Irreducible Dorsal Dislocation | Kaplan Lesion | Volar Plate Interposition
- Index MCP is most common site for complex dorsal dislocation
- Volar plate and sesamoids interpose between metacarpal head and proximal phalanx base
- Skin dimple at proximal palmar crease is pathognomonic for complex injury
- Traction alone tightens the noose around the metacarpal neck and fails
- The interposed plate sits DORSAL to the metacarpal head - so the dorsal approach, not the volar, looks directly at the block
- “Always examine for skin dimple before attempting reduction
- “Attempt closed reduction only once under adequate anaesthesia
- “Dorsal approach splits the volar plate LONGITUDINALLY, after which the joint reduces spontaneously (Becton)
- “Neither approach is proven superior: dorsal favours motion, volar favours grip - and volar carries the nerve risk
- “Post-reduction stability determines early motion versus immobilisation
Skin dimple at the proximal palmar crease indicates volar plate interposition. This is a reliable marker that closed reduction will fail and open reduction is required.
Noose effect: Traction tightens the volar plate, flexor tendons and lumbricals around the metacarpal neck, locking the proximal phalanx in hyperextension. Repeated forceful traction worsens interposition.
Classic complex dislocation described by Kaplan: metacarpal head buttonholes through the volar structures with volar plate, sesamoids and flexor sheath acting as the irreducible block.
Neither approach is proven superior — but know the anatomical argument, because it is the opposite of what most candidates say. The interposed volar plate lies dorsal to the metacarpal head, so it is the dorsal approach that looks straight at it; Becton explicitly found the volar (Kaplan) approach gives a limited view of the plate and puts the digital nerves at risk. From dorsal the plate is split longitudinally and the joint reduces spontaneously.
- Diagnosis
- Irreducible on gentle traction attempt
- Treatment
- Urgent open reduction (dorsal or volar - see the approach evidence)
- Key Pearl
- Do not repeat forceful closed attempts
- Diagnosis
- Reduces easily with traction and flexion
- Treatment
- Closed reduction, 3 weeks extension block splint
- Key Pearl
- Simple dislocation has excellent prognosis
- Diagnosis
- Possible radial collateral ligament interposition
- Treatment
- Dorsal approach for reduction
- Key Pearl
- Always confirm stability after reduction
VOLARKaplan Lesion Components
Hook:VOLAR structures create the Kaplan lesion - remember the anatomy to plan your approach!
V-DORSALSurgical Approach Choice
Hook:V-DORSAL guides the decision between volar visualisation and dorsal simplicity!
Overview and Epidemiology
Complex dorsal metacarpophalangeal dislocations are true orthopaedic emergencies in the hand. The index finger is involved in over 50 percent of cases (53.8% in the largest surgical series, PMID 41906838). The wider set of digital injuries sits in finger dislocations; for the systematic films that accompany any of them see imaging of the wrist and hand, and for the sensory mapping that localises the nerve at risk, hand examination and clinical localisation. Misdiagnosis as a simple dislocation leads to repeated failed reduction attempts, cartilage damage, and ultimately open reduction that could have been planned from the outset. Recognition of the pathognomonic skin dimple allows immediate preparation for surgery and avoids iatrogenic injury from forceful traction.
- Hyperextension force: Fall on outstretched hand with MCP hyperextended
- Direct blow: Dorsal force driving proximal phalanx into hyperextension
- Sports injury: Ball sports, gymnastics, martial arts
- High-energy trauma: Road traffic accidents with associated fractures
- Irreducible without surgery: Volar plate interposition blocks closed reduction
- Neurovascular risk: Radial digital nerve stretched over metacarpal head
- Joint surface damage: Prolonged dislocation abrades articular cartilage
- Stiffness and pain: Delayed treatment leads to permanent loss of motion
Volar Plate Anatomy and the Mechanism of Interposition
The whole pathology turns on the anatomy of the volar plate, so it is worth setting out explicitly. The same volar-plate mechanics govern the interphalangeal injuries covered in finger dislocations, and the destroyed-joint endpoint of a missed injury is the subject of MCP joint arthritis. The volar plate is a thick fibrocartilaginous structure on the palmar surface of the MCP joint with two very different attachments, and it is this asymmetry that explains why a hyperextension force makes it irreducible.
- Character
- Firm, fibrocartilaginous, strong
- Behaviour in hyperextension
- Stays attached to the phalanx and is dragged with it
- Character
- Thin, membranous, weak (the critical zone)
- Behaviour in hyperextension
- Avulses or ruptures here first
- Character
- Embedded within the volar plate substance
- Behaviour in hyperextension
- Add a bony wedge to the interposed block
In a dorsal dislocation the volar plate tears at its weak proximal (metacarpal) origin while remaining firmly attached distally to the proximal phalanx base. As the phalanx displaces dorsally the freed volar plate is carried with it and flips to lie dorsal to the metacarpal head, buttonholed between the metacarpal head and the phalangeal base. The deep transverse metacarpal ligament tethers it to its neighbours, and with the lumbrical on the radial side and the flexor tendons on the ulnar side it completes the constricting noose around the metacarpal neck.
The volar plate's strong distal and weak proximal attachments mean hyperextension avulses it from the metacarpal, not the phalanx. Because it stays tethered to the phalanx and flips over the metacarpal head, it becomes the irreducible interposed block - the anatomical basis of the simple-versus-complex distinction.
Pathophysiology
The metacarpal head is cam-shaped with a wider dorsal articular surface. In hyperextension the proximal phalanx base rides over the metacarpal head. The volar plate, which is fibrocartilaginous and contains the sesamoids in the index and middle fingers, folds into the joint space. The flexor tendons, lumbricals and deep transverse metacarpal ligament form a constricting noose around the metacarpal neck. This combination prevents any amount of traction or manipulation from achieving reduction.
- Role in Block
- Primary interposed structure
- Anatomic Location
- Folds between metacarpal head and phalanx base
- Release Method
- Longitudinal split - from dorsal it comes into full view (Becton)
- Role in Block
- Bony component of volar plate
- Anatomic Location
- Embedded in volar plate substance
- Release Method
- Divided with volar plate or excised if fractured
- Role in Block
- Form constricting noose
- Anatomic Location
- Ulnar and radial to metacarpal neck
- Release Method
- A1 pulley release if required
- Role in Block
- Radial side interposition
- Anatomic Location
- Between metacarpal head and volar plate
- Release Method
- Gentle retraction or partial release
Traction increases tension on the volar structures already encircling the metacarpal neck. The proximal phalanx remains locked in hyperextension. Forceful or repeated attempts cause further cartilage abrasion and soft-tissue swelling, converting a surgical case into a more difficult one.
The radial digital nerve is stretched over the prominent metacarpal head in index finger dislocations. The ulnar digital nerve is less commonly at risk. Both must be identified and protected during any volar approach. The radial collateral ligament is frequently torn and should be repaired after reduction.
Classification and Types
Classification by Digit Involved
- Frequency
- Most common (over 50 percent)
- Anatomic Features
- Radial sesamoid present, narrow web space
- Surgical Notes
- Protect the radial digital nerve, especially if approaching from volar
- Frequency
- Second most common
- Anatomic Features
- Two sesamoids, wider head
- Surgical Notes
- Similar volar plate interposition pattern
- Frequency
- Less common
- Anatomic Features
- No radial sesamoid in little finger
- Surgical Notes
- May reduce more easily, check for associated injury
The index finger predominance relates to its position at the radial border and the presence of a radial sesamoid that contributes to the bony block.
Clinical Assessment
- Mechanism: Hyperextension injury, fall onto outstretched hand
- Timing: Acute presentation versus delayed or missed injury
- Previous attempts: Number and force of closed reduction attempts
- Associated injuries: Other hand trauma, open wounds, nerve symptoms
- Inspect: Hyperextended MCP posture, skin dimple at proximal palmar crease
- Palpate: Metacarpal head prominence in palm, tender volar structures
- Neurovascular: Test radial and ulnar digital nerves, capillary refill
- Attempt reduction: Single gentle attempt only under digital block or sedation
Technique: Examine the palm with the MCP in maximal hyperextension. A transverse or oblique skin dimple at the proximal palmar crease directly over the metacarpal head indicates that the volar plate has buttonholed and is interposed.
Interpretation: Presence of the dimple = complex irreducible dislocation. Absence does not completely exclude complexity, but makes simple dislocation more likely.
Key point: Document the dimple before any reduction attempt. Its presence changes management from attempted closed reduction to planned open reduction.
- Posture
- MCP hyperextension, PIP flexed
- Discriminating Finding
- Skin dimple, irreducible on traction
- Key Test / Imaging
- Clinical diagnosis, X-ray confirms direction
- Posture
- MCP hyperextension, reducible
- Discriminating Finding
- No skin dimple, reduces with traction-flexion
- Key Test / Imaging
- Post-reduction X-ray, assess stability
- Posture
- MCP flexed, proximal phalanx volar
- Discriminating Finding
- Extensor interposition, rare
- Key Test / Imaging
- Dorsal approach usually required
- Posture
- PIP flexed, MCP neutral
- Discriminating Finding
- History of triggering, no trauma
- Key Test / Imaging
- A1 pulley injection trial
Always obtain orthogonal radiographs before and after any reduction attempt — see imaging of the wrist and hand for the systematic read. Associated injuries include metacarpal head fracture, proximal phalanx base fracture, collateral ligament avulsion, and sesamoid fracture. These change the post-reduction protocol and may require internal fixation. The metacarpal-head osteochondral fracture is the one that should influence your approach: Becton's third stated advantage of the dorsal approach is that it permits accurate reduction and fixation of exactly this fracture, which he described as frequently accompanying the dislocation. The main differential for a locked digit without trauma is trigger finger.
Investigations
Imaging Protocol
Views: PA, true lateral, and oblique of the affected ray
Look for: Direction of dislocation, associated fractures of metacarpal head or proximal phalanx base, sesamoid displacement, joint incongruity
Clinical correlation: The lateral view confirms dorsal versus volar displacement and guides approach planning
Indication: Intra-articular fracture, comminuted metacarpal head, or to assess sesamoid integrity
Threshold: Fragments involving greater than 20 percent of articular surface or with greater than 2 mm step-off warrant ORIF consideration
Pre-op planning: Helps decide between volar plate repair versus excision of comminuted fragments
Indication: Delayed presentation with fibrosis, to assess cartilage status and volar plate integrity
Findings: Interposed volar plate scarring, chondral loss, possible osteochondral defects
Surgical planning: Determines whether joint salvage or arthroplasty is more appropriate
X-rays are essential to confirm the diagnosis and exclude fracture, but the decision for open reduction is clinical based on the skin dimple and failed closed reduction attempt. Do not delay surgical exploration waiting for advanced imaging in an acute irreducible dislocation.
Closed Reduction Technique: One Gentle Attempt, Push Not Pull
A single gentle closed reduction attempt is appropriate for an acute dorsal MCP dislocation before complexity is confirmed - it is curative for a simple dislocation or subluxation and does no harm when done correctly. If a skin dimple is present, or this one gentle attempt fails, proceed to open reduction and do not repeat. The technique matters because the common instinct - longitudinal traction - is exactly what locks a complex injury.
- Do
- Wrist block or sedation; flex the wrist and IP joints to slacken the long flexors
- Avoid
- Manipulating an awake, guarding hand
- Do
- Accentuate MCP hyperextension first, then push the base of the proximal phalanx distally and volarly to roll it over the metacarpal head into flexion
- Avoid
- Longitudinal traction, which tightens the volar plate, flexor and lumbrical noose
- Do
- One gentle attempt only, then reassess
- Avoid
- Repeated forceful attempts that abrade cartilage and worsen interposition
- Do
- Confirm concentric reduction on radiographs, test stability, extension-block splint
- Avoid
- Discharge without a post-reduction film or stability check
The key manoeuvre is to keep the phalangeal base in contact with the metacarpal head and push it distally over the head with the wrist flexed - not to pull along the axis of the finger. Longitudinal traction tightens the noose around the metacarpal neck and can convert a reducible subluxation into an entrapped complex dislocation.
NOOSEReduction Failure Reasons
Hook:The NOOSE around the metacarpal neck explains why traction fails every time!
Management Algorithm
Acute Complex Dorsal Dislocation (Index or Middle Finger)
Goal: Achieve concentric reduction with minimal articular damage and restore stable motion
Surgical Protocol
Timing: Within 24 hours if possible, before swelling peaks Consent: Risk of stiffness, nerve injury, possible need for collateral repair, infection Equipment: Hand table, fluoroscopy, fine rongeurs, 3-0 or 4-0 nonabsorbable suture
Incision: Direct dorsal longitudinal incision through skin and extensor tendon over the MCP Rationale: The entrapped volar plate is trapped over the dorsal aspect of the metacarpal head, so this approach brings the main blocking structure into full view - the anatomical reason Becton proposed it Reduction sequence: Split the volar plate longitudinally; the dislocation then reduces spontaneously as the flexor tendons and lumbrical slip past the metacarpal head - no forceful manipulation needed Also allows: Accurate reduction and fixation of the metacarpal-head osteochondral fracture that frequently accompanies this injury Repair: Repair the extensor tendon split and any sagittal band rent to restore stability
Incision: Zigzag or Brunner incision centred over MCP, extending proximally and distally as needed Identify and protect: Radial and ulnar digital neurovascular bundles - the radial digital nerve is stretched over the metacarpal head and is the structure at risk in this approach Expose volar plate: Divide A1 pulley if needed, identify interposed volar plate and sesamoids Reduction sequence: Divide the volar plate longitudinally, retract lumbricals, reduce the phalanx by flexing and pushing the base over the head Know the trade-off: Becton's stated objection is that the view of the plate from volar is limited (the plate sits dorsal to the head) and the digital nerves are easily damaged; the counterweight is that volar reconstruction gave the better grip strength in the only head-to-head series
Splint: Extension block splint at 20-30 degrees flexion for 2-3 weeks Early motion: Protected active ROM from week 2-3 under therapist supervision Strengthening: Grip strengthening from week 6, return to sport at 10-12 weeks
After reduction, test passive MCP extension under fluoroscopy. If the joint tends to redislocate in extension, repair the radial collateral ligament and consider temporary K-wire stabilisation in 30 degrees flexion for 3 weeks. Document stability before closure.
Complications
This injury has no cohort large enough to support precise complication rates. The published literature is case reports, technique descriptions and small series — the largest comparative series in this topic has 13 patients. The figures in the table below are the ranges conventionally quoted in hand-surgery teaching; they are not derived from a series capable of estimating them, and no registry collects MCP dislocations.
Quote them as orders of magnitude with the uncertainty attached — "stiffness is the commonest problem and is the main thing we are trying to prevent with early motion" is both truer and more useful than a spuriously precise percentage. The one nerve figure with a real denominator is small and specific: transient hypoesthesia in two of three volar cases in the 2026 series (PMID 41906838).
- Conventionally quoted range
- 30-50 percent of open reductions
- Risk Factors
- Delayed presentation, repeated reduction attempts
- Management
- Early protected motion, aggressive hand therapy
- Conventionally quoted range
- 5-10 percent (mostly neuropraxia)
- Risk Factors
- Volar approach, stretched nerve over metacarpal head
- Management
- Meticulous identification, microsurgical repair if transected
- Conventionally quoted range
- Less than 10 percent with proper repair
- Risk Factors
- Unrepaired collateral ligament, inadequate splinting
- Management
- Collateral repair, extension block splint, possible temporary pinning
- Conventionally quoted range
- Less than 5 percent
- Risk Factors
- Open injury, delayed surgery, diabetes
- Management
- Prophylactic antibiotics, meticulous wound care
- Conventionally quoted range
- Common after greater than 6 weeks delay
- Risk Factors
- Prolonged dislocation, cartilage abrasion
- Management
- Arthroplasty or arthrodesis if symptomatic
The radial digital nerve is at greatest risk during the volar approach to an index finger dislocation. It is stretched over the metacarpal head and can be mistaken for a fibrous band. Always identify and protect both digital nerves before dividing any volar structures. A missed nerve transection causes permanent sensory loss and is a common source of litigation — see digital nerve compression for the sensory territory involved. This risk is approach-specific and is the single most defensible reason to consider the dorsal approach: it is the disadvantage Becton named in 1975, and the only nerve complications in the 2026 comparative series were in volar cases.
Outcomes and Prognosis
The direction of this relationship — earlier reduction does better — is consistent across every published series and is the point the examiner wants. The percentages themselves are conventional teaching estimates rather than measured figures (no cohort of this injury is large enough to generate them), and "functional ROM" is not a defined endpoint, so quote the trend and the mechanism rather than the numbers if you are pressed on where they come from.
- Treatment
- Open reduction, collateral repair if needed
- Expected Outcome
- 80-90 percent achieve functional ROM
- Long-term Function
- Excellent return to work and sport
- Treatment
- Open reduction, more extensive release
- Expected Outcome
- 60-75 percent functional ROM
- Long-term Function
- Good for daily activities, some stiffness
- Treatment
- Open reduction or salvage procedure
- Expected Outcome
- 40-60 percent useful arc, variable pain relief
- Long-term Function
- Functional improvement but rarely normal motion
Best prognosis: Acute presentation, single gentle reduction attempt, concentric reduction, repaired collateral ligament, compliant early motion protocol.
Poor prognosis: Delayed diagnosis greater than 3 weeks, multiple failed closed attempts, chondral damage on metacarpal head, patient non-compliance with therapy.
Key threshold: 3 weeks from injury - outcomes decline significantly after this window, with higher rates of stiffness and post-traumatic arthritis.
Guidelines, Registries & Global Practice
- Index finger MCP is the most common site worldwide for complex dorsal dislocation
- Hyperextension falls are the dominant mechanism across all regions and age groups
- Sports and occupational injuries account for the majority of presentations
- Missed diagnosis remains a problem in emergency settings where skin dimple is not routinely sought
- High-resource centres: early MRI, hand therapist involvement, fluoroscopic stability assessment
- Limited-resource settings: clinical diagnosis, plain radiographs only, volar approach with loupe magnification
- Universal principle: prompt recognition of the skin dimple and avoidance of repeated closed attempts determines outcome more than technology
- Surgery: concentrated in specialist hand units globally, with similar techniques reported from Europe, North America, Asia and Australia
- Diagnosis emphasis
- Skin dimple recognition, single closed attempt only
- Acute treatment
- Open reduction within 24 hours, nerve protection
- Surgical approach
- No approach mandated; choose on the obstructing anatomy
- Diagnosis emphasis
- Clinical diagnosis, radiographs to exclude fracture
- Acute treatment
- Urgent referral to hand surgery, avoid repeated manipulation
- Surgical approach
- Volar or dorsal according to surgeon preference
- Diagnosis emphasis
- High index of suspicion in hyperextension injuries
- Acute treatment
- Open reduction, collateral ligament assessment
- Surgical approach
- Both approaches accepted, stability testing essential
- Diagnosis emphasis
- Assess for associated metacarpal head fracture
- Acute treatment
- Anatomic reduction, protect soft tissues
- Surgical approach
- Approach dictated by fracture pattern and surgeon experience
There is no dedicated international registry for MCP dislocations, and no society guideline mandates a surgical approach — the row above should be read as the emphasis each body places on diagnosis and timing, not as a quotable position on volar versus dorsal. Evidence is derived from small case series, technique descriptions and anatomic studies; the largest comparative series has 13 patients. The consistent message is that recognition of the skin dimple changes management from closed to open reduction, that nerve protection during the volar approach is mandatory, and that outcomes are time-dependent with best results when reduction occurs within 24-48 hours. Where the literature is this thin, the examiner is testing whether you know how thin it is — say so, and reason from the anatomy of the block rather than citing a preference as though it were established.
Record in every dorsal MCP dislocation:
- Presence or absence of skin dimple at proximal palmar crease
- Number and result of closed reduction attempts
- Neurovascular status before and after any manipulation
- Intraoperative stability assessment and structures repaired
- Post-reduction splint position and rehabilitation plan
A missed complex dislocation leading to permanent stiffness or nerve injury is a recurring source of complaints worldwide. Always document the skin dimple examination and the rationale for proceeding to open reduction.
Controversies & Areas of Uncertainty
The one head-to-head comparison is a 13-patient retrospective series, so treat the direction of travel as a hint, not a verdict (PMID 41906838). The dorsal approach was used in 76.9% and gave greater MCP flexion (85.8° vs 78.4°), a smaller extension lag (−1.8° vs −4.2°), lower disability (QuickDASH 4.0 vs 8.8) and earlier return to sport (11.5 vs 14.4 weeks). Volar reconstruction gave the better grip strength (107.5% vs 90.9% of the other hand). None of these differences reached statistical significance — with 13 patients that is expected — though effect sizes were large (d ≥ 0.8). The one asymmetry that is not a wash: the only reported nerve complication was transient post-operative hypoesthesia, in two cases, and both were volar — two of the three volar patients in the series — which matches Becton's fifty-year-old objection. Surgeon experience still reasonably drives the choice; what is no longer defensible is claiming the volar approach gives the better view of the plate.
Some authors advocate routine repair of the radial collateral ligament after reduction, while others repair only when residual instability is demonstrated on stress testing. No comparative studies exist. Most surgeons repair obvious tears and test stability intraoperatively before deciding.
Extension block splinting at 20-30 degrees for 2-3 weeks is widely practised, but the precise angle and duration lack high-quality evidence. Early protected motion is favoured to minimise stiffness, yet too much motion risks recurrent subluxation. Therapist-led protocols vary between centres.
Temporary K-wire stabilisation across the reduced MCP joint is used by some when stability is marginal. Others avoid pinning to allow early motion. No randomised data exist. Decision is individualised based on intraoperative stability and patient compliance.
MCQ Practice Points
Q: Which structure is the primary block to reduction in a complex dorsal MCP dislocation? A: The volar plate with embedded sesamoids. In hyperextension the volar plate folds into the joint space between the metacarpal head and the base of the proximal phalanx. The sesamoids act as a bony wedge. The flexor tendons, lumbricals and deep transverse metacarpal ligament form a secondary constricting noose around the metacarpal neck.
Q: What is the pathognomonic clinical finding in a complex MCP dislocation? A: A skin dimple at the proximal palmar crease. This transverse or oblique dimple directly overlies the metacarpal head and indicates that the volar plate has buttonholed through the joint capsule. Its presence confirms that closed reduction will fail and open reduction is required.
Q: Why does longitudinal traction fail to reduce a complex MCP dislocation? A: Traction tightens the noose. The volar plate, flexor tendons and lumbricals already encircle the metacarpal neck. Longitudinal force increases tension on these structures, locking the proximal phalanx in hyperextension rather than disengaging the interposed tissue. A single gentle attempt is acceptable, but repeated traction causes further damage.
Q: What are the advantages of the volar versus dorsal approach for complex MCP dislocation? A: This is the question most candidates answer backwards. The interposed volar plate is trapped dorsal to the metacarpal head, so the dorsal approach is the one that brings the main blocking structure into full view — Becton's explicit objection to the volar (Kaplan) approach was that it gives a limited view of the plate and that the digital nerves are easily damaged during the exposure. From dorsal, the plate is split longitudinally and the joint reduces spontaneously; the approach also permits fixation of the metacarpal-head osteochondral fracture that often accompanies this injury. The volar approach still has a place: it gives direct access to the sesamoids, lumbricals and collateral ligaments, and in the only head-to-head series it produced the better grip strength. Neither is proven superior — say that, then justify whichever you choose on the obstructing anatomy in front of you.
Q: What is the recommended post-reduction protocol after open reduction of a complex MCP dislocation? A: Extension block splint at 20-30 degrees flexion for 2-3 weeks, followed by protected active motion under hand therapy supervision. Early motion prevents stiffness while the block splint maintains reduction. Strengthening begins at 6 weeks with return to full activity at 10-12 weeks. Stability must be confirmed intraoperatively before deciding on splint position.
Q: Which nerve is most at risk during the volar approach to an index finger MCP dislocation? A: The radial digital nerve. It is stretched over the prominent metacarpal head and can be mistaken for a fibrous band. Careful identification and protection of both digital nerves before dividing any volar structures is mandatory. Nerve injury causes permanent sensory loss on the radial border of the index finger.
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 32-year-old mechanic presents 6 hours after a fall onto his outstretched right hand. His index finger MCP is locked in 60 degrees of hyperextension. There is a clear skin dimple at the proximal palmar crease. Gentle traction under digital block fails to reduce the joint. What is your diagnosis and management plan?”
“A 45-year-old woman presents 5 weeks after a fall. She was told her index finger was 'sprained' and was treated with buddy strapping. She now has a stiff, painful MCP joint with 40 degrees hyperextension deformity, numbness on the radial side of the index finger, and a fixed skin dimple. Radiographs show early joint space narrowing. How would you manage this?”
Key Anatomy
- Volar plate with sesamoids is primary block to reduction
- Flexor tendons, lumbricals and deep transverse ligament form constricting noose
- Index finger most commonly affected due to radial sesamoid and border position
- Radial digital nerve stretched over metacarpal head and at risk in volar approach
Diagnosis
- Skin dimple at proximal palmar crease is pathognomonic for complex injury
- Irreducible on gentle traction confirms volar plate interposition
- X-ray: PA, lateral and oblique to confirm direction and exclude fracture
- High index of suspicion in any hyperextension MCP injury
Treatment Algorithm
- Simple dislocation: single closed reduction attempt, extension block splint 3 weeks
- Complex (skin dimple or failed reduction): open reduction, volar or dorsal approach
- Acute (under 24 hours): best outcomes with prompt open reduction
- Chronic (over 3 weeks): consider salvage arthroplasty if cartilage destroyed
Surgical Pearls
- Dorsal approach (Becton): plate lies DORSAL to the head so this gives the FULL view; split it LONGITUDINALLY and it reduces spontaneously; less nerve risk; allows MC-head fracture fixation
- Volar approach (Kaplan): direct access to sesamoids and collaterals, better grip in the one head-to-head series - but limited view of the plate and the digital nerves are at risk
- Neither approach is proven superior (best comparison n=13, no significant differences)
- After reduction: test stability, repair collateral ligament if torn
- Splint: extension block 20-30 degrees flexion for 2-3 weeks then early motion
Complications
- Residual stiffness: 30-50 percent, mitigated by early protected motion
- Digital nerve injury: 5-10 percent, mostly neuropraxia, prevent by identification
- Recurrent instability: less than 10 percent with proper collateral repair
- Post-traumatic arthritis: common after delayed presentation greater than 3 weeks
Evidence Base and Key Trials
Closed dislocation of the metacarpophalangeal joint of the index finger
- Classic early description of dorsal metacarpophalangeal dislocation of the index finger, distinguishing the simple (reducible) from the complex (irreducible) injury
- The complex/irreducible dislocation is characterised by interposition of the volar plate, which blocks closed reduction
- A puckered skin dimple in the proximal palm is a clinical sign of the complex injury
- Open reduction is required once a dislocation is irreducible by closed means
A simplified technique for treating the complex dislocation of the index MCP joint
- Described a direct dorsal longitudinal approach (through skin and extensor tendon) for the complex dislocation of the index MCP joint, as an alternative to Kaplan's volar approach
- States two explicit disadvantages of the volar (Kaplan) approach: the digital nerves are easily damaged during exposure, and there is a LIMITED VIEW of the entrapped volar plate because the plate lies dorsal to the metacarpal head
- The interposed fibrocartilaginous volar plate is brought into full view and split longitudinally, after which the dislocation reduces SPONTANEOUSLY as the flexor tendons and lumbrical slip past the metacarpal head
- Stated advantages over the volar approach: full exposure of the volar plate (the main structure blocking reduction), digital nerves less apt to be damaged, and accurate reduction and fixation of the frequently-associated metacarpal-head osteochondral fracture
Irreducible metacarpophalangeal joint dislocations: Clinical characteristics, surgical approaches, and outcomes
- Retrospective series of 13 surgically-treated irreducible MCP dislocations (mean age 29.2 years, range 7 to 78); the index finger was most often involved (53.8%) and dorsal dislocations predominated (76.9%)
- A dorsal approach was used in 76.9% and gave greater MCP flexion (85.8 vs 78.4 degrees), a smaller extension lag (-1.8 vs -4.2 degrees) and lower disability (QuickDASH 4.0 vs 8.8)
- Volar reconstruction gave superior grip strength at 107.5 percent of the contralateral hand versus 90.9 percent - exceeding baseline
- Return to sport was earlier after the dorsal approach (11.5 vs 14.4 weeks)
- No difference reached statistical significance, but effect sizes were large (d of 0.8 or more); transient post-operative hypoesthesia occurred in two cases, both volar
Kaplan's Lesion: A Case Report On The Complex Dislocation Of The Index Finger In A Weightlifter
- Case report of complex index finger MCP dislocation (Kaplan lesion) in a weightlifter successfully managed with open reduction