ACL Prostheses

Ligaments are bands of tough, elastic tissue that bind bones together at joints so that they can move.  The artificial ligament is primarily used for placement in the knee.  There are four ligaments that surround the meniscus, which is a cartilage tissue that helps support the knee when it undergoes tension and torsion.  The four ligaments are the anterior cruciate ligament (acl), the posterior cruciate ligament (pcl), the lateral collateral ligament (lcl), and the medial collateral ligament (mcl).  An artificial ligament would be used to replace any one of these four ligaments that has been damaged.

                                                   

The main mechanical connection for the femur and tibia is the ACL Ligament within the knee. The collagen fiber bundles can withstand different stress loads depending on the patient’s age.  An average breaking load of a young athletes ACL is around 1700 to 2000 N.  Artificial ACLs developed today can withstand loads of around 4,000 N, however it tends to suffer from poor mechanical performance in the long-term.

There are over 60,000 ACL reconstructions performed annually in the US. The success rate for reconstruction is between 75%-95% and failure rate is around 8% due to graft failure or instability.

Snapshot of a soccer player in the process of injuring his Anterior Cruciate Ligament

ACL injuries usually occur within young athletes who participate in sports or activities that place heavy stress on the knees. These sports or activities include football, skiing, soccer, and any activity that requires side-to-side movement or hard cutting movements that stresses the ligaments in the knees.

Image of the parts of the knee around the meniscus


Artificial ligaments are mainly constructed as woven or braided materials, but have been known to be nonwoven materials as well.  As a braided fabric structure, an artificial ligament is gifted with high flexibility, high strength, high durability, and high cover.  The fibers used (typically ePTFE, polyester, polyacetal polyethylene, polyethylene, or silk) all have a round cross-section which is ideal for use in this part of the body because it is surrounded by the human tissue in the knee so that the artificial ligament is secured in place; hopefully for the duration of the user’s life.  A nonwoven would be used in order to utilize the fibrous mat made of graphite and Teflon to promote tissue growth using the implant.


Knitted fabrics tend to be much more elastic and flexible than any of the other three fabric constructions, woven fabrics boast high abrasion resistance, strength, and cover.  Braided fabrics tend to take the advantages of both knitted and woven fabrics to create a highly function fabric.

Image of an artificial ACL

Artificial ligaments are a “last-resort” type operation.  Usually doctors will try to find a way to use ligaments from other parts of the body to repair an ACL, such as the patella tendon or the hamstring tendon.  Patients now opt for donor tissue grafts, which usually uses the patellar tendon of a cadaver.  All non-surgical treatments would have had to have failed in order for a replacement to be implanted.  The primary function of an artificial ligament is to provide mobility while decreasing the pain.  Many times, cartilage can be worn out and bone-to-bone contact can be extremely painful.  In addition to athletic injuries, osteoarthritis, or degenerative joint disease can be cause for an artificial ligament.

Pros

  • Allows return to high-level athletic activity
  • May protect future damage to the knee cartilage
  • Offers a near-normal knee
Cons
  • Surgery is not 100% effective–some people don’t improve.
  • Many activities can be accomplished without an ACL
  • There are complications that may occur.
The overall lifespan of an artificial acl is not very long, however many patients have the choice as to whether or not they want to fix their acl. Many sports that do not require bilateral movement (running, cycling, and swimming) can be done without an acl. Not repairing an acl could, however put much more unneeded stress on the knee cartilage as the knee continues to give out. Many younger patients are recommended to have the re-constructive surgery, because they will need their knee for many years to come, whereas a 60 year old would not need their knee for as intense an activity as a younger person.  An artificial acl is not free from fault.  It has the capacity to fail like many other products placed inside the body.  The most common failure mechanisms are surface abrasion against bone, flexural rotational fatigue of yarns and fibers, and fraying of textile structure due to unpredictable tissue ingrowth.

References:

http://www.ncbi.nlm.nih.gov/pubmed/19915821

http://www.technicaltextile.net/medical-textiles/hospital-textiles.aspx

http://www.swicofil.com/biomedical_textiles.html

http://www.discoveriesinmedicine.com/Apg-Ban/Artificial-Ligaments.html

http://www.sportsci.org/encyc/aclpros/aclpros.html

http://emedicine.medscape.com/article/89442-overview

http://orthopedics.about.com/cs/aclrepain/a/acldecision.htm

 http://www.youtube.com/watch?v=kNvtEMTF6YE&w=640&h=390

http://www.youtube.com/watch?v=GtYmfQof-Io

http://www.youtube.com/watch?v=q96M0jRqn7k&feature=related

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6 thoughts on “ACL Prostheses

  1. Looks great! Some of the sentences seem old grammatically, but I’m a grammar person. Also, it may flow better if references would put near the end, like when writing a paper.

  2. You could add a video showing more about the product. A table would be sufficient to have showing more properties that deal with the product. More disadvantages and advantages are also good to include for each fabric structure. I would add more mechanical and physical properties should be added.

  3. I agree with the above 2 statements. A video about the procedure used to insert the artificial ligament or just a description of the procedure would be beneficial. I also agree about putting the references at the bottom, it will help your page flow a little better.

  4. We also agree the above comments and we think your blog would flow better if you moved the pictures so that the text was not around the pictures.

  5. I have 3 comments:

    1) At the end of the first paragraph please indicate the most common instances when ACL injuries occur. It is important to stress that these injuries usually occur to athletes who experience one or several frontal (anterior) impacts to the knee due to accidents while downhill skiing, or playing football, soccer or other contact sport. These patients are usually healthy active younger people, unlike those older patients with chronic cardiovascular and arthritic diseases. Their rehabilitation will therefore normally be short in duration and quite intense.

    2) I like your reference to “last resort type operation”. This is true and most relevant. Please indicate the patient’s biological tissue of choice that the orthopedic surgeon would prefer to use, (such as the patella tendon or the hamstring), before considering the use of a totally artificial ACL prosthesis.

    3) What is the clinical experience with the use of implanted ACL prostheses? How long do they normally last and provide satisfactory mobility to the patient? What are the predominant modes of failure for these ACL prostheses?

    Thanks for considering these additional components of your blog.

    Martin W. King
    Professor of Biotextiles & Textile Technology
    North Carolina State University
    Office: (919) 515-1011
    Cellular: (919) 291-2563
    E-mail: martin_king@ncsu.edu
    URL: http://www.tx.ncsu.edu/biomedicaltextileslab/

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