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

• We investigated the influence of muscle length on scapular dyskinesis.
• We determined to what extent possible predictors for this case are.
• The shorter the pectoralis minor, the more likely the arm has scapular dyskinesis.
• Upper trapezius shortness increases the likelihood of exhibiting scapular dyskinesis.
• Routine assessment of these muscle lengths in scapular examination is recommended.

ObjectivesAlthough 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.DesignCross-sectional study.SettingUniversity research laboratory.ParticipantsAsymptomatic participants (n = 148; 296 arms) were evaluated.Main outcome measuresScapular Dyskinesis Test (SDT) was used to identify scapular dyskinesis, Pectoralis Minor Index (PMI) and Upper Trapezius Length Testing were used to determine muscle length.ResultsSDT+ 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).ConclusionsHaving a shorter pectoralis minor and upper trapezius length substantially increased the likelihood of having visually observable scapular dyskinesis.