Ankle Radiographic Characteristics of Two Different Types of Valgus Ankle Arthritis: With or Without Progressive Collapsing Foot Deformity

Category: Ankle Arthritis; Ankle Introduction/Purpose: Establishing a surgical plan for ankle arthritis requires a thorough understanding of the deforming forces involved. While ankle morphology-based classification and application are common in the surgical treatment of varus ankle arthritis (i.e., Takakura stage), such an approach has not been described for valgus ankle arthritis. Progressive collapsing foot deformity (PCFD) has been identified as the major cause of non-traumatic valgus ankle arthritis. However, mounting evidence suggests that it can also develop without PCFD, which may mean that the etiology and possibly the outcomes of treatment are different when comparing the two groups. Therefore, this study aimed to investigate whether weightbearing ankle radiographs can be used to differentiate PCFD origin from non-PCFD origin in valgus ankle arthritis. Methods: This study retrospectively reviewed patients who were surgically treated for asymmetric valgus ankle arthritis at our institution between 2017 and 2021. Patients with valgus tibiotalar tilt (TT >4 degrees and Meary’s angle>30 degrees) were included in the PCFD group (n=24). A control group (non-PCFD group [n=24]) with valgus tibiotalar tilt>4 degrees and Meary’s angle < 4 degrees was also established. In the weightbearing ankle anteroposterior (AP) view, the TT and medial distal tibial angle (MDTA) were measured. Additionally, to assess mediolateral position of the talus, the talar center migration (TCM) and lateral talar dome-plafond distance (LTD-P) ratio was measured (Figure 1A). Other PCFD radiographic parameters were also measured. In weightbearing computed tomography (WBCT), the degree of axial plane talocalcaneal subluxation was assessed using transmalleolar axis method as previously described, and the prevalence of sinus tarsi bony impingement was assessed. All parameters were compared between groups using Student t- or chi-square tests. Results: Both groups demonstrated a similar degree of TT, with a mean and standard deviation of 11.1±7.8 degrees in the PCFD group and 12.7±5.9 degrees in the non-PCFD group (p=0.2013, Table 1). However, the PCFD group showed a significantly greater TCM and LTD-P ratio compared to those of the non-PCFD group (p < 0.0001), indicating that PCFD patients have a more medially translated talus in ankle AP radiographs (Figure 1A). WBCT showed that the PCFD group had a greater axial plane talocalcaneal subluxation (p < 0.0001) and a higher prevalence of sinus tarsi bony impingement (p=0.0077) compared to the non- PCFD group, indicating a different degree of subtalar joint subluxation between the two groups. Conclusion: This study demonstrates that weightbearing ankle radiographs reveal different morphologies based on the etiology of valgus ankle arthritis. While both groups exhibited similar degrees of valgus tibiotalar tilt, PCFD patients demonstrated medial translation of the talus compared to non-PCFD patients. We propose a morphology-based classification (Figure 1B) that may assist in differentiating between the PCFD and non-PCFD origins of valgus ankle arthritis. Also, the different morphology of the valgus tibiotalar tilt in the each group may mean that they may require different treatments, as well as potentially different outcomes of treatment for the valgus tibiotalar tilt