How to Measure Diameter:

• 1). Position thumb in a resting position.
  
  
• 2). Wrap a flexible measuring tape around the widest portion of the MCP joint.
  
  
• 3). Note the measurement to the nearest centimeter.
  
  

How to Measure Flexion

• 1). Place the goniometer over the MCP joint of the thumb while it is in a neutral position.
  
  
• 2). Have her bend her thumb as far into her palm as she is able. An arrow on the goniometer should point to the degree of flexion she has achieved.
  
  
• 3). Record the measurement to the nearest centimeter.
  
  

How to Measure Thumb Extension:

• 1
  The "thumbs up" sign is an example of thumb extension.Jupiterimages/Photos.com/Getty Images
  
  Place the goniometer over the thumb MCP joint while it is in a neutral position.
  
  
• 2). Have the patient straighten the thumb as much as he is able. The more extension the joint has, the smaller the measurement should be.
  
  
• 3). Record the measurement to the nearest centimeter.