Equine joint disorders
Joint sepsis can occur due to trauma (puncture wounds and iatrogenic), extension from nearby infection and hematogenous spread. Hematogenous spread is unusual in adults; in foals it is usually related to umbilical, GI or respiratory infections. A variety of organisms can be identified with wounds, including anaerobes. Iatrogenic infections are often Staphylococcus aureus; these are associated with joint blocks and therapeutic joint injections. Systemic infections in foals are often gram negative coliforms. Rhodococcus equi can seed joints in older foals.
Early identification and aggressive treatment is required for soundness and often for life. Joint effusion and lameness are common. Foals may have a limited inflammatory response , lie down a lot, with lameness not always apparent. All joints should be carefully palpated in foals (multiple joints may be involved) and the umbilicus ultrasounded. Joint fluid is sampled and submitted for culture and cytology. A healthy joint will have viscous fluid with low protein and low cell count. An infected joint will have high protein, a high cell count and low viscosity as inflammatory cells and mediators leak into the fluid and destroy the hyaluronan components and other proteins. The joint fluid and/or blood should be cultured to determine the causative agent and appropriate antimicrobial treatment.
Radiographs are recommended as many cases of juvenile septic arthritis occur due to extension from an infected physis or metaphysis.
Any underlying infection should be treated and infected umbilical stalks removed surgically if indicated. Systemic iv antibiotics are indicated.
The joint is treated via lavage. Through and through needle lavage (two needles are put into the joint and fluid flushed into and out of the joint) is effective in foals and in very early cases of traumatic infection. If available, arthroscopic lavage is considered more effective in adults and in more chronic infections.
Local (intra-articular) antibiotic infusion of amikacin or other high powered antibiotic is usually combined with systemic administration of more broad spectrum and first line antibiotics such as penicillin/gentamicin or a cephalopsorin until culture results are available. (Amikacin is often used systemically in foals). Antibiotics alone are not effective.
Synovial resection may be required to remove deep seated bacteria and damaged synovium.
Joint samples are take every other day to determine if repeated flushing or injection is required and to ensure improvement.
If the infection cannot be controlled, the horse should be euthanized for humane reasons.
Foals can develop septic arthritis due to hematogenous spread. Adults develop septic arthritis due to wounds and injections.
Septic arthritis can result in euthanasia
Treat with lavage and antibiotics (local +/- systemic)
Haematogenous septic arthritis, physitis and osteomyelitis in foals: A tutorial review. Part 1. Equine vet. Educ. (2021) 33 (12) 659-672
Haematogenous septic arthritis, physitis and osteomyelitis in foals: A tutorial review. Part II. Equine vet. Educ. (2022) 34 (1) 37-48
Septic Arthritis, Physitis, and Osteomyelitis in Foals, VCNA August 2017, Vol.33(2), pp.299-314
Antimicrobial selection for the equine practitioner, VCNA 2021, Vol 37, pp 461-494. Includes specific recommendations for musculoskeletal infections
Effect of arthroscopic lavage and repeated intra-articular administrations of antibiotic in adult horses and foals with septic arthritis. Veterinary Surgery. 2017;46:1008–1016.