Influence of pectoralis minor and upper trapezius lengths on observable scapular dyskinesis

Objectives: Although a relationship between short pectoralis minor and upper trapezius and scapular dyskinesis has been postulated, no studies have investigated this theory. Understanding the effect of these muscle lengths on observable scapular dyskinesis may aid in determining risks and therefore making treatment decisions. Being aware of the magnitude of this effect would help gauge the significance of risks involved. Our aim was to evaluate the influence of pectoralis minor and upper trapezius lengths on scapular dyskinesis.

Design: Cross-sectional study.

Setting: University research laboratory.

Participants: Asymptomatic participants (n = 148; 296 arms) were evaluated.

Main outcome measures: Scapular Dyskinesis Test (SDT) was used to identify scapular dyskinesis, Pectoralis Minor Index (PMI) and Upper Trapezius Length Testing were used to determine muscle length.

Results: SDT+ arms had shorter pectoralis minor resting length (PMI: 7.49 ± 0.38) (p < 0.001) and greater incidence of short upper trapezius (ISUT) (66.7%) (p < 0.001) compared to SDT- arms (PMI:8.58 ± 0.75, ISUT:22.5%). With each decrease in PMI, the likelihood of having scapular dyskinesis increased 96% (p < 0.001). Arms with short upper trapezius were 2.049 times more likely to exhibit scapular dyskinesis than those with normal length (p = 0.042).

Conclusions: Having a shorter pectoralis minor and upper trapezius length substantially increased the likelihood of having visually observable scapular dyskinesis.