## 1 Introduction  
Approximately 20 million people with diabetes have diabetic foot ulceration and another 130 million are at risk to develop diabetic foot ulcers [1, 2]. Diabetic foot ulceration and re-ulcreation are leading causes of prolonged hospitalization and are associated with a socio-economic burden and a high rate of mortality [3]. Foot complications are commonly seen with increased plantar pressure, especially in a diabetic foot with neuropathy causing non-traumatic lower extremity amputation [4, 5]. Foot complications resulting in amputation begin with elevated plantar pressure and shear stresses that are directly associated with ulceration [6]. The occurrence of diabetic foot ulcers resulting from abnormal peak plantar pressure are found under the metatarsal heads and hindfoot, with a recurrence rate of more than 80% within three years after recovery [7]. More than 80% of all lower limb amputations in diabetes are led by long-term ulcerations and re-ulcreations [8]. In-shoe plantar pressure is usually measured to evaluate the plantar pressure distribution and sites of high plantar pressure. However, the plantar pressure measurement is time-consuming with prolonged trial and error procedures [9]. Furthermore, the cost of the measuring instruments and evaluation procedure is high. The finite element analysis (FEA) provides reliable results to evaluate various protocols without a patient's direct involvement. It also helps to understand the foot biomechanics and the effects of various interventions [10]. Researchers so far have focused on the effect of insole stiffness and thickness on plantar pressure distribution [11; 12]. Therapeutic footwear with insoles play an important role in the prevention of ulcers [13]. There are several design parameters that can be used to reduce peak plantar pressure in the feet of people with diabetic neuropathy. Shoe design can help to distribute weight more evenly across a foot and reduce the peak plantar pressure [14]. An insole that is designed to provide cushioning and support can help to reduce the forefoot and hindfoot peak plantar pressure [15]. In the case of material selection, different materials can also reduce peak plantar pressure. For example, foam materials may be more effective at absorbing shock than hard materials [16]. It is important to consider all these design parameters in combination when designing footwear or insoles for people with diabetic neuropathy. Insole shapes and material selections are strongly influenced by the experience of a pedorthist. Therefore, insole designs and materials are effective factors in reducing plantar pressure and in the alleviation of heel pain when compared with simulated flat insoles [17; 18]. A reduction in peak plantar pressure, foot stability, arch support, foot comfort, and shock absorption are some of the key criteria to design and prescribe customized insoles (CMIs) for people with different needs [19; 20; 21; 22]. Painful heels are addressed by providing a soft heel cup orthosis that provides comfort and a better reduction in the peak contact pressure under painful heels [23]. However, these soft heel cups are unable to provide stability for the foot. Additionally, adding dome-shaped metatarsal pads to an insole could reduce the forefoot peak contact pressure [24]. However, an addition of such a structure causes discomfort, and an inappropriate placement might result in adverse consequences with increased plantar contact pressure, especially in a diabetic foot with neuropathy [25]. The addition of a heel cup and metatarsal pads to a CMI to appropriately capture the heel morphology and the addition of a void in the base layer at the hindfoot and foot that can be filled with a softer material might be better to reduce and redistribute the pressure from the hindfoot and forefoot. To estimate plantar pressure distribution, the FEA provides a better understanding of the interaction of a foot with a CMI.