NAVLE Equine Surgery and Lameness 5

Question 1

A 12-year-old Warmblood sport horse presents with a 6-month history of intermittent right forelimb lameness that worsens after collected work. Radiographs reveal subchondral cystic lesions in the medial femoral condyle. Intra-articular anesthesia of the femoropatellar joint abolishes 70% of the lameness, but the stifle shows no significant synovial effusion. Which surgical treatment has demonstrated the best long-term outcomes for large (>15 mm diameter) subchondral cystic lesions of the medial femoral condyle in sport horses?

Accepted Answer

Intra-cyst injection of triamcinolone acetonide via arthroscopic or fluoroscopic guidance

Answer

Intra-cyst injection of triamcinolone acetonide (via arthroscopic visualization or fluoroscopic guidance) has emerged as the superior treatment for large subchondral cystic lesions of the medial femoral condyle, yielding return-to-athletic-function rates of 65–80% in sport horses. The mechanism involves suppression of the inflammatory signaling within the cyst wall, reducing osteoclastic resorption. Transcondylar screws carry significant implant-related complications and inconsistent outcomes. Simple arthroscopic debridement alone produces inferior results for large lesions (>15 mm). ESWT has limited evidence for cystic lesions specifically. Peripheral (intra-articular) corticosteroid without direct cyst access is less effective.

Question 2

During an arthroscopic surgery of the equine tarsocrural joint, you inadvertently lacerate the medial branch of the deep peroneal nerve. Which immediate postoperative complication is most specifically associated with this iatrogenic injury in the horse?

Accepted Answer

Loss of sensation over the dorsal metatarsus with no motor deficit

Answer

The medial branch of the deep peroneal (fibular) nerve in the horse is primarily sensory to the dorsal metatarsus and dorsal fetlock region. Damage to this branch produces analgesia/hypoalgesia of the dorsal metatarsus without meaningful motor loss, since the motor contributions to the digital extensors arise from the main trunk more proximally. Knuckling at the fetlock results from damage to the extensor branches of the peroneal nerve much more proximally, or from true extensor muscle denervation — not from the medial branch at the tarsocrural level. Lymphatic effects are not attributable to this nerve.

Question 3

A 5-year-old Thoroughbred racehorse undergoes emergency surgery for a complete lateral condylar fracture of the right third metacarpal bone sustained during a race. The fracture is repaired with lag screw fixation. Three weeks postoperatively, the horse develops acute non-weight-bearing lameness and radiographs show implant loosening with bone lysis around the screw tracks. Bacterial culture of joint fluid grows Staphylococcus aureus resistant to beta-lactam antibiotics. Which systemic antibiotic protocol is most appropriate while awaiting full susceptibility results?

Accepted Answer

Enrofloxacin 5 mg/kg IV once daily

Answer

Enrofloxacin is the most practical systemic option for methicillin-resistant Staphylococcus aureus (MRSA) or beta-lactam-resistant staphylococcal infections in horses pending full susceptibility data. Fluoroquinolones achieve excellent bone and synovial fluid penetration and have demonstrated efficacy against many resistant staphylococci in equine clinical practice. Vancomycin is theoretically ideal for MRSA but is nephrotoxic in horses, poorly studied pharmacokinetically, and logistically challenging (TID IV). TMP-sulfa has variable efficacy against S. aureus and poor bone penetration. Chloramphenicol has public health implications (aplastic anemia risk in humans via residues) and is rarely used in performance horses.

Question 4

A 9-year-old Quarter Horse cutting horse presents with a 4-month history of bilateral hindlimb stiffness that is worse in the morning and improves with exercise. The horse shows a characteristic 'goose-stepping' gait. Intra-articular anesthesia of the distal intertarsal and tarsometatarsal joints produces marked improvement. Medical management has failed over 6 months. Chemical arthrodesis with sodium monoiodoacetate (MIA) is elected. Which of the following correctly describes the mechanism of action of sodium monoiodoacetate in inducing arthrodesis?

Accepted Answer

It inhibits glycolysis in chondrocytes by alkylating sulfhydryl groups of glyceraldehyde-3-phosphate dehydrogenase, causing chondrocyte death and cartilage destruction

Answer

Sodium monoiodoacetate (MIA) is a chondrotoxic agent that alkylates (irreversibly inhibits) the sulfhydryl group of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis. Since articular cartilage relies almost entirely on anaerobic glycolysis for energy, this inhibition causes rapid chondrocyte death, cartilage matrix degradation, and subsequent subchondral bone-to-bone apposition — eventually leading to bony fusion. MIA does not primarily stimulate osteoblasts directly, does not chelate calcium, and does not work via complement activation.

Question 5

An 8-year-old Hanoverian mare undergoes standing laparoscopic right ovariectomy for an ovarian granulosa-theca cell tumor. Forty-eight hours postoperatively, she develops progressive signs of colic, tachycardia (72 bpm), and tachypnea. On rectal examination, distended small intestinal loops are palpable. Nasogastric reflux yields 8 liters of fluid. Which laparoscopic complication is the most likely cause of this acute deterioration?

Accepted Answer

Herniation of small intestine through the right flank cannula port site

Answer

Herniation of small intestine through a flank cannula port site (incisional hernia with bowel entrapment) is a well-recognized and serious complication of standing flank laparoscopy in horses, particularly when 10–12 mm ports are used without proper fascial closure. The 12 mm port sites in the right flank create a defect large enough for small intestinal herniation, which can rapidly progress to strangulation — explaining the large nasogastric reflux, distended small intestinal loops, and systemic signs of ischemia. CO2-induced ileus and mesenteric traction ileus would not typically produce 8 L of reflux within 48 hours. Uterine artery ligation would cause hemorrhage and uterine signs rather than small intestinal obstruction.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Equine Surgery and Lameness 5