Abstract
Background: Metal-on-metal (MoM) hip replacement, a durable alternative to conventional metal -on-polyethylene hip replacement, is increasingly common nowadays. There is a 4-8% incidence of pain and complications which usually go undetected on radiographs. MRI has a vast potential for early diagnosis in these cases. Aim: To evaluate the feasibility of MR imaging in MoM hips and to review the MR imaging features of various complications associated with metal on metal hip implants. Materials and Methods: 41 patients with 52 replaced hips using MoM prostheses underwent MRI on a 1.5T scanner using standard clinical protocols optimized to minimize metallic susceptibility artifact, known as metal artefact reduction sequences (MARS). A standardized reporting was done with specific comment on periprosthetic osteolysis, loosening, periprosthetic soft tissue mass, gluteal muscle atrophy, iliopsoas atrophy, muscle edema, muscle/ tendon tear and lymphadenopathy. Results: Diagnostic images were obtained in all patients. Of the 52 hips, 32 had total hip replacement (THR) and 20 had resurfacing. The following abnormalities were found. Periprosthetic osteolysis (5), Periprosthetic soft tissue mass (24), Gluteal muscle atrophy – moderate to severe (15), Iliopsoas atrophy (15), Muscle edema (0), Muscle / tendon tear (0), Lymphadenopathy (5). Conclusion: MRI on a 1.5T scanner is a viable technique to image the MoM hip and shows well the various complications associated with post arthroplasty hips. DOI: http://dx.doi.org/10.3126/njr.v3i2.9607 Nepalese Journal of Radiology Vol.3(2)July-Dec, 2013: 49-56
Highlights
NJR I VOL 3 I No 2 I ISSUE 5 I July - Dec, 2013Pilania et al Magnetic Resonance Imaging of Metal on Metal Implants: A BreakthroughThere is a 4-8% incidence of pain and complications which are usually asymptomatic but may require surgical revision and highlights the need for imaging followup.The various complications following arthroplasty include: Aseptic loosening, particle disease, infection, component wear, dislocation, fracture, heterotopic ossification, metalinduced reactive mass, abductor muscle tear, iliopsoas impingement and muscle atrophy.Radiographs, though still the mainstay in evaluating a post arthroplasty hip, and reasonably reliable in the detecting dislocation, fracture and heterotopic ossification, has vast limitations especially in evaluation of soft tissue details
Cross sectional imaging in postarthroplasty hips has always been a challenge because of the susceptibility artifacts on MRI and beam hardening on CT scan which prevent accurate evaluation of regions of interest near the implants.[1,2]
MR imaging in MoM hip replacements has been relatively unexplored and the purpose of this study is to show that MRI is feasible in patients with MoM hips and to provide an insight into the MR imaging features of the various complications associated with MoM hips
Summary
NJR I VOL 3 I No 2 I ISSUE 5 I July - Dec, 2013Pilania et al Magnetic Resonance Imaging of Metal on Metal Implants: A BreakthroughThere is a 4-8% incidence of pain and complications which are usually asymptomatic but may require surgical revision and highlights the need for imaging followup.The various complications following arthroplasty include: Aseptic loosening, particle disease (osteolysis), infection, component wear, dislocation, fracture, heterotopic ossification, metalinduced reactive mass, abductor muscle tear, iliopsoas impingement and muscle atrophy.Radiographs, though still the mainstay in evaluating a post arthroplasty hip, and reasonably reliable in the detecting dislocation, fracture and heterotopic ossification, has vast limitations especially in evaluation of soft tissue details. Cross sectional imaging in postarthroplasty hips has always been a challenge because of the susceptibility artifacts on MRI and beam hardening on CT scan which prevent accurate evaluation of regions of interest near the implants.[1,2] lately with the advent of specialised metal artefact reduction sequences(MARS) and newer instrumentation, the challenge of susceptibility artefacts due to the metal implants have largely been overcome and MR with its inherent ability of better soft tissue delineation has provided a phenomenal edge in providing a more accurate diagnosis of the underlying complications.[3,4] echo (GRE) images, and (b) loss of signal intensity because of intravoxel dephasing, (T2*effect) on GRE images[1,3] as these sequences, unlike SE, include no 180° refocusing pulse, which enables recovery of the transverse signal lost because of static magnetic field inhomogeneities and bulk susceptibility differences in SE sequences.[1], The metal artifact reduction sequences (MARS) reduce the size and intensity of susceptibility artifacts from magnetic field distortion allowing assessment of the periprosthetic soft tissues These sequences, which are based on view angle tilting, smaller interecho spacing, increased readout bandwidth and frequency-encoding direction oriented away from the tissues of interest, can conveniently be used in conjunction with any spin-echo sequence and requires minimal additional imaging time.[6,7,8,9,10,11,12,13,14,15]. Conclusion: MRI on a 1.5T scanner is a viable technique to image the MoM hip and shows well the various complications associated with post arthroplasty hips
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