Subchondral Bone Degradation Following Bone Marrow Stimulation -An MRI Analysis-

Abstract

Category: Ankle Introduction/Purpose: Microfracture is the most common operative procedure for the treatment of osteochondral lesions of the talus (OLT). The role of the subchondral bone (SCB)/plate (SCBP) is recognized as one of the most significant factors providing joint-loading support to the ankle. Greater attention has recently been paid to the SCBP and its effects on overlying hyaline and fibrocartilage function. However, damage to the SCB and SCBP during microfracture may irreversibly change the joint loading support of the ankle, leading to reparative cartilage degradation. The purpose of this study is to investigate the morphological change in the SCB and SCBP after microfracture for OLT by developing a novel magnetic resonance imaging (MRI) scoring system specifically for evaluating SCB and SCBP. Methods: Twenty patients who underwent microfracture for OLT and had at least a one year follow-up 3-Tesla MRI between 2008 and 2011 were selected. A SCB Health scoring system was developed to assess the condition of the SCB using 3-Tesla MRI. The SCB Health score is based on the amount of edema, subchondral cyst diameter, qualitative change in SCBP morphology and thickness change of the SCBP (Table 1). Nine of the twenty patients had two follow-up MRIs, and differences in their scores were calculated. The clinical evaluation was assessed using the Foot and Ankle Outcome Scores (FAOS) preoperatively and at final follow-up. Results: At first follow-up MRI, 65% of patients had mild or greater edema, 40% had subchondral cysts, 65% had irregularity or collapse of their SCBP and 85% had a >25% change in SCBP thickness. The overall SCB Health score of 90% of patients were abnormal. Of the nine patients who had a subsequent follow-up MRIs, the mean time between the first and second study was 22±6 months. The scores between the two time points were not statistically significant (p=0.347, p=0.559, p=0.169, p=0.347 p=0.154 for edema, subchondral cyst diameter, qualitative SCBP measurements, SCBP thickness change and overall SCB Health score, respectively). The mean FAOS score improved significantly from 55.5±16.8 preoperatively to 76.0±12.3 at final follow-up (p<0.05). Conclusion: The SCB and SCBP were not completely healed in 90% of patients at a mean 18 months follow-up following microfracture of the talus. Subsequently, morphological changes were not restored at a mean 43 months at second follow-up in a smaller subset of patients. Most previous studies have focused on the degeneration of the articular cartilage layer, and its effect on clinical outcomes. The authors of current study believe that looking at the changes in the SCB may provide additional information as to why BMS procedures fail in the long-term.