Combined Partial Knee Arthroplasty (CPKA) describes when multiple ipsilateral partial knee implants treat multi-compartmental knee osteoarthritis (OA). CPKA offers benefits over Total Knee Arthroplasty (TKA) since it preserves the cruciate ligaments and more of the healthy bone. The aim of this research was to characterise the proportion of patients suitable for CPKA, and assess the short- and long-term risks to bone in comparison to Partial Knee Arthroplasty (PKA) and TKA.

A systematic review and meta-analysis determined the prevalence of single, bi- and tricompartmental OA, and the compartmental patterns of OA. At least three-quarters of people with knee OA did not have tricompartmental OA, contrasting with arthroplasty usage in the UK, where TKAs replacing all three compartments are the default. A third had bicompartmental disease, highlighting the potential wider role for CPKA.

Finite Element models assessed how implant position, overstuffing the joint, and sex affected the risk of tibial eminence avulsion fracture in Bi-unicondylar Knee Arthroplasty (Bi-UKA) in comparison to Medial Unicondylar Knee Arthroplasty (UKA-M). The risk of fracture was similar but higher in Bi-UKA than UKA-M, and removal of anterior bone increased the risk further. The greatest risk-modifier was overstuffing the joint.

The changes in the load transfer in bone induced by CPKA were assessed in comparison to PKA and TKA. The difference between the strains predicted in the native and implanted femur and tibia was predicted. TKA was associated with more extensive and severe strain shielding than any of the PKAs or CPKAs. It was predicted that a larger proportion of the bone would experience a strain distribution that was like the native distribution in PKA than in bicompartmental CPKA, which would have more bone that experienced native-like strains than tricompartmental CPKA, and which was more native-like than TKA.