Trauma to the PIP joint can cause the joint capsule to tear, the head of the phalanx can buttonhole thru the defect and the lateral bands of the extensor tendons fall laterally & contract
The lateral bands then function as PIP flexors and not extensors
DIP hyperextension due to excessive pull of the displaced lateral bands
As a result, the pateint WILL be able to flex the DIP joint, but WILL NOT be able to extend the PIP joint
OCCURS1 - 3 weeks post injury
May not present with classic textbook deformity
The Elson test is the best way to detect the injury pattern before the deformity is evident
