Good sensitivity and specificity of ultrasound for detecting pseudotumors in 83 failed metal-on-metal hip replacements

Figures & data

Figure 1. Example of an ultrasound finding classified as a fluid-filled pseudotumor. Lateral image showing a thin-walled hypoechoic fluid collection (arrows) in the greater trochanteric region under the deep fascia. GT: greater trochanter.

Figure 2. Example of an ultrasound finding classified as a mixed-type pseudotumor. An anterior image showing a thick-walled, mixed-type pseudotumor. Solid contents (arrowheads) can be seen among the hypoechoic fluid content. This lesion was graded as mixed-type because of the thick walls and atypical contents.

Figure 3. Example of an ultrasound finding classified as a solid pseudotumor. An anterior image showing a solid pseudotumor (arrows) dislocating the iliopsoas muscle anteriorly. The thin arrows show the prosthesis. IM: iliopsoas muscle.

Table 2. Summary of test characteristics

	Trochanteric region	Iliopsoas region
Sensitivity (95% CI)	83% (63–93)	79% (62–89)
Specificity (95% CI)	92% (82–96)	94% (83–98)
Positive predictive value (95% CI)	79% (59–91)	90% (74–96)
Negative predictive value (95% CI)	93% (84–97)	87% (76–94)

Table 3. Trochanteric region pseudotumors (PTs): cross-tabulation of ultrasound and revision findings

		Revision findings
Ultrasound findings	Only intra-capsular	Fluid-filled PT	Mixed-type PT	Solid PT	Total
No PT	54	4	0	0	58
Fluid-filled PT	4	14	2	0	20
Mixed-type PT	1	0	0	0	1
Solid PT	0	0	2	1	3
Total	59	18	4	1	82

Table 4. Iliopsoas-region pseudotumors (PTs): cross-tabulation of ultrasound and revision findings

		Revision findings
Ultrasound findings	Only intra-capsular	Fluid-filled PT	Mixed-type PT	Solid PT	Total
No PT	46	7	0	0	53
Fluid-filled PT	2	8	1	1	12
Mixed-type PT	0	5	6	3	14
Solid PT	1	1	1	0	3
Total	49	21	8	4	82