Trigger points: an anatomical substratum

Abstract

This study aimed to bring the trapezius muscle knowledge of the locations where the accessory nerve branches enter the muscle belly to reach the motor endplates and find myofascial trigger points (MTrPs). Although anatomoclinical correlations represent a major feature of MTrP, no previous reports describing the distribution of the accessory nerve branches and their anatomical relationship with MTrP are found in the literature. Both trapezius muscles from twelve adult cadavers were carefully dissected by the authors (anatomy professors and medical graduate students) to observe the exact point where the branches of the spinal accessory nerve entered the muscle belly. Dissection was performed through stratigraphic layers to preserve the motor innervation of the trapezius muscle, which is located deep in the muscle. Seven points are described, four of which are motor points: in all cases, these locations corresponded to clinically described MTrPs. The four points were common in these twelve cadavers. This type of clinical correlation between spinal accessory nerve branching and MTrP is useful to achieve a better understanding of the anatomical correlation of MTrP and the physiopathology of these disorders and may provide a scientific basis for their treatment, rendering useful additional information to therapists to achieve better diagnoses and improve therapeutic approaches.

Figure 1

Scheme of anatomical location of MTrP1, MTrP2, MTrP3, MTrP3.1, MTrP4, MTrP5, MTrP5.1, MTrP5.2, and MTrP6. Motor endplate locations correspond to MTrP1, MTrP2, MTrP3, MTrP3.1, MTrP5, MTrP5.1, and MTrP5.2. MTrP4 and MTrP6 are insertional trigger points. Observe on the left side that points 5 and 3 are regions that correspond to nerve insertional points. The accessory nerve and its branches are highlighted in yellow.

Figure 2

Gross anatomy image corresponding to the previous scheme. Dissection of the trapezius muscle and the areas corresponding to the clinical trigger points. Reflection of the right trapezius muscle showing the entry points of the spinal accessory nerve branches that coincide with the MTrPs 1, 2, 3, 3.1, 5, 5.1, and 5.2. Trapezius muscle, levator scapulae, rhomboid major, and rhomboid minor are identified.