Summary

Forgotten Joint Score can be a useful preoperative tool to identify patients who may not improve with a total knee arthroplasty.

Abstract

Introduction

Total knee arthroplasty(TKA) has shown excellent results, but continues to have higher dissatisfaction rates as compared to total hip arthroplasty. Identifying patients at increased risk of not having the expected improvement is paramount to optimize patient management. Minimal important change (MIC) for patient reported outcome measures(PROM) is a useful parameter to judge improvement important to the patient following any procedure. It has been used widely to study the within-patient improvement in function and symptoms following TKA. The forgotten joint score (FJS) is a unique PROM that can help measure satisfaction post TKA and has gained popularity recently. To the best of our knowledge, there has been no study looking at the utility of FJS pre TKA in identifying patients more likely to not improve post TKA. Our aim is to study the role of FJS Pre TKA in identifying patients who will not improve post TKA.

Methods

We retrospectively reviewed our prospectively collected data of all patients undergoing primary TKA by a single senior surgeon between July 2022 & June 2023. We identified 192 TKA, all receiving a cemented TKA with patella resurfacing. All patients were assessed at 1 year(±1 month) follow-up. Patients were considered to have not improved if the increase in FJS post TKA did not meet the MIC of 14, as established by Ingelsrud et al. Clinical outcomes were measured using FJS and New Knee Society Score(NKSS). Statistical analysis was performed using SPSS. We calculated Spearman’s correlation coefficient and performed a receiver operating curve(ROC) analysis to study relationship between pre TKA FJS and those having no improvement post TKA.

Results

Of the 192 TKA, 26 TKA did not improve post TKA. The mean age was 68.7 years, 17.2% were males and mean BMI was 30.5. The Spearman’s correlation coefficient(p=0.001) was 0.52 for pre TKA FJS and those not improving post TKA.

ROC analysis showed an area under curve(p=0.001) of 0.709 (95% CI 0.609-0.809) for pre TKA FJS and those not improving post TKA. Using the ROC curve analysis, we identified a cut-off of Pre TKA FJS of 20.64 having a sensitivity of 61.5% and specificity of 40.4% in predicting no improvement post TKA.

Patient having pre TKA FJS >20.64 had an Odds Ratio of 2.36 (95% CI 1.01 – 5.52, p<0.023) of not improving post TKA.

Patients having pre TKA FJS >20.64 had higher pre TKA NKSS(p=0.0001) but comparable post TKA NKSS(p=0.12) to those with pre TKA FJS ≤20.64. The change in NKSS was lower(p=0.04) in patients with pre TKA FJS >20.64 (70.1 vs 79.1 respectively).

Conclusion

Pre TKA FJS has a significant moderate correlation with no improvement post TKA, ie higher preop FJS is associated with increased chances of not improving post TKA. Patients having a pre TKA FJS >20.64 have an increased risk (Odds Ratio 2.36) of not improving post TKA and seem to have lesser improvement in clinical outcome as measured by NKSS. Pre TKA FJS can be an important tool in identifying patients likely to not improve with TKA and needs further research.