Accuracy and potential pitfalls of fluoroscopy-guided acetabular cup placement

Figures & data

Figure 1. Inlet and outlet views of the pelvis were used to define the mid-pubic point. The inlet view is characterized by overlying superior and inferior pubic rami.

Figure 2. The two fluoroscopic views used to define the anterior superior iliac spines. A frontal view allows definition of the midpoint between the visceral and parietal compacta. A lateral view reveals the most prominent point of the spine.

Figure 3. The setup for the error analysis is shown. The cadaveric pelvis is fixed on a vacuum mattress with the APP in horizontal orientation. A tracked cup impactor is rigidly fixed to the table in a position of 15° of version and 40° of cup abduction relative to the APP. Different predefined scenarios for maldefinition of the iliac spines and the mid-pubic point were rehearsed, and the resulting cup orientation angles were displayed by the navigation system.

Figure 4. With the help of the fluoroscopy-based navigation system, a significantly higher number of cups were placed within the safe zone of 15 ± 10° of version and 40 ± 10° of abduction.

Figure 5. The anterior superior iliac spines could be registered with greater accuracy than the midpoint between the pubic tubercles.

Figure 6. The influence of malregistration of the pelvic reference coordinate system is shown. The white spots represent the real bony landmarks (the anterior superior iliac spines and the pubic tubercles) of the APP. The resulting mean angle of a maldefined point is shown in the scatter diagrams, e.g., defining the pubis point too posteriorly (point 9) would lead to a more anteverted cup.

Table I.  Resulting cup abduction and version angles with low landmark definition (starting orientation: 40° abduction, 15° version).

Point	Resulting cup abduction (°)	Resulting cup version (°)
Ipsilateral spine
Point 1	37.8 ± 0.5 (range: 37–38)	15.4 ± 0.5 (range: 15–16)
Point 2	39.6 ± 0.5 (39–40)	14.3 ± 0.5 (14–15)
Point 3	41.6 ± 0.5 (41–42)	13.6 ± 0.5 (13–14)
Point 4	39.3 ± 0.7 (38–40)	14.9 ± 0.6 (14–16)
Contralateral spine
Point 5	42.4 ± 0.5 (42–43)	13.3 ± 0.7 (12–14)
Point 6	41.4 ± 0.9 (40–43)	13.9 ± 1.1 (12–15)
Point 7	38.1 ± 0.6 (37–39)	12.3 ± 1.3 (10–14)
Point 8	40.6 ± 0.9 (40–42)	11.6 ± 1.3 (10–14)
Pubis
Point 9	42.1 ± 1.0 (41–44)	27.1 ± 3.0 (24–32)
Point 10	40.8 ± 0.5 (40–41)	20.5 ± 2.1 (18–23)
Point 11	39.9 ± 0.4 (39–40)	12.3 ± 3.1 (7–16)
Point 12	39.5 ± 0.5 (39–40)	8.8 ± 3.5 (1–12)
Point 13	40.9 ± 0.6 (40–42)	20.9 ± 2.7 (18–26)
Point 14	42.3 ± 0.9 (41–44)	25.4 ± 3.0 (23–32)

Note: The points correspond to those shown in Figure 6.

Figure 7. The inferior pubic ramus can simulate the pubic tubercle if the superior and inferior pubic rami are not correctly overlaid.

Table II.  Reported accuracies of different navigation systems for THA.

Reference	Modality	Object	n	Position	Control measurement	Abduction (°)	Version (°)
Murphy [22]	CT-based	Patients	84	Lateral	AP radiographs	0.1 ± 2.3 (−6 to 8)	–
Haaker et al. [23]	CT-based	Patients	100	–	CT-based measurement	0.4 ± 4.31; maximum error non-estimatable	− 1.6 ± 7.29; maximum error non-estimatable
Hube et al. [24]	CT-based	Patients	46	Supine	AP radiographs	2.7 (0–8); no SD documented	–
Ito et al. [25]	CT-based	Patients	30	Lateral	Post-operative CT	4.3 (0–13); no SD documented	9.1 (0–26); no SD documented
Leenders et al. [26]	CT-based	Patients	50	Supine	AP radiographs	− 1 to 5; no mean value, SD	–
Jolles et al. [20]	CT-based	Plastic bones	50	Lateral	Electromagnetic digitizing	2.5 (maximum error 4.7); no SD documented	1.5 (maximum error 8.0); no SD documented
Murphy [27]	Fluoroscopy-based	Patients	91	–	AP radiographs	− 0.7 ± 2.3 (−6 to 8)	–
Hube et al. [24]	Fluoroscopy-based	Patients	107	Supine	AP radiographs	3.9 (0–9); no SD documented	–
Grtzner et al. [28]	Combined fluoroscopy and digitizing	Patients	50	Supine	Post-operative CT	1.5 ± 1.1 (maximum error 5)	2.4 ± 1.4 (maximum error 6)
Nogler et al. [7]	Image-free	Cadaver	12	Supine	Digitizing arm	− 3.86 ± 3.44 (−8.5 to 6.8)	− 4.89 ± 4.55 (−5 to 13.5)
Mattes and Puhl [29]	Image-free	Cadaver	10	–	Post-operative CT	1.8 (−9 to 6); no SD documented	–
Amiot et al. [30]	Image-free	Patients	19	Supine	AP radiographs	2.6 ± 2.1	5.3 ± 6.0
Amiot et al. [30]	Image-free	Patients	18	Lateral	AP radiographs	3.2 ± 2.8	4.9 ± 4.7
Present study	Fluoroscopy	Cadaver	14	Lateral	CT-based fiducial	0.7 ± 2.8 (−5 to 7)	− 6.6 ± 6.0 (−18 to 2)

Note: SD: Standard deviation.

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