[Paralysis of the intrinsic muscles of the hand]

Intrinsic muscles of the fingers are the interosseous, lumbricals and hypothenar muscles. Their main action is metacarpophalangeal (MP) flexion and interphalangeal (IP) extension. If extrinsic muscles remain active, intrinsic paralysis results in a claw deformity: MP hyperextension and IP flexion. Bouvier's test is positive if IP extension is actively possible when MP hyperextension is passively prevented. Surgical operations to correct claw deformity are divided into passive and active palliative procedures. Passive palliative procedures are tenodeses and capsuloplasties. Active palliative procedures have either a proximal action (MP flexion only): lasso and direct interosseous activation, or a distal action (MP flexion and IP extension). When Bouvier's maneuver is positive, a simple claw deformity may be treated by a passive procedure and/or an active palliative with proximal action procedure. This last procedure should be preferably indicated on index and middle finger if a few muscular motors are available. When claw deformity is complicated by MP stiffness in extension, a capsulectomy-capsuloplasty is indicated. When Bouvier's test is negative, and passive IP extension is possible, an active palliative with distal action procedure is indicated. Even when there is no claw deformity, intrinsic paralysis may be treated by an active palliative with proximal action procedure, in order to stabilize pinch and grasp. Capsuloplasties, lassos and interosseous activation procedures were all invented by Eduardo Zancolli.