Obesity and arthritis of the knee Study (OAKS): study protocol for a prospective cohort study examining the treatments and outcomes of people with obesity and severe knee arthritis

TL;DR

This study will investigate how obesity affects treatment and outcomes for people with severe knee arthritis in the UK.

Contribution

The study introduces a novel protocol to examine treatment decisions and outcomes for people with obesity and severe knee osteoarthritis.

Findings

Baseline data will characterize associations between BMI, knee function, and body image.

Longitudinal follow-up will explore how weight-loss strategies and interventions affect outcomes in high-BMI participants.

Qualitative insights will reveal obstacles and preferences in managing severe knee osteoarthritis.

Abstract

People with body mass index (BMI) ≥35 kg/m2 have an approximately 19-fold increased risk of undergoing total knee replacement (TKR); however, many UK integrated care boards (37%) have restrictive policies which limit access to TKR for people based on BMI. Therefore, access to both surgical and non-surgical treatments varies widely, exacerbating existing health inequalities. It remains unclear how decisions about offering TKR are made in people with severe knee osteoarthritis, which weight-loss interventions are provided in practice and how different management pathways relate to patient outcomes among individuals with high BMI.

This study will recruit 400 participants with severe Kellgren-Lawrence grade four knee osteoarthritis from eight secondary care centres in England. All participants, irrespective of BMI, will provide baseline clinical data and patient-reported outcome measures (PROMs), enabling characterisation of baseline associations between BMI, knee function and body image.

A prespecified subgroup of participants with BMI ≥35 kg/m2 (minimum n=105) will undergo longitudinal follow-up at 6 months, 12 months and 24 months, including repeat BMI measurement, PROMs and detailed data on access to surgical and non-surgical interventions, including weight-loss strategies and TKR. For those with BMI ≥35 kg/m2, statistical modelling will be used to explore associations between baseline factors and longitudinal outcomes including Oxford Knee Score and weight change at 12 months (n≥105). Structural equation modelling will be used to quantify associations between BMI and knee pain/function mediated by psychosocial factors using data from all participants (n=400). A nested qualitative study of surgeons and patients will explore obstacles and preferences in the management of severe knee osteoarthritis.

The study received ethical approval from the West of Scotland REC 5 (Ref: 24/WS/0146) on 10 October 2024. Results will be disseminated through peer-reviewed publications.

ISRCTN42984928.