Identifying individuals with chronic pain after knee replacement: a population-cohort, cluster-analysis of Oxford knee scores in 128,145 patients from the English National Health Service

Rafael Pinedo-Villanueva,Andrew Judge,Anushka Soni,Sara Khalid,Vikki Wylde,Rachael Gooberman-Hill

doi:10.1186/s12891-018-2270-9

Abstract

BackgroundApproximately one in five patients undergoing knee replacement surgery experience chronic pain after their operation, which can negatively impact on their quality of life. In order to develop and evaluate interventions to improve the management of chronic post-surgical pain, we aimed to derive a cut-off point in the Oxford Knee Score pain subscale to identify patients with chronic pain following knee replacement, and to characterise these patients using self-reported outcomes.MethodsData from the English Patient-Reported Outcome Measures (PROMs) programme were used. This comprised patient-reported data from 128,145 patients who underwent primary knee replacement surgery in England between 2012 and 2015. Cluster analysis was applied to derive a cut-off point on the pain subscale of the Oxford Knee Score.ResultsA high-pain group was identified, described by a maximum of 14 points in the Oxford Knee Score pain subscale six months after surgery. The high-pain group, comprising 15% of the sample, was characterised by severe and frequent problems in all pain dimensions, particularly in pain severity, night pain and limping, as well as in all dimensions of health-related quality of life.ConclusionsPatients with Oxford Knee Score pain subscale scores of 14 or less at six months after knee replacement can be considered to be in chronic pain that is likely to negatively affect their quality of life. This derived cut-off can be used for patient selection in research settings to design and assess interventions that support patients in their management of chronic post-surgical pain.

Highlights

One in five patients undergoing knee replacement surgery experience chronic pain after their operation, which can negatively impact on their quality of life
Cut-off points on a visual analogue scale have been suggested to distinguish between mild, moderate and severe general pain [8], no standard cut-off points are available for patients following a Knee replacement (KR)
We conducted agglomerative clustering with all patients beginning as individual clusters, which were successively merged into all possible numbers of clusters, starting at two up to 28 clusters

Summary

Introduction

One in five patients undergoing knee replacement surgery experience chronic pain after their operation, which can negatively impact on their quality of life. With approximately 700,000 KR performed per year in the US [3] and 108,000 performed during 2016 in England, Wales, Northern Ireland and the Isle of Man [4], large numbers of people are living with chronic pain after KR. These patients experience high levels of pain-related distress [5] and reduced ability to participate. Identifying individuals with chronic pain early during their post-operative recovery will facilitate the delivery of timely and targeted interventions to improve pain outcomes This requires a robust and standardised method for identifying people in chronic pain following KR that can be used across a range of research settings

Objectives

Methods

Results

Conclusion