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PRP Knee Injections

Platelet-Rich Plasma for Knee conditions and injuries in Denver & Broomfield, COlorado

Going up and down the stairs is becoming more difficult.  Physical therapy and medications have not helped.  Your doctor recommends PRP knee injections.  What is PRP?  How is PRP made?  What is involved in the PRP injection process?  How do PRP knee injections work? Are PRP knee injections effective for osteoarthritis? How to get the best results from PRP knee injections?  Let’s dig in.

What Is PRP?

PRP stands for Platelet-Rich Plasma.  Platelets are blood cells that prevent bleeding.  They contain important growth factors that aid in healing.  Plasma is the light yellow liquid portion of our blood.  So PRP is simply a concentration of a patient’s own platelets that are suspended in plasma and are used to accelerate healing.  PRP is NOT stem cell therapy.  Regrettably, blood contains few circulating stem cells.   Rich sources of stem cells are bone marrow and fat.

PRP is rich in growth factors.  There are many different types of growth factors with different properties. VEGF is a very important one as it can increase the blood flow to an area.  Blood flow brings important nutrients to damaged tissue and can stimulate repair and healing.  Regrettably, tendons, ligaments, and most parts of the spine have a poor blood supply (1).  This makes injuries difficult to heal.  PRP can facilitate repair and healing by increasing the amount of blood flow.

To learn more about PRP please click on the video below.

How Is PRP Made?

The creation of PRP involves several steps which are summarized below.

  1. Under sterile conditions, your blood is drawn typically from the arm or hand. Volumes drawn vary depending upon the number of areas to be injected and the concentration requested.
  2. At most clinics, the blood is placed into a centrifuge.  This is a machine that spins the blood causing it to separate.  Unfortunately, the centrifuge is limited in its ability to customize the PRP.   The result is a process where one size fits all.  At the Centeno-Schultz Clinic, we utilize a state of the art laboratory with cell biologists on staff that can customize the volume and concentration of the PRP.  In this way, you get a very specific and personalized PRP intended for your personal needs.  PRP concentration matters.   We have published our own research demonstrating that higher concentrations of PRP were more effective in tendon healing in older patients (2).

To learn more about the different types of PRP please click on the video below.

The PRP Injection Process

The use of PRP knee injections is increasingly popular.  For the best clinical outcome, the PRP is injected directly into the injured or damaged tissue.   For example, in a patient with a patellar tendon tear, it is important that the PRP be injected into the tendon tear.   How it is injected is critical.  At the Centeno-Schultz Clinic, all injections are performed with either ultrasound or x-ray guidance, or both.  Accurate placement of the PRP  requires guidance.  Blind injections are substandard and should not be tolerated in 2020 as there is no assurance of the PRP getting into the damaged tissue.

Medications to avoid that regrettably are commonly mixed with PRP include:

Toxic local anesthetics:  not all anesthetics are the same and some are toxic to cartilage and stem cells (3).

High dose steroids:  steroids are toxic to cartilage (4).

How Do PRP Knee Injections Work?

Platelets are rich in growth factors and other important proteins.  In PRP the platelets and growth factor and proteins are super-concentrated.  Growth factors have critical roles in regulating inflammation and healing of tendons, ligaments, muscles, and bones (5).  The major growth factors from PRP that are involved with osteoarthritis treatment include tissue growth factor-B ( TGF-B), insulin growth factor-1, and vascular endothelial growth factor (VEGF) (6).  TGG-B promotes growth and differentiation of cartilage-like cells (chondrocytes) whereas VEGF increases blood flow (7).

Knee Conditions Treated with PRP Injections

ACL Tears

The Anterior Cruciate Ligament (ACL) is one of four major ligaments in the knee. It is an important stabilizer of the knee and prevents the shin bone (tibia) from sliding in front of the thigh bone (femur). The ACL is susceptible to injury. It is most likely to be injured during activity or by impact. A torn ACL is a common injury for athletes at all levels, but it is most common for people who are active or who experience impact injuries to the knee. ACL injuries can happen to anyone of any age, condition, or ability, and it can be injured in many ways. Examples include abruptly changing direction, slowing down while running, landing incorrectly, or getting struck by someone or some object.

Read More About ACL Tears

Baker’s Cyst

A Baker’s cyst can cause knee pain. A Baker cyst is swelling caused by fluid from the knee joint protruding to the back of the knee. They are NOT a true cyst since it has communication with the synovial sac. They typically arise from degenerative changes or injury to the articular cartilage (arthritis) or meniscus. At the Centeno-Schultz Clinic, we believe that baker’s Cysts are simply a barometer of the health of the knee joint. In a healthy knee, there are absent whereas with injury and degenerative changes they are common. They arise between the tendons of the medial head…

Read More About Baker’s Cyst

Chondromalacia

Chondromalacia is the knee usually causes pain, typically around the kneecap or deep in the kneecap. You can also have some grinding sensations or crepitus which are sounds and noises coming from around the knee with certain motions. Typically, pain and grinding sensations are worse with bending the knee, especially for prolonged periods of time, kneeling on the knee, walking downstairs, or running downhill. Standing after prolonged sitting or an immobility period where the knee is bent can cause some discomfort as well. Some people may experience swelling, others may experience locking or catching in the knee, feeling the knee wants to give out, or a feeling of weakness….

Read More About Chondromalacia

Hamstrings Tendinopathy

Your hamstrings are the thick muscles in the back of your thigh that are responsible for the movement of your hip, thigh, and knee. The hamstrings are made of three distinct muscles: Semitendinosus, Semimembranosus, and Biceps Femoris. What is Hamstrings Tendinopathy? Tendons are thick pieces of connective tissue that connect muscle to bone. They function to transfer the force generated by muscle contraction into movement. Hamstring tendinopathy, also known as a “calf strain,” is an injury to the affected tendon. It usually occurs when you bend your knee or extend your leg, putting too much force on the hamstring tendon….

Read More About Hamstrings Tendinopathy

Iliotibial Band Syndrome (ITB)

Also known as “IT Band Syndrome” also known as “ITB Syndrome,” iliotibial band syndrome is a painful medical condition that affects the lateral hip, leg, and knee. It can affect individuals of all ages and most often is caused by repetitive activities like running, cycling, hiking, and walking. Your iliotibial band is a thick band of connective tissue that runs from the outside of your hip down to the outside aspect of your knee. Its principal function is to stabilize the hip and knee. If it becomes tight and dysfunctional, you may experience pain along with this band of tissue due to strain or inflammation. You may also experience pain, limited range of motion in…

Read More About Iliotibial Band Syndrome (ITB)

Knee Arthritis

In the human body, a joint is simply where 2 ends of bone come together. At the ends of these bones, there is a thick substance called “Hyaline Cartilage” that lines the ends. Hyaline cartilage is extremely slippery which allows the two ends of the bone to slide on top of each other. Then there is a capsule that connects the two ends filled with “synovial fluid” that acts as a further lubricant to make it more slippery! Arthritis in the knee is defined by loss of the hyaline cartilage plus other changes that happen to the bone such as additional bone being laid down (bone spurs/osteophytes). The cartilage layer is worn down to the point of exposing the underlying bone they cover…

Read More About Knee Arthritis

Knee Instability

Knee instability is a condition that results when the knee joint is unstable and does not move or function normally. This can cause the knee to feel like it is going to give out or buckle. Knee instability can be caused by a variety of factors, including trauma or injury to the knee, ligament injury, arthritis or other degenerative diseases of the knee, weakness or instability of the muscles around the knee, muscle atrophy, injury to another joint in the body creates an imbalance. Knee stability, and stability in general, is very important. Lack of knee stability can lead to more problems over time, such as pain and arthritis…

Read More About Knee Instability

LCL Sprain

What is an LCL Sprain? A strain or tear to the lateral collateral ligament (LCL) is known as an LCL injury. The LCL is a band of tissue that runs along the outer side of your knee. It aids in keeping the bones together while you walk, ensuring that your knee joint remains stable. How you feel and what type of treatment you’ll require depends on how severely your LCL has been stretched or torn. If it’s only a minor sprain, self-care at home might help. However, if it’s a significant tear or sprain, you may need physical therapy, an injection-based procedure, or surgery….

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LCL Tear

A strain or tear to the lateral collateral ligament (LCL) is known as an LCL injury. The LCL is a band of tissue that runs along the outer side of your knee. It aids in keeping the bones together while you walk, ensuring that your knee joint remains stable. How you feel and what type of treatment you’ll require depends on how severely your LCL has been stretched or torn. If it’s only a minor sprain, self-care at home might help. However, if it’s a significant tear, you may need physical therapy, an injection-based procedure, or surgery. Orthopedists categorize LCL tears into 3 grades…

Read More About LCL Tear

MCL Sprain

The medial collateral ligament AKA MCL is a thick, strong band of connective tissue on the inside portion of your knee. It connects the top part of the tibia (shin) to the bottom part of the femur (thigh). This is a vital ligament that works along the lateral collateral ligament (LCL), anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL) to bring stability, structure, and movement to the knee. The MCL provides support and stability for the inside (medial) aspect of the knee. MCL sprains are a common injury in sports such as football, hockey, and skiing. The ligament can…

Read More About MCL Sprain

MCL tear

The medial collateral ligament AKA MCL is a thick, strong band of connective tissue on the inside portion of your knee. It connects the top part of the tibia (shin) to the bottom part of the femur (thigh). This is a vital ligament that works along the lateral collateral ligament (LCL), anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL) to bring stability, structure, and movement to the knee. The MCL provides support and stability for the inside (medial) aspect of the knee. MCL tears are a common injury in sports such as football, hockey, and skiing. The ligament can…

Read More About MCL tear

Meniscus Tears

The meniscus is a c-shaped piece of cartilage in the knee that functions as an important shock absorber. It is sandwiched between the thigh and shin bone. There are two menisci per knee. One on the inside portion of the knee (medial) one on the outside aspect (lateral). The knee meniscus is susceptible to injury. The most common injury is a tear in the meniscus. Not all meniscus tears however cause pain. When symptomatic a meniscus tear can cause pain, swelling, and restriction in range of motion. Tears in the knee meniscus can arise from trauma or degeneration. There are many different types of meniscus tears based upon locations….

Read More About Meniscus Tears

Patellar Tendonitis

What is the Patellar Tendon? A tendon is a piece of connective tissue that connects muscle to bone. It serves to move the bone or a given joint. The patellar tendon is a major tendon in the knee. It is located at the bottom of the kneecap (patella) and stretches down to the shin. The patellar tendon enables you to extend your knee, kick, run, and jump. What is Patellar Tendinitis? Patellar tendinitis is an irritation and inflammation of the tendon that connects your kneecap (patella) to your shinbone. Patellar tendinitis, also known as jumper’s knee, can affect anyone. The most common symptom is pain at the shin or lowest part of the kneecap…

Read More About Patellar Tendonitis

Patellofemoral Syndrome

The kneecap is also known as the patella. The thigh bone is the femur. The patellofemoral joint is formed by the kneecap and the grooved surface of the thigh bone. The patella slides up and down in a grooved track in the femur. The groove is more specifically called the trochlear groove. Like a train that travels on a track, under ideal conditions the patella tracks up and down in the trochlear groove. What is Patellofemoral Syndrome? Patellofemoral syndrome is a medical condition characterized by discomfort in the front of the knee and around the patella. Patellofemoral syndrome may also be known as “jumper’s knee” or “runner’s knee.”…

Read More About Patellofemoral Syndrome

PCL Sprain

The Posterior Cruciate Ligament is one of the paired ligaments in the middle of the knee. It is made up of 2 separate bundles: The two bundles of the PCL, and the ALB (anterior lateral bundle), and the PMB (posterior medial bundle), function synergistically to provide stability. The PCL functions as one of the main stabilizers of the knee joint and serves primarily to resist excessive posterior translation of the tibia relative to the femur. The PCL also acts as a secondary stabilizer of the knee preventing excessive rotation specifically between 90° and 120° of knee flexion. A PCL sprain happens when force is applied beyond…

Read More About PCL Sprain

PCL Tear

The Posterior Cruciate Ligament (PCL) is a paired ligament in the middle of the knee. It is made up of two separate bundles: ALB (anterior lateral bundle) and PMB (posterior medial bundle). These bundles work synergistically to provide stability. The PCL plays an important stabilizing role in the knee joint by resisting excessive posterior translation of the tibia relative to the femur. Between 90 and 120 degrees of knee flexion, it serves as secondary support for preventing excessive rotation. PCL tears happen when force is applied beyond what the PCL tensile strength is capable of resisting. The tensile strength of the PCL is well documented…

Read More About PCL Tear

Peroneal Nerve Injury

The common peroneal nerve branches behind the knee and this could be irritated from any overuse activity, surgery, instability, or any compression on the outside of the knee. Typically, this will present as pain on the outside of the knee radiating towards the baby toe, the calf, and the lateral shin towards the lateral ankle. What Causes Peroneal Nerve Compression? There are many potential causes of peroneal nerve compression, such as overuse activities, surgery, instability, or any compression on the outside of the knee. Trauma and nerve compression, especially caused by a fractured or dislocated ankle, can all cause injury to the peroneal nerve. Causes include:

Read More About Peroneal Nerve Injury

Pes Anserine Bursitis

Knee pain located at the lower inside of the knee can be caused by Pes Anserine Bursitis, which is irritation of the tendons that run on the inside aspect of the knee. Commonly mistaken for arthritic pain, meniscal pain, and sometimes nerve pain from the low back! Don’t be misdiagnosed, and let’s dive in below to get a better understanding of Pes Anserine Bursitis. The Pes Anserine Bursa is a bursa that surrounds 3 tendons of the leg. A bursa is a thin, slippery, sac-like film that contains a small amount of fluid. A bursa is found between bones and soft tissues in and around joints…

Read More About Pes Anserine Bursitis
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Are PRP Knee Injections Effective for Osteoarthritis?

To date, there are 27 randomized control studies ( RTC) on PRP knee injections to treat knee arthritis.  The studies compared PRP to common treatments such as steroid injections, hyaluronic acid (HA), and physical therapy.  PRP knee injections were better than steroids in the treatment of knee osteoarthritis.  Cortisone is a powerful anti-inflammatory agent that is commonly used in the treatment of knee osteoarthritis. Recent studies have demonstrated that it is toxic to cartilage and should be avoided (8).   Important PRP knee injections studies are summarized below:

2019 study of 120 patients with known early-stage knee osteoarthritis were randomized into three different treatment groups.  Group 1 received HA, group 2 steroid, and group three PRP.  All participants underwent injections once a week for three weeks.  At 6,9 and 12 months, PRP was more effective in reducing pain and increasing function than injected steroids (9)

A 2016 study of 41 patients with knee osteoarthritis compared a single injection of PRP vs corticosteroid.   At 6 months PRP was more effective in reducing pain, increasing function, and improving quality of life than corticosteroids (10).

A 2016 critical review of six articles with 739 patients demonstrated that PRP provided a better reduction in pain and increase in function than cortisone ( 11).

Are PRP Knee Injections Better than Exercise Alone in the Treatment of Knee Osteoarthritis?

Physical therapy is often times the first-line treatment option for knee osteoarthritis.  The is focused on increasing strength and range of motion.  Is PT better than PRP knee injections?  Nope.  Summarized below are two studies that examined the effectiveness of PRP vs exercises for patients with knee osteoarthritis.

A  2014 study randomized patients with known knee osteoarthritis into two groups:  Both groups were prescribed physical therapy.  Of the two groups, one received two PRP knee injections.   PRP combined with PT was shown to be more effective in reducing pain and increasing function than PT alone (12).

A 2015 study randomized study evaluated the use of transcutaneous electrical nerve stimulation (TENs) vs PRP injections in patients with knee osteoarthritis (13).  PRP was more effective in reducing pain and increasing function than TENS unit.

How to Get the Best Results from PRP Knee Injections?

The knee is a complex joint that contains many parts which include cartilage, meniscus, tendons, ligaments, and muscles.  All these structures need to be evaluated and treated if appropriate. Regrettably, the majority of all PRP knee injections are simply into the joint which ignores all the other structures. Many of these injections are performed without guidance.  Said another way they are blind injections with no assurance that the PRP was injected into the correct structure.  This is below the standard of care and should not be tolerated.

At the Centeno-Schultz Clinic, we are experts in the treatment of knee pain.  We utilize a comprehensive approach called SANS. It evaluates the stability, Articulation, Neurologic and Symmetry of the Knee Joint.  All PRP knee injections are performed with ultrasound and or x-ray guidance.  This ensures accurate placement of the PRP.  This will allow for the best clinical results.   To better understand the importance and skill required for ultrasound-guided injections please click on the video below.

In Conclusion

PRP knee injections are increasingly popular.  PRP is platelet-rich plasma which is a concentration of a patient’s own platelets.  It is rich in growth factors that can stimulate healing and repair.  A patient’s own blood is drawn from the arm or hand and processed removing the red cells and concentrating the platelets.  27 randomized control studies have been completed evaluating the use of PRP in the treatment of knee osteoarthritis.  PRP is more effective than steroids and exercise. For the best clinical results, all the different parts of the knee need to evaluated and treated.  All PRP knee injections must be performed under guidance to ensure the accurate placement of the concentrated platelets.

If your PCP or orthopedic surgeon discredits or ignores your questions about PRP knee injections remind them there is extensive literature to support its use.  If they are not receptive its time to look elsewhere as their biases are preventing them from providing you with the very best care.

Schedule a telemedicine consultation from the comfort of your home.  Learn if PRP is right for you.  Stop the pain and start living again.

Doctors that Treat Knee Injuries at Centeno-Schultz Clinic

Christopher J. Centeno, MD

Christopher J. Centeno, M.D. is an international expert and specialist in Interventional Orthopedics and the clinical use of bone marrow concentrate in orthopedics. He is board-certified in physical medicine and rehabilitation with a subspecialty of pain medicine through The American Board of Physical Medicine and Rehabilitation. Dr. Centeno is one of the few physicians in the world with extensive experience in the culture expansion of and clinical use of adult bone marrow concentrate to treat orthopedic injuries. His clinic incorporates a variety of revolutionary pain management techniques to bring its broad patient base relief and results. Dr. Centeno treats patients from all over the US who…

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John Schultz, MD

My passion and specialization are in the evaluation and treatment of cervical disc, facet, ligament and nerve pain, including the non-surgical treatment of Craniocervical instability (CCI). I quit a successful career in anesthesia and traditional pain management to pursue and advance the use of PRP and bone marrow concentrate for common orthopedic conditions. I have been a patient with severe pain and know firsthand the limitations of traditional orthopedic surgery. I am a co-founder of the Centeno-Schultz Clinic which was established in 2005. Being active is a central part of my life as I enjoy time skiing, biking, hiking, sailing with my family and 9 grandchildren.

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John Pitts, M.D.

Dr. Pitts is originally from Chicago, IL but is a medical graduate of Vanderbilt School of Medicine in Nashville, TN. After Vanderbilt, he completed a residency in Physical Medicine and Rehabilitation (PM&R) at Emory University in Atlanta, GA. The focus of PM&R is the restoration of function and quality of life. In residency, he gained much experience in musculoskeletal medicine, rehabilitation, spine, and sports medicine along with some regenerative medicine. He also gained significant experience in fluoroscopically guided spinal procedures and peripheral injections. However, Dr. Pitts wanted to broaden his skills and treatment options beyond the current typical standards of care.

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Jason Markle, D.O.

Post-residency, Dr. Markle was selected to the Interventional Orthopedic Fellowship program at the Centeno-Schultz Clinic. During his fellowship, he gained significant experience in the new field of Interventional Orthopedics and regenerative medicine, honing his skills in advanced injection techniques into the spine and joints treating patients with autologous, bone marrow concentrate and platelet solutions. Dr. Markle then accepted a full-time attending physician position at the Centeno-Schultz Clinic, where he both treats patients and trains Interventional Orthopedics fellows. Dr. Markle is an active member of the Interventional Orthopedic Foundation and serves as a course instructor, where he trains physicians from around the world.

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Matthew William Hyzy, D.O.

Doctor Hyzy is Board Certified in Physical Medicine and Rehabilitation (Physiatry) and fellowship-trained in Interventional Orthopedics and Spine. Dr. Hyzy is also clinical faculty at the University of Colorado School of Medicine in the Department of Physical Medicine and Rehabilitation; In addition, Dr. Hyzy is an Adjunct Clinical Assistant Professor at The Rocky Vista University College of Osteopathic Medicine. Dr. Hyzy also maintains an active hospital-based practice at Swedish Medical Center and Sky Ridge Medical Center. He is also recognized and qualified as an expert physician witness for medical-legal cases and Life Care Planning. He is published in the use of autologous solutions including…

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Brandon T. Money, D.O., M.S.

Dr. Money is an Indiana native who now proudly calls Colorado home. He attended medical school at Kansas City University and then returned to Indiana to complete a Physical Medicine and Rehabilitation residency program at Indiana University, where he was trained on non-surgical methods to improve health and function as well as rehabilitative care following trauma, stroke, spinal cord injury, brain injury, etc. Dr. Money has been following the ideology behind Centeno-Schultz Clinic and Regenexx since he was in medical school, as he believed there had to be a better way to care for patients than the status quo. The human body has incredible healing capabilities…

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Mairin Jerome, MD

Mairin Jerome, MD

Dr. Mairin Jerome is a physiatrist with subspecialty fellowship training in Interventional Orthopedics and Regenerative Medicine. This subspecialty serves to fill the gap for patients who are interested in therapeutic options that lie between conservative treatment and surgery. Dr. Jerome uses regenerative medicine techniques, including prolotherapy and orthobiologics, via X-ray or ultrasound guidance to precisely deliver injections to areas of musculoskeletal injury or degeneration. Orthobiologics refers to tissue harvested typically from a person’s own body, such as platelets (platelet-rich plasma, PRP) or bone marrow, for use in treating painful musculoskeletal conditions. The goal is to stimulate the body’s healing mechanisms to improve pain, function, and decrease inflammation.

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References

1.Mishra A, et al. Treatment of Tendon and Muscle Using Platelet-Rich Plasma. ClinCports Med 2009; 28:113-125.2. Cook JL, et al. Is Tendon Pathology a

2.Berger DR, Centeno CJ, Steinmetz NJ. Platelet lysates from aged donors promote human tenocyte proliferation and migration in a concentration-dependent manner. Bone Joint Res. 2019;8(1):32–40. Published 2019 Feb 2. doi: 10.1302/2046-3758.81.BJR-2018-0164.R1

3.Dregalla RC, Lyons NF, Reischling PD, Centeno CJ. Amide-type local anesthetics and human mesenchymal stem cells: clinical implications for stem cell therapy. Stem Cells Transl Med. 2014;3(3):365-374. doi:10.5966/sctm.2013-0058.

4.Wernecke C, Braun HJ, Dragoo JL. The Effect of Intra-articular Corticosteroids on Articular Cartilage: A Systematic Review. Orthop J Sports Med. 2015;3(5):2325967115581163. Published 2015 Apr 27. doi:10.1177/2325967115581163

5. Foster TE, Puskas BL, Mandelbaum BR, Gerhardt MB, Rodeo SA. Platelet-rich plasma: from basic science to clinical applications. Am J Sports Med. 2009 Nov;37(11):2259-72. doi: 10.1177/0363546509349921. PMID: 19875361.

6. Cook CS, Smith PA. Clinical Update: Why PRP Should Be Your First Choice for Injection Therapy in Treating Osteoarthritis of the Knee. Curr Rev Musculoskelet Med. 2018;11(4):583-592. doi:10.1007/s12178-018-9524-x.

7.Whitney KE, Liebowitz A, Bolia IK, Chahla J, Ravuri S, Evans TA, Philippon MJ, Huard J. Current perspectives on biological approaches for osteoarthritis. Ann N Y Acad Sci. 2017 Dec;1410(1):26-43. doi: 10.1111/nyas.13554. PMID: 29265418.

8. Kompel AJ, Roemer FW, Murakami AM, Diaz LE, Crema MD, Guermazi A. Intra-articular Corticosteroid Injections in the Hip and Knee: Perhaps Not as Safe as We Thought? Radiology. 2019 Dec;293(3):656-663. doi: 10.1148/radiol.2019190341.

9. Huang, Y., Liu, X., Xu, X. et al. Intra-articular injections of platelet-rich plasma, hyaluronic acid or corticosteroids for knee osteoarthritis. Orthopäde 48, 239–247 (2019). https://doi.org/10.1007/s00132-018-03659-5

10. Forogh B, Mianehsaz E, Shoaee S, Ahadi T, Raissi GR, Sajadi S. Effect of single injection of platelet-rich plasma in comparison with corticosteroid on knee osteoarthritis: a double-blind randomized clinical trial. J Sports Med Phys Fitness. 2016 Jul-Aug;56(7-8):901-8. Epub 2015 Jul 14. PMID: 26173792.

11. Meheux CJ, McCulloch PC, Lintner DM, Varner KE, Harris JD. Efficacy of Intra-articular Platelet-Rich Plasma Injections in Knee Osteoarthritis: A Systematic Review. Arthroscopy. 2016 Mar;32(3):495-505. doi: 10.1016/j.arthro.2015.08.005. Epub 2015 Oct 1. PMID: 26432430.

12. Rayegani SM, Raeissadat SA, Taheri MS, Babaee M, Bahrami MH, Eliaspour D, Ghorbani E. Does intra articular platelet rich plasma injection improve function, pain and quality of life in patients with osteoarthritis of the knee? A randomized clinical trial. Orthop Rev (Pavia). 2014 Sep 18;6(3):5405. doi: 10.4081/or.2014.5405. PMID: 25317308; PMCID: PMC4195987.

13. Angoorani H, Mazaherinezhad A, Marjomaki O, Younespour S. Treatment of knee osteoarthritis with platelet-rich plasma in comparison with transcutaneous electrical nerve stimulation plus exercise: a randomized clinical trial. Med J Islam Repub Iran. 2015 Jun 27;29:223. PMID: 26478881; PMCID: PMC4606945.