Abstract
Purpose
Full-thickness tendon tears of the supraspinatus (SP) are common and can have a significant impact on shoulder function. To optimally treat supraspinatus tendon tears an accurate understanding of its musculotendinous architecture is needed. We have previously shown that the architecture of supraspinatus is complex. It has architecturally distinct regions: anterior and posterior, each of which is further subdivided into superficial, middle and deep parts (Kim et al., 2007). Data of FBL and PA of the torn supraspinatus could enhance clinical decision making and guide rehabilitative treatments (Ward et al., 2006). Currently, however, in vivo US quantification of the fiber bundle architecture of the distinct regions of supraspinatus in subjects with full-thickness tendon tears has not been investigated.
PURPOSE: To quantify architectural parameters within the distinct regions of supraspinatus in subjects with a full-thickness tendon tear using the US protocol that we previously developed (Kim et al., 2010), and to compare findings with age and gender matched normal controls.
Method
Twelve SP from eight subjects, mean age 576.0 years, were scanned using an US scanner (12 MHz). The SP was scanned in relaxed and contracted states. For the contracted state, SP was scanned with the shoulder in neutral rotation and 60 of active abduction. Fiber bundles of the anterior region (middle and deep) and posterior region (deep) could be visualized and measured. Muscle thickness, FBL, and PA were computed from US scans. Data was analyzed using Mann-Whitney and Wilcoxon Signed Rank Tests (P<0.05).
Results
Intra-and inter-rater measurements of FBL were strongly correlated with no significant difference between measurements (P<0.001). In the anterior region, mean FBL did not significantly differ between the pathologic subjects and normal controls. In the pathologic subjects, mean PA was smaller compared to normal controls. The difference was significant between the subjects with a tear and retraction and normal controls (P<0.05). For the posterior region, mean FBL was shorter in the pathologic subjects compared to normal controls. The difference was significant between the subjects with a tear and retraction and normal controls (P<0.05).
Conclusion
Findings suggest that significant FBL and PA changes are found with full-thickness tendon tears of SP and different regions of the muscle are impacted differently. Pennation angles are largely impacted in the anterior region and FBL in the posterior. The presence of tendon retraction was found to be related to the amount of change in architectural parameters. Data from this study may be useful to model muscle-joint behavior of the pathologic shoulder. This US protocol may be beneficial to carry out a larger study to determine which comes first, architectural changes in the muscle, or tendon tearing. If we identify changes in muscle architecture predate tendon pathology, we could develop techniques to prevent tendon tearing.
