Comparison of muscle sizes and moment arms of two rotator cuff muscles measured by ultrasonography and magnetic resonance imaging.
OBJECTIVE
The purpose was to investigate ultrasound (US) and anthropometry (AN) as valid alternatives to magnetic resonance imaging (MRI) regarding muscle size characteristics of two rotator cuff muscles.


METHODS
Eight healthy females (age 27-54 yrs.) went through MRI and US scannings and AN measurements, where muscle thickness, cross-section area (CSA), moment arm, muscle length and width were measured on supraspinatus and infraspinatus muscle.


RESULTS
The agreement between the methods was very satisfactory for CSA, and satisfactory for muscle thickness, moment arm, muscle length and width, with a mean difference below 2 mm in thickness and below 5 mm in muscle length and width. Volume could be estimated satisfactory in supraspinatus muscle, but not in infraspinatus muscle, where volume had to be calculated from thickness, length and width. As a significant relation was found in the MRI measurements between thickness and CSA, thickness measurements may replace CSA in inaccessible muscles.


CONCLUSIONS
US was a valid method in measuring CSA, muscle thickness and moment arm. Combined with anthropometric measures of muscle length and width, volume can be calculated, which is important when defining the physiological cross-sectional area and muscle function. Further development and validation of the method is needed, however.
Juul-Kristensen
B
B
Department of Physiology, National Institute of Occupational Health, Lersø Parkallé 105, Dk-2100, Copenhagen, Denmark. bjk@ami.dk
Bojsen-Møller
F
F
Holst
E
E
Ekdahl
C
C
D000328:Adult; D000886:Anthropometry; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D015203:Reproducibility of Results; D017006:Rotator Cuff / Q000033:anatomy & histology* / Q000000981:diagnostic imaging* / Q000502:physiology; D012785:Shoulder Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014463:Ultrasonography