Shoulder Joint

Shoulder Joint

This is the Shoulder Joint PDF for you to download

The canine shoulder joint is a synovial ball and socket joint. It involves the head of the humerus (ball) and the glenoid cavity of the scapula (socket).

The dog is designed to move forwards in the sagittal plane and functionally (physiologically) the shoulder joint's main movements are flexion and extension, whereas anatomically it can move in all directions.

A ball and socket joint is also known as a spheroidal joint. Synovial joints are designed to facilitate movement.

Joint movements due to the muscle contractions of muscle / s that pass across a joint are known as active movements.

Synovial Joints

Synovial joints are also known as diarthrosis and are the most common joint found in the dog. There are different types of synovial joints;

1. Hinge; movement occurs primarily in a single plane, for example, elbow, stifle, interphalangeal joints

2. Ball and socket; for example hip and shoulder joint, these allow movement around 3 axes;

  • Flexion / extension
  • Abduction / adduction
  • Internal / external rotation

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The dog has specific design features to ensure the canine ball and socket hip and shoulder joints function predominantly as a hinge joint, moving in the sagittal plane, unlike in humans.

3. Pivot; a ring of bone and ligament surrounds the surface of the other bone with movement in one plane, primarily rotation, for example between the radius and ulna (radioulnar joint)

4. Gliding; flat bone surfaces allow side to side and backwards and forwards movements, for example; between carpal bones in the carpus (commonly known as the wrist in the dog); between tarsal bones in the tarsus (hock joint).

Synovial Joint Design

The synovial joint has articular cartilage between the bone ends (hyaline cartilage). All synovial joints have a joint cavity which is filled with synovial fluid and is held within the joint by the loose synovial membrane that lines the fibrous joint capsule.

The synovial membrane is delicate and produces the fluid which decreases friction and the joint is ideal for providing range of movement, as well as providing nutrition for the articular cartilage. The synovial membrane lines the fibrous joint capsule and covers all structures within the joint but does not cover the articular surfaces, as it blends with the periosteum of the bone.

A few synovial joints have their own particular modifications to the joint, depending on the function they perform, for example, the stifle joint has menisci.

Medial and lateral collateral ligaments are designed to optimise the dog to move forward in the sagittal plane. The dog is biomechanically designed to move forwards!

The nerve supply to the joint arises from the cutaneous or motor branches for the muscles which are near the joint.

Some parts of the joint are more richly innervated than others and there are 4 main types of joint receptors;

  1. Ruffini type receptors found in the joint capsule
  2. Pacinian type receptors found in the joint capsule
  3. Golgi tendon organs found in the ligaments
  4. Free nerve endings

This innervation provides the proprioceptive information needed to recognise the movements in the joint.

Schematic drawing of a typical synovial joint.
Schematic drawing of a typical synovial joint.

Shoulder Joint Supporting Structures

As loose links all synovial joints require stabilising structures to maintain the support needed for efficient natural balanced stance, postures and motion.

  • Glenoid Labrum
  • Fibrous joint capsule
  • Transverse humeral retinaculum
  • Glenohumeral ligaments
  • Schematic drawing of left shoulder joint.
    Schematic drawing of left shoulder joint.

The glenoid cavity of the scapula is deepened by the
The glenoid cavity of the scapula is deepened by the glenoid lip (labrum).
Schematic drawing of
Schematic drawing of ventral angle of left scapula.
Schematic drawing of
Schematic drawing of capsule of left shoulder joint.

Shoulder joint dynamic support from muscles tendons

  • Cranially from Biceps Brachii tendon of origin
  • Acting as a lateral collateral ligament are the short, strong tendons of Supraspinatus and Infraspinatus muscles
  • Acting as a medial collateral ligament is the tendon of Subscapularis muscle
  • Assisting these key stabilisers above are the muscles Teres major (medially) and Teres Minor (laterally), acting together caudally to encourage forward motion in the sagittal plane
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Clinical Tip: For accurate and relevant information, it's very useful to consider the bony landmarks near to the structure you are going to palpate. Finding these using Therapeutic Handling and Therapeutic Touch work empowers your palpation skills and accuracy.

Location of greater tubercle of humerus.
Location of greater tubercle of humerus.
Greater tubercle of the humerus (forefinger) + the acromium (thumb). The shoulder joint lies equidistance between these 2 structures.
Greater tubercle of the humerus (forefinger) + the acromium (thumb). The shoulder joint lies equidistance between these 2 structures.
Supporting joint structures are static and dynamic, both integrating to ensure the canine specific joint motion is efficient and enables the canine patterns of movement within the sagittal plane. This is very different to human generated patterns of movement and function.
Lily modelling a "well fitted Y shaped harness" optimising her natural balanced stance, postures and motion. This empowers her shoulder joint function.
Lily modelling a "well fitted Y shaped harness" optimising her natural balanced stance, postures and motion. This empowers her shoulder joint function.
A "well fitted Y shaped harness" maximises efficient and natural balanced stance, postures and motion.
A "well fitted Y shaped harness" maximises efficient and natural balanced stance, postures and motion.

This poorly fitting harness clearly shows how it will hinder forelimb protraction and canine shoulder joint movement.
This poorly fitting harness clearly shows how it will hinder forelimb protraction and canine shoulder joint movement.
Close up of a poor fitting harness impeding the movement of the dog.
Close up of a poor fitting harness impeding the movement of the dog.

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Anti-pull harnesses take the dog out of balance and are not therapeutically helpful.

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Clinical Tip: Always carefully check the Y shaped harness is the best fit and does not impinge on the long head of Triceps Brachii, as this will negatively impact the dogs natural balanced stance and motion. Breed variation across this amazing species means you need a selection of different Y shaped harnesses to choose from for each dog in your professional care.

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