Biomechanics of Ambulation After Partial Foot Amputation: Prevention and Management of Reulceration

Ronald A. Sage, DPM

ABSTRACT

Partial foot amputations account for half of more than 80,000 amputations per year related to diabetes in the United States. Altered biomechanics of the foot frequently lead to focal pressure keratosis and subsequent ulceration in neuropathic and dysvascular patients. The minor trauma associated with these pressure points is a major contributing factor to amputation. Partial foot amputation may further alter the biomechanics of the foot, producing new focal pressure points, leading to transfer ulceration. These transfer lesions place the patient at risk for additional amputation. Prevention of these ulcerations starts with medical management of the macrovascular and microvascular complications of diabetes. Beyond that, once a new focal pressure point is identified after partial foot amputation, prescription of an appropriate pressure-relieving orthosis or prosthesis may reduce the risk of reulceration. This is especially true when combined with other foot evaluation and management services as necessary to control focal callus formation before ulceration can occur. (J Prosthet Orthot. 2007;Proceedings:P77–P79.)

Despite efforts to control diabetes and improve limb salvage rates, the number of amputations performed in the United States because of diabetes continues to rise. More than 80,000 diabetes-related amputations are performed each year, with approximately one half partial foot procedures and one half transtibial or higher.¹ Partial foot amputation, in itself, is a risk factor for reulceration and further amputations. With appropriate postoperative management, preventive interventions may be initiated that can help lower these dismal statistics.

COMPLICATIONS OF DIABETES

Diabetic patients experience macrovascular and microvascular complications. Both of these increase the risk of serious foot problems. Prevention of further amputation starts with the medical management of the factors leading to these complications. All clinicians should be aware of these systemic disorders and encourage his or her patient's compliance with measures to control these disease processes.²

Macrovascular complications affect the larger vessels and include coronary artery disease (CAD) and peripheral arterial disease (PAD). Although diabetic patients are thought to be more susceptible to these conditions than the nondiabetic population, glucose control alone will not alter the course of these diseases. Medical interventions include exercise, prevention of thrombosis with aspirin or other medications, control of hypertension, and lipid management.

During any professional visit, hypertension education can be provided and compliance with blood pressure control measures encouraged. Undiagnosed or uncontrolled hypertension should be referred to the internist for intervention. Any blood pressure in excess of 130/80 mm Hg should be further evaluated. To take it a step further, screening for PAD by Doppler examination and determination of ankle-brachial artery index can also aid the detection of CAD. Patients 50 years old and older with ankle-brachial artery index (ABI) less than 0.5 should see a physician for cardiovascular risk evaluation. There is a 20% 5-year risk of nonfatal cardiac events in patients with PAD, and a 30% 5-year mortality rate in this group, even if they have not suffered from critical limb ischemia or amputation.³ Medical interventions can include thrombosis risk prevention, exercise, and management of lipid abnormalities. Referral for vascular intervention may also be appropriate, especially in cases of claudication or tissue loss (ulceration).

Microvascular complications include retinopathy, renal disease, and neuropathy. These appear to be directly related to hyperglycemia. Tight glucose monitoring and control is now the standard of care for both type 1 and type 2 diabetes. Encouraging compliance with such a regimen should be part of any office visit. Severe signs of neuropathy, such as profound numbness or ulceration, are indicators of poor control. Office evaluation of blood glucose or hemoglobin A1c may provide laboratory evidence of poor control. The patient must be encouraged to monitor and report glucose levels to the physician caring for his or her diabetes, and obtain appropriate management to optimize blood glucose levels. Referral to an endocrinologist may be appropriate if the primary physician is unable to normalize the glucose levels.

FOOT RISK IDENTIFICATION

The American Diabetes Association, in a position statement on foot care, has identified four conditions that are associated with an increased risk of amputation.⁴ These include:

Peripheral neuropathy
Altered biomechanics, including pressure callus and limited joint mobility, bony deformity, or severe nail pathology
Peripheral arterial disease
History of ulcer or amputation

The partial foot amputee may well be affected by each of these risk factors. In particular, pressure callus or focal pressure keratosis frequently can lead to ulcerations that fail to heal in the neuropathic patient. If a partial foot amputation has been performed because of a nonhealing focal pressure ulceration, there is a significant risk of altered biomechanics leading to a transfer of the focal pressure point to anotherlocation in the residual foot, restarting the ulcerative process. These patients may have even more problems healing if PAD is also present. The type of pressure-relieving foot orthosis required depends on the severity of the abnormality and the degree of intervention necessary to control the ulcer risk. At times, a simple athletic shoe or inlay depth shoe with a commercial insole may be adequate to control the pressure point. On the other hand, some patients with severe hemorrhagic keratosis under an isolated bony prominence may require custom orthotics, ankle-foot orthoses (AFO), or even CROW walkers in addition to debridement of the keratosis on a regular basis to prevent ulceration. Clinical observations suggest that the application of these fundamental orthotic and podiatric principles is extremely effective in preventing ulceration, infection, hospitalization and amputation. However, these devices are prescribed and fabricated on the basis of experience and consensus and lack hard evidence to support their appropriate use.

OUTPATIENT CARE AND MORBIDITY REDUCTION

In 2001, our group at Loyola University Chicago and Hines VA Hospital published a study in the Journal of the American Podiatric Medical Association in which we reviewed 233 cases of diabetic foot ulceration admitted to our hospitals during a 7-year period.⁵ We found that 82% of these ulcers were preceded by a focal pressure keratosis. Those patients who had frequent outpatient podiatric care had lower grade ulcerations and were less likely to require any form of surgical intervention. Conversely, the worst ulcerations were those without documentation of any prior podiatric care. Measures that were found effective in decreasing ulcer grade included debridement of keratosis or ulcer, prescription of protective shoes, and patient education.

The clinic or office visit consists of identification of patient complaints and pertinent history. Foot complaints and comorbidities such as renal disease or CAD should be documented, medications reviewed, and some assessment of glucose control should be noted. The podiatric physical should include at least brief vascular and sensory evaluations. Detailed exam of these systems is not necessary at every visit but should be performed once or twice a year, depending on the individual patient. In particular, the presence or absence of ulcer or ulcerative lesion should be noted. A diagnosis and risk assessment is stated.

Management of focal pressure keratosis, when present, is critical. Prescription for pressure-relieving shoes and orthoses is provided. Existing foot gear should be inspected, and replacement or revision prescribed when necessary. Debridement of chronic pressure keratosis at intervals appropriate to prevent ulceration can decrease hospitalizations and amputations.⁵ The natural history of untreated pressure callus in a diabetic neuropathic patient is ulceration, infection, and amputation. The minor trauma associated with focal pressure callus leading to ulceration, faulty healing, infection, and amputation is a classic example of Pecoraro's triad, which he suggested is responsible for 80% of all diabetes-related amputations.⁴

Patient education should be provided at every visit. Neuropathy and the importance of visual foot exams at home can be explained. Good skin care and hygiene principles can be reviewed. Compliance with diabetes control and cardiovascular risk reduction measures should be encouraged. Indications for professional treatment should be explained. Appropriate intervals for office visits should be determined and recommended.

CONCLUSION

Altered biomechanics of the foot can lead to focal pressure keratosis. In a diabetic patient, this is an event that can initiate the triad of minor trauma, cutaneous ulceration and faulty healing thought to lead to most diabetes-related amputations. This is especially true in those with poorly controlled diabetes or those with vascular disease. Partial foot amputation alters the biomechanics of weight bearing even further, making the patient susceptible to new pressure points that can ulcerate.

Orthotic and prosthetic care after partial foot amputation differs in diabetic patients, who have numerous medical issues and are at risk for further amputation, as with posttraumatic amputates who seek optimum function and performance from their prostheses and orthoses. The ideal foot orthosis or prosthesis in a person with diabetes at risk for further amputation must disperse, or prevent, focal pressure points.

To fabricate such devices, research needs to be directed at identifying the likely points of maximum pressure after various partial foot amputations. Devices and materials need to be studied to determine how an orthosis or prosthesis can effectively eliminate or redirect these pressure points and reduce the risk of reulceration. By reducing this risk, the likelihood of subsequent amputation is decreased.

Correspondence to: Ronald A. Sage, DPM, Loyola University Stritch School of Medicine, 2160 South First Avenue, Maywood, IL, 60153; e-mail:

RONALD A. SAGE, DPM, is a professor and chief of the Section of Podiatry of the Department of Orthopaedic Surgery and Rehabilitation and a staff podiatrist at Edward Hines Jr. VA Hospital, Loyola University Stritch School of Medicine, Maywood, Illinois.

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