title: New radiographic parameters assessing forefoot abduction in the adult acquired flatfoot deformity.
abstract: BACKGROUND
  Stage II flatfoot secondary to posterior tibial tendon insufficiency may be subclassified into mild (IIa) and severe (IIb) deformity based on the degree of talonavicular abduction. Current assessment of this abduction is difficult. We hypothesized that two new anteroposterior radiographic parameters, the lateral talonavicular incongruency angle (IA) and incongruency distance (ID) would demonstrate good reliability, correlate with current abduction parameters, and differ in IIb deformity, IIa deformity, and controls.
  
  
  METHODS
  Preoperative radiographs for consecutive patients undergoing flatfoot reconstruction were reviewed and subdivided into those with a Stage IIb (n = 32) or Stage IIa (n = 8) deformity. A third group of patients without flatfoot served as control (n = 30). Radiographs were measured blindly by two investigators. Reliability was assessed with intraclass correlation coefficients (ICC), correlation with existing parameters with Pearson coefficients, and comparison between groups with analysis of variance.
  
  
  RESULTS
  The mean intrarater and interrater ICC's for the IA (0.88 and 0.81, respectively) were high. The IA correlated well with the coverage angle (r = 0.86) and uncoverage percent (r = 0.76). The IA was higher in the IIb versus IIa patients (p = 0.007) and in the IIb group versus control (p < 0.001). The ID demonstrated excellent reliability (ICC's of 0.83 and 0.83), but correlated poorly with the two other abduction parameters (r = -0.59 and -0.49) and failed to differentiate between the three groups (p = 0.0528).
  
  
  CONCLUSIONS
  This data suggests that the IA is reliable and may help subclassify Stage II flatfoot deformity.
authors.affiliation: The Hospital for Special Surgery, Department of Foot and Ankle Surgery, 535 East 70th Street, New York, NY 10021, USA. elliss@hss.edu
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Ellis
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Yu
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Williams
authors.forename: Cheol
authors.initials: C
authors.lastname: Lee
authors.forename: Ya-Lin
authors.initials: YL
authors.lastname: Chiu
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Deland
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005413:Flatfoot / Q000145:classification* / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D008875:Middle Aged; D010027:Osteotomy; D011859:Radiography; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013709:Tendon Transfer