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Flexor Digitorum Brevis Inflammation

Discussion in 'Biomechanics, Sports and Foot orthoses' started by RobinP, Nov 4, 2010.

  1. RobinP

    RobinP Well-Known Member

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    Dear All,

    I would like to present a patient who I am having a little trouble diagnosing

    Presenting complaint

    Pain in the Lt Foot localised to middle of the foot on the plantar surface.
    Unilateral problem
    Has been painful for 2 years to varying degrees
    Can be painful at rest and at night

    Relevant Medical History

    Tarsal Tunnel Syndrome 2 years ago resolved by orthotic intervention

    Social History

    International level cyclist - no problems on bike - doesn't affect training
    Active 20 year old. When not cycling does a job where he stands all day
    Gets some relief from the pain by compressing the area over a golf ball


    Anatomy largely "normal". Small swelling over the area of discomfort which seems to lie directly on the flexor digitorum brevis (FDB) muscle belly. Swelling is soft and painful to palpate, more in the centre than around the margins.
    Ranges of motion are all normal as is muscle function around the foot and ankle


    Tinels sign -ve
    SLR and Slump -ve
    Plantarflexion of lesser toes against resistance is painful
    Sub talar joint axis is average to slightly laterally rotated
    Supination resistance is weak (not sure how best to describe) - inappropriately easy for his weight based on my experience
    Dorsiflexion stiffness at the 1st metatarsophalangeal joint (MPJ) is not high and jacks test produces a good and easy movement into supination
    Lunge test is positive at 130mm(no inclinometer but patient is 5 foot 11" so adequate.
    Static weight bearing shows calcaneal eversion and lowering of the medial longitudinal arch.
    Increasing plantar fascia tension did not cause discomfort. If anything patient said it relieved pain.
    Stress testing peroneus longus - no pain


    Kinematically in gait, the patient has normal initial contact and loading response. Midstance is normal but foot continues to pronate and is quite considerably pronated at heel rise(must be close to max pronation range)
    Heel rise is late.

    Differential Diagnoses

    Plantar Aponeurosis strain - I don't feel there is any plantar fascia involvement and the pain upon plantarflexion of lesser toes, I would imagine being a sign that the FDB is being excessively loaded. However, the patient desrcibes that loading the FDB muscle belly and stretching the area out feels like it is reducing the "tension"

    Medial plantar nerve tension/compression - patient doesn't describe neurological pain


    Given that the patient gets relief from compressing the area of swelling, I temporarily trialled some SCF padding on top of his existing orthoses, localised to the FDB muscle belly and forward into the metatarsal shaft and the patient felt more comfortable. I can't really work out why. The patient is happy with this reduction in discomfort but I feel that research and some type of diagnosis is necessary

    I have managed to find nothing on FDB ruptures or overusage except for isolated cases of spontaneous rupture. I can't then justify, if that were the problem, why compressing the area would make it better and I would imagine the patient's symptoms would be far more severe.

    I would welcome any guidance on FDB problems as I have no experience of it or would welcome any suggestions for a DDx.

    Many thanks

  2. Robin:

    Nice history and exam in your posting! Could you teach the others on Podiatry Arena how to give us more proper information on their clinical cases??;)

    Are you sure it is the FDB muscle and possibly not some other structure is painful? Could it be the FDL muscle or other intrinsics causing the pain with digital plantarflexion? You know that the FDB muscle is completely covered by the plantar fascia and is not directly palpable along its course, I assume. I don't think I have ever been able to diagnose a FDB muscle strain, that I know of.

    You may trial low-dye strapping and then show the patient how to tape their own feet for when they are at work standing all day. First of all, a standard set of foot radiographs would be appropriate for initial screening. However, the only other test test that would be worth doing is an MRI since all other tests, other than ultrasound, would likely not show anything unless it is of neurological origin. The night pain reminds me somewhat of neuritis or nerve entrapment, especially with a history of tarsal tunnel syndrome. Are there any neural deficits in the plantar forefoot or plantar digits?

    Good case, Robin. If you could provide a photo with exact area of most intense symptoms, then that would be extremely helpful. I see quite a few competitive cyclists in my practice.
  3. efuller

    efuller MVP

    I'd describe it as.... With manual force applied to medial plantar arch it is easy to supinate the foot. I think you got there. The description of the Jack's test is good.

    In gait is there an initial rapid pronation that stops, or slows, and then continues? Known as late stance phase pronation. Is this what you are describing. You will see this kind of gait in individuals with laterally deviated STJ axis.

    Going on the physical findings and the location of the pain... A very easy to supinate foot with laterally positioned axis may have high lateral loads. The foot supinates easily putting more load on the lateral forefoot. Something to look for would be peroneal muscle activity in static stance. Lateral column overload could cause strain in the plantar structures of the lateral arch. The problem with this theory is that it does not match all of the history and exam.

    Other structures in the area. Is the pain near the course of peroneus longus tendon? Can symptoms be reproduced with testing peroneus longus?

    Plantar ligaments: There is pain with dorsiflexion of the digits. Is there pain with dorsiflexion of the mets?

    Good presentation. It can be frustraiting when patients obviously have pain and it's hard to pin down where. Good luck with him.
  4. RobinP

    RobinP Well-Known Member

    Hi Kevin,

    Thanks for the reply. I can't be sure it is the FDB. As you said, the plantar aponeurosis completely covers the course of the muscle. However, the plantar aponeurosis aside, it is the only structure which covers all of the palpably tender area and where the swelling resides.

    Neurologically normal to all tests and palpation of the branches distal to the poterior tibial nerve that I can palpate. No neural deficits

    Because he is a cyclist, I did look at the possiblity of the FDL but the pain and swelling is distal to where I would think the FDL branches out and proximal to that, it courses too medially to make it suspect. That is assuming normal anatomy. I could be totally miles away though. I have attached an image of a foot and marked where the area of greatest discomfort is and the swelling.

    Unfortunately I have no access to imaging, so I will have to wait until I can get his GP to organise these and he may not be too keen on an MRI - I could probably organise US come to think of it.

    Why would it be more comfortable to compress the painful area when it is sore to palpate more locally. Is it possible for the long plantar ligament to be sprained and the patient feels greater support/comfort when compressed?

    Just another additional thing - I stress tested peroneus longus but no discomfort.

    Hope the image doesn't show that I hae been thinking about completely the wrong structures!



    Attached Files:

    • FDB.jpg
      File size:
      13.7 KB
  5. RobinP

    RobinP Well-Known Member

    Hi Eric,

    I replied to Kevin's post when you replied so apologies if there was a bit of cross posting.

    As I said in my post to Kevin, I tested peroneus longus but no problems there. I didn't however, test the plantar ligaments so I don't really know but again I did just raise the question in my reply to Kevin.

    With regards to the gait, you are spot on to say that he has a sharp terminal stance pronation - I didn't know that it was commonly seen in patients with a laterally deviated STJ axis. I didn't actually take any notice of whether he was an active pronator. My video footage is only frontal plane from behind and nothing is really visible

    I have actually just looked up his video footage from 12/12 ago which was much closer up and it does look like he is actively pronating at terminal stance. Static stance peroneal activity doesn't ring any bells but I didn't actually look for it specifically.

    There are certainly a couple of things you and kevin have brought up worth testing so i'll keep you updated

    thanks again for your consideration

  6. Robin:

    Could very well be the FDB from your diagram. Try the low dye strapping on while he is standing all day to see if this lessens the pain. Also, you may want to simply have him to use a higher heeled shoe at work (or use a heel lift under his orthosis) since this will likely less the arch flattening moment during standing and possibly reduce his symptoms.
  7. RobinP

    RobinP Well-Known Member

    Just a short update for anyone interested.

    US imaging showed no apparent defect in the FDB, nor in the plantar aponeurosis. Everything else looked competely normal. The practitioner doing the US is an extended scope GP who has been doing imaging for a PHD I believe, so I think this is fairly reliable information. He also had a look at the foot clinically and felt the plantar fascia was a little tighter on the symptomatic side.

    I can't say I picked that up in the examination but I added a considerable arch pad, extending over the symptomatic area and the patient felt considerably better, so perhaps the GP is right? He is symptom free now and as much as I would like a definitive diagnosis, I can't see the patient being too fussed about it in the same way I am so it will probably go no further.

    Many thanks for your help Kevin and Eric
    Last edited: Jan 21, 2011
  8. CraigT

    CraigT Well-Known Member

    I would consider a myofascial trigger point- it fits pretty well with what you have described and would respond similarly...
  9. RobinP

    RobinP Well-Known Member


    Pt presented fairly recently with significant deterioration in symptoms. Retested Tinels' and it was very positive accurately replicating symptoms.

    Referred for MRI and probable decompression

    Thanks folks
  10. pod29

    pod29 Active Member

    Hi Robin

    From your diagram and description, I would have to agree that the pain is more than likely arising from a myofascial trigger point in FDB, as Craig has suggested. Prolonged, excessive mid-stance pronation with delayed heel lift, may create an increase in external dorsiflexion force applied through the midfoot, thus increasing the loading demands on FDB (which creates an external plantarflexion force across the mid-foot). The lack of pain when cycling also make sense, as cycling shoes tend to have a very stiff shank, therefore reducing longitudinal deformation through the midfoot.

    FDB is actually relatively easy to palpate. As Kevin suggests it does lie deep to the plantar aponeurosis, but it is still quite superficial and you with care, should be able to palpate the muscle belly. I find these symptoms are really common in the footballers we treat here, due to the lightweight, flexible boots they are wearing. Clinically I find that these symptoms can actually be agrevated (in the short term) by treatments such as padding and increased MLA height in an orthosis, as they apply too much direct pressure on the painful area. Dry needling of the trigger point should provide almost immediate relief, and as you have ruled out any lesion in the muscle with ultrasound, this should be quite safe.

    As Kevin suggested, low dye taping is very effective as it will apply an external plantarflexion force to the mid-foot, without applying any direct "upward" force on the painful area. If it is a chronic problem, strengthening of the muscle and any other measures to increase mid-foot stiffness (orthoses) should be beneficial once the acute pain has subsided.

    It's also possible that this is due to irritation of the medial plantar nerve. It may be the cause of the problem, or it may just be a secondary consequence of a really angry muscle :mad:.

    I'm interested to hear how he progresses.

  11. pod29

    pod29 Active Member

    Just realised your post was a response to a much earlier one.....

    Sorry ,


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