Radial Collateral Ligament Injuries of Index Finger: Abstract Gary M. Louri, MD, Atlanta , GA Purpose The radial collateral ligament (RCL) of the metacarpo-phalyngeal joint (MCP) of the index finger and ulnar collateral ligament of the thumb MCP joint are essential for stability with pinch. Injuries to the thumb UCL are well described in the literature as this is a more common injury. The purpose of this study is to define the natural history of RCL injuries to the MCP joint of the index finger and develop a treatment algorithm for managing these uncommon injuries. Methods We have retrospectively reviewed 14 cases of RCL injuries to the index MCP joint over a four-year period. A clinical diagnosis based on instability and pain was made in all cases on the dominant hand following a forceful ulnar deviation with/without hyperextension. Patient age, delay in diagnosis, worker's compensation status, and initial treatment were correlated with post treatment pain, stability, return to work status, pinch strength, range of motion, changes in hand patterns and presence of degenerative change to devise a treatment algorithm. Clinical reassessments were made until the time of maximal recovery. Statistical analysis was performed using. Results Three of three patients who presented less than one month from the time of injury had good or excellent results with cast immobilization. Of patients who were seen less than one month from injury and treated with buddy tape, aluma-foam splint or no treatment , five of five patients had persistent pain and instability. Of patients who presented greater than one month from the time of injury, less than twenty percent had good or excellent results with conservative management alone. Four of six patients who underwent repair or reconstruction had good or excellent results. The other two patients required MCP fusion. Of note, one of the fusion patients has a second injury to the index finger following her initial surgery.   < 1 month > 1 month Buddy Tape; aluma-foam 100% F/B*     Cast 100% G/E* 20% G/E* Repair/Reconstruct/Fusion   83% G/E* *G/E-Good/Excellent *F/B-Fair/Bad Conclusions If diagnosed less than one month from injury, these injuries can be managed effectively with cast immobilization while buddy taping and aluma-foam splints are ineffective. If the diagnosis is delayed greater than one month then primary ligament repair or reconstruction is advisable. Fusion is a reasonable salvage option. The gravity of RCL injuries to the index finger is likely under appreciated due to the paucity of literature on this topic.