[Reproducibility of whole lower limb X-rays made in supine position after total knee replacement: comparison with reproducibility of whole lower limb X-rays of normal knees].

Purpose Of The Study: Outcomes after total knee replacement are correlated with the postoperative HKA angle. Therefore, it seems crucial to determine the precision of the whole lower limb X-rays which are currently used to determine the frontal knee alignment. The aim of the study was to analyze the precision of the whole lower limb X-Rays made in supine position, after total knee replacement.

Material And Method: A prospective study included 100 knees which were analyzed with two whole lower limb X-rays made at eight days interval. Seventy knees were non-replaced and 30 had total replacement with a posterior stabilized knee prosthesis. The X-rays were made in supine position and neutral rotation using the patella as a reference mark. One independent observer compared the HKA angle on the two consecutive X-Rays in order to evaluate the reproducibility of the X-Rays.

Results: In the group of patients with total knee replacement, the reproducibility was poor with a low correlation coefficient (0.5) and a poor precision of 5 degrees . On the contrary, in the non-replaced knee group, the reproducibility was very good with a high correlation factor between the two X-rays (0.99, p<0.0001) and a very good precision of 1.7 degrees (p<0.05). The group of patients with an HKA angle of less than 8 degrees had a significantly better precision (1.5 degrees ) than the group of patients with an angle HKA above 8 degrees (3 degrees , p<0.04).

Conclusion: Reproducibility and precision of whole lower limb X-rays made in supine position is poor in patients with total knee replacement. Thus, we should be very careful for the analysis of the influence of the mechanical axis on the outcomes after total knee replacement.