Determining Amputation Level To Optimize Functional Outcomes

Diabetes is the leading cause of non-traumatic amputations in the lower extremity.¹ Around 15 percent of all patients with diabetes will develop a lower extremity ulceration, with these patients being 17 to 40 times more likely to require an amputation.¹ Unfortunately for most, the decision to amputate is not always clear cut and the determination of where to make a definitive amputation is not always as it seems on plain films or advanced imaging, such as magnetic resonance imaging (MRI) or computed tomography (CT). There are several factors to consider when performing limb salvage procedures for these patients with diabetes.

During most initial amputations, I find it is often a surgeon’s preference to obtain two bone biopsy samples: one from the site of the amputation; and one from the proximal margin. The margins from the amputation site can help determine the viability of that initial procedure. In a study from Schmidt and colleagues, the authors found that obtaining clean margins (ie no residual osteomyelitis) resulted in better outcomes, including lower rates of wound dehiscence, reulceration, and needing more proximal amputation.² In addition, they also found that patients with residual osteomyelitis were 2.6 times more likely to be readmitted.²

After obtaining the bone biopsy results, the length and choice of antibiotics can benefit from consultation with the infectious disease specialist. In patients with residual positive margin cultures, intravenous antibiotics are recommended for at least, but no more than, six weeks.³ In patients with no residual infection within the proximal margin, two weeks of antibiotic therapy are typically recommended for these patients.³ Culture and sensitivity results determine antibiotic selection.

Another challenge that presents with diabetic wound healing is the vascular status of the patient. With 30 percent of all patients with diabetes and foot ulcers having concurrent peripheral vascular disease, this will play a critical role in determining the level at which an amputation will heal based on blood flow, evaluated from a series of non-invasive tests including ankle brachial index, toe brachial index, arterial dopplers, and computer tomography angiography. Obtaining pertinent blood flow studies helps determine healing potential and need for vascular intervention. Endovascular and bypass revascularization provide different ways to improve vascular perfusion to increase successful limb salvage.

If a dysvascular patient is not a candidate for revascularization, then determining an amputation level that is functional and has good potential for healing becomes more complicated. One can still attempt limb salvage with the understanding that a more proximal amputation may be necessary. Some of the more difficult discussions we have with patients involve discussing a leg amputation instead of trying limb salvage via multiple foot surgeries that lead to prolonged immobilization. The emotional and financial strain of a protracted recovery can be devastating. Furthermore, in our experience, the physical and health strain can lead to decreased survival rates. In our institution, we find a well-healed below-the-knee amputee can still have a successful functional outcome with a prosthesis.

In addition to these challenges, the postoperative course plays a role in determining the level of amputation. While many digital and partial ray amputations will heal without complications, prosthetic complications regarding transmetatarsal amputations, Chopart amputations and below-the-knee amputations are important to consider. In a study by Brodell and team, eighteen patients who presented with a complex foot wound and required a Chopart amputation.⁴ Eight ultimately required a below-the-knee amputation and only 44 percent of the patients were able to use the Chopart amputation site functionally without requiring secondary surgery.⁴ Alternatively a Chopart amputation can be converted to a below-the-knee amputation. While the below-the-knee amputation may provide a more functional amputation, as well as decreased likelihood of needing revisional amputation, additional considerations are necessary when considering this as the definitive treatment. Many studies show that a below-the-knee amputation correlates with an upwards of 71 percent increase of mortality within three years of surgery.⁵

While a Chopart amputation seems like a challenging option to brace, Pinzur and coworkers reported on how to have a successful functional outcome with posting to the shoe insert.6 Furthermore, they reported that a more proximal amputation results in increased energy expenditure when ambulating. The authors found that any level of amputation proximal to the metatarsal heads causes loss of medial support during the loading phase of gait that requires orthotic posting to limit valgus deformity.⁶ In addition to valgus deformity, these patients also often have plantarflexion contractures developing from muscle imbalances. This plantarflexion contracture will increase pressure during terminal stance causing the patient discomfort, pain, and puts the patient at risk of risk of re-ulceration.  Due to this plantarflexion contracture, it is often important to incorporate a rocker bottom sole to the patient’s orthotic to prevent the increase in pressure during terminal stance.⁶

In addition, the patient’s expectations, support system, and ability to adhere to the treatment plan need evaluation. Some patients expect a quick recovery that will allow them to return to work and regular activities. It is important to stress that the healing and recovery process will take time and not providing adequate time to heal will only result in delayed healing, increased risk of wound complications, and increased risk of additional surgery or amputation. Adherence is vital for any surgery, and we feel patients need to be included as an active participant in the recovery process. Even after the patient has healed and is functionally active, we find these patients will need monitoring at least once annually and to have a good relationship with an orthotist/prosthetist for any adjustments that need to be made to prevent possible future ulcerations and amputations. Patients need to feel that they are partners with the entire surgical and medical teams involved in their care to ensure long-term success.

“Amputations are the easiest surgery,” is a phrase I used to commonly hear early in my career. Unfortunately, as I have realized with experience, the technical aspect of the surgery is not nearly as important as understanding the the many medical factors that influence the outcome of the amputation. The amputation is just the beginning of the recovery process. We need to have an honest dialogue with the patient so that they understand the complex nature of selecting an amputation procedure for possible limb salvage versus a more definitive proximal amputation that may be less desirable, but can have a more successful healing and functional outcome. Understanding and factoring in all of these parameters with a multi-disciplinary approach with the patient will lead to better patient outcomes regardless of the final amputation level.

Dr. Husain is the Residency Director of the McLaren Oakland Hospital Podiatric Surgery and Medicine Residency Program in Pontiac, MI. He is a Fellow of the American College of Foot and Ankle Surgeons and a Fellow of the American Society of Podiatric Surgeons. Dr. Husain is also the President-Elect of the Michigan Podiatric Medical Association and Chairman of the Michigan Podiatric Residency Consortium.

Dr. Behme is a second-year podiatric resident at McLaren Oakland Hospital in Pontiac, MI.

References

1. Mariam TG, Alemayehu A, Tesfaye E, et al. Prevalence of diabetic foot ulcer and associated factors among adult diabetic patients who attend the diabetic follow-up clinic at the University of Gondar referral hospital, north west Ethiopia, 2016: institutional-based cross-sectional study. J Diabetes Res. 2017. doi: 10.1155/2017/2879249.

2. Schmidt BM, McHugh JB, Patel RM, Wrobel JS. Prospective analysis of surgical bone margins after partial foot amputation in diabetic patients admitted with moderate to severe foot infections. Foot Ankle Spec. 2019;12(2):131-137.

3. Senneville E, Joulie D, Blondiaux N, Robineau O. Surgical techniques for bone biopsy in diabetic foot infection, and association between results and treatment duration. J Bone Jt Infect. 2020;5(4):198-204.

4. Brodell JD Jr, Ayers BC, Baumhauer JF, et al. Chopart amputation: questioning the clinical efficacy of a long-standing surgical option for diabetic foot infection. J Am Acad Orthop Surg. 2020;28(16):684-691.

5. Kennedy G, McGarry K, Bradley G, Harkin DW.  All-cause mortality amongst patients undergoing above and below knee amputation in a regional vascular centre within 2014-2015. Ulster Med J. 2019;88(1):30-35.

6. Pinzur MS, Gold J, Schwartz D, Gross N. Energy demands for walking in dysvascular amputees as related to the level of amputation. Orthopedics. 1992; 15(9):1033-1036.