A minipig Model of Incisional pain
The use of animal models for the research of post-operative pain (POP) has been well described[1]. Most POP studies that have been performed to date used male rodents following plantar incision and focusing on the withdrawal response from a noxious thermal, chemical, or mechanical stimulus[2]. Although rodent models have contributed significantly to our understanding of surgical pain over the years and have the added advantage of being readily available for anatomic manipulation, there are some significant limitations, especially for assessing local therapies. For example, rodent skin structure[3], innervation[4-6] and penetration[7] is very different from human cutaneous tissue. Despite major efforts to evaluate spontaneous changes in rodents, [8] such as facial recognition and grimace scale,[9] dynamic weight bearing [10] and heat gradient place preference, [8,11] pain status is still predominantly evaluated using the withdrawal response method [12]. In contrast to the rodent, there are striking similarities between pig and human skin structure in terms of general structure, thickness, hair follicle content, pigmentation, collagen and lipid composition [13]. Indeed, pigs have been used for many years for the study of skin penetration with topical therapies because of the high prediction of permeability compared to humans [7]. The pig model for post-operative pain (POP) is therefore a rational choice.