Modified Lemaire Tenodesis Forces in Cadaveric Specimens Are Not Affected by Random Small-Scale Variations in the Femoral Insertion Point During Active Knee Joint Flexion-Extension.

Purpose: To directly measure lateral extra-articular tenodesis (LET) forces supporting anterior cruciate ligament reconstruction (ACLR) during dynamic flexion-extension cycles induced by simulated active muscle forces, to investigate the influence of random surgical variation in the femoral LET insertion point around the target insertion position, and to determine potential changes to the extension behavior of the knee joint in a cadaveric model. Methods: After iatrogenic anterior cruciate ligament deficiency and simulated anterolateral rotatory instability, 7 fresh-frozen cadaveric knee joints were treated with isolated ACLR followed by combined ACLR-LET. The specimens were tested on a knee joint test bench during active dynamic flexion-extension with simulated muscle forces. LET forces and the degree of knee joint extension were measured. Random variation in the LET insertion point around the target insertion position was postoperatively quantified by computed tomography. Results: In extension, the median LET force increased to 39 ± 2 N (95% confidence interval [CI], 36 to 40 N). In flexion over 70°, the LET was offloaded (2 ± 1 N; 95% CI, 0 to 2 N). In this study, small-scale surgical variation in the femoral LET insertion point around the target position had a negligible effect on the graft forces measured. We detected no difference in the degree of knee joint extension after combined ACLR-LET (median, 1.0° ± 3.0°; 95% CI, -6.2° to 5.2°) in comparison with isolated ACLR (median, 1.1° ± 3.3°; 95% CI, -6.7° to 6.1°; P = .62). Conclusions: LET forces in combined ACLR-LET increased to a limited extent during active knee joint flexion-extension independent of small-scale variation around 1 specific target insertion point. Combined ACLR-LET did not change knee joint extension in comparison with isolated ACLR under the testing conditions used in this biomechanical study. Clinical Relevance: Low LET forces can be expected during flexion-extension of the knee joint. Small-scale deviations in the femoral LET insertion point around the target insertion position in the modified Lemaire technique might have a minor effect on graft forces during active flexion-extension.

Modified Lemaire tenodesis reduces anterior cruciate ligament graft forces during internal tibial torque loading.

PURPOSE: The aim of the study was to directly measure graft forces of an anterior cruciate ligament reconstruction (ACLR) and a lateral extra-articular tenodesis (LET) using the modified Lemaire technique in combined anterior cruciate ligament (ACL) deficient and anterolateral rotatory instable knees and to analyse the changes in knee joint motion resulting from combined ACLR + LET. METHODS: On a knee joint test bench, six fresh-frozen cadaveric specimens were tested at 0°, 30°, 60°, and 90° of knee flexion in the following states: 1) intact; 2) with resected ACL; 3) with resected ACL combined with anterolateral rotatory instability; 4) with an isolated ACLR; and 5) with combined ACLR + LET. The specimens were examined under various external loads: 1) unloaded; 2) with an anterior tibial translation force (ATF) of 98 N; 3) with an internal tibial torque (IT) of 5 Nm; and 4) with a combined internal tibial torque of 5 Nm and an anterior tibial translation force of 98 N (IT + ATF). The graft forces of the ACLR and LET were recorded by load cells incorporated into custom devices, which were screwed into the femoral tunnels. Motion of the knee joint was analysed using a 3D camera system. RESULTS: During IT and IT + ATF, the addition of a LET reduced the ACLR graft forces up to 61% between 0° and 60° of flexion (P = 0.028). During IT + ATF, the LET graft forces reached 112 N. ACLR alone did not restore native internal tibial rotation after combined ACL deficiency and anterolateral rotatory instability. Combined ACLR + LET was able to restore native internal tibial rotation values for 0°, 60° and 90° of knee flexion with decreased internal tibial rotation at 30° of flexion. CONCLUSION: The study demonstrates that the addition of a LET decreases the forces seen by the ACLR graft and reduces residual rotational laxity after isolated ACLR during internal tibial torque loading. Due to load sharing, a LET could support the ACLR graft and perhaps be the reason for reduced repeat rupture rates seen in clinical studies. Care must be taken not to limit the internal tibial rotation when performing a LET.

[Boundary-layer damping of traveling waves in a three-dimensional passive finite-element model of the human cochlea]. / Grenzschichtdämpfung von Wanderwellen in einem dreidimensionalen passiven Finite Elemente Modell der Cochlea des Menschen.

A passive three-dimensional model of the human cochlea is described and analysed in the present article. One of its features is the implementation of a thermo-viscous boundary layer as a physically approved mechanism of mechanical damping. The model is solved numerically with the finite element method in ANSYS® and the simulation results are analysed with the help of MATLAB®. In this way curves of the basilar membrane's amplitude, phase and velocity for frequencies between 1000Hz and 8000Hz are calculated. A traveling wave develops on the basilar membrane and is damped after reaching its frequency-dependent maximum due to the boundary layer damping. A plot of the frequency-to-space transformation can be obtained which fits to the experimental data found in the literature. Furthermore, the study shows an energy analysis of the simulation verifying the boundary layer damping as a relevant physical effect for 3D-models of the cochlea.