Purpose of the study: Conventional techniques for implantation of a TKA allow a neutral mechanical axis (HKA 180±3) in 70 to 86% of patients. The purpose of this work was to evaluate the contribution of intraoperative radiologic assistance for this objective.

Material and methods: We conducted a prospective randomised study in a single-operator consecutive series of cemented TKA, model TC-SB, excluding revisions and frontal deviations > 25. The series included 65 women and 39 men, mean age 73 years. All operations were performed on a radiolucent table. An extramedullary guide was used for the tibial cut and an intramedullary guide for the femoral cup. Patient randomisation was done after the cuts. According to the randomisation, the orientation of the cuts in the frontal plane was measured radiographically using a fluoroscope and an aiming plate situated on the hip, then the ankle. Secondary cuts were made if the angular deviation was greater than 1°. The position of the TKA assisted by the fluoroscope (group R+, n=52) and that of the non-assisted TKA (group R-, n=52) was assessed on the digitalised goniometry.

Results: Mean operative time was 70 minutes in group R+ and 59 minutes in group R-. In group R+, the mean mechanical alignment was 3.9 varus preoperatively and 0.13 valgus postoperatively (5 valgus to 3 varus) with 91% in the ±3 range. In group R-, the mean mechanical alignment was 6.7 varus preoperatively and 0.06 varus postoperatively (6 varus to 5 valgus) with 80% of the cases in the ±3 range. The standard deviation was 2 in group R+ and 2.7 in group R-, with no significant difference.

Discussion: The accuracy of the implantation obtained with the conventional instrumentation for the TC-SB prosthesis is among the best reported in the literature. Intraoperative radiological assistance enabled a tighter spread of the results around the mechanical alignment. The technique was simple to use and precise. The mean duration of exposure to the fluoroscope was 3 s (PDS 3 – 35 gray cm²).

Conclusion: We reserve this assistance in priority for patients with major bone deformities or medullary obstacles.