F166. Quantifying the tendon hammer tap

Abstract

Introduction The myotatic reflex is a common neurological test performed at the bedside. This monosynaptic reflex provides a subjective assessment of the central and peripheral nervous system. The assessment of this reflex is based on the clinician’s expertise in performing and interpreting the test. It is difficult for a student or inexperienced clinician to perform and interpret the subtleties of this reflex. Even in expert hands quantification is poor, making it a limited tool for diagnosis and staging of disease. Several factors like the intervening soft-tissue, the exact location of contact and the position of the leg, make it difficult to determine how the administered tap is translated to the stretch of the tendon. We propose a simple addition to a standard tendon hammer that provides feedback to the clinician on the quality of the performed tap. This can be an useful teaching and learning tool. Methods In a freely swinging hammer of known mass, if the acceleration is known, the exact force during the tendon tap can be determined. We used an accelerometer on the head of the hammer to measure the linear acceleration during the tendon tap. Using the data from this we can plot and analyse the entire swing of the hammer along with the deceleration at the point of contact with the tendon. During use, the tendon hammer is held pivoted between thumb and forefinger and the hammer is allowed to freely swing. In this process the only external force on the hammer is the tap on the target tendon. Therefore the force of tap can be calculated accurately. Prior settings can be used for the range of forces that are deemed as adequate to produce a good response. Surface EMG electrodes on the agonist record the electrical response from the muscle which indicates a successful tap. Feedback can be provided to the user to indicate a good tap or a poor tap. Results Using this hammer, we can distinguish a good tap from a poor tap. This is quantified based on the following: magnitude and temporal course of tap force, electrical response from the muscle. Custom written software analyses the characteristics of the hammer accelerometer data to identify strike of the tendon, then confirms an electrical response on the EMG. The force of the tap is then calculated and the software checks if these fall within the preset parameters for the same. A good tap in a normal subject is one where the hammer stretches the tendon of interest with adequate force to elicit an adequate electrical response in the agonist muscle. Preliminary data support such quantitative assessment of the tendon tap. Conclusion Feedback on the quality of a tendon tap will greatly improve the interpretation and reduce the inter-person variability of interpretation of the deep tendon reflexes. Apart from being a tool that can be used for training of students, feedback of quality of tap will help in interpretation of deep tendon reflexes at the bedside.