Avulsion of the flexor digitorum profundus (FDP) tendon from its insertion on the base of the distal phalanx is known by the eponym "jersey finger". This injury of often a result from pulling on a jersey during an (American) football game. This injury was first described by VonZander in 1891, in a drummer.
Photograph of a flexor digitorum profundus tendon injury. Note that the injured finger is held in forced extension:
In the case of a FDP avulsion, MRI can be performed to see where the end of the torn, retracted tendon is.
Coronal images of the palm depict a flaccid FDP tendon in the palm, with surrounding edema:
Sagittal image of the ring finger reveals the gap (red arrows) between the torn ends of the FDP and also depicts the intact flexor digitorum superficialis tendon (green arrows):
The first detailed classification of FDP avulsion was given by Leddy and Packer in 1977, and was elaborated upon by Buscemi and Page in 1987:
Type I- characterized by retraction of the tendon into the palm. There is often a painful nodule in the palm, where the retracted tendon lies. The vascular supply to tendon is disrupted, so it should be repaired as soon as possible, no later than 7-10 days after injury.
Type II- tendon retracts to the PIP joint. Further retraction is prevented by connections through the vincula longa; preserved vascularity through the vincula prevents necrosis and tendon contracture. Occasionally, a small bone fleck is avulsed, and this can be seen at the level of the PIP joint.
Type III- avulsion of a large bone fragment from the base of the distal phalanx. Tendon will not retract past the DIP joint, due to the A4 pulley. Must be treated with open reduction, because of possible associated avulsion of profundus tendon from the osseous fragment (Type IV lesion)
Type IV- type III lesions associated with a simultaneous avulsion of the FDP tendon from the fracture fragment.
Early diagnosis and treatment of these injuries is crucial. FDP avulsion is often incorrectly labeled a "sprain" or "jammed finger", treated with splinting, and the opportunity for timely treatment is lost. The cardinal sign of a FDP rupture is the complete loss of flexion at the DIP joint.
Vic David MD