SLR - May 2018 - Stephanie Mita

Subchondral Bone Degradation After Microfracture for Osteochondral Lesions of the Talus: An MRI Analysis

Reference: Shimozono Y, Coale M, Yasui Y, O’Halloran A, Deyer TW, Kennedy JG. Subchondral Bone Degradation After Microfracture for Osteochondral Lesions of the Talus: An MRI Analysis. Am J Sports Med. 2018 Mar; 46(3).

Scientific Literature Review

Reviewed By:
Stephanie Mita, DPM
Residency Program: Kaiser Permanente North Bay Consortium, Vallejo, CA

Podiatric Relevance:
Osteochondral lesions of the talus (OLT) are a common podiatric injury, for which arthroscopic microfracture to the subchondral plate is a widely used technique to generate fibrocartilage, leading to excellent short-term clinical outcomes. Recent literature suggests that the fibrocartilaginous tissue degrades with time, resulting ultimately in poor clinical outcomes. The purpose of this study was to investigate the midterm morphological changes after microfracture, as well as to develop an MRI-based scoring system for assessing the subchondral bone to predict potential clinical outcomes.

Methods: This level IV retrospective case series included 42 patients treated with microfracture for OLT between 2007 and 2012. After preoperative MRI, the procedures were performed with standard anteromedial and anterolateral portals by the senior surgeon. After debridement and curettage of the OLT, the subchondral bone was perforated with a 2 mm awl to a depth of 3 mm, with the holes spaced 3 to 4 mm apart. A concentrated bone marrow aspirate was injected. Patients underwent postoperative MRI at four-time points—at six months to one year, at one to two years, at two to four years and at four to six years.

An MRI-based scoring system (Subchondral Bone Health score, or SCBH score) to assess morphological structure of the talar subchondral bone was developed. The SCBH score included four parameters—bone marrow edema, number and diameter of subchondral cysts, a qualitative assessment of morphology (intact, irregular, collapsed or loose in situ fragment), and the percentage change in subchondral bone plate thickness.

To evaluate clinical outcomes, the Foot and Ankle Outcome Score (FAOS) was collected preoperatively, two years postoperatively and at final follow-up.

Results: There was a significant increase in the number and size of subchondral cysts, as well as a significant decrease in the SCBH score.

The mean FAOS improved significantly from 57.8 preoperatively to 84.3 at two years. The FAOS then decreased significantly to 77.1 at final follow-up at 51.7 months.

The final FAOS did not correlate with the six-month to two-year SCBH scores; it did correlate with the two-year to six-year SCBH scores.

Conclusions: Limitations to the study include its retrospective nature, its relatively small sample size and the loss of a portion of their patient population for the third and fourth MRI, which precluded robust statistical analysis.

This study’s score to assess morphological structure of the subchondral bone correlated with the final clinical outcome score at midterm follow-up but not at short-term follow-up, suggesting that microfracture-induced trauma did not affect clinical outcomes until approximately two years postoperatively. Future studies would be needed to determine the validity and clinical application of this scoring system.

Microfracture causes damage to the subchondral bone of the talus, which in this study did not recover by four to six years postoperatively. The researchers found worsening damage over time, with a significant increase in formation and progression of subchondral cysts. Future studies are needed to investigate this possible long-lasting damage and failure of microfracture as a treatment for OLT in the long term.

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