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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Septic arthritis is infection of the articular structures, usually bacterial in origin, resulting in inflammation, pain, and effusion.

Pathophysiology!!navigator!!

  • Most commonly hematogenous seeding of the synovium and subsequent joint infection. Growing foals have increased blood flow through the transphyseal vessels and to the joint capsule
  • Organisms involved are similar to those seen with systemic sepsis. Enterobacter, Escherichia coli, Klebsiella, Salmonella, and Actinobacillus are common Gram-negative isolates. Streptococcus spp. and Staphylococcus spp. are common Gram-positive isolates
  • Increased production of cytokines and migration of neutrophils result in a painful, effusive joint. Synovial fluid has increased protein and WBCs, and the inflammatory and degradative enzymes in this fluid can eventually cause articular cartilage damage
  • Traumatic joint penetration (wounds, lacerations, punctures) can also lead to joint sepsis, although this etiology is more common in adult horses than in neonates

Systems Affected!!navigator!!

  • Musculoskeletal—synovium, cartilage, bone, and surrounding soft tissues can all be affected
  • Neonates can have multiple systems (e.g. GI, pulmonary) affected if systemic sepsis is present

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

Approximately 25% of septic foals are affected with septic arthritis.

Geographic Distribution!!navigator!!

N/A

Signalment!!navigator!!

Septic arthritis secondary to hematogenous spread is most common in foals ;<1 month of age. Foals can be affected as early as 1 day of age and foals with other systemic bacterial disease (e.g. pneumonia) may be affected at several months of age.

Signs!!navigator!!

Historical Findings

  • Frequent recumbency or reluctance to rise
  • Inadequate ingestion of colostrum—mare leaking colostrum prior to foaling; delayed ingestion of colostrum

Physical Examination Findings

  • Stilted gait or lameness; lameness may not be noted if the foal is mostly recumbent or if the lameness is bilateral
  • Joint effusion ± heat, pain on manipulation
  • Tarsocrural, stifle, and carpal and fetlock joints are most commonly affected
  • Periarticular edema
  • Fever
  • Decubital ulcers owing to frequent or prolonged recumbency

Causes!!navigator!!

  • Septicemia
  • Penetrating wounds
  • Iatrogenic—joint injections (uncommon in foals)

Risk Factors!!navigator!!

  • Systemic sepsis is the most important risk factor in neonates. Pneumonia, enteritis, and omphalophlebitis are often associated with septic arthritis
  • Failure of transfer of passive immunity
  • Premature/dysmature foals can maintain increased blood flow through the transphyseal vessels for longer periods of time, keeping the physis and joint at higher risk of sepsis

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Septic physitis—can occur concurrently with septic arthritis; radiographs can identify septic physitis
  • Osteomyelitis—can occur concurrently with septic arthritis; radiographic changes may not be evident for 10–14 days
  • Trauma
  • Foot abscess

CBC/Biochemistry/Urinalysis!!navigator!!

Hyperfibrinogenemia is consistently seen. Leukocytosis or leukopenia may be found on CBC, but these changes are not specific for septic arthritis.

Other Laboratory Tests!!navigator!!

Serum IgG concentration—often low (<800 mg/dL).

Imaging!!navigator!!

  • Radiography—bony abnormalities are often not seen in the early stages of septic arthritis. Radiographic changes associated with osteomyelitis may not been seen for 1–2 weeks. Initial radiographs are useful for determining prognosis and as a baseline for identifying changes on follow-up radiographs
  • CT and MRI—may detect early bone infection
  • US of joints—joint effusions and bony irregularity can help to identify likely septic joints or areas of abscessation
  • US of the umbilicus should be performed in neonates to rule out concurrent omphalophlebitis

Other Diagnostic Procedures!!navigator!!

  • Joint aspirate cytology. WBCs >30 000/µL and often >100 000/µL, with 80–90% neutrophils and total protein >4 g/dL. Normal synovial fluid has total protein <2 g/dL and WBCs <500/µL with <10% neutrophils. Low pH is also found in the synovial fluid of septic structures
  • Joint aspirate culture and sensitivity. Sample should ideally be taken before the foal is started on antibiotics. Do not discontinue antimicrobial therapy in order to obtain a culture if the foal is septicemic or has a septic synovial structure. Treatment with antimicrobials should begin immediately after culture is taken, but culture results can help to guide therapy if there is poor response to the initial treatment
  • If septic physitis is suspected, needle aspirate of the abnormal physeal area can be performed
  • Blood culture can be very useful for identifying the cause of septicemia

Pathologic Findings!!navigator!!

Early in the course of septic arthritis, there may not be significant gross lesions of bone or cartilage. Advanced septic arthritis can result in significant cartilage degradation and osteomyelitis/septic physitis.

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

Joint Lavage

  • Primary treatment for any septic synovial structure
  • Via 14 G needles or teat cannulas—through-and-through lavage with several liters of balanced electrolyte solution (volume depends on severity of sepsis and size of synovial structure). Multiple lavages (usually 48 h apart) are often needed

Local Antimicrobial Delivery

  • Intra-articular injection delivers the highest concentration of antibiotics to the joint. Aminoglycosides such as amikacin (250–500 mg) or gentamicin are commonly used. Continuous infusion catheters have also been used successfully to deliver high concentrations of antibiotics to septic synovial structures
  • Regional limb perfusion or intraosseous perfusion if a regional vein is not available

Systemic Antimicrobial Treatment

  • Broad-spectrum, parenteral, bactericidal antimicrobials are initiated immediately after fluid is sampled for culture. The combination of beta-lactams and aminoglycosides provides good coverage in most cases
  • Systemic antimicrobials are generally continued for approximately 2 weeks after resolution of the infection

Pain Management

  • It is important for the foal to be comfortable enough to willingly rise and nurse
  • NSAIDs are used for pain management and control of fever and inflammation related to the septic structure
  • Opioids may be used if additional analgesia is needed or if there are contraindications to using NSAIDs

Appropriate Health Care!!navigator!!

Inpatient medical and surgical therapy.

Nursing Care!!navigator!!

  • Stall should be deeply bedded to prevent decubital ulcers
  • Foals are often reluctant to rise and should therefore be encouraged or assisted to rise in order to nurse, ideally every hour
  • Immunologic support—plasma transfusion if IgG <800 mg/dL

Activity!!navigator!!

Stall rest is necessary until the joint inflammation has resolved. Concurrent systemic disease may be the limiting factor in the foal's activity.

Diet!!navigator!!

Foals should be encouraged or assisted to rise and nurse frequently (at least every 1–2 h). Debilitated foals or those unable to stand for long periods of time require supplemental feedings via nasogastric feeding tube.

Client Education!!navigator!!

Management practices of good hygiene and ensuring adequate colostrum intake should be emphasized.

Surgical Considerations!!navigator!!

  • Joint lavage—through-and-through needle lavage may be successful in the early treatment of septic arthritis. If there is significant fibrin or longstanding infection, arthroscopic lavage and visualization or arthrotomy should be performed
  • Umbilical resection should be performed in cases of severe septic omphalophlebitis or when unresponsive to antimicrobials

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antimicrobials

  • Initial broad-spectrum coverage often includes penicillin and amikacin, although third-generation cephalosporins may also be used
  • Penicillin—22 000–44 000 IU/kg IV every 6 h
  • Amikacin—25 mg/kg IV every 24 h
  • Ceftiofur—5–10 mg/kg IV every 6–12 h
  • Ceftazidime—50 mg/kg IV every 6 h
  • Cefotaxime—40 mg/kg IV every 6 h

NSAIDs

  • Ketoprofen (1.1–2.2 mg/kg IV every 12 h)
  • Flunixin meglumine (0.5–1.1 mg/kg IV or PO up to every 12 h)

Antiulcer Medication

  • Ranitidine 6.6 mg/kg PO every 8 h or omeprazole 4 mg/kg PO every 24 h
  • May be needed for foals under stress, especially if treated with NSAIDs. Septicemic foals may actually have alkaline gastric pH, so antiulcer medications may not be indicated in this group

Contraindications!!navigator!!

Enrofloxacin should not be used as part of the antimicrobial regimen in foals.

Precautions!!navigator!!

  • Aminoglycosides can cause renal compromise, especially in dehydrated or debilitated foals
  • All NSAIDs can cause renal and GI damage, although ketoprofen is less ulcerogenic and has more renal safety than phenylbutazone

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Foals should be monitored twice daily for development of additional sites of sepsis
  • If lameness and joint effusion persist, repeat radiographs (at 7–10 days) are indicated to determine presence of septic physitis or osteomyelitis
  • Repeat joint aspiration to help assess response to therapy

Prevention/Avoidance!!navigator!!

  • Consumption of adequate amounts of high-quality colostrum
  • Good hygiene in foaling area
  • Routine measurement of IgG levels

Possible Complications!!navigator!!

  • Degenerative joint disease
  • Osteomyelitis

Expected Course and Prognosis!!navigator!!

  • Response to therapy depends upon the severity of infection and the presence of concurrent systemic disease
  • Reported prognosis for survival ranges from approximately 40% to 86%
  • Septic arthritis decreases the likelihood of racing for Thoroughbreds, and appears to prolong the period of time needed to start in their first race
  • Multisystem disease decreases the prognosis for discharge from the hospital to approximately 50%
  • Multiple joint involvement and infection with Salmonella spp. appear to further decrease the prognosis. Presence of concurrent osteomyelitis also decreases the prognosis (guarded)

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Septic physitis
  • Septicemia
  • Diarrhea
  • Omphalophlebitis
  • Pneumonia

Age-Related Factors!!navigator!!

Physeal infections appear to be more common in older foals, whereas synovial sepsis alone is more common in younger foals.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

  • Joint ill
  • Septic joint

Abbreviations!!navigator!!

  • CT = computed tomography
  • GI = gastrointestinal
  • IgG = immunoglobulin G
  • MRI = magnetic resonance imaging
  • NSAID = nonsteroidal anti-inflammatory drug
  • US = ultrasonography, ultrasound
  • WBC = white blood cell

Suggested Reading ⬆ ⬇

Glass K, Watts AE. Septic arthritis, physitis, and osteomyelitis in foals. Vet Clin North Am Eq Pract 2017;33:299–314.

Hepworth-Warren KL, Wong DM, Fulkerson CV, et al. Bacterial isolates, antimicrobial susceptibility patterns, and factors associated with infection and outcome in foals with septic arthritis: 83 cases (1998-2013). J Am Vet Med Assoc 2015;246:785–793.

Smith LJ, Marr CM, Payne RJ, et al. What is the likelihood that Thoroughbred foals treated for septic arthritis will race? Equine Vet J 2004;36:452–456.

Steel CM, Hunt AR, Adams PL, et al. Factors associated with prognosis for survival and athletic use in foals with septic arthritis: 93 cases (1987–1994). J Am Vet Med Assoc 1999;215:973–977.

Author(s) ⬆

Author: Margaret C. Mudge

Consulting Editor: Margaret C. Mudge