Alojz Kralj

Standing-up of a healthy subject and a paraplegic patient

The joint torques in hip, knee and ankle were measured during the standing-up of a healthy subject. Force plate and stroboscopic photography were used in the experiment. It has been observed that the time courses of particular joint torques depend on the kind of standing-up. On the basis of these results a standing-up procedure for paraplegic patients was proposed. With the use of electrical stimulation to both paralyzed knee extensors and through use of the arm support, a completely paraplegic patient was able to rise independently from the wheel-chair. The same dual-channel stimulation also provides knee locking during standing of spinal cord injured patients.

Use of functional electrical stimulation in the rehabilitation of patients with incomplete spinal cord injuries

When patients enter the Rehabilitation Centre a therapeutic electrical stimulation programme is immediately initiated. Three groups of patients were identified: (i) those in whom an improvement of both voluntary and stimulated muscle force was observed, (ii) those with an increase in stimulation response only, and (iii) patients in whom no effect of electrical stimulation training could be recorded. Isometric measurement of voluntary and stimulated knee joint torque revealed that in a great number of patients one leg was severely paralysed while the other leg was under sufficient voluntary control. Unilateral two-channel stimulation of knee extensors and the peroneal nerve was proposed as an orthotic aid for this group of patients. Exaggerated extensor tone was observed by assessment of spasticity around the knee joint. A two-channel peroneal stimulator was found to be a useful approach in order to inhibit this tone and thereby help the patients to initiate a step.

Bending moments in lower extremity bones for two standing postures

The goal of this paper is to study how external gravitational forces stress the lower extremity bones and to ascertain and study how muscle activation compensates for the external load. For these purposes relatively accurate anatomical and biomechanical modelling is necessary. For a comparison of the calculated results to the naturally occurring muscular activity, seven-channel surface EMG activity was recorded. For simplicity a two-dimensional model was developed for the sagittal plane including 19 lower extremity muscles relevant to human standing and walking. In the calculation procedure of muscle forces an optimization procedure is also included. The results give rise to the expected assumption that muscle action is covered by two main requirements: first, to stabilize the joint actively (moment equilibrium) and, second, to compensate efficiently for bending moments produced by gravitational and external forces.

Improvement in step clearance via calf muscle stimulation

The aim is to study the influence of electrically stimulated calf muscles on the effectiveness of the swinging leg movement. The study is carried out with a group of patients with incomplete spinal cord injuries both under stationary conditions and during cruth-assisted walking. Before stimulation is applied to the ankle plantar flexors, the knee extensors are inactivated. In each cycle, after ankle plantar flexor stimulation, peroneal stimulation is started, triggering the flexion reflex. From a biomechanical point of view. functional electrical stimulation (FES) of the ankle plantar flexors results in increased ground clearance of the lower extremity. Additionally, the FES-assisted lifting of the heel results in the elimination of extensor tone and thus shortens the swing time.

Significance of FES-assisted plantarflexion during walking of incomplete SCI subjects

Abstract The significance of electrically stimulated ankle plantarflexors during functional-electrical-stimulation-assisted walking was evaluated. The dynamic (floor reaction forces) and kinematic (ankle and hip joint trajectories) data were assessed in incomplete spinal cord injury patients. The interplay of kinematic and dynamic parameters was described by mathematical modelling. An improved hand-control module providing voluntary control over functional-electrical-stimulation-restored walking pattern was developed. A specially designed two-step hand push-button enabled the division of the stride time into three distinct phases: midstance, push-off, and swing phase. Noticeable effects of functional electrical stimulation during the push-off phase were particularly evident in the vertical ground reaction force and horizontal hip joint displacement.

Chapter 34 FES gait restoration and balance control in spinal cordinjured patients

The status of gait restoration in spinal cord-injured patients by means of FES is reviewed and the main aspects are discussed. This introduction highlights the issues of balance control, stimulation sequence synthesis, and control of enhanced gait modes containing unbalancing. The use of statically unstable dynamic weight-transfer phases is important for enhanced gait modes. To show how this phase can be employed the mode of static balance currently used for FES-assisted four-point gait in paraplegic patients is discussed, and how this mode of gait can be converted to a semi-dynamic gait mode is described. The possibilities and consequences of such an approach are briefly discussed.

Modelling muscle activity in standing with considerations for bone safety.

The functional use of electrical stimulation (FES) for the restoration of movement to paraplegics has been improved in the last decade but questions about the mechanical effect of stimulation on the skeleton have arisen. In intact people, neuromuscular activity not only controls movement, but also minimizes bone and joint tissue loading. Current FES systems do not use feedback and do not even use average natural patterns of muscle activation. FES systems would be safer if muscle activation patterns were synthesized so as to minimize bending in the long bones. By modelling, we have verified that appropriate muscular activity reduces bone bending stresses, an approach we named active unloading of the skeleton. Using this criterion for control is novel. The muscle activation was calculated using measurements from intact people in different postures, and later modelling of the musculoskeletal system. The two-dimensional model of the lower limb includes 23 muscles relevant primarily for movement in the sagittal plane. The muscle model for constraint calculation is divided into first-order activation dynamics and first-order contraction dynamics. Optimization, which includes minimization of net bending moment calculated along the long bones, is static because changes in the observed postures are slow. In the calculated muscle activity patterns, muscle coactivation and cocontraction yield very uniform and low bone loading. Net bending moment values were fairly stable as the posture varies. The moment distribution in the femur was found to be U-shaped, while in the tibia it is sometimes V-shaped. The bones are naturally thicker at the points of peak moment.

Timing and kinematics of quadrupedal walking pattern

Improved walking of completely paralyzed paraplegic subjects assisted by multichannel functional electrical stimulation (FES) and crutches is proposed. In the resulting quadrupedal gait the center of body (COB) is both actively and passively transferred in the direction of progression. Active transfer of the COB is accomplished by electrical stimulation of ankle plantarflexors of the trailing leg. Passive displacement of the COB occurs during the unstable state when the paraplegic person is only supported by a single foot and the contralateral crutch. Comparison of the time parameters measured during human crawling on knees and arms with the crutch assisted walking is presented. Results of kinematic modeling of the present and the improved FES and crutch assisted walking are displayed in the form of supporting polygons with the trajectory of the COB projected to the ground.

Unstable states in four-point walking.

The presently utilized walking patterns in paraplegic subjects with complete spinal cord injury (SCI) are compared by the help of graphic representations. Improved four-point gait assisted by functional electrical stimulation (FES) and crutches is proposed by introducing unstable states into the walking sequence. The unstable states are defined as passive phases of walking where the centre of mass (COM) is gravity driven in the direction of progression. The unstable state is described by a simple inverted pendulum model. Kinematic measurements of the unstable state were performed in normal and paraplegic subjects.

Kinematic modeling of four-point walking patterns in paraplegic subjects

We present a kinematic model of a paraplegic subject walking with crutches where the subject with the crutches is modeled as a parallel kinematic structure. The model is employed to investigate if certain quadrupedal gait patterns can be implemented with functional electrical stimulation. The study is motivated by the fact that the existing crutch-assisted gait realized by the electrical stimulation is slow and energy inefficient. Gait patterns that would improve the walking are identified. The main characteristic of the patterns is that some of their states are not statically stable. During such states, the subject is supported by only a leg and a crutch. It is demonstrated that if the forward motion is provided by the stimulation of the plantar flexors the trajectory of the center of the body can closely follow the trajectory that is observed during walking of healthy subjects. We argue that the resulting gait is smooth and energy efficient. In addition, the unstable states make the walking faster.