The effect of implanting gentamicin-impregnated polymethylmethacrylate beads in the tarsocrural joint of the horse.

This study examines the effect of placing antibiotic-loaded plastic beads in a horse’s tarsocrural joint, noting that this method can maintain therapeutic levels of the antibiotic for up to 9 days. But, it also causes inflammation and superficial cartilage erosion.

Study Methodology and Objectives

• The main objective of this research was to determine the effect of inserting antibiotic (gentamicin)-impregnated Polymethylmethacrylate (PMMA), a type of plastic, beads into an equine tarsocrural joint (a joint in the hind limb). Specifically, the study aimed to understand the impact on the synovial fluid, synovial lining, and cartilage in the joint, and to identify the levels of gentamicin in the synovial fluid and plasma post-implantation.
• The study conducted a pharmacokinetic, cytologic, and histologic analysis of the effect of gentamicin-loaded PMMA on healthy equine tarsocrural joints. The research was conducted on five healthy adult horses, wherein the antibiotic-loaded beads were surgically inserted into one healthy tarsocrural joint of each horse.
• Prior to the bead administration, both joints in each horse were cleaned out with 1L of lactated Ringer’s solution. Various factors were monitored post-treatment including the concentration of total protein in the synovial fluid, white blood cell (WBC) count, gentamicin concentration, synovial histology, cartilage integrity, and the concentration of cartilage glycosaminoglycan (GAG).

Findings of the study

• The peak concentration of gentamicin was reached in the first 24 hours and remained at therapeutic levels for 9 days. Control joints and plasma did not exhibit any detectable gentamicin levels.
• Compared to control joints, WBC count in treated joints increased for 72 hours but returned to regular levels on day 6. Synovial protein level in gentamicin-treated joints remained high for 21 days.
• On histology, the synovium in treated joints exhibited diffuse synovitis while control joints showed less fibrovascular proliferation. Superficial cartilage erosion was observed in all treated joints, but there was no difference detected in the GAG content between treated and control joints’ cartilage.

Conclusions and Implications

• In the short term, the implantation of gentamicin-impregnated PMMA beads ensures therapeutic levels of gentamicin are maintained in the normal tarsocrural joint for up to 9 days. This suggests they could be a potential treatment approach for joint infections requiring constant high concentrations of antibiotics.
• However, the implantation of these antibiotic-loaded beads also induces inflammation (synovitis) and causes superficial erosion of the cartilage, pointing to potential detrimental effects on joint health.