By Marc Darrow, MD, JD

Pain at the top or side of the shoulder, especially when reaching overhead or sleeping on that side, is often called shoulder impingement. The label describes a pattern of symptoms, but it does not identify every painful structure. The supraspinatus and other rotator cuff tendons, the fluid-filled subacromial bursa, the long head of the biceps tendon, and the shoulder joint may each contribute.

During my September 12, 2026 radio program, one listener asked about pain remaining after PRP and prolotherapy for a supraspinatus tear. Another asked whether a cell-based treatment might help shoulder bursitis. Those questions belong together: before choosing another injection, we need to work out what is still hurting and why.

What does “impingement” mean?

The rotator cuff tendons and subacromial bursa occupy the space beneath the acromion, the bony roof of the shoulder. Rotator cuff tendinopathy, a partial tear, and bursal irritation can produce overlapping pain. A patient may also have biceps tendinopathy or arthritis. Bursitis visible on an image does not prove that the bursa is the sole source of pain.

I ask which movements hurt, test active and passive range of motion and strength, and examine the biceps groove and surrounding tissues. A painful but strong shoulder differs from a shoulder that suddenly became weak after an injury. Ultrasound can help examine the cuff and biceps dynamically, look for bursal fluid, and guide a needle. MRI can clarify tear size, tendon retraction, muscle changes, or other problems when the result would change treatment. Neither image replaces an examination.

Does shaving bone beneath the acromion help?

Arthroscopic subacromial decompression removes tissue or bone to enlarge the space beneath the acromion. It became common for persistent subacromial pain, but later randomized studies challenged its benefit. A systematic review of controlled trials found little or no clinically meaningful advantage over nonoperative care for typical impingement symptoms. A Cochrane review likewise found no clinically important benefit of decompression over placebo surgery for rotator cuff disease without a full-thickness tear. These findings concern decompression for this particular condition; they do not mean that every shoulder operation is ineffective. (1) (2)

Start with the diagnosis and a rehabilitation plan

Many patients can begin with activity changes, gradual rotator cuff and shoulder-blade strengthening, and exercises that restore useful motion. The goal is to increase what the shoulder can tolerate, not simply to avoid movement indefinitely. A subacromial corticosteroid injection may offer short-term pain relief in selected patients, particularly if pain prevents participation in rehabilitation; the expected benefit and risks of repeat injections need discussion.

When a patient returns after an injection helped only a little, I revisit the diagnosis. Continued pain at the front of the shoulder may point toward the biceps tendon; pain with lifting may relate to the cuff; stiffness in nearly every direction suggests another process, such as frozen shoulder. The response to one treatment does not prove that every painful tissue needs another injection.

What does the PRP research show?

Platelet-rich plasma (PRP) is prepared from the patient’s own blood. Its platelets contain signaling molecules, but PRP contains no stem cells. The preparation, injection target, and accompanying rehabilitation vary across studies.

In a 2024 randomized trial, 100 adults aged 18 to 50 with supraspinatus tendinopathy that persisted despite conservative care received either a subacromial PRP or corticosteroid injection. At 12 months, the PRP group had better average pain and function scores. The result is relevant to tendinopathy and associated subacromial pain; the trial did not establish that PRP cures isolated bursitis, closes a full-thickness tear, or has the same results in an older patient. (3)

What about bone marrow concentrate and other cell-based preparations?

Bone marrow aspirate concentrate (BMAC) is collected from the patient’s pelvis and processed into a mixture of cells and biological factors. It includes a small population of progenitor cells; calling the entire mixture “stem cells” overstates what is in the syringe. In our published 2019 shoulder study, 47 patients with 50 treated shoulders had rotator cuff tears or shoulder osteoarthritis. Patients reported improved pain and function after whole marrow or concentrate injections. Because it was an uncontrolled series with mixed diagnoses and treatments, it cannot show that the injections caused those improvements or predict results for isolated bursitis. (4)

A separate randomized trial compared a combined bone marrow concentrate and platelet-product intervention with exercise therapy for rotator cuff tears. Its combined preparation and study population make it inappropriate to attribute a benefit to marrow alone or apply it directly to bursitis. (5)

Fat-derived preparations, umbilical-cord blood, and Wharton’s-jelly products are biologically different from autologous marrow. Evidence for their use in this shoulder condition is insufficient to promise tendon repair or cartilage regrowth. No regenerative medicine product is FDA-approved for shoulder pain or another orthopedic condition. (6)

When should a surgeon evaluate the shoulder?

A sudden traumatic injury followed by pronounced weakness, a suspected complete tear with tendon retraction, progressive loss of function, or severe joint destruction warrants orthopedic assessment. Surgery can be appropriate for some of these problems. An injection should not postpone an evaluation when the timing of repair could matter.

For persistent shoulder pain without those findings, I explain what the examination and imaging do and do not show, review the rehabilitation already tried, and discuss the likely benefits and limits of each injection. Pain relief and better function would be meaningful outcomes; they should not be mistaken for proof that a tendon or joint has been restored to normal.

References

  1. Khan M, Alolabi B, Horner N, Bedi A, Ayeni OR, Bhandari M. Surgery for shoulder impingement: a systematic review and meta-analysis of controlled clinical trials. CMAJ Open. 2019;7(1):E149–E158.
  2. Karjalainen TV, Jain NB, Page CM, et al. Subacromial decompression surgery for rotator cuff disease. Cochrane Database of Systematic Reviews. 2019.
  3. Rossi LA, et al. Subacromial injection of platelet-rich plasma provides greater improvement in pain and functional outcomes compared to corticosteroids at 1-year follow-up: a double-blinded randomized controlled trial. Journal of Shoulder and Elbow Surgery. 2024. DOI: 10.1016/j.jse.2024.06.012.
  4. Darrow M, Shaw B, Schmidt N, Boeger G, Budgett S. Treatment of shoulder osteoarthritis and rotator cuff tears with bone marrow concentrate and whole bone marrow injections. Cogent Medicine. 2019;6:1628883.
  5. Percutaneous bone marrow concentrate and platelet products versus exercise therapy for the treatment of rotator cuff tears: a randomized controlled, crossover trial with 2-year follow-up. BMC Musculoskeletal Disorders. 2024;25:392.
  6. US Food and Drug Administration. Consumer Alert on Regenerative Medicine Products Including Stem Cells and Exosomes.