UKR 2-year survivorship analysis: Patient age, not BMI, affects implant longevity

In patients with unicondylar knee replacements, survivorship at 2 years postoperatively varied according to patient age, but it was not affected by body mass index, according to U.K. researchers studying those cases in the National Joint Registry for England and Wales.

The two-part analysis conducted by the Bristol Knee Group at the Avon Orthopaedic Centre, in Bristol, England, revealed the effects that a patient’s age less than 50 years had on survivorship of unicondylar knee replacements (UKR).

In the first part of the analysis, “We found a statistically significant difference in the factor of age on revision rate,” investigator Tarique Parwez, said at the Combined Orthopaedic Associations 2010 Meeting in Glasgow.

Tarique Parwez

He noted those revision rates were similar to ones reported in joint replacement registers from New Zealand, Australia and Sweden.

The second part of the analysis showed a patient’s body mass index (BMI) at the time of surgery had little bearing on the risk of UKR revision.

No effect on revision from BMI

Parwez said during his presentation that he and his colleagues hypothesized that higher BMI would cause earlier-than-expected UKR failures. However, based on their findings there was “a 4.6% revision rate at a mean of 3.05 years and we did not find any difference between the groups,” he said.

The researchers used data from February 2003 through August 2007 for 10,104 patients in the National Joint Registry for England and Wales with a UKR, and all cases reviewed had a minimum 2-year follow-up.

NJR data statistically analyzed

For the revisions by age analysis, Parwez and colleagues hypothesized that patients whose age was considered extreme — either less than 50 years or greater than 80 years at surgery — would have increased rates of revision for the time period studied.

“We found that at a mean of 3.4 years [range 2 to 5.5 years] 95.6% are still surviving and there has been a revision rate of 4.4%,” in the group as a whole, Parwez said.

The revision rate was 7.04% for the group younger than 50 years compared to 2.4% for those older than 80 years, he explained.

Based on odds ratio calculations, “We found that under 50 [years] has quite a strong chance of revision compared to the average age group of 50 to 70 years.”

A subanalysis of both factors based on gender showed that gender neither strengthened nor weakened the effect that age and BMI had on UKR survivorship, according to Parwez’ presentation. – by Susan M. Rapp

Reference:

• Parwez T, Robinson J, Murray J, et al. Early failure of unicompartmental knee replacement (UKR) – the effect of age and body mass index, an analysis of 10104 cases with minimum 2 year follow up. Presented at the 2010 Meeting of the Combined Orthopaedic Associations. Sept. 13-17, 2010. Glasgow.

• Tarique Parwez can be reached at the Avon Orthopaedic Centre, Southmead Hospital, Westbury-on-Trym, Bristol, BS10 5NB United Kingdom; 0117-32-35906; e-mail: tparwez@yahoo.co.uk.
  Disclosure: Parwez has no relevant financial disclosures.

A number of factors, including age and BMI, may affect UKR survivorship. However, findings from the published literature are variable and the impact of age and BMI on UKR survivorship remains unclear. Large cohorts are required to meaningfully examine such associations, with registry data being ideal for this purpose. Age younger than 50 years was demonstrated to be a predictor of UKR failure in the present study; but, contrary to the authors’ hypothesis, raised BMI was not associated with an increased risk of UKR failure. These associations are of clinical importance when considering individuals for UKR and consenting patients with regards to the risk of subsequent surgery. However, a patient’s dissatisfaction with a knee replacement which remains in-situ can also be classed as a failure. Joint registries are limited as they are unable to provide accurate subjective functional outcome data, and as such it is important to bear this in mind when interpreting registry findings.

– Dr. Gulraj Matharu, BSc (Hons), MB ChB
Specialist Trainee in Trauma and Orthopaedic Surgery
Birmingham, West Midlands, U.K.
Disclosure: He has no relevant financial disclosures.