The lateral extensor slips (lateral bundles) of the human finger in interphalangeal flexion

Abstract

In the present paper on functional anatomy of the human finger, we discuss the normal palmar gliding of the lateral slips (or lateral bundles) of the extensor tendon along the flexing proximal interphalangeal (PIP) joint. Finely tuned by the tendinous spiral fibers, this palmar gliding enables simultaneous flexion of the distal interphalangeal (DIP) joint. This is essential for undisturbed kinematic coupling of finger motion. In-vitro observations during manipulation of anatomical specimens of the finger reveal this phenomenon. In-vivo observations, however, have hitherto been absent. By means of high-resolution ultrasonography, we thus obtained in-vivo transversal sections of the PIP joint in extension as well as in flexion showing the palmar gliding of the lateral bundles. The images were used to compare with equivalent in-vitro transversal sections, and with current models from literature. We observed a satisfying congruence between our transverse images acquired by high-resolution MRI and by highresolution ultrasonography. Proximal interphalangeal flexion alone shows that the lateral bundles assume only slightly more palmar positions than in extension. In subsequent distal interphalangeal flexion however, the lateral bundles assume almost sagittal positions, and as a consequence, also more palmar positions along the proximal interphalangeal joint. The resulting data may contribute to finger extensor tendon repair by reconstructive surgery techniques.