The Effectiveness of an Accommodative Dressing in Offloading Pressure Over Areas of Previous Metatarsal Head Ulceration

Introduction Plantar ulceration is a common complication of diabetes and other neuropathic conditions. Nearly 15 percent of individuals with diabetes will develop foot ulceration.[1] Faulty foot ulcer healing is considered a major cause of diabetes-related lower-extremity amputations.[2] Sensory loss and foot stress (pressure) are the primary causes of plantar ulceration.[3,4] In the absence of a protective level of sensation, repetitive walking stress leads to foot injury, ulceration, and faulty healing.[5–7] Plantar ulcerations develop at areas of highest foot pressure and are most commonly found over the bony areas of the forefoot.[3,8,9] The effective reduction of pressure (offloading) is essential in the healing of plantar ulcers.[10] Individuals with insensate feet frequently have difficulty adhering to offloading recommendations because they lack the pain feedback essential to drive protective behavior changes. The contact cast has been found to be the most effective method in healing foot ulcers.[11–13] The cast is effective because it provides custom offloading to the ulcer area, imposes continuous offloading, reduces edema, and limits patient activity. While considered the gold standard, the cast is not widely used because of the skills required for application and concern about secondary skin lesions. As a result of these concerns, a variety of alternative offloading methods have been recommended.[14–17] Short leg walker boots, surgical shoes, surgical shoes with wedged soles, and accommodative felt and/or foam dressings have been found to be useful in a variety of multidisciplinary settings because they are relatively simple to apply. Short leg walkers are rigid removable plastic walking boots that have soft foot beds and rocker soles. Walkers have been found to be as effective as a cast in reducing pressure[18,19] but not as effective as a contact cast in ulcer healing.[12] Surgical shoes with soft foot beds have been used to accommodate the fit of wound dressings and provide pressure relief in the ulcerated foot. A surgical shoe has been found to reduce foot pressure when compared to a standard shoe.[20,21] A wedged-sole surgical shoe was found to be more effective than a surgical shoe in reducing forefoot pressure[18] and has been shown to promote foot ulcer healing.[22] The wedged-sole surgical shoe has been found to be less effective than the cast and the short leg walker in ulcer healing.[12] The wedged sole of these shoes is placed proximal to the metatarsal area to promote weight bearing on the rearfoot. Accommodative dressings are made from felt and/or foam materials and are designed to provide customized offloading over an ulcerated area of foot.[16,17] Offloading is obtained by cutting a hole in the material under the area of ulceration. These pads are attached to the foot by tape, cement, or adhesive backing (depending on the material used) and are generally worn in combination with a surgical shoe. An adhesive felt accommodative dressing placed over the entire forefoot and worn in a wedged-soled surgical shoe was found to be an effective method of promoting forefoot ulcer healing.[23] A felt and foam accommodative dressing applied over and proximal to the ulcer and taped to the foot was found to be more effective than a surgical shoe alone but less effective than a cast, short leg walker, or half-shoe in reducing pressure.[18] An accommodative dressing attached over the entire forefoot may be more effective in offloading pressure and promoting healing than one placed directly over and proximal to the ulcer area. Purpose This study compared the effectiveness of an adhesive felt accommodative dressing (placed over the entire forefoot) with a short leg walker, a surgical shoe, and a wedged-sole surgical shoe in reducing walking pressure over the area of previous metatarsal head ulceration in individuals with neuropathic feet. Methods Twelve volunteer subjects (eight men and four women, mean age 54.25 ± 13.9 years) who had a history of neuropathic metatarsal head (MTH) ulceration participated in the study. Subjects had previous ulcerations over the first MTH (3), third MTH (1), fourth MTH (2), and fifth MTH (6). Eleven subjects were diagnosed with diabetes mellitus (mean duration 19.7 ± 8.6 years), and one subject was diagnosed with an idiopathic polyneuropathy of unknown duration. Individuals with histories of foot amputation or surgical debridement of underlying bone were excluded from the study. Subjects did not have current ulcerations or gait instabilities. The F-Scan system (Tekscan, Inc., Boston, Massachusetts) was used to measure in-shoe walking pressure. Pressure sensors were 1mm thick and had a resolution of 3.9 sensels/cm2. F-Scan computer software was used to graphically display pressure distributions during walking and measure peak pressure and the force-time integral over the previously ulcerated area. Data was recorded at a sampling rate of 50hertz. The F-Scan system has been shown to provide good reliability for measuring in-shoe pressure during walking trials.[24] Sensors were trimmed to fit the shape of the foot, held to the foot by a thin sock, attached to a transducer on the subject’s leg, and connected to a computer via a 30-foot long cable. Sensors were calibrated on each subject prior to the walking trials. This study used a repeated-measures design with the order of treatments randomly assigned. Each subject participated in all trials and served as their own controls. Subjects provided informed consent and the study was approved by the Louisiana State University Health Sciences Center Institutional Review Board. Prior to testing, each subject’s feet were assessed for foot injuries, and heavy plantar calluses were trimmed. The subjects performed practice walks in each of the treatment footwear and were given instructions to walk consistently at their self-selected paces. After sensor calibration, subjects walked 30 feet during two trials in each footwear treatment condition. Measurements of pressure were recorded using a midgait method for footwear conditions and using a two-step method for barefoot conditions. Both the midgait and two-step methods have been shown to be reliable methods for measuring foot pressure but only one method should be used for repeated assessments.[25] The two-step method was used for barefoot comparisons to minimize the risk of injury to the previously ulcerated foot. In both the two-step and midgait methods, subjects practiced walking/stepping at their normal paces prior to testing. It is expected that the two-step method would underestimate foot pressure compared to the midgait method. Therefore, comparisons using statistical analysis were not made between the barefoot and footwear conditions because of the difference in the method used in measuring pressure. The six treatment conditions included 1) barefoot; 2) barefoot with an accommodative dressing; 3) the accommodative dressing and a surgical shoe (Medical Surgical Shoe™, Darco International, Huntington, West Virginia); 4) the accommodative dressing and a surgical shoe with a wedged sole (OrthoWedge™ Healing Shoe, Darco International); 5) the wedged-sole surgical shoe alone (OrthoWedge); and 6) a short leg walker (Pacesetter II, Carapace, Tulsa, Oklahoma) (Figure 1). The accommodative dressing consisted of a six-inch long and quarter-inch–thick adhesive piece of felt (AliMed, Inc., Dedham, Massachusetts) and was cut to fit the shape of the forefoot and a cut-out was made to provide relief over the previously ulcerated metatarsal area of interest. Skin wipes (Skin-Prep®, Smith & Nephew Inc., Largo, Florida) were applied and allowed to dry before application. The pad was place over the entire forefoot (proximal and distal to the ulcer), carefully matching the relief to the previously ulcerated area (Figure 2). The sensor and a thin sock were placed over the dressing. In the third condition, the accommodative dressing was worn with the surgical shoe, which had a firm sole, a quarter-inch–thick soft foam footbed, and Velcro strap closures. In the fourth condition, an accommodative dressing was worn with the wedged-sole surgical shoe. The wedged-sole surgical shoe had a quarter-inch–thick soft foam foot-bed and Velcro closures similar to the surgical shoe but additionally had a negative wedge sole. The wedge sole was proximal to the metatarsal heads and placed the foot in a slightly dorsiflexed position, which promoted weight bearing on the rearfoot. In the fifth condition, subjects walked in the wedged-sole surgical shoe alone. In the sixth condition, the subjects walked in the short leg walker. The walker had a fixed ankle, a quarter-inch–thick soft foam foot-bed, a rigid rocker bottom, and was secured to the foot and leg with soft foam closure and Velcro straps. Mean peak pressure and the force-time integral were recorded from a total of 10 steps (five steps x two trials) for footwear conditions and two steps (one step x two trials) for barefoot conditions. A one-way analysis of variance for repeated measures and a Duncan’s multiple comparisons test (p