Knee Pain

Mechanisms of Knee Pain

There are two primary mechanical mechanisms that cause knee pain: axial pain and instability pain. Everyone with knee pain experiences a combination of these mechanisms.

Axial Pain: This is the well-known “bone-on-bone” mechanism. As we age, our cartilage loses volume and wears down, joint fluid decreases, and we may gain weight while losing muscle tone and flexibility. As joints degenerate with wear and tear, the cartilage wears down and the bone may bruise and become edematous (Bone Marrow Edema) and deform at the edges (osteophytes). The Ligaments that hold the joint together also gradually degenerate and loosen and stretch. Yes cartilage is a cushion but it is important to realize that every joint in the body is suspended in a bed of ligaments, called a tensegrity system. When this suspension system loosens, the space between the joint narrows and there is less space protecting the joint surface. This results in reduced cushioning in the joint space and less ability to absorb loads, leading to bruising of the underlying bone plate. When the pain gets bad enough, orthopedic surgeons will often offer joint replacement for this type of pain. However, joint replacement surgery carries risks and isn’t always the perfect solution. Some patients do well, while others do not. In our view such invasive procedures should be reserved as a last resort.

Instability Pain: Equally important but less obvious is what we can call the “sprain” component. The knee capsule and surrounding connective tissues not only hold the joint together but also maintain the joint space and hold the bones apart. When the capsule stretches or loses joint space due to age or injury, it permits abnormal movement of the femur on the tibial plateau. We call small abnormal movements subluxation while larger movements are called dislocation. It is this subluxation out of its normal anatomic position that results in asymmetric stresses on tissues and causes meniscal tears and bone bruising as load is no longer properly distributed. In addition, the attachments of these capsular ligaments are highly innervated (which gives our nervous system our sense of proprioception and allows us to coordinate movement) and as the ligamentous capsule becomes loose and sloppy and the knee subluxates it pulls on these highly innervated attachments and forms tears and microtears, which become important pain generators   

So we have two major mechanisms of pain for the knee but they both stem from a weakening or stretching of the ligamentous support of the knee. The subluxation mechanism is at play when a patient says that their joint gives out suddenly or if there is a sudden increase in pain. Both these situations occur when the joint subluxates. This instability-type pain tends to get better if a patient walks for a while, unlike axial type pain that worsens as you walk more. 

No matter which mechanism is predominant in a given patient, both can be fixed by tightening and rebuilding the ligamentous support and making the joint stronger and more stable. The meniscus tears and bone bruising can actually heal itself if we can fix and reestablish the ligamentous support and stability of the knee. Also, it is true that a meniscus tear or bone bruise can cause pain but relatively speaking, the pain of instability and pulling on damaged ligamentous attachments is usually a far greater pain generator. If we can regenerate the ligamentous capsule and the supporting ligaments with stem cells and PRP, we can solve both problems, reverse the damage and heal the root causes of the pain. This is why I tell patients that as a stem cell orthopedic specialist I am a ligament and tendon specialist and regenerating  the internal and surrounding connective tissue is the key to restoring joints to health and avoiding surgery. 

Unfortunately, most orthopedic surgeons don’t fully appreciate the pain of instability and how we can regenerate and strengthen the ligamentous support of the knee. Neither x-ray or MRI studies help very much. The problem is x-ray only sees only joint space and bony changes. MRI sees the bone and joint space and the connective tissue but since it is a static examination, it gives no inkling as to the stability of the joint under movement. Also, MRI is not sensitive enough to pick up the micro-tears at the ligamentous attachments that are so important to the pain picture. Ultrasound has the advantage of seeing joints under movement and can give a greater sense of the stability of a joint. Unfortunately, like MRI, ultrasound is also not sensitive enough to pick up microtears.

So the dilemma is becoming more clear. Standard imaging tests show certain abnormalities so it is natural that we attribute the pain of a joint to the abnormalities we see. For example, a patient has knee pain and we do an x-ray. We see joint space narrowing and bony changes and we naturally attribute the pain to that. We do not appreciate that the loss of the suspension cushion of the ligaments is the major reason for the loss of the joint space nor do we understand that  the instability of the joint and pulling on the damaged attachments of a loose ligamentous capsule is a major contributor to pain.   

Likewise with the MRI. Here we see the joint space and can appreciate larger tears in the ligaments and tendons that surround the knee. However, again we cannot measure the stability of the joint or appreciate the microtears at the attachments of the major ligaments. With ultrasound we can see instability but we are limited as to the depth of the structure, so we might see superficial tears but not see the deeper tears in the deep capsular ligaments. Again, like MRI, it is not sensitive enough to see the micro-tears that might be so important to the pain picture. 

So, if we are right and the root cause of the knee breaking down is the loss of ligamentous stability and the major pain generators are damaged ligamentous attachments, what tests can we use to demonstrate this diagnosis? The only way is a tried and true technique from the world of Prolotherapy called palpation interrogation. For example, If I examine a patient with significant knee arthritis and pain and palpate the MCL complex about an inch below or an inch above the joint line and they respond with a jump sign I have demonstrated ligamentous instability and identified a major pain generator. So, how do we fix it? Certainly not with a steroid shot or a joint replacement. This patient would be a great candidate for stem cell/PRP injections in the joint as well as particular attention to peppering the MCL complex with multiple injections at the precise points of maximal ligament damage where the jump sign is most pronounced. We give them a good set of orthotics so they can walk without putting asymmetrical stress on the repairing and tightening ligaments. We follow them along to make sure they are rehabbing the knee properly and give them a booster or two as required after six or eight weeks (more on this later!). 

Evaluating the Knee

In conventional orthopedics, x-ray and MRI imaging are the primary diagnostic tests done for common problems like meniscal tears or osteoarthritis. And steroids, meniscal visco-supplementation and surgery, both arthroscopic and replacement, are the mainstays of treatment. However, a good clinical examination with stress testing of the various ligamentous components of the knee with palpation interrogation can reveal key trigger points and yield a more accurate diagnosis of pain generators than an MRI. 

Common Conditions and Treatments

Meniscal Tears and Arthroscopy

Meniscal tears are common but often not the primary pain generators. Studies have shown that many people with meniscal tears do not experience pain. Therefore, the key question is whether the meniscal tear is causing the pain or is an incidental finding. The difference is the degree of instability. Meniscus tears will often heal by themselves if the knee can be stabilized and tightened with stem cells and PRP. It’s instability and pulling on damaged capsular ligaments that causes pain, not the tear itself. The tear is a consequence of the instability. Recent studies have questioned the efficacy of arthroscopic meniscal surgery, suggesting that outcomes may not be better than placebo surgeries. You might fix the surface of the knee but the procedure of putting a 4mm scope in the joint and distending the joint might very well cause more instability. If the primary cause of pain is instability, arthroscopy may aggravate the problem. Also, it has been shown that removing meniscal tissue may accelerate long-term osteoarthritis. For these reasons, stem cells may be a better solution. 

Localized Pain

In regenerative orthopedics, our goal is to pinpoint the precise structures causing pain. This includes careful palpation of specific structures such as the medial collateral ligaments, pes anserine tendon attachments, patella, lateral collateral ligaments, posterior cruciate ligament, and the medial and lateral joint lines. A positive jump sign will signal damaged attachments. This technique also allows us to prioritize the pain generators in order of importance. Key trigger points will have the greater jump sign.

The knee is held together with four main bundles of ligaments: Medial Collateral Ligament (MCL), Lateral Collateral Ligament (LCL), Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL). A compromised MCL with microtears is found very commonly in most OA patients.The MCL tends to break down as it works double time to try and stabilize the loose knee. LCL is a little less common but many OA patients have both MCL and LCL jump signs, demonstrating that they both require stem cell/PRP for healing. PCL damage should always be checked for. Patients with PCL weakness will have trouble going down stairs as the tibia wants to slide forward on the femoral plateau. 

I also frequently encounter patients with serious ACL tears and/or rupture. ACL injuries are  graded 1-3. Grade 1 is damage and stretching of the fibers (microtears that can result in laxity), grade 2 is partial tearing, and grade 3 is a complete ligament rupture, with or without retraction. For all grades, if the pain persists, Stem cells and PRP are indicated. It has long been a discussion in regenerative circles if stem cells and PRP can regenerate a complete tear of the ACL with retraction. Orthopedic surgeons don’t think it can but they are surgeons, not regenerative specialists.  A number of years ago a colleague had a young athletic patient who had a complete ACL tear on MRI. The patient insisted that the Doctor give her three or four treatments of PRP, even though the doctor told her that they were unlikely to help. The girl began to improve and was able to return to soccer. Repeat MRI showed a normal ACL.

What possible explanation could help explain this miraculous healing? Well, for one thing, there is often a sheath surrounding a ligament and this might have guided the regeneration. Also, we have talked at length in this section and other sections such as shoulder, hip, low back etc. that the key is stability of joints. Even if we didn’t have MRI proof of regrowth, the patient might have clinically improved by strengthening all the other capsular and stabilizing ligaments. Yes, the patient was young and healthy but on the other hand, note that the doctor used PRP and not stem cells treatments to treat the patient. I often say that the regenerative power of stem cells combined with PRP is 10-fold of PRP alone. With the power of stem cells we would be even more likely to have a great result. Yes, I believe that stem cells/PRP can help ACL problems! The tissues want to heal, we just have to set it up so healing is optimized. God forbid, the stem cells and PRP don’t produce a good enough result, the patient can always resort to ACL reconstruction as a backup plan.

Osteoarthritis: Stem Cell Therapy vs. Knee Replacement:

I often consult with patients with moderate to severe osteoarthritis who are trying to choose between stem cell and knee replacement. Knee replacements carry risks and may require revision surgeries. Regenerative treatments aim to eliminate or at least defer (indefinitely is always my goal!) the need for replacement by enhancing joint stability and promoting tissue regeneration. It is important that patients understand that stem cells can’t fix every joint and that some will end up with knee replacement. They also need to understand that regenerative healing is a process and it may take time to give them the result they want. Nevertheless, if the patient is open to regenerative healing and we have an 85% success rate, it might be worth the chance. Since stem cell treatment uses their own tissues and if done properly, it is extremely safe. The risk is they may pay their money and not get the result they hope for. It is a question of quality of life. Stem cells might give them a superb result and change their lives. If we fail they can always resort to surgery as a backup plan. Of course, it doesn’t work the other way around. Once they do surgery the stem cell option is off the table as we cannot regenerate tissue on artificial surfaces.

Optimizing Stem Cell/PRP treatments, follow-up and Rehab:

In my own practice, I often use a combination of Prolotherapy, PRP and PRP/stem cells depending on the exact diagnosis and the specifics of each case. Prolo can be used as a primer prior to stem cells and can help initiate tightening of the ligamentous capsule. For younger patients or for milder problems three to five sessions of Prolo primers might well solve the problem. If we are dealing with more severe arthritis and degeneration, you need the regenerative power of stem cells and PRP to  jump-start the healing. Even if a patient has severe bone on bone OA, we have an 80-85% success rate that the patient will achieve an 80% improvement. Surprisingly, as many other regenerative doctors have noticed, the degree of severity doesn’t seem to affect the chances of success. The patients that do the best are those who have a positive lifestyle and are committed to the process of healing. Nevertheless, I do ask patients to be as proactive as possible and not to wait until they have severe pain before they consult us. For me, the earlier we intervene in a degenerative process, the better!

In many cases a single stem cell/PRP session might suffice but if after 6-8 weeks the results are mediocre, a PRP booster may be called for. The stem cells remain alive for 4-5 months, so in the case that healing is sluggish or incomplete we can reignite them with additional growth factors from PRP. In rare cases, if instability is severe we might suggest a Prolo primer a few weeks prior to stem cells or one or two Prolo boosters four or five months after the full stem cell/PRP session.

As far as rehab, the best rehab is walking but I like to make sure a patient’s gait is optimized. At RegenOrtho in Sarasota I am fortunate to work with Boris, who is a master orthotist. When I see a patient with serious knee issues (or any other weight bearing joint like the hip, low back or ankle) I not only want to fix it, I want it to stay fixed. Most knee patients might have certain characteristics of gait that aggravate and maybe even cause knee issues. I highly recommend to almost every single knee patient that they see Boris for orthotic evaluation and fitting. I could be the best stem cell guy in the world but if we don’t rectify the reason why the patient has a knee issue in the first place and they resprain the knee every time they walk, it is unlikely that the knee will be able to heal properly. My philosophy is to try and make sure we optimize as many factors as possible so the patient gets the best results possible!