Does implant design and surgical technique improve the clinical outcome in total knee arthroplasty?

Abstract

Recently, a new generation of prostheses for total knee arthroplasty (TKA) were introduced by different companies in order to improve the range of motion, clinical outcome and finally patient satisfaction. However, the basic principles in designing implants for total knee arthroplasty have not changed much over the last two decades. We still need to resect the anterior cruciate ligament (cruciate retaining, CR TKA) or remove both the anterior and posterior cruciate ligaments (posterior stabilised, PS TKA). The femoral component is designed to optimise patella tracking and to unload the patello-femoral compartment. Single and multiple radius designs are being used for the femoral condyles, both showing good reasons for preference. The multi-radius design of the femoral component respects the anatomical shape of the femoral condyles and the physiological change of flexion/extension axis during knee motion. However, CR mobile bearing TKA influence the flexion/extension axis as shown by Iacono et al. [10] in a study published in the current issue. The single-radius design presumes a fixed axis of flexion/ extension, which lies slightly posterior to the natural one. A slight posterior placed axis increases the quadriceps moment arm and improves the efficiency of quadriceps muscle function [16]. In clinical practise, better range of motion and less pain, in particular, when rising from a sitting position has been observed with the single-radius design [14]. These findings are in harmony with a biomechanical study by Ostermeier and Stukenborg-Colsman. However, other studies did not show any differences in range of motion or clinical outcome between the singleand multiple radius designs [7]. Both concepts raise the questions whether one should restore anatomy as exactly as possible or as the osteoarthritic knee’s anatomy is altered by the disease process anyway and hence one should aim for the best knee function and modify the components accordingly? What about CR or PS designs in TKA? A Cochrane analysis showed a slightly better range of motion of 8 using the PS design in comparison to the CR design (105 vs. 113 ) [11]. This finding is supported by a number of studies, but the clinical relevance of the differences in maximal degree of flexion of 8 remains questionable [5]. The prevalence of knee flexion of more than 90 was studied during a period of 35.7 h in 21 patients [9]. The patients flexed their knee more than 90 on average 10 min during this period only and eight oft them more than 120 for 2.2 min only. Range of motion during daily activity depends on patient’s activity, but it shows that small improvement in the degree of motion will not affect patients’ outcome, but may instead increase the risk of aseptic loosening. Innovations in terms of the tibial component have been very limited. Increasing the number of component sizes and the re-introduction of asymmetric tibial component are considered to improve the knee function. Posterolateral impingement of the popliteus tendon is rather unlikely when using the asymmetric plateau due to the smaller R. Becker (&) Department of Orthopedics and Trauma Surgery, City Hospital Brandenburg, Hochstrasse 26, 14770 Brandenburg, Germany e-mail: roland_becker@yahoo.de