The Effectiveness of Tripod Index in Defining Hallux Valgus Deformity: A Retrospective Study

Aim: The aim of this study is to investigate the effectiveness and reliability of the Tripod Index (TI) in defining hallux valgus (HV) deformity and accompanying deformities and evaluating the treatment outcome. Material and Methods: Fifty and fifty two patients were included to the study who underwent Chevron (group 1) and proximal dome (group 2) osteotomy, respectively. Preoperative and postoperative hallux valgus angle (HVA), intermetatarsal angle (IMA), Meary angle (MA), talar declination angle (TDA), calcaneal inclination angle (CIA), talar head uncover (THU) and TI were measured. Then, the relationship between TI and other angular variables was evaluated. Results: There was no significant difference between the mean age, body mass index (BMI), side and gender of the patients in both groups. The mean values of HVA and IMA differed between two groups both preand postoperatively. The preoperative TDA, THU and MA values were significantly higher in group 2. The preoperative mean CIA was significantly higher in group 1. The preoperative value of the TI was significantly higher in group 2. There was a significant decrease in all angular parameters in group 2 postoperatively. There was a significant decrease in mean HVA, IMA and TI postoperatively in group 1. There was strong correlation between TI and IMA, THU, CIA, TDA and MA, and moderate correlation with HVA in both groups. Conclusion: TI can provide partial data on the transverse and sagittal plane deformity of the first metatarsal deformity in HV with a single radiograph. Additionally, it can be a guiding measurement in evaluating the need for calcaneal shift osteotomy in pes planovalgus deformities accompanying HV. However, it is insufficient to define complex HV deformity alone.