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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Inflammatory intra-articular process caused by direct invasion of microorganisms such as bacteria or rarely viruses or fungi.

Pathophysiology!!navigator!!

Microorganisms invade joint by direct inoculation via intra-articular injections, traumatic wounds, joint surgery, or dissemination from periarticular infected tissue.

Systems Affected!!navigator!!

Musculoskeletal—joint.

Incidence/Prevalence!!navigator!!

Any breed.

Signalment!!navigator!!

Breed Predilections

Standardbreds overrepresented due to frequent intra-articular injections.

Mean Age and Range

None

Predominant Sex

None

Signs!!navigator!!

Historical Findings

  • Lameness± joint effusion.
  • Traumatic intra-articular wound.
  • Draining wound near joint.
  • Recent intra-articular injection

Physical Examination Findings

  • Lameness, often severe.
  • Joint effusion.
  • Periarticular edema and/or cellulitis and heat.
  • Extreme pain on palpation and manipulation of affected joint.
  • With open joint lacerations, lameness and effusion are minimal

Causes!!navigator!!

  • Traumatic articular wounds.
  • Inoculation during intra-articular injection.
  • Postsurgical infection.
  • Idiopathic.
  • Common Gram-negative organisms—Enterobacteriaceae including Escherichia coli, Pseudomonas, Acinetobacter, Proteus, Klebsiella, Citrobacter, Salmonella, Enterococcus.
  • Common Gram-positive organisms—coagulase-positive Staphylococcus, coagulase-negative Staphylococcus,β-hemolytic Streptococcus, non-β-hemolytic Streptococcus, Rhodococcus equi, Corynebacterium.
  • Staphylococcus aureus is most common after surgery or injection.
  • Anaerobic organisms—Clostridium, Bacteroides, Fusobacterium, and Peptostreptococcus are common in wounds near the foot

Risk Factors!!navigator!!

  • Performance horse.
  • Intra-articular injection

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Aseptic synovitis (“flare”)—rule out with synovial fluid analysis.
  • Traumatic osteochondral fragmentation—rule out with radiography, synovial fluid analysis

CBC/Biochemistry/Urinalysis!!navigator!!

  • Increased SAA.
  • ±Hyperfibrinogenemia

Other Laboratory Tests!!navigator!!

Synovial Fluid Analysis

  • Gross abnormalities—watery, turbid, and cloudy fluid, ± flocculent material.
  • Nucleated cells—>30 000 cells/μL, >80% neutrophils, ± toxic and degenerative changes.
  • Total protein—≥4.0 g/dL; in acute cases >3.5 g/dL.
  • Increased synovial SAA

Synovial Fluid Culture

  • Only 60–75% of infected joints yield a positive culture. For this reason, synovial fluid cytology is imperative.
  • To increase likelihood of positive culture, obtain synovial sample prior to antibiotic administration and submit in broth culture medium with large synovial fluid volume (5–10 mL)

Imaging!!navigator!!

Radiography

  • Often normal in early infection.
  • ±Concomitant fracture.
  • ±Osteolysis or osteomyelitis.
  • Serial radiography to identify preexisting or developing osteoarthritis and to monitor progression, particularly in chronic infection

Ultrasonography

  • Synovial effusion, intra-articular fibrinous material, synovial proliferation, ± cartilage defects.
  • Very helpful to confirm diagnosis when extensive edema, periarticular swelling, or joint location (hip or shoulder) make visual assessment of joint difficult

Nuclear Scintigraphy

  • Increased radiopharmaceutical uptake in subchondral and/or periphyseal bone.
  • Reduced radioactivity (photopenia) with sequestra

CT/MRI

Synovial proliferation, cartilage defects, subchondral bone changes.

Other Diagnostic Procedures!!navigator!!

Digital Exploration of the Wound

  • Aseptically prepare wound and surrounding skin, explore with sterile gloves.
  • Confirms commination when articular cartilage is palpated.
  • Avoid creating a previously nonexistent communication between wound and joint

Joint Distention with Sterile Saline

  • Easiest, most effective way to confirm wound communication.
  • Procedure—aseptic joint preparation, arthrocentesis at a location distant from wound, distend joint with sterile saline.
  • Leakage of fluid from the wound confirms joint communication

Contrast Radiography

Similar to saline joint distention, except iodinated contrast agent is injected into the joint. Radiopaque agent outside the joint confirms wound communication.

Pathologic Findings!!navigator!!

  • Synovial thickening.
  • Hyperemic synovium.
  • Cartilage degradation.
  • Bone necrosis.
  • Intra-articular fibrin

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Eliminate joint infection.
  • Avoid or minimize articular damage.
  • Reduce joint pain and inflammation.
  • Return horse to previous level of soundness

Appropriate Health Care!!navigator!!

  • Should be regarded as a medical emergency.
  • Inpatient medical management is desirable.
  • Typical case management consists of antimicrobial therapy, joint lavage ± debridement, and pain management. Periodic synovial fluid analysis, lameness evaluation, and radiographic assessment are also performed.
  • Antimicrobial therapies:
    • Systemic antimicrobials—broad spectrum until infection has completely resolved. Initial choices adjusted after bacterial culture and sensitivity results. Treatment continues for a minimum of 2–4 weeks beyond clinical resolution.
    • Local therapy—intra-articular antimicrobials via single injection, constant rate infusion, and/or antimicrobial-impregnated polymethylmethacrylate beads; daily treatment initially, then as needed.
    • Regional limb perfusion—delivery of high antimicrobial concentration via IV or interosseous delivery; procedure—place tourniquet proximal to affected joint, antimicrobials diluted into 60–100 mL of saline are administered slowly via venous or interosseous injection; remove tourniquet after 30–35 min; perform daily or every other day until infection resolves.
  • Pain management—systemic NSAIDs, intra-articular NSAIDs, topical NSAIDs, epidural narcotics, fentanyl transdermal patches

Nursing Care!!navigator!!

  • Bandaging—to reduce soft tissue swelling, edema, and joint effusion. Provides increased comfort, better visualization of infected structure(s).
  • Physical therapy—passive joint flexion once acute inflammation has resolved.
  • Cold therapy—<25 min per treatment; methods include cold hosing, ice wraps, cold/pressure delivery systems (Game Ready™)

Activity!!navigator!!

  • Rest and controlled exercise—minimum of 4 weeks of stall rest with hand-walking exercise.
  • Chronic cases, particularly those with associated degenerative changes, require extended convalescence

Diet!!navigator!!

  • Reduce high-energy feeds during convalescence.
  • Monitor hay intake to prevent large colon or cecal impactions

Client Education!!navigator!!

  • It is a medical emergency and should be treated as such.
  • Any wound near a joint should be fully investigated.
  • Unexpected lameness and/or effusion after joint injections should be fully investigated.
  • Multiple therapies are common and treatment is frequently prolonged.
  • Without proper treatment, chronic lameness, refractory infection, and contralateral limb laminitis

Surgical Considerations!!navigator!!

  • Joint lavage—most important intervention along with antimicrobials; performed immediately and then as needed depending on infection severity; procedure—copious balanced electrolyte solution infused under pressure, ± antimicrobials or anti-inflammatories, multiple large (14–18)-gauge needles placed on opposite sides of joint; performed in the sedated standing horse with local anesthesia or anesthetized horse.
  • Arthroscopic lavage and debridement—allows joint visualization and removal of foreign debris, fibrin, infected synovium; also an effective method of lavage.
  • Joint drainage—considered in chronic cases and when lavage alone has not resulted in desired results; drainage via arthroscopic incisions, preexisting wound tract, open arthrotomy, or closed suction drainage systems

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Systemic antimicrobials—broad-spectrum combination (penicillin or cephalosporin and aminoglycoside)
    • Potassium penicillin (22 000–44 000 IU/kg IV QID).
    • Ceftiofur sodium (2.2–4.4 mg/kg IV daily to BID).
    • Gentamicin sulfate (6.6–8.0 mg/kg IV SID).
    • Enrofloxacin (5 mg/kg PO SID).
  • Intra-articular antimicrobials
    • Amikacin sulfate (250–500 mg).
    • Gentamicin sulfate (500 mg).
    • Sodium penicillin (1 × 106 units).
    • Cefazolin (500 mg).
    • Ceftiofur sodium (500 mg).
  • Antimicrobials for regional limb perfusion
    • Amikacin sulfate, ceftiofur sodium, cefazolin, ceftazidime.
    • All at 1 g concentrations diluted into 60 mL of saline.
  • ±Dimethylsulfoxide as a 10% lavage solution as a free radical scavenger and anti-inflammatory agent.
  • Systemic NSAIDs—phenylbutazone (2.2–4.4 mg/kg IV or PO every 12–24 h).
  • Topical NSAIDs—1% diclofenac sodium cream (12.5 cm (5 inches) ribbon of cream over affected joint every 12 h for up to 10 days).
  • Epidural narcotics—morphine (0.1 mg/kg every 24 h) or detomidine (0.05 mg/kg every 6–24 h)

Contraindications!!navigator!!

  • Systemic fluoroquinolones in neonates due to potential osteochondrosis.
  • Intra-articular fluoroquinolones due to their toxic effects on chondrocytes

Precautions!!navigator!!

  • Systemic NSAIDs can be ulcerogenic. Monitor for inappetence, diarrhea, colic.
  • NSAIDs and aminoglycosides can be nephrotoxic; therefore, renal function (via serum creatinine levels) should be evaluated and rechecked periodically

Possible Interactions!!navigator!!

None

Alternative Drugs!!navigator!!

None

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Joint evaluation during daily bandage change. Joint effusion, drainage, heat, and swelling are assessed.
  • General comfort and lameness are initially monitored daily and then as needed.
  • To assess disease progression and response to therapy, periodic synovial fluid analysis and synovial fluid culture and sensitivity are performed.
  • Periodic radiographic and ultrasonographic evaluations are also performed. CT scans allow early recognition of bone lesions, especially in foals

Prevention/Avoidance!!navigator!!

  • Avoid unnecessary joint injections.
  • Good husbandry to reduce the likelihood of accidents and lacerations

Possible Complications!!navigator!!

  • Osteoarthritis.
  • Osteomyelitis.
  • Lameness, inability to return to previous level of performance.
  • Contralateral limb laminitis.
  • If severe, complications could necessitate euthanasia

Expected Course and Prognosis!!navigator!!

  • Prognosis is good for survival and return to athletic soundness with early recognition and aggressive treatment.
  • Preexisting osteoarthritis or cartilage damage secondary to infection will decrease athletic performance.
  • Delayed recognition, minimal therapy, and drug-resistant organisms result in worse prognosis

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Osteoarthritis.
  • Lameness.
  • Traumatic articular fracture

Age-Related Factors!!navigator!!

Infectious arthritis and osteomyelitis secondary to septicemia is common in newborn foals.

Pregnancy/Fertility/Breeding!!navigator!!

None

Synonyms!!navigator!!

Septic arthritis, joint infection.

Abbreviations!!navigator!!

  • CT = computed tomography
  • MRI = magnetic resonance imaging
  • NSAID = nonsteroidal anti-inflammatory drug
  • SAA = serum amyloid A

Suggested Reading ⬆ ⬇

Bertone AL. Infectious arthritis. In: Ross MW, Dyson SJ, eds. Diagnosis and Management of Lameness in the Horse, 2e. St. Louis, MO: Elsevier Saunders, 2011:677–684.

Richardson DW, Ahern BJ. Synovial and osseous infections. In: Auer JA, Stick JA, eds. Equine Surgery, 4e. St. Louis, MO: WB Saunders, 2012:1189–1201.

van Weeren PR. Septic arthritis. In: McIlwraith CW, Frisbie DD, Kawcak CE, van Weeren PR, eds. Joint Disease in the Horse, 2e. St. Louis, MO: Elsevier,2016:91–104.

Author(s) ⬆

Author: José M. García-López

Consulting Editor: Elizabeth J. Davidson