John G. Cahir

Grading the severity of soft tissue changes associated with metal-on-metal hip replacements:reliability of an MR grading system

IntroductionMetal-on-metal (MoM) soft tissue reactions or aseptic lymphocytic vasculitis-associated lesions (ALVAL) are being recognised using metal artefact reduction (MAR) MR with increasing frequency following the advent of second generation metal-on-metal bearings, but there is no standardised technique for reporting of MR appearances in this disease. The aim of this study was to measure the reliability of a grading system designed for scoring the severity of MoM disease on MRI.Materials and methodsMRI examinations of 73 hips in 59 patients were retrospectively selected and then anonymised, randomised and reviewed by three independent observers (musculoskeletal radiologists). Each MR examination was scored as either A: normal, B: infection, C1: mild MoM disease, C2: moderate MoM disease or C3: severe MoM disease according to pre-defined criteria. Kappa correlation statistics were used to compare the observations.ResultsThere was substantial agreement among all three observers; the correlation coefficient between the two most experienced observers was κ = 0.78 [95% confidence intervals (CI): 0.68–0.88] and when compared with the least experienced observer coefficients were κ = 0.69 (95% CI: 0.57–0.80) and κ = 0.66 (95% CI: 0.54–0.78). The strongest correlation occurred for grades A, C2 and C3. The weakest correlations occurred for grades B and C1.ConclusionThe grading system described in this study is reliable for evaluating ALVAL in MoM prostheses using MR but is limited in differentiating mild disease from infection.

Silent soft tissue pathology is common with a modern metal-on-metal hip arthroplasty.

Background and purpose Adverse reactions to metal debris have been reported to be a cause of pain in metal-on-metal hip arthroplasty. We assessed the incidence of both symptomatic and asymptomatic adverse reactions in a consecutive series of patients with a modern large-head metal-on-metal hip arthroplasty. Methods We studied the early clinical results and results of routine metal artifact-reduction MRI screening in a series of 79 large-head metal-on-metal hip arthroplasties (ASR; DePuy, Leeds, UK) in 68 patients. 75 hips were MRI scanned at mean 31 (12–52) months after surgery. Results 27 of 75 hips had MRI-detected metal debris-related abnormalities, of which 5 were mild, 18 moderate, and 4 severe. 8 of these hips have been revised, 6 of which were revised for an adverse reaction to metal debris, diagnosed preoperatively with MRI and confirmed histologically. The mean Oxford hip score (OHS) for the whole cohort was 21. It was mean 23 for patients with no MRI-based evidence of adverse reactions and 19 for those with adverse reactions detected by MRI. 6 of 12 patients with a best possible OHS of 12 had MRI-based evidence of an adverse reaction. Interpretation We have found a high early revision rate with a modern, large-head metal-on-metal hip arthroplasty. MRI-detected adverse rections to metal debris was common and often clinically “silent”. We recommend that patients with this implant should be closely followed up and undergo routine metal artifact-reduction MRI screening.

Optimization of metal artefact reduction (MAR) sequences for MRI of total hip prostheses

AIM To describe the relative contribution of matrix size and bandwidth to artefact reduction in order to define optimal sequence parameters for metal artefact reduction (MAR) sequences for MRI of total hip prostheses. METHODS AND MATERIALS A phantom was created using a Charnley total hip replacement. Mid-coronal T1-weighted (echo time 12ms, repetition time 400ms) images through the prosthesis were acquired with increasing bandwidths (150, 300, 454, 592, and 781Hz/pixel) and increasing matrixes of 128, 256, 384, 512, 640, and 768 pixels square. Signal loss from the prosthesis and susceptibility artefact was segmented using an automated tool. RESULTS Over 90% of the achievable reduction in artefacts was obtained with matrixes of 256x256 or greater and a receiver bandwidth of approximately 400Hz/pixel or greater. Thereafter increasing the receiver bandwidth or matrix had little impact on reducing susceptibility artefacts. Increasing the bandwidth produced a relative fall in the signal-to-noise ratio (SNR) of between 49 and 56% for a given matrix, but, in practice, the image quality was still satisfactory even with the highest bandwidth and largest matrix sizes. The acquisition time increased linearly with increasing matrix parameters. CONCLUSION Over 90% of the achievable metal artefact reduction can be realized with mid-range matrices and receiver bandwidths on a clinical 1.5T system. The loss of SNR from increasing receiver bandwidth, is preferable to long acquisition times, and therefore, should be the main tool for reducing metal artefact.

Metal Ion Levels Not Sufficient as a Screening Measure for Adverse Reactions in Metal-on-Metal Hip Arthroplasties

This study aims to assess the accuracy of metal ion analysis in the diagnosis of adverse reaction to metal debris (ARMD) in patients with metal-on-metal hip arthroplasties by comparing the cobalt and chromium levels in 57 patients (62 hips) to findings on metal artifact reduction magnetic resonance imaging (MRI). An ARMD was detected using MRI in 18 (29%) of the hips. Forty patients had cobalt levels less than 7 μg/L, and 33 had chromium levels less than 7 μg/L, but 8 of these had an ARMD on MRI and only minimal symptoms (Oxford Hip Score ≥ 44/48). The incidence of ARMD was significantly higher when chromium concentration was above 7 μg/L (P = .02), but normal metal ion levels can be misleading and metal artifact reduction MRI imaging is advised in all patients.

Regional migratory osteoporosis.

Regional migratory osteoporosis (RMO) is an uncommon disease characterised by a migrating arthralgia involving the weight bearing joints of the lower limb. The typical imaging findings on radiographs, magnetic resonance imaging, computed tomography and bone scintigraphy are described and illustrated. Men in their fifth and sixth decades of life are most commonly affected. The most common presentation is with proximal to distal spread in the lower limb. The world literature has been reviewed which has revealed 63 documented cases of regional osteoporosis or bone marrow oedema with migratory symptoms. Most of these cases have not been labelled as RMO and therefore the condition is probably under-diagnosed. The radiology of RMO is indistinguishable from transient osteoporosis of the hip (TOH) except for the migratory symptoms and the two conditions are likely to be part of the same spectrum of disease. Systemic osteoporosis is a more recently recognised accompanying feature that hints at an underlying aetiology and an approach to the management of this condition.

Imaging the femoral sulcus with ultrasound, CT, and MRI: reliability and generalizability in patients with patellar instability

ObjectiveRecent advances in surgical intervention for patellar instability have led to a need for long-term radiological monitoring. The aim of this study is to determine whether or not magnetic resonance imaging (MRI) or ultrasound (US) can replace computed tomography (CT) as the standard of care for the evaluation of the femoral sulcus.Materials and methodsThis was a prospective study comparing the reliability of CT, magnetic resonance (MR), and US for measuring the femoral sulcus in patients with patellar instability. Twenty-four patients were recruited to undergo a CT, MR, and US examination of each knee. Two observers independently measured femoral sulcus angles from subchondral bone and hyaline cartilage on two occasions. Intraclass correlations and generalizability coefficients were calculated to measure the reliability of each of the techniques. Thereafter, two observers measured the femoral sulcus angle from ultrasound images recorded by two independent operators to estimate interobserver and interoperator reliability.ResultsForty-seven knees were examined with CT and US and 44 with MRI. The sulcus angle was consistently smaller when measured from subchondral bone compared to cartilage (5–7°). Interobserver reliability for CT, MR, and US measurements from subchondral bone were 0.87, 0.80, and 0.82 and from cartilage 0.80, 0.81, and 0.50. Generalizability coefficients of measurements from subchondral bone for CT, MR, and US were 0.87, 0.76, and 0.81 and for cartilage 0.76, 0.73, and 0.05. Most of the variability in the US occurred at image acquisition rather than measurement.ConclusionIn patients with patellar instability, CT and MR are reliable techniques for measuring the femoral sulcus angle but US, particularly of the articular cartilage, is not. MR is therefore the most suitable tool for longitudinal studies of the femoral sulcus.

MRI of asymptomatic patients with metal-on-metal and polyethylene-on-metal total hip arthroplasties

AIMS To define and compare magnetic resonance imaging (MRI) findings of asymptomatic patients with metal-on-metal (MOM) and polyethylene-on-metal (POM) total hip replacements (THRs). MATERIALS AND METHODS Twenty-two THRs in 20 asymptomatic patients (seven men, 13 women, mean age 68 years, range 47-86 years) with normal hip radiographs were included in the study. These comprised 10 POM and 12 MOM bearings. Each patient underwent MRI with metal artefact reduction sequences (MARS) at a mean time of 46 months (POM) and 70 months (MOM) after surgery. Two musculoskeletal radiologists independently read each MRI examination for fluid collections, soft-tissue masses, muscle atrophy, and bone marrow signal changes. RESULTS A pre-MRI hip radiograph showed no significant differences from the postoperative radiograph regarding acetabular inclination, femoral stem angle, and stem mantle grade. There were eight periprosthetic collections (one POM, seven MOM). The majority of THRs had normal gluteal muscles. The ipsilateral piriformis and obturator internus muscles were more frequently abnormal in the MOM group. Overall, there were no significant differences in the number of abnormalities between the two types of bearings. CONCLUSION A range of MRI abnormalities are present in normal asymptomatic THRs but the increased frequency of these associated with MOM THR suggest that some of these changes might represent subclinical disease.

Midcarpal instability: a radiological perspective

Midcarpal instability (MCI) is the result of complex abnormal carpal motion at the midcarpal joint of the wrist. It is a form of non-dissociative carpal instability (CIND) and can be caused by various combinations of extrinsic ligament injuries that then result in one of several subtypes of MCI. The complex patterns of injury and the kinematics are further complicated by competing theories, terminology and classifications of MCI. Palmar, dorsal, ulna midcarpal instability, and capitolunate or chronic capitolunate instability are all descriptions of types of MCI with often overlapping features. Palmar midcarpal instability (PMCI) is the most commonly reported type of MCI. It has been described as resulting from deficiencies in the ulna limb of the palmar arcuate ligament (triquetrohamate-capitate) or the dorsal radiotriquetral ligaments, or both. Unstable carpal articulations can be treated with limited carpal arthrodesis or the ligamentous defects can be treated with capsulorrhaphy or ligament reconstruction. Conventional radiographic abnormalities are usually limited to volar intercalated segment instability (VISI) patterns of carpal alignment and are not specific. For many years stress view radiographs and videofluoroscopy have been the methods of choice for demonstrating carpal instability and abnormal carpal kinematics respectively. Dynamic US can be also used to demonstrate midcarpal dyskinesia including the characteristic triquetral “catch-up” clunk. Tears of the extrinsic ligaments can be demonstrated with MR arthrography, and probably with CT arthrography, but intact yet redundant ligaments are more difficult to identify. The exact role of these investigations in the diagnosis, categorisation and management of midcarpal instability has yet to be determined.

MRI of Aseptic Lymphocytic Vasculitis-Associated Lesions in Metal-on-Metal Hip Replacements

OBJECTIVE The aim of this review is to describe the clinical, histopathologic, and MRI features of aseptic lymphocytic vasculitis-associated lesions in total hip replacements. CONCLUSION The introduction of modern metal-on-metal hip arthroplasty has been accompanied by a newly described disease, aseptic lymphocytic vasculitis-associated lesions, which is characterized histologically by bland necrosis and dense perivascular lymphocytic infiltrates. Conventional radiographic findings are often normal, but the typical MRI findings include periprosthetic fluid collections, soft-tissue masses, gluteal tendon avulsion, bone loss, periosteal stripping, neurovascular involvement, and periprosthetic fractures. The severity of the histologic and MRI appearances can be graded according to defined published criteria.

Midcarpal instability:a diagnostic role for dynamic ultrasound?

PURPOSE The aim of this study was to describe the technique of dynamic ultrasound (US) examination of the triquetral clunk, and to illustrate the range of findings in four patients with midcarpal instability (MCI). MATERIALS AND METHODS Four patients were identified (3 men, 1 woman). The case notes, plain radiographs, MRI and dynamic US for each patient were reviewed. Digital video files recording the dynamic US of the triquetral clunks were analysed for the following features of abnormal triquetral mobility: direction and speed of triquetral snap, amount of anteroposterior translocation, and flexion or extension during the snap. RESULTS Five different triquetral clunks were recorded in 4 patients. In four out of five cases the clunk occurred during ulnar translocation of the wrist, and in one during radial translocation. Anteroposterior translocation was anterior (3.4 - 4.7 mm) in three of the clunks and posterior (1 - 10 mm) in two. The degree of flexion or extension varied between 1 and 16 degrees . The snapping phase of the clunk lasted between 0.17 and 0.25 seconds. CONCLUSION Dynamic US can be used to confirm the diagnosis of midcarpal instability by identifying a triquetral catch-up clunk. Quantification of carpal mobility with US may lead to further insights into the mechanics of MCI.