Myotonia is the ability of the body to maintain a certain state of muscle tension in a quiet and relaxed state. In the process of examination and assessment, the resistance felt by the assessor through the movement of the subject’s limb is called muscle tone. The necessary muscle tone is necessary to maintain the position of the limb and support the body weight, as well as to ensure the motor control of the limb, the spatial position, and to perform various complex movements. Muscle tone is divided into: resting muscle tone, postural muscle tone, and motor muscle tone.
Characteristics of normal muscle tone.
1.The muscles proximal to the joints can be contracted effectively and synchronously;
2, with complete resistance to gravity and external resistance to the movement of the limb;
3, able to maintain the balance between the prime mover and antagonist muscles;
4, with the ability to make the limb at will from fixed to movement and switch to a fixed position during the movement;
5.Passive movement with a certain degree of elasticity and a mild sense of resistance;
6.When the limb is passively placed in a certain position in space, it has the ability to maintain the same posture;
7, if necessary, both the ability to selectively complete a muscle group synergistic movement or a muscle movement alone.
Types of muscle tone abnormalities: hypertonia, bradykinesia, and dystonia.
Hypertonia means that the muscle tone is higher than the normal resting level. It is divided into two conditions: spasticity and muscle rigidity.
1, spasticity: it is a movement disorder characterized by speed-dependent enhancement of the tonic retractor reflex with abnormal tendon reflexes caused by hyperexcitability of the retractor reflex. It is caused by damage to upper motor neurons and is commonly seen in spinal cord injury stroke traumatic brain injury cerebral palsy, etc.
2, muscle stiffness: refers to muscle stiffness, a phenomenon in which the tension of active and antagonistic muscles increases simultaneously, and the resistance to passive movement of joints in all directions increases. Caused by damage to the extrapyramidal system, Parkinson’s disease is the most common cause of stiffness.
Bradykinesia is a state in which muscle tone is below normal resting levels and sensory resistance disappears when passive movements are performed on the joints. It leads to a weakened detrusor reflex, impaired overall function of movement, often accompanied by limb paralysis or paresis, loss or absence of deep reflexes, and an increased range of passive joint motion.
Dystonia i.e. a hyperactive muscle motor disorder characterized by impaired muscle tone, sustained and distorted involuntary movements. It is associated with a variety of factors, such as genetic central nervous system defects.
The assessment of dystonia is relatively simple and can be rated in two levels of severity: mild, moderate to severe.
1. Mild – reduced muscle tone, decreased muscle strength, and some functional activity still exists. When the limb is placed in a position where it can be dropped and deliberately released, the limb can only remain resistant to gravity for a short time and subsequently falls.
2. Moderate to severe – significant reduction or loss of muscle tone; unassisted muscle strength is rated as grade 0 or 1; no functional activity can be performed. When the limb is placed in a position where it can be dropped and deliberately released, the limb falls immediately.
The assessment criteria of myospasm: the passive joint movement examination method of spasticity, the neurological grading method of myospasm, and the modified Ashworth grading method.
Criteria for passive joint movement examination of spasticity
Evaluation criteria for the degree of spasticity
Mild resistance occurs in the posterior ¼ of the range of motion of the passive joint.
Moderate resistance occurs at ½ of the range of motion of the passive joint.
Severe spasticity occurs in the ¼ of the passive joint range of motion, making it difficult to complete the passive joint movement.
Modified Ashworth Classification Method
Grading criteria
Grade 0 no increase in muscle tone.
Grade 1 slight increase in muscle tone, sudden jamming at the end of joint motion during passive flexion and extension of the involved portion, then showing minimal resistance or release.
Grade 1+ has a mild increase in muscle tone, as evidenced by a sudden jam in the 50% range after shutdown activity during passive motor flexion and extension, followed by minimal resistance.
Grade 2 has a more pronounced increase in muscle tone, which is significantly increased through most of the range of motion of the joint, but the involved portion can still be moved more easily.
Grade 3 has a severe increase in tone, with difficulty in passive movement.
Grade 4 stiffness, the affected part shows stiffness during passive motion in flexion and extension and cannot be moved.