Abstract
Introduction
The use of narcotic medications to manage postoperative pain after TJA has been associated with impaired mobility, diminished capacity to engage in rehabilitation, and lower patient satisfaction [1]. In addition, side effects including constipation, dizziness, nausea, vomiting and urinary retention can prolong post-operative hospital stays. Intraarticular administration of local anesthetics such as bupivacaine – part of a multimodal postoperative pain management regimen – reduces pain and lowers patients' length of stay [2]. In addition to its anesthetic activity, bupivacaine also has antibacterial activity, particularly against gram-positive bacteria [3]. We have developed a bupivacaine-eluting ultrahigh molecular weight polyethylene (Bupi-PE) formulation; we hypothesized that elution of bupivacaine from polyethylene could have both anesthetic and antibacterial effects in vivo.
Methods
In Vivo Antibacterial Efficacy
A total of n=10 male Sprague Dawley rats (250 g) were used in this study. Polyethylene (control) or Bupi-PE plugs (2.5 mm diameter × 5 mm length) were implanted subcutaneously in the rat dorsum. After incision site closure, 5 × 107 cfu of bioluminescent S. aureus were injected around the implants. Bioluminescent signal (photos/second) was measured daily. All rats were euthanized after one week.
In Vivo Anesthetic Efficacy
A total of n=10 male Sprague Dawley rats (250 g) were used in this study. Polyethylene (control) and Bupi-PE plugs (2.5 mm diameter × 5 mm length) were implanted into rat knees via a lateral transcondylar approach (Figure 1a). Efficacy was determined by performing a walking track analysis using a highly sensitive Tekscan® sensor (VHR, 5101) (Figure 1b). Walking tracks were performed at baseline (pre-surgery) and every 24 hours for two weeks. All rats were euthanized after two weeks.
Results
In Vivo Antibacterial Efficacy
One control rat expired at day 3 and another one expired in day 7. None of the Bupi-PE rats expired during the study. Significantly less bacterial load was observed in rats receiving Bupi-PE, starting at 24 hr post implantation, continuing until the end of study (day 7) (Figure 2).
In Vivo Anesthetic Efficacy
24 hr post surgery, rats in the control group loaded their unoperated hindlimb significantly more than their operated hindlimb. Rats with the Bupi-PE implant loaded both their hindlimbs similarly (Figure 1c).
Discussion
The antibiotic activity of the Bupi-PE against an acute S. aureus infection in the subcutaneous dorsum determined that bupivacaine elution from UHMWPE effectively eradicated bacteria within the implant perimeter. In the joint, the release of bupivacaine allowed prompt weightbearing and joint mobilization compared to controls.
Conclusion
Bupivacaine-eluting UHMWPE effectively reduced bacterial load in murine subcutaneous dorsum and reduced postsurgical pain in a murine intra-articular model. This material can be promising for use as infection prophylaxis and pain management after TJA.
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