A Guide To Orthotic And Prosthetic Options For People With Partial Foot Amputations
In general, the extensiveness of the prosthetic intervention is proportional to the extent of limb loss. For example, those patients who undergo amputation of the toes or a disarticulation of the metatarsophalangeal joint will likely use devices such as insoles or toe fillers. These devices tend to be made of foams with varying degrees of compliance to fill the shoe and redistribute pressure. These devices do tend to effectively redistribute pressure away from the sensitive amputation site to the surrounding intact skin. These types of devices are commonly known as “below-ankle” interventions because they are contained entirely in the shoe.
Conversely, patients with more proximal partial foot amputations, such as transmetatarsal amputations (TMA), Lisfranc or Chopart amputations, would more likely require more robust functional bracing via AFOs or prostheses incorporating an extensive socket that encompasses the lower leg and remaining foot while limiting ankle motion. These devices are commonly known as “above ankle” devices and a review of the literature demonstrates that these modalities are gaining traction as the prosthetics of choice for more proximal amputations due to improved overall functional biomechanics.10-12
The literature suggests that the ability of the prosthesis to restore the effective foot length relies on three major design features: a stiff forefoot capable of supporting the amputee’s body mass; a socket capable of comfortably distributing the leg and foot pressures that result from loading the prosthetic forefoot; and a relatively stiff connection between the foot and leg segments to help control the moments caused by loading the prosthetic forefoot.10-12
As technological advances in material science become available, there are increasing opportunities to formulate custom functional bracing options that fulfill these requirements in patients with partial foot amputations. However, despite the abundance of anecdotal evidence in support of above-ankle type devices for those patients with TMA or higher level amputations, there remains little in the way of evidence-based medicine to guide the clinician.12,13
Key Insights On The Biomechanics Of Partial Foot Amputation
A review of the current literature suggests that patients who undergo partial foot amputations demonstrate reductions of power generated across the ankle joint during ambulation. Once the metatarsal heads have been compromised, power generation was virtually negligible irrespective of residual foot length or prosthetic intervention.10,14 Consequently, patients with partial foot amputations may compensate for reductions in power generation across the affected ankle by using the hip joints bilaterally, which generates an increased workload on the patient’s cardiovascular system.15
Additionally, patients who had partial foot amputation demonstrate increased shear forces along the distal portions of the partial foot amputation during the propulsive phase of gait, despite overall weakened ankle power.10 The objective of “above ankle” type prosthetics is to attempt to reduce these shear forces while maintaining appropriate ankle force to reduce the need for compensatory motion through a stiff connection between the foot and leg segments to help control the moments caused by loading the prosthetic forefoot.16-18 This also allows for a more efficient transfer of energy throughout the gait cycle while minimizing shearing forces along the residual stump.