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Abstract
The deep tendon reflex (DTR) is a key component of the neurological examination. However, interpretation of the results is a challenge since there is a lack of knowledge on the important features of reflex responses such as the amount of hammer force, the strength of contraction, duration of the contraction and relaxation. The tools used to elicit the reflexes also play a role in the quality of the reflex contraction. Furthermore, improper execution techniques during the DTR assessment may alter the findings and cloud the true assessment of the nervous system. Therefore, understanding the basic principles and the key features of DTR allows for better interpretation of the reflex responses. This paper discusses the brief history of reflexes, the development of the reflex hammer, and also the key features of a reflex response encompassing the amplitude of force needed to elicit a reflex response, the velocity of contraction, the strength of contraction, and the duration of contraction and relaxation phases. The final section encloses the techniques of eliciting DTR in the upper extremities, trunk, and lower extremities, and the interpretation of these reflexes.
Keywords: deep tendon reflex, myotatic reflex, muscle spindle, afferent, spinal cord, nervous system, reflex hammer, tapping force, reflex torque, contraction time, relaxation time, striking point, peripheral nerve, effector, technique, biceps reflex, brachioradialis reflex, knee jerk, Achilles reflex
Introduction
A reflex is an involuntary, unlearned, repeatable response to a specific stimulus that does not require any input from the brain (1). The deep tendon reflex (DTR), also known as a myotatic reflex, is a sequence of lengthening, contraction, and relaxation of a group of muscles. A DTR comprises of a reflex arc, which is a neural pathway that controls a reflex. The reflex arc is made up of five components:
i) Receptor: muscle spindle
ii) Afferent fibre: Ia afferent fibres
iii) Integration centre: lamina IX of the spinal cord, synapse on the a-motoneurons
iv) Efferent fibre
v) Effector: muscle
The muscle spindle is a receptor within the muscle that detects changes in the length of the muscle. The muscle spindle consists of a noncontractile centre portion and intrafusal muscle fibres which make up the contractile portion. Tapping the tendon will cause stretching of the muscle spindle, activating it, leading to the...