The world of orthotic therapy and foot biomechanics was somewhat shaken in 2006 when a randomized study found that “customized and prefabricated orthoses used in the trial (had) similar effectiveness in the treatment of plantar fasciitis.”1 Of course, there was a great deal more to this study than the one sentence but it sure stimulated discussion within podiatry and orthopedic surgery concerning the value of custom orthoses in comparison to prefabricated devices.
There are actually four relatively recent trials that compare prefabricated and custom orthoses relative to plantar fasciitis.1-4 It is quite exasperating to experience the huge difference between the successes of custom orthotics versus prefab in clinical practice and then look at the research statistical analysis, which demonstrates a minor difference between the two devices. What could contribute to this dichotomy? Is there a similar positive effect in other pathologies like hallux limitus, over-pronation, adult-acquired flatfoot, neuroma and various sports medicine injuries?
Unfortunately, the studies and data that compare custom foot orthoses (CFOs) to prefabricated foot orthoses (PFOs) are insufficient to draw any legitimate medical conclusion. The research is even more difficult to interpret due to several factors including:
• the variety of casting;
• various imaging and manufacturing techniques for custom orthoses;
• an almost infinite variety of prefabricated devices that are used in these studies; and
• the large selection of materials, shapes and flexibilities of the prefabricated devices.
Accordingly, let us take a closer look at the available literature that evaluates the effect of various prefabricated orthoses on certain foot pathologies. Then we will consider the anecdotal evidence, logical deductions and opinions that might give the clinician some criteria to use when considering the use of prefabricated orthoses. Lastly, we will consider recommendations and opinions in regard to indications, contraindications and desirable characteristics for prefabricated orthoses use, specifically when it comes to plantar fasciitis.
Discussing prefabricated orthoses becomes very complicated because of terminology. What is the difference between an arch support and a prefabricated foot orthosis? Are soft PFOs in the same category and do they have the same indications as semi-rigid devices? How do we separate accommodative PFOs from functional PFO devices?
While an in-depth discussion of soft prefabricated devices is outside of the scope of this article, these soft devices do have a place in patient care, especially when it comes to lowering pressure peaks and helping to avoid potential problems in the diabetic foot. In regard to accommodative versus functional devices, an accommodative PFO is not designed to change the morphology of the weightbearing foot but rather to alter the pressures under the foot without intentionally altering the motion of the foot. A functional device is designed to alter the motion and morphology of the foot by changing either the ground reactive force under the foot or the progression of the center of pressure plot through the foot.
What The Literature Reveals
A study performed at the University of Teesside in England compared the effectiveness and cost of accommodative prefabricated devices to functional prefabricated devices.5 The researchers found the functional semi-rigid prefabricated devices more effective than the soft accommodative PFOs but both were effective to some degree. The authors of the paper intended to consider whether the difference in cost might be important since the more expensive devices were more effective. Interestingly, study participants who wore the less expensive ($12) PFOs had a 69 percent attrition rate from the study, whereas those who wore the more expensive ($45) PFOs had a very low attrition rate in comparison to similar studies. The more expensive device was actually more cost effective.
One of the most interesting studies discussing the effect of PFOs versus CFOs came out of Emory University in 1995.6 The authors used similar definitions of accommodative versus functional orthoses, as noted above, and placed arch supports within the accommodative category. The researchers provided a thorough history and review of the literature of previous studies that compared soft accommodative orthoses to rigid (or semi-rigid) “biomechanical” orthoses. The study evaluated the effect of custom orthoses and prefabricated orthoses in comparison to no orthoses by evaluating maximum pronation, calcaneal eversion and speed of pronation.
The study design was intended to repute a previous podiatry investigation in 1986.7 When the patients wore just a shoe with no orthoses, they had the greatest maximum pronation, maximum pronation velocity and calcaneal eversion. Surprisingly, the maximum pronation velocity was lowest for the PFO and the total pronation was less in the PFO than the CFO. The major advantage of custom orthoses in this study was that it took less time to get to the maximum pronation point and maximum eversion of the heel in comparison to a PFO or just the shoe.
Unfortunately, we do not know which of these parameters, speed of pronation, time to maximum pronation or amount of eversion, is important in reducing symptoms. Current biomechanical thought and literature tell us that the amount of eversion is directly proportionate to the forefoot symptoms and deformity.8 This CFO/PPO comparison study has inconsistencies in the methods researchers used to manufacture the CFO and uses only one of a large family of prefabricated devices. We need to see researchers repeat the study with greater attention to the possible variables than are contained in these two papers.
Another study, performed at the University of Delaware in 2002, assessed the difference in rearfoot motion and comfort between a PFO and a CFO.9 Researchers dispensed two similar devices were to 19 patients. One was a custom device fabricated from a corrected plaster cast and the other was a PFO selected by size and shape by measuring the plaster cast. Both devices were made of the same material. Researchers were blinded to the type of orthoses.
Researchers tested the patients with kinematic methods three separate times: study participants with no device, with a CFO and with a PFO. The study found custom devices only provided slightly more rearfoot control than the PFO but were more comfortable.9 Again, it is important to remember that even a book of matches in the shoe will change kinematic measurements in the rearfoot and these changes may have no relationship to reversing pathology or helping with symptoms.
We know there is a huge variability in methods and materials, and this makes it very difficult to study the difference between CFOs and PFOs. We also know that prefabricated devices do seem to limit pronation and calcaneal eversion almost as much as custom devices. What we do not know is what effect this has on possibly improving the foot function.
A 2000 article from researchers at the University of Western Sydney reviewed most of the medical literature about functional orthoses, both prefab and custom, that used an established research protocol to evaluate the devices.10
A 1987 article, cited in the 2000 review, proved that placing a lateral prefabricated wedge in the shoe reduced medial knee joint pain from osteoarthritis.11 Another article contained in the same review demonstrated that prefabricated wedges that affect calcaneal position and subtalar motion had no effect on neuroma pain.12
Lastly, a 1990 study evaluated foot pain reduction when researchers compared two types of PFO devices made from the same material (6 mm polyethylene).13 Ninety-six percent of the patients treated for foot pain had either total or substantial relief of their symptoms combining the results of both types of devices. However, there was no difference in outcome between using either of the two types of prefab orthoses. This study also had a very small population and there was a huge variation between what we consider custom orthoses in the United States and the CFO they used.
It is obvious that both prefabricated and custom orthoses have an effect on the mechanics of the foot and a positive clinical outcome on patients with foot pain. Currently, no one has conclusively quantified the difference in the effectiveness of PFOs to that of CFOs. We do know that when reduction of foot pain is an evaluation instrument of success, both types of orthoses seem to be effective.
Exploring The Indications And Contraindications For Prefab Devices
Even after reading the available literature on the subject, physicians may still have several questions. There is no debate that PFOs are effective but how effective are they in comparison to custom devices? If one decides to use the less expensive and less sophisticated prefab device, what properties should the prefab have to facilitate the best possible clinical result?
It does seem that prefabricated devices are effective to some degree for knee pain.11 Logically, this seems to make sense since limiting rearfoot motion limits torque on the knee joint since the subtalar joint has a triplane axis.
Prefabricated devices also seem to change the heel position in children with hyperpronation as long as the device has a rearfoot varus component of 5 degrees.14 We do not know if this effect is solely a visual change in the patient’s stance or whether this change corrects or ameliorates pathology in the growing child.
Several previously cited studies demonstrate the effectiveness of prefabricated orthoses in reducing the symptomatology of plantar fasciitis and heel pain related to mechanical dysfunction of the foot. This clinical diagnosis has the most data confirming efficacy but does not necessarily differentiate whether the PFO or the CFO is a better treatment. Perhaps the value of the prefab device to the clinician in heel pain therapy is diagnostic. The use of a PFO is an inexpensive method to determine if the source of the symptoms is mechanical or not. Heel pain has a large number of differential diagnoses (unrelated to foot mechanics) that mimic plantar fasciitis but will not respond to orthoses of any type. If symptoms do not change after mechanical intervention, one must investigate the other diagnoses.
Prefabricated devices also seem to have a prophylactic effect on patients without obvious foot pathology and this information may be highly useful when one considers the reduction in sports medicine injuries, particularly stress fractures. A couple of studies at Hebrew University in Israel showed that dispensing prefabricated orthoses to military recruits reduced the incidence of metatarsal and femoral stress fractures.15,16 The studies evaluated the effectiveness of prefabricated, semi-rigid 3.5 mm polyolefin plastic devices with a 3-degree rearfoot varus post. Interestingly, the device was effective in reducing femoral stress fractures in high arched feet and metatarsal fractures in low arched feet.
There does seem to be sufficient data to demonstrate the professional and ethical use of prefabricated orthoses in the treatment of knee pain secondary to osteoarthritis, pediatric flatfoot and plantar fasciitis. There also appears to be validity in the use of PFOs to aid in diagnosis of the mechanical origin of foot symptoms and pathology, and even in preventing injury in the non-symptomatic foot.
With this review of the medical literature, I only found one contraindication for the use of prefabricated orthoses. This year, researchers used a pre-intervention study design to investigate the effects of a PFO on both ankle inversion and plantar forces and pressures on the fifth metatarsal.17 The study specifically involved basketball players, who are known to be prone to Jones fractures. The study found increased plantar pressures and forces on the fifth metatarsal that may increase the risk for proximal fracture of the fifth metatarsal, a common injury in basketball.
Key Considerations With Prefab Designs
What characteristics or properties do we want from a prefabricated orthotic device? Ideally, a clinician should choose the most appropriate prefab, from the large variety that are available, for the specific pathology he or she is treating.
If the orthotic characteristics are divided into shell material, design, posting, sizing and top cover, it is easier to evaluate the various prefabricated devices on the market. Available shell material ranges from soft and flexible foams to rigid durable hard thermo-formed plastic. Consider the foams as accommodating and we can eliminate most of them as incapable of changing the morphology or the function of the foot. It is very difficult to have an effect on plantar fasciitis if one cannot limit to some degree the motion of the midtarsal joint or raise the arch and plantarflex the first metatarsal.
This leaves a group of plastics called thermosets and thermoforms, better known as graphites and polys. Both materials seem to provide the semi-rigid flexibility desired for foot control as well as the durability necessary to withstand the stresses of walking and running. Polypropylene seems to have one advantage over polyethylene. It is less susceptible to deformation over time. Polypropylene will hold its shape longer in the shoe temperature/pressure environment.
The orthotic design could be the most important criteria since some of the aforementioned literature demonstrated that a change in ground reactive forces and the change in the center of pressure might be directly related to effectiveness. Some PFO devices are designed for comfort and shoe fit but not motion control. The kinematic articles suggest that the medial skive technique, sometimes known as the varus wedge effect, will create greater ground reactive force under the medial side of the orthotic and make any orthotic more effective.18 The inverted cast technique has also been accepted as a method that makes an orthotic more effective in controlling foot motion.19
These two techniques, commonly referred to as the Kirby Skive and Blake Inversion, are already incorporated in some prefabs. Physicians can add the two techniques to a prefab with felt wedges or other materials. Considering durability and longevity issues, finding a device that already has a skive or inversion might be more desirable and easier.
The Root type orthotic device has become a standard in the world of custom orthoses and it has always contained a rearfoot post.20 The intent of this addition was to stabilize the device in the shoe and allow for a slight amount of pre-midstance motion necessary in gait. One paper actually evaluated orthotic devices with and without rearfoot posts, and found that a post increased the effectiveness of the device in comparison to the same semi-rigid device without a post.21 The majority of PFOs do not contain a rearfoot post and this probably allows them to fit in the shoes more easily. Yet some PFOs do contain a rearfoot post and some even contain a 4/4 motion just like a custom Root device.
Although there are no available evaluations of sizing techniques for prefabricated orthoses, logic indicates that the closer the size of the device is to the size of the foot, the more comfortable and effective the device. Sizing choices range from the absurd “one size fits all” to selections that match male and female shoe sizes. Some choices split the difference and offer single devices that fit two shoe sizes. This latter type of selection often requires office modification in length and heel width to provide proper shoe and foot fit.
It is difficult to discuss top covers for PFOs in depth within the scope of this article. A separate discussion on the effectiveness of materials relative to pathology is in order since such little relevant data is available. For now, one must draw upon his or her own experience, anecdotal evidence and preference. Podiatric physicians must also consider shoe gear, pathology, climate, patient weight and dermatologic conditions.
What are the key take-home points from this review of PFOs?
• Semi-rigid functional PFO devices work better than soft accommodative devices.
• Semi-rigid prefabricated devices work as well in the short term for plantar fasciitis in comparison to custom orthoses.
• Semi-rigid prefabricated functional devices do slow foot pronation and limit calcaneal eversion.
• Prefabricated functional devices can reduce the eversion of rearfoot position in children with flexible flat feet.
• Prefabricated functional devices can reduce the knee pain from osteoarthritis.
• Prefabricated devices are an inexpensive tool to determine if foot symptoms are mechanical in origin.
• Semi-rigid prefabricated devices with rearfoot posts are an effective prophylaxis for metatarsal stress fractures in patients with low arches and for femoral stress fractures in active patients with high arches.
• One should not use semi-rigid and rigid prefabricated orthoses to treat basketball athletes.
There is good reason to select a PFO that includes either a medial skive or inverted technique, and selecting a PFO with a rearfoot post improves the anti-pronation performance. Also bear in mind that selecting a more rigid device for plantar fasciitis is more effective than a flexible or soft device.
Although we need more research in this arena, there is sufficient evidence to confirm that using a semi-rigid functional prefab is professionally valid and accepted.