Summary Lumbrical Plus Finger is characterized by paradoxical extension of the IP joints while attempting to flex the fingers. Diagnosis is made clinically with extension of the IP joints of one digit with attempted flexion of all fingers (making a fist). Treatment is observation if patient is minimally symptomatic. Operative tenodesis of FDP to terminal tendon or lumbrical release is indicated if symptoms affect patient's activity demands. Epidemiology Anatomic location most common in middle finger (2nd lumbrical) FDP 3, 4, 5 share a common muscle belly cannot independently flex 2 digits without pulling on the third index finger has independent FDP belly when making a fist following FDP2 transection, it is possible to only contract FDS2 (and not FDP2), thus avoiding paradoxical extension Etiology Pathophysiology mechanism FDP disruption distal to the origin of the lumbicals (most common) can be due to FDP transection FDP avulsion DIP amputation amputation through middle phalanx shaft "too long" tendon graft pathoanatomy lumbricals originate from FDP with FDP laceration, FDP contraction leads to pull on lumbricals lumbricals pull on lateral bands leading to PIP and DIP extension of involved digit with the middle finger, when the FDP is cut distally, the FDP shifts ulnarly (because of the pull of the 3rd lumbrical origin)(bipennate) this leads to tightening of the middle finger lumbrical (2nd lumbrical, unipennate), and amplifies the "lumbrical plus" effect Anatomy Lumbricals 1st and 2nd lumbricals unipennate median nerve originate from radial side of FDP2 and FDP3 respectively 3rd and 4th lumbricals bipennate ulnar nerve 3rd lumbrical originates from FDP 3 & 4 4th lumbrical originates from FDP 4 & 5 all insert on radial side of extensor expansion Presentation History recent volar digital laceration (FDP transection) or sudden axial traction on flexed digit (FDP avulsion) Symptoms notices that when attempting to grip an object or form a fist, 1 digit sticks out or gets caught on clothes Physical exam paradoxical IP extension with grip (fingers extend while holding a beer can) Treatment Operative tenodesis of FDP to terminal tendon or reinsertion to distal phalanx indications FDP lacerations do NOT suture flexor-extensor mechanisms over bone lumbrical release indications if FDP is retracted or segmental loss makes it impossible to fix NOT done in the acute setting as it does not occur consistently enough to warrant routine lumbrical sectioning acutely contraindications do not transect lumbricals 1 & 2 if there is concomitant ulnar nerve palsy with ulnar nerve paralysis, the interosseous muscles are also lost (interosseus muscles extend the IP joints) technique transect at base of flexor sheath (in the palm)