Quantitative anatomy of the growing supraspinatus muscle in the human fetus.

Abstract

The supraspinatus muscle, one of the four rotator cuff muscles, initiates abduction of the arm, simultaneously stretching the articular capsule at the glenohumeral joint, and also contributes to exorotation of the arm. In the present study we aimed to evaluate the age-specific normative values for morphometric parameters of the supraspinatus muscle in human fetuses at varying ages and to elaborate their growth models. Using anatomical dissection, digital image analysis (NIS Elements AR 3.0) and statistics (Student's t-test, regression analysis), the length, width, circumference and projection surface area of the supraspinatus muscle were measured in 34 human fetuses of both sexes (16 males, 18 females) aged 18-30 weeks of gestation. Neither sex nor laterality differences were found in numerical data of the supraspinatus muscle. In the supraspinatus muscle its length and projection surface area increased logarithmically, while its width and circumference grew proportionately to gestational age. The following growth models of the supraspinatus muscle were established: y = -71.382 + 30.972 × ln(Age) ± 0.565 for length, y = -2.988 + 0.386 × Age ± 0.168 for greatest width (perpendicular to superior angle of scapula), y = -1.899 + 0.240 × Age ± 0.078 for width perpendicular to the scapular notch, y = -19.7016 + 3.381 × Age ± 2.036 for circumference, and y = -721.769 + 266.141 × ln(Age) ± 6.170 for projection surface area. The supraspinatus muscle reveals neither sex nor laterality differences in its size. The supraspinatus muscle grows logarithmically with reference to its length and projection surface area, and proportionately with respect to its width and circumference.