title: Orientation of the Subtalar Joint: Measurement and Reliability Using Weightbearing CT Scans.
abstract: BACKGROUND
  Up to 60% of patients with an osteoarthritic ankle joint develop talar tilt with progression of the osteoarthritic process. The configuration of the subtalar joint, in particular the posterior facet, may contribute to the development of this wear pattern. Recently, the subtalar vertical angle (SVA) was used to describe the posterior facet of the subtalar joint in the frontal plane. The aim of this work was to analyze if the orientation of the subtalar joint may influence the type of asymmetric ankle osteoarthritis.
  
  
  METHODS
  In total, 60 ankles were retrospectively analyzed including 40 osteoarthritic patients and 20 healthy controls. The osteoarthritic ankles were divided into 4 groups: varus ankle joints with (incongruent) or without (congruent) a tilted talus and valgus ankle joints with (incongruent) or without (congruent) a tilted talus. The orientation of the subtalar joint was described using the SVA. The SVA was determined for every patient using weightbearing CT scans. Additionally, the inter- and intraobserver reliability was assessed using intraclass correlation coefficients (ICCs).
  
  
  RESULTS
  The inter- and intraobserver reliability was excellent (ICC > 0.989 and >0.975, respectively). The varus groups (incongruent and congruent) had significantly lower SVA values, that is, more varus orientation of the subtalar joint than the valgus groups (P < .05). The SVA of the control group was between the values of the varus and valgus ankles.
  
  
  CONCLUSIONS
  The SVA provided a reliable and consistent method to assess the varus/valgus configuration of the posterior facet of the subtalar joint. In our cohort, varus osteoarthritis of the ankle joint occurred with varus orientation of the subtalar joint whereas in patients with valgus osteoarthritis, valgus orientation of the subtalar joint was found. Our data suggest that the subtalar joint orientation may be a risk factor for the development of ankle joint osteoarthritis.
  
  
  METHODS
  Level III, retrospective case control study.
authors: Clinic for Orthopaedic and Trauma Surgery, Kantonsspital Baselland, Switzerland.
authors: Nicola
authors: N
authors: Krähenbühl
authors: Clinic for Orthopaedic and Trauma Surgery, Kantonsspital Baselland, Switzerland.
authors: Michael
authors: M
authors: Tschuck
authors: Clinic for Orthopaedic and Trauma Surgery, Kantonsspital Baselland, Switzerland.
authors: Lilianna
authors: L
authors: Bolliger
authors: Clinic for Orthopaedic and Trauma Surgery, Kantonsspital Baselland, Switzerland.
authors: Beat
authors: B
authors: Hintermann
authors: Clinic for Orthopaedic and Trauma Surgery, Kantonsspital Baselland, Switzerland markus.knupp@ksbl.ch.
authors: Markus
authors: M
authors: Knupp
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017760:Bone Malalignment / Q000000981:diagnostic imaging / Q000503:physiopathology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000000981:diagnostic imaging / Q000503:physiopathology; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013380:Subtalar Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing / Q000502:physiology*
keywords: ankle malalignment; ankle osteoarthritis; subtalar joint; weightbearing CT scan