## 3 Results
### LCS  
In 1990, [PERSON] and [PERSON] presented a second-generation bircuicate-retaining meniscal-bearing TKA as part of a comprehensive, interchangeable knee prosthesis system New Jersey Low-Contact-Stress (LCS, DePuy Synthes, Warsaw, IN, USA), with both cemented and cementless options [13]. The bircuicate-retaining tibial component had a \"U\"-shaped metallic baseplate and separate medial and lateral polyethylene meniscal bearings with articulating surfaces curved to match the femoral geometry. The authors reported on the survival of 21 cemented and 25 cementless BCR-TKAs. In the cemented group, 12-year overall survival was 90.9%, and in the cementless group 6-year overall survival  
Figure 1: Systematic literature review flowchart. was 100%. [PERSON] et al. presented 4743 TKAs that were performed between 1981 and 1997 using the LCS system with BCR (n = 324), CR (n = 2165) and PS (n = 2254) implants, and with a 14-year follow-up found the survivorship for BCR implants to be 79% (95% CI 72; 86); CR implants 82% (95% CI 78; 88); and PS knees 87% (95%CI 81; 94), respectively [14]. The overall 14-year survivorship for cementless fixation was 83% and for cemented fixation 84%. The aseptic loosening rate was the highest for the BCR system (6.1%). Conversely, in a retrospective analysis with a minimum follow-up of 15 years, a higher revision rate was found for an anterior-posterior glide CR-TKA (n = 916) compared to a BCR design (n = 180) with a hazard risk for BCR vs. PCR of 0.52 (0.34-0.80), \(p\) = 0.003 (adjusted model) [15]. Again, cemented fixation was preferred, as the 20-year cumulative revision incidence was higher at 2.9% (95% CI 1.7; 4.7) for cemented and 10.9% (95% CI 8.8; 13.4) for uncemented TKA. Table 1 provides a short overview of the clinical outcome studies for LCS BCR-TKA. In our systematic search, the Vanguard XP (Vanguard XP Total Knee System, Zimmer Biomet, Warsaw, IN, United States) showed to be the BCR-TKA system with the most clinical data available. The design includes asymmetric condyles with a larger lateral condyle than medial to allow greater roll back laterally. The tibial tray consists of a U-shaped cobalt-chromium-molybdenum tray with two pegs and two keels and an asymmetrical PE bearing aimed at the difference in kinematics between the two compartments. Several authors reported promising short-term clinical outcome after performing BCR-TKA with this implant. [PERSON] et al. found a high satisfaction rate of 94% in 146 BCR-TKAs, with an improvement in mean flexion (116\({}^{\circ}\) preoperative to 121\({}^{\circ}\) postoperative) and two revisions (1.4%) after a mean of one year follow-up [16]. Several other small case series in 20-50 patients found significant improvement in PROMs after BCR-TKA [17; 18]. Of these studies, [PERSON] et al. showed that PROMs were lower for those patients with a greater posterior tibial slope [18]. However, these level IV studies may be susceptible to reporting bias, as failure rates were not reported. Finally, one retrospective report on 107 patients with a mean follow-up of 3 years demonstrated an 88% (95% CI 82; 93) survival. Revisions were performed mainly for tibial loosening (5/19), ACL impingement (3/19) and pain (4/19) [19]. Comparative Studies of the Vanguard XP  
A variety of clinical studies compared the Vanguard XP to other designs. [PERSON] et al. found that a non-anatomical design BCR-TKA (Vanguard XP) had inferior short-term survivorship and radiolucent lines (RLLs) on X-rays when compared to a conventional CR implant [20]. Indeed, in their study including 78 BCR and 294 CR implants with a mean follow-up of 18 months (range, 2-32 months), knees in the BCR group had a higher frequency of all-cause revision (5% vs. 1.3%; hazard ratio (HR), 7.44; 95% CI 1.24; 44.80) and a greater proportion of RLLs of the tibial component (HR 2.93; 95% CI 1.62; 5.32; \(p\) < 0.001). The authors concluded that these results may be explained by learning curves or truly inferior outcomes resulting from the BCR design.