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Tendon Injuries of the Thumb

- See:
      - Excursion, of Tendons
      - Thumb Deformities in Rheumatoid Arthritis
      - Thumb Soft Tissue Defects
      - Flexor Pollicis Longus
      - Extensor Pollicis Longus

- Tendon Sheath Anatomy:
    - A1 pulley: spans the MP joint, approximately 8 mm in width;
          - note that the FPB inserts just proximal to this pulley and the adductor pollicis inserts distal to the A1 pulley;      
    - oblique pulley: located over the mid aspect of the phalanx, approximately 10 mm in width;
          - note that the adductor pollicis partially inserts into the oblique pulley;
    - A2 pulley located at the most distal aspect of the proximal phalanx, and is 9 mm in width;
          - it may partially span the thumb IP joint;

- Zone 1 Flexor Tendon Injuries:
    - in thumb, zone 1 extends from tip of finger to just distal to IP joint;
          - contains, oblique and A2 pulleys;
          - of these, the oblique is more important, but either can be sacrificed if the other remains intact;
    - most tendon injuries of thumb occur at level of IP crease, which is near point of the FPL insertion;
    - exposure:
          - skin laceration needs to be extended both proximally and distally;
          - flexor tendon sheath is "Z" step cut so that edge of the resected sheath lies about 1 cm beyond excursion of thickened area of sutured tendon;
    - tendon retrieval:
          - first, note that FPL tendon lacerations often retract into the thenar area or wrist;
                 - unlike the fingers, the FPL often lacks a vinculum and does not have a lumbrical, and therefore the tendon is free to retract;
                 - when there is tendon retraction, the tendon must be retrieved at the wrist;
          - second, note that the FPL tendon sheath is narrow in the thenar region, and therefore, passage of the tendon thru the sheath can be frustrating;
                 - it is important to avoid "scuffing" of the tendon edge as it is pulled thru the tunnel;
          - pass a curved tendon grasper retrograde through the FPL tendon, and insert a core grasping suture into the free edge of the tendon;
                - the tendon grasper is then used to pull the suture back thru the tunnel;
    - delayed reconstruction: FPL Advancement and Pull Thru

- Zone 2 Flexor Tendon Injuries:
    - over thenar eminence, injuries to FPL tendon are likely to occur in conjunction w/ injuries to thenar muscles & recurrent branch of median nerve;

- Tendon Transfers:
    - the following  musculotendinous units have adequate exursion (muscle amplitude), but lack tension strength based on cross sectional area: EPL, EIP, PL;
          - muscles that replace strength and excursion are the following
          - FDS to the long and ring fingers, ECU, and ECRL

Restoration of flexor pollicis longus function by flexor digitorum  superficialis transfer.

Flexor superficialis tendon transfers to the thumb--an alternative to the free tendon graft for treatment of chronic injuries within the digital sheath.

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