Innervation of the subscapularis: an anatomic study

Abstract

Background Successful healing of the subscapularis during anatomic total shoulder arthroplasty surgery is critical to optimize functional outcomes and avoid complications. The purpose of this study was to examine the upper and lower subscapularis nerve insertion in relation to the musculotendinous junction to estimate the risk of nerve injury. Our hypothesis was that arm position changes the risks to these nerves when exposing the anterior glenoid. Methods Twenty cadaveric shoulders were dissected, and the subscapular nerves were identified from the posterior cord of the brachial plexus to the muscle insertion. The nerve length from the origin to the muscle insertion and the distance to the myotendinous junction were measured in various shoulder positions including neutral, external, and internal rotation. Results The mean length of the upper subscapular nerve was 51.4 ± 12.8 mm; that of the lower subscapular nerve was 50.5 ± 14 mm. The mean distance from the insertion of the upper subscapular nerve to the myotendinous junction 53.0 ± 14.7 mm with external rotation, 38.5 ± 9.7 mm with neutral rotation, and 30.0 ± 9.2 mm with internal rotation. The mean distance from the lower subscapular nerve to the myotendinous junction was 44.5 ± 13.8 mm with external rotation, 31.9 ± 9.3 mm with neutral rotation, and 25.4 ± 8.8 mm with internal rotation. The internally rotated position placed these nerves closest to the glenohumeral joint. Conclusion The upper and lower subscapular nerves insert in the muscle belly close to the myotendinous junction, putting them at risk of iatrogenic injury. Care must be taken to avoid damage with retractor placement in the anterior glenoid neck as these nerves are at risk of compression or torsional injury.

A very rare case of an accessory subscapularis muscle and its potential clinical significance

“…Its origin is located on the costal surface of the scapula, which is called the subscapularis fossa. Its insertion is situated on the superior part of the humerus (in most cases, the lesser tuberosity) [ 11 , 14 , 23 ]. The SM limits the axillary fossa from behind.…”

Variations in Subscapularis Muscle Innervation—A Report on Case Series

“…Sager and colleagues [ 4 ] measured the distance from the insertion of the upper and lower subscapular nerve to the myotendinous junction with the arm adducted and externally rotated, in neutral position and internally rotated. For external rotation the distance to the upper subscapular nerve was 53.0 ± 14.7 mm (range 32–85 mm) and to the lower subscapular nerve 45.5 ± 13.8 mm (range 26–71 mm).…”

“…In rare cases an accessory subscapularis muscle can be found [ 3 ]. The subscapularis muscle is typically innervated by two distinct nerves, namely an upper and a lower subscapular nerve, both originating from the brachial plexus [ 4 ]. These two nerve branches cross the axillary vein dorsally to reach the subscapularis muscle [ 5 ].…”

“…The typical pattern described in textbooks are two subscapular nerves, both originating from the posterior cord of the brachial plexus [ 7 ]. Nevertheless, the existing literature describes the subscapular nerves as being rather variable in their origin [ 1 , 4 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ] and there are some reports about accessory subscapular nerves [ 8 , 10 , 11 , 12 , 14 , 15 , 16 ].…”

Transferência do nervo subescapular inferior para o ramo motor do músculo redondo menor: estudo anatômico

“…O nervo subescapular inferior foi constante em todas as dissecções, assim como relatado nos estudos anatômicos encontrados [22][23][24][25][26][27][28][29][30][31][32][33][34] . Seu diâmetro médio foi de 1,9 mm, mesma medida encontrada por Tubbs et al 23 .…”