Musculoskeletal Imaging Clinical Perspective

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1 Musculoskeletal Imaging linical Perspective McMonagle et al. MRI of the PL Musculoskeletal Imaging linical Perspective J. Scott McMonagle 1 lyde. Helms 1 William E. Garrett, Jr. 2 Emily N. Vinson 1 McMonagle JS, Helms, Garrett WE Jr, Vinson EN Keywords: MRI, mucoid degeneration, posterior cruciate ligament DOI: /JR Received June 21, 2011; accepted after revision October 23, Presented at the 2011 annual meeting of the merican Roentgen Ray Society, hicago, IL. 1 Department of Radiology, Duke University Health System, ox 3808, Durham, N ddress correspondence to J. S. McMonagle (jscottmcm@gmail.com). 2 Department of Orthopaedic Surgery, Duke University Health System, Durham, N. JR 2013; 201: X/13/ merican Roentgen Ray Society Tram-Track ppearance of the Posterior ruciate Ligament (PL): orrelations With Mucoid Degeneration, Ligamentous Stability, and Differentiation From PL Tears OJETIVE. The purpose of our study was to describe the MRI findings in the posterior cruciate ligament (PL) analogous to mucoid degeneration in the anterior cruciate ligament (L); to correlate MRI findings in the PL with ligamentous stability; to differentiate the PL tram-track appearance from the appearance of PL tears; and to emphasize the coexistence of PL and L mucoid degeneration, cruciate ganglia, and meniscal cysts. ONLUSION. The tram-track PL appearance commonly coexists with L mucoid degeneration; ganglia; and, less frequently, meniscal cysts. oth PL tears and MRI findings suggestive of PL mucoid degeneration show ligament thickening and increased PL signal intensity. Tram-track PLs are usually asymptomatic and typically have no ligamentous instability. lthough the MRI appearances of complete tears, partial tears, and chronic degeneration of the anterior cruciate ligament (L) have been thoroughly described, comparable studies in the literature about the posterior cruciate ligament (PL) are lacking. In particular, the MRI appearance of L mucoid degeneration was first described in 1999 [1]. Since then, our understanding of L mucoid degeneration has evolved and is now well established [2 5]. Histologic evaluations of cruciate ligaments harvested from cadavers and from patients undergoing knee replacement surgery have long described a link between degenerative changes in the L and those in the PL, particularly mucoid degeneration [6 8]. Despite the association of mucoid degeneration of the cruciate ligaments and the long-standing reports about the MRI appearance of L mucoid degeneration, only a few studies in the radiology literature describe the MRI appearance of mucoid degeneration of the PL [9, 10]. This discrepancy was highlighted at our institution s weekly sports medicine conference when an orthopedic surgeon showed a knee MRI examination that revealed diffuse PL thickening and increased signal intensity both of which are MRI findings associated with a PL tear [11]. However, this index patient had normal results on a posterior drawer examination. Homogeneous increased signal intensity that extends longitudinally throughout a thickened PL with an intact rim of peripher- al fibers (Fig. 1) is an appearance analogous to the classic celery stalk morphology of L mucoid degeneration [4]. Given the stability of the PL on physical examination and the MRI appearance of the PL being similar to mucoid degeneration in the L, we postulated that these MRI findings represent mucoid degeneration of the PL. Ultimately, findings from a physical examination performed of the index patient under anesthesia were normal and knee arthroscopy revealed an intact PL with a bulbous morphology and a diffuse yellowish hue, which was called PL mucoid degeneration by the orthopedic surgeon. The purpose of this study was to evaluate tram-track longitudinal intraligamentous PL signal-intensity abnormalities, which is similar to the MRI appearance of mucoid degeneration of the L. We also sought to differentiate this longitudinal intraligamentous PL signalintensity abnormality from PL tears and to determine the incidence of coexistent L mucoid degeneration, cruciate ganglia, and parameniscal and intrameniscal cysts. Materials and Methods Institutional review board approval and a waiver of informed consent were obtained for this retrospective study. fter our index case, we encountered five additional knee MRI examinations that had findings similar to the index case. We then conducted a retrospective review of our institution s knee MRI database of records over an 8-year period (12,972 cases). We searched for the key- 394 JR:201, ugust 2013

2 MRI of the PL Fig year-old man with posterior knee pain. Sagittal fat-suppressed T2- weighted MR image (TR/TE, 4000/70) of posterior cruciate ligament (PL) shows diffuse thickening and longitudinally increased signal intensity with peripheral rim of hypointense PL fibers (arrows). t arthroscopy, PL was intact, was bulbous in morphology, and had yellowish hue. words PL cyst, PL signal, and abnormal PL, which yielded 61 MRI studies. ll imaging studies were performed on a 1.5-T unit (Signa, GE Healthcare) according to our standard knee MRI protocol: sagittal fat-suppressed spin-echo proton density images (TR range/te, /20) and sagittal, axial, and coronal fat-suppressed fast spin-echo (FSE) T2-weighted images (TR range/te range, /57 80). The number of signals acquired was 2 for the FSE sequences and 1 for the proton density sequences. The echo-train length was 8 10 for the FSE sequences. slice thickness of 4 mm with a 0.4-mm interslice gap was used. The FOV was 16 cm, and the matrix size was These MRI examinations were retrospectively reviewed in consensus by two musculoskeletal radiologists with 5 and 33 years experience and one musculoskeletal radiology fellow. ased on our index case, the imaging criteria of PL mucoid degeneration included homogeneous longitudinal increased signal intensity in the PL in all planes on proton density and T2 images with an adjacent welldefined intact rim of hypointense PL fibers that give the PL a tram-track appearance. In an attempt to prevent potential inclusion of injured PLs, patients were excluded if they had a clinical history of knee trauma or MRI findings indicative of prior knee injury. Of the 61 patients from our database search, 47 were excluded: 23 patients had a clinical history of acute trauma, 11 had MRI findings of an acute L tear, four had an L-deficient knee, and nine had bone contusions with an intact L. Thus, there were 20 patients in the PL mucoid degeneration group: our index case, the five cases subsequently encountered in the reading room, and 14 examinations from the retrospective search. Each case fulfilled the defined imaging criteria of PL mucoid degeneration. There were eight women (40%) and 12 men (60%) with a mean age of 51.7 years (age range, years). In an effort to differentiate MRI findings of PL mucoid degeneration from those of PL tears, we included for review an equal number of patients with surgically proven PL tears. This group included seven women (35%) and 13 men (65%) with a mean age of 35.2 years (age range, years). Several different parameters for these 40 studies 20 examinations that met the imaging criteria for PL mucoid degeneration and 20 examinations of surgically proven PL tears were then retrospectively evaluated, again in consensus. Reviewers were blinded to the preliminary consensus interpretations and therefore did not know if the study had been included as PL mucoid degeneration or as a surgically proven PL tear. Using the imaging criteria of PL mucoid degeneration, the reviewers first decided whether the study represented PL mucoid degeneration or a PL tear. The transverse anteroposterior diameter of the vertical portion of each PL was measured on sagittal T2-weighted images. The PL was evaluated for the presence or absence of complete fiber disruption. The intrasubstance signal intensity of each PL on proton density weighted and T2-weighted sequences was graded as hyperintense (isointense to fluid), intermediate (increased signal intensity but less than signal intensity of joint fluid), or hypointense (normal PL signal intensity). The relative signal intensities on proton density and T2 images were then compared with each other. oexistent MRI findings of L mucoid degeneration, ganglia involving or adjacent to the PL, intrameniscal cysts, parameniscal cysts, and intraosseous cysts at either the femoral or tibial PL attachments were noted. The electronic medical records of all patients were reviewed: Each patient s presenting symptoms, the clinical assessment of the PL by an orthopedic specialist, and arthroscopic results, if available, were recorded. Results The tram-track appearance, our inclusion criterion, reliably differentiated all 20 of the PLs included as the mucoid degeneration group from the 20 PLs with surgically proven tears. Of the 20 PL tears, 19 (95%) showed amorphous or heterogeneously striated increased signal intensity without adjacent welldefined or intact peripheral fibers on both proton density weighted and T2-weighted images; these findings were easily differentiated from the tram-track appearance. Only on sagittal images, one of the PL tears (5%) showed linear, longitudinally oriented increased intraligamentous signal intensity that was somewhat similar to the tram-track appearance (Fig. 2). However, although the peripheral rim of fibers appeared intact on sagittal images, the peripheral fibers were clearly discontinuous on both the coronal and axial images. Further, the longitudinally oriented increased signal intensity throughout this PL tear was heterogeneous and had a striated look, with multiple separate lines of increased signal intensity as is often seen in PL tears; it was not a single solid and homogeneous streak of increased signal intensity, further differentiating it from the tram-track appearance [11]. y contrast, all 20 PLs in the mucoid degeneration group had a tram-track appearance created by homogeneous, longitudinal increased signal intensity with discrete borders surrounded by intact hypointense PL fibers validated on all three imaging planes (Fig. 3). Further, evaluation in all three planes distinguished adjacent structures, such as the meniscofemoral ligaments, oriented perpendicular to the PL that could erroneously appear as part of an intact peripheral rim if the PL had been evaluated in only a single plane. The tram-track appearance was seen throughout the entire length of 18 PLs (90%). One of the tram-track PLs (5%) had intraligamentous signal intensity that involved only the proximal half of the PL, whereas another (5%) had intraligamentous increased signal intensity with an intact peripheral rim of fibers that extended through the proximal and middle thirds of the PL but that spared the distal third of the PL. In the 20 patients with MRI findings that met the imaging criteria for PL mucoid degeneration, 19 PLs (95%) measured 7 mm or more in anteroposterior diameter on sagittal T2-weighted images. The average PL JR:201, ugust

3 McMonagle et al. Fig year-old man with severe knee pain after motor vehicle crash., Sagittal fat-suppressed proton density weighted MR image (TR/TE, 2000/20) shows thickening and multiple linear, longitudinally oriented intrasubstance striations of posterior cruciate ligament (PL) and few peripheral hypointense PL fibers (arrows). and, xial (4000/65) () and coronal (4000/60) () fat-suppressed T2-weighted images show abnormal thickening and multiple heterogeneous linear striations of intermediate signal intensity throughout PL, in contrast to homogeneous and solid intrasubstance signal intensity of mucoid degeneration. dditionally, peripheral rim of hypointense fibers (arrows) is not intact on axial or coronal images. t surgery, this PL was described as torn. thickness for PL mucoid degeneration was 8.5 mm, with a range of 6 12 mm. mong the surgically proven PL tears, 17 PLs (85%) had a transverse anteroposterior diameter that measured 7 mm or more. PL tears had an average PL thickness of 8.8 mm and a range of 4 13 mm. Ten of the 20 PLs (50%) from the surgically proven PL tear group appeared completely disrupted or avulsed. Partial fiber discontinuity was seen in none of the PL tear group. Four (40% of the total) of the ligaments were proximal tears with complete fiber disruption from the femoral attachment, three (30%) tears were midsubstance, and three (30%) PLs were completely disrupted from the tibial attachment; two of these three distal tears also involved small avulsed and retracted tibial cortical bone fragments. y contrast, conforming to the criteria of the tram-track appearance, PLs in the mucoid degeneration group had no disruption of the PL fibers. Hyperintense signal intensity was seen more often in the PL mucoid degeneration group than in PL tears (Table 1). Seven PLs in the mucoid degeneration group (35%) had hyperintense intrasubstance signal on proton density images, whereas only one PL tear (5%) had hyperintense signal intensity on proton density images. None of the PLs in the mucoid degeneration group had hypointense signal intensity on proton density weighted or T2-weighted images. y comparison, the PL tear group had hypointense signal intensity on T2-weighted images in six of 20 PLs (30%), and the majority of PL tears, 14 of 20 (70%), showed intermediate signal intensity. In all 20 of the PL tears (100%), the signal intensity on proton density images was relatively higher than on T2-weighted images. The majority of PLs in the mucoid degeneration group, 14 of 20 (70%), also had relatively increased signal intensity on proton density images when compared with the signal intensity on T2-weighted images. In nine of the 20 patients with PLs with a tram-track appearance (45%), coexistent MRI findings of L mucoid degeneration were also present (Fig. 4). coincident ganglion exerted mass effect on, emanated from, or was immediately adjacent to the PL in 16 (80%) of the PLs in the mucoid degeneration group (Fig. 5). Intrameniscal cysts were present in five knees in the PL mucoid degeneration group (25%), three in the lateral meniscus and two in the medial meniscus, and parameniscal cysts were noted in two patients (10%), one adjacent to the lateral meniscus posterior horn and one adjacent to the medial meniscus posterior body. Intraosseous cysts were noted in four of the 20 patients (20%) in the PL mucoid degeneration group: Two were adjacent to the tibial attachment of the PL and two were adjacent to the femoral attachment. oexistent L mucoid degeneration was not seen in any of the patients with surgically proven PL tears (0%). ganglion was adjacent to the PL in four of the 20 (20%) PL tears. Two intrameniscal cysts (10%) and one parameniscal cyst (5%) were present in the PL tear group. Review of each patient s electronic medical record showed that knee pain was the most common presenting symptom, seen in all 20 patients with tram-track PLs. However, 18 of these 20 patients (90%) had additional MRI findings that were likely the primary cause of knee pain. ll 20 patients with a tram-track PL appearance (100%) had a Table 1: Posterior ruciate Ligament (PL) Intrasubstance Signal Intensity MRI Sequence PL Intrasubstance Signal Intensity Hyperintense a Intermediate b Hypointense c PL mucoid degeneration Proton density 7 (35) 13 (65) 0 (0) FSE T2 4 (20) 16 (80) 0 (0) PL tears Proton density 1 (5) 18 (90) 1 (5) FSE T2 0 (0) 14 (70) 6 (30) Note Data presented are no. (%) of patients. FSE T2 = fast spin-echo T2-weighted. a Isointense to fluid. b Increased signal intensity but less than signal intensity of joint fluid. c Normal PL signal intensity. 396 JR:201, ugust 2013

4 MRI of the PL negative posterior drawer test on physical examination by an orthopedic specialist. Two patients (10%) in this group also had posterior knee pain with knee flexion beyond 90 and one patient (5%) had posterior midline knee tenderness to palpation. Of the 20 patients with a tram-track PL appearance, six (30%) had subsequent arthroscopy; all six patients had no ligamentous instability during their examination under anesthesia. Five of the PLs were described as normal and intact, whereas the sixth PL, our index case, was intact but also was bulbous with a diffuse yellowish hue. Discussion The true incidence of PL mucoid degeneration is difficult to assess because it is, as in our patient population, typically asymptomatic and incidentally noted. s a point of reference, ergin et al. [2] reported that the incidence of mucoid degeneration in the L is 1.0% (44/4221). The incidence of Fig year-old woman with chronic left knee pain with stable posterior cruciate ligament (PL) on clinical examination. and, xial (TR/TE, 4000/65) (), coronal (4000/68) (), and sagittal (4000/68) () fat-suppressed T2-weighted MR images show typical appearance of PL mucoid degeneration (arrows) with increased intraligamentous signal intensity and peripheral rim of intact hypointense PL fibers., Sagittal image shows anterior meniscofemoral ligament (arrowhead) that is adjacent to but separate from intact peripheral PL rim (arrows). PL mucoid degeneration in our retrospective study population was 0.1% (14/12,972). The normal appearance of the PL on MRI is that of a broad curvilinear band of low signal intensity on proton density weighted and T2-weighted images that is usually 6 mm or less in anteroposterior diameter. In 2008, Rodriguez et al. [11] reported two MRI findings that are highly suggestive of a torn PL: an anteroposterior diameter of 7 mm or more and increased intrasubstance signal intensity in the PL, particularly with PLs showing relatively higher signal intensity on proton density images than T2-weighted images. However, PL thickening and increased signal intensity do not always equate to a functionally torn PL: 19 of the 20 PLs that met the imaging criteria for mucoid degeneration (95%) were greater than 7 mm in anteroposterior diameter and 14 (70%) PLs in the mucoid degeneration group had signal intensity that was relatively higher on proton density weighted images than on T2-weighted images. s a result, neither PL thickness nor relatively higher signal intensity is a reliable discriminator and additional imaging criteria that differentiate PL degenerative changes from PL tears are requisite. The tram-track appearance was the best MRI finding for distinguishing between PL mucoid degeneration and PL tears in this small series. nalogous to intrameniscal cysts, which are isointense to fluid in only 8.4% of the cases [12], the majority of PL intrasubstance signal intensity, particularly in our tram-track PL group, was not fluid signal intensity. Instead, PLs in both study groups were usually intermediate on proton density and T2-weighted imaging, 65% and 80% for PL mucoid degeneration versus 90% and 70% for PL tears, respectively. PLs in the mucoid degeneration group were more likely to have intrasubstance signal intensity isointense to fluid on proton density images, 35%, as compared with only 5% of PL tears. Relative signal intensities, Fig year-old man with anterior knee pain and normal findings on anterior and posterior drawer clinical examinations., onsecutive coronal fat-suppressed T2-weighted MR images (TR/TE, 3700/50) show increased signal intensity and thickening of both anterior cruciate ligament (L) and posterior cruciate ligament (PL); these findings are consistent with L (black arrows) and PL (white arrows) mucoid degeneration. JR:201, ugust

5 McMonagle et al. however, cannot reliably distinguish between PL mucoid degeneration and PL tears, increasing the importance of additional MRI criteria such as the tram-track appearance. ergin et al. [2] reported that L mucoid degeneration involved the entire L in 93% of cases; similarly, the majority of our PLs with a tram-track appearance, 18 of 20 (90%), involved the entire length of the PL. One of the patients in our series had undergone subsequent knee MRI 2 and 6 years after the initial MRI examination. The transverse and longitudinal dimensions of the hyperintense intraligamentous signal intensity enlarged with each subsequent examination (Fig. 6), suggesting that just as degenerative changes of osteoarthritis progress over time, so too does the extent of PL mucoid degeneration proceed. Fig year-old man who presented with 6-week history of posterior knee pain and fullness and no history of trauma. Sagittal fat-suppressed T2-weighted MR image (TR/TE, 3700/50) shows complex ganglion (arrow) that exerts mass effect on adjacent proximal posterior cruciate ligament (PL). Longitudinal tram-track appearance of PL mucoid degeneration is also seen. PL ganglion was aspirated at surgery and PL was described as normal and intact. The posterior drawer examination is the most accurate clinical test, with a reported sensitivity of 90% and specificity of 99% for orthopedic surgeons with fellowship training in sports medicine [13]. However, the accuracy of the posterior drawer test significantly decreases with distracting injuries, when even subtle internal or external rotation of the tibia is present, or even when the knee is not precisely at 90 of flexion. The positive likelihood ratio of the posterior drawer test also significantly decreases for less experienced providers and those without dedicated training [13]. Thus, physical examination of the PL is highly valuable for assessing the functional competency of the ligament, but it is not without limitations. ll of the patients in our PL mucoid degeneration group had physical examinations that included a posterior drawer test. Further, the results were reported as either normal or no laxity for all 20 PLs that had a tram-track appearance. ll of the PLs in the surgically proven PL tear group, by contrast, had been preoperatively noted to have grade II or grade III PL laxity. Investigators have reported that the majority of PL tears (62%) involve stretching deformation and, as a result, do not have complete fiber avulsion or disruption [11]. In the group with a surgically proven PL tear, 10 of the 20 PLs (50%) showed fiber disruption. onsequently, although fiber disruption indicates a torn PL, visualization of intact PL fibers poorly correlates with functional competence of the PL. y comparison, all 20 PLs (100%) that had a tram-track appearance with an intact peripheral rim of PL fibers on all imaging planes (i.e., the inclusion criteria for this study) had a mechanically intact PL. Similar to patients with L mucoid degeneration who rarely complain of knee instability and typically have a negative Lachman sign [2], patients with PL mucoid degeneration typically do not have ligamentous instability. ll six tram-track PL patients who subsequently underwent surgery also had a normal posterior drawer examination under anesthesia. dditionally, all six patients had an intact ligament at arthroscopy; in one patient, the PL also had a bulbous appearance and yellowish hue. The arthroscopic appearance of these tram-track PLs resembles the two possible arthroscopic appearances of L mucoid degeneration: normal or bulbous with a yellowish hue [14]. lthough no specimens were obtained in our PL mucoid degeneration Fig year-old female triathlete with patellofemoral pain., Sagittal T2-weighted MR image (TR/TE, 3300/70) at initial presentation shows tram-track appearance (arrow) involving only proximal half of posterior cruciate ligament (PL) (transverse dimension, 4.3 mm; longitudinal dimension, 12.0 mm). Patient did not have meniscofemoral ligament., Sagittal T2-weighted MR image (4000/60) obtained 2 years after shows intraligamentous tram-track appearance (arrow). PL has increased in transverse dimension (5.5 mm) and longitudinal dimension (13.6 mm) since initial examination., Most recent sagittal T2-weighted MR image (3400/63) obtained 6 years after shows continued increase in transverse (7.5 mm) and longitudinal (18.2 mm) size of tram-track appearance (arrow) relative to both earlier studies. t arthroscopy, PL was reported as normal. 398 JR:201, ugust 2013

6 MRI of the PL group, Shoji et al. [10] described a PL with MRI findings identical to our group that was arthroscopically excised and revealed mucoid degeneration at histologic examination. The cause of cruciate ligament mucoid degeneration remains controversial. ergin et al. [2] described the coexistence of L mucoid degeneration with L ganglia and intraosseous cysts. The coincident association between ganglia and PL mucoid degeneration, seen in 16 of our patients (80%), suggests that these two entities may also share a common pathogenesis in the PL. Some investigators have suggested that ganglia are a product of connective tissue mucoid degeneration [15, 16], whereas others theorize that a congenital abnormality or previous injury facilitates and possibly predisposes cruciate ligaments to degenerative ganglion formation [17]. Nine of our patients (45%) had MRI findings of both L and PL mucoid degeneration, further supporting a common pathogenesis among degeneration of the L and PL, similar to what has previously been reported in cadavers and in patients undergoing knee replacement surgery [6 8]. Seven meniscal cysts (35%) five intrameniscal cysts and two parameniscal cysts were seen in our tram-track PL group. ecause meniscal cysts are reportedly found in 8% of knee MRI studies [12], the increased prevalence of meniscal cysts in our tramtrack PL patients suggests a common degenerative pathway or at least that some patients, for anatomic or biomechanical reasons, are more predisposed to soft-tissue degenerative changes throughout the knee. This study was limited by its retrospective and observational design. In an attempt to exclude injured PLs, we chose to exclude patients with a preceding episode of trauma or with MRI findings indicative of a prior knee injury. Our assumption of no prior knee injury relies heavily on each patient s reported clinical history; obviously we cannot guarantee that each patient with tram-track PL findings had absolutely no prior or remote history of knee trauma. Potential selection bias was unavoidable given the inclusion criteria for the PL tram-track group. Partial PL tears, which might have imaging features similar to or overlapping with those described with mucoid degeneration, were also potentially excluded from the study. Mild or nonspecific repetitive trauma and even healed partial tears have been espoused as potential causes of mucoid degeneration in the L [15]; similar causality for PL mucoid degeneration can be suggested and, to date, have not been definitively refuted. McIntyre et al. [3] described L mucoid degeneration that progressed to an atraumatic complete L tear. Significant selection bias was also present in our surgically proven PL tear group because progression to surgery implied clinical instability of the PL. ecause most PL tears are not treated surgically, there is uncertain clinical significance of distinguishing between PL tears and PL mucoid degeneration. This study is further limited by lack of direct histologic correlation; five of the six tram-track PLs that proceeded to arthroscopy had a normal appearance, similar to arthroscopic findings in cases of L mucoid degeneration. In summary, although the pathogenesis of cruciate ligament mucoid degeneration remains unknown, it is important that MRI findings suggestive of PL mucoid degeneration be differentiated from chronic or acute interstitial, partial, and complete PL tears given their respective and important differences in ligamentous stability and the practical implications for clinical management. linical correlation in our study population indicates that the tram-track PL appearance is usually asymptomatic and typically has no ligamentous laxity. The tramtrack PL appearance further informs clinical decision-making by allowing the radiologist to discriminate between mechanically unstable torn PLs and mechanically intact PLs. oexistent MRI findings suggest associations between PL and L mucoid degeneration, ganglia, and potentially even meniscal cysts. References 1. Kumar, ickerstaff DR, Grimwood JS, Suvarna SK. Mucoid cystic degeneration of the cruciate ligament. J one Joint Surg r 1999; 81: ergin D, Morrison W, arrino J, Nallamshetty SN, artolozzi R. nterior cruciate ligament ganglia and mucoid degeneration: coexistence and clinical correlation. JR 2004; 182: McIntyre J, Moelleken S, Tirman P. Mucoid degeneration of the anterior cruciate ligament mistaken for ligamentous tears. Skeletal Radiol 2001; 30: Papadopoulou P. The celery stalk sign. Radiology 2007; 245: Roberts, Towers JD, Spangehl MJ, arrino J, Morrison W. dvanced MR imaging of the cruciate ligaments. Magn Reson Imaging lin N m 2007; 15: Stubbs G, Dahlstrom J, Papantoniou P, herian M. orrelation between macroscopic changes of arthrosis and the posterior cruciate ligament histology in the osteoarthritic knee. NZ J Surg 2005; 75: llain J, Goutallier D, Voisin M. Macroscopic and histological assessments of the cruciate ligaments in arthrosis of the knee. cta Orthop Scand 2001; 72: Hodler J, Haghighi P, Trudell D, Resnick D. The cruciate ligaments of the knee: correlation between MR appearance and gross and histologic findings in cadaveric specimens. JR 1992; 159: Viana SL, Fernandes JL, Mendonca JL, Freitas FM. Diffuse intrasubstance signal abnormalities of the posterior cruciate ligament: the counterpart of the mucoid degeneration of the anterior cruciate ligament? case series. JR-TR 2008; 91: Shoji T, Fujimoto E, Sasashige Y. Mucoid degeneration of the posterior cruciate ligament: a case report. Knee Surg Sports Traumatol rthrosc 2010; 18: Rodriguez W Jr, Vinson EN, Helms, Toth P. MRI appearance of posterior cruciate ligament tears. JR 2008; 191: nderson JJ, onnor GF, Helms. New observations on meniscal cysts. Skeletal Radiol 2010; 39: Rubinstein R Jr, Shelbourne KD, Mcarroll JR, VanMeter D, Rettig. The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries. m J Sports Med 1994; 22: Makino, Pascual-Garrido, Rolon, Isola M, Muscolo DL. Mucoid degeneration of the anterior cruciate ligament: MRI, clinical, intraoperative, and histological findings. Knee Surg Sports Traumatol rthrosc 2011; 19: Fealy S, Kenter K, Dines JS, Warren RF. Mucoid degeneration of the anterior cruciate ligament. rthroscopy 2001; 17:E Liu SH, Osti L, Mirzayan R. Ganglion cysts of the anterior cruciate ligament: a case report and review of the literature. rthroscopy 1994; 10: Levine J. ganglion of the anterior cruciate ligament. Surgery 1948; 24: JR:201, ugust