PARTIAL MENISCECTOMY: HOW MUCH CAN BE REMOVED BEFORE A MENISCUS RECONSTRUCTION IS REQUIRED?

Introduction Partial meniscectomy, a surgical treatment for meniscal lesions, allows athletes to return to sporting activities within two weeks. However, this increases knee joint shear stress, which is reported to cause osteoarthritis. The volumes and locations of partial meniscectomy that would result in a substantial increase in knee joint stress is not known. This information could inform surgeons when a meniscus reconstruction is required. Aim Our aim was to use a previously validated knee finite element (FE) model to predict the effects of different volumes and locations of partial meniscectomy on cartilage shear stress. The functional point of interest was at the end of weight acceptance in walking and running, when the knee is subjected to maximum loading. Method An FE model of the knee joint was used to simulate walking and running, two of the most common functional activities. Forces and moments, obtained from the gait cycle of a 76.4 kg male subject, were applied at the tibia. Different sizes (0%, 10%, 30%, 60%) and locations (anterior, medial and posterior) of partial meniscectomies were simulated (Figure 1). Maximum cartilage shear stress was determined for the different meniscectomies. Graphs were plotted of the cumulative tibial cartilage volume subjected to stress values above specific thresholds. Results and analysis Maximum shear stress values for the intact knee during walking were 2.00 MPa medially and 1.71 MPa laterally. During running these magnitudes rose to 3.48 MPa medially and 4.70 MPa laterally. For a 30% anterior, central and posterior meniscectomy during walking shear stress increased by 25.9%, 44.9% and 32.5% medially, and 12.4%, 25.7% and 17.8% laterally. During running shear stress increased by 9.6%, 8.3% and 7.1%, medially and 31.6%, 37.5% and 43.6% laterally. For a 60% meniscectomy, during walking shear stress increased by 47.2% medially and 31.8%, laterally. During running shear stress increased by 10.0%, medially and 51.8%, laterally. The percentage of cartilage volume exposed to shear stress levels above a specified threshold is illustrated in Figure 2 for different volumes and locations of partial meniscectomy. Discussion and conclusions This is first study that has estimated the volume of cartilage exposed to specific stress thresholds in walking and running as a function of the amount and location of meniscectomy. Maximum shear stress was 100% higher at the end of weight acceptance in running compared to walking. Stress was higher in the lateral compartment during running while higher in the medial compartment during walking. This is because a valgus moment acts at the knee at the end of weight acceptance in running while a varus moment acts at the joint in walking. Clinical significance The model developed from this research has potential for applications in planning meniscal surgeries and developing rehabilitation strategies for athletes. It could inform surgeons about the safe volume and location of partial meniscectomy that can be performed before meniscus reconstruction becomes necessary. Results of this study also highlight the importance of considering the effect of post-surgical outcomes following different common functional activities.