Emerging Insights On Closed Incision NPWT And Transmetatarsal Amputations

We often consider transmetatarsal amputation (TMA) a definitive and predictable level of amputation. McKittrick and colleagues popularized the TMA as a limb salvage procedure.¹ Whether addressing ischemia or infection, surgeons most frequently perform TMA procedures for patients with advanced comorbidities.These factors can lead to postoperative complications including infection, dehiscence, prolonged hospitalization and further surgery.

Studies have shown that wound healing rates following a TMA range from 40 to 70 percent.² Pollard reported that 32 percent of a reviewed TMA cohort went on to subsequent major amputation with a 1.98 percent 30-day mortality rate.³ It is well documented that a patient’s ability to ambulate significantly decreases with more proximal amputations such as a transtibial amputation.⁴ Additionally, life expectancy is significantly lower following transtibial amputations.⁵

Non-healing TMA wounds increase the potential for further infection and frequently lead to more proximal amputations, increased hospitalization and subsequently higher treatment cost. Stone and colleagues reported a 92 percent return to functional ambulation following a healed transmetatarsal amputation.⁶ A TMA is not only beneficial to the patient but it is economically sound. A retrospective economic analysis estimated the costs for an amputation within the foot to be $43,100 in comparison to $63,100 for transtibial amputations.⁷ A successfully closed TMA stump will offset the compounding costs of multiple surgeries.

O’Brien and coworkers reported early failure rates of TMA procedures to be 26.4 percent, which is significantly higher than more proximal procedures such as below-knee amputations (BKA) (12.6 percent) and above-knee amputations (AKA) (8.1 percent).⁸ We can define failure of primary closure by wound dehiscence, which may result from ischemia, infection, early weightbearing or non-adherence.

While failure rates of TMAs are greater than more proximal procedures, the mortality rate of a TMA is significantly less than more proximal procedures. Feinglass and colleagues recorded a 6.3 percent mortality rate among 1,909 patients after a BKA and a 13.3 percent mortality rate among 2,152 patients after an AKA.⁹ In contrast, Geroulakos and May reported a 3 percent postoperative mortality rate following TMA.¹⁰ Given the aforementioned statistics and the adverse effects a more proximal amputation will have on a person’s quality of life, it is imperative to search for options that may improve success rates for TMAs.   

How NPWT Can Promote Wound Healing After TMA Procedures
Negative pressure wound therapy (NPWT) has gained momentum worldwide as a beneficial adjunct for chronic wound management and more recently for postoperative incision wounds. Wounds that previously were in a non-healing state have become manageable. Negative pressure modifies an array of elements in the wound healing process. The vacuum induces mechanical traction on the wound bed, leading to stimulation of granulation tissue formation, a decrease in matrix metalloproteinases (MMPs), stimulation of angiogenesis and a decrease in edema formation.^11-13 This collectively results in improved blood flow and a decrease in bacterial colonization.

Utilization of NPWT on closed incisions has potential positive outcomes, according to several studies. Stannard and coworkers found a 1.9 times higher relative risk of developing an infection in the control group in comparison to patients treated with NPWT on lower extremity incisions.¹⁴ Atkins and colleagues published retrospective data on the use of NPWT for sternal incisions in 57 patients at risk to develop infection.¹⁵ The results of the study showed all patients tolerated NPWT to completion and no patients required treatment for sternal wound infection. In a prospective study, Colli utilized closed incision NPWT on 10 patients with a high probability of postoperative dehiscence and reported that all 10 patients had complete healing without complications.¹⁶ The author concluded that one should strongly consider the use of NPWT in this patient population.

Given these outcomes and the fact that amputation surgery occurs on a “high risk” patient population, it may be reasonable to consider the use of NPWT over closed incisions following transmetatarsal amputations.

Can Closed Incision Mechanically Powered NPWT Have An Impact?
The closed incision mechanically powered NPWT system (ciSNaP^®, Spiracur) offers an advanced dressing that one applies over a sutured or stapled incision line. The system provides negative pressure therapy to increase blood flow and potentially improve wound healing. The controlled tension relief layer includes silicone wings that aid in approximation of wound edges, reduce the potential risk of dehiscence and minimize tension on the approximated wound edges. The system is small, silent and usually remains in place for seven days post-op.

At our institution, we conducted a small pilot project including closed incision NPWT into routine management of TMAs. We used the ciSNaP negative pressure wound therapy system (Spiracur) for this study. This system delivers 100 mmHg pressure over the incision and one places it over a sutured or stapled incision. This system became available to us in April 2012 and we routinely incorporated the technology on post-op day two or three. We closed all TMAs with 3-0 nylon suture and many had contemporaneous revascularization. As per the manufacturer’s recommended application protocol, dressing changes occurred weekly unless the clinical scenario warranted otherwise.  

In an effort to determine our initial results, we performed a retrospective chart review of all patients undergoing a TMA with adjunctive closed incision mechanically powered NPWT. The comparison group was a cohort of patients we treated prior to the availability of ciSNaP, from whom we obtained similar data retrospectively serving as our control group. This study defined wound dehiscence as a lack of primary closure. We noted any ensuing incisional open wound with drainage and lack of complete epithelialization, and followed patients with these wounds until closure, the need for further surgery or death.   

This initial study yielded data for eight patients in each group. Interestingly, patients who had a TMA with adjunctive ciSNaP treatment healed an average of 23 days sooner than those undergoing a TMA prior to the availability of ciSNaP. Additionally, patients with peripheral arterial disease (PAD) healed an average of 32 days sooner with ciSNaP. This was not a large randomized trial and one can draw no statistical significance from the current data.  

In Conclusion
Transmetatarsal amputations have become a common procedure for non-healing or infected wounds in a significantly comorbid population. With healing rates following a TMA ranging between 40 and 70 percent and the significant potential for a more proximal amputation with a non-healing TMA, it is imperative to seek modalities that will increase the success rate of TMAs.2 There are clear advantages in terms of cost, return to activity and improved quality of life when faster amputation healing rates occur.

While the patient population is limited in the aforementioned study with the ciSNaP negative pressure wound therapy system, we believe this will serve as the foundation for future studies to explore the financial and clinical benefits of utilizing NPWT systems over closed incisions as an adjunctive treatment.

There is clear evidence to support closed incision NPWT in high-risk populations. Plastic surgeons have adapted NPWT over closed incisions for potential improved cosmetic results. Some orthopedic surgeons have advocated the use of NPWT over joint replacements to prevent incisional dehiscence in high-risk patients such as smokers. The field of obstetrics is utilizing closed incision NPWT in obese patients having cesarean sections.¹⁷

We can clearly place podiatric patients with diabetes and PAD facing amputation in the “high risk” category. Despite a limited number of applications and experience with this particular NPWT modality, we have identified potential positive trends with incorporating a closed incision NPWT system in patients undergoing partial foot amputations. A randomized clinical trial would be advantageous to see if clinical and statistical significance would be evident. 

Dr. Rothenberg is the Director of Resident Training with the Miami VA Healthcare System.

Dr. Levine is a first-year resident with the Miami VA Healthcare System.

References

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Editor’s note: For a related article, see “A Closer Look At Advances With NPWT” in the September 2014 issue of Podiatry Today.