Numerous posterior stabilized knee systems are available for primary and revision total knee arthroplasty. Design of these systems requires an understanding of the articulating geometries and kinematic/kinetic biomechanical considerations of the normal knee. The findings for the normal knee are integrated into the design of a prosthetic system.
The natural femoral, tibial and patella articulating geometries are defined to enable subsequent kinematic and kinetic analyses. The articulating geometries are characterized from review of anthropometric studies of the tibiofemoral and patellofemoral joint.
The kinematic analysis of the natural knee defines knee motion in terms of rotation, adduction/abduction, range of motion and femoral rollback. Typical activities for total knee recipients are characterized under these headings. Instant center theory is also applied to the natural knee as it facilitates linking natural knee motion and prosthetic motion analysis. Natural knee kinetics for the gait cycle is characterized. The maximum gait cycle compressive and shear loads and knee motions attained from clinical studies using force plate, cinematography and computer optimization techniques are reviewed. The resultant loads and motions obtained from the studies form a benchmark used to establish laboratory testing parameters.
The kinematic and kinetic analysis for generic posterior stabilized design is studied. Interaction of the femoral cam, tibial spine, femoral condyles and tibia plateau geometry are reviewed for a proposed and existing posterior stabilized geometry. Additional posterior stabilized design issues including: subluxation resistance, range of motion, bone conservation for the femoral housing resection, internal/external femoral rotation, tibial polyethylene insert modularity with the tibial tray and tibial polyethylene insert conformity with the femoral condyles are reviewed. A survey of designs on the market indicates a wide range of results for bone conservation for the femoral housing resection, internal/external rotation, and degree of conformity
