An anatomical description of the pennation angles and central tendon angle of the supraspinatus both in its normal configuration and with full thickness tears

HypothesisIt is hypothesized that supraspinatus central tendon retraction is related to functional deficit; yet, there is no literature comparing the normal and pathological pennation and central tendon angles using magnetic resonance imaging (MRI). Therefore, the aim of this study was to quantify the anterior and posterior muscle pennation angles, central tendon angle, and retraction of the supraspinatus using MRI.MethodsAnterior pennation angle (APA), posterior pennation angle (PPA), and central tendon angle (CTA) were measured from 2 groups: no tear (NT, n = 157), full thickness tears (FTT) with retraction (FTT, n = 156).ResultsNo tear (NT) average APA, PPA, and CTA were 19.0° (SD 5.9), 4.0° (SD 3.2), and 17.8° (SD 5.1). All differences were statistically significant (PPA < APA, P < .001; PPA < CTA, P < .001; CTA < APA, P < .001). FTT averages were 17.6° (SD 8.6), 16.7° (SD 12.2), and 7.3° (SD 4.9). Increasing retraction correlated to PPA (P < .001), APA (P < .002), and CTA (P < .001).ConclusionThe size of a supraspinatus tear is directly correlated with muscle pennation and tendon retraction, and provides a direct measurement from MRI that can now be employed in further studies of functional deficit and tendon tear size.