Mallet finger (closed or open terminal tendon disruption) will often result in a chronic distal interphalangeal (DIP) joint extensor lag, even with adequate initial treatment, due to slight lengthening of the healed tendon. Tenotomy of the central slip, described by Fowler, can clinically improve chronic DIP extensor lag by allowing the finger extensor mechanism to slide proximally, thereby reducing the ‘slack’ in the terminal tendon. To our knowledge, no anatomic or biomechanical study has studied the amount of extensor lag that is correctable with a central slip tenotomy. The goal of this study is to evaluate the potential of central slip tenotomy to restore DIP joint extension, with respect to the severity of the pre-existing extensor lag.

Fifteen fresh frozen cadaver fingers (age range 27 to 46 years) that were free of joint contractures were used for this study. The skin over the dorsal aspect of the fingers was removed. The extensor tendon insertion was identified and a suture anchor placed into the bony insertion. The extensor tendon was then sectioned over the DIP joint, producing a mallet deformity. The braided suture-anchor suture was then secured to the extensor tendon over the middle phalanx with 2 hemoclips to simulate lengthening of the tendon that might occur with healing. The degree of extensor lag produced was measured with an analog goniometer. A 5 pound weight attached to the proximal extensor tendon over the hand provided a uniform traction force. Central slip tenotomy was then performed by lifting the extensor tendon from the ulnar side and completely sectioning the insertion on the middle phalanx. Measurements of the degree of extensor lag pre- and post-tenotomy were made.

Following sectioning of the extensor tendon over the DIP joint, the average amount of extensor tendon lag produced was 45° with 5 pounds of proximal traction. After performing central slip tenotomy, the average amount of extensor lag correction was 35.7°. The largest extensor lag able to be corrected measured 46°.

Several clinical studies have demonstrated that central slip tenotomy is an effective treatment for chronic mallet finger, but may not fully restore DIP joint extension. In this study, a DIP joint extensor lag of up to 46° was fully correctable with central slip tenotomy, but the average degree of correction was 36°. Patients with a pre-existing extensor lag of greater than 36° may not achieve full correction with central slip tenotomy.