Background

A navigation system is useful tool to evaluate the intraoperative knee kinematics. Rheumatoid arthritis (RA) patients often need to have TKA operation, however, there are few TKA kinematics studies comparing RA and Osteoarthritis (OA) patients.

Background

Septic knee arthritis is one of the most serious complications after total knee arthroplasty (TKA), and the effectiveness of its treatment affects the patient's quality of life. In our super-aging society, the frequency of TKA in the elderly, often combined with various comorbidities, is increasing. Careful management should be considerd during the management of septic arthritis after TKA in these patients.

Introduction: It is difficult to measure the knee kinematics after TKA, navigation system can measure the knee kinematics during TKA operation. The purpose of this study is to describe the knee kinematic analysis in TKA using navigation system.

Patients and methods: TKA kinematics was measured in 24 patients (7 men and 17 women) 27 knees (7 rheumatoid arthritis knees and 20 osteoarthritis knees) in this study. Mean age was 72.8 (55–81). The TKA implant was Vanguard PS (Biomet, Warsaw) and navigation system was Vector Vision Knee ver. 1.6 (BrainLab Inc). All patients were operated using navigation system. This system was CT-based navigation system. We cut the bone independently and released medial collateral ligament, joint capsule and other tight structures to equal the joint balance. Femoral component was implanted parallel to clinical epicondylar line. Kinematic Analysis: We measured the joint gap (mm), coronal alignment (degree), antero-posterior translation (mm) and femoral rotation angle (degree) using navigation workstation just after all prostheses implantation and closure of joint capsule. The patient’s leg was held by operator and moved passively. All joint kinematic data were recorded at every 10 degrees in full range of motion (0 to 130 degrees). The joint gap is the distance between proximal tibial cut surface and that of distal femur (extension range: 0–40) and posterior femur (flexion range: 50–130). Medial and lateral distances were measured.

Results: In extension range, medial joint gap was 21.7mm at 0 degrees and decreased to 15.2mm with knee flexion. Lateral joint gap was 22.1mm at 0 knee extension, slightly decreased up to 40 degrees. Coronal alignment was 0.47 varus at 0 deg. and increased to 6.64 varus at 40 flexion. In flexion range, medial and lateral joint gap were increased 20.7 to 25.3, 17.2 to 31.2mm. Coronal alignment was c hanged from 4.94 valgus (60 flexion) to 8.94 varus (130 full flexion). Regarding to AP translation, femoral component was once moved 7.4 mm forward in early knee flexion and 15.2mm backward with flexion. Femoral components were rotated internally to 50 degrees flexion and then rotated externally with flexion.

Conclusion: The balance of TKA was still varus alignment after soft tissue release. Femoral components were moved backward and external rotation. Our results demonstrated that femoral rollback movement and medial pivot knee motion were recognized. The limitation of this study was the situation of under anesthesia and no muscle strain were loaded during the measurement of knee kinematics. However navigation system is available not only for the accurate implantation but also the measurement of intra operative knee kinematics.

Wear of ultra-high molecular weight polyethylene (UHMWPE) is a major factor that affects longevity of the total joint replacement. In total hips, cross-linking of polyethylene acetabular cup has been shown highly effective in reducing wear both clinically and experimentally. In TKR, Schmidig 2000 showed 90% reduction of wear rate in 10 Mrad irradiated tibial inserts compared to 3 Mrad irradiated tibial inserts. Thus crosslinking should provide substantial improvement also in the wear resistance of UHMWPE tibial inserts. Our objective was to compare 3 Mrad UHMWPE with 10 Mrad HCLPE in same design but comparing standard kinematics to more severe mal-rotation kinematics. The latter offsets the tibial tray with 15 degrees internal rotation such the central tibial eminencies became involved in the wear process. Our hypothesis was that HCLPE would be more resistant than the standard UHMPE even in the mal-rotation model. The control material was Duracon 3 Mrad UHMWPE. HCLPE was radiation crosslinked to 10 Mrad mater

According to the knee simulator test results in 1970s, the total decrease in thickness of UHMWPE tibial tray in combination with ceramic femoral component [F-Comp] was less than one tenth as that of the combination with metal [1]. These advantages led to development of total knee prosthesis [TKP] with alumina ceramics. In this study, we report the wear surface observation, the clinical wear and the oxidation of the retrieved TKP used clinically for 23 years, comparing with a metal TKP.

The retrieved TKP was implanted in 1979, and retrieved on January 9th in 2002. This TKP consisted of an alumina ceramic F-Comp and a UHMWPE tray combined with a alumina ceramic tibial component. Observations of the surface of alumina F-Comp and UHMWPE tray were carried out using SEM. Shape of UHMWPE tray was determined three-dimensionally. Comparing the result with original shape based on the product’s plan, liner wear and volumetric wear were calculated. Oxidation index was determined by Fourier transform infrared spectrophotometry.

Alumina F-Comp did not have any scratch on the surface by seeing with naked eye. UHMWPE tray had deformation and scratches obviously. The liner wear rate was 37 micrometer/year and volumetric wear rate was 18.8 mm3/year. The oxidation indexes were 0.6 in the unworn area, 1.2 in the worn area and 0.2 in the inner area.

SEM observations of the F-Comp demonstrated no scratch or pit. In contrast, many scratches were clearly observed on the UHMWPE tray. However, higher magnification observations did not demonstrate severe wear, which was shown on the wear analysis of a metallic F-Comp. Oxidation degradation is a problem to solve. However, the low wear rate and mild wear pattern demonstrate that ceramic F-Comp reduced UHMWPE wear.