Sagittal Band Rupture - Hand

summary
- Sagittal Band Ruptures lead to dislocation of the extensor tendons and may be caused by trauma or by a chronic inflammatory process such as rheumatoid arthritis.
- Diagnosis is made clinically with the inability to initiate MCP extension but the ability to hold MCP in extension once passively extended.
- Treatment of acute traumatic injuries is generally splinting where chronic injuries often require surgical reconstruction.

Epidemiology
- Demographics
  - more common in pugilists
    
    index and middle finger in professionals
    
    ring and little finger in amateurs
- Anatomic location
  - the middle finger is most commonly involved
    
    index 14%
    
    middle 48%
    
    ring 7%
    
    little 31%
  - the radial SB is more commonly involved
    
    radial:ulnar = 9:1

Etiology
- Mechanism
  - traumatic
    
    forceful resisted flexion or extension
    
    laceration of extensor hood
    
    direct blow to MCP joint
  - atraumatic
    
    inflammatory (e.g. rheumatoid arthritis)
    
    spontaneously during routine activities
- Associated conditions
  - MCP joint collateral ligament injuries

Anatomy
- Extensor mechanism comprises
  - tendons
    
    EDC/EIP/EDM
    
    lumbricals
    
    interossei
  - retinacular system
    
    sagittal bands
    
    the sagittal bands are part of a closed cylindrical tube (or girdle) that surrounds the metacarpal head and MCP along with the palmar plate
    
    origin
    
    volar plate and intermetacarpal ligament at the metacarpal neck
    
    insertion
    
    extensor mechanism (curving around radial and ulnar side of MCP joint)
    
    retinacular ligaments
    
    triangular ligament
- Sagittal band
  - function
    
    the SB is the primary stabilizer of the extensor tendon at the MCP joint
    
    juncturae tendinum are the secondary stabilizers
    
    resists ulnar deviation of the tendon, especially during MCP flexion
    
    prevents tendon bowstringing during MCP joint hyperextension
  - biomechanics
    
    ulnar sagittal band
    
    partial or complete sectioning does not lead to extensor tendon dislocation
    
    radial sagittal band
    
    distal sectioning does not produce extensor tendon instability
    
    complete sectioning leads to extensor dislocation
    
    sectioning of 50% of the proximal SB leads to extensor tendon subluxation
    
    extensor tendon
    
    instability after sectioning is greater with wrist flexion
    
    instability after sectioning is greater in the central digits (than border digits)
    
    the least stable tendon is the middle finger
    
    the most stable tendon is the little finger
    
    junctura tendinum stabilize the small finger

Classification

Rayan and Murray Classification
Type I	Sagittal band injury without extensor tendon instability
Type II	Sagittal band injury with tendon subluxation
Type III	Sagittal band injury with tendon dislocation

Presentation
- Symptoms
  - pain
    
    MCP soreness
  - swelling
    
    focal MCP swelling or tenderness
  - snapping senstion with extension
- Physical exam
  - tendon snapping
  - ulnar deviation of the digits at the MCP joint (rheumatoid arthritis)
  - inability to initiate extension
    
    can hold MCP in extension once placed there
    
    unable to extend finger from flexed MCP position (causes tendon to subluxate)
  - pseudo-triggering - key to recognize to avoid unnecessary trigger release surgery
    
    this is the snapping that takes place from subluxation and relocation
  - extensor tendon dislocation into intermetacarpal gully
    
    most unstable during MCP flexion with wrist flexed
    
    least unstable during MCP flexion with wrist extended
  - provocative test
    
    pain when extending MCP joint against resistance (with both IP joints extended)

Imaging
- Radiographs
  - required views
    
    hand PA, lateral, oblique
  - optional view
    
    Brewerton view
    
    AP with dorsal surface of fingers touching the cassette and MCP joints flexed 45deg
    
    stress view
    
    to rule out collateral ligament avulsion/injury
  - findings
    
    exclude mechanical/bony pathology limiting extension, or predisposing to sagittal band rupture
    
    may show dropped fingers and ulnar deviation in rheumatoid arthritis
- Ultrasound (dynamic)
  - indications
    
    when swelling obscures the physical exam
  - findings
    
    subluxation of EDC tendon relative to metacarpal head on MCP flexion
- MRI
  - indications
    
    to establish diagnosis of SB disruption (radial or ulnar SB)
    
    may show underlying etiology e.g. synovitis in rheumatoid arthritis
  - views
    
    axial images at the level of the long MCP
    
    with MCP joint flexed for maximum EDC tendon displacement
  - findings
    
    poor definition, focal discontinuity and focal thickening in acute injury
    
    subluxation of extensor tendon in radial direction due ulnar SB defect
    
    dislocation of extensor tendon into ulnar intermetacarpal gully radial SB defect

Differentials
- Digital collateral ligament injury
- EDC tendon rupture
- Trigger finger
- Junctura tendinum disruption
- Congenital sagittal band deficiency
- MCP joint arthritis

Treatment
- Nonoperative
  - extension splint or yoke splint for 4-6 weeks
    
    indications
    
    acute injuries (within 6 weeks)
- Operative
  - direct repair (Kettlekamp)
    
    indications
    
    chronic injuries (more than 6 weeks) where primary repair is possible
    
    professional athlete
  - extensor centralization procedure (realignment)
    
    indications
    
    chronic injuries (more than 6 weeks) where primary repair is NOT possible
    
    professional athlete

Techniques
- Extensor Centralization Procedures (Realignment)
  - anesthsia
    
    local
  - approach
    
    dorsal incision
  - reconstruction (various techniques described)
    
    trapdoor flap
    
    ulnar based partial thickness capsular flap created
    
    tendon placed deep to flap
    
    flap resutured to capsule
    
    Kilgore tendon slip
    
    distally based slip of EDC tendon on radial side
    
    looped around radial collateral ligament
    
    sutured to itself after tensioning to centralize tendon
    
    Carroll tendon slip
    
    distally based slip of EDC tendon on ulnar side
    
    routed deep to affected tendon and around radial collateral ligament
    
    sutured to itself after tensioning to centralize tendon
    
    McCoy tendon slip
    
    proximally based slip of EDC tendon
    
    looped around lumbrical insertion
    
    sutured to itself after tensioning to centralize tendon
    
    Watson EDC tendon transfer
    
    distally based slip of EDC tendon slip
    
    looped under deep transverse metacarpal ligament
    
    weaved to remaining EDC tendon after tensioning to centralize tendon
    
    Wheeldon junctural reinforcement
    
    for a middle finger radial SB rupture, the juncturae tendinum (JT) of the ring finger is divided close to the ring finger,
    
    bring JT over the extensor tendon
    
    attach JT to the torn SB
    
    fascial strips or free tendon graft
  - rehabilitation
    
    0-4 weeks
    
    resting splint MPs an IPs at 0 degrees
    
    2 weeks
    
    motion splint, MPs at 0 degrees, IPs free, most of day
    
    4-8 weeks
    
    AROM >8 weeks - progressive strengthening

Complications
- MCP flexion contracture
  - usually from non-operative treatment or delayed presentation
  - secondarily intrinsic tightness develops