Low-dose CT-based implant motion analysis is a precise tool for early migration measurements of hip cups: a clinical study of 24 patients

Figures & data

Figure 1. Implant types used in the studies: (a) the uncemented TOP cup used in the Uppsala study, (b) a cemented Muller Exceed ABT polyethylene cup from the Danderyd study, (c) the graft-compressing titanium shell and a cemented Lubinus cross-linked UHMWP polyethylene cup used in the Gävle study.

Table 1. CT settings from 3 clinical trials. A bone filter has been used for all scans without any metal artefact reduction algorithm.

Site of CT scanner	kVp ^a (V)	Tube current (mA)	Exposure (mAs)	Slice thickness (mm)	Increments (mm)	Pitch	Rotation time (s)
Uppsala University Hospital ^b	120	23	23	0.6	0.6	0.9	1
Danderyd’s Hospital ^c	120	10	10	0.625	0.312	0.98	1
Gävle Hospital ^d	120	80–500 ^e	55	0.5	0.5	0.81	0.5

^akVp: Kilovoltage peak is the peak voltage applied to the X-ray tube.

^bSomatom Definition Flash, Siemens, Forchheim, Germany.

^cDiscovery CT750HD, GE Healthcare, Chicago, IL, USA.

^dAquilon One CT scanner (Toshiba).

^eDynamic tube current.

Figure 2. Processing schematic for CTMA. (Step 1) First an optimization of bone thresholding is performed manually. (Step 2) Thereafter the pelvic bone is defined here by the surface of the pelvic anatomy; a first registration is subsequently performed. (Step 3) A manual thresholding of metal is performed. (Step 4) The implant rigid body (the cup) is defined. The user indicates the region of interest for the second registration in the 2 datasets, i.e., the implant. Next the second registration occurs. Green color indicates a successful registration.

Table 3. Precision of CTMA of different cups using bone markers for registration

Hospital	Translation, mm					Rotation, °
	n	x	y	z	TT	x	y	z
Uppsala University Hospital	5	0.11	0.09	0.08	0.03	0.43	0.23	0.22
Danderyd’s Hospital	9	0.08	0.13	0.13	0.13	0.25	0.21	0.29
Gävle Hospital	10	0.10	0.20	0.14	0.12	0.20	0.22	0.26

TT: total translation.

Table 2. Precision of CTMA of different cups using the pelvic anatomy without beads for registration

Hospital	Translation, mm					Rotation, °
	n	x	y	z	TT	x	y	z
Uppsala University Hospital	5	0.07	0.13	0.31	0.20	0.37	0.22	0.39
Danderyd’s Hospital	9	0.23	0.11	0.08	0.16	0.31	0.28	0.29
Gävle Hospital	10	0.12	0.31	0.15	0.22	0.28	0.20	0.23

TT: total translation.