Abstract
Some approaches in total knee arthroplasty aim for an oblique joint line to achieve an even medio-lateral load distribution across the condyles during the stance phase of gait. While there is much focus on the angulation of the joint line in static frontal radiographs, precise knowledge of the associated dynamic joint line orientation and the internal joint loading is limited. The aim of this study was to analyze how static alignment in frontal radiographs relates to dynamic alignment and load distribution, based on direct measurements of the internal joint loading and kinematics. A unique and novel combination of telemetrically measured in vivo knee joint loading and simultaneous internal joint kinematics derived from mobile fluoroscopy (“CAMS-Knee dataset”) was employed to access the dynamic alignment and internal joint loading in 6 TKA patients during level walking. Static alignment was measured in standard frontal postoperative radiographs while external adduction moments were computed based on ground reaction forces. Both static and dynamic parameters were analyzed to identify correlations using linear and non-linear regression. At peak loading during gait, the joint line was tilted laterally by 4°–7° compared to the static joint line in most patients. This dynamic joint line tilt did not show a strong correlation with the medial force (R 2: 0.17) or with the mediolateral force distribution (pseudo R 2: 0.19). However, the external adduction moment showed a strong correlation with the medial force (R 2: 0.85) and with the mediolateral force distribution (pseudo R 2: 0.78). Alignment measured in static radiographs has only limited predictive power for dynamic kinematics and loading, and even the dynamic orientation of the joint line is not an important factor for the medio-lateral knee load distribution. Preventive and rehabilitative measures should focus on the external knee adduction moment based on the vertical and horizontal components of the ground reaction forces.
Highlights
In Total Knee Arthroplasty (TKA), frontal plane geometry is usually determined using static standing radiographs, where the alignment is mainly quantified by: 1) the relative orientation of the femoral and tibial mechanical axes and 2) the orientation of the joint line to the mechanical axes
The standard implantation approach in orthopedics has been to use the Mechanical Alignment Technique (MAT), which aims for a joint line that is orthogonal to a neutral mechanical axis
Alternative techniques involving a joint line that is oblique to the mechanical axis, like Anatomical Alignment Technique (AAT) (Hungerford et al, 1982) and Kinematic Alignment Technique (KAT) (Howell and Hull, 2014), have been proposed to address the issues of MAT
Summary
In Total Knee Arthroplasty (TKA), frontal plane geometry is usually determined using static standing radiographs, where the alignment is mainly quantified by: 1) the relative orientation of the femoral and tibial mechanical axes (varus-valgus of the leg) and 2) the orientation of the joint line to the mechanical axes. These measures are used to infer the mechanical conditions in the joint, and form the basis for different alignment techniques in knee joint reconstruction. One rationale behind an oblique joint line is that during the single leg support phase of gait, the mechanical axis of the leg is assumed
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