Iliopsoas Part 2

It's Muscle Monday again! Time for part 2 of our Psoas muscle group. It's a long read (sorry!), but well worth it I promise. Let's get started!

C L I N I C A L  S I G N S:
In a case where there is an injury to a muscle, it would be expected to see lameness… locomotive signs of discomfort and pain. However, the Iliopsoas muscle group can be injured without causing apparent lameness. Instead, more subtle signs may be evident.
- Loss of muscle tone to Iliopsoas muscle group. (This leads to the horse adjusting his movement = compensatory locomotive patterns.)
- “Hip drop” on the side of injury as hindlimb flexion is limited.
- Unleveled points of tuber coxae when assessed statically. (The Iliopsoas muscle group influences the position of the pelvis.)
- Over-compensation of the uninjured hindlimb or diagonal pair. (Demonstrated by the uninjured hindlimb taking a wider and larger step, increased tarsal flexion, increased MCP joint “sinking” indicating increased weight-bearing)
- Tail carried to the uninjured side.

In ridden work, the rider may feel:
- An uncomfortable twisting motion instead of impulsion
- Resistance to specific movements that encourage
- Hindlimb muscle engagement ie. collection.
- Inability to track up or “step under”
- This can cause the horse to stiffen the back, and increase the weight bearing load onto the forelimbs.

Acute clinical signs can then develop into chronic problems such as:
- Increased muscle tension/hypertonicity of uninjured side and surrounding hip (coxofemoral) joint.
- Eventually muscular tension will be mirrored in the shoulder and neck area. Palpable in the brachiocephalic, pectorals and deltoid.
- If left long enough, this muscular tension can progress to the point of causing lameness.
- Muscular tension can then have a knock on effect on the poll and jaw area.
- This can be attempted to be solved superficially by the use of training aids such as side reins to improve the head and neck position. This can often lead to worsening of current problems, or developing of new ones.
- Atrophy of middle gluteal and hamstrings muscle group.
- Atrophy to the superficial gluteal and proximal bicep femoris on the side of injury may occur due to lack of elasticity of the Iliopsoas prevents full hindlimb retraction.
- This may present by the horse being uncomfortable for the farrier.
- Engagement of the hindquarters becomes increasingly difficult due to muscular atrophy and tension caused by distorted neuromuscular feedback. Consequently, core (hypaxial) muscle engagement is difficult reducing the horses ability to work naturally in self carriage.
- Under saddle, the horse may tilt their head slightly and over-flex on one rein… whilst feeling stiff and unbalanced on the other.

The Link between Iliopsoas Pain and Back Sensitivity:
Sensitivity located over the lumbar portion of the spine and behind the saddle can potentially be associated with Iliopsoas discomfort.

The Link between Iliopsoas Discomfort, Diet and Kidneys:
In close contact with the Iliopsoas muscle group are the kidneys. As the kidneys hold a lot of toxins, the Iliopsoas muscles can act as a “biological dustbin”. Preservatives in feed will increase the amount of toxins in the body, for example, increasing the amount of waste products to be broken down by the kidneys.

The Link between Hormones and Iliopsoas Sensitivity:
The ovaries of a horse sit just behind the last rib. When a mare is in season, she may be particularly sensitive over this area of skin. The Iliopsoas muscle is also located in this area, and may become hypertonic (harder/increased tone) or contain excess fluid (oedema) when in season.
The nerves that determine whether a horse develops ovaries or testicles when they are an embryo are the same. With this in mind, the process of gelding a horse involves the cutting of a neuromuscular bundle. This can mean that branches of nerves that come from the same area of nerves that innervate the ovaries in a mare can be damaged. Hence, a gelding can also become sensitive in the same area that a mare would during her seasons.
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It's a vicious circle when muscles do not function correctly, additional strain on associated tendons, ligaments and joints will undoubtedly occur (See Diagram below).
Source: https://vetphysiophyle.co.uk