Effect of surgical parameters on the biomechanical behaviour of bicondylar total knee endoprostheses - A robot-assisted test method based on a musculoskeletal model.

The complicated interplay of total knee replacement (TKR) positioning and patient-specific soft tissue conditions still causes a considerable number of unsatisfactory outcomes. Therefore, we deployed a robot-assisted test method, in which a six-axis robot moved and loaded a bicondylar cruciate-retaining (CR)-TKR in a virtual lower extremity emulated by a musculoskeletal multibody model. This enabled us to systematically analyse the impact of the posterior cruciate ligament (PCL), tibial slope, and tibial component rotation on TKR function while considering the physical implant components and physiological-like conditions during dynamic motions. The PCL resection yielded a decrease of femoral rollback by 4.5 mm and a reduction of tibiofemoral contact force by 50 N. A reduced tibial slope led to an increase of tibiofemoral contact force by about 170 N and a decrease of femoral rollback up to 1.7 mm. Although a higher tibial slope reduced the contact force, excessive tibial slopes should be avoided to prevent joint instability. Contrary to an external rotation of the tibial component, an internal rotation clearly increased the contact force and lateral femoral rollback. Our data contribute to improved understanding the biomechanics of TKRs and show the capabilities of the robot-assisted test method based on a musculoskeletal multibody model as a preoperative planning tool.

[Total knee replacement with ceramic femoral components: a national prospective multicenter study of clinical and radiological outcomes]. / Knieendoprothetik mit keramischen Femurkomponenten: Nationale prospektive Multicenterstudie zum klinischen und radiologischen Outcome.

BACKGROUND: The purpose of this prospective multicenter study was to evaluate the clinical and radiological outcomes of an unconstrained bicondylar total knee prosthesis with a new ceramic femoral component made of BIOLOX® delta. MATERIAL AND METHODS: Fifty patients underwent cemented total knee arthroplasty in three hospitals/centers. Clinical and radiological evaluations were undertaken preoperatively and at 3 as well as 12 months postoperatively using the HSS, WOMAC, and SF-36 scores. RESULTS: During 12 months follow-up three patients had to undergo revision surgery due to non-implant-related reasons (infection, periprosthetic fracture, and retropatellar replacement). The mean preoperative HSS score amounted to 56.2±11.0 points. At 3 and 12 months follow-up the mean HSS score was 75.5±11.5 and 83.6±10.9 points, respectively. Therefore, HSS and WOMAC scores improved significantly from preoperative values at both postoperative evaluations. The first significant improvement of SF-36 score was seen after 12 months. Radiolucent lines around the femoral ceramic components were found in one case. CONCLUSION: Subsequent long-term studies must be carried out in order to clarify the potential benefits of ceramic femoral components and confirm the good early clinical result. Moreover, the specific material properties of ceramic implants must be considered during implantation.

[Bicondylar knee arthroplasty - influence of preoperative functional restriction on early functional postoperative outcome]. / Bikondylärer Oberflächenersatz - Einfluss präoperativer Funktionseinschränkungen auf das frühfunktionelle postoperative Outcome.

AIM: The point of time for total knee arthroplasty has a significant importance due to limited implant survival rate. To what extent the preoperative stage of physical and psychological function limitation, which is increasing with the progression of the osteoarthritis, has an influence on the early functional outcome after total knee arthroplasty should be clarified in a clinical evaluation. PATIENTS AND METHOD: 47 Patients were treated with the same bicondylar knee endoprosthesis system (Type Genia, ESKA Implants, Lübeck). A clinical evaluation was undertaken preoperatively and at 3 and 6 months postoperatively using HSS score, WOMAC index and SF-36 score. In relation to the preoperative HSS score the patients were allocated into three groups depending upon whether their level of function was "good", "average" or "poor". Additionally, all patients were assigned to three body mass index (BMI) groups (< 30, 30 - 35, > 35) which were descriptively analysed. RESULTS: The preoperative differences in HSS score and SF-36 score in all three groups show a high reduction after 3 and 6 months. Postoperatively there were no significant differences in all three groups at both timepoints. Patients with "poor" preoperative function achieved on average a lower score niveau than patients with preoperative "good" function, but have the benefit of the best function improvement. The early postoperative period (3 months) showed the highest decrease in physical and psychological function derogation. The BMI had no significant influence on the early functional outcome. CONCLUSION: Therefore, older people should receive early total knee arthroplasty to gain a high postoperative score niveau. In younger patients the indication for implant should be considered essentially because of the limited survival rate. Even in progressive osteoarthritis and extreme functional limitation the bicondylar surface replacement gives the possibility of a good early functional postoperative outcome. Total knee arthroplasty of obese patients is under attention of the perioperative internistic risks, a safe procedure with good functional results and can increase patient's mobility.

[Alternative materials and solutions in total knee arthroplasty for patients with metal allergy]. / Alternative Werkstoffe und Lösungen in der Knieendoprothetik für Patienten mit Metallallergie.

The annual number of total knee replacement implantations is rising continuously. A progressive cutaneous hypersensitivity rate against metallic materials in the population has been registered which can lead to an increase of allergy-induced reactions associated with implant loosening in the future although the correlation with an allergic cutaneous sensitisation has not been proven in all cases. On apparent allergy against metallic implant components different alternative solutions to standard endoprostheses should be taken into account for primary implantation or revision of total knee replacement, for example the application of implant components without metallic elements (e.g. ceramics), the use of non-allergic metallic implants, such as titanium or ZrNb alloys, or potential allergy-inducing metallic materials after masking the implant surface using a suitable coating. In the case of primary or revision surgery most patients with metal allergy are treated with a Ti(Nb)N-coated knee implant made of cobalt-chrome or titanium alloys in our hospital. Within an international multi-centre study we are currently implanting a newly developed knee endoprosthesis system with a ceramic femoral component as an alternative.

[The importance of wear couples for younger endoprosthesis patients]. / Die Bedeutung der Gleitpaarung beim jüngeren Endoprothesenpatienten.

The success and long-term survival rates of modern joint arthroplasty leads to a high patient satisfaction and, together with its technical improvements, has broadened the indications to an increasingly younger population. Limitations to the established systems are the long-term survival rates, which are mainly influenced by wear of the articulating parts and the resulting problems. Beside "classic" long-stemmed cemented shafts articulating with metal against polyethylene, short-stemmed or cup designs with a hard-hard self pairing are increasingly used in total hip arthroplasty. This paper reflects the current state of the art in joint arthroplasty for younger patients with the focus on wear couples and discusses future perspectives. Special interest is focused on the advantages and disadvantages of ceramic bearings, problems with allergies to implant components and the design of endoprostheses with regard to avoidance of impingement.