Septic Arthritis

Septic arthritis is infection of a native joint space.

Bacterial replication and the host inflammatory response can destroy articular cartilage rapidly, making septic arthritis both an infectious and orthopaedic emergency.

The knee is the most commonly affected large joint in adults, followed by the hip, shoulder, ankle and wrist.

Common organisms include:

Staphylococcus aureus
Streptococci
Gram negative bacilli in selected hosts
Neisseria gonorrhoeae in sexually active younger adults

Risk increases with:

Older age
Diabetes
Immunosuppression
Recent joint injection
Skin infection
Intravenous drug use
Pre existing joint disease
Bacteraemia

Gächter arthroscopic classification

Stage I

Turbid joint fluid
Synovial hyperaemia
Possible petechiae
No radiographic destruction

Stage II

Severe synovitis
Fibrin deposits
Purulent fluid
No established radiographic destruction

Stage III

Thickened synovium
Adhesions
Compartment or pouch formation

Stage IV

Aggressive pannus
Cartilage invasion and destruction
Subchondral osteolysis, erosions or cystic changes

Stages I and II, and many stage III infections, can usually be managed arthroscopically. Advanced stage III and stage IV disease may require open debridement.

Typical presentation is:

Acute severe joint pain
Restricted active and passive movement
Effusion
Warmth
Swelling
Fever, which may be absent

Pain with passive motion in all directions strongly suggests an intra articular process.

The absence of fever does not exclude infection.

Any acutely painful swollen joint should be treated as possible septic arthritis until infection is adequately excluded.

Differential diagnoses include:

Gout
Pseudogout
Haemarthrosis
Reactive arthritis
Inflammatory arthritis
Osteoarthritis flare

Crystals in synovial fluid do not completely exclude simultaneous bacterial infection.

Joint aspiration

Aspiration is the central diagnostic investigation.

Send synovial fluid for:

White blood cell count
Differential
Gram stain
Aerobic and anaerobic culture
Crystal analysis

A synovial WBC above approximately 50,000 cells/µL with a high neutrophil percentage strongly supports infection, but lower values do not exclude septic arthritis.

Culture is more important than any single cell count threshold.

Obtain blood cultures when systemic infection or haematogenous spread is possible.

Except in sepsis or septic shock, obtain synovial fluid and blood cultures before starting antibiotics.

Imaging

Plain radiographs: baseline joint status and exclude fracture or advanced destructive disease.

Ultrasound: detects effusion and assists aspiration, particularly hip.

MRI: useful for:

Adjacent osteomyelitis
Deep joint infection
Abscess
Sacroiliac infection
Difficult diagnostic cases

Do not delay drainage of an obviously septic accessible joint solely to obtain MRI.

Management requires:

Joint drainage
Antimicrobial therapy
Treatment of bacteraemia or primary source
Early rehabilitation once infection is controlled

Empirical antibiotics

After cultures in a stable patient:

A practical adult regimen where MSSA and streptococci predominate is:

Cefazolin 2 g IV every 8 hours

plus, where significant Gram negative risk exists:

Ceftriaxone 2 g IV every 24 hours.

If MRSA risk is significant:

Vancomycin IV, using weight based loading when severe and subsequent AUC guided dosing.

In septic shock, begin broad therapy immediately after blood cultures without waiting for joint aspiration if this would delay resuscitation.

Drainage

Large joint septic arthritis usually requires operative washout.

Arthroscopic lavage and debridement is appropriate for most knee, shoulder and selected hip infections.

Perform:

Complete joint inspection
Removal of pus
Fibrin debridement
Synovectomy according to severity
Thorough saline irrigation

Advanced infection with:

Dense adhesions
Extensive cartilage destruction
Bone involvement

may require open arthrotomy.

Hip septic arthritis

The adult native hip usually requires urgent operative drainage because:

Joint is deep
Needle aspiration alone gives unreliable source control
High intra articular pressure threatens cartilage and femoral head

Repeat washout

Failure to improve after drainage should prompt urgent reassessment.

Concerning features are:

Persistent fever
Persistent or rising CRP
Ongoing purulent drainage
Persistent bacteraemia
Reaccumulating effusion
Continued severe joint pain
Deteriorating systemic status

These indicate possible inadequate source control and may require repeat arthroscopy or arthrotomy.

Antibiotic duration

After adequate drainage and clinical improvement, IV treatment can often be continued for approximately 1 to 2 weeks, followed by an active oral agent.

A further 2 to 4 weeks of oral therapy is a reasonable reference for uncomplicated adult native joint infection.

Longer therapy is required with:

Adjacent osteomyelitis
Endocarditis
Difficult organisms
Immunosuppression
Inadequate source control

Rehabilitation

Begin joint motion as soon as:

Infection is controlled
Drains are removed
Wound permits movement

Prolonged immobilisation causes severe stiffness and muscle wasting.

Major complications include:

Rapid cartilage destruction
Secondary osteoarthritis
Osteomyelitis
Joint stiffness
Instability
Sepsis
Death
Need for later arthroplasty

Clinical toolsCalculators

BMI GCS EDD Parkland Formula

Corrected Sodium Corrected Calcium Anion Gap Creatinine Clearance Insulin Calculations qSOFA Wells PE Wells DVT CHA₂DS₂-VASc HAS-BLED CURB-65 Centor/McIsaac

Knee Dislocation

A knee dislocation is disruption of the tibiofemoral articulation associated with major multiligament injury.

Many knee dislocations spontaneously reduce before hospital arrival, so a normal looking knee does not exclude a limb threatening injury.

A patient with significant injuries to two or more major knee ligaments should be assessed as a potential reduced knee dislocation.

The immediate threats are:

Popliteal artery disruption
Common peroneal nerve injury
Compartment syndrome
Irreducible dislocation
Severe instability

The popliteal artery is tethered proximally at the adductor hiatus and distally near the soleus arch, making it vulnerable to traction and intimal disruption.

Palpable distal pulses do not completely exclude arterial injury because collateral circulation can maintain flow.

Kennedy classification

Based on direction of tibial displacement relative to the femur.

Anterior

Usually hyperextension.

Often associated with PCL disruption.

Arterial injury can result from traction and intimal tearing.

Posterior

Often dashboard type axial load to a flexed knee.

Particularly associated with popliteal artery disruption.

Medial

Tibia displaced medially.

Usually severe collateral and cruciate injury.

Lateral

Tibia displaced laterally.

Usually ACL and PCL plus collateral injury.

Rotational

Posterolateral rotational dislocation is particularly important.

The medial femoral condyle can buttonhole through capsule and soft tissue, producing the dimple sign.

This injury may be irreducible by closed methods.

Schenck classification

Based on multiligament injury pattern.

KD I

One cruciate ligament remains intact with multiligament injury involving the opposite cruciate plus collateral structures.

KD II

Both ACL and PCL disrupted, collateral structures largely intact.

KD III

Both cruciates plus one collateral side disrupted.

KD IIIM

ACL + PCL + medial collateral or posteromedial complex injury.

KD IIIL

ACL + PCL + lateral collateral or posterolateral corner injury.

KD IV

ACL + PCL + medial and lateral collateral complexes disrupted.

Extremely unstable.

KD V

Multiligament knee injury associated with periarticular fracture.

Modifiers are often added:

C for arterial injury
N for significant nerve injury

A grossly dislocated knee is obvious.

A spontaneously reduced knee may present only with:

Massive swelling
Ecchymosis
Instability
Peroneal nerve deficit
Abnormal vascular findings

Vascular assessment

Perform before and after reduction:

Dorsalis pedis pulse
Posterior tibial pulse
Capillary refill
Skin temperature
Ankle brachial index

Hard vascular signs

Active haemorrhage
Expanding haematoma
Absent distal perfusion
Cold pale limb
Obvious arterial disruption

These require immediate vascular intervention.

A normal pulse examination alone is insufficient.

ABI

After reduction:

ABI below 0.9

Requires vascular imaging, usually CT angiography.

ABI at least 0.9 with symmetric normal pulses

Allows close serial vascular examinations in a reliable patient without other concerning findings.

ABI below 0.9 has very high specificity for significant arterial injury.

Continue serial examinations because intimal injury can thrombose later.

Neurological assessment

The common peroneal nerve is particularly vulnerable in posterolateral injuries.

Assess:

Ankle dorsiflexion
Great toe extension
Foot eversion
First web space sensation
Dorsum of foot sensation

Assess tibial nerve function as well.

Complete peroneal palsy has a worse prognosis than incomplete injury.

Obtain AP and lateral radiographs before reduction if this does not delay treatment of a threatened limb.

In a neurovascular emergency, reduce immediately.

Obtain post reduction films to confirm a concentric joint.

CT angiography: obtain for:

ABI below 0.9
Abnormal pulses
Soft vascular signs
Concerning high energy injury
Equivocal vascular assessment

MRI knee: obtained after reduction and initial stabilisation to define:

ACL
PCL
MCL
LCL
Posterolateral corner
Menisci
Cartilage
Tendons

MRI is not the immediate priority when limb perfusion is threatened.

Immediate reduction

Reduce the knee urgently using longitudinal traction with correction of displacement.

Avoid repeated forceful attempts.

After reduction:

Repeat pulses
Repeat ABI
Repeat neurological examination
Confirm radiographically
Immobilise in a well padded brace or splint

Irreducible dislocation

Posterolateral dislocation with medial skin puckering or a dimple sign may indicate medial femoral condyle buttonholing.

Do not persist with multiple forceful closed attempts.

Proceed to urgent open reduction.

Pulseless or ischaemic limb

Immediately reduce the knee.

If perfusion does not return, proceed directly to vascular exploration and repair.

Do not delay arterial restoration for MRI.

Temporary vascular shunting can be used when:

Ischaemia time is prolonged
Orthopaedic stabilisation is needed before definitive vascular repair

A stable knee spanning external fixator can protect the vascular reconstruction.

Popliteal artery repair

Repair options include:

Primary repair in a small clean defect
Interposition graft
Bypass, often using reversed autologous great saphenous vein

Perform four compartment leg fasciotomy liberally when:

Ischaemia has been prolonged
Revascularisation has occurred
Major swelling exists
Compartment pressure is concerning

Temporary external fixation

Use a knee spanning external fixator when:

Vascular repair requires protection
Open dislocation
Severe soft tissue injury
Gross instability cannot be maintained in a brace
Fracture dislocation
Polytrauma prevents immediate reconstruction.

Pins should be positioned outside future ligament reconstruction tunnels where possible.

Definitive ligament treatment

Nonoperative management is mainly reserved for:

Frail patients
Low functional demand
Major comorbidity
Selected incomplete ligament injuries

Most active patients with true KD III or KD IV injury benefit from operative reconstruction.

The primary objective is restoration of:

Central pivot, ACL and PCL
Medial stability
Posterolateral stability

Failure to recognise posterolateral corner injury is a major cause of cruciate reconstruction failure.

Repair versus reconstruction

Collateral avulsions

Acute repair may be appropriate when:

Ligament is avulsed from a clearly repairable attachment
Tissue quality is good
Surgery occurs early

Midsubstance collateral or cruciate disruption

Reconstruction is usually more reliable than simple suture repair.

Timing

Definitive multiligament reconstruction is individualised.

Early surgery within approximately 3 weeks can improve stability and functional outcomes but carries a greater risk of arthrofibrosis.

Delay or stage reconstruction when there is:

Vascular repair
Major soft tissue injury
Open wound
Severe swelling
Fracture requiring healing
Significant loss of knee motion

A common staged strategy uses temporary stabilisation followed by reconstruction after soft tissue recovery, often around 3 to 6 weeks in severe injuries.

Peroneal nerve injury

Observe incomplete palsies with serial examination because recovery can occur.

Complete palsy requires careful assessment.

Explore when there is:

Open injury
Nerve transection suspected
Entrapment
Progressive neurological deterioration

Persistent foot drop may eventually require:

Nerve reconstruction in selected cases
Posterior tibial tendon transfer
Ankle foot orthosis

Rehabilitation

Rehabilitation must balance:

Prevention of stiffness
Protection of reconstructed ligaments
Restoration of quadriceps function

Early controlled range of motion is generally preferable to prolonged rigid immobilisation once the knee is stable.

Weight bearing progression depends on:

Ligaments reconstructed
Meniscal repair
Fracture
Vascular repair
External fixation

Major complications include:

Limb loss from missed arterial injury
Popliteal thrombosis
Compartment syndrome
Peroneal nerve palsy
Arthrofibrosis
Chronic instability
Graft failure
Heterotopic ossification
Post traumatic osteoarthritis

Septic Arthritis

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management