Abstract
Research Type:
Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies
Introduction/Purpose:
Multiple conventional radiographic (CR) parameters are employed for evaluating and staging Progressive Collapsing Foot Deformity (PCFD). The threshold values of the different measurements utilized by surgeons in defining the presence of the different deformity classes are not well established, and the specific cutoffs for each may vary depending on individual preferences and expertise. With that in mind, the objective of this study was to identify what are the measurements and most importantly the threshold values of these measurements that influence the decision-making of orthopaedic foot and ankle surgeons in reporting the absence or the presence of Class A (hindfoot valgus), Class B (midfoot/forefoot abduction), Class C (arch collapse), class D (peritalar subluxation) and Class E deformities (valgus talar tilt) in PCFD.
Methods:
Five fellowship-trained foot and ankle surgeons conducted an independent and blinded assessment of clinical and CR images from 96 PCFD patients (108 feet). A total of 5 images were assessed per patient: anteroposterior (AP) and lateral foot views, AP ankle view, hindfoot alignment view, and posteroanterior clinical view of patient's heel. Observers were restricted from conducting measurements and were directed to identify the presence/absence of PCFD classes A to E solely through their experience and visual analysis. A sixth independent investigator performed semi-automatic and manual measurements assessing measurements for Class A (Hindfoot Moment Arm, HMA), Class B (Talonavicular Coverage Angle, TNCA; talus-first metatarsal angle axial plane, TFMA-A), Class C (Calcaneal Inclination Angle, CIA; talus-first metatarsal angle sagittal plane, TFMA-S), Class D (Subtalar Impingement, STI; Subfibular Impingement, SFI) and Class E (Talar Tilt Angle, TTA). Threshold values of the different measurements influencing observer’s decision-making to stage PCFD patients were assessed.
Results:
Interobserver agreement was high, with values of 0.98 (Class A), 0.88 (Class B), 0.77 (Class C), 0.74 (Class D), and 0.96 (Class E). All feet were staged as Class A (100%), followed by Class B (96.3%), Class C (82.4%), Class D (37.0%), and Class E (6.5%). The most frequently observed combined stagings were ABC (46.0%), ABCD (28.0%), and AB (14.0%). The average HMA (Class A) was 12.6mm. The best cut-off values and Area Under the Curve (AUC) identified to influence the observer’s decision-making for the other different PCFD classes were respectively: TFMA-A >13.31o, AUC=0.90 (Class B), TFMA-S >16.45o, AUC=0.90 (Class C), absence of STI (88.5% chances of no Class D), and TTA >0.52o, AUC=0.92 (Class E).
Conclusion:
In the words of William Shakespeare, "the eye sees all, but the mind shows us what we want to see." This concept was evident in the current study where five fellowship-trained foot and ankle surgeons examined conventional radiographs and clinical pictures of PCFD patients. The results showed that the mind tends to focus on hindfoot valgus, which was present in all patients. The study also identified specific cut-off values, such as TFMA-A >13.31o, TFMA-S >16.45o, absence of STI, and TTA >0.52o, that were crucial in determining the presence or absence of PCFD Classes B, C, D, and E.
