Kinematics of the three components of a total ankle replacement: in vivo fluoroscopic analysis.
BACKGROUND
Careful kinematic analysis of ankle joints with newly developed prostheses should be carried out to assess the actual performance in vivo. This study analyzed the pattern of motion of the three components of a ligament-compatible ankle replacement, developed to replicate normal joint kinematics.


METHODS
Twelve patients treated with this design were analyzed at 6, 12, and 24 months followup. A series of images were acquired by videofluoroscopy at extremes of the range of motion, and during flexion/extension against gravity and stair-climbing/descending. Three-dimensional positions and orientations of the tibial and talar metal components and of the polyethylene mobile-bearing were obtained from the images by a standard shape-matching procedure. Motion between the three components was calculated and descriptively analyzed.


RESULTS
Large tibiotalar joint mobility of the replaced ankle was observed in all three anatomical planes, particularly in the sagittal. In flexion/extension against gravity, the mean range of flexion was 17.6, 17.7, and 16.2 degrees, respectively, over the three followups. The inclination angle of the mean axis of joint rotation was 3.7 degrees down and lateral in the frontal plane and 4.7 degrees posterior and lateral in the transverse plane, similar to those in the normal ankle. The corresponding antero-posterior translation of the meniscal-bearing with respect to the tibia was 3.3, 3.3, and 3.2 mm, with statistically significant correlation with joint flexion.


CONCLUSIONS
Physiological motion can be achieved in ligament-compatible ankle joint replacements. The considerable antero-posterior bearing-to-tibial motion and its coupling with flexion support the main original claims of this design.
Istituto Ortopedico Rizzoli, Movement Analysis Laboratory, Via di Barbiano, Bologna, Italy. francesco.cenni@ior.it
Francesco
F
Cenni
Alberto
A
Leardini
Claudio
C
Belvedere
Francesca
F
Bugané
Karin
K
Cremonini
Maria T
MT
Miscione
Sandro
S
Giannini
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint / Q000502:physiology*; D058737:Arthroplasty, Replacement, Ankle; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D005471:Fluoroscopy; D005500:Follow-Up Studies; D006801:Humans; D021621:Imaging, Three-Dimensional; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology