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[CLINICAL TECHNIQUES]

Hand-Based Thumb Spica Casting

William O. Roberts, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 3 - MARCH 2021


A hand-based thumb spica cast can be used to protect the metacarpophalangeal (MCP) and interphalangeal (IP) joints of the thumb after uncomplicated ulnar collateral ligament (UCL) sprains and certain other thumb injuries. The cast allows continued participation in many activities, letting the patient grip an implement and move the wrist joint but immobilizing the thumb joints.

UCL injuries of the thumb are common in downhill and cross-country skiing, snowboarding, and ice hockey, but they can happen in almost any sport. UCL sprains generally heal well as long as the thumb is protected from radial stresses and other forces that can cause reinjury. Reinjury occurs frequently in the unprotected joint, even in activities of daily living.

Other injuries for which the hand-based cast may be used include marginal, nondisplaced chip fractures of the IP joint that do not involve the articular surface, radial collateral ligament sprains, and chip fractures of the proximal thumb. A hand-based splint is not suitable for a nondisplaced fracture of the first metacarpal shaft; this injury requires a cast that immobilizes the wrist.

Athletes and active patients can return to work and sports activity with a "hard" or "soft" hand-based thumb spica cast. "Stick"-handling athletes in ice hockey, lacrosse, and cross-country and downhill skiing often can compete while wearing the cast.

Hard vs Soft Casts

The hand-based cast is most comfortable when fabricated from soft fiberglass casting tape, but hard fiberglass casting tape can also be used. The softer material is more comfortable at the extremes of wrist flexion and extension during sports and daily activities, but a hard cast provides greater protection. The soft cast is permitted in most sports, but a hard cast may need additional padding to be permitted in football, soccer, and other collision or contact sports.

Neither type of cast is very useful for activities that require thumb dexterity, but the athlete will most likely be unable to participate without it. The cast will also allow most patients to write.

Cast Application

[FIGURE 1]

To apply the cast, first place the hand in the position of function (ie, with the thumb opposed). Start with a synthetic stockinette extending from the proximal interphalangeal (PIP) joints of the hand to the wrist joint; cut a hole for the thumb. A 1/2- to 1-in. stockinette covers the thumb. The gap at the thumb MCP joint can be covered by splitting the thumb tube to extend it proximal to the MCP joint (figure 1). Next, wrap synthetic cast padding to cover the cast area two to three layers thick, with extra layers at the proximal wrist to protect the wrist joint during flexion and extension (figure 2).

[FIGURE 2]

The cast tape will cure faster when dipped in water. For the purpose of learning to apply the splint, therefore, the cast tape can be applied dry to slow the resin curing and then wet down to accelerate hardening.

Use 1- or 2-in. casting tape to wrap the hand and thumb in a thumb spica. Start with one full turn around the metacarpals and then wrap the tape around the thumb and hand in a figure-eight pattern, alternating the direction of the wrap around the thumb (figure 3). Tuck the free ends of the stockinette under the second layer of wrap.

[FIGURE 3]

The extent to which the thumb is casted is a matter of comfort and the severity of injury. Early in the UCL-MCP joint injury, limiting the movement of the IP joint will increase comfort but will sacrifice some grasping ability. An injury to the IP joint requires that the cast extend to the tip of the thumb. Take care to keep the edge of the cast distal to the joint lines of the wrist and proximal to the metacarpal heads to allow comfortable movement (figure 4). The cast rarely requires more than one 1-in. roll of tape for a child's hand or a 2-in. roll for an adult hand.

[FIGURE 4]

Check the Grasp

Before the cast hardens, test the patient's grip on the stick or pole to be used in his or her sport. Have the patient grasp a tube about the size of the hockey stick, ski pole, or other implement to be used. If a ski pole handle or hockey stick is used, cover the grip with stockinette to keep the surface free of resin (figure 5). As long as the cast has not dried, the thumb position can be adjusted slightly to improve the grip. Alternatively or in addition, the grip may be tightened by using tape to increase the diameter of the stick or handle.

[FIGURE 5]

For a sprain, the splint will need to be worn for 2 to 12 weeks, depending on the activity and the degree of the initial injury. It may need to be replaced for longer treatment and protection courses. The dorsal aspect of the hand portion of the splint may be split, the padding cut, and the edges taped to make a removable splint for the later stages of treatment.

Codes used for this procedure include 29075 for a short arm cast and 99110 for small cast supplies.

Dr Roberts is a family physician at MinnHealth SportsCare in White Bear Lake, Minnesota, and medical director of the Twin Cities Marathon. He is a fellow of the American College of Sports Medicine, a charter member of the American Medical Society for Sports Medicine, and an editorial board member of The Physician and Sportsmedicine.


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