Contact characteristics of the subtalar joint: the effect of talar neck misalignment

The scapholunate allograft: a biomechanical feasibility study

The feasibility of a new method for reconstruction of the isolated scapholunate ligament tear with a scapholunate allograft was studied biomechanically using a fresh cadaver upper extremity model. Seven specimens were first tested intact for wrist range of motion, contact characteristics of the radiocarpal articulation, and relative motion of the scaphoid with respect to the lunate. Then a segment consisting of the radial third of the lunate, the adjoining scapholunate interosseus ligament, and the proximal pole of the scaphoid was resected. This segment was matched to a donor allograft of similar size and geometry, which was then placed into the recipient carpus and secured with one central transverse Kirschner wire and two shorter interfragmentary Kirschner wires placed into the lunate and scaphoid. The allografted specimen was subjected to the same tests as the intact wrist. Results showed that there were no significant differences in wrist range of motion, radiocarpal articular surface contact area and pressure, and relative flexion-extension rotation between the scaphoid and lunate during passive radioulnar deviation between the intact and allografted wrists.

Contact areas and pressure distributions in the subtalar joint

We investigated how foot position and ankle arthrodesis affect the contact characteristics of the subtalar joint. Nine fresh-frozen specimens of amputated lower legs were used. Pressure-sensitive films were inserted into the anterior and posterior articulation of the subtalar joint. The contact areas and pressure for various foot positions and under axial loads of 600, 1200, and 1800 N were determined based on the gray level of the digitized film. In neutral position and under a 600 N load, the maximum contact pressure in the subtalar joint was 5.13 +/- 1.16 MPa. The contact area (1.18 +/- 0.35 cm2) was only 12.7% of the whole subtalar articulation area (9.31 +/- 0.66 cm2), and the total force (348.5 +/- 41.7 N) transmitted via this contact area was about 58% of the applied load (600 N). Dorsiflexion of the foot increased the contact area and the force transmitted, but decreased the average contact pressure in the subtalar joint, while the reverse occurred in plantar flexion. Eversion increased the subtalar contact stress, whereas inversion up to 10 degrees decreased it. Ankle joint arthrodesis shifted the contact areas in the subtalar joint posteriorly in all inversion/eversion positions. Moreover, total force transmitted through the subtalar joint as well as the contact pressure increased.