Osteoarthritis (OA) of the shoulder can be divided into:

1. OA affecting the acromioclavicular joint
2. OA affecting the glenohumeral joint

It is a degenerative joint condition causing pain, stiffness and limitation of movement with subsequent disability. Degeneration of the cartilage and subchondral bone is seen, with narrowing of the joint space. In general, shoulder osteoarthritis is not as common as OA of other major joints such as the hip or knee. Osteoarthritis of the shoulder can either be primary (no predisposing factors) or secondary to other causes such as overuse, surgery, trauma, inflammatory arthropathies or avascular necrosis

Acromioclavicular joint OA is common and can be asymptomatic, occurring mainly in people that repetitively reach overhead, for example in those that lift weights. On examination there may be pain over the acromioclavicular joint when palpated. The cross adduction test requires the patient to reach the arm across their chest towards the opposite shoulder. In acromioclavicular joint OA this movement will be painful at the site of the acromioclavicular joint.

In contrast, glenohumeral joint OA is relatively uncommon. It presents as:

• Deep shoulder pain
  • Felt especially on external rotation of the shoulder.
• Progressive stiffness

On examination, there may be a reduction in passive external rotation. This is not specific for osteoarthritis (it also occurs in adhesive capsulitis, for example) but indicates glenohumeral involvement.

Shoulder OA is the cause in approximately 2-5% of patients presenting to primary care with shoulder pain. Glenohumeral joint OA is most commonly found in older patients over the age of 60 years, whereas acromioclavicular joint OA can occur in younger patients. For both types of OA, women are affected more commonly than men.

The 2016 British Elbow and Shoulder Society/British Orthopaedic Association (BESS/BOA) guidelines state that if shoulder OA is suspected, plain radiographs are the investigation of choice for diagnosis. The x-ray findings are similar to osteoarthritis affecting other joints and include narrowing of the joint space and osteophyte formation. Plain radiographs can also be used to diagnose or exclude other causes of shoulder pain such as humeral head avascular necrosis or shoulder dislocation.

When performing plain radiographs for OA, two views are required:

• True anteroposterior view (in scapular plane)
• Axillary view

Specialist imaging with ultrasound, CT or MRI is reserved for secondary care, where they may be used prior to surgical intervention or to assess the rotator cuff.

The main differential diagnoses to consider are:

• Adhesive capsulitis (also known as frozen shoulder)
  • Similarities: Like in glenohumeral joint OA there is shoulder pain, stiffness and passive external rotation is limited on examination
  • Differences: In adhesive capsulitis, over time the shoulder pain improves, but the stiffness gradually worsens (usually resolving over months/years). It occurs in younger patients than glenohumeral OA, with the median age being 50-55 years. There should be no abnormalities of note on plain radiographs
• Rotator cuff disorders: These include impingement, rotator cuff tendinopathy and rotator cuff tears.
  • Similarities: Rotator cuff disorders are also a cause of shoulder pain
  • Differences: In rotator cuff disorders it is shoulder abduction that is affected: there may be a painful arc of abduction on examination. In acute tears there may be a history of trauma, although they can be atraumatic in the elderly
• Referred neck pain
  • Similarities: Like in OA, there may be a restriction in shoulder movement
  • Differences: In referred pain from the neck, the neck and suprascapular area are usually painful and tender

Other important differentials not to miss are the shoulder ‘red flags’ that require urgent same day assessment:

• Suspected joint infections (septic arthritis)
  • The patient may be systemically unwell or they may have fever, joint pain and erythema overlying the site
• Unreduced shoulder dislocations

If a mass, swelling or unexplained deformity is found on examination of the shoulder, consider the possibility of malignancy. Suspected malignancy should be referred under the two-week wait referral pathway.

Treatment of shoulder osteoarthritis aims to:

• Control pain
• Improve the function of the shoulder

Treatment of choice is dependent upon the severity of symptoms and limitations in activities of daily living. Conservative management is used in the first instance, however those with established osteoarthritis are less likely to respond well to conservative treatment alone.

Options in primary care include:

• Physiotherapy for strengthening exercises
• Weight loss in those that are overweight
• Oral analgesia
  • Regular paracetamol is the first line drug of choice due to its minimal side effect profile.
  • If paracetamol alone is ineffective, oral NSAIDs or codeine can be used (considering their contraindications before prescribing)
• Intra-articular corticosteroid injections: these are for short term use only, usually for an acute exacerbation of pain. There is currently no evidence for the use of corticosteroid injections specifically for shoulder OA

NICE do not currently recommend the use of acupuncture for shoulder osteoarthritis due to the evidence base being limited to its use in chronic shoulder pain caused by a variety of other shoulder conditions and not specifically osteoarthritis.

Referral to secondary care shoulder specialists is required when:

• Pain is severe and not controlled by the above methods
• The patient is significantly affected by the stiffness
• The diagnosis is not clear

Secondary care specialists can offer surgery. For acromioclavicular joint OA this can be a day case procedure with excision of the joint or distal clavicle. For glenohumeral joint OA surgical options include:

• Arthroscopy with debridement +/- resurfacing
• Joint replacement
  • Hemiarthroplasty or
  • Total shoulder replacement

Joint replacement is a well-established and effective method for improving pain, function and quality of life.

Secondary care may also offer short term non-surgical interventions whilst the patient is awaiting surgery:

• Corticosteroid injections if not offered in primary care
• Sodium hyaluronate therapy
• Autologous platelet preparations
• Nerve blocks or local injections