Abstract
Background
The goal of this study was (1) to investigate the relationships between the bony contours of the knee and the popliteus tendon before and after TKA and (2) to analyse the influence of implant sizing. Our hypothesis was that an apparently well-sized prosthesis, will modify the position or the tracking of popliteus tendon.
Methods
4 fresh frozen cadavers were selected. The popliteus tendon was injected with contrast dye and a CT-scan was performed from full extension to full flexion with increments of 20°. Afterwards a total knee arthroplasty (TKA) was performed. Each cadaver received either a normal-sized, oversized, undersized or mobile bearing prosthesis. After TKA the limb was scanned again using the same protocol as before. 3D-reconstructions were created using Materialise Mimics software. These 3D-models were then imported into custom made Matlab software to measure and compare the deviation of the popliteus tendon before and after TKA.
Results
TKA resulted in significant postero-lateral displacement of the tendon from full extension to 100° flexion in both normal- and oversized prosthesis. In normal-sized prosthesis in full extension the mean posterior deviation was 6.2 mm (SD: 1.2). For oversized prosthesis the mean posterior deviation was 16.7mm (SD: 0.6). For the undersized prosthesis mean posterior deviation was −0.8mm (SD: 0.3). Finally for the mobile bearing prosthesis mean posterior deviation was −3.1mm (SD: 1.3).
Conclusions
To our knowledge, this is the first investigation which analyses the relationships between implants and soft tissues after TKA. The main finding is that surgeons must approach sizing in terms of volume rather than in terms of surface. The current study seems to indicate that it may be advantageous to aim at undersizing implants, both in the mediolateral dimension and in the anteroposterior dimension.
Level of Evidence
4
