Introduction

Shoulder pain as a cause of lameness is becoming more frequently diagnosed in dogs. Instability of the shoulder is thought to be a common cause of shoulder pain and lameness.¹ Shoulder instability allows abnormal translation of the humeral head in relation to the glenoid cavity due to disruption of the soft tissue supporting structures of the joint.² Diagnosis of the condition can be difficult and controversial. It is important to carefully rule out elbow pathology as a cause of forelimb lameness as well, as many dogs having shoulder pathology also have elbow pathology. Treatment of shoulder instability is equally controversial at the present time. Treatment options include ligament reconstruction, joint capsular imbrication, joint capsular shrinkage, simple debridement of damaged tissues, and conservative management with antiinflammatory therapy, controlled activity and physical rehabilitation exercises.^3-10 Surgical treatment can be performed using a traditional arthrotomy or arthroscopy, depending on the surgical technique.

Diagnosis

The gait of a dog having shoulder instability is usually abnormal at the walk and the trot. Most patients have an obvious weight bearing lameness with a prominent head bob on the affected limb. The first step in diagnosis of shoulder instability is localizing pain to the shoulder joint. When evaluating the shoulder for pain, the shoulder should be isolated and evaluated independent of the elbow. The shoulder should be assessed for pain and instability in the awake patient. The shoulder is assessed as it is manipulated in flexion, extension, abduction, adduction, internal rotation and external rotation. Abduction angles can be measured and used as a tool for diagnosis on medial shoulder instability.¹¹ Abduction angles greater than 50° has been suggested as pathologic and indicative of medial shoulder instability.¹¹ Although an excessive abduction angle is found with patients with medial shoulder instability, excessive abduction angles can also be seen with other causes of forelimb lameness (e.g., elbow dysplasia, bone cancer, carpal injury) due to muscle atrophy and loss of active (dynamic) restraints of the shoulder.

Diagnostic imaging is useful in assessment of the active restraints of the shoulder. Magnetic resonance can be used to evaluate the biceps brachii, infraspinatus, supraspinatus, teres minor and subscapularis muscles.¹² Arthroscopy is used to evaluate the static stabilizers of the shoulder, including the medial glenohumeral ligament, lateral glenohumeral ligament and joint capsule. Arthroscopy is also useful in assessing the biceps brachii tendon, subscapularis tendon and articular surfaces of the glenoid and humeral head.

Pathologic changes that may be seen include mineralization, tendonitis, partial or complete tears of ligament or tendons, joint capsular stretching, cartilage erosion, or fragmentation. Many patients have multiple pathologic changes, complicating the decision-making process.

Decision-making Process

The decision-making process is complicated because of the difficulty in assessing all of the potential anatomical structures of the shoulder and the lack of evidence-based studies evaluating treatment modalities. At the present time, management of most clinical patients is based on surgeon opinion. Some surgeons elect to treat dogs diagnosed with shoulder instability surgically, while others prefer a more conservative approach. Both groups report anecdotal success and at the present time there are no criteria to distinguish between surgical and non-surgical management.

Surgical Stabilization

The goal of surgical stabilization of the shoulder is immediate return of shoulder stability. This can be accomplished with an arthrotomy or arthroscopy. Techniques that have been described include biceps tendon transposition, ligament reconstruction, imbrication of the subscapularis tendon, joint capsule imbrication and joint capsule shrinkage. Stabilization of the medial glenohumeral ligament with good results has been recommended by ligament reconstruction,⁵ imbrication of the subscapularis tendon⁶ or imbrication of the MGHL and medial joint capsule.⁹ Stabilization of the lateral glenohumeral ligament by joint capsule imbrication using a suture anchor technique was recently reported with good results in 2 dogs having tears of the LGHL.⁷ Thermal shrinkage of the joint capsule was previously recommended as a means of stabilizing the shoulder,^3,4 but this technique has fallen out of favor due to inconsistent results.⁶ Following any type of surgical repair of surgical instability, it is recommended that the shoulder be protected with restricted, controlled activity and a thoracic jacket or bandage. Immobilization of the shoulder has been recommended for 6 weeks, followed by rehabilitation exercise for an additional 6 weeks.⁶

Medial Glenohumeral Ligament Repair

Stabilization of the medial glenohumeral ligament with good results has been recommended by medial glenohumeral ligament (MGHL) reconstruction. Reconstruction of the MGHL is typically performed through a craniomedial approach to the shoulder, followed by ligament reconstruction using suture anchors and Fiberwire or FiberTape. It is important to reconstruct both arms of the ligament if they are both damaged. Most commonly a small suture anchor is placed at the cranial and caudal aspects of the edge of the medial glenoid rim. The sutures are attached to the medial aspect of the proximal humerus using another suture anchor. When attaching to a Corkscrew anchor (Arthrex Vet Systems, Naples, FL), the suture is tensioned and tied using 4–5 knots. When attaching to a Swivel Lock anchor (a knotless suture anchor system), the suture is tensioned, but no knot is needed.

Conservative Treatment

Conservative management of shoulder instability has been proposed using arthroscopic debridement of damage tissues, controlled activity, shoulder bandaging, intraarticular steroid injections, NSAIDs, physical rehabilitation exercise, stem cell therapy and extracorporeal wave therapy (shockwave therapy). The basic premise of conservative therapy is control of inflammation to decrease pain, rehabilitation exercise to increase muscle strength and improve range of motion of the shoulder, shoulder restraint to prevent excessive translation during healing and adjunctive treatments to stimulate production of growth factors or reparative tissues (shock wave or stem cell therapy). Unfortunately, the above techniques have not been critically evaluated and recommendations for their use are based on surgical opinion and experience.

At the current time, it would be reasonable to use a surgical stabilization technique in dogs having obvious shoulder instability, especially if articular cartilage wear is seen, supporting the theory that abnormal translation of the humeral head is occurring. If shoulder pain is present, but minimal signs of translation are evident, conservative treatment of shoulder instability can be considered. Patients that fail to respond to conservative treatment after 3 months should be considered for surgical stabilization.

References

1.  Bardet JF. Diagnosis of shoulder instability in dogs and cats; a retrospective study. J Am Anim Hosp Assoc 1998;34:42–54.

2.  Sidaway K, McLaughlin RM, Elder SH, et al. Role of the tendons of the biceps brachii and infraspinatus muscles and the medial glenohumeral ligament in the maintenance of passive shoulder joint stability in dogs. Am J Vet Res. 2004;65:1216–1222.

3.  Cook JL, Tomlinson JL, Fox DB, et al. Treatment of dogs diagnosed with medial shoulder instability using radiofrequency-induced thermal capsulorrhaphy. Vet Surg. 2005;34:469–475.

4.  O'Neill T, Innes JF. Treatment of shoulder instability caused by medial glenohumeral ligament rupture with thermal capsulorrhaphy. J Small Anim Pract. 2004;45:521–524.

5.  Fitch RB, Breshears L, Staats A, et al. Clinical evaluation of a prosthetic medial glenohumeral ligament repair in the dog (ten cases). Vet Comp Orthop Traumatol. 2001;14:222–228.

6.  Pettitt RA, Clements DN, Guilliard MJ. Stabilisation of medial shoulder instability by imbrication of the subscapularis muscle tendon of insertion. J Small Anim Pract. 2007;48(11):626–631.

7.  Pettitt RA, Innes JF. Arthroscopic management of a lateral glenohumeral ligament rupture in two dogs. Vet Comp Orthop Traumatol. 2008;21(3):302–306.

8.  Innes JF, Brown G. Rupture of the biceps brachii tendon sheath in two dogs. J Small Anim Pract. 2004;45:25–28.

9.  Devitt CM. Suture anchor techniques for medial shoulder imbrication. Proceedings of the Advanced Arthroscopy Course Naples, Italy, Aug 24–26, 2006.

10. Buttersworth SJ. The use of intra-articular methylprednisolone in the management of shoulder lameness in the dog. Proceedings of the 46th Annual BSAVA Congress, Birmingham, UK, April 3–6, 2003:598.

11. Cook JL, Renfro DC, Tomlinson JL, et al. Measurement of angles of abduction for diagnosis of shoulder instability in dogs using goniometry and digital image analysis. Vet Surg. 2005;34:463–468.

12. Shaefer SL, Forrest LJ. Magnetic resonance imaging of the canine shoulder: an anatomic study. Vet Surg. 2006;35(8):721–728.