carpal-metacarpal joints

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

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 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)

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
- 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

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