Background: Normal thoracic motion during shoulder elevation has not been elucidated yet. Purposes of this study were to clarify the normal motion of the ribs, thoracic spine, and scapula during elevation and to compare thoracic and scapular motion between males and females.
Methods: Ten males and 7 females (average age 25 years old) participated in this experiment. All subjects had 3D-CT of the thorax at 3 positions: resting position, 120°, and 160° of shoulder elevation to measure the translated distance of each rib and the extension angle of the thoracic spine and to calculate scapulohumeral rhythm (SHR).
Results: Average elevation of each rib was 3.1 mm in men and -0.2 mm in women at 120° of shoulder elevation (p < 0.05), 8.8 mm in males and 2.4 mm in females (p < 0.05) at 160°, respectively. The 5th rib maximally elevated at both 120° and 160° of shoulder elevation. The average extension angle of the thoracic spine was 4.2° in men and 2.2° in women at 160° of shoulder elevation (p < 0.05). The average value of SHR was 2.7 in men and 3.5 in women (p < 0.01) at 160° of shoulder elevation, which indicated that women dominantly moved the glenohumeral joint during shoulder elevation.
Conclusion: As thoracic and scapular motions in females are smaller than those of males, women move the glenohumeral joint dominantly during shoulder elevation.
