Distal radius fracture pathophysiology

The pattern of fracture and degree of comminution are the resultant of several factors or variables such as the nature of the fall, the bone quality, the age and weight of the patient, the energy involved, and the position of the hand and wrist at the time of impact. Various combinations of these variables lead to a variety of different fracture patterns.

• The fracture pattern and severity of comminution depends on multiple factors including:
  • Nature of the fall
  • Bone quality
  • Age of the patient
  • Weight of the patient
  • Energy involved
  • Position of the hand and wrist at the time of impact
• Decrease in bone mass density involves following process:^[1]
  • Autophagy is the mechanism through which osteocytes evade oxidative stress.
  • The capability of autophagy in cells decreases as they age, a major factor of aging.
  • As osteocytes grow, viability of cells decrease thereby decreasing the bone mass density.

• Mechanism of fracture may be described as follows:^{[2][3][4][5][6][7][8][9]}
  • The majority of the distal radius fractures are caused by a fall on the outstretched hand with the wrist in dorsiflexion.
  • The form and severity of fracture of distal radius as well as the concomitant injury of disco-ligamentary structures of the wrist depends on the position of the wrist at the moment of hitting the ground.
  • The width of the angle influences the localization of the fracture.
  • Pronation, supination, and abduction determine the direction of the force and the compression of carpus and different appearances of ligamentary injuries.
  • The radius initially fails in tension on the volar aspect, with the fracture progressing dorsally where bending forces induce compressive stresses, resulting in dorsal comminution.
  • As the deformation of the wrist continues, the ulnar styloid may also fracture due to the attachment of the triangular fibrocartilage complex to its base and the distal radius.
  • In elderly osteoporotic patients, the distal ulna may fracture through the metaphysis.
  • Cancellous impaction of the metaphysis further compromises dorsal stability.
  • Additional shearing forces influence the injury pattern, resulting in articular surface involvement.
  • Distal radius fractures typically occur with the wrist bent back from 60 to 90 degrees.
  • Radial styloid fracture would occur if the wrist is ulnar deviated and vice versa.
  • If the wrist is less dorsifelxed, then proximal forearm fracture would occur, but if the dorsiflexion is more, then the carpal bones would fracture.

• The articular surface of the distal aspect of the radius tilts 21 degrees in the antero-posterior plane and 5 to 11 degrees in the lateral plane.^[3][4]
• The dorsal cortical surface of radius thickens to form the Lister tubercle as well as osseous prominences that support the extensors of the wrist in second dorsal compartment.
• A central ridge divides the articular surface of the radius into a scaphoid facet and a lunate facet.
• The triangular fibrocartilage extends from the rim of the sigmoid notch of the radius to the ulnar styloid process.
• Only the brachioradialis tendon inserts onto the distal aspect of the radius; the other tendons of the wrist pass across the distal aspect of the radius to insert onto the carpal bones or the bases of the metacarpals.
• In addition to the extrinsic ligaments of the wrist, the scapholunate interosseous and lunotriquetral interosseous ligaments maintain the scaphoid, lunate, and triquetrum in a smooth articular unit that comes into contact with the distal aspect of the radius and the triangular fibrocartilage complex.
• Because of the different areas of bone thickness and density, the fracture patterns tend to propagate between the scaphoid and lunate facets of the distal aspect of the radius.
• The degree, direction, and extent of the applied load may cause coronal or sagittal splits within the lunate or scaphoid facet.

Conditions associated with poor bone quality leading to distal radius fracture include:^[4]

• Osteoporosis
• Osteopenia
• chronic stroke
• Diabetes
• Rheumatoid arthritis
• Chronic kidney disease
• Hyperparathyroidism
• Hypophosphatemic rickets
• Immobility
• Menopause
• Multiple myeloma
• Mixed connective tissue disease
• Paget’s disease of bone
• Primary hypoparathyroidism
• Short stature
• Chronic corticosteroid use

On gross pathology, decreased bone density and small pores in diaphysis of bones are characteristic findings of osteoporosis, leading to distal radius fracture.^[4]

• On microscopy, characteristic findings of bone with osteoporosis is increased number of osteoclasts and decreased number of osteoblasts under the microscope.^[1]

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