What’s an ACL and why is the injury so devastating? 

click to enlarge Rams quarterback Sam Bradford's season ended before it really began as he sustained a torn ACL during a preseason game. - DAVID RICHARD/AP FILE PHOTO
  • David Richard/AP file photo
  • Rams quarterback Sam Bradford's season ended before it really began as he sustained a torn ACL during a preseason game.

The NFL season had not even begun and already one of its biggest stars had sustained a devastating injury, taking him out for the entire season. Sam Bradford, starting quarterback for the St Louis Rams, tore the anterior cruciate ligament in his left knee, re-rupturing the same ligament he'd injured in November.

The anterior cruciate ligament extends from the thighbone (femur) to the shinbone (tibia) and keeps the bones together, along with other tissues in the knee. It also helps stabilize the knee.

A torn ACL is often the result of a sudden twist or change in direction or a hard blow to the knee, such as being hit by another player. The thighbone moves past where the ligament can stretch, producing the famous pop. The ACL is a strong weave of collagen fibers. When injured, it is usually damaged so much that even repair of the torn ends is unsuccessful at producing a strong enough ligament. However, what used to be a career-ending injury for many athletes is now usually reduced to a season-ending. Even this may change with ever improving techniques.

Replacement is now the normal treatment. There continues to be significant debate on which tissue to use: autograft, from the patient's own body, such as their hamstring, or allograft, from donor tissue. Our preference is a sterilized patellar tendon, with bone on each end, from a young cadaver. In our hands, this tissue has produced highly reliable results, though it still takes a year for the tissue to mature. Athletes often return to sports as soon as they have the muscle and coordination control. Fortunately the rerupture rate is quite small.

However, injury to the ACL often involves injury to other structures in the knee, including the meniscus cartilage, the articular cartilage and the underlying bone. These injuries determine the long-term health of the knee more than the ACL. Damage to the supporting tissues often fails to heal normally and meaning that arthritis is a very common outcome years after ACL injury with or without reconstruction.

So what is new in terms of surgical techniques and what is the future? New is the recognition that harvesting tissue from one part of the body to repair another part is definitely an extra injury to the knee and has long-term consequences. Whether it is the patellar tendon or the hamstrings that are used, the knee never returns to normal and permanent weakness results. This has stimulated a stronger push to find replacement tissues for the injured ACL. Allografts, or donor tissues, are of a mixed bag. We have identified young bone patellar bone grafts, which have not been irradiated above a minimal level, to be ideal for ACL reconstruction. Tissues weaken at 1 percent per year with every year of age after 20. Since there are few young donors, there is always a shortage of the best tissues.

Our team of scientists is also studying how adding stem cells and growth factors to donor tissues can speed healing. This work may reveal that the tissues remodel faster and athletes can return sooner. These studies are still underway and are likely to bear fruit.

Future techniques include the use of animal tissue to replace damaged ligaments. Sterilized pig bone patellar tendon bone grafts replacements have just been approved in Europe after a two-year, 66-patient double-blinded trial confirmed that they were as effective as the ideal young human donor tissues. A U.S. clinical trial is pending.

Rehabilitation from an ACL injury, meanwhile, has moved into the CrossFit era where we recognize that fitness is a combination of ten skills: cardiovascular-respiratory endurance, stamina, strength, flexibility, power, coordination, agility, balance, and accuracy. We use the ACL injury as an opportunity to set goals in each of these areas and test to determine when an athlete is ready to return to full sports. What is new in rehab and fitness training is the cleverness in which multiple exercises are combined into one so that a highly efficient program can be completed in as little as 20 minutes of intensive exercise per day.

Sam Bradford may have suffered one of the first ACL injuries of the regular season, but there will be more. So when you hear of the athlete who has injured their ACL and plans to return to sports soon, remember that while we are making strides in reducing the severity of this injury, and that the tissues, cells and rehabilitation are all improving, it is still a major insult to the knee, with long-term consequences, that unfortunately prevent it from ever being normal again.

Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco. He pioneers advanced orthopedic surgical and rehabilitation techniques to repair, regenerate and replace damaged cartilage and ligaments. For more info, visit www.stoneclinic.com.

About The Author

Dr. Kevin R. Stone

Bio:
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco. He pioneers advanced orthopedic surgical and rehabilitation techniques to repair, regenerate and replace damaged cartilage and ligaments.
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