Association of Total Hip Arthroplasty Flexural Rigidity With Magnetic Resonance Imaging and Histological Findings.

BACKGROUND: Modular connections in total hip arthroplasty (THA) offer surgical advantages, but can contribute to implant fretting and corrosion due to micromotion at the head-stem interface. Previous studies implicated lower flexural rigidity as a key contributing factor to THA corrosion and fretting, but none associated flexural rigidity with direct histological evaluation or magnetic resonance imaging (MRI) outcomes. The purpose of this study was to determine how implant flexural rigidity is associated with MRI imaging metrics and histopathological outcomes in patients who have a failed THA. METHODS: Patients requiring revision THA surgery underwent preoperative MRIs with 3-dimensional multispectral imaging techniques to suppress metal artifacts. The MRI images were graded for adverse local tissue reactions. For each hip, trunnion flexural rigidity was measured from the retrieved femoral stem, and a periprosthetic tissue sample was retrieved and evaluated using semiquantitative histology. Generalized linear models and analyses of variance were used to assess associations between flexural rigidity and MRI and histology outcomes. RESULTS: A total of 106 THA stems were retrieved (46 women and 60 men, age: 68 years (range, 60 to 73 years). After adjustment for length of implantation, flexural rigidity was negatively correlated with histologic aseptic lymphocyte-dominant vasculitis-associated lesion severity (ß = -26.27, P = .018), Fujishiro lymphocyte grading (ß = -13.4, P = .039), perivascular lymphocyte layers (ß = -17.8, P = .022), the grade of tissue organization (ß = -22.5, P = .009), the presence of diffuse synovitis (ß = -66.5, P = .003), and the presence of lymphoid aggregates (ß = -75.9, P = .022). No association was found between MRI metrics and flexural rigidity. CONCLUSIONS: Among these implants, decreased trunnion stiffness was associated with increased histologic features of adverse host-mediated soft tissue reactions.

MRI Advancements in Musculoskeletal Clinical and Research Practice.

Over the past decades, MRI has become increasingly important for diagnosing and longitudinally monitoring musculoskeletal disorders, with ongoing hardware and software improvements aiming to optimize image quality and speed. However, surging demand for musculoskeletal MRI and increased interest to provide more personalized care will necessitate a stronger emphasis on efficiency and specificity. Ongoing hardware developments include more powerful gradients, improvements in wide-bore magnet designs to maintain field homogeneity, and high-channel phased-array coils. There is also interest in low-field-strength magnets with inherently lower magnetic footprints and operational costs to accommodate global demand in middle- and low-income countries. Previous approaches to decrease acquisition times by means of conventional acceleration techniques (eg, parallel imaging or compressed sensing) are now largely overshadowed by deep learning reconstruction algorithms. It is expected that greater emphasis will be placed on improving synthetic MRI and MR fingerprinting approaches to shorten overall acquisition times while also addressing the demand of personalized care by simultaneously capturing microstructural information to provide greater detail of disease severity. Authors also anticipate increased research emphasis on metal artifact reduction techniques, bone imaging, and MR neurography to meet clinical needs.

The role of advanced metal artifact reduction MRI in the diagnosis of periprosthetic joint infection.

Identification and diagnosis of periprosthetic joint infection (PJI) are challenging, requiring a multi-disciplinary approach involving clinical evaluation, laboratory tests, and imaging studies. MRI is advantageous to alternative imaging techniques due to superior soft tissue contrast and absence of ionizing radiation. However, the presence of metallic implants can cause signal loss and artifacts. Metal artifact suppression (MARS) MRI techniques have been developed that mitigate metal artifacts and improve periprosthetic soft tissue visualization. This paper provides a review of the various MARS MRI techniques, their clinical applicability and accuracy in PJI diagnosis and evaluation, and current challenges and future perspectives.

Significantly Worse Fixation of Cemented Patellar Components on Multiacquisition Variable-Resonance Image Combination Magnetic Resonance Imaging Compared to Femoral and Tibial Components: A Cause for Concern?

BACKGROUND: The etiology of anterior knee pain after total knee arthroplasty (TKA) remains unclear. Few studies have examined patellar fixation quality. The purpose of the present study was to evaluate the patellar cement-bone interface after TKA on magnetic resonance imaging (MRI) and to correlate the patella fixation grade with the incidence of anterior knee pain. METHODS: We retrospectively reviewed 279 knees undergoing metal artifact reduction MRI for either anterior or generalized knee pain at least 6 months after cemented, posterior-stabilized TKA with patellar resurfacing with one implant manufacturer. MRI cement-bone interfaces and percent-integration of the patella, femur, and tibia were assessed by a fellowship-trained senior musculoskeletal radiologist. The grade and character of the patella interface were compared to the femur and tibia. Regression analyses were used to determine the association between patella integration with anterior knee pain. RESULTS: There were more patellar components with ≥75% zones of fibrous tissue (50%) compared to the femur (18%) or tibia (5%) (P < .001). There were a greater number of patellar implants with poor cement integration (18%) compared to the femur (1%) or tibia (1%) (P < .001). MRI findings showed more evidence of patellar component loosening (8%) compared to the femur (1%) or tibia (1%) (P < .001). Anterior knee pain was correlated with worse patella cement integration (P = .01), with women predicted to have better integration (P < .001). CONCLUSION: The quality of the patellar cement-bone interface after TKA is worse compared to the femoral or tibial component interface. Poor patellar cement-bone interface may be a source of anterior knee pain after TKA, but further investigation is required.

Diagnostic Performance of MRI for Component Loosening in Total Knee Arthroplasty Compared with Radiography.

Background Because loosening of total knee arthroplasty (TKA) occurs due to poor osseous integration at component-bone interfaces, interface assessment may be helpful in diagnosing loosening at MRI. Purpose To determine interreader reproducibility for characterizing component interfaces and diagnosing loosening and to evaluate the diagnostic performance of MRI for diagnosing loosening after TKA compared with radiography. Materials and Methods Consecutive knees with TKA that underwent revision between July 2018 and June 2019 and were imaged at MRI and radiography were included in this retrospective study. Interface type (normal, fibrous membrane, fluid, or osteolysis), percent integration (<33%, 33%-66%, or >66%), and presence of bone marrow edema pattern were assessed. Loosening was diagnosed at MRI if no or almost no normal interface was present. Sensitivity and specificity were compared with radiographs by using surgical findings as reference. Gwet agreement coefficient evaluated interreader reproducibility between two readers and multivariable logistic regression assessed risk factors for loosening. Results Among 116 knees in 114 patients (mean age, 63 years ± 10 [SD]; 59 women), 61 of 116 knees (52.6%) had at least one loose component. Interreader reproducibility of MRI was substantial to excellent (Gwet agreement coefficient, 0.67-0.96). Loosening was associated with fluid interface (odds ratio [OR], 20.1; 95% CI: 5.7, 70.9) or osteolysis (OR, 3.1; 95% CI: 1.8, 5.3), absence of any normal interface (OR, 11.8; 95% CI: 6.3, 22.2), poor (<33%) osseous integration (OR, 20.4; 95% CI: 9.7, 42.6), and bone marrow edema pattern (OR, 4.7; 95% CI: 2.8, 7.8). Sensitivity and specificity of MRI for loosening were 84% (27 of 32; 95% CI: 72, 97) and 85% (71 of 84; 95% CI: 77, 92) for the patellar, 31% (eight of 26; 95% CI: 13, 49) and 100% (90 of 90; 95% CI: 100, 100) for the femoral, and 81% (22 of 27; 95% CI: 66, 96) and 98% (87 of 89; 95% CI: 95, 100) for the tibial component, respectively. MRI had higher sensitivity (84% vs 31%; P < .001) but lower specificity (85% vs 96%; P = .003) for patellar component loosening than did radiography, respectively, whereas no evidence of a difference was found for femoral (sensitivity and specificity, MRI vs radiography: 31% vs 46% [P = .20] and 100% vs 99% [P > .99], respectively) or tibial (sensitivity and specificity, MRI vs radiography: 81% vs 70% [P = .16] and 98% vs 97% [P = .32], respectively) component loosening. Conclusion MRI demonstrated substantial to excellent interreader reproducibility and higher sensitivity than did radiography for diagnosing patellar component loosening after total knee arthroplasty. © RSNA, 2022 Online supplemental material is available for this article.

A Postmortem Analysis of Polyethylene Damage and Periprosthetic Tissue in Rotating Platform and Fixed Bearing Tibial Inserts.

BACKGROUND: Mobile bearing designs are intended to reduce wear, but mixed results were reported from retrieval analyses. Postmortem evaluation (PM) provides the opportunity to assess polyethylene damage in successful implants. We compared damage patterns, MRI presentation, and histology between mobile-bearing and fixed tibial inserts retrieved postmortem and compared these results to our prior findings from implants retrieved at revision. METHODS: Eleven postmortem knees with rotating platform (RP) implants and 13 with fixed bearing (FB) implants were examined. All were MRI scanned, and tissue samples were collected from standardized regions for histology. Polyethylene inserts were subjectively scored to assess articular, backside, and PS post surfaces for damage modes and severity. RESULTS: Average duration of implantation was 9.3 years (1.7-19.6 years). Surface burnishing was the most common polyethylene damage mode. Average damage scores were higher for RP (53.4) compared to FB inserts (34.4) due to greater backside damage (13.4 for RP vs 1.4 for FB). A minimal difference in damage was observed on the articular surfaces (37.4 RP vs 30.0 FB). Mild innate macrophage reactions were seen in 8 (72.7%) RP and 5 (45.5%) FB specimens. Polyethylene particles were identified in 7 (63.6%) RP and 3 (27.7%) FB specimens. CONCLUSIONS: Postmortem inserts showed low damage levels and mild tissue reactions compared to those reported for implants removed at revision arthroplasty. Nonetheless, trends in comparing RP and FB inserts were consistent with those seen in retrieval analyses, demonstrating the usefulness of retrieval studies in capturing performance differences among TKA designs.

Magnetic Resonance Imaging Synovial Classification Is Associated With Revision Indication and Polyethylene Insert Damage.

BACKGROUND: Patients with total knee arthroplasty (TKA) stiffness are commonly presumed to have arthrofibrosis though no specific test exists. In patients undergoing revision TKA, we asked the following question: (1) Do patients who are revised for stiffness display a synovial reaction on MRI that is different than patients revised for other reasons? (2) Do these patients have a different magnitude of polyethylene insert damage than patients revised for other reasons? and (3) Is the MRI synovial classification associated with polyethylene insert damage? METHODS: Patients undergoing revision TKA for stiffness had a preoperative MRI performed, and the synovium was classified on MRI in a blinded fashion as arthrofibrosis, focal scarring, polymeric reaction, infection, or abnormal. At surgery, the polyethylene inserts were removed, and graded by 2 reviewers for total surface damage. RESULTS: Revision indication and MRI synovial classification were associated (P < .0001), with a greater proportion of patients assigned an MRI classification of arthrofibrosis revised for arthrofibrosis and a greater proportion of patients assigned a polymeric classification revised for aseptic loosening. Patients assigned an MRI synovial classification of polymeric had the greatest damage to the tibial insert (P < .0001), and patients revised for the clinical indication of aseptic loosening had the greatest damage to the tibial insert (P < .0001). CONCLUSION: Synovial grading on MRI is strongly associated with revision indication and polyethylene insert damage. In patients with stiffness in the absence of another complication, MRI can be a helpful diagnostic adjuvant in confirming the diagnosis of stiffness.

Effects of the Competitive Season and Off-Season on Knee Articular Cartilage in Collegiate Basketball Players Using Quantitative MRI: A Multicenter Study.

BACKGROUND: Injuries to the articular cartilage in the knee are common in jumping athletes, particularly high-level basketball players. Unfortunately, these are often diagnosed at a late stage of the disease process, after tissue loss has already occurred. PURPOSE/HYPOTHESIS: To evaluate longitudinal changes in knee articular cartilage and knee function in National Collegiate Athletic Association (NCAA) basketball players and their evolution over the competitive season and off-season. STUDY TYPE: Longitudinal, multisite cohort study. POPULATION: Thirty-two NCAA Division 1 athletes: 22 basketball players and 10 swimmers. FIELD STRENGTH/SEQUENCE: Bilateral magnetic resonance imaging (MRI) using a combined T1ρ and T2 magnetization-prepared angle-modulated portioned k-space spoiled gradient-echo snapshots (MAPSS) sequence at 3T. ASSESSMENT: We calculated T2 and T1ρ relaxation times to compare compositional cartilage changes between three timepoints: preseason 1, postseason 1, and preseason 2. Knee Osteoarthritis Outcome Scores (KOOS) were used to assess knee health. STATISTICAL TESTS: One-way variance model hypothesis test, general linear model, and chi-squared test. RESULTS: In the femoral articular cartilage of all athletes, we saw a global decrease in T2 and T1ρ relaxation times during the competitive season (all P < 0.05) and an increase in T2 and T1ρ relaxation times during the off-season (all P < 0.05). In the basketball players' femoral cartilage, the anterior and central compartments respectively had the highest T2 and T1ρ relaxation times following the competitive season and off-season. The basketball players had significantly lower KOOS measures in every domain compared with the swimmers: Pain (P < 0.05), Symptoms (P < 0.05), Function in Daily Living (P < 0.05), Function in Sport/Recreation (P < 0.05), and Quality of Life (P < 0.05). CONCLUSION: Our results indicate that T2 and T1ρ MRI can detect significant seasonal changes in the articular cartilage of basketball players and that there are regional differences in the articular cartilage that are indicative of basketball-specific stress on the femoral cartilage. This study demonstrates the potential of quantitative MRI to monitor global and regional cartilage health in athletes at risk of developing cartilage problems. LEVEL OF EVIDENCE: 2 Technical Efficacy Stage: 2.

Genicular Artery Embolization for Refractory Hemarthrosis following Total Knee Arthroplasty: Technique, Safety, Efficacy, and Patient-Reported Outcomes.

PURPOSE: To investigate the safety and efficacy of genicular artery embolization for treatment of refractory hemarthrosis following total knee arthroplasty. MATERIAL AND METHODS: Patients who underwent genicular artery embolization with spherical embolics between January 2010 and March 2020 at a single institution were included if they had undergone total knee arthroplasty and subsequently experienced recurrent hemarthrosis. Technical success was defined as the significant reduction or elimination of the hyperemic blush. Clinical success was defined as the absence of clinical evidence of further hemarthrosis. Clinical follow-up was performed 7-14 days after the procedure and at 3-month intervals thereafter via a telephone interview. A total of 117 embolizations, comprising 82 initial, 28 first repeat, and 7 second repeat, were performed. RESULTS: An average of 2.5 arteries was treated per procedure. The superior lateral genicular artery was the most frequently embolized. The most utilized embolic size was 100-300 µm. Follow-up was available for all patients, with a median duration of 21.5 months. 65.9%, 25.6%, and 8.5% of patients underwent 1, 2, and 3 treatments, respectively. Complications occurred following 12.8% of treatments, of which the most common was transient cutaneous ischemia. Technical success was achieved in all cases. Clinical success was achieved in 56%, 79%, and 85% of patients following the first, second, and third treatment, respectively. 83% of patients reported being either satisfied or very satisfied with the overall result. CONCLUSIONS: Targeted genicular artery embolization with spherical embolics is an effective treatment for recurrent hemarthrosis with infrequent serious complications. Repeat embolization should be considered in cases of recurrence following initial therapy.

MRI Visualization of Polyethylene Post Fractures in Posterior Stabilized Total Knee Arthroplasty.

Polyethylene post fracture is a recognized complication of posterior stabilized total knee arthroplasty. Two radiologists retrospectively reviewed MRI examinations of 19 reported post fractures in 18 patients; all fractures were subsequently confirmed surgically with no false-positive cases. All post fractures were visualized as a combination of post deformity and signal-void fragment in a joint recess. A metal artifact reduction 3D multispectral imaging sequence improved fracture visualization versus conventional sequences in 47% of cases.

Adverse Local Tissue Reactions are Common in Asymptomatic Individuals After Hip Resurfacing Arthroplasty: Interim Report from a Prospective Longitudinal Study.

BACKGROUND: The evaluation of the natural history prevalence of adverse local tissue reactions (ALTRs) using MRI has focused only on metal-on-metal (MoM) bearing surfaces without comparison to nonMoM bearing surfaces. QUESTIONS/PURPOSES: To determine (1) the longitudinal changes and differences in blood metal ion levels in patients with hip resurfacing arthroplasty (HRA), ceramic-on-ceramic (CoC) THA, and metal-on-polyethylene (MoP) THA compared with those undergoing ceramic-on-polyethylene (CoP) THA; (2) how the longitudinal change of synovial reaction classification in patients with HRA, CoC THA, and MoP THA compares with those undergoing CoP THA, and whether there is an association between the presence of an ALTR or metallosis on MRI with corresponding patient-reported outcomes, or the presence of capsular dehiscence; and (3) differences in blood metal ion levels between patients undergoing HRA with an ALTR or metallosis on MRI and those with HRA without these conditions. METHODS: Between March 2014 and February 2019, 22,723 patients underwent primary HRA and THA at one center. Patients received an HRA based on their desired athletic level after surgery and the presence of normal acetabular and proximal femoral bone morphology without osteopenia or osteoporosis. Two percent (342 of 22,723) of patients were contacted to participate, and 71% (243 of 342 hips in 206 patients) were enrolled for analysis at baseline. The patients underwent arthroplasty for degenerative joint disease, and 25 patients withdrew over the course of the study. We included patients who were more than 1 year postarthroplasty. All participants had an MRI examination and blood serum ion testing and completed a Hip Disability and Osteoarthritis Outcome Score survey annually for four years (baseline, year 1, year 2, year 3). Morphologic and susceptibility-reduced MR images were evaluated by a single radiologist not involved in the care of patients for the presence and classification of synovitis (Gwet AC1: 0.65 to 0.97), synovial thickness, and volume (coefficient of repeatability: 1.8 cm3). Linear mixed-effects models were used to compare the mean synovial thickness, synovial volume, and Hip Disability and Osteoarthritis Outcome Score subscales between bearing surfaces at each timepoint and within each bearing surface over time. Marginal Cox proportional hazards models were used to compare the time to and the risk of developing ALTR only, metallosis only, and ALTR or metallosis between bearing surfaces. All models were adjusted for age, sex, BMI, and length of implantation based on known confounders for hip arthroplasty. Adjustment for multiple comparisons was performed using the Dunnett-Hsu method. RESULTS: Patients with unilateral HRA had higher cobalt and chromium serum ion levels (baseline: 1.8 ± 0.8 ppb, year 1: 2.0 ± 1.5 ppb, year 2: 2.1 ± 1.2 ppb, year 3: 1.6 ± 0.7 ppb) than those with unilateral CoP bearings (baseline: 0.0 ± 0.1 ppb, year 1: 0.1 ± 0.3 ppb, year 2: 0.0 ± 0.2 ppb, year 3: 0.0 ± 0.0 ppb) at all timepoints (p < 0.001 for each time point). More patients who received an HRA developed ALTR or metallosis on MRI than did patients with CoP bearings (hazard ratio 4.8 [95% confidence interval 1.2 to 18.4]; p = 0.02). There was no association between the longitudinal change of synovial reaction to ALTR or metallosis on MRI with patient-reported outcomes. In addition, there was no association between the presence of dehiscence at baseline and the subsequent development of ALTR or metallosis, as seen on MRI. There were elevated cobalt (4.7 ± 3.5 ppb) and chromium (4.7 ± 2.6 ppb) serum levels in patients with unilateral HRA who had an ALTR or metallosis present on MRI at year 1 compared with patients without an ALTR or metallosis on MRI (cobalt: 1.8 ± 1.0 ppb, mean difference 4.7 ppb [95% CI 3.3 to 6.0]; p < 0.001; chromium: 2.3 ± 0.5 ppb, mean difference 3.6 ppb [95% CI 2.2 to 5.0]; p < 0.001) as well as for chromium at year 3 (3.9 ± 2.4 ppb versus 2.2 ± 1.1 ppb, mean difference 1.3 ppb [95% CI 0.3 to 2.4]; p = 0.01). CONCLUSION: We found a higher proportion of ALTR or metallosis on MRI in patients with HRA compared with patients with CoP, even when patient self-assessed symptomatology of those with an ALTR or metallosis on MRI was not different than the absence of these features. MRI detected ALTRs in high-function patients, emphasizing that an annual clinical assessment dependent on survey or blood ion testing alone may not detect soft tissue complications. The results of this study are in line with prior consensus recommendations of using MRI as part of a routine follow-up protocol for this patient population. LEVEL OF EVIDENCE: Level III, therapeutic study.

Reverse total shoulder arthroplasty: an imaging overview.

Although not as common as hip or knee arthroplasty, shoulder arthroplasty is becoming a more common procedure. Reverse total shoulder arthroplasty (RTSA) is known to be an effective surgical procedure for massive irreparable rotator cuff tears, comminuted proximal humerus fractures, and revision shoulder arthroplasty. The utilization of RTSA has been increasing, and although complications following reverse arthroplasty have been reported, there are few reports in the literature that focus on the imaging features of RTSA. Herein, we demonstrate the biomechanics of RTSA, prosthesis components, indications, and imaging features of the normal postoperative appearance and various complications after RTSA. Familiarization with the normal and abnormal imaging appearances after RTSA can be helpful for appropriate management of patients.

Non-treatment of stable ramp lesions does not degrade clinical outcomes in the setting of primary ACL reconstruction.

PURPOSE: The purpose of this study was to evaluate the clinical outcomes of various methods of treatment of stable and unstable ramp lesions compared to patients with no meniscal pathology at the time of primary ACL reconstruction. METHODS: All patients with a preoperative MRI performed at our facility who were enrolled in an institutional ACL registry and 1-year clinical follow-up were identified. A musculoskeletal radiologist reviewed preoperative MRI scans for evidence of a ramp lesion. Ramp lesions were classified as stable if a peripheral tear of the posterior horn of the medial meniscus was identified by MRI, but did not displace into the medial compartment with anteriorly directed probing at the time of surgery. Ramp lesions were classified as unstable if a tear was identified by preoperative MRI at the meniscocapsular junction and the meniscus was displaceable into the medial compartment with probing. Reoperation rates for ACL graft failure or recurrent medial meniscus pathology were collected. Patient-reported outcome scores (IKDC, SF12 PCS, SF12 MCS, and Marx Activity scale) were recorded at baseline and final follow-up. RESULTS: A total of 162 patients were included in the analysis with median 2-year (range 1-5 years) clinical follow-up. Patients with a repaired unstable ramp lesion had a significantly higher likelihood of reoperation for recurrent medial meniscus pathology than patients without meniscal pathology at the time of index surgery. Patients with an untreated stable ramp lesion had a similar rate of reoperation when compared to patients without meniscal pathology. At final follow-up, there was no difference between groups in IKDC score, SF12 PCS/MCS, or Marx activity score or change in any score. CONCLUSIONS: Patients with untreated stable ramp lesions have similar clinical outcomes at median 2-year (range 1-5 years) follow-up when compared to patients without a ramp lesion. Treatment of stable ramp lesions at the time of ACL reconstruction does not have clinical benefit. LEVEL OF EVIDENCE: III.

How Useful Is Magnetic Resonance Imaging in Evaluating Adverse Local Tissue Reaction?

Biologic failures of hip arthroplasty have emerged as an increasing threat to the longevity of the prosthesis. While wear of modern-day bearings has been greatly reduced with the advent of cross-linked polyethylene, local reaction to metal particles either from the bearing itself or to any of the modular tapers appears to be on the rise. Monitoring of these reactions by the use of plain radiographs or serum markers appears to be insufficient to gauge the gravity of the response. Over the past decade, the use of magnetic resonance imaging (MRI) techniques has emerged as the superior noninvasive instrument to assess the extent of soft tissue reaction around hip implants. The use of MRI around implants was initially challenging due to the presence of relatively high ferrous metals especially cobalt which causes local distortion of the magnetic fields. Novel changes in pulse sequencing have greatly improved the sensitivity and specificity of MRI so that at this time, MR is the most predictive diagnostic tool in evaluating the extent of tissue destruction. We feel strongly that modern MRI techniques are the most important tool in the workup of the patient suspected of having an adverse tissue reaction after hip arthroplasty.

3D-multi-spectral T2 mapping near metal implants.

PURPOSE: Due to host-mediated adverse reaction to metallic debris, there is an increasing need for noninvasive assessment of the soft tissue surrounding large joint arthroplasties. Quantitative T2 mapping can be beneficial for tissue characterization and early diagnosis of tissue pathology but current T2 mapping techniques lack the capability to image near metal hardware. A novel multi-spectral T2 mapping technique is proposed to address this unmet need. METHODS: A T2 mapping pulse sequence based on routinely implemented 3D multi-spectral imaging (3D-MSI) pulse sequences is described and demonstrated. The 3D-MSI pulse sequence is altered to acquire images at 2 echo times. Phantom and knee experiments were performed to assess the quantitative capabilities of the sequence in comparison to a commercially available T2 mapping sequence. The technique was demonstrated for use within a clinical protocol in 2 total hip arthroplasty (THA) cases to assess T2 variations within the periprosthetic joint space. RESULTS: The proposed multi-spectral T2 mapping technique agreed, within experimental errors, with T2 values derived from a commercially available clinical standard of care T2 mapping sequence. The same level of agreement was observed in quantitative phantoms and in vivo experiments. In THA cases, the method was able to assess variations of T2 within the synovial envelope immediately adjacent to implant interfaces. CONCLUSIONS: The proposed 3D-MSI T2 mapping sequence was successfully demonstrated in assessing tissue T2 variations near metal implants.

Electrodiagnostic evidence of suprascapular nerve recovery after decompression.

INTRODUCTION: The purpose of this study was to determine whether surgical arthroscopic decompression or ultrasound-guided aspiration of a paralabral cyst would result in suprascapular nerve recovery from axonal regeneration based on electrodiagnostic testing. METHODS: Nine patients with preoperative electromyography (EMG) evidence of suprascapular neuropathy due to paralabral cysts at the suprascapular or spinoglenoid notch were prospectively studied. Eight patients underwent arthroscopic surgical decompression, and 1 patient underwent ultrasound-guided aspiration. Postoperative EMG was performed in all patients to evaluate nerve regeneration. RESULTS: Three (33%) patients had cysts at the suprascapular notch, whereas 6 (67%) patients had cysts at the spinoglenoid notch. All patients showed complete electrophysiological recovery after decompression. DISCUSSION: Decompression of paralabral cysts at the suprascapular or spinoglenoid notch resulted in postoperative EMG evidence of nerve recovery. Long-term studies with a greater number of patients are required to elucidate time to recovery. Muscle Nerve 59:247-249, 2019.

MRI of Hip Arthroplasties: Comparison of Isotropic Multiacquisition Variable-Resonance Image Combination Selective (MAVRIC SL) Acquisitions With a Conventional MAVRIC SL Acquisition.

OBJECTIVE. The objective of our study was to compare the quality and diagnostic utility of the following three metal artifact reduction sequences in evaluating hip arthroplasties: conventional multiacquisition variable-resonance image combination selective (MAVRIC SL), isotropic MAVRIC SL, and reduced-TR isotropic MAVRIC SL. SUBJECTS AND METHODS. Ninety-three hip arthroplasties (85 total hip replacements and eight hip resurfacings [nine bilateral hips]) in 84 patients (38 men and 46 women; mean age ± SD, 69.1 ± 9.7 years old) were imaged and evaluated. A calibration scan determined the number of spectral bins needed for each implant, and isotropic and conventional MAVRIC SL images were acquired. Reduced-TR isotropic MAVRIC SL scans were acquired for 40 arthroplasties. Two board-certified radiologists blinded to MRI acquisition evaluated images for clinical and image quality features and compared images using a mixed-effects ordinal logistic regression model and odds ratios. Rater agreement was assessed with Gwet agreement coefficients. Scanning times were compared using mixed-effects linear regression. Significance was set at p < 0.05. RESULTS. Calibration scans decreased the number of bins needed (median, 12 bins; interquartile range, 10-16 bins). Isotropic MAVRIC SL (mean scanning time, 7 minutes 16 seconds; 95% CI, 7 minutes 7 seconds-7 minutes 25 seconds) acquisitions had the longest scanning time, and conventional (mean, 5 minutes 46 seconds; 95% CI, 5 minutes 37 seconds-5 minutes 55 seconds) and reduced-TR isotropic (5 minutes 28 seconds; 95% CI, 5 minutes 15 seconds-5 minutes 41 seconds) MAVRIC SL acquisitions had scanning times that were similar. Both isotropic and reduced-TR isotropic MAVRIC SL images showed decreased blurring and improved visualization of the synovium and periprosthetic bone compared with conventional MAVRIC SL images (p < 0.001). Isotropic MAVRIC SL acquisitions more effectively improved signal-to-noise ratio (SNR), visualization of the synovium and periprosthetic bone, and lesion conspicuity and decreased blurring compared with reduced-TR isotropic MAVRIC SL acquisitions (p < 0.032). CONCLUSION. Isotropic MAVRIC SL acquisitions improve SNR, conspicuity of lesions, and visualization of synovium and periprosthetic bone and decrease blurring compared with conventional MAVRIC SL acquisitions.

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.