We are interested in the mechanism of failure of metal-on-metal hip replacements

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 01 2010 3:20PM - 3:30PM ROOM E451A KeshthraSatchithananda, 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 Painful MOM hip clinic 160 MARS MRI scans; 79 lesions found Hart, Skinner et al JBJS Br. 2009 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): 1566-74, 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): 1566-74, 2009. 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): 1019-24, 2009. 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): 313-20, 2008. 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): 356-61. 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): 847-51, 2008. Pandit, H.; Vlychou, M.; Whitwell, D. et al.: Necrotic granulomatouspseudotumours in bilateral resurfacing hip arthoplasties: evidence for a type IV immune response. Virchows Arch, 453(5): 529-34, 2008. 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

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.

13. MRI Type 1 pseudotumour 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

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