Quantitative anatomy of the infraspinatus muscle in the human foetus

The study presents one of the 6 scapulohumeral muscles, which occupies most of the osteofibrous infraspinatus compartment. Along with the supraspinatus, teres minor, and subscapularis muscles, the infraspinatus muscle contributes to the rotator cuff. It protects the posterior aspect of the articular capsule of the shoulder joint, and adducts and externally rotates the arm. The aim of the study was to perform a quantitative analysis of the infraspinatus muscle in human foetuses and to elaborate growth dynamics for its morphometric parameters.

Using anatomical dissection, digital image analysis (NIS Elements AR 3.0), and statistics (Student's t-test, regression analysis), the vertical, transverse, and oblique diameters, muscle circumference, and projection surface area of the infraspinatus muscle were measured in 36 human foetuses of both sexes (17♂, 19♀) aged 18-30 weeks. The infraspinatus muscle revealed neither sex nor laterality differences.

All examined morphometric parameters of the infraspinatus muscle increased commensurately in accordance with the following linear functions: y = -4.024 + 0.903 × age ± 0.621 (R2 = 0.96) for transverse diameter, y = -3.089 + 1.321 × age ± 0.897 (R2 = 0.97) for vertical diameter, y = -1.161 + 0.632 × age ± 0.444 (R2 = 0.97) for oblique diameter, y = -13.575 + 3.851 × age ± 1.938 (R2 = 0.98) for muscle circumference, and y = -293.512 + 23.228 × age ±19.650 (R2 = 0.95) for projection surface area.