INCREASED BMI IS A MODIFIABLE RISK FACTOR OF SUBCHONDRAL INSUFFICENCY FRACTURE OF THE KNEE

Abstract

INTRODUCTION

Subchondral insufficiency fractures of the knee (SIFK) are increasingly recognized as an important, but often underdiagnosed, cause of acute knee pain and functional decline, particularly in middle-aged and older adults. Existing studies on SIFK are often limited in number and lack a sufficient number of controls. Because of its rare occurrence in the general population and in major epidemiological studies, our understanding of the risk factors of SIFK remains limited. It has been hypothesized that excessive joint loading leads to focal stress concentrations within the subchondral bone plate, overwhelming its capacity for repair and ultimately predisposing to a microfracture. However, it remains unclear whether BMI is modifiable risk factor of SIFK.

OBJECTIVE

Our aim is to investigate the association between BMI and the occurrence of MRI-detected SIFK in a clinical setting.

METHODS

We conducted a case–control study at a tertiary academic hospital network from November 2022 to October 2024. Cases were identified using an institutional repository, based on MRI reports containing the diagnosis “subchondral insufficiency fracture”. The diagnosis of SIFK was confirmed by a MSK radiologist who reviewed all images. Matched controls were defined as patients within 5 years of age who underwent knee MRI for knee pain over the same period (±10 days) and who did not have subchondral insufficiency fracture on MRI (both in the MR report and after review of images). Electronic medical records were manually checked for the primary independent variable, BMI, and other variables such as age, sex, dyslipidemia, statin use, diabetes mellitus, and hypertension. Univariable and multivariable logistic regression estimated odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using SIFK as the primary dependent variable. Missing data on variables in the logistic regression model will be handled by listwise deletion.

RESULTS

The mean age (±SD) in years was 63.2 (±10.2) for the cases and 64.3 (±10.4) for the controls. Females made up 64% of the cases and 67% of the controls. Median (Q1–Q3) BMI was 29.5 kg/m² (26.0–34.4) for the cases and 27.1 kg/m² (23.7–31.4) for the controls. A two-sample t-test showed that BMI was significantly higher in the cases than in controls (p-value = 0.015). Univariable logistic regression with SIFK as the dependent variable and BMI as the independent variable estimated an OR of 1.06 (95% CI: 1.01–1.10). This statistically significant result remained after adjusting potential confounders such as sex, dyslipidemia, and statin use with an estimated OR of 1.05 (95% CI: 1.01–1.10) (figure 1 and table 1). Figure 2 shows an example of SIFK.

CONCLUSION

Our preliminary results indicate that elevated BMI may be linked to greater odds of having SIFK. As we continue to enroll additional participants, we anticipate refining our effect estimates and strengthening the evidence for this association.