The soft-tissue restraints of the knee and its balancing capacity in total knee arthroplasty procedures

Abstract

Total knee arthroplasty is a successful surgical treatment for patients with severe knee joint arthrosis. However, restoring soft-tissue function is a major challenge. Depending on the positioning of the prosthesis, the implantation procedure and the pathology of the patient, it is necessary to adjust the soft-tissue structures of the joint in order to restore the function of the knee. The assessment and adaptation of the soft-tissue envelope is a subjective process that is strongly dependent on the surgeon. This dissertation addresses these challenges and seeks quantitative guidelines for softtissue management based on a meta-analysis of the laxity of the natural knee joint. A further aim of the present study was to clarify in the scope of in-vitro investigations to what extent the loosening and removal of individual structures alters joint laxity and how far the joint can be balanced by targeted resection of soft-tissue structures. In addition, in-silico investigations within the scope of this thesis form the basis for a numerical tool to better understand the function of the ligaments and to better plan soft-tissue balancing preoperatively in the future. The investigations of the natural laxity of the knee jointin different flexion angles and loading directions by utilizing a meta-analysis show a strong dependency of the joint laxity on the flexion angle. Furthermore, the results show a distinct asymmetry of joint laxity when comparing translations in opposite directions within a certain degree of freedom. The data collected provide the surgeon with quantitative target parameters for natural soft-tissue balancing in knee arthroplasty procedures. The in-vitro investigations on 19 human knee specimens show that the restoration of soft-tissue function of the knee after arthroplasty cannot be achieved by kinematic alignment alone. The use of a bicruciate-retaining knee arthroplasty is the only way to keep the anterior and posterior stability of the joint in balance. To correct varus deformities, balancing of the medial collateral ligament appears to be a safe method. Correction of valgus laxity can be achieved by partially or completely resecting the lateral collateral ligament, however this increases the risk of instability in joint flexion. Within the scope of this work, subject-specific multi-body simulation models could be developed with which the laxity of the knee joint can be predicted, especially for low flexion angles. The presented procedure for the approximation of the ligament attachment sites represents a time-saving alternative to the segmentation of the attachments in MRI images.