PMC5961132_01
Comparative diagnostic imaging of the right stifle joint. (A): Mediolateral radiograph. (B): Midsagittal multiplanar reformatted CT image. (C): Midsagittal T2-weighted and (D): gradient-echo STIR MRI images. (E, F): Longitudinal sonograms of the cranial aspect of the stifle joint. On radiographic image only the proximal part of the patellar ligament (PL) is visible with distinct margins while its distal part is ill-defined and surrounded by periligamentous soft tissue opacity (short arrow). The infrapatellar fat pad (h) shows loss of triangular shape. On CT image, the distal half of the patellar ligament is ill-defined ad surrounded by periligamentous accumulation of irregularly marginated material isoattenuating to the soft tissue (short arrow). The infrapatellar fat pad is caudally displaced. There are no signs of bone fractures or detached bone fragments at the tibial osteoligamentous junction. On MRI images, there is evident enlargement of the distal part of the PL (arrowheads) with intraligamentous signal inhomogeneity. The damaged part of the PL is surrounded by pathologic material, isointense on T1 and T2 weighted and hyperintense on STIR sequences, resembling a clot (short arrow).The pathologic material displaces the cranial aspect of the infrapatellar fat pad (h). A focal area of bone hyperintensity suggestive of bone marrow edema-like lesion (me) is evident on STIR image at level of the cranial aspect of tibial plateau, close to the osteoligamentous junction. On US the PL shows enlargement of its distal part and heterogeneous echotexture with intraligamentous anechoic defect (asterisks). The paratenon (long arrows) appears unaffected. The infrapatellar fat pad (h) appears inhomogeneous, hypoechoic with a small inner fluid collection. T: Tibia; F: Femur.
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F1
On medio-lateral view, only the proximal part of the PL was clearly seen with distinct margins, while its distal part, along with the cranio-ventral margin of the infrapatellar fat pad, was ill-defined and indistinguishable from the background of periligamentous soft tissue opacity (Fig. 1-A). T2-weighted sequences with inhomogeneous contrast-enhancement, resembling a clot (Fig. 1-C,D). At the level of the PL insertion, the tibial tuberosity showed a focal area of intraosseous pathological hyperintense signal in fat-suppressed sequences, compatible with a bone-marrow edema-like lesion (Starr et al., 2008) (Fig. 1-D). Discontinuities in PL structure were not evident (Fig. 1-B; Fig. 2-B,D; Fig. 3-F,G). The distal PL area appeared thickened with heterogeneous echotexture and a loss of fibrillary pattern (Fig. 1-E,F).
Midagittal oblique multiplanar reformatted bSSFP MRI (A) and CT (B) images of the patellar ligament (PL). Dorsal oblique multiplanar reformatted bSSFP MRI (C) and CT (D) images obtained orienting slice plane in the centre of the ligament (dotted line in image A). There is thickening of the distal half of PL (A - asterisk) and pathologic material (c), resembling a clot, adjacent to the inner surface of PL and displacing the infrapatellar fat pad (f). A small linear defect is clearly visible on MRI images (C-arrow) in disto-medial position within PL structure. Such detail is not detectable on CT image obtained at the same level (D).
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F2
Multiplanar reformatting of the volumetric bSSFP sequence aligned according to the inner mid-dorsal axis of the PL showed complete disto-proximal extension of the lesion from the osteotendineous junction on the tibial tuberosity to the middle third of the PL (Fig. 2).
(A): Midagittal multiplanar reformatted bSSFP MRI image of the patellar ligament (PL). (B,C,D): Transverse multiplanar reformatted bSSFP MRI images at different levels of PL course. Image B is obtained orienting the oblique transverse plane at level 1 of image A. Image C is obtained orienting the oblique transverse plane at level 2 of image A. Image D is obtained orienting the oblique transverse plane at level 3 of image A. (E): Midsagittal multiplanar reformatted CT image of the patellar ligament (PL). (F,G,H): Transverse multiplanar CT images at different levels of PL course. Image F is obtained orienting the oblique transverse plane at level 1 of image A. Image G is obtained orienting the oblique transverse plane at level 2 of image A. Image H is obtained orienting the oblique transverse plane at level 3 of image A. (I): Transverse sonographic image of the PL at level 1 of image A. (L): Transverse sonographic image of the PL at level 2 of image A. (M): Transverse sonographic image of the PL at level 3 of image A. On midsagittal MRI and CT images thickening of the distal PL half is evident. Transverse MRI images at different levels show in detail the caudo-cranial extension of the tear within PL sections: at most distal part of the PL (B - level 1 of Fig. A) the defect affects a large portion of ligament section while it became smaller proximally being confined to the most caudal part of PL section (C - level 2 of Fig. A). Images D and H shows normal PL sections (arrowhead) with homogeneous signal and attenuation respectively (level 3 of Fig. A). Such details are not evident on CT images (F, G) but easily assessable on correspondent transverse sonographic images as hypoechoic linear defects (I,L-arrows).
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F3
Discontinuities in PL structure were not evident (Fig. 1-B; Fig. 2-B,D; Fig. 3-F,G). At the distal insertion level the defect measured 3.8 mm and affected the entire PL section from caudal to cranial margin (Fig. 3-I,L).