Biomechanical study of a fresh-frozen cadaveric knee with discoid lateral meniscus.

BACKGROUND: To evaluate the biomechanical characteristics of the discoid lateral meniscus (DLM) using a cadaveric specimen and clarify the effects of partial meniscectomy on the resultant force of the DLM and knee kinematics. METHODS: Fresh-frozen cadaveric knee with a DLM was tested using a robotic system with six degrees of freedom. The knee was tested under 5-Nm valgus torque at 0°, 30°, 60° and 90° flexion to measure the resultant force and tibiofemoral valgus angle. Knee kinematics were evaluated during passive flexion-extension from 0 to 120° with a 10-N axial load. Five conditions were sequentially evaluated: intact, 25%, 50%, 75% partial lateral meniscectomy, and 100% lateral meniscectomy. RESULTS: The resultant force of the DLM under 5-Nm valgus torque in each condition (intact/25%/50%/75% lateral meniscectomy) was 79.1/78.0/72.9/36.4 N at 0°; 61.6/57.0/54.9/21.6 N at 30°; 37.8/43.3/42.1/17.7 N at 60°; and 36.7/35.4/26.4/11.6 N at 90°, respectively. Additionally, the tibiofemoral valgus angle under 5-Nm valgus torque (intact/25%/50%/75% lateral meniscectomy/100% lateral meniscectomy) was 2.8/2.9/3.1/4.7/5.9° at 0°; 1.8/2.0/2.2/3.4/4.3° at 30°; 1.9/1.6/2.0/2.7/3.1° at 60°; and 3.4/3.7/4.1/6.2/7.1° at 90°, respectively. The tibiofemoral valgus angle under passive flexion-extension was -0.2/-0.1/0.3/1.0/2.8° at 0°; -1.3/-1.2/-1.0/0.1/0.8° at 30°; -2.0/-2.2/-2.0/-1.1/-0.8° at 60°; -1.9/-2.4/-2.2/-1.6/-1.0° at 90°; -1.2/-2.2/-2.2/-1.2/-0.6° at 120°, respectively. Finally, the external tibial rotation angle under passive flexion-extension in each condition was -8.8/-5.6/-3.7/-4.2/-1.3° at 0°; -7.1/-4.2/-2.4/-2.0/1.7° at 30°; -9.1/-5.7/-4.0/-3.2/-0.6° at 60°; -14.0/-9.7/-8.5/-7.8/-6.6° at 90°; and -18.5/-14.0/-12.7/-12.1/-10.9° at 120°, respectively. CONCLUSIONS: Limited partial meniscectomy appeared to largely maintain the resultant force and tibiofemoral valgus angle of the DLM, whereas extensive resection was associated with reduced resultant force and a valgus shift. Tibial external rotation tended to increase progressively with increasing resection volume.