The influence of the femoral force application point on tibial cementing pressure in cemented UKA: an experimental study

Background

Aseptic loosening is the major cause for implant failure in cemented unicompartmental knee arthroplasty (UKA). Central positioning of the femoral pressure during the tibial cementation process is recommended to achieve equal pressure and a good cementation result. The aim of this study was to verify the central position of the femoral force application point (FFAP) at 45° flexion of the knee and to investigate the influence of ligament tension and cement penetration pressure (CPP) for UKA.

Materials and methods

Cemented Oxford UKAs were performed in 24 human legs. CPP and ligament tension forces (LTF) were measured. The FFAP was measured in a standardised manner in relation to the tibial implant length on lateral digital X-rays.

Results

The FFAP at 45° of knee flexion is located at 53.5 % and is not significantly different from the FFAP at 0° (p = 0.768). The CPP shows mean values at the anterior portion of 13.97 kPa (SD 16.11), at the implant keel of 24.34 kPa (SD 25.21) and at the posterior portion of 36.58 kPa (SD 26.51). The LTF shows a mean value of 194.35 N (SD 83.77).

Conclusion

The central position of the FFAP for the investigated cemented UKA with single radius femoral component at 45° flexion of the knee could be confirmed. A flexion angle of <45° does not influence the position of the FFAP significantly. More than 45° of flexion should be avoided because the FFAP shifts backwards significantly and may cause increased pressures posteriorly and therefore tilting of the component occurs during the cementation process.