Cadaveric Sheep Research Articles

System Setup to Deliver Air Impact Forces to a Sheep Limb: Preparation for Model Development of Blast-Related Heterotopic Ossification.

BackgroundHeterotopic ossification (HO) is a significant complication for wounded warriors with traumatic limb loss. Although this pathologic condition negatively impacts the general population, ectopic bone has been observed with higher frequency for service members injured in Iraq and Afghanistan due to blast injuries. Several factors, including a traumatic insult, bioburden, tourniquet and wound vacuum usage, and bone fractures or fragments have been associated with increased HO for service members. A large combat-relevant animal model is needed to further understand ectopic bone etiology and develop new pragmatic solutions for reducing HO formation and recurrence.ObjectiveThis study outlines the optimization of a blast system that may be used to simulate combat-relevant trauma for HO and replicate percussion blast experienced in theater.MethodsWe tested the repeatability and reproducibility of an air impact device (AID) at various pressure settings and compared it with a model of blunt force trauma for HO induction. Furthermore, we assessed the ability of the higher-power air delivery system to injure host tissue, displace metal particulate, and disperse bone chips in cadaveric sheep limbs.ResultsData demonstrated that the air delivery setup generated battlefield-relevant blast forces. When the AID was charged to 40, 80, and 100 psi, the outputs were 229 (SD 13) N, 778 (SD 50) N, and 1085 (SD 114) N, respectively, compared with the blunt force model which proposed only 168 (SD 11) N. For the 100-psi AID setup, the force equaled a 5.8-kg charge weight of trinitrotoluene at a standoff distance of approximately 2.62 m, which would replicate a dismounted improvised explosive device blast in theater. Dispersion data showed that the delivery system would have the ability to cause host tissue trauma and effectively disperse metal particulate and host bone chips in local musculature compared with the standard blunt force model (13 mm vs 2 mm).ConclusionsOur data showed that a high-pressure AID was repeatable or reproducible, had the ability to function as a simulated battlefield blast that can model military HO scenarios, and will allow for factors including blast trauma to translate toward a large animal model.

Royal Perth Hospital airway & head and neck anesthesiology fellowship

Royal Perth Hospital airway & head and neck anesthesiology fellowship

Intraluminal three-dimensional optical coherence tomography – a tool for imaging of the Eustachian tube?

The cause of Eustachian tube dysfunction often remains unclear. Therefore, this study aimed to examine the feasibility and possible diagnostic use of optical coherence tomography in the Eustachian tube ex vivo. Two female blackface sheep cadaver heads were examined bilaterally. Three conditions of the Eustachian tube were investigated: closed (resting position), actively opened and stented. The findings were compared (and correlated) with segmented histological cross-sections. Intraluminal placement of the Eustachian tube with the optical coherence tomography catheter was performed without difficulty. Regarding the limited infiltration depth of optical coherence tomography, tissues can be differentiated. The localisation of the stent was accurate as was the lumen. The application of optical coherence tomography in the Eustachian tube under these experimental conditions is considered to be a feasible, rapid and non-invasive diagnostic method, with possible diagnostic value for determining the luminal shape and superficial lining tissue of the Eustachian tube.

Conduit-based Nerve Repairs Provide Greater Resistance to Tension Compared with Primary Repairs: A Biomechanical Analysis on Large Animal Samples.

Background:When primary repair of transected peripheral nerves is not possible due to large gaps, nerve grafts or repair using conduits are other options to bridge the gap such that the nerve is repaired without tension. When nerve gaps are repaired primarily, there is a worry about tension, failure, and poor healing. In this biomechanical study comparing nerves repaired primarily versus those repaired with conduits, we hypothesized that conduit repair provided greater mechanical breaking strength.Methods:We dissected fresh cadaveric sheep hooves and transacted their peripheral nerves. Subsequently, we divided these transacted nerves into 2 groups: primary repair versus repair using a nerve conduit. After repair using a standardized technique, we tensioned each of these repairs via a load tester and recorded the force required till repair failure occurred.Results:Six nerves using primary nerve repair and 6 nerves repaired with a nerve conduit (10 mm length × 2.5 mm diameter) were studied. The average breaking strength of the nerves repaired with the nerve conduit was 0.92 N and that using the primary nerve repair technique was 0.46 N (P = 0.001). All the nerves repaired using nerve conduit repair had an additional 5 mm added to their total length as compared with the nerves in the other group.Conclusions:Nerve repair using a nerve conduit ensures a higher breaking strength and potentially a greater tension-free repair as compared with primary nerve repairs in a sheep model. This study supports the use of conduits in the bridging of nerve gaps.

In Vivo Measurement of Middle Ear Pressure Changes during Balloon Eustachian Tuboplasty.

Background Balloon Eustachian tuboplasty (BET) is known as a treatment for chronic obstructive Eustachian tube dysfunction (OETD). The precise mechanism of action is not fully understood. Observations in sheep cadavers and human cadavers have shown specific middle ear pressure changes related to BET. Methods In this prospective study using a microfibre optical pressure sensor, pressure changes during BET were for the first time monitored transtympanically in five normal human middle ears in vivo. Results Middle ear pressure changes during 21 BETs consisted of five stages (insertion, inflation, deflation, withdrawal, and recovery). The highest pressure change occurred in most of the cases during the withdrawal of the balloon catheter. Withdrawal pressure yielded a mean middle ear pressure of 4.76 mmHg (61.89 daPa) with a maximum of 13.88 mmHg (179.55 daPa). Pressure amplitudes capable of causing barotrauma to ear structures were not detected. Internal carotid artery dehiscences were detected as causative of sinusidual pressure changes. Conclusion The middle ear pressure changes detected in vivo during BET can be attributed to the balloon inflation. Further human studies with patients affected by OETD are necessary to gain more insight into the mechanism of action of BET to clarify a possible pressure related second mechanism of action of BET.

Changes in Joint Contact Mechanics in a Large Quadrupedal Animal Model After Partial Meniscectomy and a Focal Cartilage Injury.

Acute mechanical damage and the resulting joint contact abnormalities are central to the initiation and progression of post-traumatic osteoarthritis (PTOA). Study of PTOA is typically performed in vivo with replicate animals using artificially induced injury features. The goal of this work was to measure changes in a joint contact stress in the knee of a large quadruped after creation of a clinically realistic overload injury and a focal cartilage defect. Whole-joint overload was achieved by excising a 5-mm wedge of the anterior medial meniscus. Focal cartilage defects were created using a custom pneumatic impact gun specifically developed and mechanically characterized for this work. To evaluate the effect of these injuries on joint contact mechanics, Tekscan (Tekscan, Inc., South Boston, MA) measurements were obtained pre-operatively, postmeniscectomy, and postimpact (1.2-J) in a nonrandomized group of axially loaded cadaveric sheep knees. Postmeniscectomy, peak contact stress in the medial compartment is increased by 71% (p = 0.03) and contact area is decreased by 35% (p = 0.001); the center of pressure (CoP) shifted toward the cruciate ligaments in both the medial (p = 0.004) and lateral (p = 0.03) compartments. The creation of a cartilage defect did not significantly change any aspect of contact mechanics measured in the meniscectomized knee. This work characterizes the mechanical environment present in a quadrupedal animal knee joint after two methods to reproducibly induce joint injury features that lead to PTOA.

Surgical access via right thoracotomy facilitates tricuspid valve surgery in sheep.

In quadrupeds, the three-dimensional orientation of the heart with respect to the thorax is fundamentally different from that in humans. In this study, we assessed the best surgical approach to the tricuspid valve in sheep. Firstly, different surgical access sites to the tricuspid valve were tested in sheep cadavers, the anatomy was analyzed, and the optimal surgical approach to the tricuspid valve was determined. Secondly - along with cardiopulmonary bypass and cardioplegic arrest -the chosen approach was tested in six adult sheep in vivo. Anatomical analyses revealed that a left thoracotomy provided optimal access to the aorta and left heart. However, visualization of the right heart was significantly impaired. In contrast, a right thoracotomy provided good access to the right heart, but the ascending aorta was difficult to approach. Therefore, in the in vivo studies, arterial cannulation was performed through a carotid (n = 4) or femoral (n = 2) artery. In conclusion, a right-sided thoracotomy allows good visualization of all components of the tricuspid valve complex in sheep, but not of the ascending aorta. Consequently, peripheral vessels are preferred for arterial cannulation. This work may stimulate the investigation of pathomechanisms and/or novel treatment options for tricuspid valve pathologies.

Complex Spine Pathology Simulator: An Innovative Tool for Advanced Spine Surgery Training.

Background Technical advancements in spine surgery have made possible the treatment of increasingly complex pathologies with less morbidity. Time constraints in surgeons' training have made it necessary to develop new training models for spine pathology. Objective To describe the application of a novel compound, Stratathane resin ST-504 derived polymer (SRSDP), that can be injected at different spinal target locations to mimic spinal epidural, subdural extra-axial, and intra-axial pathologies for the use in advanced surgical training. Material and Methods Fresh-frozen thoracolumbar and cervical spine segments of human and sheep cadavers were used to study the model. SRSDP is initially liquid after mixing, allowing it to be injected into target areas where it expands and solidifies, mimicking the entire spectrum of spinal pathologies. Results Different polymer concentrations have been codified to vary adhesiveness, texture, spread capability, deformability, and radiologic visibility. Polymer injection was performed under fluoroscopic guidance through pathology-specific injection sites that avoided compromising the surgical approach for subsequent excision of the artificial lesion. Inflation of a balloon catheter of the desired size was used to displace stiff cadaveric neurovascular structures to mimic pathology-related mass effect. Conclusion The traditional cadaveric training models principally only allow surgeons to practice the surgical approach. The complex spine pathology simulator is a novel educational tool that in a user-friendly, low-cost fashion allows trainees to practice advanced technical skills in the removal of complex spine pathology, potentially shortening some of the aspects of the learning curve of operative skills that may otherwise take many years to acquire.

Patch-augmented rotator cuff repair: influence of the patch fixation technique on primary biomechanical stability.

There is an ongoing debate about the potential of patch augmentation to improve biomechanical stability and healing associated with rotator cuff repair. The biomechanical properties of three different patch-augmented rotator cuff repair techniques were assessed in vitro and compared with a standard repair. Dermal collagen patch augmentation may increase the primary stability and strength of the repaired tendon in vitro, depending on the technique used for patch application. Forty cadaveric sheep shoulders with dissected infraspinatus tendons were randomized into four groups (n=10/group) for tendon repair using a knotless double-row suture anchor technique. A xenologous dermal extracellular matrix patch was used for augmentation in the three test groups using an "integrated", "cover", or "hybrid" technique. Tendons were preconditioned, cyclically loaded from 10 to 30N at 1Hz, and then loaded monotonically to failure. Biomechanical properties and the mode of failure were evaluated. Patch augmentation significantly increased the maximum load at failure by 61% in the "cover" technique test group (225.8N) and 51% in the "hybrid" technique test group (211.4N) compared with the non-augmented control group (140.2N) (P≤0.015). For the test group with "integrated" patch augmentation, the load at failure was 28% lower (101.6N) compared with the control group (P=0.043). There was no significant difference in initial and linear stiffness among the four experimental groups. The most common mode of failure was tendon pullout. No anchor dislocation, patch disruption or knot breakage was observed. Additional patch augmentation with a collagen patch influences the biomechanical properties of a rotator cuff repair in a cadaveric sheep model. Primary repair stability can be significantly improved depending on the augmentation technique.

Finite element modeling of blast lung injury in sheep.

A detailed 3D finite element model (FEM) of the sheep thorax was developed to predict heterogeneous and volumetric lung injury due to blast. A shared node mesh of the sheep thorax was constructed from a computed tomography (CT) scan of a sheep cadaver, and while most material properties were taken from literature, an elastic-plastic material model was used for the ribs based on three-point bending experiments performed on sheep rib specimens. Anesthetized sheep were blasted in an enclosure, and blast overpressure data were collected using the blast test device (BTD), while surface lung injury was quantified during necropsy. Matching blasts were simulated using the sheep thorax FEM. Surface lung injury in the FEM was matched to pathology reports by setting a threshold value of the scalar output termed the strain product (maximum value of the dot product of strain and strain-rate vectors over all simulation time) in the surface elements. Volumetric lung injury was quantified by applying the threshold value to all elements in the model lungs, and a correlation was found between predicted volumetric injury and measured postblast lung weights. All predictions are made for the left and right lungs separately. This work represents a significant step toward the prediction of localized and heterogeneous blast lung injury, as well as volumetric injury, which was not recorded during field testing for sheep.

Local Tissue Electrical Resistances in Transpedicular Screw Application in the Thoracolumbar Region.

To determine local tissue electrical resistance differences generated during a screw pass from the pedicle to another tissue rather than determining all individual electrical tissue resistance values. We attempted to measure electrical resistance values of regional tissues in addition to fluoroscopic imaging during application of fixation via a transpedicular screw. We also attempted to detect local tissue electrical resistance alterations in case of malposition of the screw inside the pedicle. For this purpose, local tissue electrical resistances of 10 transpedicular tracks opened with standard track openers bilaterally in 5 vertebrae, and of spinal cord accessed by puncturing the medial walls of three vertebrae in a cadaver were measured. These resistance differences were not only measured in human cadaveric tissue but also in 36 pedicles belonging to a total of 18 vertebrae between Th 1-S1 vertebrae of a sheep cadaver. Both medial and lateral walls were drilled to measure local tissue resistance differences in a sheep cadaver. Our results indicated that local tissue electrical resistance changes were statistically significant in both human and sheep cadaver. It is possible to prevent screw malposition using a simple and cheap electrical resistance measurement. Local tissue electrical resistance measurement during transpedicular screw insertion is a safe, simple, cheap, and practical method.

Microsurgical training model for residents to approach the orbit and the optic nerve in fresh cadaveric sheep cranium

Microsurgical training model for residents to approach the orbit and the optic nerve in fresh cadaveric sheep cranium

Sheep Hemifacial and Auricular Transplantation Models

Currently, only a few large animal models, including swine, dog, and nonhuman primate, are described for composite face transplantation studies and the literature lacks reports on the large animal model of composite auricular transplantation. Large animal models offer better understanding of the immunological mechanisms and major histocompatibility complex characterization and, for this reason, are preferred to the small animal models for the assessment of new immunosuppressive tolerance induction protocols. Thus, the aim of this study was to demonstrate feasibility of dissection and exploration of vascular territories of the hemifacial and auricle transplantation models in the sheep cadavers. Ten cadaver sheep heads were studied. The vascular territories of the composite hemifacial flap and composite auricle flap were defined by anatomical dissection. Methylene blue staining and laser-assisted indocyanine green angiography using SPY Elite System were used for vascular territories assessment. The dissection of cadaver sheep heads confirmed that the hemifacial flap and auricle flap can be raised on the same pedicle consisting of the common carotid artery and jugular vein. An adequate vascular network was observed in the flaps after injection of methylene blue dye via the arterial pedicle. Laser-assisted indocyanine green angiography identified vascular territories of the hemifacial and auricular vascular network. We described a new hemifacial and an auricular transplantation models in the sheep cadavers and have confirmed presence of the adequate vascular network as demonstrated by the laser-assisted angiography. This study introduces 2 new large animal models into the armamentarium of vascular composite allotransplantation.

Anatomy of the fetlock in goats and sheep: comparison of sonography and macroscopic anatomy (914.2)

Sonography is an important tool for diagnosing diseases of the locomotor system. It helps to evaluate tendons, ligaments, joint capsules and any free fluid. The aim of this study was to describe the anatomy of the fetlock region in sheep and goats based on sonographic pictures. During the first phase, sonographic examination was conducted on the fetlock of six sheep cadavers and compared to frozen feet sections. In the case of eight feet, the joint pouches were experimentally filled. During the second phase, the same examination was conducted on ten living sheep and eight goats. Clear differentiation of the joint space, the capsule, the articular cartilage, the extensor tendons, the flexor tendons and the interosseus medius muscle was possible. Several anatomical structures were compared to each other. No significant differences were observed between the right and left and between the front and back extremities. Differences between sheep and goats could neither be neglected nor demonstrated. In the case of goats, a correlation between the age of the animals and the size of the structures could not be proven. It was shown that a minimum filling of 3 ml was necessary for imaging a distended fetlock joint cavity. The clear differentiation of the soft tissue structures by ultrasonography is a valuable tool for the examination of the fetlock joint. However, more studies are necessary for demonstrating any pathological aspects.

Microsurgical training model for residents to approach to the orbit and the optic nerve in fresh cadaveric sheep cranium.

Background:Neurosurgery and ophthalmology residents need many years to improve microsurgical skills. Laboratory training models are very important for developing surgical skills before clinical application of microsurgery. A simple simulation model is needed for residents to learn how to handle microsurgical instruments and to perform safe dissection of intracranial or intraorbital nerves, vessels, and other structures.Materials and Methods:The simulation material consists of a one-year-old fresh cadaveric sheep cranium. Two parts (Part 1 and Part 2) were designed to approach structures of the orbit. Part 1 consisted of a 2-step approach to dissect intraorbital structures, and Part 2 consisted of a 3-step approach to dissect the optic nerve intracranially.Results:The model simulates standard microsurgical techniques using a variety of approaches to structures in and around the orbit and the optic nerve.Conclusions:This laboratory training model enables trainees to gain experience with an operating microscope, microsurgical instruments and orbital structures.

Interprofessional Education: Oral Health and Mechanically Ventilated Critically Ill Adults

Abstract Introduction The PowerPoint presentation with audio and embedded video clips presents an overview of the relationship of oral health to overall systemic health in mechanically ventilated a...

Ultrasound-guided block of sciatic and femoral nerves: an anatomical study

The sheep is a popular animal model for human biomechanical research involving invasive surgery on the hind limb. These painful procedures can only be ethically justified with the application of adequate analgesia protocols. Regional anaesthesia as an adjunct to general anaesthesia may markedly improve well-being of these experimental animals during the postoperative period due to a higher analgesic efficacy when compared with systemic drugs, and may therefore reduce stress and consequently the severity of such studies. As a first step 14 sheep cadavers were used to establish a new technique for the peripheral blockade of the sciatic and the femoral nerves under sonographic guidance and to evaluate the success rate by determination of the colorization of both nerves after an injection of 0.5 mL of a 0.1% methylene blue solution. First, both nerves were visualized sonographically. Then, methylene blue solution was injected and subsequently the length of colorization was measured by gross anatomical dissection of the target nerves. Twenty-four sciatic nerves were identified sonographically in 12 out of 13 cadavers. In one animal, the nerve could not be ascertained unequivocally and, consequently, nerve colorization failed. Twenty femoral nerves were located by ultrasound in 10 out of 13 cadavers. In three cadavers, signs of autolysis impeded the scan. This study provides a detailed anatomical description of the localization of the sciatic and the femoral nerves and presents an effective and safe yet simple and rapid technique for performing peripheral nerve blocks with a high success rate.

Evaluation of an intraoperative ultrasound training model based on a cadaveric sheep brain.

Background:The present study evaluates the effectiveness of an ultrasound (US) practice course based on a sheep brain cadaver. Neurosurgical education is considerably restrained following patient safety objections and work time restrictions. It is therefore of vital importance to offer residents an opportunity to practice certain US techniques in a controlled environment without ethical or legal restrictions. We developed an US training model based on a sheep brain cadaver in order to demonstrate the feasibility of such a model, facilitate crucial anatomic knowledge, and demonstrate a learning curve from it.Methods:Over the course of 2 months from December 2012-January 2013, a total of 13 residents took part in a three part training session, each consisting of 20-30 min of individual US-training and performance evaluation based on a biological phantom. The first cadaver was a physiologic sheep brain. After initial familiarization with the US, the residents performed an US on a second cadaveric brain and tried to find a 0.5 cm big (in diameter) echogenic structure. In a third brain they were asked to identify a cyst (Fogarty catheter filled with water).Results:Thirteen neurosurgical residents participated in the study. After the first training session, the learning curve improved significantly in the second and the third session. The ability to actuate the US device, the time needed to display crucial anatomic landmarks, and to locate the two different artificial masses increased, and respectively decreased remarkably by up to 80%.Conclusion:After 2 months and three training sessions, the handling of the US from the residents was excellent in the operating room. The accuracy and the dexterity in use of the US improved significantly. The participants found the model to be realistic and agreed on the need for further promotion of such courses.

Microsurgical training model for residents to approach the orbit and the optic nerve in fresh cadaveric sheep cranium.

Microsurgical training model for residents to approach the orbit and the optic nerve in fresh cadaveric sheep cranium.

Generation of a 3D Printed Temporal Bone Model with Internal Fidelity and Validation of the Mechanical Construct

To generate a rapid-prototyped temporal bone model from computed tomography (CT) data with a specific focus on internal anatomic fidelity. Research ethics board-approved prospective cohort study. Current iterations of a rapid-prototyped temporal bone model are complicated by absent void spaces and inconsistent bone density due to limited infiltrant exposure. The creation of a high-fidelity model allows surgical trainees to practice in a standardized and reproducible training environment. This learning paradigm will significantly augment resident understanding of surgical approaches and techniques to prevent adverse outcomes. We describe a technique for generating internally accurate rapid-prototyped anatomical models with solid and hollow structures, including void spaces. The novel slicing algorithm digitally deconstructs a model into segments and permits removal of extraneous print material and allows infiltrant penetration of the entire bone structure. Precise reassembly is facilitated by digitally generated fiducials. Infiltrant of choice was determined by expert assessment and subjected to objective mechanical property assessment with comparison to cadaveric sheep bone. The printed bone models are highly realistic. Void space representation was excellent with 88% concordance between cadaveric bone and the resultant rapid-prototyped temporal bone model. Ultimately, cyanoacrylate with hydroquinone was determined to be the most appropriate infiltrant for both cortical and trabecular simulation. The mechanical properties of all tested infiltrants were similar to real bone. This model serves as an excellent replica of a human temporal bone for training and preoperative surgical rehearsal and can be dissected in a true-to-life fashion.