MRI evaluation of the knee with non-ferromagnetic external fixators: cadaveric knee model

Safety of Magnetic Resonance Imaging in Orthopaedic Trauma Patients With External Fixation: A Two-Center Case Series

OBJECTIVES

To report on adverse events during magnetic resonance imaging (MRI) in patients with external fixators.

METHODS

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DESIGN

Retrospective case series.

SETTING

Two Level 1 trauma centers.

PATIENT SELECTION CRITERIA

Patients with external fixators on the appendicular skeleton or pelvis undergoing MRI between January 2005 and September 2023.

OUTCOME MEASURES AND COMPARISONS

Adverse events, defined as any undesirable event associated with the external fixator being inside or outside the MRI bore during imaging, including (subjective) heating, displacement or pullout of the external fixator, or early MRI termination for any reason.

RESULTS

A total of 97 patients with 110 external fixators underwent at least one MRI scan with an external fixator inside or outside of the MRI bore. The median age was 51 years (interquartile range: 39-63) and 56 (58%) were male. The most common external fixator locations were the ankle (24%), knee (21%), femur (21%), and pelvis (19%). The median duration of the MRI was 40 minutes (interquartile range: 26-58), 86% was performed using 1.5-Tesla MRI, and 14% was performed using 3.0-Tesla MRI. Ninety-five percent of MRI was performed for the cervical spine/head. Two MRI scans (1.6%), one of the shoulder and one of the head and cervical spine, with the external fixator outside of the bore were terminated early because of patient discomfort. There were no documented events of displacement or pullout of the external fixator.

CONCLUSIONS

These findings suggest that MRI scans of the (cervical) spine and head can be safely obtained in patients with external fixators on the appendicular skeleton or pelvis. Given the low numbers of MRI scans performed with the external fixator inside the bore, additional studies are necessitated to determine the safety of this procedure. The results from this study can aid orthopaedic surgeons, radiologists, and other stakeholders in developing local institutional guidelines on MRI scanning with external fixators in situ.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Magnetic resonance imaging quality in the context of a knee-spanning external fixator placed inside the MR bore: a literature review

After emergent assessment of potentially limb-threatening injuries in knee dislocation or multi-ligament knee injury patients, magnetic resonance imaging is necessary to visualize ligamentous structures and plan for soft tissue repair. However, the application of a knee-spanning external fixator may introduce artifact and reduce overall image quality, which can limit the evaluation of soft tissue injury. As a result, the utility of MRI in the context of a knee-spanning external fixator has been called into question. Signal-to-noise ratio, contrast-to-noise ratio, and qualitative scales have been used to assess image quality of MRI in the context of a knee-spanning external fixator. Despite the potential for artifact, studies have demonstrated that useful diagnostic information may be obtained from MRI in the presence of an external fixator. This review examines the general principles of anatomical assessment, magnetic field strength, device composition and design, radiofrequency coil use, and MRI sequences and artifact reduction as they pertain to MRI in the presence of a knee-spanning external fixator.

Perspectives and institutional policies on patient safety and image quality regarding the use of knee-spanning external fixators in MRI: A survey study of the Society of Skeletal Radiology

OBJECTIVE

Concerns regarding patient safety and image quality have made the use of knee-spanning external fixators in MRI a challenging clinical scenario. The purpose of our study was to poll practicing musculoskeletal radiologists on their personal experiences regarding the use of knee-spanning external fixators in MRI in an effort to consolidate practice trends for the radiologists' benefit.

METHODS

A 27-item survey was created to address the institutional use, safety, adverse events, quality, and perspectives of the radiologist related to MRI of an externally fixated knee. The survey was distributed to 1739 members of the Society of Skeletal Radiology.

RESULTS

A total of 72 members of the Society of Skeletal Radiology completed the survey. Most notably, 40 of 72 (55.56%) respondents are permitted to place a knee-spanning external fixator inside the MR bore at their institution, while19 of 72 (26.39%) respondents are not permitted to do so. Fourteen of 32 (43.75%) respondents have institutional guidelines for safely performing an MRI of an externally fixated knee. Twenty-five of 32 (78.13%) respondents are comfortable permitting an MRI of an externally fixated knee.

CONCLUSION

We found a general lack of consensus regarding the decision to scan a patient with a knee-spanning external fixator in MRI. Many institutions lack safety guidelines, and providers rely upon a heterogeneous breadth of resources for safety information. A re-examination of the FDA device labeling nomenclature and expectations of the individual manufacturers may be needed to bridge this gap and help direct management decisions placed upon the provider.

Patient Safety in MRI with the Use of a Joint-Spanning External Fixator for Knee Dislocation: A Critical Analysis Review

» Universal safety guidelines for the use of a knee-spanning external fixator in magnetic resonance imaging (MRI) are unlikely to be established considering the high variability in device construct configurations.» Per the US Food and Drug Administration, manufacturers are to provide parameters for safe MRI scanning for "MR Conditional" devices; however, such labeling may be limited in detail. Physicians should reference manufacturer labels as a starting point while making an educated clinical decision.» Scanning of a knee-spanning external fixator inside the MR bore has been safely demonstrated in previous studies, although with small sample sizes.» When considering MRI in a patient treated with a knee-spanning external fixator, physicians should use all available resources and coordinate with their medical team to make a clinically reasonable decision contrasting patient benefit vs. potential harm.

External Fixator Usage and Delayed MRI Scans: A National Survey Study

OBJECTIVE

To report the current state of institutional protocols regarding the use of MRI in patients with external fixation devices (EFDs) in the United States.

DESIGN

National Survey Study.

PARTICIPANTS

Practicing orthopaedic surgeons frequenting the Orthopaedic Trauma Association website were invited to participate in this study.

RESULTS

Sixty-two eligible orthopaedic surgeons completed the survey. No respondents reported any known harmful complications of MRI use with an EFD. Eight respondents (13%) reported at least one early scan termination because of mild warmth or vibration without any lasting complications. Fifty-six respondents (90%) reported delays to care related to MRI-EFD compatibility labeling, and 27 respondents (48%) reported delayed MRI scans in every patient with an EFD who needed one. Twenty-six surgeons (42%) had modified their practice in some way in response to these barriers. Examples include delaying EFD placement until after MRI, relying on CT arthrograms over MRI for surgical planning, and taking patients to the operating room to remove EFDs temporarily and then replace them. Nineteen respondents (31%) had developed formal protocols to address this issue, but having a written protocol was not associated with any decrease in delays ( P = 0.119). Eighty-nine percent of respondents thought there was a need for a national consensus guideline on this issue.

CONCLUSION

Despite no previous reports of harmful complications, MRI utilization is frequently delayed or prevented in patients with EFDs in place. This is a pervasive problem nationally, which persists despite the implementation of written institutional protocols. Additional research is needed, potentially at the national level, to address this common issue.

LEVEL OF EVIDENCE

V.

The value of magnetic resonance imaging in the preoperative diagnosis of tibial plateau fractures: a systematic literature review

Purpose

The outcome of a tibial plateau fracture (TPF) depends on the fracture reduction achieved and the extent of soft-tissue lesions, including lesions in the ligaments, cartilage, and menisci. Sub-optimal treatment can result in poor knee function and osteoarthritis. Preoperative planning is primarily based on conventional X-ray and computed tomography (CT), which are unsuitable for diagnosing soft-tissue lesions. Magnetic resonance imaging (MRI) is not routinely performed. To date, no literature exists that clearly states the indications for preoperative MRI. This systematic review aimed to determine the frequency of soft-tissue lesions in TPFs, the association between fracture type and soft-tissue lesions, and the types of cases for which MRI is indicated.

Methods

A systematic review of the literature was based on articles located in PubMed/MEDLINE and the Cochrane Central Register of Controlled Trials (CENTRAL), supplemented by searching the included articles’ reference lists and the ePublication lists of leading orthopedic and trauma journals.

Results

A total of 1138 studies were retrieved. Of these, 18 met the eligibility criteria and included a total of 877 patients. The proportion of total soft-tissue lesions was 93.0%. The proportions of soft-tissue lesions were as follows: medial collateral ligament 20.7%, lateral collateral ligament 22.9%, anterior cruciate ligament 36.8%, posterior cruciate ligament 14.8%, lateral meniscus 48.9%, and medial meniscus 24.5%. A weak association was found between increasing frequency of LCL and ACL lesions and an increase in fracture type according to Schatzker's classification. No standard algorithm for MRI scans of TPFs was found.

Conclusion

At least one ligament or meniscal lesion is present in 93.0% of TPF cases. More studies with higher levels of evidence are needed to find out in which particular cases MRI adds value. However, MRI is recommended, at least in young patients and cases of high-energy trauma.

Magnetic Resonance Imaging of the Knee in the Presence of Bridging External Fixation: A Comparative Experimental Evaluation of Four External Fixators, Including Dolphix®

Performing MR investigation on patients instrumented with external fixators is still controversial. The aim of this study is to evaluate the quality of MR imaging of the knee structures in the presence of bridging external fixators. Different cadaveric lower limbs were instrumented with the MR-conditional external fixators Hofmann III (Stryker, Kalamazoo, MI, USA), Large external Fixator (DePuy Synthes, Raynham, MA, USA), XtraFix (Zymmer, Warsaw, IN, USA) and a newer implant of Ketron Peek CA30 and ERGAL 7075 pins, Dolphix^®, (Citieffe, Bologna, Italy). The specimens were MR scanned before and after the instrumentation. The images were subjectively judged by a pool of blinded radiologists and then quantitatively evaluated calculating signal intensity, signal to noise and contrast to noise in the five regions of interest. The area of distortion due to the presence of metallic pins was calculated. All the images were considered equally useful for diagnosis with no differences between devices (p > 0.05). Only few differences in the quantification of images have been detected between groups while the presence of metallic components was the main limit of the procedure. The mean length of the radius of the area of distortion of the pins were 53.17 ± 8.19 mm, 45.07 ± 4.33 mm, 17 ± 5.4 mm and 37.12 ± 10.17 mm per pins provided by Zimmer, Synthes, Citieffe and Stryker, respectively (p = 0.041). The implant of Ketron Peek CA30 and ERGAL 7075 pins showed the smallest distortion area.

Computed Tomography in Limb Salvage and Deformity Correction-3D Assessment, Indications, Radiation Exposure, and Safety Considerations

Computed tomography (CT) is an essential tool in orthopedic surgery but is known to be a method with that entails radiation exposure. CT increases the risk of developing fatal cancer, which should not be underestimated. However, patients with bone defects and/or deformities must frequently undergo numerous investigations during their treatment. CT is used for surgical planning, evaluating callus maturation, alignment measurement, length measurement, torsion measurement, and angiography. This study explores the indications in CT scans for limb lengthening and deformity correction and estimates the effective radiation dose. These results should help avoid unnecessary radiation exposure by narrowing the examination field and by providing explicit scanning indications. For this study, 19 posttraumatic patients were included after the bone reconstruction of 21 lower limbs. All patients underwent CT examinations during or after treatment with an external ring fixator. The mean effective dose was 3.27 mSv, with a mean cancer risk of 1:117,014. The effective dose depended on the location and indication of measurement, with a mean dose of 0.04 mSv at the ankle up to 6.8 mSv (or higher) for vascular depictions. CT evaluation, with or without 3D reconstruction, is a crucial tool in complex bone reconstruction and deformity treatments. Therefore, strict indications are necessary to reduce radiation exposure-especially in young patients-without compromising the management of their patients.

MRI of Traumatic Knee Dislocation: A Study to Evaluate Safety and Image Quality for Patients with Knee-Spanning Stabilization Devices

This study evaluated safety and image quality of MRI exams performed for patients with traumatic knee dislocations in knee-spanning stabilization devices. It is an IRB-approved retrospective design with waived informed consent that included 63 patients with traumatic knee dislocation. 56 patients had metallic external fixators, and 7 patients had non-metallic knee immobilizers. 7 patients had bilateral dislocations yielding a total of 70 knee MRIs. 1.5 Tesla MRI exams were performed for all patients who were awake and alert at the time of imaging. All knee-spanning external fixators were considered "MR conditional" by the FDA. The electronic medical record was reviewed for notes from the technologist and nursing staff documenting any patient complaints or adverse events during the MRI exam as required by departmental protocol. Qualitative analysis of the six most frequently performed sequences were independently conducted by 2 musculoskeletal radiologists using a 5-point Likert scale. Overall image quality and select time intervals between the two groups were compared using an independent sample t test and the Mann-Whitney U test, respectively. No adverse events were reported for a 40-minute average estimated patient scan time with the stabilization devices in the MR gantry. Mean values of Likert scale scores were generated from two readers' data for comparison between the external fixation and the immobilizer groups. Most knee MRI exams with external fixators were within diagnostic quality despite artifacts (grade 3). MRI exams generally were of higher diagnostic quality in the immobilizer group than the external fixator group (p < 0.05). The external fixator models included DePuy Synthes, Smith and Nephew, Stryker Hoffman III, Zimmer FastFrame, and Zimmer XtraFix. MRI examinations in patients with external fixators for traumatic knee dislocations can be safely performed under certain conditions and provide diagnostic quality images.

Safety and image quality of MR-conditional external fixators for 1.5 Tesla extremity MR

PURPOSE

To evaluate the safety and image quality of extremity MR examinations performed with two MR conditional external fixators located in the MR bore.

MATERIALS AND METHODS

Single-center retrospective study of a prospectively maintained imaging dataset that evaluated MR examinations of extremities in patients managed with external fixations instrumentation and imaged on a single 1.5T MR scanner. The fixation device was one of two MR-conditional instrumentation systems: DuPuy Synthes (aluminum, stainless steel, carbonium and Kevlar) or Dolphix temporary fixation system (PEEK-CA30). Safety events were recorded by the performing MR radiologic technologist. A study musculoskeletal radiologist assessed all sequences to evaluate for image quality, signal- and contrast-to-noise ratios (SNR/CNR), and injury patterns/findings.

RESULTS

In the 13 men and 9 women with a mean age of 42 years (range 18 to 72 years), most patients (19/22 patients; 86%) were involved with trauma resulting in extremity injury requiring external fixation. MR examinations included 19 knee, 2 ankle, and 1 elbow examinations. There were no adverse safety events, heating that caused patient discomfort, fixation dislodgement/perturbment, or early termination of MR examinations. All examinations were of diagnostic quality. Fat-suppressed proton density sequences had significantly higher SNR and CNR compared to STIR (p = 0.01 to 0.04). The lower SNR of STIR and increased quality of fat-suppressed proton density during the study period led to the STIR sequence being dropped in standard MR protocol.

CONCLUSION

MR of the extremity using the two study MR conditional external fixators within the MR bore is safe and feasible.

Optimal configuration for stability and magnetic resonance imaging quality in temporary external fixation of tibial plateau fractures

INTRODUCTION

Temporary external fixation has been widely utilized in the stabilization of plateau fractures while waiting for an optimization of the soft tissue conditions before subsequent permanent internal fixation. Simultaneously, MRI is beneficial in the assessment of concomitant damage to ligaments and menisci so that these injuries could be promptly identified, and surgical planning executed at the time of definitive fixation of the bony injury. Increasing numbers of side-bars and pins have been previously suggested to increase frame rigidity, but at the same time, several studies have indicated the presence of MRI artifacts which may obscure key anatomical structures, even when MRI-compatible fixation devices are used. This study aims to identify, among six potential configurations, the construct that maximizes stability while most minimizing the number of MRI artifacts generated among different configurations commonly used.

HYPOTHESIS

There is one or more configurations among the others that maximize stability while preserving a clinically acceptable level of MRI quality.

MATERIAL AND METHODS

Six constructs were recreated on cadaveric specimens and identified by the disposition of the bars: H, Anterior, Flash, Hashtag, Rhomboid, and Diamond. Stage one evaluated the amount of artifact produced during MRI on instrumented cadaveric legs, as well as the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) at five specific regions of interest. Stage two assessed the amount of compressional and torsional stiffness of the configurations on bone surrogate models.

RESULTS

Image artifacts were not detected within the knee joint for all considered constructs. In terms of SNR The H, Anterior, Hashtag, and Diamond configurations were not significantly different from their control (p>0.366) while the others were significantly different (p<0.03). The values of CNR found for the H and Hashtag configurations were not significantly different from their controls (p>0.07) while the remaining configurations were significantly different (p<0.03). In compression, the H and Diamond configurations had similar stiffness (p=0.468) of 35.78N/mm and 31.44N/mm, respectively, and were stiffer than the other configurations. In torsion, the constructs have shown different stiffness (p<0.001) with a minimum value of 0.66 Nm/deg for the Rhomboid configuration, which was significantly less stiff than the Anterior configuration (1.20 Nm/deg [p<0.001]). There was no difference between the Diamond and H configurations (p=0.177) or between them and the Hashtag configuration (p=0.215).

DISCUSSION

An external fixator construct directly bridging the femur and tibia without interconnections is the most stable and produces MRI scans without image artifacts that would interfere with diagnostic quality.

LEVEL OF EVIDENCE

V, basic science study, diagnostic imaging and mechanical testing.

External Orthopaedic Implants in the Magnetic Resonance Environment: Current Concepts and Controversies

MRI provides diagnostic three-dimensional imaging and remains extremely important in the diagnosis and management of spinal trauma as well as other acute traumatic injuries, including those of the extremities. The American Society for Testing and Materials has created standards against which all implantable medical devices are tested to ensure safety in an MR environment. Most implantable passive orthopaedic devices can undergo MRI without consequence to the patient. However, the American Society for Testing and Materials has recently updated its terminology resulting in confusion among providers and institutions. Primary safety concerns are radiofrequency-induced heating and magnetically induced torque or displacement. These safety concerns have emerged as a recent source of debate, particularly regarding the imaging of patients with external fixation and cervical immobilization devices in place. Surveys have shown a lack of consensus among radiologists regarding this issue. Having an institutional protocol in place for the imaging of these patients streamlines the diagnosis and early stabilization of certain polytraumatized patients. The purpose of this review is to summarize the pertinent literature as well as the current industry recommendations regarding the safety of commonly used external fixation, cervical immobilization, and traction devices in the MR environment.

Safety and Complications Associated With MRI-Conditional External Fixators in Patients With Tibial Plateau Fractures: A Case Series

OBJECTIVES

To address the safety of obtaining magnetic resonance imaging (MRI) in patients with temporary knee-spanning external fixators placed for tibial plateau fractures.

DESIGN

Institutional Review Board-approved retrospective review.

SETTING

Level 1 trauma center.

PATIENTS/PARTICIPANTS

Records were reviewed on patients with knee-spanning external fixators applied during staged management of tibial plateau fractures from 2009 to 2015 and who also had an MRI performed.

MAIN OUTCOME MEASUREMENTS

Complications associated with the MRI; secondary outcomes were pain scores, narcotic requirements, and fracture healing.

RESULTS

A total of 56 patients with 57 fractures were included, and 55 scans (96.5%) were completed without complication. Two scans (3.5%) were stopped prematurely for patient-reported pain and subjective warmth of the external fixator. For all 57 studies, pain scores and narcotic usage were unchanged, and all fractures healed without complication.

CONCLUSIONS

Knee-spanning external fixator placement does not preclude MRI for patients with tibial plateau fractures. MRIs can be safely performed on patients with external fixators if patients are educated before imaging. Even in the small percentage of patients who experienced discomfort, there were no long-term complications.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Magnetic Resonance Imaging of Trauma Patients Treated With Contemporary External Fixation Devices: A Multicenter Case Series

OBJECTIVES

To report the safety and clinical outcomes of placing current magnetic resonance imaging (MRI) components inside and outside the MRI bore during MRIs.

DESIGN

Retrospective case series.

SETTING

Four trauma centers (3 Level I and 1 Level II), from January 2005 to January 2015.

PATIENTS

All patients who had MRIs with external fixators in place either inside or outside the MRI bore.

INTERVENTION

MRI of patients with external fixator in place.

MAIN OUTCOME MEASUREMENTS

Adverse events were defined as catastrophic pullout of the external fixator during the MRI, thermal injury to the skin, severe field distortions precluding the intended imaging, alterations of the magnetic field, or visible structural damage to the magnet casing.

RESULTS

Thirty-eight patients with 44 external fixators were identified who had MRI with the fixator inside or outside the MRI bore. Twelve patients with 13 external fixators had MRI with the external fixator inside the MRI bore. Twenty-seven patients with 32 external fixators had MRI with the external fixator outside the MRI bore. There were no adverse events.

CONCLUSIONS

Although no universal guidelines exist, there are circumstances in which obtaining MRIs of patients with external fixators can be safe. This is the first clinical series with the primary outcome of safety when placing modern external components both inside and outside an MRI bore during a scan.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.