This study was supported by a grant (CNUH-BRI-2012-02-005) funded by the Biomedical Research Institute of Chonbuk National University Hospital (CNUH-BRI), Republic of Korea.

The Institutional Animal Care and Use Committee of Chonbuk National University approved this study. The treatment, use, and handling of animals followed all guidelines and policies. Maintain the operating room at 24 &#176;C.
1. Anesthesia
<ol>
	<li>Acclimatize miniature pigs, aged 12 months, in the experimental unit for at least one week. Perform a clinical examination measuring the respiratory rate, heartrate, and body temperature. Do not feed each miniature pig for 12 h before the anesthes...

<ol>
	<li>Greenfield, R. T., Grant, R. E., Bryant, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pedicle+screw+fixation+in+the+management+of+unstable+thoracolumbar+spine+injuries.">Pedicle screw fixation in the management of unstable thoracolumbar spine injuries.</a> Orthop Rev. 21 (6), 701-706 (1992).</li><li>Upasani, V. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pedicle+screw+surface+coatings+improve+fixation+in+nonfusion+spinal+constructs.">Pedicle screw surface coatings improve fixation in nonfusion spinal constructs.</a> Spine. 34 (4), 335-343 (2009).</li><li>Halvorson, T. L., Kelley, L. A., Thomas, K. A., Whitecloud, T. S., Cook, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+bone+mineral+density+on+pedicle+screw+fixation.">Effects of bone mineral density on pedicle screw fixation.</a> Spine. 19 (21), 2415-2420 (1994).</li><li>Weinstein, J. N., Spratt, K. F., Spengler, D., Brick, C., Reid, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spinal+pedicle+fixation:+reliability+and+validity+of+roentgenogram-based+assessment+and+surgical+factors+on+successful+screw+placement.">Spinal pedicle fixation: reliability and validity of roentgenogram-based assessment and surgical factors on successful screw placement.</a> Spine. 13 (9), 1012-1018 (1988).</li><li>Fini, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+assessment+of+the+bone-screw+interface+after+insertion+of+uncoated+and+hydroxyapatite-coated+pedicular+screws+in+the+osteopenic+sheep.">Biological assessment of the bone-screw interface after insertion of uncoated and hydroxyapatite-coated pedicular screws in the osteopenic sheep.</a> J Biomed Mater Res A. 66 (1), 176-183 (2003).</li><li>Kim, D. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+Titanium-Coated+Pedicle+Screws:+In+Vivo+Porcine+Lumbar+Spine+Model.">Evaluation of Titanium-Coated Pedicle Screws: In Vivo Porcine Lumbar Spine Model.</a> World Neurosurg. 91, 163-171 (2016).</li><li>Upasani, V. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pedicle+screw+surface+coatings+improve+fixation+in+nonfusion+spinal+constructs.">Pedicle screw surface coatings improve fixation in nonfusion spinal constructs.</a> Spine. 34 (4), 335-343 (2009).</li><li>Smit, T. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+a+quadrupted+as+an+in+vivo+model+for+the+study+of+the+spine-biomechanical+considrations.">The use of a quadrupted as an in vivo model for the study of the spine-biomechanical considrations.</a> Eur Spine J. 11 (2), 137-144 (2002).</li><li>Aldini, N. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pedicular+fixation+in+the+osteoporotic+spine:+a+pilot+in+vivo+study+on+long-term+ovariectomized+sheep.">Pedicular fixation in the osteoporotic spine: a pilot in vivo study on long-term ovariectomized sheep.</a> J Orthop Res. 20 (6), 1217-1224 (2002).</li><li>Fini, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+assessment+of+the+bone-screw+interface+after+insertion+of+uncoated+and+hydroxyapatite-coated+pedicular+screws+in+the+osteopenic+sheep.">Biological assessment of the bone-screw interface after insertion of uncoated and hydroxyapatite-coated pedicular screws in the osteopenic sheep.</a> J Biomed Mater Res A. 66 (1), 176-183 (2003).</li><li>Branemark, R., Ohrnell, L. O., Skalak, R., Carlsson, L., Branemark, P. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomechanical+characterization+of+osseointegration:+an+experimental+in+vivo+investigation+in+the+beagle+dog.">Biomechanical characterization of osseointegration: an experimental in vivo investigation in the beagle dog.</a> J Orthop Res. 16 (1), 61-69 (1998).</li><li>McLain, R. F., Yerby, S. A., Moseley, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+morphometry+of+L4+vertebrae:+comparison+of+large+animal+models+for+the+human+lumbar+spine.">Comparative morphometry of L4 vertebrae: comparison of large animal models for the human lumbar spine.</a> Spine. 27 (8), E200-E206 (2002).</li><li>Giavaresi, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+preclinical+evaluation+of+the+influence+of+osteoporosis+on+the+anchorage+of+different+pedicle+screw+designs.">In vivo preclinical evaluation of the influence of osteoporosis on the anchorage of different pedicle screw designs.</a> Eur Spine J. 20 (8), 1289-1296 (2011).</li><li>Hasegawa, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydroxyapatite-coating+of+pedicle+screws+improves+resistance+against+pull-out+force+in+the+osteoporotic+canine+lumbar+spine+model:+a+pilot+study.">Hydroxyapatite-coating of pedicle screws improves resistance against pull-out force in the osteoporotic canine lumbar spine model: a pilot study.</a> Spine J. 5 (3), 239-243 (2005).</li><li>Smorgick, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-+versus+multilevel+fusion+for+single-level+degenerative+spondylolisthesis+and+multilevel+lumbar+stenosis:+four-year+results+of+the+spine+patient+outcomes+research+trial.">Single- versus multilevel fusion for single-level degenerative spondylolisthesis and multilevel lumbar stenosis: four-year results of the spine patient outcomes research trial.</a> Spine. 38 (10), 797-805 (2013).</li><li>Busscher, I., Ploegmakers, J. J., Verkerke, G. J., Veldhuizen, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+anatomical+dimensions+of+the+complete+human+and+porcine+spine.">Comparative anatomical dimensions of the complete human and porcine spine.</a> Eur Spine J. 19 (7), 1104-1114 (2010).</li></ol>

The authors have nothing related to this paper to disclose.

The evaluation of transpedicular screws in the porcine spine requires much time and effort. First, the miniature pig is a large animal. For animal care and anesthesia, the researcher needs a specialized protocol. Second, surgery should maintain an environment similar to that of human surgery. The purpose of evaluating pedicle screws in the porcine spine is to develop an efficient screw that can be applied to humans. Third, evaluating the long-term stability of transpedicular screws requires about three months after the s...

Transpedicular screw fixation is a gold-standard treatment for degenerative lumbar spine and bursting fracture because it involves three columns of the spine and achieves stabilization1,2. However, most patients who undergo such surgery also have osteoporosis3,4. Many studies have evaluated the fixation strength and the osseointegration status of transpedicular screws, because the loosening of pedicle screws currently in use has been reported in patients with osteoporosis5,6.
The porcine spine is similar to the human spine in terms of size. It is less expensive compared to a primate model7. Furthermore, an in vivo mechanical study has demonstrated that the quadruped porcine spine is essentially loaded in the same way as that of the human spine8, which is why many researchers use porcine spines for studies on the prevention of pedicle screw loosening. However, it takes several months to study pedicle screws in the porcine spine because identifying the long-term stability of pedicle screws takes times. In order to compare different types of screws in the vertebral body, it is necessary to insert the screws in similar positions. Therefore, researchers should be well-acquainted with proper anesthesia techniques, standardized surgical protocols, and harvest procedures before performing any experiments. Here, we describe a detailed method for anesthesia, surgery, and harvest for the evaluation of pedicle screw fixation using a porcine spine model, including ex vivo imaging, histology, and strength testing.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Miniature pig</td>
			<td>OrientBio</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Atropine</td>
			<td>Jeil pharmaceutical</td>
			<td>A04900241</td>
			<td>Anesthesia</td>
		</tr>
		<tr>
			<td>Over-the needle plastic catheter</td>
			<td>BD</td>
			<td>REF382412</td>
			<td>Maintenance of IV line</td>
		</tr>
		<tr>
			<td>Ketamine</td>
			<td>Yuhan</td>
			<td>A04502441</td>
			<td>Anesthesia</td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Bayer Korea</td>
			<td>A00800071</td>
			<td>Anesthesia</td>
		</tr>
		<tr>
			<td>Laryngoscope</td>
			<td>Karl storz</td>
			<td></td>
			<td>Intubation</td>
		</tr>
		<tr>
			<td>Endotracheal tube</td>
			<td>Covidien</td>
			<td></td>
			<td>Intubation</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>JW pharmaceutical Co</td>
			<td>A02104781</td>
			<td>Anesthesia</td>
		</tr>
		<tr>
			<td>Eye ointment</td>
			<td>Hanlim pharma</td>
			<td>A37851721</td>
			<td>Protection of pig&#39;s eye</td>
		</tr>
		<tr>
			<td>Cefazolin</td>
			<td>Donga pharma</td>
			<td>A01503951</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>JW pharmaceutical Co</td>
			<td>A02151392</td>
			<td>Maintenance of fluid homeostasis</td>
		</tr>
		<tr>
			<td>Fentanyl</td>
			<td>Hana pharm</td>
			<td>C03200032</td>
			<td>Pain control</td>
		</tr>
		<tr>
			<td>Enrofloxacin</td>
			<td>Bayer</td>
			<td>93106-60-6&#160;</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>Morphine</td>
			<td>Myungmoon pharma</td>
			<td>C03700091</td>
			<td>Pain control</td>
		</tr>
		<tr>
			<td>Meloxicam</td>
			<td>Boehringer Ingelheim</td>
			<td>A07600711</td>
			<td>Antibiotics</td>
		</tr>
		<tr>
			<td>Povidone-iodine</td>
			<td>Hyundai pharma</td>
			<td></td>
			<td>Wound dressing</td>
		</tr>
		<tr>
			<td>Scalpel blade size 15</td>
			<td>Braun</td>
			<td>&#160;I1 BB515</td>
			<td>Skin incision</td>
		</tr>
		<tr>
			<td>Cobb elevator</td>
			<td>Codman</td>
			<td>65-2546</td>
			<td>Dissection of muscle</td>
		</tr>
		<tr>
			<td>Burr</td>
			<td>Medtronic</td>
			<td></td>
			<td>Making of starting point of screw</td>
		</tr>
		<tr>
			<td>Rongeur</td>
			<td>Aesculap</td>
			<td>FO515R</td>
			<td>Making of starting point of screw</td>
		</tr>
		<tr>
			<td>Guide pin (K-wire)</td>
			<td>CE</td>
			<td>01067803</td>
			<td>Guidance of screw trajectory</td>
		</tr>
		<tr>
			<td>C-arm</td>
			<td>GE</td>
			<td>OEC 9800 plus</td>
			<td>Guidance of screw trajectory</td>
		</tr>
		<tr>
			<td>Portable X-ray</td>
			<td>Siemens</td>
			<td>Mobile XP hybrid</td>
			<td>Guidance of screw trajectory</td>
		</tr>
		<tr>
			<td>Pedicle probe</td>
			<td>OtisBiotech</td>
			<td>SPI-02-01</td>
			<td>Guidance of screw trajectory</td>
		</tr>
		<tr>
			<td>Pedicle sounding device</td>
			<td>OtisBiotech</td>
			<td>SPI-03-01</td>
			<td>Guidance of screw trajectory</td>
		</tr>
		<tr>
			<td>Pedicle screw</td>
			<td>OtisBiotech</td>
			<td>MS-40025</td>
			<td></td>
		</tr>
		<tr>
			<td>Posterior fixator systems</td>
			<td>OtisBiotech</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Rod&#160;</td>
			<td>OtisBiotech</td>
			<td>ROD-60140</td>
			<td>Rigid fixation between screws</td>
		</tr>
		<tr>
			<td>Universal handle</td>
			<td>OtisBiotech</td>
			<td>SPI-08-01</td>
			<td>To fix the screws to the rod</td>
		</tr>
		<tr>
			<td>Straight socket wrench</td>
			<td>OtisBiotech</td>
			<td>SPI-06-01</td>
			<td>To fix the screws to the rod</td>
		</tr>
		<tr>
			<td>counter torque wrench</td>
			<td>OtisBiotech</td>
			<td>SPI-07-01</td>
			<td>To fix the screws to the rod</td>
		</tr>
		<tr>
			<td>Bulb irrigation syringe</td>
			<td>Hyupsug medical</td>
			<td>HS-IR-140</td>
			<td>Irrigation</td>
		</tr>
		<tr>
			<td>Silicone drain</td>
			<td>Sewon medical</td>
			<td>2205-006</td>
			<td>To drain the fluid at the surgical site</td>
		</tr>
		<tr>
			<td>3.0 metric absorbable suture</td>
			<td>Ethicon</td>
			<td>BA1673H</td>
			<td>Muscle suture</td>
		</tr>
		<tr>
			<td>2.0 metric nonabsorbable nylon suture</td>
			<td>Ethicon</td>
			<td>W1626T</td>
			<td>Skin suture</td>
		</tr>
		<tr>
			<td>Gauze</td>
			<td>Kingphar Korea</td>
			<td>KP120-06</td>
			<td></td>
		</tr>
		<tr>
			<td>Pentobarbital</td>
			<td>Hanlim pharma</td>
			<td>645301221</td>
			<td>Euthanasia</td>
		</tr>
		<tr>
			<td>Oscillating saw</td>
			<td>Zimmer</td>
			<td></td>
			<td>Harvest spine</td>
		</tr>
		<tr>
			<td>Tower forceps</td>
			<td>Aesculap</td>
			<td>BF461R</td>
			<td>Harvest spine</td>
		</tr>
	</tbody>
</table>

an anesthesia, surgery, and harvest method for the evaluation of transpedicular screws using an in vivo porcine lumbar spine model

Pedicle screw fixation is the gold standard for the treatment of spinal diseases. However, many studies have reported the issue of loosening pedicle screws after spinal surgery, which is a serious concern. To address this problem, diverse types of pedicle screws have been examined to identify those with good fixation strength and osseointegration in spine bone. The porcine spine is a good alternative for the human spine in the evaluation of pedicle screws due to the anatomical size, mechanical characteristics, and cost. Although several studies have reported that pedicle screws are efficient in the porcine model, no study has described detailed protocols for the evaluation of a pedicle screw using the porcine model. Here, we describe a detailed method for evaluating transpedicular screws using an in vivo porcine lumbar spine model. The technical details for anesthesia, spine surgery, and harvest provided here will facilitate with the evaluation of the transpedicular screw fixation model.

A detailed protocol for anesthesia, surgery, and harvest for the evaluation of transpedicular screws using an in vivo porcine lumbar spine model is described here. This protocol is suitable for a number of downstream analyses, including mechanical testing (Figure 1), quantitative micro-CT evaluation (Figure 2), and histology (Figure 3). Representative mechanical testing (Figure 1) shows the mean extraction torsio...

Watch this Scientific Journal Video about An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model at JoVE.com

An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model

Here, we introduce a method to evaluate transpedicular screws by using an in vivo porcine lumbar spine model.

An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model

Pedicle screw fixation is the gold standard for the treatment of spinal diseases. However, many studies have reported the issue of loosening pedicle ...

The overall goal of this surgical intervention is to evaluate transpedicular screws using an in vivo porcine lumbar spine model. This method can help answer key questions about such complications of the spine, such as the loosening of pedicle screw. The main advantage of this technique is that we can compare long-term stability of different type of screws.Maintain 12-month-old miniature pigs in the experimental unit for at least one week. After this acclamation period, give each pig a clinical exam, measure respiratory rate, heart rate, and body temperature. Prior to the anesthesia, starve the pigs for 12 hours.To sedate a pig, inject atropine into the lateral cervical muscle region behind the ear. Once sedated, press a hand around the base of the ear and then clean the ear with alcohol. Then, place an over the needle plastic catheter into the ear vein.Then, flush the catheter with heparinized saline and secure it with tape. Now, induce anesthesia using ketamine and xylazine via the catheter. To intubate the pig, position it in sternal recumbency.And with the help of an assistant, hold open the jaw using a suitable sling. Then, pass the tip of the laryngoscope into the pharyngeal cavity to displace the epiglottis from the soft palate. Once intubated, listen to the respiration in both lungs.Then, fill the cup of the endotracheal tube with air using a 10 milliliter syringe, and fix the tube to the snout, using adhesive tape. Next, begin providing 2%isoflurane through the tube. Then, test the pig's corneal and palpebral reflexes to confirm a surgical plane of anesthetization.Now, apply ointment on the eyes and set up vital sign monitors, which should be checked at least every five minutes. 30 minutes before the surgery, provide a bolus of cefazolin via the ear vein catheter. Then, switch the IV line to administer 37 degree Celsius saline and fentanyl for pain management.To begin, shave the pig's back 10 centimeters to either side of the midline. Then, clean the skin with alternating scrubs of povidone iodine solution and 70%ethanol. Now, make a longitudinal midline incision from the second spinous process of the lumbar spine to the first median sacral crest.Then, dissect through the subcutaneous tissue and fascia down to the tip of the spinous processes. Next, using a Cobb elevator, elevate the paraspinal muscles subperiosteally from the underlying lamina. Then, dissect along the spinous process and lamina at the facet joints.At the entry point, which is just inferior to the mamillary process from L3 to L5, use a burr or rongeur to open the superficial cortex. Then, insert the guide pen parallel to the superior end plate and at a 20 degree angle to the spinous process. Now, take posterior anterior lateral X-rays to define the insertion points for the pedicle screws.Then, insert a pedicle probe up to 25 millimeters and confirm a complete intraosseous trajectory using the sounding device and palpation. Now, insert six pedicle screws. Make sure that the screw heads are well-seated.Pay attention to the orientation of the site opening and the horizontal position which must line up with the rod. Then, insert two rods into both sides of the pedicle screw heads. Next, attach sleeves and nuts to the screw's head.First tighten the nuts loosely with a straight socket wrench and then tighten them with a counter torque wrench. Then, confirm the positions of the pedicle screws using X-rays. Once the site is ready to close, irrigate it with three liters of normal saline.Then attach a silicone drain and take out the silicone tip. Now, close the paraspinal muscles and subcutaneous tissues using absorbable sutures, and then close the skin with nonabsorbable nylon sutures. After suturing, disinfect the site with povidone iodine and apply a dressing.Once a strong swallowing reflex is apparent, extubate the pig and transfer it to a recovery room. Once fully conscious, provide the pig food and water and check its gate patterns. Monitor the hind limb movement to assess the implant and provide pain relievers for three days.12 weeks after the implantation, euthanize the pig. To harvest a spinal section, make a longitudinal midline incision at the previous surgery scar legion. Then, dissect the soft tissue and paraspinal muscles to fully expose the implant from L3 to L5.Now, remove the nuts using a counter torque wrench.And then remove the rods. Next, using an oscillating saw, cut the L2-3 disc space and the L5-S1 disc space. Then, dissect both sites in the middle and anterior part of the L3-5 spine with a Cobb elevator and tower forceps.If the spinal section cannot be immediately analyzed, store it in saline-soaked gauze at minus 20 degrees Celsius. The bonding strength between the pedicle screws and bone was evaluated for three screw types. Uncoated, hydroxyapatite-coated, and titanium-coated.The main extraction torsional peak torque, or bond strength, was greatest with the titanium-coated pedicle screws. The region of interest can be evaluated by a micro-CT program for the analysis of the bone volume fraction, bone surface density, and specific bone surface. Scanning a spinal section with Goldner trichrome shows the interface between the pedicle screw and bone.The fibrous tissue is red, and the bone is blue. When using uncoated pedicle screws, only fibrous tissue was observed at the interface. However, new bone formation was found at the interface for both types of coated screws.It was even observed that with titanium-coated pedicle screws, the space between the screw threads in the bone was completely compacted. Once mastered, this technique can be done in three hours if it is performed properly. While attempting this procedure, it's important to focus on proper positioning of the the pedicle screws so the misplacement of the pedicle can be prevented.After its development, this technique paved the way for researchers in the field of the spine surgery to explore loosening of pedicle screws in patients with osteoporosis.

an-anesthesia-surgery-harvest-method-for-evaluation-transpedicular

Research

Education

JoVE Core

JoVE Journal

Pharmacology

Medicine

Unit 1

Local Anesthetics

SCIENTISTS IN ACTION

7.5K ビュー.  Chonbuk National University School of Medicine, Chonbuk National University Hospital. The overall goal of this surgical intervention is to evaluate transpedicular screws using an in vivo porcine lumbar spine model. This method can help answer key questions about such complications of the spine, such as the loosening of pedicle screw. The main advantage of this technique is that we can compare long-term stability of different type of screws.Maintain 12-month-old miniature pigs in the experimental unit for at least one week. After this acclamation period, give each pig a ...