Patellar Tendinopathy surgery and treatment options
Ross A. Hauser, MD; Danielle R. Steilen-Matias, MMS, PA-C
- In this article, we will examine research and clinical observations of various treatments for patellar tendinopathy, a degeneration process of the kneecap tendon.
- We will also look at the connection between patellar tendinopathy, continuing degenerative knee ligament damage, and degenerative knee instability that makes it very difficult for a jumper to jump, a runner to run, or a worker to work without pain.
Understanding points: People will often come into the office with confusion because they have been diagnosed with patellar tendinosis or with patellar tendinitis.
- Patellar tendinitis is inflammation, pain, and swelling.
- Patellar tendinitis occurs, for instance, when a runner has knee pain after a run or someone in a sport that involves jumping suffers a more acute injury, especially a first-time acute injury. On examination, the patella tendon is very sore.
- Patellar tendinosis is pain and weakness without inflammation.
- This is a chronic degenerative condition. If this person/athlete gets cortisone shots in the patellar tendon or they take anti-inflammatories for a very long time, the tendinitis (pain and degenerative knee disease symptoms with inflammation) becomes tendinosis (pain and degenerative knee disease symptoms without inflammation).
My doctors are arguing over my MRI, I need to get a surgery
The problem of chronic patellar tendinopathy is that it is usually not an isolated knee injury. The problem of patella tendinopathy is that is part of a series of problems in the knee caused by knee instability. We will often have people email us describing an injury to the knee. The limitations this is giving them including the inability to perform sports, work without pain, or even just walk up a flight of steps without knee pain. These people also tell us about the confusion in their diagnosis and the true cause of what is causing their pain. Some tell us about the arguments between their doctors as to what their MRI “really,” says. Some people will have a meniscus tear on their MRI and their doctors focus on that, minimizing the potential of a problem with the patella tendon. The longer this goes on, the greater the need to get in line for surgery.
“I do not want to take more time off from working out”
Many people have patellar tendinopathy. They take some anti-inflammatories, look up video exercises, buy tape and knee braces and they go about their way with a chronic nagging injury that they can pretty much control. For others, the situation has progressed to a point of surgical recommendations. Such as these types of stories we hear.
I have been trying to get back to running, I have patellar tendonitis that is not responding. I don’t want to take more time off. The orthopedist I am seeing is prescribing anti-inflammatories, I have been on them for months, stronger doses, I still can’t run. He tells me to rest, I have been resting. I still can’t run. I have had two MRIs. I have patellar tendon inflammation. My doctor and I both knew it but nothing is working for me. Not ice, not yoga, not physical therapy. I am getting quickly out of shape.
Others go something like this.
I am being recommended for surgery. My orthopedist tells me I should have no illusions that I will be the same or better player after surgery. I will just have more better days than worse days. I have no illusions, I play volleyball, I have already had two meniscus procedures and my doctor says the tendinitis is probably a response to my post-surgically weakened knee.
From self-management to doctor’s care. Your knee is not responding.
When someone has knee pain, from whatever source, a self-management program is usually taken before a trip to the doctor. This will include some type of stabilizing brace or knee sleeve and anti-inflammatory medication. Of course, these are only symptom suppression means to keep swelling down and to give the wearer a false sense of security that the brace will hold their knee together. Education is part of the management plan, a person will usually spend a lot of time online trying to find out what is wrong with their knee and the best course of action they can take. The one suggestion most patients with Jumper’s Knee do not want to follow is “REST.”
If you are reading this article, it is likely that here you are, with knee pain that is getting progressively worse, wearing a sleeve on your knee, and a knee that is becoming much less functional. Shutting down your knee and resting seems the best option now.
Rest did not help. Anti-inflammatories are making your knee worse.
After a few weeks of rest, you are back on your knee and nothing has changed. You still have pain, you still have instability. Now perhaps it is time for a trip to the doctor. For some people, they do not go to the doctor. They continue on with more anti-inflammatories because they want to play. These people are going to “suck it up.”
At the beginning of his article, we discussed the difference between tendinitis and tendinosis – this is why it is important to you.
- Patellar tendinitis is inflammation, pain, and swelling.
- Your body is still trying to heal the knee
- Patellar tendinosis is pain and weakness without inflammation.
- Your body HAS STOPPED trying to heal the knee. You have no inflammation, inflammation, as bothersome and troubling as it is, is the way the body heals damage. If you stop inflammation, you cannot heal.
If you would like to learn about When NSAIDs make pain worse and lead to a worsening joint condition, please read our article When NSAIDs make pain worse.
If you are reading this article, perhaps this is what is happening to you now. You are in this situation because you are looking for the quick fix recovery from patellar tendinopathy.
Cortisone injection concerns
A recent paper in the International Journal of Sports Physical Therapy (1) offered this summary of the concerns of ng cortisone for patella tendinopathy.
- “As tendon pathology has been historically labeled as tendinitis, an inflammatory condition, it is not surprising that anti-inflammatory medicines are commonly prescribed for patients with tendon pain. This includes the use of oral non-steroidal anti-inflammatory medicines (NSAIDs) and injections of corticosteroids.
- In a systematic review of the literature on treatment of tendinitis,(one study) reported that the use of oral NSAIDs may result in some pain relief but the effect on the tendon is not known as the follow-up time in all the studies was less than one month.
- Similarly, the use of injected corticosteroids may also result in pain relief in tendinopathy, but there is concern regarding the effect of corticosteroids on tendon strength.
Cortisone can mutate stem cells and make the tendon weaker.
- A new challenge to the injection of corticosteroids into the patellar tendon was revealed in a recent study (2) on the effect of dexamethasone on patellar tendon stem cells. These authors found that dexamethasone had a “paradoxical” effect on the tendon stem cells, inducing them to differentiate into non-tenocytes including chondrocytes and adipocytes. This evidence suggests that injection of dexamethasone into a tendon may lead to the formation of non-tendon tissue within the tendon, ultimately weakening the tendon.
Research: “no treatments exist for patellar tendinopathy that guarantees quick and full recovery”
This is not what you probably wanted to hear. But let’s look deeply at this. What most researchers warn is that there is no “magic bullet,” single injection or single therapy that will repair this type of knee damage overnight. If you have Jumper’s Knee, you did this type of damage over time, it takes time to repair.
The above statement comes from an October 2017 study in the Clinical Journal of Sports Medicine (3) from the Center for Sports Medicine at the University Medical Center Groningen in the Netherlands. Here is the whole sentence:
“Currently, no treatments exist for patellar tendinopathy that guarantees quick and full recovery. Our objective was to assess which treatment option provides the best chance of clinical improvement and to assess the influence of patient and injury characteristics on the clinical effect of these treatments.”
These were the treatments they tested:
Participants were divided into 5 groups:
- Extracorporeal shockwave therapy (ESWT) (A machine delivers acoustic pressure waves to the affected area) (31 participants),
- ESWT plus eccentric training (Eccentric training is an exercise technique where the return to the starting pose is done slowly. For instance, if you perform a knee lift, instead of letting your foot drop back down to the floor quickly, you slowly lower it to build muscle strength. (43 participants),
- Eccentric training (17 participants),
- Topical glyceryl trinitrate patch (Salonpas for instance) plus eccentric training (16 participants),
- and placebo treatment (31 participants).
- In comparison, clinical improvement was significantly higher in the eccentric training group and the ESWT plus eccentric training group compared to Extracorporeal shockwave therapy alone, topical glyceryl trinitrate patch, or placebo.
- The higher training volume, a longer duration of symptoms, and older age negatively influence a treatment’s clinical outcome.
NO CLEAR BENEFIT to any of those treatments.
We do find that eccentric exercise training offered some degree of relief, however, the more exercise the less benefit (not what an athlete wants to hear), the longer the patient had the symptoms and the patients’ age also presented problems.
Take away points:
- Extracorporeal shockwave therapy – the role remains unclear
- Exercise the more important of the treatments, but not too much exercise
- No comparison in this study was made to comprehensive Prolotherapy or Platelet Rich Plasma treatments which will be discussed below.
The research above continues the work from the University of Groningen researchers. (4) Earlier the University medical researchers investigated the impact patellar tendinopathy has on a patient’s sports and work performance. Their findings were published in the journal Research in Sports Medicine.
- Reduced sports performance was reported by 55% of their study’s participants;
- 16% reported a reduced ability to work and
- 36% decreased work productivity, with 23% and 58%
The Dutch researchers concluded that the impact of Patellar Tendinopathy on sports and work performance is substantial and stresses the importance of developing preventive measures.
More research on extracorporeal shockwave therapy
In March 2018, publishing in the British Journal of Sports Medicine, (5) a multi-national team of researchers evaluated extracorporeal shockwave therapy (ESWT) in treating Achilles tendinopathy, greater trochanteric pain syndrome, medial tibial stress syndrome, patellar tendinopathy, and proximal hamstring tendinopathy.
- (1) no difference between focused ESWT and placebo ESWT at short and mid-term in patellar tendinopathy and
- (2) radial ESWT is superior to conservative treatment at short, mid, and long term in proximal hamstring tendinopathy.
Low-level evidence suggests that ESWT
- (1) is comparable to eccentric training, but superior to a wait-and-see policy at 4 months in mid-portion Achilles tendinopathy;
- (2) is superior to eccentric training at 4 months in insertional Achilles tendinopathy;
- (3) less effective than corticosteroid injections in short term, but ESWT produced superior results at mid and long term in greater trochanteric pain syndrome;
- (4) produced comparable results to control treatment at long term in greater trochanteric pain syndrome; and
- (5) is superior to control conservative treatment for the long term in patellar tendinopathy.
The conclusion simply suggests, extracorporeal shockwave therapy may or may not help. Many people get good success with extracorporeal shockwave therapy, however, similar findings were made in an August 2018 study from doctors at the National Taiwan University and Taipei Medical University in Taiwan. They published findings in the journal BioMed Central Musculoskeletal Disorders (6) in London. The suggestion of their findings is that caution is given in providing ESWT to knee soft tissue disorders. ESWT may or may not work for Patellar tendinopathies.
An October 2019 study in the Annals of Translational Medicine (7) also offers this summary:
“The mechanism of action of ESWT is not fully understood, and current research as to its efficacy in treating tendinopathies is conflicting. It is suspected that it can have both analgesic effects along with potential tissue regenerative effects. The efficacy of shockwave therapy is inconsistent, with some research finding no improvements. Other research is promising.”
The main problem with patellar tendinopathy – it is a degenerative disorder rather than an inflammatory disorder – should you have surgery?
If the doctor suggests your problem is due to patellar tendinopathy, you have a problem with the tendon that passes from the quadriceps muscle (the large muscle at the front of the thigh) over the kneecap (patella) to connect to the shinbone (tibia).
What are we seeing in this image?
The patella is pulled and pushed in all directions. It is pulled by the Iliotibial band, it is stabilized in place by the lateral patellar retinaculum and the medial patellar retinaculum. The quadriceps move the patella upwards, the patellar ligament moves it downward. When one of these structures is weakened or damaged through degenerative wear and tear, the knee cap becomes unstable.
Further recommendations and guidelines for the treatment of patellar tendinopathy were published in The Journal of the American Academy of Orthopaedic Surgeons (8).
- The main problem in patellar tendinopathy is tendinosis, which is a degenerative disorder rather than an inflammatory disorder; therefore, the other popular term for this disease, tendinitis, is not appropriate. Tendinosis – degeneration without inflammation (the body has given up trying to heal this injury), Tendinitis – degeneration with inflammation (the body is trying to heal this injury). As we mentioned above.
- The nonsurgical treatment of patellar tendinopathy is focused on eccentric exercises and often has good results.
- Surgical treatment is indicated for cases that are non-responsive to nonsurgical treatment. Open or arthroscopic surgery can be performed; the two methods are comparable.
As far as the surgical technique goes, doctors from the Department of Orthopedic Surgery and the Department of Physical Medicine and Rehabilitation, Mayo Clinic, Florida State University, and the Florida State University College of Medicine, published their findings in the journal Orthopedics. They found open surgery and arthroscopic techniques achieved similar satisfactory results in 81% of patients, respectively. The average time to return to play was 5.6 months and 5 months, respectively. (9)
The unappealing aspects of Patellar Tendinopathy surgery – Average time to return to play was 5.6 months and 5 months. Second: If the surgery fails, it is difficult to fix.
The problem with surgery for the athlete are three-fold,
- one the length of time to recovery is not appealing,
- second, patellar tendinopathy is often a chronic problem.
- Third, if the surgery fails, it is difficult to fix.
This is what a paper from the University of Salerno and the University of London suggested in the journal Sports Medicine and Arthroscopy Review.
- Many patients respond well to conservative treatment, but about 10% of them do not.
- In these cases, surgery is indicated.
- In a small percentage of patients, surgery is unsuccessful. This group of patients presents a major challenge, as options are limited. (10)
I was a very active woman. In the past year, I underwent arthroscopic knee repair
Many people have patella arthroscopic surgery with outstanding results. These are typically not the patients we see in our office. we see people like this:
I was a very active woman. In the past year, I underwent arthroscopic knee repair. I had a torn meniscus that needed repair and medial meniscus repair and patella debridement for my patellar tendinopathy. I was very happy with the surgery initially because I was able to return to my activities within six months. However a month into my return to activities I had significant knee pain. My knee swelled up. I could not run, I could barely walk. Steps and inclines became impossible.
Non-surgical bio-treatments Prolotherapy and PRP Therapy
Before we look at the research and explanation discussing the use of injection techniques such as Prolotherapy, Platelet Rich Plasma, and Stem Cell Therapy. Let’s look at a paper from the Rubin Institute for Advanced Orthopedics, Sinai Hospital, Baltimore. It was published in the journal Annals of Translational Medicine,(11) October 2019.
In this paper, various methods of treating common knee injuries are discussed. One section has very good information on the concept of the patella and the importance of keeping the patella where it should be in the knee.
“Patellar taping is commonly used in conjunction with manual and exercise therapies in the management of Patellofemoral pain syndrome. Taping is predominately used to help decrease pain. Other studies show it can also help with patellar alignment and muscle activation. As patellar hypermobility has been shown as a predisposing factor for developing Patellofemoral pain syndrome, taping can be indicated to promote patellar positioning and decrease pain. . . .Overall, the effects of taping, are conflicting, with some studies showing no benefit and others unsure of the mechanisms of improvements noted. The positive changes including decreased pain and improved VMO (vastus medialis obliquus, the muscle above the knee used to extend the leg at the knee and to stabilize the patella) function is only short-term but can be helpful with acute management of symptoms with functional activity.”
The goal of tape or brace or surgery is to get the patella back into place.
Prolotherapy treatment options
Prolotherapy is the injection of a simple sugar solution, hypertonic dextrose, into and around specific important structures in the knee to stimulate their repair. Many studies have documented Prolotherapy treatments effectiveness
Prolotherapy is a multiple injection technique that is demonstrated in the video below. The treatment stimulates healing and repair of the tendon attachments, the knee ligaments and addresses problems of the cartilage that sits behind the knee cap and in the trochlear groove. When more significant degenerative damage has occurred, we may utilize Platelet Rich Plasma Therapy, the use of your own blood platelets reintroduced into the knee. Ross Hauser, MD discusses a case of 70% tear treated with stem cell therapy and Prolotherapy.
- Prolotherapy injections to restore stability to the knee cap will usually take 4 – 6 treatments.
- Patients come back every 4 to 6 weeks as we strengthen the attachments of the patella tendon and the quadriceps tendon as well as address the cartilage issues behind the knee cap and in the trochlear groove where the patella slides against the thigh bone.
- Typically I would have patients rest after treatment for 5 – 7 days and then begin a responsible closed chain exercise program that would include squats, leg presses, etc, focusing on strengthening the muscles of the downward motion. I would have the patient avoid exercises that twist the knee and avoid running on uneven or up and down surfaces.
Most recent research
A November 2020 study in the Journal of Experimental Orthopaedics (12) examined the use of Prolotherapy and Sclerotherapy injections. A note of understanding. At one time Prolotherapy and Sclerotherapy were used as somewhat synonymous terms. They are however not the same treatment. Prolotherapy injections center on the joints with the repair of the tendon, ligaments, and cartilage. Sclerotherapy focuses on the blood vessels and is considered an excellent treatment for varicose veins.
In this study, the researchers noted that: “Sclerotherapy and Prolotherapy are, among a wide range of conservative treatment options, two promising therapies and have shown positive results in other tendinopathies. Since the treatments’ efficacy and safety are still not defined, this review sought to answer questions on recommendations for use in clinical utility, safety, and how to perform the injection in the most effective way.”
The findings: The researchers examined ten previously published papers and found positive results with an increase in functional ability scores and decreases in pain scores in the patients examined. “Among all ten studies, no serious adverse events were reported. Based on this limited set of studies, there seems to be some evidence that Sclerotherapy and Prolotherapy may be effective treatment options to treat pain and to improve function in patients with Chronic Patellar tendinopathy.”
One of my more memorable cases over the course of 30 years doing Prolotherapy and more recently stem cell therapy was a patient who came in and had a 70% tear of their patella tendon.
- At 0:30 Dr. Hauser shows an ultrasound scan revealed a significant tear of the tendon.
- The patient revealed that her orthopedic surgeon described her tendon as “spaghetti” and that she would need arthroscopic reconstruction surgery for her patella tendon.
- This particular person is very, very active. She does triathlons, golfs, runs, and she is very holistic and conservative so she wanted me to treat her with our treatments as opposed to surgery.
- It should be pointed out that a tear this significant does take 6 to 8 months to repair with injection therapy. The patient received multiple PRP treatments and ultimately stem cell treatments into the patellar tendon.
- At 1:15 ultrasound before and after revealing that the tear is repairing. The person is back to playing golf, back to running, back to doing everything that she loves. So even really severe tears as this was a 70% tear, responded to Prolotherapy with PRP and with stem cells. The treatment can be objectively verified and confirmed with ultrasound analysis.
When you have bone spurs in the knee
What are we seeing in this image?
This image graphically shows what can happen when knee instability is left untreated or improperly treated. The unstable knee in this image has created a large bone spur to help stabilize the knee by limiting the knee’s natural range of motion. Because of the severity of the knee instability, the knee grew itself a very large bone spur. The bone spur became so large it started to rub and fray the patella tendon of this patient to the point of near-total rupture.
Research on Prolotherapy and PRP injections
Here is what New York University doctors wrote in the Bulletin of the Hospital for Joint Diseases.
“Due to its common refractory response (non-responsive or difficult to treat) to conservative treatment, a variety of new treatments have emerged recently that include dry-needling, sclerosing injections (Prolotherapy), platelet-rich plasma therapy, arthroscopic surgical procedures, surgical resection of the inferior patellar pole (cutting away tendon tissue at the kneecap), extracorporeal shock wave treatment (as discussed in the other studies cited here), and hyperthermia thermotherapy (exposing the knee to high temperature) in addition to physical therapy.”(13)
Obviously, the list includes treatments that we offer at Caring Medical, Prolotherapy, and Platelet Rich Plasma.
Non-surgical solutions to the problem of chronic and recurrent Patellar Tendinopathy
In Germany, doctors supported the New York University findings. Writing in the medical journal Der Unfallchirurg (English: The trauma surgeon), the German researchers suggested that treatment with platelet-rich plasma showed a significantly better outcome when used correctly. Additionally, treatments such as Extracorporeal shockwave therapy, operative treatment, and sclerotherapy (Prolotherapy) have also shown positive effects. Treatment with corticosteroid injections and with oral non-steroidal anti-inflammatory drugs (NSAIDs) showed positive short-term effects. (14)
Prolotherapy can treat various knee disorders including problems of the tendons. Prolotherapy Injections of a dextrose solution directed at the weakened tendons and involved ligaments. This causes a mild, localized inflammatory response at the injured area which stimulates a string of healing events, which include an increase of blood supply, an influx of reparative cells, and the deposition of collagen cells. When the collagen matures, it will strengthen and tighten the damaged tendons and ligaments.
PRP and Prolotherapy
- PRP treatment takes your blood, like going for a blood test, and re-introduces the concentrated blood platelets from your blood into areas of chronic joint and spine deterioration.
- Your blood platelets contain growth and healing factors. When concentrated through simple centrifuging, your blood plasma becomes “rich” in healing factors, thus the name Platelet RICH plasma.
- The procedure and preparation of therapeutic doses of growth factors consist of an autologous blood collection (blood from the patient), plasma separation (blood is centrifuged), and application of the plasma rich in growth factors (injecting the plasma into the area.) In our office, patients are generally seen every 4-6 weeks. Typically three to six visits are necessary per area.
The most important finding is that PRP injections are statistically better than the control group (ESWT and dry needling) at longer-term (6 months or more) follow-up, suggesting that PRP is an effective and worthwhile treatment for Patellar Tendinopathy.
Doctors at the University of Pittsburgh writing in the Journal of Knee Surgery (15) say athletes and doctors are turning to biomaterials, that is stem cells and blood platelets (PRP therapy). In fact, “They are becoming the mainstay of nonoperative therapy in the high-demand athletic population. The most well-studied agents include platelet-rich plasma (PRP) and stem cells-both of which have shown promise in the treatment of various conditions. Animal and clinical studies have demonstrated improved outcomes for patients with chronic patellar tendinopathy.”
In a one-year study of patients who decided on non-surgical PRP treatments to get them back to their sport, European doctors found that all 20 patients in their study benefited from one injection of PRP coupled with a standardized eccentric rehabilitation (exercise). They concluded: “This study confirms that a local injection of PRP coupled with a program of eccentric rehabilitation for treating a chronic jumper’s knee, improves pain symptoms and the functionalities of the subjects’ knee up to 1 year after injection.”(16)
The most important finding in our meta-analysis is that PRP injections are statistically better than the control group (ESWT and dry needling) at longer-term (6 months or more) follow-up suggesting that PRP is an effective and worthwhile treatment for Patellar Tendinopathy.
Doctors in the United Kingdom writing in the journal Knee Surgery and Related Disease (17) released their study in which they state: “The most important finding in our meta-analysis is that PRP injections are statistically better than the control group (ESWT and dry needling) at longer-term (6 months or more) follow-up suggesting that PRP is an effective and worthwhile treatment for Patellar Tendinopathy.”
Multiple Injections of PRP may hold the answer
Doctors at The Rizzoli Orthopaedic Institute in Italy published their paper: Nonsurgical Treatments of Patellar Tendinopathy: Multiple Injections of Platelet-Rich Plasma Are a Suitable Option: A Systematic Review and Meta-analysis. It appeared in the March 2018 issue of the American Journal of Sports Medicine. (18)
What they were looking for was the evidence on nonoperative options to treat chronic patellar tendinopathy: Three treatments came to the forefront as the most studied: They are mentioned in the research above:
- eccentric exercise,
- extracorporeal shockwave therapy (ESWT),
- and platelet-rich plasma (PRP).
- Single and multiple PRP injections were evaluated separately.
“Eccentric exercises may seem the strategy of choice in the short-term, but multiple PRP injections may offer more satisfactory results at long-term follow-up and can be therefore considered a suitable option for the treatment of patellar tendinopathy.”
In December 2018, doctors at the University of Connecticut Health Center published this summary on the effect of PRP on Patellar tendinopathy in the journal Current Reviews in Musculoskeletal Medicine. (19)
The summary of their findings suggested:
- PRP has become a common non-surgical intervention for Jumper’s knee in recent years
- Research indicates that overall, patients had significant improvement in pain and function, with up to 81% of patients able to return to their pre-symptom level of activity. However, it should be noted that these results are at the high end of inconsistent findings. Another study suggested 22% were able to return to their pre-symptomatic activity.
- Compared to extracorporeal shockwave therapy, PRP had a significant impact on pain and function
- The number of PRP injections has also been shown to have an effect on the outcome of the treatment, with two injections found to improve outcomes significantly more than a singular injection.
A quick word on Patellar Tendinopathy and ligament weakness
- Chronic patella pain and tendinosis are rooted in knee instability. Upon examination, we find patients who have patellar tendinitis may have laxity in the anterior cruciate ligament (ACL), medial collateral ligament (MCL), or a posterolateral ligament injury.
- The ligaments are the primary stabilizers of the knee. If the knee is unstable, the patellar tendon will be under strain and weaken.
To address this, a series of injections are placed at the tender and weakened areas of the patella tendon and knee ligaments. These injections contain a proliferant to stimulate the body to repair and heal by inducing a mild inflammatory reaction. The body heals by inflammation, and Prolotherapy stimulates this healing. As the ligaments tighten and the patella tendon heals, the knee structures function normally rather than moving out of place. When the knee functions normally, the pain goes away.
Summary and contact us. Can we help you?
We hope you found this article informative and it helped answer many of the questions you may have surrounding your knee problems and knee instability. If you would like to get more information specific to your challenges please email us: Get help and information from our Caring Medical staff
Brian Hutcheson, DC | Ross Hauser, MD | Danielle Steilen-Matias, PA-C
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This article was updated January 8, 2021