Modern navigated ligament balancing in total knee arthroplasty with the PiGalileo system

Abstract

Ligament balancing of the knee is one of the cornerstones for the function and longevity of a knee endoprosthesis. «Size and shape of the flexion gap should be equal to the extension gap» as Insall [1] put it. In Insall's concept the gaps should be rectangular for the same ligament tension at the medial and lateral side. The decisive point of the gap technique is that it is oriented towards the status and condition of the soft tissue. During the process the posterior cruciate ligament is resected [2]. Reconstruction of the joint line is not taken into account. No data regarding the measure of the ligament tension are provided. The gap technique then met some competition from the «Measured Resection Technique» [3]. The principle of this implantation philosophy consists in the measurement of the resection being replaced by the corresponding implant thickness, both at the femur and the tibia. Unlike the gap technique, the posterior cruciate ligament is preserved in this process. The joint line can consequently largely be preserved and reconstructed. For knee joints that are not significantly deformed, it is thus possible to restore the original conditions of the ligaments. Ligament tension in the joint compartments themselves results from the selected thickness of the implant, and is thus determined by subjective assessment of the surgeon. The LCS Total Knee Arthroplasty according to Buechel and Pappas [4] simultaneously integrates the rotation of the femur component when determining flexion gap and ligament tension. During this, following the tibial incision, the rotation of the femoral resection level and the width of the flexion gap for evenly stretched ligaments in flexion are initially simultaneously determined through a spacer block. The thus obtained height of the flexion gap is subsequently transferred to the extension gap. In this implantation technique as well, the extent of the ligament tension is determined by subjective assessment of the surgeon. Little significance is attached to the reconstruction of the joint line. What all these methods have in common is the fact that ligament tension in flexion and extension is defined through individual subjective assessment of the surgeon. No special attention is given to any external influences, such as that of an everted patella, especially in flexion, or the use of a thigh tourniquet. Such subjective assessment of ligament tension is frequently the source of complications. Major revision statistics indicate instability as the reason for a revision in 1/5 - 1/3 of revision operations [5, 6]. As revision operations are usually only performed where clinically particularly abnormal instabilities are present, it must be assumed that the estimated number of unknown cases of sub-clinical instable knees is high. Using surgical navigation systems, it is possible to quantify and thus objectify factors that have conventionally been determined through subjective assessment, such as ligament tension and joint stability. Software modules to support both implantation techniques are usually available. «Bone referencing» modules are oriented towards the «Measured Resection Technique» and are used for «straight forward» knees, i.e. for knees without any major bone or ligament deformities. In addition to landmark-oriented navigation, «ligament-based» modules, in particular those of the PiGalileo Systems (Plus Orthopedics Aarau, Switzerland), also offer the possibility of force-controlled recording of ligament tension using a ligament balancer, and integrating it in the operative implantation management. Those integrative operation steps comprise for the flexion gap: . determination of ligament tension, . determination of femur rotation, and . implant planning with joint line optimising. The thus determined flexion gap is then transferred to the extension gap. In the following, the individual operation steps will be presented and described, and first clinical results will be reported on. Finally, future aspects involving individual ligament tension measurement will be discussed. © 2007 Springer Medizin Verlag Heidelberg.