Minimally invasive image guided surgery and regenerative technologies have rapidly developed requiring changes in post-operative management protocols. With such a variety of options available for patients and varying ideas on which product is best suited for each procedure, practitioners play in important role in optimizing patient care when prescribing solutions. Function, aesthetics, and ease of mobility play key roles in patient acceptance of orthotic devices and determine the success of a product and recovery journey. This paper aims to investigate commonly utilized options for various foot and ankle conditions and compare their applications, advantages, and disadvantages. By analyzing available options, knowledge can be gained to create an optimized modular product that takes advantage of the best features of existing devices and offers a complete solution for every patient.

Orthosis; Diabetic ulcer; Bracing; Regenerative medicine; Regenerative Biology

The advent of biologic treatments and regenerative medicine can require longer treatment times and bracing requirements. The challenge is to minimize the inconvenience of longer treatment times with bracing.

The paper investigates current marketed post-operative, preventative, and management options for various foot and ankle conditions and proposes a solution to accommodate most patient needs in a complete system.

By analyzing the applications, advantages and disadvantages of plaster casting, Controlled Ankle Movement (CAM) walking boots, ankle braces, offloading shoes and typical “diabetic” shoes, more information can be gained on gaps in patient care and which options are best suited for which disease, aiding in the development of a complete solution.

Although patients with diabetes often need shoes to accommodate for ulcer treatment, general, everyday shoes to prevent injury are essential to maintaining healthy feet. Unsuitable footwear which is ill fitted, too tight, or causes any unnecessary pressure on the foot increases the risk of ulcer formation and possible amputation [1]. Conventional shoe designs, mismatches between feet and shoes and materials are involved in nearly 80% of all ulcers that precede amputations [2]. The goal of a proper therapeutic shoe is to protect the skin from external trauma, enhance function mobility and provide an acceptable level of cosmesis [3].

According to Bauman et al. [4], “prevention of trophic ulceration largely depends on the even distribution of pressure over the sole of the foot”. Thus, pressure redistribution must be balanced with protection, function, and aesthetics. Although a total contact cast offers excellent pressure redistribution, mobility and aesthetics are compromised. Similarly, a rigid rocker sole can significantly reduce foot pressures, but patients with existing balance issues will have trouble with mobility [1]. A study published in 2011 by Bus et al. [5] analysed the effectiveness of a therapeutic shoe in offloading plantar pressures and found that when compared to a baseline shoe, mean peak pressure can be reduced by an average of 30.2%(18-50% across regions). Thus, therapeutic footwear and stock “diabetic” shoes (SDS) can have a significant impact in reducing ulcerations and complications in diabetic patients. In 2003, Busch et. al presented a study assessing a new type SDS, the German LucRo®, consisting of a rocker-shaped walking sole, shock absorbing insole and soft, deformable uppers.

The innersole was designed to be less triangular and more rectangular to better accommodate the shape of elderly feet, which tend to be wider and flatter than younger generations [6].

In the first year of the study, foot ulcer relapse in the SDS group was 15% compared with 60% in the group without specialized shoes. In addition, 95% of patients reapplied for additional pairs showing a high satisfaction rate. It was concluded that the LucRo® could reduce ulcer incidence by 45% in the first year, solidifying the importance shoe choice has on diabetic feet. Such a high compliance rate may have contributed to its success.

Figure 1: LucRo® Shoe, women’s version, easily deformable upper [1].

Figure 2: Shape of the LucRo^® Inner sole, bar indicated 5cm [1].

Offloading shoes are commonly prescribed for conditions affecting the forefoot, such as deformations of toes 2-5, surgical correction of hallux valgus and treatment of diabetic ulcers. They have been shown to significantly reduce pressure in the forefoot when walking. [7-9]. A half shoe, wedge shoe or Type 1 shoe can reduce forefoot plantar load by as much as 62% of a patient’s body weight [10]. Due to its forefoot offloading abilities, the wedge shoe has widespread use in minimally invasive hallux valgus deformity (bunion) correction surgery allowing immediate post-operative weight-bearing [11]. Offloading capabilities of the wedge shoe are also important when considering treatment of diabetic ulcers in which offloading of plantar pressures is key in healing. Statistically, around 15% of diabetes suffers will develop an ulcer at some point in their lives with 85% of all global diabetes amputations being preceded by an ulcer [12,13].

Diabetic ulcers can have significant adverse effects on patients including struggles with adjusting to illness, altered satisfaction of personal life, depression, and poorer quality of personal life overall [14].There are numerous variations of offloading shoes available to prescribe to patients. A study investigating the Barouk® second generation postoperative forefoot relief shoe determined that from their results and existing research this shoe was more effective at reducing peak forefoot pressures than the Darco®, WalkWell® and Hannover® brands with a mean peak pressure reduction of between 76-96% [8,9,15]. This impressively high reduction in forefoot load bodes well for managing diabetic ulcers.

Figure 3: Barouk® second generation post-operative forefoot relief shoe [9].

Another offloading shoe, in this case a flat shoe, that offers up to 51% decreased plantar pressures compared to a control shoe is the DH Pressure Relief Shoe™. Designed specifically for people with plantar ulcerations or high pressure, the shoe allows for customisation by addition and removal of hexagonal shaped pieces from its insole. Priced at AUD $100 in 2012, this shoe is cost effective, convenient, and easy to use. Due to its flat bottom design, it doesn’t pose such a hazard when walking like the above wedge style shoes, but also may not be suitable for post-surgery hallux valgus which requires a much higher reduction in forefoot pressure [16].

Figure 4: (a) DH Pressure Relief Shoe™ (b) Insole of DH Pressure Relief Shoe™ with hexagonal plugs removed from under the right first metatarsophalangeal joint [16].

Accounting for up to 23% of all sports injuries presented to UK emergency departments, ankle ligament sprains are considered the most common of sports injuries. Minimal swelling, localised tenderness and minor function deficit are commonly associated with a mild sprain which generally will not require an x-ray. However, moderate and severe ankle sprains can be presented by significant pain and swelling, haematoma formation and an inability to weight bear. Despite the high incidence of injury, often there is no clear regimen for their management. In most instances, patients are provided with an elastic support bandage, but a wool and crepe wrap around bandage may also be used. Historically, elastic support bandages have been provided as the first line of treatment in for than 70% of British emergency departments [17-21].

In 2004 Boyce et al. [22] conducted a study comparing elastic support bandages and ankle braces, specifically an Aircast ankle brace, and recorded a significant improvement in ankle joint function at both 10 days and one month. The Aircast ankle brace consists of two plaster lateral straps which foam pads designed to sit against the medial and lateral malleoli of the ankle. Padding is contoured at the ankle and rigid sidewalls held in place with Velcro. The brace can be self-applied, is reusable and adjustable. Although ankle braces are superior to an elastic support or compression bandage [23] and patients treated with an elastic support bandage took longer to return to work [24-26]. Boyce et. al highlights that use of ankle orthosis is rarely used on the public, more so in sports groups and teams supervised by practitioners. Additionally, Aircast ankle braces have never been used in more than 70% of all British emergency units [20].

Figure 5: Aircast ankle brace [22].

Figure 6: Elastic Support Bandage [22].

In addition to sprains, ankle braces may in some circumstances be applied to treat ankle fractures. A trial conducted by Kearney et. al and published in 2021 [27] concluded that when comparing traditional plaster casting to removable bracing when treating ankle fractures, there is no statistically significant difference between the two. This poses a question of whether ankle braces can, in some instances, replace both plaster casts and walker boots.

Although knowledge and studies of how effective an ankle brace reduces plantar pressure are scarce, many studies have analyzed the effectiveness of the Aircast on stabilizing the ankle. Fritsch et Al. [28] found the Aircast may provide greater stability to the hind and midfoot. According to them and drawing knowledge from a 1993 study by Scheuffelenet al.[28], “almost all studies which analyze the stabilizing effect of ankle orthoses show an average reduction in the tilt angle of the talus of 50 to 70%”. To establish whether in some circumstances a brace could be more effective than a cast, more research is needed.

Ankle fractures are one of the most common injuries of the lower limb, prevalent in middle-aged to older women and young men. An ankle fracture can be categorized by a fracture of the distal tibia of the fibula commonly caused by sports injuries, falls and twisting injuries. Pain, stiffness, weakness, swelling and limitations when climbing stairs and walking, even post-rehabilitation, are often experienced[29-34]. Naturally, ankle fractures have an immense impact on the quality of people’s lives affect all areas from social and family life and independence to sleep and psychological wellbeing [35]. As such, much research has gone into selecting and developing the best post-operative option for patient rehabilitation after foot and ankle injuries, with many arguing for the Controlled Ankle Movement (CAM) Walker boot, or similar [36-39].

A CAM Walker Boot, also called a Moon Boot, is a type of removeable Ankle-Foot Orthosis (AFO) allowing total contact with the posterior and anterior calf, ankle, and whole foot. Some variations are equipped with inflatable blades to assist in managing swelling and maintaining total contact with the leg and foot. These boots provide a stable platform to distribute forces evenly across the plantar region during weight bearing and often have a rocker bottom for more natural movement when walking.

High-leg boots can offload plantar pressure to the tibial region, further reducing stress on the foot and. Although commonly used for fractures, CAM boots can also be prescribed for a range of foot and ankle injuries, including but not limited to ankle sprains, diabetic ulcers, and general post-operative stabilization after procedures such as ankle reconstruction, endoscopic plantar fascia release and percutaneous opening wedge calcaneal osteotomy [39-46].

Figure 7: An Example of a modern CAM Walking Boot; the Össur Rebound Air Walker ® [47].

A study by Amaha et al. [48] published in 2017 compared the effectiveness of a plaster cast (PC) and a short leg walking boot (WB) used in post-op rehabilitation for an ankle fracture. It was determined that although there was no significant difference in the final range of motion (ROM) of the two groups, the WB showed significantly better functional recovery with significantly shorter full unipedal weightbearing times. Even though this group suffered from significantly more severe fractures and patients were older, they still showed a faster recovery after full weight bearing was permitted. These results may be attributed to the ease of removal of the boot for patients to conduct ROM exercises and reduce joint stiffness and muscle weakness often associated with plaster casts. Additionally, walker boots can reduce plantar pressure by more than 50% at some ulcer sites when compared to a cast or baseline shoe by redistributing it to other areas of the foot, and the lower leg [38,49].

While CAM Walkers have been demonstrated to have considerable advantages and can allow for a great amount of freedom and independence post-surgery, there are some disadvantages than cannot be overlooked. Leg length discrepancy due to the thick rocker-bottom sole has been shown to result in secondary site pain in most commonly in the lower back, contralateral hip, and ipsilateral knee. 67% of patients included in a 2018 study who wore a CAM walker boot for at least 2 weeks reported new or worsened secondary site pain. As well as leg length discrepancy, these results may also be attributed to overall boot design and altered gait mechanics [50]. To combat this common issue, prominent injury solutions company Össur® developed a product called the EvenupShoelift™ which when used in conjunction with their Rebound Air Walker ® helps to level a patient’s gait and prevent back, hip and knee injury [47].

Figure 8: The ÖssurEvenupShoelift™ [47].

The first record of plaster casting being utilized for conditions requiring immobilization or force application was in the ninth century by the Arabian surgeon Abu Ali Sina, or Avicenna, as known in the West [51,52].

Historically, Plaster of Paris has been the most widely used material for casting. Like other plaster materials, when dipped in water an exothermic crystallisation reaction occurs resulting in the hardening of the plaster which becomes warm as it sets. Plaster of Paris is relatively light and easy to remove compared other plaster types.

With advances in technology more modern materials like fibreglass and resins have been developed that are indeed lighter than Plaster of Paris, but much more difficult to remove [53].

When applied to foot and ankle conditions, Plaster can be used to treat fractures, correct deformities, and manage and treat diabetic foot ulcerations [53-56]. It is also effective at reducing plantar pressures. A 2005 study by Beuker et al. concluded that when compared to an Oxford leather shoe, a total contact cast can reduce plantar pressure by as much as 65.8% [57].

Figure 9: Application of Plaster of Paris [58].

Although Plaster has proved a reliable and effective method of immobilization for centuries, it does not come without negative side effects. The exothermic reaction of the cast hardening can, if not handled correctly, cause skin burns. Care should be taken to use water cooler than 24 ̊C and apply liberal padding [59]. Patients may also experience allergic reactions, pressure ulcers, compartment syndrome, which can result in permanent necrosis and even amputation and Deep Vein Thrombosis (DVT) [58]. In a 2002 study by Jørgensen et al. [60] investigating the incidence of DVT in patients immobilized in a plaster cast found that DVT in legs has an incidence rate of almost 20%, hence requiring an effective prophylactic routine. Additionally, pain, joint stiffness, weak muscles and swelling of the ankle may be experienced due to a fracture injury coupled with an extended immobilization period [29]. A cast, being a rigid bracing technique, does not accommodate the natural post-op cadence of limb diameter in the post-operative period.

The following table outlines the options discussed so far in this article.

Table 1: Comparing Options.

Compared to other areas of human endeavour, there has been a remarkable paucity in development of post-operative splints. As seen above, finding a product that is light, discreet, functional, and cost effective for the patient, plus effective in treating if not all, but most foot and ankle conditions is difficult.

Each condition has certain treatment requirements and patients have different needs. As such, there is a demand to create a bridge between CAM walker boots, plaster casts and weightbearing in a shoe. With populations increasing and hospitals and clinics requiring an increasing number of products, there is further need for light weight, modular splints to decrease inventory levels. Splints that are strong, light weight and convenient are required with the advent of biologic regenerative treatments that need longer protection times.

To combat the deficit in development of post-operative brace solutions, a modular system can be proposed designed to work in conjunction with a walker boot for treating multiple foot and ankle diseases. Consisting of a leg brace Ankle Foot Orthosis (AFO), plus a SDS style adjustable shoe with removable rocker or wedge bottom, the system targets fractures, ankle stability, hallux valgus post-op and treatment and prevention of diabetic ulcers.

When considering construction, Kevlar® is the most desirable choice for the brace material. First developed in 1965 by Stephanie Kwolek and DuPont among a family of polymer fibres with incredible strength and stiffness, it has over 200 known applications and can perform under extreme conditions [61]. Kevlar has a tensile strength comparable to carbon fibre, a modulus between it and glass and yet a lower density than them both, making it extremely light weight and strong [62].

Unique properties of Kevlar® include its low stretch, very high strength to weight ratio and excellent fatigue and abrasion resistance. It is, however, weak in compressive strength and susceptible to Ultraviolet (UV) light [63].

According to DuPont’s “Technical Guide for Kevlar® Aramid Fiber” [64] need to form proper reference format], Kevlar® can be manufactured in various combinations of properties to meet specific requirements, but the most common yarns are Kevlar® [29] and Kevlar® [49]. Although affected by UV light, regular exposure from incandescent and fluorescent lightbulbs or sunlight filtered through a window should not impact the quality of the Kevlar®. Extra UV protection can be provided depending on manufacturing technique.

Hovorka et al in a 2021 article [65] considered an AFO designed to constrain ankle plantar and dorsiflexion within 5˚C. They determined a conventional, solid, thermoplastic brace was insufficient for applications requiring significant motion control, so instead proposed a carbon composite with modulus of 18.5x106psi, very similar to a Resin Impregnated Kevlar® [49] with a modulus of 18x106 psi [64].

They developed a design consisting of two cylindrical shells encapsulating the shank and the foot to create a stiffer AFO more resistant to bending when compared to a half shell. To further minimize ankle motion, Hovorka et al, employed a three-force system to counter bending of the ankle and transmit forces to skeletal structures. Although effective at minimising ankle motion, their design purely experiment, designed to set the standard for ankle mobility minimisation and inspire further design innovation.

Figure 10: (a)Hovorka et al. “Experimental ankle foot orthosis (exAFO) provides increased leverage (b) bymaximizing moment arm length (10cm) from ankle joint to the end point of linear bearing anchored to a cylindrical shell at foot. (c) Tibial plate at anterior proximal shank” [65].

As such, the Kevlar® AFO style brace would incorporate the same three-point force system and rigidity, but be more conservative in aesthetics, possibly being able to be worn under clothes. With the ability to remove components (brace, shoe, and rocker bottom) the brace system would be modular to fit patient recovery needs and stages. Multiple sizes would be available to accommodate various foot sizes.

The main aim of the system is to allow patient independence in an easy to use, assemble and modify system dependent on individual patient requirements. The collapsibility, modularity, and adaptability of the design reduces inventory requirements for hospitals and clinics. Further, the strong, lightweight Kevlar® brace creates ease and convenience for patients whose biologic regenerative treatments require longer protection times. Research is still being conducted to refine and develop the brace system.

This paper has investigated current marketed post-op, preventative and management options for various foot and ankle conditions and proposed a solution to accommodate patient needs in the form of a Kevlar® brace modular system. This system aims to minimise the inconvenience of longer bracing times often required with biologic treatments and regenerative medicine.

Dr. Gordon Slater is a medical director of Integrant Pty Ltd, an orthobiologics company.

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