Final answer:
In a Sharp Purser test, the patient's head should be in a neutral position to assess the stability of the atlantoaxial joint, helping to detect issues like atlantoaxial subluxation.
Step-by-step explanation:
When performing a Sharp Purser test, the patient's head should be in a neutral position initially. The test is designed to assess the stability of the atlantoaxial joint and is often used by healthcare professionals for patients who may have upper cervical spine instability. The practitioner stabilizes the patient's cervical spine with one hand and applies a gentle posterior force to the forehead with the other hand while the patient is seated. It is important for the head to start in a neutral position to effectively test for the presence of abnormal motion between the atlas and the axis, which could suggest a problem such as atlantoaxial subluxation.