ACL Tear in Knee Hyperextension

Hi there my name is Tom, I am a physio student studying in Dunedin, New Zealand and was wondering if someone could explain to me how you can tear the ACL in a hyperextension injury. I understand how this could occur if it was a very severe hyperextension injury that tore the PCL as well. But not if it is just the ACL. We have not been taught about this at all only that the ACL prevents anterior translation of the tibia and the PCL prevents posterior translation...

Hope someone can help out,

Cheers

So you looking for info, a book? Do you have online library subscription? Check journal of athletic training is free via pubmed. Book wise look at Magee orthopedic physical examination or clinical sports medicine of Brukner and Khan
As anatomy is quite simple the PCL is almost Vertical while the ACL is diagonal arising from the tibia to attach in lateral femoral condyle at its medial surface. Get a piece of paper and make your hands the correspoding bones and perfrom the movements.

I think you would benefit from really looking into the anatomy of the ACL, and the idea that it is structured with mlti-directional fibres. It's role is not purely to prevent anterior translation. It is also one of the main involvers in the final 'screw home' movement in knee hyper extension.

It is also important to look at the stability of the other ligaments too, especially the MCL as if there is laxity here then it may be that the ACL is brought into play to prevent genu valgus deformity

The knee - range of motion | KNEEguru notebook

This website explains the mechanics of the screw home element of knee extension...


also I forgot to mention, relating to the question about how hyperextension can cause ACL injury. as the MCL and LCL also restrict hyper-extension, if there is laxity here then the ACl is brought into play for a role in preventing hyper-extension. Normally it will be combined with a rotational or valgus force, but in this sense the ACl can be damaged in hyperextension

Brilliant. Cheers guys will have a look into that stuff. Thanks very much.

hey there, remember as already stated that the acl is not one bundle of fibres. it is more accurate to describe it as a ligament that is composed of three bundles of fibres that each are taught in different positions. one of these bundles of fibres is indeed taught in full knee extension. with a forceful hyperextension its therefore possible to tear this bundle. some people think that with a hyperextension injury, this part of the ligament is torn and it then wont provide the normal stability and can easily be finished off with a typical functional valgus position injury. an interesting video to look at is michael owens acl tear in the 2006 world cup. he stated that he felt a tear and heard a pop before his foot hits the ground, so its possible to say that he may have torn part of his acl before his foot comes down, he goes into a valgus position and blows the whole acl out. there area a couple of acl tear videos out there like that and its interesting to look at the mechanics of the injuries in slow mo.

some info on the anatomical bundles. http://www.ncbi.nlm.nih.gov/pubmed/21695467