When producing modern leg orthoses for patients with neurological paralyses, it is important to know the paralysis category concerned:
- peripheral paralysis, e.g. poliomyelitis or multiple sclerosis (MS);
- spinal paralysis, e.g. caused by spina bifida or paraplegia;
- central paralysis, e.g. caused by a stroke or cerebral palsy.
In the case of peripheral paralyses, the muscle chains securing the main joints of the legs while standing and walking, operate only poorly. In spinal paralyses, they are not sufficiently supplied with impulses and in central paralyses, they are activated by the wrong impulses from the brain.
In peripheral and spinal paralyses, the focus is often on the support function providing security, whereas in central paralyses, the support function is used to reprogram physiological movement sequences in the brain. This is to improve the physiological activation of the muscles.
In many cases, patients affected by one of these three paralysis categories develop compensation mechanisms, which result in an atypical stance or gait. These mechanisms compensate lost stability while standing and walking. The patients fear to fall and use these gait patterns to join in everyday things of life without falling. This inevitably results in an increased wear of the joints, back pains and other physical troubles.
Some commonly seen examples demonstrate exactly that:
- A person with fully functional muscles uses the entire length of the feet to enlarge the stance area and thus keeping a stable balance while standing. The occurring lever forces are realised especially through the cooperation of the forefoot lever with the calf muscles. People with limited functionality of the calf muscles often display a forward bending of the torso while leaning on crutches or similar devices. In doing so, they artificially enlarge the supporting area on the ground. This is necessary for these patients, because their muscles cannot activate the forefoot lever, which is vital for standing upright.
- In many patients with paralyses, it can be observed that they rotate their feet inwards when they walk to protect their knees from the kinematic forces affecting the direction of movement, which would force the knee to give way.
- Some patients overextend the knee of their paralysed leg while standing and/or walking to protect the knee from giving way in flexion direction.
Especially in central paralyses, these compensation mechanisms are often passively caused and manifest as spasticities. In these cases, the brain unintentionally gives an impulse for an exaggerated security measure in exactly the moment when a signal is sent of the need for security.