Analysis of joint laxity after total ankle arthroplasty: cadaver study.
BACKGROUND
Clinical results of total ankle arthroplasty with early designs were disappointing. Recently-developed ankle prostheses have good mid-term results; however, limited information is available regarding effects of total ankle arthroplasty on ankle laxity.


METHODS
Eight cadaveric lower extremities were tested with a custom device which enabled measurement of multi-axial forces, moments, and displacement during applied axial, shear, and rotational loading. Tests consisted of anterior-posterior and medial-lateral translation and internal-external rotation of the talus relative to the tibia during axial loads on the tibia simulating body weight (700 N) and an unloaded condition (5 N). Tests were performed in neutral, dorsiflexion, and plantarflexion. Laxity was determined for the intact ankle, and following insertion of an unconstrained total ankle implant, comparing load-displacement curve.


RESULTS
Laxity after total ankle arthroplasty did not approximate the normal ankle in most conditions tested. Displacement was significantly greater for total ankle arthroplasty in both posterior and lateral translation, and internal rotation, with 5 N axial loading, and anterior-posterior, medial-lateral translation, and internal-external rotation for 700 N axial loading. For the 700 N axial load condition, in the neutral ankle position, total anterior-posterior translation averaged 0.4 mm (SD 0.2 mm), but 6.0 mm (SD 1.5 mm) after total ankle arthroplasty (P<0.01). This study demonstrated more laxity in the replaced ankle than normal ankle for both unloaded and 700 N axially loaded conditions.


CONCLUSIONS
These data indicate the increased responsibility of the ligaments for ankle laxity after total ankle arthroplasty and suggest the importance of meticulous ligament reconstruction with total ankle arthroplasty operations.
Watanabe
Kota
K
Mayo Clinic College of Medicine, Biomechanics Laboratory, Division of Orthopedic Research, 200 First Street SW, Rochester, MN 55905, USA.
Crevoisier
Xavier M
XM
Kitaoka
Harold B
HB
Zhao
Kristin D
KD
Berglund
Lawrence J
LJ
Kaufman
Kenton R
KR
An
Kai-Nan
KN
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000843:Ankle Joint / Q000601:surgery*; D002102:Cadaver; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000503:physiopathology*; D007595:Joint Prosthesis / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009068:Movement; D016059:Range of Motion, Articular; D019415:Torque; D016896:Treatment Outcome