[Extension of the fingers. V. Anatomic approach to lesions of the extensor apparatus].

The physiopathology of the main deformities of the fingers, induced by the injury of the dorsal aponeurosis of the fingers, is caused by an imbalance of forces: proximally between extrinsic and intrinsic muscles; distally between central and collateral structures. The ulna Claw, caused by the whole paralysis of the intrinsic muscles, can be corrected by an interosseous tenodesis on the basis of the finger. The boutoniere is induced by the exaggeration of the action of the collateral structures with respect to this of the central structures. The swan neck is induced by the exaggeration of action of the central structures with respect to this of the collateral structures. The surgical treatment consist to give back those structures their normal lengthening and way, or else to create new detours or shortenings, allowing to give back the balance. So, any structures, spared by the traumatism, will not injure by the surgeon.