Misconceptions about patellofemoral resurfacing in total knee replacement

Abstract

mation is minimized and more uniform load transmission occurs. Metal backing provides a surface for secure and durable biological fixation. The metal-backed patella consist of a cancellous structured t i tanium porous sintered to a t i tanium base. The metal backing should support the polyethylene circumferentially. The addition of three smooth pegs ensures initial stability without stress shielding and allows for easy, bone-sparing revisions. We feel that application of a bone slurry of autogenous cancellous bone to the cut surface of the bone is an integral step in achieving cementless fixation [3]. We have shown that the bone slurry increases the initial contact of the metal backing to the cut bone surface, recreating a new subchondral plate. Through osteoinduction and osteoconduction, bone slurry application promotes and reliably achieves durable bony ingrowth and ongrowth over the porous coating. A microradiographic analysis of postmortem retrievals of patellas indicated that 84 ± 12% of the porous coating was in direct contact with bone [4]. Backscattered electron image analysis showed the bone ingrowth measured 13 ± 10%, which confirmed that reproducible bone ongrowth and ingrowth can be achieved in clinically functioning porous-coated metal-backed patellar components. Allpolyethylene patellas are standard for the fully cemented knee. A recent 6to 10-year retrospective review of 302 consecutive cementless TKAs, using the modified domeshaped metal-backed patella, indicated a 96% patellar survivorship [5]. There was no lucency or loosening. These results contrast strongly with those of earlier metal-backed designs, and compare favorably with cemented all-polyethylene patellae. Our results are also better than the reported results of unresurfaced patellas. This is accomplished with the dome-shaped patella that articulates with a deep-dished trochlear grooved asymmetrical femoral component. Patellofemoral forces are further minimized by medializing the patellar component such that it matches the patient's anatomic high point, maintaining limb alignment at 6 ° of valgus and optimizing patellar tracking. In summary, improvements in implant design, instrumentation, and surgical technique allow reproducible and excellent results with patellar resurfacing performed with or without cement.