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What is a Extensor Tendon Laceration?
Related articles: flexor tendon laceration, broken finger, broken hand, jersey finger (finger tendon injury), mallet finger (finger tendon injury), broken finger tip and broken nailbed
Tendons attach muscle to bone so that we can move our fingers. An extensor tendon allows you to straighten your fingers (while a flexor tendon allows you to grip with your finger). A laceration (cut) to the tendon prevents that muscle from being able to control the finger, and with an extensor tendon laceration, you will not be able to straighten that finger. The tendon runs along the back of your hand, and they run all the way from the forearm (where the muscle is located, while the tendon forms out of the muscle about 4 cm before the wrist joint) to the tip of the finger. Cutting the tendon at different locations will affect how its treated. The tendons to each of the fingers are held together so they work as one unit, the ligaments that do this are the juncturae tendinae. It’s these ligaments that prevent independent extension of the middle or ring finger...try to completely straighten one finger while your other fingers remain flexed. Cant do it right. But you can with the index finger, that’s why we point with it (thats because it has an extra, independent tendon. The index finger is so free spirited. With the tendon running along the top of your skinny finger, you must wonder: "How does it stay up there and not slip to the side?" Well, Its held in its central position by a thick piece of tissue called the “Saggital band”, the extensor tendon fans out into three thick connective tissue bands that insert over your middle knuckle. The middle band is called the central slip (while the two side bands are called the “lateral bands” and they actually joint up with the lumbricle tendons). The lateral bands get held into place by the triangular ligament (dorsally) and the transverse retinacular ligament (volar). If the triangular ligament breaks, the lateral bands slip forward and you get a boutineere deformity (see talk). If the transverse retinacular ligament breaks the lateral bands slip back and you get a swan neck deformity (see talk). The lateral bands then converge to form the terminal tendon. This tendon stops only 1.2 mm before you reach the finger nail.
How is an Extensor Tendon Laceration diagnosed?
Injury to an extensor tendon will prevent you from straightening out a finger. A person will come to the emergency room or office with a cut on the top of their wrist, hand, or finger and will say that they cannot full straighten their finger. The diagnosis is made by examining the finger and seeing what it can do. We look for tenodesis effect: we flex the wrist, this pulls tension on the extensor tendons and automatically starts to straighten the fingers.
A cut over a finger will cause a more complex injury because the tendon spreads out into all of those other smaller tendons, as we described above). An injury to the central slip affects the middle knuckle (PIP) and can be isolated with a test called the Elson test. You bend the middle knuckle over a table edge and then ask the person to straighten their finger. This keeps the lateral bands slack (you notice that you cannot extend the DIP with a flexed PIP) and focuses PIP extension on the central slip alone. If torn the DIP is able to extend b/c the lateral bands aren’t lax, but you cannot extend the PIP.
How is an Extensor Tendon Lacteration treated?
Treatment depends on the severity of the tendon injury. If the laceration involves less than 50% of the tendon, then we immobilize the hand for a few days to give time for healing and then start early passive motion. The splint is kept for 6 weeks, then another 6 weeks of wearing the splint sometimes. If the tendon is torn more than 50% it needs to be repaired. Incisions across a joint are always transverse or oblique to prevent scarring that blocks motion, about 4-6 loops of suture are used to hold the repair together.
What is the long term outcome?
The weakest time of the tendon, meaning greatest risk for re-tearing is days 6-12 because the tissue is remodeling and therefore the weakest (if everything is done correctly there is only a 5% risk of this happening). The other common complication is scarring, which prevents full finger flexion. This is avoided with early range of motion exercises.