Rotterdam Intrinsic Hand Myometer (RIHM)
Dynamometer for intrinsic hand muscles
The Rotterdam Intrinsic Hand Myometer (RIHM) is a hand-held dynamometer to measure intrinsic hand muscle strength. In contrast to pinch and grip strength measurements, this instrument can directly quantify maximal strength of a number of intrinsic hand muscles, such as abduction of the thumb, abduction of the index finger, abduction of the little finger, and the intrinsic action of the fingers.
The RIHM is a hand-held, ergonomically designed dynamometer and is made of a strong lightweight plastic, which contains the battery, the force sensor and electronics. The peak forces can be read from a digital display on top of the device. The grip is positioned at a 97 degree angle with the horizontal, allowing the tester to hold the wrist in a comfortable and stable position.
Due to its design, the RIHM can be used to measure all the intrinsic muscle groups in the hand using an approach that is similar to manual strength testing of the intrinsic hand muscles. More specifically, the RIHM can measure the abduction and adduction of the little finger and index finger as well as the opposition, palmar abduction (anteposition), adduction and flexion of the metacarpophalangeal (MCP) joint of the thumb, allowing measurement of both median and ulnar nerve innervated intrinsic muscles. In addition, the intrinsic plus position of each finger can be measured to assess a combination of the interosseous and lumbrical muscle strength by pulling at the proximal interphalangeal (PIP) joint level and giving resistance to MCP flexion and PIP extension.
The device can store a maximum of 99 measurements, which can be downloaded to a PC using an USB cable for off-line analysis. The data can also be exported to other software packages such as MS Excel and SPSS. To minimize erroneous forces introduced by the tester, a small cylindrical part is connected to the handgrip of the instrument by means of a ball joint containing the button load cell (type BC301 from DS Europe). This construction, together with a rotating handgrip, ensures loading perpendicular to the load cell and prevents the examiner from introducing torques.
An important difference with other intrinsic muscle strength dynamometers mentioned above is the pulling technique of the RIHM, whereby the forces are measured by pulling on a leather band placed on the digit. An advantage of this pulling technique is that testers can pull towards their own body while supporting the upper arm against the side of the thorax, enabling better force control than pushing. For practical reasons (e.g. hand size) a 15-cm long leather band is used, allowing visual control of the direction of force application. Assessments with the RIHM are performed as a break test. To do so, the examiner pulls with increasing force while verbally encouraging the patient to hold the finger or thumb in place. The force will be increased such that after approximately one second, the subject will not be able to maintain the position (the resistance will break) and the pulling is ended so that the subject can relax. The RIHM stores the maximum force that is recorded during this period. Within our measurement protocol, the break test is repeated three times for each muscle group and the average of three values is reported, similarly to the American Society of Hand Therapists recommendations for evaluating pinch and grip force.
For information about the RIHM, please contact Ton Schreuders, email: email@example.com