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

Abstract

Functional alignment (FA) is a novel philosophy to deliver a total knee arthroplasty (TKA) that respects individual bony and soft tissue phenotypes within defined limitations. The purpose of this paper is to describe the rationale and technique of FA in the valgus morphotype with the use of an image-based robotic-platform. For the valgus phenotype the principles are personalized pre-operative planning, reconstitution of native coronal alignment without residual varus or valgus of more than 3°, restoration of dynamic sagittal alignment within 5° of neutral, implant sizing to match anatomy, and achievement of defined soft tissue laxity in extension and flexion through implant manipulation within the defined boundaries. An individualized plan is created from pre-operative imaging. Next, a reproducible and quantifiable assessment of soft tissue laxity is performed in extension and flexion. Implant positioning is then manipulated in all three planes if necessary to achieve target gap measurements and a final limb position within a defined coronal and sagittal range. FA is a novel TKA 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 respects variations in individual anatomy and soft tissues within defined limits.

Why Kinematic Alignment Makes Little Sense in Valgus Osteoarthritis of the Knee: A Narrative Review

“…The principles of FA in valgus knees are, after customized preoperative planning, the reconstruction of the native coronal alignment without remaining varus or valgus alignment of more than three degrees and the reconstruction of dynamic sagittal alignment with boundaries of five degrees of neutral [ 45 ] followed by matching the anatomy with the size of the components and attaining the defined soft tissue laxity in extension and flexion by manipulating the components within the limits that have been established [ 45 ]. It has been shown for varus knees that, in contrast to KA, FA is more dependable in terms of preserving bone, the natural trochlea groove and tibiofemoral balance [ 70 , 71 ].…”

“…The introduction of robotic instruments has enhanced the measurement and management of implant positioning and balancing goals [ 45 ]. These technologies allow for preoperative planning using imaging modalities that enable an evaluation of bone architecture in all three planes to customize implant size and positioning [ 46 ].…”

“…In addition, with the use of these technologies, soft tissue balancing can be quantitatively evaluated during surgery [ 46 ]. Using robotic devices, functional alignment (FA) is an alignment strategy that attempts to restore three-dimensional constitutional alignment with respect to the individual soft tissues of each patient [ 45 , 46 ]. This method combines components of gap-balancing and measured resection [ 47 ].…”

Definitions and consequences of current alignment techniques and phenotypes in total knee arthroplasty (TKA) – there is no winner yet

“…Preoperatively, surgery is planned to achieve neutral MA or KA, but intraoperatively it combines methods of gap balancing, measured resection, and predictive modeling, utilizing robotic or computer‐assisted platforms to virtually position implants and minimize soft‐tissue releases, eventually allowing restoration of sagittal knee balance [9]. The functional approach is more about 3D positioning of implants than limited to coronal alignment, since it combines coronal, rotational and sagittal positioning of both femur and tibia component [54, 55].…”

Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs

“…The persistence of suboptimal satisfaction outcomes among patients following total knee arthroplasty (TKA) has led to the development of innovative surgical techniques [ 1 – 3 ]. Personalized alignment strategies in total knee arthroplasty have emerged as alternatives to neutral mechanical alignment [ 4 , 5 ]. Kinematic alignment and related approaches aim to recreate native knee morphology by removing the amount of bone and cartilage that will be exactly replaced by the implant, with the intent of restoring natural kinematics and joint laxities [ 6 , 7 ] .…”