A computed tomography based study on rotational alignment accuracy of the femoral component in total knee arthroplasty using computer-assisted orthopaedic surgery

Rotation of the femoral component in total knee arthroplasty (TKA) is of high importance in respect of the balancing of the knee and the patellofemoral joint. Though it is shown that computer assisted surgery (CAOS) improves the anteroposterior (AP) alignment in TKA, it is still unknown whether navigation helps in finding the accurate rotation or even improving rotation. Therefore the aim of our study was to evaluate the postoperative femoral component rotation on computed tomography (CT) with the intraoperative data of the navigation system. In 20 navigated TKAs the difference between the intraoperative stored rotation data of the femoral component and the postoperative rotation on CT was measured using the condylar twist angle (CTA). This is the angle between the epicondylar axis and the posterior condylar axis. Statistical analysis consisted of the intraclass correlation coefficient (ICC) and Bland-Altman plot. The mean intraoperative rotation CTA based on CAOS was 3.5° (range 2.4–8.6°). The postoperative CT scan showed a mean CTA of 4.0° (1.7–7.2). The ICC between the two observers was 0.81, and within observers this was 0.84 and 0.82, respectively. However, the ICC of the CAOS CTA versus the postoperative CT CTA was only 0.38. Though CAOS is being used for optimising the position of a TKA, this study shows that the (virtual) individual rotational position of the femoral component using a CAOS system is significantly different from the position on a postoperative CT scan

Polyethylene thickness is a risk factor for wear necessitating insert exchange

PURPOSE: The aim of this observational study was to investigate the optimal minimal polyethylene (PE) thickness in total knee arthroplasty (TKA) and identify other risk factors associated with revision of the insert due to wear. METHODS: A total of 84 TKA were followed for 11-16 years. All patients received the same prosthesis design (Interax; Howmedica/ Stryker) with halfbearings: separate PE-inserts medially and laterally. Statistical analysis comprised Cox-regression to correct for confounding. RESULTS: Eight knees (9.5%) had been revised due to thinning inserts and an additional patient is scheduled for revision. PE thickness, diagnosis, BMI and weight are risk factors for insert exchange. For each millimetre decrease in PE thickness, the risk of insert exchange increases 3.0 times, which remains after correction for age, gender, weight, diagnosis and femoral-tibial angle. Insert exchange was 4.73 times more likely in OA-patients compared to RA-patients. For every unit increase in BMI and weight the risk for insert exchange increases 1.40 times and 1.14 times, respectively. CONCLUSIONS: In conclusion we therefore advise against the use of thin PE inserts in modular TKA and recommend PE inserts with a minimal 8-mm thickness.Optimising joint reconstruction management in arthritis and bone tumour patient

Migration and clinical outcome of mobile-bearing versus fixed-bearing single-radius total knee arthroplasty

<p><b>Background and purpose — Mobile-bearing total knee prostheses (TKPs) were developed in the 1970s in an attempt to increase function and improve implant longevity. However, modern fixed-bearing designs like the single-radius TKP may provide similar advantages. We compared tibial component migration measured with radiostereometric analysis (RSA) and clinical outcome of otherwise similarly designed cemented fixed-bearing and mobile-bearing single-radius TKPs.</b></p> <p><b>Patients and methods — RSA measurements and clinical scores were assessed in 46 randomized patients at baseline, 6 months, 1 year, and annually thereafter up to 6 years postoperatively. A linear mixed-effects model was used to analyze the repeated measurements.</b></p> <p><b>Results — Both groups showed comparable migration (p = 0.3), with a mean migration at 6-year follow-up of 0.90 mm (95% CI 0.49–1.41) for the fixed-bearing group compared with 1.22 mm (95% CI 0.75–1.80) for the mobile-bearing group. Clinical outcomes were similar between groups. 1 fixed-bearing knee was revised for aseptic loosening after 6 years and 2 knees (1 in each group) were revised for late infection. 2 knees (1 in each group) were suspected for loosening due to excessive migration. Another mobile-bearing knee was revised after an insert dislocation due to failure of the locking mechanism 6 weeks postoperatively, after which study inclusion was preliminary terminated.</b></p> <p><b>Interpretation — Fixed-bearing and mobile-bearing single-radius TKPs showed similar migration. The latter may, however, expose patients to more complex surgical techniques and risks such as insert dislocations inherent to this rotating-platform design.</b></p