Selective dorsal rhizotomy and its effect on muscle force during walking: A comprehensive study.

Selective dorsal rhizotomy (SDR) is commonly used to permanently reduce spasticity in children with cerebral palsy (CP). However, studies have yielded varying results regarding muscle strength and activity after SDR. Some studies indicate weakness or no changes, while a recent study using NMSK simulations demonstrates improvements in muscle forces during walking. These findings suggest that SDR may alleviate spasticity, reducing dynamic muscle constraints and enhancing muscle force without altering muscle activity during walking in children with CP. In this study, we combined NMSK simulations with physical examinations to assess children with CP who underwent SDR, comparing them to well-matched peers who did not undergo the procedure. Each group (SDR and No-SDR) included 81 children, with pre- and post-SDR assessments. Both groups were well-matched in terms of demographics, clinical characteristics, and gait parameters. The results of the physical examination indicate that SDR significantly reduces spasticity without impacting muscle strength. Furthermore, our findings show no significant differences in gait deviation index improvements and walking speed between the two groups. Additionally, there were no statistically significant changes in muscle activity during walking before and after SDR for both groups. NMSK results demonstrate a significant increase in muscle force in the semimembranosus and calf muscles during walking, compared to children with CP who received other clinical treatments. Our findings confirm that although SDR does not significantly impact muscle strength compared to other treatments, it creates a more favorable dynamic environment for suboptimal muscle force production, which is essential for walking.

Selective dorsal rhizotomy: Analysis of two rootlet sectioning techniques.

OBJECTIVE: To analyze and compare the efficacy of two selective dorsal rhizotomy (SDR) techniques with intraoperative neurophysiological monitoring, using instrumented three-dimensional gait analysis. INTRODUCTION: SDR is a common, irreversible surgical treatment increasingly used to address gait disturbances in children with chronic non-progressive encephalopathy by reducing spasticity. Various techniques have been used, which mainly differ in the percentage of rootlets selected for sectioning. A greater proportion of rootlets sectioned leads to a more effective reduction of spasticity; however, there is a potential risk of unwanted neurological effects resulting from excessive deafferentation. While there is evidence of the short- and long-term benefits and complications of SDR, no studies have compared the effectiveness of each technique regarding gait function and preservation of the force-generating capacity of the muscles. MATERIALS AND METHODS: Instrumented three-dimensional gait analysis was used to evaluate two groups of patients with spastic cerebral palsy treated by the same neurosurgeon in different time periods, initially using a classic technique (cutting 50% of the nerve rootlets) and subsequently a conservative technique (cutting no more than 33% the nerve rootlets). RESULTS: In addition to an increase in knee joint range of motion (ROM), in children who underwent SDR with the conservative technique, a statistically significant increase (p = 0.04) in the net joint power developed by the ankle was observed. Patients who underwent SDR with the conservative technique developed a maximum net ankle joint power of 1.37 ± 0.61 (unit: W/BW), whereas those who were operated with the classic technique developed a maximum net ankle joint power of 0.98 ± 0.18 (unit: W/BW). The conservative group not only showed greater improvement in net ankle joint power but also demonstrated more significant enhancements in minimum knee flexion during the stance phase and knee extension at initial contact. CONCLUSION: Our results show that both techniques led to a reduction in spasticity with a positive impact on the gait pattern. In addition, patients treated with the conservative technique were able to develop greater net ankle joint power, leading to a better scenario for rehabilitation and subsequent gait.

Individual muscle force-energy rate is altered during crouch gait: A neuro-musculoskeletal evaluation.

Children with pathological movement patterns like crouch gait present with excessive knee and hip flexion during stance phase due to multiple factors. A good treatment requires that the primary factor is reduced or eliminated to optimise the relationship between muscle energy expenditure and muscle force production during walking. In this way, neuro-musculoskeletal simulations are reliable tools to evaluate how individual muscles contribute to gait. However, previous studies have reported that changes in energy consumed per unit time have not correlated with crouch gait severity. In this study, EMG-informed musculoskeletal simulations combined with analytical approaches (which include altered muscle composition and morphology presented in children with CP) were used to evaluate individual muscle force, energy expenditure and their relationship in five typically developing children and eleven children with different degrees of crouch gait severity. In agreement with the literature, our results show an increase in Watts required per Newton of muscle force during walking in children with crouch gait when compared to unimpaired gait. This is true for all levels of crouch but does not correlate with severity. Hamstrings required more than three times the muscle energy per Newton of muscle force during crouch gait compared with unimpaired gait. Also, a different strategy in muscle force-energy rate of quadriceps and plantarflexors muscle groups was present in crouch gait. Finally, our results showed weakness in hamstrings and gastrocnemius with an increment in their muscle energy expenditures during moderate and severe crouch gait. This could suggest that well controlled strength training (i.e. personalised and designed to improve both the muscle strength and functional mobility) focused in these muscle groups could improve knee extension of these children by providing a more efficient plantarflexor-knee extension couple during stance phase (action of the ankle plantarflexor muscles to control the progress of the tibia over the foot and the knee kinetics) and more control of the distal limb at initial contact. However, strength training of hamstrings only could be better for children with mild crouch gait.

A regularized functional method to determine the hip joint center of rotation in subjects with limited range of motion.

The symmetrical center of rotation estimation (SCoRE) is probably one of the most used functional method for estimating the hip join center (HJC). However, it requires of complex multi-plane movements to find accurate estimations of HJC. Thus, using SCoRE for people with limited hip range of motion will lead to poor HJC estimation. In this work, we propose an anisotropic regularized version of the SCoRE formulation (RSCoRE), which is able to estimate the HJC location by using only standard gait trials, avoiding the need of recording complex multi-plane movements. RSCoRE is evaluated in both accuracy and repeatability of the estimation as compared to functional and predictive methods on a self-recorded cohort of fifteen young healthy adults with no hip joint pathologies or other disorders that could affect their gait. Given that, no medical images were available for this study, to quantify the global error of HJC the SCoRE residual was used. RSCoRE presents a global error of about 12 mm, similarly to the best performance of SCoRE. The comparison of the coordinate's errors at each coordinate indicates that HJC estimations from SCoRE with complex multi-plane movements and RSCoRE are not statistical significantly different. Finally, we show that the repeatability of RSCoRE is similar to the rest of the tested methods, yielding to repeatability values between 0.72 and 0.79. In conclusion, not only the RSCoRE yields similar estimation performance than SCoRE, but it also avoids the need of complex multi-plane movements to be performed by the subject of analysis. For this reason, RSCoRE has the potential to be a valuable approach for estimating the HJC location in people with limited hip ROM.

Minimum toe clearance and tripping probability in people with unilateral transtibial amputation walking on ramps with different prosthetic designs.

BACKGROUND: Minimum Toe Clearance (MTC) is defined as the minimum vertical distance between the lowest point under the front part of the foot and the ground, during mid-swing. Low values of MTC and walking on inclines are both related to higher probability of tripping and falling in lower limb amputees. New prosthetic designs aim at improving MTC, especially on ramps, however the real effect on MTC still needs investigation. The objective of this study was then to evaluate the effect of different prosthetic designs on MTC in inclined walking. METHODS: Thirteen transtibial amputees walked on a ramp using three different prostheses: non articulating ankle (NAA), articulating hydraulic ankle (AHA), and articulating hydraulic ankle with microprocessor (AHA-MP). Median MTC, coefficient of variation (CV), and tripping probability (TP) for obstacles of 10 and 15 mm were compared across ankle type in ascent and descent. FINDINGS: When using AHA-MP, larger MTC median values for ascending (P ≤ 0.001, W = 0.58) and descending the ramp (P = 0.003, W = 0.47) were found in the prosthetic limb. Also significantly lower CV was found on the prosthetic limb for both types of AHA feet when compared to NAA for descending the ramp (P = 0.014, W = 0.45). AHA-MP showed the lowest TP for the prosthetic leg in three conditions evaluated. On the sound limb results showed the median MTC was significantly larger (P = 0.009, W = 0.43) and CV significantly lower (P = 0.005, W = 0.41) when using an AHA in ascent. INTERPRETATION: Both AHA prosthetic designs help reduce the risk of tripping of the prosthetic limb by increasing the median MTC, lowering its variability and reducing TP for both legs when ascending and descending the ramp. For most of the conditions, AHA-MP showed the lowest TP values. Findings suggest that AHA prostheses, especially AHA-MP could reduce the risk of tripping on ramps in amputees.

Assessment of the energy-related cost function over a range of walking speeds.

Cost funtions are needed for calculation of muscle forces in musculoskeletal models. The behavior of the energy-related cost function, proposed by Praagman et al. (J Biomech 39(4):758-765, 2006. https://doi.org/10.1016/j.jbiomech.2004.11.034 ) (CFP), can be used as an optimization criteria in musculoskeletal models for studying gait. In particular, in this work, its performance is compared against two empirical phenomenological models at different walking speed conditions. Also, the sensitivity of the CFP function to model parameters, such as muscle mass, maximal isometric muscle force, optimal muscle fiber length and maximum muscle velocity of the contractile element, was analyzed. The obtained results showed that CFP presents different behavior (in terms of the normalized root-mean-squared deviation (NRMSD) and the coefficient of multiple correlation (CMC)) for different muscles. Also, it provided estimates with median of NRMSD between 0.176 and 0.299 and median of CMC between 0.703 and 0.865 both metrics for slow, free and fast walking speed, which could be considered as acceptable results. Furthermore, the results indicated that CFP is insensitive to changes in muscle mass and relatively sensitive to maximal isometric muscle force. However, CFP presented a noisy behavior on estimations of muscle energy rate for some muscle as compared to phenomenological models. Finally, estimations by CFP during gait are within the values obtained by the empirical phenomenological models.

A subject-specific integrative biomechanical framework of the pelvis for gait analysis.

Analysis of the human locomotor system using rigid-body musculoskeletal models has increased in the biomechanical community with the objective of studying muscle activations of different movements. Simultaneously, the finite element method has emerged as a complementary approach for analyzing the mechanical behavior of tissues. This study presents an integrative biomechanical framework for gait analysis by linking a musculoskeletal model and a subject-specific finite element model of the pelvis. To investigate its performance, a convergence study was performed and its sensitivity to the use of non-subject-specific material properties was studied. The total hip joint force estimated by the rigid musculoskeletal model and by the finite element model showed good agreement, suggesting that the integrative approach estimates adequately (in shape and magnitude) the hip total contact force. Previous studies found movements of up to 1.4 mm in the anterior-posterior direction, for single leg stance. These results are comparable with the displacement values found in this study: 0-0.5 mm in the sagittal axis. Maximum von Mises stress values of approximately 17 MPa were found in the pelvic bone. Comparing this results with a previous study of our group, the new findings show that the introduction of muscular boundary conditions and the flexion-extension movement of the hip reduce the regions of high stress and distributes more uniformly the stress across the pelvic bone. Thus, it is thought that muscle force has a relevant impact in reducing stresses in pelvic bone during walking of the finite element model proposed in this study. Future work will focus on including other deformable structures, such as the femur and the tibia, and subject-specific material properties.

Estimation of muscle forces in gait using a simulation of the electromyographic activity and numerical optimization.

Clinical gait analysis provides great contributions to the understanding of gait patterns. However, a complete distribution of muscle forces throughout the gait cycle is a current challenge for many researchers. Two techniques are often used to estimate muscle forces: inverse dynamics with static optimization and computer muscle control that uses forward dynamics to minimize tracking. The first method often involves limitations due to changing muscle dynamics and possible signal artefacts that depend on day-to-day variation in the position of electromyographic (EMG) electrodes. Nevertheless, in clinical gait analysis, the method of inverse dynamics is a fundamental and commonly used computational procedure to calculate the force and torque reactions at various body joints. Our aim was to develop a generic musculoskeletal model that could be able to be applied in the clinical setting. The musculoskeletal model of the lower limb presents a simulation for the EMG data to address the common limitations of these techniques. This model presents a new point of view from the inverse dynamics used on clinical gait analysis, including the EMG information, and shows a similar performance to another model available in the OpenSim software. The main problem of these methods to achieve a correct muscle coordination is the lack of complete EMG data for all muscles modelled. We present a technique that simulates the EMG activity and presents a good correlation with the muscle forces throughout the gait cycle. Also, this method showed great similarities whit the real EMG data recorded from the subjects doing the same movement.

Model to estimate hamstrings behavior in cerebral palsy patients: as a pre-surgical clinical diagnosis tool.

Crouch gait is the most common motion abnormality in children with cerebral palsy (CP). This paper presents a new biomechanical model based on a simple rescaling and adjustment to CP patients who develop crouch gait by subject-specific anthropometric data. The model estimates the length of hamstrings, as the distance between the origin and insertion of the muscle, and the velocity of shortening of hamstrings by the first derivative of the length with respect to time. This model has the potential to increase the benefits of three-dimensional biomechanical models as it can discriminate between short, spastic or normal hamstrings. The main advantage of this model in clinical use is that it does not require costly magnetic resonance imaging.