Using the Anatomical Axis as an Alternative to the Mechanical Axis to Assess Knee Alignment

Aim: The aim of this study was to derive a pure, unbiased, reliable and accurate objective relationship between the local knee axis measurements through a short knee anteroposterior roentgenogram and the lower limb axis measurement through an orthoroentgenogram. Patients and Methods: Radiographs of 114 patients (114 knees) were evaluated by two independent raters for measurement of lower limb axis on an orthoroentgenogram and the local knee axis on short knee anteroposterior X-ray, which was derived by cropping the orthoroentgenogram by a blinded radiology assistant. The raters measured at two different time-points separated by an interval of 30-day period. Intra-rater and inter-rater reliabilities were calculated by intra-class correlation coefficients and three models were built to establish the relationships of X-ray anatomical axis with orthoroentgenogram anatomical axis, orthoroentgenogram anatomical axis with orthoroentgenogram mechanical axis and X-ray anatomical axis with orthoroentgenogram mechanical axis. Results: For three different measurements, intra-class correlation coefficients of Rater 2 were higher than 0.90 which shows perfect reliability, while that for Rater 1 was low. Furthermore, first measurements were more consistent than the second measurement. There was a strong positive correlation in all the three models except for varus cases in the last. Conclusion: The standardized correlation derived between the two different techniques for measuring knee alignment is fairly comparable with the studies in the past and would serve as a reliable template for future studies concerning relationships between the two, in addition to helping knee surgeons make more reliable and accurate interpretations through local knee axis measurements.

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Mechanical and Anatomical Axis in Total Ankle Arthroplasty

Foot & Ankle Orthopaedics ◽

10.1177/2473011418s00089 ◽

2018 ◽

Vol 3 (3) ◽

pp. 2473011418S0008

Author(s):

Ali-Asgar Najefi ◽

Andrew Goldberg

Keyword(s):

Lower Limb ◽

Mechanical Axis ◽

Normal Group ◽

Total Ankle Arthroplasty ◽

Coronal Plane ◽

Patient Specific ◽

Ankle Arthroplasty ◽

Patient Specific Instrumentation ◽

Significant Difference ◽

Anatomical Axis

Category: Ankle Arthritis Introduction/Purpose: Inadequate correction of alignment in the coronal, sagittal or axial planes will inevitably lead to failure of the Total Ankle Arthroplasty (TAA). The mechanical axis of the lower limb (MAL), the mechanical axis of the tibia (MAT) and the anatomical axis of the tibia (AAT) are three recognized coronal plane measurements using plain radiography. The relationship between anatomical and mechanical axes depends on the presence of femoral or tibial deformities from trauma or inherited conditions, or previous corrective or replacement surgery. Ankle arthroplasty relies heavily on preoperative radiographs or CT scans and the purpose of this study was to assess whether MAL, MAT and AAT are the same in a cohort of patients upon which placement of TAA is considered. Methods: We analysed 75 patients operated on between 2015 and 2016 at a specialist tertiary centre for elective orthopaedic surgery. All patients had a pre-operative long leg radiograph. They were split into 2 groups. The first group had known deformity proximal to the ankle (such as previous tibial or femoral fracture, severe arthritis, or previous reconstructive surgery) and the second group had no clinically detectable deformity. The MAL, MAT and AAT were assessed and the difference between these values was calculated. Results: There were 54 patients in the normal group, and 21 patients in the deformity group. Overall, 25 patients(33%) had a difference between all three axes of less than 1 degree. In 33 patients(44%), there was a difference in one of the axes of ≥2 degrees. There was no significant difference between MAT and AAT in patients in the normal group(p=0.6). 95% of patients had a difference of <1 degree. There was a significant difference between the MAT and AAT in patients in the deformity group(p<0.01). In the normal group, 39 patients(73%) had a difference of <2 degrees between the AAT and MAL. In the deformity group, only 10 patients (48%) had a difference of <2 degrees.In fact, 24% of patients had a difference ≥3 degrees. Conclusion: Malalignment in the coronal plane in TAA may be an issue that we have not properly addressed. Up to 66% of patients without known deformity may have a TAA that is placed at least 1 degree incorrectly relative to the MAL. We recommend the use of full-length lower limb radiographs when planning a TAA in order to plan the placement of implants. The decision to perform extramedullary referencing, intramedullary referencing, or patient specific Instrumentation must be part of the pre-operative planning process.

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Robotic Arm-Assisted Total Knee Arthroplasty in the Setting of Combined Extra-articular Deformities of the Femur and Tibia

Case Reports in Orthopedics ◽

10.1155/2020/5489646 ◽

2020 ◽

Vol 2020 ◽

pp. 1-6

Author(s):

Sharma Cook-Richardson ◽

Rasesh Desai

Keyword(s):

Total Knee Arthroplasty ◽

Surgical Treatment ◽

Treatment Option ◽

Knee Arthroplasty ◽

Mechanical Axis ◽

Robotic Arm ◽

Implant Positioning ◽

Total Knee ◽

Anatomical Axis ◽

Bone Deformities

In this case, we will describe a 68-year-old man with combined femoral and tibial bone deformities who underwent robotic arm-assisted total knee arthroplasty (RATKA) to treat his severe osteoarthritis in the setting of extra-articular deformities that altered the native anatomical axis and the kinematics of the deformed extra-articular bony structures which chronically generated a neomechanical axis. The combination of severe osteoarthritis with extra-articular deformities made the RATKA method the best surgical treatment option taking into account altered kinematics of the native joint which conventional jig-based total knee arthroplasty would not have prioritized during bony cuts and implant positioning. The patient underwent successful knee arthroplasty with robotic arm-assisted technology with restoration of the mechanical axis.

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Comparison of Mechanical Axis of the Limb Versus Anatomical Axis of the Tibia for Assessment of Tibiotalar Alignment in End-Stage Ankle Arthritis

Foot & Ankle International ◽

10.1177/1071100720972664 ◽

2020 ◽

pp. 107110072097266

Author(s):

Alessio Bernasconi ◽

Ali-Asgar Najefi ◽

Andrew J. Goldberg

Keyword(s):

Ankle Joint ◽

Mechanical Axis ◽

Articular Surface ◽

Intraclass Correlation ◽

Coronal Plane ◽

The Mean ◽

The Difference ◽

End Stage ◽

Long Leg Radiographs ◽

Anatomical Axis

Background: Coronal plane ankle joint alignment is typically assessed using the tibiotalar angle (TTA), which relies on the anatomical axis of the tibia (AAT) and the articular surface of the talus as landmarks. Often, the AAT differs from the mechanical axis of the lower limb (MAL). We set out to test our hypothesis that the TTA using the MAL would differ from the TTA measured using the AAT in patients with ankle osteoarthritis. Methods: Standardized standing long leg radiographs of 61 ankles with end-stage osteoarthritis were analyzed. We measured the MAL and the AAT. A line was drawn along the talar articular surface (TA) and the TTA was calculated using both the MAL (MAL-TA) and the AAT (AAT-TA). The mechanical axis of the tibia (MAT) was also recorded and the MAL-MAT angle calculated. The difference between MAL-TA and AAT-TA and its correlation with the MAL-MAT angle were assessed. Intra- and interobserver agreement were measured for MAL-TA and AAT-TA. Results: The mean MAL-TA was 91.4 degrees (95% CI, 88.5-94.4) and the mean AAT-TA was 91.2 degrees (95% CI, 88.6-93.9). The difference ranged from −8.1 to 7.8 degrees, and was greater than 2 and 3 degrees in 42% and 18% of the patients, respectively. The difference, as an absolute value, also strongly correlated with the MAL-MAT angle ( r = 0.91, P < .001). Intra- and interobserver reliability were excellent for both MAL-TA (intraclass correlation coefficient [ICC], 0.93 and 0.91, respectively) and AAT-TA (ICC, 0.91 and 0.89, respectively). Conclusion: We recommend that surgeons consider using the MAL-TA, which relies on long leg radiographs, especially with proximal deformity, to more accurately measure coronal plane ankle joint alignment. Level of Evidence: Level III, retrospective comparative study.

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

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120s00301 ◽

2020 ◽

Vol 8 (5_suppl4) ◽

pp. 2325967120S0030

Author(s):

Lukas Moser ◽

Silvan Hess ◽

Henrik Behrend ◽

Michael Hirschmann

Keyword(s):

Mechanical Axis ◽

Mean Value ◽

Limb Alignment ◽

Knee Alignment ◽

Coronal Alignment ◽

Mean Values ◽

Key Factor ◽

Femoral Mechanical Angle ◽

Tibial Mechanical Angle ◽

Hospital Registry

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.

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Reliability of Roentgenographic Knee Alignment Measurements in Gonarthrosis

The Journal of Knee Surgery ◽

10.1055/s-0037-1603638 ◽

2017 ◽

Vol 31 (04) ◽

pp. 302-305

Author(s):

Teng-Le Huang ◽

Chen-Chie Wang ◽

Kai-Chiang Yang ◽

Chang-Chin Wu

Keyword(s):

Lower Limb ◽

Estimating Equation ◽

Equation Model ◽

Generalized Estimating Equation ◽

Tibial Osteotomy ◽

Knee Alignment ◽

Ankle Joints ◽

Medial Gonarthrosis ◽

Anatomical Axis ◽

Better Than

AbstractA reliable method of measuring knee alignment is critical in the preoperative planning of high tibial osteotomy (HTO). This radiological study, based on the measurements of the mechanical and anatomical axes of the lower limb, aimed to determine which method would be more reliable and reproducible. From 2004 to 2013, 50 consecutive patients (50 knees) with medial gonarthrosis were treated with valgus-producing HTO. Four independent investigators assessed preoperative standing lower limb radiography (including hip, knee, and ankle joints) to measure both anatomical and mechanical axes. We defined a response as a difference in the angle measured by the same investigator using the same method. The covariates were the investigators and methods. To account for both inter- and intraobserver variabilities, all data were evaluated using a generalized estimating equation model. The results revealed that the effect of the investigators was not statistically significant; however, the effect of the measurement method was highly significant (p < 0.0001). The estimated coefficient of the anatomical axis method was negative, indicating that the reproducibility of the anatomical axis method was better than that of the mechanical axis.

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The accuracy of femoral component rotational measurements using computed tomography—a cadaveric study

Arthroplasty ◽

10.1186/s42836-020-00052-6 ◽

2020 ◽

Vol 2 (1) ◽

Author(s):

Onyedikachi Eseonu ◽

Calum Cree ◽

Martin Sambrook ◽

Mark Blyth ◽

Bryn Jones

Keyword(s):

Femoral Component ◽

Clinical Decision Making ◽

Mechanical Axis ◽

Measurement Techniques ◽

Cadaveric Study ◽

Ct Scans ◽

Significant Difference ◽

Posterior Condylar ◽

Anatomical Axis ◽

Posterior Condylar Angle

Abstract Background CT scans can be used to assess the rotational alignment of the femoral component following total knee arthroplasty (TKA). This is done by calculating the posterior condylar angle (PCA). However, the methods used may not account for the biomechanical functionality of the TKA components. This cadaveric study aimed to determine whether the axis of scanning (mechanical or anatomical) alters the results of PCA calculations. Methods CT scans of 12 cadaveric adult femora were performed along the anatomical axis and the mechanical axis. The PCA was determined on each CT scan by measuring the relationship of the prosthetic posterior condyles to the surgical epicondylar axis of the femur. The mechanical and anatomical axis groups were further subdivided into best-fit and multi-slice subgroups. As a control, the posterior condylar angle was also calculated on photographic images of each femur. Bland-Altman plots were used to determine the correlation between the PCA values obtained from the different scanning axes and measurement techniques. Results There was no significant difference between the PCA measurements derived from anatomical and mechanical axis CT scans. The Pearson correlation co-efficient also indicated good correlation between the two scanning axes. Conclusion The axis of scanning does not significantly affect the PCA measurements. Therefore, the measurements may be reliably used for clinical decision-making, regardless of the axis of CT scanning.

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Is Valgus Cut Angle Based on Radiographic Measurements in Total Knee Arthroplasty Really Inaccurate? A Comparison of Two- and Three-Dimensional Measurements

The Journal of Knee Surgery ◽

10.1055/s-0041-1728785 ◽

2021 ◽

Author(s):

LiMing Liu ◽

Kai Lei ◽

Xin Chen ◽

HuaQuan Fan ◽

Liu Yang ◽

...

Keyword(s):

Total Knee Arthroplasty ◽

Knee Arthroplasty ◽

Mechanical Axis ◽

Three Dimensional ◽

Anatomical Landmarks ◽

Radiographic Measurements ◽

Significant Difference ◽

Total Knee ◽

Femoral Mechanical Axis ◽

Anatomical Axis

AbstractRadiographs are widely used to measure distal femoral valgus cut angle (VCA) in total knee arthroplasty (TKA), but its accuracy is controversial. This study used three-dimensional (3D) reconstruction models to verify the accuracy of VCA measurements on radiographs, and explore the correlation of VCA with hip–knee–ankle (HKA) angle and lateral femoral bowing angle (FBA). A total of 444 osteoarthritis knees of 444 patients from August 2016 to June 2018 was included retrospectively. On radiographs, two-dimensional VCA (VCA-2D) was measured between the femoral mechanical axis and the distal femoral anatomical axis, and HKA was measured between the femoral mechanical axis and the tibial mechanical axis. On the coronal projection of computed tomography 3D models, the anatomical landmarks used for VCA-3D measurements were the same as those on the radiographs, FBA was measured between the proximal and distal femoral anatomical axis. The distributions of VCA-2D and VCA-3D were evaluated by means and variances. The correlation between HKA and VCA and between FBA and VCA was explored. There was a statistical difference between VCA-2D and VCA-3D (p < 0.001), but the deviation was very small (0.15 ± 0.69 degrees), 83.3% of the deviations were less than 1 degree. VCA would increase both in 2D and 3D with increasing of FBA and HKA varus. There was no statistically significant difference between VCA-2D and VCA-3D in patients with moderate varus knees (0–8 degrees of varus) and mild bowing femurs (FBA <5 degrees). Overall, the deviation caused by using radiography to measure VCA was negligible. VCA measurements using radiographs were accurate in patients with moderate varus knees and mildly bowed femurs. This study reflects level of evidence III.

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Proximal tibia vara involves the medial shift of the tibial articular surface

Journal of Orthopaedic Surgery ◽

10.1177/2309499020902592 ◽

2020 ◽

Vol 28 (1) ◽

pp. 230949902090259 ◽

Cited By ~ 2

Author(s):

Makoto Kawasaki ◽

Ryuji Nagamine ◽

Weijia Chen ◽

Yuan Ma ◽

Akinori Sakai ◽

...

Keyword(s):

Proximal Tibia ◽

Mechanical Axis ◽

Articular Surface ◽

Varus Deformity ◽

Tibia Vara ◽

True Alignment ◽

Digital Radiograph ◽

Total Knee ◽

Two Parameters ◽

Anatomical Axis

Purpose: According to the concept of the constitutional varus, the tibial articular surface (TAS) has varus inclination. On the other hand, it has been reported that proximal tibia vara involved medial shift of the TAS. However, it has not been assessed whether varus inclination of the TAS has a correlation with the medial shift. We investigated whether varus inclination of the TAS has a correlation with the medial shift. If there is a correlation between two parameters, the influence of the medial shift of the TAS on the value of the hip–knee–ankle (HKA) angle and the femorotibial angle should be considered. Methods: A total of 112 patients who underwent total knee arthroplasty had anteroposterior view tibia digital radiograph on which five parameters were analyzed. Varus angle of the TAS, the distance between the mechanical axis and the anatomical axis on the articular surface, and the width of the articular surface were measured. Results: The more the proximal tibia had varus deformity, the more the TAS shift medially would be. Therefore, the mechanical axis does not match the anatomical axis. Because the HKA angle was assessed based on the concept that the mechanical and anatomical axes match on the tibia, this angle may not express the true alignment of the lower extremity in knees with proximal tibia vara. Conclusion: In varus knees, the proximal tibia has a medial shift of the TAS that may influence the value of the HKA angle.

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Tibial Mechanical Axis Is Nonorthogonal to the Floor in Varus Knee Alignment

Arthroplasty Today ◽

10.1016/j.artd.2021.03.009 ◽

2021 ◽

Vol 8 ◽

pp. 237-242

Author(s):

Stefano A. Bini ◽

Christopher C. Chung ◽

Scott A. Wu ◽

Erik N. Hansen

Keyword(s):

Mechanical Axis ◽

Varus Knee ◽

Knee Alignment ◽

Tibial Mechanical Axis

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