ista 2007 program at a glance

B14-1
A NEW DESIGN OF ANKLE PROSTHESIS TARGETING LIGAMENT ISOMETRY: INTRA-
AND POST-OPERATIVE VALIDATION MEASUREMENTS
Leardini Alberto, Catani Fabio, Romagnoli Matteo, Bianchi Loris, Miscione Maria Teresa, Giannini Sandro
Corresponding Author: Alberto Leardini
Istituti Ortopedici Rizzoli, Movement Analysis Lab, Bologna , 40136, Italy
Ph: ++39 051 6366522
Fax: ++39 051 6366561
Email: leardini@ior.it
Total ankle (TAA) is still not as satisfactory as total hip and total knee arthroplasty. For TAA to be considered a
valuable alternative to ankle arthrodesis, an effective range of mobility must be recovered. The disappointing clinical
results of the current generation of TAA are mostly related to poor understanding of the anatomical structures
guiding joint mobility. A new design has been developed by these authors, potentially able to restore physiologic
ankle mobility and a natural relationship between the implanted components and the retained ligaments.
According to extensive prior research, the new design features a spherical convex tibial component, a talar component
with radius of curvature in the sagittal plane longer than that of the natural talus, and a meniscal component
fully conforming to these two. In the sagittal plane, the shapes of the tibial and talar components are compatible
with a four-bar linkage model formed by the calcaneofibular and tibiocalcaneal ligaments. After computer-based
modelling and preliminary observations in trial implantation on anatomical preparations, 75 patients were implanted
in the period July 2003 – May 2007, with mean age 62 years (range 37 – 80), mean follow-up 18 months
(range 1 – 46). For the meniscal bearing to slide smoothly on both the components, a special operative technique
was designed together with relevant instrumentation in order for the three components to be implanted in an exact
position also with respect to the retained ligaments. This was achieved by ensuring that a constant gap is maintained
between the tibial and the talar components throughout the flexion arc. The AOFAS score system was used
to assess patient outcome at 3, 6, 12, 24, 36 month follow-ups.
Intra-operatively, the components seated properly onto the prepared osteotomies. Over the entire motion arc, the
prosthesis maintained complete congruence at the two articulating surfaces of the meniscal bearing which moved
considerably antero-posteriorly. Range of dorsi- and plantar-flexion improved from respectively 0.4 and 15.3 preop
to 10.1 and 24.2 post-op, maintained at the follow-ups. Radiographs at maximal dorsiflexion and maximal plantar
flexion and fluoroscanning confirmed the meniscal bearing moves anteriorly during dorsiflexion and posteriorly
during plantarflexion, over a distance of 2 to 11 mm. Frontal and lateral radiographs of all patients at all follow-ups
showed good alignment of the components, and no signs of radiolucency or loosening. The mean AOFAS score
was observed to go from 40.6 pre-op to 78.5 at last follow-up.
Because the meniscal bearing moved in the direction and approximately for the distance predicted by computerbased
models, physiological roles of the ligaments must have been restored, i.e. controlling joint mobility by isometric
fibre rotations and assuring joint stability by appropriate load resistance. As full conformity of the three
prosthesis components was observed over the entire motion arc, it is encouraged also the prospect of minimizing
wear of these components. Slight misplacement of the bone-anchored components did not affect considerably these
observations. The satisfactory though preliminary observations both intra- and post- operatively from this novel
TAA encourage continuation of the implantation.
212