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December 13, 2011
Rounding Up the Usual Suspects: Cartilage Injuries
We’re hearing reports of microfracture surgery, arthritis, and osteochondral and articular cartilage injuries increasingly often. Given today’s emphasis on year-round training at an earlier and earlier age, cartilage injuries are going to become only more common in the future. We’ve made numerous advances in repairing cartilage injuries, but we still aren’t 100 percent there. Local cartilage defects are more of a problem than degenerative arthritis in the young, athletic population we report on here, so in this installment, we will primarily look at focal cartilage injuries and their management.
Source 1 Nanoall
Cartilage comes in different thicknesses depending on the location, but the thickest is usually in the knee at just 0.07 inches to 0.15 inches, which doesn’t leave a lot of room to spare. There is no direct blood supply to, nor innervation of, the cartilage itself. This is why many cartilage tears do not become painful until the first few layers of the cartilage are compromised. The lack of blood supply also means that the cartilage has very little ability to heal itself and usually requires assistance from medication, injections, or surgical intervention to correct the gliding mechanisms.
In Irving Herman’s 2007 book, Physics of the Human Body, table 3.4 lists various coefficients of friction of different substances and surfaces. Healthy articular cartilage on articular cartilage has a coefficient of friction of 0.005-0.02, an extremely low measure that shows how easily healthy cartilage can glide. For comparison’s sake, ice sliding over ice at 4 m/s is 0.02, while skis traveling over snow is over 10 times higher at 0.05-0.20. The only other surfaces that come close to the coefficient of friction of articular cartilage are ice skates and ice itself, at 0.003-0.007.
Source 2 Orthohouse.co.nz
When cartilage is damaged, the joint surfaces are no longer smooth and the gliding mechanism between the two bones is interrupted to some degree. In acute injuries, compressive or shearing forces can force the surface to be roughened, depressed, or torn. Cartilage can also be injured in conjunction with other injuries, such as episodes of instability, patellar dislocations, and ACL, meniscus, or severe ankle sprains.
It can also erode gradually over a long period of time, which typically leads to the osteoarthritis that so many people are afflicted with. Over a sufficiently long period, almost everyone would develop some sort of arthritis, because the cartilage cannot heal itself and we are always on our feet. However, the degenerative process is often sped up by the constant impact activities and repetitive loading of the joint that come with countless hours of practice and competitions.
The cartilage is most commonly injured with traumatic rotational forces while the joint is being loaded. Examples include cutting, pivoting, or landing in an awkward position for the lower extremities. Cases of upper extremity cartilage injuries are more likely to be the result of episodes of instability, such as shoulder dislocations, or gradual erosion, as with with elbow laxity.
X-rays cannot provide a direct method of evaluating cartilaginous injuries, especially in the acute setting. With gradual degeneration, standing x-rays can provide a clue as to how thin the cartilage is and how close the bones are to rubbing against each other. Basic MRIs are able to provide a much clearer picture without the risk of radiation exposure. Of course, the only definitive, direct method of evaluating the cartilage is through surgery, usually under arthroscopic evaluation.
Source 3 Orthohouse.co.nz
Pressure must be taken off of the area for several weeks in order to prevent the newly formed clot from being squeezed out. Over a few months, the clot hardens and smoothes into a form of cartilage called fibrocartilage, which slightly less effective than normal articular cartilage but much better than nothing. In the hands of a good surgeon, microfracture can be very successful in returning the athlete to play with reduced pain and improved function in anywhere from two to six months, depending on the size and surface of the area. Typically, the fibrocartilage can last for at least a few years before it too wears down—since it’s not the same substance as the surrounding cartilage—and something else needs to be done.
One of the greatest benefits of microfracture is that very little is lost if it is unsuccessful. Other techniques that we will discuss later involve taking cartilage from one area that is not as important in order to replace or plug the original cartilage defect, in effect robbing Peter to pay Paul. Healthy articular cartilage is hard to come by, and microfracture does not disturb other areas of healthy tissue. It focuses solely on the injured area, so if it fails, other, more aggressive measures can still be performed in the future.
Recovery from microfracture is almost always quicker than other procedures. Athletes in cutting and pivoting sports are usually reintroduced at roughly the six-month mark, with adjustments based on the sport and the size of the defect.
While we most often hear about microfracture involving the knee, it is also often used in the ankle, hip, thumb, elbow, shoulder, and big toe, to name a few places. Two other procedures, drilling and abrasion arthroplasty, follow the same premise and much of the same procedure but come with other risks. In the former, tiny drills are used to create the holes, but the heat from the drill may damage other healthy tissue and cause further damage (although this is relatively unlikely). Abrasion arthroplasty burrs away all the damaged tissue to reach the subchondral bone and produces bleeding, but it is less precise than microfracture and may not provide a sustained reparative response. It is believed that the abrasion arthroplasty provides only about two to three weeks of healing, which is not much time for the clot to transform into new cartilage compared to the six weeks commonly used with microfracture. Thus, microfracture is considered the benchmark to hold other cartilage repair procedures up against.
Autologous Chondrocyte Implantation (ACI)
Much more takes place in the second surgery. The area of the lesion is cleared of any scar tissue that may have formed in the interim, and a bony cover is actually sewn into place over the cartilage defect and sealed with fibrin glue. The cells grown in the lab are then injected underneath this bony cap and allowed to settle into place.
Source 4 Kneeandshouldersurgery.com
Rehabilitation from ACI surgery is similar to microfracture but much longer. Weight bearing is limited for the first few months, but high-impact pivoting sports cannot be resumed until 12 months after the second surgery. Many athletes do not fully recover until 16-18 months after surgery.
Osteochondral Autograft Transplantation
Source 5 Restorecartilagenj.com
Osteochondral Allograft Transplantation
Corey Dawkins is an author of Baseball Prospectus. Follow @CoreyDawkinsBP