title: Tripod index: a new radiographic parameter assessing foot alignment.
abstract: BACKGROUND
  No single radiographic measurement takes into account complete foot alignment. We have created the Tripod Index (TI) to allow assessment of complex foot deformities using a standing anteroposterior (AP) radiograph of the foot. We hypothesized that TI would demonstrate good intraobserver and interobserver reliability and correlate with currently accepted radiographic parameters, in both flatfoot and cavovarus foot deformities.
  
  
  METHODS
  Three groups of patients were studied: 26 patients (30 feet) with flatfoot, 29 patients (30 feet) with cavovarus foot, and 51 patients (60 feet) without foot deformity as controls. Weight-bearing radiographs were obtained: foot AP with a hemispherical marker around the heel plus standard lateral and hindfoot alignment views. Radiographic measurements were made by 2 blinded investigators. Statistical analysis included intraclass correlation coefficients (ICCs), correlation of the TI with existing radiographic measurements using Pearson coefficients, and comparison between patient groups using analysis of variance.
  
  
  RESULTS
  Intraobserver and interobserver ICCs of TI (0.99 and 0.98, respectively) were excellent. In the flatfoot group, TI significantly correlated with AP talonavicular coverage angle (r = 0.43), medial cuneiform-fifth metatarsal height (r = -0.59), coronal plane hindfoot alignment (r = 0.53), and clinical hindfoot alignment (r = 0.39). In the cavovarus foot group, TI correlated significantly with AP talonavicular coverage angle (r = 0.77), calcaneal pitch angle (r = 0.39), medial cuneiform-fifth metatarsal height (r = -0.65), coronal plane hindfoot alignment (r = 0.55), and clinical hindfoot alignment (r = 0.61). Statistically significant differences between flatfoot-control and cavovarus foot-control were found in TI, AP talonavicular coverage angle, lateral talo-first metatarsal angle, calcaneal pitch angle, medial cuneiform-fifth metatarsal height, coronal plane hindfoot alignment, and clinical assessment of hindfoot alignment (all with P < .001).
  
  
  CONCLUSIONS
  The TI was demonstrated to be a valid and reliable radiographic measurement to quantify the magnitude of complex foot deformities when evaluating flatfoot and cavovarus foot.
  
  
  CONCLUSIONS
  The TI may be helpful as an integrated assessment of complex foot deformities. Further clinical studies are recommended.
  
  
  METHODS
  Level III, retrospective comparative study.
authors: Department of Orthopaedics and Rehabilitation, University of Iowa, Iowa City, Iowa, USA.
authors: Marut
authors: M
authors: Arunakul
authors: Annunziato
authors: A
authors: Amendola
authors: Yubo
authors: Y
authors: Gao
authors: Jessica E
authors: JE
authors: Goetz
authors: John E
authors: JE
authors: Femino
authors: Phinit
authors: P
authors: Phisitkul
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005413:Flatfoot / Q000000981:diagnostic imaging; D005530:Foot Deformities / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: Tripod Index; cavovarus foot; flatfoot; radiographic parameter