Scapulothoracic Joint

Scapulothoracic Joint

This is the Scapulothoracic Joint PDF for you to download

The canine Scapulothoracic Joints are where the forelimbs (thoracic limbs) are attached to the canine trunk by muscles alone. This form of attachment is known as synsarcosis.

In many species including humans, there is a bony union between the forelimb and the trunk through the scapula, clavicle and stenum, via the stenoclavicular and acromioclavicular joints.

Other species have a well developed coracoid bone. However, in the dog, this amazing species has a vestigial clavicle you can find sited at the component attachments of the Brachiocephalicus Muscle. The dog's coracoid process is small and insignificant and found on the medial aspect of the supraglenoid tubercle (attachment of the tendon of origin of Biceps Brachii Muscle).

The canine scapulothoracic joint is defined as a synsarcotic joint and will have a profound impact on the dog's natural balanced motion.

The quadruped have evolved a system of freedom for the scapula to move along the thoracic wall and this movement pattern is often referred to as "scapular glide". This simplistic term does not convey the importance of the integrated movement pattern of a combined simultaneous action of the glide and rotation components. Furthermore, these integrated component movements will be different for protraction and retraction of the forelimb.

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Clinical Tip: Determine the integrated scapular movement actioned by the thoracic muscle sling so you can apply clinically reasoned manual and movement therapies to improve canine scapulothoracic function. This is turn can positively impact stride length and therefore speed.

Canine speed = stride frequency + stride length

Canine Extrinsic Muscles

These have a very important role in the dog by supporting the trunk as it is slung between the two forelimbs. The thoracic sling of muscles work in an integrated and cohesive way and attach the forelimbs to the dog's trunk.

The thoracic sling of muscle includes;

  • Trapezius (superficial to Rhomboideous)
  • Rhomboideous (deep to Trapezius and commonly called Rhomboids)
  • Omotransversarius (one of the 3 muscles that attach to the spine of scapula in the dog)
  • Brachiocephalicus (careful not to confuse this with Sternocephalicus!)
  • Superficial Pectoral (constitutes the Descending and Transverse components)
  • Deep Pectoral (Ascending)
  • Latissmus Dorsi
  • Serratus Ventralis

Canine Biomechanics

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.The canine scapula is able to glide over the wall of the thorax and rotate on that surface to increase the range of movement of the thoracic limb.

OneShot Inside K9HS 002 video

OneShot Inside K9HS 004 video

Summary

Unusually most of the scapulothoracic joint stability comes from a series of muscles that sling the trunk from the scapula and the forelimbs are therefore slung off the trunk.

Stability in the scapulothoracic joint does NOT come from ligaments, but from an integrated muscle sling composed of several extrinsic muscles.

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