful in the thumb MP joint than other MP joints.
    • In one series of 9 thumb MP dislocations, 8 were successfully treated with closed reduction.6,17
  • However, all patients with thumb MP joint dislocations should be warned that the MP joint on the injured side will likely remain slightly larger than the opposite MP joint because the stretched collateral ligaments are likely to heal with a little extra bulk (collagen).
  • The longer a thumb MP joint remains dislocated, the harder it is to obtain a closed reduction and the greater the chances it will require surgical intervention. These injuries are also more likely to develop osteoarthritis and have less satisfactory outcomes after surgery in terms of pain, joint stability, and ROM.12
Key Educational Points
  • Simple longitudinal traction as a reduction maneuver should be avoided because it might convert a simple dislocation into an irreducible one.12
  • Simple closed thumb MP joint dislocations can be mobilized early and should get a good outcome with minimal loss of ROM and residual deformity.
  • Unstable thumb MP joint dislocations require prolonged extension block splinting with continuous monitoring by hand therapy for splint adjustment, etc.
  • Open and complex thumb MP joint dislocations require urgent surgical treatment.
  • The literature on volar dislocations of the thumb MP joint is scant, but these injuries should be considered very carefully since they can lead to impaired grip and pinch function, and associated chronic MP joint instability.9
References

New and Cited Articles

  1. Barrera-Ochoa, S, Nunez, JH and Mir, X. Isolated open metacarpophalangeal dislocation of the little finger. Hand Surg Rehabil 2018. [Epub] PMID: 30174199
  2. Patterson, RW, Maschke, SD, Evans, PJ, et al. Dorsal approach for open reduction of complex metacarpophalangeal joint dislocations. Orthopedics 2008;31(11):1099.PMID: 19226090
  3. Murali, M, Abdul Khader, F, Sunderajan, T, et al. A rare case of closed isolated dislocation of the third metacarpophalangeal joint of the hand. J Clin Orthop Trauma 2013;4(4):199-203.PMID: 26403883
  4. Ramzi, Z, Chafik, R, Madhar, M, et al. Volar metacarpophalangeal joint dislocation: A case report. Hand Surg Rehabil 2018. [Epub] PMID: 29853350
  5. Ip, KC, Wong, LY and Yu, SJ. Dorsal dislocation of the metacarpophalangeal joint of the thumb: a case report. J Orthop Surg (Hong Kong) 2008;16(1):124-6.PMID: 18453677
  6. Dinh, P, Franklin, A, Hutchinson, B, et al. Metacarpophalangeal joint dislocation. J Am Acad Orthop Surg 2009;17(5):318-24. PMID: 19411643
  7. Potini, VC, Sood, A, Sood, A, et al. Volar dislocation of the thumb metacarpophalangeal joint with acute repair of the ulnar collateral ligament. Case Reports Plast Surg Hand Surg 2014;1(1):5-7. PMID: 27252947
  8. Merrell G, Slade J.F. 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.
  9. Yuksel, S, Adanir, O, Beytemur, O, et al. Volar dislocation of the metacarpophalangeal joint of the thumb: A case report.Acta Orthop Traumatol Turc 2017;51(4):352-354.PMID: 28457796
  10. Senda, H and Okamoto, H. Palmar dislocation of the thumb metacarpophalangeal joint: report of four cases and a review of the literature. J Hand Surg Eur Vol 2014;39(3):276-81.PMID: 23906784
  11. Diaz Abele, J, Thibaudeau, S and Luc, M. Open metacarpophalangeal dislocations: literature review and case report. Hand (N Y) 2015;10(2):333-7. PMID: 26034455
  12. Izadpanah, A and Wanzel, K. Late presentation of a complete complex thumb metacarpophalangeal joint dislocation: A case report. Can J Plast Surg 2011;19(4):139-42.PMID: 23204885
  13. Basar, H, Inanmaz, ME, Kose, KC, et al. Isolated dorsal approach for the treatment of neglected volar metacarpophalangeal joint dislocations. World J Orthop 2014;5(1):62-6.PMID: 24649416
  14. Stiles, BM, Drake, DB, Gear, AJ, et al. Metacarpophalangeal joint dislocation: indications for open surgical reduction. J Emerg Med 1997;15(5):669-71. PMID: 9348056
  15. Vandeweyer, E, Zygas, P and Libotte, M. Palmar metacarpophalangeal joint dislocation. J Hand Surg Br 1998;23(4):546-7. PMID: 9726568
  16. Beck, JD and Klena, JC. Closed reduction and treatment of 2 volar thumb metacarpophalangeal dislocations: report of 2 cases.J Hand Surg Am 2011;36(4):665-9. PMID: 21353397
  17. Takami, H, Takahashi, S and Ando, M. Complete dorsal dislocation of the metacarpophalangeal joint of the thumb. Arch Orthop Trauma Surg 1998;118(1-2):21-4.PMID: 9833099

Reviews

  1. Dinh, P, Franklin, A, Hutchinson, B, et al. Metacarpophalangeal joint dislocation. J Am Acad Orthop Surg 2009;17(5):318-24. PMID: 19411643
  2. Senda, H and Okamoto, H. Palmar dislocation of the thumb metacarpophalangeal joint: report of four cases and a review of the literature. J Hand Surg Eur Vol 2014;39(3):276-81.PMID: 23906784

Classics

  1. Dutton RO, Meals RA. Complex dorsal dislocation of the thumb metacarpophalangeal joint. Clin Orthop Relat Res1982;(164):160-4. PMID: 7067279
  2. Moneim MS. Volar dislocation of the metacarpophalangeal joint. Pathologic anatomy and report of two cases. Clin Orthop Relat Res1983;(176):186-9. PMID: 6851324
  3. Wolfe, S. W., Hotchkiss, R. N., & Green, D. P. (2011). Greens operative hand surgery(6th ed., Vol. 1). Elsevier Churchill Livingstone.
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