title: Muscle thickness measurements of the lower trapezius with rehabilitative ultrasound imaging are confounded by scapular dyskinesis.
abstract: Alterations in scapular muscle activity have been theorized to contribute to abnormal scapular motion and shoulder pain, but pose challenges to quantify in the clinic. Rehabilitative Ultrasound Imaging (RUSI) has proved useful identifying dysfunction of lumbar regional stabilizing muscle activity, specifically contractile behavior. Although, recent examinations of scapular stabilizing trapezius muscle function using RUSI did not detect alterations individuals with shoulder pain or differences in muscle thickness between varying external loads in asymptomatic individuals, a potential confounder to prior results, scapular dyskinesis has not been controlled. It is unknown if dyskinesis alters scapular muscle thickness during activation measured with RUSI. Thus, the purpose of this study was to compare change in scapular muscle thickness between individuals with and without scapular dyskinesis. Thirty-nine asymptomatic adults with (n = 19) and without (n = 20) scapular dyskinesis, defined with a reliable and validated method, participated. Two separate ultrasound images of the serratus anterior (SA) and lower trapezius (LT) were captured under two randomized conditions, rest and isometric contraction against gravity, and saved for blinded measurement. Change in thickness with contraction was calculated and expressed as a percentage. The dyskinesis group demonstrated a greater increase (p = 0.005) in LT thickness with the isometric contraction than the group without (mean difference = 31.6%; 95%CI = 10.3, 53.0). No differences in SA or resting thickness of either muscle were found between groups. The presence of scapular dyskinesis alters thickness changes of the lower trapezius during activation. Furthermore, potential underlying reasons beyond muscle contractile behavior must be considered.
authors: Department of Physical Therapy & Human Movement Sciences, Northwestern University, 645 N. Michigan Ave, Suite 1100, Chicago, IL 60611, USA. Electronic address: amee.seitz@northwestern.edu.
authors: Amee L
authors: AL
authors: Seitz
authors: Mountaintop Physical Therapy and Wellness Center, 1794 Olympic Parkway, Suite 140, Park City, UT 84098, USA.
authors: Caralyn J
authors: CJ
authors: Baxter
authors: Physical Therapy Department, Brigham and Women's Faulkner Hospital, 1153 Centre Street, Boston, MA 02130, USA.
authors: Kristen
authors: K
authors: Benya
mesh_terms: D053587:Arthrometry, Articular; D020820:Dyskinesias / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D012540:Scapula / Q000000981:diagnostic imaging* / Q000473:pathology; D064171:Superficial Back Muscles / Q000000981:diagnostic imaging* / Q000473:pathology
keywords: Scapular muscle; Scapululothoracic; Serratus anterior; Shoulder