Gerlinde Lenaerts

Evaluation of the effect of backpack load and position during standing and walking using biomechanical, physiological and subjective measures

Recommendations on backpack loading advice restricting the load to 10% of body weight and carrying the load high on the spine. The effects of increasing load (0%–5%–10%–15% of body weight) and changing the placement of the load on the spine, thoracic vs. lumbar placement, during standing and gait were analysed in 20 college-aged students by studying physiological, biomechanical and subjective data. Significant changes were: (1) increased thorax flexion; (2) reduced activity of M. erector spinae vs. increased activation of abdominals; (3) increased heart rate and Borg scores for the heaviest loads. A trend towards increased spinal flexion, reduced pelvic anteversion and rectus abdominis muscle activity was observed for the lumbar placement. The subjective scores indicate a preference for the lumbar placement. These findings suggest that carrying loads of 10% of body weight and above should be avoided, since these loads induce significant changes in electromyography, kinematics and subjective scores. Conclusions on the benefits of the thoracic placement for backpack loads could not be drawn based on the parameter set studied.

Subject-specific hip geometry and hip joint centre location affects calculated contact forces at the hip during gait

Hip loading affects the development of hip osteoarthritis, bone remodelling and osseointegration of implants. In this study, we analyzed the effect of subject-specific modelling of hip geometry and hip joint centre (HJC) location on the quantification of hip joint moments, muscle moments and hip contact forces during gait, using musculoskeletal modelling, inverse dynamic analysis and static optimization. For 10 subjects, hip joint moments, muscle moments and hip loading in terms of magnitude and orientation were quantified using three different model types, each including a different amount of subject-specific detail: (1) a generic scaled musculoskeletal model, (2) a generic scaled musculoskeletal model with subject-specific hip geometry (femoral anteversion, neck-length and neck-shaft angle) and (3) a generic scaled musculoskeletal model with subject-specific hip geometry including HJC location. Subject-specific geometry and HJC location were derived from CT. Significant differences were found between the three model types in HJC location, hip flexion-extension moment and inclination angle of the total contact force in the frontal plane. No model agreement was found between the three model types for the calculation of contact forces in terms of magnitude and orientations, and muscle moments. Therefore, we suggest that personalized models with individualized hip joint geometry and HJC location should be used for the quantification of hip loading. For biomechanical analyses aiming to understand modified hip joint loading, and planning hip surgery in patients with osteoarthritis, the amount of subject-specific detail, related to bone geometry and joint centre location in the musculoskeletal models used, needs to be considered.

Subject-specific hip geometry affects predicted hip joint contact forces during gait

Hip loading affects bone remodeling and implant fixation. In this study, we have analyzed the effect of subject-specific modeling of hip geometry on muscle activation patterns and hip contact forces during gait, using musculoskeletal modeling, inverse dynamic analysis and static optimization. We first used sensitivity analysis to analyze the effect of isolated changes in femoral neck-length (NL) and neck-shaft angle (NSA) on calculated muscle activations and hip contact force during the stance phase of gait. A deformable generic musculoskeletal model was adjusted incrementally to adopt a physiological range of NL and NSA. In a second similar analysis, we adjusted hip geometry to the measurements from digitized radiographs of 20 subjects with primary hip osteoarthrosis. Finally, we studied the effect of hip abductor weakness on muscle activation patterns and hip contact force. This analysis showed that differences in NL (41-74 mm) and NSA (113-140 degrees ) affect the muscle activation of the hip abductors during stance phase and hence hip contact force by up to three times body weight. In conclusion, the results from both the sensitivity and subject-specific analysis showed that at the moment of peak contact force, altered NSA has only a minor effect on the loading configuration of the hip. Increased NL, however, results in an increase of the three hip contact-force components and a reduced vertical loading. The results of these analyses are essential to understand modified hip joint loading, and for planning hip surgery for patients with osteoarthrosis.

Relation between subject-specific hip joint loading, stress distribution in the proximal femur and bone mineral density changes after total hip replacement

In the prediction of bone remodelling processes after total hip replacement (THR), modelling of the subject-specific geometry is now state-of-the-art. In this study, we demonstrate that inclusion of subject-specific loading conditions drastically influences the calculated stress distribution, and hence influences the correlation between calculated stress distributions and changes in bone mineral density (BMD) after THR. For two patients who received cementless THR, personalized finite element (FE) models of the proximal femur were generated representing the pre- and post-operative geometry. FE analyses were performed by imposing subject-specific three-dimensional hip joint contact forces as well as muscle forces calculated based on gait analysis data. Average values of the von Mises stress were calculated for relevant zones of the proximal femur. Subsequently, the load cases were interchanged and the effect on the stress distribution was evaluated. Finally, the subject-specific stress distribution was correlated to the changes in BMD at 3 and 6 months after THR. We found subject-specific differences in the stress distribution induced by specific loading conditions, as interchanging of the loading also interchanged the patterns of the stress distribution. The correlation between the calculated stress distribution and the changes in BMD were affected by the two-dimensional nature of the BMD measurement. Our results confirm the hypothesis that inclusion of subject-specific hip contact forces and muscle forces drastically influences the stress distribution in the proximal femur. In addition to patient-specific geometry, inclusion of patient-specific loading is, therefore, essential to obtain accurate input for the analysis of stress distribution after THR.

A biomechatronical transtibial prosthesis powered by pleated pneumatic artificial muscles

Due to its high power-to-weight ratio, a pleated pneumatic artificial muscle (PPAM) offers an interesting alternative actuation source for robotic devices. Its inherent compliant behaviour excites another broad field of interest: assistive clinical devices such as powered exoskeletons and prosthetics. In this paper, the design of a pneumatically powered transtibial prosthetic device is presented. A first prototype has been built and provides a preliminary test bed for control algorithm development and testing with able-bodied subjects in laboratory conditions. The characteristics and working principle of a PPAM are described. The design specifications and the mechanical model of the prosthesis are discussed. The mechanical design and the control structure are outlined. Furthermore, some initial walking trials with an able-bodied subject wearing the prosthesis prototype are presented and discussed.

Aberrant pelvis and hip kinematics impair hip loading before and after total hip replacement.

Musculoskeletal loading is an important factor affecting the development of osteoarthritis, bone remodelling and primary fixation of total hip replacement (THR). In this study, we analyzed the relation between muscular force, gait kinematics and kinetics and hip loading in 20 patients before and six weeks after THR. Hip contact forces were calculated from gait analysis data using musculoskeletal modelling, inverse dynamics and static optimization. We found aberrant pelvis and hip kinematics and kinetics before and six weeks after surgery, confirming previous findings in literature. Furthermore, we found a decrease in the total contact force and its vertical component. These changes result in a decrease of the associated inclination angles of the total hip contact force in the sagittal and transverse planes, changing the orientation towards more vertical implant loading after THR. These changes in hip loading were related to observed gait kinematics and kinetics. Most importantly, excessive pelvic obliquity and associated hip adduction related to impaired implant loading. We concluded, therefore, that physical therapy in the early post-operative phase should primarily focus on stretching of anterior and medial structures and strengthening of hip flexors and abductors to achieve normalization of the hip and pelvis kinematics and consequently normalize hip loading.

A pneumatically powered below-knee prosthesis: Design specifications and first experiments with an amputee

This paper reports on the development of a powered below-knee (BK) prosthesis. The initial prosthesis prototype is a pneumatically powered system, which serves as test bed for proof-of-concept and evaluating control algorithms in laboratory conditions. The mechatronical design of the prosthesis is described, including the selection, the characteristics and working principle of its actuators. The control approach is discussed. First experimental results with an amputee are presented that demonstrate the promising performance properties of the powered prosthesis in restoring ankle power to the user in level walking.

Successful Preliminary Walking Experiments on a Transtibial Amputee Fitted with a Powered Prosthesis

This paper presents the results of preliminary walking experiments on a transtibial amputee wearing a powered prosthesis. The prosthesis prototype serves as a proof-of-concept implementation for investigating the potential of pleated pneumatic artificial muscles to power a transtibial prosthesis. The device is equipped with pleated pneumatic artificial muscles, and tethered to a laboratory pressure source. The prosthesis is capable of providing the amputee with 100% of the required push-off torque and it can adapt its joint stiffness to the walking speed. This study supports the hypothesis that a powered transtibial prosthesis with adaptable stiffness might be beneficial to the amputee.

Influence of altered gait patterns on the hip joint contact forces.

Children who exhibit gait deviations often present a range of bone deformities, particularly at the proximal femur. Altered gait may affect bone growth and lead to deformities by exerting abnormal stresses on the developing bones. The objective of this study was to calculate variations in the hip joint contact forces with different gait patterns. Muscle and hip joint contact forces of four children with different walking characteristics were calculated using an inverse dynamic analysis and a static optimisation algorithm. Kinematic and kinetic analyses were based on a generic musculoskeletal model scaled down to accommodate the dimensions of each child. Results showed that for all the children with altered gaits both the orientation and magnitude of the hip joint contact force deviated from normal. The child with the most severe gait deviations had hip joint contact forces 30% greater than normal, most likely due to the increase in muscle forces required to sustain his crouched stance. Determining how altered gait affects joint loading may help in planning treatment strategies to preserve correct loading on the bone from a young age.

From conventional prosthetic feet to bionic feet: A review study

In general, prosthetic feet can be classified in three categories. These are, following the time line: Conventional Feet (CF), Energy-Storing-and-Returning (ESR) feet, and recent so-called dasiabionicpsila feet. Research studies have shown enhanced performance properties of ESR feet compared to early CF. However, even with the advanced technology today, none of the ESR feet is capable of significantly reducing energy cost of walking or enhancing amputeepsilas gait pattern. From the 1990s gradually more attention has been paid to the incorporation of active elements in prosthetics as passive devices are not capable of providing the amputee with sufficient ankle power during gait. Most of these bionic devices are still on research level nowadays but one can expect that they will become available on the market soon. In this paper, the evolution of prosthetic feet over the last two decades is reflected. The importance of mimicking human ankle biomechanics in prosthetic foot design is discussed. Prior work on both objective and subjective evaluation of TT (transtibial = through the lower leg) amputee gait when fitted with different prosthetic feet is reported.