In vivo kinematics of the salto total ankle prosthesis.
BACKGROUND
Recent technological advancements in total ankle arthroplasty (TAA) have included the introduction of the mobile bearing concept. This bearing has several advantages, but researchers have questioned whether or not increased mobility sacrifices joint stability or durability of the implant. The present study evaluated the kinematics of this type of prosthesis implanted in patients.


METHODS
Fluoroscopy and 3D-to-2D registration techniques were used to determine the in vivo kinematics for 20 TAA subjects performing two activities: gait and step-up. The motion of the prostheses was described in terms of clinical rotations and as rotation about the helical (screw) axis. Then, the anterior-posterior translation and axial rotation of the mobile bearing insert were determined.


RESULTS
Among the clinical rotations, the dorsi-/plantarflexion was the most dominant, revealing the greatest pattern change and the largest magnitude. During gait, the orientation of the prosthetic components changed smoothly from plantarflexion to dorsiflexion. The average range of this motion was 9.2 degrees. For step-up activity, the range was 8.0 degrees. However, between 33% and 66% of stance phase, the talar component's orientation changed from dorsiflexion to plantarflexion. The average absolute range of anterior-posterior translation of the mobile bearing insert was 1.5 mm and 2.3 mm for gait and step-up, respectively.


CONCLUSIONS
These measured translations were relatively small and may suggest that the rotational portion of the motion was more dominant than translational and provided sufficient mobility.
Leszko
Filip
F
Komistek
Richard D
RD
Mahfouz
Mohamed R
MR
Ratron
Yves-Alain
YA
Judet
Thierry
T
Bonnin
Michel
M
Colombier
Jean-Alain
JA
Lin
Sheldon S
SS
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint; D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D005684:Gait / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D016474:Weight-Bearing / Q000502:physiology