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.

The muscle-tendon junction (MTJ) is a highly specific tissue interface where the muscle\'s fascia intersects with the extracellular matrix of the tendon. The MTJ functions as the particular structure facilitating the transmission of force from contractive muscle fibers to the skeletal system, enabling movement. Considering that the MTJ is continuously exposed to constant mechanical forces during physical activity, it is susceptible to injuries. Ruptures at the MTJ often accompany damage to both tendon and muscle tissues. In this review, we attempt to provide a precise definition of the MTJ, describe its subtle structure in detail, and introduce therapeutic approaches related to MTJ tissue engineering. We hope that our detailed illustration of the MTJ and summary of the representative research achievements will help researchers gain a deeper understanding of the MTJ and inspire fresh insights and breakthroughs for future research.

Transcranial magnetic stimulation (TMS) of the motor cortex during a maximal voluntary contraction (MVC) permits functionally relevant measurements of muscle group relaxation rate (i.e., when muscles are actively contracting under voluntary control). This study\'s purpose was twofold: (1) to explore the impact of muscle length on TMS-induced plantar flexor relaxation rate; and (2) to incorporate ultrasonography to measure relaxation-induced lengthening of medial gastrocnemius (MG) fascicles and displacement of the muscle-tendon junction (MTJ). Eleven males (24.8 ± 7.0 years) performed 21 brief isometric plantar flexor MVCs. Trials were block-randomized every three MVCs among 20° dorsiflexion (DF), a neutral ankle position, and 30° plantar flexion (PF). During each MVC, TMS was delivered and ultrasound video recordings captured MG fascicles or MTJ length changes. Peak relaxation rate was calculated as the steepest slope of the TMS-induced drop in plantar flexor torque or the rate of length change for MG fascicles and MTJ Torque relaxation rate was slower for PF (-804 ± 162 Nm·s-1) than neutral and DF (-1896 ± 298 and -2008 ± 692 Nm·s-1, respectively). Similarly, MG fascicle relaxation rate was slower for PF (-2.80 ± 1.10 cm·s-1) than neutral and DF (-5.35 ± 1.10 and -4.81 ± 1.87 cm·s-1, respectively). MTJ displacement rate showed a similar trend (P = 0.06), with 3.89 ± 1.93 cm·s-1 for PF compared to rates of 6.87 ± 1.55 and 6.36 ± 2.97 cm·s-1 for neutral and DF, respectively. These findings indicate muscle length affects the torque relaxation rate recorded after TMS during an MVC Comparable results were obtained from muscle fascicles, indicating ultrasound imaging is suitable for measuring evoked contractile properties during voluntary contraction.

BACKGROUND: The complex structure of the bone-tendon and muscle-tendon junctions makes their reproduction for tissue engineering applications very difficult. Relatively few studies have investigated the characteristics of these regions from a tissue engineering view point.
METHODS: PubMed, Thomson Reuters, Scopus and Google Scholar databases were searched using various combinations of the keywords \'Tendon\', \'Myotendinous junction\', \'Osteotendinous junction\', \'Tissue engineering\' and \'Scaffold\'.
RESULTS: The available studies can be divided according to whether the objective is to build an entire composite tissue unit or to assist the recreation of interfaces, such as improving integration of autografts with the surrounding bone or with the muscle. The most used techniques are based on the electrospinning and the self-reorganized constructs process, which were applied to both bone-to-tendon junction (BTJ) and muscle-to-tendon junction (MTJ) regeneration. The use of nanofibers that mimic the hierarchical structure of the extracellular matrix (ECM), eventually functionalized by encapsulation of bioactive components, allowed cell attachment and differentiation.
RESULTS: There have been no translational investigations.
CONCLUSIONS: There is a need to devise suitable techniques that allow suitable tissue engineering of BTJ and MTJ.
CONCLUSIONS: Appropriately planned studies are needed to translate tissue engineering from a scientific challenge to a clinically applicable technique.

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