Marc Darrow, MD, JD
A caller to my Living Pain-Free radio program described a herniated disc and a strained sacroiliac joint. This is a common and important diagnostic problem. A person may have low back, buttock, groin, or leg pain and an MRI showing a disc bulge, yet the disc may not be the structure producing the symptoms. Another patient may be told that the sacroiliac joint is the problem when the pain is actually referred from the lumbar spine or hip.
The first question should therefore not be, “What can we inject?” It should be: What structure is generating the pain?
The low back, hip, and SI joint can produce overlapping symptoms
The sacroiliac (SI) joints connect the sacrum at the bottom of the spine to the pelvis. They transfer load between the trunk and legs and are supported by strong ligaments. Pain in the SI region may be felt below the belt line, in the buttock, near the posterior pelvis, or occasionally toward the groin and thigh.
Unfortunately, those locations are not exclusive to the SI joint. Similar symptoms may come from:
- A lumbar disc
- Lumbar facet joints
- Spinal or pelvic ligaments
- Hip osteoarthritis or labral disease
- Gluteal tendons or other surrounding soft tissues
- Lumbar nerve irritation or sciatica
- Muscle injury or persistent guarding
A study of patients whose pain was concentrated around the SI region illustrates the difficulty. After a more complete diagnostic evaluation, most were found to have lumbar spinal pain rather than primary SI-joint pain. (1) The lesson is not that SI-joint pain never occurs. It is that pain location alone does not establish its source.
A herniated disc on MRI is not automatically the cause of pain
Disc bulges, protrusions, degeneration, and other age-related findings are frequently seen in people without back pain. A systematic review of asymptomatic individuals found that many degenerative spinal imaging findings become increasingly common with age. (2)
An MRI is valuable when used in context. It can identify nerve compression, fracture, tumor, infection, severe stenosis, and other important structural findings. What it cannot do by itself is prove which abnormality hurts.
Discogenic pain often behaves differently from SI-joint or ligament pain. It may be central, aggravated by sitting or bending, or associated with leg symptoms when a nerve is irritated. SI-region pain may worsen during rolling in bed, stairs, getting out of a car, prolonged standing, or single-leg loading. Facet pain, hip disease, and ligament injury have their own patterns. These are clues rather than stand-alone diagnostic tests.
How SI-joint pain is evaluated
There is no single physical test that conclusively diagnoses SI-joint pain. Clinicians generally look for a consistent history and a cluster of pain-provocation tests. The examination should also evaluate the lumbar spine, hips, neurologic function, strength, gait, and the surrounding ligaments and tendons.
In selected cases, an image-guided diagnostic anesthetic injection may help determine whether pain originates within the SI joint. Even this has limitations. An intra-articular injection tests the joint space; it does not necessarily test the posterior SI ligaments or every adjacent structure.
This distinction matters because “SI pain” can describe several different problems:
- Inflammation or degeneration inside the joint
- Ligament injury and impaired load transfer around the joint
- Pain referred from the lumbar spine or hip
- Pain following lumbar fusion, pelvic trauma, or hip replacement
- Inflammatory sacroiliitis associated with a rheumatologic disorder
These conditions should not automatically receive the same treatment.
Could damaged ligaments contribute to low back and SI-region pain?
Spinal and pelvic ligaments guide movement and help control excessive motion. Biomechanical research has examined how disc degeneration and ligament failure can affect the functional mechanics of the lumbar spine. The findings support the concept that a stiff, degenerated segment and a ligament-compromised, excessively mobile segment are mechanically different problems. (3)
This does not mean that every person with low back pain has “instability,” nor does it prove that ligament treatment is appropriate for everyone. It does explain why a physical examination may reveal information that a static MRI cannot: tenderness, painful loading, abnormal movement, weakness, and loss of neuromuscular control.
First-line treatment does not begin with stem cells
Most patients without urgent neurologic or structural problems begin with conservative care. Depending on the diagnosis, this may include activity modification, progressive exercise, physical therapy, improved hip and trunk strength, medication when appropriate, and attention to sleep, body weight, and general health.
An SI belt may provide temporary support for some patients. Corticosteroid injections can reduce inflammation and may also have diagnostic value, but relief is often temporary. Radiofrequency procedures attempt to reduce pain transmission from selected nerves. SI-joint fusion may be considered for carefully selected patients with confirmed, disabling SI-joint pain who have not improved with nonsurgical care.
These treatments have different purposes. A short response to anesthetic does not prove that a fusion will succeed, and failure of a steroid injection does not automatically establish ligament damage.
PRP research for SI-joint pain
Platelet-rich plasma (PRP) is made from the patient’s blood and contains concentrated platelets and signaling proteins. It is being studied as an alternative to corticosteroid injections for SI-joint pain.
A 2026 retrospective comparative study evaluated PRP, corticosteroid, and hyaluronic-acid injections in 60 adults with sacroiliitis. All three groups improved, with corticosteroids producing faster relief and PRP showing greater improvement at six months. (4) The study was small, retrospective, and involved only 20 patients per treatment group. It therefore provides supportive—not definitive—evidence.
PRP preparation also varies considerably. Platelet concentration, white-cell content, injection target, number of treatments, and rehabilitation protocols can all influence results.
What are MSCs and bone marrow concentrate?
Mesenchymal stromal/stem cells (MSCs) are studied for their signaling and tissue-supporting properties. The term “stem cell treatment,” however, can obscure important differences among products.
Bone marrow aspirate concentrate (BMAC or BMC) is produced from a patient’s own bone marrow, commonly collected from the pelvis and concentrated during the same procedure. It contains platelets, cytokines, white blood cells, growth factors, and a small population of progenitor and stromal cells. It is not a purified MSC product, and it is not equivalent to laboratory-isolated, culture-expanded cells.
This article intentionally excludes culture-expanded MSC research. Conclusions from expanded or donor-derived cellular products should not be used to promise outcomes from same-day autologous BMAC.
Non-expanded bone marrow concentrate for discogenic low back pain
A retrospective study followed 33 patients who received non-expanded concentrated bone marrow aspirate injections for discogenic low back pain. Some patients reported meaningful improvements in pain and function, but response rates varied over time. The study had no control group and incomplete follow-up data, so its findings are preliminary. (5)
This evidence is encouraging enough to support further study, but it does not establish that BMAC rebuilds a degenerated disc or reverses an MRI abnormality. Intradiscal injection also differs from treating a facet joint, SI joint, ligament attachment, muscle, or fascia. These procedures should not be grouped together simply because each uses bone marrow concentrate.
Placing a needle into an intervertebral disc carries specific considerations, including the uncommon but serious risk of infection. A physician must determine whether the clinical findings truly support discogenic pain and whether the potential benefit justifies the procedure.
What does our low back BMC case series show?
In 2018, Marc Darrow, MD, and Brent Shaw reported four patients treated with bone marrow concentrate injections into painful lumbar and sacroiliac-region structures, including ligaments, fascia, and muscles. At follow-up, all four patients reported reduced resting and active pain and improved function. (6)
These outcomes are clinically interesting, but the limitations must be clear. This was a four-patient case series without randomization, a control group, or blinding. It cannot determine how much improvement came from BMC, the injection procedure, rehabilitation, natural symptom fluctuation, or other contextual effects. It supports further investigation; it does not prove effectiveness for all low back or SI-joint pain.
Direct BMAC evidence for SI-joint dysfunction remains limited
Research specifically testing non-expanded autologous BMAC for confirmed SI-joint pain is sparse. There is biologic rationale and limited clinical experience, but it would be premature to state that BMAC reliably rebuilds SI-joint cartilage, tightens ligaments, or restores the joint’s structure.
When BMAC is discussed, the physician should specify the proposed target:
- The intra-articular SI joint
- Supporting ligament attachments
- A painful lumbar facet joint
- A suspected discogenic source
- Another soft-tissue structure
The target matters because the diagnosis, research, procedural risks, and rehabilitation plan are different for each one.
Who may be considered for PRP or BMAC?
An orthobiologic consultation may be reasonable when pain has persisted despite appropriate conservative care, the likely pain generator has been identified, and the patient understands the uncertainties, alternatives, costs, and rehabilitation requirements.
PRP or BMAC is less likely to solve pain caused primarily by major nerve compression, severe spinal stenosis, infection, fracture, tumor, hardware failure, or a mechanical problem requiring surgical correction. Inflammatory sacroiliitis may require rheumatologic treatment rather than a local regenerative injection.
Summary
Low back and SI-region pain should not be treated according to an MRI label alone. A herniated disc may be incidental, and pain near the SI joint may originate in the lumbar spine, hip, ligaments, or another structure.
PRP has emerging but still limited clinical research for SI-joint pain. Non-expanded autologous bone marrow concentrate has preliminary supportive evidence for selected discogenic and soft-tissue low back pain, while direct BMAC evidence for confirmed SI-joint dysfunction remains sparse. Neither treatment should be presented as proven cartilage regeneration or guaranteed ligament reconstruction.
The most important step is identifying the probable pain generator and matching the treatment to the diagnosis.
References
- DePhillipo NN, Corenman DS, Strauch EL, Zalepa King LA. Sacroiliac Pain: Structural Causes of Pain Referring to the SI Joint Region. Clin Spine Surg. 2019;32(6):E282-E288.
- Brinjikji W, Luetmer PH, Comstock B, et al. Systematic Literature Review of Imaging Features of Spinal Degeneration in Asymptomatic Populations. AJNR Am J Neuroradiol. 2015;36(4):811-816.
- Ellingson AM, Shaw MN, Giambini H, An KN. Comparative role of disc degeneration and ligament failure on functional mechanics of the lumbar spine. Comput Methods Biomech Biomed Engin. 2016;19(9):1009-1018.
- Yadav PJ, Thampi G. Therapeutic Evaluation of Intra-articular Platelet-Rich Plasma, Steroid, and Viscosupplement Injections for Sacroiliitis: A Retrospective Comparative Study. Cureus. 2026;18(3).
- Wolff M, Shillington JM, Rathbone C, Piasecki SK, Barnes B. Injections of concentrated bone marrow aspirate as treatment for discogenic pain: a retrospective analysis. BMC Musculoskelet Disord. 2020;21(1):135.
- Darrow M, Shaw B. Treatment of Lower Back Pain with Bone Marrow Concentrate. Biomed J Sci Tech Res. 2018;7(2):001461.
Medical disclaimer: This article is for educational purposes only and is not a diagnosis or an individualized treatment recommendation. PRP and bone marrow concentrate procedures remain evolving areas of medicine. Their risks, regulatory status, alternatives, and expected outcomes should be discussed with a qualified physician.
