The animal experiment was carried out in accordance with the revised Animals (Scientific Procedures) Act 1986 in the UK and Directive 2010/63/EU in Europe. With approvals from the Institutional Animal Care and Use Committee of Hebei Medical University, and from the Research Ethics Committee of the Second Hospital of Hebei Medical University, 12 healthy male canines were provided by the University. They were randomly divided into two groups with proper labeling: the Exterior Group (EG), in which the metal plates were applied on the outward facing side of the rib; the Interior Group (IG), in which the metal plates were applied on the inward facing side of the rib.
Material
The medal plates used in the experiment were custom made with titanium to fit the size and shape of the canine rib. Custom made tools, devices and operation scenes were as shown in Figure 1, including a cordless electric drill, guiding wire loop, threaded metal plates, flexible soft shaft extension, and solid plate stand screwed onto a threaded plate.
Methods
1. Preoperative Preparation
1.1 Preparation before Anesthesia
Food was withheld for 24 hours, and water was withheld for 6 hours before surgery in order to reduce the possibility of regurgitation and aspiration pneumonia. All canines were closely monitored for signs of anxiety, hypothermia (defined as body temperature below 37.2 Degree Celsius), and dehydration. (22)
1.2 Premedication before General Anesthesia
Oxygen was delivered to the canine via face mask, in order to provide mild sedation, reduce aggression and facilitate drug injection. (23) Blood was withdrawn for ABG analysis.
1.3 General Anesthesia
After premedication and mild sedation, the canine’s accurate body weight was measured for precise calculation of drug dosage. General anesthesia was given via intravenous injection of Buprenorphine (0.2mg/kg) at the sacrococcygeal site. The injection was slowed once symptoms of anesthesia started to appear. The surgical anesthesia symptom was defined as lack of palpebral reflex, muscle relaxation of the jaw tone, and the absence of purposeful movement. (22)
The canine was then secured to the operation bed and shaved. Its response was closely monitored as it was becoming unconscious. Observation and interpretation of the canine’s physiologic status were critical to avoid any anesthesia related complications. Body temperature below 37.2 Degree Celsius should be especially alerted and appropriate measures should be taken to avoid hypothermia.
2. Animal Model Preparation
2.1 Canine Rib Fracture Model
Under general anesthesia, standard osteotomy was prepared on the canine at the 5th and 6th rib on the left anterior side of the body resulting in oblique fractures. Two 0.5-cm incisions 3 cm apart were made by an electric knife between the 5th and 6th ribs. Through the two incisions, two fracture sites (3 cm apart) were made on the 5th rib, to closely mimic real world trauma injuries. Similarly through the same two incisions, two fracture sites were made on the 6th rib with a total of 4 fracture sites on the canine. The procedure was performed carefully to minimize the damage to the pleura during the operation. The Canine was closely monitored during surgical fixation.
2.2 Endotracheal Intubation
A single-lumen endotracheal tube was placed for proper airway management to avoid any respiratory obstruction. Intubation was gently performed to avoid damage to the larynx. About 5-8 mL of air was injected into the catheter balloon at the distal end, and tubes were secured with tapes. An extended thin tube was used for the relatively long trachea of the canine. Breathing was maintained via a mechanical ventilator.
2.3 Preoperative Measurements
Measurements include: RR (Respiratory Rate, Breath Per Minute), ABG analysis (PO2, PCO2, and SpCO2), Heart Rate (bpm), Body Temperature (℃), Duration of Surgery (Hours), and Total Blood Loss volume (mL).
3. Operation Procedures
3.1 Exterior Plate Fixation
For canines in the Exterior Plate group, the plate was contoured to the appropriate shape and cut into the right size prior to the surgery. Under open surgery, a 5 cm incision was made with an electric knife. The muscles surrounding the broken rib segments were carefully divided. The exposed rib bones were approximated and aligned to the proper positions. The pre-contoured plate was positioned on the 6th rib, and screws of proper size were slowly drilled with 2 screws per fracture side. The same procedure was performed on the 5th rib.
3.2 Interior Plate Fixation
3.2.1 Incision Preparation
There were totally three incisions made to perform the surgery as shown in Figure 2 marked in red. The 1st incision of 0.5 cm was prepared below the 8th rib along the midaxillary line. A trocar was inserted through the hole and a thoracoscope (shown as A in Figure 2) was inserted for visualization and inflation of CO2 (6mm Hg pressure) in the thoracic cavity for the collapse of one lung. The 2nd incision of 0.5 cm was prepared below the 7th rib close to the fracture site. A metal wire device with a distal loop (shown as B in Figure 2) was inserted here to control direction of the flexible shaft extension. The 3rd incision of 2 cm was made along the infrascapular line below the 7th rib on the posterior side for major operations. A circumferential surgical wound retractor was used here. A surgical glove was used to cover the opening to conserve the CO2 inflation pressure. A shaft extension with a screwdriver attached to the distal end (shown as C in Figure 2) and a contoured titanium plate with a solid plate stand (shown as D and E in Figure 2) were inserted here through the glove cover.
3.2.2 Plate Description
The titanium plate had seven threaded holes (shown as E in Figure 2). The solid plate stand (D in Figure 2) was screwed into the middle threaded hole for firm support during the application process. Other screws were pre-inserted into the threaded holes on the plate (E) to secure their positions so that screws could be easily fastened during the operation.
3.2.3 Pre-drilling and Fixation
The periosteum on the inward facing side of the 5th rib was carefully divided with an electric knife under thoracoscopic view. The inward facing side of the rib bone was then exposed, and small holes were drilled on the bone at locations guided by the plate holes (E) with the help of flexible shaft extension (C with drill bits attached to the distal end). The threaded plate (E) with pre-inserted screws was then approximated to the desired positions. While the plate was pushed firmly against the interior side of the rib by the rigid plate stand (D), the shaft extension with attached screwdriver (C) was inserted and was guided by the wire loop device (B). The screws were then slowly fastened to avoid thermal damage. After confirming that all screws were securely fastened, the solid plate stand was unscrewed and retrieved. Suction was used to remove any debris from the drilling and screwing. The same procedure was repeated on the 6th rib.
4. Postoperative Measurements
Postoperative outcomes were recorded 6, 12, 24, and 48 hours after surgery. In addition, the Glasgow Composite Measure Pain Scale was assessed within 48 hours and up to 14 days after surgery (A blank assessment sheet was shown in Figure 3). (24) Other postoperative outcomes were measured to compare the rates of recovery, including: Time to First Food and Water intake, Intake Frequencies, Vomiting and Regurgitation, Time to First Urine and Stool, Excretion Frequencies, Time to First Standing and Gentle Ambulation, and Mobilization Frequencies up to 14 day after operation. The outcomes were measured and recorded by assessors blinded to the groups. Long term recovery outcomes were not recorded due to limited resources.
Statistical Analysis
The IBM SPSS Statistics 26 software for Windows (SPSS Inc., Chicago, IL, USA) was used for data processing and analysis. Independent-Samples T Test was used to compare functions and outcomes. Data was given as Mean ± S.D. or Median (Interquartile Range) with 95% confidence interval. All testing was two tailed, and a P value less than 0.05 was considered to be statistically significant.