Robotic-Assisted Total Knee Arthroplasty: Cruciate-Retaining Versus Bi-Cruciate Stabilized

Arthritis is a clinical syndrome of joint pain accompanied by varying degrees of functional limitation and reduced quality of life. Two common etiologies of arthritis are degeneration of the joint, osteoarthritis (OA), and inappropriate inflammatory response, rheumatoid arthritis (RA). OA is characterized by loss of cartilage, remodeling of adjacent bone, and inflammation in the affected joint. RA is a progressive inflammatory disease that eventually causes systemic joint damage and disability. Post-traumatic arthritis is a form of osteoarthritis following an injury to a joint. Inappropriate joint biomechanics due to deformities is the main risk factor for OA. The joint biomechanics are directly affected by the malalignment of the lower extremities due to anatomical deformities. Varus deformity is an excessive inward angulation of the lower leg and results in a bowlegged appearance. It may cause an overloading and cartilage wear in the medial knee compartment, which could support a degeneration of the knee joint leading to OA.

As of 2010, there were approximately 250 million people globally with osteoarthritis of the knee joint (3.6% of the global population). The prevalence was higher in females than in males. Initial treatment of arthritis may include physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and corticosteroids which can be taken orally or by injection.

Avascular necrosis (AVN) has several etiologies but fundamentally results from a decrease in blood flow to the affected bone, leading to cellular death. Studies have reported a 3.4% and 9.4% incidence of spontaneous osteonecrosis in persons older than 50 and 65 years of age, respectively. Initial treatment of AVN may include medication, stretching, and avoiding walking on the affected leg.

Complex epiphyseal fractures around the knee joint involve the distal femur or proximal end of the tibia. The management of these fractures, especially in elderly patients, is challenging. When the damage to the joint is advanced or available conservative treatment options are exhausted, knee arthroplasty is considered the most effective treatment for patients with any of these indications.

Total knee arthroplasty (TKA) is a highly successful and frequently performed surgical treatment to reduce disability caused by end-stage osteoarthritis and other conditions affecting articular cartilage. Technical outcomes for TKA are excellent, with favorable postoperative health-related quality of life. Also, survivorship of primary knee replacements is excellent with reported survivorship of 82.3% at 25 years. TKA has traditionally been indicated in the elderly population with relatively sedentary lifestyles, but more active, younger patients (<55) are receiving TKA due to the desire for a pain-free, active lifestyle with the demand projected to continue to increase for this group. A recent systematic review has shown that functional outcomes are similar in this population compared to elderly patients with no increase in the burden of revision.

In Australia, 660,000 primary TKAs have been performed in 2018. Since 2003, the number of knee replacement procedures undertaken has increased by 128%. The escalating prevalence of end-stage OA places an increased burden on healthcare providers, especially on less experienced surgeons and facilities that perform low numbers of arthroplasties. Lower volume hospitals (<25 procedures/year) report higher revision rates and more complications by 5 to 8 years compared to high volume hospitals (>200 procedures/year). Therefore, technology or techniques that could improve outcomes and reduce the risk of revision are becoming increasingly important.

Surgical factors that must be considered in knee arthroplasty include lower leg alignment, soft tissue balancing, maintenance of the joint line, and component size and fixation. Malalignment of components in any anatomical plane can cause major complications including aseptic loosening, instability, poor function, polyethylene wear, and pain. Additionally, implant malposition and malalignment of the joint can result in failure of the prosthesis. When not aligned within a narrow tolerance of ≤3° of the mechanical axis, poor functional outcomes, decreased implant survivorship, increased wear, and early failure from component loosening may occur.

Evidence has shown that neutral mechanical alignment provides optimal outcomes in knee arthroplasty, which is achieved with conventional alignment guides in approximately 75% of TKA cases. For partial knee procedures, approximately 30-60% of UKAs have been reported to be mal-aligned using conventional manual instruments. The importance of alignment can be demonstrated by observing higher revision rates of UKA attributed to malposition or malalignment of partial knees while roughly 25% of TKAs have been revised for instability or malalignment.

As an alternative to mechanical alignment, kinematic alignment technique for knee arthroplasty aims to restore the individual knee anatomy and ligament tension, to restore native knee kinematics. Kinematic alignment restores the obliquity and level of the joint line anatomically so the femoral component is slightly more valgus (1° to 2°) and the tibial component is slightly more varus (1° to 2°) than mechanically aligned components.

A significant innovation in knee arthroplasty has been the introduction of computer navigation and robotic-assisted surgery. One such technology is CORI. This system is a semi-autonomous image-free system. During the surgery, the surgeon maps the condylar landmarks and determines alignment indices to define the volume and orientation of bone to be removed. The tools to remove the bone and place the implants are controlled and manipulated by the surgeon with the guidance of a 3-dimensional digital map of the surgical surface.

Comparisons of navigation systems to conventional instruments have demonstrated that robotic platforms produce fewer positioning errors in both UKA and TKA. When used in medial or lateral UKA procedures, robotics reported short learning curves, increased accuracy in posterior tibial slope, and coronal tibial alignment in comparison to other alignment methods.

There are various total knee designs available in the market that promote their own benefits in restoring the natural kinematics of the knee to mimic the movement of the normal knee. Currently in our region, there are four commonly used robotic-assisted total knee arthroplasty designs available, which depend on the patient's factors and surgeon's preference. There is the Bi-Cruciate Retaining Total Knee Arthroplasty (BCR TKA), the Bi-Cruciate Stabilized Total Knee Arthroplasty (BCS TKA), the Posterior Stabilized Total Knee Arthroplasty (PS TKA), and the Cruciate Retaining Total Knee Arthroplasty (CR TKA).

The PS and BCS total knee arthroplasties are common choices as they sacrifice both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) for simplification of implantation and reduction of surgical difficulty. The conventional PS TKA is a common feasible choice as it has shown long-term survivorship and acceptable patient outcomes. The BCS TKA similarly substitutes both the ACL and PCL but uses a unique dual cam-post mechanism to preserve normal knee kinematics and increase anterior-posterior stability throughout knee flexion.

On the other hand, preservation of the PCL in Cruciate Retaining (CR) total knee arthroscopy was traditionally believed to improve flexion and range of motion by restoring normal knee biomechanics and anatomical femoral rollback. PCL retention is also associated with better stairs performance, although the function of the PCL without the ACL is in debate. However, more recent studies have shown that there was a paradoxical anterior translation of the femur on the tibia during knee flexion, leading to the newer development of designs to retain both cruciate ligaments.

The Bi-Cruciate Retaining (BCR) total knee arthroplasty was designed for more kinematically functional implants that better reconstruct natural knee kinematics for activities of daily living by preserving both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). BCR TKA historically has not been favored in the past due to its difficult surgical technique and complication rate, however, due to the recent emergence of new implant designs, it has gained back its popularity with improving functional outcomes and reducing complication rate. The ACL has been shown to be a factor for optimal knee kinematics and natural movement through its proprioceptive qualities. ACL deficient knees demonstrate posterior femoral position in full extension and increased medial femoral condyle translation during knee flexion. Preservation of both the ACL and PCL results in better flexion range, stability, and capacity to climb stairs.

On the other end of the spectrum, implant designs that resect the cruciate ligaments have emerged to simplify implantation and reduce surgical difficulty, such as the posterior cruciate retaining (PCR), posterior stabilized (PS), and the newer Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA). In the normal knee, the lateral femoral condyle moves posterior across the tibial plateau with knee flexion, while the medial femoral condyle moves posterior in early flexion then anteriorly briefly before resuming posterior in the end of flexion. The BCS TKA is a convenient design that substitutes the sacrificed ACL and PCL with a unique dual cam-post mechanism to preserve normal knee kinematics and increase anterior-posterior stability throughout knee flexion.

The improvement of the biomechanical properties mimicking the natural kinematics of both the BCS and CR TKA may provide an effective solution to patient dissatisfaction and impaired functional outcomes after surgery. Therefore, an analysis of the knee kinematics of these patients with gait analysis, proprioception, and comparison of functional outcomes would aid the choice of implant.

Objective:

PRIMARY OBJECTIVE The primary objective of this study is to evaluate the use of CR and BCS in TKA procedure in achieving post-operative leg.

SECONDARY OBJECTIVE(S) The secondary objective of this study is to generate safety and performance evidence supporting the use of robotic assisted CR and BCS TKA procedures. To assess the safety and performance of robotic assisted CR and BCS TKA procedures up to 24 months after TKA surgery.