Musculoskeletal
Question 167 of 180
You have been asked to give a teaching session to junior colleagues on atraumatic joint pain. You are discussing septic arthritis. What is the most common site of isolated septic arthritis?
Answer:
The commonest reported site of isolated septic arthritis is the knee. The hip, shoulder, ankle, elbow, and wrist are also common sites of joint infection.Septic Arthritis
Musculoskeletal
Last Updated: 8th September 2021
Septic arthritis is defined as the infection of 1 or more joints caused by pathogenic inoculation of microbes. Complications include sepsis, osteomyelitis and permanent joint destruction.
Aetiology
- Haematogenous spread from a bacteraemia (most common)
- Contiguous spread from infected periarticular tissue (e.g. osteomyelitis, cellulitis, bursitis)
- Direct inoculation from external skin puncture wound
Infective agent
- The predominant causative organisms of septic arthritis are staphylococci or streptococci. These organisms account for 91% of cases.
- In sexually active patients, gonococcal arthritis may be suspected.
- In older and immunocompromised people, gram-negative organisms are more common than among young people, although staphylococci and streptococci still predominate.
- Anaerobic organisms rarely cause septic arthritis except in the case of penetrating trauma.
- Community-associated MRSA is becoming more common in many parts of the world and should be suspected in patients recently discharged from hospital, nursing home residents, those with leg ulceration, and those with indwelling urinary catheters.
Risk factors
- Underlying joint disease e.g. osteoarthritis, rheumatoid arthritis
- Joint prostheses
- Immunosuppression e.g. HIV, diabetes mellitus, alcohol misuse, immunosuppressants
- Intravenous drug misuse
- Cutaneous ulcers or skin infection
- Recent joint surgery or intra-articular injection
- Exposure to ticks (may indicate arthritis associated with Lyme disease)
Clinical features
Delayed diagnosis and treatment can result in permanent joint damage with resulting disability. Regard a hot, swollen, acutely painful joint with restriction of movement as septic arthritis until proven otherwise. Do so even in the absence of fever and irrespective of microbiology and blood test results.
- History:
- Pain and swelling are the most common symptoms.
- The commonest reported site of isolated septic arthritis is the knee. The hip, shoulder, ankle, elbow, and wrist are also common sites of joint infection. The metatarsophalangeal joint of the great toe is the commonest joint to present as hot, swollen, and painful in primary care, but this presentation is unlikely to be caused by septic arthritis. This is almost always due to gout and can be diagnosed clinically without needle aspiration.
- Patients typically present with an acute (<2 weeks) history.
- In patients with underlying joint disease, suspect a septic joint if symptoms are out of proportion to disease activity elsewhere.
- Do not exclude the diagnosis of septic arthritis in patients with polyarticular disease. Up to 22% of patients with septic arthritis have oligoarticular or polyarticular disease
- On examination:
- Septic joints will be held in a position of maximum joint volume: fully extended knee; hip abducted, flexed, and externally rotated.
- Positively identify an intra-articular effusion (not just surrounding soft-tissue swelling). Localised swelling external to the joint suggests bursitis rather than septic arthritis.
- Passive and active movement of the joint will be limited and very painful in septic arthritis. In practice, most patients with septic arthritis of a weight-bearing joint will not be able to walk.
- Fever, chills, and rigors may be present in some patients.
Differential diagnosis
- Infective
- Lyme arthritis
- Tuberculous arthritis
- Fungal arthritis
- Viral arthritis
- Inflammatory
- Gout or pseudogout
- Reactive arthritis
- Rheumatoid arthritis
- Psoriatic arthritis
- Arthritis associated with connective tissue disorders such as systemic lupus erythematosus
- Haemarthrosis
- Trauma
- Bursitis
- Cellulitis
- Osteomyelitis
- Osteoarthritis
- Perthes disease or SUFE in children with hip pain
- Transient synovitis in children with hip pain
- The Kocher criteria is a tool useful in the differentiation of septic arthritis from transient synovitis in the child with a painful hip. A point is given for each of the four following criteria:
- Kocher’s criteria:
- History or presence of fever > 38.5°C
- Child not weight-bearing on the affected side
- ESR > 40 mm/h
- WCC > 12 x 10⁹/L
- Score interpretation:
- Score 1 - 3% likelihood of septic arthritis
- Score 2 - 40% likelihood of septic arthritis
- Score 3 - 93% likelihood of septic arthritis
- Score 4 - 99% likelihood of septic arthritis
Investigations
- Bloods – WCC, CRP, U&Es, LFTs
- Blood cultures and sensitivities
- Diagnostic joint aspiration & synovial fluid evaluation
- Take a synovial fluid sample, bloods, and any other relevant culture samples before starting antibiotics, unless this would cause undue delay.
- Refer patients with a prosthetic joint or inaccessible joint to orthopaedics.
- Only a specialist should manage suspected septic arthritis in a prosthetic joint, as the diagnostic approach and management is significantly different to native joint infection, and may or may not require surgery.
- If the hip is involved, refer to orthopaedics immediately for ultrasound-guided joint aspiration and possible surgical debridement.
- Aspirate the joint through a closed-needle approach using sterile technique if it is safe and you have had appropriate training and experience of this procedure.
- Assess the colour, viscosity, and clarity of the joint aspirate to support/weaken your presumptive diagnosis.
- Aspirate to dryness. Repeat aspiration to dryness as often as is required: for pain relief, removing source of sepsis and for diagnosis.
- Send joint aspirate to the microbiology laboratory for urgent processing. Order:
- Gram stain, microscopy, and white cell count
- Polarising microscopy for crystals
- Culture and sensitivities
- White cell count is the first result available and is the most useful in differentiating between septic arthritis and other diagnoses.
- Swabs
- For MRSA in patients who have recently been in hospital or a nursing home, as joint aspirate does not always yield cultures and MRSA carriage will affect management.
- From any other sources of potential infection identified on history and examination (e.g. pressure sores, skin lesions, genitourinary tract, respiratory tract).
- X-ray
- X- rays are not diagnostic for septic arthritis and not urgent, but should be carried out as a baseline investigation for assessing future joint damage.
- Ultrasound
- Arrange an ultrasound if you suspect hip sepsis, as aspiration should be performed under ultrasound guidance.
Management
- Admit the patient for intravenous antibiotic treatment and joint drainage.
- Antibiotic treatment
- Immediately after you have aspirated the joint, taken blood for culture, and taken any necessary swabs or samples for biological processing, start empiric intravenous antibiotics in patients with suspected septic arthritis.
- Consult local protocols and local infectious disease services or microbiology regarding prevalent organisms and their sensitivities. For example:
- Likely typical organisms - flucloxacillin
- High risk of gram-negative organisms - second or third generation cephalosporin +/- flucloxacillin
- MRSA risk - vancomycin plus second or third generation cephalosporin
- Suspected gonococcus - ceftriaxone
- Switch to pathogen-targeted antibiotics when microbiology culture and sensitivity results become available and continue intravenous treatment for up to a total of 2 weeks or until signs improve, unless there is an inadequate clinical response.
- After 2 weeks of successful intravenous treatment start an oral antibiotic with the same spectrum of activity.
- Therapeutic joint aspiration
- Repeat joint aspiration to dryness as often as necessary. This helps remove infection and manage pain by relieving pressure within the joint.
- Repeated arthroscopic washouts are indicated if temperature and inflammatory markers do not improve after the initial aspiration and treatment.
- Evacuation of pus with arthrocentesis or surgery by a specialist may be necessary.
- Analgesia
- Prescribe simple analgesics such as paracetamol or a non-steroidal anti-inflammatory drug (NSAID) if the patient reports ongoing pain. Use NSAIDs with caution in older people and people with comorbidities such as hypertension and heart disease. NSAIDs may increase the risk of acute kidney injury in people with sepsis.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
