Quantifying knee meniscus tissue behaviour: A combined experimental and computational study

Damage to knee meniscus tissue has been associated with the onset and progression of musculoskeletal diseases such as osteoarthritis. Through previous computational studies, the meniscus material property parameters have been found to directly affect knee contact mechanics and meniscus kinematics considered as key variables that reflect knee and meniscus health. However, characterising these properties remain challenging.
Previous studies have used techniques that compromise tissue integrity, require sectioning of meniscus tissue or make compromising assumptions leading to potential inaccuracies in measurements.

The aim of the study was to develop new methods to characterise meniscus mechanical properties. This involved imaging the tissue under load and using inverse finite element analysis with corresponding meniscus kinematic measurements from MRI data.
A sensitivity analysis was conducted to establish meniscus radial distance sensitivity to linear transverse isotropic material property parameters. An added feature that distinguishes the current study was the study of both meniscus kinematics and contact mechanics concurrently with changes to meniscus property parameters to understand their relationship. The outcomes suggest a 3T MRI scanner of isotropic resolution ~0.3 mm would sufficiently capture meniscus kinematics and that the Efibre, Eplane and Gplane-fibre material parameters would be sufficient for capturing meniscus response in situ. Meniscus kinematics and contact mechanics were found to be linked in their response.

A novel MRI-compatible loading rig was designed, built and calibrated for loading the knee joint in vitro following the finite element sensitivity analysis. The MRI-compatible rig provides for two flexion configurations (i.e., neutral and 45 degrees in flexion) and allows axial rotation, a key component relevant to the screw-home mechanism, to investigate its effect on meniscus loading and response.

Meniscus radial distance measurements were obtained for various loading and knee configurations from the MR images for three porcine samples. A novel feature was that the measurements were made with reference to tibial tubercles locations such that the tibia internal-external rotations could be assumed to have no effect on the measures.
Knee FE models were built, and the meniscus radial distance measurement technique replicated programmatically for material property identification purposes using the finite element method updating procedure with the particle swarm optimiser.

Outcomes from the material property parameter identification study suggested consistency in the Eplane term at 20 MPa for all the three porcine samples considered. The derived Efibre term was in the range 161 MPa to 250 MPa while the Gplane-fibre term occurred in the range 13 MPa to 30 MPa. Normalised root mean squared error (NRMSE) in the range 7% to 11% was measured for the three knee samples used. Outcomes were verified using a brute force parameter identification technique.
A validation study performed using meniscus radial distances obtained from a different knee configuration was deemed inconclusive due to modelling difficulties. However, a partial validation based on the medial meniscus radial distances showed NRMSE of ~9 % which was comparable to the optimised ranges. Porcine lateral meniscus kinematics were not sufficiently captured using the developed knee FE model.

To conclude novel methods were developed for the non-invasive characterisation of subject-specific meniscus material property parameters using a combination of measurements from medical imaging and computational techniques. The methods developed provides for the characterisation of representative human meniscal tissue material properties and the assessment of meniscus replacement devices laying the foundations for patient stratification studies.