Effects of Stifle Flexion Angle and Scan Plane on Visibility of the Normal Canine Cranial Cruciate Ligament Using Low‐field Magnetic Resonance Imaging

Abstract

Low-field magnetic resonance imaging (MRI) is commonly used to evaluate dogs with suspected cranial cruciate ligament injury; however, effects of stifle positioning and scan plane on visualization of the ligament are incompletely understood. Six stifle joints (one pilot, five test) were collected from dogs that were scheduled for euthanasia due to reasons unrelated to the stifle joint. Each stifle joint was scanned in three angles of flexion (90°, 135°, 145°) and eight scan planes (three dorsal, three axial, two sagittal), using the same low-field MRI scanner and T2-weighted fast spin echo scan protocol. Two experienced observers who were unaware of scan technique independently scored visualization of the cranial cruciate ligament in each scan using a scale of 0-3. Visualization score rank sums were higher when the stifle was flexed at 90° compared to 145°, regardless of the scan plane. Visualization scores for the cranial cruciate ligament in the dorsal (H (2) = 19.620, P = 0.000), axial (H (2) = 14.633, P = 0.001), and sagittal (H (2) = 8.143, P = 0.017) planes were significantly affected by the angle of stifle flexion. Post hoc analysis showed that the ligament was best visualized at 90° compared to 145° in the dorsal (Z = -3.906, P = 0.000), axial (Z = -3.398, P = 0.001), and sagittal (Z = -2.530, P = 0.011) planes. Findings supported the use of a 90° flexed stifle position for maximizing visualization of the cranial cruciate ligament using low-field MRI in dogs.

Comparison of High-field and Low-field Magnetic Resonance Imaging of Stifle Joint Disorders in Dogs

“…The MRI coil has a significant impact on the signal-to-noise ratio, and thus on graininess (Mink et al 1993, Banfield andMorrison 2000). Therefore, it is advisable to use a coil well-adjusted to the size of the stifle, which allows for better visibility of the cranial cruciate ligament (Podadera et al 2014). Worthy of mention is a study in human medicine during which the sensitivity of the detection of meniscal tears in the knee with a standard knee coil and a surface coil were compared, and it amounted to 76% and 88%, respectively (Nemec et al 2008).…”

“…Among them the following may be mentioned: dorsal recumbency with extended (Baird et al 1999, Martig et al 2006 or flexed hindlimbs (Bottcher et al 2010, Tremolada et al 2014, lateral recumbency with various flexion angles of the stifle (Barrett et al 2009, Podadera et al 2014, or even in sternal recumbency (Harper et al 2011). Pujol et al (2011 reported that lateral recumbency with the stifle flexed at 145 o changed the tension of the cranial cruciate ligament and improved its visibility.…”

“…Although it is assumed that the problems associated with the cranial cruciate ligament occur in large or giant breed dogs, it is true that they can affect any dog (Hayashi et al 2004, Podadera et al 2014, especially neutered dogs (Witsberger et al 2008). On MRI images, undamaged caudal and cranial ligaments are uniform low signal intensity bands of oblique course, which makes it difficult to image them entirely on one slice.…”

“…Therefore, a study was performed to determine the optimal stifle flexion angle to improve the visibility of ligaments. Podadera et al (2014) . Slightly more often it is possible to see the caudal cruciate ligament in its entirety (Pujol et al 2011).…”

“…Other authors used T2-weighted fast spin echo (FSE) sequence due to the difference in signal intensity between the cranial cruciate ligament and synovial fluid. Furthermore, it avoids the risk of magic angle artifact (Podadera et al 2014). Besides that, the T2-weighted FSE and PD-weighted with fat-suppressed sequences were the best to visualize joint effusion, edema and inflammation of stifle joint (Bredella et al 2000, Blond et al 2008, D'Anjou et al 2008.…”