A Simplified Technique for Producing an Ischemic Wound Model

Summary

We have developed a minimally invasive technique to create a rabbit ischemic ear wound model by dividing the central artery and nerve and the cranial neurovascular bundle. A subcutaneous tunnel then cuts all subcutaneous tissues. This procedure causes minimal skin disruption and can be safely used in diabetic animals.

Abstract

One major obstacle in current diabetic wound research is a lack of an ischemic wound model that can be safely used in diabetic animals. Drugs that work well in non-ischemic wounds may not work in human diabetic wounds because vasculopathy is one major factor that hinders healing of these wounds. We published an article in 2007 describing a rabbit ear ischemic wound model created by a minimally invasive surgical technique. Since then, we have further simplified the procedure for easier operation. On one ear, three small skin incisions were made on the vascular pedicles, 1-2 cm from the ear base. The central artery was ligated and cut along with the nerve. The whole cranial bundle was cut and ligated, leaving only the caudal branch intact. A circumferential subcutaneous tunnel was made through the incisions, to cut subcutaneous tissues, muscles, nerves, and small vessels. The other ear was used as a non-ischemic control. Four wounds were made on the ventral side of each ear. This technique produces 4 ischemic wounds and 4 non-ischemic wounds in one animal for paired comparisons. After surgery, the ischemic ear was cool and cyanotic, and showed reduced movement and a lack of pulse in the ear artery. Skin temperature of the ischemic ear was 1-10 °C lower than that on the normal ear and this difference was maintained for more than one month. Ear tissue high-energy phosphate contents were lower in the ischemic ear than the control ear. Wound healing times were longer in the ischemic ear than in the non-ischemic ear when the same treatment was used. The technique has now been used on more than 80 rabbits in which 23 were diabetic (diabetes time ranging from 2 weeks to 2 years). No single rabbit has developed any surgical complications such as bleeding, infection, or rupture in the skin incisions. The model has many advantages, such as little skin disruption, longer ischemic time, and higher success rate, when compared to many other models. It can be safely used in animals with reduced resistance, and can also be modified to meet different testing requirements.

Protocol

1. Anatomic Basis

The rabbit ear has been a favored study material for wound care since the early 20^th century. The ear is supplied by three vascular bundles (central, cranial, and caudal); the central bundle is the largest, while the vessels in the cranial and caudal bundles vary in size. Occasionally, the caudal artery may be absent.¹ All of these vessels are easily identified on the dorsal side after the ear is shaved (Fig. 1). On the ventral side, the distal skin does not receive blood supply from the proximal vessels. The three vessel bundles on the dorsal ear have numerous branches that penetrate t....

Discussion

Diabetes affects 23.6 million people in the US,^2,3 and 15-20% of these patients develop foot ulcers in their lifetime,^4,5 at an annual treatment cost of more than $25 billion.^3,6 However, even the best available treatments achieve only a 50% healing rate and this is often temporary,⁷ with recurrence rates as high as 66% in diabetics.^3,6 When ulcers occur in diabetic patients, major complications such as infection and amputation increase dramatically. Despite almost a.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
For monitoring during surgery
A heating pad to maintain normal temperature. A transcutaneous oxygen monitor. A temperature monitor.
For surgery
A #3 knife with #15 blade. Two pairs of forceps (one for skin and another for other soft tissues). 2-3 pairs of small clamps. One or two pairs of micro scissors (for tissue cutting). One pair of small scissors (for cutting sutures). A needle holder. A few stainless steel punches (for making wounds).