The Functional Anatomy of the Extensor Mechanism of the Finger

Our investigations indicate that the oblique retinacular ligament does not extend the distal phalanx in the normal hand. It, therefore, need not be reconstructed in attempting to restore distal interphalangeal extension. Our efforts should, in general, be directed toward a restoration of the lateral band mechanism. 2. Dorsal and volar migration of the lateral bands at the proximal interphalangeal joint level is not dependent on the triangular ligament or the transverse retinacular ligaments. It is based on simple mechanical principles, and will take place even though the lateral bands are completely free throughout their length. In the surgical repair of old boutonnière deformities, our efforts should be directed toward re-establishment of the central slip. The lateral bands, which are normal, should not be disturbed. 3. The central slip at the base of the proximal phalanx has no extensor function in the normal finger, except when the metacarpophalangeal joint is in extreme hyperextension. We must not, therefore, fix this mechanism rigidly to the base of the proximal phalanx by surgically produced insertions.