Are CT Scans a Satisfactory Substitute for the Follow-Up of RSA Migration Studies of Uncemented Cups? A Comparison of RSA Double Examinations and CT Datasets of 46 Total Hip Arthroplasties

Table 2

(a) Relative prosthetic movement expressed in 6 degrees of freedom (DOF). Translation is expressed with respect to the centroid of the prosthetic landmark group. This relative movement is theoretically zero between the examinations; hence the calculated movement presents the precision of our setup [16]. (b) Precision as described in [17] of RSA double examinations and RSA-CT double examinations. (c) Precision as confidence limits based on RSA double examinations and RSA-CT double examinations presented as in many earlier RSA studies [5, 18–20].

(a)

	Rotation (degrees)			Translation (mm)			MTPM
	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)
RSA-CT ()
Mean	−0.14	0.05	0.05	−0.01	−0.08	−0.04	0.30
Median	−0.02	−0.03	0.09	0.02	−0.09	−0.03	0.26
95% conf. interval; (mean ± 1.96 SD)
Lower	−1.02	−1.31	−0.56	−0.37	−0.40	−0.47	−0.02
Upper	0.75	1.21	0.65	0.34	0.24	0.39	0.61
Standard deviation (SD)	0.45	0.64	0.31	0.18	0.16	0.22	0.16
Min	−1.23	−1.58	−0.73	−0.71	−0.35	−0.47	0.10
Max	1.00	1.38	0.66	0.32	0.66	0.41	0.78
RSA1-RSA2 (double examination); ()
Mean	0.02	−0.09	−0.04	−0.04	0.00	−0.01	0.14
Median	−0.04	−0.11	−0.02	−0.01	0.00	−0.01	0.12
95% conf. interval (mean ± 1.96 SD)
Lower	−0.84	−0.90	−0.41	−0.29	−0.10	−0.23	−0.10
Upper	0.88	0.72	0.32	0.22	0.10	0.20	0.37
Standard deviation (SD)	0.44	0.41	0.18	0.13	0.05	0.11	0.12
Min	−0.92	−1.44	−0.80	−0.77	−0.16	−0.24	0.02
Max	2.23	0.90	0.42	0.18	0.17	0.32	0.78

(b)

	Rotation (degrees)			Translation (mm)			MTPM
	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)
RSA-CT ()
95% confidence limit (2.01 × SD)	0.90	1.29	0.62	0.36	0.33	0.44	0.32
Mean	−0.14	0.05	0.05	−0.01	−0.08	−0.04	0.30
Min	−1.23	−1.58	−0.73	−0.71	−0.35	−0.47	0.10
Max	1.00	1.38	0.66	0.32	0.66	0.41	0.78
RSA1-RSA2 (double examination); ()
95% confidence limit (2.01 × SD)	0.88	0.83	0.37	0.26	0.10	0.22	0.24
Mean	0.02	−0.09	−0.04	−0.04	0.00	−0.01	0.14
Min	−0.92	−1.44	−0.80	−0.77	−0.16	−0.24	0.02
Max	2.23	0.90	0.42	0.18	0.17	0.32	0.78

(c)

	Rotation (degrees)			Translation (mm)			MTPM
	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)	(Transverse axis)	(Longitudinal axis)	(Sagittal axis)
RSA-CT ()
95% confidence limit; (mean of absolute differences + 1.96 × SD)	1.23	1.78	0.86	0.48	0.46	0.61	0.61
99% confidence limit; (mean of absolute differences + 2.575 × SD)	1.51	2.17	1.05	0.59	0.56	0.74	0.71
RSA1-RSA2 (double examination); ()
95% confidence limit; (mean of absolute differences + 1.96 × SD)	1.09	1.10	0.48	0.32	0.14	0.30	0.37
99% confidence limit; (mean of absolute differences + 2.575 × SD)	1.36	1.36	0.60	0.40	0.17	0.37	0.45