Persistent shoulder pain: when an ultrasound-guided injection makes sense

The shoulder has a very particular architecture: it is the joint with the greatest range of motion in the body, which makes it remarkably versatile — and also vulnerable. When it hurts, several structures may be involved, and it pays to identify the culprit precisely: the rotator cuff tendons, the bursae, the joint capsule, the acromioclavicular joint, or the glenohumeral joint itself.

In everyday practice I see many patients referred for a shoulder injection without a precise diagnosis of which structure is actually causing the pain. "I have shoulder tendinitis" is one of the phrases I hear most often, and it tends to lump together very different conditions: subacromial bursitis, supraspinatus tendinopathy, early adhesive capsulitis, acromioclavicular joint disease, or a combination of several. The distinction matters, because each of these conditions has a different anatomical target — and if the injection goes into the wrong place, the result will be poor no matter how meticulous the technique.

Persistent shoulder pain is one of the most common reasons patients come to a pain medicine practice, and most cases respond well to nonsurgical treatment when it is properly indicated. Here is when an ultrasound-guided injection is the most reasonable option, and what to expect from the process.

Common causes of shoulder pain

Rotator cuff tendinopathy

The rotator cuff is a group of four tendons that stabilize and move the shoulder. With repetitive use or aging, these tendons degenerate, become inflamed, or can partially tear. It is the most common cause of shoulder pain in adults. The hallmarks are pain when raising the arm, when sleeping on that side, and with certain specific movements.

Subacromial bursitis

A bursa is a small fluid-filled sac that reduces friction between structures. The subacromial bursa can become inflamed, usually in association with rotator cuff tendinopathy. It causes pain when raising the arm and with direct pressure.

Frozen shoulder (adhesive capsulitis)

This is a progressive tightening of the shoulder joint capsule that causes pain and, above all, a marked loss of mobility. It typically evolves through three phases: painful, stiff, and recovery. It can last months to years. It is more common in women over 40 and in people with diabetes.

Glenohumeral or acromioclavicular osteoarthritis

Joint wear can occur in any of the shoulder's joints. It usually causes deeper pain and grinding sensations.

Subacromial impingement syndrome

This occurs when the rotator cuff structures are mechanically pinched as they pass beneath the acromion. It is frequently associated with tendinopathy or bursitis.

A nuance I repeat often in the office: a shoulder MRI in someone over 50 very rarely comes back "normal." The usual findings are some degree of rotator cuff tendinopathy, a partial tear or even a full tear, and signs of acromioclavicular joint disease. The clinical challenge is working out which of all those findings is actually generating the patient's pain — and that is done with the physical exam, using specific maneuvers, more than with the imaging. When I indicate an injection, the clinical picture chooses the target; the ultrasound only tells me exactly where to place the needle.

Why ultrasound guidance matters

Traditional shoulder injections were done "blind," relying on anatomical landmarks. Current evidence shows that ultrasound-guided injections have significantly higher accuracy rates than blind ones. That difference translates into:

• Greater effectiveness: the medication reaches the exact spot where it is needed.
• Less pain during the procedure: neighboring structures are not punctured unnecessarily.
• Lower risk of complications: vessels and nerves to avoid are seen in real time.
• Simultaneous diagnosis: ultrasound shows the state of the tissues and confirms the condition.

The injections available

Subacromial corticosteroid injection

The most widely used. Indicated for rotator cuff tendinopathy, subacromial bursitis, and impingement syndrome. Relief usually sets in within 2 to 7 days and lasts several months. Repeating it more than 3 times a year in the same shoulder is not recommended.

Intra-articular injection

Indicated for frozen shoulder and glenohumeral osteoarthritis. In frozen shoulder, early intra-articular injections can significantly speed up recovery, especially when combined with physical therapy.

Hydrodilatation

A technique specific to frozen shoulder. A larger volume of fluid is injected into the joint to stretch the tightened capsule. It can significantly improve mobility when properly indicated.

Acromioclavicular joint injection

Indicated for acromioclavicular osteoarthritis or injuries to that specific joint.

Regenerative medicine (PRP)

In chronic tendinopathies that have not responded to conventional treatment, ultrasound-guided PRP delivered to the site of the tendinopathy can speed up recovery. It is an option for selected cases.

When to consider an injection

In general, injections come into the picture when:

• Pain persists despite a well-conducted initial course of medication and physical therapy (4 to 8 weeks).
• Pain significantly interferes with sleep or daily activities.
• There is a clear clinical diagnosis that calls for one (active bursitis, capsulitis, symptomatic tendinopathy).
• Pain control is needed to make proper physical therapy possible.

Injections do not replace physical therapy — they enhance it. After a well-indicated injection, the best next step is to resume (or start) a physical therapy program targeted at the specific condition.

When it is not the best option

There are situations where an injection is not the first choice:

• Full-thickness rotator cuff tears that require surgical evaluation.
• Suspected infection.
• Systemic conditions that need general medical treatment first.
• A history of multiple previous injections with no response.

My criterion for performing an injection under ultrasound guidance, rather than blind, is practically systematic: in the shoulder, the difference in accuracy between the two techniques is substantial, and the target structures often sit just a few millimeters apart. Ultrasound not only increases effectiveness — it reduces the risk of injecting into the tendon itself, something especially worth avoiding with corticosteroids. I perform the injection when there is a clear anatomical diagnosis, a reasonable initial course of conservative treatment has failed, and the patient understands that the injection is part of a plan, not the whole plan.

What to expect afterward

The procedure takes 10-15 minutes, is done on an outpatient basis, and is usually very well tolerated. There may be some soreness at the injection site for the first few days. The intended effect sets in within a few days and lasts from several weeks to months.

A well-indicated, well-performed injection can be a turning point in a case of persistent shoulder pain. What matters is that the decision comes from a careful clinical examination — not as a default treatment for "any shoulder that hurts."

To my mind, a well-indicated, well-performed shoulder injection should give the patient a window of relief to be used for what really changes the prognosis: active physical therapy, rotator cuff strengthening, and correction of movement patterns. An injection done in isolation, without rehabilitation work afterward, tends to bring temporary relief followed by relapse. When a patient comes back six months later pain-free and with a functional shoulder, it is almost always because they understood that the procedure opened the door — but they walked the path themselves with physical therapy.

Dr. Mauricio Casarsa

Anesthesiologist, specialist in Pain Medicine and Interventional Pain Management. Postgraduate training at UBA (Fundación Dolor) and UNLP (CAIDBA). Staff physician at Hospital Alemán, Buenos Aires.

MN 137756 · San Isidro · Villa Urquiza