Second-generation bi-cruciate stabilized total knee system has a lower reoperation and revision rate than its predecessor

The study hypothesis was confirmed. JOURNEY™ II has a lower risk of reoperation and a lower risk of revision compared to JOURNEY™ (I). The risk of revision was found to be 4.2 times higher and the risk of reoperation was 3.5 times higher for JOURNEY™ I than JOURNEY™ (II). Overall, the cumulative revision risk in JOURNEY™ II was 1.89 per 100 TKAs at 4 years, which compares favorably with standard total knee systems.

This is the first study with long-term follow-up that compares the clinical performance of both the older and newer versions of the JOURNEY™ BCS TKS, taking into consideration the risks of reoperation and revision. While the high revision rate of JOURNEY™ I raised concerns, it appears that the device modification applied in JOURNEY™ II was successful in reducing excessive revision risk.

The goal of TKA has historically been restoration of neutral mechanical alignment. Complicating this goal is that patients presenting with osteoarthritis often have either varus or valgus deformity. Significant deformities are more difficult to correct to neutral mechanical alignment if conventional instrumentation is used [37, 38]. Depending on the degree of deformity, the surgical technique, and the choice of implant, the amount of necessary constraint might differ [38, 39]. Thienpont et al. conducted bone morphotype analysis on 96 patients with varus or valgus alignment who underwent TKA. Bone morphotype analysis provides better understanding of the deformity level, allows the surgeon to estimate how much deformity correction can be obtained, helps the surgeon decide if intra-articular correction is possible, and helps with planning of ligamentous release and the amount of constraint to choose. Fifty patients had one osteoarthritic and one non-arthritic knee, and both knees had the same type of varus or valgus alignment. The controls were 46 patients with only ligamentous problems, and both knees had neutral alignment. The authors found that bone morphology in varus and valgus deformity is different before and after OA, and that perpendicular cuts to mechanical axes do not necessarily lead to a neutral mechanical axis. Deformities over 10° usually had an extra-articular component, thus correction to neutral alignment with conventional instruments might not be sufficient to compensate for femoral bowing or extra-articular deformity [38]. The JOURNEY™ II BCS provides more mobility in the lateral compartment than other total knee systems provide, to replicate normal knee kinematics. For patients who presented with significant varus or valgus deformities (> 15°), morbid obesity, or deficient collateral ligaments, the surgeon decided if additional implant constraint was appropriate. The flexion space was assessed under full ligament tension (e.g., laminar spreaders) with the patella reduced, and a constrained implant option was kept on hand [36].

Minoda et al. investigated how the design of the post-cam mechanism affects the risk of impingement of the patellar component on the tibial post (patella post impingement, PPI) during deep flexion after TKA. PPI can cause anterior knee pain, increased patellofemoral pressure, wear of the polyethylene patellar component and tibial post, and reduced range of motion [40]. Using navigation, five posterior-stabilized total knee prostheses were implanted. The tibial component was 10 mm thick in all prostheses; patellar tendon length was represented by the tibial-patellar clearance (TPC), which varied from 18 to 40 mm. The authors found that the tibial-patellar clearance (TPC) and the design of the tibial post both affected the PPI after posterior-stabilized TKA. A longer tibial-patellar clearance (TPC), which is affected by the amount of bone resected from the proximal tibia and distal femur, resulted in a larger PPI angle. Furthermore, a larger tibial post (as in constrained prostheses) resulted in a smaller PPI angle, meaning that the anterosuperior part of the tibial post impinged on the patellar component during deep flexion. To maintain an appropriate TPC and avoid PPI, the authors recommended that surgeons adjust the amount of bone resected from the proximal tibia and distal femur during TKA [41]. The second-generation iteration of the JOURNEY™ BCS addresses this risk of impingement. The cam in the JOURNEY™ II BCS has been re-positioned superior to the original location and thus decreases femoral rollback in the targeted ranges of motion, increases femoral external rotation, and lowers the point of tibial post contact in deep flexion. The tibial post is now anterior to the original location and the height increased by taller PS femoral box walls. The new post position further maintains more anatomically correct femoral rollback, thus reducing iliotibial band (ITB) and iliotibial-patellar band (ITPB) tension. In addition, the tibial post height balances patellar impingement in flexion, while maximizing the dislocation safety factor [42].

Hommel and Wilke assessed differences between JOURNEY™ I and JOURNEY™ II in 257 patients with osteoarthritis of the knee [35]. The first 153 patients received JOURNEY™ I and the remaining 104 patients received JOURNEY™ II. All knees were operated with an extension-first surgical technique. The authors found good early functional results and an acceptable rate of complications with both devices. However, the mean follow-up time for JOURNEY™ II patients was brief at 15 months (range 12–18 months), and follow-up times and other variables differed between the groups.

JOURNEY™ II offers an innovative design that better resembles normal knee kinematics compared to traditional knee replacement devices. One study investigated the JOURNEY™ I device; however, the authors were not able to demonstrate that the improved dynamics could translate into improved functional and quality of life outcomes in patients [31].

Murakami et al. compared clinical outcomes and in vivo knee joint kinematics during stair climbing in rotating platform cruciate-retaining (CR) and posterior-stabilized (PS) mobile-bearing TKAs on clinical outcomes and in vivo knee joint kinematics during stair climbing [43]. Outcomes were evaluated in 20 successful TKAs, including ten CR knees and ten PS knees. The parameters investigated included isometric extensor torque, anterior translation, posterior translation, and total external rotation. The authors found that both CR and PS types of rotating platform mobile-bearing TKAs provided reproducible knee joint kinematics during stair climbing and equivalent clinical patient-reported outcomes. In fact, the patient-reported outcomes using the Knee Society Score 2011 (KSS 2011) were generally comparable to those found by Matsuda et al. [2] and Kawahara et al. [44] in their evaluations of fixed-bearing TKAs.

This is the first study with longer-term follow-up that describes patient outcomes of the current JOURNEY™ II BCS device.

This analysis has some limitations. This study was a non-randomized comparison of the reoperation and revision risks of two devices, and the compared cohorts did not begin concurrently. Non-randomized comparisons are subject to confounding that arise from comparing cohorts that possibly differ in characteristics of importance for the measured outcomes. Further, the risk of reoperation and revision increase over time. The JOURNEY™ I cohort had a longer follow-up time than the JOURNEY™ II cohort.

To minimize these limitations, three different statistical approaches were applied to describe and compare the reoperation and revision risks: the person-time incidence rate, Kaplan–Meier non-parametric estimates, and Cox regression analysis. Each of these approaches has its strengths and weaknesses. The strength of the person-time incidence rate is that it provides a simple way to compare two devices using the same, easily understandable statistic. The major limitation is that the approach assumes that the risk is constant over time. Such an assumption is not accurate for TKA as the risk is higher in the first year than in the later years. Since the JOURNEY™ II cohort had a shorter follow-up than the JOURNEY™ I cohort, the incidence rate estimates were biased in favor of the JOURNEY™ I. Despite this bias, the comparable person-time statistics favored JOURNEY™ II, although statistical significance was not reached for any of the person-time comparisons. Kaplan–Meier non-parametric estimates overcome this limitation and provide a less-biased comparison. Both K–M estimates favored JOURNEY™ II; the estimate for risk of reoperation reached statistical significance. Due to a larger number, the analysis of reoperations had more statistical power than the analysis of revisions and it is reasonable to assume that the lack of statistical significance for the risk of revision is due to type II error. The limitation of K–M estimates is that they are insensitive to effects of confounders. Cox regression analysis allows for the adjustment for confounders. After the adjustment for confounders, the risk estimates remained substantially lower in the JOURNEY™ II cohort. None of these statistical approaches address possible historical confounding effects due to a non-concurrent study design. Theoretically, it is possible that significant time trends or events have occurred that would bias these results. No major health care advances or changes have occurred that would account for the observed difference. Furthermore, all surgeries were performed by the same surgeon using the same surgical technique. A possible learning curve effect was addressed by excluding the first 108 cases in the JOURNEY™ I cohort. From a surgical perspective, there was no difference between the JOURNEY™ I and JOURNEY™ II surgeries. All available consecutive cases were included in the analysis. Revisions that occurred elsewhere were captured and reported. The compared cohorts were similar in age, gender, and the need for bilateral surgery.

These results have important clinical implications. In short-term follow-up, JOURNEY™ II has a low and acceptable risk of revision. Studies with longer follow-ups and those investigating functional and quality of life outcomes are warranted to fully qualify the safety and effectiveness of JOURNEY™ II BCS total knee system.