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

Abstract

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.

Determination of the ideal plate for medial femoral condyle fracture fixation: an anatomical fit and biomechanical study

“…Traditionally, the quality of the CT images have been affected by scattering caused by the presence of the fixator pins. Recent studies have suggested that MRI scans offer good analysis of the fracture patterns around the knee despite presence of the fixator pins [21,22].…”

Patient Safety in MRI with the Use of a Joint-Spanning External Fixator for Knee Dislocation

“…Historically, external fixators were composed of metals that contained delta ferrite, which resulted in significant ferromagnetism 7,10,11,15,18,27 . Ferromagnetic devices may interact with the MR field and have the potential to cause patient harm through heating, movement, or projectile events 28 .…”

“…The collective 141 patients of the 4 studies that we reviewed used a combination of body (66), torso (57), cardiac (18), and knee coils (3) (Table I). The 2 adverse events previously described by Gillig et al occurred in externally fixated KD patients imaged with body coils over the knee 16 .…”

“…However, in clinical practice, the use of knee-spanning external fixators in MRI has been complicated by evolving terminology, as well as heterogeneous and often limited manufacturer safety guidelines. Previous studies have demonstrated that radiologists have refused to perform MRIs on externally fixated patients because of unclear safety guidelines 12,[14][15][16]18 . Resulting inability to obtain a timely MRI may delay diagnosis and surgery and negatively impact patient outcomes because improved results have been observed in KD patients who undergo acute ligamentous repair/reconstruction 21,22 .…”

“…In the orthopaedic and radiology literature, safety concerns with the use of knee-spanning external fixators inside the MR bore have been examined in several ex vivo studies 7-13 , but few human studies have addressed clinical outcomes 14-17 (Table I). The limited literature available notes that patients placed in an “MR Conditional” knee-spanning external fixator have been safely scanned in MRI and the resulting images may provide sufficient diagnostic information 9,14-20 (Figs. 1 and 2).…”