The Chemistry of the ACL

• The ACL, or the Anterior Cruciate Ligament, is tough fibrous material that connects a bone to a bone. The ACL is an important ligament in the knee, and it would be difficult to complete daily tasks without one. The knee itself is made of the femur, tibia, and patella and forms the knee joint. The kneecap is there for protection in front of the joint. Each of these bones are connected by four ligaments- the lateral collateral, posterior cruciate, medial collateral, and the anterior cruciate. They are mainly on the side of the knee and are particularly keen to the bending and straightening motion.
• I chose to study the ACL because I have had teammates face injuries due to their ACL, and I myself have torn my ACL. You can tear your ACL by changing direction rapidly, stopping suddenly, slowing down while running, landing from a jump, direct contact or collision, or hyperextension. I tore mine because of direct contact and hyperextension. There are over 250,000 ACL injuries per year in the U.S. and that created the interest to learn further information about the ACL. Maybe there is something in the Chemistry of the ACL to prevent future injuries.
• I tore my ACL during a basketball game and it has now enabled me from playing softball this season and any other sport this summer. My routine changed drastically, because instead of going to practice I now go to physical therapy. It has turned my life upside down, so gaining more knowledge about what is happening in my body will help my future and recovery. The more I know about what is going on inside my body, the more I am able take precautions and not become frustrated with the process of my rehab.

Composition of ...

• Water = H2O
• Proteoglycans = D-glucuronate+GlcNAc
• Proteins = NH2CHRCOOH (aq) + H (aq) → NH3CHRCOOH (aq)
• Glycoproteins (Actin, Laminin, & the Integrins) = C4H8N2O3 (polypeptides)
• Anteromedial band
• Posterolateral portion
• Lysyl-oxidase
• Elastin (EtO2C)2+CH2=CHCN → (EtO2CH2)2 CHCH2 CH2 CN

Main Chemicals, Compounds, Components

• Proteins = NHCHRCOOH2 (aq) + H (aq) → NH3CHRCOOH (aq)

Proteins are Platelet-rich plasma (PRP). It is a fraction of plasma that is produced by centrifugal separation of whole blood. It is a useful delivery system for growth factors important in tissue engineering. PRP contains plasma proteins which are known to act as cell adhesion molecules important for osteoblast, fibroblast, and epithelial cell migration and viability. These proteins allow a graft to be put in the place of the previous ACL and form to the body and its functions. As the graft is placed in as the ACL the body takes over and breaks it down, so cells from the body can begin to rebuild the ligament for strength.

• Elastin (EtO2C)2+CH2=CHCN → (EtO2CH2)2 CHCH2 CH2 CN

The patellar tendon is a thick and strong band of connective tissue on the front of the knee. It starts at the bottom of the patella to just below the knee to the front of the tibia, called the tibial tubercle. When using the patellar tendon as an ACL graft, surgeons remove a strip from the middle of it. The graft includes the bone attachments from the bottom of the patella and the tibial tubercle. The connection it has with both bones allows your knee to straighten. The bending and straightening motion stretches and contracts your muscle which is also interacts with the elastin in your knee. Elastin is in connective tissues like the patellar tendon. It allows things to return back to their normal position, and therefore is a big factor in the recovery in the ACL.

Chemistry's Role

All of the compounds of the ACL are not man-made, you have the option of using an autograft or an allograft. The autograft is bone or tissue from your own body, where an allograft is used from a donor. The proteins and tendons of your knee are made and strengthened by your body even after a new one is placed in the spot of the torn ACL. There is a period where your body breaks down the foreign ligament after surgery, and rebuilds it for future strength.

Background Research

The ACL provides 85% of total restraining force of anterior translation. It has a structure of ⅔ water, ⅓ solid components- proteoglycans, elastin, proteins and glycoproteins. It has a specialized enzyme called lysyl-oxidase, and promotes cross link formation. The ligament itself has a length of 38mm, and a width of 10mm. Lysyl is a healing protein in the knee. Another tendon is brought to replace the torn ACL, so the Lysyl-oxidase will not heal the ACL itself, it will help rebuild the “new” ACL. The Patellar Tendon is commonly used as the graft replacement for the ACL. The patellar tendon, Bone Tendon Bone (BTB), graft has consistently shown excellent surgical outcomes with 90-95% success rates in allowing athletes to return to playing sports post surgery. Because of the bone on each side the patellar tendon holds in place and prevents the tibia from moving too far forward. After surgery, the body develops network of blood vessels in the new graft called revascularization, this takes about 12 weeks. At this time the graft is at its weakest, which means it has a greater chance of stretching or tearing. A stretched or torn graft can occur if you push yourself too hard during this period of recovery. When revascularization is complete, strength in the graft gradually builds. A second surgery may be needed to replace the graft if it is stretched or torn. Post surgery many will be on crutches from 2-4 weeks. Gradually you will be able to put weight on the injured leg and start walking while still in a brace. Most choose to go to a physical therapist. After about 6 months athletes should be cleared to resume their sports or activities. The new graft will eventually allow complete range of motion and many will not be able to notice the prior injury.

Resources

http://orthoinfo.aaos.org/topic.cfm?topic=a00549

The ACL - Anterior Cruciate Ligament

Anatomy- The femur, tibia, and patella meet to form the knee joint. The kneecap is there for protection in front of the joint. These bones are connected by four ligaments- the lateral collateral, posterior cruciate, medial collateral, and the anterior cruciate (ACL).

Causes of tears- Changing direction rapidly, stopping suddenly, slowing down while running, landing from a jump, direct contact or collision, or hyperextension.

http://www.sportsandortho.com/minneapolis/anterior-cruciate-ligament-ACL-injury.htm

Made of- tough fibrous material that connects bone to a bone.

There are over 250,000 ACL injuries per year in the U.S.

http://www.physio-pedia.com/Anterior_Cruciate_Ligament_%28ACL%29

Composition- The ACL is a band of connective dense tissue that goes from the the femur to the tibia.

It receives nerve fibers from the posterior articular branches of the tibial nerve.

The ACL provides 85% of total restraining force of anterior translation.

http://www.ismni.org/jmni/pdf/16/21FRANK.pdf?q=ligament

⅔ water

⅓ solid components- proteoglycans, elastin, proteins and glycoproteins.

specialized enzyme called lysyl-oxidase, promotes cross link formation.

http://www.cryst.bbk.ac.uk/pps97/assignments/projects/emilia/Proteoglycans.HTM

Proteoglycans- D glucuronate + GlcNAc

http://www.rsc.org/Education/Teachers/Resources/cfb/proteins.htm

Proteins- NH2CHRCOOH (aq) + H (aq) = NH3CHRCOOH (aq)

http://www.chemistryexplained.com/Ge-Hy/Glycoprotein.html

Glycoproteins-N-linked- endoplasmic reticulum and Golgi apparatus.

Addition of amino acids = polypeptide (C4H8N2O3)

O-linked- addition of sugar residues to the hydroxyl side chain of serine or threonine residues in polypeptides in the Golgi apparatus.

http://en.wikipedia.org/wiki/Actin#In_smooth_muscle

Actin amino acid sequence is a highly conserved protein as it has little charge over its course of evolution.

http://www.wheelessonline.com/ortho/anatomy_of_acl

Length of 38mm

width of 10mm

Small anteromedial band- tight in flexion (crossed)

Larger bulky posterolateral- tight in extension (both are parallel)

http://www.sciencedirect.com/science/article/pii/S0020138312003579

Lysyl is a healing protein in the knee.

Although another tendon is brought to replace the torn ACL, so the Lysyl-oxidase will not heal the ACL itself, it will help rebuild the “new” ACL

http://en.wikipedia.org/wiki/Elastin

Highly elastic protein in connective tissue

Allows tissues to resume shape after stretching or contracting

ELN gene encodes a protein that is 1 of the 2 components of elastic protein.

http://en.wikipedia.org/wiki/Proline

Hydrophobic amino acid (glycine & proline)

(EtO2C)2+CH2=CH.CN------>(EtO2CH2)2 CH.CH2 CH2 CN

Tropoelastin is another name for elastin

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2952126/

Healing of the ACL post surgery

http://www.methodistorthopedics.com/patellar-tendon-graft-reconstruction-of-the-acl

http://www.orthoassociates.com/SP11B35/

Patellar tendon common replacement for a torn ACL.

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