Plantar Incision Model in Mice

Mice (≥8 weeks) were briefly (5–10 s) anesthetized with 1.5 % isoflurane in 100 % O₂ at a flow rate of 1.0 L/min (SurgiVet Isotech 4). Anesthetized mice were placed on bite bar in a rebreathing anesthetic circuit with nose cone (Vetamac, Rossville, IN). Artificial tears ointment (Dechra, UK) was applied after induction of anesthesia and a feedback controlled heating pad (FHC) was used to maintain body temperature at 37 °C. The plantar surface of the left hind paw was aseptically prepared by using three skin preparation protocols: povidone iodine (7.5 %, Purdue Products LP) and 70 % isopropyl alcohol wipes (Curity). We implemented the plantar Incision model (PIM) adapted from previously described methods (Pogatzki and Raja, 2003 (link), Cowie and Stucky, 2019 ). After aseptic preparation, a 5 mm longitudinal Incision was made using a No.11 scalpel blade through the skin and fascia on the plantar surface of the left hind paw, starting 2 mm from the proximal end of the heel and extending toward the toes. The underlying plantaris muscle was elevated using pointed tips tweezers, leaving the muscle intact. A 5 mm longitudinal Incision was made along the center of the exposed plantaris muscle. The skin Incision was closed with two horizontal simple interrupted sutures of 5–0 nylon (McKesson) on the proximal and distal end of the Incision covered with triple antibiotic ointment (Actvis Pharma, Inc). Mice were allowed to recover from anesthesia in their home cages with wet feed and on a heating pad (FHC) before being returned to the vivarium. Sham mice underwent anesthesia, antiseptic preparation and topical triple antibiotic ointment application, but without Incisions on the skin, fascia, or the muscles. Mice were checked every day, and any mouse with evidence of infection or dehiscence, or lose of sutures were excluded from the study. For pain recovery studies, nylon sutures were removed when mice were anesthetized after postoperative day 1 (POD1) behavior measurement.