Purpose
Assesses the integrity of the Atlanto-Axial joint and more notably the stabilizers of the dens on the Atlas. This test specifically assesses the integrity of the Transverse Ligament. If the transverse ligament that maintains the position of the odontoid process relative to C1 is torn, C1 will translate forwards on C2 in flexion.
Atlantoaxial instability is the most significant complication of rheumatoid arthritis (RA) in the cervical spine[1], occuring in 29-70% of RA patients.[2] Cervical spinal cord compromise due to atlantoaxial subluxation can have serious neurological consequences, including quadriplegia and even death.
!!This test should be performed with extreme caution!!
Technique
The patient is seated. The examiner places the palm of one hand on the patient’s forehead, and the index finger or thumb of the other hand on the tip of the spinous process of the axis (C2). The patient is asked to slowly flex the head performing a slight cervical nod, at the same time the examiner presses posteriorly on the patient’s forehead.
A sliding motion of the head in relation to the axis indicates atlantoaxial instability.[1] A positive result may also be accompanied by a reduction in symptoms[3], a “clunk” sensation, or patient reports of a “click” or “clunk” felt in the roof of their mouth. It is thought that this technique reduces atlantoaxial subluxation caused by forward flexion of an unstable cervical spine.
Aspinall[4] suggests that if upper cervical instability is suspected, the Sharp-Purser test should be performed first before any of the other ligamentous tests. If, and only if, the Sharp-Purser is negative, Aspinall then suggests that, in the absence of neurological symptoms, a test that passively moves the atlas on the axis be used to assess for laxity of the transverse ligament, such as the transverse ligament stress test.
The Sharp-Purser test is not without controversy, it is stated that this test is intended to relieve neurological symptoms, however Meadows called the use of the Sharp-Purser in the presence of neurological symptoms an “exercise in futility and risk.”[5]
Evidence
Uitvlugt and Indenbaum[1] compared the Sharp-Purser Test to a gold standard of lateral flexion/extension radiographs in 123 patients with rheumatoid arthritis. They report a sensitivity of 69%, and a specificity of 96% for laxity >3mm. This yields a positive likelihood ratio of 17.3 and negative likelihood ratio of 0.32. For laxity >4mm, sensitivity increased to 88%. All cases with neurological involvement and all laxities >5mm were detected.
However, Cattrysse et al.[6] found no tendancy towards a consistent level of significant intra- and interobserver reliability.
Resources
The Sharp-Purser Test: A Useful Clinical Tool or an Exercise in Futility and Risk?
References
