Position of the prosthesis components in total ankle replacement and the effect on motion at the replaced joint
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In some cases of total ankle replacement, perfect alignment of the prosthetic components is not achieved. This study analyses the extent to which component positioning is critical for the final range of motion.
Fourteen patients undergoing total ankle replacement were assessed preoperatively and postoperatively at seven and 13 months follow-up. X-ray pictures of the ankle were taken in static double leg stance, i.e. at neutral joint position, and in maximum plantarflexion and dorsiflexion. Measurements were obtained by a specially devised computer program based on anatomical reference points digitised on the radiograms. These allowed calculation of the position and orientation of the components in the sagittal and coronal planes, together with the joint range of motion.
The mean range of motion was about 34 degrees at the first follow-up and maintained at the second. Tibial and talar components were more anterior than the mid-tibial shaft in 11 and nine patients, respectively. Mean inclination was about four degrees posterior for the tibial component and nearly one degree anterior for the talar component. A significantly larger range of motion was found in ankles both with the talar component located and inclined more anteriorly than the tibial.
Correlation, though weak, was found between motion at the replaced ankle and possible residual subluxation and inclination of the components. However, a satisfactory range of motion was also achieved in those patients where recommended locations for the components could not be reached because of the size of the original joint deformity.
KeywordsTibial Component Prosthetic Component Total Ankle Replacement AOFAS Score Talar Component
The authors thank John J. O’Connor for the invaluable and useful discussions on the manuscript.
Conflict of interest
The Istituto Ortopedico Rizzoli has a licence agreement with the company producing the prosthesis, under which it receives royalties. However, the study was performed on a voluntary basis, and the company was not involved in any of the phases, i.e. planning of the experiment, collection or analyses or interpretation of the data, and writing of the manuscript.