Functional Evaluation of Lateral Pinch in Subjects with Tetraplegia

Deborah E. Kenney, MS OTR; M. Elise Johanson, MS PT; Niels Smaby, MS; Wendy M. Murray, PhD

Objectives: Tetraplegia greatly affects a person's ability to perform activities of daily living (ADL). In an effort to improve functional independence surgical reconstruction may be performed to increase lateral (key) pinch forces. We developed an assessment protocol to test the ability to complete tasks that require a variety of postures and pinch forces. The objective of the study was to provide a link between functional abilities and quantitative measures of lateral pinch.

Methods: Seven tasks were evaluated in the study. These included unlocking a door with a key, using an ATM card; horizontal zipper; vertical zipper; activating a remote control button; picking up theraputty with a fork; and inserting and removing a plug from an outlet. Activities were further broken into 13 sub-component tasks. For example unlocking a door is comprised of putting the key into the lock, turning the key and removing the key. Each task was performed at a set height based on typical ADL performance of that task. The tasks may only be performed using lateral pinch in the "normal" hand position for that object. Tasks were analyzed on a scale of 0-3 for the ability to be completed and the time necessary for completion. Up to three attempts may be used to complete the task. The best performance was used in the additive score (0-39). For comparison the GRT and lateral pinch strength were also measured. Six subjects with C5-6 tetraplegia were tested.

Results: Our assessment could be performed in less than 15 minutes using mostly readily available materials. The preliminary results indicate a similar ordinal ranking of subjects with the GRT. All except one pre-surgical subject, with no measurable pinch force, was able to complete at least one of the tasks. Compensatory strategies (tenodesis, elbow extension etc.) were used by all subjects on most of the 7 tasks. This was especially evident in the ATM task where more force is applied to the thumb than the index finger through elbow extension and shoulder elevation.

Pinch force measurements do not show a strong relationship with functional ability. Most tasks require less than 8.3N of force to perform with the exception of the zipper and plug. Five of six subjects could produce at least 20 N of force. Yet, not all could perform each of the 7 tasks. This may be due to the fact that pinch meter's measurements are performed at a much wider grasp opening than the actual tasks. Subjects had most difficulty with the tasks with very narrow pinch openings (ATM, key) irrespective of the force requirement. Hand and upper limb positioning also affects ability to perform the task. For example the horizontal zipper proved more difficult for subjects than the vertical zipper.

Conclusions: We have developed a comprehensive lateral pinch assessment protocol to test the ability to complete tasks that require a variety of pinch forces and postures. These measures should provide an important link between function and quantitative laboratory measures of force magnitude, direction, and pinch openings. Subject testing and data analysis is currently ongoing with both chronic and pre and post surgical subjects with tetraplegia.

Funding Acknowledgment: Rehabilitation R&D Service of the Department of Veterans Affairs, VA Merit Review B898-3RA