Sagittal Band Rupture - Hand

Introduction

Overview
- Sagittal band rupture leads to leads to dislocation of the extensor tendon and may be caused by trauma or by a chronic inflammatory process such as rheumatoid arthritis.
  - when it is caused by trauma it is also known as a "boxer's knuckle".
  - acute traumatic injuries are treated with splinting where chonic injuries often require surgical reconstruction
Epidemiology
- demographics
  - more common in pugilists
    - index and middle finger in professionals
    - ring and little finger in amateurs
- 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
Mechanisms
- 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 of Closed SB Injury
Type	Description	Image
Type I	SB injury without extensor tendon instability
Type II	SB injury with tendon subluxation
Type III	SB 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

MCP joint 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 one week)
Operative
- direct repair (Kettlekamp)
  - indications
    - chronic injuries (more than one week) where primary repair is possible
    - professional athlete
- extensor centralization procedure (realignment)
  - indications
    - chronic injuries (more than one week) 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