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Making an Ulnar Gutter Splint for a Boxer's Fracture

Michael J. Petrizzi, MD; Mark G. Petrizzi, MD; Allen Miller

Department Editor: William O. Roberts, MD


Isolated fractures of the distal fourth or fifth metacarpal bones, also known as boxer's fractures, are among the more common fractures seen by primary care physicians. This injury has been described as "a tolerable fracture in an intolerable patient" because it is generally the result of the patient's having struck someone or something with a fist. One simple and proven method for immobilizing boxer's fractures is the ulnar gutter splint.

The splint effectively immobilizes the patient's fourth and fifth fingers, the fourth and fifth metacarpophalangeal (MCP) joints, and the wrist. It is easily fabricated from fiberglass or plaster casting or splinting material, and it can be molded during application to reduce fractures or hold reductions. A properly applied ulnar gutter splint will usually provide some pain relief and prevent further injury and/or displacement of the fracture. The splint is easier to apply than a short arm cast with an outrigger.

Boxer's Fractures

A boxer's fracture is the most common type of metacarpal fracture. It often occurs when someone throws a punch that connects over the fourth or fifth knuckle rather than the second or third. The point of maximal tenderness is just proximal to the knuckle. As always, a detailed neurovascular exam should be conducted and documented. The patient should then be asked to flex the fingers, which should point toward the thenar eminence. If a rotational deformity is present, the affected finger will be rotated out of line.

Only isolated, uncomplicated fractures to the distal fourth or fifth metacarpal are appropriately treated with an ulnar gutter splint. Fractures that require referral include those involving the second or third metacarpal, those with accompanying rotational deformity of the finger, those associated with neurovascular compromise, and those that are multiple or comminuted. These injuries may require open reduction and internal fixation or K-wires.

Angulation of up to 40° is generally acceptable for boxer's fractures because of the high degree of mobility of the fourth and fifth MCP joints. These fractures may therefore be immobilized with or without reduction, depending on the patient's level of concern with cosmetic results. Isolated boxer's fractures with more than 40° of angulation must be reduced prior to long-term immobilization in an ulnar gutter splint.

It is important to explain to the patient before treatment for a displaced boxer's fracture that these fractures tend to be difficult to maintain in reduction and that, with or without anatomic reduction, the outcome often involves a permanent bump over the fracture site and depression of the associated knuckle. The patient should also know that a palmar prominence at the distal metacarpal will sometimes lead to problems with grasping objects. In addition, many patients have stiffness of the MCP joints after immobilization and will later need to use rehabilitation exercises to regain full range of motion and grip strength.

Constructing the Splint

Ulnar gutter splints can be made quickly and easily. The necessary supplies include prefabricated splinting material with padding, a bucket of water, some cotton for placement between the fingers, and enough elastic wrap to hold the splint on.

Place the affected extremity, with the help of an assistant if possible, in a functional position (figure 1). This entails having the patient hold the hand in the air, with the elbow flexed 90° and the wrist dorsiflexed 10° to 15°.

[Figures 1 and 2]

The splint length should be from the end of the fifth finger to within two to four finger-widths of the antecubital space (figure 2). The splint can be slightly shorter if preferred, but it should cover at least the distal two thirds of the forearm. It should be wide enough to cover half the circumference of the wrist.

[Figures 3 and 4]

Before applying the splint, place cotton between the fourth and fifth fingers. After wetting the splinting material, mold it onto the hand and wrist (figure 3) while wrapping on the elastic wrap. It is best to wrap from distal to proximal, as this pushes the edema up and out of the distal extremity. When wrapping the splint, include the fourth and fifth fingers only, leaving the other fingers free.

Once the splint has been secured to the hand, wrist, and arm, the hand must be positioned correctly (figure 4). This includes 10° to 15° of dorsiflexion of the wrist, flexion of the MCP joints to as close to 90° as possible, and 10° to 15° of flexion of the proximal interphalangeal joints. The tips of the fourth and fifth fingers should not be pointed toward the ulnar side of the palm, but rather toward the thenar eminence. This position is known as the cobra position because when viewed from the side it resembles the head of a striking cobra.

When using fiberglass, be sure to hold the patient's extremity in this position for 3 to 6 minutes to allow the splint to become reasonably hard. Also, be careful to loosen and reapply the elastic wrap after the splint dries if it was initially placed too tightly. Although postsplint x-rays to verify alignment are not generally necessary, some physicians may prefer to obtain them if significant reduction was attempted.

Take-Home Instructions

The patient should be instructed not to remove the splint and to return for checkups at 24 hours and 2 weeks. As previously, x-rays to verify alignment are optional at these times. When showering, the patient should cover the affected arm with a plastic bag, which can be secured at the top with rubber bands or tape. The patient should also be given written instructions about cast and splint care, along with advice to return to the office or go to a hospital emergency department if signs of neurovascular compromise are noted.

The callus formation around the fracture site should be strong enough to allow the splint to be removed within 3 to 4 weeks. If cared for properly, these splints should last 4 weeks, but if necessary a new splint can be applied at the 2-week checkup.

Dr Michael Petrizzi is director of the family practice residency program at Hanover Family Physicians in Mechanicsville, Virginia, an associate professor of family medicine at the Medical College of Virginia in Richmond, and a charter member of the American Medical Society for Sports Medicine. Dr Mark Petrizzi is on the residency program faculty at Hanover Family Physicians and is an assistant professor of family practice at the Medical College of Virginia. Mr Miller is a certified orthopedic technician and a management services officer at UCLA Medical Center in Los Angeles. Dr Roberts is a family physician at MinnHealth SportsCare in White Bear Lake, Minnesota, and an editorial board member of The Physician and Sportsmedicine.