Analysis of shoulder motion with inertial sensors in Poland syndrome patients

Poland syndrome is a congenital malformation characterized by agenesis or hypoplasia of pectoralis muscles. There is a limited literature on how the anatomic anomalies of PS may impact the movement of the shoulder. This study analyzes the effects of absence of the pectoralis muscles on the shoulder kinematic.

Clinical evaluation was performed analyzing range of motion (RoM), stability, cuff disease and internal rotation strength. In all patients, we used inertial sensors to analyze scapular motion in three degrees of freedom: medium-lateral rotation, posterior tilting and protraction-retraction. The same analysis was performed by dividing the patients into two groups by age to evaluate the presence of age-related alterations.

No differences in RoM between pathological and healthy side were observed. All patients were positive for posterior instability. No significant differences in strength in internal rotation were observed with average + 6,91% (s = 2,14) on the healthy side's strength. Kinematic analysis showed higher values of scapular medium-lateral rotation and anticipation of retraction of the pathological side during flexion and abduction. Reduced scapular tilt in under 18 years old was found.

The absence of the pectoralis muscles seems not to affect the RoM. The increased scapular rotation on the medium-lateral axis is probably due to the absence of humeral insertion of the pectoralis major and the absence of the scapular insertion of the pectoralis minor. The increased retraction in abduction it can be explained by a hypercontraction of the scapular stabilizers. The reduced tilt in under 18 years old is influenced by the lack of adaptation by the muscle groups involved.