Shoulder Tendinopathies in Dogs: Supraspinatus, Biceps, Medial Shoulder Syndrome, and Associated Osteoarthritis

Shoulder tendinopathies are a frequent cause of forelimb lameness in active and working dogs. These injuries often result from repetitive strain or overload and can lead to chronic pain, decreased performance, and, over time, secondary osteoarthritis (OA) of the shoulder joint. The most affected structures include the supraspinatus tendon, biceps brachii tendon, and the medial shoulder stabilizers (subscapularis muscle and medial glenohumeral ligament), resulting in conditions such as medial shoulder syndrome (MSS).

Supraspinatus Tendinopathy

The supraspinatus muscle functions as a key stabilizer of the shoulder and aids in extension. Tendinopathy results from overuse or microtrauma, often leading to fiber disruption, thickening, or mineralization.

Diagnosis:

• Radiographs (mineralization)
• Musculoskeletal ultrasound (tendon fiber architecture)
• MRI (soft tissue detail)

Treatment:

• Rehabilitation: Targeted exercises for shoulder stability, stretching, and strengthening
• ESWT (Extracorporeal Shockwave Therapy): Promotes neovascularization and tissue regeneration
• Injections:
  • Platelet-rich plasma (PRP): Enhances tendon healing
  • Stem cell therapy (MSC): Used in degenerative cases
  • 2.5% Polyacrylamide hydrogel (PAAG, e.g., Arthramid): May be considered for cases with concurrent joint capsule thickening or OA
• Surgical debridement or removal of calcified tissue in refractory or impinging lesions

Biceps Brachii Tendinopathy

The biceps tendon, located within the bicipital groove, is prone to strain and inflammation, especially in active dogs. This tendon can also be affected secondarily by supraspinatus enlargement.

Diagnosis:

• Pain on shoulder flexion and elbow extension
• Dynamic ultrasound of the bicipital groove
• MRI for intra-articular detail

Treatment:

• Rehabilitation: Controlled return to function, soft tissue mobilization, and strengthening
• ESWT: Applied to the biceps origin to reduce pain and stimulate healing
• Injection Therapies:
  • PRP: Intra-sheath injection under ultrasound guidance
  • Stem cells: Particularly in chronic or degenerative tendinopathy
  • Polyacrylamide hydrogel (PAAG): Used intra-articularly to improve joint function and reduce pain, especially when biceps pathology contributes to synovitis or OA
  • Corticosteroids: Reserved for severe inflammatory cases but used cautiously due to risk of tendon weakening
• Surgical options: Tenotomy or tenodesis in chronic, refractory cases

Medial Shoulder Syndrome (MSS)

MSS involves injury to the medial glenohumeral ligament, joint capsule, and subscapularis tendon. This condition resembles medial shoulder instability in human athletes and is common in agility and working dogs.

Diagnosis:

• Stress ultrasound (dynamic abduction)
• Pain on shoulder abduction/internal rotation
• MRI or arthroscopy (for definitive diagnosis)

Treatment:

• Physical rehabilitation:
  • Proprioceptive and strengthening exercises
  • Core stabilization and scapular control
  • Modalities such as PEMF and therapeutic laser
• ESWT: Applied to medial shoulder structures for healing stimulation
• Injection therapies:
  • PRP or MSCs: Targeting joint capsule or periarticular tissues
  • PAAG: Offers viscoelastic support to the joint capsule, reduces synovitis, and may improve joint congruency
• Shoulder brace: May be used for joint support during recovery
• Surgery: Indicated in severe instability, with thermal capsulorrhaphy or synthetic stabilization procedures

Shoulder Tendinopathies and Osteoarthritis (OA)

Chronic tendinopathies, especially when undiagnosed or undertreated, can lead to joint incongruity, capsular fibrosis, and degenerative joint disease (DJD). Supraspinatus impingement, biceps strain, or joint instability can all contribute to secondary OA of the shoulder.

Injectable Therapies for Shoulder OA:

• Polyacrylamide Hydrogel (2.5% PAAG, Arthramid): Long-acting, non-resorbable, and safe for intra-articular use. Reduces pain and inflammation by integrating with the synovial lining.
• Platelet-Rich Plasma (PRP): Stimulates anti-inflammatory and reparative responses; commonly used intra-articularly.
• Mesenchymal Stem Cells (MSC): Provide immunomodulatory and regenerative effects; ideal for chronic, multi-joint OA or cases with significant synovitis.
• Radiosynoviorthesis (Synovetin OA®, Sn-117m colloid):
  • A novel radioisotope-based intra-articular therapy
  • Targets and selectively destroys activated macrophages in the synovium, which are central to chronic inflammation in OA
• Corticosteroids: Fast-acting anti-inflammatory but used sparingly due to concerns of cartilage catabolism and tendon weakening.

Summary

Shoulder tendinopathies in dogs—including supraspinatus, biceps, and medial shoulder injuries—require early detection and a multimodal treatment approach. Combining diagnostics like ultrasound or MRI with targeted physical rehabilitation, ESWT, and injection therapies can lead to favorable outcomes. Importantly, all these conditions may progress to osteoarthritis, which can be addressed through intra-articular injectables like polyacrylamide hydrogel, PRP, stem cells, radiosynoviorthesis (RSO) to preserve joint health and function.