MSI or Medial Shoulder Instability in Dogs

Chronic unresolving front leg lameness

By Kelly Thompson, DC




(link to the beginning of Article)  The reason it was always chronic front leg lameness for me was because people would find their way to me only after exhausting all other Veterinary approaches, including stints on medications, cage rest, physical therapy, and even acupuncture.  I have even treated cases where MSI surgery was performed and the pet continued to limp anyway.  I don’t believe I ever dealt with a fresh or newly acute case of MSI. It was always the chronic front leg lameness with intermittent acute flare-ups followed by periods of constant lesser degrees of waxing and waning lameness.


If you do some online research you might be interested in the following excerpt taken from Colorado Canine Orthopedics website about MSI:


“Compared to our human counterparts, veterinary surgeons are behind the curve regarding shoulder disorders…”

“Radiographs are commonly non-diagnostic.”

Regarding Shoulder MRI and /or CT scans: “…the shoulder joint can be difficult to scan and the scan interpretation can be highly dependent on the radiologists’ experience and comfort level with the shoulder joint. Thus, a shoulder scan can have false negatives.”


This goes a long ways in explaining what I have experienced over the years. A lot of inconsistent diagnostic and therapeutic protocols and frustrated pet owners seeking answers for a diagnostically elusive condition. Presumptive diagnoses without clinical evidence is common. In other words guessing as to whether the canine patient has MSI or not, and often going on arthroscopic “fishing expeditions” with hefty price tags that yield poor to limited clinical outcomes.


To understand this condition more thoroughly, let’s drill down and see if we can make sense of this usually intractable condition.  In humans the shoulder or Glenohumoral Joint is the most unstable and consequently the most flexible joint of our body. Have you ever done windmill exercises or jumping jacks? Can you think of another joint of the body that has this degree motion or flexibility? You can not, because it takes the record. We tend to take it for granted as we use these two joints to accomplish nearly every activity of daily living. If you have ever had “Frozen Shoulder” you can appreciate how it impacts your life when the flexibility is restricted. In Dogs the shoulder joint is much less flexible and much more stable as a result, because unlike human shoulders these are weight bearing joints. In fact in canines upwards of 60% of their body weight is carried on the front limbs.


So what is injured and how does it happen in the life of one’s dog? It is fairly easy to understand, when you understand what is called Abduction.  This is defined physiologically as moving a limb (or other part of the body) away from the midline of the body. This is opposite of the action of adduction which is moving a limb toward the midline of the body. A simple thought experiment will suffice to explain this in human terms. If you bring your wrists together with your arms locked straight in front of you, at shoulder level this is adduction. Now get the idea of reversing this action and spreading your arms wide from in front of you as far as you can at shoulder level to the point that your arms are actually pointing in a direction behind you. This is Abduction. Notice that with your arms straight out to both sides you have moved your arms through an arc of 90 degrees from directly in front of you. Most people can move their arms further beyond 90 degrees to as much as 110 to 125 degrees in abduction. Unfortunately our canine companions have nowhere near this degree of flexibility and this explains what happens when an injury that yields MSI occurs. Studies show that dogs can only abduct their forelegs in similar fashion to a maximum of approximately 30 degrees. The following research citation explains the essential elements of this:


Cook, James & Renfro, Daniel & Tomlinson, James & Sorensen, Jill. (2005). Measurement of Angles of Abduction for Diagnosis of Shoulder Instability in Dogs Using Goniometry and Digital Image Analysis. Veterinary surgery : VS. 34. 463-8. 10.1111/j.1532-950X.2005.00070.x.


Conclusion of the study: “Mean abduction angles for shoulders with instability (53.7+/-4.7 degrees goniometric, 51.2+/-4.9 degrees image) were significantly (P<.001) larger than for all unaffected shoulders (32.6+/-2.0 degrees goniometric, 30.9+/-2.3 degrees image). In dogs diagnosed with instability, affected shoulders had significantly (P<.001) larger abduction angles than the contralateral (unaffected) shoulders.”


What this means is that normal abduction angles in dogs is up to around 30 degrees. Beyond that point medially supporting elements are damaged.


Bottom line, past roughly 30 degrees abduction in dogs, elastic and then plastic deformation occurs to the medially supporting, active (muscles) and passive (primarily ligaments and tendons), structures. Elastic deformation is defined as a temporary shape change that is self-reversing after the force is removed so that the tissue returns to its original shape and function (think of a rubber band being stretched then released). Plastic deformation occurs when structures are taken beyond the point of elastic deformation to the point where the tissue can not return to its original shape and function when the force is removed (think of a rubber band being stretched to the point it tears and ultimately ruptures). This is called a sprain when ligaments are involved. It is called a strain when muscles and tendons are involved. Ankles get sprained, hamstrings get strained (aka pulled) is an easy way to remember this.


So how does this happens in Dogs? I have found over the decades when questioning pet owners who’s dogs suffer from this condition is that they live in houses with lots of slippery floor space. That is houses with a lot of slick hard wood floors or tile floors. This condition is seen predominantly in larger or heavier or taller dogs. The injurious activity is precisely when these canine companions “lose it” as they excitedly careen around the house and one or both front legs lose traction on the slick floor surface and forcefully slide out from under them, i.e “doing the splits.”  Most commonly one side gets injured, which is the side that went well beyond 30 degrees of abduction.


The reason Medial Shoulder Instability in dogs becomes so chronic is because they have to walk on their front legs to go about their business despite the injury. Additionally, they will baby it until it feels better but will continuously re-injure it doing what they do best… careening around the house on the slippery floor again. This is why just throwing pain and anti-inflammatory Meds at it makes problems worse inasmuch as the discomfort they feel would force them to limit their injurious activity if the Meds weren’t short circuiting the pain signal.


Now what resolves MSI? The trick is to accelerate healing process enough so that the the forces of construction (physiologic tissue repair) move faster than the forces of destruction (injurious activity). Additionally, companies make hobbling harnesses that prevent abductive movement and prevent them from running through the slippery house. The attached photo is one such product at: What I have found extremely effective in resolving these cases is 20 minute Petlight Therapy sessions a minimum of 3 times per week along with severely restricting activity.  Petlight is the latest technology using pulsed high intensity red and infrared light in light emitting pads that flexibly mold into the space between the upper foreleg and chest. Having used cold lasers for over a decade prior to learning about this newer technology, I can tell you unequivocally that Petlight is far superior in resolving MSI. Here is a link to the article I wrote on the difference between Petlight and Laser: Petlight vs laser


© 2018 Dr KellyThompson,DC all rights reserved

371 1st St, Los Altos, CA 94022, and 412 S Adams St, #118, Fredericksburg, Tx 78624 Phone: CA: 650-218-5512 and TX: 830-992-0987

© 2018, Chiropractor for Animals, Dr KellyThompson,DC all rights reserved

371 1st St, Los Altos, CA 94022, and 412 S Adams St, #118, Fredericksburg, Tx 78624 Phone: CA: 650-218-5512 and TX: 830-992-0987