Functional Alignment Philosophy in Total Knee Arthroplasty – Rationale and technique for the varus morphotype using a CT based robotic platform and individualized planning

Abstract

Introduction: Alignment techniques in total knee arthroplasty (TKA) continue to evolve. Functional alignment (FA) is a novel technique that utilizes robotic tools to deliver TKA with the aim of respecting individual anatomical variations. The purpose of this paper is to describe the rationale and technique of FA in the varus morphotype with the use of a robotic platform. Rationale: FA reproduces constitutional knee anatomy within quantifiable target ranges. The principles are founded on a comprehensive assessment and understanding of individual anatomical variations with the aim of delivering personalized TKA. The principles are functional pre-operative planning, reconstitution of native coronal alignment, restoration of dynamic sagittal alignment within 5° of neutral, maintenance of joint-line-obliquity and height, implant sizing to match anatomy and a joint that is balanced in flexion and extension through manipulation of implant positioning rather than soft tissue releases. Technique: An individualized plan is created from pre-operative imaging. Next, a reproducible and quantifiable method of soft tissue laxity assessment is performed in extension and flexion that accounts for individual variation in soft tissue laxity. A dynamic virtual 3D model of the joint and implant position that can be manipulated in all three planes is modified to achieve target gap measurements while maintaining the joint line phenotype and a final limb position within a defined coronal and sagittal range. Conclusion: Functional alignment is a novel knee arthroplasty technique that aims to restore constitutional bony alignment and balance the laxity of the soft tissues by placing and sizing implants in a manner that it respects the variations in individual anatomy. This paper presents the approach for the varus morphotype.

Alignment philosophy influences trochlea recreation in total knee arthroplasty: a comparative study using image-based robotic technology

“…Furthermore, whilst differences in ability to restore the sulcus could be demonstrated, the effect on clinical outcomes remains unknown and will need to be the focus of future research. Finally, this study utilised previously described safe zones on implant limits [ 9 ], and these limits are subject to ongoing debate in TKA and may vary over time and between implant designs.…”

“…Implant position outside following thresholds were defined as unsafe and are based on previous literature and guidelines [ 9 , 16 ]. Limit for femoral flexion was 10° and femur coronal positioning great between 6° valgus and 3° varus.…”

“…In 2008, kinematic alignment (KA) was described by Howell and aimed to restore the kinematics of the native pre-osteoarthritic knee [ 7 , 8 ]. More recently, functional alignment (FA) was described [ 9 , 10 ], which considers the patients soft tissue laxity in flexion and extension and adjusts the implant position within defined boundaries to achieve balanced compartments. This technique utilises robotic tools and also considers the native trochlea groove when adjusting the position of the femoral component.…”

Trends in Computer-Assisted Surgery for Total Knee Arthroplasty in Germany: An Analysis Based on the Operative Procedure Classification System between 2010 to 2021

“…Recently, the functional alignment technique has been proposed as a new evolution of the kinematic concept. Software-based gap balancing and soft tissue balancing by modern robotic systems allow a more precise implant positioning, reducing the total amount of soft tissue release during TKA [ 42 , 43 ].…”

Functional Alignment Philosophy in Total Knee Arthroplasty—Rationale and Technique for the Valgus Morphotype Using an Image Based Robotic Platform and Individualized Planning

“…The additional control of all these elements with robotic tools has allowed the development of a new philosophy of alignment, termed functional alignment (FA) [ 19 , 20 , 21 ]. Functional alignment aims to reconstruct 3D constitutional alignment within set boundaries, with a key difference being the adjustment of implant positioning based on consideration of the patient’s soft tissue envelope to achieve gaps that are considered balanced [ 22 ]. Its use for the varus morphotype has recently been detailed [ 23 ] and was shown to be both bone preserving and more consistent in achieving tibiofemoral balancing and preserving the native trochlea groove compared to KA [ 23 , 24 ].…”