Deltoid

Original Editor - Wendy Walker

Lead Editors - Lucinda hampton, Sai Kripa, Wendy Walker, Naomi O'Reilly, Joao Costa, Chrysolite Jyothi Kommu, Andeela Hafeez, Kim Jackson, Vidya Acharya, WikiSysop, Wanda van Niekerk, Aminat Abolade, Admin, Evan Thomas, George Prudden and Uchechukwu Chukwuemeka  

Description

The Deltoid muscle is a large triangular shaped muscle which lies over the glenohumeral joint and which gives the shoulder its rounded contour.

• It is comprised of three distinct portions (anterior or clavicular, middle or acromial, and posterior or spinal)
• Acts mainly as an abductor of the shoulder and stabiliser of the humeral head. as well as assists in forward elevation.
• The deltoid is a very powerful muscle and is used in many ADLs (eg putting clothes on line, carrying shopping bags, washing hair) and many athletic activities. (eg netball, swimming, water polo).

Image 1: Deltoid Muscle overlying shoulder complex.

Anatomy

Origin

1. 
   Anterior Fibres/Head: Lateral third, Anterior Surface of the Clavicle (close to the lateral fibres of pectoralis major).
2. Mid/Lateral Head: Acromion Process scapula, Superior Surface.
3. Posterior Head: Spine of the Scapula, Posterior Border.

Insertion

• 
  Fibres from all heads converge to insert into the deltoid tuberosity on the humerus.
• The deltoid fascia is continuous with the brachial fascia and connects to the medial and lateral intermuscular septa.

Nerve Supply

Axillary Nerve, C5 & 6, posterior cord of the brachial plexus.

Blood Supply

Deltoid receives its blood supply from the posterior circumflex humeral artery.

Function

An important function of deltoid is the stabilisation of the shoulder joint preventing subluxation or even dislocation of the head of the humerus particularly when carrying a load. Deltoid is the prime mover of shoulder abduction.

All heads of deltoid work together to produce abduction of the Shoulder Joint. It helps lifting arm front, side and backwards. Deltoid pain can affect anyone who does repetative overhead activities eg house painters, swimmers, waterpolo players and pitchers. It also is active with carrying objects eg suitcase or reaching up for objects, to prevent subluxation/dislocation.

The deltoid compensates for loss of strength in the rotator cuff.

Images 4 and 5: Deltoids in action in water polo; in carrying deltoid prevent subluxation of shoulder joint.

This 3 minute video is worth watching

Clinical Relevance

Deltoid pathologies can lead to functional disfunction of the shoulder complex

• Tears are not infrequently associated with large or massive rotator cuff tears and may further jeopardize shoulder function.
• Rotator cuff tears place more strain on the deltoid to prevent abduction motion loss. Fatigue or injury to the deltoid may result in a precipitous decline in abduction.
• A variety of other pathologies may affect the deltoid muscle including enthesitis, calcific tendinitis, myositis, infection, tumors, and chronic avulsion injury.
• The deltoid muscle and its innervating axillary nerve may be injured during shoulder surgery, which may have disastrous functional consequences.
• 
  Axillary neuropathies leading to deltoid muscle dysfunction and cause denervation of the deltoid muscle.
• Abnormalities of the deltoid may originate from nearby pathologies of subdeltoid bursa, acromion, and distal clavicle.
• During dislocation of the shoulder or fracture of surgical neck of the humerus axillary nerve may be injured. The damage to axillary nerve leads to paralysis of deltoid muscle.

Image: Trigger Point Referral Patterns (is a hyper-irritable spot, a palpable nodule in the taut bands of the skeletal muscles' fascia).

Assessment

Palpation

Flex elbow to 90 degrees and have patient abduct the shoulder against resistance.

Anterior Fibers: Deltoid palpated with elbow extended, shoulder 90 degrees abduction and then resist horizontal adduction.

Posterior Fibers: Position same as above and then resist horizontal abduction.

Length Tension Testing

Length Tension Testing

Anterior Deltoid- The position of patient will be high sitting

• The therapist will be standing behind the patient holding the testing shoulder
• The primary function of anterior deltoid is flexion, internal rotation and horizontal adduction, to stretch this muscle, reverse the action by extension, external rotation and horizontal abduction shoulder, without letting the torso rotate
• While performing extension and external rotation, place your one hand on the patient forearm and with the other hand push the shoulder anteriorly from posterior, thereby lengthening the muscle

Posterior Deltoid- The position of patient will be high sitting

• The therapist will be standing in front of the patient initially and moving back to the patient later for better length assessment
• The primary function of posterior deltoid is extension, external rotation and horizontal abduction, to stretch this muscle, reverse the action by flexion, internal rotation and horizontal adduction shoulder joint.
• While performing flexion, internal rotation and horizontal adduction, place your one hand on the patient's shoulder and the other hand on patient's forearm
• Alternatively, perform flexion, internal rotation and horizontal adduction shoulder by bringing the patient's shoulder against the chest and therapist moving to the back of the patient by holding the patient's shoulder and forearm, lengthening the muscle.

Exercises

The following deltoid strengthening exercises are designed to improve the strength of the deltoid muscles

Isometric Deltoid Contraction

Standing next to a wall with back and elbow straight. Gently push arm to the side against the wall as hard as possible and comfortable without pain. Hold for 5 seconds and repeat 10 times on each side provided it is pain free. 

Progress Resistance Band Forward Raises, lateral raises and pull backs