Extensor tendon lacerations are caused by an injury to the finger, hand or arm. The injury is typically the result of a traumatic event that results in the lacerations, i.e. deep cuts.

The Anatomy of the Extensor Tendons

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 (dorsum) of the hand, down to the knuckle, or MCP joint. It attaches to a fibrous band called the Sagittal Band.
• This band wraps 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 (Distal Phalanx). They form the Terminal Tendon, which is used to extend or straighten the last joint (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.

The Causes: About Lacerations

Lacerations, i.e. deep cuts, of the extensor tendon may be classified by their location. Common locations are:

• over the DIP joint or terminal tendon
• over the PIP joint or central slip
• in the hand or Extensor Digitorum

Lacerations can also vary in their causes and their presentation. For example:

• Lacerations may be the result of something sharp, such as a knife or glass; or of something jagged, such as a chainsaw or table saw.
• Lacerations may be complete or partial. 
• Lacerations may be clean or dirty (i.e. 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 and 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. 

The Diagnosis

One thing we must keep in mind when evaluating patients is that there are also 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. Therefore, it’s our responsibility as medical professionals to make this distinction.

With that in mind, diagnosis of extensor tendon lacerations involves careful examination of the hand and testing for extensor function.

The Treatment

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 procedure 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, or 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, an 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, an extensor tendon is rerouted to the necessary finger along with its muscle to substitute for the damaged extensor tendon.