The extensor mechanism of the hand is a complex apparatus; there are extrinsic and intrinsic contributions and ligamentous stabilizers which contribute to the integrity of the system. Extensor tendon injuries are divided into nine zones, extending from the DIP joint (zone I) to the proximal forearm (zone IX) (1). In this entry, we will briefly explore the management strategies for Zone III injuries of the central slip.
The extensor mechanism trifurcates at the mid-dorsal aspect of the proximal phalanx. Arising from the extrinsic extensor tendon and lateral bands, the central slip is a tendinous attachment to the base of the middle phalanx. The transverse retinacular ligament stabilizes the extensor mechanism over the PIP joint and limits any dorso-palmar translation (1).
Central slip disruptions can occur as either open or closed injuries. Closed injuries are usually caused by forceful flexion induced by sports injuries or falls, while open injuries can arise from lacerations over the PIP joint (2,3). Failure to recognize this injury can have potentially devastating consequences due to the imbalance of flexor and extensor forces which will lead to a boutonniere deformity (Figure 1). More specifically, the volar migration of the lateral bands and subsequent attenuation of the triangular ligament causes this deformity (Figure 2). These injuries can also arise from fractures of the middle phalangeal base at the insertion of the central slip. Moreover, degenerative conditions such as rheumatoid arthritis can also result in disruption of the central slip (3,4).
Patients usually present with pain and swelling over the dorsal PIP joint of the affected finger or a laceration. Digital block is often helpful to further assess extent of injury.
After a thorough neurovascular examination, attention can be turned to the digit with a suspected central slip injury. This digit will often be held in flexion at the PIP joint, and exhibit a positive Elson Test (5). Following adequate digital blockade, one can assess the integrity of the central slip by having the patient flex his or her fingers over a table at the PIP joint. As a brief reminder, finger extension is normally governed by the central slip at the PIP joint and pivotal contributions from the lateral bands, traveling volar to the PIP joint, at the DIP joint via the terminal tendon. An intact central slip will allow for extension against resistance at the middle phalanx while simultaneously allowing the distal phalanx to remain supple when this resistance is applied (Video 1); by contrast, a disruption of the central slip will create proximal migration of the origin of the lateral bands, which will create a hyperextension at the DIP joint with resisted extension.
30 y.o. right handed male who had a motor vehicle accident; was a restrained lone driver when he struck another vehicle and rolled over x2 in his vehicle.
Open laceration over the PIPJ of the left middle finger. Left small finger with nail plate injury and radial sided laceration. Left middle finger held in flexion, unable to extend actively or passively. Elson test not possible due to pain. Sensation largely intact in radial, median and ulnar distribution. Extension intact in all other fingers. Median/radial and ulnar motor function grossly intact with “OK” sign, thumbs up and finger adduction/abduction aside from left middle finger.
