Bert Otten

Development of postural adjustments during reaching in sitting children

We evaluated the development of postural adjustments accompanying reaching movements in sitting children. Twenty-nine typically developing children aged, 2–11 years, and ten adults were studied with multiple surface electromyograms (EMGs) and kinematics during reaching in four conditions: sitting with the seat-surface oriented horizontally with and without an additional task load, and sitting with the seat-surface tilted 15° forward and 15° backward. The development of postural adjustments during reaching in a sitting position turned out to have a non-linear and protracted course, which is not finished by the age of 11 years. The development of these adjustments is characterised by variation, yet specific developmental sequences could be distinguished. Firstly, the development of postural adjustments during reaching from the age of 2 years onwards lacked a preference for an en bloc strategy, which consists of an in concert activation of the direction-specific neck and trunk muscles. Secondly, anticipatory postural muscle activity, which was consistently present in adults, was virtually absent between 2 and 11 years of age. Thirdly, the data demonstrated that with increasing age the head gradually becomes the dominant frame of reference. In addition, the study suggested that, in terms of postural control, the forward-tilted position is the most efficient one.

Kinematic characteristics of reaching movements in preterm children with cerebral palsy

Kinematic characteristics of reaching movements of the dominant arm were assessed in 51 sitting preterm children who were aged 2–11 y and had cerebral palsy (CP), including 33 with spastic hemiplegia and 18 with bilateral CP (Bi-CP). Reference data of 29 typically developing children were present. The results indicated that the quality of reaching movements from the dominant arm of children with CP was significantly worse than that of typically developing children. This held true in particular for the children with Bi-CP. For example, reaching movements of children with CP took more time and consisted less often of one movement unit. The quality of reaching was related to the severity of lesion present on the neonatal ultrasound scan of the brain, the severity of motor disorder, the degree of spasticity, and the ability to perform activities of daily life. The last indicates that movements of the dominant arm in children with spastic hemiplegia and Bi-CP deserve clinical attention.

Optimization of the Anterior Cruciate Ligament Injury Prevention Paradigm: Novel Feedback Techniques to Enhance Motor Learning and Reduce Injury Risk

SYNOPSIS Primary anterior cruciate ligament (ACL) injury prevention programs effectively reduce ACL injury risk in the short term. Despite these programs, ACL injury incidence is still high, making it imperative to continue to improve current prevention strategies. A potential limitation of current ACL injury prevention training may be a deficit in the transfer of conscious, optimal movement strategies rehearsed during training sessions to automatic movements required for athletic activities and unanticipated events on the field. Instructional strategies with an internal focus of attention have traditionally been utilized, but may not be optimal for the acquisition of the control of complex motor skills required for sports. Conversely, external-focus instructional strategies may enhance skill acquisition more efficiently and increase the transfer of improved motor skills to sports activities. The current article will present insights gained from the motor-learning domain that may enhance neuromuscular training programs via improved skill development and increased retention and transfer to sports activities, which may reduce ACL injury incidence in the long term.

Comparative roll-over analysis of prosthetic feet

A prosthetic foot is a key element of a prosthetic leg, literally forming the basis for a stable and efficient amputee gait. We determined the roll-over characteristics of a broad range of prosthetic feet and examined the effect of a variety of shoes on these characteristics. The body weight of a person acting on a prosthetic foot during roll-over was emulated by means of an inverted pendulum-like apparatus. Parameters measured were the effective radius of curvature, the forward travel of the center of pressure, and the instantaneous radius of curvature of the prosthetic feet. Finally, we discuss how these parameters relate to amputee gait.

Kinematic characteristics of postural control during reaching in preterm children with cerebral palsy

The relationships between kinematic characteristics of sitting posture during reaching movements of the dominant arm and 1) the kinematics of the reaching movement itself and 2) functional performance during daily life activities (PEDI) were assessed in 51 sitting preterm children with cerebral palsy (CP). The children were 2–11 y, 33 had spastic hemiplegia (SH) and 18 bilateral CP (Bi-CP). The data were compared with those of 26 typically developing children (TD). Sitting posture before the onset of reaching of children with CP differed from that of TD children: they sat with a more reclined pelvis and a more collapsed trunk. The more reclined pelvic position was associated with a better quality of reaching movements. The different sitting postures of pelvis and trunk were not related to functional performance during daily life activities. Displacement of the head, trunk, and pelvis of the children with CP did not differ from that of the TD children. Nevertheless, in the children with CP a more stable head, a more mobile trunk, and a more stable pelvis were related to better functional performance and/or a better quality of reaching. This suggests that physiotherapeutic guidance of children with CP should focus rather on the latter postural parameters than on the different sitting posture of pelvis and trunk.

Mechanical energy in toddler gait - A trade-off between economy and stability?

SUMMARY Mechanical energy expenditure was investigated in children who are just learning to walk and compared with adult mechanical energy expenditure during walking. First, we determined whether the inverted pendulum (IP) mechanism of energy exchange was present in toddlers. It seems that new walkers partially make use of this energy saving mechanism, but it is less efficient than in adults. The reduced recovery values (R=40% at optimal speeds in toddlers compared to 70% in adults) can be explained by their low self-selected walking speed in combination with their tossing gait (large vertical oscillations of the body) and by the observation that during as much as 25–50% of the gait cycle kinetic and potential energy are oscillating in-phase. The second step was to calculate positive external mechanical work (Wext). Since the IP mechanism is less efficient in toddlers, more mass-specific positive work has to be performed to lift and accelerate the centre of mass than in adults walking at the same speed, even when differences in body size are taken into account. The amount of positive internal work (Wint,k) necessary to move the body segments relative to the centre of mass was the third parameter we calculated. In toddlers Wint,k is largely determined by the kinetic energy of the lower limb. Compared to adults, toddlers have to perform less mass-specific work per unit distance to accelerate the body segments since the upper body is kept relatively stiff during walking and there is no arm swing. Apart from work performed on the centre of mass and work performed to move the body segments relative to the centre of mass, when walking some work is also performed during double contact as both legs are pushing against each other. Two methods were used to calculate this amount of work, both leading to the same conclusions. Mass-specific work during double contact is small in toddlers compared to adults because of their low walking speed. Finally the total amount of mechanical work performed in toddlers was compared to the work production observed in adults. Wext seems to be the major determinant for total mechanical energy expenditure. At intermediate froude numbers work production is comparable between adults and toddlers, but at low and high froude numbers Wtot increases due to the steep increases in Wext. Despite the fact that mechanical work requirements in toddler gait are underestimated if work during double contact is not taken into account, it is not a major determinant of the energy cost of walking.

Recovery of Motor Imagery Ability in Stroke Patients

Objective. To investigate whether motor imagery ability recovers in stroke patients and to see what the relationship is between different types of imagery and motor functioning after stroke. Methods. 12 unilateral stroke patients were measured at 3 and 6 weeks poststroke on 3 mental imagery tasks. Arm-hand function was evaluated using the Utrecht Arm-Hand task and the Brunnström Fugl-Meyer Scale. Age-matched healthy individuals (N = 10) were included as controls. Results. Implicit motor imagery ability and visual motor imagery ability improved significantly at 6 weeks compared to 3 weeks poststroke. Conclusion. Our study shows that motor imagery can recover in the first weeks after stroke. This indicates that a group of patients who might not be initially selected for mental practice can, still later in the rehabilitation process, participate in mental practice programs. Moreover, our study shows that mental imagery modalities can be differently affected in individual patients and over time.

Effect of Seat Surface Inclination on Postural Control During Reaching in Preterm Children With Cerebral Palsy

Background and Purpose Because it is debatable whether seat surface inclination improves motor function in children with cerebral palsy (CP), the effect of seat surface tilting on postural control and quality of reaching was studied. Subjects The subjects were 58 children with CP aged 2 to 11 years (34 with unilateral spastic CP, 24 with bilateral spastic CP). Methods During the task of reaching movements, surface electromyographic and kinematic data were recorded for posture and reaching with the dominant arm in 3 sitting conditions: horizontal seat surface, seat surface tilted forward 15 degrees, and seat surface tilted backward 15 degrees. Results In the children with unilateral spastic CP, forward tilting improved postural efficiency and quality of reaching. In the children with bilateral spastic CP, both forward and backward tilting of the seat surface was associated with more postural instability and did not affect the quality of reaching. Discussion and Conclusion The results suggest that, in terms of postural control and quality of reaching, children with unilateral spastic CP benefit from a forward-tilted position and children with bilateral spastic CP benefit from a horizontal sitting position.

A computer study of fracture mobility and strain on biodegradable plates used for fixation of mandibular fractures

PURPOSE This computer-based study was done to determine whether a small biodegradable plate system was suitable for internal fixation of mandibular fractures. MATERIALS AND METHODS In a three-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. Simulated solitary angle, body, and symphysis fractures were fixed with one titanium miniplate, one polylactide (PLA) midiplate, one PLA maxiplate, or two PLA midiplates. Fractures with and without interfragmentary bone contact were studied. In the case of fractures with bone contact, the loads were transmitted through the fracture surfaces and the plate; when there was no contact, the loads were transmitted only through the plate. Maximum fracture mobility was set at 150 microm. Maximum plate strain was set at the yield strain of PLA and titanium. RESULTS For fractures without interfragmentary bone contact, all plate fixations resulted in a fracture mobility and plate strain higher than the limits set, except for the symphysis fracture fixed with two PLA midiplates. Interfragmentary bone contact significantly reduced fracture mobility and plate strain. For the angle fracture with bone contact, all PLA plate fixations resulted in a fracture mobility above the limit, whereas the titanium miniplate fixation had a fracture mobility below the limit. For the body and symphysis fracture with bone contact, only double PLA midiplate fixation resulted in a fracture mobility below the limit. CONCLUSIONS From a mechanical point of view, based on the computer model, small PLA plates are only suitable for symphysis fractures with and without interfragmentary bone contact and for body fractures with interfragmentary contact. However, fixation with two PLA plates is always necessary to provide sufficient reduction of fracture mobility and plate strain.

D-flow: immersive virtual reality and real-time feedback for rehabilitation

D-Flow is a software system designed for the development of interactive and immersive virtual reality applications, for the purpose of clinical research and rehabilitation. Key concept of the D-Flow software system is that the subject is regarded as an integral part of a real-time feedback loop, in which multi-sensory input devices measure the behavior of the subject, while output devices return motor-sensory, visual and auditory feedback to the subject. The D-Flow software system allows an operator to define feedback strategies through a flexible and extensible application development framework, based on visual programming. We describe the requirements, architecture and design considerations of the D-Flow software system, as well as a number of applications that have been developed using D-Flow, both for clinical research and rehabilitation.