A novel 3D MRI-based approach for assessing supraspinatus muscle length

Rotator cuff (RC) tears are a common source of pain and decreased shoulder strength. Muscle length is known to affect muscle strength, and therefore evaluating changes in supraspinatus muscle length associated with RC pathology, surgical repair, and post-operative recovery may provide insights into functional deficits. Our objective was to develop a reliable MRI-based approach for assessing supraspinatus muscle length. Using a new semi-automated approach for identifying 3D location of the muscle-tendon junction (MTJ), supraspinatus muscle length was calculated as the sum of MTJ distance (distance between 3D MTJ position and glenoid plane) and supraspinatus fossa length (distance between root of the scapular spine and glenoid plane). Inter- and intra-operator reliability of this technique were assessed with intraclass correlation coefficient (ICC) and found to be excellent (ICCs > 0.96). Muscle lengths of 6 patients were determined before RC repair surgery and at 3- and 12-months post-surgery. Changes in normalized muscle length (muscle length as a percentage of pre-surgical muscle length) at 3 months post-surgery varied considerably across patients (16.1 % increase to 7.0 % decrease) but decreased in all patients from 3- to 12-months post-surgery (0.3 % to 17.2 %). This study developed a novel and reliable approach for quantifying supraspinatus muscle length and provided preliminary demonstration of its utility by assessing muscle length changes associated with RC pathology and surgical repair. Future studies can use this technique to evaluate changes over time in supraspinatus muscle length in response to clinical intervention, and associations between muscle length and shoulder function.

In Vivo Static Retraction and Dynamic Elongation of Rotator Cuff Repair Tissue After Surgical Repair: A Preliminary Analysis at 3 Months

Background:

Rotator cuff repair is a common orthopaedic procedure that provides pain relief for many patients, but unfortunately, an estimated 20% to 70% of repair procedures will fail. Previous research has shown that elongation (ie, retraction) of a repaired tendon is common even in patients with a repair construct that appears intact on magnetic resonance imaging. However, it is unknown how this repair tissue functions under dynamic conditions.

Purpose:

To quantify static retraction and maximum dynamic elongation of repair tissue after rotator cuff repair.

Study Design:

Case series; Level of evidence, 4.

Methods:

Data from 9 patients were analyzed for this study. During surgery, a 3.1-mm tantalum bead was sutured to the supraspinatus tendon, medial to the repair site. Glenohumeral kinematics were assessed at 1 week (static) and 3 months (static and during scapular-plane abduction) after surgery using a biplanar videoradiographic system. The 3-dimensional position of the bead was calculated relative to the tendon’s insertion on the humerus (ie, bead-to-insertion distance). Static retraction was calculated as the change in the bead-to-insertion distance under static conditions between 1 week and 3 months after surgery, and maximum dynamic elongation was calculated as the maximal positive change in the bead-to-insertion distance during dynamic motion relative to the start of motion. The magnitudes of static retraction and maximum dynamic elongation were assessed with 1-sample t tests.

Results:

At 3 months after surgery, static retraction occurred in all patients by a mean of 10.0 ± 9.1 mm (P = .01 compared with no elongation). During scapular-plane abduction, maximum dynamic elongation averaged 1.4 ± 1.0 mm (P < .01 compared with no elongation). Descriptively, dynamic elongation consistently took 1 of 2 forms: an initial increase in the bead-to-insertion distance (mean, 2.0 ± 0.6 mm) before decreasing until the end of motion or an immediate and substantial decrease in the bead-to-insertion distance at the onset of motion.

Conclusion:

Repair tissue elongation (static retraction and maximum dynamic elongation) appeared to be a common and significant finding at 3 months after arthroscopic rotator cuff repair. Dynamic elongation of repair tissue during scapular-plane abduction exhibited 1 of 2 distinct patterns, which may suggest different patterns of supraspinatus mechanical and neuromuscular function.