Carpalmetacarpal Joints: Understanding Injuries & Managing CMC Pain

Facts *** Usually the result of high-energy injuries
* Simple dislocations are rare, most are fracture-dislocations
* Hand compartments: dorsal interossei (4), palmar interossei (3), adductor pollicis, thenar and hypothenar
* Compartment syndrome: sustained increase in compartment pressure due to inflammation and edema in one or more of the hand compartments leading to vascular compromise and muscle death
* Signs include tense swelling, pain out of proportion to injury and loss of motion
* Sensory exam may be normal
* Hand may assume intrinsic minus position (MCP extension, IP flexion)
* Compartment pressures must be measured when clinical signs of compartment syndrome are present
* Pressure > 15-20 mmHg warrants release of all 10 compartments
* Transverse carpal ligament requires release as well
Thumb (1st MC-trapezium) :
* Most occur from axial loading of a partially flexed thumb
* Joint is structured as a reciprocal saddle joint between the 1st MC and the trapezium
* Volar oblique ligament maintains stability
* Dorsal dislocations involve disruption of the dorsoradial ligament
* Most stable in pronation and extension
* Radial artery passes beneath abductor pollicis longus (APL) and extensor pollicis brevis (EPB) just proximal to the CMC joint
* Deforming forces:
* Adductor pollicis: adduction and supination
* APL: radial and proximal
Fingers (2nd MC-trapezoid, 3rd -capitate, 4th/5th -hamate) :
* Dislocations of the lesser CMC joints are rare due to relatively rigid anatomic configuration
* Strong ligaments provide stability and form a rigid transverse arch
* 2nd and 3rd CMC joints allow < 5° of motion and form the stable keystone of the transverse and longitudinal arch of the hand
* 4th and 5th CMC joints allow 15° and 25° of motion respectively
* Injuries of the 4th and 5th CMC joints occur more frequently
* 2nd CMC base is particularly stable due to its wedge shaped articulation with the trapezoid
* Patients present with pain, swelling and deformity
* Most CMC dislocations are dorsal
* Thumb dislocations often present reduced, requiring stress testing to determine residual instability
* Compare with contralateral side
* The ulnar nerve (motor) is at risk with 5th CMC joint dislocations
* Deep palmar arterial arch is at risk with 3rd CMC joint dislocations
* Fracture-dislocations involving the MC bases and/or the corresponding carpal bones are common
* Disruption of the normal dorsal cascade of MCP joints suggests shortening Imaging** Radiographs
* PA, oblique and lateral views of the hand are standard examinations

Normal PA hand

Normal oblique hand

Normal lateral hand

• Thumb series: true AP, oblique, lateral
  • Robert view: true AP taken with hand in IR, dorsum of the thumb on the plate
• Finger series: PA, oblique and lateral
  • Lateral demonstrates avulsion fractures
  • MC fractures may be better visualized with lateral and off-lateral views
  • 5th MC base best visualized with 30° pronated view Classification * Descriptive Open or closed
    Involved digit
    Direction
    Presence of fractures
• Base of thumb MC fracture-dislocations :
  • Often associated with thumb CMC dislocations
    Type I : Bennett's fracture: partial articular fracture with volar lip fragment
• Represents avulsion of the strong volar oblique ligament from its insertion on the MC
• MC is pulled proximally by abductor pollicis longus (APL)
  Type II : Rolando's fracture: complete articular fracture (comminuted Bennett's) with Y or T pattern

Base of thumb fracture-dislocations

• Base of 5th MC fracture-dislocation :
  • Reverse-Bennett's fracture: the radial-volar fragment remains reduced while remainder of the MC is pulled proximally by extensor carpi ulnaris (ECU)

Reverse Bennett's fracture

• OTA : carpal-metacarpal joints (70-C)
  1. 1st Metacarpal-trapezial dislocation
  2. 2nd MC-trapezium dislocation
  3. 3rd MC-capitate dislocation
  4. 4th MC-hamate dislocation
  5. 5th MC-triquetrum dislocation
  6. Multiple carpal-metacarpal dislocations Treatment * Acute treatment : dislocations and fracture-dislocations should be grossly reduced and splinted
  7. Reduction maneuver: longitudinal traction with pressure on the base of the MC to reverse deformity
     Thumb CMC dislocations :
• Operative : preferred in almost all cases to decrease instability and arthrosis
  • Closed reduction and pinning does not adequately treat this injury
  • Options include open ligament repair with pinning of the joint or early open ligament reconstruction with flexor carpi radialis graft
    Thumb CMC fracture-dislocations :
• Operative : preferred in almost all cases to decrease instability and arthrosis
  • Percutaneous pinning: preferred for Bennett's and comminuted Rolando's fractures
  • Following acceptable closed reduction, K-wires are passed across the MC shaft and into the adjacent 2nd MC and/or the trapezium
  • ORIF: indicated for less comminuted Rolando's fractures
  • Fixation is achieved with screws ± plate
    Finger CMC dislocations and fracture-dislocations :
• Nonoperative : indicated for simple dislocations and some minimally displaced fracture-dislocations that are stable after reduction
  • Reductions of unstable fracture-dislocations cannot be held effectively reduced with a splint
• Operative : generally preferred for most injuries
  • Percutaneous pinning: following acceptable closed reduction, K-wires are passed across the metacarapal shaft and into the adjacent stable MCs and/or the carpus
  • ORIF: indicated for failed closed reduction or open injuries
  • Stabilization can be performed with K-wires
  • Reverse Bennett's fracture: often requires ORIF with wire or lag screw due to deforming forces Complications
• Compartment syndrome: rare
  • Compartment pressure > 15-20 mmHg warrants release of all 10 compartments
• Nerve injuries: the ulnar nerve (motor) is at risk with 5th CMC joint dislocations
• Posttraumatic arthritis: 2nd and 3rd CMC joints are highly amenable to arthrodesis
• Residual instability: can be addressed with arthrodesis
  • 5th CMC can be fused in 20° of flexion with little loss of hand motion
• Vascular injuries: the deep palmar arterial arch is at risk with 3rd CMC joint dislocations