Overview
Medial shoulder instability (MSI) is a common cause of forelimb lameness in dogs, particularly active and athletic breeds. Overuse during repetitive activities (jumping, rapid turns, landing on outstretched forelimbs) damages the soft tissue structures on the medial (inner) aspect of the shoulder. This damage leads to weakening of the structures and, ultimately, excessive laxity and instability.
These injuries are sometimes compared to human rotator cuff injuries, although our anatomies differ from dogs. Commonly affected structures include the medial glenohumeral ligament and subscapularis muscle-tendon complex. They can impact both companion animals, working dogs, and agility/sporting dogs.
Clinical Signs
- Intermittent, or persistent, forelimb lameness
- Pain on shoulder manipulation, especially abduction (away from the body)
- Decreased performance in athletic dogs
- Reluctance to jump or climb stairs
- Muscle atrophy in chronic cases
Diagnosis
Soft tissue injuries (tendons, muscles, and ligaments) of the shoulders are frequently missed or misdiagnosed causes of lameness in dogs. These injuries create a cycle where dogs improve with rest but become lame again with exercise due to progressive scarring that further weakens the structures. Additionally, osteoarthritis can form over time with continued instability. Early diagnosis is crucial, as the longer the condition persists, the less likely a full recovery becomes.
Diagnosis begins with a comprehensive orthopedic examination, in particular shoulder discomfort response, shoulder abduction angles, and comparison with the other forelimb. Radiographs, while unable to visualize soft tissue specifics, are helpful to rule out other conditions of the shoulder that can have similar clinical signs. Next steps include non-invasive advanced imaging (musculoskeletal ultrasound or MRI) or arthroscopy (both diagnostic and therapeutic).
Treatment Options
Conservative Management consists of anti-inflammatory medications and rest/ activity restriction. Activity restriction is augmented with a protective shoulder stabilization system, or hobbles, to limit abduction of the limb. Rehabilitation is essential for recovery and includes controlled range-of-motion maneuvers and strengthening exercises.
Surgery is indicated for severe or refractory cases. Most commonly, arthroscopic thermal capsulorrhaphy is performed to tighten the medial structures. In severe cases or those that do not respond adequately to thermal capsulorrhaphy, an open surgical approach may be performed to reconstruct the medial glenohumeral ligament.
Recovery and Prognosis
Recovery is slow, and unlike bone fractures, tendons and ligaments often never return to full strength after injury, making early intervention critical for better outcomes. Complete recovery typically requires 3-12 months. A gradual rehabilitation protocol is essential for improved outcomes. Conservative management is effective in over 70% of mild to moderate MSI cases. Surgical intervention, when appropriate, has a 75-90% positive outcome. Lifelong management may be necessary, particularly in working or athletic dogs.