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- Anatomy:
    - flexor sheath of thumb usually extends from distal phalanx to a point 2-4 cm proximal to volar wrist crease;
    - proximal half of tendon sheath is commonly referred to as the radial bursa;
    - occasionally proximal half of FPL sheath is separate from distal sheath, making them entirely separate sheaths;
    - in 80% of patients, the ulnar bursae communicates w/ the radial bursae;
           - this accounts for the horse shoe tenosynovitis;

- Tenosynovitis:
     - pus may extend from thumb sheath to proximal end of radial bursae;
     - pus in thumb flexor tendon sheath can also lead to infection in carpal tunnel;
     - incision:
           - extends on ular side of FPL sheath & distal part of thenar eminence;
           - do not to extend incision along ulnar border of thenar eminence proximally beyond the mid point of first metacarpal;
                 - this avoids motor branches of median nerve