Spinalis

​Okay okay, Muscle Monday is a day late this week. Forgive me it's been a bit hectic! This week's muscle is the Spinalis. It's a deep muscle that is often just given a passing note in the textbooks, but it has a pretty significant part in saddle fit. Let's get started.

L O C A T I O N:
You'll find the muscle in a hidden area of the spine at the base of the neck, the cervico-thoracic junction, deep between the scapulae. It's a small, triangular area at the base of the withers that you can actually palpate (feel). It’s actually a muscle of three parts – dorsalis, thoracis and cervicis. These names denote its many insertions (attachment spots), for it links the spinous processes of the lumbar, thoracic and cervical vertebrae.

R O L E:
In his 1980s’ Guide to Lameness videos, Dr. James Rooney referred to Spinalis as part of the suspension bridge of muscles supporting the spine (Longissimus dorsi achoring from the lumbosacral vertebrae, Spinalis thoracis et dorsalis from the upper thoracics). He also refers to this extensively in The Lame Horse (1988). The Spinalis is often credited with a role in turning the head to left to right, and raising the head. BUT if you go into older texts you can find it mentioned for its help in stabilizing the spine.
Given that the nuchal ligament doesn’t attach to C6 and often only weakly with C5, Spinalis suddenly appears pretty important in stabilizing and lifting the base of the neck, particularly as it does so at the point of greatest lateral bending.
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S P I N A L I S  &  S A D D L E  F I T
When a horse has been ridden in an overly tight saddle, this small area of muscle can become pretty hypertrophic – raised and hardened. Typically, the neighbouring muscles are atrophied. When Spinalis is palpated, the horse often gives an intense pain response, flinching down and raising the head.
Next week we are going to take this one step further and look at Inverted Posture and Asymmetry. Stay tuned!