Phenotyping of hip–knee–ankle angle in young non-osteoarthritic knees provides better understanding of native alignment variability

Abstract

Purpose There is a lack of knowledge about the native coronal knee alignment in 3D. The currently used classiication system (neutral, valgus and varus) oversimpliies the coronal knee alignment. The purpose of this study was therefore (1) to investigate the coronal knee alignment in non-osteoarthritic knees using 3D-reconstructed CT images and (2) to introduce a classiication system for the overall knee alignment based on phenotypes. Methods The hospital registry was searched for patients younger than 45 years and older than 16, who received a CT according to the Imperial Knee Protocol. Patients with prosthesis, osteoarthritis, fractures or injury of the collateral ligaments were excluded. Finally, 308 non-osteoarthritic knees of 160 patients remained (102 males and 58 females, mean age ± standard deviation (SD) 30 ± 7 years). The overall lower limb alignment was deined as the hip-knee-ankle angle (HKA), which is formed by lines connecting the centers of the femoral head, the knee and the talus. The angle was measured using a commercially planning software (KneePLAN 3D, Symbios, Yverdon les Bains, Switzerland). Descriptive statistics, such as means, ranges, and measures of variance (e.g., standard deviations) are presented. Based on these results, the currently used classiication system was evaluated and a new system, based on phenotypes, was introduced. These phenotypes consist of a phenotype-speciic mean value (a HKA value) and cover a range of ± 1.5° from this mean (e.g., 183° ± 1.5°). The mean values represent 3° increments of the angle starting from the overall mean value (mean HKA = 180°; 3° increments = 183° and 177°, 186° and 174°). The distribution of these limb phenotypes was assessed. ResultsThe overall mean HKA was 179.7° ± 2.9° varus and values ranged from 172.6° varus to 187.1° valgus. The mean HKA values for male and female were 179.2° ± 2.8° and 180.5° ± 2.8°, respectively, which implied a signiicant gender difference (r 2 = 0.23). The most common limb phenotype in males was NEU HKA 0° (36.4%), followed by VAR HKA 3° (29.2%) and VAL HKA 3° (23.1%). The most common limb phenotype in females was NEU HKA 0° (36.4%), followed by VAL HKA 3° (22.1%) and VAR HKA 3° (15.0%). ConclusionThe measurements using 3D-reconstructed CT images conirmed the great variability of the overall lower limb alignment in non-osteoarthritic knees. However, the currently used classiication system (neutral, varus, valgus) oversimpliies the coronal alignment and therefore the introduced classiication system, based on limb phenotypes, should be used. This will help to better understand individual coronal knee alignment. Level of evidence Level III, retrospective cohort study.

Custom total knee arthroplasty facilitates restoration of constitutional coronal alignment

“…The theoretical benefits of custom TKA based on computed tomography (CT) reconstructions include the differentiation of constitutional versus arthritic bony deformities, as well as identification of the native femoral and tibial axes [11]. This concept has the potential to reduce boneimplant mismatch and preserve or restore CA within predetermined limits, to maintain the native overall phenotype while allowing correction of severe deformities [14][15][16]. The purpose of this study was to describe the strategy for coronal alignment using a CT-based custom TKA system and to evaluate the agreement between the planned and postoperative Hip-Knee-Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA).…”

Reoperations are few and confined to the most valgus phenotypes 4 years after unrestricted calipered kinematically aligned TKA

“…The TMA was the medial angle between the proximal tibial joint line and the mechanical axis of the tibia (varus < 90° and valgus > 90°) The HKA angle was the intersection of a line connecting the mechanical axes of the femur and tibia (varus was positive and valgus was negative). Each measurement was assigned to a phenotype category [6,7]. Between September 2019 and March 2020, one observer (MKG) independent from the treating surgeon and blinded to the patient's alignment contacted each patient by e-mail, postal service, and phone.…”

“…The novel concept of categorizing the femoral mechanical angle (FMA), tibial mechanical angle (TMA), and hip-knee-ankle angle (HKA) into phenotypes by Hirschmann brought to light a wide variability in coronal alignment in the young nonosteoarthritic population, suggesting the need for a more individualized approach in total knee arthroplasty (TKA) [6][7][8]. The five FMA, five TMA, and seven HKA phenotypes each have a 3° range constructed from the mean value of the nonosteoarthritic knee.…”

Personalized alignment in total knee arthroplasty: current concepts

“…A systematic review by Moser et al reported that the mean hip knee ankle angle (HKA) ranged from 176.7 to 180.7°in a native nonosteoarthritic knee [9]. The majority of studies in the review (12)(13)(14)(15) did not report a neutral native limb alignment of 180°, apart from Hovinga and Lerner [10] or Khattak et al [11]. The coronal alignment variability in non-osteoarthritic knees raises the question of a limb alignment of 180°is "normal".…”