EFFECTS OF PATELLAR THICKNESS ON COMPRESSION AND SHEAR FORCES IN TOTAL KNEE ARTHROPLASTY

Ten unembalmed cadaveric knees were dissected to the capsule preservin g the ligamentous and tendinous structures, A posterior cruciate ligam ent sparing total condylar knee arthroplasty was implanted routinely, A force transducer that measured compression force and shear was impla nted into each patella, For each knee, 3 thicknesses of the patellar c omposite (osteotomized patella, transducer, polyethylene component) we re evaluated: (1) precut patellar thickness, (2) precut plus 2 mm, and (3) precut plus 4 mm, The knees were tested in an Oxford Knee Testing Rig, which allowed dynamic testing with 6 degrees of freedom. Values of patellar forces were obtained throughout a range of motion of 0 to 95 degrees flexion, At higher flexion angles (45 degrees and above), t he total patellofemoral shear forces for the precut plus 2 mm and the precut plus 4 mm composites were altered significantly from the precut thickness, Increasing the patellar thickness results in a significant increase in shear forces, potentially leading to early loosening of t he component or increased wear or both, Therefore, bone conserving res ections that increase the patellar composite thickness above the precu t thickness should be avoided.