title: Kinematic analysis of the agility total ankle during gait.
abstract: BACKGROUND
  With the increasing use of total ankle prostheses, kinematic analysis of these implants is important to our understanding of their specific biomechanics. Fluoroscopic analysis as used in this study has distinct advantages over previous experimental approaches and allows kinematic determination in vivo of dynamic weightbearing motions.
  
  
  METHODS
  Ten patients with unilateral Agility (Depuy, A Johnson & Johnson Company, Warsaw, IN) total ankle replacements were tested using video fluoroscopy in weightbearing dynamic gait conditions. Their prosthetic ankle and normal ankle kinematics were then analyzed by computer with two-dimensional and three-dimensional model-fitting techniques.
  
  
  RESULTS
  All of the total ankle prostheses in this study demonstrated less than 3.5 mm of posterior-to-anterior translation from heel strike to toe-off. In comparison, more variability was seen in posterior-to-anterior motion of the normal contralateral ankles, with three ankles translating more than 6 mm. When inversion and eversion and internal and external rotation of the ankle were measured, wide variations were seen among patients.
  
  
  CONCLUSIONS
  While the relative incongruence theoretically decreases the shear stresses transmitted to the bone-prosthesis interface, it does allow more inversion-eversion and rotational freedom that can lead to edge loading and higher contact stresses. Despite good medium-term results having been published for this prosthesis, polyethylene wear and osteolysis have been observed. Further studies looking at the effect of the inversion and eversion and rotational freedom on polyethylene wear and prosthesis survival will assist in our understanding of the factors leading to successful outcome of total ankle prostheses.
authors.affiliation: Allegeheny General Hospital, Federal North, 1307 Federal Street, 2nd Floor, Pittsburgh, PA 15212, USA. sconti@wpahs.org
authors.forename: Stephen
authors.initials: S
authors.lastname: Conti
authors.forename: Karl-Andre
authors.initials: KA
authors.lastname: Lalonde
authors.forename: Robroy
authors.initials: R
authors.lastname: Martin
mesh_terms: D000368:Aged; D000843:Ankle Joint / Q000502:physiology* / Q000601:surgery*; D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena; D005471:Fluoroscopy; D005684:Gait; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007595:Joint Prosthesis / Q000009:adverse effects; D008875:Middle Aged; D010014:Osteolysis / Q000209:etiology; D020959:Polyethylene; D012399:Rotation; D014741:Video Recording; D016474:Weight-Bearing
chemical_list: D020959:Polyethylene