By Shelagh McNally for Knee1An exciting new discovery is changing how doctors will treat knee injuries. Knee injuries are often the trickiest for healing, especially with the anterior cruciate ligament (ACL). The ACL is one of the four ligaments connecting the upper leg to the lower leg and it’s particularly important since it prevents the lower leg from sliding and the knee from being stretched, straightened or bent beyond its normal limits.
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Recognizing an ACL Injury
Symptoms of an ACL tear:
A loud pop at time of injury.
Severe pain.
Knee swelling within six hours of injury.
Pain when walking.
Pain when bending the knee.
Knee joint instability.
Arthritis (long-term symptom).
ACL function:
Connects the femur (upper leg bone) to the tibia (lower leg bone).
Stabilized knee motion.
Prevents tibia from sliding forward or turning inward when leg is straight.
Prevents knee from being hyper-extended or stretched beyond its limit.
Supports the knee ligaments that keep knee from bending sideways.
Causes of an ACL tear:
Tears can be due to contact or non-contact injuries.
Blow to the side of the knee.
Coming to a quick stop combined with a sudden change in direction.
Landing from a jump.
Overextending the knee joint.
Basketball, football, soccer and skiing are the sports that most commonly cause ACL tears.
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Unfortunately, tears in the ACL are a common knee injury. More than 100,000 Americans were afflicted last year with this painful and debilitating injury which causes swelling and loss of motion. Even worse, ACL injuries almost never heal properly so the chances of a repeat injury are high. In the past, doctors first tried suturing the ligament back together as a healing process, but the ACL almost always tore. Now doctors opt for replacing the entire ligament using tendons from another part of the leg. While this surgery can be done using arthroscopic techniques, it still takes six months for recovery and the ACL always remains weak. There is often the risk of developing arthritis in the knee and the new ACL never functions at the same level as the original one.
But, a promising new discovery by a surgeon at Children’s Hospital Boston is offering a new way to way permanently heal ACL tears. In a recent edition of the Journal of Orthopaedic Research, orthopedic surgeon Martha Murray, M.D. reported that natural healing of the ACL was stimulated using a collagen gel, enriched with blood platelets. The body responded to the gel by encouraging the cells to repair the ligament and restore strength. “This is a first important step in showing that the ACL can heal if we give it the right conditions,” said Murray. “That’s an important shift from thinking that the ACL has to be completely replaced after an injury.”
Murray first became interested in ACL healing while pursuing a doctorate in materials science, and she eventually went to medical school to study the problem. Murray and her colleagues began studying torn ACLs at a microscopic level and witnessed how the body would send cells to the injured area to begin the healing process. Although the healing process began, the problem with ACLs was that the process could not be completed and so the ligaments never joined.
In most torn ligaments a blood clot forms and acts as a temporary bridge until the ligaments are healed together. But in the case of ACL injuries, fluid inside the knee keeps dissolving the blood clot so the bridge never forms and the ligament can’t heal. Murray realized all that was missing was the bridge, so she set out to discover what could be used to create that bridge. After trying various materials, her team found that a collagen hydrogel mixed with platelet-rich blood plasma was perfect – it wasn’t easily dissolved by the joint fluid and helped the ACL cells do their job.
“Even though ACL cells are happy to participate in the repair process, there's no place for them to do it. The repair cells are looking for a place to go and heal, but they get lost in the fluid,” said Murray. “Our big finding was recognizing that the cells are fine – they just need a bridge that they like. We developed a collagen bridge to give the cells a place to crawl into and be happy and functionally heal. With this bridge, the cells just go crazy. We found that to be incredibly exciting.”
Murray’s team began using the gels on pigs and tracking the progress. At six weeks, the gel-treated ACL injuries had a 40 percent increase in mechanical strength compared with 14 percent for untreated injuries. The preliminary results are extremely promising and while Murray cautions that more research is needed, she is hopeful that the ACL regeneration technique can be applied to human patients in the near future.
With funding from the National Institutes of Health (the NIH), the National Football League, the Orthopedic Research and Education Foundation and the Center for Minimally Invasive Technology, Murray is developing an arthroscopic approach that would squirt the gel into the wound via two small incisions in the knee. Her team is also trying to enhance the gel to speed the healing process. In the future, Murray hopes to extend her technique to other injuries like meniscus and rotator cuff tears.
