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.
Highlights
In total knee arthroplasty (TKA), a postoperative neutral alignment was a standard principle [1,2,3]
Lustig et al.: SICOT-J 2021, 7, 19 components are positioned at 90° to the tibial and femoral mechanical axis. This alignment philosophy for knee arthroplasty was driven by equalizing load on the implant to decrease wear and loosening rather than restoring normal knee kinematics and function
Sappey-Marinier et al performed a systematic review of the clinical and radiological outcomes after TKA with Kinematic alignment (KA) versus with Mechanical Alignment (MA) at 2 years of follow-up [25]. They reported that four of five prospective randomized controlled trial studies did not find any difference between the two groups (MA or KA) for all scores [26,27,28,29]
Summary
In total knee arthroplasty (TKA), a postoperative neutral alignment was a standard principle [1,2,3]. Lustig et al.: SICOT-J 2021, 7, 19 components are positioned at 90° to the tibial and femoral mechanical axis This alignment philosophy for knee arthroplasty was driven by equalizing load on the implant to decrease wear and loosening rather than restoring normal knee kinematics and function. Tibial and femoral resection thicknesses are validated with caliper measures and must match the thickness of the implants after compensating for saw cut and wear. It restores pre-arthritic ligament lengthening, does not create gap imbalance, minimizes the need for release [21,22,23,24]. This results in two important limitations that can occur with KA and have led to the development of restricted KA and inverse KA which is discussed later
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