The aim of this study is to investigate meniscal extrusion in relation to the biomechanical properties of meniscus in varus gonarthrosis patients. Furthermore, a comparison of patients and healthy individuals in neutral position with and without axial loading is aimed to provide evidence for increased extrusion in existing gonarthrosis and to investigate the effect of axial loading. The extrusion will be differentiated with respect to the degree of joint degeneration. Then, the regional and degeneration-specific differences of the biomechanical parameters of the menisci in relation to the locally identified meniscus extrusion will be enlightened.
After IRB approval, a total of twelve patients with TKA indication and six healthy volunteers were recruited. The determination of extrusion at the medial and lateral meniscus was based on MRI and differentiated at the meniscus anterior horn (AH), posterior horn (PH) and pars intermedia (PI). The images were taken in a 10° flexion position first without and then under 25% individual body weight. The KOOS as well as the WOMET score of the patients and volunteers were determined beforehand. During patient surgery, the tibial plateau with the associated menisci was carefully extracted and subsequently biomechanically tested: first the menisci specimens were prepared in accordance to the same regional areas (AH, PI, PH) as defined in the extrusion experiments. Afterwards, an established confined compression stress-relaxation test (equilibrium modulus - EEq and hydraulic permeability - k) was performed on plane parallel, round meniscus samples. Then, the water content of these samples was determined by lyophilization. Youngs modulus (E), tensile strength (smax) and maximum strain at material failure lmax) were determined for dumbbell-shaped meniscus samples by means of an uniaxial tensile test to failure. In addition to the initial radiological knee joint degeneration classification, the macroscopic and microscopic meniscus degeneration was evaluated using the Pauli scoring.
Unsurprisingly, the patients showed a significantly larger meniscal extrusion compared with the volunteers. Under axial loading, this effect was further enhanced and was significant for all regions and also >3mm for the patients. Direct correlations between the macroscopic meniscus degeneration and extrusion indicated that the more degenerated the meniscus was, the more distinct the extrusion was. The biomechanical properties of the meniscus showed no significant regional differences, while only indicating some trends with progressing degeneration. Significant correlations of extrusion with meniscal biomechanical properties were found for E and lmax.