A QUANTITATIVE HEAD POSITION MEASUREMENT TECHNIQUE FOR THE EVALUATION OF TORTICOLLIS

Robert P. Patterson, Tanya L. Baxter and Dennis D. Dykstra Department of Physical Medicine and Rehabilitation University of Minnesota, Minneapolis MN 55455 USA

ABSTRACT

Torticollis is a condition in which involuntary muscle action causes the head to rotate into an abnormal position. No quantitative system exists which can measure head position in order to evaluate techniques used to treat this problem. Using an electromagnetic tracking device, a measurement system and activity protocol were developed to obtain objective data. Examples of the results of the measurements and the improvement with Botulinum injections will be presented.

BACKGROUND

Spasmodic torticollis is a condition in which the neck muscles involuntarily rotate and/or tilt the head into an abnormal right or left position. Bizarre head movements that occur in some patients tend to increase with certain activities or emotional conditions. Torticollis may interfere with work and activities of daily living. It also frequently results in pain. In most cases the cause is unknown, but it is thought to be associated with problems in the brain stem.

In order to keep their head in a neutral position, patients frequently use what are referred to as "tricks". These typically involve sensory stimulation, such as lightly touching the face.

Torticollis is treated with oral medications, injections of Botulinum toxin in the involved neck muscles, which results in muscle weakness, surgery, and by using various therapies, such as biofeedback, and electrical stimulation. The effectiveness of the various procedures has been difficult to determine because no good objective method exists to evaluate head position.

METHODS

A Torticollis Evaluation System (TES) was developed which records the position of the head using the Polhemus 3Space Isotrak 3-dimensional tracking system to provide continuous positional data. As part of the TES system, a protocol was developed to evaluate head position during four dynamic activities as well as measuring active range of neck motion in lateral tilt, flexion/extension and rotation.

The Isotrak device is based on electromagnetic techniques that are capable of continuously measuring angular position with an error of less than 1 degree. A small reference transmitter (3.5 x 3.5 x 6 cm) is mounted on either the back below the neck or on the anterior thorax. A small sensor (1.5 x 2.5 x 2.5 cm) is mounted on the head using an adjustable plastic band. The Isotrak system measures the distance and angular position between the source and receiver at a continuous rate of 10 samples/s. In this study of torticollis only the angular data of yaw, pitch and roll was used.

The testing protocol has two phases: Phase I measures the active range of neck motion as the patient moves his/her head through three cycles in each of the three planes of motion; lateral tilt, flexion/extension, and rotation. The system measures not only the primary angles, (angular change in the directed plane of motion) but the secondary angles (angular change in the two other planes where motion should not occur). For example, if the patient is doing flexion/extension, movements in rotation or lateral tilt would be considered secondary angular movements.

Phase II involves measuring head position during four dynamic activities: 1. sitting at rest for one minute without trying to control the head position starting from the best neutral position using "tricks", 2. sitting for two minutes attempting to hold the head in neutral, 3. walking in place for 30 s and 4. watching a video for 5 minutes.

RESULTS

Figure 1 shows an example of the range of motion results before and 4 weeks after Botulinum toxin injection. The labels above each group of curves indicates the desired plane of motion. Figure 2 shows an example of changes in average lateral tilt position during activities in Phase II following Botulinum injections. Also shown are the limits of the active range of neck motion.

DISCUSSION

In the example, the range of motion results show that the change in secondary angles is significantly reduced and that for lateral tilt, the active range of motion is more symmetrical. The Phase II activity measures indicate the head position for these activities is on average in the neutral position. Five patients have been studied to date. Each patient has unique characteristics in their head position with variable results to Botulinum injections.

Robert Patterson, Ph.D. University of Minnesota UMHC Box 297 Minneapolis, MN 55455