Joint Dislocations: Classification by Severity, Cause, Skin Integrity, and Direction

What are the Classification of Dislocations?

Dislocations, which involve the displacement of bones at a joint, are classified based on several key factors including the completeness of separation, the underlying cause, the integrity of the overlying skin, and the specific direction of displacement, each influencing diagnosis and treatment strategies.

Understanding Joint Dislocation

A joint dislocation, medically known as a luxation, occurs when the bones that form a joint are forced out of their normal alignment, resulting in a complete separation of the joint surfaces. This disrupts the structural integrity and function of the joint. A less severe form, known as a subluxation, involves a partial or incomplete dislocation where the joint surfaces remain in partial contact, but their normal relationship is altered. Understanding the various classifications of dislocations is crucial for accurate diagnosis, appropriate treatment, and predicting recovery.

Classification by Severity

The most fundamental classification relates to the degree of displacement:

• Complete Dislocation (Luxation): This signifies a total loss of contact between the articular surfaces of the bones forming the joint. For example, in a complete shoulder dislocation, the head of the humerus is entirely out of the glenoid cavity.
• Partial Dislocation (Subluxation): In a subluxation, the joint surfaces are still partially in contact, but their normal anatomical alignment is compromised. This is common in conditions like patellar subluxation, where the kneecap partially shifts out of its groove.

Classification by Cause (Etiology)

The mechanism or underlying reason for the dislocation provides another critical classification:

• Traumatic Dislocations: These are the most common type, resulting from an external force or injury that exceeds the joint's stability limits. Examples include falls, sports injuries, or motor vehicle accidents. The force can be direct or indirect, causing the bones to be suddenly displaced.
• Pathological Dislocations: These occur due to underlying disease or condition that weakens the joint structures (ligaments, capsule, bone). This can include inflammatory conditions (e.g., rheumatoid arthritis), infections (e.g., septic arthritis), tumors, or neuromuscular disorders that lead to joint instability without significant trauma.
• Congenital/Developmental Dislocations: Present at birth or developing early in life, these dislocations are due to abnormalities in joint development. The most well-known example is Developmental Dysplasia of the Hip (DDH), where the hip joint does not form correctly, leading to instability or dislocation.
• Voluntary/Habitual Dislocations: Less common, these dislocations occur due to an individual's ability to intentionally dislocate and reduce their own joint, often without pain. This can be due to generalized ligamentous laxity or learned behavior. Habitual dislocations, on the other hand, are recurrent dislocations that occur with minimal force or even during normal activities, often following an initial traumatic event that stretched or damaged the joint capsule and ligaments.

Classification by Integrity of Overlying Skin

This classification is vital for assessing the risk of infection and guiding immediate medical management:

• Closed (Simple) Dislocations: The skin overlying the dislocated joint remains intact. While severe, these carry a lower risk of infection compared to open dislocations.
• Open (Compound) Dislocations: The dislocated bone or joint capsule has punctured the skin, creating an open wound. This type is a medical emergency due to the high risk of contamination and infection, requiring immediate surgical intervention and antibiotic prophylaxis.

Classification by Direction of Displacement

For many joints, the specific direction in which the bones are displaced is a crucial descriptive classification, informing reduction techniques and prognosis:

• Anterior Dislocation: The dislocated bone segment moves forward (anteriorly) relative to its normal position. This is the most common direction for shoulder dislocations (anterior glenohumeral dislocation).
• Posterior Dislocation: The dislocated bone segment moves backward (posteriorly). This is less common in the shoulder but can occur with specific trauma, and is also seen in hip dislocations (posterior hip dislocation is common in dashboard injuries).
• Inferior/Superior Dislocation: The bone moves downwards (inferiorly) or upwards (superiorly). For example, luxatio erecta is a rare inferior shoulder dislocation where the arm is fixed in an overhead position.

Common Joints Prone to Dislocation

While any synovial joint can dislocate, some are more susceptible due to their anatomy and range of motion:

• Shoulder (Glenohumeral Joint): Most commonly dislocated joint due to its high mobility.
• Fingers and Toes: Often dislocated during sports or falls.
• Patella (Kneecap): Can dislocate laterally.
• Elbow: Often seen in falls, especially in children.
• Hip: Requires significant force, often associated with major trauma.
• Jaw (Temporomandibular Joint - TMJ): Can dislocate during yawning or wide opening of the mouth.

Importance of Accurate Classification

Accurate classification of a dislocation is paramount for several reasons:

• Diagnosis: Guides the physical examination and imaging studies (X-rays, MRI) needed to confirm the dislocation and assess associated injuries.
• Treatment Planning: Determines the appropriate method of reduction (manual manipulation vs. surgical intervention), the need for immobilization, and rehabilitation protocols.
• Prognosis: Helps predict the likelihood of recurrence, potential complications (e.g., nerve damage, avascular necrosis), and long-term joint stability.

Seeking Professional Medical Attention

Any suspected dislocation requires immediate medical attention. Attempting to reduce a dislocation without proper medical training can cause further damage to nerves, blood vessels, ligaments, or the joint surfaces. A healthcare professional will correctly diagnose the type of dislocation and implement the safest and most effective treatment plan.