Paper # 277: Biomechanical Consequence of Posterior Medial Meniscal Root Tears with Subsequent Repair Using a Physiologic Loading Model

Abstract

A physiologic load, simulating a knee squat and a pressure sensitive, capacitive, electronic sensor were used to investigate the biomechanical consequence of a meniscal root tear, subsequent repair and total meniscectomy. Posterior root tears of the medial meniscus cause a detachment of the meniscus at its insertion onto the posterior tibial plateau. Recent literature has identified these tears as common and 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 these same studies also report that repair of the meniscal root corrects compartment loading (Marzo, 2008; Allaire et. al. 2008). The current study investigates the effect of posterior medial meniscal root tears on medial compartment loading using a physiologic model that recreates a knee squat. An all arthroscopic meniscal root repair technique which uses a retrograde reaming device (FlipCutterTM, Arthrex, Naples, FL, USA) to create a blind socket at the tibial insertion into which the meniscal root is advanced, recreating the tibial attachment, was then performed to repair the posterior root tear(Nicholas et al 2009). The knees were then similarly loaded after root repair and subsequent total meniscectomy, examining their effect on medial compartment loading. Nine fresh-frozen cadaver knees were dissected of soft tissue to the joint capsule while preserving the insertion and entire length of the 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 the ground reaction force). Anterior and posterior, submeniscal arthrotomies were made allowing for passage of a pressure sensitive, capacitive, electronic sensor, custom 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 medial meniscectomy. Each condition was tested at 15, 45 and 90 degrees of knee flexion. Transection of the meniscal root significantly 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. Our study differs from previous studies 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 transection was approximately 25% of that seen with total meniscectomy. The previously described meniscal root repair technique (Nicholas et al 2009) recreated normal compartment loading.