Subluxation: Understanding Joint Displacement, Biomechanical Angles, and Management

What is the angle of subluxation?

While there isn't a single, universally defined "angle of subluxation" in medical or biomechanical terminology, subluxation refers to a partial or incomplete dislocation of a joint, where the joint surfaces lose their normal alignment but remain in partial contact. The concept of "angle" in relation to subluxation often pertains to specific anatomical measurements or the direction of displacement that predisposes or characterizes a particular joint's subluxation.

Understanding Subluxation: A Foundation

Subluxation is a clinical term describing a state where the articulating surfaces of a joint are no longer perfectly aligned, but still maintain some degree of contact. This differs from a full dislocation (luxation), where there is a complete separation of the joint surfaces. Subluxations can occur in various joints throughout the body, from the spine to the major appendicular joints like the shoulder and knee.

The impact of a subluxation can range from mild discomfort and temporary instability to significant pain, restricted movement, and potential long-term joint damage if left unaddressed. It often involves injury to the surrounding soft tissues, including ligaments, tendons, and joint capsules, which are critical for joint stability.

The Nuance of "Angle" in Subluxation

The phrase "angle of subluxation" is not a standard diagnostic or descriptive term used to quantify the degree of partial displacement in a subluxated joint. Unlike specific anatomical angles (e.g., Q-angle of the knee, angle of inclination of the femoral neck) that are measured for diagnostic purposes or to assess biomechanical alignment, a singular "angle of subluxation" does not exist as a universal metric.

Instead, when discussing subluxation, the focus is typically on:

• Direction of Displacement: For example, anterior, posterior, lateral, or inferior subluxation.
• Degree of Displacement: Described qualitatively (e.g., mild, moderate, severe) or sometimes quantitatively in millimeters, particularly in spinal imaging.
• Associated Biomechanical Angles: Certain pre-existing anatomical angles or alignments can predispose a joint to subluxation, or changes in these angles may be observed alongside a subluxation. These are not the "angle of subluxation" itself, but rather factors influencing joint stability.

Joint-Specific Considerations and Relevant Biomechanical Angles

While there's no universal "angle of subluxation," understanding the specific biomechanics and common angles associated with certain joints helps clarify the concept.

Patellar Subluxation

The patella (kneecap) commonly subluxates laterally (outward). Several angles and anatomical features are highly relevant here:

• Q-angle (Quadriceps Angle): This is the angle formed by a line from the anterior superior iliac spine (ASIS) to the center of the patella, and a second line from the center of the patella to the tibial tubercle. A larger Q-angle (typically >15-20 degrees) can increase the lateral pull on the patella, predisposing it to subluxation.
• Trochlear Dysplasia: The trochlear groove of the femur, where the patella glides, can be abnormally shallow or flat, reducing its ability to contain the patella and increasing the risk of subluxation.
• Patellar Tilt: An angle indicating how much the patella is tilted laterally within the trochlear groove, observable on imaging.

Shoulder (Glenohumeral) Subluxation

The shoulder is the most mobile joint in the body, making it prone to subluxation, often anteriorly or inferiorly. While no specific "angle of subluxation" is measured, biomechanical factors include:

• Glenoid Version: The orientation of the glenoid fossa (shoulder socket) relative to the scapula. Excessive retroversion (pointing backward) or anteversion (pointing forward) can affect stability.
• Humeral Head Retroversion: The angle of the humeral head relative to the humeral shaft.
• Labral Tears: Damage to the glenoid labrum, a rim of cartilage that deepens the socket, can reduce stability and lead to recurrent subluxations.

Vertebral Subluxation (Chiropractic Context)

In chiropractic, vertebral subluxation refers to a misalignment of spinal vertebrae that is believed to interfere with nerve function. While highly debated within the broader medical community, chiropractors often assess spinal alignment using:

• Angles of Curvature: Measuring the natural curves of the spine (cervical lordosis, thoracic kyphosis, lumbar lordosis) and identifying deviations.
• Segmental Misalignment: Assessing the relative position of one vertebra to an adjacent one in sagittal, coronal, or axial planes, often described in terms of degrees of rotation or millimeters of translation.

Radial Head Subluxation (Nursemaid's Elbow)

This common injury in young children occurs when the radial head (forearm bone at the elbow) is pulled partially out of the annular ligament, often due to a sudden pull on the arm. There is no "angle" associated with this specific subluxation; it's a mechanical displacement of the radial head from the ligament.

Diagnosing Subluxation

Diagnosis of subluxation typically involves:

• Clinical Examination: A thorough physical assessment by a healthcare professional (e.g., physician, physical therapist, chiropractor). This includes palpation, range of motion assessment, special tests to assess joint stability, and neurological examination.
• Imaging Studies:
  • X-rays: To visualize bone alignment and rule out fractures.
  • MRI (Magnetic Resonance Imaging): To assess soft tissue structures like ligaments, tendons, and cartilage, which are often injured in subluxations.
  • CT Scans (Computed Tomography): Provides detailed bone imaging, useful for assessing complex joint anatomy or subtle displacements.

Causes and Risk Factors

Subluxations can be caused by:

• Trauma: Direct impact, falls, or sudden twisting movements (e.g., sports injuries, car accidents).
• Repetitive Strain: Overuse or repetitive motions that stress a joint over time.
• Ligamentous Laxity: Inherited hypermobility or acquired laxity due to previous injuries, leading to reduced joint stability.
• Muscle Imbalance/Weakness: Insufficient strength or coordination of muscles surrounding a joint can compromise its stability.
• Anatomical Abnormalities: Congenital or developmental variations in joint structure (e.g., shallow joint sockets, abnormal bone shapes) that predispose to instability.
• Neuromuscular Conditions: Conditions affecting nerve and muscle control can lead to poor joint stabilization.

Management and Rehabilitation

Management of subluxation depends on the joint, severity, and underlying cause, but generally involves:

• Acute Care:
  • Reduction: In some cases, a healthcare professional may need to manually guide the joint back into proper alignment.
  • Immobilization: Bracing or splinting may be used temporarily to protect the joint and allow healing.
  • Pain and Inflammation Management: RICE (Rest, Ice, Compression, Elevation), NSAIDs (non-steroidal anti-inflammatory drugs).
• Rehabilitation: A cornerstone of recovery, often guided by a physical therapist or kinesiologist.
  • Restoration of Range of Motion: Gentle exercises to regain full movement.
  • Strengthening: Progressive exercises to build strength in surrounding muscles, improving joint stability.
  • Proprioception and Neuromuscular Control: Exercises to re-educate the body's awareness of joint position and improve muscle coordination for dynamic stability.
  • Activity Modification: Adjusting activities to prevent re-injury.
• Surgery: In cases of recurrent subluxations, significant soft tissue damage (e.g., severe labral tears), or persistent instability, surgical intervention may be necessary to repair damaged structures or improve joint mechanics.

When to Seek Professional Help

It is crucial to seek immediate medical attention if you suspect a subluxation or dislocation, especially if accompanied by:

• Severe pain
• Visible deformity of the joint
• Inability to move the joint
• Numbness or tingling in the limb (indicating potential nerve involvement)
• Swelling and bruising

Even if symptoms are mild, consulting a healthcare professional is advisable to receive an accurate diagnosis, rule out more serious injuries, and develop an appropriate treatment and rehabilitation plan to prevent chronic instability and future complications.

Conclusion

While the term "angle of subluxation" is not a precise, universally accepted medical measurement, understanding subluxation involves appreciating the partial displacement of joint surfaces. The severity and direction of this displacement, alongside specific biomechanical angles and anatomical features that predispose to instability, are the true focus. Proper diagnosis and a comprehensive rehabilitation strategy, often guided by an exercise science professional, are essential for restoring joint function and preventing recurrence.