Lingering knee pain, weakness, and instability can have many causes. When rest and rehabilitation have failed to restore function, many patients wonder what the next step is. For many patients, platelet-rich plasma (PRP) may offer an effective next step. Understanding what PRP is and how it’s uniquely useful for restoring the knee is critical.
In this article, we’ll cover how PRP is uniquely positioned to repair the knee, the process and evidence behind PRP therapy, and how it stacks up against surgery and other treatments, like steroid injections.
Why PRP?
The knee is the largest and one of the most complex joints in the human body. It’s a modified hinge at the intersection of three bones—the tibia, femur, and patella—cushioned by shock-absorbing cartilage and menisci, all held in place by four critical ligaments—the ACL, PCL, MCL, and LCL.
When these crucial ligaments become worn and loose, the knee can fail to function properly. The joint moves poorly and awkwardly, like a door with loose hinges. This misalignment can prematurely degrade the shock-absorbing surfaces of the knee joint, causing pain and instability as pieces of the meniscus catch with each step.
Steroids are great at relieving inflammation. A meniscectomy can remove damaged portions of the meniscus that are catching. But if the knee continues to move improperly, the pain and inflammation may return. And with time, they may only get worse.
By restoring strength and tension to the ligaments of the knee, we can work to return the joint to its optimal, intended function. This approach aims to address the underlying mechanical contributors to inflammation and pain rather than simply suppressing symptoms.
What’s one of the best tools we have for restoring strength and tension to ligaments? PRP.
What Is a Platelet-Rich Plasma (PRP) Knee Injection?
Platelet-rich plasma is prepared by drawing a sample of your blood and processing it to concentrate the platelets, small blood components that contain powerful proteins and growth factors involved in tissue repair. This concentrated solution is then injected under imaging guidance into the carefully selected structures underlying your knee pain.
Because the preparation of PRP and the expertise with which it’s injected vary greatly from clinic to clinic, not all PRP treatments produce the same result. The most critical parts of any PRP injection are the right diagnosis, the highest-quality PRP, and the precise application of the PRP into the suspected pain generator.
What Happens During a PRP Knee Injection?
A PRP knee injection is typically performed in a single office visit and generally follows the same sequence of steps:
- A small blood sample is drawn from the patient’s arm, similar to a routine blood test.
- The blood is placed in a centrifuge, which spins it at a controlled speed to separate and concentrate the platelets from the other blood components.
- The provider prepares the injection site and, in many cases, uses ultrasound or fluoroscopic imaging to guide the needle precisely into the affected tissue.
- The concentrated platelet solution is injected directly into the damaged area.
The full visit, including blood draw, processing, and injection, usually takes about an hour. Patients are able to leave shortly after the injection and may gradually resume normal activities in a few days as repair takes place.
How Does PRP Work at the Cellular Level?
When platelets are activated, they release growth factors and signaling proteins that drive the body’s natural healing response, including factors that stimulate cell migration, blood vessel formation, and collagen production. A PRP knee injection delivers a concentrated dose of these factors directly to an area of joint degeneration or soft tissue injury, where they modulate local inflammation and interact with the surrounding tissue’s repair processes. This platelet activity is standard, well-documented biology.
When that repair stimulus is triggered in the ligaments and tendons supporting the knee, it can promote collagen production and tissue remodeling. Think of a brand-new rubber band compared to one that’s been stretched until the rubber starts to fray. As these ligaments and tendons strengthen, the tracking and stability of the knee joint may begin to improve toward its pre-injury state.
What Knee Conditions Does PRP Treat?
PRP for knee pain has been studied across several distinct types of knee problems, and the efficacy looks different for each.
Ligament and Soft Tissue Injuries
Certain ligament and soft tissue injuries around the knee may respond well to PRP when used alongside physical rehabilitation. The growth factors in PRP can stimulate collagen production and cellular activity involved in repairing damaged connective tissue. PRP can therefore play an important role in restoring the strength and integrity of the ligaments and tendons that support the functional unit of the knee.
Patellar and Other Tendinopathy
Chronic tendon irritation around the knee, such as patellar tendinopathy, sometimes called jumper’s knee, is another area where PRP may be useful. By modulating inflammation and stimulating the body’s repair response, PRP can help reduce pain and promote healing in chronically injured tendons.
Knee Osteoarthritis
PRP can be an integral part of treating osteoarthritis by improving the health and function of the joint and, when underlying instability is addressed, helping restore proper joint mechanics. However, PRP is not an effective tool for rebuilding already degenerated cartilage or bone. For more advanced degeneration, we may consider cellular therapies, including treatments targeting the subchondral bone.
PRP vs. Cortisone vs. Surgery for Knee Pain
Cortisone (corticosteroid) injections are a longstanding and widely used option for knee pain, particularly osteoarthritis. By quickly reducing inflammation, they can provide meaningful short-term relief, typically over a period of several weeks.
The problem with steroid injections is that they do not necessarily address the underlying cause of knee pain, so symptoms may return when the steroid wears off. More importantly, repeated steroid use may have detrimental effects on joint tissues and has been associated with progression of cartilage loss in some research.
Research suggests that PRP can provide more durable improvements in pain and function at three to twelve months compared with cortisone injections.
A few factors influence when a provider may recommend a steroid or PRP:
- How quickly the patient needs relief, since cortisone typically works faster
- Whether the patient has already had multiple cortisone injections, since repeated steroid use carries risk
- Whether the patient has had previous success with PRP or is looking for a longer-term solution to their knee pain
- Whether the structural integrity of the knee has been compromised by ligament or tendon issues that could potentially be addressed with PRP
Surgery
When the structural damage to a knee is too severe for biologic treatment, surgery can be an excellent option to restore function to the knee. Typically, these cases involve complete rupture of major ligaments in the knee or osteoarthritis too advanced to benefit from biologic intervention.
Many knee injuries, however, are sub-surgical. This is because knee surgery can sometimes take a micro approach to a macro problem. For example, the surgical approach to a damaged or extruded meniscus may involve removing the damaged portion; a macro approach would look at the total knee architecture and determine whether improving stability and joint mechanics could help the meniscus function more effectively.
This is why one five-year clinical study of patients with degenerative meniscal tears found that exercise-based physical therapy remained noninferior to arthroscopic partial meniscectomy in terms of knee function.
Because the outcomes of knee surgery vary greatly, proper candidate selection is critical. Typically, the best candidates are those who have failed appropriate conservative care, which may include physical therapy, activity modification, medications, injections, or orthobiologic treatments such as PRP.
Recovery, Risks, and What to Expect
PRP is generally considered low risk because it uses the patient’s own blood, but as with any injection, it carries some potential for soreness, swelling, bruising, bleeding, or infection at the injection site. Many patients experience temporary soreness in the days following the injection, followed by a gradual response over the following weeks as the body’s healing processes are engaged. Results are not immediate, and realistic expectations about timing are worth discussing with a provider before treatment.
How Many Sessions You May Need
The majority of patients require only a single treatment of PRP. However, some patients who benefit from an initial injection may repeat the procedure to pursue additional improvement. Typically, we wait a full healing course of approximately 12 weeks to assess the progress of PRP treatment. If knee function has improved substantially but symptoms remain, the procedure may be repeated when clinically appropriate. Each additional injection carries the same general procedural risks and should be considered based on the patient’s response and individual clinical circumstances.
Who May Be a Candidate for a PRP Knee Injection?
PRP is often considered for patients who:
- Have knee pain related to early to moderate osteoarthritis, chronic tendon irritation, or ligamentous laxity or weakness
- Have not achieved adequate relief from conservative measures such as physical therapy or activity modification
- Want to explore options before considering surgery or want an alternative to repeated cortisone injections
As with any orthobiologic treatment, candidacy depends on an individualized evaluation of the patient’s diagnosis, imaging findings, and overall health, and PRP is not appropriate for every type or stage of knee condition.
Deciding if a PRP Knee Injection Fits Your Knee Pain
A platelet-rich plasma knee injection is a reasonable option for many patients with knee instability, osteoarthritis, and chronic tendon pain. No orthobiologic treatment, including PRP, can be described as a guaranteed solution or a replacement for a proper diagnosis.
Compass offers PRP as part of its regenerative medicine services. Because the right approach depends on the specific cause and severity of a patient’s knee pain, a personalized evaluation is the most reliable way to determine whether a platelet-rich plasma knee injection is worth pursuing.
