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Subluxation of the Middle Facet of the Subtalar Joint as a Marker of Peritalar Subluxation in Adult Acquired Flatfoot Deformity
Journal article   Peer reviewed

Subluxation of the Middle Facet of the Subtalar Joint as a Marker of Peritalar Subluxation in Adult Acquired Flatfoot Deformity

Cesar de Cesar Netto, Alexandre Leme Godoy-Santos, Guilherme H. Saito, Francois Lintz, Sorin Siegler, Martin J. O'Malley, Jonathan T. Deland and Scott J. Ellis
Journal of bone and joint surgery. American volume, Vol.101(20), pp.1838-1844
10/16/2019
DOI: 10.2106/JBJS.19.00073
PMID: 31626008

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Abstract

Background: Progressive peritalar subluxation (PTS) is part of adult acquired flatfoot deformity (AAFD). We investigated the use of the middle facet as an indicator of PTS using standing, weight-bearing computed tomography (CT) images. We hypothesized that weight-bearing CT would be an accurate method of measuring increased subluxation ("uncoverage") and incongruence of the middle-facet among patients with AAFD. Methods: We included 30 patients with stage-II AAFD (20 female and 10 male; mean age, 57.4 years [range, 24 to 78 years]) and 30 matched controls (20 female and 10 male; mean age, 51.8 years [range, 19 to 81 years]) who underwent standing, weight-bearing CT. Two independent and blinded fellowship-trained foot and ankle surgeons measured the amount of subluxation (percentage of uncoverage) and the incongruence angle of the middle facet at the midpoint of its longitudinal length, using coronal-plane, weight-bearing, cone-beam CT images. Intraobserver and interobserver reliabilities were assessed using intraclass correlation coefficients (ICCs). Comparisons were performed using independent t tests or Wilcoxon tests. P values of <0.05 were considered significant. Results: Substantial to almost perfect intraobserver and interobserver reliability was observed for both measurements. We found that the middle facet demonstrated significantly increased PTS in patients with AAFD, with a mean value for joint uncoverage of 45.3% (95% confidence interval [CI], 38.5% to 52.1%) compared with 4.8% (95% CI, 3.2% to 6.4%) in controls (p < 0.0001). A significant difference was also found for the incongruence angle, with a mean value of 17.3 degrees (95% CI, 14.7 degrees to 19.9 degrees) in the AAFD group and 0.3 degrees (95% CI, 0.1 degrees to 0.5 degrees) in controls (p < 0.0001). A joint incongruence angle of >8.4 degrees was found to be diagnostic for symptomatic stage-II AAFD. Conclusions: We investigated the use of the middle facet of the subtalar joint as a marker for PTS in patients with AAFD. We confirmed that standing, weight-bearing CT images allowed accurate measurements and that significant differences were found in the percentage of joint uncoverage and the incongruence angle compared with controls.
 Orthopedics Surgery Life Sciences & Biomedicine Science & Technology

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