TABLE II.

The H:A Ratio for Standard THA Articulations in Each Available Head and Shell Combination^*

Head Diameter (mm)	Acetabular Shell Diameter (mm)
	42	44	46	48	50	52	54	56	58	60	62	64	66	68	70	72
22	0.52	0.50	0.48	0.46	0.44	0.42	0.41	0.39	0.38	0.37	0.35	0.34	0.33	0.32	0.31	0.31
28	0.67	0.64	0.61	0.58	0.56	0.53	0.52	0.50	0.48	0.47	0.45	0.44	0.42	0.41	0.40	0.39
32		0.73	0.70	0.67	0.64	0.61	0.59	0.57	0.55	0.53	0.52	0.50	0.48	0.47	0.46	0.44
36				0.75	0.72	0.69	0.67	0.64	0.62	0.60	0.58	0.56	0.55	0.53	0.51	0.50
40						0.77	0.74	0.71	0.69	0.67	0.65	0.63	0.61	0.59	0.57	0.56
44								0.79	0.76	0.73	0.71	0.69	0.67	0.65	0.63	0.61

^*As surgeons today are most likely to select a larger femoral head implanted into an acetabular shell in a standard THA, standard articulations are more likely to have a ratio of ≥0.6 (boldfaced numbers). The most common size head, 36 mm, will always produce an H:A ratio of ≥0.50. Italicized numbers represent a ratio between 0.50 and 0.59.