Michael W Bowman M.D. FACS
The anatomy of the extensor tendons (tendons that extend or straighten your finger) is very complex. Tendons attach muscles to bone. The muscles for the extensor tendons of the hand are located in the forearm and become tendons just prior to the wrist joint. The extensor tendon to the finger (Extensor Digitorum) runs on the back or dorsum of the hand, down to the knuckle, or MCP joint. It attaches to a fibrous band called the Sagittal Bands that wrap around the base of the first finger bone (Proximal Phalanx). This attachment allows the Extensor Digitorum to pull the finger up at the MCP joint and extend the finger at the knuckle. The Extensor Digitorum then travels further to attach to the Middle Phalanx or middle finger bone. At that point it is called the Central Slip. Pulling or tension on the Central Slip straightens or extends the middle joint or PIP joint. Extensions of the Extensor Digitorum called the Lateral Bands extend out from either side of the Extensor Digitorum and are joined by tendons from the small intrinsic muscles located deep in the hand. The Lateral Bands run toward and connect at the last bone or Distal Phalanx. They form the Terminal Tendon, which is used to extend or straighten the last joint or DIP joint. The extensor tendons at this level are covered by peritenon, a slick layer of tissue which allows gliding. The extensor tendons in general are thinner than the powerful flexor tendons and glide together as a sheet over the finger. The extensor mechanism is very complex, elegant and delicate.
Lacerations of the extensor tendon may be classified by their location (over the DIP joint or terminal tendon, over the PIP joint or central slip, or in the hand or Extensor Digitorum). Lacerations may be sharp, such as those produced by a knife or glass; or jagged, such as those produced by a chainsaw or table saw. Lacerations may be complete or partial. Lacerations may be clean or dirty, with foreign material in the wound. Lacerations of the extensor tendon may produce pain and stiffness of the finger or inability to extend the finger. Lacerations over the DIP joint involving the Terminal Tendon may produce a mallet finger or swan-neck deformity. For more information see mallet finger/fracture or swan-neck deformity. Lacerations over the PIP joint involving the Central Slip may produce a Boutonniere Deformity. For more information see Boutonniere Deformity. Lacerations over the MCP joint or in the hand may result in a droopy finger at the knuckle or MCP joint. Occasionally laceration of the Extensor Digitorum around the MCP joint will not cause a droopy finger and may be missed. There are intertendinous connections between the extensor tendons to the different fingers called Juncturae Tendineae. These are located proximal to the MCP joint in the back of the hand. The extensor tendons for the adjacent finger can pull on the affected tendon through its juncturae and mask a tendon laceration.
Treatment of extensor tendon lacerations involves careful examination of the hand and testing for extensor function. Small tendon lacerations that involve only part of the tendon may be treated conservatively after repairing the skin. Splinting or buddy taping to an adjacent finger may be used while the tendon is healing and allow finger motion. In cases where the finger extension is weak or absent, surgery is usually required to restore function. In the surgery the laceration is usually extended slightly to allow exposure and access to the ends of the tendon. The wound is explored and any other injured structures are repaired. The tendon is then repaired with several small but strong sutures. Afterwards a protective dressing and splint are applied. Range of motion of the tendon is allowed when the tendon is sufficiently healed. This will vary from case the case, depending on the strength of both the tendon and the repair at that location. After the tendon is healed aggressive therapy will be used to regain motion and strength. This surgery is usually performed as an outpatient with local standby or twilight anesthesia or axillary block. Risks with this injury and surgery include anesthesia related risks, wound healing problems or infection, stiffness of the finger, failure of the repair. In cases of scarring, a later surgery to free the tendon (tenolysis) or joint (capsulotomy) may be required.
In cases where a portion of the extensor tendon has been lost, such as a grinder injury, or cannot be repaired, and extensor tendon graft or transfer may be required. in this situation a portion of extensor tendon from another donor area is spliced into the extensor tendon for repair. In cases of a transfer, and extensor tendon is rerouted to the necessary finger along with its muscle to substitute for the damaged extensor tendon.