Knee Replacements: Big Data Favors Larger Procedures?

October 27, 2014

More careful patient selection is making knee replacement ever safer, judging from data in a huge British registry. But the analysis may generate an unfair bias favoring total over partial replacement.

Cobb JP. Comment: Patient safety after partial and total knee replacement. The Lancet (2014) 384:1405-1407. doi:10.1016/S0140-6736(14)60885-0

Liddle AD, Judge A, Pandit H, Murray DW. Adverse outcomes after total and unicompartmental knee replacement in 101, 330 matched patients: a study of data from the National Joint Registry for England and Wales. The Lancet (2014) 384:1437-1445. doi:10.1016/S0140-6736(14)60419-0

Hunt LP, Ben-Shlomo Y, Clark EM, et al. 45-day mortality after 467, 779 knee replacements for osteoarthritis from the National Joint Registry for England and Wales: an observational study. The Lancet. (2014) 384:1429-1436. doi:10.1016/S0140-6736(14)60540-7

Unicompartmental knee replacement (UKR) has a lower mortality risk than total knee replacement (TKR), particularly in the first 30 days, but carries a higher rate of revisions, according to analyses of a national registry.

Two papers look at data from the National Joint Registry of England and Wales, which contains information on more than 500,000 knee replacements registered since 2003.

The authors point out that if 100 patients receive UKR instead of TKR, there would be around one fewer death, but three more re-operations in the first 4 years after surgery.

Overall, the authors report that the mortality from primary knee replacements declined over 9 years, from 0.37% in 2003 to 0.20% in 2011. The “healthy-surgery effect,” where surgery is not an option for high-risk patients, may be at work here, they suggest. 

Also, age and male gender are major risk factors for mortality after knee replacement surgery, and related risk factors, including myocardial infarction and renal disease, also increase with age. The authors argue for careful patient selection and counseling.

However, an accompanying commentary claims that using revision rates to compare UKR to TKR may led to a bias against UKR. A successful joint revision becomes a failure in the registry, while a joint replacement that cannot be revised is deemed a success, the author explains, adding that “the TKR industry will continue to grow steadily encouraged by statistics based upon revision rates alone."