Biomechanical Consequence of Posterior Medial Meniscal Root Tears with Subsequent Repair Using a Physiologic Loading Model (SS-32)

Abstract

<h3>Introduction</h3> Posterior root tears of the medial meniscus cause a detachment of the meniscus at its insertion to the posterior tibia. These tears have been identified as clinically significant entities associated with meniscal extrusion and the development of degenerative arthritis. Recent studies demonstrated that meniscal root tears are biomechanically equivalent to total meniscectomy in axial load models, while also reporting that root repair can correct compartment loading (Marzo, 2008; Allaire et al., 2008). This study investigates the effect of posterior medial meniscal root tears on medial knee compartment loading using a physiologic model that recreates a knee squat. A meniscal root repair technique which uses a retrograde reaming device to create a socket at the tibial insertion, into which the meniscal root is advanced, recreating the tibial attachment, was then performed (Nicholas et al., 2009). The knees were then loaded after the root repair and subsequent total meniscectomy examining the effect on medial compartment loading. <h3>Methods</h3> Nine fresh-frozen cadaver knees were dissected of soft tissue to the joint capsule while preserving the insertion and entire quadriceps and hamstring tendons. Knee moments during squatting were simulated in a custom testing jig by application of angle specific loads to the quadriceps and hamstring tendons (based on body mass) with an axial compressive load at the tibia used to flex the knee to the desired angle (simulating ground reaction force). Anterior and posterior submeniscal arthrotomies allowed for passage of a pressure sensitive, capacitive, electronic sensor, made to approximate the medial tibial plateau shape and surface area. This sensor measures both contact area and peak pressures. Each specimen was then tested in four conditions: medial meniscus intact, after creation of posterior root tear, after repair of the meniscal root, and after total meniscectomy. Each condition was tested at 15, 45, and 90 degrees of knee flexion. <h3>Results</h3> Transection of the meniscal root decreased the contact area of the medial compartment by 13% (p=0.002). After meniscal root repair, contact area was not significantly different from the intact meniscal state (decreased 6%, p=0.302). Additionally, total meniscectomy reduced contact area by 53% (p=0.025). Root transection also resulted in an overall increase in peak contact pressure of 21% (p=0.167) in the medial compartment. Meniscal root repair showed no difference when compared to the intact meniscal state (increased 10%, p=0.425) and total meniscectomy increased peak contact pressure by 97% at 15 degrees (p=0.015) with no significant effect at 45 or 90 degrees of knee flexion. <h3>Conclusion</h3> Our study differs from others in the use of a physiologic load model that recreates the loads seen in the knee during the performance of a squat rather than an axial load model using supraphysiological loads and/or non-angle specific loading. In contrast to previous reports, our results show that meniscal root tears are not equivalent to total meniscectomies. The reduction in tibiofemoral contact area with meniscal root transaction was approximately 25% of that seen with total meniscectomy. The previously described meniscal root repair technique (Nicholas et al., 2009) recreated normal compartment loading.