Septic Arthritis

Objectives

This guideline outlines the diagnostic considerations and procedural guidance for the management of Septic Arthritis.   

The key aims are:  

• To ensure timely diagnosis and treatment of Septic Arthritis 
• To reduce morbidity by identifying and managing septic arthritis, gout, or other inflammatory conditions promptly.
• To provide clear protocols for advanced assessment, prolonged casualty care, and paediatric considerations.  

Scope

This guideline applies to the management of Septic Arthritis in military or deployed settings. It includes protocols for initial assessment, advanced diagnostics with the focus on differentiating the diagnosis of Septic Arthritis from other medical causes of a hot swollen joint.   Management strategies of suspected Septic Arthritis, including joint aspiration and surgical wash out are outlined. 

Audience

The target audience is deployed medical teams. It is particularly aimed at deployed surgical units but the material also has relevance to personnel in further forward medical locations.

Initial Assessment & Management

There is a wide-ranging differential diagnosis of an acute atraumatic monoarthritis including: gout, pseudogout and other crystal arthropathies, autoimmune causes including rheumatoid, exacerbation of osteoarthritis; bursitis; cellulitis; acute injury, Charcot joint; bone or soft tissue malignancy and septic arthritis.  

History: Key features to elicit and document: 

Time course of the pain and dysfunction

• Any recent or preceding trauma
• Previous episodes
• Any known arthropathy causes
• Systemic symptoms: malaise, fever, rigors
• Other joints affected (if more than one joint is involved then the likelihood of a infectious cause is extremely low)
• Treatment so far, particularly administration of antibiotics (document duration of treatment, name of agent, and date/time of last dose) 
   

Examination: Key features to elicit and document: 

Presence or absence of heat, erythema, swelling, tenderness 

Active and passive range of movement 
Distal neurovascular status 
Weight bearing status 
  

Role 1: Investigations at Role 1 will be limited. If a working diagnosis of septic arthritis is raised, the patient should be evacuated urgently to deployed orthopaedic care. If the patient is not septic, withhold antibiotics until an aspirate can be performed. If the patient is septic on presentation, they should be treated early in accordance with the CGO “Immediate Management of Septic Shock Patient” in conjunction with the deployed antimicrobial guidelines.  The need for joint aspiration should not delay the administration of antibiotics in a septic patient.  

Role 2: At Role 2, a hot swollen joint should be initially investigated with plain film radiograph and blood tests, which is limited to FBC with a 3-part differential.  The aim of aspiration without further laboratory analysis technique is to aspirate pus as diagnostic aid opposed to guiding antimicrobial administration.  CRP is only available at R2E or R3.  If the echelon of care is scaled for microbiology capability, then blood cultures and a joint aspirate should be analysed. 

A pragmatic approach to joint aspiration in the absence of deployed microbiological capability is as follows:

• Aspirate is frank pus: a diagnosis of septic arthritis confirmed
• Aspirate is turbid fluid: a diagnosis of septic arthritis confirmed 
• Aspirate is normal synovial fluid: consider alternative diagnosis 

This approach risks over-treating hot swollen joints that may not be proven to be infected but it is the safest and most robust approach in the deployed setting. 

If deployed microbiological capability allows, then the presence or absence of crystals and/or organisms can feed into the clinical decision making in the same manner as in firm base practice. 

Figure 1. Septic Arthritis Initial Management in the Deployed Setting

Advanced Assessment & Management

Joint Aspiration  

In the diagnostic work up of a hot swollen joint, consideration should always be given to joint aspiration.  Role 3 is likely to be the only echelon that would have the deployed capability to perform microscopy, cultures and sensitivities. Aspirate should be sent for Microscopy, Culture and Sensitivities and testing for WBC and PMN with WBC > 50,000 u/L and PMN > 90% considered strongly predictive of septic arthritis.  A BMS may be able to comment on the presence of crystals, depending on their scope of practice.    

Joint aspiration should be undertaken by an appropriately trained clinician, with a sterile technique and informed consent regarding the risk of introducing infection to a sterile joint.  A joint aspiration should not be performed through cellulitic or broken skin. 

Equipment required:

• Wound pack for sterile field and sterile gloves  
• Cleaning solution i.e. chlorprep, alcoholic betadine
• An 18 or 20 gauge needle with 10-50ml syringe  
• Appropriate containers i.e. universal container for microscopy and culture bottles 
   

The landmarks for joint aspirations are noted below:

Hip: The hip is a deep joint and in UK Firm base is accessed under fluoroscopic or USS guidance. A landmark technique can be utilised based on the mid inguinal point and femoral artery, however,  aspiration should be discussed with an orthopaedic surgeon.

Knee: An anterolateral or anteromedial approach is a simple approach for knee aspiration. Position the knee in extension, or slightly flexed with the patient on a stretcher. After cleaning and prepping the area, insert the needle 1-2cm lateral or medial to the proximal 1/3 of the patella into the suprapatellar pouch. Enter the skin perpendicularly and aim to go along the posterior aspect of the patella until joint aspirate is obtained.  

Ankle: Position the patient supine and place a cushion under the ankle to hold it in a dorsiflexed position. Identify the medial malleolus and the tibialis anterior tendon. The insertion site is the dimple between tibialis anterior and the medial malleolus. Insert the needle perpendicular to the skin aiming towards the joint site.  

Shoulder: Position the patient sitting with their arm at the side and hand on the lap across the patient. The joint is accessible posteriorly. Identify the humeral head, acromion and the coracoid process via palpation. Insert the needle in the sulcus between the acromion and humeral head, aiming toward the coracoid process anteriorly.  

Elbow: Position the patient supine or sat up with the elbow flexed to 90* and the wrist pronated. Identify the radial head, ulna/olecranon process and the lateral epicondyle of the elbow. The insertion site is the depression between these three landmarks. Insert the needle perpendicular to skin and aim direct towards the antecubital fossa.  

Wrist: Position the patient supine or sitting with wrist on the side. Identify lister’s tubercle of the radius (distal tubercle on dorsal radius) and identify extensor pollicis longus tendon (can be identified by extending thumb). Identify the hollow between these two structures. Apply slight traction and flex the wrist slightly. Needle entry occurs distal to lister’s tubercle and ulnar to extensor pollicis longus tendon.  Aiming slightly proximally to mirror the wrists joints natural anatomy of a volar tilt. Ensure you do not insert the needle into the anatomical snuffbox (radial to EPL tendon) due to risk of neurovascular injury.  

Summary of Investigations at different echelons of care:   

Table 1. Summary of Investigations available at different echelons of care 

Clinical Decision-Making Tool  

 A web-based Septic Arthritis Risk calculator can be used to help decision-making once results from aspirate are available in difficult clinical cases. https://septicknee.org/risk-calculator

Factors to consider include synovial fluid WBC >30,000, positive synovial gram stain, synovial crystals found, history of septic arthritis in any joint, clinical effusion on exam, duration of knee pain > 2 days.  

Advanced Management  

This section will consider the management of Septic Arthritis.  In cases where the working diagnosis is an inflammatory arthropathy or crystal arthropathy, the mainstay of treatment is analgesia and evacuation, situation dependant.  

Septic Arthritis  

There are three goals to management of a septic arthritis:   

1. Source Control – achieved through aspiration and surgical washout, arthrotomy in the deployed setting  
2. Identification and treatment of Sepsis 
3. Minimising cartilage damage – timely decision for surgical washout.  

Medical Management of Septic Arthritis:   

Prompt identification of a septic patient is essential and should be managed in accordance with CGOs (Immediate Management of Septic Shock Patient). Empirical antibiotics should not be delayed for joint aspiration or surgical washout in a septic patient.  In stable patients, strong consideration should be given for antibiotic administration after joint aspiration if microbiological capability is available. All patients with septic arthritis will subsequently require joint drainage; either serial aspiration or surgical drainage; whist monitoring for sepsis.

Deployed antimicrobial guidance should be followed with the "deployed secondary care cellulitis/abscesses/furunculosis" section giving the relevant agents. Typically antibiotics are given for 3-4 weeks, and an oral agent can usually be considered once clinically stable which is typically after 3-4 days once source control has been achieved. Advice can be found via the infection reach-back service available by telephone or message systems, where deployed without local military infection specialists.

Surgical Management of Septic Arthritis:   

The definitive treatment for a septic arthritis is a surgical washout, although consideration could be given by the senior deployed orthopaedic surgeon for the role of aspiration to dryness.  

Serial Aspirations  

In situations such as prolonged evacuation timelines, or specific operational constraints, it may be appropriate to consider serial aspiration of a joint alongside intravenous antibiotics.    Outcomes from serial aspiration of septic joints has been shown to be non-inferior to surgical management. However, to help guide decision making, certain parameters to predict surgery in medically managed patients have been identified including more comorbidities, a prolonged fever, and a delta CRP (increased CRP day 1 after aspiration). This approach has a high failure rate in hip and shoulder septic arthritis and should be avoided in these joints. 

Whilst it is acknowledged that aspiration to dryness is not gold standard in UK Firm Base practice, within a deployed setting, clinical and tactical consideration may justify the approach. This should be discussed with a senior clinician.

Surgical Techniques - Arthrotomy

Any casualty with a suspected septic arthritis treated with an initial washout, should be reviewed for consideration of a further washout after 24-48 hrs of antibiotic treatment.  The approaches for Hip, Knee, Shoulder and Ankle Arthrotomy are outlined in the accordion section below.

Drugs

Analgesia – give analgesia in accordance with guidelines and the treating clinicians scope of practice. 

Antibiotics – See above regarding timing of antimicrobial therapy. Refer to the Deployed Antimicrobial Guidelines for choice of agent.   

Prolonged Casualty Care

In the situation of a prolonged hold, the treatment for suspected septic arthritis should be joint aspiration for diagnosis and surgical washout with broad spectrum antibiotics. Clinicians should bear in mind the requirement for a further surgical washout in a proportion of cases.  

Casualties should be closely monitored for complications such as systemic sepsis.  

Casualties should be evacuated to definitive surgical care as soon as feasible.

Paediatric Considerations

In the paediatric setting, septic arthritis is a medical emergency due to the risk of growth plate damage.  Early signs may be subtle - irritability, altered gait, refusal to bear weight or pseudoparalysis.  Diagnostic criteria such as Kocher's criteria – weight bearing status, Temperature > 38.5°C, ESR >40mm/hr and WCC >12,000 cells/mm3 - should be used with clinical judgment to differentiate between a septic arthritis and a transient synovitis.    Antibiotic treatment should be delivered as per current guidelines and is weight based.   Surgical treatment of septic arthritis in the paediatric population is through surgical drainage with arthrotomy.