22 fresh cadaver specimens have been examined to study the anatomy, histology and biomechanical features of the ligaments of the proximal and distal poles of the scaphoid. The biomechanical study was carried out by two methods: an analytical one on an Instron machine, and a global one in situ. The different experiments show the predominant rôle of the distal ligamentous complex of the scaphoid over the scapho-lunate ligament. This contrasts with the generally accepted concept and modifies the management of lateral carpal instability.

The movements of flexion of the digital articular chain are dependent upon a vast functional complex comprising the long flexor tendons, their antagonist long extensor tendons, and the coupled action of the interosseous and lumbricales muscles. Based on theoretical biomechanical data backed up by experimental investigation, the authors emphasize the important role of the digital fibrous sheath in the mechanism of action of the long flexor tendon. Any proximal resection (even of minor degree) of the proximal pulley of the digit induces severe mechanical disturbances by enhancing flexion of the metacarpophalangeal joint to the detriment of the proximal interphalangeal joint. Conversely, distal resection of the pulley enhances flexion of the interphalangeal joint to the detriment of the metacarpophalangeal articulation, although the resulting abnormalities are less pronounced than those due to proximal resection. The fibrous pulley plays a role in tendinous orientation in the frontal plane and in digital orientation of the index finger where the angulation between the pulley and flexor tendon is most pronounced. In this latter case ulnar deviation of the second finger occurs on flexion. Reconstructive surgery of the long flexor tendons requires that the digital fibrous sheath, especially its proximal segment, be preserved. The metacarpophalangeal joint seems to be the most vulnerable to morphological modifications of the pulley, as stressed from the anatomical standpoint by the absence of insertion of the long flexor tendons on the proximal phalanx.

No abstract

In the synergistic complex formed by the intervertebral disc and posterior articular processes, the latter play a significant role to protect the disc and block forward movement of the spine. This role is of special importance at the level of the lumbosacral interface whose inclination contributes to increase shearing forces acting on the disc. The orientation of the lumbosacral articular processes modifies the distribution of the mechanical stress acting at their level. The relationship between the orientation of the articular processes and the stress transmitted to the disc was studied by computerized tomography (31 subjects without disc prolapse, 35 subjects with disc prolapse, 110 operative reports). Sagittal orientation of the facet joints, which is consistently more pronounced on the right side, seems to promote the occurrence of disc prolapse at the lumbosacral level.

No abstract