- Clinical science
Finger injuries are very common and because there are many different possible injuries, only some of the more common flexor and extensor tendon as well as ligament injuries will be covered here. Injury is typically caused by lacerations (work place injury, road traffic accidents) or blunt force (e.g., ball sports, falling). For instance, forced extension of the distal interphalangeal joint (DIP) can damage the flexor digitorum profundus (FDP) tendon and lead to a loss of DIP flexion (Jersey finger). Forced flexion of the DIP causes extensor digitorum (ED) tendon injury, which results in a loss of DIP extension (mallet finger). Rupture/slippage of the central band of the ED tendon is primarily due to laceration or blunt injury and results in a hyperextension of the DIP with flexion of the PIP (Boutonniere deformity). Sudden forced hyperextension and abduction of the metacarpophalangeal joint (MCP) of the thumb can tear the ulnar collateral ligament (UCL) and cause laxity (Gamekeeper's thumb). While all flexor tendon injuries need to be surgically repaired, most extensor tendon and some ligament injuries can be managed conservatively with splints. Complete laceration or no response to conservative therapy are indications for surgical repair. Postoperative complications of tendon or ligament injuries include adhesions, joint contractures, and chronic joint deformities (e.g., swan-neck deformity, chronic mallet finger). Early recognition and treatment of injuries and their complications is necessary to prevent permanent disability.
- Physical examination (see "clinical features" below) 
- Flexor digitorum profundus (FDP): Fix the MCP and PIP joints in extension and ask the patient to flex the DIP
- Flexor digitorum superficialis (FDS): Fix all the finger joints in extension (MCP, PIP and DIP) with the palm facing upwards. The patient is asked to flex the PIP of the injured finger
- Flexor pollicis longus (FPL): The patient is asked to flex the interphalangeal joint of the thumb
- Flexor carpi radialis and ulnaris: The patient is asked to flex the wrist
- Extensor pollicis longus (EPL): The hand is place palm-down on a flat surface and the patient is asked to raise his thumb
- Extensor pollicis brevis (EPB) and abductor pollicis longus: The hand is placed palm-down, and the patient is asked to abduct the thumb away from the other fingers (without raising it)
- Extensor digitorum (ED): The patient is asked to make a loose fist (partial flexion of PIP and DIP) and then asked to extend the MCP joints
- Extensor indicis (EI): The patient is asked to make a fist with all fingers except the index finger (as in pointing at something) This prevents extensor contribution from the ED
- Extensor digiti minimi (EDM): The patient is asked to make a fist with all fingers except the little finger
- Extensor carpi radialis longus (ECRL), brevis (ECRB), and extensor carpi ulnaris (ECU): The patient is asked to extend the wrist Inspect for deviation of the wrist during extension (occurs if only one of the wrist extensors is injured).
- X-ray: three views are taken (posterior-anterior, oblique, and lateral) to identify coexistent fractures
- Ultrasound: can detect complete lacerations 
- MRI: provides accurate description of the extent of tendon or ligament injury
|Affected tendon(s) or ligament(s)||Condition||Mechanism of injury||Clinical features||Treatment||Possible complications|
|Flexor digitorum profundus tendon||Jersey finger|| || || || |
|Extensor digitorum tendon||Mallet finger|| || |
|Central band of extensor digitorum tendon||Boutonniere deformity|| || || |
Ulnar collateral ligament (UCL) of the thumb
|Gamekeeper's thumb (Skier's thumb)|| || |
The differential diagnoses listed here are not exhaustive.