Osteomyelitis, septic arthritis and bone and joint tuberculosis

Overview

Bone and joint infection is common in Pakistan. Children get acute haematogenous osteomyelitis and septic arthritis; adults more often get post-traumatic or post-operative osteomyelitis; and tuberculosis of the spine and large joints is still frequent.

The key exam ideas are: where infection starts, which organism to expect, why the early X-ray is normal, when to drain, and how TB of the spine looks.

Acute haematogenous osteomyelitis

Who and where

• Mostly children; boys more than girls.
• Starts in the metaphysis of a long bone, most often the upper tibia or the lower or upper femur (around the knee and hip).
• In adults, the vertebral column is the usual site.

Organisms

Pathology: how it progresses

1. Acute inflammation and pus in the metaphysis; pressure rises inside the bone.
2. Pus tracks through the cortex and lifts the periosteum (subperiosteal abscess).
3. Bone deprived of blood from both inside and outside dies: a sequestrum.
4. The lifted periosteum lays down a sheath of new bone: the involucrum.
5. Holes in the involucrum through which pus escapes are cloacae; pus may reach the skin as a sinus.

Where the metaphysis lies inside the joint capsule (hip, shoulder, elbow, ankle), pus can burst straight into the joint and cause septic arthritis. In infants (under about 1 year), vessels cross the growth plate, so infection also spreads to the epiphysis and joint.

Clinical features

• Child: severe pain, refuses to use the limb, high fever, toxic; deep tenderness over the metaphysis.
• Neonate: may be only irritable and not feeding; look for multiple sites.
• Adult: often back pain from vertebral infection.

Investigations

Differential diagnosis

Cellulitis, septic arthritis, sickle cell crisis and Ewing sarcoma (fever, raised ESR and periosteal reaction can mimic infection).

Management

1. Take blood cultures (and aspirate if possible), then start IV antibiotics at once.
2. Supportive care: analgesia, IV fluids.
3. Splint the limb (traction or a plaster slab) for comfort and to prevent contracture.
4. Antibiotics:
   • Older children and fit adults: flucloxacillin (Apley pairs it with fusidic acid, which concentrates well in bone).
   • Neonates: flucloxacillin plus a third-generation cephalosporin (cefotaxime).
   • Children under about 6 years: cover H. influenzae as well (flucloxacillin with cefotaxime or cefuroxime).
   • Sickle cell: third-generation cephalosporin or ciprofloxacin (for Salmonella).
   • MRSA risk: vancomycin.
   • Give IV until the child improves and CRP normalises (about 2-4 weeks), then oral for another 3-6 weeks.
5. Surgical drainage if there is no improvement within about 36 hours of starting antibiotics, if deep pus is suspected (fluctuant swelling), or if aspiration yields pus.

Complications

• Chronic osteomyelitis (the main one).
• Septic arthritis of the neighbouring joint.
• Growth plate damage: limb shortening or angular deformity.
• Pathological fracture.
• Metastatic infection and septicaemia.

Subacute osteomyelitis: Brodie abscess

• A low-grade infection in a patient with good resistance.
• Brodie abscess: a walled-off cavity in the metaphysis (usually tibia), seen as a round lucent area surrounded by sclerosis.
• Presents in teenagers or young adults with long-standing dull pain, often worse at night, and little systemic upset.
• Treatment: antibiotics; curettage if it does not settle.

Chronic osteomyelitis

Causes

• Inadequately treated acute osteomyelitis.
• Today, most often after an open fracture or bone surgery, especially with metal implants.
• Infection becomes mixed with time: Staph. aureus, E. coli, Strep. pyogenes, Proteus, Pseudomonas.

Bacteria on dead bone and implants hide in a biofilm, shielded from antibiotics, so dead bone must be removed.

Clinical features

• Recurrent flares of pain, fever and redness.
• A discharging sinus that seals and reopens; skin puckered and stuck to bone.

Imaging

• X-ray: sclerosis, thickened bone, sequestra appear denser than surrounding bone, cavities.
• CT shows sequestra; MRI is the imaging test of choice for extent and abscesses.
• Sinogram can show the track.

Management

• Best handled by a multidisciplinary team.
• Deep tissue samples for culture (superficial sinus swabs are unreliable).
• Surgical debridement: remove sequestra, dead bone and infected tissue (sequestrectomy, saucerisation).
• Dead space management (antibiotic beads or carriers, muscle flap), stabilisation (external fixator such as Ilizarov), soft-tissue cover.
• Prolonged targeted antibiotics.
• Cierny-Mader staging combines the anatomy of the lesion (stages 1-4) with the host type (A, B, C).

Complications of chronic osteomyelitis

• Pathological fracture; joint stiffness; growth disturbance.
• Amyloidosis (rare).
• Squamous cell carcinoma in a long-standing sinus (Marjolin ulcer).

Garré sclerosing osteomyelitis: a rare non-suppurative form with dense sclerosis and thickening, no pus or sequestrum.

Septic arthritis (acute suppurative arthritis)

Causes

• Blood-borne spread (commonest), spread from neighbouring metaphyseal osteomyelitis, or direct entry (wound, injection, surgery).
• Organisms: Staph. aureus (commonest); H. influenzae and Kingella kingae in young children; Neisseria gonorrhoeae in sexually active adults.
• At risk: infants, rheumatoid arthritis (especially on steroids), diabetes, drug users, immunocompromised.

Clinical features

• Child: acute pain in one large joint (hip or knee), swinging fever, refuses to move the limb (pseudoparesis).
• The hip is held flexed, abducted and externally rotated (position of maximum capsular volume); all movements are painful and limited.
• Neonate: features of septicaemia; joint signs may be subtle.
• Adult: usually a superficial joint (knee, wrist, ankle). Ask about gonorrhoea and drug use.

Investigations

• Ultrasound is the best early test for a hip effusion.
• Joint aspiration is the key test: Gram stain, culture, cell count.
• Synovial fluid WCC above about 50,000 per mL strongly suggests sepsis (normal is under 300; inflammatory arthritis often above 10,000).
• Raised ESR, CRP and WCC; blood cultures.
• X-ray is normal early; later joint space widening and subluxation (effusion), then narrowing and erosion.

Kocher criteria (septic hip vs transient synovitis in children)

The more predictors present, the higher the chance of sepsis (about 93% with all four).

Management

1. Aspirate first, then start IV antibiotics immediately (same choices as osteomyelitis).
2. Drain the joint: open arthrotomy and washout (always for the infant hip and thick pus) or arthroscopic washout (knee).
3. Splint (hip in abduction and slight flexion on traction to prevent dislocation), then early movement.
4. Antibiotics IV for about 4-7 days, then oral for about 3 weeks (longer if bone is involved).

Differential diagnosis

Complications

Cartilage destruction (chondrolysis), ankylosis, dislocation of the hip, avascular necrosis of the femoral head, growth plate damage and limb shortening, secondary osteoarthritis.

Tuberculosis of bones and joints

General points

• Bones or joints are involved in about 5% of people with TB.
• Blood-borne spread from a primary focus (lung or gut).
• Spine is the commonest site (about half of skeletal TB), then hip and knee.
• Pathology: granuloma with caseous necrosis, epithelioid and Langhans giant cells.
• Pus without heat or redness tracks along tissue planes: a cold abscess.

Clinical features of TB joint

• Child or young adult; slow onset; marked muscle wasting, synovial thickening, movement limited in all directions.
• Night cries: protective spasm relaxes in sleep and the joint moves painfully.
• Low-grade fever, night sweats, weight loss.

Investigations

• Raised ESR, relative lymphocytosis; Mantoux positive (a negative test makes TB unlikely).
• X-ray: periarticular osteoporosis, narrowed joint space, erosions on both sides of the joint, little periosteal reaction.
• Synovial biopsy is more reliable than fluid: histology and culture (positive in about 80% of untreated cases); acid-fast bacilli in fluid in only 10-20%.
• Chest X-ray; GeneXpert on tissue or pus where available.

Tuberculosis of the spine (Pott disease)

Pathology

• Usually starts in the front of the vertebral body next to the disc (paradiscal type).
• Spreads beneath the anterior longitudinal ligament to the disc and the next vertebra: two adjacent vertebrae with the disc between them involved.
• The disc is spared longer than in pyogenic infection because mycobacteria lack disc-digesting enzymes, but the disc space narrows as the end plates are destroyed.
• Anterior collapse gives an angular kyphosis: a gibbus (knuckle).
• Commonest region: thoracic (lower thoracic and thoracolumbar).
• Cold abscess can track: psoas abscess pointing in the groin or thigh; retropharyngeal abscess in cervical TB.

Clinical features

• Back pain (often mild), stiffness, gibbus, cold abscess.
• Constitutional symptoms; concurrent pulmonary TB in some.
• Neurological deficit: spastic paraparesis in thoracic disease.

Imaging

• MRI is the investigation of choice (abscess, cord compression, skip lesions).
• CT-guided needle biopsy confirms the diagnosis.

Pott paraplegia

Treatment of skeletal TB

• Antituberculous drugs are the mainstay: always include rifampicin and isoniazid, with pyrazinamide and ethambutol in the intensive phase. Bone and joint TB is usually treated for longer than lung TB (often 9-12 months). Follow the current National TB Programme Pakistan guideline, which can change.
• Rest and splintage in the acute phase, then mobilise.
• Cold abscess: aspirate through healthy skin from a non-dependent site to avoid a sinus.
• Surgery for the spine:
  • Abscess that can be drained.
  • Neurological deficit not improving (or worsening) on drugs.
  • Severe or progressive kyphosis, instability, or diagnostic doubt.
  • Usual operation: anterior debridement and strut bone grafting (the classic "Hong Kong operation"), with fixation when needed.
• Joint TB: drugs and rest; arthrodesis or replacement later for a destroyed joint, with drug cover before and after surgery.

Quick revision

• Acute osteomyelitis: child, metaphysis, Staph. aureus, X-ray normal for 7-10 days, MRI best early.
• Treat at once after cultures; drain if no response in about 36 hours or pus present.
• Sequestrum (dead bone), involucrum (new bone sheath), cloaca (hole); sinus + sequestrum = chronic osteomyelitis.
• Chronic osteomyelitis now usually follows open fractures or implants; treat by debridement plus antibiotics.
• Brodie abscess: tibial metaphysis, lucency with sclerotic rim, night pain.
• Septic arthritis: aspirate, IV antibiotics, washout; hip held flexed, abducted, externally rotated.
• Kocher: fever over 38.5 °C, non-weight-bearing, ESR over 40, WCC over 12.
• TB spine: thoracic, two vertebrae and disc, cold abscess, gibbus; metastasis spares the disc.
• Early Pott paraplegia recovers well after decompression; late onset does poorly.

Written by The House Job from standard orthopaedic references (Apley; Bailey & Love).

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