ACL Recovery: Why does it take so long?
When SF 49ers quarterback Jimmy Garoppolo tore his anterior cruciate ligament on September 23rd in the second game of the 2018 season, the immediate verdict was, “He’s out for the season. He’ll be back next year.” Why does it take so long to recover from a simple ligament rupture?
Answer: It is not the injury; it is the surgery. Here is the state of the art and what to look for next:
When the knee goes one way and the body another, the ACL—which connects the femur to the tibia—often ruptures. A high percentage of the time, it is not just the ACL that gets injured, but the supporting meniscus tissues and the ligaments and soft tissue around the knee as well. Left untreated, most knees will be unstable and develop further injuries with sports.
To repair the ligament, the surgeon has several choices with pros and cons to each.
- Primary suture repair of the ruptured tissues only works when it is a partial rupture, very close to the femoral origin of the ligament. This is because the forces required to rupture the ligament shred the inside fibers throughout the length of the ligament. Only a very few, low-energy partial tears heal well. Efforts to augment the healing with scaffolds have not led to strong ligaments and would not be recommended for a high-level athlete.
- Replacement of the ligament by harvesting the patient’s own hamstrings or patella tendon tissue is the most common treatment. Robbing Peter to pay Paul, however, definitely weakens the knee permanently and creates a second injury site that must heal and recover. It may also increase the risk of arthritis. The grafted tendon tissues must then remodel into a ligament, and this process takes a year or more to complete. Still, this is the most common surgery done in the US for ruptured ACLs in 2018.
- Donor tissues are available from young cadavers—usually people who fall off their motorcycles. The best of these tissues is the bone-patellar tendon-bone. The advantage is that the athlete does not have to sacrifice other critical tissues around their knee. The disadvantage is that donor tissues have been reported, in some studies, to rupture at a higher rate than the patient’s own tissues. One must balance the downsides: Would the patient rather have a permanent weakness from a harvest of their own patellar or hamstring tendons or risk a possibly higher re-injury rate? (My patients almost always choose the donor tissue approach, since if they rupture it again they have another graft pulled through the same holes.) We are evaluating the addition of amniotic stem cells and growth factors to all donor tissues to see if they accelerate the healing and reduce the re-injury rate. The answer is not in yet.
- Artificial ligaments remain popular is some areas of Europe, Australia, and Asia for top-level professional athletes. While most of these ligaments will fail over time, they often permit the athlete to return to sport the same season. They have not caught on in the US yet, although research is ongoing. Given the amount of money and prestige on the line for an NFL quarterback, it is easy to see how they might favor this choice.
- Xenograft ligaments, using pig tissue, have been approved in Europe after extensive testing here and there is awaiting commercialization. The pig tissue can be stronger than human tissue and may provide a new option for avoiding the second site surgery described in option #2. Remodeling would still need to occur over the course of a year.
The tissue choices are one part of this slow recovery process. The other part is the related injuries. Often the corner of the knee is stretched with an ACL injury and, if not identified and repaired, leads to a high failure rate. If the meniscus tissue is torn, it too must be repaired—and if a significant piece is removed, the knee is doomed to develop arthritis.
The state of the art is not very artful, unfortunately. The best choice would be an immediate fix of all the injured tissues, with rapid healing. We are pursuing this goal by developing combinations of better tissues plus stem cells, better scaffolds for regrowing tissues that are partially torn, and novel artificial materials that may support regeneration while functioning immediately as successful replacements.
For now, the quarterback's choice is to either go short for a sure gain with an uncertain future or go long and hope for the best. Which would you choose?
