Frozen Shoulder MRI: What It Shows

Frozen shoulder — known medically as adhesive capsulitis — is a condition where the capsule surrounding the shoulder joint becomes thickened, inflamed, and tight, causing progressive stiffness and pain that can last 1-3 years. It affects 2-5% of the general population and up to 20% of people with diabetes. MRI can help confirm the diagnosis, rule out other causes of shoulder stiffness, and identify the stage of the condition to guide treatment.

If your shoulder has been gradually seizing up over weeks or months, with pain that disturbs your sleep and an increasing inability to reach behind your back or above your head, frozen shoulder is a likely explanation — but an MRI can confirm it and make sure nothing else is going on.

What Happens in Frozen Shoulder

The shoulder joint capsule is a flexible sleeve of tissue that surrounds the joint and normally allows many different movement. In frozen shoulder, the capsule becomes inflamed and then progressively thickens and contracts, forming adhesions (bands of scar tissue). This shrinks the joint space and restricts movement in a characteristic pattern — external rotation is usually lost first and most severely.

The Three Stages

• Stage 1 — Freezing (2-9 months) — gradual onset of shoulder pain, often worse at night. Pain increases progressively and range of movement starts to reduce. This is often the most painful stage and the point where most people seek help.
• Stage 2 — Frozen (4-12 months) — pain may start to improve slightly, but stiffness is at its worst. Activities like reaching behind the back, putting on a coat, or fastening a bra become very difficult or impossible.
• Stage 3 — Thawing (5-24 months) — gradual return of movement. Pain continues to decrease. Most people recover most or all of their range of movement, though this can take months.

Total duration from onset to resolution is typically 1-3 years. Some people have residual stiffness beyond this, particularly those with diabetes.

Who Gets Frozen Shoulder?

• Peak age 40-60 years
• Women are slightly more commonly affected than men
• Diabetes — the strongest risk factor. Affects up to 20% of diabetics, and frozen shoulder in diabetics tends to be more severe and longer-lasting.
• Thyroid disease — both hypothyroidism and hyperthyroidism increase risk
• Previous shoulder surgery or trauma — immobilisation can trigger adhesive capsulitis
• Dupuytren's contracture — association with both conditions
• Bilateral involvement occurs in 20-30% of cases, though usually not simultaneously

What Frozen Shoulder Looks Like on MRI

Frozen shoulder is primarily a clinical diagnosis (based on symptoms and examination), but MRI can show characteristic findings and, more importantly, rule out other causes of stiffness:

• Thickening of the joint capsule — particularly at the rotator interval (the gap between the supraspinatus and subscapularis tendons at the front of the shoulder) and the axillary recess (the lowest part of the capsule, which normally forms a pouch).
• Capsular enhancement — on contrast-enhanced MRI, the inflamed capsule lights up with gadolinium, particularly in the freezing stage.
• Thickening of the coracohumeral ligament — this ligament, which bridges the rotator interval, is typically thickened to over 4mm (normal is under 2-3mm).
• Obliteration of the subcoracoid fat triangle — the normal fat pad at the front of the shoulder disappears as the capsule thickens.
• Reduced joint volume — the contracted capsule holds less fluid than normal.
• Bone marrow oedema — occasionally seen in the humeral head during the active inflammatory phase.

Important Differentials

MRI is valuable because it rules out other conditions that mimic frozen shoulder:

• Rotator cuff tear (especially subscapularis tear, which causes similar loss of external rotation)
• Calcific tendinitis (can cause acute severe stiffness)
• Glenohumeral arthritis
• Labral pathology
• Tumour (very rare, but important to exclude)

What MRI Cannot Show

• Early frozen shoulder — MRI findings can be subtle or normal in the very early freezing stage. A normal MRI does not rule out frozen shoulder if the clinical picture fits.
• Degree of pain — MRI shows structural changes, not pain levels. Clinical assessment remains essential for assessing severity.
• Prognosis — MRI cannot reliably predict how long your frozen shoulder will last or how fully you will recover.

What to Expect During the Scan

A shoulder MRI takes 25-40 minutes. You lie on your back with your arm at your side. The limited range of movement from frozen shoulder is actually not a problem for positioning — the standard MRI position does not require you to lift or rotate your arm.

If your shoulder pain is severe (common in the freezing stage), take painkillers beforehand. Let the radiographer know you have a frozen shoulder so they can make you as comfortable as possible.

Alternative Diagnostic Approaches

• Clinical examination — the primary diagnostic tool. Frozen shoulder has a characteristic pattern: loss of both active and passive range of movement, particularly external rotation and abduction. If the examiner cannot move your arm either (passive movement restricted), this strongly suggests capsular disease.
• X-ray — usually normal in frozen shoulder but useful to rule out glenohumeral arthritis and calcific tendinitis.
• Ultrasound — can show rotator cuff pathology but is less reliable for capsular assessment.
• Arthrogram — injecting contrast into the joint shows reduced joint capacity (normally 15-20ml, frozen shoulder often under 5-10ml). Rarely done now as MRI provides sufficient information.

Treatment Pathways

• Physiotherapy — the cornerstone of treatment at all stages. Gentle range-of-movement exercises, pendulum exercises, and gradual stretching. Aggressive stretching in the freezing stage can make things worse. Physiotherapy is most effective in the thawing stage.
• Pain management — NSAIDs, paracetamol, and sometimes short courses of oral corticosteroids (e.g. prednisolone 30mg for 2 weeks) in the acutely painful freezing stage.
• Corticosteroid injection (intra-articular) — injection into the glenohumeral joint (not the subacromial space). Most effective in the early freezing stage. Can significantly reduce pain and improve range in the short to medium term. Typically image-guided (ultrasound or X-ray) for accuracy.
• Hydrodilatation (distension arthrogram) — saline, steroid, and local anaesthetic are injected into the joint under X-ray guidance to stretch and distend the contracted capsule. Evidence suggests it can accelerate recovery by 2-3 months. Usually done as a single procedure.
• Manipulation under anaesthetic (MUA) — the shoulder is forcefully moved through its range while you are under general anaesthetic, breaking the adhesions. Quick procedure, but carries a small risk of fracture, dislocation, or rotator cuff tear. Usually combined with a steroid injection.
• Arthroscopic capsular release — keyhole surgery to cut the thickened, contracted capsule. Most reliable way to restore movement in resistant cases. Usually combined with MUA. Recovery involves intensive physiotherapy starting immediately.

UK Statistics

• Frozen shoulder affects 2-5% of the general population
• Prevalence in diabetics: 10-20%
• Peak age: 40-60 years
• Bilateral involvement in 20-30% of cases
• Natural resolution typically takes 1-3 years without intervention
• Around 10-15% of patients have significant residual stiffness beyond 3 years

Frequently Asked Questions

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