December 23, 2011
Rounding Up the Usual Suspects: Thumb Injuries
Some would argue that the thumb’s primary purpose is to be raised in the manner of Arthur “Fonzie” Fonzarelli from Happy Days, but we are most concerned with its role in gripping and grabbing objects in baseball. In order for that to happen, the thumb has to be working right. You can’t play baseball at a high level with your thumb sticking up in the air like the Fonz, or if you just hit it with a hammer. One of the most common injuries to the thumb involves the ulnar collateral ligament of the metacarpophalangeal joint. In today’s installment, we are going to look at a few specific injuries to the UCL of the thumb, namely Gamekeeper’s thumb and Stener lesions.
Again, despite the thumb’s small size, there are a number of muscles involved in its motion and stability. The thumb, much like the shoulder, relies on its muscles and tendons for a large part of its stability as a whole, in part because it has such a wide range of motion. The muscles that begin in the forearm and travel to the thumb include the abductor pollicis longus (abducts the CMC joint), extensor pollicis brevis (extends thumb MCP joint), extensor pollicis longus (extends the IP joint), and flexor pollicis longus (flexes the IP joint).
The muscles that begin in the hand are the abductor pollicis brevis (abducts CMC joint), adductor pollicis (adducts the CMC joint), first dorsal interosseous (adducts CMC joint and flexes, pronates, and abducts the MCP joint), flexor pollicis brevis (flexes MCP and CMC joint, assists in opposition), and the opponens pollicis (opposition, flexion and pronation).
Injuries and non-surgical treatment
The UCL is actually composed of two different bands of the ligament that resist valgus force in different ranges of motion. The proper collateral ligament resists valgus force in flexion, while the accessory collateral ligament and volar plate resist that force in extension. Stress testing in each of these positions can tell you which of the bands is injured. If laxity is present during both flexion and extension, then the entire UCL is ruptured, assuming no fracture is present. The valgus force can also result in a small piece of bone being avulsed off from the insertion point of the UCL. X-rays can tell you if there is a bony injury, and MRIs can also be used to evaluate this soft tissue injury.
When the ligament tears, it most often tears and separates at the insertion of the proximal phalanx. Often the torn portion becomes squeezed and gets stuck in the adductor pollicis aponeurosis as it runs over the UCL, which limits its ability to heal. This is called a Stener lesion, and because it almost never heals on its own, it generally requires surgery.
Unlike the Stener lesion, sprains of the UCL and even Gamekeeper’s thumb fractures heal well on their own with immobilization and physical therapy. If there is significant opening of the joint with valgus stress testing—usually due to the presence of a Stener lesion—then surgery is warranted.
Conservative treatment involves immobilization for a period of time depending on the degree of injury. With a moderate partial tear—Grade II out of III—immobilization in a cast or rigid splint for four weeks is commonly prescribed. Physical therapy begins almost immediately in order to decrease the swelling and restore normal motion. Most UCL injuries that do not require surgery can heal in anywhere from one month to three months, again depending on the severity of injury.
Most of the time, the ligament tears at the insertion point, but it can, and does, tear in the mid-substance. If this is the case, the ligament is often sutured back together with non-absorbable sutures. With the more common distal rupture, the ligament is then prepared for reattachment and the bone is roughened to enable a better bite or grab when the ligament is reattached. Bone anchors are placed in the proper position to provide better anatomic reconstruction, and the ligament is reattached. A pin may be used to stabilize associated fracture fragments.
In chronic conditions, this repair may not be feasible. In those cases, the attachment is moved distally from the original insertion point to foster the necessary stability. If the tissue is frayed, shredded, and unusable, then a reconstruction similar to other ligament replacement surgeries may be used. The preferred tendon is the palmaris longus, which is absent in about 25 percent of the population. (Quick side note: this is also why other grafts must be used instead of the palmaris longus for Tommy John surgery).
In cases where the palmaris longus is absent, the surgeon may use one of several other tendons, including the extensor pollicis brevis tendon, the plantaris in the foot, a toe extensor, a small portion abductor pollicis longus, or even a part of the flexor carpi radialis tendon. The graft is passed through a tunnel from the metacarpal to the base of the proximal phalanx before being anchored. The skin is then closed, and the patient is place in a post-operative splint.
The long-term prognosis for recovery is usually very good, although some patients do develop stiffness that takes a long time to resolve. There can also be associated arthritis, especially with chronic tears, so continued soreness may also be an issue.
Corey Dawkins is an author of Baseball Prospectus. Follow @CoreyDawkinsBP