Stem Cell Therapy for 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!).