Abstract
Introduction
Opponents of patellar resurfacing during Total Knee Arthroplasty (TKA) note unique complications associated with resurfacing. Problems include over-stuffing (the creation of a composite patellar-prosthesis thickness greater than the native patella) that may contribute to reduced range of motion; and creation of a patellar remnant that is too thin (in order to avoid over-stuffing) that may contribute to post-operative fracture. Factors including surgical technique, prosthesis design and patient anatomy may contribute to these problems. This study was performed to define the native patellar anatomy, and to compare the effect of differences in component thickness between manufacturers.
Methods
This retrospective, IRB approved study reviewed 803 knees that underwent primary TKA between 2005 and 2011 with a single surgeon. Patellar resurfacing was performed with a round, polyethylene component from one of two different implant designs using the same surgical technique. Data recorded for each patient included: gender; patellar thickness before and after resurfacing; the dimensions and manufacturer of the prosthesis. The residual patellar bone thickness after resection was calculated.
Results
Mean (SD) native patellar thickness was 25.24mm (2.11) in males, versus 22.13mm (1.89) in females (P = <0.001). 47/313 (15%) of males had increases in the composite patellar thickness after resurfacing, versus 120/480 (25%) of females (P < 0.001). 123/480 (26%) of females had a residual patella thickness <= 13mm, versus 12/313 (4%) of males (P <0.001). Finally, 79/265 (30%) of patients with a patellar prosthesis from manufacturer B had increases in the composite thickness, versus 88/522 (17%) of patients with manufacturer A (P < 0.001).
Conclusions
Both patient gender (due to smaller native patellae in females) and prosthesis design (thicker components from manufacturer B) are risk factors for over-stuffing of the patella or over-resection of the patella. These findings suggest that patellar component design can be improved for female patients.
