Purpose: This comparative study of femoropatellar function in four types of total knee arthroplasty (TKA) was conducted to demonstrate the relation between the form of the femoropatellar articulation and the function outcome achieved with these prostheses.

Material and methods: Forty patients who had undergone first-intention TKA for primary degenerative joint disease were selected at random. Minimum follow-up was one year. The functional IKDC score was greater than 85/100. All TKA had been inserted without preservation of the posterior cruciate ligament. Four types of prostheses were used:

- posterior stabilised prosthesis with a fixed plateau, toric trochlea, cemented dome patella (n=10);

The following parameters were studied prospectively:

- pain assessed on a visual analogue scale;

Results: The kinematic data demonstrated a significant difference between:

- TKAs with a dome patella and those with an anatomic patella;

This difference basically involved the patellar tilt, lateral subluxation of the patella, and especially, the patellar trajectory between 20° and 90°, the toric trochlae with a dome patella having a more anterior trajectory than the normal knee.

The clinical and functional study showed that:

- the percentage of totally pain-free femoropatellar articulations was higher for the hollow anatomic trochlae (96%) than for the three other types (75%) (p = 0.04);

Discussion and conclusion: This study confirms the theoretic work reported by Walker and the clinical work reported by Andriacchi on the anterior curvature of the trochlae and the kinematic work reported by Stichl on the advantage of anatomic trochlae. These findings point out the advantage of the hollow anatomic trochlae where the patella is applied on the trochlear groove situated at the same depth as the normal trochlae, which is not the case with most TKAs. This advantage is seen by the absence of pain and by the propulsion when climbing stairs.