Flexor Tendon Injuries
What is it: The flexor digitorum profundus attaches to the distal phalanx and the flexor digitorum superficialis attaches to the middle phalanx. Either of these two flexor tendons can be injured or ruptured.
How does it present: The more common injury is a rupture of the flexor digitorum profundus called a Jersey finger, which classically occurs when an athlete's finger gets stuck in another players jersey causing sudden forced extension of the finger. A complete rupture of the FDP will result in loss or weakened flexion of the DIP. A hyperextension injury further down the finger may also cause a rupture to the FDS at its insertion on the middle phalanx. If the FDP and FDS are both ruptured, the patient will not be able to flex at the DIP or PIP; however, if just the FDS is ruptured they will continue to have normal appearing flexion of the finger at all joints. The patient will often complain of pain and swelling at the joint of injury.
Common exam findings: Boyes' Test should be performed to evaluate the integrity of the FDP. In this test the hand is placed in a "palm up" position on the table and the injured finger is held in full extension at the MCP and PIP and the ability to flex at the DIP is evaluated. Inability to flex at the DIP indicates an injury to the FDP. The FDS should be evaluated with the hand in the "palm up" position on the table with the uninjured fingers held down fully extended. If the FDS is ruptured and the injured finger is not isolated, the FDP can flex the injured finger at the DIP, PIP and MCP. If the injured finger is isolated by holding the uninjured fingers in extension, then FDP can not function independently, thus limiting flexion at the PIP under these conditions.
Tests and treatment: X-rays should be done to evaluate for other finger or hand fractures and for associated avulsion fractures that may give a clue to the flexor tendon injury. As the tendon is ruptured, a small avulsion fracture off the DIP for the FDP or off the PIP for the FDS may occur. If a flexor tendon injury is suspected by exam and or appropriate avulsion fracture, referral to orthopedics is appropriate as treatment of flexor tendon injuries is surgical.