Abstract
Introduction and Aims: Mobile bearings have been introduced in total knee arthroplasty (TKA) as a means to improve kinematics and reduce wear. Another theoretical advantage may be a reduction of the torsional and shear stresses at the baseplate – bone interface, and thereby improving the fixation of the tibial component. The aim of this study was to analyse and compare the fixation of tibial components with fixed or mobile bearings in a prospective randomised study using RSA.
Method: Fifty-two consecutive patients (31 women, 21 men, mean age 72) with knee osteoarthrosis underwent primary cemented total knee arthroplasty. Included were patients with arthrosis stage III–V and age over 62. Patients were randomised at operation by opening of sealed envelopes to either Mobile Bearing (MB) or Fixed Bearing (FB). The FB knees received a NexGen TKA with titanium tibial baseplate, and the MB knees a NexGen mobile bearing TKA with CrCo tibial baseplate. All components were cemented using vacuum-mixed Palacos-Gentamicin bone cement. The stem of the component was not cemented. Patellar components were not used. Each tibial baseplate was equipped with five tantalum markers on the undersurface by the manufacturer. The peri- and post-operative management was in all cases identical. Radiostereometric analysis (RSA) was performed three, 12, and 24 months post-op. Clinical results were assessed with Knee Society Knee and Function Scores.
Results: There were no complications. One patient (MB) died two months after operation in myocardial infarction. The Knee Society Knee and Function scores and range of knee motion improved after surgery in both groups with no differences between the groups, reaching 89 at both 12 and 24 months. The rotations of the tibial baseplates did not differ significantly between the two groups. In both groups, anterior-posterior tilting was somewhat larger than varus-valgus tilting. Maximum subsidence was 0.3 ± 0.1 mm (MB) and 0.2 ± 0.1 mm (FB), and maximum migration was 0.6 ± 0.2 mm (MB) and 0.5 ± 0.1 mm (FB) (P = 0.3 – 0.4).
Conclusion: This study could not detect any positive effects on the fixation of the cemented tibial baseplate when a mobile polyethylene insert was used. It may be that in cemented fixation the theoretical advantages of lower shearing and torsional forces at the interface are not important, at least during the initial 24 months post-op.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
