Designing a More Effective Joint: The Knee

In this project I researched the anterior cruciate ligament to figure out how to make it better. The knee is a complex joint of the human body that can easily be hurt. The anterior cruciate ligament (ACL) is one of the most common serious knee injuries. It can easily be hurt through sports and the recovery time is a long one. I researched key ways the ACL is damaged and came to the conclusion that it should be modified by increasing the thickness of it, adding more muscle tissue, and adding more motor neurons. These theoretical additions will decrease the chance of injury and improve the joint. In reality, the knee cannot be redesigned, so ways to protect this ligament include keeping the thigh muscle strong, warming up before exercise, and maintaining flexibility.

The knee is one of the most complex joints in the human body and it can easily be damaged. One part of the knee that is commonly injured is the Anterior Cruciate Ligament, or ACL. Of all serious knee injuries, the ACL is damaged 70% of the time. The ACL is an essential ligament in the knee, as its job is to stabilize the knee. It extends posteriorly and laterally from the tibia and femur. By being in this location, it prevents the tibia from sliding in front of the femur. It also provides rotational stability. While people can live their daily lives without this ligament, life goes a lot smoother with it since it prevents the knee from ‘giving out.’ There are many ways in which the ACL can be torn. It is most commonly injured from playing sports. Ways to injure it include changing direction rapidly, stopping suddenly, slowing down while running, landing from a jump incorrectly, or direct contact. All of these display the how easy it is to hurt the ACL. Studies have shown that girls are 8 times more likely have to have an ACL injury than boys. Factors that contribute to this include how women have more flexible muscles, wider hips that put more pressure on the knees, weaker hamstrings, and smaller ACLs. The ACL is such a commonly hurt ligament because it is in control of keeping the knee stable from such common movements. It is at the center and its job is crucial for knee functionality. Ironically, I currently have a torn ACL at this moment. I hurt my ACL while playing soccer, but still am unsure about how I hurt it. I think that it was from either stopping suddenly, changing direction, or landing awkwardly. Unlike some other injuries, the ACL will not heal on its own if it is torn or stretched. If full use is desired, surgery is needed to reconstruct the ligament. In the surgery, it is common to take some tissue from either the hamstring muscle or patellar tendon and place it where the ACL should be.

My knee 2 days after the injury occurred

My new redesign of the ACL could theoretically reduce likelihood of injury in the first place. In the new design of the knee, the ACL, which is usually about 10 mm thick on average, would be 2 mm thicker right and left, which a total addition of 4 mm of ligament. The addition of this extra ligament could hopefully reduce the likelihood of the ligament tearing and over stretching. The new knee would also have a larger muscle mass. The muscle of the hamstring in particular would be increased by about 6 cm in diameter. This would allow the hamstring to naturally be stronger and help allow it to absorb more of the shock placed on the knee. The quadricep would also be increased by about 4 cm in diameter. Like the hamstring, the quadricep would help protect the ACL from injury by being able to absorb more shock and have more strength to make safe movements. The hamstring is increased more than the quadricep because many people naturally have weaker hamstrings, so more muscle should be added. I would also increase the number of motor neurons so that individuals would have a quicker reaction time if they were in a situation that could lead to injury. These neurons would allow an individual to have a better sense of their own body, reducing the chance of injury.

This new diagram of the ACL displays how it is approximately 4 mm larger than it was originally. The thinness of the original ligament plays a role in how it tears and stretches easily. The new thickness allows the ligament to be tougher.

Before

After

This diagram displays the difference in structure in the additional muscles added to the improved knee. The increase of the muscle mass makes the leg stronger than it was before so that the ACL will not be as traumatized in different situations.

Before

After

I arrived at this design through my prior knowledge of the ACL and additional research that I did. Ideally, I would have decreased the width of women’s hips, but that would simply not work out since they are that way so that they can give birth to children. A problem that I ran into was trying to figure out reasonable sizes of the muscles and ligaments. I could not find any source that explicitly stated the size of the hamstring or quadriceps muscle, so I had to use common sense. A problem with increasing the width of the ACL is that it may reduce the mobility of the knee if the thickness reduced movement; every part of the body is made how it is for a reason. The increase in motor neurons may also be a problem if it creates too much information for the brain to process, which could possibly lead to seizures if it gets too much. This relates to what we have learned in class because we have learned about what ligaments are and how muscles always have another one to work inversely with it. The increase in size of the hamstring and quadriceps is an example since when the hamstring flexes, the quadricep relaxes. Because we are unable to actually redesign different joints, different things can be done to prevent this injury. One way to prevent injury is to keep the thigh muscles strong. The strengthening of these muscles allows legs to stay strong and add extra protection to the ACL. Another way to stay healthy is to warm up before doing strenuous exercise. This will allow muscles to get moving so that they are able to support sudden movements. Maintaining flexibility will also help so that an individual’s body is able to have full range of motion without straining it.

Works Cited

"Anterior Cruciate Ligament (ACL) Injuries - Topic Overview." WebMD. WebMD, n.d. Web. 09 May 2017.

"Anterior Cruciate Ligament (ACL) Injuries." Anterior Cruciate Ligament (ACL) Injuries-OrthoInfo - AAOS. N.p., 01 Mar. 2014. Web. 09 May 2017.

Hindawi. "Adequacy of Semitendinosus Tendon Alone for Anterior Cruciate Ligament Reconstruction Graft and Prediction of Hamstring Graft Size by Evaluating Simple Anthropometric Parameters." Anatomy Research International. Hindawi Publishing Corporation, 29 July 2012. Web. 09 May 2017.

Horwitz, D.C. Steven. "ACL Injuries: Female Athletes At Increased Risk." MomsTeam. N.p., n.d. Web. 09 May 2017.

"KneeAnatomy Side." Wikipedia Commons. Wikipedia Commons, n.d. Web. 8 May 2017.

Mysid. "Knee Diagram." File:Knee Diagram.svg - Wikimedia Commons. Wikipedia Commons, n.d. Web. 09 May 2017.

Tortora, Gerard J., and Bryan Derrickson. Introduction to the Human Body: The Essentials of Anatomy and Physiology. New York: Wiley, 2007. Print.

"What Are Knee Ligament Injuries?" WebMD. WebMD, n.d. Web. 09 May 2017.