A Closer Look At The WIfI Classification System For Threatened Limbs

Diabetes has become an epidemic resulting in devastating physical and financial loss. While researchers project the incidence of diabetes to increase by nearly 200 percent from 2005 to 2050, the concern deepens as approximately 60 percent of non-traumatic lower extremity amputations in the United States occur in patients with diabetes.^1,2 The U.S. healthcare system spent an estimated $29 billion in 2007 on foot ulcers and amputations.³

Patients with diabetes commonly have a list of comorbidities. Peripheral arterial disease (PAD) has become increasingly prevalent in the diabetic population and places patients at risk for developing ischemic or neuroischemic foot ulcers, and ultimately loss of limb. As we move toward improving standards for managing limb-threatening conditions, it has become imperative that we correctly identify this multifarious population.

Classification systems are powerful tools for providers to use when managing patients with threatened limbs. The ability to define and delineate a heterogeneous group into fine-grained cohorts not only aids communication between providers, it allows for a more accurate analysis of outcomes across treatment strategies. Thus, classification systems are essential for clinical decision making as well as setting meaningful goals and expectations with patients and their families.

Current classification schemes fall short in capturing the full spectrum of disease for threatened limbs. The Fontaine and Rutherford classifications, commonly in use for threatened limbs and PAD, are purely ischemic models.^4,5 Neither classification includes infection or provides sufficient detail of wound severity.^4,5 Similarly, the widely used Wagner and University of Texas wound classification systems lack proper assessment of perfusion status and infection. The Wagner system does not account for severity of PAD nor does it delineate gangrene due to infection versus ischemia.⁶ The University of Texas system includes PAD and infection, but lacks severity gradation for either category.⁶ No classification system sufficiently incorporates all etiologies of threatened limbs: wound extent, ischemia and infection.

A Pertinent Overview Of The WIfI Classification Grading System

In 2014, The Society for Vascular Surgery Lower Extremity Guidelines Committee published a classification system for threatened lower limbs, categorizing and grading (0–3) the three major risk factors leading to amputation: wound, ischemia and foot infection (WIfI).⁷ The WIfI system merges existing classification systems, including the Infectious Diseases Society of America (IDSA) classification for diabetic foot infections, into a single concise system. After grading each category, one can then clinically stage the affected limb to estimate risk of amputation at one year.

Not only does WIfI predict amputation risk, it is the only system that can standardize outcome comparisons for accurate analysis of the increasing number of available therapies.⁸ The WIfI classification has the capability to improve guideline-based management of these complex and resource-intensive patients.⁹

The Society for Vascular Surgery WIfI system is intended for any patient with a diabetic foot ulcer, non-healing foot ulcer present for two or more weeks, foot/lower extremity gangrene, or ischemic rest pain.⁷ It is not meant for patients with acute ischemia, emboli, trauma, non-atherosclerotic diseases such as vasospastic disorders, or pure venous ulcers.

Wound. The first category accounts for the degree of tissue loss and anticipated level of intervention/amputation required for healing.⁷
Grade 0: No ulcer, no gangrene. Ischemic rest pain.
Grade 1: Minimal tissue loss. No exposed bone (unless limited to distal phalanx). Intervention requires no more than a toe amputation or soft tissue covering. No gangrene.
Grade 2: Moderate tissue loss. Ulcer extends to tendon, joint, or bone. Localized gangrene to digits only. Intervention requires transmetatarsal amputation (TMA) or less.
Grade 3: Extensive tissue loss. Gangrene to forefoot, midfoot and hindfoot. Intervention requires more than a transmetatarsal amputation and/or complex soft tissue rearrangement.

Ischemia. The second category assesses perfusion status to the foot using objective hemodynamic indices such as ankle brachial index (ABI), transcutaneous oximetry, pulse volume recording, skin perfusion pressure or toe pressure. Toe pressure measurements are preferable for those with calcified vessels or non-compressible ABIs (as one may encounter in patients with diabetes and end-stage renal disease).⁷
Grade 0: No ischemia. ABI ≥ 0.80; toe pressure ≥ 60 mmHg.
Grade 1: Mild ischemia. ABI ≥ 0.6–0.79; toe pressure 40-59 mmHg.
Grade 2: Moderate ischemia. ABI ≥0.4–0.59; toe pressure 30-39 mmHg.
Grade 3: Severe ischemia. ABI ≤ 0.39; toe pressure <30 mmHg.

Foot infection. The last category describes the foot infection and derives from the IDSA and PEDIS clinical staging systems.⁷ (The PEDIS system, a classification system developed by the International Working Group on the Diabetic Foot, measures perfusion, extent/size, depth/tissue loss, infection and sensation.)
Grade 0: No infection.
Grade 1: Superficial infection. Localized cellulitis ≤ 2 cm.
Grade 2: Moderate (deep) infection. Erythema > 2 cm. Abscess present or infection extends to joint or bone.
Grade 3: Severe infection. Local infection with systemic inflammatory response syndrome (SIRS).

After calculating the WIfI score, one will use the classification system to assess the clinical stage 1–5 (with stage 5 being an unsalvageable foot) and estimate the risk of major amputation at one year. The stages derive from a grid of 64 theoretically possible outcomes assigned by a 12-member expert group using a Delphi consensus method.⁷ If this seems daunting, the Society for Vascular Surgery has created a free WIfI calculator on its app, available for download on iTunes.
 

Stage 1: Amputation risk: very low
Stage 2: Amputation risk: low
Stage 3: Amputation risk: moderate
Stage 4: Amputation risk: high
Stage 5: Unsalvageable foot

Case Study Examples With The WIfI Classification System

To further illustrate the mechanics of the WIfI classification, here are a couple of case examples.

Case 1. A 59-year-old male with diabetes mellitus and peripheral neuropathy presented to the emergency department with a plantar left foot ulcer and surrounding cellulitis. The ulcer probed to the second metatarsal head with evidence of deep space abscess. He exhibited systemic symptoms of infection that satisfied SIRS criteria. There was no radiographic evidence of subcutaneous emphysema and non-invasive vascular studies showed an ABI of 1.02 and toe pressures of 65 mmHg.

Given these findings, his WIfI score was: wound 2, ischemia 0, foot infection 3, correlating to a clinical stage 4. This suggests a high risk of major amputation at one year.

Case 2. An 82-year-old male presented with right lower extremity rest pain. He had a past medical history of type 2 diabetes, peripheral neuropathy and known PAD with prior bilateral femoral popliteal bypass performed at an outside hospital. He also had a non-healing, right dorsal foot wound with exposed and desiccated extensor tendons, and dry gangrene of his second toe. His wound did not probe to bone. He had periwound hyperemia with no evidence of local infection. He was afebrile with normal vital signs, indicating no systemic signs of infection. There were no radiographic findings suggestive of osteomyelitis. Noninvasive vascular studies showed an ABI 0.31 and toe pressure of 0. An aortogram with a lower extremity runoff arteriogram showed occlusion of his right femoral-popliteal bypass.

Given these findings, his WIfI score was: wound 2, ischemia 3, foot infection 0, correlating to a clinical stage 4. This suggests a high risk of major amputation at one year.
 
What The Studies Reveal About The WIfI Classification System

Several independent studies have validated the ability of the WIfI classification system to accurately assess amputation risk at one year.^7,8,10-13 Not only did these studies verify amputation risk but they also showed prolonged wound healing in the higher staged wounds.^10-12

Causey and coworkers also found that WIfI staging was a strong predictor of initial hospital duration stay and with higher WIfI stages, there was an increased number of revascularization procedures and podiatric procedures.⁸ Results from Darling and colleagues supported the prognostic amputation risk ability of the WIfI classification system for those undergoing infrapopliteal endovascular procedures.¹² Confirming that the WIfI classification is not inclusive to patients with diabetes, Beropoulis and coworkers successfully evaluated one-year amputation risk in non-diabetic patients with critical limb ischemia (CLI).¹³ These studies not only verify the WIfI classification system’s ability to accurately stage patients but they demonstrate its potential use to predict hospital duration and costs, wound healing rates and need for timely revascularization.

In Conclusion

The Society for Vascular Surgery WIfI classification offers a more robust system than existing classifications and functions to integrate the key factors affecting tissue loss: foot wound, ischemia, and infection. As the WIfI staging systematically classifies the heterogeneous population with limb-threatening conditions, it provides a framework to evaluate patients and interventions, set meaningful goals and expectations, and develop specific treatment algorithms.

Ms. Behan is a third-year podiatric medicine student at the California School of Podiatric Medicine at Samuel Merritt University.

Dr. Kwon is an Assistant Professor at the California School of Podiatric Medicine at Samuel Merritt University.

Dr. Reyzelman is an Associate Professor at the California School of Podiatric Medicine at Samuel Merritt University. He is the Co-Director of the University of California San Francisco (UCSF) Center for Limb Preservation.

References

1. Centers for Disease Control and Prevention. National Diabetes Statistics Report: Estimates of Diabetes and Its Burden in the United States, 2014. U.S. Department of Health and Human Services.
2. Narayan KM, Boyle JP, Geiss LS, et al. Impact of recent increase in incidence on future diabetes burden: US 2005-2050. Diabetes Care. 2006;29(9):2114-6.
3. Rogers LC, Lavery LA, Armstrong DG. The right to bear legs—an amendment to healthcare: how preventing amputations can save billions for the US health-care system. J Am Podiatr Med Assoc. 2008;98(2):166-168.
4. Fontaine R, Kim M, Kieny R. Surgical treatment of peripheral circulation disorders. Hely Chir Acta. 1954;21(5–6):499-533.
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6. Oyibo SO, Jude EB, Tarawneh I, et al. A comparison of two diabetic foot ulcer classification systems: the Wagner and the University of Texas wound classifications systems. Diabetes Care. 2001;24(1):84-8.
7. Mills JL, Conte MS, Armstrong DG, et al. The Society for Vascular Surgery Lower Extremity Threatened Limb Classification System: Risk stratification based on Wound, Ischemia, and foot Infection (WIfI). J Vasc Surg. 2014;59(1):220034.e1-2.
8. Causey MW, Ahmed A, Wu B, et al. Society for Vascular Surgery limb stage and patient risk correlate with outcomes in an amputation prevention program. J Vasc Surg. 2016;63(6):1563-73.
9. Vartanian SM, Robinson KD, Ofili K, et al. Outcomes of neuroischemic wounds treated by a multidisciplinary amputation prevention service. Ann Vasc Surg. 2015;29(3):534-42.
10. Zhan LX, Branco BC, Armstrong DG, Mills JL. The Society for Vascular Surgery lower extremity threatened limb classification system based on Wound, Ischemia, and foot Infection (WIfI) correlates with risk of major amputation and time to wound healing. J Vasc Surg. 2015;61(4):939-44.
11. Cull DL, Manos G, Harley MC, et al. An early validation of the Society for Vascular Surgery Lower Extremity Threatened Limb Classification System. J Vasc Surg. 2014;60(6):1535-42.
12. Darling JD, McCallum JC, Soden PA, et al. Predictive ability of the Society for Vascular Surgery Wound, Ischemia, and foot Infection (WIfI) classification system following infrapopliteal endovascular interventions for critical limb ischemia. J Vasc Surg. 2015; 64(3):616-622.
13. Beropoulis E, Stavroulakis K, Schwindt A, et al. Validation of the Wound, Ischemia, foot Infection (WIfI) classification system in nondiabetic patients treated by endovascular means for critical limb ischemia. J Vasc Surg. 2016;64(1):95-103.