1. Metal-on-metal hips. “What’s to see on MRI?”
S. Sabah, A. Mitchell, J. A. Skinner, J. Henckel, J. Cobb, A. Hart
Department of Musculoskeletal Surgery, Imperial College London, United Kingdom
MOM Hips: “What’s to see on MARS MRI?”

2. MOM Hips: “What’s to see on MARS MRI?”
introduction
Use of metal-on-metal hip resurfacing for primary hip arthroplasty is increasing
ref
Proposed advantages over THR include:
Bone conservation
Reduced incidence of dislocation
MOM Hips: “What’s to see on MARS MRI?”

3. MOM Hips: “What’s to see on MARS MRI?”
Introduction
Epidemiology
Metal-on-metal hip resurfacing now accounts for 8% of primary hip replacement in the UK
UK National Joint Registry 5th Annual Report:
MOM-HR have the highest revision rates for primary hip prostheses
Estimated 2.8% at 3-years
Reason for revision surgery
Aseptic loosening
32%
Periprosthetic fracture
25%
Pain
23%
Other
20%
“Unexplained” 43%
MOM Hips: “What’s to see on MARS MRI?”

4. MOM Hips: “What’s to see on MARS MRI?”
Our experience
We are a tertiary referral centre for painful MOM-HR
We run weekly “unexplained painful MOM hip” clinics and have performed MARS MRI in over 100 MOM-HR
We are linked to the London Implant Retreival Centre which has analysed over 200 explanted hip resurfacings from across UK
MOM Hips: “What’s to see on MARS MRI?”

5. MOM Hips: “What’s to see on MARS MRI?”
Introduction
MARS MRI
Metal artefact-reduction sequences for MRI can produce diagnostic quality images of the periprosthetic tissues
Toms et al, Clin Radiol [2008], Hart et al, JBJS(Br) [2009]
Recent papers have proposed soft tissue disease (especially so-called “pseudotumours”) may account for high failure rates of MOM-HR
Fang et al, Skel Rad [2008], Pandit et al, JBJS(Br) [2008], Hart et al, JBJS(Br) [2009]
Axial T1W – Iliopsoas fluid collection
MOM Hips: “What’s to see on MARS MRI?”

6. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours”
Aetiology
Unknown
Histopathology
Classification as aseptic lymphocyte-dominated vasculitis association lesions (ALVAL)
Willert, JBJS(Am) [2005]
Subsurface band of macrophages with perivascular lymphocytes
Hart, AAOS Annual Meeting[2009]
Subtypes
Solid, fluid and mixed
Fang [2008], Pandit [2008], Hart [2009]
Hip neocapsule specimen. H&E [top]. CD68 immunohistochemistry (macrophage marker) [bottom]
MOM Hips: “What’s to see on MARS MRI?”

7. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours”
solid masses
Axial T1W + contrast
MOM Hips: “What’s to see on MARS MRI?”

8. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – solid masses
imaging features
Intermediate signal intensity on T1W and T2W
No fluid characteristics
Poorly demarcated border
Local regional soft tissue invasion
Axial T1W
MOM Hips: “What’s to see on MARS MRI?”

9. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – solid masses
Complications
Lymphatic stasis
Limb swelling
Nodal enlargement
Sciatic nerve involvement
Axial T1W + contrast
Coronal T1W
MOM Hips: “What’s to see on MARS MRI?”

10. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – solid masses
Clinical
With late presentation:
Severe pain
Reduced range of movement
Very low hip scores
MOM Hips: “What’s to see on MARS MRI?”

11. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – solid masses
Management
Dictated by clinical evaluation
Surgical debridement with maximal preservation of normal tissue
Ensure attention to other soft tissue structures involved within mass
INSERT OPERATION PICTURE
MOM Hips: “What’s to see on MARS MRI?”

12. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours”
Fluid collections
Axial T2W
MOM Hips: “What’s to see on MARS MRI?”

13. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – fluid collections
classification
Radiological
Location
Anterior
Posterior
Lateral
Signal characteristics
Core
Pseudocapsule
Clinical
Aetiology
Infected or sterile
Status
Symptomatic/asymptomatic
Axial T2W
Coronal STIR
MOM Hips: “What’s to see on MARS MRI?”

14. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – fluid collections
classification
Radiological
Location
Anterior
Posterior
Lateral
Signal characteristics
Core
Pseudocapsule
Clinical
Aetiology
Infected or sterile
Status
Symptomatic/asymptomatic
MOM Hips: “What’s to see on MARS MRI?”

15. Signal characteristics
“Pseudotumours” – fluid collections
Signal characteristics
Core
Signal intensity on T1W
Intermediate
High
Mixed
Axial T1W
NEED BESAGNI T1W FOR ‘MIXED’
MOM Hips: “What’s to see on MARS MRI?”

16. Signal characteristics
“Pseudotumours” – fluid collections
Signal characteristics
Pseudocapsule
Smooth, linear?
Irregularly thickened?
Areas of susceptibility artefact?
Coronal STIR
Coronal STIR
MOM Hips: “What’s to see on MARS MRI?”

17. MOM Hips: “What’s to see on MARS MRI?”
“Pseudotumours” – fluid collections
classification
Radiological
Location
Anterior
Posterior
Lateral
Signal characteristics
Core
Pseudocapsule
Clinical
Aetiology
Infected
Sterile
Status
Symptomatic/asymptomatic
Axial T2W. Infected fluid collection in “dumb-bell” about iliopsoas tendon (asterisk)
appear identical
MOM Hips: “What’s to see on MARS MRI?”

18. MOM Hips: “What’s to see on MARS MRI?”
Other pathology
Muscles
Oedema
Atrophy
Tendons
Avulsion
Bones
Fracture
Metastases
Osteolysis
Coronal STIR. Extensive muscle oedema posterior to right joint
MOM Hips: “What’s to see on MARS MRI?”

19. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - muscles
Muscle atrophy
Individual muscles easily differentiated on MARS MRI
2 labelled diagrams of normal max, med, min, oe, qf
max = Gluteus maximus
med = Gluteus medius
min = Gluteus minimus
oe = Obturator externus
qf = quadratus femoris
MOM Hips: “What’s to see on MARS MRI?”

20. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - muscles
Muscle atrophy
Assess on T1W images
Compare to contralateral side
Example grading system:
Bal et al, Intr Course Lect [2008]
Grade
Comment
Normal 1
≤30% decrease in muscle size 2
30-70% fatty change with decrease in muscle mass 3
>70% fatty change with an 80% decrease in size
MOM Hips: “What’s to see on MARS MRI?”

21. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - muscles
Muscle atrophy
Significance unknown
surgically induced or indicator of disease?
Axial T1W – Atrophy of obturator externus and quadratus femoris on right-side
MOM Hips: “What’s to see on MARS MRI?”

22. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - tendons
tendons
Tendon avulsion is best seen on T1W images as discontinuity of the low signal muscle attachment
Toms [2008]
Avulsion may be found with:
Inadequate/absent surgical repair
Local space-occupying lesion (e.g. fluid collection)
Axial T1W – Lateral fluid collection (arrow) associated with marked atrophy of gluteus medius muscle and avulsion of its tendon
MOM Hips: “What’s to see on MARS MRI?”

23. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - bones
bones
Screen MARS MRI images for fracture, osteolysis and metastatic disease
Always refer to plain radiographs of pelvis and hips for comparison
Coronal T1W showing diffuse metastases – NEED TO CHANGE
MOM Hips: “What’s to see on MARS MRI?”

24. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - bones
bones
Fracture
Acetabulum
Often difficult to visualise due to artefact
Pubic rami
Axial T1W image of a fracture of the inferior pubic ramus on the right (circled)
MOM Hips: “What’s to see on MARS MRI?”

25. MOM Hips: “What’s to see on MARS MRI?”
Other pathology - bones
bones
AP Radiograph (left) and Axial T1W images of racture of acetabulum and inferior pubic ramus (circled)
MOM Hips: “What’s to see on MARS MRI?”

26. MOM Hips: “What’s to see on MARS MRI?”
Other pathology
Incidental pathology
Dermoid
MOM Hips: “What’s to see on MARS MRI?”

27. MOM Hips: “What’s to see on MARS MRI?”
conclusion
MARS MRI can produce diagnostic quality images of the periprosthetic tissues
“Pseudotumours” have characteristic features on MARS MRI and may be important causes for failure of MOM-HR
Musculotendinous and incidental pathologies should not be overlooked
MOM Hips: “What’s to see on MARS MRI?”

28. MOM Hips: “What’s to see on MARS MRI?”
Questions
Please
See also:
MOM Hips: “What’s to see on MARS MRI?”