Summary

One in three total knee arthroplasty patients progressed to bilateral total knee arthroplasty within 7 years of the index surgery, and progression could be predicted by pre-operative measures.

Abstract

It is estimated that as many as 40% of patients who receive a total knee arthroplasty in the management of osteoarthritis return for a subsequent total knee arthroplasty in the contralateral knee within 10 years. The risk factors for a first total knee arthroplasty are well understood, but much less is known about the risk factors for patients who progress to bilateral knee arthroplasty. Identifying the risk factors associated with for this progression may provide an opportunity for more thorough planning and expectation setting.

All patients of a single orthopaedic surgeon who had undergone a total knee arthroplasty in the management of osteoarthritis were evaluated for inclusion in this study. Patients who had undergone a knee arthroplasty prior to their first documented surgery with this surgeon were excluded, as were patients who had undergone simultaneous bilateral knee arthroplasty. Patients were assessed (i) immediately prior to surgery, (ii) 12 months following surgery, and (iii) 6-7 years following surgery. At the pre-operative and 12 months post-operative assessments, patients were assessed on the Oxford-12 Knee Score, the Knee Society Knee Score, the SF-12, the presence or absence of contralateral knee pain and body mass index. At 6-7 years post-operative assessment, patients were asked about any surgery or pain in each knee since their total knee arthroplasty. A Classification and Regression Tree was developed to identify factors associated with a higher likelihood of progression to bilateral total knee arthroplasty.

Seven hundred and fourteen patients were included; 69% of these were assessed at 6-7 years. Of these patients 31.6% progressed to bilateral total knee arthroplasty within 7 years of the index surgery. The strongest prediction model of who progressed to bilateral knee arthroplasty included three classification levels – pain in the contralateral knee prior to the index surgery, body mass index, and Mental Component Score on SF12 measure prior to the index surgery. None of the measures from the 12 month assessment improved the prediction model. Patients who reported an absence of pain in the contralateral knee prior to the index surgery had a 20% chance of progressing to bilateral total knee arthroplasty within 7 years. Patients who reported the presence of pain in the contralateral knee prior to the index surgery, and had a body mass index greater than 30.7 had a 70% chance of progressing to bilateral knee arthroplasty. Patients with pain in the contralateral knee but with a body mass index of less than 30.7 were just as likely to progress to bilateral knee surgery as those with high body mass index if they had a Mental Component Score of greater than 55.

In this cohort, one in three total knee arthroplasty patients progressed to bilateral total knee arthroplasty within 7 years of the index surgery. Progression to bilateral knee arthroplasty was predicted by 3 key outcomes – the presence of pain in the contralateral knee, body mass index and SF12. These outcomes were measured prior to the index surgery, and can therefore help to inform expectations of outcome, and planning for multiple surgeries.