Change of tibial tuberosity-trochlear groove (TT-TG) distance during total knee arthroplasty had no influence on clinical outcome and anterior knee pain

Purpose The main purpose of this study was to determine whether there is a correlation between the change of tibial tuberosity-trochlear groove (TT-TG) distance and clinical outcomes after total knee arthroplasty (TKA). Methods A total of 52 knees undergoing TKA due to primary osteoarthritis were included in this retrospective study. All patients had pre- and postoperative CT scans. TT-TG distance was measured by two independent observers and the following alignment parameters were measured: hip-knee ankle angle (HKA), femoral mechanical angle (FMA), tibial mechanical angle (TMA), and posterior condylar angle (PCA). Clinical outcome was assessed using Knee Society Score (KSS) pre- and post-operatively and at a minimum of 12-month follow-up. Evidence of AKP was noted from follow-up reports. Pre- and postoperative scores were compared using a paired Student t-test. Pearson correlations were calculated to assess the influence of TT-TG on clinical outcome and of alignment parameters on the change in TT-TG. TT-TG between patients with and without AKP was compared using unpaired Student’s t-test (p < 0.05). Results Neither the absolute postoperative TT-TG nor the amount of change in TT-TG correlated with the post-operative KSS or the change in KSS. Post-operative TT-TG and change in TT-TG did not differ significantly between patients with and patients without AKP. Only the change in FMA showed a correlation with the change in TT-TG (p = 0.01, r = 0.36). Conclusion Despite a missing correlation between outcomes and TT-TG distance in this study, excessive TT-TG distance should be avoided. Furthermore, surgeons need to be aware that changes in femoral joint line orientation might affect TT-TG distance.

Variability of functional knee phenotypes in osteoarthritic knees shows that a more personalized approach in TKA is needed

Aims and Objectives: Recently, the functional knee phenotype concept was introduced as a new system to classify the coronal alignment of the lower limb. Until now, this concept has only been applied to non-osteoarthritic knees. The purpose of this study was therefore to phenotype osteoarthritic knees according to this concept and investigate the distribution of these phenotypes. Materials and Methods: Preoperative CT scans of osteoarthritic knees scheduled for TKA collected between January 2017 and December 2019 in the KneePLAN 3D database (Symbios Orthopédie S.A.) were reviewed for patients meeting the following inclusion criteria: age>50 and <90, no signs of previous fractures, osteotomies and rheumatoid arthritis. A total of 2764 patients (1438 right and 1326 left lower limbs, Male:female ratio 1096 :1668) with a mean age ± standard deviation of 70±8.5years (range 50-90 years) were included. The following coronal alignment parameters were measured using a validated software (KneePLAN 3D, Symbios Orthopédie S.A): hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). Based on these measurements each leg was phenotyped according to the functional knee phenotype concept and the distribution of these phenotypes assessed. A phenotype thereby consists of a phenotype specific mean value (HKA, FMA or TMA value) and covers a range of ± 1.5° from this mean (e.g. 180°± 1.5). The phenotype specific mean values represent 3° increments of the angle starting from the rounded overall mean value of the angle. Results: There were 162 different functional knee phenotypes (122 male, 138 female and 97 mutual). The most common functional knee phenotype in males was VARHKA6°VARFMA3°NEUTMA0° accounting for 8% of all males. The most common functional knee phenotype in females was VARHKA3°NEUFMA0°NEUTMA0° accounting for 9% of the population. The ten most common functional phenotypes account for 50% and 42.8% of all females and males, respectively. Overall, 134 phenotypes accounted each for less than 1% of the total population (all 134 together for 26.4%). Conclusion: The broad variability of functional knee phenotypes in osteoarthritic knees shows that a more personalized TKA realignment strategy is needed. The challenge will be to identify the optimal alignment strategy for each functional knee phenotype.

Functional knee phenotypes - A novel classification for the lower limb alignment based on the native alignment in young non-osteoarthritic patients

Aims and Objectives: In total knee arthroplasty (TKA), the postoperative coronal alignment is a key factor for good clinical outcome. At the same time, the optimal alignment has been under debate recently. This debate usually focuses on the overall limb alignment while the details of the alignment, such as femoral or tibia alignment, are neglected. This might be partly because there is no concept which incorporates all parameters in a comprehensive and simple way. The purpose of this study was therefore to establish such a concept for the coronal knee alignment. Materials and Methods: The hospital registry was searched for patients older than 16 and younger than 45 years, 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 following coronal alignment parameters were measured using a validated software (KneePLAN 3D, Symbios Orthopédie S.A): hip-knee-ankle angle (HKA, angle formed by the lines connecting the centers of the femoral head, the knee and the talus), femoral mechanical angle (FMA, angle between the mechanical axis of the femur and the tangent to the distal femoral condyles) and tibial mechanical angle (TMA, angle between the mechanical axis of the tibia and the tangent to the tibial plateau). Phenotypes for the limb, femur and tibia were defined based on these measurements. A phenotype thereby consists of a phenotype specific mean value (HKA, FMA or TMA value) and covers a range of ± 1.5° from this mean (e.g. 180°± 1.5). The phenotype specific mean values represent 3° increments of the angle starting from the rounded overall mean value of the angle. Results: Out of 125 possible phenotypes, 43 were found in these non-osteoarthritic knees (35 male, 26 female and 18 mutual phenotypes). The most common functional knee phenotype in males was NEUHKA0°NEUFMA0°NEUTMA0° (19%), followed by VARHKA3°NEUFMA0°VARTMA0° (8.2%). The most common phenotype in females was NEUHKA0°NEUFMA0°NEUTMA0° (17.7%), closely followed by NEUHKA0° NEUFMA0°VALTMA0° (16.6%). Conclusion: The functional knee phenotype concept better represents the variability of the coronal knee alignment than the conventional system of valgus, varus and neutral. Furthermore, it should enable a more detailed discussion about the coronal alignment and TKA alignment goals.