• Daniel N Bracey, Matthew L Brown, Hoyt R Beard, Sandeep Mannava, Omar F Nazir, Thorsten M Seyler, and Jason E Lang.
• Department of Orthopaedic Surgery, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC, 27157, USA.
• Int Orthop. 2015 Sep 1; 39 (9): 1715-22.

PurposeThe purpose of this study was to test the hypothesis that overstuffing the patellofemoral joint during total knee arthroplasty (TKA) would decrease passive knee flexion and alter patellar kinematics during knee flexion.MethodsTen cadaveric knees were implanted with cruciate-retaining TKAs, and the patellofemoral joint was overstuffed in 2-mm increments with custom-augmented patellar prostheses (+2 mm through +8 mm). Changes to knee flexion, patellar shift, tilt and rotation were measured with an imageless optical-tracking computer navigation system.ResultsKnee flexion decreased an average 1.2° with each additional 2 mm of patellar thickness. Compared with control TKA (+0 mm), no significant decrease in knee flexion was detected until the patellofemoral joint was overstuffed with the +8-mm patellar prosthesis. Kinematic tracking data showed significantly greater lateral shift of patella with the +6- and +8-mm prostheses and significantly greater lateral tilt with the +8-mm prosthesis. Overstuffing had no appreciable effect on patellar rotation.ConclusionsPassive knee flexion after TKA is significantly reduced when overstuffing the patellofemoral joint by +8 mm, and patellofemoral kinematics are altered when overstuffing the joint by +6 mm. These results demonstrate the relatively modest effects of patellofemoral overstuffing on knee flexion and patellar tracking kinematics after TKA.

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