For many active individuals, knee pain begins as a nagging ache at the front of the knee—often dismissed as overuse or aging. Over time, that discomfort can evolve into a limiting condition that interferes with walking, climbing stairs, exercising, and even routine daily activities. Patellar tendinopathy and chondromalacia patellae (softening of the cartilage behind the kneecap) are two of the most common culprits, and they frequently resist conventional treatments.
Patients who come to our clinic often share similar stories. They have tried cortisone injections, physical therapy, extended rest, anti-inflammatory medications, and supportive braces. Some have wrapped their knees in compression bandages and iced them faithfully for months. Despite these efforts, the pain persists—or returns. For these individuals, the question becomes: Is there another option that addresses the underlying problem rather than simply masking symptoms?
Understanding the Biology of Tendon and Cartilage Healing
To appreciate why regenerative approaches are being studied, it helps to understand why tendons and cartilage heal so slowly. Tendons, including the patellar tendon that connects the kneecap to the shinbone, have relatively poor blood supply compared to muscles or skin. This limited vascularity means that the natural healing response is slow and often incomplete, especially in chronic cases where the tendon structure has begun to degenerate.
Similarly, the articular cartilage that cushions the back of the patella has no direct blood supply at all. Once this cartilage begins to soften or wear—a condition known as chondromalacia patellae—the body’s ability to restore it is inherently limited. This biological reality is why researchers have turned to cell-based therapies that may help stimulate or support the body’s own repair mechanisms.
What the Research Says: Patellar Tendinopathy
A 5-Year Follow-Up Study
One of the most frequently referenced studies in this area followed eight athletes in their mid-20s who had been living with chronic patellar tendon degeneration (1). These individuals had already exhausted non-surgical options and received injections of autologous bone marrow-derived stem cells directly into the affected tendon. The stem cells were harvested from each patient’s own iliac crest and prepared for injection on the same day.
The results, published after five years of follow-up, were encouraging. Statistically significant improvement was observed across most clinical scoring systems used to measure pain and function. Seven of the eight patients reported complete satisfaction with the procedure and stated they would undergo it again if the opposite knee developed the same problem. The authors concluded that bone marrow stem cells should be considered as a potential therapy for patients with chronic patellar tendinopathy that has not responded to non-operative treatments.
It is important to note the limitations of this study. With only eight participants and no control group receiving a placebo or alternative treatment, these findings provide preliminary evidence rather than definitive proof. However, the long follow-up period—five years—is unusual in regenerative medicine research and adds meaningful context to the durability of the observed improvements.
A Phase 1/2 Clinical Trial: 12-Month Results
A more recent investigation expanded our understanding of stem cell therapy for patellar tendinopathy (2). This study enrolled patients with chronic patellar tendinopathy that included a structural gap in the tendon greater than 3 millimeters—a finding that typically indicates more advanced tissue damage.
In the initial phase, ten patients received bone marrow-derived mesenchymal stem cells, while a separate group of ten patients received leukocyte-poor platelet-rich plasma (Lp-PRP). At the six-month mark, MRI evaluation revealed that the stem cell group showed improved tendon structure and evidence of regeneration within the gap area. The PRP group, by contrast, did not demonstrate comparable structural healing at that timepoint.
The researchers then offered the PRP-treated patients the option to cross over and receive stem cell therapy, which all ten chose to do. At the 12-month follow-up, all 20 patients who had ultimately received stem cells were evaluated together. The outcomes were notable: participants showed highly statistically significant clinical improvement in pain scores, and MRI imaging confirmed continued improvement in tendon structure. No adverse effects were reported, supporting the safety profile of this biological treatment approach.
This study design—allowing the PRP group to cross over—means that a direct long-term comparison between the two treatments at 12 months was not possible. However, the within-group improvements and the structural changes observed on MRI provide meaningful signals that warrant further investigation in larger, randomized trials.
Understanding How Stem Cells May Support Tendon Healing
Research into the mechanisms of mesenchymal stem cell therapy has revealed that these cells may contribute to healing in ways that extend beyond simply transforming into new tendon cells (3). When introduced into an environment of injury or inflammation, stem cells appear to secrete a range of bioactive molecules—including cytokines and growth factors—that can modulate the local immune response and create conditions more favorable for tissue repair.
In simpler terms, stem cells may act as both participants and coordinators in the healing process. They can home in on areas of tissue stress, reduce excessive inflammatory signaling, and promote the organized deposition of new collagen. This dual role—direct participation and environmental modulation—helps explain why researchers remain interested in their therapeutic potential for conditions like patellar tendinopathy, where the natural healing response is often insufficient.
What the Research Says: Chondromalacia Patellae
A Case Report on BMAC for Grade III Cartilage Changes
While clinical trial data for stem cell therapy in chondromalacia patellae is more limited than for tendinopathy, emerging case reports offer preliminary insights. A 2024 publication described a 36-year-old laborer who developed Grade III chondromalacia of the right patella following a fall more than a year earlier (4). His symptoms included severe anterior knee pain (rated 8 out of 10), limited range of motion, and a sensation of knee instability.
After an initial period of improvement with physical therapy and anti-inflammatory medications, his symptoms returned six months before presentation. At that point, conventional treatments no longer provided relief, and Bone Marrow Aspirate Concentrate (BMAC) therapy was recommended.
Following BMAC treatment, the patient experienced substantial pain reduction and functional improvement at both six and twelve weeks. The authors noted that this case illustrates how BMAC therapy may offer a less invasive treatment option for cartilage-related knee conditions. They also appropriately emphasized that larger clinical trials with longer follow-up periods and control groups are needed to validate these findings and establish BMAC as a reliable treatment for this condition.
A 2025 narrative review examined the broader clinical use of Bone Marrow Aspirate Concentrate for knee conditions, including osteoarthritis and cartilage defects (5). The review highlighted that BMAC contains not only mesenchymal stem cells but also a rich concentration of growth factors such as VEGF, PDGF, and TGF-β, which play roles in tissue repair and anti-inflammatory processes.
The authors noted that BMAC has demonstrated effectiveness in improving functional outcomes in clinical trials, though they cautioned that conflicting results in the existing literature make it difficult to definitively establish superiority over other orthobiologic treatments. Younger patients with medium-sized cartilage defects appeared to respond more favorably, suggesting that patient selection may be an important factor in treatment success.
How does this compare to cortisone or PRP?
Cortisone injections can provide short-term pain relief by suppressing inflammation, but they do not promote tissue healing and may have detrimental effects on tendon structure with repeated use. PRP, which uses concentrated platelets from your own blood, has shown mixed results for patellar tendinopathy and did not demonstrate tendon regeneration in the comparative trial discussed above. Stem cell therapy, because it introduces a broader array of regenerative cells and signaling molecules, may offer a more robust biological stimulus—though direct comparative studies with long-term follow-up remain limited.
References
- Pascual-Garrido C, Rolón A, Makino A. Treatment of chronic patellar tendinopathy with autologous bone marrow stem cells: a 5-year followup. Stem Cells International. 2012;2012:953510.
- Soler R, Rodas G, Rius-Tarruella J, Alomar X, Balius R, Ruíz-Cotorro Á, Masci L, Maffulli N, Orozco L. Safety and Efficacy of Bone Marrow–Derived Mesenchymal Stem Cells for Chronic Patellar Tendinopathy (with Gap >3 mm) in Patients: 12-Month Follow-up Results of a Phase 1/2 Clinical Trial. Orthopaedic Journal of Sports Medicine. 2023;11(9):23259671231184400.
- Abat F, Alfredson H, Cucchiarini M, Madry H, Marmotti A, Mouton C, Oliveira JM, Pereira H, Peretti GM, Spang C, Stephen J. Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part II: treatment options. Journal of Experimental Orthopaedics. 2018;5(1):38.
- Soundharya V, Arthi R, Haran H, Kumar S, James S. Enhanced Bone Marrow Aspirate Concentrate (BMAC) Preparation Strategy in the Management of Chondromalacia Patella: A Case Report. Cureus. 2024;16(4):e59321.
- Park D, et al. Bone Marrow Aspirate Concentrate (BMAC) for Knee Osteoarthritis: A Narrative Review of Clinical Efficacy and Future Directions. Medicina. 2025;61(5):853.
Marc Darrow, M.D., J.D., is one of the world’s most experienced Regenerative Medicine doctors. He has more than 30 Years of expertise in regenerative medicine techniques and has treated thousands of patients. He uses non-surgical therapy to reduce pain in joints, tendons, ligaments, and a variety of other ailments and disorders throughout the body, including back and neck discomfort. He taught at UCLA and received Board Certification in Physical Medicine and Rehabilitation.
