Little fishing lines in the knee

Little fishing lines in your knee
If you take your finger nail and rub across either the femur or the tibia on the medial side of your knee cap you may feel a twang as your nail flicks across what feels like fishing lines. These are likely to be branches of the infrapatellar branch of the saphenous nerve. Now that is a mouthful – and did you know that the saphenous nerve is the longest nerve in the body. These little nerves may well be responsible for a range of problems such as medial knee pain and swelling, post arthroscopy pain and fat pad problems. Check out the picture of them – there are usually two branches, and see if you can give them a twang. Next time you see me ask me to get on your nerves!

Is the brain too trendy?
These days the brain is trendy to research, who would want to focus on the knee when there is a brain to explore? It’s sexy to link yourself to a gadget that peers into the workings of the brain and even the word ‘neuromatrix’ has a Keanu Reeves feel about it. It’s all good stuff in our view but it may be at the expense of clinical consideration of the body. We are serious here about the reciprocal interactions between brain and the rest of the body.

One of our guiding philosophies at NOI is that the pain mechanism has a physicality. What this means is that pathophysiology is nearly always linked to movement. For example, in a pain state where nociception contributes, say a good knee sprain, the clinical findings, assessment and treatment are linked to movement. In pain where there is contribution from a peripheral nerve, the clinical findings are often linked to movement of the nerve. Even in centrally generated pain, the meninges, neural and glial cells still have a physicality, i.e. they can move and stretch and this may well be a necessary feature for neural health. But let’s take another look at the infrapatellar branch of the saphenous nerve (IBSN).

The IBSN – A very slidey little nerve?
Think what happens when you squat – the saphenous branches really move like worms in the skin fascia and soft tissue as we move. If your knee is extended the nerves run 45 degrees across the knee joint but when the knee is flexed it will be parallel to the joint line and it could glide a centimetre (Tifford, Spero et al. 2000). I occasionally marvel at its physical abilities when I squat (doesn’t everyone!). It is worth remembering that the nerve still has to function electrically and chemically despite this extraordinary movement and worth reflecting on the possible role of this nerve in people with painful squatting and/or kneeling.
Image from Butler, D.S., The Sensitive Nervous System, Noigroup Publications, 2000

Problems with the IBSN
Knee surgery seems to be the biggest challenge for this little nerve. Meniscal surgery used to regularly ‘wipe out’ the nerve. Of course, it is all done arthroscopically these days but 25 years ago, up to 44% of people reported discomfort in the IBSN zone as late as 6 months post-surgery (Mumenthaler and Schliack 1991).

Most researchers agree that surgery such as total knee replacements, the insertion of arthroscopy portals and incisions for cruciate surgery place the nerve at risk with the incidence of sensory changes in the distribution of the IBSN reported as “common” – between 25 and 70%. Of course, this may be inevitable and it often resolves but some do go on to neuropathic pain states which may be inconvenient (problems squatting) or very painful such as CRPS. There is a good summary in Tifford et al (Tifford, Spero et al. 2000) for those who want to read further.

Adding some pain sciences
Involvement of the IBSN may be more common than we realise. It should be considered a possible contributor to any anteromedial knee pain. This may make us look afresh at patella fat pad problems or patella tendinopathy – could they be neurogenically inflamed by the nerve injury (antidromic firing causing a substance P initiated mast cell degranulation, bleeding and immune reaction in the fat pad)?

And of course some patients with knee problems will have brain changes in the representational meaning of the knee (Woolf 2011) and it is likely that as the brain tries to rearrange its notion of body that further immune based swelling and nerve sensitivity is possible. This may well be minimised if patients are told prior to surgery that they can expect some sensory changes and that it is likely to go.

Checking it out
It’s rare that fancy electrodiagnosis will be needed. Just do a sensory examination, touch the nerve to see if there is any difference in sensitivity compared to the other side. Palpate it in knee flexion and extension. Local tissue snags and thickening may well benefit from some soft tissue work and simply identifying and explaining the problem for patients may dethreaten the situation enough to calm it right down. Maybe some knee taping could unload the tissues around a discharging area of nerve.

So in summary
Let’s not forget the body, and remember that even minor nerves can cause heaps of trouble. Get your fingers off the keyboard and go twanging.

Send in your best clinical story involving the infrapatellar branch of the saphenous nerve and the winner will get a NOI Neurodynamics DVD and handbook.

Neurodynamics and the Neuromatrix conference
At NOI 2012 we will have sessions on neurodynamics, although there is not as much research as there is on the more trendy brain. One of the sessions will be a lunchtime display where you can watch movies of nerves sliding and have someone ultrasound your own nerves – what a lovely way to review your anatomy and come to grips with how much even the small nerves glide.

Mumenthaler, M. and H. Schliack (1991). Peripheral Nerve Lesions. New York, Thieme.
Tifford, C. D., L. Spero, et al. (2000). “The relationship of the infrapatellar branch of the saphenous nerve to arthroscopy portals and incisions for anterior cruciate ligament surgery ” The American Journal of Sports Medicine 28: 562-567.
Woolf, C. J. (2011). “Central sensitization: Implications for the diagnosis and treatment of pain.” Pain 152(3Suppl): S2-15.

Winners on the female homunculus
We’re all winners with these new maps! But seriously, thanks so much to everybody for sending in your thoughts and sharing your personal experiences. The three winners will be sent a copy of Explain Pain (book, audio or ebook in English, Spanish or Portuguese).

Huge congratulations to Melissa from the United States, Emily from Australia and Carolyn from Canada for answering the three questions in that order.

[PDF of responses from August 2011 – Females reclaim the homunculus]

There are also more comments you can read on the blog page where the NOI Notes get posted each month.

Explicando a Dor ebook
Explicar el Dolor ebook
Explain Pain ebook

NOI 2012 September scientific update

recap on the recent Australian GMI tour
Handstands in your day

New Flashcards – back, neck and shoulder

NOI Neurodynamics video

NOI Research


3 Responses to “Little fishing lines in the knee”

  1. MARCOME (@Marcome) Says:

    Great! I’m getting a second knee surgery so I will bring your article to the surgeon! I’ve had so many problems because of the Epidural (rachidienne) over the last 8 months!

  2. Braedan@PhysioSurrey Says:

    Noi Groupies,

    Thanks for mentioning this vital system for knee mechanics. I have been noticing the connection between knee function, the distal ITB, lateral knee, and the “little fishing lines” for years. The IP branch of the Saph nerve is relatively often involved in my patients knee pain. Some surprisingly gentle soft tissue mobilizations can make big differences in how my patients knee might function.

    Keep the peripheral nerve posts coming! I believe that they have been clinically under emphasized for too long.

  3. jamie Says:

    i had an accident 13months at work on a constuction site.i fell down hill with a manhole lid & bracket braking my femur-i had an operation 10month orthopaedic surgeon wouldnt even look at my knee never mind hands on so i done my own tests & then went on the net and found this page which was one of the problems i have.i went back to see my orthopaedic and he said there was nothing wrong with my knee and dischared me.i went to my GP & he said i have nerve damage & my cartilage dont look right.he sent me back to the mri to see another orthopaedic &he has agreed with my GP-thank you for posting this helped me tell my GP.i have a v-good orthopaedic now and it looks like im on the right road at last—thank you again—

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