On the design and evaluation of adjustable footwear for the prevention of diabetic foot ulcers

Worldwide there are over 422 million people with diabetes. Up to 34% of them will develop a diabetic foot ulcer. These ulcers are extremely dangerous and can result in amputation of the affected leg. Elevated pressures at the plantar surface of the foot are a major cause of diabetic foot ulcerations. Diabetic foot ulcers can be prevented by reducing plantar pressures that are too high. Special footwear such as custom-made insoles and rocker profile shoes are commonly used to reduce plantar pressure. However, the design of this footwear is mainly based on the experience of the prescribing specialist and orthopaedic shoe technician. This leads to a large variety of results and sometimes to insufficient offloading of the foot. Even when the insole or rocker profile shoe initially is effective, over time the location of the pressure spots can shift, resulting in poor offloading and putting the person at risk again of developing an ulcer. The work in this thesis aimed to overcome the problems with the current offloading footwear and includes the design and evaluation of an adjustable rocker profile and a self-adjusting insole

Insole for reducing peak pressures under a foot

The invention provides an insole (1) comprising a plurality of supporting elements (5A, 5B, 5C) distributed over the insole surface for resiliently supporting a foot. Each supporting element comprises a main supporting portion (9) having a narrowing outer shape, and a widening circumferential buckling wall (7) designed to have a buckling behaviour such that: (i) the buckling wall collapses in reaction to a condition in which an external compressive force exceeds a first force threshold (F1); and (ii) if thus being collapsed, the buckling wall resiliently expands in reaction to a condition in which said external compressive force falls below a second force threshold (F2), which is lower than the first force threshold. In use the insole provides a highly effective dynamically self-adjusting pressure distribution reducing peak pressures under a foot, dynamically when the patient walks. In addition, the insole is compact, non complex, easy to produce, durable and reliable

Effects of flexible and rigid rocker profiles on in-shoe pressure

Rocker profiles are commonly used in the prevention of diabetic foot ulcers. Rockers are mostly stiffened to restrict toe plantarflexion to ensure proper offloading. It is also described that toe dorsiflexion should be restricted. However, the difference in effect on plantar pressure between rigid rockers that restrict this motion and flexible rockers that do not is unknown. In-shoe plantar pressure data were collected for a control shoe and the same shoe with rigid and flexible rockers with the apex positioned at 50% and 60%. For 29 healthy female adults peak plantar pressure (PP), maximum mean pressure (MMP) and force-time integral (FTI) were determined for seven regions of the foot. Generalized estimate equation was used to analyse the effect of the different shoes on the outcome measures for these regions. Compared to the control shoe a significant increase of PP and FTI was found at the first toe for both rigid rockers and the flexible rocker with the apex positioned at 60%, while MMP was significantly increased in rockers with an apex position of 60% (p <0.001). PP at the first toe was significantly lower in flexible rockers when compared to rigid rockers (p <0.001). For both central and lateral forefoot PP and MMP were significantly more reduced in rigid rockers (p <0.001), while for the medial forefoot no differences were found. The use of rigid rockers results in larger reductions of forefoot plantar pressures, but in worse increase of plantar pressures at the first toe compared to rockers that allow toe dorsiflexion

Rocker profiles

With rocker profiles the biomechanics of gait can be altered. Proximally placed forefoot rockers can reduce the forces on the Achilles tendon and when combined with a stiff foot plate, strain on the plantar fascia can be reduced. These proximal rockers can also reduce the pressure at the Metatarsal Phalengeal (MTP) region. By adjusting the apex and rocker angle and rocker radius, plantar pressure and Achilles tendon and plantar fascia force reduction can be individually optimized. Rocker profiles can also reduce the ankle joint motion during the heel- and ankle rocker and, combined with a stiff foot plate, rocker profiles can eliminate the motion in the MTP-joint