MRI-DETECTED SUBCHONDRAL INSUFFICIENCY FRACTURE OF THE KNEE INCREASES RISK OF TOTAL KNEE REPLACEMENT

To determine whether MRI-confirmed subchondral insufficiency fracture of the knee (SIFK) is an independent predictor of total knee replacement (TKR).

Using hospital electronic medical records (EMRs), we assembled a cohort of patients with MRI-detected SIFK and identified a comparator group without SIFK, matched 1:1 for age. All MRIs were performed between November 2021 and November 2024 and subsequently reviewed by four musculoskeletal radiologists 1. to confirm the presence of SIFK and 2. to assess meniscal tear and extrusion using the MRI Osteoarthritis Knee Score (MOAKS). Exclusion criteria included secondary osteonecrosis, prior knee surgery, high-energy trauma, and suboptimal imaging quality. In the present analysis, SIFK was treated as the exposure, and subsequent ipsilateral TKR was the outcome. Patients without documented TKR in the EMR were censored at the date of their last available knee imaging study or clinical encounter. TKR-free survival was estimated using a Kaplan-Meier curve and log-rank testing. A multivariable Cox proportional hazards model was adjusted for sex, age, body mass index, meniscal radial/root tear, meniscal extrusion, and ipsilateral radiographic osteoarthritis.

We analyzed a total of 694 patients (344 with SIFK, 350 without SIFK). Patients with SIFK and those without were similar in age at baseline (SIFK+ mean age = 65.35 ± 10.06 years, SIFK- = 66.30 ± 9.96 years). The proportion of women was similar among participants with SIFK and without SIFK (227/344 [66.0%] vs 230/350 [65.7%], respectively). BMI was slightly higher among those with SIF (29.73 ± 6.44 kg/m² versus 28.63 ± 5.72 kg/m² among comparators). The overall mean duration of follow-up was 2.00 ± 1.24 years, with a median of 2.01 years; follow-up was slightly shorter among SIFK+ than SIFK- comparators, with mean durations of 1.82 ± 1.27 years and 2.18 ± 1.19 years, respectively. In total, 90 patients progressed to TKR (64 SIFK+ and 26 SIFK-). Among participants who progressed to TKR, the overall mean time to progression was 0.79 ± 0.70 years, with SIFK+ and SIFK- showing similar mean times to progression of 0.76 ± 0.64 years and 0.88 ± 0.84 years, respectively. In unadjusted analysis, SIFK was associated with conversion to TKR (HR 2.88; 95% CI 1.83-4.55; p<0.001). After adjustment for sex, age, BMI, meniscal root tear, meniscal extrusion, and ipsilateral radiographic osteoarthritis, SIFK remained an independent predictor of TKR (HR 2.06; 95% CI 1.19-3.57; p=0.010) (figure 1).

In this clinical sample, we found that MRI-confirmed SIFK is an independent predictor for subsequent TKR Future mechanistic studies are needed to further elucidate whether the biomechanical consequences of SIFK on knee joint health are reversible and whether SIFK could serve as a target for preventive strategies to delay TKR.