HAND/WRIST
Synergy may be defined as two or more components working together to produce an outcome or result not attainable by any of those components individually. A group’s ability to outperform even its strongest, most powerful member represents synergy. Hand synergy is imperative for optimal performance of all daily activities. Often the hand is subjected to overuse, trauma or degenerative changes, which result in tendon imbalances. There are several types of tendon imbalances, which occur in the finger. Untreated, these imbalances will lead to deformity and impaired function of the entire hand.
Mallet Finger refers to loss of terminal joint extension in the digit. This type of injury may consist of soft tissue injury only (Tendinous Mallet) or may be associated with an articular fracture (Bony Mallet). “Baseball finger” or “drop finger” are names frequently associated with a Mallet finger. These injuries are generally treated with immobilization splinting or operative stabilization. The primary goal of rehab is to promote healing of the injured tendon minimizing loss of extension at the fingertip (DIP joint) and ensuring no loss of flexion at the middle of the finger (PIP joint).
Boutonniere Deformity, also commonly referred to, as “buttonhole” deformity is a loss of central slip function. The digit will appear with the middle joint (PIP joint) bent or flexed and the end joint (DIP joint) hyperextended. Causes of boutonniere deformity include extensor tendon injury (to zone 3), traumatic avulsion injuries (to zone 3) and rheumatoid arthritis. Generally, these injuries are treated conservatively with hand therapy utilizing various splinting techniques to restore PIP joint extension and DIP joint full active flexion. Your therapist will encourage you to actively bend your fingertip while immobilizing the middle portion of your finger in a splint. Surgery will be considered if the deformity was caused due to an acute, open injury.
Swan Neck Deformity, is characterized by hyperextension of the PIP joint along with flexion of the DIP joint. Usual causes of this deformity include laxity of the volar plate, and/or an imbalance of muscle forces on the PIP (usually extension>flexion force). Swan neck deformity can be seen in conjunction with mallet finger, laceration of the flexor digitorum superficialis (FDS) tendon, intrinsic muscle contractures and rheumatoid arthritis (RA). This deformity is often associated with snapping and locking of the fingers. There are several surgical approaches to operative management of this condition. Non-surgical treatment involves splinting the PIP joint in a flexed position (temporarily) to encourage tightening of the volar plate, restoring tendon and joint capsule balance and for prevention of fixed contractures.
Lumbrical Plus Finger or Paradoxical Extension occurs when the PIP and DIP joints extend while the individual is attempting active flexion of the fingers. For example, an individual may attempt to grip an object or form a fist and one finger sticks out (getting caught on clothing, finger extends while attempting to hold a can or glass). This is most commonly seen in the middle finger (likely due to a shared muscle belly with the ring and small fingers). The lumbrical muscles are responsible for extending or straightening the IP joints and flexing or bending the MCP joints. This condition can be caused due to digital lacerations involving the deep flexor tendons or sudden traction on a flexed or bent finger. There are multiple surgical techniques utilized in correction of the Lumbrical Plus Finger or Paradoxical Extension. These muscles work intricately with other muscle groups (interossei, lateral bands, and flexor digitorum profundus). The lumbricals epitomize synergy in the hand and subsequently, the dysfunction that can occur when this synergy is disrupted.
Intrinsic Minus Hand or Claw Hand is caused by an imbalance between strong extrinsics and insufficient intrinsic muscles. The intrinsic minus hand presents with the MCP joints hyperextended and the IP joints flexed (often time worse in the ring and small finger with ulnar nerve palsy). An individual with an intrinsic minus hand will demonstrate an inability for prehensile grasp along with diminished pinch and grip strength. Conservative treatment consist of splinting techniques to correct the unopposed MCP hyperextension and IP unopposed flexion as well as strengthening and ROM activities to prevent permanent deformity. Conversely, Intrinsic Plus Hand is caused due to a muscle imbalance between spastic or tight intrinsics and weak extrinsics. This will present as MCP flexion and IP extension. This can be caused by trauma, arthritis or neurological deficits. Individuals with an intrinsic plus hand will demonstrate difficulty gripping large objects. As with most other pathologies discussed, there are several operative interventions to correct this deformity. Mild cases generally respond well to a passive stretching program.
This brief overview of tendon imbalances in the hand is in no way comprehensive but rather intended to provide a brief overview of the intricacies and synergy that allow your hand to function. All of these conditions (and most hand conditions) achieve greater outcomes with earlier treatment (so don’t wait!). If you have any questions about diagnosis or treatment for these or any hand conditions, please consult with your physician or your hand therapist.
