METAL-ON-METAL HIPS. “WHAT’S TO SEE ON MRI?” S. Sabah, A. Mitchell, J. A. Skinner, J. Henckel, J. Cobb, A. Hart MOM Hips: “What’s to see on MARS MRI?” 1 The following presentation was given at the Radiological Society of North America (RSNA) in 2009

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 – ref MOM Hips: “What’s to see on MARS MRI?” 2 INTRODUCTION

Reason for revision surgery Aseptic loosening32% Periprosthetic fracture25% Pain23% Other20% Metal-on-metal hip resurfacing now accounts for 8% of primary hip replacement in the UK UK National Joint Registry 5 th Annual Report: – MOM-HR have the highest revision rates for primary hip prostheses – Estimated 2.8% at 3-years MOM Hips: “What’s to see on MARS MRI?” 3 EPIDEMIOLOGY INTRODUCTION “UNEXPLAINED” 43%

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?” 4 OUR EXPERIENCE

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] MOM Hips: “What’s to see on MARS MRI?” 5 MARS MRI INTRODUCTION Axial T1W – Iliopsoas fluid collection

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] MOM Hips: “What’s to see on MARS MRI?” 6 “PSEUDOTUMOURS” Hip neocapsule specimen. H&E [top]. CD68 immunohistochemistry (macrophage marker) [bottom]

MOM Hips: “What’s to see on MARS MRI?” 7 SOLID MASSES “PSEUDOTUMOURS” Axial T1W + contrast

Intermediate signal intensity on T1W and T2W No fluid characteristics Poorly demarcated border Local regional soft tissue invasion MOM Hips: “What’s to see on MARS MRI?” 8 IMAGING FEATURES “PSEUDOTUMOURS” – SOLID MASSES Axial T1W

Lymphatic stasis Limb swelling Nodal enlargement Sciatic nerve involvement MOM Hips: “What’s to see on MARS MRI?” 9 COMPLICATIONS “PSEUDOTUMOURS” – SOLID MASSES Coronal T1W Axial T1W + contrast

With late presentation: – Severe pain – Reduced range of movement – Very low hip scores MOM Hips: “What’s to see on MARS MRI?” 10 CLINICAL “PSEUDOTUMOURS” – SOLID MASSES

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?” 11 MANAGEMENT “PSEUDOTUMOURS” – SOLID MASSES

MOM Hips: “What’s to see on MARS MRI?” 12 FLUID COLLECTIONS “PSEUDOTUMOURS” Axial T2W

Coronal STIRAxial T2W Radiological –L–Location Anterior Posterior Lateral –S–Signal characteristics Core Pseudocapsule Clinical –A–Aetiology Infected or sterile –S–Status Symptomatic/asymptomatic MOM Hips: “What’s to see on MARS MRI?” 13 CLASSIFICATION “PSEUDOTUMOURS” – FLUID COLLECTIONS

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?” 14 CLASSIFICATION “PSEUDOTUMOURS” – FLUID COLLECTIONS

Core – Signal intensity on T1W Intermediate High Mixed MOM Hips: “What’s to see on MARS MRI?” 15 SIGNAL CHARACTERISTICS Axial T1W NEED BESAGNI T1W FOR ‘MIXED’ “PSEUDOTUMOURS” – FLUID COLLECTIONS

Pseudocapsule – Smooth, linear? – Irregularly thickened? – Areas of susceptibility artefact? MOM Hips: “What’s to see on MARS MRI?” 16 SIGNAL CHARACTERISTICS Coronal STIR “PSEUDOTUMOURS” – FLUID COLLECTIONS

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

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

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

Assess on T1W images Compare to contralateral side Example grading system: – Bal et al, Intr Course Lect [2008] MOM Hips: “What’s to see on MARS MRI?” 20 MUSCLE ATROPHY OTHER PATHOLOGY - MUSCLES GradeComment 0Normal 1≤30% decrease in muscle size % fatty change with decrease in muscle mass 3>70% fatty change with an 80% decrease in size

Significance unknown – surgically induced or indicator of disease? MOM Hips: “What’s to see on MARS MRI?” 21 MUSCLE ATROPHY OTHER PATHOLOGY - MUSCLES Axial T1W – Atrophy of obturator externus and quadratus femoris on right-side

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) MOM Hips: “What’s to see on MARS MRI?” 22 TENDONS OTHER PATHOLOGY - TENDONS Axial T1W – Lateral fluid collection (arrow) associated with marked atrophy of gluteus medius muscle and avulsion of its tendon

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

Fracture – Acetabulum Often difficult to visualise due to artefact – Pubic rami MOM Hips: “What’s to see on MARS MRI?” 24 BONES OTHER PATHOLOGY - BONES 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 BONES OTHER PATHOLOGY - BONES AP Radiograph (left) and Axial T1W images of racture of acetabulum and inferior pubic ramus (circled)

Dermoid MOM Hips: “What’s to see on MARS MRI?” 26 INCIDENTAL PATHOLOGY OTHER PATHOLOGY

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?” 27 CONCLUSION