Impact of structural factors around the accessory nerve on the pathogenesis of essential neck and upper-back stiffness: a sonographic investigation.

Introduction: Neck and upper-back stiffness involves discomfort/ache in the trapezius muscle (TM). The pathogenesis of 'essential neck and upper-back stiffness' without obvious causes remains uncertain. In symptomatic subjects, TM hardness correlates with decreased transverse cervical artery (TCA) blood flow to the TM. Neck and upper-back stiffness could be associated with both hemodynamic and neurological factors affecting the TM. We therefore sonographically evaluated structural factors around the accessory nerve innervating the TM impacting neck and upper-back stiffness.

Methods: Participants comprised 69 healthy young adults (33 men, 36 women; 21 ± 1 y) who completed questionnaires and underwent elastography to determine TM hardness as a strain ratio and pulsed Doppler sonography to determine TCA hemodynamics. Intermuscular length was measured as the distance between sternocleidomastoid and levator scapulae muscles around the accessory nerve. Relationships of intermuscular length with symptoms, TM hardness, and TCA hemodynamics were analyzed.

Results: Intermuscular length was greater in symptomatic subjects (median 2.3 mm, interquartile range 1.5-3.1 mm) than in asymptomatic subjects (median 1.8 mm, interquartile range 1.5-2.3 mm; p = 0.032). Intermuscular length correlated positively with symptom severity (r = 0.43, p = 0.014) and negatively with strain ratio for the TM (r = -0.39, p = 0.025) and peak systolic velocity in the TCA (r = -0.40, p = 0.022). Intermuscular length contributed independently to the presence of symptoms (p = 0.025, odds ratio 2.26, 95% confidence interval 1.11-4.62).

Conclusion: In symptomatic subjects, symptom severity, TM hardness and TCA hemodynamics all correlated with greater intermuscular length. Structures around the accessory nerve could be associated with the pathogenesis of essential neck and upper-back stiffness.