12.5 Bone & Joint Infections

Question 1

A 10-year-old boy presents with a 3-day history of fever, localized pain, and swelling over his right tibia. He has difficulty bearing weight on the affected leg. On examination, the right tibia is warm, swollen, and tender. Laboratory investigations show a white blood cell count of 15,000 cells/mm³ and a C-reactive protein level of 120 mg/L.

Which of the following is the most likely causative organism?

A) Staphylococcus aureus
B) Streptococcus pyogenes
C) Pseudomonas aeruginosa
D) Mycobacterium tuberculosis
E) Escherichia coli

Correct Answer: A) Staphylococcus aureus

Explanation:
Acute hematogenous osteomyelitis is most commonly seen in children and typically presents with fever, localized bone pain, swelling, erythema, and difficulty bearing weight. The elevated white blood cell count (15,000 cells/mm³) and markedly raised C-reactive protein (120 mg/L) indicate an active systemic inflammatory response consistent with infection.

The most frequent causative organism in otherwise healthy children with acute osteomyelitis is Staphylococcus aureus, responsible for approximately 80-90% of cases. This pathogen has a high affinity for bone tissue and can rapidly cause local destruction if not treated promptly.

Other organisms such as Streptococcus pyogenes may occasionally cause osteomyelitis but are less common. Pseudomonas aeruginosa is typically associated with puncture wounds or infections in immunocompromised hosts. Mycobacterium tuberculosis usually causes a more chronic, indolent infection rather than an acute presentation. Escherichia coli is often seen in neonates or patients with urinary tract infections leading to secondary bone involvement.

Early identification of the causative organism allows targeted antibiotic therapy, which is critical to preventing chronic infection and complications such as bone necrosis or septic arthritis.

Question 2

A 45-year-old man with poorly controlled diabetes presents with a 5-day history of severe pain, swelling, and redness in his left knee. He reports fever and inability to move the joint. On examination, the knee is warm, swollen, and tender with limited range of motion. Synovial fluid aspiration reveals a turbid fluid with a white blood cell count of 80,000 cells/mm³, predominantly neutrophils. Gram stain shows gram-positive cocci in clusters.

Which of the following is the most appropriate initial management?

A) Oral antibiotics and rest
B) Intravenous antibiotics and joint aspiration
C) Immediate joint replacement surgery
D) Nonsteroidal anti-inflammatory drugs only
E) Physical therapy without antibiotics

Correct Answer: B) Intravenous antibiotics and joint aspiration

Explanation:
Septic arthritis is a medical emergency characterized by joint infection causing rapid joint destruction if untreated. It commonly presents with acute onset of joint pain, swelling, fever, and reduced range of motion.

In this patient, synovial fluid analysis shows a high white cell count with neutrophil predominance, and gram stain reveals gram-positive cocci in clusters, suggesting Staphylococcus aureus infection, the most common pathogen in septic arthritis.

The initial management involves prompt joint aspiration to drain purulent material and reduce pressure in the joint. This also allows for culture and sensitivity testing to guide antibiotic therapy. Empiric intravenous antibiotics should be started immediately, targeting common pathogens including S. aureus.

Oral antibiotics alone are insufficient for acute septic arthritis, and surgical joint replacement is not indicated initially. NSAIDs and physical therapy may help with symptoms but do not treat the infection and can delay appropriate care.

Early diagnosis and aggressive treatment are critical to preserve joint function and prevent complications such as joint destruction and systemic spread of infection.

Question 3

A 6-year-old girl presents with a painful, swollen left hip and refuses to bear weight. She has had a fever of 38.5°C for two days. On examination, the left hip is held in slight flexion and external rotation with limited movement due to pain. Laboratory tests show a white blood cell count of 14,500 cells/mm³ and a C-reactive protein of 90 mg/L. An ultrasound of the hip reveals a joint effusion.

Which of the following is the most appropriate next step in management?

A) Observation and analgesia
B) Immediate hip joint aspiration and intravenous antibiotics
C) Oral antibiotics and outpatient follow-up
D) Magnetic resonance imaging (MRI) of the hip
E) Referral for elective hip replacement surgery

Correct Answer: B) Immediate hip joint aspiration and intravenous antibiotics

Explanation:
This presentation is consistent with septic arthritis of the hip, a surgical emergency in children that requires prompt diagnosis and treatment to prevent joint destruction.

The clinical features include fever, acute hip pain, refusal to bear weight, and restricted joint movement, often with the hip held in a position that maximizes joint space to reduce pain (flexion and external rotation).

Laboratory tests showing elevated white blood cell count and C-reactive protein support an infectious process. The presence of joint effusion on ultrasound confirms fluid accumulation within the joint.

The most appropriate next step is urgent joint aspiration to obtain synovial fluid for microscopy, culture, and sensitivity, combined with intravenous antibiotics to treat the infection aggressively.

Observation or oral antibiotics alone are inadequate and risk progression to irreversible joint damage. MRI can be helpful but should not delay urgent aspiration and treatment. Elective hip replacement is not indicated in the acute phase.

Early intervention improves outcomes and reduces the risk of complications such as avascular necrosis and chronic arthritis.

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12. Orthopedics Module

12.1 ATLS Principles

12.2 Upper Limb Fractures

12.3 Lower Limb Fractures

12.4 Dislocations & Soft Tissue Injuries

12.5 Bone & Joint Infections

12.6 Bone Tumors