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FDP Avulsion/Rupture


- See: Phalangeal Injury

- Mechanism:
    - results from forceful hyperextension of DIP joint w/ FDP in maximal contraction;
    - classic examples include pts injured by the sudden jerk of a rope, such as starting a lawnmower
           or retraining an animal;
    - tendon may rupture directly from its insertion into bone, or it may avulse bone fragment from base of distal phalanx;
           - it may also rupture at the musculotendinous junction;
    - there is more soft tissue injury and hemorrhage than seen w/ simple laceration, & therefore there is more scarring
           of flexor tendon sheath;
    - ring finger is most often involved (75%);
           - this is due to a weaker insertion, a common flexor muscle belly of middle, ring, and little fingers;
    - anatomy: 
           - avulsed tendon ends retract proximally, & may become entrapped at chiasma of FDS at the level of PIP joint,
                   causing a flexion contracture of the PIP;
           - tendon retracts to the base of the digit or into palm, depending on the force of the avulsion;
           - vinculum prevents excessive retraction;
           - lumbricals prevent proximal retraction of lacerated FDP past the mid-palmar area;
    - diff dx:
           - anterior interosseous nerve paralysis (index and long fingers);
           - trigger finger
           - swan neck deformity (can resemble chronic PIP rupture);
    - classification:
           - Type I   - retracts to the palm;
           - Type II  - retracts to the PIP joint;
           - Type III - bony fragment distal to A4;
    - references:
           - "Rugby finger"--Avulsion of the profundus of the ring finger.  
           - Avulsion of the profundus tendon insertion in athletes.   
           - Misleading fractures after profundus tendon avulsions: a report of six cases.

- Exam:

    - attempt to feel the lump of the tendon in palm;
    - consider AIN palsy
    - references: A simple clinical test to differentiate rupture of flexor pollicis longus and incomplete anterior interosseous paralysis.

- Radiograph:

- Indications for Repair:
    - FDP is difficult to repair if tendon retracts into palm for longer than 7 days because tendon becomes swollen, vinculum
           remains avulsed, & tendon cannot be rethreaded (which would comprimise PIP movement);
    - attempts at repairing the tendon after 2 wks will be unsuccessful;
    - if tendon has retracted into  palm consider tendon excision and DIP fusion
           - DIP fusion most indicated in index finger or use of free tendon graft;
    - reference:
           - [Traumatic avulsion of the flexor digitorum profundus tendon. Report of 20 cases].

- Operative Repair:
    - goal is to reattach the flexor tendon to the point of avulsion;
    - tendon is isolated proximally and the phalanx is exposed distally;
    - tendon is rethread using a silicone flexible tendon;
    - avoid A4 pulley disruption (which will impair DIP flexion);
    - in type I tendon rupture (w/ retraction into palm), the vinicular system has been disrupted, and the tip of the profundus
           tendon will be avascular;
           - hence, the distal end of the tendon should be trimmed;
    - in type II rupture, the blood supply to the tendon is left intact, but fibrosis may develop at the FDS chiasm which might
           limit flexion gliding;
           - any such fibrosis should be debrided;

- Pull Through Technique:
    - repair is uses a 3-O polypropylene suture thru distal end of tendon as double figure of eight, and attached to tendon just
            proximal to bone fragment;
    - pass suture on either side of phalanx thru the periosteum;
    - tie sutures over a plastic button placed directly over finger nail to avoid pressure on the tip of the digit;
    - complications:
           - quadriga may develop if the FDP is excessively advanced;

- Alternatives:
    - chronic rupture:
           - in that case of late FDP rupture with intact FDS, consider whether the functional deficit warrents FDP reconstruction;
           - consider no treatment, or tenodesis or arthrodesis of the distal interphalangeal joint to free tendon grafting;

- DIP Arthrodesis:

- Complications:
    - w/ chronic neglected injury there may be dorsal subluxation of the DIP;

The effect of mitek anchor insertion angle to attachment of FDP avulsion injuries.

Bone suture anchors versus the pullout button for repair of distal profundus tendon injuries: a comparison of strength in human cadaveric hands.

Comparison of pullout button versus suture anchor for zone I flexor tendon repair.

Comparison of an all-inside suture technique with traditional pull-out suture and suture anchor repair techniques for flexor digitorum profundus attachment to bone.