A Guide To Offloading The Diabetic Foot

   Increased plantar foot pressure is a leading cause of ulceration in the diabetic population.1 Healing these ulcers requires adequate blood supply, control of infection, excellent wound care and offloading or pressure redistribution of the ulcerative area.2-16 Out of all these factors, offloading presents a particularly unique challenge in treating chronic wounds. As diabetic foot care has evolved over the years, podiatrists have used numerous approaches including complete bed rest, cutout felt pads and total contact casting to offload these wounds.3,15,17    However, in order to select an appropriate offloading modality, it is important to be aware of the potential causes of increased plantar pressure in the diabetic foot.    Ground reactive forces (GRF) impact the plantar foot during weightbearing activities in all ambulatory individuals. The difference in response for diabetic versus non-diabetic individuals is our primary concern as limb salvage specialists. Ground reactive forces can be perpendicular to the foot (known as vertical stress) or they can work parallel to the foot (known as shear stress). When these forces work together in a repetitive fashion, ulcers may form on the plantar foot in people with diabetes due to the inability to appreciate the increased stress on the foot.18    When people stand, each foot takes on 50 percent of the body weight. However, when people walk, they transfer all of the body weight from one foot to the other.19 During the stance phase of the gait cycle, the entire foot is only on the ground (foot flat) 23 percent of the time.20,21 The heel is in contact with the ground the first 64 percent of the phase while the forefoot is in contact the last 59 percent of the phase. This means all of the body weight is on one heel or one forefoot a significant period of time. This pressure can equal 1.2 to 1.5 times the body weight depending on the walking speed.19    When a deformity is present, there is increased pressure on the foot. Researchers have shown that diabetes causes a decrease in conduction speed in the tibial and peroneal nerves.22 This correlates to increased lower extremity muscle weakness.22 Muscle weakness may lead to foot deformity and subsequently cause areas of increased pressure.    Greenman, et. al., have shown that small muscle atrophy occurs in the diabetic foot before clinical peripheral neuropathy is detected.23 Using MRI to look at the cross-sectional anatomy of the foot, they compared the muscle area to total area in non-diabetic controls, diabetic patients without sensory neuropathy and diabetic patients with sensory neuropathy.    The diabetic group with no sensory neuropathy developed muscle atrophy before clinical sensory loss. Therefore, structural changes may occur with this early muscle weakness before protective sensation becomes diminished. This muscle atrophy may lead to increased plantar foot pressure even in the “low-risk,” sensate diabetic foot. When coupled with the insensate foot, increased pressure patterns typically lead to foot ulceration.

Emphasizing The Initial Approaches And Goals Of Offloading

   In regard to offloading, we intuitively place something on the foot such as padding or devices. However, the first and most important offloading technique is actually taking something off the skin.4 Debriding the hyperkeratotic skin surrounding the wound edge is the first aspect of offloading that one should address. When left untreated, the thick and callused edges of a wound will roll inward and inhibit the wound edges from migrating towards the center. This hyperkeratotic edge may also cause increased plantar pressure. Based upon Dr. Paul Brand’s work that demonstrated the greatest amount of pressure placed on a foot ulcer is at the leading edge, Armstrong and Athanasiou later coined the term “edge effect.”18    One might think the greatest pressure would be in the center of the wound but many plantar ulcers have such significant depth that the weightbearing forces do not affect the center of the wound. Due to the natural offloading of the central wound cavity, plantar foot pressures intensify at the leading edge of the wound. This is why many plantar foot ulcers need weekly, or at least frequent, debridement for offloading purposes.    The same effect can occur when attempting to offload a plantar ulcer with a simple cutout pad or aperture pad. Simply stated, decreasing the weight in any one area of the foot will necessarily increase it on another part of the foot. The gold, or old, standard of wound accommodation by padding has been implicated in creating its own edge effect.18 Classically in our training, we were instructed to place prefabricated or customized pads at the edge of wounds to “facilitate” healing. However, these pads actually increase the pressure on the fragile skin surrounding a plantar foot ulcer and may actually cause the ulcer to increase in size or, at the very least, remain unchanged in size.18    Podiatrists should offload the plantar foot ulcer by employing devices that encompass the entire foot with total contact pressure relief. Balancing the forces on the plantar foot is the goal of total contact pressure relief. By redistributing the forces, one will offload the ulcerative site. Keep in mind that total contact pressure relief does not necessarily mean total contact casting as many devices can redistribute plantar foot pressure.    Gait modification offers another simple means of offloading the foot. A reduction in walking speed or shuffling-type gait can reduce the pressure on the forefoot.19 Unfortunately, it is sometimes difficult for patients to change their walking patterns abruptly. Physical medicine can be helpful in retraining patients in gait when needed. It is the senior author’s position that we should make all attempts to keep our patients ambulatory with the exception being cases of the most unresponsive wounds. Continued ambulation can reduce other morbidity. Also be aware that frequently when a wound heals and patients begin walking again or participating in normal activities, ulcerations will reoccur. It is possible to provide all the necessary elements for wound healing while keeping our patients ambulatory.    The goal of any offloading modality should be redistributing plantar pressure from one specific location to a broad area encompassing the entire plantar foot. As we mentioned earlier, the “edge effect” results in tissue damage from both shearing and vertical stress.18 Therefore, effective offloading must take both of these destructive forces into account.

A Closer Look At Total Contact Casting

   Total contact casting has long been viewed as the ideal vehicle for facilitating redistribution of the weightbearing load. However, when utilizing other offloading modalities, all practitioners should strive for total contact pressure relief.    Total contact casts (TCCs) are considered the gold standard for offloading plantar neuropathic ulcers.5 While there are many variations in the application of TCCs, the general concept is a below knee cast that conforms to the patient’s anatomical contours with little padding. The intimate fit of the cast material to the plantar surface of the foot increases the plantar weightbearing surface area. This helps distribute the plantar pressure from one or two distinct areas to the plantar foot as a whole.    There are many benefits to TCCs. These benefits include protection from trauma, limitation of edema, pressure reduction at the site of ulcers and immobilization of the wound edges.6 However, many physicians believe the best feature of the TCC is the inability of the patient to remove the device.    The literature is full of support for using TCCs to treat neuropathic plantar ulcers. Myerson, et. al., used TCCs on 71 Wagner Grade I or II plantar ulcers. Ninety percent of the ulcers healed at a mean duration of 5.5 weeks.7 Nabuurs-Franssen, et. al., reported an 88 percent healing rate with a median number of three cast applications.8 Armstrong, et. al., reported similar results, with 89.5 percent of patients healing within 12 weeks.5    Some would argue that it is a bad idea to fully enclose an open wound with a TCC. Wukich prospectively evaluated the complication rate of 13 patients with neuropathic ulcers placed in TCCs.9 There were 14 minor complications out of 82 total casts applied with all but one being new pressure ulcers. The study found no major complications requiring the cessation of casting and there was an 83 percent healing rate at a mean of 5.2 weeks.9    While most studies report low rates of complications, TCCs are not without contraindications. One should not use TCCs in patients with deep abscess, gangrene, osteomyelitis, chronic venous stasis ulcers or severe peripheral arterial disease with an ABI of < 0.45. Use them with caution in patients who have an unsteady gait and in noncompliant patients who routinely miss scheduled appointments.6 In order to avoid new skin breakdown and ensure patient safety, an experienced cast technician or physician should apply the TCC.

Can Removable Cast Walkers Expedite Wound Healing?

   Removable cast walkers (RCWs) have become increasingly popular in the treatment of neuropathic ulcers. Many practitioners laud the easy application of the device, the ability to continue daily wound care and the potential use for patients with infected ulcerations.10 However, the ability of the non-compliant patient to remove the device is a significant deterrent for other practitioners. This problem has led to the development of the “instant TCC,” which is a RCW with a few layers of plaster, fiberglass or cohesive bandage to discourage removal of the device.11    Removable cast walkers are hypothesized to decrease forefoot plantar pressure by keeping the ankle at 90 degrees and subsequently limiting propulsion. Lavery, et. al., compared four different brands of available RCWs and assessed their ability to decrease dynamic foot pressure.12 They found the Active Off-Loading Walker exhibited the lowest mean peak pressure of the four brands, followed by the Pneumatic Walker, the Three D Dura-Stepper and the CAM Walker respectively. The researchers also found no significant difference in peak pressure between the Active Off-Loading Walker and TCC.    In separate study by Fleschli, et. al., the Active Off-Loading Walker also had the lowest mean peak pressure measurement under the metatarsal heads of all tested offloading devices including the TCC.13    Still, it is not certain if this decrease in measured plantar pressure results in clinically accelerated wound healing. Armstrong, et. al., followed 63 patients with plantar ulcers for a period of 12 weeks.5 All patients were randomized to one of three groups: TCC, RCW or half shoe. At the end of the 12-week period, 89.5 percent of patients in the TCC had healed their wound. Only 65 percent of the patients in the RCW healed after 12 weeks.    Alternatively, one may want to consider the DH Shoe, which is similar to the Active Off-Loading Walker in that the one-half inch pressure relief insert is identical. The senior author uses this shoe frequently as an intermediary solution between a walking cast and other shoe modalities. Some patients are not able to tolerate a walking cast for several reasons. The DH shoe provides good pressure relief while allowing continued weightbearing. To our knowledge, there is currently no research that evaluates the effectiveness of this shoe in comparison to the Active Off-Loading Walker. However, in our center, we have seen similar results with the shoe.

What Advantages Do Half Shoes Offer?

   Podiatrists have long utilized half shoes to reduce pressure postoperatively following forefoot surgery. The design of the shoe consists of a wedged sole that ends proximal to the level of the metatarsal heads. Theoretically, this shoe dissipates ground-reactive forces on the forefoot by eliminating propulsive gait.    Many wound care specialists place patients with plantar forefoot ulcers in half shoes for the aforementioned reason. Fleischli, et. al., did show a decrease in mean peak pressure for ulcers plantar to the metatarsal heads of patients in half shoes versus those who used felted foam and postoperative shoes.13 However, when the researchers compared half shoes with TCCs and RCWs, half shoes finished last in reducing plantar pressure. In another study, Armstrong, et. al., found that half shoes had a significantly poorer rate of wound healing at 12 weeks, in comparison to the TCC and RCW.5    Armstrong, et. al., also found that patients with half shoes exhibited a significant increase in the amount of daily activity in comparison to those treated with TCC.5 One should take care to evaluate patients for lower extremity weakness or instability as fall precautions when using this modality.

What The Research Reveals About Therapeutic Footwear

   Frequently, patients will wear extra-depth, extra-wide shoes after the successful healing of a neuropathic ulcer in an attempt to prevent re-ulceration. However, Reiber, et. al., showed this may not be as beneficial as previously believed.14 They conducted a randomized clinical trial involving 400 patients with a history of ulceration. The patients in the study were randomized into three groups: those wearing therapeutic shoes and customized insoles, those wearing therapeutic shoes and prefabricated insoles, and a control group wearing their own footwear. After two years, there was no significant difference in the reulceration rate between the three groups.    Extra-depth shoes have also performed poorly in trials evaluating the reduction of plantar pressures. Lavery, et. al., examined the dynamic foot pressures of multiple devices as quantified by an in-shoe measurement device.12 The mean peak pressure under the first metatarsal head was 5.5 times greater for the extra-depth shoe than it was with the TCC. In fact, the extra-depth shoe finished sixth out of seven modalities in reducing plantar pressures, beating only a canvas oxford tennis shoe.    We are not suggesting that clinician should keep all of these patients in RCWs permanently. Further research is needed to determine the failure of shoes to prevent reulcerations. Certainly, patient compliance might be one of the reasons behind these results. Another possibility is the requisite thickness of materials for pressure relief based upon an individual’s body mass.    It should be stressed that appropriate footwear is very important in the prevention of pre-ulcerative skin and active ulcers. Any practitioner would be doing her patients with diabetes a disservice if he or she did not examine their footwear during each office visit. However, in the case of open ulceration, there are much better options for providing the patient with total contact pressure relief.

What You Should Know About Insoles And Custom Devices

   There are a variety of materials available for use as accommodative insoles for patients with diabetes. Typically, these insoles are a multi-layered design based on a positive model of the patient’s foot.15 When initially placing plastazote in a shoe, there are a few important points to remember. One should re-examine the insert at each subsequent visit. It is not uncommon for one-quarter inch plastazote inserts to become flat and ineffective in a short period of time.    We usually recommend starting with one-half inch plastazote/PPT or equivalent materials for larger, overweight diabetic patients. This thickness can present a problem in wearing normal depth toe-boxes so it is important to gauge the need for extra-depth shoes. When prescribing thick inserts, examine the foot for new areas of increased rubbing or pressure, especially the dorsal aspects of the lesser digits.    The senior author has developed a “pinch test” for inserts to determine if they are worn out or adequate. Placing an insert between the thumb and index figure, and compressing them together should not yield bone on bone contact of the distal phalanges in one’s fingers. When performing this test, keep in mind that any insert that does not have at least some minimal sponginess is not adequate. To our knowledge, no study has been conducted to determine the appropriate thicknesses of inserts for different body masses.    Frykberg, et. al., conducted one of the only studies measuring the plantar pressures of patients wearing insoles.16 They used a rocker insole design consisting of an anterior wedge of cell foam extended just proximal to the metatarsal heads. The maximum decrease in peak pressure was present when they combined a rocker insole with a postoperative boot.    Multiple factors can make pressure relief a difficult task. A good working relationship with the local pedorthist is ideal for those tough cases. Large bony prominences, gross peripheral edema, previous amputation, wound location and wound care all play important parts in the decision making process for offloading. No one device will ever be adequate for all patients. Keeping this in mind (and also having a good imagination) will enable DPMs to utilize the tenets of total contact pressure relief when ordering custom offloading orthoses.

In Conclusion

   Evidence-based medicine has demonstrated that total contact casting is the best method to offload the plantar foot while keeping a patient ambulatory. Unfortunately, one cannot extrapolate these results to pressure relief shoegear once wounds are healed. More research is needed to examine what thickness of material is necessary to adequately redistribute plantar pressures based upon body mass.    Assuming patient compliance is not a factor, we need to make a more concerted effort to provide preventive care for our patients. Just ordering a diabetic shoe and insert is no longer good enough to satisfy the need to offload the insensate foot. Accordingly, we must be diligent in checking shoes and insoles as a part of our regular at-risk foot care visits. Dr. Claxton is in private practice in Belleville, Ill. Dr. Martin is a second-year resident at Forest Park Hospital, St. Louis, Mo. Dr. Oldani is a second-year resident at Forest Park Hospital, St. Louis, Mo. References 1. Brand PW. The diabetic foot. In: Ellenberg M, Rifkin H, eds. Diabetes mellitus, theory and practice. 3d ed. New York; Medical Examination Publishing, pp803-28, 1983. 2. Steed DL, Donohoe D, Webster MW, Lindsley L. Effect of extensive debridement and treatment on the healing of diabetic foot ulcers: diabetic ulcer study group. J Am Coll Surg 183:61-4, 1996. 3. American Diabetes Association. Consensus development conference on diabetic foot wound care. Diabetes Care 22:1354-60, 1999. 4. Armstrong DG, Lavery LA, Nixon BP, Boulton AJM. It’s not what you put on, but what you take off: Techniques for debriding and offloading the diabetic foot wound. Clin Inf Dis 39:S92-9, 2004. 5. Armstrong DG, Nguyen HC, Lavery LA et al. Off-loading the diabetic foot wound: a randomized clinical trial. Diabetes Care 24(6):1019-21, 2001. 6. Dhawan S, Conti SF. Use of total contact casting in the diabetic foot. Foot Ankle Clin 2(1):115-36, 1997. 7. Myerson M, Papa J, Eaton K, Wilson K. The total-contact cast for management of neuropathic plantar ulceration of the foot. JBJS 74-A(2):261-9, 1992. 8. Nabuurs-Franssen MH, Huijberts MSP, Sleegers R, Schaper NC. Casting of recurrent diabetic foot ulcers. Diabetes Care 28(6):1493-4, 2005. 9. Wukich DK, Motko J. Safety of total contact casting in high-risk patients with neuropathic foot ulcers. Foot Ankle Int 25(8):556-60. 10. Armstrong DG, Lavery LA. Evidence-based options for off-loading diabetic wounds. Clin Pod Med Surg 15(1):95-103, 1998. 11. Lipsky BA, van Baal JG, Harding KG. Diabetic foot infection: epidemiology, pathophysiology, diagnosis, treatment and prevention. Clin Inf Dis 39 S71-139, 2004. 12. Lavery LA, Vela SA, Lavery DC, Quebedeaux TL. Reducing dynamic foot pressures in high-risk diabetic subjects with foot ulcerations: a comparison of treatments. Diabetes Care 19(8):818-21, 1996. 13. Fleischli JG, Lavery LA, Vela SA, et al. Comparison of strategies for reducing pressure at the site of neuropathic ulcers. JAPMA 87(10):466-72, 1997. 14. Reiber GE, Smith DG, Wallace C, et al. Effect of therapeutic footwear on foot re-ulceration in patients with diabetes: a randomized control trial. JAMA 287(19):2552-8, 2002. 15. Pinzur MS, Dart HC. Pedorthic management of the diabetic foot. Foot Ankle Clin 6(2):205-14, 2001. 16. Frykberg RG, Bailey LF, Matz A, et al. Offloading properties of a rocker insole: a preliminary study. JAPMA 92(1):48-52, 2002. 17. Armstrong DG, Liswood PL, Todd WF. Potential risks of accommodative padding of neuropathic ulcerations. Ostomy Wound Management 41:44-9, 1995. 18. Armstrong DG, Athanasiou KA. The edge effect: how and why wounds grow in size and depth. Clin Pod Med Surg 15(1):105-108, 1998. 19. Van Deursen, R. Mechanical loading and off-loading of the plantar surface of the diabetic foot. Clin Inf Dis 39:S87-91, 2004. 20. Root ML, Orien WP, Weed JH. Normal and abnormal function of the foot. Clinical Biomechanics Corp. Los Angeles, 1977. 21. Blanc Y, Balmer C, et al. Temporal parameters and patterns of the foot roll over during walking: normative data for healthy adults. Gait and Posture 10:97-108, 1999. 22. Van Schie CHM, Vermigli C, Carrington AL, Boulton AJM. Muscle weakness and foot deformities in diabetes. Diabetes Care 27(7):1668-73, 2004. 23. Greenman RL, Khaodhiar L, Lima C, et al. Foot small muscle atrophy is present before the detection of clinical neuropathy. Diabetes Care 28(6):1425-30, 2005.
 

References:

CE Exam #134 Choose the single best response to each question listed below. 1. During the stance phase of the gait cycle, the entire foot is only on the ground __ percent of the time. a) 23 b) 32 c) 54 d) None of the above 2. What is the first aspect of offloading one should address with diabetic foot wounds? a) Applying a total contact cast b) Having the patient wear a removable cast walker c) Debriding the hyperkeratotic skin surrounding the wound edge d) Gait modification 3. Many plantar foot ulcers need _______ debridement for offloading purposes. a) Weekly or at least frequent b) Daily c) Monthly d) None of the above 4. The goal of any offloading modality should be to … a) Redistribute plantar pressure away from the heel b) Redistribute plantar pressure to a specific location c) Redistribute plantar pressure from one specific location to a broad area encompassing the entire plantar foot d) None of the above 5. What is considered the gold standard for offloading plantar neuropathic ulcers? a) Removable cast walker b) Half shoes c) Therapeutic footwear d) Total contact cast 6. The total contact cast (TCC) offers many benefits including … a) An indication for use in patients with chronic venous stasis ulcers b) Easy removal by patients for bathing c) Immobilization of the wound edges d) All of the above 7. Removable cast walkers (RCWs)… a) Are reserved only for non-compliant patients with neuropathic ulcers b) Have been lauded for easy application and the ability to continue daily wound care c) Have performed poorly when compared to the half shoe in studies assessing the ability of offloading modalities to reduce plantar pressure d) None of the above 8. In separate studies by Fleischli, et. al., and Armstrong, et. al., which of the following modalities finished last in reducing plantar pressure and had a significantly poorer rate of healing plantar forefoot ulcers at 12 weeks? a) TCCs b) RCWs c) Half shoes d) None of the above 9. In one trial by Lavery, et. al., which modality finished sixth out of seven modalities in reducing plantar pressures? a) Instant TCC b) Half shoes c) RCW d) Extra-depth shoe 10. Which of the following statements is true about the authors’ “pinch test” for inserts? a) One may use this test to determine if inserts are worn out or adequate. b) Placing an insert between the thumb and index finger and compressing them together should yield bone on bone contact of the distal phalanges in one’s fingers. c) Any insert that does not have at least minimal sponginess is adequate. d) All of the above. Instructions for Submitting Exams Fill out the enclosed card that appears on the following page or fax the form to NACCME at (610) 560-0502. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam. Responses will be accepted up to 12 months from the publication date.