Abstract
The most recent Australian registry has a database of 547,407 knee arthroplasties, having added over 52,000 in 2016. Total knee arthroplasties (TKA) comprise 83.8%, revisions (RevTKA) 8.1% and “partials of all types” 8.1%. Since 2003, the percent of TKA has increased from 76.7%, RevTKA has stayed stable and partial replacements have declined from 14.5%. In the last year, however, TKA declined slightly.
There is a slightly higher percentage of women (56.1%) undergoing TKA and this has remained very stable since 2003. Revision rates are slightly higher for men. Percentages of the youngest (<55) and oldest (>85) are small and stable. The 75–84 year olds have declined as 55–74 year olds have increased. This represents a gradual shift to earlier TKA surgery. More patella are resurfaced and this is a gradual trend with a cross over in 2010 when half were resurfaced. Computer navigation is progressively more popular and now accounts for almost 30% of cases. Cement fixation is also increasing and accounts for about 65% of cases. Crosslinked polyethylene is gradually replacing non crosslinked and in 2014 was used in 50% of cases.
Revisions are performed most commonly for loosening and infection. Revision rates correlate directly with age. Loosening is the most common indication for revision in both genders, but males have a distinctly higher revision rate due to infection. Revision rates are slightly higher in all forms of mobile bearing than fixed bearing.
Minimally constrained (cruciate retaining) devices are used in the majority of TKAs. Posterior stabilised implants are in slight decline, having peaked in about 2008–2010. Minimally constrained implants are in slight decline as medial pivot/medial congruent devices have been used more frequently. Revision rates are similar amongst all three implant types: PS implants are revised at a slightly higher rate. When an early Medial Pivot (MP) implant is excluded the newer version has better results. The reasons for revision are similar amongst all 3 groups with slightly higher loosening rates for PS designs. (Could this represent backside wear with older locking mechanisms, surface finish and non crosslinked poly?) The MP designs had slightly higher revision rates for “pain”, which is not recognised as a reasonable indication for revision.
Revision rates are steadily higher for TKAs without patella resurfacing over 16 years, but the questions as to whether: i. the surgeries were secondary resurfacings or full revisions or ii. if secondary resurfacings eliminated pain are unknown. The combinations at greatest risk of revision were a posterior stabilised or medial pivot arthroplasty without patellar resurfacing. Cementless fixation leads to a higher revision rate.
If age and computer navigation are evaluated in terms of revision rates, young patients with and without computer navigated arthroplasties failed at the highest rates, distinct from patients >65. However, if failure rates due only to loosening are evaluated, then computer navigation leads to a lower revision rate in the <65 group. This has been interpreted as the protective effect of better component position that only shows up in patients who use the arthroplasty more aggressively.
Patient specific instrumentation (PSI) or Individual Designed Instrumentation (IDI) were revised at marginally higher rates than conventional instrumentation. Crosslinked polyethylene appears to be superior at 12 years (CRR= 4%) versus non crosslinked polyethylene (CRR>7%). This is the result of fewer failures due to loosening with crosslinked poly. The superiority of crosslinked poly was greater in the younger, more active patient.
