The Manchester Charcot Ankle Neuroarthropathy (M-CAN) Classification: A Radiographic-Based System for Assessing Charcot Ankle Neuroarthropathy

Background Charcot neuroarthropathy (CN) is a complication of long-standing, poorly controlled diabetes, associated with increased risks of amputation and mortality. Currently, there is no dedicated classification system specifically for ankle CN, nor a standardized description of the possible deformities involving the ankle in relation to CN. This study aims to develop and propose the Manchester Charcot Ankle Neuroarthropathy (M-CAN) classification - a descriptive, radiograph-based system designed to categorize ankle deformities and patterns of bone loss in patients with diabetic CN. The M-CAN classification may aid clinicians in early identification of deformities, facilitating more effective treatment planning and improved outcomes. Methods This retrospective review included 71 patients with diabetic ankle CN who were managed at the Manchester University NHS Foundation Trust over a 10-year period. Patterns of ankle deformity and bone loss were assessed using weight-bearing radiographs, and this information formed the basis for developing the classification system. The proposed classification is structured as follows: "A" refers to the alignment of the ankle joint - Type 1: varus ankle, Type 2: valgus ankle, Type 3: anterior angulation, Type 4: posterior angulation, Type 5: combined plane deformity, and Type N: neutral ankle. "B" denotes bone loss around the ankle joint - Subtype a: tibial bone loss, Subtype b: talar bone loss, Subtype c: calcaneal bone loss, and Subtype d: combined bone loss. "C" represents the cutaneous condition around the ankle, including ulceration and infection. "D" reflects diabetic control, measured by glycated hemoglobin levels. "E" captures the modified Eichenholtz stage of Charcot - Stages 0, 1, 2, and 3. "F" indicates foot perfusion status as assessed by Doppler studies. The classification primarily describes the deformity pattern "A", bone loss "B", and CN stage "E" using standard weight-bearing ankle radiographs, with optional supplementary information from the cutaneous condition "C", glycemic control "D", and pedal perfusion status "F". Results A total of 75 ankle X-rays from CN patients were reviewed. The coronal and sagittal planes of deformity "A" were assessed, and the patterns of bone loss "B" were documented, along with the Eichenholtz stage "E". Based on this A+B+E framework, the most common classification among patients was Type 1-d Stage 3, indicating a varus ankle with combined tibial, talar, and calcaneal bone loss in the consolidation stage of CN. Inter- and intra-observer agreement for components A and B showed near-perfect reliability, with a Kappa value of 0.94. Conclusions This new classification system for ankle CN facilitates the understanding of deformity patterns using plain radiographs and serves as a descriptive tool. It allows the condition to be categorized based on the specific deformities and associated osseous loss.