Clicking and Squeaking: In Vivo Correlation of Sound and Separation for Different Bearing Surfaces

luoroscopy has proven to be an accurate method to determine in vivo motions1 and has enabled the extraction of accurate three-dimensional hip-joint kinematics unaffected by erroneous skin movements1,2. Previ-ously, fluoroscopy was used to determine that the femoral head of a total hip prosthesis slides within the acetabular cup, leading to separation of certain aspects of the articular geometry3-5. This finding has often been referred to as hip separation, where there is a loss of contact area, leaving only edge contact. Although separation has been well docu-mented, it has not been correlated to clinical complications nor has a more in-depth understanding of the cause and ef-fect been developed. Another phenomenon observed primarily in total hip prostheses is the presence of squeaking. Mismatched ceramic