Purpose

The purpose of this study was to assess clinical outcomes of SIFK based on progression to surgical treatment and arthroplasty, and to evaluate risk factors which increase the progression to arthroplasty in a large retrospective cohort.

Methods and Materials

A retrospective review was performed on patients with an MRI confirmed diagnosis of SIFK. Baseline and final radiographs were reviewed and graded according to Kellgren-Lawrence scores. Baseline MRIs were reviewed for evaluation of meniscus or ligament injuries. Failure was defined as progression to operative management or conversion to arthroplasty.

Results

223 patients (71% female) with mean age of 65.1 years were included. SIFK affected 69% of femurs and 55% of tibias, with medial compartment involvement in 89% of the knees. 74% of medial menisci had root or radial tears with mean extrusion of 3.6mm. Varus malalignment was identified in 60% of knees. 34% progressed to surgical intervention and 29% underwent arthroplasty. The rate of surgery and arthroplasty increased to 47% (p=0.04) and 37% (p=0.09) respectively in patients with greater than 5 years of follow- Up. Ten-year arthroplasty-free survival rate for patients with SIFK on the MFC, SIFK on MT, medial meniscus extrusion, varus alignment, and older was significantly higher than the survival rates compared to their counterparts (p<0.01, p<0.01, p=0.01, p=0.02, p=0.003, respectively).

Figure 1. Survival curves by A. Kellgren-Lawrence (K-L) Grades and subchondral insufficiency fracture of the knee (SIFK) on B. Medial Femoral Condyle (MFC) and C. Medial Tibial Plateau (MT).

Conclusion

Subchondral insufficiency fractures predominantly involve the medial compartment of the knee and commonly present with medial meniscus root and radial tears. Approximately one third of the patients progress to total knee arthroplasty. Baseline arthritis, older age, location of insufficiency fracture on the medial femoral condyle and metal tibial plateau, meniscal extrusion, and varus malalignment are all associated with progression to arthroplasty.

Purpose

To create a predictive model utilizing baseline demographic and radiographic characteristics for the likelihood that a patient with SIFK will progress to knee arthroplasty with emphasis on clinical interpretability and ease of use.

Methods and Materials

A retrospective review was performed on patients with MRI-confirmed diagnosis of SIFK. Baseline and final radiographs in addition to MRIs were reviewed for evaluation. Patient and radiographic factors were used in building predictive models for progression to arthroplasty with 50:25:25 splits in Train:Validation:Test data subsets. Six types of models were evaluated for their accuracy/misclassification rate.

Results

Figure 1. Receiver operator curves (ROC) by model type.

Table 1. SIFK Score: Final clinical model with associated risk of arthroplasty. P-values <0.05 considered significant.

A total of 249 patients (68% female) with a mean age of 64.6 years (SD 10.5) were included. Sixty-six patients (27%) underwent knee arthroplasty at a mean of 4 years of follow-up. All models had an area under the curve (AUC) > 80%. Lasso Regression model was non-inferior to other models and was chosen for easy interpretability. In order of importance, predictors for progression to arthroplasty included (1) lateral meniscus extrusion, (2) Kellgren-Lawrence (K-L) Grade 4, (3) SIFK on MFC, (4) lateral meniscus root tear, and (5) medial meniscus extrusion. The resulting final SIFK Score stratified patients into low-, medium-, and high-risk categories with associated arthroplasty rates of 8.8%, 40.4%, and 78.9% (p<0.001) and an area under the curve (AUC) of 82.5%.

Conclusion

Subchondral insufficiency fractures of the knee can be a source of functional limitation and progress to arthroplasty. This validated clinic-ready model identifies the most important factors in predicting progression to arthroplasty and assists in providing accurate prognostic information based on patient-specific risk factors.