Knee joint line obliquity alters lateral meniscal root tension, tibiofemoral subluxation and compartment-specific contact pressures.

Abstract

The objective was to measure effects of joint line obliquity (JLO) on meniscus posterior root tension, tibiofemoral subluxation and contact pressures. It was hypothesised that a medial JLO would increase medial meniscal (MM) root tension, medial tibiofemoral subluxation and medial compartment contact pressure, and vice versa for lateral downslope. Eight knees were mounted in a compression machine with JLO from 16° medial to 12° lateral downslope. The loading axis was aligned to the centre of the tibial plateau, while JLO was altered by tilting the tibial plateau relative to the loading axis. Subluxation was measured optically. Sub-meniscal sensors measured contact pressures. The posterior MM or lateral meniscus (LM) root was transected and repaired using transosseous suture tapes attached to a tensiometer. The repair was tightened 30 N, then the tension measured at 2× body weight load. This was repeated for each JLO and both menisci, at 0° and 20° flexion. Data analyses used Shapiro-Wilk tests, RM-ANOVA and RM-t post-tests. 2× body weight load (1.48 ± 0.30kN) caused posterior root tensions higher at 20° flexion than 0°: MM 83 ± 15 N and 64 ± 9 N (p < 0.001), LM 75 ± 16 N and 63 ± 13 N (p = 0.006). Changing JLO at 20° flexion from 16° medial to 12° lateral caused 5.4 mm subluxation and increased LM root tension: 55 ± 14 N to 81 ± 12 N (p = 0.016). JLO did not affect MM tension significantly. Medial JLO did not increase medial compartment articular pressure; the lateral compartment saw reduced pressure with lateral JLO. JLO affected lateral compartment contact stresses, but less than meniscal root transection. Beyond 8° lateral JLO the LM root tension was above that with native 4° medial downslope. Root repairs restored contact pressures following root transection. Excessive lateral JLO may influence contact mechanics and meniscal loading. This should be considered during surgical planning of osteotomies. Level N/A, controlled laboratory study.