Table 3.

Damage mode groups

Group	Observed damage modes	Mechanically or chemically driven	Number of femoral heads in group	Number with no volume measurement calculable
Group A	Column damage (with/without fretting)	Chemical (+ mechanical)	15	5
Group B	Imprinting	Mechanical	37	8
Group C	Imprinting and column damage	Chemical + mechanical	37	18
Group D	Uniform surface fretting	Mechanical	19	2