What is it: The extensor tendons have a central portion that attaches to the middle phalanx and also lateral portions that run along the middle phalanx and attach and inserts at the base of the distal phalanx. A rupture can occur at the distal phalanx attachment or at the middle phalanx attachment.
How does it present: A rupture of the extensor tendon at the base of the distal phalanx causes inability or decreased extension at the DIP, called a mallet finger. Patients will often present with this complaint, associated with pain and swelling of the DIP after and injury. The classic injury is hitting the tip of the finger, causing a forced flexion, such as with trying to catch a ball. A rupture of the central slip at the level of the middle phalanx ultimately causes a Boutonniere injury where the PIP is forced into flexion, but the DIP is hyperextended due to the lateral bands of the extensor tendon still being functional. This may take weeks to develop the classic deformity. Patients may complain of pain and swelling at the PIP. In either condition, the patient may have pain over the dorsum of the distal or middle phalanx where the tendon had been avulsed.
Common exam findings: Physical exam findings may show swelling and tenderness at the DIP or PIP joint, depending on the injury. Tenderness over the dorsum of the joint instead of laterally over the collateral ligaments may help differentiate the tendon rupture from a collateral ligament strain. With the mallet finger, a partially flexed DIP may be present and ability to extend at the DIP should be evaluated with that joint in isolation. Elson's Test involves isolating the PIP of the injured finger over the edge of a table to assess the ability to extend. Inability or difficulty to extend at the PIP indicates an injury of the extensor tendon and the attachment on the middle phalanx.
Tests and treatment: X-rays should be examined to evaluate for fractures and avulsion fractures of the dorsum of the distal phalanx may indicate a mallet finger and avulsion fractures off the dorsum of the middle phalanx may indicated a Boutonniere injury. A mallet finger should be treated with a splint that produces slight hyperextension of the DIP. This can be accomplished with a dorsal padded splint or a stack splint. This splint should stay on continuously for six to eight weeks, followed by nighttime splinting for an additional two to three weeks. Residual loss of extension can occur if splinting is delayed or inadequate. For the Boutonniere injury, the finger should be splinted in full extension at the PIP for six weeks continuously and then nightly for an additional three to four weeks. While the finger is splinted in full extension at the PIP, it is fine to allow flexion at the DIP. In both cases if there is a large avulsion fracture present or it is significantly displaced, referral to orthopedics should be considered.