Innervation of the subscapularis: an anatomic study.

Area of Science:

• Orthopedic Surgery
• Neuroanatomy
• Surgical Anatomy

Background:

• Subscapularis muscle healing is crucial for successful anatomic total shoulder arthroplasty (TSA).
• Iatrogenic injury to subscapular nerves can compromise functional outcomes.
• Understanding nerve insertion points is key to preventing complications during TSA.

Purpose of the Study:

• To analyze the insertion of the upper and lower subscapular nerves relative to the musculotendinous junction.
• To assess the risk of nerve injury during TSA based on shoulder position.
• To determine if arm position influences the vulnerability of subscapular nerves.

Main Methods:

• Dissection of 20 cadaveric shoulders to identify subscapular nerves.
• Measurement of nerve length from origin to muscle insertion.
• Quantification of nerve distance to the myotendinous junction in neutral, external, and internal rotation.

Main Results:

• Mean upper subscapular nerve length: 51.4 mm; lower: 50.5 mm.
• Nerve-to-myotendinous junction distance decreased significantly with internal rotation.
• Internal rotation placed both nerves closest to the glenohumeral joint, increasing risk.

Conclusions:

• Upper and lower subscapular nerves insert near the myotendinous junction, posing an iatrogenic risk.
• Retractor placement in the anterior glenoid neck requires caution.
• Nerve compression or torsional injury is a risk during TSA, especially in internal rotation.