title: Influence of Ankle Position and Radiographic Projection Angle on Measurement of Supramalleolar Alignment on the Anteroposterior and Hindfoot Alignment Views.
abstract: BACKGROUND
  Using digitally reconstructed radiographs (DRRs), we determined how changes in the x-ray beam projection angle from the horizon, tibiotalar joint angle, and axial rotation of the foot influenced measurements of the medial distal tibial angle (MDTA) on the anteroposterior (AP) and hindfoot alignment views (HAV).
  
  
  METHODS
  Seven cadaver foot-ankle specimens were scanned by computed tomography (CT) at fixed tibiotalar joint positions, ranging from 15 degrees of dorsiflexion to 25 degrees of plantarflexion. DRRs were created from each CT scan to simulate alterations in the horizontal projection angle (0 to 25 degrees) and foot axial rotation (-30 to 30 degrees). The MDTA was measured on each DRR and compared with that quantified on the baseline HAV and AP view.
  
  
  RESULTS
  Altering the horizontal projection angle by ≥5 degrees and >10 degrees significantly altered the MDTA for the AP view and the HAV, respectively. Shifting dorsiflexion and plantarflexion caused minor changes in the MDTA that were only statistically significant for the HAV. Axial rotation significantly changed the MDTA on both views, but deviations were more pronounced for the HAV.
  
  
  CONCLUSIONS
  Compared with the HAV, the MDTA on the AP view was less sensitive to changes in foot-ankle position. However, increasing the tilt of the x-ray beam from the horizon altered the MDTA on the AP view substantially.
  
  
  CONCLUSIONS
  To avoid misinterpretation of the MDTA, we recommend using the AP view to quantify supramalleolar alignment as it is less sensitive to changes in positioning of the foot-ankle. When acquiring an AP film, the x-ray beam should be directed along the horizon to ensure consistent assessment of the MDTA across patients.
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA Harold K. Dunn Orthopaedic Research Laboratory, University of Utah, Salt Lake City, UT, USA.
authors.forename: Alexej
authors.initials: A
authors.lastname: Barg
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA Harold K. Dunn Orthopaedic Research Laboratory, University of Utah, Salt Lake City, UT, USA.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Amendola
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA Harold K. Dunn Orthopaedic Research Laboratory, University of Utah, Salt Lake City, UT, USA.
authors.forename: Heath B
authors.initials: HB
authors.lastname: Henninger
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Kapron
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Saltzman
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT, USA Harold K. Dunn Orthopaedic Research Laboratory, University of Utah, Salt Lake City, UT, USA Department of Bioengineering, University of Utah, Salt Lake City, UT, USA Department of Physical Therapy, University of Utah, Salt Lake City, UT, USA Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT, USA Andrew.Anderson@hsc.utah.edu.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Anderson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D017760:Bone Malalignment / Q000000981:diagnostic imaging*; D002102:Cadaver; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D013977:Tibia / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
keywords: alignment; ankle; digitally reconstructed radiographs; medial distal tibia angle; radiographs