An injury to the tip of the finger is common during sporting activities such as baseball. If the tip of the finger (known as the distal interphalangeal (DIP) joint) is struck with the ball, the tendon that attaches to the small bone underneath can be injured. Untreated, this can cause the end of the finger to fail to straighten completely, a condition called mallet finger.
In this study from Japan, surgeons use a particular surgical approach known as the Thompson procedure developed in 1978 by Dr. J. S. Thompson. Seven adults ranging in age from 25 to 71 had a chronic mallet finger that was not resolved with a previous surgery. They ended up with both the mallet position as well as a swan neck deformity.
With the mallet deformity, the end of the finger is bent and cannot be straightened voluntarily. The DIP joint can be straightened easily with help from the other hand. If the DIP joint gets stuck in a bent position and the proximal interphalangeal (PIP) joint (middle knuckle) extends, the finger may develop a deformity that is shaped like a swan’s neck. This is what is meant by a swan neck deformity.
The Thompson procedure uses a graft from the palmaris longus tendon. The graft tendon is split, spiraled under and over the middle bone of the finger, and then tied over the skin with an external button. The procedure reconstructs the spiral oblique retinacular ligament (SORL). This makes it possible for motion of both the distal and proximal interphalangeal joints (DIP and PIP) to work together creating coordinated flexion and extension of the finger.
The authors say that the biggest benefit of the Thompson procedure is that it corrects the extension lag of the tip of the finger (patient can’t fully extend the finger tip) while also addressing the swan neck deformity. And it does so without scarring the extensor tendon (which would restrict finger extension) or preventing flexion of the proximal interphalangeal (PIP) joint. The goal is to get smooth finger flexion and extension of both the DIP and the PIP joints.
In these seven cases, the Thompson procedure proved to be successful in restoring full, smooth active motion of the affected finger in six of the seven patients. Failure to fully extend the tip of the finger (called extensor lag) was resolved for six people. The seventh patient had improved motion but not a complete “cure.” The reasons for this included a seven year delay between injury and surgical repair and injury to the end of the torn tendon.
An important point from this study is the fact that patients who had previous (failed) surgeries all benefitted from the Thompson technique. The authors also commented that appropriate graft tension is essential to avoiding problems or complications after surgery.
They applied enough tension to the graft before buttoning it down so that the proximal interphalangeal (PIP) joint was in a neutral position with the distal interphalangeal (DIP) joint in five degrees of flexion. With one of the seven patients, the graft tension was adjusted with both joints in a neutral position. The result was a buttonhole deformity (obvious inward indentation or “dimple” along the side of the finger where the graft is tied).
In summary, the purpose of this study was to report on results of using the Thompson procedure in seven cases of chronic mallet finger deformity. The Thompson procedure is safe and effective. It is recommended in cases of severe extensor lag (30 degree or more) of the distal interphalangeal (DIP) joint and for patients who have had an unsuccessful prior surgery for mallet finger.
The authors also point out that patients with a rigid swan neck deformity, contracture of the DIP joint, or DIP joint deformity caused by bone fracture and joint dislocation are NOT good candidates for the Thompson procedure.