Background: The posterolateral corner (PLC) resists tibial varus angulation, external rotation, and, to a lesser extent, posterior translation. It is important that reconstructions of posterolateral knee injuries restore joint laxity and patient function, but residual laxities are often observed.
Hypothesis: The knee laxity after a new 4-strand PLC reconstruction would be closer to normal than after a 2-strand “modified Larson” reconstruction.
Study Design: Controlled laboratory study.
Methods: Fourteen intact cadaveric knees were mounted in a 6 degrees of freedom rig and subjected to the following external loading conditions: a 90-N posterior tibial force, a 5-N·m external rotation torque, and 5-N·m varus moment. Knee kinematics were recorded with an active optical tracking system for the intact, PLC-deficient, modified Larson PLC reconstruction and 4-strand PLC reconstruction.
Results: With external tibial torque, the rotational laxity in 4-strand reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P = .0112) and did not differ significantly from intact laxity at any angle of flexion. In response to posterior load, posterior translation did not change in any of the tested conditions, while the coupled external rotation laxity in 4-strand PLC reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P < .0486) and was not significantly different from the intact movements for both reconstructions. The varus angulation-versus-flexion curves were significantly different between the PLC-deficient and both PLC reconstructions (P < .0001). The varus laxity was not significantly different between the modified Larson reconstruction, the 4-strand reconstruction, and the intact knee.
Conclusion: This study showed that the rotational knee laxity in response to both external rotation and posterior translation load were significantly better after the 4-strand PLC reconstruction than after the modified Larson reconstruction, although significant differences were not found between the 2 procedures for varus laxity.
Clinical Relevance: The 4-strand PLC reconstruction may produce a better biomechanical outcome, especially during external rotation and posterior translation tibial load. The authors suggest that this relates to load sharing among 4 graft strands crossing the joint.
Background
Although the use of meniscal allografts to replace severely damaged or absent menisci is commonplace, little is known about the effects of donor age on the biochemical and biomechanical properties of human menisci.
Hypothesis
The mechanical and biochemical properties of human medial and lateral menisci from donors less than 45 years of age do not vary with donor age.
Study Design
Controlled laboratory study.
Methods
Thirty-three lateral and 25 medial menisci from 34 donors (26 male and 8 female) ranging from 15 to 44 years of age were harvested and immediately stored at –80°C. The outer third of each meniscus was subjected to static and dynamic tensile analysis. In addition, the biochemical composition (collagen, proteoglycan, and water content) of these samples was analyzed.
Results
There was no correlation between donor age and static tensile stiffness for either the lateral (R2 = .003) or medial (R2 = .002) meniscus. Likewise, there was no correlation between donor age and dynamic tensile modulus for either the lateral or medial meniscus. Although there was a weak, positive correlation between water content and age in both lateral (R2 = .22) and medial (R2 = .25) menisci, there was no effect of age on collagen or proteoglycan content. There were no differences (P > .05) between female and male menisci in any of the measured biomechanical or biochemical parameters tested.
Conclusion
The tensile properties, as well as the collagen and proteoglycan content, of menisci from donors less than 45 years of age were not age dependent.
Clinical Relevance
The age of the donor does not appear to affect the initial tensile properties of menisci from donors less than 45 years of age.
Background: Double-bundle posterior cruciate ligament reconstructions are performed to more closely replicate the anatomy of the native posterior cruciate ligament and to better restore normal knee biomechanics and kinematics than a single graft. The femoral tunnel for the anterolateral graft is normally located near the anterior margin of the posterior cruciate ligament footprint. However, there is considerable variability with regard to placement of the posteromedial tunnel within the footprint margins.
Hypothesis: A double-bundle posterior cruciate ligament reconstruction will better replicate normal knee biomechanics and kinematics than a single anterolateral graft, and the separation distance between femoral tunnels will significantly affect the recorded measurements.
Study Design: Controlled laboratory study.
Methods: The posterior cruciate ligament’s femoral origin was mechanically isolated using a cylindrical coring cutter, and a cap of bone containing the ligament fibers was attached to a load cell that recorded resultant force in the posterior cruciate ligament as the knee was loaded. Cast acrylic replicas of the femoral bone cap, with 9-mm and 6-mm holes for the anterolateral and posteromedial grafts, respectively, were attached to the load cell. Graft isometries, anterior-posterior laxities, graft forces, and tibial rotations were measured for an anterolateral graft alone, and for anterolateral and posteromedial grafts with narrow (0-mm) and wide (3-mm) bridges between tunnels.
Results: Mean laxities with an anterolateral graft alone were within 1.2 mm of normal, between 0° and 90°; means with double-bundle grafts were 1.7 mm to 2.4 mm less than normal, between 10° and 45°. Relative length change of the anterolateral graft between 0° and 90° was within +1.3 mm, while the posteromedial graft, placed in either tunnel, tightened approximately 6 mm with knee extension from 90° to 0°. At 0°, mean forces with a single anterolateral graft were not significantly different from posterior cruciate ligament forces for any loading mode tested; mean forces with double-bundle grafts were 74 N to 154 N higher than posterior cruciate ligament forces at 0°. During passive knee extension, the double-bundle reconstruction externally rotated the tibia (relative to intact) between 0° and 50°. There were no significant differences in mean knee laxities, graft forces, or tibial rotations between narrow and wide tunnel separations.
Conclusion: In contrast to the anterolateral graft, which experienced minimal length changes, the posteromedial graft tightened 3.1 mm to 4.3 mm from 30° to 0°. When the posteromedial graft was tensioned and fixed at 30°, it developed relatively high graft forces as the knee was extended to 0°; this tended to reduce knee laxity and increase graft forces. With double-bundle grafts, tunnel separation distance was not an important variable with respect to the biomechanical and kinematic measurements recorded in this study.
Clinical Relevance: The need for a posteromedial graft during posterior cruciate ligament reconstruction is questioned, especially in view of the relatively high graft forces at full extension that could cause it to permanently elongate with time. If a double-bundle reconstruction is performed, there is no biomechanical advantage in making the bone bridge between tunnels less than 3 mm.
