An Investigation Of The Design And Function Of Knee Joint-sparing Massive Endoprostheses

Distal femoral and proximal tibial joint-sparing bone tumour implants allow to preserve the knee, in limb salvage surgery. The aim of this thesis was to compare implant survival, functional outcomes, acceptance, proprioception and gait in patients with knee sparing implants and conventional knee sacrificing implants. Using FEA, a distal femoral implant and cadaver bone were modelled and parametrised to find the design that improves implant fixation. A survivorship study of 104 consecutive patients following knee sparing surgery (mean follow-up 36.1 ± 11.0 months) found an implant survival rate of 78% and this is comparable to the reported survival for joint sacrificing prostheses. Younger patients showed improved implant survival compared to older individuals. Plate fracture was not observed and aseptic loosening was the main reason for revision. Radiographic analysis indicated that implantation accuracy increased implant survival. Patient questionnaires showed that patients with knee sparing implants had more normal functional outcome and acceptance compared with patients with knee sacrificing implants. However, proprioception (joint position sense) was reduced in these patients. Using optoelectronic gait analysis system, hip, knee and ankle joint angle in 19 patients and 3 healthy subjects were measured. Ground reaction force and time in stance were also investigated. Joint symmetry in the joint sacrificing group was improved compared to the joint-sparing group, however overall, the joint-sparing tibial group demonstrated a more normal gait pattern. FEA results indicated that lower resection levels, reduced plate thickness and implant materials with lower modulus, decreased the stresses in the bone adjacent to the implant while loaded the bone more to reduce risk of stress shielding. To conclude, knee sparing endoprostheses provide a reliable alternative to knee sacrificing implants in limb reconstruction in selected patients. However, the current design of joint-sparing implants can be optimised to potentially improve bone remodelling and implant fixation