1. What Is the Clinical Significance of a Raised Blood C-Reactive Protein (CRP) Level in Patients with Inflammatory Lesions Adjacent to Metal-on-Metal Hip Replacements on MARS MRI? Radiological Society of North America (RSNA) Wed Dec :20PM - 3:30PM ROOM E451A
Keshthra Satchithananda, Tahir Mahmud, Adam Mitchell, Anastasia Papadaki, Donald Mcrobbie, Shiraz Sabah, John Skinner, Johann Henckel, Justin Cobb, Angus Lewis, Alister Hart

2. We are interested in the mechanism of failure of metal-on-metal hip replacements
The London Implant Retrieval Centre
>750 components
We have collected 280 MOM retrievals
Last week we received 6. We are now receinving hips from the US
We are funded by the British Orthopaedic Association with a contract that involves 8 Orthopaedic companies to allow them to use the data for regulatory obligations
The Imperial College standard academic contract includes protection of our statements, ie the companies are prevented from manipulating our conclusions
Painful MOM hip clinic
160 MARS MRI scans; 79 lesions found
Hart, Skinner et al JBJS Br Jun;91-B(6):738-44;
Sabah, Skinner, Hart et al Epub J Athroplasty 2010

3. Plain radiographs do not explain failure: Well positioned cups, non-infected & well fixed

4. But MRI can detect pseudotumours

5. Oxford definition of pseudotumour
“we use the term ‘‘pseudotumour’’ to encompass all masses, whether cystic or solid. Lesions described in different ways by other groups (eg. cyst, bursa, ALVAL), would be classified as a pseudotumour in our centre.”
Glynn-Jones, J Bone Joint Surg Br, 91(12): , 2009.
It is an inflammatory problem

6. Difficulty differentiating between inflammation and infection for painful MOM hips
Sierra
Biant

7. Purpose
a) To report the clinical correlation of CRP and MARS MRI findings on 97 patients with painful metal-on- metal (MOM) hip replacements.
b) To guide radiologists and surgeons through the complex clinical interpretation of MARS MRI findings in patients with painful MOM hips.
When investigating a painful hip replacement, Surgeons use raised blood CRP to indicate infection and help decide between a 1 and 2 stage revision procedure. The British Orthopaedic Association has recently recommended MARS MRI in patients with painful MOM hips because sterile inflammatory lesions can be the cause of premature failure. However, it is not known whether blood CRP is elevated in such cases.

8. Many papers on pseudotumours
Glyn-Jones, S.; Pandit, H.; Kwon, Y. M. et al.: Risk factors for inflammatory pseudotumour formation following hip resurfacing. J Bone Joint Surg Br, 91(12): , Grammatopolous, G.; Pandit, H.; Kwon, Y. M. et al.: Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg Br, 91(8): , Harvie, P.; Giele, H.; Fang, C. et al.: The treatment of femoral neuropathy due to pseudotumour caused by metal-on-metal resurfacing arthroplasty. Hip Int, 18(4): , Kwon, Y. M.; Glyn-Jones, S.; Simpson, D. J. et al.: Analysis of wear of retrieved metal-on-metal hip resurfacing implants revised due to pseudotumours. J Bone Joint Surg Br, 92(3): Pandit, H.; Glyn-Jones, S.; McLardy-Smith, P. et al.: Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br, 90(7): , Pandit, H.; Vlychou, M.; Whitwell, D. et al.: Necrotic granulomatous pseudotumours in bilateral resurfacing hip arthoplasties: evidence for a type IV immune response. Virchows Arch, 453(5): , Park, S. J.; Lee, H. K.; Yi, B. H. et al.: Pseudotumour in the bladder as a complication of total hip replacement: ultrasonography, CT and MR findings. Br J Radiol, 80(954): e119-21, 2007.

9. Simple hypothesis
Do patients with a lesion (pseudotumour) on MRI have a raised CRP?

10. Method 97 patients Painful, non-infected, MOMHR
Infection was excluded by hip aspiration and extended seven day cultures or low (<10mg/l) blood CRP level
Metal artifact reduction sequence (MARS) MRI were performed.
Sensitivity and specificity were calculated using a contingency table and the Chi square test was used to test for statistical significance.

11. MRI classification 97 MARS MRI scans of painful MOM hips
Classification developed by 2 MSK radiologists
Blinded to clinical details
Lesion category
Wall
Contents
Shape
Class 1
Thin walled
Fluid like:
T1 hypo / T2 hyper
Flat with walls mainly in apposition
Class 2A
Thick walled or irregular
Not flat and >50% of the walls are not in apposition
Class 2B
Atypical fluid:
T1 hyper / T2 variable
Any size
Class 3
Solid
Mixed signal

12. Results
A raised CRP was found in 34 out of 97 patients of which 88% of these had lesions on MARS MRI.
In the 63 patients with a normal CRP, 53% had lesions on MARS MRI.
CRP >10 predicts lesion on MRI with:
Sensitivity 59%
Specificity 48%
Difference in the frequency of lesions between the normal and raised CRP groups was not statistically significant.
CRP>10
CRP<10
Lesion on MRI 30 33 63
No lesion on MRI 4 34 97

13. MRI Type 1 pseudotumour Lesion Lesion a. Well functioning hip
b. Painful hip
Lesion
Lesion

14. MRI Type 2a pseudotumour
a. Well functioning hip
b. Painful hip
Lesion on T2
Lesion on T2
Lesion on T1
Lesion on T1

15. MRI Type 2b pseudotumour
a. Well functioning hip
b. Painful hip
Lesion on T2
Lesion on T2
Lesion on T1
Lesion on T2 (coronal)

16. MRI Type 3 Pseudotumour
A painful hip
Solid Lesion

17. Conclusion
A raised CRP was commonly found in all patients with non-infected, painful MOM hips (probably as a result of a synovitis to the metal wear debris).
However, a raised CRP did not reliably predict the presence of a soft tissue lesion adjacent to a painful MOM hip replacement on MARS MRI.

18. CLINICAL RELEVANCE/APPLICATION
This study shows that a raised CRP level in a non-infected painful MOM hip replacement does not necessarily correlate with the presence of a soft tissue lesion.
Our latest work shows no difference in the prevalence of lesions on MRI between 28 well functioning and 30 painful MOM hip.
CRP may indicate a synovitis as the cause of a painful MOM hip

19. Details of the patients groups
Variable Median
(interquartile range)
97 patients
Type of implant
Adept
ASR
Biomet
BHR
Cormet
Durom
Oxford hip score
3D CT measured cup inclination angle (degrees)
3D CT measured cup version angle (degrees)

20. Conclusions
50% of well functioning and painful MOM hips had pseudotumour
Only difference was for solid lesions: 1 painful versus zero well functioning hips
The current definition of Pseudotumour is not clinically useful and misleading