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  • Sagittal band (SB) rupture leads to dislocation of the extensor tendon post
    • also known as "boxer's knuckle"
  • 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
  • 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 
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
  • Symptoms 
    • MCP soreness
  • Physical exam
    • tendon snapping
    • ulnar deviation of the digits at the MCP joint (rheumatoid arthritis)
    • inability to initiate extension
    • pseudo-triggering
    • 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) 
  • 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 defec
      • dislocation of extensor tendon into ulnar intermetacarpal gully radial SB defect  
  • MCP joint collateral ligament injury
  • EDC tendon rupture
  • Trigger finger
  • Junctura tendinum disruption
  • Congenital sagittal band deficiency
  • MCP joint arthritis
  • Nonoperative
    • extension 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
      • indications
        • chronic injuries (more than one week) where primary repair is NOT possible
        • professional athlete
  • Extensor Centralization Procedures
    • various techniques described including
      • 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 post 
        • 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

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Questions (2)

(OBQ12.262) A 28-year-old NFL running back complains of continued hand pain three days following an injury sustained while being tackled. He was splinted on the field. He has tenderness over the long finger metacarpal head, with subluxation of the extensor tendon into the intermetacarpal area during active metacarpophalangeal joint flexion. A representative MRI is shown in Figure A. What is the next best step in management of this patient? Review Topic


Observation alone




Continued splinting in flexion




Continued splinting in extension




Open repair of the disrupted junctura tendinae




Open repair of the disrupted sagittal band



Select Answer to see Preferred Response


Based on the history and physical exam findings this patient has sustained a traumatic rupture of the sagittal band. In this professional athlete, the next best step would be to perform an open repair of the sagittal band. This will allow for earlier aggressive rehabilitation and a quicker return to sport.

Sagittal band ruptures may be traumatic (as in this case) or attritional in nature (as in rheumatoid arthritis). A direct blow to the MCP leads to forced flexion of the digit and subsequent stretching/rupture of the affected structure. On physical exam the tendons are most unstable with the wrist flexed; MCP flexion will lead to dislocation of the tendon into the intermetacarpal gutter. Acute injuries may be treated with extension bracing for 4-6 weeks, but in professional athletes, direct open repair of the sagittal band is indicated.

Catalano et al. review sagittal band injuries treated with a thermally molded plastic splint that held the MCP in ~25-35 degrees of hyperextension. Patients were evaluated over 14 months; out of 11 sagittal band injuries, splinting was successful in eight of them. They recommend initial nonsurgical management with custom splinting.

Hame et al. review the results of the management of sagittal band injuries in the professional athlete. The lesion commonly found was the disruption of the extensor mechanism with predictable sagittal band tears. In their series, all patients regained full range of motion and returned to their respective sports. They recommend surgical intervention in elite athletes in the form of extensor tendon centralization and sagittal band repair.

Figure A shows a T1 weighted axial cut of the affected hand; subluxation of the tendon (arrow) can be identified with disruption of the sagittal band (arrowhead).

The video provided briefly reviews injury to the sagittal band.

Incorrect Answers
Answer 1: Observation is not indicated in this patient
Answer 2, 3: Splinting in extension would be an acceptable option in the non-athlete, but direct repair is indicated in a professional athlete
Answer 4: The junctura tendinae are not injured in this patient


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(OBQ06.92) A 20-year-old man has pain, swelling, and popping over his index metacarpophalangeal joint after striking a wall 3 days ago. Radiographs are normal, but physical exam reveals a palpable defect over the dorsum of the joint with clenching of the fist, and this defect is resolved with extension of the metacarpophalangeal joint. What is the next most appropriate step in treatment? Review Topic


Trigger finger steroid injection




Extension splinting of the metacarpophalangeal joint




Metacarpophalangeal synovectomy




Extensor hood reconstruction




Metacarpophalangeal joint arthrodesis



Select Answer to see Preferred Response


“Boxer’s knuckle” refers to injury to the extensor hood mechanism that results following resisted extension ("flicking") of the finger or direct trauma to the MP joint, usually involving the radial sagittal band of the middle or ring finger. Often, both the sagittal band and the dorsal capsule are torn. The hallmark of the physical examination is pain over the MCP with a palpable defect in the dorsal capsule, and it is important to examine for EDC subluxation with MP flexion. Sagittal band injuries seen within 3 weeks of injury may be treated nonoperatively with an MP joint flexion blocking splint. Patients presenting later than 2 to 3 weeks after the injury or patients who failed a trial of splinting are candidates for surgical repair.

Hame et al reviewed 27 patients who were treated for Boxer’s Knuckle. The authors concluded that in cases in which conservative treatment has failed, these injuries should be treated with sagittal band repair with centralization of the extensor tendon without repair of the capsule. In the acute period however (less than 3 weeks), as is the scenario for this patient, conservative management with extension splinting should be attempted first.

Araki et al performed a study of 16 cases of rupture of the extensor hood initially treated conservatively with splinting. While 8/16 responded successfully to nonoperative management, the remaining 8 did not improve with conservative treatment and were eventually treated with surgical repair and closure of the joint capsule when injured.

Illustration A shows a clinical image of a boxer's knuckle and Illustration B displays an axial T2 MRI with a sagittal band rupture. Video V demonstrates a sagittal band reconstruction.


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