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Shoulder instability in dogs and cats, Dr Bardet, Clinic Abvet, Neuilly-sur-Seine

What is shoulder instability?

In the past, shoulder pain in dogs was mostly attributed to osteoarthritis or tendinitis of the bicep’s tendon. Since the use of arthroscopy in the 1990s, shoulder diseases in dogs have been identified and their treatment has become morespecific.

Shoulder pain is a common cause of lameness in dogs. Instability is the first shoulder disease in adult dogs. The shoulder is one of the most mobile joints, but its anatomy makes it very susceptible to instability as it is not constrained by bony structures (photos 1 and 2) such as the elbow or hip, but its stability depends mainly on ligament structures and secondarily on peripheral muscle forces (photos 3 and 4). Instability is either the result of trauma (less frequent) or multiple microtrauma exceeding the repair capacity of the ligament structures, which is frequently observed in hyperactive dogs. Instabilities can be classified according to the location of the injury as medial, lateral, or multidirectional. This classification is fundamental as it is the basis of treatment which varies according to the nature of the instability. Shoulder instability is associated with the tearing or distension of either a medial or lateral ligament or a combination of both. The joint does not dislocate, but there is "play" between the scapula and the humerus, which leads to abnormal stress on the cartilage, wear and tear, and the appearance of arthrosis when the cause is not treated.

Photo 1: Anatomical view of the two shoulder bones, the scapula and the humerus, showing the low level of bone-related restrain.

Photo 3: Anatomic specimen of a left shoulder and its capsular and ligament structures

Photo 2: Diagram of the shoulder with humerus and glenoid and the analogy of the golf ball on the left on its T showing the inherent instability of the anatomy.

Photo 3: Anatomic specimen of a left shoulder and its capsular and ligament structures

Photo 4: Anatomical specimen of a left scapula and its capsular and ligament structures

How can I tell if my dog or cat has shoulder instability?

Shoulder instability is characterized by a more or less severe lameness of the affected limb, resistant to anti-inflammatory treatments. Most animals are presented after several weeks or months of lameness. The lameness may be without support when it is acute and some dogs are sometimes presented with signs of a herniated disc, indicating the intensity of the pain, especially when the origin is traumatic. In cases of persistent and chronic lameness, the limb may atrophy.

How does shoulder instability in dogs and cats is diagnosed by Dr Bardet at Abvet Clinic?

Shoulder instability is diagnosed and classified based on history, orthopedic and neurological examinations, X-rays, arthroscopy and possibly tendon ultrasound or M.R.I. After characterizing the lameness during the orthopedic examination, the pain is localized to the shoulder thanks to several tests including the biceps tendon test (photo 5). The stability of the shoulder is then tested thanks to the search for the drawer movement and the adduction test (VIDEO: limping of a foreleg in a 7-year-old Malinois boy with instability of the right shoulder associated with a significant drawer movement and a positive adduction test compared to a healthy left shoulder) on the awaken animal and then under anesthesia. X-rays are then taken. They make it possible to characterize the presence or absence of arthrosis and the lesions associated with instability while excluding any other cause of lameness. It is important to understand that shoulder osteoarthritis is not a disease in itself but is secondary to an internal disturbance, most often instability of the shoulder. Ultrasound, scans of the ligaments, tendons and muscles of the shoulder rotator cuff or MRI of these same structures provide useful additional information when instability is not certain. Arthroscopy is the "gold standard" for detecting injuries inside the joint. All joint structures are examined and a joint injury assessment is carried out, making it possible to classify and characterize the instability (photos 6 to 9) before any treatment.

Photo 5: representation of the biceps tendon test with the foreleg along the body

Photo 6: Arthroscopic view of an abnormal and softened cartilage associated with shoulder stability

Photo 7: Arthroscopic view of a normal shoulder with its ligament under tension

Photo 8A: Arthroscopic view of the biceps tendon of an unstable shoulder

Photo 8B: Arthroscopic view of the shoulder of the dog in photo 8A with the tear of the subscapular tendon muscle

Photo 8C: Arthroscopic view of the dog's shoulder from photo 8A with distension of the medial shoulder ligament

Photo 8D: Arthroscopic view of the shoulder of the dog in photo 8A with a fracture of the caudal edge of the glenoid

Photo 9: Arthroscopic view of the shoulder of a dog with lateral instability of the shoulder with avulsion of the joint capsule of the caudal glenoid rim

How is instability of the shoulder of dogs and cats treated by Dr Bardet at Abvet Clinic?

Conservative treatment of shoulder instability in dogs and cats

Conservative treatment uses a combination of activity restriction for several weeks, weight reduction, combined with the use of medication or even rehabilitation. Drug treatment uses non-steroidal anti-inflammatory drugs combined with chondro-protective substances or growth factor-enriched plasma and stem cells. This treatment is rarely a permanent cure.

Surgical treatment of shoulder instabilities in dogs and cats

The surgical treatment varies according to the nature of the instability, age of the patient, the presence of aggravating associated lesions and the destination of the patient. Many techniques described in the past are no longer used because they are very unsatisfactory, such as the transposition of the biceps tendon which systematically tears, sectioning of the biceps tendon which aggravates the instability and many other techniques which are even less recognized.

  • Thermocapsulography of the medial compartment of the shoulder: This technique is reserved for medial instabilities of the shoulder when the medial ligament is distended, torn, incompetent or absent. It uses a specialized probe which is applied to the surface of the articular capsule and causes its contraction (VIDEO: visualization of a Thermocapsulography in a dog suffering from medial instability of the shoulder). The surgery is performed only under arthroscopic control without surgical incision. A Velpeau sling is applied for a fortnight and activity is limited for a total of two months before resuming controlled activity.
  • Reinsertion of the joint capsule on the edge of the articular surface of the glenoid under arthroscopy. This technique is reserved for lateral and caudal instabilities of the shoulder. Suturing is performed using surgical anchors inserted under arthroscopy on which the disinserted joint capsule is sutured. The postoperative treatment is identical to the previous technique.
  • Surgical reinsertion of the joint capsule on the edge of the glenoid. This technique is reserved for severe lateral instabilities of the shoulder of traumatic origin. The approach to the shoulder is cranio-lateral. The joint capsule is reinserted on the edges of the articular surface of the scapula.
  • Combination of the three previous techniques. Multi-directional instabilities use a combination of the three previous techniques because the medial and lateral anatomical structures are damaged. This type of instability is often associated with severe trauma to the shoulder. The anatomical reconstruction of the lesions ensures a good recovery in spite of the severity of the lesions.

What is the prognosis after treatment of shoulder instability at the ABVet Clinic?

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The prognosis after treatment of shoulder instability depends on many factors, but mainly on the severity of the initial lesions and the speed with which the operation is carried out after the appearance of lameness, i.e., before the appearance of severe osteoarthritis. We have reported a 92% success rate with normal dogs or dogs presenting slight discomfort after marked effort. Bibliography:

Bardet JF: Diagnosis of shoulder instability in Dogs and Cats: a retrospective study. J Am Anim Hosp Assoc 1998; 34 :42-54.

Bardet JF: Shoulder diseases in dogs. Vet Med 2002; 97:909

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