A Closer Look At Preserving Foot Function With A Transmetatarsal Amputation

For patients with diabetes and neuropathy, partial first ray amputations can lead to less than optimal results. With this in mind, these authors discuss emerging insights from the literature and offer a compelling case study that illustrates the key considerations in choosing between partial amputations and more proximal procedures.

Diabetes mellitus, particularly when coupled with neuropathy, is a disease that predisposes affected individuals to a cascade of lower extremity ulcerations, infections and amputations. The complex nature of lower extremity biomechanics is compromised by the natural progression of this disease. Myopathy, tendinopathy and autonomic alterations that result in skin changes can cause insult to both foot form and function. Inherently, first ray biomechanics predispose patients with diabetic neuropathy to submetatarsal head breakdown.

Partial first ray amputations in patients with diabetes mellitus and coexisting peripheral neuropathy have relatively poor postoperative outcomes. Often, these amputations lead to more proximal foot amputations or even limb loss. As foot and ankle surgeons, we seek to preserve as much of the limb as possible when a patient presents with infected wounds, gangrene or other foot conditions requiring possible amputation. The surgical plan should consider postoperative biomechanical implications in order to avoid a cascade of amputations that increase morbidity, anesthesia complications and readmissions, which contribute to lengthy hospital stays.

In the case of partial first ray amputations, the option for a transmetatarsal amputation is one that offers the patient a foot with far less biomechanical risk for reulceration in the long term. A solitary first ray amputation may not always be the best decision, especially when considering functionality and the increased probability of the development of future wounds. The risk of lesser toe contracture, transfer ulceration and distal toe ulceration in the partial first ray amputation are well-documented complications that can lead to skin breakdown and subsequent amputation.¹

Surveying The Research On First Ray Amputations
The literature consensus on the success rates of partial first ray amputation as an initial procedure in patients with type 2 diabetes mellitus and peripheral neuropathy is discouraging.

A recent 11-year retrospective study of 59 patients with diabetes and peripheral neuropathy demonstrated a 42.4 percent repeat amputation rate after partial first ray amputation in this patient population.² A systematic review of a total of 435 amputations also demonstrated that one of every five patients undergoing a partial first ray amputation went on to have a more proximal amputation due to tissue breakdown secondary to biomechanical instability.³ In addition, studies have shown that peak plantar forces during ambulation increase about the first ray following hallux amputation.⁴

Accordingly, we must compare the relative benefits of function versus ray preservation in each individual patient. The main goal of amputation in patients with diabetes is function and this may entail performing a more proximal amputation in order to achieve a more functional limb.¹ Attinger and Brown related that with a team approach, limb salvage can facilitate a 64 percent ambulation rate and an 80 percent two-year survival rate.¹ They also note that below-knee amputation led to a similar ambulatory rate but a lower two-year survival rate of 52 percent.

The utilization of adjunctive wound healing modalities, such as negative pressure wound therapy (NPWT) with instillation, can be beneficial for patients undergoing serial debridement.⁵ A study involving 162 patients found that the postoperative use of NPWT in treating complex diabetic foot wounds is associated with a higher proportion of healed wounds, faster healing rates and potentially fewer re-amputation rates in comparison to standard wet-to-dry dressings.⁶

If the tissue shows any signs of vascular compromise, hyperbaric oxygen therapy (HBOT) is a viable, simple and non-invasive option. Several studies support HBOT as an adjunctive treatment for diabetic foot wounds. One study of 94 patients revealed a 52 percent healing rate at a one-year follow-up in patients who had HBOT for their wounds in comparison to a 29 percent healing rate in the control group.⁷ In addition, HBOT is associated with very low complication rates in the literature.⁷

Take advantage of these adjunctive measures whenever necessary, especially in the immediate postoperative period. Patients are at greatest risk for additional same limb amputation within the first six months following their initial amputation.² Therefore, it is prudent to develop an appropriate and at times aggressive treatment protocol postoperatively in these high-risk patients.

The limiting factor to arriving at a functional amputation level can often be the patient’s understanding of the situation and evidence. It can be very difficult to educate a patient on the possible necessity of amputating digits that appear normal, are not infected, and inflict no pain on the patient. A thorough debriefing of the patient’s current situation and educating the patient in a manner that provides him or her with the same evidence that you have as a physician will often help progress the care in the right direction.

The physician should not underestimate the layperson’s ability to understand the biomechanical implications of first ray amputations and the importance of considering all surgical options available in order to achieve the best long-term result. It is important for patients to understand that preserving a limb by performing a free flap, skin graft or other limb-preserving procedure may not always be the best treatment option, especially if they have had a partial first ray amputation. It is tempting to proceed with the option that preserves most of the limb. However, in many cases, performing a more proximal amputation, especially in a relatively younger patient who is active, provides better form and function, and leads to a more desirable outcome in the long term.

Case Study: How A Proximal Amputation Preserved Function After First Ray Amputation
The following case study focuses on the performance of a more proximal procedure following a first ray amputation in order to preserve foot function and avoid future re-ulceration.

A 41-year-old male with a past medical history of poorly controlled type 2 diabetes mellitus, hypertension, hyperlipidemia and a 25-year history of tobacco use presented to our tertiary wound care center in June 2015. His chief complaint was new onset discoloration to his right foot. The patient had a two-week history of progressively worsening redness, swelling and pain to his right hallux.

The patient presented with subjective fever and chills, and denied trauma or any other inciting events. His random finger-stick blood glucose was 493. The hallux was cool to the touch but his vascular examination revealed triphasic signals to the dorsalis pedis, posterior tibialis and peroneal arteries on a handheld Doppler. Radiographs were negative for gas in the soft tissue and any cortical disruption of the associated bones. Preoperative labs revealed a leukocytosis of 25,100, increased glucose of 505, hemoglobin A1C of 13.3 and a C-reactive protein (CRP) of 284 mg/L. After the patient started on an insulin drip, we brought him to the operating room for emergent incision and drainage with possible amputation of the hallux.

The left photo of the initial clinic presentation demonstrates necrosis to the first ray and dorsal erythema with proximal streaking.

The emergent surgery resulted in a right hallux amputation at the level of the metatarsophalangeal joint (MPJ) with debridement of all infected and necrotic soft tissue. The underlying tissue was surprisingly healthy given the patient’s presenting condition. Intraoperatively, the patient had adequate bleeding with no evidence of a deep abscess. Two days later, the patient returned to the OR for re-debridement and partial resection of the first metatarsal. The below right photo shows the foot’s appearance following partial first metatarsal resection and thorough debridement.

Four days following this second procedure, the patient had an angiogram of the right lower extremity, which demonstrated patent three-vessel runoff to the foot. The lower extremity demonstrated a patent superficial femoral artery with patent peroneal, posterior tibial and anterior tibial vessels extending down the extremity, and past the ankle to supply adequate flow to the foot.

Three days following the angiogram, the patient returned to the OR for further debridement and additional first metatarsal bone resection with application of NPWT with instillation of normal saline.

The plan for definitive closure included discussion with our multidisciplinary clinical team including plastic surgery. We planned to use a free flap to close the large surgical wound that remained after serial debridement. Pre-free flap planning included venous mapping of the lower extremity as well as coagulation studies. We also discussed the procedure in detail with the patient and his family.

When Certain Risk Factors Shift The Surgical Plan From A Free Flap Procedure To A TMA
Re-examination of this patient’s foot structure stimulated revision of our plan. The left photo adequately demonstrates the digital contractures already present in the patient’s lesser digits. These contractures will inevitably lead to the formation of wounds to the distal tips of the toes, the dorsal aspect of the proximal interphalangeal joints and in the submetatarsal areas. In addition, given the patient’s extensive tobbacco use, we noted the increased risk for flap failure and decided to proceed with a transmetatarsal amputation instead.

We performed a transmetatarsal amputation, closed the wound primarily with minimal tension and placed the patient in a posterior splint. Frequent daily dressing changes allowed surveillance for postoperative complications. The patient’s post-debridement cultures were negative at the time of closure. Both bone pathology and cultures of the clean margin of the first metatarsal were without evidence of osteomyelitis.

During postoperative clinic follow up, the patient’s incision site began to progressively show signs of suboptimal healing. We immediately began HBOT to mitigate the progression of incision site necrosis.

The patient completed multiple dives of HBOT with noticeable improvement to the right foot. A small granular wound was present at the medial forefoot but this healed uneventfully with local wound care. The photo below at left shows the foot one month after transmetatarsal amputation with adjunctive HBOT.

Currently, the patient has completed HBOT and continues to follow up regularly at our tertiary wound care center. He is currently in a diabetic offloading shoe and we will ultimately fit him for a custom shoe. We will evaluate the need for an Achilles tendon lengthening if contracture should present at follow-up.

In Conclusion
While foot and limb preservation remain important goals of any surgery, this case study illustrates that performing a more proximal amputation may result in a more functionally favorable limb. In addition, with this particular patient’s history of tobacco use, performing an extensive surgery, such as a procedure involving a free flap, would be more likely to fail and potentially lead to further amputation.

Furthermore, the primary motivation in many emergent cases such as the aforementioned case is to eradicate infection and this is often a life-saving measure. Serial debridement offers re-examination of the native tissue and serves to sequentially progress the patient out of an infected and compromised wound state. Once the patient is clear of infection, clinicians can consider adjunctive treatment methods to encourage faster wound granulation and increase healing time.

Dr. Tawancy is a second-year resident at the MedStar Washington Hospital Center Podiatric Residency Program.

Dr. Elmarsafi is a second-year resident within the Division of Podiatric Surgery at MedStar Washington Hospital Center in Washington, DC.

Dr. Garwood is a third-year resident with the INOVA Fairfax Residency Program in Falls Church, Va.    

Dr. Steinberg is a Professor at Georgetown University School of Medicine and the Podiatric Residency Program Director at MedStar Washington Hospital Center.

References

1.     Attinger CE, Brown BJ. Amputation and ambulation in diabetic patients: Function is the goal. Diabetes Metab Res Rev. 2012; 28(Suppl 1):93-96.
2.     Borkosky SL, Roukis TS. Incidence of repeat amputation after partial first ray amputation associated with diabetes mellitus and peripheral neuropathy: an 11-year review. J Foot Ankle Surg. 2013; 52(3):335-338.
3.     Borkosky SL, Roukis TS. Incidence of re-amputation following partial first ray amputation associated with diabetes mellitus and peripheral sensory neuropathy: a systematic review. Diabetes Foot Ankle. Epub. 2012; epub Jan 20.
4.     Lavery LA, Lavery DC, Quebedeax-Farnham TL. Increased foot pressures after great toe amputation in diabetes. Diabetes Care. 1995; 18(11):1460-1462.
5.     Kim P, Attinger CE, Steinberg JS, et al. Negative pressure wound therapy with instillation: international consensus guidelines. Plast Reconstr Surg. 2013; 132(6):1569-1579.
6.     Armstrong DG et al. Negative pressure wound therapy after partial diabetic foot amputation: A multicenter, randomized controlled trial. Lancet. 2005; 366(9498):1704-1710.
7.     Londahl M, Katzman P, Nilsson A, Hammarlund C. Hyperbaric oxygen therapy facilitates healing of chronic foot ulcers in patients with diabetes. Diabetes Care. 2010; 33(5):998-1003.

For further reading, see “Point-Counterpoint: Is An Initial TMA Better Than A Partial Ray Amputation in Patients With Diabetic Neuropathy?” in the June 2014 issue of Podiatry Today or “Understanding The Biomechanics Of The Transmetatarsal Amputation” in the March 2013 issue.  

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