INFLUENCE OF INITIAL BONY DEFORMITY ON RADIOLOGICAL OUTCOME IN TOTAL KNEE ARTHROPLASTY WITH PRESERVATION OF THE POSTERIOR CRUCIATE LIGAMENT

Abstract

Purpose: A pre- and postoperative radiographic analysis of 50 total knee arthroplasties (TKA) was performed to determine the femorotibial correction angle and the tibial and femoral mechanical angles obtained as a function of the initial bony deformity. The preoperative angle beyond which correction was not achieved was determined.

Material and methods: This prospective single-centre study included 50 TKA (25 men and 25 women), mean age 69.1 years (range 53–83). Degenerative disease involved the right knee in 21 cases and the left knee in 29. A Wallaby I TKA (semi-restrained with preservation of the posterior cruciate ligament) was implanted in all cases. Three angles were calculated on the AP loaded knee: AFT (femorotibial angle), AFM (femoral mechanical angle), ATM (tibial mechanical angle). For each angle, statistic analysis was performed on four groups of patients: group I: overall population, group II: patients with normal axis (178°< AFT< 182°; 88°< AFM< 92°; 88)< ATM< 92°), group III: patients with varus (AFT> 182°; AFM> 92°; ATM> 92°), and group IV: patients with valus (AFT< 178°; AFM< 88°; ATM< 88°). Non-parametric tests (Spearman rank test and MacNemar symmetry test) were performed on SAS software for statistical analysis with p< 0.05 considered as significant.

Results: Pre- and postoperative AFT showed: significant improvement of the mean (> 3.44° in group I, > 6.87° in group III, and > 6.12° in group IV). There was no significant difference in group II. Pre- and postoperative AFM showed: constant but non-significant improvement in groups I and III (> 3°) and constant and significant improvement in groups III and IV (> 2.5°). Pre- and postoperative ATM showed: significant improvement in groups I and III (> 3°), constant but non-significant improvement in group IV (n=4). There was no group II. An ATM > 94° was the threshold angle beyond which correction was not obtained.

Discussion: Taken together, the results of this study confirm the reliability of the Wallaby I instrumentation for achieving a correct postoperative mechanical axis. These results are comparable with data in the literature (with or without preservation of the posterior cruciate ligament). However, the correction of the bony deformity obtained depended uniquely on the initial deformity of the tibia. Extreme deformity of the tibia should be corrected with osteotomy or with a more restrained prosthesis.