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  Discussion on Analgesia of the DF tendon sheath
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Member:
lynnland

Posted on Wednesday, Jan 19, 2011 - 1:06 pm:

Hi Dr. O,

Just came across an article on the use of analgesia of the digital flexor tendon sheath to help determine whether foot pain was due to soft tissue damage within the hoof rather than the sole, coffin bone, or navicular bursa (https://www.ncbi.nlm.nih.gov/pubmed/18065312). Just wondering why this isn't more widely used. Has there been any updates suggesting this is not the case or is the procedure difficult to do in the field?

Thanks
Moderator:
DrO

Posted on Thursday, Jan 20, 2011 - 8:04 am:

Lynn, I think you misread the conclusion. The study concludes, "Analgesia of the digital flexor tendon sheath has little effect on lameness caused by pain originating in the sole, distal interphalangeal joint (coffin joint), or navicular bursa". I don't see how this differentaites pain from the different structures of the foot.

However there are anesthetic technques that are used to seperate pain from the NB and the coffin joint which are explained in the article on foot lameness. Seperating solar pain from pain elsewhere requires careful examination and is explained in the article also.
DrO
Member:
lynnland

Posted on Thursday, Jan 20, 2011 - 8:24 am:

Hi Dr. O.,

I think I didn't ask my question very well, let me try to rephrase it. If a horse has an undiagnosed lameness that has been blocked to the foot (PD block), why would a vet not recommend a tendon sheath block to try to rule out all of the above (that you listed) if a soft tissue lameness is suspected? It would be a whole lot cheaper than an MRI.

Here is a quote from "The Horse" website (https://www.thehorse.com/ViewArticle.aspx?ID=10841):

"Anesthesia in the digital flexor tendon sheath limits pain only to structures within the sheath, such as the flexor tendon or distal sesamoidean ligaments. This study suggests that analgesia of the digital sheath is a useful alternative diagnostic tool for identifying tendonitis in the foot instead of relying on a more expensive MRI."
Moderator:
DrO

Posted on Thursday, Jan 20, 2011 - 9:55 pm:

Since this experiment shows that the nervous innervation of the flexor sheath is different than for the other structures of the foot, if a PD block relieves the lameness it is not a problem within the flexor sheath or at least not one alone. In other words it appears from this work that is you have a positive DP block it rules out the flexor sheath structures as a cause of problems. see correction of this statement below..DrO

I disagree with your last paragraph (from The Horse I am Guessing) when it states that this can replace the MRI. While the sheath anesthetic block will localize the pain to structures within the flexor sheath it will not replace an MRI which may identify the actual pathology causing the lameness. Until the pathology is accurately identified proper treatment and prognosis cannot be identified.
DrO
Member:
lynnland

Posted on Friday, Jan 21, 2011 - 1:28 pm:

Hi Dr. O,

Thanks for the reply. I totally understand that and MRI provides a significant amount more information than a block ever would. The images I have seen a pretty incredible.

Your article suggests that a low PD block will block lameness due to the DDF tendon distal to the block, but that does not appear to be what your last post says. If I read it correctly, you are saying that a PD block would not resolve a lameness due solely to tendon damage within the hoof?
Moderator:
DrO

Posted on Saturday, Jan 22, 2011 - 10:31 am:

This study does not answer the question of whether you can rule out distal flexor sheath structures with a DP. It asks and answers whether a flexor sheath block differentiates distal flexor lameness from other causes of foot lameness.

Lee I do think I over interpreted the study in the last post when I said "the experiment shows the innervation is different than the DPN". There is another explanation for the study results that occurs to me this morn. What if the nerves branch off the DP distal to where you do the block, then enter the sheath. Blocking the sheath would block these nerves but not the other structures innervated by the DPN. Traditionally we have assumed these distal flexor structures would be blocked with a PDN block and it will require more careful experimentation to test these 2 hypotheses or others that might exist I have not thought about.
DrO
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