Cemented fixation improves bone stress and stability in distal femoral replacement.

PURPOSE: Distal femoral replacement (DFR) is commonly used not only for metastatic bone tumours but also for complex revision surgery and treatment of periprosthetic fractures, serving as a limb-salvage procedure or a solution to restore knee function, as a valid alternative to amputation. The success and longevity of DFR depend on proper implant positioning and fixation at the bone-implant interface to ensure physiological load transfer. Clinically, both cemented and press-fit fixations are used; however, there is no consensus biomechanical guideline to determine the optimal fixation strategy. This study provides a biomechanical comparison of different fixation methods to inform surgical decision-making.

METHODS

Finite element models of a standard femur implanted with a DFR system-including femoral component, stem, collar and shaft-were used to evaluate bone stress distribution and implant micromotion under physiologically relevant loading conditions (0° and 90° of flexion, simulating walking and chair-rise). Four fixation configurations were analysed: fully cemented, press-fit with full contact, press-fit with proximal contact only, and press-fit with distal contact only, the latter two simulating implant positioning errors.

RESULTS

Each fixation technique and load condition influences stress distribution and stability differently. Cemented fixation generally reduced bone stress and therefore fracture risk, but exhibiting higher micromotion though within safe limits for long-term stability. Press-fit fixation offered comparable bone stress and, when properly positioned, higher implant stability. However, inadequate stem or collar contact increased bone stress and micromotion, potentially compromising stability. These findings highlight the importance of precise surgical technique across tumour surgery, complex revision procedures and periprosthetic fracture treatment.

CONCLUSION

Both fixation methods have trade-offs: cemented implants minimise bone stress, while press-fit configurations enhance stability if properly positioned. These findings underline the importance of precise surgical technique to minimise implant errors to optimise outcomes.

LEVEL OF EVIDENCE: NA, preclinical biomechanical computational study.