Cadaver Cartilage Grafts for Large Cartilage Tears of the Knee

Cadaver Cartilage Grafts Prove Promising for Large Cartilage Tears of the Knee

A recent review of the most up-to-date research found that large cartilage tears at the knee joint are best repaired with donations from cadavers.  The review found that a technique called “Osteochondral Allograft Transplantation,” or OCA, is versatile in terms of what kinds of repairs it can help and has the best long-term effects when compared to alternative surgical options.

Chondral is a fancy word for cartilage.  Cartilage is a protective layer of rubbery tissue that covers the ends of bones to prevent rubbing.  There are two important layers of cartilage in the knee - one layer of articular cartilage that covers the end of each leg bone, and your knee meniscus, which resemble rubbery washers that sit on top of the articular cartilage.  Both of these can be damaged from trauma (like a side blow to the knee or excessive twisting forces) or they can degrade over time from normal wear and tear. Sometimes, due to abnormal forces across the knee joint, or excessive use with improper form, these pieces of tissue rub and tear earlier in life.  This often happens to athletes who perform the same repetitive movements again and again or in athletes with high impact activities. In addition, if there are any muscle imbalances the knee joint moves at the less than optimal angle speeding up the wear and tear on the cartilage.  This breakdown in the cartilage causes swelling at the knee, pain, and interferes with a person's ability to perform their sport or typical functional tasks of life.

Cartilage does not have a good blood supply which means that it does not heal well.  What's more, it has no nerve endings so you do not really realize there is a problem until damage is done. Chondral degradation is graded on a scale from one to five, with five being the worst. Repair options hinge on the size and location of the tear as well as the goals of the patient.

Smaller lesions are often repaired by clipping out the frayed pieces of cartilage (debridement), taking a piece of cartilage from another part of the knee and placing over the tear (osteochondral autograft transplantation), or by poking tiny holes in the bone below the cartilage so the blood clots formed will provide some healing and regrowth of fibrocartilage (microfracture). These techniques, however, are less effective for larger tears or deep tears. Bigger tears are treated by either OCA or by an autologous chondrocyte implantation (ACI).  An ACI procedure involves harvesting your own cartilage cells and growing them outside the body and then planting them in the affected area.  It is worth noting, however, that an OCA is the only back-up procedure for a failed ACI.  Authors of this review found that an OCA is less invasive (only one procedure), is more versatile, and has better long-term outcomes than an ACI.   

The OCA procedure has become refined with time. The cartilage donation must be collected within 24 hours of the person passing away and is taken from people with healthy knees.  The tissue is screened for a host of diseases.  This process takes anywhere from 14 to 28 days, during which the cartilage is kept at body temperature, its ideal environment. The cartilage is then selected based on a size and location match, as there is a very minimal risk of tissue rejection since there is little to no immune response in cartilage.  If the tear is deep and a bone graft is also required then the risk of rejection is only slightly higher.

An OCA procedure includes several different techniques depending on the type of tear.  The most common technique is called a plug, where the chunk of torn cartilage, and perhaps bone, is removed and the new piece of cartilage is fitted perfectly in its place with as tight of a fit as possible.  If the fit is not completely snug the surgeon can fasten it in using dissolvable materials or tiny hardware that will not disturb the knee function.

Rehabilitation after the surgery is broken into three phases.  The first phase is a period of rest to allow the tissue to heal, with the amount of use of the leg depending on the type of repair.  Typically phase one lasts six weeks.  Phase two is from week six to twelve and involves return to daily activities, strengthening, and full motion of the knee.  Phase three is from three months on and involves full return to sport with the guidance of a physical therapist.  From six months up to one year after surgery repetitive high impact activities should be avoided.

Long-term outcomes for OCA procedures are promising with the greatest percentage of success in a younger, active population with traumatic onset of cartilage damage less than one year prior to surgery. That being said, however, the numbers are also promising for the non-traumatic middle-aged population with tears greater than 2cm. Authors suggest that an OCA become the standard practice for larger tears of these populations.

Reference: Seth L. Sherman, MD, et al. Fresh Osteochondral Allograft Transplantation for the Knee: Current Concepts. In Journal of American Academy of Orthopedic Surgery. February 2014. Vol 22. No. 2. Pp. 121-133.

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