Marc Darrow, MD, JD

Many people, or should I say many runners, will reach out to me to ask whether stem cell therapy or Platelet Rich Plasma therapy will help them with their knee problems. They have what you probably have. They have pain in the front of their knee, it is coming from behind their knee cap. They hear grinding noises, popping noises, and crunching noises coming out of that knee. These runners can be any age but are typically someone who has a lot of wear and tear damage in their knees. They will have an MRI that may be inconclusive of the grade of their problem and a recommendation for some type of arthroscopic clean up. The more athletic of these people will stop running and move over to cycling or swimming. The person who has a job that puts a lot of wear and tear on their knee will probably switch over to a bigger knee brace and worse, more medications to get them through their work day.

Patellofemoral Pain Syndrome is one of the most common problems we see in our new patients.

In our office we have understood this to be a wide reaching problem and this has been confirmed by researchers who say patellofemoral pain is diagnosed in up to 7% of patients seeking medical care within the United States. Females experienced patellofemoral pain more often than males. The diagnosis of patellofemoral pain increased with age and the 50-59 year old age group had the most cases.(1)

Patellofemoral pain can be a tricky problem to surgically repair as noted in the literature: “Management of chondral (cartilage) defects in the athlete is complex and multifactorial. There is little high-level evidence to support one (surgical) procedure over another. (2)

The patella is covered with a layer of smooth (articular) cartilage. This cartilage normally glides effortlessly across the knee during activities such as running or stair climbing, where bending the knee is involved in the activity.

Why physical therapy may not work

I do see a number of patients who have tried the “full course” of physical therapy. Some patients experienced a lot of good. However, they did not get enough pain relief or functional improvement. They had to continue looking for more options. But why didn’t the physical therapy help them?

A study from August 2020 (3) explains why physical therapy, while reducing pain, may not offer the help many people need.

“Patellofemoral pain is a common but challenging condition to manage. This is partly due to the various physical impairments along the entire lower extremity biomechanical chain (knee to ankle to foot), variables such as training errors, improper shoe wear or type of running surface, and possible central pain processing dysfunction. As high quality research and clinical practice guidelines assist in optimizing outcomes, the recurrence rate and functional impact of Patellofemoral pain syndrome remains high. When coupled with other interventions, joint mobilization has been shown to help reduce pain and improve functional outcomes for patients with Patellofemoral pain syndrome, with moderate to large effect sizes. However, available research frequently emphasizes mobilizations performed in a supine position which would allow for greater patellofemoral joint  excursion, but may inherently lack carryover to the functionally limited task.”

When exercise may or may not help

In a December 2020 study (4), researchers evaluated the effects of a 12-week home exercise therapy program on pain, function and neuromuscular activity of the vastus medialis and vastus lateralis. Pain and function improved significantly after a home exercise therapy program in patients with patellofemoral pain syndrome. In addition, patients with a delayed onset or reduced activity of the vastus medialis compared to the vastus lateralis experienced a reduction in this imbalance.

If you have had a lot of knee pain you may be aware of the function and relationship between the vastus medialis and the vastus lateralis knee muscles and you may have been told that this imbalance between these muscles in what is causing your problem.

One paper (5) suggests that this muscle imbalance however is not the problem. I will let this research paper go into more depth in explaining these muscles roles.

“Patellofemoral joint pain is a common knee disorder, but its underlying causes remain unknown. One proposed mechanism is an imbalance in force in the knee extensor muscles. Specifically, the vastus medialis and vastus lateralis are thought to play a crucial role in proper patellar tracking, and weakness in vastus medialis is thought to lead to a lateral shift in the patella causing increased contact pressures and pain. The purpose of this study was to create an animal model of vastus medialis weakness and to test the effect of this weakness on patellofemoral contact pressures.”

The researchers of this study then conducted a trial on rabbit knees to test whether this muscle imbalance actually caused patellar mal-tracking and patellofemoral joint pain. They concluded “that vastus medialis weakness does not cause changes in patellofemoral contact pressures. Since the muscular and knee joint geometry in rabbits and humans is similar, we question the idea of vastus medialis weakness as a cause of patellar mal-tracking and patellofemoral joint pain.”

Maybe it is not the patella causing pain in Patellofemoral pain syndrome

Another problem is the problem of accurate diagnosis. Knee pain is very complex.

A July 2020 (6) study investigated the gait of participants with Patellofemoral pain syndrome before and after the application of Kinesio Tape in order to assess the impact of Kinesio Tape on cadence, stance time, and pain. While our study failed to demonstrate a significant difference in the gait of participants with Patellofemoral pain syndrome in comparison to those without Patellofemoral pain syndrome, we did demonstrate a significant reduction in pain after the application of Kinesio Tape. These results suggest other variables addressed by the Kinesio Tape may be causing the pain associated with Patellofemoral pain syndrome.

PRP for Patellofemoral Pain Syndrome

PRP treatments involve collecting a small amount of your blood and spinning it in a centrifuge to separate the platelets from the red cells. The collected platelets are then injected back into the injured area to stimulate healing and regeneration. PRP puts specific components in the blood to work. Blood is made up of four main components; plasma, red blood cells, white blood cells, and platelets. Each part plays a role in keeping your body functioning properly. Platelets act as wound and injury healers. They are first on the scene at an injury, clotting to stop any bleeding and immediately helping to regenerate new tissue in the wounded area.

A study from 2015 (9) did test the effectiveness of PRP for Patellofemoral pain syndrome. This is what the study found.

“Patellofemoral pain syndrome is the most common problem in musculoskeletal system. Platelet-rich plasma (PRP) has been suggested to be beneficial in the treatment of sports injuries. The purpose of this study is to compare single and triple PRP injections in the treatment of Patellofemoral pain syndrome and to show whether or not triple application of PRP injection may be more effective.

  • A total of 30 patients with Patellofemoral pain syndrome for more than 3 months, with age of 20 to 35 years, were included in this study.
  • The patients were divided into three groups as single injection application group (number=20) or triple injection application group (n=10) and the unaffected opposite knees were used as controls (number=30). 2 mL of PRP injected into the knee joints.
  • In triple injection group the injections were done a month apart. All patients received a six-week standard exercise program.
  • Results: Among the patients with PFPS treated with an exercise program, a triple PRP injection compared with a single PRP injection did not result in greater improvement in knee functions, balance and proprioception, isokinetic muscle strength and endurance during a 4-month follow-up.”

In this study one injection of PRP was found to provide similar healing as three injections of PRP given at one month intervals. In our practice we too have seen where one treatment of PRP would be enough for many patients but not all patients. In this study group this was a younger, already active group who tended to heal faster. Realistically some people with a more advanced denegation would require a more comprehensive treatment. Sometimes one treatment will be enough.

Do you have questions? Ask Dr. Darrow



A leading provider of stem cell therapy, platelet rich plasma and prolotherapy

PHONE: (800) 300-9300 or 310-231-7000


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2 Harris JD, Brophy RH, Siston RA, Flanigan DC. Treatment of chondral defects in the athlete’s knee. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2010 Jun 1;26(6):841-52.
3 Jayaseelan DJ, Holshouser C, McMurray MW. FUNCTIONAL JOINT MOBILIZATIONS FOR PATELLOFEMORAL PAIN SYNDROME: A CLINICAL SUGGESTION. Int J Sports Phys Ther. 2020 Aug;15(4):643-649. PMID: 33354396; PMCID: PMC7735690.
4 Kölle T, Alt W, Wagner D. Effects of a 12-week home exercise therapy program on pain and neuromuscular activity in patients with patellofemoral pain syndrome. Archives of Orthopaedic and Trauma Surgery. 2020 Dec;140(12):1985-92.
5 Sawatsky A, Bourne D, Horisberger M, Jinha A, Herzog W. Changes in patellofemoral joint contact pressures caused by vastus medialis muscle weakness. Clinical Biomechanics. 2012 Jul 1;27(6):595-601.
6 Kellish AS, Kellish P, Hakim A, Miskiel S, Shahi A, Kellish A. What Is the Effect on Kinesio Taping on Pain and Gait in Patients With Patellofemoral Pain Syndrome?. Cureus. 2020 Jul;12(7).
7 Shaw B, Darrow M, Derian A. Short-term outcomes in treatment of knee osteoarthritis with 4 bone marrow concentrate injections. Clinical Medicine Insights: Arthritis and Musculoskeletal Disorders. 2018 Jun 14;11:1179544118781080.
8 Doyle EC, Wragg NM, Wilson SL. Intraarticular injection of bone marrow-derived mesenchymal stem cells enhances regeneration in knee osteoarthritis. Knee Surgery, Sports Traumatology, Arthroscopy. 2020 Jan 31:1-6.
9 Orscelik A, Yildiz Y. Comparison of single and triple platelet rich plasma injections in the treatment of patellofemoral pain syndrome. Turkiye Klinikleri Journal of Medical Sciences. 2015;35:78-87.


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