More Research Needed on Extensor Tendon Injuries
Using your hand every day, you may not realize how intricate the extensor mechanism is, the part of the hand that allows you to extend your hand and fingers. In your forearm, the extrinsic extensor tendons are either superficial or deep muscular. The superficial group is divided into several other types of extensors. These many extensors feed through several compartments to get into the hand to allow extension.

The first dorsal compartment holds two tendons (the abductor pollicis longus and extensor pollicis brevis) and many injuries are common to this area. The second tunnel or compartment has two more tendons (the extensor carpi radialis longus, and brevis), the third tunnel one tendon (the extensor pollicis longus), and the fourth tunnel, two more tendons (the extensor indicis proprius, EIP, and extensor digititorum communis, EDC). This compartment also houses the posterior interosseous nerve. A fifth tunnel houses a tendon that rests above the distal radial ulnar joint (the extensor digiti minimi, EDM), and the last tunnel holds the last tendon (the extensor carpi ulnaris).

The further the tendons go through the compartments or tunnels, the higher they move to the surface of the hand and the more they flatten out. These changes can make the tendons vulnerable to injury. As the tendons go through the hand to the fingers, the more complex the system becomes and they wind around, allowing you the ability to extend your fingers and hand. By understanding the detail of the extensor mechanisms, doctors are better able to recognize and diagnose injuries to an extensor tendon.

When first inspecting an extensor injury in the hand or wrist, doctors should closely investigate for the size and location, and determine the underlying injury. To do this, the extensor mechanism is divided into nine zones, so the injuries may be classified. Those zones with odd numbers are found directly over joints while the even number ones are over bone. Zone 1 starts at the tip of the fingers and zone 9, the forearm.

As the doctor inspects the arm and hand, the normal resting cascade is one of the first things checked. This is how the fingers natural flex from the index (pointing) finger to the little finger. Each finger is tested individually. If a tendon injury is suspected, there is a good chance there is more injury, because it seems that rarely is only one tendon damaged. At this point, an x-ray is usually indicated.

Zone I injuries involve the distal interphalangeal joint (DIP). A common injury, a mallet finger, is an injury of the DIP, the joint on the fingers closest to the tip, or the most distal part of the finger. This is usually caused by forced flexion (bending) and is classified into one of four types:

I: closed
II: open
III: open with skin loss and tendon affected
IV: involves large mallet fractures

Usually, type I is treated with a splint and the other types with surgery. But, if there are other injuries involved, other treatment options may be necessary. One analysis of previous studies looking at various treatment methods and outcomes, done by researchers Handoll and Vaghela, found only four studies in 2004 that were usable and no studies in 2005 to 2008. Therefore, there are still not a lot of usable data to determine the best way to treat mallet finger.

When looking at surgery for stage II and above mallet fingers, the different procedures are controversial among some surgeons. Here, too, there are not a lot of data available. In general, however, primary repair is often using a variety of suture (stitches) techniques, using K wires for stabilization or suture anchors.

Zone II injuries are usually due to lacerations or cut wounds and affect the DIP joint as well. If the tendon isn't completely cut through or injured, surgery may not be needed and the tendon can be repaired with a short course of splinting, but only if more than half the tendon is intact, and there is no indication of extensor lag, or drooping at the joint.

If the tendon has been cut through, surgery is required, which will most often be followed by splinting, as long as the DIP joint is extended as it should.

Zone III injuries affect the proximal interphalangeal joint (PIP) joint, the one at the middle of your finger. Doctors use the Elson test, which checks for the rigidity of the DIP joint while trying to bend the PIP joint. This can tell the doctor if there may be a central slip injury. Splinting when such an injury is suspected is usually recommended, to prevent further damage. As with zone I injuries, treatment depends on if the injury is open or closed, and how much damage has occurred. Unfortunately, no one particular splint has been found to be better than any other with this joint, unlike the mallet finger. If surgery is needed, splinting will be done for a set period of time during recovery, but some surgeons have been concerned about patients not using the joint for between four to six weeks, resulting in stiffness. One surgeon, Evans, has been experimenting with shorter splint times of about three weeks and results are promising.

Zone IV injuries are similar to zone II but closer to the wrist. They are most often due to lacerations and, at this level, the tendon is flat and wraps around the bone, so injuries are usually partial. It is vital that the doctor check the tendon thoroughly, checking if there is any weakness to the PIP. If the PIP can extend and flex normally, then nonsurgical treatment is usually acceptable. On the other hand, any sign of loss of flexion is usually an indicator that surgery is needed to repair the tendon.

Zone V injuries occur over the metacarpophalangeal joint (MCP), the middle knuckle of your fingers, and this is the most common spot for extensor mechanism injuries. One of the more common injuries is the so-called fight bite, which is the result of a punch to another's mouth. Treatment of this type of injury may be different from a non-bite injury because of the potential of infection from a bite injury. A bite injury can become easily infected and this can destroy the tissue, requiring surgery to remove the dead tissue and to clean out the area. Both the bite and non-bite injuries are divided into one of three categories:

Type 1: a bruise without a break in the skin
Type 2: displacement of the joint but not complete dislocation
Type 3: dislocation of the tendon

Which treatment is recommended depends on the type of injury and how long ago the injury was sustained. If the injury is acute, less than six weeks, splinting may be the recommended treatment, and this has been reported to be fairly successful for the long (middle) and ring fingers that don't have any other issues, such as rheumatoid arthritis. An eight-week splinting is good for displacements of 25 degrees to 35 degrees. If the splinting doesn't work or if the injury is chronic, then surgery may be needed.

Zone VI injuries occur over the metacarpals, which are the bones in your hand. These injuries have a better prognosis than the ones in the fingers because there aren't usually associated joint injuries, which allows for better healing. These injuries, however, are not always obvious as the patients may still be able to extend their hand and fingers.

Zone VII injuries occur just below the metacarpals in the extensor retinaculum. This structure consists of fibers that connect the smaller bone of your forearm radius, with the longer bone, the ulna. This must be opened to be able to see if there is damage inside. If there is an acute injury, a repair can be done, but if the injury is chronic, having been present for a while, this is difficult to treat. Grafting or a tendon transfer may be needed here.

Zone VIII and Zone IX injuries are at the forearm level and can be difficult to repair because of a lack of tissue that can be used to make the surgical repair. Repairs can be made though, if there is enough tissue. Another issue that doctors must look for in this type of injury, is nerve damage because of the location of the nerves in the wrist/forearm area.

Rehabilitation after any of these types of injuries depends on the severity and location of the injury and repair. Most often, the extensors were supported with splinting after surgery but researchers, Newport and colleagues, found there was only a 64 percent success rate and some left over difficulty with bending the joint with this type of rehabilitation. Researchers are looking at shorter splinting times and the results have been promising. Mowlavi and colleagues found that there was a better total active motion and grip strength after eight months, but at six months, the patients were no different than patients who had longer splinting times.

An issue to take into account with early mobilization is the possibility of complications, such as tendon rupture or lag, but this shorter splinting time may be appropriate for highly motivated patients.

The authors conclude the article by pointing out that extensor injuries are often not considered to be taken as seriously as flexor injuries and the damage is often underestimated. Therefore, more research needs to be done to ensure doctors know what to look for and how best to treat it, to prevent long-term complications or disability.
Jonas L. Matzon, MD, and David J. Bozentka, MD. Extensor Tendon Injuries. In The Journal of Hand Surgery. May 2010. Vol. 35. No. 5. Pp. 854-861.