Is the ACL Crisis in Women’s Sports Solvable?

ACL ruptures are in the news during the 2023 FIFA Women's World Cup. They have been an enormous problem for women athletes for decades and are not even close to being solved. Here is some background and the future.

The ACL is the key guidewire in the knee joint. It guides the tibia as the knee bends, providing stability and proprioception: the sense of where the knee is in space, especially when landing from a jump.

The shape of the ACL resembles a ribbon which, when twisting as the knee bends, gives the impression of multiple bundles of fibers. In fact, the ACL is a complex weave of collagen fibers interspersed with cells and electrically-charged sugars. This biological formula permits the tissue to stretch a little bit and resist the tremendous forces experienced by the knee joint during the 2-3 million steps that most people take each year.

When ruptured the ACL does try to heal itself, and often adheres to the surrounding tissues and the posterior cruciate ligament (PCL). This natural healing process is sometimes enough to provide adequate stability for the knee joint. But it doesn’t work as well for pivoting athletes or for those knees that are called “ACL dependent.” 

Surgery to repair the ACL, or sometimes to replace it, is usually recommended. While surgery works for most people, there are significant problems with weakness and scar tissue formation if tissues are taken from the patient’s own hamstrings, patellar tendon, or quadriceps tendon. And no matter which tissue is taken, there is the risk of recurrent rupture. Allografts (donor tissues) solve the “robbing Peter to pay Paul” weakness problem, but still have an uncomfortable re-rupture rate. 

All of these natural tissue strategies require the body to remodel the tissue with the patient’s own collagen, repopulate it with the patient’s own cells, and heal the tissue to the bone. This process takes 12-18 months to occur fully. But the muscle atrophy that athletes suffer from the injury, as well as the surgery and post-op period, all contribute to their delayed return to sports.

The solutions are the following. 

Prevention. This works currently by training all athletes to land in knee-stable positions, thus lowering the potential for rupture.

Better natural tissues. Pig tissues have been stripped of most of the pig antigens that cause rejection. This unique enzyme-stripping process has been tested successfully in humans, finally receiving approval for sale in Europe. The first batch of tissues, however, suffered an unfortunate water-borne contaminant in processing, leading to a reduced success rate. Investors pulled back, and are waiting for tissues from genetically engineered pigs: a much more expensive solution. 

But this technology will return and is likely to provide an unlimited supply of natural tissues for tissue and joint reconstruction.

Artificial materials. The right material will permit bone to heal into it, stretch just like the normal ACL, and not break over a normal human lifetime. Sadly, all efforts to develop this material—using carbon fiber, polyester, Dacron, and Gore-Tex—have mostly failed. There is a solution here, but it hasn’t yet been found. While this problem is not rocket science, it has so far eluded material scientists.

Anabolic therapies to stimulate healing. The body can be stimulated to heal faster. PRP (platelet-rich plasma) is a well-known therapy now and new ones—most likely from birth tissues—may soon become widely available. Blood vessels can be induced to grow tissues and cells, and growth factors can be added to augment healing. Biologic intelligence—the knowledge of how to augment and restore the body’s regenerative abilities—will lead this effort to accelerate healing.

Therapy to block atrophy. When surgery occurs, there is an enormous release of cortisol, the natural stress hormone. Cortisol binds to the muscle receptors and muscle atrophy begins within eight hours—and recovery takes a full year. We are now researching a muscle receptor blocker, given just before surgery in a clinical trial, to determine if the atrophy can be reduced or eliminated. Either this drug or another is likely to work and solve the misery of missing an entire year of sports due to an ACL rupture.

So yes, the ACL crisis is a huge issue. Yes, it is solvable. And yes, many of us are working on solutions. Please help support this research, if you can. Women athletes are counting on us.