Two collateral ligaments, accessory collateral ligaments, volar plate which prevent hyperextension of digital joints, fibrous flexor sheath which attached to volar plate, intrinsic and extrinsic muscles were contribute to the stability of the digital joints. Among them, two collateral ligaments were most important as a static stabilizer. Especially, the instability of fingers due to the rupture of ulnar collateral ligament of metacarpophalangeal joint of thumb and radial collateral ligament of index will attenuate the pinch power and maybe a cause of chronic painful limited finger motions. So, they should be repaired if ruptured completely. During the period of May 1980 to Oct. 1985, 17 cases of ruptured collateral ligaments 5 cases in thumb, 12 cases in fingers were treated surgically and followed up for average 8 weeks. The results were that normal range of digital joint motion were obtained in 14 cases and instabilities were disappeared in 16 cases and pain free in 12 cases. Therefore, careful clinical evaluation to detact therupture of collateral ligament of dig.ital joint after hand injury and then appropriate management could restore the best function of hand.