Design and biomechanical investigation of a patient-specific total talar prosthesis for total talar replacement: A finite element analysis.

BACKGROUND

Total talar replacement (TTR) is an emerging treatment for end-stage talar diseases, although concerns persist regarding ankle stability due to essential ligament transection. Further investigation is necessary regarding the biomechanical impact of patient-specific total talar prosthesis (TTP) on ankle stability and bone-implant mechanics.

OBJECTIVE

The purpose of this study is designing a patient-specific TTP and assess its biomechanical performance on ankle stability and stress distribution under various loading conditions using finite element analysis.

METHODS

A CT scan is used to create a 3D finite element model of the foot and ankle complex. The TTP made of A dual-material (UHMWPE talar body and titanium alloy cage) was created and fixed with five screws. Four loading conditions were simulated: inversion, eversion, dorsiflexion, and plantarflexion, with forces of 10 N, 50 N, 100 N, and 150 N. Talar tilt angles and von Mises stresses were examined for intact and implanted models.

RESULTS

In comparison to the intact ankle, TTR significantly decreased the talar tilt angles in inversion (12.5%-16%), eversion (6.6%-14%), and dorsiflexion (33%-47%). On the other hand, plantarflexion produced a larger tilt (34%-44%). While bone stresses stayed below 5 MPa, maximum implant stresses ranged from 20 to 80 MPa. The validation of the model against cadaveric studies was reliable.

CONCLUSION

The patient-specific TTP with screw fixation improves ankle stability in most loading directions, potentially compensating for ligament insufficiency. However, greater plantarflexion instability necessitates post-operative measures. These findings provide biomechanical evidence that fixation-enhanced TTP designs can improve therapeutic outcomes.