A Guide To Orthotic And Prosthetic Options For People With Partial Foot Amputations

It is estimated that greater than 26 million Americans — over 8 percent of the total population — suffer from diabetes and the literature demonstrates that nearly 25 percent of patients with diabetes will develop a foot ulcer at some point during their lifetime.1 It has been well documented that more than half of these wounds will become infected and require hospitalization, and that nearly 20 percent of these infections result in lower extremity amputation.1

   The partial foot amputation is the most common type of amputation in the United States and occurs nearly twice as frequently as either the transfemoral or transtibial amputations.2,3 In the United States, there are approximately 618,000 individuals who have had some form of partial foot amputation and, considering the current population, that translates to approximately two out of every 1,000 people who suffer with partial foot amputations.4

   This is a staggering statistic, especially considering that the number of people living with limb loss will likely double by 2050 as the population ages and the number of people living with comorbidities, such as diabetes and vascular disease, increases.5 Consequently, clinicians involved in the management of lower extremity wounds are truly facing an epidemic of limb loss.

   There is a clear prevalence of partial foot amputations and the numerous complications associated with these procedures as 30 to 50 percent of partial foot amputees will experience some form of subsequent skin breakdown following partial foot amputation.6 Despite this, there has been little consensus on the type of prosthetic and orthotic intervention after partial foot amputation that patients should utilize to provide the greatest risk reduction for subsequent secondary amputation.

   Sadly, studies estimate that 15 to 45 percent of people with partial foot amputation experience some form of secondary amputation with two-thirds undergoing a higher level of amputation on the same limb.7,8 The mortality for partial foot amputation is significant and studies estimate that of those who undergo partial foot amputation, between 15 percent and 30 percent will die within 12 months.8,9

   Clearly, there is a need to determine the most effective way to limit further skin breakdown and limb loss in this challenging patient population with effective offloading and stabilization via custom prosthetics and orthotics. However, formal study and critical analysis of these modalities is a relatively recent phenomenon and there is little evidence-based medicine to guide the practitioner in the selection of appropriate prosthetic interventions.

A Pertinent Overview Of Prosthetic And Orthotic Interventions

Historically, physicians have utilized a wide variety of prosthetic/orthotic modalities to manage partial foot amputations. Among these devices, insoles, toe fillers, slipper sockets, ankle foot orthoses (AFOs) and clamshell sockets are the most commonly utilized prosthetic interventions.

   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.

In Conclusion

Partial foot amputation is the most commonly performed amputation — affecting approximately two in every 1,000 people — and complications such as ulceration and re-amputation are all too common sequelae in these challenging patients. There is little consensus regarding the appropriate post-partial foot amputation modalities. Following partial foot amputation, clinicians must attempt to maintain function and reduce force loading along the residual foot stump in order to reduce further skin breakdown and subsequent secondary limb loss in these challenging patients.

   While there is a paucity of evidence-based medicine regarding the use of prosthetic interventions, there is increasing research into these topics. Much of the current literature suggests that the above ankle prosthetic interventions that eliminate ankle motion improve ankle power generation during the gait cycle and reduce overall strain on the patient’s cardiovascular system while also reducing potential shear forces along the residual stump, thus reducing risk of re-ulceration.8,15-18

   While further research is necessary, the clinician will always need to weigh various considerations including level of amputation and realistic functional expectations when prescribing a specific type of orthosis or prosthetic device following partial foot amputation to maintain the highest level of function.

   Dr. Fitzgerald is an Assistant Professor of Surgery at the University of South Carolina School of Medicine-Greenville in Greenville, S.C. He is also affiliated with the Center for Amputation Prevention with the Greenville Health System in Greenville, S.C. Dr. Fitzgerald is a Fellow of the American College of Foot and Ankle Surgeons.

References
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6. Mueller MJ, Allen BT, Sinacore DR. Incidence of skin breakdown and higher amputation after transmetatarsal amputation: implications for rehabilitation. Arch Phys Med Rehabil. 1995; 76(1):50-4.
7. Sage R, Pinzur MS, Cronin R, et al. Complications following midfoot amputation in neuropathic and dysvascular feet. J Am Podiatr Med Assoc. 1989; 79(6):277-80.
8. Dillingham TR, Pezzin LE, Shore AD. Reamputation, mortality, and health care costs among persons with dysvascular lower-limb amputations. Arch Phys Med Rehabil. 2005; 86(3):480-6.
9. Aulivola B, Hile CN, Hamdan AD, et al. Major lower extremity amputation: outcome of a modern series. Arch Surg. 2004; 139(4):395-9; discussion 399.
10. Dillon MP, Barker TM. Comparison of gait of persons with partial foot amputation wearing prosthesis to matched control group: observational study. J Rehabil Res Dev. 2008; 45(9):1317-34.
11. Cannada LK, Vaidya R, Covey DC, et al. The traumatic lower extremity amputee: surgical challenges and advances in prosthetics. Instr Course Lect. 2013; 62:3-15.
12. Carroll K. Adaptive prosthetics for the lower extremity. Foot Ankle Clin. 2001; 6(2):371-86.
13. Bedotto RA. Biomechanical assessment and treatment in lower extremity prosthetics and orthotics: a clinical perspective. Phys Med Rehabil Clin N Am. 2006; 17(1):203-43.
14. Mann RA, Poppen NK, O’Konski M. Amputation of the great toe. A clinical and biomechanical study. Clin Orthop Relat Res. 1988; 226:192-205.
15. Dillon MP, Barker TM. Preservation of residual foot length in partial foot amputation: a biomechanical analysis. Foot Ankle Int. 2006; 27(2):110-6.
16. Spaulding SE, Chen T, Chou LS. Selection of an above or below-ankle orthosis for individuals with neuropathic partial foot amputation: a pilot study. Prosthet Orthot Int. 2012; 36(2):217-24.
17. Janisse DJ, Janisse EJ. Shoes, orthoses, and prostheses for partial foot amputation and diabetic foot infection. Foot Ankle Clin. 2010; 15(3):509-23.
18. Sage RA. Risk and prevention of reulceration after partial foot amputation. Foot Ankle Clin. 2010; 15(3):495-500.

   For further reading, see “A Guide To Digital Amputations In Patients With Diabetes” in the September 2011 issue of Podiatry Today.