Kinematic alignment fails to achieve balancing in 50% of varus knees and resects more bone compared to functional alignment

Abstract

Purpose Evidence is emerging that tibio-femoral compartmental balancing is related to clinical outcomes after total knee arthroplasty (TKA). The purpose of this study was to assess if kinematic alignment (KA) delivered a balanced knee in lexion and extension after TKA on varus deformity, compared to functional alignment (FA). Methods This single-centre retrospective cohort study assessed 110 consecutive TKAs performed with an image-based robotic system for pre-operative varus deformity. The ligament balancing in the medial and lateral femorotibial compartments was assessed intra-operatively with a robotic system to evaluate if a KA plan would deliver a balanced knee. Balance was considered achieved if tibio-femoral compartments (medial/lateral) were equal to or less than 1.5 mm, or if the estimated inal gap position more than 2 mm from the global implant thickness (17 mm). Implant positioning was modiied within limits previously deined for a FA philosophy to achieve balancing. Resection thickness and implant positioning were compared with the KA plan and after the FA adjustments; and also, between the patients with a inal balanced knee in extension and at 90° of lexion. Results A total of 102 patients were eligible for inal analysis. Mean age was 67.3 ± 8.2 years, average BMI was 29.1 ± 5.2 kg/ m 2 , mean pre-operative coronal alignment was 174.0° ± 3.3° and sagittal alignment 3.4° ± 5.9°. Mean post-operative coronal alignment was 177.7° ± 1.0° and sagittal alignment 0.8° ± 1.9°. A KA plan delivered medial-lateral tibio-femoral compartment balancing in 67 cases (65.7%) for the extension gap and in 50 cases (49.1%) for the lexion gap. All measured bone resection depths were signiicantly less for FA compared to KA. To achieve balancing targets, inal femoral component position was more externally rotated relative to the posterior condylar axis, (0.5° with KA compared to 1.7° with FA (p < 0.0001), and the tibia in more varus (3.0° KA vs. 3.5° FA p = 0.0024). Only one soft tissue release was required. Conclusion KA failed to deliver a balanced TKA in more than 50% of cases, especially regarding the lexion gap. Consideration of soft tissue laxity led to signiicantly less bone resection, with more externally rotated femoral component and more varus tibial component.

The language of knee alignment

“…Most commonly, femoral component external rotation is performed to maintain balanced medial extension and flexion gaps, so often, the final femoral component axial rotation lies between PCA and TEA axes. 80…”

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

“…With the advent of assistive robotic technology, it has become possible for pre-emptive soft tissue balancing to be incorporated into implant position prior to bone cuts being performed. This has recently been shown to reduce the amount of bone resected as well as reducing the need for soft tissue releases in TKA for the varus morphotype [ 23 ].…”

“…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 ]. The technique and rationale for the valgus morphotype is yet to be described.…”

Estrategias de alineamiento en prótesis total de rodilla: La era robótica cambió el juego

“…However, it has been reported that this alignment can fail to balance the prosthesis in up to 50% of cases. 9 Another feature of this technique is that resections follow the measurement of the bone sections of the medial distal femur, made with a caliper, an element that may not be error-free.…”

“…No obstante, se ha reportado que este alineamiento puede fallar en balancear la prótesis, en hasta un 50% de los casos. 9 Otra de sus características es que las resecciones se hacen en relación a la medición de los cortes óseos de fémur distal medial, realizadas con un cáliper, elemento que podría no estar exento de errores en su uso.…”