Ortho Hors D'oeuvres (Answer):

To review, this is a 26 year-old male with right small finger pain and restricted movement after basketball injury. Questions and Answers: 1) What is the suspected injury by history and radiographs? This patient suffered an injury of forced flexion which improved when a friend "pulled on his finger," which is immediately concerning for a dislocation with subsequent successful field reduction.

The radiographs do not show any obvious fracture, but do show some mild extension at the distal interphalangeal joint and flexion at the proximal interphalangeal joint which is concerning for a possible central slip injury and associated boutonniere's deformity.

Although frequently used interchangeably, an injury to the central slip is the acute traumatic incident, that if untreated, will eventually lead to the classic boutonierre's deformity (flexion at the proximal interphalangeal joint (PIP) with extension at the distal interphalangeal jiont (DIP)). In a normally functioning hand, the extension of the finger is controlled by a complex of extensor tendons. This complex trifurcates over the dorsal aspect of the proximal phalanx to become the central slip with 2 lateral bands. The central slip attaches to the dorsal aspect of the base of the middle phalanx and performs extension at the PIP. The lateral bands joint insert at the dorsal end of the distal phalanx and perform extension of the DIP. When the central slip is ruptured or stretched, the lateral bands move volarly and perform unopposed flexion of the PIP and extension at the DIP.

2) What are the confirmatory tests to perform as part of the physical exam?

When patients initially present with this injury, they may not have any notable boutonniere deformity; in the earliest stages of central slip injury, they will only have tenderness to palpation over the distal insertion of the central slip. After radiographs have demonstrated no associated phalangeal fractures, patients should be evaluated for central slip injury with Elson's test or a modified Elson's test.

The basic principle of Elson's test is as followed--if a patient is attempting to extend the isolated PIP against resistance and has a ruptured central slip, their lateral bands will fire, causing a rigid DIP and generally performing weaker extension at the PIP. Contrarily, if a patient has an intact central slip, the lateral bands should remain unactivated and the patient's DIP should be floppy while they are performing isolated extension of the PIP.

The classic Elson's test is as follows: The patient's PIP is placed at 90 degrees over a table, the patient actively extends the PIP against resistance. If a central slip injury is present, there will be weak PIP extension and a rigid distal interphalangeal jiont.

In recent years several modified Elson's test have been proposed; neither of which have been evaluated in large case series. The first approach is very similar to Elson's test; the only change is that the table is not involved. The provider pinches the patient's distal and middle phalanx between their fingers at 90 degrees. Again the patient attempts to extend the PIP and the provider assesses for DIP rigidity. A rigid DIP indicates a central slip injury.

The second approach evaluates the patient's ability to extend the DIP while extending the PIP against resistance. If a patient is able to asymmetrically extend the DIP of the injured finger, this is concerning for possible central slip injury.

3) What is the appropriate management for this injury? How would this change if the patient had associated fractures?

Patients with diagnosed central slip injury are at risk for permanent boutonniere's deformity if not treated appropriately and relatively quickly after injury. They should be placed in a splint with full extension at the PIP. The DIP should have freedom to flex and extend as necessary in order to prevent further contractures.

Patients with small nondisplaced bony fracture at the insertion of the central slip tendon can be treated in the same fashion if the fractures are displaced by less than 2mm and involve less than 50% of the joint surface. These patients should be seen by a hand surgeon within 3-5 days to discuss possible operative management, although they generally do very well with conservative nonoperative therapy.

The splint is generally required for 4-6 weeks to allow the central slip to re-approximate.

References:

Coons MS, Green SM. Boutonniere deformity. Hand Clin. 1995 Aug;11(3):387-402 Massengill JB. The boutonniere deformity. Hand Clin. 1992 Nov;8(4):787-801 Harrison BP, Hilliard MW. Emergency department evaluation and treatment of hand injuries. Emerg Med Clin North Am. 1999 Nov;17(4):793-822, v Lin JD, Strauch RJ. Closed Soft Tissue ExtensoR Mechanism Injuries (Mallet, Boutonniere and Sagital Band). J hand Surg. 2014 May;39(5):1005-1011 McMurtry JT, Isaacs J. Extensor Tendons Injuries. Clin Sports Med 2015. 34:167-180 Williams K, Terrono AL. Treatment of boutonniere finger deformity in rheumatoid arthritis. J Hand Surg Am. 2011 Aug;36(8):1388-93.

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