Aim: The aim of this study was to determine whether increasing obesity has an influence on the age at which joint replacements are undertaken at our centre.

Materials and Methods: The database was analyzed for age, oxford score and body mass index (BMI) at the time of surgery.

The patients were divided into 5 groups based on their BMI, BMI< 25(normal), 25–29.9(overweight), 30–34.9(obese), 35–39.9(moderately obese), 40 or more(morbidly obese).

BMI < 25 was treated as a control group for comparison.

Statistical analysis was done using t test.

Results: In total, 1369 patients were analyzed, 1025 with hip replacement and 344 with knee replacement The difference in mean oxford score at surgery was not statistically significant between the groups (p> .05). For those undergoing hip replacement, the mean age of morbidly obese was 10 years less as compared to those with BMI < 25. For those with knee replacement, the same difference was 13 years. The age at surgery fell as the BMI > 35 for both hip and knee replacement (p< . 05). This association was found to be stronger for patients with knee replacement than with hip replacement.

Conclusion: This study shows that there is a positive association between obesity and the age at which hip and replacements are required. Obese people with BMI > 35 are likely to require joint replacement at an earlier age as compared to people with BMI < 25. The age at which joint replacement in required falls as the BMI increases over 35. This association is strong for patients requiring total knee replacement, and moderate for patients with hip replacement.

INTRODUCTION: The American Knee Society score (AKSS) and the Oxford Knee score (OKS) are widely used health outcome measures for total knee replacements. The AKSS is a surgeon-assessed, variable weighted knee score. The OKS is a patient assessed equally weighted score. Our aim was to evaluate whether patient self assessment is a viable alternative to clinical review and whether it can provide enough information to identify which patient would require a clinic visit.

As there had been no previous studies correlating the two scoring systems, we investigated whether a correlation exists between the two scores at 2, 5 and 10 year periods. A correlation would allow us to determine what OKS value would achieve 90% sensitivity in identifying patients requiring clinical review at the above time points. This strategy would reduce the number of clinical visits required and its associated cost.

METHODS: We reviewed the data gathered prospectively from January 2000 to April 2006. All patients were part of an ongoing multi-surgeon single institution Knee Arthroplasty Outcome Programme. Preoperative, 2, 5 and 10 year post-operative OKS and AKSS were gathered from different cohorts. This method of comparison has been validated by previous publications. The scores were then analyzed using the Pearson correlation and linear regression. Different OKS values were analyzed for sensitivity and specificity.

RESULTS: 175 patients completed both the OKS and AKSS questionnaires preoperatively. 312 completed both scores at 2 years; 124 at 5 years and 57 patients at 10 years. The mean OKS, and the two AKSS components, the Knee score and Functional score improved significantly 2 years postoperatively when compared to their preoperative values. The Functional score deteriorated significantly from 5 to 10 years (p< 0.0001). There was good correlation between the OKS and the Knee score and Functional score at 2 years and a moderate correlation at 5 to 10 years. OKS > 24 showed more than 90 % sensitivity in identifying poor Knee scores in the 2, 5 and 10 year periods.

CONCLUSION: In this study, the good correlation of OKS and AKSS at 2-years suggests that postal Oxford questionnaire is sufficient in following up patients in the short term after total knee replacement. However, the moderate correlation at 5 and 10 years suggests that clinical evaluation is necessary.

We recommend that at 2 years, all patients complete an OKS questionnaire and if this is above 24, a clinical evaluation maybe required. Using this OKS value as a screening technique would allow a reduction of up to 50% in clinic visits and outpatient costs at the 2 year follow-up. This reduction is not as great at the 5 and 10 year periods. At these time periods, we recommend a clinical follow-up.