# Patient-reported outcomes following patellofemoral and total knee replacement: an analysis of the 6–18 months postoperative period from the National Joint Registry

## TL;DR

This study compares patient-reported outcomes for patellofemoral and total knee replacements, finding similar results up to 18 months post-surgery but a higher revision rate for patellofemoral replacements.

## Contribution

The study provides new insights into the revision thresholds and patient-reported outcomes for patellofemoral versus total knee replacements.

## Key findings

- PFR had a lower median Oxford Knee Score (35) compared to TKR (38) at 6–18 months.
- PFR showed a higher revision hazard ratio (3.4) compared to TKR, indicating a lower threshold for revision.
- There was no significant difference in EQ5D-3L scores between PFR and TKR up to 18 months post-surgery.

## Abstract

Patellofemoral joint replacements (PFR) and total knee replacements (TKR) are surgical treatment options for patellofemoral joint osteoarthritis. We aimed to compare patient-reported outcome measures (PROMs) for these procedures, and revision thresholds for PFR.

Data from the National Joint Registry (2009–2021) was linked with the Hospital Episodes Statistics (HES) database. Data was then merged with the PROMs dataset and adjusted using inverse proportional treatment weighting methods. Primary PROMS were Oxford Knee Score (OKS) and EQ5D-3L at the 6–18-month mark with a minimal clinically important difference of 5 for OKS. Secondary outcome measures included threshold to revision, defined as the cut-off score at which an arthroplasty was revised. Differences in patient characteristics between those classed as best and worst outcomes were compared and regression analyses examined the influence of factors such as age, provider type (public or private healthcare), and comorbidities on PROMs with results stratified by sex.

340,449 matched records were analyzed (1,085 PFR, 339,364 TKR). The median postoperative OKS was 35 (PFR) and 38 (TKR), with a difference of –2.4. Patients with the best PFR outcomes were older (62.0 vs 57.2 years, P = 0.01). The median 6-month EQ5D-3L was 0.77 (PFR) and 0.80 (TKR). PFR had a higher revision hazard ratio (3.4, 95% confidence interval 2.7–4.4, P = 0.01), indicating a lower threshold for revision.

Up to 18 months, in terms of OKS and EQ5D-3L, there was no significant difference between the 2 procedures. PFR had a lower threshold for revision compared with TKR. Future research should incorporate more objective measures, such as activity level, where objective differences might be identified.