Acute osteomyelitis is characterized primarily by bone resorption and destruction. Chronic osteomyelitis is mainly characterized by the formation of dead bone and new bone. In acute suppurative osteomyelitis, if pus penetrates beneath the periosteum early and then breaks through the skin, bone destruction is less severe; however, abscesses often spread within the medullary cavity, creating high pressure that can occlude or embolize the bone's nutrient vessels. If pus penetrates the bone cortex to form a subperiosteal abscess, it can cause extensive periosteal detachment, depriving the bone cortex of blood supply from the periosteum, severely affecting bone circulation and leading to bone necrosis. The extent and size of necrosis depend on the ischemic range, potentially resulting in necrosis of the entire bone shaft. Due to periosteal detachment, osteoblasts in the deep layer of the periosteum are stimulated by inflammation to produce a large amount of new bone, which encases the dead bone, forming a shell that supports the diseased bone. This shell may have many openings leading to the wound, forming sinuses, and the wound may fail to heal for a long time, resulting in chronic osteomyelitis.

bubble_chart Pathogenesis

It commonly occurs in children and adolescents, starting at the metaphysis of long bones, where clusters of bacteria stagnate and proliferate. After the lesion forms, the abscess is surrounded by bone tissue, with poor drainage, often presenting severe symptoms of toxemia. Subsequently, the abscess expands and spreads in different directions depending on local resistance.

1. The abscess spreads towards both ends of the long bone. Since the epiphyseal plate in children has a strong resistance to infection and is difficult to penetrate, pus often flows into the medullary cavity, affecting the bone marrow. As the pressure of pus in the medullary cavity increases, it can travel along the Haversian canals to the subperiosteal layer, forming a subperiosteal abscess.
2. The pus breaks through the compact bone at the metaphysis and penetrates beneath the periosteum to form a subperiosteal abscess. As the subperiosteal abscess gradually enlarges and the pressure increases, it can also invade the medullary cavity along the Haversian canals or rupture through the periosteum into the soft tissues.
3. It can penetrate into the joint, causing suppurative arthritis. The epiphyseal plate in children has a strong resistance to infection, so the chance of developing arthritis through direct spread is very low. However, adults lack this defense mechanism, making them more prone to developing arthritis. If the metaphysis is within the joint capsule, the infection can quickly enter the joint. For example, osteomyelitis of the upper femur can complicate into hip arthritis.

bubble_chart Treatment Measures

1. Comprehensive supportive therapy: Includes adequate rest and good nursing care, attention to water and electrolyte balance, small and frequent blood transfusions, prevention of bedsores and oral infections, providing easily digestible diets rich in protein and vitamins, use of analgesics to ensure the patient gets better rest.
2. Drug therapy: Timely use of sufficient and effective antibacterial drugs, initially broad-spectrum antibiotics can be chosen, often two or more in combination, later adjusted based on bacterial culture and drug sensitivity test results and treatment efficacy. Antibiotics should continue to be used until about 2 weeks after the body temperature normalizes and symptoms subside. Most cases can gradually control toxemia, a few may not require surgical treatment. If the body temperature does not decrease after treatment, or if an abscess has formed, drug application needs to be coordinated with surgical treatment.
3. Local treatment: Use appropriate splints or gypsum casts to limit movement, elevate the affected limb to prevent deformity, reduce pain, and avoid pathological fractures. If symptoms subside after early drug treatment, surgery can be delayed or may not be necessary. However, if an abscess has formed, timely incision and drainage should be performed. If the abscess is not obvious, symptoms are severe, drugs cannot control within 24 to 48 hours, and there is significant local tenderness in the affected bone, early incision and drainage should be performed to prevent the pus from spreading on its own, causing extensive bone destruction. In addition to incising soft tissue abscesses, surgery also requires drilling holes and opening windows in the affected bone, removing part of the bone to expose the infected part of the medullary cavity, to achieve full decompression and drainage. Early closed drip drainage can be performed, and the wound heals faster.

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bubble_chart Complications

Acute hematogenous osteomyelitis had a high mortality rate in the past (approximately 25%). However, due to a deeper understanding of the disease in recent years, early diagnosis, aggressive treatment, and the appropriate use of antimicrobial drugs and comprehensive therapies, the mortality rate has significantly decreased (approximately 2%).

Bone destruction caused by bone infection leads to the formation of sequestra, often progressing to chronic suppurative osteomyelitis, and even resulting in various complications that affect function. Common complications include:

1. suppurative arthritis.
2. Pathological fracture.
3. Limb growth disorders: such as epiphyseal destruction, which affects the length of limb growth, leading to shortening of the affected limb; or due to inflammation near the epiphysis, with abundant blood supply, causing faster growth of the epiphysis, resulting in the affected limb being slightly longer. Sometimes, partial involvement of the epiphysis can lead to deformities, such as genu varum or valgus.
4. Joint contracture and ankylosis.
5. Traumatic osteomyelitis: often due to infection, leading to delayed union or non-union of fractures, as well as restricted joint movement.

bubble_chart Differentiation

1. Cellulitis: Systemic toxic symptoms are mild, local inflammation is extensive, and the range of tenderness is also larger.
2. Acute suppurative arthritis: Swelling and tenderness are in the joint space rather than at the bone ends, joint movement is almost completely lost, and when in doubt, joint cavity puncture and fluid examination can confirm the diagnosis.
3. Wind-dampness arthritis: Generally, the condition is mild, fever is low, local symptoms are also mild, the affected area is in the joints, and multiple joints are often involved.