Complications in total knee arthroplasty (TKA), which may include the inaccuracy of the implantation and the poor component design, can cause major failures in the TKA. Therefore, the present investigation studies the onlay knee implants commonly used clinically to find the major causes of the damage to artificial patella by the computer aided analysis of the three-dimensional finite element model of the artificial patello-femoral joint built through reverse engineering. Results showed that although a significant difference is found in the condition and the state of the stress distribution generated as the patello-femoral joint changes with the flexion of the knees, this variation is still within the tolerable range; but the patellar lateral tilt is something that caught our attention. Furthermore, through the comparison between the study and the clinical results, this investigation concludes that the bone cement on the implant interface is the major cause for the breaking of the pegs, and is not related to the original design of the patella. This study also discovers that slight design modification on the parts of commonly used artificial joints may effectively reduce surgical failure rate; therefore, a more robust design configuration for patellar pegs is proposed.