Phenotyping the knee in young non-osteoarthritic knees shows a wide distribution of femoral and tibial coronal alignment

Purpose To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (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). Methods From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT-based posterior-stabilized cemented custom TKA. In addition to a preoperative CT-scan, pre-and post-operative radiographs of weight-bearing long leg, anterior-posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CTbased three-dimensional (3D) models enabled to correct for cases with bony wear by referring to the non-worn areas and to estimate the native pre-arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a 'target zone' based on three criteria: 1) a ± 3° (range 87°-93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°-95°); 3) a planned HKA angle range of 175°-183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra-class correlation coefficients (ICC). Results Preoperative radiograph and CT-scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the 'target zone', whereas postoperative radiographs revealed that 217 (84%) TKAs were in the 'target zone'. Deviation from the planned angles were − 0.5° ± 1.8° for FMA, − 0.5° ± 1.8° for TMA, and − 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472). Conclusion Using this strategy for coronal alignment, 84% of custom TKAs were within the 'target zone' for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory 'personalised alignment' that can further be improved by customisation of implant components. Level of evidence IV.

Section: Introductionmentioning

confidence: 99%

Custom total knee arthroplasty facilitates restoration of constitutional coronal alignment

Bonnin

Beckers

Leon

et al. 2020

“…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.…”

Section: Methodsmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Howell

Gill

Shelton

et al. 2021

Purpose The present study determined the postoperative phenotypes after unrestricted calipered kinematically aligned (KA) total knee arthroplasty (TKA), whether any phenotypes were associated with reoperation, implant revision, and lower outcome scores at 4 years, and whether the proportion of TKAs within each phenotype was comparable to those of the nonarthritic contralateral limb. Methods From 1117 consecutive primary TKAs treated by one surgeon with unrestricted calipered KA, an observer identified all patients (N = 198) that otherwise had normal paired femora and tibiae on a long-leg CT scanogram. In both legs, the distal femur–mechanical axis angle (FMA), proximal tibia–mechanical axis angle (TMA), and the hip–knee–ankle angle (HKA) were measured. Each alignment angle was assigned to one of Hirschmann’s five FMA, five TMA, and seven HKA phenotype categories. Results Three TKAs (1.5%) underwent reoperation for anterior knee pain or patellofemoral instability in the subgroup of patients with the more valgus phenotypes. There were no implant revisions for component loosening, wear, or tibiofemoral instability. The median Forgotten Joint Score (FJS) was similar between phenotypes. The median Oxford Knee Score (OKS) was similar between the TMA and HKA phenotypes and greatest in the most varus FMA phenotype. The phenotype proportions after calipered KA TKA were comparable to the contralateral leg. Conclusion Unrestricted calipered KA’s restoration of the wide range of phenotypes did not result in implant revision or poor FJS and OKS scores at a mean follow-up of 4 years. The few reoperated patients had a more valgus setting of the prosthetic trochlea than recommended for mechanical alignment. Designing a femoral component specifically for KA that restores patellofemoral kinematics with all phenotypes, especially the more valgus ones, is a strategy for reducing reoperation risk. Level of evidence Therapeutic, Level III

“…In a recent computed tomography (CT) study of 308 non-arthritic knees, Hirschmann et al [10] estimated that native limb alignment in men and women, respectively, corresponds to MA in 4% and 6%, to AA in 17% and 18%, and to rKA in 45% and 51%. Although patient-specific alignment techniques would maintain native alignment of all knees, safe ranges for postoperative residual varus or valgus remain unknown [2,[8][9][10] leading some surgeons to opt for hybrid alignment [18].…”

Section: Introductionmentioning

confidence: 99%

Higher satisfaction after total knee arthroplasty using restricted inverse kinematic alignment compared to adjusted mechanical alignment

Grave

Luyckx

Claeys

et al. 2020

Purpose Various alignment philosophies for total knee arthroplasty (TKA) have been described, all striving to achieve excellent long-term implant survival and good functional outcomes. In recent years, in search of higher functionality and patient satisfaction, a shift towards more tailored and patient-specific alignment is seen. The purpose of this study was to describe a restricted 'inverse kinematic alignment' (iKA) technique, and to compare clinical outcomes of patients that underwent robotic-assisted TKA performed by restricted iKA vs. adjusted mechanical alignment (aMA). Methods The authors reviewed the records of a consecutive series of patients that received robotic-assisted TKA with restricted iKA (n = 40) and with aMA (n = 40). Oxford Knee Score (OKS) and satisfaction on a visual analogue scale (VAS) were collected at a follow-up of 12 months. Clinical outcomes were assessed according to patient acceptable symptom state (PASS) thresholds, and uni-and multivariable linear regression analyses were performed to determine associations of OKS and satisfaction with six variables (age, sex, body mass index (BMI), preoperative hip-knee-ankle (HKA) angle, preoperative OKS, alignment technique). Results The restricted iKA and aMA techniques yielded comparable outcome scores (p = 0.069), with OKS, respectively, 44.6 ± 3.5 and 42.2 ± 6.3. VAS Satisfaction was better (p = 0.012) with restricted iKA (9.2 ± 0.8) compared to aMA (8.5 ± 1.3). The number of patients that achieved OKS and satisfaction PASS thresholds was significantly higher (p = 0.049 and p = 0.003, respectively) using restricted iKA (98% and 80%) compared to aMA (85% and 48%). Knees with preoperative varus deformity, achieved significantly (p = 0.025) better OKS using restricted iKA (45.4 ± 2.0) compared to aMA (41.4 ± 6.8). Multivariable analyses confirmed better OKS (β = 3.1; p = 0.007) and satisfaction (β = 0.73; p = 0.005) with restricted iKA. Conclusions The results of this study suggest that restricted iKA and aMA grant comparable clinical outcomes at 12-month follow-up, though a greater proportion of knees operated by restricted iKA achieved the PASS thresholds for OKS and satisfaction. Notably. in knees with preoperative varus deformity, restricted iKA yielded significantly better OKS and satisfaction than aMA. Level of evidence Level III, comparative study.