Interrater and intrarater reliability of the pectoralis minor muscle length measurement in subjects with and without shoulder impingement symptoms.

Measuring the pectoralis minor muscle length (PML) is of clinical interest, as a short PML has been associated with a decrease of scapular posterior tilting and shoulder pain. However, as no reliability data are available at present, the objective of this study was to examine the inter- and intrarater reliability of the PML measurement in both subjects with and without shoulder impingement symptoms (SIS). Therefore, two assessors performed the PML measurement (3 times/shoulder) in 25 patients with SIS and 25 pain-free controls. Both assessors were blinded for each other's findings. For reliability testing, intra-class coefficients (ICCs; model 2,1) and standard errors of measurements were calculated. Intrarater reliability analysis resulted with ICCs ranging from 0.87 (Standard error of measurement (SEM) 0.21-0.27%) (symptomatic) to 0.93 (SEM 0.19-0.30%) (asymptomatic) in patients with SIS, representing excellent test-retest agreement. Healthy subjects presented with ICCs ranging from 0.76 (SEM 0.29-0.32%) (dominant side) to 0.87 (SEM 0.21-0.32%) (non-dominant side), representing good test-retest agreement. ICCs and SEMs on the symptomatic and asymptomatic side (0.48 and 0.46%; 0.56 and 0.61%) in SIS patients, and on the two sides (non-dominant; 0.47 and 0.45%, dominant; 0.53 and 0.38% respectively) in healthy subjects showed moderate interrater reliability and low dispersion of the measurement errors. We concluded that the PML measurement has good to excellent intrarater reliability and poor to moderate interrater reliability.