Prosthetic alignment and sizing in computer-assisted total knee arthroplasty

Abstract

We implanted 60 posterior stabilized total knee prostheses (P.F.C. Sigma, DePuy, Warsaw, USA). In 30 cases, we used a CT-free navigation system (Vector Vision, Brain LAB, Heimstetten, Germany), and in 30 matched-paired controls, we used a conventional manual implantation. We compared postoperative long-leg radiographs in the two groups. The results revealed a significant difference in favor of navigation. In addition, we compared the preoperative anteroposterior dimension of the femoral condyle with the postoperative value. While there were no significant differences in the preoperative anteroposterior dimension of the femoral condyle between the two groups, the postoperative value in the navigation group was significantly larger than that of the preoperative value. Therefore, surgeons using navigation systems should guard against the possibility of oversizing when determining the size of the femoral component.Résumé Nous avons implanté 60 prothèses totales postéro-stabilisées du genou (P.F.C. Sigma, DePuy). Dans 30 cas nous avons utilisé un système de navigation sans scanner (Vector vision R, Laboratoire du Cerveau, Heimstetten, Allemagne) et dans 30 contrôles appairés nous avons utilisé une implantation manuelle habituelle. Nous avons comparé les grandes radiographies postopératoires des membres inférieurs dans les deux groupes. Les résultats ont révélé une différence notable en faveur de la navigation. De plus nous avons comparé la dimension antéro-postérieure du condyle fémoral avant l'intervention avec la valeur postopératoire. Tandis qu'il n'y avait pas de différence notable dans la dimension antéro-postérieure préopératoire du condyle fémoral entre les deux groupes, la valeur postopératoire dans le groupe de la navigation était nettement plus grande que la valeur préopératoire. Par conséquent les chirurgiens qui utilisent des systèmes de navigation doivent prendre garde à ne pas implanter un composant fémoral sur-dimensionné.

Computer Navigation Did Not Improve Alignment in a Lower-volume Total Knee Practice

“…A power analysis was conducted to determine the required sample size. Because the reported percentages of satisfactory lower limb mechanical alignment were 70% to 75% in the majority of conventional technique TKA series [1-3, 5-10, 12, 13, 16-24, 28, 29, 31-34] and 90% to 100% in computer navigation TKA series [1,17,22,23,28,29,34], it was assumed there should be an improvement in satisfactory alignment of at least 15% using the computer navigation technique. The sample size estimation was performed using a power of 80%, a level of significance of 5%, an estimate of a significant reduction of 15% of outliers greater than 3°i n mechanical alignment of the lower limb in the computer navigation group when compared with the conventional jig-based group, and an estimate of a standard deviation of 30% in the variation of reported results in the conventional jig-based series.…”

“…We identified 13 clinical series for comparison with the current navigation series (Table 2). Seven studies were prospective, randomized studies [1,7,23,25,28,29,34] and six were retrospective case-control series [2,12,17,[20][21][22]. We compared the characteristics of the patients and the radiographic results of the current case series with those in the literature.…”

“…However, some authors agree this objective may not be practically obtainable in every TKA [15]. Satisfactory position of a TKA prosthesis is commonly accepted to be an alignment within 3°from this ideal [1,6,7,12,17,18,22,23,28,33]. Aseptic loosening of the prosthesis has been reported to be more common in knees implanted in an alignment greater than 3°varus [26].…”

“…If an outlier in the lower limb mechanical alignment is defined as greater than 3°from the neutral position, the majority of the TKA series performed using the conventional jig-based technique reported a satisfactory alignment rate of approximately 70% [1-3, 5-10, 12, 13, 16-24, 28, 29, 31-34]. However, the results of most of the computer navigation TKA series were much more favorable, reporting satisfactory alignment of 90% to 100% [1,17,22,23,28,29,34]. Some surgeons have suggested this improved predictability of postoperative radiographic alignment with computer navigation TKA occurs with experienced and inexperienced surgeons [30].…”

“…Because many studies regarding this subject have been performed in high-volume tertiary referral centers, there is concern whether similarly good results can be obtained by the average orthopaedic surgeon [3]. Despite the fact that radiographic alignment of the implanted prosthesis is superior in computer navigation TKA, outliers greater than 3°are still unavoidable in most of the reported series [1,7,8,12,17,22,23]. The potential reasons leading to these outliers are not discussed in adequate detail in the literature.…”