How does the Myotonometer® work and what exactly does it measure?

The Myotonometer^® is a hand-held electronic device that can be interfaced with a computer (ranging from a personal assistant to a PC). It is non-invasive, painless, easy to use and provides accurate, reliable and reproducible results.

The examiner pushes a blunt metal probe perpendicular to the surface of the skin overlying the muscle to be tested. The probe does not penetrate the skin and only a light pressure by the examiner is needed. The basic measurements that are taken are the amount of deformation that occurs within a muscle (millimeter deflection) to a given unit of force of the relaxed and maximally contracted muscle.

These measurements relate to the "stiffness" of the muscle. Resting values provide an accurate assessment of muscle tone and compliance. Muscle contraction values provide an assessment of muscle strength. The differences in the slopes of the two lines provides an assessment of the level of severity of the spasticity. This assessment is done automatically by the program's computational software. Other analyses within the program allow the determination of whether changes in tone or muscle strength contribute most to a disability. This allows quantifiable assessment of changes taking place over time or following treatment interventions.

The Myotonometer^® represents a unique combination of newly developed hardware and computational software. All computations are done on-line and require little or no interpretation by the clinician or scientist. Its ease of use is one of its main features. Unlike other methods that are limited to limb assessments only, the Myotonometer^® can assess any surface muscle in the body. Graphs and charts are generated immediately and can be printed out for patient/subject medical/research documentation.

The peripheral component of the Myotonometer^® is a hand-held device that consists of a metal probe (1 cm in diameter) that is surrounded by metal/plastic sleeve (3.5 cm in diameter). The surfaces between the probe and the sleeve are machined to be as frictionless as possible. The handheld probe is brought into contact with the skin overlying the muscle to be tested and downward pressure is then applied by the examiner. Within the probe are transducers that monitor the amount of downward force being applied. Measurements are taken every .25 kg ranging from .25 to 2.0 kg. The amount of maximal force exerted can be lessened to 1.0 kg if needed for small children or painful muscular conditions. Also contained within the unit is an electric measurement circuit that monitors the amount of displacement occurring between the inner probe and the outer sleeve. The sleeve, with a broader surface area, stays relatively stationary on the surface of the skin whereas the inner probe moves as it deforms the muscle. The higher the tone within the muscle, the less penetration per unit force. A contracted muscle of a non-disabled individual will permit less penetration than in a relaxed state. Clinical trials conducted thus far have shown that the spastic muscle does not respond similarly and that the Myotonometer^® can distinguish between levels of severity of spastic involvement (see Results of Myotonometer^® Clinical Tests).