ANZCVS 2017

Question 1

a) Briefly describe four (4) biopsy methods used to collect tissue for diagnosis of a solid skin or subcutaneous tumor.

Answer 1

• Fine Needle Aspirate (FNA): typically performed using 22 to 18G needle using jabbing or aspiration technique. Reserved for cutaneous and SQ masses, but also useful for organ masses under U/S guidance. Samples are small and non-organized (“loose cells”), therefore often non-diagnostic. Does not allow tumor grading.

• Needle core biopsy
- cutting needle: Tru-Cut (favor spring loaded) or Franklin-Silverman. Favor 14G needles. Asseptic prep, local block, introduce needle with outer cannula extended over the inner needle until the periphery of the lesion is reached. Advance inner needle into lesion at least 1.5cm and fire spring-loaded device. Remove needle from lesion, retract sleeve and remove sample with 25G needle. Obtain further samples by redirecting needle into mass at different angles. Use same skin incision and make sure to keep needle sterile.

• Needle core biopsy – aspiration needle: Menghini, Klatskin, Jamshidi needles. Sterile skin prep, needle introduced into lesion, syringe used to suction the sample into the shaft of the needle. Klatskin and Jamshidi have internal bevels that improve patient safety in comparison to Menghini.
• Needle core biopsies result in diagnostic samples in 56 to 94% of cases

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- Punch Biopsy: Aseptic prep unless obtaining samples for dermatological analysis. Local anesthetic block, place punch over site and push into lesion using a twisting motion. Remove punch and use metzembaum scissors to transect the base of the sample. Avoid grasping sample with forceps – creates artifact. Topical hemostatic agents can be used if necessary. Close skin with single sutures.

• Incisional biopsy: Used to obtain larger samples from tumors. Often possible with patient awake because tumors lack innervation. Aseptic skin prep, local anesthetic block, skin incision limited to the minimum length necessary to obtain samples. Samples of soft-tissue masses should be obtained at the junction of the mass and normal tissue using scalpel blade. Aim for a narrow and deep sample. Make sure to penetrate mass, not just pseudocapsule. The biopsy location should be planned as to allow removal of the entire biopsy tract during surgical treatment. Samples of bone lesions should be obtained from the center (periphery is usually reactive periosteum). Use mattress sutures to provide hemostasis to deep layers. Close SQ and skin routinely.
• Excisional biopsy: Excision of the entire lesion prior to knowledge of histopathology. Provides a large amount of information but is highly likely to result in incomplete excision, local recurrence, and the need for additional treatment. May impair CT results as it is best performed before mass is disrupted. Typically reserved for lesions confirmed to be benign via FNA or very small skin masses.

Question 2

b) List four (4) sampling techniques for diagnosis of a primary bone tumor. List an advantage and disadvantage of each technique

Answer 2

• Jamshidi needle-core biopsy: Preferred method, 82% accurate, small biopsy tract (minimal trauma), low risk of fractures.
• Michelle Trephine: Large sample size, more traumatic, increased risk of iatrogenic fractures.
• Fine-needle percutaneous aspiration biopsy: Only possible for highly lytic tumors. Small sample, no intact core (rarely). Less traumatic and inexpensive.
• Incisional (surgical) biopsy: Requires a surgical approach to the affected area (more traumatic). Samples usually obtained using drill/rongeur. Large samples obtained, but higher chance of iatrogenic fractures, infection, discomfort.

Question 3

c) Solid tumors can be removed along with different margins/amount of the surrounding tissue. List and briefly describe four (4) levels of surgical aggressiveness (or surgical dose) that can be applied to the removal of a solid tumor.

Answer 3

1. Intralesional (debulking) surgery: Tumor debrided inside the pseudocapsule, with residual gross disease. Typically, not performed because leaves a large-enough tumor burden to render chemo or radiation therapy ineffective.
2. Marginal resection: The tumor is resected just outside the pseudocapsule, without “margins”. Only effective for lipomas and other benign tumors since satellite tumors are left behind. This approach should be avoided for potential malignancies since it complicated future curative surgery and adjuvant therapy.
3. Wide resection: Curative procedure meant to resect the macroscopic (tumor) and microscopic (satellites) disease, including biopsy tracts. Recommended over intralesional or marginal resection for the treatment of solid tumors.
4. Radical resection: Wide resection of an entire tissue compartment such as organ or limb. Typically performed because the tumor location does not allow the resection of the entire tumor/pseudocapsule/satellites in any other way.

Question 4

d) State which surgical resection (extent or dose of treatment) technique is appropriate for curative-intent tumor resection?

Answer 4

Wide or radical depending on tumor type and location.

Question 5

e) Tumour margins are three-dimensional. Explain the term ‘surgical margins’. Briefly describe the minimum surgical margins that are recommended for removal of a mast cell tumour and soft tissue sarcoma in a dog, (you can use a diagram to explain the tumour margin).

Answer 5

“Surgical margins” are defined as the minimum necessary amount of grossly normal tissue around and below the mass which will contain the entire tumor and satellite tumors.

Recommended surgical margins for Mast Cell Tumors (Grades 2 to 3) are 2 cm lateral and 1 fascial plane. Grade 1 MCT can be excised with 1cm margins.

Recommended surgical margins for Soft Tissue Sarcomas are 3cm peripheral and 1 fascial plane. Feline vaccine-associated STS require 2 fascial planes.

Question 6

a) List and briefly describe the four (4) classifications of surgical wounds, in terms of their level of contamination.

Answer 6

• Clean wound: Surgical wound, sterile, closed by primary intention. No evidence of inflammation or infection. Does not penetrate the respiratory, GI, urinary or genital tracts.
• Clean-contaminated wound: A surgical wound that has entered the respiratory, GI, genital or urinary tract.
• Contaminated wound: A surgical wound with breakage of sterile technique or leakage of GI contents. A fresh open wound without gross debris or evidence of infection.
• Dirty/Infected wound: A improperly-managed traumatic wound with devitalized tissue and evidence of infection.

Question 7

b) In a clean orthopaedic surgical procedure, what genus of bacteria is the primary consideration for antibiotic use?

Answer 7

Staphylococcus sp.

Question 8

c) What type of bacteria is of most concern when operating in the large intestine?

Answer 8

E. Coli

Question 9

d) List two (2) antibiotics or antibiotic combinations that would have suitable spectrum of activity for procedures involving the large intestine.

Answer 9

Cefoxitin (2nd generation cephalosporin)
Cefoxitin + metronidazole
Cefuroxime (2nd generation cephalosporin)
Gentamycin

Question 10

e) Describe an appropriate prophylactic antibiotic regime for an elective orthopaedic procedure (e.g. tibial-plateau-levelling osteotomy - TPLO). Your answer should include:
• the name of the antibiotic:
• route of administration:
• dose:
• timing of the initial dose:
• frequency and duration of administration:

Answer 10

•  the name of the antibiotic: Cefazolin
•  route of administration: IV
•  dose: 22mg/kg
•  timing of the initial dose: 60 min before incision
•  frequency and duration of administration. Every 90 minutes

Question 11

f) Provide a rationale for the timing the administration of cefazolin 60min before incision and every 90min intra-op

Answer 11

Cefazolin achieves peak concentration within 60 minutes. Elimination half-life is 45-70 minutes, and administration within 90 to 120 min maintains plasma concentration around 10x MIC

Question 12

g) List the factors reported to significantly increase the risk of surgical site infection.

Answer 12

• VetSurg May 2021 – Only prolonged surgery time was reported to increase the chance of SSI.
• Immune-suppressive diseases (Cushing’s)
• Age
• Malnutrition
• Obesity
• Ongoing infection elsewhere

Question 13

a) Give a brief definition for the following modes of bone plate application, and, describe a clinical scenario for each in which it may be used. You may provide diagrams if you wish:

Neutralization plating
Bridge plating
Buttress plating

Answer 13

i. Neutralization plating: Applicable to fractures that can be anatomically reconstructed but not amenable to load sharing (most forces are still counteracted by the implant). Examples include long-oblique, spiral and butterfly fractures.
ii. Bridge plating: Utilized when the fracture is not reconstructable and a gap will exist between the fracture segments (even if the gap is only on the trans cortex). Load sharing is not possible, and the implants must bear all of the forces acting upon the fracture. Examples include comminuted fractures and distraction osteogenesis.
iii. Buttress plating: Utilized on the metaphyseal area to counteract compression and shear forces while support fracture healing. The plate is anchored to the main stable fragment and contoured to engage and minimize displacement of the smaller fragments. Interfragmentary screw fixation is commonly used. Example: fracture of the tibial plateau

Question 14

b) Briefly describe the mechanism for how a bone screw may lock into a plate.

Answer 14

Locking mechanisms may include:
• Lock nuts (Surfix) – the screw has a flat head upon which a lock nut is placed and tightened. Uncommonly used in Vet Med.
• AO System (Synthes) – Conical screw head threads machined to match plate holes treads (most common used. Includes – Arthrex, Synthes and others).
• Morse tapers designs (Kyon ALPS) – the screw head and plate holes are chamfered to the same angle during machining, leading to locking via friction.
• Expansion ring design (Newclip, Striker) – the screw head is locked by an expansion ring upon tightening.
• Screw head lock to polymer (Biotech)– conical self-threading screw head locks into PEEK insert on plate.

Question 15

c) Discuss the mechanism of load transfer for both a locking plate system and a conventional non-locking plate system. You may use a diagram if you wish.

Answer 15

• Conventional non-locking system: Load transfer between bone and plate is provided by the compression between the two surfaces, which converts axial forces into shearing forces (shearing effect). Most of the force transfer occurs at the cis cortex, immediately below the plate. The part of the screw engaging the trans cortex primarily resists pullout forces.
• Locking plate systems: Shearing forces (load transfer) resisted by the entire length of the screw, which is subjected to flexing forces. This is far superior to the conventional system and allows the use of larger screw core diameter (smaller threads) which significantly increases the Area Moment of Inertia (AMI)

Question 16

d) Compare the advantages and disadvantages of locking plate systems and conventional non-locking plate systems.

Answer 16

Conventional non-locking system

Advantages:

            - More affordable
	- Allows the addition of lag screws through plate
	- Not angle-stable, allowing more flexibility regarding screw placement 

Disadvantages:

           - More prone to implant failure than locking implants if used in bridging fashion 
           - Resistance to screw pullout is determined by screw outer diameter, requiring larger threads and thinner core (lower AMI)
           - Caused more periosteal and periosteal blood supply damage
           - Less well-suited for MIO 

Locking plate systems

Advantages:
- Does not rely on plate-bone friction
- Decreases damage to the periosteum and extraosseous bone blood supply.
- Does not require anatomical reconstruction, only functional alignment
- Well-suited to the principles of biological osteosynthesis / MIO
- Double the construct stiffness when compared to non-locking plates
- Very low risk of screw back out
Disadvantages:
- More costly
- Angle-stable design may complicate screw placement near joints

Question 17

a) Use a diagram to illustrate the anatomy of the liver lobes, gall bladder and important vasculature of the hepatobiliary tract.

Answer 17

Question 18

b) Use a diagram to illustrate the anatomy of the extrahepatic biliary system in the dog.

Answer 18

Question 19

c) Briefly describe the main anatomical difference of the biliary and pancreatic ductal anatomy between the cat and the dog.

Answer 19

Question 20

d) List three (3) conditions that can lead to bile peritonitis.

Answer 20

• Ruptured biliary mucocele
• Necrotizing cholecystitis
• Gallbladder rupture due to cholelithiasis
• Neoplasia
• Trauma

Question 21

e) Describe the pathophysiology of bile peritonitis. In your answer include the factors that influence prognosis or morbidity.

Answer 21

Bile spillage, regardless of cause, causes significant local inflammation (chemical peritonitis). This usually starts as a localized process which may last days to weeks, later leading to peritoneal effusion and generalized peritonitis. The process is usually sterile at the beginning, subsequently becoming infected with bacteria.

Factors that may negatively affect prognosis or morbidity include cause (i.e. neoplasia Vs trauma), presence of septic peritonitis, refractory hypotension, cardiovascular collapse and DIC.

Plasma lactate above 4 mmol/L on admission was associated with 73% mortality in one study. Inability to normalize plasma lactate within 6 hours of admission was associated with mortality with 79% sensitivity and 100% specificity (Cortellini et al, VECC 2015)

Question 22

c) A four-year-old Maltese terrier presents to you post dog-attack, with a large traumatic wound over his caudal lateral abdomen. There is no involvement with the abdominal cavity. Primary closure is not an option in this case due to the size of the defect.
i. Name an axial pattern flap that could be used to repair this defect and describe the anatomical landmarks of the flap base.

Answer 22

Caudal Superficial Epigastric flap. The base is located at the level of the inguinal ring. The medial incision is at midline. The lateral incision is parallel to the medial and equidistant to the mammary chain. The flap may extend as far cranially as the second mammary gland.

Question 23

c) A four-year-old Maltese terrier presents to you post dog-attack, with a large traumatic wound over his caudal lateral abdomen. There is no involvement with the abdominal cavity. Primary closure is not an option in this case due to the size of the defect.
ii. List some of the advantages of axial pattern flaps over other types of wound closure

Answer 23

• Allow primary closure of large cutaneous wounds
• Can be performed immediately without the need for a granulated recipient bed
• Cover the wound with full-thickness skin (robust)
• Do not require bandaging
• Usually completely healed in 14 days
• Greater survivability as compared to subdermal plexus flaps
• Does not require specialized equipment

Question 24

iii. Outline four (4) reasons why axial pattern flap necrosis can occur.

Answer 24

• Compromise of blood supply during harvesting
• SQ seroma/hematoma
• Infection
• Edema due to venous or lymphatic obstruction

Question 25

iv. Briefly describe how the delay phenomenon can be utilized to increase the viability of axial pattern flaps.

Answer 25

The delay phenomenon has been described as a potential method to increase flap viability. This method involves the creation of an axial-pattern flap including its lifting from the donor bed, followed by suturing back down. The flap is re-harvested two weeks later and transplanted to the new position. The theory is that such method improves the blood supply within the flap, making it more “robust” and resistant to transfer. This is advocated in cases where terminal flap survival is considered paramount.

Question 26

3. You are presented with a male four-year-old working Border collie dog that has a closed mid-diaphysis comminuted fracture of the right femur. The injury was sustained jumping down from the back of a utility vehicle. Physical and radiographic examinations reveal no other injuries. You elect to stabilize the fracture with an intramedullary (IM) pin and bone plate.
   a) Discuss possible advantages and disadvantages to using an IM pin and plate combination in this case.

Answer 26

Advantages: The IM pin offers very good resistance to bending forces as compared to plating alone. IM pin application is relatively simple, inexpensive and minimally disturbs the fracture site. The bridging plate can be applied in a “open but do not touch” fashion since only functional alignment is required, thereby minimizing the disturbance to the external callus.

Disadvantages: The fracture characteristics (comminuted) do not allow reconstruction and therefore load sharing, requiring the implants to bear 100% of the forces applied to the fracture during healing. This may predispose the construct to failure. Axial forces are predominantly opposed by the plate/screw interface (shear effect) which is biomechanically inferior to implants applied closer to the mechanical axis of the bone (i.e. Interlocking nail).

Question 27

3. You are presented with a male four-year-old working Border collie dog that has a closed mid-diaphysis comminuted fracture of the right femur. The injury was sustained jumping down from the back of a utility vehicle. Physical and radiographic examinations reveal no other injuries. You elect to stabilize the fracture with an intramedullary (IM) pin and bone plate.
   b) Describe the difference between normograde and retrograde application of IM pins. With reference to this case, describe which method you would select and justify your answer.

Answer 27

Retrograde application refers to the insertion of the IM pin through the fracture site, exiting proximally and redirected into the distal fracture segment. Normograde application refers to the insertion of the pin through the proximal aspect of the bone (trochanteric fossa in this case) and down the length of the medullary cavity. Femoral IM pin insertion should be performed in a normograde fashion to avoid injury to the sciatic nerve.

Question 28

c) When using a combined IM pin and plate fixation method, what percentage of the intramedullary cavity can the pin accommodate?

Answer 28

30 to 40%

Question 29

3. You are presented with a male four-year-old working Border collie dog that has a closed mid-diaphysis comminuted fracture of the right femur. The injury was sustained jumping down from the back of a utility vehicle. Physical and radiographic examinations reveal no other injuries. You elect to stabilize the fracture with an intramedullary (IM) pin and bone plate.
   d) You compliment your fracture fixation with an autogenous cancellous bone graft. Discuss the biological functions of a cancellous bone graft in fracture repair.

Answer 29

Osteogenesis: provides a mixture of cells (fibroblasts, undifferentiated MSC) to improve bone regeneration.

Osteoinduction: provides growth factors line BMPs and TGF-beta which induce the formation of osteoprogenitor cells from surrounding host tissue mesenchymal cells.

Osteoconduction: provides a three-dimensional porous scaffold to support cellular proliferation and vascular ingrowth.

Osteopromotion: induce the secretion of osteopromotive substances that enhance bone regeneration

Question 30

e) Give three (3) examples of locations the bone graft may be harvested from in this case.

Answer 30

Lateral aspect of the distal femoral condyle

Ilial wing

Proximal tibia

Question 31

4. A five-year-old Burmese cat is presented to your clinic with open mouth breathing. On thoracic auscultation the heart and lung sounds are muffled. Thoracic radiography reveals a bilateral pleural effusion.
   d) Part of your treatment plan involves placing a unilateral chest drain. Describe the technique for surgical placement of a chest drain.

Answer 31

The placement of a thoracostomy tube begins with the determination of the appropriate side. Most thoracic effusions can be managed with one tube, except for pyothorax and chylothorax. Bilateral tubes may be necessary. The lateral thorax is clipped and aseptically prepared. An intercostal local anesthetic block is applied, extending at least two intercostal spaces cranial and caudal to the placement site. If extra holes are to be made in the tube, care is taken to make sure they do not exceed 1/3 of the tube diameter. A small skin incision is made on the dorsal one-third of the thoracic wall at the level of the 10th or 11th intercostal space. The tube is inserted with the aid of a stylet or a large hemostat and advanced in a cranio-ventral direction through the subcutaneous to the level of the 8th intercostal space. If using a tube trocar, the end of the tube is firmly grasped 1-2 cm from the body wall to protect internal organs from plunging. The tube is introduced through the intercostal muscles and pleura until a “pop” is felt. The tube is clamped with hemostats or a tube clamp device (preferred) the introduction instrument is retracted and the tube advanced in a cranioventral direction to a predetermined point. A purse-string suture is placed around the tube, followed by a Chinese fingertrap or Roman sandal suture. The tube is connected to a three-way stopcock which is also secured with suture. Tube placement is verified radiographically. A loose bandage is applied.

Question 32

4. A five-year-old Burmese cat is presented to your clinic with open mouth breathing. On thoracic auscultation the heart and lung sounds are muffled. Thoracic radiography reveals a bilateral pleural effusion.
   e) When managing pyothorax, give two (2) examples when further surgical intervention is indicated.

Answer 32

Lung abscess
Lung-lobe torsion
Foreign bodies
No response to medical management for 3-4 days (suspect fibrosing pleuritis)