Anatomy of Common Fractures
Fractures are among the most common presentations in emergency medicine and orthopaedics. Understanding the anatomy of the bones most frequently broken — and why they break where they do — is essential for recognising injury patterns, anticipating complications, and planning treatment. This guide is for educational purposes only.
## Why Anatomy Predicts Fracture Patterns
Bone geometry, blood supply, and the forces transmitted through joints determine not only which bones fracture but precisely where the fracture line will run. Cortical (compact) bone is stronger under compression than tension; cancellous (trabecular) bone is better at distributing load. Fractures occur when applied force exceeds the bone's tensile, compressive, or shear strength. The pattern — transverse, oblique, spiral, comminuted — reflects the direction and magnitude of force.
## Colles Fracture: Distal Radius
The Colles fracture is the most common fracture in adults under 75, typically produced by a fall on an outstretched hand (FOOSH mechanism). The fracture occurs within 2–3 cm of the distal radial articular surface. The distal fragment is displaced dorsally and radially, producing the classic "dinner fork" deformity on lateral radiograph. The radial styloid is often fractured simultaneously. Key anatomical neighbours at risk include the median nerve (which runs through the carpal tunnel just distal to the fracture site), the extensor tendons in their compartments (particularly the extensor pollicis longus, which runs around Lister's tubercle and is at risk of delayed rupture), and the distal radioulnar joint (DRUJ), which is disrupted in approximately 60% of cases. In elderly patients with osteoporosis, the fracture is often comminuted. In younger patients, the same mechanism more commonly produces a scaphoid fracture because the stronger distal radius transmits force to the carpus.
## Scaphoid Fracture
The scaphoid is the most commonly fractured carpal bone, accounting for approximately 70% of carpal fractures. It is fractured by FOOSH with the wrist in dorsiflexion and radial deviation. The fracture most commonly occurs at the waist (middle third) of the scaphoid — a point of anatomical weakness. The blood supply to the scaphoid is tenuous: the major vascular supply enters distally via the dorsal ridge branches of the radial artery and flows retrogradely (distal to proximal) to the proximal pole. A waist or proximal pole fracture therefore jeopardises the blood supply to the proximal fragment, predisposing to avascular necrosis (AVN) — a complication that occurs in 30–40% of untreated waist fractures and in the majority of displaced proximal pole fractures. Clinical diagnosis relies on tenderness in the anatomical snuffbox (bordered by extensor pollicis longus posteriorly and abductor pollicis longus and extensor pollicis brevis anteriorly) and on the scaphoid tubercle volarly. Plain radiographs miss up to 20% of scaphoid fractures acutely; MRI or CT is recommended when clinical suspicion is high and X-rays are negative.
## Hip Fracture: Proximal Femur
Hip fractures — fractures of the proximal femur — are a major public health problem, predominantly affecting elderly women with osteoporosis. Anatomically, proximal femur fractures are classified by their relation to the joint capsule. Intracapsular fractures (subcapital, transcervical, basicervical) carry a high risk of AVN of the femoral head because the blood supply to the femoral head (primarily the medial femoral circumflex artery, a branch of the profunda femoris, which anastomoses with the lateral femoral circumflex artery to form a ring at the base of the neck) is disrupted. The artery of the ligamentum teres (from the obturator artery) contributes a minor supply that is insufficient to maintain the femoral head alone. Extracapsular fractures (intertrochanteric, subtrochanteric) have a better blood supply prognosis but are associated with greater blood loss (the trochanteric and subtrochanteric regions are well-vascularised cancellous bone) and more complex biomechanical forces. Surgical management (hemiarthroplasty for displaced intracapsular fractures, dynamic hip screw or intramedullary nail for extracapsular fractures) is guided entirely by this anatomical classification.
## Ankle Fractures: Weber Classification
Ankle fractures involve the lateral malleolus (distal fibula), medial malleolus (distal tibia), and/or posterior malleolus (posterior lip of the tibial plafond). The Danis-Weber classification is based on the level of the fibular fracture relative to the syndesmosis (the fibrous joint between the distal tibia and fibula, stabilised by the anterior and posterior inferior tibiofibular ligaments, the interosseous membrane, and the transverse tibiofibular ligament). Weber A fractures are below the syndesmosis (the fibula fractures below the level of the ankle joint) — the syndesmosis is intact and the fracture is typically stable. Weber B fractures are at the level of the syndesmosis — the syndesmosis may or may not be disrupted; stability is assessed clinically and under fluoroscopy. Weber C fractures are above the syndesmosis — the syndesmosis is disrupted, the ankle mortise (the "mortise" formed by the tibia and fibula that receives the talus) is widened, and surgical stabilisation is usually required. The medial side of the ankle is stabilised by the deltoid ligament (a powerful fan-shaped ligament from the medial malleolus to the talus, navicular, and calcaneus); its disruption (as a tear or as an avulsion fracture of the medial malleolus) combined with a Weber C fibular fracture produces the unstable bimalleolar equivalent fracture.
## Vertebral Compression Fractures
Vertebral compression fractures (VCFs) are the most common osteoporotic fracture, occurring predominantly in the thoracic (T8–T12) and thoracolumbar (T12–L2) regions. The thoracolumbar junction is particularly susceptible because the relatively immobile, kyphotic thoracic spine meets the mobile, lordotic lumbar spine here, concentrating stress at this transition zone. Compression fractures involve failure of the anterior column (the anterior two-thirds of the vertebral body) under compressive loading, typically from forward flexion. The posterior elements (pedicles, laminae, facets, spinous process) and the posterior longitudinal ligament remain intact in a simple wedge fracture, making it mechanically stable. Burst fractures involve failure of both anterior and posterior cortices of the vertebral body under axial loading; bony fragments may be retropulsed into the spinal canal, threatening the spinal cord (at thoracic levels) or the conus medullaris and cauda equina (at the thoracolumbar junction and lumbar levels). Neurological assessment and CT/MRI imaging determine whether the fracture requires surgical decompression and stabilisation.
## Fracture Healing
Bone healing progresses through four overlapping phases. The haematoma phase (days 1–5) involves clot formation at the fracture site and an acute inflammatory response. The soft callus phase (days 5–21) sees invasion of the haematoma by fibroblasts and chondroblasts forming a fibrocartilaginous callus (visible on X-ray as a fluffy opacity around the fracture ends). The hard callus phase (weeks 3–12) involves mineralisation of the callus by osteoblasts, initially as woven (immature) bone. The remodelling phase (months to years) replaces woven bone with lamellar (mature) bone according to Wolff's law, restoring cortical continuity and gradually resorbing surplus callus. This process requires adequate blood supply, mechanical stability, and nutritional support (calcium, vitamin D, protein). Impaired healing (delayed union, non-union) occurs with infection, poor blood supply, excessive motion, or systemic disease.