Imaging in suspected rotator cuff pathology: Choosing between ultrasound and MRI in primary care

Patients presenting with shoulder pain are a regular occurrence in primary care. A leading cause of shoulder pain (70%) is rotator cuff injury, most commonly caused by chronic wear and tear, often related to repetitive overhead movements during work or sports, with a significantly smaller proportion of cases due to acute injury to the shoulder.

Rotator cuff injuries can substantially impact a patient’s day-to-day ability to work and engage in sports, exercise and leisure activities. Timely diagnosis is therefore essential for effective treatment and rehabilitation. Imaging plays an important role in diagnosing the type and extent of rotator cuff injury and other similar shoulder pathologies.

When is imaging indicated?

Many cases of shoulder pain can be managed with appropriate pain relief and shoulder exercises. However, referring patients for imaging is appropriate when persistent shoulder pain exists that:

• Hasn’t responded to conservative treatment.

• Is the result of an acute injury to the shoulder, accompanied by significant pain and weakness.

Imaging also supports your suspicions that a patient might require surgical intervention to treat or manage their symptoms.

Shoulder problems such as rotator cuff tears and impingement may present with individual symptoms but may be subtle; imaging is useful for differentiation and diagnosis.

Rotator cuff tears

Patients with a rotator cuff tear often present with pain over the top of the shoulder and upper arm that can occur when raising, lowering, and rotating the arm. They may also demonstrate shoulder weakness when lifting and pain that worsens at night or when the arm is at rest.

Most rotator cuff tears, either partial or full-thickness, occur over time as the tendons of the shoulder degenerate with age-related wear and tear. More common in the over-40s, they can be caused by bone spurs rubbing against the tendon, decreased blood flow, or overuse from repetitive motions during work or sports. They may be treated with painkillers, rest, refraining from making overhead arm movements, and physiotherapy.

Significant pain, weakness, instability, and reduced range of motion suggest that surgery might be beneficial. An acute rotator cuff injury caused by a fall, accident, or injury might also require surgery. These signs indicate that medical imaging would be an appropriate next step. Ultrasound is often a first-line scan, and an MRI can be useful if an ultrasound is inconclusive or if surgical intervention is likely.

Subacromial pain / impingement

Patients experiencing a shoulder impingement will present with pain across the top and outside of the shoulder, made worse by reaching the arm behind their back or lifting it above their head and often worsens at night. Pain relief, physiotherapy and steroid injections may help to relieve the pain.

Shoulder impingement can often be diagnosed using a range of clinical tests performed in your primary care setting. If initial tests prove inconclusive or more clarity is required for treatment options or surgical guidance, an ultrasound scan is usually sufficient.

AC joint pathology

Patients with acromioclavicular pain present with localised shoulder pain that worsens with crossing the arm over the body, lifting it above the head or while sleeping on the affected side. Pain in the AC joint may be attributed to osteoarthritis, trauma, post-traumatic arthritis, or stress-related osteolysis.

AC joint pathologies can be diagnosed clinically in your primary care setting, and suspicions and diagnoses confirmed with medical imaging. An ultrasound is effective at evaluating inflammation and swelling and for guiding joint injection treatments, but an MRI may be more appropriate if a ligament tear is suspected.

Choosing the right scan and when

Acute shoulder trauma and failure of conservative management usually deem a scan appropriate for diagnosing or supporting clinical suspicions.

If the clinical presentation and symptoms suggest a rotator cuff injury or shoulder impingement due to bursitis or tendinopathy, an ultraljud of the shoulder joint is the recommended first-line scan to evaluate the soft tissues in real time at rest and during movement.

An MRI is most suitable for patients with suspected intra-articular pathologies, inconclusive ultrasound results, persistent symptoms and a likely surgical referral.

Ultrasound: strengths and limitations

Ultrasounds produce highly detailed, dynamic images of soft tissues and are therefore routinely used to assess and diagnose rotator cuff tears and their extent, as well as shoulder impingements related to bursitis and tendinopathies. They’re cost-effective, quick and accessible.

However, they’re operator-dependent and show variable sensitivity and specificity: highly specific for detecting full-thickness tears but less sensitive for partial tears.

MRI: strengths and limitations

MRIs are superior for detecting intra-articular pathologies, labral injuries, and complex or full-thickness rotator cuff tears. They’re also more appropriate for rotator cuff pathologies that require surgical planning and intervention, and as a second-line scan when an ultrasound has proven inconclusive.

Static images from an MRI cannot provide insight into the restricted movement of soft tissues; therefore, an MRI isn't usually considered a first-line scan for shoulder pain or suspected rotator cuff injuries. MRI scans are also more expensive than ultrasound and often have longer NHS waiting lists. However, private imaging provider Scan.com offers affordable scans with no waiting lists at over 250 centres across the UK.

Comparison: ultrasound vs MRI

Choosing the right modality in practice

Using your experience and clinical expertise in primary care, if you suspect a rotator cuff tear and you need confirmation, an ultrasound is usually an appropriate first-line scan.

If you suspect a more complex or intra-articular pathology, it would be more appropriate to refer for an MRI. Similarly, if a surgical referral is likely or an ultrasound has proven inconclusive and symptoms persist, an MRI would be most beneficial.