Sweater Finger Sign
Clinically Relevant Anatomy
Flexor Digitorum Profundus is a fusiform muscle located deep within the anterior (flexor) compartment of the forearm . The FDP muscle divides into 4 tendons that run down the forearm and closer to the bone. These tendons insert into the base of the distal phalanges of the index, middle, ring, and little fingers, and assist in bending them at the fingertip joint.. As the tendons of the FDP arise at or below the wrist joint, they allow a power grip by the contraction of the muscle .
The patient's position while tested should be sitting.
The following steps are taken to confirm if the sign is positive or not: 
Step 1. The therapist holds the patients' Metacarpophalangeal (MCP) and Proximal interphalangeal (PIP) in full extension.
Step 2. Then the patient is asked to flex at the DIP or make a fist.
Step 3. The PIP must be tested in full extension to isolate FDP function.
Step 4. If the FDP is intact, the patient will be able to flex at the DIP.
Interpretation of results
The sweater finger sign is said to be positive when the finger is not bent; when there is a loss of flexion at DIP of one of the fingers.
The Jersey test is indicated in the diagnosis of the Flexor digitorum profundus injury .
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