Estimating soft tissue artifact of the thigh in high knee flexion tasks using optical motion Capture: Implications for marker cluster placement

Quantification of soft tissue artifacts using CT registration and subject-specific multibody modeling

The potential use of gait analysis for quantitative preoperative planning in total hip arthroplasty (THA) has previously been demonstrated. However, the joint kinematic data measured through this process tend to be unreliable for surgical planning due to distortions caused by soft tissue artifacts (STAs). In this study, we developed a novel motion capture framework by combining computed tomography (CT)-based postural calibration and subject-specific multibody dynamics modeling to prevent the effect of STAs in measuring hip kinematics. Three subjects with femoroacetabular impingement syndrome were recruited, and CT data for each patient were collected by attaching marker clusters near the hip. A subject-specific multibody hip joint model was developed based on reconstructed CT data. Spring-dashpot network calculations were performed to minimize the distance between the anatomical landmark and its corresponding infrared reflective marker. The STAs of the thigh was described as six degrees of freedom viscoelastic bushing elements, and their parameter values were identified via smooth orthogonal decomposition. Least squares optimization was used to modify the pelvic rotations to compensate for the rigid components of STAs. The results showed that CT-assisted motion tracking enabled the successful identification of STA influences in gait and squat positions. Furthermore, STA effects were found to alter maximal pelvis tilt and hip rotations during a squat. Compared to other techniques, such as dual fluoroscopic imaging, the adopted framework does not require additional medical imaging for patients undergoing robot-assisted THA surgery and is thus a practical way of evaluating hip joint kinematics for preoperative surgical planning.

IMU positioning affects range of motion measurement during squat motion analysis

Inertial Measurement Units (IMUs) provides embedded and accessible (financially and technically speaking) motion analysis for sports or clinical applications (rehabilitation, therapy…). Despite being advertised for it ease of use, the very nature of IMU sensor makes it prone to errors which are usually corrected through calibration processes thus adding extra complexity for the users. The main goal of this study is to estimate the effect of sensor positioning on the thigh for a simple assessment of squat motion range of motion (ROM) as could be done in a pragmatic clinical approach (i.e., without prior calibration). Kinematics, squat counts and timing of three IMU sensors along the thigh were recorded during squat motion and compared to an optoelectronic reference system. Results showed concordance coefficients of the IMU system over 0.944 without the need for calibration with a preference for placement on the distal part of the segment regarding kinematics data.

Can Anthropometry be Used to Dictate Participant-Specific Thigh Marker Placements Which Minimize Error in Hip Joint Center Estimation?

Specific participant characteristics may be leveraged to dictate marker placements which reduce soft tissue artifact; however, a better understanding of the relationships between participant characteristics and soft tissue artifact are first required. The purpose of this study was to assess the accuracy in which measures of whole-body and thigh anthropometry could predict mislocation error of the hip joint center, tracked using skin-mounted marker clusters. Fifty participants completed squatting and kneeling, while pelvis and lower limb motion were recorded. The effect of soft tissue artifact was estimated from 6 rigid thigh marker clusters by evaluating their ability to track the position of the hip joint center most like the pelvis cluster. Eighteen backward stepwise linear regressions were performed using 10 anthropometric measures as independent variables and the mean of the peak difference between the thigh and pelvis cluster-tracked hip joint centers. Fourteen models significantly predicted error with low to moderate fit (R = .38-.67), explaining 14% to 45% of variation. Partial correlations indicated that soft tissue artifact may increase with soft tissue volume and be altered by local soft tissue composition. However, it is not recommended that marker placement be adjusted based on anthropometry alone.

Model-Based Acetabular Cup Orientation Optimization Based On Minimizing the Risk of Edge-Loading and Implant Impingement Following Total Hip Arthroplasty

In this paper, a computationally-efficient model-based method for determining patient-specific optimal acetabular cup alignment for total hip arthroplasty (THA) is presented. The proposed algorithm minimizes the risk of implant impingement and edge-loading, which are reported as the major causes of hip dislocation following THA. First, by using motion capture data recorded from the patient performing different daily activities, the hip contact force and the relative orientation of the femur and pelvis are calculated by a musculoskeletal model. Then, by defining two quantitative indices i.e., angular impingement distance and angular edge-loading distance, the risk of impingement and edge-loading are assessed for a wide range of cup alignments. And finally, three optimization criteria are introduced to estimate the optimal cup alignment with a tradeoff between the risk of impingement and edge-loading. The results show that patient-specific characteristics such as pelvic tilt could significantly change the optimal cup alignment, especially the value of cup anteversion. Therefore, in some cases, the well-known Lewinnek safe zone may not be optimal, or even safe. Unlike other dynamic model-based methods, in this work, the need for force plate measurements is eliminated by estimating the ground reaction forces and moments, which makes this method more practical and cost-efficient. Furthermore, the low computational complexity due to analytical formulas makes this method suitable for both preoperative and intra-operative planning.