Helpful information on foot orthoses.
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Previous Foot Orthotic Tips Newsletters:
January 2006: Sesamoiditis
This is an inflammation and swelling of the peri-sesamoid structures. It is generally considered to be an 'overuse' type of problem and is more common in feet with plantarflexed first ray/forefoot valgus and a limited range of motion at the midtarsal joint (cavus feet).
Clinical Features:
- Painful/aching on walking
- Local tenderness to palpation
- May have limitation of first MPJ motion
- May be painful on dorsiflexion against resistance
- May be thickening or inflammation of a bursa on the plantar surface
- X-rays are generally normal.
Differential diagnosis:
- Arthritis (osteoarthritis may occur in the sesamoid articulation)
- Infection (osteomyelitis may occur following a puncture wound)
- Nerve Compression (the digital nerves in the region of the sesamoid may be impinged)
- Bipartite Sesamoids and Fractures
- Stress Fracture
- Osteochondritis (Treve's disease)
- Planter hyperkeratosis
- Flexor Hallucis Longus Tendonitis
- Myofascial pain syndrome (pain referred to sesamoid area from trigger point in intrinsic muscles)
Management:
- Correct diagnosis is crucial (see ddx above).
- Accommodative padding to off load the area
- Treat inflammation - (RICE; Activity modification; NSAID's);
- Low heel shoes
- Physical therapy (strapping to prevent first MPJ dorsiflexion; manipulation/mobilisation of first ray; electrotherapeutic modalities)
- Foot orthosis to offload the medial column and cushion
The Interpod Control Tech soft has the following features to help manage sesamoiditis:
- Shock absorption and cushioning under the forefoot
- Posterior arch support to off load the medial column
- Inverted rearfoot to improve biomechanical function
- A grinder can be used to reduce the thickness under the area of the sesamoids to offload
- Padding can be adhered to the top of the orthoses to offload
If initial attempts at management fail, consider:
- Correct diagnosis
- Rocker sole shoe
- Below knee cast
- Surgery (dorsiflexory wedge osteotomy of the first ray; removal of sesamoid)
October 2005: Facilitating the windlass mechanism:
The windlass mechanism is an important concept in how the foot functions. The plantar aponeurosis attaches to the plantar surface
of the calcaneus and the bases of the proximal phalanx. During gait, when the heel comes of the ground the dorsiflexion of the proximal phalanx 'winds' the
plantar fascia around the head of the first metatarsal - this raises the height of the arch and makes the foot into a stable structures. It is widely believed
that afoot orthoses should, at worst, not interfere with this mechanism and, at best, actually facilitate it function. The follow are ways that foot orthoses
can facilitate the windlass mechanism:
- Invert the heel
- Elevate the lateral forefoot column of the foot
- Use an orthoses with a plantar fascial groove
The Interpod range of prefabricated foot orthoses range have design features that do all three of these, thereby
facilitating the windlass. Prefabricated foot orthoses can be modified to further enhance the windlass mechanism by:
- Reducing the thickness below the first metatarsal head and shaft
- Elevating the thickness under the lateral forefoot column
- Inverting the rearfoot more
- Heel raise
Calf muscle stretching also has an effect on facilitating the windlass mechanism (it powers the force needed for the windlass
mechanism to get established). More on the windlass mechanism
here
July 2005 - Can all orthoses invert the rearfoot?
Research has shown that only foot orthoses that have wedging under the rearfoot can invert the
rearfoot (this also make intuitive sense). It has also been shown that a number of prefabricated foot orthoses that claim to have rearfoot wedging and can invert the rearfoot, do not.
Check the research
here.
Foot orthoses need to invert the rearfoot to overcome the force that is everting or pronating the foot. This force from the orthoses has become known as the supination resistance force.
More on this
here.
The forces that are pronating a foot vary greatly from person to person with an excessively pronated foot.
In some, this force is low and it is easy to overcome with a lot of different foot orthoses.
When this force is high, it is harder and a foot orthoses that is more controlling and more inverted in the rearfoot is needed.
How do you tell how much force is needed? Put two fingers under the medial plantar side of the talonavicular joint and try to supinate the foot.
Do this to lots of patients and you can soon get a feel for what is high and what is low. Use this information as part of the prescription for a foot orthoses - the higher the force, the more rigid and inverted the foot orthoses should be;
the lower the force, the more flexible foot orthoses is suitable.