Previous studies showed that the insertion of the intramuscular tendons of the deltoid muscle formed three discrete lines. The purpose of the present study was to establish a new dividing method of the deltoid muscle into various anatomical segments based on the distribution of the intramuscular tendons with their insertions (anatomical study). We further hoped to clarify the relationship between the anatomical segments and their activity pattern assessed by positron emission tomography with [18 F]-2-fluoro-deoxyglucose (FDG-PET; PET study). Sixty cadaveric shoulders were investigated in the anatomical study. Three tendinous insertions of the deltoid muscle to the humerus were identified. Then, the intramuscular tendons were traced from their humeral insertions to the proximal muscular origins. The extent of each anatomical segment of the muscle including its origin and insertion was determined through careful dissection. Six healthy volunteers were examined using FDG-PET for the PET study. PET images were obtained after exercise of elevation in the scapular plane. On the PET images, margins of each anatomical segment of the deltoid muscle were determined using magnetic resonance images. Then, the standardized uptake value in each segment was calculated to quantify its activity. The anatomical study demonstrated that the deltoid muscle was divided into seven segments based on the distribution of its intramuscular tendons. The PET study revealed that the intake of FDG was not uniform in the deltoid muscle. The area with high FDG intake corresponded well to the individual muscular segments separated by the intramuscular tendons. We conclude that the deltoid muscle has seven anatomical segments, which seem to represent the functional units of this muscle.

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No difference in the recurrence rate was seen with the use of a shoulder motion restriction band after 3 weeks of immobilization in external rotation after an initial dislocation of the shoulder.

Osteonecrosis of the humeral head in an adolescent without clear pathogenesis has not been reported in the literature. In this case report, we present such a case of humeral head osteonecrosis in a 15-year-old adolescent. The lesion was located at the subchondral area of the medial part of the humeral head with characteristic appearances on MRI. The shoulder was immobilized in a sling until the pain disappeared, and the patient was told to refrain any kind of sport activities. Bone remodeling was noted five months after the first visit, and it took 2 years for the lesion to be totally healed.