REIDER PART 1
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150 Chapter 4 Hand and Wrist

laxity at thc MCP joint and notes the angle that the devi-ated index finger makes with the adjacent long finger.

In the normal patient, a smali amount of separation between the indcx and thc long fmgers occurs owing to rotation of the metacarpals or minor degrees of residual laxity in the collateral ligaments, but thc angle between the two adjacent fmgers should not exceed 15° or 20°. In thc presence of a mild sprain of the ulnar collateral ligament, this stress reproduces thc patients pain on the ulnar side of the metacarpal head, but stability feels normal. In morę severc injuries of thc ulnar collateral ligament of thc MCP joint, the resistance of the collateral ligament feels spongy and thc bones appear to separatc morę than in the normal hand. If thc fccling of an endpoint is completely lacking, or if the angle between the index and the long fmgers exceeds 35°, a complete rupture of the ulnar collateral ligament of the MCP joint of thc index finger is present. Most injuries to the collateral ligaments of the MCP joints are traumatic, but in rheumatoid arthritis the radial collateral ligaments stretch out gradually as the subluxing extcnsor tendons puli the fmgers into ulnar deviation.

The collateral ligaments of the MCP joint of the thumb are tested in a manner almost idcntical to that just deseribed for thc MCP joints of the fmgers. In the thumb, thc vast majority of thesc injuries occur to the ulnar collateral ligament; injuries to thc radial collateral ligament are uncommon. In many individuals, the MCP joint of the thumb cannot flex to 90°. Flexing the joint to 30°, howevcr, tenses thc collateral ligaments and allows for proper testing.

To test the ulnar collateral ligament of the thumb, the examiner flexes the patients thumb to 30° at the MCP joint by grasping the proximal phalanx (Fig. 4-80A). The examiner then pushes the thumb away from the index finger, thus tensing the ulnar collateral ligament (Fig. 4-80B). In some individuals, somc laxity of the ulnar collateral ligament is felt before the ligament tightens lully and firmly resists further motion.

In thc normal thumb, this laxity is usually limited to 15° or less. If a mild sprain of the ulnar collateral ligament is present, this mancuver reproduces the patients pain on the ulnar side of the joint, but no abnormal laxity is felt. In morę severe degrees of ligament injury, thc ulnar side of the joint is felt to separate as thc thumb is pushed away from the index finger. Asymmetric deviation of the joint of morę than 30° reflects a severe injury to the ulnar collateral ligament. In the most severe injuries, virtually no resistance is perceived and the examiner may feel that the thumb can be pushed to the side almost without restriction.

Radial collateral ligament injuries of the MCP joint of the thumb are unusual. When they do occur, abnormal laxity can be evaluated by a similar test conducted by applying force in the opposite direction.

Figurę 4-80. A and B, Stability testing of the ulnar collateral ligament of the thumb (arrow indicatcs the direction of the force applied to the proximal phalanx of the thumb). Q Thumb of patient with tom UCL.