Musculus deltoideus
The deltoideus is a thick, triangular muscle covering the lateral shoulder. It originates from the scapular spine and the caudal border of the scapula (via the infraspinatus fascia) and inserts on the deltoid tuberosity of the humerus. Its main actions are to flex the shoulder joint and abduct the humerus. It is visible as the muscular contour over the point of the shoulder and is innervated by the axillary nerve (C6–C7). It contributes to limb protraction and lateral stability. Direct trauma or axillary-nerve injury can affect it, though it is less commonly the primary focus than the biceps or supraspinatus region.
Origin: Scapular spine and caudal border of the scapula via the infraspinatus fascia
Insertion: Deltoid tuberosity of the humerus
Action: Flexes the shoulder; abducts the humerus
Innervation: Axillary nerve (C6-C7)
Contusions or strains can occur with falls or collisions. Axillary-nerve damage (rare) produces atrophy and weakness. Ultrasound can evaluate the muscle belly.
## Overview Intramuscular injections can cause local swelling, pain, abscess, or Clostridial myonecrosis. Signs include heat, swelling, reluctance to move the limb, and sometimes a draining tract. #
Swelling or pain over the outside of the shoulder after trauma should be examined. Most soft-tissue injuries improve with rest and controlled exercise.
## Overview Intramuscular injections can cause local swelling, pain, abscess, or Clostridial myonecrosis. Signs include heat, swelling, reluctance to move the limb, and sometimes a draining tract. ## Causes Bacterial contamination, irritating drugs, or poor injection technique. ## Diagnosis History of recent injection, local signs, and ultrasound or aspiration if abscess is suspected. ## Treatment Anti-inflammatories, hot packing, and drainage plus antibiotics for abscesses. Clostridial infections are emergencies requiring aggressive surgical and medical therapy. ## Recovery and Prognosis Good for simple reactions. Clostridial myositis has a guarded prognosis. ## Prevention Proper site selection, sterile technique, and appropriate drug choice. Signs include: swelling and heat at injection site; reluctance to move the limb; stiff gait; possible abscess with draining tract
Contusions or strains can occur with falls or collisions. Axillary-nerve damage (rare) produces atrophy and weakness. Ultrasound can evaluate the muscle belly.
Swelling or pain over the outside of the shoulder after trauma should be examined. Most soft-tissue injuries improve with rest and controlled exercise.
See the Deltoideus on our interactive 3D horse model. Open 3D Model