Osteomyelitis and Diabetic Foot Ulcer

Osteomyelitis is an inflammation of the bone,usually the long bones of the arms and legs, which is caused by a pyogenic organism. If left untreated, it may lead to bone destruction or stiffening of the joints due to spread of the infection. In extreme cases, where infection occurs before the end of the growth period and the growth center of the bone is destroyed, it results in shortening of the affected limb. Osteomyelitis occurs in two forms: acute and chronic infection. There is no abrupt shift from acute to chronic disease, but rather a gradual blending of one into the other.

Acute osteomyelitis is usually a bloodborne disease, most often affecting rapidly growing children. Chronic osteomyelitis commonly develops as a complication of infections from other sites, such as the pharynx (pharyngitis), ear (otitis media), or skin (impetigo). Though osteomyelitis can develop through blood-borne bacteria in adults, in these patients it is more often the result of tissue contamination at the time of injury or surgery. Chronic osteomyelitis usually requires surgery to remove dead bone (sequestrectomy) and to promote drainage (saucerization). On the basis of the pathogenesis of the lesion, cases of osteomyelitis fall into one of three categories:

  1. Hematogenous Osteomyelitis
  2. Osteomyelitis resulting from a secondary focus of infection
  3. Osteomylitis associated with peripheral vascular disease

Hematogenous Osteomyelitis

85% of hematogenous osteomyelitis cases occur in children where it affects the rapidly growing bone tissue. Osteomyelitis commonly occurs in the metaphyseal region of long bones where turbulent, slow flow is felt to favor bacterial deposition.

Epiphyseal and joint involvement is common in children younger than 18 months due to the presence of trans-physeal vessels. In older children the growth plate prevents the spread of infection into the epiphysis. In neonates with osteomyelitis, systemic disturbances may be mild or absent. Detection is therefore frequently delayed, and often spread of the infection has occurred. The local decrease in pH, the occurrence of edema and the accumulation of leukocytes contribute to tissue necrosis and breakdown of the bone trabeculae.

Spreading into the neighboring bone and the occluding of vascular channels causes the death of more osteocytes. When larger bone segments become isolated due to blood supply deprivation, they form sequestra. They act as foreign bodies,and the infection develops from an acute condition into a chronic one, rendering eradication by antibiotics impossible until the devitalized bone is removed.

The degenerative process may also cause a septic thrombophlebitis. Subsequent formation of a sub-periosteal abscess, is associated with considerable local pain, tenderness, and swelling due to the accumulation of pus under pressure.

Sub-periosteal infection can induce exuberant circumferential growth of the periosteum. Progressive chronic destruction of the cortex will ultimately lead to spontaneous pathological fracture in some instances.

About one-third of the patients suffer from a bacterial infection, S. aureus being the one most commonly found. Group B streptococcal infection is seen more commonly in neonates.

In drug addicts and nosocomial infections, gram negative bacteria such as Pseudomonas and Klebsiella are commonly encountered. E. coli is usually the cause of spinal osteomyelitis following urinary tract infection. In patients with sickle cell anemia, infections with S. aureus and Salmonella are common.

Osteomyelitis Secondary to a Contiguous Focus of Infection

Osteomyelitis secondary to a contiguous focus of infection occurs most commonly after surgical procedures, such as open reduction of fractures, craniotomy, and reconstruction of joints that are severely affected by degenerative arthritis. Additional causes are skin burns, infection of the ears or para-nasal sinuses, animal bites, and infection of soft tissue due to trauma. In contrast to hematogenous osteomyelitis, which is predominantly a disease of the young, most patients with this form of bone disease are over 50 years old. These infections tend to be chronic, recurrent, and difficult, if not impossible, to eradicate. Complete recovery is only possible when all foreign bodies are removed.

The most frequent clinical manifestations are local pain and drainage from a sinus tract. S. aureus is the bacterium most commonly involved. However, less invasive bacteria can cause this syndrome, as mostly found in infections of orthopedic prosthesis.

The usual manifestations of acute infection are often absent in this setting. Minimal local erythema, low-grade fever, pain and limitation of motion secondary to spasm of muscles in and around the affected bone are the most important features.

Osteomyelitis Associated with Vascular Insufficiency

Osteomyelitis associated with vascular insufficiency is most frequently found in patients with long-standing diabetes mellitus, occasionally in individuals with severe artherosclerosis and sporadically in persons with vasculitis secondary to a connective tissue disorder.

The pathogenesis of the process involves extension of infection into bone secondary to ischemic ulceration of the skin. The disease is almost invariably localized to the toes or the small bones of the feet. Local symptoms of pain, swelling, and erythema dominate the clinical picture. There are few systemic manifestations of infection.

Diabetic Foot Ulcers

Diabetes is caused by reduced levels of insulin, a hormone produced by the pancreas (an endocrine gland located in the upper-middle abdomen) which is responsible for the proper metabolism of blood sugar and the maintenance of blood sugar level.

Two types can be discriminated: Type I (autoimmune; manifest early in life, body produces no insulin; 5 -1 0% of all cases) and Type II (metabolic; body fails to make sufficient amounts of insulin; 90-95% of all cases). Aside from the immediate effects of elevated blood sugar levels, the long term effects of diabetes relate to blood vessel changes, vasculopathy, and degeneration of the neuronal system, neuropathy.

Thickening of the walls of the arteries causes an increased risk of a heart attack or stroke, kidney problems and reduced circulation to the legs. People with diabetes are 2 to 3 times more likely to develop heart and stroke problems and are 12 to 13 times more at risk for amputation.

As a result of reduced blood circulation to the legs, the skin on the foot becomes very thin and vulnerable. Moreover, the neuropathy impairs sensation and foot trauma is likely to go unnoticed. This frequently results in foot ulcers. The most vulnerable areas are the first three metatarsal heads and the plantar medial aspect of the great toe.

The appearance of a diabetic foot ulcer does not mean an infection is present. Unless signs of ischemia or infection are present, most of these ulcers can be successfully managed by relief of pressure. Severe cases require a below-knee cast to redistribute forces and reduce shear stresses to the skin.

The plaster should conform exactly to the patient's needs and be changed weekly. Using this approach, approximately 90 percent of plantar ulcers heal within five weeks.

Infection in diabetic foot ulcers is usually caused by multiple organisms. Deep cultures for both anaerobic and aerobic organisms are advised in addition to conventional surface wound swabs.

The most common bacteria found are S. aureus, S. epidermidis, Streptococci, Enterococci and anaerobic organisms. Debridement of devitalized tissue is essential before therapy with antibiotics is started. For initial treatment broad-spectrum antibiotics, such as ciprofloxacin, metronidazole or amoxicillin-clavulanate are used. Specific regimens guided by culture and sensitivity results should be initiated as soon as data are available. Treatment should be carried out for at least two to four weeks, but it may need to be continued for several months if osteomyelitis is present.

Annual screening for a diabetic foot should include a skin and soft tissue evaluation at least once per year, but preferably several times per year. Tests should include neurological, vascular, musculoskeletal, skin and soft tissue examination.

Neurological examination for sensation are the Semmes-Weinstein monofilament test to examine the extent of neuropathy, the tuning fork or biothesiometer to identify Vibration Perception Thresholds (VPTs), Q-tip test to discriminate between a sharp and a blunt object, the reflex-test and the proprioceprion test. Physical vascular examinations include palpation of the pulses, inspection for any gross ischemic changes and possible vascular consultation.

Radiographic vascular examination (arteriogram) should also be carried out. A musculoskeletal evaluation should include include the estimation of the foot and ankle joint range of motion, assessment of gait, inspection for bone abnormalities and possible orthopedic consultation.

Early diagnosis and treatment are imperative in this clinical setting since untreated patients have high morbidity and often require amputation.

Epidemiology

The incidence of chronic osteomyelitis is 2 out of 10,000 people.

Country Population Diabetes Mellitus

(Million) (Million)

Germany 82 2,4

UK 59 2,4

France 59 2,4

Italy 58 2,3

Spain 40 1,6

Poland 39 1,5

The Netherlands 16 0,63

Hungary 10 0,41

Sweden 9 0,36

Switzerland 7 0,29

Denmark 5 0,21

As indicated in the table, between 3 and 5% of the population suffers from Type I or Type II diabetes and diabetic foot infections exert high costs on the European healthcare systems.

Diabetic patients account for about half of all the lower extremity amputations performed for non-traumatic indications. One-third of all diabetics eventually undergo an amputation (G.A. Holloway, 'The Diabetic Foot.' Abstract presented during the Symposium on advanced Wound Care & Medical Research Forum on Wound Repair, San Diego, California, USA, May 1995).

19% of all diabetics suffer from foot ulcers (http://www.amc.uva.nl/posters/17/index.html), and in Sweden 60% of the diabetics over 70 years of age have an amputation (J. Apelqvist et al., 'Putative Risk Factors Associated with Foot Ulcers in Diabetic Patients.' Abstract 1049 in the Minutes of the European Association for the Study of Diabetes, 31st Annual Meeting, Stockholm, Sweden, 12-16 September 1995). The surgical mortality of major leg amputation is 11-13%, which is probably not related to the amputation itself, but to the patients' overall debilitation due to concomitant renal and vascular disease.

The complications of osteomyelitis are clinically silent; it cannot be determined readily in foot ulcers. In a more recent study, it was found that that leukocytosis is a poor indicator of acute osteomyelitis of the foot in patients with diabetes mellitus

The consequences of not diagnosing osteomyelitis promptly and correctly are amputation of the affected limb, disability and, possibly, death.

Indeed, it has been estimated in the U.S. that diabetic patients account for about half of all the lower extremity amputations performed for non-traumatic causes.

In Germany this number is estimated to be 75%, thus indicating the serious medical and economic implications of osteomyelitis in this patient population, and the need for rapid and accurate means of diagnosis, and the early implementation of effective antibiotic therapy.

Submitted By:
DR. M.R. BHUIYAN

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