The Triplanar Hallux Abducto Valgus Classification System: Is it Valid?

CATEGORY: Bunion INTRODUCTION/PURPOSE: Historically, two-dimensional radiographic study techniques have been used to classify and describe hallux valgus deformities and guided treatment based on severity of deformity in the transverse plane only. These two-dimensional radiographic studies and were not able to assess rotational deformity and may explain the high recurrence and dissatisfaction rates which have been reported. Recently, a triplanar hallux abducto valgus classification (THAVC) system was proposed. This key elements of this classification system are the pathologic alignments in all three anatomic planes. The THAVC system is intended to clarify the deformity and apply a triplanar anatomic algorithm for treatment. To our knowledge, this classification system has not been validated. Our objective was to assess the intra-reader and inter-reader reliability of the THAVC. METHODS: After approval by the Institutional Review Board, patients with hallux abducto valgus (HAV) were identified from a foot and ankle registry. Electronic medical records and digital radiographs were reviewed by the principal investigator (PI). Selected radiographs were then deidentified of patient information and assembled in a digital slide presentation and presented to the reviewers. The eligibility criteria required complete weightbearing radiographic studies and represented varying degrees of HAV. The reviewers included three board certified, fellowship trained orthopaedic foot and ankle surgeons. Images of twenty cases of hallux valgus and five normal cases were distributed electronically, who independently classified all 25 cases according to the THAVC system for a total of 75 observations. After an eight week washout period, the order of the HAV cases was randomized and redistributed to the reviewers. The three reviewers were blinded to the results of the both radiographic reviews until after statistical analysis had occurred. RESULTS: We evaluated the intra-reader consistency by Cohen's kappa for the agreement between two measurements from the same reader. The average kappa value from three readers was 0.241 with 95% CI (0.093-0.374), indicating a fair agreement. The inter-reader agreement was 0.046 with 95% CI (-0.041-0.112), showing poor agreement between readers. CONCLUSION: The Triplanar HAV Classification is the first classification system that utilizes anatomic, multi-plane evaluation. Our results indicate while this is the first known HAV classification system, by this analysis it lacks reliability. This study shows that the reading of 2D radiographs still present a difficulty in assessing a 3D problem. Perhaps a scoring system utilizing advanced imaging such as 3D WBCT could prove more reliable and applicable.