Personalized alignment in total knee arthroplasty: current concepts

Abstract

Traditionally in total knee arthroplasty (TKA), a post-operative neutral alignment was the gold standard. This principle has been contested as functional outcomes were found to be inconsistent. Analysis of limb alignment in the non-osteoarthritic population reveals variations from neutral alignment and consideration of a personalized or patient-specific alignment in TKA is challenging previous concepts. The aim of this review was to clarify the variations of current personalized alignments and to report their results. Current personalized approaches of alignment reported are: kinematic, inverse kinematic, restricted kinematic, and functional. The principle of “kinematic alignment” is knee resurfacing with restitution of pre-arthritic anatomy. The aim is to resurface the femur maintaining the native femoral joint line obliquity. The flexion and extension gaps are balanced with the tibial resection. The principle of the “inverse kinematic alignment” is to resurface the tibia with similar medial and lateral bone resections in order to keep the native tibial joint line obliquity. Gap balancing is performed by adjusting the femoral resections. To avoid reproducing extreme anatomical alignments there is “restricted kinematic alignment” which is a compromise between mechanical alignment and true kinematic alignment with a defined safe zone of alignment. Finally, there is the concept of “functional alignment” which is an evolution of kinematic alignment as enabling technology has progressed. This is obtained by manipulating alignment, bone resections, soft tissue releases, and/or implant positioning with a robotic-assisted system to optimize TKA function for a patient’s specific alignment, bone morphology, and soft tissue envelope. The aim of personalizing alignment is to restore native knee kinematics and improve functional outcomes after TKA. A long-term follow-up remains crucial to assess both outcomes and implant survivorship of these current concepts.

The Role of Stability and Alignment in Improving Patient Outcomes After Total Knee Arthroplasty

“…To avoid this issue, tibial “resurfacing” in inverse kinematic alignment is performed with equal medial and lateral resection, which maintains the native joint line obliquity. The flexion and extension gaps are then balanced by adjusting the posterior and distal femoral resections 45 . One of the drawbacks of this technique is that readjustment of the femoral cuts after the initial cuts have been performed is difficult with manual resection guides and may require robotic-assisted systems to be more accurate.…”

Current concept of kinematic alignment total knee arthroplasty and its derivatives

“…The goal is eventually different between patients, so it is considered to be a personalized, individualized, or patient-specific approach. 15,22,23 This approach has received a great deal of attention in recent years, and many surgeons have reported good short-term and medium-term clinical results. [24][25][26][27][28] With the spread of KA-TKA, several derivatives with different modifications have been proposed, which has led to some confusion.…”

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

“…Functional alignment is an emerging philosophy that aims to reconstruct 3-dimensional constitutional alignment while respecting the behavior of the soft tissue envelope with the assistance of a robotic platform. While its concept has been described [ 18 , 19 ], rationale and technique are yet to be defined.…”

“…Furthermore, 10.8% and 4.4% of males and females, respectively, had an HKA between 172.5° and 175.5° [ 22 ]. Safe zones that set a limit of ±3° do not allow constitutional alignment to be recreated in at least 20% of the population [ 18 , 23 ]. Several studies have demonstrated good clinical results out to 10-year follow-ups outside this range [ 20 , 24 – 28 ].…”