Acute musculoskeletal injuries — Ottawa rules, acute joint injury and septic arthritis

Definition / Overview

Acute musculoskeletal emergencies presenting to general practice span two broad categories:

• Infectious (septic) arthritis: bacterial, mycobacterial, or rarely fungal infection of a synovial joint, representing a true orthopaedic emergency with potential for irreversible joint destruction within 24-48 hours if untreated
• Acute joint and soft-tissue injury: fractures, dislocations, ligamentous tears, tendon ruptures, and haemarthrosis requiring triage, initial management, and appropriate escalation

Both categories demand rapid recognition, decisive triage, and seamless coordination between the GP clinic, emergency department, and specialist services.

Pathophysiology and Mechanism

Septic Arthritis

Bacteria reach the joint by three routes:

1. Haematogenous spread: the most common route; bacteraemia seeds the synovium (e.g. from skin, respiratory, or urinary tract infection)
2. Direct inoculation: penetrating trauma, joint aspiration, or intra-articular injection
3. Contiguous spread: from adjacent osteomyelitis or soft-tissue infection

Once bacteria enter the joint space, a cascade of neutrophil-driven inflammation and proteolytic enzyme release rapidly degrades articular cartilage. Staphylococcus aureus (including MRSA) is the dominant pathogen across all age groups. Neisseria gonorrhoeae is the leading cause in sexually active adults under 40. Gram-negative bacilli predominate in neonates, the elderly, and immunocompromised individuals.

Acute Joint Injury

Traumatic joint injury results from:

• Compressive, shear, or tensile forces exceeding the structural tolerance of bone, cartilage, ligament, or tendon
• Haemarthrosis after anterior cruciate ligament (ACL) rupture, tibial plateau fracture, or patellar dislocation indicates significant intra-articular pathology

Clinical Features and Diagnosis

Septic Arthritis: Red Flags

Key clinical rule: Any acutely hot, swollen, and painful joint must be considered septic arthritis until proven otherwise. Do not attribute it to gout or pseudogout without excluding infection.

Differential Diagnosis of the Acutely Hot Joint

Acute Joint and Soft-Tissue Injury

History essentials:

• Mechanism of injury (direct blow, twisting, hyperextension)
• Timing, onset, and progression of swelling
• Ability to weight-bear or use the limb
• Previous injury, surgery, or joint disease
• Medications (anticoagulants, steroids)

Examination principles:

• Inspect for deformity, swelling, bruising, open wound
• Palpate for point tenderness (fracture risk), effusion, warmth
• Assess active and passive range of motion, neurovascular status distal to injury
• Specific ligament tests (Lachman, anterior drawer, valgus/varus stress, McMurray)
• Ottawa Ankle Rules and Ottawa Knee Rules to guide X-ray decision-making

Investigation and Monitoring

Septic Arthritis: Investigations in General Practice and ED

The GP's role is rapid clinical recognition and urgent transfer; do not delay referral to await results.

Acute Injury Investigations

• Plain X-ray: first-line for fracture exclusion; apply Ottawa Rules to reduce unnecessary imaging
• MRI: gold standard for soft-tissue (ligament, meniscus, tendon) injury; arranged after acute phase or by specialist
• CT: complex fractures, fracture-dislocation, suspected occult fracture
• Ultrasound: dynamic assessment of tendons (rotator cuff, Achilles), effusions

Management

Septic Arthritis: Urgent Management Algorithm

1. Recognise: Hot, swollen, restricted joint with fever or risk factors
2. Do not delay referral: Transfer urgently to emergency department or contact orthopaedic team
3. Initiate workup while arranging transfer: FBC, CRP, blood cultures, X-ray if available
4. Do not give oral antibiotics in the community: IV antibiotics in hospital, culture-guided
5. Document clearly: Time of recognition, vital signs, clinical findings, contact made

Empirical antibiotic therapy (hospital-initiated, per Therapeutic Guidelines):

Note: Antibiotic duration is typically 2 weeks IV followed by 2-4 weeks oral, guided by clinical response and organism sensitivity. Decisions made in the inpatient setting.

Surgical drainage: Repeated joint washout (arthroscopic or open) is required for most cases. The GP does not perform this but should communicate urgency clearly to the receiving team.

Prosthetic Joint Infection

• Any suspected infection around a prosthetic joint is an emergency
• Presents with pain, warmth, swelling, or wound discharge around a prosthesis
• Contact the relevant orthopaedic team directly; do not attempt aspiration without specialist guidance
• Blood cultures and inflammatory markers, but do not initiate antibiotics unless the patient is systemically septic, as this can mask cultures

Acute Joint Injury Management in the GP Setting

Fractures

Suspected fracture:

1. Immobilise the limb in the position of comfort (splint, backslab)
2. Assess and document neurovascular status distal to the injury
3. Analgesia: paracetamol 1 g orally; consider ibuprofen 400 mg if not contraindicated; consider short-acting opioid for severe pain
4. X-ray if available in clinic; if not, arrange urgent imaging or transfer
5. Open fracture: cover with moist sterile dressing, do not reduce, initiate analgesia, give antibiotics (cephazolin 2 g IV if available), arrange emergency transfer

Specific fractures requiring urgent referral:

• Open or comminuted fractures
• Neurovascularly compromised limb
• Femoral neck fracture (especially elderly; risk of avascular necrosis and non-union)
• Scaphoid fracture (or suspected; X-ray often normal initially; immobilise and refer for MRI if clinical suspicion high)
• Displaced or intra-articular fractures

Dislocations

• Shoulder dislocation: most common large joint dislocation; assess axillary nerve (lateral deltoid sensation) before and after reduction; X-ray before reduction to exclude fracture-dislocation; GPs with appropriate skills and monitoring can attempt reduction (e.g. Cunningham, FARES, or Milch technique) with analgesia/sedation; refer if unsuccessful or if fracture-dislocation present
• Patella dislocation: typically lateral; assess for osteochondral fracture; reduce with knee extension and medial pressure; X-ray post-reduction
• Hip, knee dislocation: emergency transfer; vascular injury risk with knee dislocation is high

Soft-Tissue Injuries

RICE + analgesia in the first 48 hours:

• Rest (relative, not absolute)
• Ice (20 minutes on/off, barrier to skin)
• Compression bandage
• Elevation

Complications and Special Considerations

Complications of Septic Arthritis

• Irreversible articular cartilage destruction within days if untreated
• Osteomyelitis (contiguous spread)
• Septicaemia and multi-organ failure
• Chronic osteomyelitis, joint ankylosis, avascular necrosis
• Mortality: up to 10-15% in elderly or immunocompromised patients

Populations at Elevated Risk

Rheumatoid arthritis on biologics/DMARDs:

• Blunted inflammatory response; fever may be absent
• Superimposed septic arthritis can mimic RA flare
• High index of suspicion required; aspiration is essential

Immunosuppressed patients (transplant, HIV, malignancy):

• Atypical organisms including mycobacteria and fungi
• Presentation may be subacute or indolent

Diabetes mellitus:

• Impaired neutrophil function; higher risk; worse outcomes
• Consider Gram-negative organisms

People who inject drugs:

• S. aureus (including MRSA) and Gram-negative organisms
• Axial joints (sacroiliac, sternoclavicular) more commonly involved

Older adults:

• Gram-negative bacilli more prevalent
• Concurrent dehydration, delirium risk; ensure IV access and hydration while arranging transfer

Paediatric Considerations

• Septic arthritis in children requires same-day emergency referral
• Hip is the most commonly affected joint in children
• Kocher criteria help differentiate septic arthritis from transient synovitis: fever $> 38.5°C$, non-weight-bearing, ESR $> 40\,\text{mm/h}$, WBC $> 12{,}000/\mu L$ (each criterion increases probability of septic arthritis)
• Neonates: GBS (Streptococcus agalactiae) and S. aureus; presentation subtle
• Do not attempt aspiration in children without appropriate facilities; arrange emergency paediatric orthopaedic review

Long-Term Care and Follow-Up in General Practice

Post-Septic Arthritis

• Ensure completion of oral antibiotic course once discharged
• Monitor inflammatory markers (CRP, ESR) until normalised
• Arrange physiotherapy for joint rehabilitation
• Counsel regarding joint damage risk; may require specialist monitoring for post-infectious arthritis or secondary osteoarthritis
• Review and optimise risk factors: diabetes control, skin integrity, harm reduction for IVDU

Post-Injury Rehabilitation

• Arrange physiotherapy referral for all significant ligamentous and tendon injuries
• Review at 4-6 weeks to assess recovery; re-image or refer if not progressing
• For athletes and working-age adults: consider referral to sports medicine for return-to-sport planning
• Address osteoporosis in fragility fractures: bone density (DXA), calcium/vitamin D, anti-resorptive therapy per Therapeutic Guidelines
• Falls risk assessment in older adults post-fracture: MBS item 731 (75+ health assessment) can be used to address falls, medication review, and functional assessment

MBS and Referral Pathways

• MBS item 23 or 36: Standard GP consultation for acute injury assessment and initial management
• MBS item 105: After-hours urgent attendance
• Enhanced Primary Care (EPC) plan: GP Management Plan (item 721) and Team Care Arrangement (item 723) for complex post-infectious arthritis patients requiring allied health input (physiotherapy, podiatry)
• Radiology: Bulk-billed plain X-ray under standard referral; MRI requires specialist or GP referral depending on state/territory agreements
• Always document time-critical clinical decisions, referral made, and patient/carer communication in the medical record

Key Exam Points

• The hot swollen joint is septic arthritis until proven otherwise: do not attribute to gout without aspiration
• Never delay referral to obtain investigations: blood cultures and aspiration are done at the hospital
• Do not start oral antibiotics before cultures in community septic arthritis: masks organism identification
• Gonococcal arthritis: think in any sexually active adult under 40 with migratory polyarthritis; STI screen mandatory
• Kocher criteria guide paediatric hip septic arthritis versus transient synovitis
• Ottawa Rules: apply to ankle and knee to avoid unnecessary X-rays
• Achilles rupture: immobilise in plantarflexion immediately; Thompson test (absence of plantarflexion on calf squeeze) confirms rupture
• Scaphoid fractures: X-ray can be normal; clinical suspicion mandates immobilisation and MRI or specialist review
• Post-fracture in older adults: always address bone health and falls risk

Sources

• MBS Online (Medicare Benefits Schedule)
• Therapeutic Guidelines (eTG)