portfolio: Muscle Recovery Measurement (MRM) Project

project summary

client: The Methodist Hospital, Houston

the muscle recovery measurement system was designed in collaboration with Dr. Robert Grossman (Chairman of the Department of Neurosurgery, The Methodist Hospital, Houston) to aid clinicians in evaluating recovery of strength due to increased innervation, and of reinnervation of the motor neuron pool of specific muscles after a spinal cord injury.

background

the Motor Recovery Measurement (MRM) System is a computer based muscle strength measuring platform. The device incorporates a variety of features and modes of operations to assist the clinician with evaluating and assessing a patients progress after a spinal cord injury (SCI).

the system is designed to measure force outputs that result from a “flicker of movement” to maximum voluntary muscle contraction. What makes this device unique is that it is designed to objectively and reliably quantify muscle strength in individuals with Spinal Cord Injury (SCI) allowing clinicians to accurately record a large spectrum of muscle strength changes during the motor recovery process.

motivation

presently there are two ways in which muscle strength testing is conducted: a fully manual approach and a device assisted approach. In manual muscle testing, the assessor locates and palpates the target muscle belly, positions the joint into a position of mechanical advantage for the muscle and asks the subject to generate a maximal effort to produce a primary action of the target muscle. The task is graded so that the subject can try to move with little gravitational load if the target muscle is weak, then tested against gravity if it is stronger, and then tested against manual resistance (in a make or break test) if the target muscle can work against the higher loads. The grading of the task is generally evaluated along a 0-5 point scale where 0 represents total paralysis (nonactivation) and 5 represents “normal” levels of maximal effort against resistance. These manual tests, one for each major muscle of the body, are nonquantitative and do not have equal intervals that represent the grading across the 6 levels (0 – 5). Most importantly, in cases where gradual changes in muscle strength occur with some intervention, these scales are unable to detect the changes because the scales are not sensitive enough.

the state of the art devices used to assist assessors with muscle strength testing are variations of the manual muscle test with an imposed force transducer between the assessor’s manual contact and the body surface. As the assessor applies resistance to the muscle, the transducer records peak force applied by the assessor. Typically these devices are not widely used because they are uncomfortable for the subject when the assessor bears down with the device on the body surface. In addition, the devices are only useful when a target muscle is strong enough to withstand a resistive force and cannot record forces when a target muscle can move against gravity without resistance, or cannot move against gravity or can only generate trace contractions.

the nature of muscle strength recovery after spinal cord injury, for example, demands a strength testing apparatus that can assess the entire range of forces that a muscle might generate as it gradually recovers neural innervation, can do so in a quantitative manner, and is sensitive enough to identify gradual and subtle changes in strength over time. Also, the time course of muscle force generation, along with fatigue measures and alternating movement forces may generate important insights into the acquisition of control of forces which may be both diagnostic and prognostic for the clinician.

advantages:

• repeatability of measurement: allows for testing of muscle strength to become an indicator of innervation, and of re-innervation of the motor neuron pool of specific muscles.
• portability: the device can be used at bedside.
• integrated visual feedback: gives feedback to the patient so that they are aware of when they have achieved a maximum voluntary contraction, and/or as motivation to complete a challenging task.
• configurable: useable in supine and/or seated position.
• measures small changes of muscle force output: allows for testing of muscle strength to become an indicator of innervation, and of re-innervation of the motor neuron pool of specific muscles.

customer/user description:

clinicians who work with patients and want a valid and reliable tool to measure muscle strength for using on a variety of different patient types, these include:

• Spinal Cord Injury
• Stroke
• Traumatic Brain Injury
• Multiple Sclerosis
• Guillan-Barre
• Amyotrophic Lateral Sclerosis
• Orthopedic Patients
• Sports Medicine

device description

Figure 1– Picture of the prototype MRM system.

the MRM sytem is comprised of a computer, signal processing electronics, and a mechanical structure designed to accommodate the limbs to be measured (Figure 1). The configuration shown in Figure 1 is specifically for performing isometric measurements of elbow torque during flexion/extension, effectively measuring bicep/triceps contractions, respectively.

the patient is harnessed into a structural mechanism which is composed of a strength measuring sensor (ex. load or torque sensor), and an orientation measuring sensor. The sensors are then connected to the signal conditioning electronic enclosure which is subsequently connected to a computer for processing and display.

electronics and software

Figure 2 – MRM system overview.

electronics

electronic system consists of four parts: Computer, Data acquisition electronics, signal conditioning electronics and device sensors.

software

the software running on the computer is used to:

• acquire and display device data
• serve as a user display during data collection
• store device data

Figure 3 – Picture of the user interface.

The screen capture of the software application is shown on Figure 3.

The display consists of four areas:

1. elbow Torque graph and data acquisition and display controls.

• graph control displays the torque data collected by the hardware in real time
• start Acquisition button initiates and stops data collection
• time Span numeric control lets the therapist specify the amount of data in seconds to collect
• rolling Acquisition check box lets the user specify a continuous data acquisition mode. When time span worth of data is collected a new data acquisition period is automatically initiated
• zoom Level control lets the user specify the Y axis (torque data) scaling. This control also affects the Patient Display (see below)
• zero Out Static Torque button subtracts an initial torque offset from subsequently collected data.

2. elbow Angle displays the output of the potentiometer in degrees

3. patient Display is for patient visual feedback during a measurement session

• forearm Length numeric control is used to convert torque to force applied by patient’s hand
• flexion/Extension bar display current torque measurements converted into force and scaled according to the value selected by the Zoom Control (see above)
• flexion/Extension targets and numeric controls let the therapist select a force goal for the patient. The computer beeps each time a goal is reached

4. data Files controls save, discard and document collected data.

• patient ID control and ring control let a therapist enter a new ID or lookup and existing ID respectively. Each patient ID corresponds to a subdirectory in the application data directory. Subdirectories corresponding to a new ID are automatically created.
• save To File button click stores the collected data simultaneously in two files. The file name has the following form: PatientID_date_time.extension. One file, with a .txt extension, is a plain ASCII text file formatted to be importable into Excel and Matlab applications for post processing. The second file, with a .jpg extension is a picture file that contains the same information in a graphical format. It is created to facilitate fast browsing of data as well as convenient means of including the data in a report with minimum effort. The following data is captured in each datafile:
  1. application name and version number
  2. Filename
  3. Patient ID
  4. Date
  5. Time
  6. Elbow Angle
  7. Recorded Peak Torques
  8. Patient Display Targets
  9. Fforearm Length
  10. Notes
  11. Time and Torque data collected at 50 Hz
• discard Data button click marks the previously collected data for removal. If this button is not clicked prior to clicking the Start Acquisition button the user is prompted to save the data.
• notes text control lets the therapist enter arbitrary session documentation text together with the data in the files described above.

hardware user interface

Figure 4 – (left) Picture of the mechanical joint, (right) picture of a person’s arm harnessed to the mechanism and set at an angle approximately 80°.

the structural mechanism is designed to accommodate measurements of elbow torque generated isometrically (without joint motion) during flexion and/or extension of the arm. It consists of a one lockable rotational degree-of-freedom joint, three adjustable straps, and two cushion pads. The straps are used to stabilize the wrist, lower arm, and upper arm. The current embodiment uses a ‘carpal tunnel’ style harness in order to have a positive engagement of the wrist thereby discouraging motion away from the neutral (supinated) position.

data logging and display

sensors incorporated into the device are used to monitor and record patient’s progress during a evaluation session, aiding the clinician with performance analysis and documentation. The parameters, such as limb orientation, and torque exerted by the limb are directly measured by the sensors mounted on the mechanism.

the collected data can be used to monitor the patient’s progress during an evaluation session, for example to determine if the patient is getting fatigued, as well as between sessions to determine overall treatment progress. The available data can be displayed on a computer screen visible to either the patient, the therapist of both, in a real time fashion.

gallery

videos:

• for a video demo of the MRM system, click here (11MB).
• for a technical description video, click here (25MB).

pictures: