Residency · Residency · Physical Medicine Rehabilitation

Regenerative Medicine in PMR: PRP and Orthobiologics

Introduction

Regenerative medicine in physiatry encompasses biologic therapies aimed at restoring tissue structure and function rather than merely managing symptoms. Platelet-rich plasma (PRP), bone marrow aspirate concentrate (BMAC), and other orthobiologics represent a growing area of clinical practice and research. While evidence is evolving, these treatments are increasingly used for tendinopathy, osteoarthritis, and musculoskeletal injuries refractory to conventional therapy.

Platelet-Rich Plasma (PRP)

Preparation and Classification

PRP is autologous blood concentrated to contain supraphysiologic platelet levels (3-8x baseline). Preparation: Venipuncture, centrifugation (single or double spin), collection of platelet-rich layer. Leukocyte-rich PRP (LR-PRP): Higher white blood cell concentration; more pro-inflammatory. Leukocyte-poor PRP (LP-PRP): Fewer white blood cells; more anti-inflammatory.

Platelet concentration, leukocyte content, and activation method vary significantly across systems. No standardized preparation protocol; heterogeneity limits cross-study comparison.

Mechanism of Action

Platelets release growth factors upon activation: PDGF, TGF-beta, VEGF, EGF, IGF-1. Growth factors stimulate cell proliferation, extracellular matrix synthesis, and angiogenesis. Anti-inflammatory cytokines modulate the local inflammatory environment. Recruitment of mesenchymal stem cells to the injury site. Duration of biologic effect: weeks to months depending on tissue and injury type.

Clinical Applications with Evidence

Lateral epicondylitis: Level I evidence supporting PRP over corticosteroid at 6-12 months. Knee osteoarthritis: Multiple RCTs show benefit over hyaluronic acid at 6-12 months (LP-PRP preferred). Patellar tendinopathy: Moderate evidence of benefit; LR-PRP may be preferred for tendinopathy. Rotator cuff tendinopathy: Mixed evidence; may augment surgical repair healing.

Plantar fasciitis: Moderate evidence; comparable or superior to corticosteroid injection. Hamstring injuries: Some evidence for accelerated return to sport (in athletes).

Applications with Limited Evidence

ACL reconstruction augmentation. Meniscal repair augmentation. Hip osteoarthritis. Achilles tendinopathy. Muscle injuries. Intervertebral disc degeneration (early research). 

Bone Marrow Aspirate Concentrate (BMAC)

Preparation

Aspiration of bone marrow from the posterior iliac crest under ultrasound or fluoroscopic guidance. Centrifugation to concentrate mesenchymal stem cells (MSCs), growth factors, and cytokines. MSC concentration in BMAC is relatively low (0.001-0.01% of nucleated cells). Higher cost and procedural complexity compared to PRP.

Mechanism

Mesenchymal stem cells have multipotent differentiation capacity (cartilage, bone, fat, tendon). Paracrine signaling: MSCs secrete anti-inflammatory and immunomodulatory factors. Trophic effects may be more important than direct differentiation. Growth factor milieu from concentrated marrow elements.

Clinical Applications

Knee osteoarthritis: Limited RCTs; some studies show improvement in pain and function. Osteochondral defects: Augmentation of microfracture or scaffold-based repair. Bone non-unions: Established use in orthopedic surgery. Avascular necrosis: Early-stage femoral head AVN (core decompression + BMAC). Evidence base is less robust than PRP; more research needed.

Other Orthobiologics

Adipose-Derived Stem Cells

Harvested via lipoaspiration; processed to obtain stromal vascular fraction (SVF). Higher MSC yield than bone marrow per volume. FDA regulatory concerns: Minimal manipulation versus more-than-minimal manipulation. Clinical evidence limited; mostly case series and small trials.

Amniotic and Placental Tissue Products

Processed from donated birth tissue (amniotic membrane, Wharton jelly). Contain growth factors, cytokines, and extracellular matrix components. Do NOT contain viable stem cells in commercially available products (despite marketing claims). Anti-inflammatory and scaffolding properties. Regulatory and marketing controversies regarding stem cell claims.

Prolotherapy

Injection of hypertonic dextrose (12.5-25%) to stimulate tissue healing. Proposed mechanism: Osmotic cell injury triggers inflammatory cascade and tissue repair. Evidence: Moderate for knee osteoarthritis and chronic tendinopathy. Low cost and accessible; used for decades in musculoskeletal medicine.

Evidence-Based Decision Making

Strongest Evidence

PRP for lateral epicondylitis: Superior to corticosteroid at long-term follow-up. LP-PRP for knee osteoarthritis: Mild-to-moderate OA; improvements in pain and function at 6-12 months. PRP shows consistently better long-term outcomes than corticosteroid for most tendinopathies.

Areas of Uncertainty

Optimal PRP formulation (LR vs. LP, platelet concentration, activation method). Number and frequency of injections. Patient selection criteria (disease severity, age, BMI). Long-term outcomes beyond 12 months. BMAC versus PRP comparative effectiveness. Cost-effectiveness relative to conventional treatments.

Limitations

Lack of standardization across PRP preparation systems. Heterogeneity in study protocols limits meta-analysis. Many studies are small, single-center, and unblinded. Publication bias toward positive results. Insurance coverage varies; often out-of-pocket expense. 

Regulatory and Ethical Considerations

PRP and BMAC are regulated under FDA Section 361 as minimally manipulated homologous use. More-than-minimally manipulated products require FDA approval as biologics. Culture-expanded stem cells are not FDA-approved for orthopedic indications in the U.S. Informed consent must include discussion of uncertain evidence, out-of-pocket costs, and alternatives. Marketing should accurately reflect the evidence base; avoid unsubstantiated claims.

Procedure Technique

Ultrasound guidance recommended for accurate delivery to target tissue. PRP: Typically 3-6 mL injected into tendon, joint, or peritendinous space. BMAC: 3-8 mL after concentration; delivered under ultrasound or fluoroscopic guidance. Post-procedure activity modification: Relative rest for 48-72 hours; gradual return to activity.

Rehabilitation protocol: Progressive loading beginning 1-2 weeks post-injection. Avoid NSAIDs for 1-2 weeks post-injection (may inhibit the inflammatory healing response).

Key Clinical Pearls

1. Leukocyte-poor PRP is generally preferred for intra-articular joint injections (osteoarthritis), while leukocyte-rich PRP may be more appropriate for tendinopathy, though optimal formulations remain under investigation. 2. PRP demonstrates superior long-term outcomes compared to corticosteroid injection for lateral epicondylitis and is emerging as the preferred injection therapy for this condition. 3. Commercially available amniotic and placental tissue products do not contain viable stem cells; practitioners should accurately represent the contents and evidence when discussing these options with patients. 4. NSAIDs should be avoided for 1-2 weeks after PRP or BMAC injection, as anti-inflammatory medications may inhibit the biologic healing cascade that these treatments are designed to initiate.

References

1. Fitzpatrick J, et al. "The Effectiveness of Platelet-Rich Plasma in the Treatment of Tendinopathy: A Meta-Analysis." Am J Sports Med. 2017;45(1):226-233.
2. Filardo G, et al. "Platelet-Rich Plasma vs Hyaluronic Acid to Treat Knee Degenerative Pathology: Study Design and Preliminary Results." BMC Musculoskelet Disord. 2012;13:229.
3. Chahla J, et al. "A Call for Standardization in Platelet-Rich Plasma Preparation Protocols and Composition Reporting." J Bone Joint Surg Am. 2017;99(20):1769-1779.
4. Centeno CJ, et al. "A Prospective Study of Bone Marrow Concentrate for Knee Osteoarthritis." Regen Med. 2018;13(7):831-838.

Read this lecture as Markdown