The authors argue that PCL retention better preserves the normal kinematics of the knee with maintenance of femoral rollback, clearance of the femur for increased range of motion and quadriceps strength, increased stair-climbing ability, fewer patellar complications, and reducing anteroposterior shear forces thus reducing bone-prosthesis interface shear stress.36-41
Balancing of the flexion and extension gaps is criticially dependent upon the preoperative state of the posterior cruciate ligament. If the PCL is contracted in valgus knees or knees with fixed flexion deformities, flexion-extension balancing is difficult, and the PCL should be sacrificed. The PCL is often inadequate or absent in cases of inflammatory arthritis, as well as in some cases of advanced degenerative arthritis. When the PCL is sacrificed or incompetent, stability of the knee depends upon PCL substitution.42-44 In traditional PCLsubstituting TKA systems, a central polyethylene post of the posterior middle portion of the tibial insert articulates with a transverse cam on the femoral component. As the knee flexes to 75 degrees, the post and cam come into contact, preventing the tibia from subluxating posteriorly and maintaining femoral rollback. Although this design has proven useful, it is not without problems and complications including post failure and dislocation. In order to improve results with posterior stabilization, a more congruent (ultracongruent) tibial polyethylene insert was designed45 (Fig. 7.4). The insert is designed with an anterior buildup of 12.5 mm, and a more congruent articular surface to stabilize the femur in the anteroposterior plane, and has proven clinically successful for over 5 years.45
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