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Extensor Mechanism of Fingers


- See: Extensor Tendon Lacerations:

      - the extensor apparatus is a "plexus of tendons with an aponeurotic sheet." - from Stack, 1962.

MP Joint Level:

- extensor digitorum communis: (at the MP joint)
       - there may be some adhesion to the joint capsule, but there is no formal insertion;
              - the deep portion of the extensor tendon becomes adherent to and supplements the dorsal roof of the MP joint capsule;
              - these fibers may help centralize the extensor tendons, but probably do not contribute to finger extension;
                     - other argue that this insertion is of functional significance;
                          - The Anatomy of the Extensor Apparatus of the Fingers
                                Tubiana R, and Valentin P. Surg Clin North Am. 1964;44:897.
       - at the MCP joint, four tendons, one to each finger, divides into three slips;
       - middle slip connects to the proximal phalanx via the lasso like saggital bands (which encircle the digit and attach to the volar plate)
              - it is the only extensor of the proximal phalanx;
       - middle slip goes on to attach to the dorsal surface of the 2nd phalanx;
       - two lateral slips unite to attach to dorsal surface of base of distal phalanx;
              - on the radial side, the lateral slip of the EDC unites w/ the lateral slip from the lumbrical to form the lateral band;
- saggital bands: (at the MP joint)
    - saggital bands anchor the extensor tendon over the central MCP joint;
    - saggital bands arise from volar plate and spans both sides of MP joint;
    - they adhere to collateral ligaments and deep transverse intermetacarpal ligament;
    - these bands function to extend the proximal phalanx;
    - conjoined tendons of intrinsics and saggital band hold the extensor tendons in a central position over the MP joint;
    - rupture:
            - most often involves saggital hood tear of radial side of middle finger following trauma;
            - patients will be unable to actively extend the digit from a flexed position (since the tendon is subluxed) but the patient will
                    be able to keep the digit extended after the digit is passively extended (since the tendon is relocated);
            - w/ acute injury consider nonoperative treatment w/ the MP joint splinted in extension;

- interossei: (at the MP joint)
    - on both sides of MCP joint, a portion of the interossei insert into the base of the proximal phalanx and joint capsule;
    - the remainder of the interossei alond w/ the lumbricals insert into the extensor apparatus at the level of the proximal phalanx,
            and continues distally (as the lateral bands:) to insert into the distal phalanx;

Phalangeal Level:

- extensor digitorum communis:
      - divides into 3 slips;
            - central slip continues on to insert into dorsum of middle phalanx;
            - two lateral bands travel on either side of proximal phalanx;
- transverse fibers:
      - these lie distal to the saggital bands;
      - arise from the dorsal surface of the lateral bands and envelop the dorsal extensor apparatus;
      - they act to flex the MP joint
- lateral bands:

The finger extensor mechanism.
    Littler JW. Surg Clin North Am. 1967;47:415-432.

Muscle Function in the Fingers.
    Stack HG. J Bone Joint Surg 1962;44-B:899.

The microvascular anatomy of the distal extensor tendon.  
    Warren RA, Kay RNM, Norris SH. J Hand Surg. 1988;13-B:161.

Common variations of the radial wrist extensors.
    Albright JA. J Hand Surgery. 1978;3:134.

Variations of the extensor tendons of the fingers. Surgical significance.
    SchenckRR. J Bone Joint Surg Am. 1964;46:103.

Anatomy of the extensor tendons to the index finger.

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