The Effect of Lateral Meniscus Tear Patterns on Tibio-Femoral Contact

+1Goyal, K; 1Forsythe, B; 1Costanzo, J; 1Lo, M; 1Muriuki, M; 1Zhang, X; 1Harner, C+1Department of Orthopaedics, University of Pittsburgh Medical Center, Pittsburgh PA

Senior author: harnercd@upmc.edu

INTRODUCTION:Poor outcomes after meniscectomy have resulted in increased interest

in repair of meniscal tears. Furthermore, irreparable tears are debrided in a limited manner with the goal of preserving as much meniscal function as possible. The literature is clear regarding the deleterious effects of meniscectomy; what is currently lacking is a definitive understanding of the effects of various clinically relevant meniscal tears on contact area and kinematics in the knee joint. We hypothesize that altered knee contact pressures and kinematics as a result of meniscal injury and subsequent treatment with meniscectomy are likely contributors to the development of degenerative changes and progression to osteoarthritis.Using a static in-vitro model, we examine joint congruity in the intact knee, and we investigate how vertical cleavage tears, partial tears, and root tears of the lateral meniscus affect joint compartment pressures and contact areas in both the medial and lateral compartments.

METHODS:Four fresh-frozen cadaveric knees were dissected free of skin and

subcutaneous tissue without disrupting the intraarticular and extraarticular anatomic structures that stabilize the knee joint. The specimens were potted in epoxy and mounted in a custom testing apparatus.

Arthroscopic techniques were used to create the following meniscal states sequentially: intact state, vertical tear medial to hiatus (1), vertical tear extending lateral to hiatus (2), partial meniscectomy (3), and complete posterior root tear (4). Through a small arthrotomy, low and super low Fuji Prescale pressure sensitive film (Fuji Photo Film Co. Ltd, Tokyo, Japan) was inserted under the menisci to measure joint contact area and stress. Using an Instron Apparatus, a 1000N load was applied vertically to the femur. Data was collected at four knee flexion angles, 0°, 15°, 30°, and 60°, for each meniscal state. A custom Matlab™(MathWorks Inc., Natick, MA, USA) program was developed anddetermined maximum contact stress, its location and the total contact area. ANOVA was performed to identify significant differences within groups, followed by post hoc, paired, two-tailed, t-tests.

RESULTS:In the lateral compartment there was no interactive effect between

meniscal state and flexion angle. Pressure and contact area were significantly affected by meniscal state (p=0.002 and p=0.021, respectively) but not flexion angle (p=0.84 and p=0.135, respectively).There was no statistical significance in the measures in the medial compartment.

With the knee in full extension, there was significantly greater lateral contact area in the posterior root vs. partial meniscectomy state (p=0.038). At 15° flexion, there was significantly greater lateral contact area in the vertical cleavage medial to hiatus vs. vertical cleavage lateral to hiatus and posterior root tear states, respectively (p=0.026 and 0.024, respectively). At 30° flexion, there was significantly greater lateral contact area in the intact vs. vertical cleavage lateral to hiatus, partial meniscectomy, and posterior root states (p=0.007, p=0.017, and p<0.001, respectively), as well as greater contact area in the vertical cleavage medial to hiatus vs. posterior root tear state (p=0.013). At 60°flexion, there was significantly greater lateral contact area in the intact vs. posterior root tear state (p=0.021).

With the knee in full extension, there were significantly greater lateral maximum pressures in the posterior root tear vs. intact state, and medial and lateral cleavage tear states (p<0.001, p<0.001, p=0.028, respectively). At 15° flexion, there was significantly greater lateral maximum pressure in the posterior root tear vs. all other states (p <0.04for all) and greater lateral maximum pressure in the partial mensicectomy vs. vertical cleavage medial to hiatus state (p=0.016).With the knee in 30° flexion, there were significantly greater lateral maximum pressures in the partial meniscectomy and posterior root tear states vs. intact and vertical cleavage medial and lateral to the hiatus states (p<0.01 for all, respectively). With the knee in 60° flexion, there was significantly greater lateral maximum pressure in the posterior root tear vs. intact and vertical cleavage medial and lateral to hiatus states (p<0.001, for all).

DISCUSSION:The importance of the meniscus to tibiofemoral congruency is well

established, and the biomechanical literature clearly demonstrates the detrimental effects of meniscectomy. However, the effects of clinically relevant meniscus tears are poorly understood. The data from this study demonstrates how lateral tibiofemoral contact areas and maximum joint pressures are affected by clinically relevant meniscal states. Interestingly, no effect of lateral meniscal state was observed on medial compartment contact areas or maximum pressures. Further research is necessary to develop a scientific rationale for clinical decisions made in the treatment of patients with meniscal tears. This information will enable the clinician to offer better treatments with improved patient outcomes, and will likely provide support for surgical repair of meniscus tears over partial meniscectomy.

Poster No. 1190 • 55th Annual Meeting of the Orthopaedic Research Society