ANZCVS 2012

Question 1

1. a) Name the end products of primary and secondary hemostasis and briefly describe how they are formed. (8 marks)

Answer 1

Primary hemostasis – end product: platelet clot; Endothelial disruption exposes subendothelial collagen to which platelets adhere via platelet glycoprotein VI receptor and to collagen-bound Von Willebrand’s factor via glycoprotein Ib receptor. Adherence stimulates the release of platelet cytosolic granular contents (ADP) which stimulate arachidonic acid metabolism and production of prostanoids like Thromboxin A2, recruiting and activate further platelets.

Secondary Hemostasis – end product: fibrin mesh; Simultaneously with platelet aggregation, blood cells are exposed to Tissue Factor (TF) immediately after tissue injury. TF is a cofactor to Factor VII, which then activated factors IX and X leading to the activation of prothrombin to generate thrombin. Thrombin is the central protein in the coagulation cascade, cleaving fibrinogen into fibrin and activating further platelets.

Question 2

2. b) Describe the clinical signs expected in animals with significant defects in primary and secondary haemostasis. (8 marks)

Answer 2

Primary Hemostasis: Petechia, mucosal damage, prolonged bleeding at injury sites.
Secondary Hemostasis: hematomas, hemarthrosis, intramuscular hemorrhage, effusions.

Question 3

c) State the beneficial properties of transfusions of fresh frozen plasma, fresh whole blood and packed red blood cells and give an example of a surgical clinical situation in which each of these products could be used. (9 marks)

Answer 3

Fresh Frozen Plasma (FFP): contains all constituents of plasma, including coagulation proteins, vWF, natural anticoagulants, albumin and globulins. Indicated for inherited or acquired coagulation disorder, vWD and hypoproteinemia. Example: Doberman Pincher with vWD, presented with GDV.

Fresh Whole Blood: Same as FFP but including RBC’s. Low platelet concentration, requiring large volume to affect platelet levels. Example: Hemoabdomen (replaces volume, RBC’s and “some” platelets and clotting factors. Supplementation with FFP or Cryoprecipitate likely necessary depending on the level of platelet/clotting factor consumption).

Packed Red Blood Cells (pRBC’s): Does not contain clotting factors, vWF, natural anticoagulants, albumin or globulins. Exposes recipient to large amounts of RBC antigens. Example: Anemic but normovolemic patient who requires a surgical procedure (avoids fluid-overload); anemic patient with cardiac disease who needs surgery (volume -sensitive

Question 4

2. b) Describe, at a cellular level, the stages of wound healing in a small intestinal anastomosis from scalpel incision to wound maturity. (9 marks)
   Mention the approximate time period for each stage. (3 marks)

Answer 4

Inflammatory phase – 48 hours – hemostasis and vasoconstriction, followed by diapedesis of inflammatory cells like neutrophils (first 24 hours) and macrophages (48 hours). Macrophages are fundamental for production of growth factors and cytokines, stimulating the migration and function of fibroblasts. Fibroblasts produce fibrin to seal the serosal layer.

Proliferative phase – 3 to 5 days- granulation tissue is formed (collagen + blood vessels) and collagen undergoes synthesis and lysis. Different from skin, where collagen is exclusively produced by fibroblasts, in the GI tract fibroblasts and smooth muscle produce collagen and elastin. Smooth muscle present in the muscularis mucosa and muscularis propria is primarily responsible for collagen production in the small intestines. Skin has collagens type I and III. GI tract has I, III and V.

Maturation phase – 5 to 21 days – Collagen is remodeled and reorganized to improve strength. Intestinal wall becomes thinner (less edema, better collagen fiber orientation).

Question 5

3. c) Describe how the integrity and strength of the sutured anastomosis changes over the timeline from incision to wound maturity. (7 marks)

Answer 5

Immediately following surgical incision, the strength of the wound is reliant upon the holding power of the sutures upon the collagen-rich layer (submucosa), as well as on a relatively fragile fibrin seal. Significant collagen breakdown occurs in the first 4 days due to upregulation of MMP’s, leading to relevant decrease in the strength of anastomosis (up to 70% for small intestines and colon). This is when dehiscence is most likely to occur. Risk factors include hypotension, poor O2 saturation, infection, excessive tissue trauma and tissue tension. Around 1 week post-surgery the intestines will have regained nearly 100% of the original bursting strength, but the strength of the scar will continue to increase for several months.

Question 6

1. a) Describe the process of direct bone healing of fractures. Include in your answer reference to inter-fragmentary strain theory. (20 marks)

Answer 6

Direct bone healing: Occurs under conditions of “absolute stability”, when strain at the fracture site has been functionally eliminated via anatomical reduction, compression of bone fragments and rigid fixation of the bone column. Healing occurs through intramembranous ossification, in which surviving osteoblasts and osteoblast precursors directly deposit new bone at the fracture gap. Since complete and perfect congruence of the entire bone surface is nearly impossible, primary bone healing occurs via a combination of Contact Healing and Gap Healing.
• Contact Healing – Only possible is fracture gap < 0.01mm (10 microns) and interfragmentary strain has been eliminated (less than 2%). Osteoclasts immediately ahead of injured osteons for a “spearhead” and advance across the fracture gap (cutting cones), removing devitalized one. Osteons elongate and directly bridge the fracture gap. Osteoblasts follow closely behind and deposit new bone. This results in a process of concomitant resorption and deposition of bone. Osteoblast orientation and multiple cutting cone elongation result on the formation of lamellar bone across the fracture gap (oriented parallel to the long axis of the bone).
• Gap Healing – Occurs when small gaps exist between zones of contact healing. Absolute stability is provided by the contact zones. Interfragmentary strain must have been eliminated (<2%) and the gap must not exceed 1mm. The gap is initially filled with fibrin matrix and vascular sprouts, which are quickly remodeled with collagen Type I and III. Within days lamellar bone fills the gap in a process similar to intramembranous ossification. This lamellar bone is initially oriented perpendicular to the long axis of the bone (in contrast to contact healing), making it mechanically weak. Within 3 to 4 weeks cutting cones cross the fracture gap and unite perpendicularly-oriented lamellar bone with each end of the fracture. Over time, remodeling transforms the perpendicular lamellar structure into longitudinally oriented lamellae.

Question 7

1. a) Describe the process of indirect bone healing of fractures. Include in your answer reference to inter-fragmentary strain theory. (20 marks)

Answer 7

Indirect Bone Healing: Occurs when fractures are not anatomically reconstructed or stabilized by rigid internal fixation. Implants are used to bridge zones of comminution and provide “relative stability”. (this is also how fractures not treated with internal fixation will heal). The process is organized in five overlapping stages:

1. Inflammation: Loss of vascular integrity leads to hemorrhage and reduction of local oxygen tension. Primary hemostasis occurs and platelets release cytokines and growth factors, recruiting macrophages, neutrophils and other inflammatory cells. Fibroblast and platelet growth factors activate progenitor mesenchymal cells within periosteum, muscle and soft tissues. These progenitor cells will differentiate into osteoprogenitor cells, modulate inflammation and provide anabolic factors to encourage bone healing. Secondary hemostasis produces a hematoma composed of fibrin matrix, which provide further degranulating platelets and serves as a scaffold for mesenchymal cell infiltration as well as macrophages, endothelial cells and fibroblasts. The end result of this phase is the production of a provisional cell, growth factor and matrix-rich scaffold along the cortex, medullary cavity and periosteum into adjacent soft tissues. This scaffold is eventually remodeled into granulation tissue to form a reparative granuloma, termed external callus.
2. Intramembranous ossification: Mimics the process of skeletal development. Progenitor cells from the overlaying periosteum proliferate and differentiate into osteoblasts to start new bone production adjacent to the fracture gap, between the periosteum and cortex (no cartilaginous intermediate). This leads to the formation of an early hard callus, but is insufficient to bridge and stabilize the fracture.
3. Soft Callus Formation (chondrogenesis): Starts as soon as a robust bed of granulation tissue is formed across the fracture gap (external callus). Granulation tissue transitions to fibrovascular tissue and finally to fibrocartilage containing collagens type I and III over several weeks. The matrix is initially avascular as resembles the proliferative zone of the physis. The persistent tissue hypoxia, presence of growth factors and cell-matrix interaction cause stem cell population to differentiate into chondrocytes. These chondrocytes produce extracellular matrix rich in collagen Type II, aggrecan and other cartilage-specific proteins. The resulting callus is termed “soft callus” and bridges the fracture gap. This callus is fragile, however, and remains insufficient to decrease strain to a level that permits osteoblast survival.

• Interfragmentary strain: The formation of various tissue types during bone healing is directly dependent on the degree of interfragmentary strain. Strain is defined as the effect of loading on a fracture gap. Practically it is calculated by dividing the resulting length of the gap after loading by the original length. Smaller fracture gaps experience greater strain (concentrate strain) than large gaps. Granulation tissue can withstand almost 100% deformation, and is therefore the tissue found it to be formed within fracture gaps undergoing significant strain. As strain is reduced, tissues region collagen can develop and form a soft callus. Specifically, fibrocartilage is capable of accommodating 10 to 15% deformation. Osteoblasts and osteocytes can only survive in a very low strange environment, and bone can only tolerate 2% deformation.

4. Hard Callus formation (endochondral ossification): Chondrocytes within the soft callus undergo hypertrophy and begin to mineralize the adjacent extracellular matrix next to the zone of intramembranous ossification. This occurs due to down-regulation of cartilage-specific genes, leading to decreased production of collagen type II and aggrecan and increased production of collagen type X. Collagen type X is unique to hypertrophic chondrocytes and a marker of endochondral ossification. MMP’s are expressed and degrade the matrix in preparation for calcification. Hypertrophic chondrocytes also secrete Vascular Endothelial Growth Factor (VEGF) which stimulates vascular invasion of peripheral parent bone. Mineralized cartilage has the necessary stiffness and strength to limit strain to levels that will support the survival of osteoclasts and osteoblasts. These cells can now advance from the periphery to the center of the callus. Osteoclasts remove mineralized cartilage and osteoblasts lay new woven bone. Radiographically this woven bone appears larger than normal and is often misshapen.
5. Bone remodeling: This final phase of bone healing lasts months to years. The abnormally large and misshapen woven bone produced during ostechondral ossification is weaker than primary bone, and therefore gradually replaced by lamellar bone. Resorption occurs withing each of the four bone envelopes (periosteal, endocortical, trabecular and intracortical). Osteoclasts and osteoblasts work together as Bone Multicellular Units (BMU) is a continuous process of activation, resorption, reversal, formation and quiescence. The result is the formation of Osteon, a structure composed of concentric layers of bone enclosed by a cement line with a central Harversian canal. Bone remodeling is strongly influenced by Wolff’s Law, which states that bone in a healthy animal will adapt to the loads under which it is placed. This occurs through the process of mechanotransduction. Bone generates a small electrical potential when it deforms, with an electropositive environment on the concave surface (compression) and electronegative environment on the convex side (tension). Electropositivity is associated with an increase in osteoclastic activity, whereas electronegativity induces osteoblastic activity. This justifies the fact the cortical bone under compression (concave surface) typically appears osteopenic on radiographs, while bone under tension (convex side) appears sclerotic.

Question 8

2. b) With respect to direct and indirect bone healing explain your choice of repair method for a fracture of the lateral aspect of the humeral condyle in an adult dog. (5 marks)

Answer 8

The lateral humeral condyle is responsible for a significant amount of weight bearing, increasing the chance of complications which mostly stem from inadequate stability. This is particularly a problem in adult dogs. The approach is usually craniolateral. The goal with this fracture is to achieve anatomical reduction, interfragmentary compression and rigid stability. This is typically achieved via the use of a transcondylar screw placed in lag fashion across the condyles (intercondylar compression), followed by a caudolateral plate extending from the lateral epicondyle to a few centimeters proximal to the fracture line (enough to ideally allow the application of 3 screws per segment). Screws are directed craniomedially. Care must first be taken to carefully align the articular surface, followed by the lateral epicondylar crest. Meticulous anatomical reconstruction and interfragmentary compression will eliminate fracture gaps. This, coupled with adequately sized and positioned implants will effectively eliminate strain (below 2%), allowing primary bone healing to take place.
Similar fractures involving any degree of comminution cannot be anatomically reconstructed nor compressed. Care must be taken to align the articular surfaces (critical step). Intercondylar compression may be possible, but the remaining epicondylar fracture will have to be bridged using an adequately sized plate. Healing will be indirect, involving the production of a bone callus.

Question 9

4. Discuss the use of perioperative antibiotics in routine, elective orthopedic surgery in dogs. Include in your answer a discussion of the relevant indications for use, the likely micro-organisms to be targeted, the level of contamination required for sepsis to occur and your choice, dose and scheduling of antibiotic agent. (25 marks)

Answer 9

Perioperative antibiotics are generally indicated in elective orthopedic surgeries where implant infection can lead to catastrophic results. These are typically clean procedures when contamination and infection are not suspected at the time of the procedure. The use of antibiotics should NEVER replace the need to meticulous surgical technique and adherence to surgical asepsis. The most-likely microorganism to be encountered include Staphylococcus pseudointermedius, but S. aureus, Enterobacteriaceae, Enterococcus spp and Pseudomonas spp are also possible. A bactericidal antibiotic predominantly effective against gram positive bacteria should be administered at least 30 minutes before the beginning of surgery and repeated every 90 minutes. Good options include beta-lactam antibiotics like first-generation cephalosporins (Cefazolin 22mg/kg IV). Clean surgical wounds without breakage of sterile technique or known contamination do not require post-operative antibiotics. Contaminated wounds should be swabbed for culture at the end of the procedure. Antibiotics should be prescribed for 48 hours, and extended for 7 days based on culture results (if positive).
One exception to this rule may be the TPLO procedure. Recent data appears to indicate that the use of post-operative antibiotics may have a protective effect against surgery-site infections.
Theoretically any level of contamination may cause infection. In practical terms, however, only contaminated or dirty wounds require post-operative antibiotics (guided by culture). Minor breaks in sterile technique can be managed with thorough lavage and perioperative antibiotics alone. A swab should still be obtained for culture prior to surgery site closure.

Question 10

A five-year-old male Dalmatian is presented to your clinic in a near comatose state. He has a very large bladder on palpation and you quickly discover this is due to a blockage in the urethra as you are unable to pass a catheter beyond the base of his penis due to the presence of a urethrolith.

1. a) What is the most likely underlying primary composition of this urethrolith?

Answer 10

a) Ammonium Urate

Question 11

A five-year-old male Dalmatian is presented to your clinic in a near comatose state. He has a very large bladder on palpation and you quickly discover this is due to a blockage in the urethra as you are unable to pass a catheter beyond the base of his penis due to the presence of a urethrolith.

b) Provide a pathophysiological explanation for this dog’s presentation. Include expected biochemical, electrolyte and ECG abnormalities. (6 marks)

Answer 11

b) Dalmatians do not convert most of their metabolic urate into allantoin like other breeds, and excrete urate in bulk (30-40% urate conversion versus 90% for other breeds).
Prolonged urethral blockage leads to severe hyperkalemia, metabolic acidosis and post-renal azotemia. Hypocalcemia (ionized) may also be present. Hyperkalemia may lead to life-threatening cardiac arrhythmias due to its effect on cardiac electrical conductivity. These may begin as bradycardia and spiked T-waves, progressing to depressed R-waves, prolonged QRS and PR intervals and ST segment depression.

Question 12

A five-year-old male Dalmatian is presented to your clinic in a near comatose state. He has a very large bladder on palpation and you quickly discover this is due to a blockage in the urethra as you are unable to pass a catheter beyond the base of his penis due to the presence of a urethrolith.

c) Discuss how you would go about emergency medical stabilization of this patient given the derangements noted in part 1b) above, prior to attempting urethrolith removal. (6 marks)

Answer 12

c) Management of this patient should include evaluation of hemodynamic status, correction of metabolic derangements (particularly hyperkalemia, and metabolic acidosis) and urinary diversion. The passage of a retrograde urinary catheter for urohydropulsion can be attempted in such moribund status. The use of lubrication, local anesthetics and sacro-coccigeal epidural block with local anesthetic may facilitate the process. If urinary catheter passage is not possible, intermittent cystocentesis can be performed to relieve and prevent recurrence of bladder distension. In the case the bladder should be completely emptied with each drainage to decrease the risk of urine leakage within the abdomen. A cystostomy tube can also be placed using sedation and local block or simply local block in such moribund patient. Intravenous fluids should be provided for at least 15 minutes prior to the induction of anesthesia. LRS is currently considered the fluid of choice (over 0.9 % NaCl) for these cases. Its potassium concentration is too low to create further hyperkalemia (about 4 mEq/L) and the lactate is converted into NaHCO3 by the liver, exerting a much needed alkalinizing effect. If this patient’s hyperkalemia exceeds 8 mEq/L, 10% Ca Gluconate should be administered which the EKG is closely monitored. Ca Gluconate does not affect potassium levels, but raises the threshold for cardiac myocyte depolarization, thereby acting as a cardioprotective agent. Intravenous dextrose can be administered to drive potassium intracellularly by cotransportation. Sodium Bicarbonate can be administered if severe metabolic acidosis is present, particularly is concurrent ionized hypocalcemia.

Question 13

A five-year-old male Dalmatian is presented to your clinic in a near comatose state. He has a very large bladder on palpation and you quickly discover this is due to a blockage in the urethra as you are unable to pass a catheter beyond the base of his penis due to the presence of a urethrolith.

d) You are successful in your attempts at emergency medical stabilization. Describe the technique to non-surgically relieve the urethrolith obstruction. (6 marks)

Answer 13

d) An adequately-sized urethral catheter should be lubricated and sterily introduced into the urethra. Once the obstruction is met a syringe containing sterile fluid (LRS or 0.9% NaCl) can be attached and the plunger “pulsed” with mild to moderate pressure to cause intermittent urethral distension. This is done concomitantly with progressive advancement of the catheter with the intention of driving the calculus back into the bladder.

Question 14

A five-year-old male Dalmatian is presented to your clinic in a near comatose state. He has a very large bladder on palpation and you quickly discover this is due to a blockage in the urethra as you are unable to pass a catheter beyond the base of his penis due to the presence of a urethrolith.

e) If your method to relieve the obstruction non-surgically is unsuccessful, describe the technique for surgical removal of a urethrolith at the base of the os penis, including the relevant anatomical features. (6 marks)

Answer 14

e)The technique of choice would be a pre-scrotal urethrotomy. The patient is positioned in dorsal recumbency and the area extending from the scrotum to the prepuce is clipped and aseptically prepared. The scrotum is included in the surgical field in case conversion to scrotal urethrotomy/urethrostomy becomes necessary. The prepuce is flushed with dilute antiseptic solution to decrease contamination prior to skin prep with chlorhexidine and alcohol swabs. The urethra is catheterized in retrograde fashion to facilitate identification during the surgical approach. A 1 to 2 cm long incision is performed on the midline immediately cranial to the scrotum. Dissection is continued through the subcutaneous until the paired retractor muscles are identified and laterally retracted. The urethra and surrounding corpus spongiosum are identified as a purple, 3 to 4 mm wide longitudinal structure bordered on either side by the white tunica albuginea. A longitudinal incision is made on the urethral midline, over the catheter, the calculus or just proximal to the calculus using #15 blade. Hemorrhage is expected due to the highly vascular carpus spongiosum and should be controlled using only pressure (avoid electrocautery). The calculi are removed, and the catheter is advanced into the bladder. A cystotomy can be performed to retrieve cystic calculi. The urethrotomy can be either closed primarily or allowed to heal by second intention. The latter option will be associated with much more hemorrhage, but the wound will heal within 14 to 21 days. The skin surrounding the stoma must be kept lubricated to prevent urine scalding. If primary closure is elected, both the urethral mucosa, submucosa and muscularis, as well as the surrounding corpus spongiosum should be closed using 5-0 monofilament absorbable sutures on a taper needle. Suture pattern can be simple-interrupted or continuous. Subcutaneous and skin are closed in routine fashion.

Question 15

2. A six-year-old Labrador is presented to your clinic with progressive dyspnea. On thoracic auscultation the heart and lung sounds are muffled. Thoracic radiography confirms a bilateral pleural effusion.
   Answer all subparts of this question:
3. a) List the different types of pleural effusions. (5 marks)

Answer 15

Pure transudate, modified transudate, exudate, hemorrhagic, chylous, “other” (i.e. pseudochylous, biliary effusion across the diaphragm)

Question 16

2. A six-year-old Labrador is presented to your clinic with progressive dyspnea. On thoracic auscultation, the heart and lung sounds are muffled. Thoracic radiography confirms a bilateral pleural effusion.
   b) Discuss the diagnostic tests you would perform to differentiate between each type of pleural effusion you have listed. Include in your answer the results you would expect for each effusion type. (10 marks)

Answer 16

Transudates and Exudates have traditionally been differentiated based on neutrophil percentage (Cytology). Pure and Modified transudates have less than 30% neutrophils (Pure transudates have less than 1500 cells/uL, while Modified transudates have 1500 to 5000 cells/uL). Exudates have more than 30% neutrophils, and typically > 5000 cells/uL. This classification scheme has been proven only 40-53% accurate. Newer methods utilize the Modified Light Criteria, based on effusion Lactate Dehydrogenase (LDH) and serum protein measurements. Exudates have more than 200 UI/L of LDH. This method has been shown to be over 90% accurate in differentiating transudates from exudates.

Hemorrhagic exudates have a PCV similar to whole blood (PCV). Diseases leading to chronic effusions, in contract with thoracic trauma, will not contact platelets and will not clot. Erythrophagocytosis may be observed.

Chylous exudates are milky-white to light pink and contains chylomicrons. The fluid will contain primarily lymphocytes, but neutrophils and macrophages may also be present (Cytology). Cholesterol/triglyceride ratio= <1 (opposite of serum); Protein content is typically 2.5 to 6 g/dL; Cell count <10,000 cells/uL. (biochemistry analysis)

“Other” effusions are rare in dogs and cats. Pseudochylous effusions are caused by the breakdown of cells, and can look similar to chyle. They can be differentiated via cholesterol measurement (higher than chyle), normal levels of triglycerides (similar to serum) and no chylomicrons. Lipid-laden macrophages may be present.

Question 17

2. A six-year-old Labrador is presented to your clinic with progressive dyspnea. On thoracic auscultation, the heart and lung sounds are muffled. Thoracic radiography confirms a bilateral pleural effusion.
   c) Your diagnostic tests confirm idiopathic chylothorax. Briefly discuss each of the treatment options you would give to the owner of this patient. (5 marks)

Answer 17

A 2019 systematic review published on Veterinary Surgery evaluated over 300 articles describing therapeutic methods to address idiopathic chylothorax, and found to advantage of one method over another. These included Thoracic Duct Ligation, trans-diaphragmatic omentalization, Pleuroperitoneal shunt and Partial Pleurectomy. No evidence was found to support medical therapy.

Question 18

2. A six-year-old Labrador is presented to your clinic with progressive dyspnea. On thoracic auscultation, the heart and lung sounds are muffled. Thoracic radiography confirms a bilateral pleural effusion.
   d) As part of your treatment plan, a lateral intercostal thoracotomy is to be performed. Describe and justify your perioperative analgesia plan for a patient undergoing a lateral intercostal thoracotomy. (5 marks)

Answer 18

Intercostal thoracotomies carry the potential to cause significant discomfort, and therefore require a robust preemptive approach. This can be accomplished via a combination of inhalant anesthesia, opioid analgesia (ideally CRI), local anesthetic blocks and epidular blocks. Start by administering a pure u-agonist opioids like hydromorphone, fentanyl, methadone or morphine, followed by a CRI of similar drugs and ideally including lidocaine and ketamine (after adequate leading doses). The skin over the proposed incision should be blocked using bupivacaine or liposome-encapsulated bupivacaine (Nocita – extra-label). Intercostal local anesthetic blocks should also be administered using similar local anesthetics. The block is administered immediately ventral and caudal to the costal tubercle, and must extend at least 2 intervertebral spaces cranial and caudal to the proposed thoracotomy site. Epidural opioids are administered at adequate volumes to reach the thoracic segments (morphine or buprenorphine – avoid local anesthetics due to the required volume to reach such cranial region). Liposime-encapsulated bupivacaine should be administered to each tissue layer during closure. Administer NSAID post-op and for at least 5 days. Oral narcotics (codeine), Ca-channel blockers (Gabapentin) can also be utilized as needed, as well as repeated doses of opioids (typically for the first 24-72 hours).

Question 19

4. A four-year-old Cavalier King Charles spaniel has been presented to your clinic experiencing intermittent right hind leg skipping lameness. On physical examination, you discover mild tibial rotation, a predominantly reduced patella that is easily luxated in a medial direction with flexion of the stifle joint and spontaneously reducing on stifle extension. You diagnose medial patella luxation.
   Answer all subparts of this question:
5. a) Describe a commonly used grading system for categorizing medial patella luxation. (8 marks)

Answer 19

Grade 1: the patella can be manually luxated during stifle extension but tends to spontaneously reduce itself. Typically asymptomatic incidental finding.

Grade 2: Spontaneous luxation occurs with clinical signs ranging from non-painful “skipping” lameness to mild discomfort. Mild deformities typically exist, consisting of internal tibial rotation and abduction of the hock.

Grade 3: The patella is permanently luxated by can be manually reduced. More severe bony deformities are usually present, including marked internal tibial rotation, distal femur varus and a shallow troclear groove. The patient usually stands with a “crouched” posture due to internal rotation of the stifle.

Grade 4: The patella is luxated and cannot be manually reduced. Similar anatomical abnormalities as for Grade 3, but more severe. The tibia is internally rotated between 60 and 90 degrees relative to the sagittal plane.

Question 20

4. A four-year-old Cavalier King Charles spaniel has been presented to your clinic experiencing intermittent right hind leg skipping lameness. On physical examination you discover mild tibial rotation, a predominantly reduced patella which is easily luxated in a medial direction with flexion of the stifle joint and spontaneously reducing on stifle extension. You diagnose medial patella luxation.
   b) What would you grade this dog using the system mentioned in part 4a) above?

Answer 20

Grade 2

Question 21

4. A four-year-old Cavalier King Charles spaniel has been presented to your clinic experiencing intermittent right hind leg skipping lameness. On physical examination you discover mild tibial rotation, a predominantly reduced patella which is easily luxated in a medial direction with flexion of the stifle joint and spontaneously reducing on stifle extension. You diagnose medial patella luxation.
   c) Briefly discuss three (3) commonly used soft tissue and two (2) commonly used bone reconstructive procedures that you could use to surgically help this animal.

Answer 21

Medial Desmotomy/capsulotomy: The contracted medial fascia and femoro-fabelar ligament (medial retinaculum), as well as joint capsule, are incised in a proximo-distal direction, beginning 2 to 3 cm proximal to the tibial attachment of the patellar ligament and 5 mm medial to the edge of the same ligament. The incision is extended proximally as far as necessary to relieve the tension on the patella, remaining 6 to 8 mm medial to the medial border of the patella. The incision may be left open or very loose horizontal mattress sutures may be applied.

Rectus Femoris muscle release: The patella is reduced and the quadriceps group is palpated for areas of tension. If present, the rectus femoris can be released from its origin on the ventral aspect of the ilium. The fascia of the vastus medialis and lateralis can also be incised between the rectus femoris / caudal sartorius and biceps femoris, respectively.

Lateral retinacular imbrication: An incision is performed through the fascia lata and joint capsule (as individual layers) beginning at the level of the attachment of the patella ligament on the tibia and 6 to 8 mm caudally. The incision is extended proximally to 8 to 10 mm proximal to the patella, remaining 4 to 5 mm lateral to the lateral border of the patella. The joint capsule can be imbricated with horizontal mattress sutures using absorbable monofilament material. The fascia lata can be imbricated on the cranial border of the biceps femoris using a “vest-over-pants” pattern (modified Mayo Mattress), also using monofilament absorbable suture material. Sutures are placed 4 to 6 mm from cut edges. Care is taken to avoid creating too much soft tissue tension, leading to lateral patella luxation and restriction of range of motion.

Trochleoplasty: This may include the abrasion, wedge and block recession variants. The wedge and block recession trochleoplasties preserve much of the hyaline cartilage over the trochlear groove, and are therefore considered preferable in comparison to the abrasion option. In the case of a block recession trochleoplasty, for example, the patella is luxated and the abaxial margins of the block are marked over the trochlear ridges using a scalpel blade of X-ACTO handsaw. The width of the block must be sufficient to accommodate the entire patella. This is important to prevent the patella from simply riding over the ridges, not making contact with the bottom of the trochlea. Each abaxial cut is angled 10 degrees towards the sagittal plane of the femur, resulting in a “press fit” of the block after recession of the underlining bone. The osteotomy should extend from the suprapatellar region (proximal limit) to the intercondylar notch (but not entering the intercondylar fossa). A straight basilar osteotomy is performed using a narrow osteotome or sagittal saw blade. The basilar subchondral bone is recessed using scalpel blade or a bone rasp, following by press-fitting onto the recipient bed.

Tibial Tuberosity Transposition: The point of attachment of the patellar ligament fibers is identified (Sharpey’s fiber insertion), followed by incision and light elevation of the medial tibial tuberosity periosteum over the proposed osteotomy line. This line should start 3 to 4 mm proximal to the Sharpey’s fiber insertion point and extend to the distal limit of the tibial crest. It is imperative that sufficient bone be mobilized to allow the placement of adequate stabilization. This can be measured on lateral tibial pre-op radiographs: the width of the tibial tuberosity segment to be transposed must equal roughly half the distance between the cranial limit of the tibial tuberosity and the tibial articular surface. The cranial tibial muscle is elevated from the lateral tibial surface and the osteotomy is preformed with osteotome or sagittal saw (preferred method). The osteotomy is extended to the most distal limit of the tibial crest, ideally leaving the periosteal attachment intact. The stifle is extended and the tuberosity is transposed laterally until the patellar ligament is realigned. Fixation is achieved with two Kirshner wired (0.039 to 0.062”)placed in the widest part of the tuberosity, directed slightly distal and caudomedial to avoid the fossa of the cranial tibial muscle. Care is taken to avoid intra-articular placement of implants. (the fibular head can be used as proximal landmark, but is not engaged). Next a bone tunnel is drilled from medial to lateral across the tibial, 3 to 10 mm caudal and slightly distal to the most distal aspect of the osteotomy. Cerclage wire of sufficient size (18 or 20 G) is placed through the tunnel and around the pins to for a “figure 8” on the cranial aspect of the transposed tuberosity. The wire is tied with one or two twist knots based on surgeon’s preference. The pins are bent proximally and cut leaving 2 to 3 mm beyond the bends.

Question 22

4. A four-year-old Cavalier King Charles spaniel has been presented to your clinic experiencing intermittent right hind leg skipping lameness. On physical examination you discover mild tibial rotation, a predominantly reduced patella which is easily luxated in a medial direction with flexion of the stifle joint and spontaneously reducing on stifle extension. You diagnose medial patella luxation.
   d) What potential complications could arise from your corrective surgery and what measures could you take to minimize these complications? (5 marks)

Answer 22

Potential complications may range from incision-related issues such as infection, seroma and dehiscence to osteomyelitis, fixation failure, patella reluxation and osteoarthritis. The prognosis for Grades 3 and 4 is typically not as favorable since various degrees of cartilage wear, muscle atrophy and rotational deformity are typically already present.

Ways to minimize the chance of infection include observance of strict aseptic technique, the use of injectable IV antibiotics (First-generation cephalosporin) 30 minutes before starting surgery and every 90 minutes intra-op as well as the use of an Elizabethan collar post-op.

Trochleoplasties must be wide enough to accommodate the entire width of the patella, and long enough to restrain the patella during the entire stifle range-of-motion. Patella alta or baja should be corrected at the time of surgery (together with tibial tuberosity transposition).

The medial retinaculum must be released as far proximately as necessary to eliminate undue tension on the patella. The lateral fascia must be sufficiently imbricated to prevent medial luxation, but not so much as to cause lateral luxation.

Careful surgical planning base on pre-op exam awake and under sedation, as well as on diagnostic-quality radiographs. This will allow adequate estimation of the osteotomy position for the tibial tuberosity transposition, as well as the ideal location of implants. The selection of a relatively large diameter cerclage wire and correct application of the tension band, based on AO principles, will sufficiently counteract the quadriceps group pull. The use of very thin osteotomes or ideally a sagittal saw will minimize the chance of iatrogenic tibial fractures.

The cranial cruciate ligament and menisci must be carefully examined at the time of surgery. Concomitant CrCLR is common, and if missed can lead to persistent discomfort.