Review Question - QID 1151

Figure A demonstrates a non-linked, constrained total knee arthroplasty prosthesis. This drawing depicts the degree of coronal plane and rotational constraint provided by the tall, wide tibial spine in the deep femoral box. This design constrains varus-valgus (allows 2°-3°) and internal-external rotation (allows 2°). A linked, rotating-hinge prosthesis (Illustration A) constrains anterior-posterior translation in addition to varus-valgus and internal-external rotation.

The article by Scuderi reports that in revision TKA, the goal is to restore the original anatomy, restore function, and provide a stable joint. To this point of stability, it is preferable to implant the prosthesis that provides adequate stability with the least mechanical constraint possible to avoid bone-implant stresses that may cause early loosening. Therefore, it is preferable to use a posterior-stabilized (cruciate substituting) articulation (Illustration B) if the knee remains stable without constrained components.

McAuley et al suggest that more predictable results are obtained with the use of cruciate-substituting components. However, if there is functional loss of the medial collateral ligament or lateral collateral ligament, inability to balance the flexion and extension spaces, or a severe valgus deformity, then a constrained condylar prosthesis is needed.

Rodriguez et al reports Level 4 evidence of 44 patients revised with varus-valgus constrained implants followed for an average of 5.5 years. There was a theoretical concern that the increased constraint of the prosthesis would lead to component loosening, however their series had only one femoral component and no tibial components that loosened.