Navicular Drop Test 

Purpose: To assess the height of the navicular bone.

Test Position: Standing.

Performing the Test:  First, mark the navicular tuberosity. Next, measure the height of the navicular bone with the subtalar joint in neutral and the patient bearing most of the weight on the contralateral limb. Finally, have the patient assume equal weight on both feet and remeasure the height of the navicular. The difference between the first and second measurement is the navicular drop. A difference of >10 mm is considered significant excessive foot pronation. 

Diagnostic Accuracy: Intra-examiner: .33-.9; Inter-examiner: .31-.74.

Importance of Test: The medial longitudinal arch is the primary shock absorber and load-bearing structure of the foot. Without this arched configuration, large forces at the foot would exceed the physiologic weight bearing capabilities of the tarsal bones. During the navicular drop test, the examiner is first measuring the height of the navicular bone without the subject's body weight pushing down on the medial longitudinal arch. Because the arch should have some flexibility, the examiner should expect a decreased navicular height when the subject places his/her full body weight on the medial longitudinal arch. While >10 mm difference is considered excessive foot pronation, there is also speculation that <5 mm of navicular drop could be associated with a limited foot type or a supinated foot. Specific criteria for a supinated foot has not been well established.

Note: these tests should only be performed by a properly trained health care practitioner.

References: 
Flynn , Timothy. User's Guide to the Musculoskeletal Examination. Evidence in Motion, 2008. Print.
Neumann, Donald. Kinesiology of the Musculoskeletal System. Second . Mosby Publishing Inc., 2010. 609-613. Print.
Tiberio, David. "Pathomechanics of Structural Foot Deforities." Physical Therapy. 68. (1988): 1840-1849. Print.