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Researching the Anterior Cruciate Ligament

May 3, 2023

This semester I took a course called Locomotion Neuromechanics. Like me, you might think that it would be a course where you would learn more about the movement within one’s body, different things that can affect mobility, etc. However, after attending the first class, I realized it was focused on the student’s own interest in a topic relating to Locomotion Neuromechanics. I found this method interesting because it allows the student to either dive deeper into their own research or explore other topics, related to locomotion, that they wouldn’t be able to in another class.

After the first round of presentations, the class had a broad range of topics that would be focused on like robotics, animal/insect locomotion, neurodegenerative diseases that impact mobility, flying snakes, spinal cord injuries, etc. At first, I had no idea on what topic I would be focusing on. I initially presented on something related to spinal cord injuries, but instead of focusing on humans, I was looking at animals like cats and mice. This changed after I was researching stuff that I would enjoy more. I then focused on the anterior cruciate ligament or commonly known as the ACL. This topic can go any way from what is the ACL, how it works, ACL injuries, etc.

Before I start, you might be wondering what the ACL is. The ACL is a ligament that connects the femur to the tibia. The femur and tibia in layman’s terms are the thigh bone and shinbone, respectively, found in your leg. This ligament is important for knee and joint stability. You might wonder why your knee doesn’t move forward when you walk, jump, play sports, etc. The ACL is in charge of preventing the movement of the knee to go from the front to the back or side to side. It is most commonly known to have ACL injuries while playing sports such as soccer, football, basketball, gymnastics, etc.

Below are some of the interesting research facts that I found on my literature search about the ACL:

  • The two most common ACL reconstruction surgeries: bone patellar tendon bone graft and the hamstring graft
  • Hamstring strength recovered at a faster rate than quadricep strength (3)
  • Anterior knee pain influences the recovery of muscle performance of a patient after ACL reconstruction (3)
  • Younger patients had a higher rate of subsequent ACL injury rate, distinctly that young males had higher rate of rupture than females (6)
  • Researchers are trying to focus on rehabilitation programs that focus on the different forces that might heal an ACL (6)
  • Depending on some factors like the type of graft used, how the graft works post-operatively and the different fixation techniques (6)
  • In addition to rehabilitation programs, literature states that they are examining pre and post operative rehabilitation, neuromuscular training, electrostimulation and other protocols that an individual can go through after ACL reconstruction. (5)
  • A long term consequence of ACL reconstruction is osteoarthritis which is known to be a disease of the joints. Factors that can influence the outcome consists of sex, age, family history and muscle strength (4)

These were just a couple of interesting literature facts that my research came across focusing on ACL before and after reconstruction surgeries.
I am working on the final project for this class so if anyone is interested in other facts about the ACL or interested to learn more, let me know.

 

References:

  1. Cavanaugh JT, Powers M. ACL Rehabilitation Progression: Where Are We Now? Curr Rev Musculoskelet Med. 2017 Sep;10(3):289-296. doi: 10.1007/s12178-017-9426-3. PMID: 28791612; PMCID: PMC5577427.   https://pubmed.ncbi.nlm.nih.gov/28791612/
  2. Freeman. “ACL Injuries.” NJ’s Top Orthopedic Spine &; Pain Management Center, 7 Mar. 2023, https://redefinehealthcare.com/acl-injuries/.
  3. Kobayashi A, Higuchi H, Terauchi M, Kobayashi F, Kimura M, Takagishi K. Muscle performance after anterior cruciate ligament reconstruction. Int Orthop. 2004 Feb;28(1):48-51. doi: 10.1007/s00264-003-0502-5. Epub 2003 Aug 26. PMID: 12942198; PMCID: PMC3466568. https://doi.org/10.1007/s00264-003-0502-5
  4. Lohmander, L. S., Englund, P. M., Dahl, L. L., & Roos, E. M. (2007). The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis. The American journal of sports medicine, 35(10), 1756–1769. https://doi.org/10.1177/0363546507307396 
  5. Perry A, DeFroda S, Leporace G, Metsavaht L, Coxe CR, Bierman AM, Chahla J. ACL Rehabilitation: How Can We Lessen Injury Rates? Operative Techniques in Sports Medicine, 30,1, 2022. ISSN 1060-1872, https://doi.org/10.1016/j.otsm.2022.150892. https://www.sciencedirect.com/science/article/pii/S1060187222000041
  6. Webster KE, Feller JA. Exploring the High Reinjury Rate in Younger Patients Undergoing Anterior Cruciate Ligament Reconstruction. Am J Sports Med. 2016 Nov;44(11):2827-2832. doi: 10.1177/0363546516651845. Epub 2016 Jul 7. PMID: 27390346.  https://pubmed.ncbi.nlm.nih.gov/27390346/
  7. https://www.shutterstock.com/image-illustration/torn-anterior-cruciate-ligament-176343242
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About Author

Claudia is an Biology graduate student at Georgia Tech. She loves photography, traveling, baking, and swimming. In her spare time she enjoys swimming, watching soccer, exploring new places and hanging out with friends. She is excited to research and learn new things in the world of science.

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.