Advanced MRI Techniques for the Hip Joint: Focus on the Postoperative Hip

Imaging approach to prosthetic joint infection

The diagnosis of prosthetic joint infection (PJI) remains challenging, despite multiple available laboratory tests for both serum and synovial fluid analysis. The clinical symptoms of PJI are not always characteristic, particularly in the chronic phase, and there is often significant overlap in symptoms with non-infectious forms of arthroplasty failure. Further exacerbating this challenge is lack of a universally accepted definition for PJI, with publications from multiple professional societies citing different diagnostic criteria. While not included in many of the major societies' guidelines for diagnosis of PJI, diagnostic imaging can play an important role in the workup of suspected PJI. In this article, we will review an approach to diagnostic imaging modalities (radiography, ultrasound, CT, MRI) in the workup of suspected PJI, with special attention to the limitations and benefits of each modality. We will also discuss the role that image-guided interventions play in the workup of these patients, through ultrasound and fluoroscopically guided joint aspirations. While there is no standard imaging algorithm that can universally applied to all patients with suspected PJI, we will discuss a general approach to diagnostic imaging and image-guided intervention in this clinical scenario.

MRI of total hip arthroplasty: technical aspects and imaging findings

Total hip arthroplasty (THA) is the best surgical approach for treating advanced hip degeneration, providing pain relief, and improved function in most cases. In the past, MR imaging quality has been highly compromised by in-plane distortions, inadequate fat saturation, and other artifacts due to metal components of THA. Technological advancements have made pathologic conditions, which were previously hidden by periprosthetic artifacts, outstanding features due to the optimization of several sequences. To date, several short and long-term complications involving bony and soft-tissue structures may be detected through magnetic resonance imaging (MRI). The use of MRI with adapted sequences and protocols may drastically reduce artifacts thereby providing essential pre-operative elements for planning revision surgery of failed THA. This review has the purpose of conveying new insights to musculoskeletal radiologists about the techniques to suppress metal-related artifacts and the hallmark MRI findings of painful THA. CRITICAL RELEVANCE STATEMENT: Advancements in metal-suppression have given radiologists the opportunity to play an emerging role in THA management. This article provides technical and imaging insights into challenges that can be encountered in cases of THA, which may present complications and characteristic imaging findings. KEY POINTS: Imaging total hip arthroplasty requires adapted MRI protocol and awareness of the common complications. We have reported the available metal-suppression sequences for evaluating total hip arthroplasty. Many structures and conditions should be considered when dealing with painful aseptic or septic arthroplasty.

[Advances in study of surgical approaches and MRI evaluation of total hip arthroplasty]

Objective

To review the research on different surgical approaches and MRI evaluation of total hip arthroplasty (THA), to clarify the possible muscle damage caused by different approaches, and to help clinicians avoid intraoperative muscle damage and identify the causes of certain muscle-related complications after operation.

Methods

The research literature on different surgical approaches and MRI evaluation of THA at home and abroad was extensively reviewed to summarize the MRI performance of the posterior approach, modified direct lateral approach, direct anterior approach, and minimally invasive anterolateral approach (also called Orthopadische Chirurgie Munchen approach).

Results

The traditional posterior approach mainly damages the short external rotator muscle group and increases the incidence of postoperative dislocation; the piriformis-keeping posterior approach significantly improves the quality of the pyriformis tendon in the postoperative period, but it may lead to damage to the intrapelvic portion of the piriformis muscle. The modified direct lateral approach mainly damages the gluteus medius muscle, which increases the risk of postoperative claudication. The direct anterior approach mainly damages the vastus tensoris muscle and may result in damage to the short external rotator muscle group and the muscles around the incision. The minimally invasive anterolateral approach primarily damages the superior gluteal nerve, which subsequently leads to denervation of the broad fascial tensor fasciae latae, and this approach may also result in injury to the gluteus medius and gluteus minimus muscles. The muscle damage status significantly affects prognosis, and the minimally invasive approach is more suitable for elderly patients.

Conclusion

MRI can clarify the different types of muscle damage caused by different surgical approaches. Minimally invasive approaches can reduce muscle damage and improve postoperative function compared with traditional approaches, and can benefit elderly patients more, but due to the small field, forcing to expand the surgical field will lead to unintended muscle damage and reduce postoperative function.

Revision rate in metal compared to ceramic humeral head total shoulder arthroplasty and hemiarthroplasty

Aims

Metal and ceramic humeral head bearing surfaces are available choices in anatomical shoulder arthroplasties. Wear studies have shown superior performance of ceramic heads, however comparison of clinical outcomes according to bearing surface in total shoulder arthroplasty (TSA) and hemiarthroplasty (HA) is limited. This study aimed to compare the rates of revision and reoperation following metal and ceramic humeral head TSA and HA using data from the National Joint Registry (NJR), which collects data from England, Wales, Northern Ireland, Isle of Man and the States of Guernsey.

Methods

NJR shoulder arthroplasty records were linked to Hospital Episode Statistics and the National Mortality Register. TSA and HA performed for osteoarthritis (OA) in patients with an intact rotator cuff were included. Metal and ceramic humeral head prostheses were matched within separate TSA and HA groups using propensity scores based on 12 and 11 characteristics, respectively. The primary outcome was time to first revision and the secondary outcome was non-revision reoperation.

Results

A total of 4,799 TSAs (3,578 metal, 1,221 ceramic) and 1,363 HAs (1,020 metal, 343 ceramic) were included. The rate of revision was higher for metal compared with ceramic TSA, hazard ratio (HR) 3.31 (95% confidence interval (CI) 1.67 to 6.58). At eight years, prosthesis survival for ceramic TSA was 98.7% (95% CI 97.3 to 99.4) compared with 96.4% (95% CI 95.2 to 97.3) for metal TSA. The majority of revision TSAs were for cuff insufficiency or instability/dislocation. There was no significant difference in the revision rate for ceramic compared with metal head HA (HR 1.33 (95% CI 0.76 to 2.34)). For ceramic HA, eight-year prosthetic survival was 92.8% (95% CI 86.9 to 96.1), compared with 91.6% (95% CI 89.3 to 93.5) for metal HA. The majority of revision HAs were for cuff failure.

Conclusion

The rate of all-cause revision was higher following metal compared with ceramic humeral head TSA in patients with OA and an intact rotator cuff. There was no difference in the revision rate for HA according to bearing surface.

Hip Capsulolabral Complex: Anatomy, Disease, MRI Features, and Postoperative Appearance

The hip is a uniquely constrained joint with critical static stability provided by the labrum, capsule and capsular ligaments, and ligamentum teres. The labrum is a fibrocartilaginous structure along the acetabular rim that encircles most of the femoral head. Labral tears are localized based on the clock-face method, which determines the extent of the tear while providing consistent terminology for reporting. Normal labral variants can mimic labral disease and can be differentiated by assessment of thickness or width, shape, borders, location, and associated abnormalities. The Lage and Czerny classification systems are currently the most well-known arthroscopic and imaging systems, respectively. Femoroacetabular impingement is a risk factor for development of labral tears and is classified according to bone dysmorphisms of the femur ("cam") or acetabulum ("pincer") or combinations of both (mixed). The capsule consists of longitudinal fibers reinforced by ligaments (iliofemoral, pubofemoral, ischiofemoral) and circular fibers. Capsular injuries occur secondary to hip dislocation or iatrogenically after capsulotomy. Capsular repair improves hip stability at the expense of capsular overtightening and inadvertent chondral injury. The ligamentum teres is situated between the acetabular notch and the fovea of the femoral head. Initially considered to be inconsequential, recent studies have recognized its role in hip rotational stability. Existing classification systems of ligamentum teres tears account for injury mechanism, arthroscopic findings, and treatment options. Injuries to the labrum, capsule, and ligamentum teres are implicated in symptoms of hip instability. The authors discuss the labrum, capsule, and ligamentum teres, highlighting their anatomy, pathologic conditions, MRI features, and postoperative appearance. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

Midterm results of the Birmingham hip resurfacing: a single-surgeon series

INTRODUCTION

Birmingham hip resurfacing (BHR) is readily used as alternative to total hip replacement in younger patients. The current study aims to compare outcomes in terms of adverse local tissue reactions (ALTR), elevated metal ion levels and survival rates between low-risk (femoral component size ≥ 48 mm) and high-risk (femoral component size < 48 mm) BHR patients at a minimum 5-year follow-up (FU).

MATERIALS AND METHODS

We report the minimum 5-year, single surgeon outcome results of 183 BHRs, performed between 2007 and 2012. 154 patients, 18 women (20 hips) and 136 men (163 hips) were included in the study. Patients were grouped in 149 low-risk cases (femoral component size ≥ 48 mm) and in 34 high-risk cases (18 female/12 male) patients with a femoral head size < 48 mm).

RESULTS

At a minimum of 5-years FU time, 91% of the patients were available for FU. The overall survival rate was 91.8%. There were five revisions (survival rate 96.6%) in the low-risk group and ten revisions (survival rate 70.6%) in the high-risk group. In the low-risk group, six patients (6.5%) showed elevated metal ion levels (> 7 μg/l), compared to five patients (20.8%) in the high risk-group (p = 0.03).

CONCLUSION

Including the surgeon's initial learning curve, the BHR shows very good mid-term survival rates in the low-risk group but should, as previously demonstrated, not be considered for patients with less than 48 mm femoral head size.

LEVEL OF EVIDENCE

Level III: retrospective cohort study.

Inducible displacement CT increases the diagnostic accuracy of aseptic loosening in primary total hip arthroplasty

BACKGROUND AND PURPOSE

Inducible displacement CT compares 2 CTs acquired in series but with alternated rotation of the femur. This provides visual and quantitative clues as to the mechanical situation, i.e., loosening, of a total hip arthroplasty. We report the accuracy of this method as well as the experience of integrating it into a clinical workflow.

PATIENTS AND METHODS

This was a retrospective single centre study of 72 cases of suspected aseptic loosening were the surgeon after reviewing a standard plain radiograph saw a need for more information. The displacement CT and plain radiograph were compared either to intraoperative findings or a 1-3 year follow up questionnaire for patients that did not have revision surgery. Patients reporting degradation in status since the time of the displacement CT were called for a follow up plain radiograph. Sensitivity and specificity were assessed, and user experience gathered.

RESULTS

Of 72 enrolled patients 15 were lost to follow up. Of the remaining 57, 17 were judged by in-traoperative findings or follow-up to have had loose implants. For plain radiography the sensitivity and specificity were 59% (95% CI 35-82) and 85% (74-96). For displacement CT the corresponding values were 77% (56-97), and 100% (100-100) respectively. The tool was adaptable to clinical routine.

CONCLUSION

Displacement CT with alternated rotations of the femur is a viable option to improve the diagnostic process for identifying aseptic loosening in a total hip arthroplasty.

Imaging of total hip arthroplasty: Part I – Implant design, imaging techniques, and imaging of component wear and fracture

Despite being one of the most reliable procedures in orthopedic surgery, complications can occur after total hip arthroplasty, and radiology plays an essential role in their evaluation. This article will review the various types of hip arthroplasty and their normal appearances on imaging, followed by mechanisms and imaging appearances of component wear and fracture.

Metal Articulations as a Source of Total Hip Arthroplasty Pain

The consensus systematic risk stratification algorithm from the American Association of Hip and Knee Surgeons, the American Academy of Orthopaedic Surgeons, and The Hip Society summarizes clinical challenges in evaluation and treatment of metal-on-polyethylene total hip arthroplasty (THA) patients with adverse local tissue reaction (ALTR) due to mechanically assisted crevice corrosion (MACC), reviews up-to-date evidence, and identifies the areas for future research in order to provide a useful resource for orthopedic surgeons providing care to these patients. A painful THA has various intrinsic and extrinsic causes. ALTR is one of the intrinsic causes in patients with painful THA. The occurrence of ALTR due to MACC at modular junctions is likely to be multifactorial, including implant, surgical, and patient factors. Therefore, a systematic evaluation needs to involve a focused clinical history, detailed physical examination, laboratory tests, and imaging in order to identify potential differential diagnoses. There should be a low threshold to perform a systematic evaluation of patients with painful non-metal-on-metal THA, including patients with metal-on-polyethylene THA, and modular dual-mobility THA with the CoCr metal acetabular insert, as early recognition and diagnosis of ALTR due to MACC will facilitate initiation of appropriate treatment prior to significant adverse biological reactions. Specialized tests such as blood metal analysis and metal artifact reduction sequence magnetic resonance imaging are important modalities in evaluation and management of ALTR in patients with painful THA.

Imaging in Hip Arthroplasty Management Part 2: Postoperative Diagnostic Imaging Strategy

Hip arthroplasty (HA) is a frequently used procedure with high success rates, but 7% to 27% of the patients complain of persistent postsurgical pain 1 to 4 years post-operation. HA complications depend on the post-operative delay, the type of material used, the patient’s characteristics, and the surgical approach. Radiographs are still the first imaging modality used for routine follow-up, in asymptomatic and painful cases. CT and MRI used to suffer from metallic artifacts but are nowadays central in HA complications diagnosis, both having their advantages and drawbacks. Additionally, there is no consensus on the optimal imaging workup for HA complication diagnosis, which may have an impact on patient management. After a brief reminder about the different types of prostheses, this article reviews their normal and pathologic appearance, according to each imaging modality, keeping in mind that few abnormalities might be present, not anyone requiring treatment, depending on the clinical scenario. A diagnostic imaging workup is also discussed, to aid the therapist in his imaging studies prescription and the radiologist in their practical aspects.

Simultaneous 18F-FDG-PET/MRI for the detection of periprosthetic joint infections after knee or hip arthroplasty: a prospective feasibility study

Purpose

This study investigated the diagnostic value of simultaneous 18F-fluordeoxyglucose positron emission tomography/magnetic resonance imaging (PET/MRI) in suspected periprosthetic joint infection (PJI) of the hip and knee.

Methods

Sixteen prostheses from 13 patients with suspected PJI were prospectively examined using PET/MRI. Image datasets were evaluated in consensus by a radiologist and a nuclear physician for the overall diagnosis of ‘PJI’ (yes/no) and its anatomical involvement, such as the periprosthetic bone margin, bone marrow, and soft tissue. The imaging results were compared with the reference standard obtained from surgical or biopsy specimens and subjected to statistical analysis.

Results

Using the reference standard, ten out of the 13 prostheses (ten hips, threes knees) were diagnosed with PJI. Using PET/MRI, every patient with PJI was correctly diagnosed (sensitivity, 100%; specificity, 100%). Considering the anatomical regions, the sensitivity and specificity were 57% and 50% in the periprosthetic bone margin, 75% and 33% in the bone marrow, and 100% and 100% in the soft tissue.

Conclusion

PET/MRI can be reliably used for the diagnosis of PJI. However, assessment of the periprosthetic bone remains difficult due to the presence of artefacts. Thus, currently, this modality is unlikely to be recommended in clinical practice.

The Utility of MRI With Multiacquisition Variable-Resonance Image Combination (MAVRIC) in Diagnosing Deep Total Hip Arthroplasty Infection

Background: The 2010 American Academy of Orthopaedic Surgeons Clinical Practice Guidelines report insufficient evidence to address the diagnostic efficacy of magnetic resonance imaging (MRI) for periprosthetic joint infection (PJI). Questions/Purposes: The purpose of this study was to determine the utility of MRI with multiacquisition variable-resonance image combination (MAVRIC) metal artifact suppression techniques in diagnosing PJI in the setting of total hip arthroplasty (THA). Methods: Multiacquisition variable-resonance image combination MRIs obtained of THAs between November 2012 and November 2016 were queried. Radiology reports were classified as positive (suspicious for infection), negative (no features of infection), or inconclusive (infection cannot be excluded or correlation with aspiration suggested if clinically concerned). Chart review identified cases of deep PJI according to the modified Musculoskeletal Infection Society criteria. Results: Of 2156 MRIs of THAs included, MRI was concerning for infection in 1.8% (n = 39), inconclusive in 1.2% (n = 26), and negative in 97.0% (n = 2091). Deep PJI was identified in 53 (2.5%) patients, 30 of whom (56.6%) had conclusively positive finding on MRI (false-negative rate: 43.4%, sensitivity: 56.6%). Of 2103 aseptic THAs, only 9 (0.4%) MRIs were read as suspicious for infection (false-positive rate: 0.4%; specificity: 99.6%). Conclusion: Magnetic resonance imaging with MAVRIC is a highly specific test for PJI with a low false-positive rate. This indicates that when clinicians are provided with an MRI that unexpectedly suggests infection, a formal evaluation for infection is indicated. In patients with otherwise equivocal diagnostic findings, MRI may help confirm, but not refute, a diagnosis of PJI. Prospective study with more experienced image reviewers may further support the use of MRI in PJI.

Risk Stratification Algorithm for Management of Head-Neck Taper Tribocorrosion in Patients with Metal-on-Polyethylene Total Hip Arthroplasty: Consensus Statement of the American Association of Hip and Knee Surgeons, the American Academy of Orthopaedic Surgeons, and The Hip Society

Adverse local tissue reactions (ALTRs) were initially reported as complications associated with metal-on-metal (MoM) bearings; however, there is increasing concern regarding the occurrence of adverse local tissue reactions from mechanically assisted crevice corrosion (MACC) at the femoral head-neck junction or between other modular junctions of the implant containing cobalt chromium parts in patients with metal-on-polyethylene (MoP) bearings. ALTR due to MACC at the head-neck junction has primarily been reported in association with cobalt chromium alloy femoral heads. As pain following total hip arthroplasty may have various intrinsic and extrinsic causes, a systematic approach to evaluation (risk stratification algorithm) based on the currently available data is recommended to optimize patient management. Evaluation should begin by ruling out common causes of pain, including component loosening and periprosthetic joint infection. While specialized tests such as blood metal analysis and metal artifact reduction sequence magnetic resonance imaging (MARS MRI) are useful modalities in evaluating for ALTRs, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. There should be a low threshold to perform a systematic evaluation for ALTR due to MACC in patients with metal-on-polyethylene total hip arthroplasty as early recognition and diagnosis is critical, as delays in appropriate treatment initiation may result in soft-tissue damage, which complicates surgical treatment and is associated with a higher risk of complications and poorer patient outcomes.

Does load-bearing materials influence hip capsule thickness in total hip replacement? An MRI case-matched study

BACKGROUND

Ceramic-on-ceramic (COC) total hip replacements (THR) have exhibited less instability and late dislocation. Hip capsule plays an important role in hip stability. Different surrounding soft tissue reactions have been observed according to the bearing material used but no study compared these data using MRI investigation. Therefore, we performed a retrospective case control study to compare hip capsule thicknesses according to the bearing materials in THR and in native hips.

HYPOTHESIS

Hip capsule is thicker after COC THR compared to ceramic- or metal-on-polyethylene (PE) bearings, or native hips.

MATERIALS AND METHOD

Magnetic resonance imaging (MRI) images, combined with a multi acquisition variable resonance image combination (MAVRIC) sequence, was used to measure the hip capsule thickness in 16 patients (29 hips) who had either COC (13 hips, median age at surgery: 64.8 years old, median follow-up at imaging: 2482 days), PE bearings (11 hips, median age at surgery: 48.4 years old (significantly different from COC THR), median follow-up at imaging: 1860 days (NS)), or a native hip with no implant (5 hips). Two independent radiologists measured capsular thicknesses in 4 different zones and were blinded regarding the bearing components. The imaged hips were classified into three groups: native, COC and PE.

RESULTS

The COC THR group had the thickest capsules (median 7.0mm, range 2.9-15.5mm). This result was statistically significant (p<0.0001) when compared to PE THR (median 4.9mm, range 2.2-10.5mm), and to native hips (median 4.1mm, range 2.7-6.9mm) measurements, respectively. Furthermore, painful hips had thinner capsules (4.6mm, range 2-10.5) compared to not painful hips (6.8mm, range 2.3-15.5) (p=0.0006).

DISCUSSION

This is the first in-vivo study measuring capsular thickness in THR with the objective of measuring variations according to the hip implant materials used. The results revealed a significantly thicker capsule for the COC bearing compared to either PE or native hips, and a thinner capsule in painful hips.

LEVEL OF EVIDENCE

III, retrospective non-consecutive cohort study.

Best Practices: Best Imaging Modality for Surveillance of Metal-on-Metal Hip Arthroplasty

OBJECTIVE. Metal-on-metal hip arthroplasty has been shown to result in soft-tissue complications in some patients, making revision surgery necessary. Imaging is critical in the detection and surveillance of soft-tissue complications, which are collectively termed adverse reaction to metal debris (ARMD) and adverse local tissue reaction. Studies have investigated the use of ultrasound, MRI, and CT for detecting ARMD, and each modality has advantages and disadvantages. This article provides evidence-based recommendations for imaging surveillance of ARMD. CONCLUSION. Compared with ultrasound, MRI has been found to be a better imaging modality for surveillance of ARMD. In addition, MRI is not operator dependent, allows visualization of soft-tissue details, and allows more consistent measurement of fluid collections on follow-up examinations. Limitations of ultrasound include operator skill, the inability to visualize osseous structures, and the challenge of visualizing posterior soft tissues for synovitis and fluid collections in larger patients. Finally, CT is only useful for focused evaluation of osteolysis or periprosthetic fracture.

What is the Diagnostic Accuracy of MRI for Component Loosening in THA?

BACKGROUND

Implant loosening is a common cause of reoperation after THA. Plain radiographs have been the default modality to evaluate loosening, although radiographs provide a relatively insensitive assessment of integration; cross-sectional modalities may provide a more detailed evaluation but traditionally have suffered from metal-related artifacts. We sought to determine whether MRI is capable of reliably detecting operatively confirmed component loosening in patients after hip arthroplasty.

QUESTIONS/PURPOSES

(1) Is assessing implant integration using MRI (with multiacquisition variable resonance image combination, [MAVRIC]) repeatable between readers? (2) What is the sensitivity and specificity of MRI with MAVRIC to evaluate component loosening, using intraoperative assessment as a gold standard? (3) How does the sensitivity and specificity of MRI with MAVRIC for surgically confirmed component loosening compare with those of radiographs?

METHODS

Between 2012 and 2017, 2582 THAs underwent revision at one institution. Of those, 219 had a preoperative MRI with MAVRIC. During that period, the most common indication for obtaining an MRI was evaluation of potential adverse local tissue reaction. The surgeons' decision to proceed with revision was based on their overall assessment of clinical, imaging, and laboratory findings, with MRI findings cited as contributing to the decision to revise commonly occurring in the setting of recalled implants. Of the THAs that underwent MRI, 212 were included in this study, while seven were excluded due to equivocal operative notes (5) and excessively poor quality MRI (2). MRI was performed at 1.5T using a standardized arthroplasty imaging protocol, including MARS (metal artifact reduction sequencing) and MAVRIC techniques. Two independent musculoskeletal fellowship-trained readers (one with 26 and one with 5 years of experience) blinded to operative findings scored a subset of 57 hips for implant integration based on Gruen zone and component loosening (defined as complete circumferential loss of integration around a component) to evaluate interobserver reliability. A third investigator blinded to imaging findings reviewed operative notes for details on the surgeon's assessment of intraoperative loosening.

RESULTS

Gwet's agreement coefficients (AC) were used to describe interobserver agreement; these are similar to Cohen's kappa but are more resistant to certain paradoxes, such as unexpectedly low values in the setting of very high or low trait prevalence, or good agreement between readers on marginal counts. Almost perfect interobserver agreement (AC2 = 0.81-1.0) was demonstrated for all acetabular zones and all femoral Gruen zones on MRI, while perfect (AC1 = 1.0) agreement was demonstrated for the overall assessment of acetabular component loosening and near perfect agreement was shown for the assessment of femoral component loosening (AC1 = 0.98). MRI demonstrated a sensitivity and specificity of 83% (95% CI, 65-96) and 98% (95% CI, 97-100), respectively, for acetabular component loosening and 75% (95% CI, 55-94) and 100% (95% CI, 100-100), respectively, for femoral component loosening. Radiographs demonstrated a sensitivity and specificity of 26% (95% CI, 12-47) and 100% (95% CI, 96-100), respectively, for acetabular component loosening and 20% (95% CI, 9-47) and 100% (95% CI, 100-100), respectively, for femoral component loosening.

CONCLUSION

MRI may provide a repeatable assessment of implant integration and demonstrated greater sensitivity than radiographs for surgically confirmed implant loosening in patients undergoing revision THA at a single institution. Additional multi-institutional studies may provide more insight into the generalizability of these findings.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Radiological Imaging Evaluation of the Failing Total Hip Replacement

Total hip replacements (THR) have been performed in the UK from the 1960s and since then we have seen surgical techniques, the design of implants, and imaging modalities rapidly develop. This paper will aim to review the different complications and imaging appearance which help to evaluate each problem. As for all investigations for bone and joints, a radiograph is the first imaging to be performed for any patient with a THR and can detect a majority of complications. CT is relatively low-cost, simple to perform and easily available making it an excellent tool to supplement radiographs when trying to evaluate a hip prosthesis. Single photon emission computed tomography with CT (SPECT-CT) is an emerging modality which has shown to combine the sensitivity that bone scintigraphy offers with the high specificity of CT. SPECT imaging also has the advantage of showing the bone's metabolic activity and is less prone to metal artifact than Magnetic resonance imaging (MRI). MRI has evolved to become an important diagnostic tool for the evaluation of THR in the post-operative period. Optimized pulse sequences and metal artifact reduction techniques have made MRI a useful tool in diagnosis of soft tissue abnormalities and is particularly useful in identifying adverse local tissue reactions in metal on metal implants. CT and MRI are accurate in identifying the diagnosis of most causes of THR complications except infection. Research confirms that leukocyte-marrow scintigraphy is the modality of choice for accurately diagnosing prosthetic joint infection and reassures us of its superiority over other nuclear medicine imaging. However, due to the limited availability and increased costs when performing leukocyte-marrow scintigraphy, CT and SPECT-CT would be a more preferred option when suspecting prosthesis infection. Ultrasound (US) has a limited role in the assessment of most THR complications but can be useful to identify peri-prosthetic fluid collections and the presence of soft tissue sinus tracts. Being aware of the imaging modalities that are available to orthopedic surgeons, and discussing these challenging cases with specialist radiologists will enable optimal management of THR complications.

Discovery of biomarkers to identify peri-implant osteolysis before radiographic diagnosis

Peri-implant osteolysis is commonly diagnosed after substantial bone loss has occurred, making revision surgery more challenging. The goal of the current study was to identify urinary biomarkers that differentiate total hip replacement patients who eventually develop osteolysis from patients who do not. We used a repository of 24-h urine samples collected prior to surgery and annually thereafter in 26 patients, 16 who developed osteolysis, and 10 who did not. We examined the markers at radiographic diagnosis, annually for 6 years preceding diagnosis, at the first post-operative sampling point, and pre-operatively. Patients in the osteolysis and non-osteolysis groups were matched according to time post-surgery and did not differ in the male:female ratio or age at surgery. Seven candidate biomarkers were measured, including free deoxypyridinoline (DPD), cross-linked N-telopeptides (NTX), interleukin-6 (IL-6), interleukin-8 (IL-8), osteoprotegerin (OPG), α-crosslaps (α-CTX), and β-crosslaps (β-CTX). As an individual biomarker, DPD demonstrated the highest ability to predict osteolysis, with an area under the curve (AUC) in Receiver Operating Characteristic (ROC) analyses of 0.844 at 6 years prior to diagnosis. A panel of α-CTX and IL-6 was able to identify at-risk patients with an AUC of 0.941 or greater at all post-operative time points and an AUC of 1.000 pre-operatively. The results demonstrate the potential of using non-invasive biomarkers to identify patients at risk for peri-implant osteolysis long before the emergence of radiographic signs. Further, the high accuracy of the pre-operative biomarker levels demonstrates the potential importance of pre-existing, patient-specific factors driving subsequent osteolysis. Study Design © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2754-2761, 2018.

MRI Findings at the Bone-Component Interface in Symptomatic Unicompartmental Knee Arthroplasty and the Relationship to Radiographic Findings

BACKGROUND

The most common modes of failure of cemented unicompartmental knee arthroplasty (UKA) designs are aseptic loosening and unexplained pain at short- to mid-term follow-up, which is likely linked to early fixation failure. Determining these modes of failure remains challenging; conventional radiographs are limited for use in assessing radiolucent lines, with only fair sensitivity and specificity for aseptic loosening.

QUESTIONS/PURPOSES

We sought to characterize the bone-component interface of patients with symptomatic cemented medial unicompartmental knee arthroplasty (UKA) using magnetic resonance imaging (MRI) and to determine the relationship between MRI and conventional radiographic findings.

METHODS

This retrospective observational study included 55 consecutive patients with symptomatic cemented UKA. All underwent MRI with addition of multiacquisition variable-resonance image combination (MAVRIC) at an average of 17.8 ± 13.9 months after surgery. MRI studies were reviewed by two independent musculoskeletal radiologists. MRI findings at the bone-cement interface were quantified, including bone marrow edema, fibrous membrane, osteolysis, and loosening. Radiographs were reviewed for existence of radiolucent lines. Inter-rater agreement was determined using Cohen's κ statistic.

RESULTS

The vast majority of symptomatic UKA patients demonstrated bone marrow edema pattern (71% and 75%, respectively) and fibrous membrane (69% and 89%, respectively) at the femoral and tibial interface. Excellent and substantial inter-rater agreement was found for the femoral and tibial interface, respectively. Furthermore, MRI findings and radiolucent lines observed on conventional radiographs were poorly correlated.

CONCLUSION

MRI with the addition of MAVRIC sequences could be a complementary tool for assessing symptomatic UKA and for quantifying appearances at the bone-component interface. This technique showed good reproducibility of analysis of the bone-component interface after cemented UKA. Future studies are necessary to define the bone-component interface of symptomatic and asymptomatic UKA patients.