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Hip and Knee Arthroplasty - Surface Hippy Guide to Hip Resurfacing

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number is greater than 100, in which case we<br />

extend the graph until the number at risk reaches<br />

100. This avoids uninformative, imprecise<br />

estimates at the right tails of the distribution<br />

where the number of primary prostheses at risk is<br />

low. However, analytical comparisons of<br />

prostheses survival using log-rank tests <strong>and</strong><br />

proportional hazards models are based on all<br />

available data (ref Pocock SJ, Clay<strong>to</strong>n TC, Altman<br />

DG. Survival plots of time <strong>to</strong> event outcomes in<br />

clinical trials: good practice <strong>and</strong> pitfalls, Lancet<br />

2002; 359: 1686-89).<br />

Confidence intervals for the Kaplan-Meier<br />

estimates are point-wise Greenwood estimates<br />

<strong>and</strong> their appearance should not be used <strong>to</strong> infer<br />

whether overall differences in survival between<br />

prosthesis types are significant. Rather, the logrank<br />

tests <strong>and</strong> hazard ratios reported with each<br />

curve should be used for this purpose.<br />

When we refer <strong>to</strong> the cumulative percent revision<br />

(CPR) at a certain time, for example five years,<br />

we mean the complement (in probability) of the<br />

Kaplan-Meier survivorship function at that time,<br />

multiplied by 100. The cumulative percent<br />

revision, generically a “cumulative failure rate”,<br />

also accounts for the right censoring due <strong>to</strong> death<br />

<strong>and</strong> the ‘closure’ of the database at the time of<br />

analysis.<br />

Acknowledgements<br />

The Registry could not function without the<br />

cooperation of a large number of organisations<br />

<strong>and</strong> individuals. The Registry acknowledges the<br />

continued cooperation <strong>and</strong> support provided by<br />

those undertaking the surgery <strong>and</strong> completing<br />

the data forms, in particular all orthopaedic<br />

surgeons, registrars <strong>and</strong> nursing staff. The<br />

Registry would also like <strong>to</strong> acknowledge the<br />

continued support of all hospitals both public <strong>and</strong><br />

private that undertake arthroplasty surgery<br />

nationally. The support provided by each of the<br />

hospitals through their nominated coordina<strong>to</strong>r(s)<br />

is appreciated. A list of participating hospitals<br />

<strong>and</strong> coordina<strong>to</strong>rs is included on the following<br />

pages.<br />

The Registry has also continued <strong>to</strong> receive<br />

support <strong>and</strong> invaluable assistance from the<br />

Federal Government, State <strong>and</strong> Terri<strong>to</strong>ry Health<br />

Departments <strong>and</strong> Orthopaedic Companies.<br />

Report Review Prior <strong>to</strong> Publication<br />

As previously mentioned, members of the<br />

<strong>Arthroplasty</strong> Society were invited <strong>to</strong> attend a two<br />

day workshop <strong>to</strong> review, comment <strong>and</strong> provide<br />

advice <strong>and</strong> feedback on all sections of the report.<br />

This report is the report finalised <strong>and</strong> approved at<br />

that meeting. Prior <strong>to</strong> publication the report was<br />

provided <strong>to</strong> the Board of the AOA for<br />

consideration <strong>and</strong> approval.<br />

6

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