Thursday we received the good news that Minnesota Vikings quarterback Teddy Bridgewater's surgery to repair the anterior cruciate ligament (ACL), torn when his left knee dislocated, was a success. The surgeon called Vikings' coach Mike Zimmer to say that the surgery went well, the ACL was repaired, and there was no structural damage beyond what the team had already found from MRI images. By Friday, the team's head athletic trainer Eric Sugarman released his statement on Bridgewater's successful knee repair surgery. With Bridgewater's knee repaired and the hopeful statement from Sugarman about the surgery and rehab, fans have reason to heave a collective sigh of relief and hope for Bridgewater to have a good recovery.

For a lot of fans, that is probably good enough. I, however, am a bit odd and I wanted to understand more about Bridgewater’s injury and his road to recovery.

In the frantic scramble to figure out what had happened and what the Vikings would do after losing their franchise quarterback to a freak non-contact injury, I found myself wondering about the medical side of this injury just as much as the football aspects of what would happen next. While the Vikings were fairly candid about the nature of the injury, it felt like I didn’t understand the context of the information. So, I did some research and I talked with my dad and my sister.

Big, fat disclaimers

My dad worked in emergency medicine at a Level 1 trauma center for more than 30 years and has seen a lot of knee injuries. Since he didn't treat Bridgewater or see Bridgewater's MRI and x-rays, the information he shared is general in nature. My sister is a physical therapist. Again, Bridgewater isn't her patient, so she can only speak generally about rehabbing ACL injuries. Because there was a lot back and forth discussion and explanation involved in these conversations, I opted to paraphrase their answers rather than quote them (most of the time) for the sake of easier reading. I also reference a MMQB article that is linked.

Now that the disclaimers are out of the way, if you're curious about this type of injury, read on.

How does a knee become dislocated?

There are a variety of connective tissues in the knee that both enable and restrict movement as well as acting like shock absorbers. Those tissues have to allow the knee to move as well as restricting movement so the bones stay in correct position and the joint avoids injury. A knee dislocation causes the bones of the thigh (femur) and lower leg (tibia) to move in relation to each other, tearing connective tissues that would normally stabilize movement in the knee joint. There can be an anterior, posterior, or rotatory dislocations. Considering Bridgewater was dropping back when he dislocated his left knee, it could be a rotatory dislocation due to twisting, but that's just a highly speculative guess.

How does a knee dislocation differ from a patellar dislocation?

Much less severe an injury than a full knee dislocation, a patellar dislocation is when the knee cap (patella) is out of place and not the femur and tibia. A patellar dislocation is much more common than a full knee dislocation. Although a patellar dislocation also looks scary, it is a much less severe injury than a full knee dislocation. A full knee dislocation is often caused by trauma like the kind sustained in car accidents. However, it sounds like Bridgewater's injury is a true dislocation because the Vikings described it as a “non-contact injury” when they released their official statement.

What does the ACL do for the knee?

An ACL stabilizes the knee from front to back--it prevents the tibia (shin) from sliding out in front of the femur (thigh). Basically, the ACL is directly related to the movements of the femur and tibia. When people walk and move their legs, there is a normal amount of rotation that occurs and the ACL helps provide stability for that rotational and anterior movement.

What kinds of "other structural damage" can occur during a knee dislocation?

At the time of the injury, Bridgewater was rushed to a Level 1 trauma center. A Level 1 trauma center not only has orthopedic surgeons always available, but also other surgical specialties and imaging capabilities. This is important with a knee dislocation because there is the possibility of vascular and nerve damage. Vascular damage could, in some cases, cause a patient to lose his/her leg by cutting off the blood supply to the lower leg. If the dislocation tears a major vessel like the femoral artery, the patient could die from blood loss. Nerve damage could cause loss of movement or numbness in the leg. For an ordinary person, that’s a problem, but, for an elite athlete, loss of movement and numbness could have career implications. Fortunately, the Vikings said Bridgewater did not have either of those complications.

As for the Vikings saying Bridgewater had suffered "other structural damage," that could indicate what is known as a "terrible triad injury." That is when the ACL, the medial collateral ligament (MCL), and the medial meniscus are all damaged. A triad injury is more complicated because more of the knee's side-to-side stability is affected. In his post-surgery statement, Eric Sugarman said that, "The knee dislocation resulted in Teddy needing a multi-ligament reconstruction," making it sound like a triad injury is a possibility.

How is an ACL repaired during surgery?

In 2013, MMQB had a fascinating in-depth feature article on Dr. James Andrews (Adrian Peterson's knee surgeon) repairing an ACL. The article is a long read, but worth it if you are curious. While the process is an amazingly simple concept when you read about it, that hardly makes it easy. Here's the short version: guided by a scope, a surgeon cleans out the damaged knee tissue, harvests the middle third of the patellar tendon (including bone from where it attaches to the bottom of the patella and the top of the tibia), and uses that patellar tissue to create a new ACL graft for the patient. After the harvested tendon tissue is crafted into the correct shape, it is carefully secured in place to give the patient a new ACL.

How long does ACL surgery take?

According to the MMQB article, it took Dr. Andrews and his surgical team 63 minutes to perform the surgery the writer observed. I'm guessing surgery time varies depending on what other damage is found when the scope is inserted in the knee and the surgical team gets a first-hand look at the knee and connective tissue. Bridgewater’s surgeon was Dr. Dan Cooper of the Carrell Clinic in Dallas, Texas and his methods as well as surgery time could vary from Dr. Andrews’ because, according to Sugarman’s statement, Bridgewater had a “multi-ligament reconstruction.”

What are the biggest potential pitfalls for patients during the ACL rehab process?

It’s incredibly important not to rush the rehab process. Because ligaments and tendons do not have a great blood supply, healing takes time.

The first part of the rehab process will focus on reducing inflammation and keeping the range of motion in the reconstructed knee. Sutures need to be secure before the knee is over-stressed. Over-stressing increases the likelihood of re-injuring the repaired tissues.

When the trainers/therapists feel that it is time to increase the activity, with the patient already bearing weight and walking decently, the new priorities will be rebuilding stability and strength. And, of those two concerns, stability is the real issue.

As mentioned above, the different ligaments of the knee (anterior, posterior, medial) allow the knee a certain amount of twisting and turning motion rather than just bending and straightening in a single plane—they work together to both allow and limit motion, kind of a give and take. When one of those ligaments is injured, it throws off the power balance of the joint. High-performing athletes, like NFL players, often have to strengthen other ligaments as well to restore balance.

In the rehab process, stability will be regained through several methods: externally bracing the knee will limit the knee’s range of motion, all the repair work that the surgeon did will provide internal stability, and then musculature surrounding the knee evenly will also stabilize the repaired knee. Because a lot of the stability comes from the core muscles, the strengthening will include the whole body. As part of that, the training staff will check for and address any muscle imbalances that could contribute to instability.

What are some of the long-term knee issues ACL patients experience?

In the long-term, many athletes develop arthritis in their knees and hips related to repetitive trauma. My sister concluded, “In Michigan, college football was big. I saw lots of guys in their forties and fifties needing knee and hip replacements. But they’re a therapist’s dream. They have such a great work ethic and are often still in decent shape overall.”

My thanks to my dad and my sister for sharing their expertise with me.