Sharp Purser Test: Purpose, Performance, and Clinical Significance

What is the Sharp Purser Test?

The Sharp Purser Test is a specific orthopedic clinical test used to assess the integrity of the transverse ligament of the atlas (C1) and the stability of the atlantoaxial joint (C1-C2) in the upper cervical spine. It is a critical screening tool for atlantoaxial instability.

Introduction to the Sharp Purser Test

Developed by Sharp and Purser, this diagnostic maneuver is a cornerstone in the physical examination of the cervical spine, particularly when evaluating potential instability at the craniovertebral junction. Its primary purpose is to identify excessive anterior translation of the atlas (C1) on the axis (C2), which can occur if the transverse ligament – a crucial stabilizing structure – is compromised. Identifying such instability is paramount because a displaced C1 could impinge upon the spinal cord, leading to severe neurological deficits or even life-threatening complications.

Anatomy and Biomechanics: Why This Test Matters

To understand the significance of the Sharp Purser Test, a brief review of the upper cervical anatomy is essential. The atlantoaxial joint is formed by the first two cervical vertebrae: the atlas (C1) and the axis (C2).

• Atlas (C1): A ring-shaped bone that supports the skull and articulates with the occiput above and the axis below. It lacks a vertebral body and spinous process.
• Axis (C2): Characterized by the dens (odontoid process), a tooth-like projection that extends superiorly from its body and acts as a pivot point for the atlas.
• Transverse Ligament: This strong, fibrous band stretches across the ring of the atlas, posterior to the dens. Its primary function is to hold the dens firmly against the anterior arch of the atlas, preventing excessive anterior translation of C1 on C2 and thus protecting the spinal cord from compression by the dens.

The atlantoaxial joint allows for significant rotation of the head, but its stability is heavily reliant on the integrity of the transverse ligament. If this ligament is lax or ruptured, the atlas can move excessively forward on the axis, potentially compressing the spinal cord located just posterior to the dens.

Purpose and Clinical Significance

The Sharp Purser Test serves as a vital screening tool for atlantoaxial instability (AAI). Conditions that can compromise the transverse ligament and lead to AAI include:

• Trauma: Especially high-impact injuries like whiplash, falls, or direct blows to the head/neck.
• Inflammatory Arthropathies: Rheumatoid arthritis is a common culprit, as chronic inflammation can erode ligaments and bone.
• Congenital Conditions: Such as Down syndrome, which is often associated with ligamentous laxity throughout the body.
• Connective Tissue Disorders: Ehlers-Danlos syndrome or Marfan syndrome.
• Other Conditions: Ankylosing spondylitis, psoriatic arthritis, or os odontoideum (a congenital anomaly of the dens).

Early identification of AAI is critical. Undiagnosed instability can lead to progressive neurological symptoms, including myelopathy (spinal cord dysfunction), radiculopathy (nerve root compression), vertigo, nystagmus, or even sudden death due to brainstem compression.

How to Perform the Sharp Purser Test

The test is typically performed by a trained healthcare professional, such as a physical therapist, chiropractor, or physician.

• Patient Positioning: The patient is usually seated, with their head in a comfortable, neutral position or slight flexion. Some clinicians may prefer a supine position.
• Therapist Positioning: The examiner stands beside the patient.
• Hand Placement and Execution:
  1. The examiner places one hand on the patient's forehead, stabilizing the head.
  2. The thumb or index finger of the other hand is placed on the spinous process of the axis (C2). This can be palpated just below the occiput.
  3. The examiner then applies a posteriorly directed force through the patient's forehead (moving the head backward) while simultaneously stabilizing C2.
• Observation: The examiner observes for any excessive movement, a "clunk" or "thud," or a reduction in the patient's symptoms during the application of the posterior force.

Interpreting the Results

Interpreting the findings of the Sharp Purser Test requires careful observation and clinical judgment.

• Positive Test: A positive test is indicated by:
  • Excessive anterior translation: The examiner feels the head move excessively posteriorly on C2.
  • A "clunk" or "thud": This audible or palpable sensation occurs as the atlas (C1) reduces posteriorly onto the axis (C2), indicating that it was previously displaced anteriorly.
  • Reduction of symptoms: If the patient was experiencing neurological symptoms (e.g., paresthesia, dizziness, nystagmus) prior to the test, these symptoms may temporarily decrease or disappear when the posterior force is applied and the C1-C2 joint is stabilized, only to return upon release of the force.
  • A positive test suggests laxity or rupture of the transverse ligament and atlantoaxial instability.
• Negative Test: A negative test occurs when there is no excessive translation, no clunk, and no change in the patient's symptoms during the maneuver. This suggests integrity of the transverse ligament and stability of the atlantoaxial joint.
• False Positives/Negatives: Like all clinical tests, the Sharp Purser Test is not 100% accurate. Factors such as muscle guarding, patient apprehension, or concurrent injuries can influence the results.

Limitations and Considerations

While valuable, the Sharp Purser Test has important limitations:

• Not a Definitive Diagnosis: It is a screening tool, not a definitive diagnostic test. A positive finding warrants immediate referral for further diagnostic imaging (e.g., X-rays in flexion/extension, CT, MRI) to confirm the diagnosis and assess the degree of instability.
• Clinical Judgment: The interpretation relies on the examiner's ability to perceive subtle movements and patient responses.
• Contraindications: The test should be performed with extreme caution or avoided entirely if there are clear signs of severe neurological deficit, acute trauma with suspected fracture, or if the patient expresses significant apprehension or pain during initial positioning.
• Comprehensive Assessment: It should always be part of a broader clinical examination, including a thorough history, neurological assessment, and other specific cervical spine tests.

Who Benefits from This Test?

The Sharp Purser Test is particularly indicated for individuals who present with:

• A history of significant cervical trauma, especially those involving hyperflexion or hyperextension.
• Systemic inflammatory conditions like rheumatoid arthritis affecting the cervical spine.
• Congenital conditions such as Down syndrome.
• Symptoms suggestive of upper cervical instability, including:
  • Occipital headaches or neck pain.
  • Neurological symptoms (numbness, tingling, weakness in the limbs).
  • Dizziness, vertigo, or nystagmus.
  • Gait disturbances or balance issues.
  • Feeling of "instability" or a "clunking" sensation in the neck.

Conclusion

The Sharp Purser Test remains an indispensable tool in the assessment of upper cervical spine stability. Its ability to screen for potentially life-threatening atlantoaxial instability makes it a critical component of any thorough musculoskeletal or neurological examination of the neck. However, its application demands a skilled and knowledgeable practitioner, and any positive findings necessitate immediate referral for comprehensive medical evaluation and advanced imaging to ensure appropriate management and prevent adverse neurological outcomes. Always consult with a qualified healthcare professional for diagnosis and treatment of any health concerns.