Approach to Fractures

Approach to Fractures

• This presentation covers the approach to fractures, specifically bone structure, function, development, diagnosis, different forces, types, classification, healing, and repair methods.

Learning Objectives

• Students should be able to describe normal bone structure and development.
• Students should be able to classify fractures according to type, location, and nature.
• Students should be able to explain primary and secondary bone healing.
• Students should be able to discuss the principles of fracture repair.
• Students should be able to identify delayed unions, nonunions, and malunions.

Bone Structure

• Bone is composed of cells and organic/mineral matrix.
  • Cells include osteoblasts (make bone), osteocytes (bone cells), and osteoclasts (resorb bone).
  • Organic matrix (⅓ of bone mass) includes collagen fibers and proteoglycans.
  • Mineral matrix (⅔ of bone mass) includes calcium phosphate as hydroxyapatite.
• Bone types include long bones (epiphysis, physis, metaphysis, diaphysis), short bones (carpus/tarsus), sesamoid bones (usually in or adjacent to tendons), flat bones (skull/scapula), irregular bones (vertebrae), and non-flat bones of the skull (zygomatic arch).

Bone Function

• Axial skeleton: Provides structure for the skull, hyoid apparatus, vertebral column, ribs, and sternum. Also protects organs in the cranial and thoracic cavities.
• Appendicular skeleton: Includes the thoracic and pelvic limbs.
• Heterotopic skeleton: Includes the os penis.

Bone Development

• Initially bone develops as woven bone (immature) and is then replaced by lamellar bone (mature).
  • Lamellar bone has two types: compact cortical bone (made up of osteons) and spongy/cancellous bone (made up of trabeculae, found in ends of long bones and inner layers of long bones and vertebrae).
• Intramembranous ossification: Formation of bone directly from osteogenic mesenchymal cells (most flat bones). Periosteal cells increase the width of long bones.
• Endochondral ossification: Formation of bone from a cartilage precursor (vertebrae, ribs, sternebrae, pelvis, and the primary means of long bone growth). Prominences on the long bones may have separate centres of ossification.

Bone Development: Endochondral Ossification - Primary Centre

• Chondrocytes form columns characterized by resting/reserve zone (normal hyaline cartilage), proliferation zone (chondsrocytes multiply), hypertrophy and calcification zone (chondrocytes grow and matrix mineralises),
• cartilage erosion zone(chondroclasts remove matrix, and blood vessels invade), and endochondral ossification (bone replaces removed cartilage, bone elongation occurs).

Bone Development: Secondary Centres

• Separate ossification centres arise in epiphyseal areas.
• These centres enable localized joint and bone shaping.
• They contain their own blood supply which doesn't cross the growth plate.

Modelling

• Wolff's law states that bone responds to the loads placed upon it.
• Bone and cartilage need load to remain healthy.
• When bone is loaded, piezoelectric effects induce electric currents.
• Electropositivity on convex surfaces leads to osteoclastic activity.
• Electronegativity on concave surfaces leads to osteoblastic activity.
• Trabeculae/struts/plates form in line with applied forces.

Types of Fractures

• Various types include monotonic (supramaximal loading), pathological (weakened by disease), and stress fractures(accumulation of fatigue damage exceeding body's remodelling ability).

Classification of Fractures

• Based on location (general-articular, epiphyseal, metaphyseal, diaphyseal; special-condylar, trochanteric), displacement (greenstick, folded, fissure, depressed, compression, impacted, complete, incomplete), direction (transverse, oblique, spiral, comminuted), number of fracture lines (multiple, comminuted), stability (stable, unstable), and open vs. closed (Gustilo-Anderson classification).

Bone Healing: Phases

• Inflammatory/hematoma phase: Hemorrhage, neutrophils/macrophages, growth factors.
• Reparative/granulation/callus formation phase: Granulation tissue, vascularisation, collagen fibers, chondrogenesis, gradual mineralisation.
• Remodelling phase: Woven bone replaced by lamellar bone.

Bone Healing: Direct vs. Indirect Healing

• Direct Bone Healing: Primary bone union, occurs under rigid fixation, no callus formation.
• Gap healing: Bone ends less than 0.8 mm
• Contact healing: Bone ends less than 0.01 mm, Haversian remodelling begins immediately
• Indirect Bone Healing: Secondary bone union, callus formation.

Fracture Repair and Aims

• Aims to rehabilitate patient as quickly as possible, achieving sufficient reconstruction to meet functional requirements.
• Fixation needed for immobilisation until healing occurs, and mobilization of joints, with respect to stability/instability of each fracture type in different patients.
  • Biomechanics of Repair: Prevent rotation, prevent bending, maintain length, and withstand distraction forces.
• Repair Methods: Conservative, closed reduction with external fixation, open reduction without rigid fixation, rigid external fixation, open reduction with internal fixation, and closed reduction with internal fixation.

Tools and Methods of Fixation

• Tools: Cast/splints, External fixators, Intramedullary pins, Screws, Plates, Wire.

Conservative Approach for Pelvic Fractures

• Pelvic fractures are inherently stable.
• Surgical fixation is considered if the integrity of the weight-bearing axis is lost, the pelvic canal is narrowed, or there is an acetabular fracture, bilateral sacroiliac separation, intractable pain, or multiple injuries.
• Medical considerations include iliac fractures with minimal displacement, ischial fractures, public fractures, and cost prohibitions to surgery.

Fracture Repair Methods: Casts and Splints

• Stable fractures (distal limbs, diaphyseal, single bone, paired bone, simple and uncomplicated fractures in young dogs).
• Considerations: Pressure sores, patient interference, change of cast affecting fracture site, joint stiffness, cost.

Fracture Repair Methods: Rigid External Fixation

• Linear and circular fractures; may be open or closed.
• Multiple configurations, biomechanically strong dynamic repair.
• Wound management is necessary, along with considerations for owner compliance, patient interference, drainage tracts, and soft tissue injury.

Fracture Repair Methods: Screws

• Types include self-tapping vs non-self-tapping, cortical vs cancellous.
• Techniques such as lag screws, plates, and locking plates are used to provide stabilisation and structural integrity.

Fracture Repair Methods: Plates

• Plates can be applied in various ways neutralisation, compression, buttress, and bridging to overcome forces at the fracture site and stabilize the fracture during healing.
• Neutralization overcomes bending, rotation, and shear forces.
• Compression, Buttress, and Bridging support under compressive forces and span bone gaps to ensure stability.

Fracture Repair Methods: Wire

• Cerclage wire: encircles bone, used for some mandibular/maxillary, and long oblique fractures to compress and provide stability.
• Tension band wire: used for neutralising avulsion forces (tendons, ligaments) by applying vector forces to coapt the fracture site.

Fracture Repair Methods: Pins

• Pins are generally inexpensive and simple to use.
• Are often used for diaphyseal fractures, as they easily neutralise bending forces.
• Cannot resist rotation, axial collapse, or distraction.
• May be supplemented with interlocking nails or external fixators to overcome these limitations.

Fracture Repair: Planning

• Evaluation of patient type, and characteristics of the fracture, location, direction, stability, complications, and species/breed, age, activity, expertise, and budget.

Treatment Considerations

• Carpenter vs. Gardener: Preservation of soft tissue envelope and temporary extraosseous blood supply is important.
• Challenges: Open fractures pose higher risks of infection and joint problems. Young animals may be difficult for owners to manage.

Fracture Complications

• Delayed union (fracture takes more time to heal).
• Non-union (fracture does not heal).
  • Subtypes: Viable, non-viable.
• Different causes for different types.

Fracture Assessment Score

• Mechanical, Biological, Clinical factors are evaluated.
• Mechanical: Strength of fixation required.
• Biological: Healing rate.
• Clinical: Patient/client factors considered.

Problems with Healing

• Mechanical failure: Poor blood supply, soft tissue coverage, and systemic disease.
• Biological failure: Poor blood supply, soft tissue coverage, and systemic disease.
• Clinical failure: Poor owner compliance.