Sharp purser test: Procedure, interpretation, and diagnostic accuracy

Key Takeaways

The sharp purser test detects atlantoaxial instability by assessing the integrity of the transverse ligament of the atlas at the C1-C2 joint

A positive result is indicated by a clunk or slide sensation and/or relief of the patient’s presenting symptoms during posterior head glide

Published diagnostic accuracy values (Uitvlugt & Indenbaum, 1988) report sensitivity of ~69% and specificity of ~96% in an RA population; a single positive result is not diagnostic in isolation

Pabau’s digital patient records and clinical documentation tools help physiotherapy and musculoskeletal clinics capture contraindication screens and assessment findings accurately

Performing a manual upper cervical stability assessment on the wrong patient can carry serious neurological risk. The sharp purser test is one of the most frequently taught clinical tools for detecting atlantoaxial instability, yet misapplication, poor documentation, and incomplete contraindication screening remain persistent problems in clinical practice.

This guide covers the anatomy, procedure, result interpretation, and diagnostic accuracy of the sharp purser test, with practical guidance on when it is and is not appropriate to use.

This reference is written for physiotherapists, chiropractors, sports medicine clinicians, and musculoskeletal practitioners who perform or supervise upper cervical assessments. It assumes familiarity with cervical spine anatomy and clinical examination principles. Links throughout connect to physiotherapy clinic compliance resources and practice management tools that support safe clinical workflows.

What is the sharp purser test and what does it assess?

The sharp purser test is a clinical orthopedic examination used to assess the integrity of the transverse ligament of the atlas at the atlantoaxial (C1-C2) joint. When this ligament is lax or ruptured, the atlas can translate anteriorly on the axis, compressing the spinal cord. The test applies a controlled posterior force to the patient’s head to detect abnormal anterior translation of the atlas relative to C2.

First described by Sharp and Purser in 1961 in their research on spontaneous atlanto-axial dislocation in ankylosing spondylitis and rheumatoid arthritis, the test has since become a standard component of upper cervical screening protocols in physiotherapy and chiropractic education. The American Physical Therapy Association (APTA) includes it in their evidence-based practice resources as an assessment for atlantoaxial instability secondary to transverse ligament laxity or rupture.

The test targets a specific anatomical failure mode: transverse ligament insufficiency. It does not assess alar ligament integrity, odontoid fracture, or broader cervical instability patterns. This distinction matters for clinical decision-making.

Anatomy: The transverse ligament of the atlas and atlantoaxial joint

The transverse ligament of the atlas (TAL) is the primary stabiliser of the atlantoaxial joint. It runs horizontally across the ring of C1, holding the odontoid process (dens) of C2 against the anterior arch of the atlas. Without intact TAL function, anterior translation of C1 relative to C2 is unconstrained, and the dens can impinge on the spinal cord.

Normal atlanto-dens interval (ADI) in adults is 3mm or less on lateral flexion-extension radiographs. Values above 3mm in adults (or 5mm in children) indicate pathological anterior translation and raise suspicion for TAL disruption. The sharp purser test attempts to reproduce and then reduce this translation manually, making the anatomy of the C1-C2 articulation central to interpreting what you feel during the examination.

Three anatomical facts shape how you interpret the test:

• The TAL is the primary restraint to anterior translation; the alar ligaments contribute secondarily.
• The dens occupies approximately 50% of the available space in the C1 ring; the other 50% is divided between the spinal cord and surrounding soft tissue (“Steele’s rule of thirds”).
• Rheumatoid pannus formation can erode the odontoid and compromise TAL attachment, producing instability even before the ligament itself ruptures.

Clinical indications: when to perform the sharp purser test

The sharp purser test is not a routine screening tool for all neck pain presentations. It is indicated when the clinical history raises suspicion for upper cervical ligament instability. For practitioners starting a physiotherapy clinic or expanding into musculoskeletal assessment, having clear criteria for when to apply the test is essential.

Three clinical populations carry the highest pre-test probability of atlantoaxial instability:

In practice, the most common indication remains rheumatoid arthritis. Many physiotherapy guidelines recommend screening for upper cervical instability before any cervical mobilisation or manipulation in RA patients. Clinics with a significant musculoskeletal caseload should have a clear referral pathway and documentation protocol for this population. The sports medicine and physiotherapy contexts also encounter hypermobility-related instability in younger athletic populations.

Contraindications and safety precautions for the sharp purser test

The sharp purser test involves applying a posterior translatory force to the upper cervical spine. Applied incorrectly, or in the presence of absolute contraindications, this manoeuvre risks compressing a spinal cord that is already compromised. Clinical compliance workflows should include a contraindication check as a mandatory pre-test step.

Absolute contraindications include:

• Known atlanto-axial dislocation on imaging
• Severe RA with bony erosion and confirmed instability on flexion-extension radiograph
• Acute cervical fracture or acute trauma to the upper cervical spine
• Severe osteoporosis with risk of pathological fracture
• Active myelopathy with progressive neurological deficit

Relative contraindications requiring clinical judgment:

• Acute inflammatory flare in RA without recent imaging
• Congenital odontoid anomalies identified on prior imaging
• Severe apprehension or inability to relax in the patient
• Recent cervical surgery

Red-flag neurological signs that should prompt imaging before any manual upper cervical test include bilateral hand paraesthesia, lower limb weakness, bilateral upper motor neuron signs, or unexplained gait disturbance. If any of these are present, stop and refer. The sharp purser test is not the starting point for this clinical picture.

How to perform the sharp purser test: Step-by-step procedure

Correct hand placement and force direction are critical. Small technical errors change what you are testing. Use a cervical assessment intake form to record the pre-test contraindication screen and findings systematically.

Patient positioning

Seat the patient in a chair with a backrest. The patient’s head should be in a position of slight forward flexion, approximately 20-30 degrees from neutral. This position slackens the posterior ligamentous structures and places the atlas in a position where anterior translation is more likely to be detected. The patient should be relaxed with their gaze level or slightly downward.

Therapist hand placement and force direction

Stand to the side of the seated patient. Place the palm of one hand flat across the patient’s forehead to stabilise and monitor for anterior head movement. Place the thumb of your other hand on the posterior aspect of the spinous process of C2 (the axis). Your thumb provides the posterior-directed force; your forehead hand detects the glide.

Apply a gentle, controlled posterior force through the palm on the forehead, sliding the patient’s head posteriorly while your thumb on C2 remains stationary (providing a relative anterior stop for the axis). The movement is a translatory posterior glide of the cranium and atlas together, not a nodding or rotation. Force should be gentle: this is a diagnostic test, not a manipulation.

The complete procedure in sequence:

1. Confirm no absolute contraindications are present.
2. Seat patient with slight cervical flexion (~20-30 degrees).
3. Place palm of dominant hand on patient’s forehead.
4. Place thumb of non-dominant hand on the C2 spinous process posteriorly.
5. Apply gentle posterior translatory force through the forehead hand while stabilising C2 with the thumb.
6. Note any sensation of clunk, slide, or glide under your forehead hand.
7. Observe and ask the patient whether symptoms are reproduced or relieved.
8. Release slowly. Document findings immediately.

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Interpreting the results: What is a positive sharp purser test?

A positive sharp purser test result occurs when one or both of the following are detected during the posterior head glide:

• A clunk or sliding sensation under the forehead hand, suggesting the atlas is repositioning relative to the axis as the posterior force reduces anterior subluxation.
• Symptom reproduction followed by relief, indicating that the anterior atlas position was contributing to the patient’s presenting symptoms, and the posterior glide temporarily reduced the load on neural structures.

A negative result is the absence of both findings during the glide. The head moves posteriorly smoothly, and the patient’s symptoms are neither reproduced nor relieved by the movement.

Important interpretation caveats: a positive sharp purser test does not confirm a diagnosis of atlantoaxial instability in isolation. It raises the pre-test probability that TAL insufficiency is present and should prompt imaging: MRI for soft-tissue detail of the ligament, or dynamic flexion-extension radiographs to quantify the atlanto-dens interval.

Clinical correlation with the patient’s history, neurological screen, and existing imaging findings is essential before drawing any diagnostic conclusion.

Diagnostic accuracy: Sensitivity, specificity, and likelihood ratios

The most widely cited diagnostic accuracy data come from Uitvlugt and Indenbaum (1988), who studied the sharp purser test specifically in a rheumatoid arthritis population. These values should not be generalised beyond this population without caution, as the evidence base is limited and derives primarily from small studies. For broader context on clinical decision rules, see guidance on clinical decision rules in practice.

Source: Uitvlugt G, Indenbaum S. Clinical assessment of atlantoaxial instability using the Sharp-Purser test. Arthritis Rheum. 1988;31(7):918-922. These values were derived from a specific RA population. Applying them to other populations (Down syndrome, post-trauma, hypermobility) requires caution; the broader peer-reviewed literature on NCBI/PubMed contains additional smaller studies with varying results.

The modified sharp purser test

The modified sharp purser test adjusts the original protocol to reduce the risk of provoking neurological symptoms in patients with suspected severe instability. In the modified version, the examiner applies a smaller amplitude posterior force and begins from a position of less cervical flexion (closer to neutral), reducing the degree of anterior atlas displacement at the start of the test.

The rationale is that beginning from a more neutral position means there is less anterior subluxation to reduce, and therefore the risk of transient cord contact during the procedure is lower. However, this modification comes with a trade-off: a less provocative starting position may reduce test sensitivity, making it less likely to detect mild or borderline instability.

The peer-reviewed evidence supporting the modified protocol’s superiority in safety or diagnostic accuracy is limited. Current evidence does not allow a definitive claim that the modified test is safer or more accurate than the original. Clinicians should choose between the two based on their clinical assessment of the patient’s severity and their own training and competency. Safer clinical notes practices apply equally to both versions: document which protocol was used and why.

Related upper cervical stability tests

The sharp purser test does not exist in isolation. Upper cervical instability assessment typically involves a battery of tests, each targeting a different ligamentous structure or movement plane. Understanding the distinction helps clinicians select the right test for the right clinical question. For a broader view of physical therapy assessment protocols in musculoskeletal practice, systematic frameworks are essential.

In clinical practice, the sharp purser test and the alar ligament test are most commonly performed together as part of a pre-manipulative upper cervical screening battery. Neither test is sufficient alone. A comprehensive assessment includes neurological screening, symptom provocation, and consideration of imaging findings before any manual intervention to the upper cervical spine.

How the sharp purser test fits into clinical practice management

The clinical value of the sharp purser test depends not just on technique, but on the systems that surround it. Three documentation failures are the most common in upper cervical assessment practice:

• No documented contraindication screen: performing the test without a written pre-test checklist creates medicolegal exposure if an adverse event occurs.
• Incomplete positive finding records: noting “positive SPT” without specifying which finding (clunk, slide, symptom relief) undermines the clinical record’s value for ongoing management.
• No imaging follow-up pathway: a positive result should trigger a clear next step; if the record doesn’t reflect this, the patient may fall through the gap.

Clinics using physiotherapy practice management software can build structured assessment forms that enforce contraindication screening before the assessment section loads. Digital patient forms allow clinicians to create templated upper cervical screening checklists that capture presenting symptoms, red flags, and contraindication responses as part of a structured clinical record rather than free text.

Patient record management systems that link assessment findings to follow-up tasks help ensure that a positive sharp purser test result generates an automatic referral flag or imaging request, rather than relying on the clinician to remember.

For practices working with high-risk populations such as RA patients or patients with Down syndrome, physical therapy EMR tools that support condition-specific templates and documentation standards reduce the risk of clinical error and strengthen audit readiness. Physiotherapy clinic compliance requirements increasingly include documented evidence of pre-treatment screening for at-risk presentations.

The goal is a clinical workflow where safe technique and safe documentation are both systematically supported, not left to individual memory.

Conclusion

The sharp purser test remains a clinically useful tool for detecting transverse ligament insufficiency at the C1-C2 joint, particularly in rheumatoid arthritis and Down syndrome populations. Its high specificity means a positive finding is meaningful, but its moderate sensitivity means a negative result does not rule out instability in high-risk presentations. Technique, contraindication screening, and post-test documentation are as important as the test itself.

Clinics that treat MSK and at-risk populations need more than good technique; they need systems that enforce safe workflows. Pabau’s clinical documentation and chiropractic practice software tools help build those systems. To see how structured assessment forms and patient records work in practice, book a demo.

Continue your research

Need to document upper cervical assessments more safely? Safer clinical notes covers best practices for capturing clinical findings accurately and reducing medicolegal risk.

Managing compliance requirements for your physiotherapy practice? Physiotherapy clinic compliance outlines what UK physiotherapy clinics need to document and demonstrate for regulatory bodies.

Looking for an EMR built for physical therapy workflows? Physical therapy EMR shows how Pabau supports documentation, scheduling, and compliance for PT clinics.

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