BCR TKA Designs: A Comprehensive Review of the Literature

Diego Zamagni. M.Sc. *¹, Eslam Shalaby MD ², Mohamed Elfekky. M.D ³, Samih Tarabichi M.D. ⁴

1,4. Tarabichi center, Al Zahra Hospital Dubai, Sheikh Zayed Rd - Al Barsha - Al Barsha 1 - Dubai – UAE.

2,3. Hatta hospital Dubai Health. Dubai – UAE.

*Correspondence to: Diego Zamagni. Via Fleming 50, Savignano Sul Rubicone, 47039, FC, Italy.

Copyright

© 2024 Diego Zamagni. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: 23 February 2024

Published: 10 March 2024

Abstract

Background: More than 20% of total knee replacement (TKR) patients reveal to be unsatisfied by their implant; an unacceptably high rate nowadays. The main underlying reason of this failure can be attributed to abnormal kinematics, poor proprioceptive outcomes and discomforts associated to the current standard arthroplasties. While in the latter the anterior cruciate ligament (ACL) is sacrificed, a diametrically opposed approach called bicruciate retaining (BCR) TKR spares both cruciate ligaments. Although this anatomical approach is supported by many publications in terms of knee motion, patient preference and joint feeling, it failed to solidly establish on the market, mainly due to design flaws and a highly challenging surgical procedure.

Objectives: The aim of this review is to describe in detail the most important BCR designs ever developed and present their reported clinical limitations. A special focus is set on the most relevant weaknesses of these implants, in the attempt to finally highlight the key features of a new ideal BCR design and reveal possible solutions to the current technical challenges related to ACL retention.

Methodology: For this purpose, a comprehensive literature research was performed through Embase, Scopus, Science Direct, Medline databases, arthroplasty journals, books and additional sources.

Conclusion: From the collected data, it clearly emerges that BCR designs have significantly evolved over the years. The resulting contemporary BCR prosthesis succeed in solving many past design flaws, however the early results suggest that further improvements are still required to reduce the dissatisfaction rate after total knee arthroplasty (TKA) once and for all.

Key-words: Bicruciate Retaining (BCR); Total Knee Replacement (TKR); Total Knee Arthroplasty (TKA); Anterior Cruciate Ligament (ACL); Design.

Introduction

1.Current TKAs and their limitations

Nowadays, standard procedures for TKR in patients with advanced osteoarthritis (OA) and rheumatoid arthritis (RA) of knee joint, consist in the insertion of posterior cruciate substituting (PS) or cruciate retaining (CR) prosthesis.[1,2] Both implants require ACL sacrifice (Fig. 1).

Figure 1: a standard total knee arthroplasty TKA and its components.[3]

Although PS and CR total knee replacements are well established worldwide, approximately 20% of patients who undergo TKA are unsatisfied, a consistently higher percentage than discontent patients after total hip arthroplasty (THA).[4-7] This is surely correlated to the higher expectations of young and active people experiencing TKR.[8] According to dr. Kurtz et al., a 17-fold increase in the number of TKAs in the 45-54 age category, from 59,077 procedures in 2006 to 994,104 procedures in 2030 is anticipated.[4] This young generation aims for a return to demanding activities such as cycling, running and sports trainings and competitions, even at high level, all exercises that strongly require a close to normal knee kinematics and proprioception. However, the current PS and CR prosthesis show many limitations in this direction. On the contrary, unicondylar knee arthroplasty (UKA), which spares both ACL and PCL, has demonstrated kinematic and proprioceptive outcomes that more closely resemble the normal knee.[9-11] Therefore, it is clear that bicruciate retention might be the key to reduce the gap with satisfaction rates after THA.[11]

In this optics, a different approach called bicruciate retaining (BCR) TKA offers a promising solution. BCR TKA, as the name suggests, is a specialized prosthetic implant which preserves both ACL and PCL. BCR prosthesis belongs to the “anatomical approach” aiming to recreate the physiological anatomy of knee joint, juxtaposed to CR and PS designs which focus on functionality instead, hence belonging to the so called “functional approach”.[12,13]

2.BCR TKA advantages

Bicruciate retaining designs are supported over ACL-sacrificing ones by many reports in literature. In terms of kinematics, [14-20] BCR TKA demonstrates more normal posterior femoral roll back during deep bending, compared to a CR TKA, which shows anterior femoral movement on flexion and exaggerated medial condyle translation on deep knee bend instead.[21-23] Anteroposterior laxity has also been shown to be closer to normal in BCR TKA than CR and PS TKA.[21,24] Stiehl et al reported a femorotibial contact close to the tibial midline in full extension in BCR designs similarly to healthy knee, while for CR implants the contact was significantly posterior.[14] Several studies univocally prove satisfying performance of BCR arthroplasties in gait and stair climbing analysis, where CR TKAs revealed extensor moment weakness with forward leaning and decreased stance phase knee flexion, typical of ACL-deficient knees.[14,15,22,25-28]

At the same time, it has been shown that in absence of ACL, the PCL and collateral ligaments are abnormally loaded through the ROM, leading to a reduction in femoral rollback by an average of 36% and a 15% loss in extensor efficiency.[29] In posteriorly stabilized PS arthroplasties, both cruciate ligaments are extracted and compensated by a post-cam mechanism. This design demonstrated less abnormal kinematics than PCL-retaining TKAs2, but still Mahoney et al. shown a 12 % loss in rollback and an 11 % decrease in extensor efficiency.[29] Another kinematic study performed by Stacey M. Acker et al., assessing deep flexion daily activities performed by Asian patients, demonstrated a significantly higher femoral external rotation in PS knees with respect to the normal 20-30° range of normal joints. This is attributable to the absence of ACL constraint during knee motion in PS arthroplasties. [29,31] Furthermore, these functional designs are constraining and forcing the knee motion alone, resulting in higher stresses at the bone-implant interface and therefore possible prosthetic failures. On the other hand, a design which replicates the normal anatomy and spares the knee-stabilizing soft tissues will allow for physiological force transmission through ligaments, reducing the stresses on the implant.[32]

In terms of proprioception, several recent researches reported superior outcomes in patients undergoing BCR TKAs rather than CR or PS procedures.[2,3,9,33-35] In addition to kinematics and proprioception and significantly linked to them are the patient reported outcomes (PROs), describing the patient satisfaction and feelings about the implant. In this context, dr. Pritchett reported that in 440 patients undergoing bilateral TKA with different prosthesis, with a minimum of 2-year follow-up, 89.1% preferred a BCR design in one knee to a PS in the other.[2] In a similar study, Pritchett, analyzing 50 patients, could show that 70% percent of them preferred the BCR knee, whereas only 10% preferred the posterior cruciate-retaining knee.[28] In addition, reduced joint awareness was observed in patients receiving a contemporary BCR implant with respect to PS prosthesis.[36]

Last but not least, Lombardi et al. found that if an intact ACL is removed during TKA the patient will have poorer postoperative results and more restricted ROM compared to patients who had an absent or dysfunctional ACL at operation time, strongly justifying a BCR arthroplasty for the former.[11] All these data firmly support BCR approach for patients with intact ACL, representing more than half of patients with knee OA undergoing TKA,[37] or at least with a functional anterior cruciate, findable in roughly 78% of knees at the time of TKA, according to Johnson et al.[38]

3.BCR TKA disadvantages

Unfortunately, bicruciate retaining TKA doesn’t come with advantages only. Some critical drawbacks have limited its wide-spreading on the market and made it outpaced by CR and PS techniques. Although BCR limitations will be discussed in details further on in this review, the main disadvantages carried by this approach are anticipated here.

The biggest drawback of BCR TKA is the more challenging knee surgery with respect to other designs such as PS and CR.[10,32-34,39,40] Indeed, in order to spare the ACL, the tibia eminence must be preserved and this make it impossible to subluxate the tibia intraoperatively, therefore narrowing the surgical space.[11,32] At the same time, the anatomical joint line (on average 3° of varus) should be restored, meaning that the exact amount of cartilage and bone resected should be supplemented by the implant.[41] Any significant discrepancy, will alter the normal kinematics and ligament tension. During BCR TKA, accurate balancing of the knee through the ROM is vital, but extremely challenging at the same time.[42,43] Hence, fracture of the tibial eminence and rupture of the ACL are not infrequent intraoperatively under not experienced hands, making the surgical technique not easily reproducible.[39,43-45] Given the narrow space available intraoperatively, the size of fixation pegs or keels in the tibial component is constrained, while the application of a long stem as in PS and CR is out of question.[11,46] This might result in tibial tray loosening.[33,47,48] At the same time, as the tibial eminence must be retained, instead of fully covering the bone surface, the tibial baseplate must have a central cutout and a narrow bridge connecting the medial and lateral plateau, that therefore limits the bone-implant contact area, favoring instability and fatigue fractures of the anterior bridge.[46,49-52] Furthermore, patient selection criteria is considerably stricter for BCR TKA rather than bicruciate sacrificing knee replacements. It’s obvious that ligaments must be present and functionally intact, a requirement not always fulfilled by elderly patients with advanced OA or RA. Concurrently, varus, valgus deformity and flexion contracture must be minimal.[12,39,53] Last but not least, BCR TKA is not only technically but also economically demanding. Design and development of these implants is usually associated with additional costs.[1]

To sum up, BCR arthroplasty represents a complex reality with weaknesses but strong benefits at the same time, that could finally bring the relatively high dissatisfaction rates after TKA to an end. The goal of this report is to review in detail the major BCR designs from the historical to the contemporary ones, aiming for a deep understanding of their limitations in order to set some key design specifics which could help to overcome the latter.

Materials and Methods

1.Research strategy

A comprehensive literature research was performed through 5 main online databases: Embase, Science Direct, Medline, Scopus and Google scholar. Arthroplasty journals, orthopedic books, additional material provided by Tarabichi center (AZHD) and other sources were also consulted and included into this work. The research strategy did not follow a standard protocol because, contrarily to a conventional systematic review, this paper doesn’t focus on a specific topic or aspect only, but covers a huge variety of themes, a significant number of different BCR designs, each one described in as much detail as possible, making it impossible to adopt a single, unique research plan. However, a personalized strategy was performed during databases consultation, to make the review as systematic as possible. Initially a broad investigation of BCR arthroplasties was performed in order to obtain basic knowledge about this field that was then exploited for the Introduction, Discussion and Conclusion paragraphs. Examples of search strings employed are: (BCR OR bicruciate retaining OR bi-cruciate retaining) AND (TKA OR TKR OR total knee replacement OR total knee arthroplasty OR implant OR implants OR prosthesis) AND (review OR systematic review); (ACL OR anterior cruciate ligament OR anterior cruciate) AND (preserv* OR spar* OR retain*) AND (TKA OR TKR OR total knee replacement OR total knee arthroplasty OR implant OR implants OR prosthesis). In a subsequent step, more precise information about BCR designs was searched, with the aim to find all the major implants that have ever been developed until now. For this purpose, orthopedic books revealed to be more suitable than journal papers. The main research step comes now. After the individuation of all main BCR designs in TKA history, for each one a methodical research was performed in the databases, through every paper reference and images found online. For the contemporary BCR implants, the company website was consulted aiming to find product information and the design rationale.

2.Inclusion/exclusion criteria:  

Every study presenting BCR TKA approach was assessed in first place. Since, a basic knowledge of the field was initially sought, priority and preference was given to reviews and TKA books until collected data were considered enough by the author. In a second place, papers regarding each separate BCR design was read and evaluated. In this phase, studies not regarding directly the BCR design under consideration, in a non-English language, without an open institutional access or with low level of evidence (grey literature, conference abstracts, case reports and expert opinions) were excluded. On the other hand, every source providing reliable additional data to the already collected one was took into consideration, resulting in a wide range of references. In this way, double checks could be performed between different publications to confirm the validity of most of the findings and therefore increase the solidity of the data provided in this work. 

Results

1.History of BCR TKA designs:

The end of 1960s and beginning of 1970s represented a turning point for TKR. Huge excitement soared in the field after the introduction of high density polyethylene (HDPE) in 1963 and the first application of bone cement PMMA for implant fixation in 1960.[12,54] In this highly motivating atmosphere, several new TKA designs of both anatomical and functional approach were developed. In this review, we will focus only on the anatomical category, particularly on BCR implants. A chronological overview of these is presented below, dwelling on major design features, clinical outcomes and limitations. The prosthesis will be divided in two families according to the year of commercial release: historical and modern BCR designs (Fig. 2). While the contemporary implants will be described in details, the historical designs will be summarized in tables, in order to relieve and efficiently organize the information load and therefore smooth the reading process. For these old prosthesis, the “main design weaknesses” column refers to the initial proposed version, unless otherwise stated.

Figure 2: chronological representation of the historical and modern BCR designs assessed in this review.

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