SLR - February 2019 - Jeffery Hunter

Correlation of MRI Appearance of Autologous Chondrocyte Implantation in the Ankle with Clinical Outcome  

Reference: Chan K, Ferkel R Kern B, Chan S, Applegate G. Correlation of MRI Appearance of Autologous Chondrocyte Implantation in the Ankle with Clinical Outcome. Cartilage. 2018 Jan;9(1):21–29.

Reviewed By: Jeffery Hunter, DPM
Residency Program: Wake Forest Baptist Health, Winston-Salem, NC

Podiatric Relevance: A common condition seen and treated by foot and ankle surgeons is chronic ankle pain and disability secondary to osteochondral lesions of the talus (OLTs). Despite the highly specialized nature of articular cartilage, it has poor reparative capabilities. One surgical technique utilized for this condition is autologous chondrocyte implantation (ACI). Magnetic resonance imaging (MRI) is commonly performed postoperatively for evaluation and follow-up of the graft. Most literature on MRI follow-up of ACI has mainly been described in the knee. Several studies in the knee have shown that postoperative MRIs correlate with clinical outcome scores. Prior to this study, there has been no systematic way to describe MRI findings following ACI procedures. This study provides the foot and ankle surgeon with a metric to help evaluate ACIs on MRI and possibly predict patients’ clinical outcomes.

Methods: This was a prospective study to characterize MRI findings and correlate the findings with clinical results in patients who underwent ACI of OLTs. Twenty-four consecutive grafts were evaluated by an experienced musculoskeletal radiologist for six criteria: defect fill, surface regularity, signal pattern, bone marrow edema, subcondral plate irregularity and presence of cystic lesions. Clinical outcome was measured by the American Orthopaedic Foot and Ankle Society (AOFAS) clinical outcome score. Mean follow-up with MRI was 65.8 months.

Results: The mean postoperative AOFAS score was 87.5 with a mean improvement of 39.4. When evaluating the MRI criteria, 92 percent of the grafts demonstrated >75 percent defect fill. Eighteen (75 percent) of the grafts had a mildly irregular and six (25 percent) had a moderately irregular articular surface. Of the 24 grafts, 23 (96 percent) showed a heterogeneous signal pattern. Bone marrow edema was decreased in 58 percent while no difference was found in 17 percent and 21 percent had an increase in bone marrow edema. Only two grafts were free of abnormalities of their subchondral plate. Seven grafts had an increase in cystic changes while the others had no change, decrease in cystic findings or no cysts seen at all.  

Conclusions: To the author's knowledge, this was the first prospective study to evaluate the MRI appearances of OLTs after ACI and to compare the relatively long-term MRI follow-up findings with clinical outcome scores. While the results demonstrated a wide variation of MRI appearances after ACI surgery, most patients were clinically doing good or excellent. The results seemed to suggest that certain categories of MRI evaluation, such as bone marrow edema and cystic lesions, may correlate stronger to clinical outcomes than other MRI evaluation categories. The results of this study suggest that patients who did not have an increase in bone marrow edema or an increase in cystic lesions on their follow-up MRI correlated more strongly with the patients who had excellent AOFAS outcome scores. While MRI is a good tool for postoperative assessment of ACI grafts, one must interpret MRI abnormality findings with caution when using them to predict clinical outcomes.

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