Experimental model of peri-prosthetic infection of the knee caused by Staphylococcus aureus using biomaterials representative of modern TKA

Abstract

Prosthetic joint infection (PJI) following total knee arthroplasty (TKA) remains the leading cause for revision surgery, with Staphylococcus aureus the bacterium most frequently responsible. We describe a novel rat model of implant-associated S. aureus infection of the knee using orthopaedic materials relevant to modern TKA. Male Sprague-Dawley rats underwent unilateral knee implant surgery, which involved placement of a cementless, porous titanium implant into the femur, and an ultra-highly cross-linked polyethyelene (UHXLPE) implant into the proximal tibia within a mantle of gentamicin-laden bone cement. S. aureus biofilms were established on the surface of titanium implants prior to implantation into the femur of infected animals, whilst control animals received sterile implants. Compared to controls, the time taken to full weight-bear and recover pre-surgical body weight was greater in the infected group. Neutrophils and C-reactive protein levels were significantly higher in infected compared to control animals at day 5 post surgery, returning to baseline levels for the remainder of the 28-day experimental period. Blood cultures remained negative and additional plasma inflammatory markers were comparable for control and infected animals, consistent with the clinical presentation of delayed-onset PJI. S. aureus was recovered from joint tissue and implants at day 28 post surgery from all animals that received pre-seeded titanium implants, despite the use of antibiotic-laden cement. Persistent localised infection was associated with increased inflammatory responses and radiological changes in peri-implant tissue. The availability of a preclinical model that is reproducible based on the use of current TKA materials and consistent with clinical features of delayed-onset PJI will be valuable for evaluation of innovative therapeutic approaches.

Evaluation of bacteriophage as an adjunct therapy for treatment of peri-prosthetic joint infection caused by Staphylococcus aureus

“…Sterile titanium implants were pre-seeded with S . aureus under in vitro conditions prior to implantation into rat femurs, as described previously [21]. The mean bacterial density on each implant at the time of surgery (day 0) was 1.2 x10 6 CFU (range, 8.9 x 10 5 –1.9 x 10 6 CFU).…”

“…Animals were individually caged, fed a standard pellet diet and provided water ad libitum . After a 7-day acclimation period, knee implant surgery was performed on rats under isoflurane anaesthesia using surgical techniques and materials, as described previously [21]. Surgeries were performed on 10 to 12 animals per surgery day.…”

“…Clinical signs including body weight, temperature and weight-bearing activity were monitored daily throughout the experimental period. Establishment of infection was confirmed by differential white blood cell at day 5 post-surgery (S1 Table) [21]. Animals were sacrificed at 28 days post-surgery (7 days after commencing treatment) with an overdose of pentobarbital (100 mg/kg) for gross pathology, haematology, microbiology, inflammatory, and histological evaluation.…”

“…Bacterial loads were determined in blood, tissues and implants from animals at day 28 post-surgery, using methods described previously [21]. Briefly, liver, spleen, popliteal and inguinal (draining) lymph nodes of the operated (right leg) and non-operated (left leg) limb were dissected aseptically and weighed.…”

“…Using the same titanium implants and additional biomaterials employed in modern TKA, a novel rat model of S . aureus biofilm-associated PJI was also recently characterised [21]. The aim of the current study was to compare the in vivo efficacy of single or combination therapy using a bacteriophage cocktail and vancomycin for reducing S .…”