Evaluation of Asymptomatic Contralateral Foot Deformities Using the Tripod Index

The primary aim of this study was to determine the prevalence of asymptomatic pes planus and cavovarus foot deformities using the tripod index (TI).

A retrospective study was conducted on 122 adult subjects over the age of 18 from January 2010 to December 2016 with symptomatic pes planus (n=78) or cavovarus (n=44) foot deformities. We subdivided both groups into subjects who presented with unilateral symptomatic deformities (pes planus unilateral symptomatic; cavovarus unilateral symptomatic) and bilateral symptomatic foot deformities (pes planus bilateral symptomatic feet and cavovarus bilateral symptomatic feet). The severity of TI was compared between sides.

The prevalence of asymptomatic pes planus and cavovarus foot deformities was 52% and 67.6%, respectively. Subjects with unilateral symptomatic foot deformities had significantly more severe TI values for the symptomatic cavovarus foot -98.96% (-288.89 to 0%) compared to asymptomatic cavovarus -67.41% (-270.59 to 14.71%) (p=0.015). Subjects with unilateral symptomatic pes planus deformity also had more severe TI on the symptomatic foot 57.49 (-9.38 to 141.67%) compared to the asymptomatic foot 30.43 (-51.52 to 119.23%) (p<0.01). Subjects with bilateral symptomatic foot deformities had no significant difference in severity of Tripod Index between feet.

Although half of subjects with unilateral symptomatic deformities had a foot deformity on the contralateral side, the severity of deformity between symptomatic and asymptomatic feet was significantly different for both pes planus and cavovarus feet. Further studies should prospectively follow postoperative radiographs to determine whether a correction in foot alignment directly improves symptoms.Level of evidence: III.