Avulsion

Avulsion (from Latin avulsio, meaning tearing away) is a type of traumatic injury characterized by the complete or forcible separation of a part of an organ or tissue from its main body. The term is used across multiple fields of medicine, most commonly in traumatology to describe avulsion fractures, and in surgery to denote detachment of soft tissues.

The defining mechanism of an avulsion injury is the application of excessive tensile force to an anatomical structure, such that the tensile strength of the tissue itself or its site of attachment is exceeded.

Types of Avulsion Injuries

Depending on the tissue involved, avulsion injuries present differently and require distinct treatment approaches.

• Avulsion fracture: The most common usage of the term. Occurs when a strong ligament or tendon, during sudden muscle contraction, pulls off a fragment of bone at its attachment site. Examples: avulsion fracture of the base of the fifth metatarsal bone following an ankle inversion injury; pelvic avulsion fractures in young athletes during jerky movements.
• Soft Tissue avulsion (degloving Injury): Partial or complete separation of a skin and subcutaneous tissue flap from the underlying fascia and muscles. These injuries frequently occur in motor vehicle accidents. Examples: degloving injuries of an extremity or the scalp.
• Tendon or nerve avulsion: Complete detachment of a tendon from its bony insertion, or avulsion of a nerve root from the spinal cord (e.g., in brachial plexus trauma).
• Dental avulsion (dislocation): Complete displacement of a tooth from its socket (alveolus) as a result of trauma. This constitutes a dental emergency.

Pathophysiology and Clinical Significance

The pathophysiology of avulsion fractures is related to the fact that, in certain regions of the skeleton (particularly in children and adolescents at apophyseal sites) the tensile strength of a tendon or ligament exceeds that of the bone to which it attaches. Under critical load, this results in bone avulsion rather than ligament or tendon rupture.

Clinical presentation depends on the type of injury. Avulsion fractures are characterized by acute localized pain, swelling, hematoma formation, and impaired function of the corresponding muscle. Skin avulsions result in extensive open wounds with compromised blood supply to the avulsed flap.

Diagnosis of avulsion fractures is based primarily on radiography, which typically demonstrates a displaced bone fragment. Treatment may be conservative (immobilization) in cases of minimal displacement, or surgical in cases of significant displacement, usually involving osteosynthesis with screws or Kirschner wires. Management of soft tissue avulsions is always surgical and often requires complex plastic and reconstructive procedures.

Differential Diagnosis

Avulsion fractures must be differentiated from complete ligament or tendon ruptures and from muscle strains. Clinical presentation may be similar. However, localized bone tenderness and characteristic radiographic findings usually allow accurate diagnosis. In equivocal cases, ultrasound or MRI may be used to assess soft tissue integrity. A simple laceration should be distinguished from a true avulsion injury, in which there is extensive undermining and separation of a tissue flap. The latter indicates a more severe injury with a high risk of flap necrosis.