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Introduction to the concept of biologic knee replacement (part 1a of a course)

Biologic Knee Replacement involves replacing the articular cartilage or regrowing it, replacing the meniscus cartilage or reconstructing it, replacing the anterior cruciate ligament or other ligaments when needed, or reconstructing them or repairing them, in order to have a biologically stable smooth joint rather than an artificial or bionically-reconstructed joint.

Just to clarify when I am referring to 'cartilage' during this course, the articular cartilage and the meniscus cartilage are different structures -

Articular cartilageMeniscus cartilage

 

On the left I am pointing on a model to the firm white articular cartilage that covers the bone at the end of the femur (thighbone). On the right I am pointing to the mobile white meniscus cartilages that act as shock absorbers between the femur and the tibia (shinbone).

Under my pointing finger in the image on the right, you can see the flat top of the tibia bone - the tibial plateau - and it, too, is covered with white articular cartilage. The pink-coloured structures represent the ligaments of the knee.

An artificial joint replacement replaces these structures with 'bionic' components of metal and plastic, whereas a 'biologic' joint replacement repairs, reconstructs or replaces these structures with living tissue. The rationale for biologic joint replacement is that many of our patients want to continue playing impact sports and would like to delay the time in which an artificial joint replacement is done. Additionally they have heard that artificial joint replacements sometimes fail or that they all wear out by 15 to 20 years and that the first one is the best one, because as you get older you lose bone stock and the revision artificial joints are not as reliable as the primary joints. Additionally there is at least a 20-30% incidence of continued pain for people who have artificial joints.

So the most common comment I hear in my practice here in San Francisco is a patient who says “Doc, isn’t there just a shock absorber you can put in my knee just to buy me some time? I want to continue playing impact sports, I want to continue running marathons. I might be 40 [or 50 or 60 or 70] years old but I am still qualifying in a Masters level of athletics and I just don’t want to have that joint replacement until I absolutely have to.”

And so for those patients we study their joint by physical examination and history and gait analysis, by pre-evaluation with physical therapy and rehabilitation to determine their rehabilitation potential, and then we study their joints with X-rays and MRI to figure out where the cartilage loss is, where the ligament damage is and where the meniscus damage is. Then we design a surgical replacement programme for them which may include rebuilding or replacing any one of the damaged tissues in the knee, and sometimes all of them.

For biologic knee reconstruction the tools that we have at our disposal are cells and growth factors, tissues and scaffolds. So if we are going to use a tissue such as an ACL allograft then we like to speed the healing of that tissue if we could with growth factors and cells. Or if we are going to use a primary suture repair of an injured tissue, then we would like to speed that healing by adding growth factors and cells to that healing site. In the knee joint and in many tissues it is very difficult to add growth factors or cells and keep them in place, and so using a scaffold - such as a collagen meniscus implant or a collagen scaffold - we can load that scaffold with cells or growth factors and sew it into the repaired tissue site in order to deliver a boost to the healing response. We see regeneration templates - collagen scaffolds - as excellent carriers for the cells and growth factors that we want to augment healing. So we’ll use those tools whenever we are doing a primary ligament repair, a primary meniscus repair, a primary tissue repair where we might be worried about the quality of the healing- we think that augmenting that healing site is probably a pretty good way to go.

When we are augmenting healing, we always use the patient’s own cells and the patient’s own growth factors. These are natural substances in the blood that we can easily extract. So we will take the growth factors either by just forming a fibrin clot of the patient's own blood, or by reducing the platelet concentration of a sample of blood in a centrifuge and taking the supernatant and the PRP (platelet rich plasma) or PRGF (platelet rich growth factor) depending upon the site in which we want to induce healing. But we always use the patient’s own cells and their own growth factors.

 

Updated: 01 May, 2013
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