Table 2.

Summarized pattern categories of observed metal transfer on the bearing surface of the analyzed femoral heads. Patterns are presented by type, description, and an exemplar photograph for each cohort (images taken with a digital microscope (Keyence; Itasca, Illinois, USA)).

Pattern observed	Description	CoCr	Ceramic
Solid patch	Similar in length and width, with a rough dark gray appearance. Often only one per femoral head, and commonly the only metal transfer on the bearing surface. Occasionally accompanied by one or two random patches
Directional scratches	Multiple thin lines of transfer with similar macrodirectionality. Typically clustered in groups or in a circular ring around the apex of the femoral head
Longitudinal stripe	Longitudinal dark marks appearing black on ceramic and dark gray, brown, or dull gray on CoCr. Often extending from taper to apex of the femoral head with strong macrodirectionality, opposing microdirectionality, and one or both longitudinal edges straight and well defined. Often only one mark of this type per head, accompanied by additional transfer patterns (see random patches, patterned coverage)
Random stripe	Similar coloring to a longitudinal stripe, with a high length : width ratio and no preferred orientation (lateral or longitudinal). It can be straight, curved, or looped; one to two seen per upper hemisphere
Random patches	No overall directionality, often overlapping marks. Found in clustered groups or independently with no location preference. Typically one to a few marks, either the only pattern observed or a secondary pattern
Patterned coverage	Small straight lines or pinpoints markings, evenly distributed over the entire upper hemisphere. Spaced approximately 1 mm apart in every direction. Most often a secondary pattern to a longitudinal transfer stripe
Miscellaneous	Iatrogenic damage, stripe wear accompanied by metal transfer, additional surface damage, or unconfirmed metal transfer