The effect of alignment of the implant on fractures of the patella after condylar total knee arthroplasty.

The results in thirty-six knees that had a fracture of the patella after a total condylar arthroplasty were reviewed, and were analyzed according to the type of fracture and the alignment of the implant and the limb. Most of the fractures occurred two years or less after the initial operation. Fourteen knees were rated fair or poor and twenty-two, good or excellent. None of the thirty-six implants had been aligned in the neutral range. In sixteen knees, the alignment had a minor variation from the neutral range--that is, the knees were in minor malalignment. In general, these knees had the least severe fractures and the best over-all results. All had a good or excellent result except one, which was revised because of a loose patellar component. That knee was rated as fair at the latest follow-up. There was a major discrepancy in the alignment of twenty implants. These knees had more severe fractures and less satisfactory results than those in the other group. In two of these knees, the fracture was treated non-operatively; one had a good and the other, a poor result. Twelve of the remaining knees, which were treated surgically, were rated as fair or worse. Two knees that had revision of three components and restoration of alignment to the neutral range had an excellent result. The results of this study indicate that the alignment and fit of a component are important in determining the severity of a fracture of the patella after condylar total knee replacement and the long-term results after treatment of the fracture.