Canine Fracture Management Study Guide

Overview and Clinical Importance

Fracture management is a fundamental component of veterinary orthopedic practice. Long bone fractures represent approximately 24% of all fractures in dogs, with the femur, tibia, radius/ulna, and humerus being most commonly affected. Successful fracture management requires understanding of fracture classification, bone healing biology, fixation techniques, and recognition of complications. This knowledge is essential for the NAVLE examination and clinical practice.

The goal of fracture treatment is to restore anatomical alignment, maintain stability, promote bone healing, and return the patient to normal function while minimizing complications. Understanding when to use different fixation methods and recognizing when referral is appropriate are critical skills for the general practitioner.

Fracture Classification Systems

Proper fracture classification is essential for communication between veterinarians, treatment planning, and prognosis determination. Fractures should be described systematically using multiple classification criteria.

Anatomic Classification

Fractures are first classified by anatomic location within the bone:

Fracture Configuration (Morphology)

Salter-Harris Classification of Physeal Fractures

The Salter-Harris classification system is essential for describing growth plate fractures in skeletally immature dogs. Physeal injuries account for up to 30% of long bone fractures in young animals. The classification guides treatment and predicts prognosis for growth disturbance.

Open Fracture Classification: Gustilo-Anderson System

Open (compound) fractures involve disruption of skin integrity with communication between the fracture and external environment. These injuries carry significantly higher risk of infection, delayed healing, and complications. The Gustilo-Anderson classification guides treatment and predicts prognosis.

Open Fracture Management Principles

• Antibiotics within 3 hours of injury - reduces infection rate 6-fold
• Wound lavage with isotonic saline (minimum 1 liter per Type I; more for higher grades)
• Aggressive surgical debridement of all nonviable tissue
• Temporary or definitive fracture stabilization
• Wound management (delayed primary closure often preferred for Type III)
• External skeletal fixation is ideal - keeps implants away from contaminated zone

Bone Healing Biology

Understanding the two types of bone healing is crucial for selecting appropriate fixation methods and monitoring fracture repair progress.

Direct (Primary) Bone Healing

Direct healing occurs with rigid fixation and anatomic reduction resulting in a fracture gap less than 1mm and interfragmentary strain less than 2%. This is achieved with compression plating and lag screws.

• Contact healing: Gap less than 0.01mm; direct osteonal remodeling across fracture line
• Gap healing: Gap less than 1mm; lamellar bone fills gap followed by Haversian remodeling
• No callus formation: Fracture line gradually disappears on radiographs
• Timeline: Slower process; implants typically remain 5-14 months

Indirect (Secondary) Bone Healing

Indirect healing is the most common type in veterinary patients and occurs with less rigid fixation (casts, external fixators, IM pins). It involves callus formation through three overlapping phases:

Radiographic Assessment of Bone Healing

Clinical union is confirmed when callus bridges the fracture on at least 3 of 4 cortices visible on orthogonal radiographic views.

• 5-7 days: Fracture gap widening and smudging of fracture edges (resorption phase)
• 2-3 weeks: Early periosteal callus visible
• 4-8 weeks: Callus becoming more radiopaque; fracture line becoming less distinct
• 8-16 weeks: Bridging callus; clinical union in most adult dogs

Fracture Fixation Methods

Selection of fixation method depends on fracture configuration, patient factors, and the forces that must be neutralized. Understanding the biomechanical properties of each method is essential.

Forces Acting on Fractures

Fixation Methods Comparison

The 50/50 Rule

Fracture ends should have at least 50% cortical contact for bone healing to occur. If anatomic reduction cannot achieve 50% contact, internal fixation is required. This is the absolute minimum for healing to be possible (not probable).

Fracture Healing Complications

Delayed Union

Delayed union is diagnosed when a fracture is taking longer to heal than expected for a fracture of that type, in a patient of similar age and health, with similar fixation. Healing activity is still present but slower than normal.

Causes:

• Inadequate immobilization or stability
• Excessive fracture gap or distraction
• Impaired blood supply
• Infection
• Excessive implant material interfering with biology

Nonunion

Nonunion is a fracture where all osteogenic activity has ceased and healing will not occur without intervention. Generally diagnosed after 3 months or when no progression is seen on 2-3 consecutive radiographic evaluations.

Osteomyelitis

Osteomyelitis is bacterial infection of bone, most commonly posttraumatic (open fractures) or postsurgical in veterinary patients. It is the most common cause of nonunion when associated with infection.

Risk factors:

• Open fractures with significant contamination
• Presence of implants (biofilm formation)
• Extensive soft tissue trauma
• Necrotic tissue, hematoma, poor vascularity
• Fracture instability

Radiographic signs: Excessive periosteal reaction, radiolucency around implants (loosening), sequestra, involucrum, draining tracts.

Treatment principle: Infected fractures CAN heal if they are STABLE. Treatment involves debridement, culture-based antibiotic therapy (long-term), and adequate stabilization. External fixation is ideal. Implant removal once clinical union is achieved.

Malunion

Malunion occurs when a fracture heals in abnormal alignment (angulation, rotation, or shortening). May cause lameness, abnormal joint loading, and degenerative joint disease. Corrective osteotomy may be required if functional impairment is significant.

Special Clinical Considerations

Radius/Ulna Fractures in Toy Breeds

Distal radius/ulna fractures in toy and miniature breeds have the highest complication rate of any long bone fracture. This is due to poor intraosseous blood supply in the distal radius of small dogs, minimal soft tissue coverage, and tendency for delayed union and nonunion. NEVER use IM pins for these fractures. Bone plate fixation is the treatment of choice, often with bone grafting.

Fracture Disease

Fracture disease encompasses complications that affect limb function after fracture healing, including muscle atrophy, reduced range of motion, osteoporosis, and quadriceps contracture (tie-down). Quadriceps contracture is especially associated with distal femoral fractures in young dogs. Prevention requires early passive range of motion exercises, adequate analgesia, and avoiding prolonged immobilization.