Osteomyelitis, an infection of bone, is caused most commonly by pyogenic bacteria and mycobacteria.

Introduction
As a useful framework for evaluating a patient and planning treatment, cases are classified on the basis of
1.The causative agent
2.The route by which organisms gain access to bone
3.The duration of infection
4.The anatomic location of infection
5.The local and systemic host factors that have a bearing on pathogenesis and outcome.

Pathogenesis and Pathology
Microorganisms enter bone by hematogenous dissemination, by spread from a contiguous focus of infection, or by a penetrating wound.

Trauma, ischemia, and foreign bodies enhance the susceptibility of bone to microbial invasion by exposing sites to which bacteria can bind and by impeding host defenses.

Phagocytes attempt to contain the infection and, in the process, release enzymes that lyse bone.

Pus spreads into vascular channels, raising intra osseous pressure and impairing the flow of blood; as the untreated infection becomes chronic, ischemic necrosis of bone results in the separation of large devascularized fragments (sequestra).

When pus breaks through the cortex, subperiosteal or soft tissue abscesses form, and the elevated periosteum deposits new bone (an involucrum) around the sequestrum.

Microorganisms, infiltrates of neutrophils, and congested or thrombosed blood vessels are the principal histologic findings of acute osteomyelitis.

The distinguishing feature of chronic osteomyelitis is necrotic bone, which is characterized by the absence of living osteocytes.

Mononuclear cells predominate in chronic infections, and granulation and fibrous tissues replace bone that has been resorbed by osteoclasts.

In the chronic stage, organisms may be too few to be seen on staining.

Hematogenous Osteomyelitis
Hematogenous infection accounts for greater than 20% of cases of osteomyelitis and primarily affects children, in whom the long bones are infected, and older adults and intra venous drug users, in whom the spine is the most common site of infection.
Acute Hematogenous Osteomyelitis
Infection usually involves a single bone, most commonly the tibia, femur, or humerus in children and vertebral bodies in injection drug users and older adults.

CLINICAL FEATURES:

The child with osteomyelitis usually appears acutely ill, with fever, chills, localized pain and tenderness, and in many cases restriction of movement or difficulty bearing weight

A history is often obtained of recent blunt trauma to the area involved; presumably, this event results in a small intra osseous hematoma or vascular obstruction that predisposes to infection.

Adults with hematogenous osteomyelitis may present either in the context of an infection elsewhere presents with the respiratory or urinary tract, a heart valve, or an intravascular catheter site or without an obvious source of bacteremia.

Vertebral Osteomyelitis
The vertebrae are the most common sites of hematogenous osteomyelitis in adults.

Organisms reach the well-perfused vertebral body via spinal arteries and quickly spread from the end plate into the disk space and then to the adjacent vertebral body.

Sources of bacteremia include the urinary tract especially among men over age 50, dental abscesses, soft tissue infections, and contaminated IV lines, but the source of bacteremia is not evident in more than half of patients.

Diabetes mellitus requiring insulin injection, a recent invasive medical procedure, hemodialysis, and injection drug use carry an increased risk of spinal infection.

Osteomyelitis Secondary to a Contiguous Focus of Infection
Introduction:
This broad category of osteomyelitis accounts for greater than 80% of all cases and occurs most commonly in adults. It includes infections introduced by penetrating injuries, such as bites, puncture wounds, and open fractures; by surgical procedures; and by direct extension of infection from adjacent soft tissues.
Generalized vascular insufficiency and the presence of a foreign body are important predisposing factors and also make infection more difficult to cure.

Clinical feature and diagnosis:
Frequently, the diagnosis of this type of osteomyelitis is not made until the infection has already become chronic.
The pain, fever, and inflammatory signs due to bony infection may be attributed to the original injury, to underlying bone or joint disease such as degenerative arthritis, or to overlying soft tissue infection.

Osteomyelitis may become apparent only weeks or months later, when a sinus tract develops, a surgical wound breaks down, or a fracture fails to heal.

A special type of contiguous-focus osteomyelitis occurs in the setting of peripheral vascular disease and nearly always involves the small bones of the feet of adults with diabetes.
This type of infection is a major cause of morbidity for patients with diabetes and results in many thousands of amputations per year.

Diabetic neuropathy exposes the foot to frequent trauma and pressure sores, and the patient may be unaware of infection as it spreads into bone.

INVESTIGATIONS:
*Complete blood picture
*Blood tests for glucose levels
*Plain radiographs
*Ct scan
*MRI SCAN of bones