Dislocation and Subluxation

A dislocation is the complete displacement of the bones forming a joint so that their articular surfaces lose all contact, while a subluxation is a partial displacement in which some contact between the surfaces is retained. Both result from forces that overcome the joint's stabilizing capsule and ligaments, and both can damage the surrounding soft tissues, cartilage, nerves, and vessels.

Definition

A dislocation is the complete loss of contact between the articular surfaces of a joint, and a subluxation is a partial displacement in which the surfaces remain in incomplete contact; both denote a disruption of normal joint congruity.

Scope

This entry covers the definitions and distinctions of dislocation and subluxation, the soft-tissue and bony structures whose failure permits displacement, the concept of fracture-dislocation, and the recurrence that may follow a first dislocation. It treats these as reference concepts within orthopedic trauma and does not provide reduction techniques or management instructions.

Core questions

• How do dislocation and subluxation differ in degree of displacement?
• Which structures normally maintain joint congruity, and how does their failure allow displacement?
• What is a fracture-dislocation?
• Why may a joint dislocate repeatedly after a first event?

Key concepts

• Loss of articular congruity
• Complete dislocation versus subluxation
• Capsuloligamentous restraint
• Fracture-dislocation
• Recurrent dislocation
• Associated neurovascular injury
• Reduction (concept of restoring congruity)

Mechanisms

A joint stays congruent through the combined restraint of its bony architecture, capsule, ligaments, and surrounding muscles. When an applied force exceeds these restraints, the articular surfaces displace: complete separation produces a dislocation, partial separation a subluxation. The same force may avulse or fracture the bone at the joint margin, producing a fracture-dislocation, which is recognized within the dislocation portion of the Marsh et al. (2007) classification framework. Displacement can stretch or tear the capsule and ligaments and may injure adjacent nerves and vessels. Once the stabilizing structures are damaged, the joint may be predisposed to displace again under lower loads, the basis of recurrent dislocation.

Clinical relevance

Dislocation and subluxation are common acute joint injuries whose recognition and classification inform communication and research in orthopedics and emergency care. Because displacement can compromise nearby nerves and vessels and damage cartilage, the concepts are important for understanding injury severity. This entry describes the phenomena and is not a basis for individual diagnosis or treatment.

Epidemiology

Dislocations occur at characteristic joints with characteristic mechanisms; the shoulder (glenohumeral joint) is the most frequently dislocated major joint, reflecting its wide range of motion and relatively shallow socket. Court-Brown and Caesar (2006), in summarizing adult musculoskeletal injury, situate dislocations alongside fractures in the broader epidemiology of skeletal trauma.

History

Reduction of dislocated joints is among the oldest recorded orthopedic interventions, described since antiquity. Modern practice added systematic classification of dislocations and fracture-dislocations, integrated into the AO/OTA compendium, and a growing understanding of how capsuloligamentous damage at the time of dislocation predisposes to instability and recurrence.

Key figures

• J. Lawrence Marsh
• Charles Court-Brown

Seminal works

• marsh-2007
• court-brown-caesar-2006

Frequently asked questions

What is the difference between a dislocation and a subluxation?

A dislocation is complete loss of contact between the joint surfaces, whereas a subluxation is partial displacement in which the surfaces remain in incomplete contact.

What is a fracture-dislocation?

A fracture-dislocation is an injury in which a joint is dislocated and a bone forming that joint is also fractured, often at the joint margin, combining loss of congruity with a break in the bone.