Abstract
Purpose
to evaluate the kinematics of a knee with a polyurethane meniscal scaffold for partial meniscus defect substitution during flexion under weightbearing conditions in an upright MRI. In addition, radial displacement and the surface of the scaffold was compared to the normal meniscus.
Materials and Methods
One cadaver with a normal lateral meniscus and medial scaffold in the left knee and with a normal medial meniscus and lateral scaffold in the right knee. The scaffolds were implanted to substitute a 3 cm meniscus defect in the posterior horn. The cadaver was scanned in an 0,7T open MRI with a range of motion from 0-30-60-90 to hyperflexion. Kinematics were evaluated on sagittal images by the following two parameters: the position of the femoral condyle, identified by the centre of its posterior circular surface, which is named the flexion facet centre (FFC), and the point of closest approximation between the femoral and tibial subchondral plates, the contact point (CP). Both were identified in relation to the posterior tibial cortex.
The displacement, measured on coronal images, is defined as the distance between the tibial plateau and the outer edge of the meniscus. The surface was also measured on coronal slices and contains the triangular surface of the meniscus.
Results
Medially from 0 degrees to hyperflexion the FFC does not move anteroposteriorly. Laterally the FFC moves 12 mm backwards. The CP moves 15 mm backwards both lateral and medial. The lateral femoral condyle does roll-back with flexion but the medial does not, so the femur rotates externally around a medial centre. By contrast, both medial and lateral contact points move back, roughly in parallel, from 0 degrees to hyperflexion. The kinematics of the involved compartment is not influenced by the presence of the scaffold compared to the controlateral normal compartment.
The radial displacement remains stable during full flexion: both the normal and scaffold meniscus have no different (p > 0,05) position.
Both for the normal and the scaffold meniscus there is no difference (p > 0,05) in surface; there is no compression of the meniscus during flexion.
Conclusion
The polyurethane implant, indicated for partial meniscus defect substitution, has no effect on the normal kinematics of the knee. Additionally, the degree of flexion has no effect on the external displacement, the surface and compressibility of both the implanted scaffold and the meniscus.
