Computational modelling of mobile bearing TKA anterior–posterior dislocation

Abstract

Anterior–posterior stability in an unconstrained mobile-bearing total knee arthroplasty (TKA) and one with rotational constraints is compared in a computational model based on an ASTM test. Both TKA designs dislocate at loads greater than reported maximum in vivo forces. The posterior drawer forces (mean: 3027 N vs. 1817 N) needed to induce subluxation increase with a greater anterior jump distance (12 mm vs. 7 mm; refers to the vertical height of the anterior or posterior border of the tibial insert's articulating surface). The posterior jump distance for both tested TKA differed by 1.5 mm and had minimal effect on the magnitude of the anterior drawer forces at dislocation in mid-flexion (unconstrained vs. constrained: 445 N vs. 412 N). The unconstrained insert dislocated by means of spin-out whereas in the constrained TKA the femur dislocated from the bearing during posterior drawer and the bearing from the baseplate during anterior drawer. MCL function is an important consideration during ligament balancing since a ± 10% variation in MCL tension affects dislocation forces by ± 20%. The simulation platform provided the means to investigate TKA designs in terms of anterior–posterior stability as a function of knee flexion, collateral ligament function and mechanical morphology.

Keywords:

• total knee arthroplasty
• mobile bearing
• anterior–posterior stability
• computational model

Acknowledgement

All analyses have been done by the lead author and validation and interpretation done by all authors.

Conflict of interest disclosure statement

No potential conflict of interest was reported by the authors.

Notes

^1. Email: [email protected]

^2. Email: [email protected]

^3. Email: [email protected]

^4. Grand challenge competition to predict in vivo knee loads. https://simtk.org/home/kneeloads, accessed on 08/10/2014.

Additional information

Funding

The authors thank Tornier Inc. for their financial contribution to this study. This study is funded by the manufacturer of the constrained mobile-bearing TKA.