Causes for weak foot dorsiflexion
There are three main underlying causes of peroneal nerve paresis: Firstly, injury to upper motor neurons. These motor neurons are located in the cerebral cortex and control conscious triggering of motor movements. If, for example, these cells are damaged by a stroke or multiple sclerosis this is referred to as a central lesion. A second possible cause of weak foot dorsiflexion may be a peripheral lesion injuring lower motor neurons. These motor neurons are located in the spinal cord and may be compromised in cases of spinal disc herniation. The lower motor neuron transmits impulses it receives from the upper motor neuron to nerves and muscles. If motor neurons in both the brain and spinal cord are affected, this is referred to as a mixed motor neuron disease.
Patients with peroneal nerve paralysis are unable to lift or roll their feet when walking. The toes often drag over the floor which leads to what is known as foot drop. This significantly increases the risk of tripping and falling. Adopting a walking posture to alleviate pain places additional strain on the hips and the spine. The innoSTEP-WL is an innovative, wireless therapeutic device for functional electrical stimulation to treat weak foot dorsiflexion and can be prescribed by your treating physician. The peroneal nerve is stimulated via electrodes attached to the leg allowing the leg muscles to contract and the foot to lift. The innoSTEP-WL foot drop system enables the patient to walk naturally and safely – for enhanced mobility and quality of live.
The following sections provide an overview of the various causes and clinical pictures that can lead to a weak foot dorsiflexion.
Weak foot dorsiflexion resulting from spinal disc herniation
Spinal disc herniation is one of the most common spinal conditions in Germany, affecting approximately 180,0001 patients per year. Symptoms range from severe pain, neurological disorders and loss of sensitivity to impairment of motor skills – as is the case for weak foot dorsiflexion and peroneal nerve paresis.
Loading and tension are decisive factors influencing the development of spinal disc herniation (also sometimes called a prolapsed disc). Sitting in a car or at a desk for prolonged periods of time, in particular exerts pressure on the lumbar vertebrae. Muscle tensions – such as those caused by poor posture or adopting postures which alleviate pain – contribute to amplify the effect. A spinal disc herniation can thereby be both the cause and the concomitant symptom of a peroneal nerve lesion – with both clinical pictures able to adversely affect one another.
How do spinal disc hernias occur?
The spine is made up of individual vertebral bodies, which are separated from each other by an intervertebral disk. A single unit consists of two adjacent vertebrae separated by an intervertebral disc, and is called a “segment”. Viewed from the side, the spine is divided into several arches: Abnormal curvatures of the cervical and lumbar regions of the spine are referred to as lordosis, while excessive curving the thoracic spine is referred to as kyphosis. Segments downstream of the cervical spine are inherently exposed to ever greater pressures. This is why spinal disc hernias occur particularly frequently in the lumbar vertebrae.
The intervertebral disc itself consists of a gelatinous core surrounded by a stable fibrous ring. Micro-fibre cracks can occur in these areas, and these can expand under prolonged loading. If the gelatinous fluid escapes through these cracks in the fibres, this results in a spinal disc herniation. If the escaping fluid is still retained by the posterior longitudinal ligament of the vertebral column, this is referred to as a subligamentous disc herniation. If the gelatinous core extends into the spinal canal and constricts the spinal cord, this is a subligamentous herniation.2
Nerve damage resulting from spinal disc herniation
Four of the five pairs of the spinal nerves that control and supply the lower extremities are found in the lumbar region of the spine. The sciatic nerve – which is the longest and widest single nerve of the human body – is located between the fourth lumbar vertebra and the second sacral vertebra. From there, it passes through the buttocks and thighs until it finally bifurcates into its two main branches, the nervus tibularis and the nervus fibularis communis (also called the nervus peroneus or the common peroneal nerve), at the height of the knee joint. A spinal disc herniation affecting the lumbar region of the spine can constrict the sciatic nerve and thereby compromise the ability to transmit stimuli to the peroneal nerve – this manifests as weak foot dorsiflexion.3
Weak foot dorsiflexion following hip surgery
There are approximately 220,000 hip replacements in Germany every year. Hip surgery is a major procedure which carries an inherent risk of nerve damage: The sciatic nerve (nervus ischiadicus), which bifurcates into the nervus peroneus (also called the nervus fibularis) at knee-level, extends out of the pelvis and runs under the gluteal muscles. For patients with variant nerve trajectories, nerve adhesions or an oversight of the surgeon may result in an injury to the nerve cord, which may lead to peroneal nerve paresis.4
Multiple sclerosis and weak foot dorsiflexion
Multiple sclerosis (MS) is a chronic inflammatory disease during which the body attacks and permanently damages the protective nerve fibre sheaths. In Germany, an estimated 200.000 to 300.000 individuals are affected by this autoimmune disease.5
The degradation of, what is called, myelin disrupts nerve impulse transmission thereby impairing nerve function. Motor commands cannot be transmitted to the target muscle – a study by the MS registry found that about half of those affected report restricted walking ability.6
How does MS manifest throughout the body?
Multiple sclerosis causes the body's own defence cells (i.e. scavenger cells) to destroy the protective membrane surrounding the nerve fibres, the myelin sheath. Over time, this myelin sheath can no longer regenerate – leading to the formation of scarred regions called plaques. This hardening or sclerosing process considerably restricts the ability to transmit stimuli through affected regions. This may also manifest as peroneal nerve paresis, where patients can no longer lift the foot when walking. Functional electrical stimulation can compensate for this loss of stimulation and help the patient regain a safe and stable gait.7
MS Symptoms
MS symptoms vary greatly depending on which parts of the nerves are hardened, i.e. where signal transmission is impaired. Roughly speaking, symptoms can be divided into two categories. Early symptoms include:
- Sensory and somatosensory disorders
- Transient paralysis
- Weak foot dorsiflexion
- Visual impairment
- Fatigue and poor concentration
During the advanced stages of MS, symptoms may include incontinence and loss of the ability to taste. In the most severe cases, symptoms may extend to irreversible paralysis and motor dysfunction.8
Weak foot dorsiflexion in Parkinson's disease
In Germany, approximately 250,000 people are affected by Parkinson's disease, a degenerative disease of the basal ganglia (an accumulation of nerve cells) in the brain. This nerve cell aggregate controls motor processes and for this the neurotransmitter dopamine is required. Dopamine is released by a brain structure called the substantia nigra. In Parkinsons disease, the brain cells of this very structure die, leading to a dopamine deficiency.
The lack of dopamine means that the brain can no longer control or coordinate physical movements. This manifests as symptoms ranging from tremors, muscle stiffness (rigor) to slowing of physical movements (bradykinesia)9. As motor processes become increasingly difficult to control, the patient's gait also deteriorates – resulting in weak foot dorsiflexion. Functional electrical stimulation can in this case, as it were, replace the failed motor stimuli and support movement sequences: The peroneal nerve is directly controlled via electrodes applied to the skin and is therefore not dependent on cues from the brain – this enables the patient to walk more naturally and safely.9
Peroneal nerve paralysis following a stroke
In Germany, an estimated 270,000 individuals10 suffer a stroke (also called apoplexy, cerebrovascular accident or insult) every year: This is when an acute circulation disorder interrupts the supply of oxygen and nutrients to brain cells. If they are badly damaged, brain cells die. This leads to loss of brain function, often in the form of numbness, loss of speech and vision or paralysis – and makes stroke the most common cause of weak foot dorsiflexion.
Causes for a stroke
Essentially, there are two causes of stroke – poor blood flow to the brain and brain haemorrhage. If a blood clot obstructs an artery supplying the brain, it disrupts the supply of oxygen and nutrients to the affected area of the brain – this is known as an ischaemic stroke. This acute lack of blood supply is the underlying cause for 80 to 85 per cent of all strokes. Brain haemorrhages account for the remaining 15 to 20 per cent of all strokes. This causes the tissue surrounding the haemorrhage to be severely undersupplied, while the rising brain pressure further damages cells. This is called a haemorrhagic stroke.
Consequences of a stroke
Approximately 50 per cent of stroke patients struggle with permanent impairments, be they physical or psychological. The severity of a stroke depends on its location in the brain. If the locomotor centre in of the cerebral cortex is affected, for example, paralysis and motor restrictions such as peroneal nerve paralysis occur.11
As the nerve fibres cross to opposing sides of the body on their way to the muscle, the damage always affects the other side of the body. A weak right-sided foot dorsiflexion is therefore suggestive of a stroke in the left hemisphere of the brain. The brain can no longer initiate the motor processes necessary for foot lifting. Functional electrical stimulation can provide support for these failed processes and thereby alleviate paralysis symptoms. EMG and Biofeedback can similarly help patients to retrain impaired bodily functions.
Stroke in children
Despite a higher incidence of stroke in older adults, children – some even before birth – can already suffer from apoplexy. Possible causes include cardiovascular diseases and infectious diseases. In Germany, around 300 children suffer a stroke every year.12 The innoSTEP-WL is suitable for treating children as young as 5 years of age. Featuring a unique cuff and functional electrical stimulation with virtually no side effects, children with weak foot dorsiflexion can now move more freely and effortlessly. The muscles and ligaments are simultaneously strengthened by the continuous stimulation of movement, which helps combat atrophy.
Weak foot dorsiflexion – symptomsSources
2 www.apotheken-umschau.de, www.bandscheibenvorfall.de, Anatomie-Atlas Dorling Kindersley Verlag GmbH, München, 2002
7 Anatomie-Atlas Dorling Kindersley Verlag GmbH, München, 2002
