Articular cartilage damage, resulting from injury or osteoarthritis, challenges the body’s natural healing systems. This smooth, protective tissue covering joint ends lacks a direct blood supply and contains few cells capable of repair. Because it is avascular, damaged cartilage cannot easily access the cellular building blocks and growth factors needed to rebuild itself. Minor defects often lead to chronic pain, stiffness, and eventual joint deterioration.
Injections for cartilage regeneration are a modern, non-surgical approach designed to overcome this biological limitation. These treatments harness the body’s healing mechanisms by concentrating and delivering biological agents directly to the damaged joint. The goal is to stimulate local cells to repair tissue, reduce inflammation, and slow joint degeneration, rather than merely masking symptoms. Regenerative orthopedics aims to provide this biological intervention before invasive surgical options, such as joint replacement, are needed.
Main Types of Regenerative Injections
The two most common injection therapies promoting cartilage repair are Platelet-Rich Plasma (PRP) and cell-based therapies, primarily Mesenchymal Stem Cells (MSCs). PRP is an autologous product, derived solely from the patient’s own blood. A blood sample is processed in a centrifuge to separate and concentrate the platelets, often resulting in a solution three to ten times higher than normal blood concentration. This concentrated plasma is then injected into the affected joint space.
Cell-based therapies utilize Mesenchymal Stem Cells (MSCs), which are multipotent cells capable of differentiating into various cell types, including cartilage cells. These cells are typically sourced from the patient’s bone marrow or adipose (fat) tissue. Bone Marrow Aspirate Concentrate (BMAC) is prepared by extracting bone marrow, often from the posterior iliac crest, and concentrating the MSCs and other healing factors. Adipose-Derived Stem Cells (ADSCs) are similarly harvested through a minor liposuction procedure and then concentrated for injection.
Biological Mechanisms of Cartilage Repair
Platelet-Rich Plasma delivers a concentrated burst of anabolic and anti-inflammatory signaling molecules directly into the joint. Once activated, platelets release alpha-granules containing numerous growth factors, including Transforming Growth Factor-beta (TGF-β), Platelet-Derived Growth Factor (PDGF), and Insulin-like Growth Factor (IGF). These factors encourage resident joint cells, such as chondrocytes, to proliferate and synthesize cartilage matrix components like Type II collagen and aggrecan. PRP also has an anti-inflammatory effect by mitigating catabolic cytokines, such as Interleukin-1 beta (IL-1β), and reducing Matrix Metalloproteinases (MMPs), which break down cartilage.
Cell-based therapies primarily function through the paracrine effect, which is the secretion of bioactive factors influencing nearby cells. Although MSCs can differentiate into cartilage cells, their short survival time suggests their signaling role is more significant for initial repair. These injected cells secrete a complex mix of growth factors, chemokines, and anti-inflammatory cytokines that modulate the local immune response. This action reduces the destructive inflammation associated with osteoarthritis and helps recruit the body’s existing stem cells, promoting a favorable environment for tissue maintenance.
Patient Selection and Procedure Logistics
Candidates for these regenerative injections are typically patients with mild to moderate cartilage damage or osteoarthritis, often classified as Kellgren-Lawrence grades I to III. Younger patients with focal cartilage defects not severe enough for surgery often see the most benefit due to their robust healing capacity. Patients are generally excluded if they have active systemic infections, a history of certain cancers, or a diagnosed bleeding disorder. Patients must also temporarily stop taking anti-inflammatory medications, such as NSAIDs, before and after the injection, as these drugs can interfere with the treatments’ pro-inflammatory healing mechanism.
The logistical process varies by product, but both are performed as outpatient procedures. The PRP process involves a simple venipuncture (blood draw), centrifugation, and injection into the joint, often guided by ultrasound imaging for precise placement. The BMAC procedure is more involved, requiring bone marrow aspiration, typically from the posterior iliac crest, using a specialized needle under local anesthesia. After aspiration, the sample is concentrated in a centrifuge and then injected into the joint using image guidance, with the entire process usually taking about two hours.
Current Evidence and Realistic Expectations
Current evidence supports the efficacy of regenerative injections primarily for pain reduction and functional improvement, though evidence for true, long-term cartilage regeneration remains variable. Platelet-Rich Plasma frequently provides short-term symptomatic relief that often surpasses the effects of traditional hyaluronic acid injections, sometimes lasting a year or more. However, PRP is generally viewed as an anti-inflammatory and anabolic agent that improves the joint environment. It is not considered a reliable method for complete structural restoration of hyaline cartilage.
Cell-based therapies, particularly MSCs, have demonstrated more consistent evidence of disease modification and longer-lasting effects in some studies. Magnetic resonance imaging occasionally shows qualitative improvement in cartilage defects. A challenge is the regulatory landscape, as the U.S. Food and Drug Administration (FDA) has not approved any stem cell product for routine orthopedic use outside of limited clinical trials. Treatments involving the culturing or expansion of cells, or the use of allogeneic (donor) cells, are generally not permitted for commercial use, meaning these therapies are still largely considered experimental.