Hallux Valgus Interphalangeus Measurement: Comparison of the Two Radiographic Methods

CATEGORY: Midfoot/Forefoot INTRODUCTION/PURPOSE: To determine the reliability of Delta PP (difference in medial and lateral proximal phalanx wall length) compared to HIA (hallux interphalangeal angle) in the assessment of HVI (hallux valgus interphalangeus) in both pre and postoperative radiographs. METHODS: This was a retrospective observational study of 186 feet with hallux valgus. The number of cases required to adequately power the study was 128. Preoperative and postoperative hallux alignment were evaluated by two different radiological parameters, Delta PP and HIA. Inter-observer variability was assessed independently by two authors and compared using a intraclass correlation coefficient. RESULTS: The intra-class correlation coefficient was more than 0.8 for all parameters, thus both HIA and Delta PP measurement provide reliable and reproducible data. Mean HIA significantly increased following surgical correction of hallux valgus. In comparison, the mean Delta PP decreased after correction. This postoperative increase in HIA indicates that pre-operative HIA underestimates the magnitude of HVI and therefore is an inaccurate tool for measuring HVI's contribution to the TVDH (total valgus deformity of the hallux) and to preoperative planning. However, the Delta PP was a greater determinant of the phalanx deformity's contribution to the TVDH. CONCLUSION: The outcome of our study shows that both HIA and Delta PP are reproducible when assessing the hallux valgus interphalangeus deformity, however, Delta PP quantifies the amount of correction obtained more precisely. The additional benefit of measuring the Delta PP is that it allows for accurate planning in determining the dimensions of the medial based wedge of the Akin osteotomy that needs to be resected.