Equine Joint Disease Quiz

Learning Objectives

• Students should be able to describe the types and clinical findings of bone and joint pathologies in horses.
• Students should be able to determine an appropriate diagnostic approach to bone/joint pathologies in horses, including imaging options and interpretation of findings.
• Students should be able to describe how different bone/joint diseases are managed in horses and determine the prognosis.

Bone Pathologies in Horses: Categories

• Developmental: Angular Limb Deformities, Physitis, Osteochondrosis
• Congenital: Skeletal dysplasia, Chondrodysplasia, Traumatic fracture, Periosteal reaction, Sequestrum, Subchondral bone injury, Cysts
• Infectious: Osteitis, osteomyelitis
• Metabolic: Fibrous osteodystrophy
• Neoplasia: Keratoma
• Other: Marie's Disease

Diagnosis of Bone Pathologies: History

• Owner observations
• Signalment (age, sex, breed)
• Lameness
• Duration (worsening or improving)
• Effect of exercise
• Recent trauma/wound
• Current diet
• Medication/previous problems/surgery

Diagnosis of Bone Pathologies: Observation

• Obvious clinical signs (e.g., hard swellings in physitis weanlings)

Diagnosis of Bone Pathologies: Clinical Examination

• Orthopaedic examination (symmetry, muscular atrophy, posture, limb palpation—heat, pain, swelling)
• Gait assessment (presence of wounds/lacerations, depth assessment, discharge/nature, fragments of bone, fracture palpability, other clinical disease)

Approach to Diagnosis of Bone Pathologies: Radiography

• Assess each structure in terms of Röntgen signs (size, shape, contour/margins, number, position, opacity—air, fat, water, soft tissue, bone, metal)
• Identify pathology or features of normal anatomy
• Be aware of incidental findings, normal variations vs abnormalities, composite shadows/superimposition, artefacts, or pathological lesions
• Look for soft tissue swelling, and acquire orthogonal views
• Radiograph contralateral limb for comparison.

Radiographic Findings with Bone Disease

• Periosteal New Bone Formation: Blunt trauma can lead to sub-periosteal hemorrhage, lifting periosteum, stimulating production of periosteal new bone, creating less dense, irregular outlines (that become more radiopaque with smooth outlines), and potentially showing signs of healing fractures, infection, inflammation, neoplasia, or osteoarthritis.
• Sclerosis (Endosteal New Bone Formation): Densification, localised new bone formation, increased bone mass, increased radio-opacity, protection of weakened areas, or walling off infection.
• Bone Lysis: Destruction of bone area, signs of infection, presence of neoplasia or keratoma.
• Osteophyte Formation: Spur of bone on a joint margin, intra-articular disease like osteoarthritis, and joint instability.
• Enthesophyte Formation: New bone development on tendon/ligament/joint capsule to bone attachment, a response to stress on these structures, or soft tissue injury

Aggressive vs Non-Aggressive Bone Lesions

• Characteristics of aggressive bone disease (e.g., malignant bone tumors, bone infection):
  • Destruction of the cortex
  • Irregular margin of reaction of periosteal reaction
  • Lack of distinctness/boundary of the bone lesion to normal bone.

Diagnosis of Bone Pathologies: Ultrasonography

• Useful for assessing bone surface—smooth, uniform, hyperechoic line (only surface; not internal).
• Useful for areas difficult to radiograph (e.g., pelvis).
• Allows assessment of fractures (non-displaced break, displaced fragment with visualization of hyperechogenic bony bony structure from underlying bone), presence or absence of concurrent soft tissue damage and depth of wounds.

Diagnosis of Bone Pathologies: Nuclear Scintigraphy

• Radioisotope (Technetium 99m) is injected intravenously.
• Increased radiopharmaceutical uptake (IRU) in areas with increased osteoblastic activity.
• High in sensitivity but low in specificity imaging modality.
• Indications include fracture suspicion with negative radiographs or obscure lameness, those that are difficult to localize with diagnostic analgesia and episodic lameness, and horses with poor performance or inaccessible pelvic regions.
• Requires careful interpretation and knowledge of "normal" areas with increased bone turnover.

Diagnosis of Bone Pathologies: Computed Tomography

• 3D image from a series of 2D radiographic images, taken around a single axis of rotation.
• Advantages include non-superimposed structures, facilitating complex structure examination (e.g., skull), and the use of multiple planes to help delineate fracture orientation—useful for fracture repair planning.

Diagnosis of Bone Pathologies: Magnetic Resonance Imaging

• Allows better imaging of soft tissue structures, but less detailed examination of bone structures—lower resolution compared to radiography, CT, or ultrasound.
• Dynamic imaging modality, identifying intra-osseous fluid.
• Only distal limb possible in horses.

Bone Pathologies: Common Conditions, Treatment & Prognosis

• (This section is addressed throughout the notes)

Developmental Bone Disease

• Angular limb deformities, physitis, osteochondrosis, cuboidal bone malformation (premature foals)

• Sequelae to developmental bone disease predisposes animal to degenerative joint disease later in life. Early intervention is important to reduce long-term damage to a joint.

Angular Limb Deformities

• Valgus (lateral deviation of limb)
• Varus (medial deviation of limb)
• Carpus and fetlocks most commonly affected

Physitis

• Inflammation of growth plate
• Irregularly thickened growth plate
• Metaphyseal sclerosis
• Periosteal bone formation

Infectious Causes of Bone Disease: Osteitis and Osteomyelitis

• Inflammation of bone caused by pyogenic organisms.
• Inflammation, necrosis, removal of bone, compensatory production of new bone.
• Bone involved (pedial osteitis).

Radiographic Findings for Osteitis and Osteomyelitis

• Soft tissue swelling
• New bone formation
• Bone resorption
• Possible consequence: Sequestrum, involucrum, area of sclerosis to wall off infection, sinus

Septic Arthritis

• Contamination of synovial cavity with bacteria (from trauma, iatrogenic procedures, hematogenous spread, local soft-tissue infections).

Septic Arthritis: Pathogenesis

• Inflammatory response (vasodilation, neutrophil influx, release of cytokines/enzymes).
• Fibrin clots trapping bacteria.
• Cartilage destruction and extension to subchondral bone.
• Pain and swelling in affected joint—possibly leading to degenerative osteoarthritis.

Septic Arthritis: Treatment

• Joint lavage (ASAP)
• Arthroscopic debridement and lavage
• Systemic antibiotics (based on culture/sensitivity)
• Intra-articular antibiotics
• Intravenous regional perfusion
• Analgesics

Septic Arthritis: Prognosis

• Early, aggressive management for best outcome.
• Concurrent damage worsens prognosis (osteomyelitis, soft tissue damage).
• Care – most present NWB lame; low-grade lameness if open and draining; untreated—chronic lameness, DJD -> euthanasia.

Osteochondrosis/OCD

• Developmental disorder.
• Defect in endochondral ossification; focal ischaemic necrosis of cartilage initiated by necrosis of cartilage canal blood vessels.
• Osteochondritis dissecans (OCD): Fragment separates from adjacent subchondral bone.
• Osseus cyst-like lesions (OCLLS).
• Retention of a focal area of degenerate cartilage within the subchondral bone (subchondral bone cyst).
• Leads to osteoarthritis
• Predisposing factors: Trauma, body size, growth rate, nutrition (high plane of nutrition & high phosphorus diet, copper deficiency) and genetics (predisposition).
• Environment is important.

Osteochondrosis/OCD: Radiographic Findings

• Flattening of joint surface
• Mineralised cartilage flap/ subchondral bone defect
• OCLL/subchondral bone cysts
• Joint effusion.

Osteochondrosis/OCD: Ultrasonography

Osteochondrosis and OCD Management

• Long-term consequences (predisposition to osteoarthritis); free-floating fragments, extensive cartilage damage, fragments lodged in synovial membrane).
• Conservative management (Dietary modification, Rest, Analgesia.)
• Intra-articular medication with chondroprotectants +/- corticosteroids.
• Surgery (Arthroscopic debridement, cartilage flap removal.)

Osteoarthritis

• Degenerative joint disease
• Afflicted joints (small tarsal joints, tarsometatarsal joints, distal intertarsal joints, proximal intertarsal joints, distal interphalangeal joints, proximal interphalangeal, MCP, carpal joints, stifles, cervical spine).

Osteoarthritis: Radiographic Findings

• New bone formation/ periarticular osteophytes
• Enthesophytes
• Erosion of subchondral bone surface
• Subchondral sclerosis
• Subchondral cyst formation
• Reduced joint space/joint narrowing
• Increased synovial mass
• Mineralisation of tissues

Osteoarthritis: Radiography

Osteoarthritis: Management

• Aims (analgesia, control inflammation, limit damage to articular tissues, promote healing, improve quality of life, return to athletic function).
• Physical Therapy (Acute: rest, cold therapy; Chronic: gentle exercise, hydrotherapy).
• Anti-inflammatory/Analgesia (NSAIDs).
• Corticosteroids (intra-articular).
• Adjunctive Treatments (Hyaluronic Acid, Pentosan polysulphate sodium, Bisphosphonates…)

Useful Resources

• (A list of relevant research articles and publications is presented)

Synoviocentesis

• Essential for septic arthritis diagnosis.
• Detects inflammation within the joint (synovitis).
• Aseptic Collection is critical.
• Essential Tests (cytology and sensitivity).
• Contrast study (contrast agent injection into joint & radiographs, leaks if wound communicates with joint).
• Pressure test.

Synoviocentesis: Appearance

• Normal appearance: Pale yellow/transparent, high viscosity, low in white blood cells, low total protein.
• Abnormal appearance: Serosanguinous/turbid/low viscosity, High in white blood cells and high total protein; >90% Neutrophils.

Arthroscopy

• Direct visualisation of joints
• Diagnostic and therapeutic

Joint Disease: Common Conditions, Treatment & Prognosis

Osteoarthritis (Degenerative Joint Disease): Which joints are commonly affected in horses?

• Small tarsal joints ("Bone Spavin")
• Tarsometatarsal joints
• Distal intertarsal joints
• Proximal intertarsal joints
• Distal interphalangeal joints
• Proximal interphalangeal joint
• Metacarpophalangeal joints
• Carpal joints
• Stifles
• Cervical spine (articular facets.)

Joint Lavage

• Removes bacteria, debris, inflammatory mediators
• Uses large volume of sterile polyionic solution to dilute

Arthroscopic Debridement and Lavage

• Superior visualization
• Removal of debris, foreign materials, adhesions.
• Synovial biopsy for culture and sensitivity