When the best shoe needs to be better

Author: By Steve “The Footman” Manning Founder of intraini  

You have run in your new pair of runners after trying on every shoe in the shop.  Unfortunately, they still do not seem quite right.  Besides despairing what are you going to do?  Shoe modification may be the simple answer.

While the ideal situation is to purchase the right shoe in the first place this is not always possible.  Sometimes the best shoe available needs to be tweaked in order to make it satisfactory.  This is most often the case when the runner has an unusual type of problem that no shoe can accommodate. When there is a major difference between one foot and the other, one shoe of the pair may need modification so both feet can be supported adequately.  

Outsole modifications

The outsole is the area of the shoe least frequently needing modification.  This is because it does not really do much other than offer traction.  Because it is separated from the foot by the midsole it is also hard to perceive what it is doing.

Changes to the outsole most commonly deal with adjusting the configuration of the lugs on the outsole.  If some lugs stick out more than others it can cause excessive pressure under those areas.  This is commonly found under the forefoot.  It is usually a simple matter of grinding these lugs down to the same level.

Additions can also be made to the outsole to change the path of motion during the gait cycle. Gait plates can be used in the forefoot to treat intoeing or outoeing by making it harder to toe off in the wrong position.  Additions to the midfoot can make the heel to toe transition smoother by creating a Rocker Sole.  The heel may need additions to reduce the amount of wedging that exists particularly in worn out shoes.  The outsole can be replaced with a softer material to increase traction on flat surfaces.  It can also be replaced with a harder material to reduce traction in areas where movement against the ground is needed.  Shoe Goo is a cheap way to make minor outsole modifications.

Midsole modifications

The midsole is the most important part of the shoe to modify if you want to get a major change in function.  Because of its thickness there is a greater scope to make multiple types of modifications.  The type and extent of modification is dependent on the severity of the condition. The big problem

with current midsoles is the presence of extra cushioning compounds like gel and air pads, which complicate modifications.

The most common shoe modification is for leg length discrepancy.  If the difference in leg length is greater than 2cm then it will usually require the addition of more EVA to the midsole on one foot.  This is done by removing the outsole with heat, gluing on the extra EVA and then gluing the outsole back on.  This is becoming more difficult as the outsoles become more complex, coming in more than one unit.  Because running involves propulsion from the toes the lift should be full length rather than just in the heels.

Heel Lifts can be used for ankle equinus (reduced ankle range of motion) or shortened calf muscles.  In this case the midsole can be split, and a wedge added to the back.  The midsole can also have a wedge added or removed to the inside or outside of the heel to increase the tilt at the rearfoot.  This is called a varus or valgus wedge and is similar in idea to the dual density midsoles that offer more support on the medial (inside) of the shoe.

Another problem with some current shoes is the flaring of the posterior or lateral heel.  This flare of midsole can stick out and cause premature strike and excessive velocity of pronation or plantarflexion.  The result is overpronation and slapping because the leg muscles are not strong enough to slow the movement of the foot.  This can usually be fixed by grinding off the flare as long as the additional cushioning compound is not compromised.

In rare occasions stability may have to be reduced by removing bars and pillars that are causing aggravation.  It is more difficult to increase stability, but it can be done by adding plastics or EVA to appropriate locations.

The arch in contemporary shoes is part of the midsole rather than the insole.  As midsole EVA is less soft this can cause blistering when there is a poor match between the shape of the runner’s arch and the shape of the arch in the shoe.  The reduction of arch height is the most frequent shoe modification that I do and also the most successful.

Rocker soles can be created by adding material to the midsole as well as the outsole.

Softer and harder EVA wedges can be added to different parts of the midsole to change foot function and to change the path of the foot during the gait cycle.  The best known of these is the kinetic wedge.  This is discussed in the case study.

Upper modifications

Upper modification is usually to do with making the shoe fit better but can sometimes affect the support of the shoe as well.

Support Strapping may need to be removed in order to accommodate bunions and toe deformities.  There is a current trend to use support straps on the top of the forefoot.  These straps will often press down onto the toes during propulsion.  There is little functional need for these straps as they are really to make the shoe look nicer and more streamlined.  Removing them has little effect on function but improves comfort greatly.

The Heel Tab can also dig into the achilles tendon or the ankle bones.  A simple cut can relieve the pressure and it will rarely tear any further.

The Tongue has the role of padding the top of the foot from pressure from the laces.  Problems are usually from it being too thin or too thick or sometimes because it is reinforced with harder materials so the logo will stand out more.  Occasionally the whole tongue can be removed but usually reduction will be sufficient.  Triathletes in particular have problems with the tongue because they race without socks.

Lace eyelets can also dig into the top of the foot.  It is more difficult to modify them because the forces of the laces need the strength.  It is usually better to remove the offending material and no longer use that eyelet.  This may have an affect on the support and fit of the shoe.  Eyelets can also be added to grip the heel better.

For people with asymmetrical reduction in the length, width or depth of the foot, shoe fillers can be added to make up the space.  This is often done with inserts to make a narrow heel fit better but is also effective in other places inside the shoe.

Insole modifications

Orthotics are a form of insole modification.  They can entirely replace the insole in many cases.  More minor adjustments can be made directly to the insole by adding felt to the surface.  Arches can be raised, minor deformities accommodated, and function changed even with small additions to the insole.  Often these modifications are temporary to see if orthotic treatment will be successful.  Adding a thicker insole on top of the existing one can fill out shoes.  The thing to remember is that the insole is not for any cushioning but rather is there to customize the shoe to the foot.  Stiffer and harder modifications will not reduce the overall cushioning of the shoe.

How to decide if a modification is necessary

Some shoes need to be replaced rather than modified.  There is no sense in making modifications to a shoe that is too old or worn out.  Modifications become necessary if there are minor aggravating issues with a new pair of shoes that can be fixed simply without throwing out the shoes.  They are also needed to accommodate deformities due to trauma, surgery or poor genetics.  Modifications can range in scope from simple adjustments to the uppers, outsole, insole or midsole, to major changes to the structure and function of the shoe.  At some stage modification to the shoe will not be enough 

and a custom made orthopedic shoe may be required.  Shoe modification is a service often overlooked by the sports medicine practitioner. It can be highly effective in dealing with recalcitrant cases that will not get better despite the use of a variety of treatments including orthotics.

Case Study: The kinetic wedge

Back in the 1980s, Brooks brought out a top of the range shoe that incorporated a new device called the kinetic wedge.  The theory was that a softer material under the first metatarsal-phalangeal (big toe) joint would allow the joint to work more effectively reducing injury and improving performance.  The shoe was very popular but not long after it’s introduction there were a spate of injuries that seemed to be linked to the shoe.  The problem was that while the shoe was ideal for people with problems at that joint it caused problems for the majority of runners.  This was basically a feature that had its place but was over-utilised due to the shoe’s popularity.  Unfortunately, it received such a bad reputation amongst runners and sports medicine practitioners that it was never again used in a shoe.

Runners with a plantar flexed first ray where the big toe joint is in a lower position than the other toe joints may require a greater change in support then is possible to achieve with an orthotic within a running shoe.  There may be pain under the metatarsal heads themselves or even in the sesamoids due to the increased ground reaction force.  Sometimes these runners will have reduced range of motion at this joint because there is so much pressure.  In this instance they have to change the way that they run in order to toe off properly.  This change in the running gait leads to other injuries and problems.  To make the modification, midsole material is removed and replaced by softer low-density foam.  Rather than to improve cushioning it is designed to let the midsole depress under the big toe joint and work more functionally.

The picture was a case where there was reduced range of motion at the rearfoot that was also in varus (tilted out).  The first metatarsal and big toe was plantarflexed or lower then the other toe joints.  Because of the general inflexibility there was little ability to compensate for the position of the big toe.  This caused them to externally rotate the leg and roll off the side of the foot.  Various orthotic treatments proved unsatisfactory.  With the kinetic wedge they were able to run straighter without pain and without knocking their knees.


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