Risk Factors for Subchondral Insufficiency Fracture of the Knee in the Setting of Medial Meniscus Posterior Root Tear.

Background: Subchondral insufficiency fracture of the knee (SIFK) is commonly associated with medial meniscus posterior root tears (MMPRTs). However, there is limited research investigating risk factors for SIFK in patients with MMPRTs.

Purpose/hypothesis: The purpose of this investigation was to identify the risk factors for SIFK in patients with MMPRTs. It was hypothesized that age, body mass index, and extent of meniscal extrusion would emerge as significant risk factors for SIFK.

Study design: Case series; Level of evidence, 4.

Methods: Patients with a primary isolated MMPRT confirmed via magnetic resonance imaging were included. Data on patient demographics, medical and surgical history, and imaging parameters were assessed for associations with SIFK. Imaging parameters included mechanical axis, medial tibial slope, tibiofemoral joint space, and meniscal extrusion. Patients were identified and divided into 2 groups based on the presence or absence of findings of SIFK on magnetic resonance imaging. Continuous variable distribution normality was assessed using the Shapiro-Wilk test. Demographic comparisons were made by t tests and chi-square tests. Multivariable logistic regression was used to identify SIFK risk factors. The threshold of joint space for predicting SIFK was determined through receiver operating characteristic analysis. The optimal threshold was determined with the Youden index.

Results: A total of 153 patients were included (mean ± SD age, 56.2 ± 9.1 years): 90 patients (26 male, 64 female) in the non-SIFK group and 63 patients (16 male, 47 female) in the SIFK group. There were no differences in patient demographics between the cohorts. Patients with SIFK had a greater incidence of previous knee injections (P = .047), a significantly smaller tibiofemoral joint space (P < .001), and a significantly greater degree of meniscal extrusion (P = .041). Multivariable logistic regression analysis identified diminished joint space as the only independent predictor of SIFK (odds ratio, 0.41; P = .017). Receiver operating characteristic analysis determined a predictive threshold for joint space <3.93 mm, yielding an acceptable area under the curve of 0.766.

Conclusion: The development of SIFK is likely multifactorial; however, decreased tibiofemoral joint space is a significant independent risk factor for SIFK in patients with MMPRTs, with a greater risk in patients with a tibiofemoral joint space <3.93 mm.