Diagnostic Imaging (Lesson 3 & 6)
What is the optimal radiographic projection to evaluate for an un-united anconeal process (UAP) without superimposition in a young dog, and why is this view chosen?
A fully flexed lateromedial projection. Flexing the elbow pulls the anconeal process cranially and out of the humeral olecranon fossa, eliminating superimposition by the medial and lateral humeral epicondyles and allowing a clear view of the radiolucent cleft.
i. By what age (in days/months) should the separate center of ossification for the anconeal process be completely fused with the ulnar olecranon in large breed dogs?
It should be completely fused by approximately 150 days (5months) of age. Failure to fuse by this time is diagnostic ofUAP.
How do parallel and pennate muscle fiber arrangements differ in their biomechanical capacity for force (power) production and range of motion (shortening velocity)?
Parallel arrangements feature long fibers that run parallel to the muscle's long axis and tendon, allowing a much greater range of shortening (excursion) and a faster contraction velocity.
Pennate arrangements feature short fibers oriented obliquely at an angle to the tendon's line of pull; this packs a higher density of fibers into a given area (larger cross-sectional area), maximizing force and strength potential at the direct expense of range of motion
How are the three sub-types of pennate muscles classified based on fiber organization around the central tendon, and what is an example of a unipennate muscle?
unipennate (fibers on one side of the tendon, e.g., ulnar and radial muscles), bipennate (fibers on both sides of the tendon), and multipennate (multiple tendons distributed throughout the muscle)
What is the primary pathological definition of epiphysiolysis, and in what specific veterinary patient demographic and anatomical location is it most commonly diagnosed?
Epiphysiolysis is the separation of the epiphysis from the metaphysis due to the formation of a horizontal fissure or fracture through an abnormal physis. It is most commonly diagnosed affecting the femoral head in market-weight pigs and gilts
This is the correct vertebral formula for the different species (ovine, canine, equine, bovine, caprine, and porcine)?
Ovine (sheep): C7 T13 L6-7 S4 Cd16-18
Canine (dog): C7 T13 L7 S3 Cd20
Equine (horse): C7 T18 L6 S5 Cd (about 20)
Bovine (ox): C7 T13 L6 S5 Cd18-18
Caprine (goat): C7 T13 L6-7 S5 Cd16-18
Porcine (pig): C7 T14-15 L6 S4 Cd20-23
Of the three main synovial compartments of the equine carpus (antebrachiocarpal, middle carpal, and carpometacarpal), which cavities communicate directly, and what is the clinical significance of this during joint injections?
The middle carpal joint and the carpometacarpal joint communicate directly with one another. The antebrachiocarpal (radiocarpal) joint does not communicate with the other two cavities and is completely separate.
Clinically, injecting a therapeutic drug into the middle carpal joint will successfully distribute it into the carpometacarpal joint, but a second, separate injection is required to treat the antebrachiocarpal joint.
What are the characteristic radiographic findings of aseptic necrosis of the femoral head in a young, toy-breed dog, and what surgical salvage procedure is indicated?
Increased radiolucency (lysis), flattening, collapse, and fragmentation of the femoral head, often with joint space widening, subluxation, and severe osteophytosis. The surgical salvage is a Femoral Head and Neck Ostectomy (FHO).
i. What is the underlying pathogenesis of Legg-Calvé-Perthes disease?
Non-inflammatory, aseptic ischemia resulting in avascular necrosis of the subchondral bone of the femoral head.
What is the anatomical term for the flat, broad, sheet-like dense connective tissue structures used by wide muscles (such as the abdominal wall) to attach to bone or support internal organs?
An aponeurosis (plural: aponeuroses).
How are the origin and the insertion of a muscle functionally defined in relation to joint movement and distal/proximal limb positioning?
The origin is the more fixed, least movable attachment point (typically proximal on a limb). The insertion (or termination) is the more movable attachment point (typically distal on a limb) that is pulled toward the origin during muscle contraction
Explain the mechanical and inflammatory sequence of events that leads to the formation of a subchondral bone cyst secondary to chronic degenerative joint disease.
When degenerative joint disease creates tears or fissures in the articular cartilage, high-pressure synovial fluid herniates through these defects into the subchondral bone. This fluid becomes lined by a synovial-like membrane, and the surrounding bone is resorbed (bone lysis) via osteoclasis driven by mechanical pressure and inflammatory cytokines released by the expanding cyst.
A 5-year-old Quarter Horse gelding is evaluated for acute, grade 4/5 lameness of the left forelimb after landing awkwardly over a jump. On physical examination, there is marked digital pulse elevation in the left distal limb, heat over the hoof wall, and a positive response to hoof testers over the toe region. Radiographs of the foot reveal a non-displaced sagittal fracture of the distal phalanx. What is the common clinical name for the distal phalanx (P3) in horses, and what are the names of the proximal (P1) and middle (P2) phalanges?
Coffin bone (P3); Long pastern bone (P1); Short pastern bone (P2)
What is a grade 4/5 lameness?
Obvious at a walk
If a horse suffers a traumatic distal limb laceration resulting in complete grounding (collapse) of the fetlock joint—where the palmar aspect of the fetlock actively touches the ground during weight-bearing—which specific structures have been severed?
Complete grounding of the fetlock joint occurs only when both digital flexor tendons (SDFT and DDFT) and the interosseus muscle (suspensory ligament) are completely severed.
How does the clinical presentation differ if only the superficial digital flexor tendon (SDFT) is completely severed?
If only the SDFT is severed, the fetlock joint will sink slightly, but the foot remains flat on the ground and does not achieve complete grounding
What two primary radiographic parameters are measured on a lateromedial projection of the equine foot to assess the severity of laminitis?
(1) Rotation angle (the degree of angular rotation of the dorsal cortex of P3 away from the dorsal hoof wall); and (2) Founder (sinker) distance (the vertical distance from the coronary band to the extensor process of P3).
What anatomical structure is damaged in laminitis, allowing P3 to rotate or sink?
The laminae (dermal and epidermal laminae), which normally anchor the dorsal surface of P3 to the inner hoof wall
Describe type I and type II muscle fibers
Type I fibers contract slowly, are highly resistant to fatigue, rely on aerobic (oxidative) metabolism, and contain abundant myoglobin (giving them a red color).
Type II fibers contract rapidly and forcefully, fatigue easily, rely heavily on anaerobic glycolytic energy sources, and have low myoglobin content (giving them a pale/white color).
How do the proportions of Type I and Type II fibers differ between an endurance horse breed (like the Akhal-Teke) and a sprinting breed (like the American Quarter Horse)?
Racing horses possesses a higher proportion of Type I (slow- twitch, oxidative) fibers to support endurance and stamina. The American Quarter Horse possesses a higher proportion of Type II (fast-twitch, glycolytic) fibers to support explosive speed and power
what are the primary cellular and structural differences that distinguish osteoporosis, osteochondrosis, and osteopetrosis?
Osteoporosis: A metabolic bone disease characterized by reduced bone mass (osteopenia) with thin, fragile trabeculae that are otherwise normally mineralized. It is driven by an imbalance where osteoclastic bone resorption exceeds osteoblastic bone formation.
b. Osteochondrosis: A developmental skeletal disease defined by a focal failure of endochondral ossification. It begins as focal necrosis of epiphyseal cartilage, which fails to mineralize and be replaced by bone, leaving a localized region of retained necrotic cartilage.
c. Osteopetrosis: A metabolic/genetic disorder characterized by a pathologic increase in bone density (diffuse skeletal sclerosis). It is driven by a functional or genetic defect in osteoclast bone resorption (such as defective osteoclast acidification), preventing normal bone modeling and cavity formation
An orthopedic surgeon is reviewing the surgical approach to the hip joint in a dog. To ensure proper exposure of the coxofemoral joint during a total hip replacement, the surgeon must identify the distinct components of the pelvis (os coxae) that fuse to form the acetabulum. In dogs and cats, which four distinct bones fuse together to form each os coxae and contribute directly to the cup-shaped acetabulum?
Ilium, Ischium, Pubis, and Acetabular bone
What are the types of atypical bones?
Sesamoid ( develop within a tendon to reduce wear and tear), pneumatic ( contain air filled spaces to reduce the weight) and splanchnic ( develop in soft organs)
Describe the anatomical communication pattern between the three synovial sacs of the equine stifle joint (femoropatellar, medial femorotibial, and lateral femorotibial).
The femoropatellar sac communicates directly with the medial femorotibial sac in 100% of horses. In contrast, the femoropatellar sac communicates with the lateral femorotibial sac only approximately 25% of the time.
How does this communication pattern compare to that of companion animals (dogs/cats)?
In dogs and cats, all three synovial sacs of the stifle joint communicate directly with one another (100% communication across all compartments)
What are the most common radiographic indicators of bone spavin, and which specific joints of the tarsus are primarily affected?
Joint space narrowing, subchondral bone sclerosis, and medial periarticular osteophyte formation. It primarily affects the distal intertarsal joint (DIJ) and the tarsometatarsal joint (TMTJ).
Do the DIJ and TMTJ consistently communicate with each other or the tarsocrural joint in horses?
No. The DIJ and TMTJ communicate in only 25%–38% of horses, and they do not communicate with the high-motion tarsocrural joint, meaning they must often be targeted with separate needle placements for local anesthesia or therapy.
Bog spavin vs. Bone spavin?
1. Bone Spavin: This is the clinical term for osteoarthritis (degenerative joint disease) of the low-motion distal joints of the hock (tarsus), specifically the distal intertarsal joint (DIJ) and the tarsometatarsal joint (TMTJ). On a radiograph, the classic diagnostic changes you will see include joint space narrowing, subchondral bone sclerosis, and periarticular osteophytes, which classically form along the medial aspect of these distal tarsal bones.
2. Bog Spavin: This refers to chronic joint swelling or synovial effusion of the high-motion tarsocrural (tibiotarsal) joint. On radiographs, while bone spavin is characterized by chronic bone remodeling and sclerosis, bog spavin presents primarily as a distension of the tarsocrural joint capsule with soft tissue swelling, visible as a prominent fluid bulge on the dorsal and medial aspects of the hock.
What specialized membranous invaginations of the sarcolemma are responsible for carrying a depolarization wave deep into the interior of a muscle cell to stimulate calcium release?
Transverse tubules (T-tubules).
Where is intracellular calcium stored within the muscle cell prior to being released into the cytoplasm for contraction?
Inside the terminal cistern of the sarcoplasmic reticulum (SR)
What is the primary cell of origin for canine osteosarcoma, its classic appendicular anatomical distribution, and its characteristic metastatic behavior?
Osteosarcoma originates from malignant osteoblasts. In large-breed dogs, it predominantly targets the metaphyses of larger appendicular bones, characteristically following the "away from the elbow, towards the knee" rule (specifically the proximal humerus, distal radius, distal femur, and proximal tibia). It is highly malignant, producing osteoclastic bone lysis alongside disorganized tumor osteoid (woven bone), and typically exhibits early hematogenous metastasis (commonly trapped in the vascular sinusoids of the lungs).
A 9-year-old male German Shepherd dog is evaluated for chronic hindlimb lameness, difficulty jumping into the car, and an arched back. Orthopedic exam reveals severe pain upon palpation of the lumbosacral junction and tail-jack. Advanced imaging reveals degenerative lumbosacral stenosis (DLSS). The radiologist notes significant hypertrophy of a short ligament located between the vertebral arches, which is directly contributing to stenosis of the canal and compression of the cauda equina. Which short ligament of the vertebral column is pathologically affected in DLSS?
Interarcuate ligament – can lead to compression of the cauda equina, spinal instability, pain, hindlimb lameness, and urinary incontinence
If you need to perform a cerebrospinal fluid (CSF) tap in the caudal region of a dog, what vertebral space is used and what cistern are you accessing?
CSF is collected via the lumbosacral space (located between the last lumbar vertebra and the sacrum)
What is the "reciprocal apparatus" in the equine pelvic limb, which two structures form it, and what mechanical effect does it enforce?
The reciprocal apparatus is a specialized tendon linkage forcing the stifle and hock joints to move in perfect unison. It is formed by the peroneus tertius muscle/tendon cranially and the superficial digital flexor (SDF) muscle/tendon caudally. This linkage ensures that whenever the stifle flexes, the hock must flex, and whenever the stifle extends, the hock must extend.
What oblique radiographic projection of the equine fetlock is required to isolate and profile the medial proximal sesamoid bone?
The Dorsolateral-palmaromedial oblique (DLPMO) projection. (Oblique projections profile the structures on the "opposite side" of the beam entry).
What major ligamentous structure originates on the proximal palmar aspect of the cannon bone and inserts on these proximal sesamoid bones?
The interosseus muscle (suspensory ligament)
At the molecular level, what specific event must occur to prompt tropomyosin to move away and expose the active binding sites on the actin thin filament?
Intracellular calcium ions released from the sarcoplasmic reticulum must bind directly to Troponin C. This binding triggers a conformational shift in the troponin complex that physically pulls tropomyosin off of the actin molecule's active sites, allowing myosin heads to bind and initiate the cross-bridge cycle.
What immunological mechanism drives the pathogenesis of non-erosive IMPA, and what is its hallmark histopathological difference compared to erosive joint diseases like rheumatoid arthritis?
Non-erosive IMPA is driven by the deposition of circulating antigen- antibody (immune) complexes directly in the synovial membranes of multiple joints. Unlike erosive arthritides, non-erosive IMPA lacks the formation of a destructive pannus (vascular granulation tissue) and does not cause aggressive cartilage or subchondral bone erosion, preserving joint structure despite severe inflammation.
A 9-month-old male Yorkshire Terrier is evaluated for progressive neck pain, tetraparesis, and a "wobbly" gait. Gentle cervical palpation elicits severe distress. Lateral cervical radiographs reveal dorsal displacement of the body of C2 (axis) relative to C1 (atlas), suggesting atlanto-axial subluxation. What is the name of the distinct, cranial peg-like projection of the axis that normally sits inside the ventral ring of C1, and what head movement does this joint primarily allow?
Dens (odontoid process); rotation ("no" head movement)
Why does damage to the suprascapular nerve lead to shoulder instability (lateral slipping) in horses?
The suprascapular nerve innervates the supraspinatus and infraspinatus muscles, which act as crucial "active collateral ligaments" to stabilize the shoulder joint. Nerve injury leads to rapid, severe neurogenic atrophy of these muscles (creating a prominent scapular spine). Without their stabilizing tension, the shoulder joint loses lateral support, causing the joint to slip laterally (subluxate) whenever the horse bears weight on the limb.