Synovial Cavities: Adults

Question 1

• Risk

- causes

Answer 1

• Rapid onset, severe lameness
• Risk of permanent lameness
– Osteoarthritis (2°)
– Fibrosis, adhesions (sheath, bursa)

causes:
• Wounds – lacerations, punctures
• Iatrogenic
– Medication, diagnostic local anaesthesia
– Surgery, e.g. arthroscopy
• Spread from other site of infection
– Haematogenous spread - foals
– Extension from adjacent site of infection

Question 2

• CS (3)

- investigation (3)

Answer 2

• Severe lameness
– 4/5 -5/5
– May be reduced if drainage
• Distension of synovial membrane
– This is what causes the lameness
• Oedema/ Cellulitis

Investigation:
• Synovial fluid analysis
• Distension of synovial cavity to identify leakage (“pressure test”)
• Radiography, ultrasonography

Question 3

Normal synovial fluid

Answer 3

• Translucent, pale yellow
• Viscous
• 10-20g total protein/L
• WBCs
– Total: 0.2 x 109/L
– Differential: <10% PMNs; mainly lymphocytes & large mononuclears
• Sterile

Question 4

Synovial fluid changes

Answer 4

• ↑Volume, ↓viscosity
• Clot formation: Increased synovial membrane permeability results in entry of fibrinogen and clotting factors
• Cannot read newsprint through sample → >30x109 WBCs/L

Question 5

Septic synovitis

Answer 5

– Cloudy, turbid, haemorrhagic, amber, may clot
– WBCs: >10x109/L, ≥90% PMNs
– TP: >40g/L
– PMNs often degenerate and may show toxic changes

Question 6

Traumatic synovitis

Answer 6

– Haemorrhagic (dk yellow or amber in time)
– 0.5-10x109/L, ↑%PMNs
– 40g/L upper limit for severe traumatic arthritis

Question 7

Timing of SF changes (4)

Answer 7

• % neutrophils >90% within 8h
• Total WBCs > 10x109/L 4-8h
• Total protein >40g/L 4-8h
• Lameness took 12h to develop
–	When synovial changes develop

Sampling too early is not a concern!

Question 8

Other test

• four and reasons why you would do them

Answer 8

• bacteriology (before ABs)
• synovial pressure test
• radiography
• -> concurrent traumatic injuries
• -> soft tissue swelling, gas & foreign bodies in soft tissues
• -> Periarticular osteophytes and subchondral lysis, reflecting infection of subchondral bone, may occur after weeks if infection not controlled (DDx OA)
• US
• -> Foreign bodies
• -> Joint effusion, cellularity of synovial fluid
• -> Direction of tracts
• -> Synovial proliferation, cartilage defects
• ->Early periarticular new bone formation (chronic infection)
• -> May aid sampling by identification of fluid pocket

Question 9

Contrast radiography

• how (2)
• middle 1/3 penetration (4)
• palmer 1/3 penetration (1)
• dorsal 1/3 penetration (2)

Answer 9

• Metal probe → synovial cavity approached/penetrated
• Contrast agent – synovial cavities 1st, wound last
– Use water soluble iodine containing agent

middle 1/3 of sole:
• DDFT → localised necrosis which has a tendency to spread & erode into deeper structures
• Navicular bursa → septic bursitis; → osteomyelitis; → extension to DIP joint
• Impar ligament & DIP joint → septic arthritis
• Digital sheath →septic tenosynovitis

palmer 1/3:
→ Septic tenosynoviti

dorsal 1/3:
• Puncture into P3 (toe region or peripheral sole) → bacterial osteitis with sequestration; occasionally fracture
• Puncture into digital fat cushion → heel abscess

Question 10

Concurrent injuries (4)

Answer 10

• Large soft tissue deficit
• Fractures
• Tendon or ligament laceration
• Extensor tendon lacerations

Question 11

Tx (4)

Answer 11

• Flush
– >10L Hartmann’s
– Vital to eliminating infection, restoration of normal joint environment
– Through and through flush using wide bore needles
• Antibiotics: Systemic & local
• Bandaging, rest, intra-synovial medication?
• Tetanus prophylaxis

Question 12

Arthroscopic vs needle flush

Answer 12

• More complete flush, identification of injuries to cartilage, tendon, ligaments; foreign material, infected/devitalised tissue +specific treatment (may not be seen radiography & ultrasonography)
• Cost effective?

Question 13

ABs

• systemic (4)
• local (3)
• regional (5)

Answer 13

Systemic:
– Broad spectrum, bactericidal agents until bacteriology results are known
– Long course
– Penicillin (Gram +ve) & gentamicin (Gram -ve) given intravenously
– inactivation by pus, resistance makes pot SNMs unsuitable first line antibiotic

Local:
• Amikacin, gentamicin
• Not affected by vascular thrombosis & necrosis that occur within synovial mb/bone
• High local concentration for longer compared to systemic administration without risk of systemic toxicity & @ reduced cost

Regional:
– Cannot access synovial cavity easily, multiple cavities in one region
– Cellulitis
– Osteomyelitis
– Higher concentration & for longer than with intra-synovial technique
– foals have fragile veins: I/O may be better with them

Question 14

Monitoring (2)

Answer 14

• Clinical signs
– Degree of lameness
➢ Beware masking by NSAIDs
– Resolution of cellulitis
• Sequential synovial fluid sampling