We report the results of a longitudinal study of 40 patients with osteoarthritis who had primary prosthetic replacement without patellar resurfacing, and were followed at 6 months postoperatively with a densitometric study and clinically at a minimum follow-up of 2 years. Densitometric analysis showed a mean preoperative density at the affected knee of 0.69 g/cm(2) (CI: 0.62-0.76), compared to 0.86 g/cm(2) (CI: 0.79-0.93) for the opposite knee (p = 0.002). In our study population, the return to load and motion to the retained patella led to a significant increase in patellar bone density as measured by densitometry studies. This observation correlated with significant improvement in knee functional score.