When We Are Faced With the Unknown: Clinical Reasoning of an Equine Shoulder Pathology

by | Jun 30, 2022 | Equine Therapy

When it comes to cases that are out of the ordinary and present with clinical signs that are unknown or very uncommon, we can be challenged on multiple levels to identify a pathoanatomical diagnosis, a reasonable and realistic treatment plan, and a potential prognosis for the patient. 

 

Cases that present as outside of the norm force us to lean on our clinical reasoning, our evaluation techniques and procedure, and our knowledge of anatomy. Leaning on our community and colleagues is a valuable part of the clinical reasoning process. 

 

In today’s blog, we discuss and clinically reason a presentation, recently shared on social media, of a horse with what seems to be a collapsing shoulder or thoracic sling.

 

Clinical reasoning procedure

The more complex a patient seems, the more important it is for us to revert to basics. The less information we have on a patient, the more important this becomes!

The number one tool that has helped me stay on track during clinical reasoning is the development of a problem list.

Secondary to that is an understanding (not only knowledge) of anatomy and its interrelation to the entire body.

Thirdly, up-to-date knowledge of the current literature in our field can help us to think outside the box for potential tools and techniques that might help and support a particular patient.

And finally, probably the most important tool would be a supportive community who can add their thoughts, experience, observations and knowledge to the clinical reasoning process. This is why the Onlinepethealth Vetrehabbers Facebook communities are so incredibly valuable.

 

Case discussion: Equine Shoulder

I would love to clinically reason through a particular case with you today that has drawn quite a bit of interest on social media, with a very abnormal presentation. All the information that we have, as Onlinepethealth, is in this video:  https://www.facebook.com/onlinepethealthequine/posts/569041301622358

NB: This is not a case that we, or any of our Vetrehabbers (to our knowledge), have seen. We do not have a history or information from a full evaluation. Below we discuss only what we can see and guess from this video.

The Vetrehabber community was as flummoxed as we were when watching this video, but several potential causes came up for discussion, including:

  • scapulohumeral dislocation/subluxation
  • failure of the pectoral muscles
  • failure of the serratus ventralis
  • failure of the biceps tendons
  • trauma to the thoracic sling
  • trauma to the cervicothoracic vertebrae
  • failure of the lacertus fibrosis
  • sweeney

Let us keep all of these thoughts in the back of our minds, take a look at the video, and try to break down what exactly we are seeing.

In the relaxed or released posture, we see

  • an acute shoulder angle with a very flat scapula
  • the points of the shoulders are protruding cranially and bilaterally.
  • The elbows and distal joints are straight and stable.
  • The thorax is dropped significantly.
  • The neck seems short in front of the shoulder.
  • The back and ribcage seem long behind the shoulder
  • Angulation of the hindlimbs appears straight

When the handler applies force to the point of the shoulder and the top of the whither, we can see:

  • The scapula rotates into a more upright position,
  • The thorax lifts
  • A more neutral spinal alignment with the posture only slightly croup high
  • The neck still seems short coming out of the shoulder,
  • The back and ribcage still seem long behind the shoulder.
  • It appears to be relatively easy (a matter of changing a lever angle) for the handler to achieve the change.
  • The scapula and thorax drop immediately on release of the handler’s hold.
  • The humerus and scapula seem to move in unison, and there is no visible subluxation/relaxation with pressure applied by the handler.
  • Angulation of the hindlimbs appears straight.

Illustration of the change in posture.

From these observations, I would narrow down that the primary problem may lie in the stabilisation of the scapula or glenohumeral joint, or maintaining the scapular in extension during stance.

Next, we can start to ask ourselves which structures might be involved in this pathology.

We should look at two areas; first, the thoracic sling, and secondly, the shoulder or glenohumeral joint. While we consider these individual anatomical structures, we need to keep in mind the tensegrity of the body, and the interconnected function of different structures.

 

 

The Thoracic sling

The deeper components of the thoracic sling include the pectoral muscles, serratus ventralis and rhomboid muscles. These muscles connect the limb and the trunk and provide support to both. If we individually consider these muscles:

  • Serratus ventralis is the primary trunk support and elevates the neck when a limb is WB. It is innervated by the ventral branches of the Cx nerves.
  • Rhomboideus draws the shoulder dorsally and elevates the neck, and is innervated by the ventral branches of C6-7.
  • Pectoralis profundus supports the trunk and draws the limb caudally. It is innervated by the cranial and caudal pectoral nerves.

If we look at this illustration and consider what would happen if each of these muscles failed to function, we can ‘rule out’ the serratus ventralis for two reasons: Its absence or inactivity would not cause the scapular angle to become more acute, and secondly, when the handler rotates the scapula, the thorax lifts, indicating that the connection between the serratus ventralis and the scapula is intact.

The rhomboideus acts to pull the dorsal border of the scapula dorsally and cranially – its failure may result in a drop in the scapular angle.

The pectoral muscle acts primarily on the humerus, which seems to maintain its position and angle sufficiently.

The more superficial muscles of the thoracic sling include the brachiocephalicus, latissimus dorsi and trapezius.

  • Trapezius draws the scapula cranially and caudally and is innervated by the accessory nerve.
  • Brachiocephalicus draws the limb cranially and is innervated by the cervical nerves.
  • Latissimus dorsi is innervated by the thoracodorsal nerve.

If we look at these three muscles, brachiocephalicus seems shortened, and, from what we can see in the video, may be atrophied.

The trapezius muscles are likely under a great deal of strain and may have sustained damage.

Latissimus dorsi will play a role in maintaining shoulder extension in a standing position, as it pulls the humerus caudally. In this illustration, it appears that the lats dorsi is strained and elongated, as well as potentially atrophied. The pull on the thoracolumbar fascia as a result of the cranially displaced shoulder joint seems significant.

If I consider these structures and the changes that are visible in this horse, I am more likely to consider them as secondary changes rather than a primary cause in this case.

 

Soft tissues stabilising the shoulder joint

If we consider the shoulder joint and the structures surrounding it, as well as their function, we think about the following musculotendinous units and structures:

  • Infraspinatus provides lateral support and flexion of the shoulder, innervated by the suprascapular nerve.
  • Supraspinatus provides extension and stabilisation, innervated by the suprascapular nerve
  • Biceps brachii provides shoulder extension and forms a part of the stay apparatus, innervated by the musculotendinous nerve.
  • Deltoid and teres minor provide flexion and are innervated by the axillary nerve.

On the medial aspect of the joint

  • Subscapularis provides medial joint support and is innervated by the subscapular and axillary nerves.
  • Coracobrachialis provides support and flexion and is innervated by the musculocutaneous nerve.

On the caudal aspect of the joint, we have the primary flexors of the shoulder, including the triceps and teres major.

Considering these structures, my mind leans towards a failure of the biceps brachii and supraspinatus muscles/tendons. Without their role in maintaining shoulder extension, the weight of the thorax and the large number of attachments supporting shoulder flexion, a clinical picture such as this one.

However, the fact that this pathology occurs bilaterally adds another dimension of challenge to the clinical picture and nudges us to consider the neurological component of this presentation.

 

The brachial plexus

Each of the muscles discussed thus far is innervated by different nerves originating in the caudal cervical region, which forms a part of the brachial plexus. It is incredibly difficult to predict how a neurological injury may present, but if we consider some scenarios:

  1. Injury to the cervical spine leads to compression of the spinal cord.

In this case, the presentation before us makes this unlikely, as compression of the spinal cord, even within the cervical spine, would affect the pelvic limbs before the thoracic limbs.

  1. Trauma to the brachial plexus

Again, it is unlikely that trauma to the brachial plexus will occur to the same degree bilaterally. Of course, we are unable to see the opposite limb in this video, but let’s continue to assume that both legs are affected in a very similar way.

  1. Impingement of the nerve roots

If trauma to the cervical spine occurred and resulted in impingement of the nerve roots, we are again more likely to see a lateralized presentation. However, if that impingement was caused by inflammation and swelling, we might potentially see a bilateral presentation.

Potentially, trauma occurred to the cervical spine, leading to swelling and inflammation that caused nerve root impingement. The brachial plexus is affected, and the muscles of the shoulder start to atrophy, in particular the biceps brachii.

This still feels like a ‘far-fetched’ and unlikely scenario, but what if we add another neurological layer?

There were a few observations in the community that this horse does not seem to be in pain – and I had the same thought. When we can see her face, her expression is attentive but calm. If we think back to our most recent series on neurodynamics with Amie Hesbach and Gillian Tabor, we will remember that they discussed changes in the cortical map in response to injury, including cortical silencing. What if, as a result of cervical trauma, this horse experienced cortical silencing of her scapulohumeral and thoracoscapular areas, resulting in further atrophy of those muscles? Potentially the postural change we see now is one that developed over some time instead of acutely after a trauma.

Whether the presentation before us originated as a result of neurological trauma or musculoskeletal trauma, we have to consider the neurological system in any rehabilitation programme to ensure successful re-education.

Nerve roots and Brachial Plexus

Tensegrity

One thing that the presentation of this mare highlights to me is the tensegrity of the horse’s body. With just one correction of the angle of the scapula, the entire body comes back into alignment and remains there for as long as the scapula remains in its normal position. As soon as the scapula drops, so does the entire thorax. Each of the structures we discussed above will be affected by this change in tensegrity within the body, and there will be changes throughout the horse’s entire myofascial and skeletal system, from ears to hooves.

 

Rehabilitation?

In this case, I don’t believe it appropriate for us to discuss rehabilitation, as we do not have enough information on this patient. As with most cases, an accurate diagnosis will determine the prognosis as well as the rehabilitation of this patient.

Taking a problem list approach, we would ask ourselves how we might externally stabilise the scapula in the correct position. 

If correction of the scapular position is not a possibility, and our rehab goals are not to correct the dysfunction but to help the horse live with it, we would take a very different approach.

In Amie Hesbach’s first webinar in our series on neurodynamics in the equine, she discusses the role of adaptation and compensation within the neurological system and the musculoskeletal system. When we have dysfunction that prevents the original anatomical structures from ever returning to their function, we can help adjacent, complementary and agonist structures to step in and help restore functionality. We are, in essence, training or creating compensation patterns.

 

Conclusion

I do hope that this has been interesting to you, and has caused you to consider your clinical reasoning process and the support you have in place for the day you may be presented with a case that is completely outside of your norm or comfort zone. To me, continuing education is crucial to open your mind to new pathways of thinking, and new solutions to common and not-so-common problems. Without it, our experience might increase but our knowledge will lessen over time. We must maintain an in-depth knowledge of anatomy – engage regularly in dissections, and have your anatomy books always close at hand to refer to. In complex cases, we must rely heavily on our evaluation process to ensure we cover all potential bases. This helps our minds focus on what we do know in a moment when we might be overwhelmed by what we don’t know. And finally, a supportive community to help you problem solve, brainstorm and consider both alternative differential diagnoses as well as treatment options can make all the difference in the world.

 

Resources

If you feel there is a gap in your continuing education and what is available to you, I recommend considering membership with Onlinepethealth, where you will be able to access a library of webinars, research summaries and business support tools.

If you would like to join a supportive, global community of Vetrehabbers, why not join our Facebook groups?

If you want to dive into some continuing education straight from here, I highly recommend:

 

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