Bicruciate-retaining total knee arthroplasty compared to cruciate-sacrificing TKA: what are the advantages and disadvantages?

KEYWORDS:

• Bicruciate-retaining total knee arthroplasty (BCR-TKA)
• patient’s perception
• joint awareness
• patient-reported outcome measurement (PROM)
• proprioception
• knee kinematics

1. Introduction

Total knee arthroplasty (TKA) with sacrifice of the anterior cruciate ligament (ACL) is the standard treatment of advanced osteoarthritis (OA) of knee joint. In the past, patients of advanced age with reduced demands for activity of daily living (ADL) were considered for TKA. However, more and more younger, and physically active patients suffer from OA of the knee. These patients expect to return to the high level of physical activity following TKA. Further advancements in the implant design aim for a closer to anatomic movement pattern. There is ongoing discussion about the role of preservation of cruciate ligaments in arthroplasty of the knee. When talking about cruciate-retaining TKA, usually it is the preservation of the posterior cruciate ligament (PCL). However, a number of studies have shown that PCL-retaining implants provide no clinical or functional advantage. In recent years, a new generation of bicruciate-retaining (BCR) TKA with preservation of the anterior and PCL has been developed. Early clinical results are promising and have stimulated a controversial discussion about the advantages and disadvantages of BCR-TKA.

2. Technical evolution and knee kinematics

Gunston [1] was the first to develop a BCR-TKA which aimed for a closer to natural knee movement pattern. Besides limitations in early postoperative range of motion (ROM), early results regarding survivorship were promising. The decrease in the level of constraint was seen as a possible reason for its increased survivorship. Preservation of the cruciate ligaments in BCR-TKA leads to a shock absorbing function leading to reduced transmission of shear forces. Preservation of the ACL in BCR-TKA requires preservation of the central part of the tibial plateau narrowing the area for tibial component fixation. Further attempts were made based on the same principle involving simultaneous implantation of medial and lateral sledge prostheses with preservation of both cruciate ligaments which showed good clinical and proprioceptive results [2]. Lack of anterior cross-linking between both compartments led to early tibial loosening in this bicondylar sledge construct. Tibial anchoring is still a critical issue in BCR-TKA [3]. Latest generation implants contain a firm cross-link between the medial and lateral tibial surfaces which provides more stability. However, we have seen rare cases of cross-link breakage even in the latest generation of BCR-TKA. There are also reports on intraoperative island fractures at primary implantation of BCR-TKA [4]. In case of an intraoperative island fracture, the surgeon has to resort to a cruciate sacrificing implant.

Implantation of a BCR-implant is a challenging procedure associated with a long learning curve. Ligamentous tension balancing and precise reconstruction of the joint line hold more importance in BCR compared from cruciate sacrificing arthroplasty. Additional problems such as cyclops syndrome – specifically to the new implantation technique – have also emerged which were not encountered in routine arthroplasty techniques [5,6].

Besides the abovementioned problems, this implantation technique provides more natural knee kinematics. Physiologically, the ACL prevents an anterior translation of the tibia and creates a rollback of the femur. Sacrifice of the ACL can result in abnormal kinematics. BCR implants have shown a more physiologic anterior femorotibial contact point and a greater posterior translation in motion compared to ACL-sacrificing implants [7–11]. Recently, Peersman et al. [8] showed that changes by removal of the conforming meniscus and cartilage have more impact on tibiofemoral kinematics than different inlay sizes of a BCR TKA. However, they confirmed close to normal knee kinematics for BCR-TKA.

3. Clinical results

Cloutier et al. [12] reported excellent clinical results for the first generation of BCR-TKA with a survivorship rate of 95% after 10 years and 82% after 22 years. However, 38% of patients had limited ROM and pain. The authors attribute this high number to an elevated ligamentous tension caused by ‘an inadequate use of the distractor.’ Despite technical advances, a higher proportion of patients have reduced ROM compared to standard implants. This problem is especially common in patients who have limited preoperative ROM. Recently, Christensen [5] found a higher rate of early revisions in BCR-TKA compared to PCL-retaining implants. However, this study has various limitations which curb its generalizability. The study design is retrospective and nonrandomized. The authors have also included the initial patients who were treated with BCR-TKA in their institution. Some of the initial revisions can be attributed to the long learning curve of the new implantation techniques. Unfortunately, the authors do not describe any temporal occurrence of the complications to make this relationship evident. Due to high rate of early revision, the authors cautioned its readers against widespread adoption in clinical practices unless its superiority over conventional implants is proven.

The largest series of BCR-TKA patients (160 patient; 214 knees) with long-term survivorship (20 years) was presented by Pritchett [13]. The Kaplan–Meier survivorship was 89% (95% CI, 82–93) with revision for any reason as an end point. The main reason for revision was polyethylene (PE) wear of a non-cross-linked PE. Excluding these revisions, the 20 years survivorship rises to 96%. Further studies are needed to investigate long-term survivorship for the latest generation of BCR implants with highly cross-linked PE.

With all these advantages of BCR-TKA, it has to be underlined that this procedure is not only technically but also economically demanding. Development of these implants is associated with additional costs. The implant cost of BCR TKA is more than the average cost of standard implants which are the reference for most of the insurance-based systems. The question is whether companies are willing to take the risks of development costs if the product has a limited target group of patients.

4. Patient’s perception

Anatomic studies have shown cruciate ligaments; especially ACL contains a considerable number of proprioceptive nerve cells. In a recent prospective cohort study, we found that BCR implants can provide a level of proprioception comparable to a medial unicondylar knee arthroplasty where the ACL is also preserved [14]. The BCR-TKA group showed a superior proprioceptive capacity compared to our standard cruciate-sacrificing implant.

There is a high proportion of patients who report residual knee symptoms after TKA without any identifiable objective clinical or radiological reasons. Initial results of BCR TKAs have shown that these implants are associated with a higher ‘overall satisfaction’ [15]. However, these findings are derived from retrospective case studies focusing on the global patient’s satisfaction. So the question remains if improvements in functional properties like knee kinematics and proprioception lead to an improved patient’s perception. Besides proprioceptive abilities, the patient’s sensation of the artificial joint is crucial for the patient’s perception of the joint. Prior studies on patient satisfaction after TKA have used conventional clinical scores (e.g. Knee Society Score). Conventional scores are based on clinical or radiological parameter and do not reflect the patient’s perception. This can lead to impairments in validity of the score, e.g. discrimination of good and very good results. This makes it difficult to reveal minor differences in TKA. In the past years, there was rising impact of patient-reported outcome measurement (PROM) in joint arthroplasty. The new PROM instruments have a high discriminatory power in long-term results and are therefore able to discern between good and very good results. In a recent prospective cohort study, we have seen the same level of joint awareness measured by the Forgotten Joint Score as for proprioceptive capacity: The patients with BCR implants have a lower level of distracting joint awareness in ADL compared to cruciate-sacrificing implants [4]. However, it seems to be dependent on the outcome instrument used. Christensen et al. did not see any difference in PROM using the National Institute of Health’s Patient-Reported Outcomes Measurement Information System.

5. Conclusion

In conclusion, BCR-TKA is a technical advancement for patients with knee OA showing early promising results regarding postoperative function and patient satisfaction. However, these results are related to some basic requirements like patient selection and the surgeon’s experience with the implant. Further prospective randomized trials are necessary to investigate long-term survivorship and limitations in early postoperative ROM of some patients to determine who is the ideal patient for this type of implant.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Acknowledgement

I want to thank Himanshu Bhayana who was involved in finalization of the manuscript.

Additional information

Funding

This paper was not funded.