Fractures — Classification, Biomechanics, Diagnosis

Introduction

A fracture is a discontinuity in the structural integrity of bone. The understanding of fractures encompasses their etiology, the biomechanical forces producing them, the patterns of injury, the principles of classification, the systematic clinical and radiographic diagnosis, and the conceptual framework that guides treatment decisions. This chapter, synthesizing content from AO Principles of Fracture Management (the foundational text for the modern science of fracture surgery), Rockwood and Green’s Fractures in Adults, Apley & Solomon’s, and Miller’s Review, addresses the general principles that underlie the more specific fracture topics in subsequent chapters. The trauma section that follows is organized anatomically, addressing each major fracture region in detail; the principles in this chapter apply across all regions.

Epidemiology of Fractures

Fractures are extremely common, with the lifetime risk of at least one fracture approaching 50% in many populations. The principal patterns of fracture epidemiology are: bimodal age distribution, with peaks in young adults (high-energy trauma) and in older adults (low- energy fragility fractures); male predominance in young adults, female predominance in older adults; and the increasing burden of fragility fractures as the population ages. The principal fragility fractures — distal radius, proximal humerus, vertebral body, hip — produce substantial morbidity and mortality in older adults, with the hip fracture in particular producing 1-year mortality of 20-30% in elderly patients with comorbidities.

Biomechanics of Fractures

The biomechanical analysis of fractures considers the mechanical properties of bone, the forces applied to it, and the resulting patterns of failure. Mechanical Properties of Bone Bone is an anisotropic material — its mechanical properties differ in different directions of loading. Compressive strength along the long axis of the bone is substantially greater than tensile strength (bone is approximately twice as strong in compression as in tension) or shear strength. The Young’s modulus of cortical bone is approximately 15-20 GPa, intermediate between metals (much stiffer) and tendons (much more compliant). Cancellous bone has substantially lower stiffness and strength than cortical bone, reflecting its trabecular structure and the role of the marrow in load-sharing. Bone is a viscoelastic material — its mechanical properties depend on the rate of loading. At high strain rates (high-energy trauma), bone behaves in a more brittle manner, with relatively little energy absorbed before fracture. At low strain rates, more energy is absorbed before failure. This property explains the different patterns of fracture seen in high-energy versus low-energy injuries.

Modes of Failure Bone can fail under several different loading modes, producing characteristic fracture patterns: Tension produces transverse fractures perpendicular to the long axis of the bone. Pure tension fractures are uncommon in clinical practice; they typically arise at sites of muscular insertion (avulsion fractures). Compression produces oblique fractures (at approximately 45° to the long axis) along the lines of maximum shear stress in compressive loading. Pure compression typically produces wedge-type vertebral compression fractures or compression fractures of metaphyseal bone (proximal tibial plateau). Bending produces a combination of tension on the convex side and compression on the concave side of the bend, with a characteristic transverse fracture on the tension side that may progress to a butterfly fragment on the compression side. The classical “boxer’s fracture” of the fifth metacarpal neck and many torus (buckle) fractures of children are examples of bending failures. Torsion produces spiral fractures around the long axis of the bone. The spiral fracture is highly characteristic of torsional failure and is seen classically in ski-related tibial fractures (with the ski as a long lever arm rotating the foot) and in non-accidental injuries in children (with rotational force applied to the limb). Shear produces fractures parallel to the loading direction. Pure shear fractures are uncommon as a single mode of loading. Combined loading in clinical reality produces fractures with components of multiple loading modes. The pattern of the fracture provides useful information about the mechanism of injury. Energy Considerations The energy delivered to the bone during the injury is a critical determinant of fracture severity and complexity. Low-energy injuries (a simple fall, a sports collision) typically produce simple fracture patterns with limited soft-tissue injury. High-energy injuries (motor vehicle accident, fall from height) produce comminuted fractures with extensive soft-tissue injury. The kinetic energy of an injury follows the equation E = (1/2)mv², emphasizing that velocity is the dominant determinant of energy — small increases in velocity produce dramatic increases in energy delivered to tissues. The classical example is the difference between a low-velocity gunshot wound (handgun) and a high-velocity gunshot wound (military rifle): the soft-tissue damage in the high-velocity injury is dramatically greater and extends far beyond the apparent wound track. Pathological Fractures A pathological fracture, by definition, is a fracture that occurs through abnormal bone — bone weakened by tumor (primary or metastatic), metabolic disease (osteoporosis,

osteomalacia, Paget’s disease), infection, or congenital anomaly (osteogenesis imperfecta). The forces required to produce a pathological fracture are often substantially less than for a normal-bone fracture, and the recognition of an underlying pathological process is essential to appropriate management.

Classification of Fractures

General Principles Fracture classification serves several purposes: communication between surgeons; prognosis (predicting outcomes from the fracture pattern); treatment guidance (specific patterns directing specific treatments); and research (allowing comparison of similar fracture patterns across studies). The principles of a useful classification system, articulated by Müller and others, include: completeness (covering all fractures in the relevant area); mutual exclusivity (each fracture fitting into one and only one category); reliability (different observers reaching the same classification); and validity (the classification predicting prognosis or guiding treatment). General Descriptive Categories Several descriptive categories apply to all fractures: Open vs closed: The presence or absence of a skin disruption communicating with the fracture. Open fractures (formerly “compound fractures”) have substantially higher rates of infection and other complications and require specific management. Simple vs comminuted: The number of fracture fragments. A simple fracture has two main fragments; a comminuted fracture has more than two fragments. Displaced vs non-displaced: Whether the fracture fragments have moved relative to each other or remain in anatomical alignment. Angulation, translation, rotation, shortening: The specific components of fracture displacement. Stable vs unstable: Whether the fracture can be expected to maintain reduction with simple immobilization (stable) or requires surgical fixation (unstable). Location: Diaphyseal, metaphyseal, epiphyseal, or intra-articular. The AO/OTA Classification The AO/OTA Comprehensive Classification of Fractures, developed by the AO Foundation and adopted as the international standard, classifies fractures by a five-element alphanumeric code: Bone: A number identifying the bone (1 — humerus, 2 — radius/ulna, 3 — femur, 4 — tibia/fibula, etc.; with further codes for the pelvis, spine, hand, and foot).

Segment: A number identifying the segment of the bone (1 — proximal, 2 — diaphyseal, 3 — distal). Type: A letter indicating the type of fracture (A, B, or C, with C being the most severe). For diaphyseal fractures: A — simple, B — wedge, C — complex. For metaphyseal and epiphyseal fractures: A — extra-articular, B — partial articular, C — complete articular. Group: A further subdivision (A1, A2, A3, B1, B2, B3, C1, C2, C3) reflecting specific patterns within each type. Subgroup: Further detail (e.g., A1.1, A1.2, A1.3) for specific anatomical variants. The system has the advantage of completeness, hierarchical organization, and international standardization. The disadvantages include complexity, with the full alphanumeric code being cumbersome in routine clinical practice. Specific Fracture Classifications Many specific classifications are used for particular fracture types, and these are addressed in the relevant anatomical chapters: Garden classification of femoral neck fractures; Pipkin classification of femoral head fractures; Russell-Taylor classification of subtrochanteric fractures; Schatzker classification of tibial plateau fractures; Lauge-Hansen and Weber classifications of ankle fractures; Sanders classification of calcaneal fractures; Frykman classification of distal radius fractures; Salter-Harris classification of physeal fractures; Tile and Young-Burgess classifications of pelvic ring fractures; and many others. Each classification provides specific information relevant to its anatomical region.

Classification of Soft-Tissue Injury

The classification of soft-tissue injury accompanying fractures is at least as important as the bony classification, since the soft-tissue damage often determines the complications and the ultimate outcome. Two principal classifications are used: Gustilo-Anderson classification of open fractures: Type I (clean wound <1 cm), Type II (wound 1-10 cm, no extensive soft-tissue damage), Type IIIA (extensive soft-tissue laceration with adequate bone coverage by soft tissues), Type IIIB (extensive soft-tissue damage requiring flap coverage), Type IIIC (vascular injury requiring repair). The classification correlates with infection rate and is the standard for open fracture management. Tscherne classification of closed fracture soft-tissue injury: Grade 0 (no soft-tissue injury), Grade I (superficial abrasion or contusion), Grade II (deep contused abrasion or focal skin or muscle contusion), Grade III (extensive skin contusion, muscle damage, severe degloving, compartment syndrome). The classification is useful for closed injuries and informs the timing of definitive surgery and the choice of fixation.

Dislocations and Subluxations

A dislocation is the complete loss of normal articular relationship between the joint surfaces. A subluxation is a partial loss of articular contact with persistent partial articular relationship. The classification of dislocations is generally by the direction of displacement (anterior, posterior, etc.) and by whether they are simple (without associated fracture) or complex (with associated fracture — fracture-dislocation). Specific classifications apply to specific joints: anterior, posterior, inferior shoulder dislocation; anterior, posterior, central hip dislocation; etc. The management principles of dislocations include: prompt reduction (delayed reduction increases the risk of avascular necrosis and other complications); assessment of associated injuries (fractures, neurovascular injury); and post-reduction immobilization and rehabilitation appropriate to the joint and the underlying injury.

Clinical Diagnosis of Fractures

The clinical diagnosis of fractures follows a systematic approach. History The history identifies the mechanism of injury (which suggests the likely fracture pattern and energy), the time of injury, the patient’s symptoms (pain, deformity, inability to bear weight), any associated injuries, the patient’s general medical condition, and any factors that might predispose to fragility fracture (advanced age, prior fragility fracture, corticosteroid therapy, metabolic disease). Physical Examination The physical examination assesses: Inspection: Deformity, swelling, ecchymosis, soft-tissue injury, open wounds, skin tension over fragment ends. Palpation: Tenderness localized to the fracture site (point tenderness over the bony prominence is highly suggestive of fracture); palpable step-off, gap, or crepitus (the abnormal mobility and grating sensation of fragments rubbing together — a sign that should be sought gently and only when needed because of the discomfort and the risk of additional soft-tissue injury). Range of motion: Loss of motion at the joint adjacent to the fracture; abnormal motion at the fracture site itself. Neurovascular assessment: The single most important component of the clinical examination of any fracture. Assessment of pulses distal to the fracture; capillary refill; sensation in the cutaneous distribution of each major nerve crossing the fracture; motor function of each muscle group innervated by these nerves. This examination must be documented in every case, and changes over time must be tracked and acted upon.

Compartments: Assessment of compartmental tension. Severe pain disproportionate to the apparent injury, pain on passive stretch of muscles within the compartment, sensory disturbance in the distribution of nerves within the compartment, and palpable compartmental tension are the cardinal features of compartment syndrome — discussed in detail in the chapter on compartment syndrome. Associated injuries: A systematic survey to identify other injuries that may have been missed during initial assessment. Cardinal Clinical Features of Fracture The classical clinical features of fracture include: pain (well-localized to the fracture site); swelling; deformity; loss of function; abnormal mobility; and crepitus. Not all features are present in every fracture; non-displaced fractures may have only pain and swelling, while severely displaced fractures show all of the cardinal features. Each fracture type has its own pattern of clinical presentation.

Radiographic Diagnosis

Plain Radiographs Plain radiographs remain the foundation of fracture imaging. The general principles include: Two orthogonal views: A single view can conceal substantial deformity in the perpendicular plane; two views at right angles to each other are mandatory for adequate assessment of any fracture. Include the joints above and below: A fracture in the diaphysis may have associated injury at the adjacent joints (the classical “Monteggia equivalent” of radius shaft fracture with proximal radioulnar dislocation, or the “Galeazzi equivalent” with distal radioulnar dislocation, are examples of why this principle matters). Apply standard projections appropriate to the region: Each anatomical region has specific projections that optimize visualization (mortise view for the ankle, Judet views for the acetabulum, etc.). Compare with the contralateral side when in doubt: Particularly useful in pediatric fractures where physeal lines can be confusing. Reassess as needed: Follow-up radiographs at 7-10 days can reveal initially occult fractures as fracture line resorption makes them more visible. CT and MRI CT is the imaging modality of choice for complex articular fractures (acetabulum, tibial plateau, distal radius, calcaneus), for fractures of complex anatomical regions (pelvis, spine), for assessment of fracture morphology when plain radiographs are inadequate, and increasingly as a primary imaging modality in major trauma. Three-dimensional reconstruction provides additional information for surgical planning.

MRI is the modality of choice for occult fractures (stress fractures, occult hip fractures), for assessment of associated soft-tissue and ligament injury, and for specific situations including suspected spinal cord injury and complex articular injuries. Other Imaging Bone scintigraphy is useful for occult fractures, stress fractures, and metastatic disease but is less commonly used in modern practice with the availability of MRI. Ultrasound has a limited role in fracture diagnosis but is increasingly used for soft-tissue and rib fractures and for selected pediatric fractures.

The Tertiary Survey

The tertiary survey — a comprehensive systematic examination of the trauma patient 24- 72 hours after admission — is a critical concept in trauma care. The principle is that injuries can be missed in the chaos of the initial trauma resuscitation, and a deliberate systematic re-examination after the patient is stable identifies these missed injuries. The tertiary survey includes head-to-toe examination, review of all imaging, and consideration of any new symptoms. Missed orthopedic injuries (rib fractures, hand fractures, foot fractures, vertebral fractures) are particularly common findings on tertiary survey.

General Principles of Fracture Management

The principles of fracture management, articulated by the AO Foundation and elaborated in modern fracture surgery, include the four cardinal goals: (1) anatomical reduction of fracture fragments, particularly for intra-articular fractures; (2) stable fixation appropriate to the fracture pattern and personality; (3) preservation of vascularity of the bone fragments and surrounding soft tissues; (4) early functional rehabilitation of the involved joint(s) and limb to prevent stiffness and atrophy. These principles have evolved over decades, with the more recent emphasis on “biological fixation” — preserving the soft-tissue envelope and the vascularity of fracture fragments, accepting less than perfect reduction in many cases in favor of preserving the biology necessary for healing. The development of locking plates, intramedullary nails, and minimally invasive techniques reflects this biological approach.

Summary and Take-Home Points

The classification, biomechanics, and diagnosis of fractures form the foundation of trauma orthopedics. Bone is an anisotropic, viscoelastic material that fails in predictable patterns under different loading modes — transverse from tension, oblique from compression, spiral from torsion, bending wedges, and combinations of these. The AO/OTA comprehensive classification provides international standardization, with specific classifications for each anatomical region addressing the particular features of that fracture type. Soft-tissue injury accompanying fractures is at least as important as the bony injury and is graded by the Gustilo-Anderson classification (open fractures) and Tscherne classification (closed injuries). Clinical diagnosis follows systematic history and physical examination with attention to neurovascular status and compartments. Plain radiographs

in two orthogonal views remain the foundation of imaging, with CT for complex articular and pelvic fractures and MRI for occult fractures and soft-tissue assessment. The four cardinal goals of fracture management — anatomical reduction (particularly for articular fractures), stable fixation, preservation of vascularity, and early functional rehabilitation — guide treatment decisions across all fracture types. The tertiary survey identifies missed injuries in the recovering trauma patient.