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Meniscus morphology: Does tear type matter? A narrative review with focus on relevance for osteoarthritis research
Author’s Accepted Manuscript Meniscus Morphology: Does Tear Type Matter? A Narrative Review with Focus on Relevance for Osteoarthritis Research Mohamed Jarraya, Frank W. Roemer, Martin Englund, Michel D. Crema, Heather I. Gale, Daichi Hayashi, Jeffrey N. Katz, Ali Guermazi www.elsevier.com/locate/semarthrit
PII: DOI: Reference:
S0049-0172(16)30440-1 http://dx.doi.org/10.1016/j.semarthrit.2016.11.005 YSARH51131
To appear in: Seminars in Arthritis and Rheumatism Cite this article as: Mohamed Jarraya, Frank W. Roemer, Martin Englund, Michel D. Crema, Heather I. Gale, Daichi Hayashi, Jeffrey N. Katz and Ali Guermazi, Meniscus Morphology: Does Tear Type Matter? A Narrative Review with Focus on Relevance for Osteoarthritis Research, Seminars in Arthritis and Rheumatism, http://dx.doi.org/10.1016/j.semarthrit.2016.11.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Meniscus Morphology: Does Tear Type Matter? A Narrative Review with Focus on Relevance for Osteoarthritis Research Mohamed Jarraya 1,2, Frank W. Roemer1, 3, Martin Englund 4,5, Michel D. Crema1, Heather I. Gale 6, Daichi Hayashi 7, Jeffrey N. Katz 8, Ali Guermazi 1
1) Quantitative Imaging Center, Department of Radiology, Boston University Medical Center, Boston, MA 2) Department of Radiology, Mercy Catholic Medical Center, Darby, PA 3) Department of Radiology, University of Erlangen-Nuremberg, Erlangen, Germany 4) Lund University, Faculty of Medicine, Department of Clinical Sciences Lund, Orthopedics, Clinical Epidemiology Unit, Lund, Sweden 5) Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston, MA, USA 6) Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 7) Department of Radiology, Bridgeport Hospital, Yale New Haven Health System, Bridgeport, CT 8) Departments of Medicine (Rheumatology, Immunology and Allergy) and Orthopedic Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
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ABSTRACT: Objective: To give a narrative overview of meniscal tears with a radiologic emphasis on the morphologic type, technical considerations, and on the relevance of the type of meniscal tear in the context of osteoarthritis (OA) research. Design: Twenty years of the PubMed database were searched for epidemiological, radiological, arthroscopic and biomechanical reports, and review articles focusing on meniscal tears in middle aged and older individuals, in the setting of OA. Case reports, publications on meniscal tears in young active individuals, and publications not in English were excluded. Results: Meniscal intra-substance signal abnormalities are associated with an increased risk of a degenerative meniscal tear in the same segment. Posterior radial tears of the medial meniscus appear to be a highly relevant event in OA of the knee, with associated cartilage loss and meniscal extrusion. Radial tears are more commonly missed on MRI than other types, and should be carefully looked for on coronal and axial images. While medial meniscus posterior root tears are of “radial” morphology, there is growing interest in looking at them as a separate entity, mainly because they require a different therapeutic approach. Conclusion: There is a lack of data on the relevance of different morphologic types of meniscal tears to the natural history of knee OA, both cross-sectionally and – especially – longitudinally. Further epidemiologic studies should focus on specific meniscal tears based on their morphology to better understand their relevance in the genesis and progression of knee OA. Key Words: Magnetic resonance imaging, meniscal tear, osteoarthritis, degenerative tears.
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Introduction: Knee menisci are intra-articular fibro-cartilaginous structures, with important functions in knee biomechanics including load distribution, shock absorption, lubrication, and joint stability [1; 2]. Several computer-based semi-automated and automated magnetic resonance imaging (MRI) – based algorithms have been developed recently to characterize meniscal changes – including volume and position – in knee osteoarthritis (OA) [3-9], as well as their predictive value in disease progression [10; 11]. While promising, these novel techniques are not able to reliably show intrameniscal signal changes that are thought to represent intrameniscal mucoid degeneration (when the signals do not reach the meniscal surface), or different types of meniscal tears (when a signal abnormality reaches the meniscal surface on at least two consecutive slices on MRI). Meniscal tears are highly relevant when discussing the natural history, incidence and progression of knee OA [12-22]. In addition, there has been a significant increase in the use of knee arthroscopy during the last two decades in the United States, with nearly half of all knee procedures performed for meniscal tears [23]. However there is no consensus on optimal management of meniscal tears in OA, as most of the recently published randomized clinical trials showed no benefit of partial meniscectomy over physical therapy or even a sham meniscectomy procedure [24-28]. Only one prospective study, involving middle-aged patients with meniscal symptoms, found any benefit from partial meniscectomy [29]. A recent study even showed that meniscal surgery is associated with increased risk of radiographic osteoarthritis in absence of preceding trauma [30]. At the time this manuscript was written, there were no Appropriateness Use Criteria for the management of meniscal tears published by the American Academy of Orthopedic Surgeons (AAOS). However a webpage containing educational content, and co-provided by the AAOS stated that arthroscopic surgery may be suggested if symptoms persist with a non-surgical treatment [31].
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Some authors suggest that the severity of the cartilage degeneration is related to the specific morphology of the tear, including the degree of circumferential fiber disruption [32]. Recently, a large epidemiologic study of the use of knee arthroscopy in Sweden showed meniscal tear types may differ by age group, and have a variable association with cartilage lesions and anterior cruciate ligament (ACL) tear [33]. Meniscal tears are often discussed as if they are a single entity [13; 34]. Our aim is to give an illustrative overview of the different types of meniscal tears, and to discuss their differences particularly in regard to knee OA. Also, we will briefly touch on other MRI-detected meniscal changes, such as intra-substance signal abnormalities, and meniscal substance loss due to surgery or as part of the natural history of OA, and commonly referred to as partial or complete maceration. Methods: A search for original articles published between January 1995 and December 2015 was performed in PubMed. The search was based on but not limited to the query terms “meniscal tear”, “horizontal meniscal tear”, “complex meniscal tear”, “radial meniscal tear”, “longitudinal meniscal tear”, “bucket-handle meniscal tear”, “meniscal root tear”, “meniscal destruction”, “meniscal substance loss”, “meniscal intrasubstance signal abnormality”, “meniscal mucoid degeneration”, “meniscal extrusion”, “magnetic resonance imaging (MRI)”, and “osteoarthritis (OA)”. The literature search using these search terms yielded 3,633 publications. Animal studies were excluded, as were letters to the editors, proof of concept studies of less than 10 patients, case reports, publications on meniscal tears in young active individuals, and publications not in English. The focus was on epidemiological, radiological, arthroscopic and biomechanical original research, and review articles focusing on meniscal tear in middle aged and older individuals, in the setting of OA. Additional references were included when they were considered of importance. The literature was sorted and analyzed and is presented here according to technical
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considerations, anatomy, and meniscal tears, with an emphasis on the effects of different types of meniscal tears in the pathogenesis and progression of knee OA. Anatomy: The meniscus is a wedge-shaped, semilunar, fibrocartilaginous structure, with a thicker peripheral portion and tapered central free edge, as well as a superior concave surface conforming to the femoral condyle and a flat base attached to the tibia via a central root ligament. The attachment is essential for normal meniscal function and distribution of axial compressive loads across the tibial plateau. Circumferentially-oriented type I collagen fibers provide the meniscus with hoop strength, and are critical to resisting axial load and preventing meniscal extrusion [35]. When exposed layer by layer with electron microscopy, the meniscus reveal three distinct layers: A superficial meshwork of thin fibrils covering the tibial and femoral sides, with lamella-like collagen fibril bundles beneath, and a main central portion of collagen fibrils oriented in a circular manner, which explains the circumferential orientation of the majority of tears in the meniscal tissue [36]. A capillary network originating within the synovium supplies the meniscus and capsular tissues of the knee along the meniscal periphery, only part receiving a direct blood supply. As a result the meniscus is usually divided into three zones based on their vascular supply, and the location of the tear within one of those areas plays a determining role in the prognosis of spontaneous or surgical healing. The peripheral vascular portion called the “red-red” zone, has an excellent prognosis. An intermediate portion at the border of the vascular supply-– the “red-white” zone– has a generally positive prognosis. However the inner portion – the “white-white zone” – is relatively avascular and has a poor prognosis for healing [37-39].
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Technical Considerations: The diagnosis of meniscal tears by MRI requires high spatial resolution and an optimized signalto-noise ratio [40], achieved by the use of a dedicated knee coil, a slice thickness no more than 3 mm, a field-of-view of 16cm or less, and a matrix size of at least 288x288 [41]. While sagittal and coronal images are essential [1], axial images can help in characterizing meniscal injuries, particularly in regard to radial tear detection [35; 42]. Reported sensitivity and specificity for detection of medial meniscal tears are 93% and 90% at 1.5T, and 96% and 88% at 3.0T, suggesting similar accuracy [43]. Other studies reported slightly better results with 3.0T [44; 45]. Most common sequences include spin-echo or fast spin echo (FSE) proton density with or without fat saturation, T1, and gradient echo [46]. These sequences usually share short echo times, i.e, 3~6 ms [47], which has the advantage of decreasing susceptibility and flow artifacts, improving noise-to-signal ratio, and reducing scan time, [46; 48]. With shorter echo times (<1ms) the entire meniscus can be seen with high signal intensity, which limits detection of pathology [47]. The “magic angle” artifact, however, has to be considered when using short echo times. It results in artifactual abnormal meniscal signal, usually in the upsloping portion of the posterior horn of the lateral meniscus, and can be mistaken for a tear by inexperienced readers [49]. Meniscal Intra-substance Signal Abnormality: Meniscal intra-substance signal abnormalities are defined as an increased signal that does not fulfill the criteria for a meniscal tear according the “two-slice-touch” rule (i.e it does not reach the meniscal surface on two consecutive views) and is a common finding on routine MRI of the knee (figure 1) [50-52]. Its reported prevalence in middle aged (45-55 years) individuals with or without OA, is between 26% and 43% [50; 52]. Histologically, intra-meniscal signal intensity may represent foci or bands of mucoid degeneration or microcyst formation and separation of
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collagen bundles [53; 54]. These changes may weaken the meniscal structure and may serve as a risk factor for degenerative meniscal tears [52]. The natural history of intra-substance signal abnormalities is still not fully understood. Initial studies failed to show an association between intrameniscal signal intensity and incident meniscal tears [50; 55]. These studies may have been biased by short follow-up interval (12 months) [50], or subject selection (younger subjects after knee trauma) [55]. More recently a six-year longitudinal study that included 269 middle-aged participants without radiographic knee OA from the Osteoarthritis Initiative, reported by Kumm et al. showed intrameniscal signal changes at baseline to be highly unlikely to regress (only one of 130 showed regression). Indeed, it was associated with an increased risk of developing a degenerative meniscal tear in the same segment, typically a horizontal cleavage or a flap tear [52]. Meniscal Tears: In one population-based study that included 991 randomly selected adults regardless of knee symptoms. Englund et al. reported an overall prevalence of meniscal tears of 31%, increasing with age and consistently higher in men, ranging from 19% in women aged 50-59 years to 56% among men between 70 and 90 years[34]. Regardless of pain status, the prevalence of meniscal tears was markedly higher in subjects with established radiographic OA [34]. When present, meniscal tears involved the medial meniscus and/or the posterior horn in two thirds of the cases, with horizontal and complex tears the most common. In another cohort sample from the same study, Guermazi et al. reported a prevalence of meniscal tears of 24% of the knees, regardless of pain status [56]. It should be mentioned that most subjects with a meniscal tear are asymptomatic [34]. Meniscal tears in the context of osteoarthritis usually occur without predisposing trauma. The American College of Radiology’s appropriateness criteria show that non-contrast enhanced MRI is “usually appropriate” for non-traumatic knee pain with a negative initial x ray (or x-ray
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with joint effusion). Meniscal tears are among the MR findings in this case, along with ligamentous injury, cartilage damage, bone marrow edema, joint effusion. Regardless of morphologic type, meniscal tears are strongly associated with OA cross-sectionally and predict OA longitudinally and are considered to be part of the spectrum of early or preradiographic disease [15-17]. Furthermore, any type of meniscal tear is associated with, and is a risk factor for, meniscal body extrusion commonly measured in the coronal plane on MRI [57; 58]. Often enough meniscal tear types are categorized into varying groups for comparison rather than separately compared to each other. For example horizontal tears are sometimes combined with complex tears, or with flap and radial tears, which prevents comparison of tear type characteristics [59; 60]. In the following sections we will highlight the different types of tears and discuss their role in the context of OA incidence and progression based on the published literature. Horizontal Tear: A horizontal tear runs parallel to the tibial plateau, involves either one of the articular surfaces and/or the periphery, dividing the meniscus into superior and inferior halves. Commonly, in the radiologic community, a horizontal-oblique tear only differs by a slight difference in direction of meniscal cleavage (figure 2). In semiquantitative MRI scoring systems of knee OA, a horizontaloblique tear is scored as horizontal [61]. Table 1 provides a comparison between the different semiquantitative MRI scoring systems for the evaluation of meniscal damage. Experimental studies have shown that horizontal cleavage of the medial meniscus results in a statistically significant increase in peak contact pressure, compared with an intact meniscus [62; 63], which may be one explanation for associated cartilage damage. In the Framingham cohort, horizontal tears were found in 40% of all knees with meniscal tears [34]. In a cross-sectional arthroscopic study including 103 patients with isolated medial meniscal tears, and investigating the relationship between tear morphology and cartilage degeneration,
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Henry et al. reported a prevalence of isolated horizontal tears of 24% [32]. The study showed similar findings for horizontal and complex tears in regard to severity of chondral degeneration in the ipsilateral compartment [32]. Other arthroscopic studies reported conflicting results regarding overall prevalence and severity of associated cartilage degeneration in horizontal tears compared to other tears. The conflicts are mainly due to inconsistent categorization of tear morphology [59; 60]. There is no longitudinal data comparing horizontal meniscal tears to other morphologic types in regard to structural joint outcomes, such as cartilage loss and bone marrow changes. Complex Tear: Complex tears include any combination of radial, horizontal, and longitudinal components. The meniscus often appears fragmented with the tear extending into more than one plane (figure 3) [35]. Complex tears were present in 37% of the subjects with meniscal tears in the Framingham cohort [34], and in 22% in the arthroscopic study by Henry et al. [32]. Unfortunately, as for horizontal tears, there is no longitudinal data on OA progression of complex tears as compared with other morphologic types. Flap Tear: Flap tears are commonly regarded as within the spectrum of degenerative tears [1; 33], caused by either horizontal or oblique fissures of the meniscus with superior or inferior displacement of the fragment into the meniscal recess or the intercondylar space (figure 4)[64; 65]. Usually flap tears involve the body and posterior horn of the medial meniscus and displacement occurs inferiorly adjacent to the tibial plateau [64]. However, flap tears of the lateral meniscus more likely involve the posterior horn [64]. Radial Tear: Radial meniscal tears are oriented perpendicularly to the meniscal axis and tibial plateau, transecting the longitudinal collagen bundles extending from the free edge toward the periphery
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(figure 5). This pattern disrupts the meniscal hoop strength resulting in a dramatic loss of function and may result in meniscal extrusion. Complete radial tears impair the ability of the medial meniscus to withstand loading, and have been described as equivalent to total meniscectomy [66]. Radial tears were present in 15% of subjects with meniscal tears in the Framingham study [34], while Bergkvist et al reported radial tears in 7% of arthroscopy-detected meniscal tears in patients with a preoperative diagnosis of knee OA and/or chronic meniscal tears [33]. In other clinical cohorts, radial tears were identified by arthroscopy in 15-25 % of the cases [67; 68]. Bergkvist et al. reported that medial meniscus radial tears predominantly affect the posterior horn, and had the highest association with ipsilateral cartilage damage compared to all other morphologic types (although there is no mention of statistical significance). The mean age of affected individuals (51 years) was no different from subjects with degenerative horizontal or flap tears. In addition arthroscopic findings of medial radial tears were consistent with degenerative tears [33]. It is worth noting however that the study made no distinction between radial and root tears. Furthermore, in a study including 407 patients who underwent knee arthroscopy for tears of the medial meniscus, Wu et al. reported that higher grade cartilage damage was found in radial tears than in horizontal tears [69]. In a retrospective series of 102 patients with medial posterior horn tears, meniscal extrusion was greater and more severe in patients with a radial tear component than in those without a radial component [70]. Taken together, these studies suggest the significance of radial tears of the medial posterior horn in the natural history of knee OA. Unfortunately, there is no longitudinal data in the literature to confirm this significance. In contrast with medial meniscus radial tears, lateral radial tears are encountered in younger patients (mean age 32 years) and have a higher association with ACL injuries (36%) than medial meniscus radial tears (8%) [33]. They are thus considered to be of traumatic origin.
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The location of the tear relative to the imaging plane may affect the MRI findings. For example a radial tear of the posterior horn may appear as “cleft” on coronal view, and “ghost/truncated” on sagittal view [35]. Another example, a radial tear involving the junction of the meniscal body and posterior horn results in a “marching cleft” appearance, progressing away from the free edge on contiguous sagittal images [35]. This variability may explain, at least in part, the reported underdiagnosis of radial tears by MRI, when compared to arthroscopy [67; 68; 71]. Harper et al. reported only 37% of radial tears were diagnosed correctly. Sometimes, radial tears may be seen in only one view, such as coronal or axial [42; 45]. Because of the possibly more deleterious consequences resulting from radial tears compared with other morphological types, we suggest that MRI-detected complex tears with radial component should be classified as radial tears. While biomechanical studies have reported on the importance of meniscal repair in restoring the meniscal function [72; 73], treatment of radial tears in individuals with OA usually consists of partial meniscectomy [70; 74]. Root Tear: Meniscal root tear is an avulsion injury or radial tear occurring within 1 cm of the bony tibial attachment (figure 6) [75; 76]. Biomechanically, it compromises the loading profile with subsequent increased tibiofemoral contact pressure [77-82]. Clinically, posterior medial meniscus root tears result in severe instability of the knee joint [83]. The prevalence of meniscal root tears varies between 1% in the middle aged and elderly among the general population [34] to 6% in adults with radiographic OA [84], and was up to 27.8% in a group of Korean patients with medial meniscal tears treated arthroscopically [68]. The latter high prevalence was attributed to local cultural factors, such as squatting and sitting on the floor with folded legs [68]. Henry et al. reported more ipsilateral cartilage damage of the femoral condyle in medial posterior root tears than in all other types [32]. A retrospective arthroscopic study further showed that medial meniscus posterior root tears were associated with a greater degree of meniscal extrusion
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and more cases of osteonecrosis in comparison with horizontal tears [85]. However, in a retrospective series of 102 patients with medial posterior horn tears, Lee et al. reported a similar incidence of major meniscal extrusion in knees with root tear and non-root tears [70]. Biomechanical studies showed that alteration of the loading profile secondary to posterior medial meniscus root tears can be almost totally reversed with anatomic repair [77]. This is consistent with clinical studies reporting refixation to be more effective than partial meniscectomy in regard to clinical and radiologic outcomes [86; 87]. Vertical (Longitudinal And Bucket-Handle) Tear: Vertical tears run perpendicular to the tibial plateau and parallel to the long axis of the meniscus, dividing the meniscus into central and peripheral halves. Unlike horizontal or radial tears, pure longitudinal tears do not involve the free edge of the meniscus (figure 7). Bergkvist et al. reported longitudinal and bucket handle tears in 25% of patients [33]. Regardless of the compartment, vertical tears were encountered in a younger age group (mean age 35 to 37 years) compared to degenerative (horizontal or flap) meniscal tears (mean age 49 to 50 years). Longitudinal and bucket handle tears were twice as common in the medial as the lateral compartment, and ACL injuries were present in almost half of the cases [33]. Shelbourne and Carr reported in a retrospective study involving 155 patients with bucket handle tears and ACL injuries that the white-white zone was involved in 80% [88]. On MRI images, a bucket handle tear represents a longitudinal separation with central migration of the inner handle fragment in the intercondylar notch, resulting in a “double PCL” sign, or “double anterior horn” with flipped meniscus. The non-displaced fragment (usually the posterior horn) appears disproportionally small [35]. Displaced lateral meniscal fragments are commonly found along the posterior joint line or within the lateral recess [89]. In a retrospective comparative study between MRI and arthroscopy, MRI was shown to be highly specific (78%), but only moderately sensitive (65%)
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for the detection of displaced meniscal fragments [89]. Identification of free meniscal fragments on MRI is paramount as they often result in persistent pain and potential knee locking. Distinguishing longitudinal or bucket handle tears from other types of meniscal tears on MRI is essential as the preferred treatment in this case is suturing (if the tear is located peripherally), rather than resection as for other types of meniscal tears, besides root tears [33]. Meniscal Substance Loss: Meniscal substance loss can result from previous surgical resection or from degenerative processes of the meniscus, and is termed partial/complete maceration. Although not classified as a tear, meniscal maceration is typically associated with radiographic evidence of knee OA (figure 8) [1], and has been shown to be a predictor of knee replacement within the following year [90]. Its incidence is reported as up to 10% in the general population aged 50 years and older in the Framingham cohort [34]. Crema et al. showed a significant association between high-grade medial meniscus maceration and increased cartilage loss, longitudinally [20]. A detailed discussion of meniscal maceration is beyond the scope of this paper but there are ongoing research efforts focusing on 3D volume approaches, which should shed further light on the relevance of the loss of meniscal volume in knee OA [8; 9; 11]. Summary: There is a striking lack of data on the relevance of different morphologic types of meniscal tears in OA, both cross-sectionally and, more importantly, longitudinally. Horizontal and complex tears are common findings in knees with OA with similar characteristics in regard to associated cartilage damage. Posterior radial tears of the medial meniscus are associated with a high degree of cartilage loss and meniscal extrusion, and appear to be a highly relevant event in the progression of OA in the knee. On the other hand, lateral meniscus radial tears affect younger individuals and are considered post-traumatic. Despite their suggested high relevance, radial tears
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are more commonly misdiagnosed on MRI than any other type of tear. We recommend that complex tears with radial components should be classified as radial tears. While medial meniscus posterior root tears are of “radial” morphology, there is growing interest in regarding them as a separate entity. Longitudinal and bucket handle tears – whether of the medial or lateral menisci – affect younger individuals and are highly associated with ACL injuries, favoring a traumatic etiology. MRI is paramount in detecting and locating a possible displaced tear. Further epidemiologic studies should focus on the morphology of specific meniscal tears to better understand their relevance in the genesis and progression of knee OA. In addition further studies should focus on increasing the accuracy of MRI with regard to the diagnosis of radial tears, which may be underestimated in large MRI-based epidemiologic studies on knee OA. Authors Contributions: (1) All authors were involved in the conception and design of the study, or acquisition of data, or analysis and interpretation of data. (2) All authors contributed to drafting the article or revising it critically for important intellectual content. (3) All authors gave their final approval of the manuscript to be submitted. Competing Interest Statement: A. Guermazi: President of Boston Imaging Core Lab (BICL) LLC., Consultant for Astra Zeneca, Genzyme, Novartis, Stryker, and Merck Serono. Research grant by General Electric; F. Roemer: CMO BICL LLC. None of the other authors declare any conflict of interest. Funding and role of the funding source: No funding was received.
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Yim JH, Seon JK, Song EK et al (2013) A comparative study of meniscectomy and nonoperative treatment for degenerative horizontal tears of the medial meniscus. Am J Sports Med 41:1565-1570 Gauffin H, Tagesson S, Meunier A, Magnusson H, Kvist J (2014) Knee arthroscopic surgery is beneficial to middle-aged patients with meniscal symptoms: a prospective, randomised, single-blinded study. Osteoarthritis Cartilage 22:1808-1816 Zikria B, Hafezi-Nejad N, Roemer FW, Guermazi A, Demehri S (2016) Meniscal Surgery: Risk of Radiographic Joint Space Narrowing Progression and Subsequent Knee Replacement-Data from the Osteoarthritis Initiative. Radiology. 10.1148/radiol.2016160092:160092 OrthoInfo. American Academy of Orthopedic Surgeons. Available via http://orthoinfo.aaos.org/topic.cfm?topic=a00358 Henry S, Mascarenhas R, Kowalchuk D, Forsythe B, Irrgang JJ, Harner CD (2012) Medial meniscus tear morphology and chondral degeneration of the knee: is there a relationship? Arthroscopy 28:1124-1134 e1122 Bergkvist D, Dahlberg LE, Neuman P, Englund M (2015) Knee arthroscopies: who gets them, what does the radiologist report, and what does the surgeon find? Acta Orthop. 10.3109/17453674.2015.1055179:1-5 Englund M, Guermazi A, Gale D et al (2008) Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med 359:1108-1115 Nguyen JC, De Smet AA, Graf BK, Rosas HG (2014) MR imaging-based diagnosis and classification of meniscal tears. Radiographics 34:981-999 Petersen W, Tillmann B (1998) Collagenous fibril texture of the human knee joint menisci. Anat Embryol (Berl) 197:317-324 Brindle T, Nyland J, Johnson DL (2001) The meniscus: review of basic principles with application to surgery and rehabilitation. J Athl Train 36:160169 DeHaven KE, Arnoczky SP (1994) Meniscus repair: basic science, indications for repair, and open repair. Instr Course Lect 43:65-76 Arnoczky SP, Warren RF (1983) The microvasculature of the meniscus and its response to injury. An experimental study in the dog. Am J Sports Med 11:131-141 Escobedo EM, Hunter JC, Zink-Brody GC, Wilson AJ, Harrison SD, Fisher DJ (1996) Usefulness of turbo spin-echo MR imaging in the evaluation of meniscal tears: comparison with a conventional spin-echo sequence. AJR Am J Roentgenol 167:1223-1227 Shapiro L, Staroswiecki E, Gold G (2010) Magnetic resonance imaging of the knee: optimizing 3 Tesla imaging. Semin Roentgenol 45:238-249 Tarhan NC, Chung CB, Mohana-Borges AV, Hughes T, Resnick D (2004) Meniscal tears: role of axial MRI alone and in combination with other imaging planes. AJR Am J Roentgenol 183:9-15 Van Dyck P, Vanhoenacker FM, Lambrecht V et al (2013) Prospective comparison of 1.5 and 3.0-T MRI for evaluating the knee menisci and ACL. J Bone Joint Surg Am 95:916-924
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Wong S, Steinbach L, Zhao J, Stehling C, Ma CB, Link TM (2009) Comparative study of imaging at 3.0 T versus 1.5 T of the knee. Skeletal Radiol 38:761-769 Magee T, Williams D (2006) 3.0-T MRI of meniscal tears. AJR Am J Roentgenol 187:371-375 Fox MG (2007) MR imaging of the meniscus: review, current trends, and clinical implications. Radiol Clin North Am 45:1033-1053, vii Bae WC, Du J, Bydder GM, Chung CB (2010) Conventional and ultrashort time-to-echo magnetic resonance imaging of articular cartilage, meniscus, and intervertebral disk. Top Magn Reson Imaging 21:275-289 Helms CA (2002) The meniscus: recent advances in MR imaging of the knee. AJR Am J Roentgenol 179:1115-1122 Peterfy CG, Janzen DL, Tirman PF, van Dijke CF, Pollack M, Genant HK (1994) "Magic-angle" phenomenon: a cause of increased signal in the normal lateral meniscus on short-TE MR images of the knee. AJR Am J Roentgenol 163:149154 Crema MD, Hunter DJ, Roemer FW et al (2011) The relationship between prevalent medial meniscal intrasubstance signal changes and incident medial meniscal tears in women over a 1-year period assessed with 3.0 T MRI. Skeletal Radiol 40:1017-1023 De Smet AA, Tuite MJ (2006) Use of the "two-slice-touch" rule for the MRI diagnosis of meniscal tears. AJR Am J Roentgenol 187:911-914 Kumm J, Roemer FW, Guermazi A, Turkiewicz A, Englund M (2015) Natural History of Intrameniscal Signal Intensity on Knee MR Images: Six Years of Data from the Osteoarthritis Initiative. Radiology. 10.1148/radiol.2015142905:142905 Hajek PC, Gylys-Morin VM, Baker LL, Sartoris DJ, Haghighi P, Resnick D (1987) The high signal intensity meniscus of the knee. Magnetic resonance evaluation and in vivo correlation. Invest Radiol 22:883-890 Stoller DW, Martin C, Crues JV, 3rd, Kaplan L, Mink JH (1987) Meniscal tears: pathologic correlation with MR imaging. Radiology 163:731-735 Dillon EH, Pope CF, Jokl P, Lynch JK (1991) Follow-up of grade 2 meniscal abnormalities in the stable knee. Radiology 181:849-852 Guermazi A, Niu J, Hayashi D et al (2012) Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study). BMJ 345:e5339 Crema MD, Roemer FW, Felson DT et al (2012) Factors associated with meniscal extrusion in knees with or at risk for osteoarthritis: the Multicenter Osteoarthritis study. Radiology 264:494-503 Zhang F, Kumm J, Svensson F, Turkiewicz A, Frobell R, Englund M (2015) Risk factors for meniscal body extrusion on MRI in subjects free of radiographic knee osteoarthritis: longitudinal data from the Osteoarthritis Initiative. Osteoarthritis Cartilage. 10.1016/j.joca.2015.12.003 Christoforakis J, Pradhan R, Sanchez-Ballester J, Hunt N, Strachan RK (2005) Is there an association between articular cartilage changes and degenerative meniscus tears? Arthroscopy 21:1366-1369 18
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Lewandrowski KU, Muller J, Schollmeier G (1997) Concomitant meniscal and articular cartilage lesions in the femorotibial joint. Am J Sports Med 25:486494 Jarraya M, Hayashi D, Wolfgang Roemer F, Guermazi A (2015) MR Imagingbased Semi-quantitative Methods for Knee Osteoarthritis. Magn Reson Med Sci. 10.2463/mrms.rev.2015-0058 Arno S, Bell CP, Uquillas C, Borukhov I, Walker PS (2015) Tibiofemoral contact mechanics following a horizontal cleavage lesion in the posterior horn of the medial meniscus. J Orthop Res 33:584-590 Brown MJ, Farrell JP, Kluczynski MA, Marzo JM (2016) Biomechanical Effects of a Horizontal Medial Meniscal Tear and Subsequent Leaflet Resection. Am J Sports Med. 10.1177/0363546515623782 Lance V, Heilmeier UR, Joseph GB, Steinbach L, Ma B, Link TM (2015) MR imaging characteristics and clinical symptoms related to displaced meniscal flap tears. Skeletal Radiol 44:375-384 Le Hir P, Charousset C, Duranthon LD et al (2007) [Magnetic resonance imaging of medial meniscus tears with displaced fragment in the meniscal recesses]. Rev Chir Orthop Reparatrice Appar Mot 93:357-363 Bedi A, Kelly NH, Baad M et al (2010) Dynamic contact mechanics of the medial meniscus as a function of radial tear, repair, and partial meniscectomy. J Bone Joint Surg Am 92:1398-1408 Harper KW, Helms CA, Lambert HS, 3rd, Higgins LD (2005) Radial meniscal tears: significance, incidence, and MR appearance. AJR Am J Roentgenol 185:1429-1434 Bin SI, Kim JM, Shin SJ (2004) Radial tears of the posterior horn of the medial meniscus. Arthroscopy 20:373-378 Wu J, Huang JM, Zhao B, Cao JG, Chen X (2016) Risk Factors Comparison for Radial and Horizontal Tears. J Knee Surg. 10.1055/s-0036-1572415 Lee DH, Lee BS, Kim JM et al (2011) Predictors of degenerative medial meniscus extrusion: radial component and knee osteoarthritis. Knee Surg Sports Traumatol Arthrosc 19:222-229 von Engelhardt LV, Schmitz A, Pennekamp PH, Schild HH, Wirtz DC, von Falkenhausen F (2008) Diagnostics of degenerative meniscal tears at 3-Tesla MRI compared to arthroscopy as reference standard. Arch Orthop Trauma Surg 128:451-456 Beamer BS, Masoudi A, Walley KC et al (2015) Analysis of a new all-inside versus inside-out technique for repairing radial meniscal tears. Arthroscopy 31:293-298 Alentorn-Geli E, Choi JH, Stuart JJ et al (2015) Inside-Out or Outside-In Suturing Should Not Be Considered the Standard Repair Method for Radial Tears of the Midbody of the Lateral Meniscus: A Systematic Review and Meta-Analysis of Biomechanical Studies. J Knee Surg. 10.1055/s-00351570113 Sofu H, Oner A, Camurcu Y, Gursu S, Ucpunar H, Sahin V (2016) Predictors of the Clinical Outcome After Arthroscopic Partial Meniscectomy for Acute
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Trauma-Related Symptomatic Medial Meniscal Tear in Patients More Than 60 Years of Age. Arthroscopy. 10.1016/j.arthro.2015.11.040 Koenig JH, Ranawat AS, Umans HR, Difelice GS (2009) Meniscal root tears: diagnosis and treatment. Arthroscopy 25:1025-1032 Smigielski R, Becker R, Zdanowicz U, Ciszek B (2015) Medial meniscus anatomy-from basic science to treatment. Knee Surg Sports Traumatol Arthrosc 23:8-14 Allaire R, Muriuki M, Gilbertson L, Harner CD (2008) Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am 90:1922-1931 Hein CN, Deperio JG, Ehrensberger MT, Marzo JM (2011) Effects of medial meniscal posterior horn avulsion and repair on meniscal displacement. Knee 18:189-192 LaPrade CM, Jansson KS, Dornan G, Smith SD, Wijdicks CA, LaPrade RF (2014) Altered tibiofemoral contact mechanics due to lateral meniscus posterior horn root avulsions and radial tears can be restored with in situ pull-out suture repairs. J Bone Joint Surg Am 96:471-479 Marzo JM, Gurske-DePerio J (2009) Effects of medial meniscus posterior horn avulsion and repair on tibiofemoral contact area and peak contact pressure with clinical implications. Am J Sports Med 37:124-129 Schillhammer CK, Werner FW, Scuderi MG, Cannizzaro JP (2012) Repair of lateral meniscus posterior horn detachment lesions: a biomechanical evaluation. Am J Sports Med 40:2604-2609 LaPrade CM, James EW, Cram TR, Feagin JA, Engebretsen L, LaPrade RF (2015) Meniscal root tears: a classification system based on tear morphology. Am J Sports Med 43:363-369 Ra HJ, Ha JK, Jang HS, Kim JG (2015) Traumatic posterior root tear of the medial meniscus in patients with severe medial instability of the knee. Knee Surg Sports Traumatol Arthrosc 23:3121-3126 Guermazi A, Hayashi D, Jarraya M et al (2013) Medial posterior meniscal root tears are associated with development or worsening of medial tibiofemoral cartilage damage: the multicenter osteoarthritis study. Radiology 268:814821 Sung JH, Ha JK, Lee DW, Seo WY, Kim JG (2013) Meniscal extrusion and spontaneous osteonecrosis with root tear of medial meniscus: comparison with horizontal tear. Arthroscopy 29:726-732 Chung KS, Ha JK, Yeom CH et al (2015) Comparison of Clinical and Radiologic Results Between Partial Meniscectomy and Refixation of Medial Meniscus Posterior Root Tears: A Minimum 5-Year Follow-up. Arthroscopy 31:19411950 Chung KS, Ha JK, Ra HJ, Kim JG (2015) A meta-analysis of clinical and radiographic outcomes of posterior horn medial meniscus root repairs. Knee Surg Sports Traumatol Arthrosc. 10.1007/s00167-015-3832-0 Shelbourne KD, Carr DR (2003) Meniscal repair compared with meniscectomy for bucket-handle medial meniscal tears in anterior cruciate ligament-reconstructed knees. Am J Sports Med 31:718-723 20
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Vande Berg BC, Malghem J, Poilvache P, Maldague B, Lecouvet FE (2005) Meniscal tears with fragments displaced in notch and recesses of knee: MR imaging with arthroscopic comparison. Radiology 234:842-850 Roemer FW, Kwoh CK, Hannon MJ et al (2015) Can structural joint damage measured with MR imaging be used to predict knee replacement in the following year? Radiology 274:810-820
Table 1: Comparison of different semiquantitative systems of knee osteoarthritis for the evaluation of meniscal damage [61]. WORMS
KOSS
BLOKS
MOAKS
Subregional Division
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
No subregional division
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
Meniscal tears / changes
1. Minor radial or parrot beak tear
1. Horizontal
1.Intrameniscal signal
1. Intrameniscal signal
2. Vertical tear
2. Vertical tear
3. Horizontal tear
3. Horizontal tear
2. Vertical 2. Nondisplaced tear or prior surgical tear 3. Displaced tear or partial resection 4. Complete maceration or destruction or complete resection
3. Radial 4. Complex
4. Complex tear 5. BucketHandle
4. Complex tear 5. Root tear 5. Root tear
6. Meniscal Intrasubstance degeneration (scored from 0 to 3)
6. Maceration 7. Meniscal cyst
6. Partial Maceration 7. Progressive partial maceration 8. Meniscal cyst 9. Hypertrophy
Other meniscal
-
Meniscal
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Meniscal
Meniscal extrusion
features
extrusion (from 0 to 3)
extrusion (from 0 to 3)
(from 0 to 3)
Figure 1. Meniscal intra-substance signal abnormality. A and B. Drawings showing (A) 3D and (B) sagittal views of the meniscal posterior horn with intra-substance abnormality not reaching the articular surface (arrows). C. Coronal intermediateweighted image shows punctate intrameniscal hyperintense signal changes in the body of the medial and lateral meniscus that do not reach the meniscal surface (arrows). Note marked extrusion medially. D. Sagittal intermediate-weighted fatsuppressed image shows intrameniscal linear hyperintense signal not reaching the meniscal surface and thus not qualifying for the diagnosis of meniscal tear. It has been shown that intrameniscal signal changes are a risk factor for subsequent tear development. Figure 2. Horizontal oblique tear. A and B. Drawings showing (A) 3D and (B) sagittal views of the meniscal posterior horn with a horizontal tear. C and D. Drawings showing (C) 3D and (D) sagittal views of the meniscal posterior horn with an oblique tear. E. Sagittal intermediate-weighted fat-suppressed image shows a horizontal oblique tear of the posterior horn of the medial meniscus reaching the inferior meniscal surface (arrow). Note that the tear only reaches one surface but not the superior or posterior meniscal margins. These tears are also referred to as “parrot beak” tears based on their shape. F. Sagittal intermediate-weighted fatsuppressed image depicts another horizontal oblique tear of the medial posterior
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horn (long arrow). In this case the tear reaches the inferior and posterior meniscal surfaces. There is also meniscal intra-substance signal abnormality of the anterior horn not reaching any meniscal surface (short arrow). Figure 3. Complex Tear. A and B. Drawings showing 3D (A) and sagittal (B) views of a posterior meniscal horn with a complex tear. C. Sagittal intermediate-weighted fat-suppressed image of the lateral tibio-femoral compartment shows a complex tear of the lateral posterior horn characterized by tear components that reach the superior and inferior meniscal surface and an oblique component reaching the posterior meniscal margin (arrows). Figure 4. Flap tear. Coronal intermediate-weighted fat-suppressed image shows a small dislocated meniscal flap component next to the tibial margin (arrow). Note the adjacent tibial bone marrow edema (small arrows) and synovitis (arrowhead). Figure 5. Radial tear. A and B. Drawings showing (A) superior and (B) sagittal views of the meniscal posterior horn with a radial tear (arrows). C. Sagittal intermediate-weighted fat-suppressed image shows the amputated free edge of the medial posterior horn (arrow). D. Corresponding axially reformatted dual echo at steady state (DESS) image confirms small radial tear of the posterior horn (arrow). Figure 6. Root tear. A and B. Drawings showing (A) superior and (B) coronal views of a medial posterior meniscal horn with a root tear. C. Coronal intermediateweighted image shows a tear of the ligamentous attachment of the posterior horn of the medial meniscus consistent with meniscal root tear. D. Axially reformatted dual echo a steady state (DESS) image confirms complete disruption of the meniscal root
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(arrow). E. Another case of medial posterior root tear is shown in this axially reformatted DESS image (arrow). F. Corresponding coronal intermediate-weighted image shows consequent marked extrusion of the medial meniscal body leading to a status of functional total meniscectomy (double-headed arrow). Note diffuse cartilage thinning in the central weight-bearing region of the medial femur and tibia. Figure 7. Bucket handle tear. A and B. Drawings showing (A) superior and (B) sagittal views of the posterior meniscal horn with a bucket handle tear, making a “double PCL” sign in the sagittal image, resulting from a displaced meniscal fragment lying under the PCL. C. Coronal proton density-weighted fat-suppressed image shows a dislocated bucket-handle fragment in the intercondylar notch (long arrow). The fragment originates from the body of the medial meniscus, which clearly shows substance loss. Note the anterior cruciate ligament directly adjacent to the meniscal fragment (short arrow). D. Sagittal proton density-weighted image shows meniscal bucket handle component anteriorly to the PCL resulting in the socalled “double PCL sign”. Figure 8. Development of meniscal damage over time. A. Baseline coronal intermediate-weighted fat-suppressed image shows intrameniscal signal change of the meniscal body and discrete meniscal extrusion in regard to tibial margin. B. Follow-up image one year later shows increase in extrusion and deformation of the meniscal body without apparent tear component and without meniscal substance loss. C. Another year later a flap tear has developed with fragment dislocated adjacent to the medial femoral margin (short arrow). Note substance loss at the
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medial free edge consistent with partial meniscal maceration as a consequence of the flap tear (long arrow).
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PII: DOI: Reference:
S0049-0172(16)30440-1 http://dx.doi.org/10.1016/j.semarthrit.2016.11.005 YSARH51131
To appear in: Seminars in Arthritis and Rheumatism Cite this article as: Mohamed Jarraya, Frank W. Roemer, Martin Englund, Michel D. Crema, Heather I. Gale, Daichi Hayashi, Jeffrey N. Katz and Ali Guermazi, Meniscus Morphology: Does Tear Type Matter? A Narrative Review with Focus on Relevance for Osteoarthritis Research, Seminars in Arthritis and Rheumatism, http://dx.doi.org/10.1016/j.semarthrit.2016.11.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Meniscus Morphology: Does Tear Type Matter? A Narrative Review with Focus on Relevance for Osteoarthritis Research Mohamed Jarraya 1,2, Frank W. Roemer1, 3, Martin Englund 4,5, Michel D. Crema1, Heather I. Gale 6, Daichi Hayashi 7, Jeffrey N. Katz 8, Ali Guermazi 1
1) Quantitative Imaging Center, Department of Radiology, Boston University Medical Center, Boston, MA 2) Department of Radiology, Mercy Catholic Medical Center, Darby, PA 3) Department of Radiology, University of Erlangen-Nuremberg, Erlangen, Germany 4) Lund University, Faculty of Medicine, Department of Clinical Sciences Lund, Orthopedics, Clinical Epidemiology Unit, Lund, Sweden 5) Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston, MA, USA 6) Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 7) Department of Radiology, Bridgeport Hospital, Yale New Haven Health System, Bridgeport, CT 8) Departments of Medicine (Rheumatology, Immunology and Allergy) and Orthopedic Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
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ABSTRACT: Objective: To give a narrative overview of meniscal tears with a radiologic emphasis on the morphologic type, technical considerations, and on the relevance of the type of meniscal tear in the context of osteoarthritis (OA) research. Design: Twenty years of the PubMed database were searched for epidemiological, radiological, arthroscopic and biomechanical reports, and review articles focusing on meniscal tears in middle aged and older individuals, in the setting of OA. Case reports, publications on meniscal tears in young active individuals, and publications not in English were excluded. Results: Meniscal intra-substance signal abnormalities are associated with an increased risk of a degenerative meniscal tear in the same segment. Posterior radial tears of the medial meniscus appear to be a highly relevant event in OA of the knee, with associated cartilage loss and meniscal extrusion. Radial tears are more commonly missed on MRI than other types, and should be carefully looked for on coronal and axial images. While medial meniscus posterior root tears are of “radial” morphology, there is growing interest in looking at them as a separate entity, mainly because they require a different therapeutic approach. Conclusion: There is a lack of data on the relevance of different morphologic types of meniscal tears to the natural history of knee OA, both cross-sectionally and – especially – longitudinally. Further epidemiologic studies should focus on specific meniscal tears based on their morphology to better understand their relevance in the genesis and progression of knee OA. Key Words: Magnetic resonance imaging, meniscal tear, osteoarthritis, degenerative tears.
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Introduction: Knee menisci are intra-articular fibro-cartilaginous structures, with important functions in knee biomechanics including load distribution, shock absorption, lubrication, and joint stability [1; 2]. Several computer-based semi-automated and automated magnetic resonance imaging (MRI) – based algorithms have been developed recently to characterize meniscal changes – including volume and position – in knee osteoarthritis (OA) [3-9], as well as their predictive value in disease progression [10; 11]. While promising, these novel techniques are not able to reliably show intrameniscal signal changes that are thought to represent intrameniscal mucoid degeneration (when the signals do not reach the meniscal surface), or different types of meniscal tears (when a signal abnormality reaches the meniscal surface on at least two consecutive slices on MRI). Meniscal tears are highly relevant when discussing the natural history, incidence and progression of knee OA [12-22]. In addition, there has been a significant increase in the use of knee arthroscopy during the last two decades in the United States, with nearly half of all knee procedures performed for meniscal tears [23]. However there is no consensus on optimal management of meniscal tears in OA, as most of the recently published randomized clinical trials showed no benefit of partial meniscectomy over physical therapy or even a sham meniscectomy procedure [24-28]. Only one prospective study, involving middle-aged patients with meniscal symptoms, found any benefit from partial meniscectomy [29]. A recent study even showed that meniscal surgery is associated with increased risk of radiographic osteoarthritis in absence of preceding trauma [30]. At the time this manuscript was written, there were no Appropriateness Use Criteria for the management of meniscal tears published by the American Academy of Orthopedic Surgeons (AAOS). However a webpage containing educational content, and co-provided by the AAOS stated that arthroscopic surgery may be suggested if symptoms persist with a non-surgical treatment [31].
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Some authors suggest that the severity of the cartilage degeneration is related to the specific morphology of the tear, including the degree of circumferential fiber disruption [32]. Recently, a large epidemiologic study of the use of knee arthroscopy in Sweden showed meniscal tear types may differ by age group, and have a variable association with cartilage lesions and anterior cruciate ligament (ACL) tear [33]. Meniscal tears are often discussed as if they are a single entity [13; 34]. Our aim is to give an illustrative overview of the different types of meniscal tears, and to discuss their differences particularly in regard to knee OA. Also, we will briefly touch on other MRI-detected meniscal changes, such as intra-substance signal abnormalities, and meniscal substance loss due to surgery or as part of the natural history of OA, and commonly referred to as partial or complete maceration. Methods: A search for original articles published between January 1995 and December 2015 was performed in PubMed. The search was based on but not limited to the query terms “meniscal tear”, “horizontal meniscal tear”, “complex meniscal tear”, “radial meniscal tear”, “longitudinal meniscal tear”, “bucket-handle meniscal tear”, “meniscal root tear”, “meniscal destruction”, “meniscal substance loss”, “meniscal intrasubstance signal abnormality”, “meniscal mucoid degeneration”, “meniscal extrusion”, “magnetic resonance imaging (MRI)”, and “osteoarthritis (OA)”. The literature search using these search terms yielded 3,633 publications. Animal studies were excluded, as were letters to the editors, proof of concept studies of less than 10 patients, case reports, publications on meniscal tears in young active individuals, and publications not in English. The focus was on epidemiological, radiological, arthroscopic and biomechanical original research, and review articles focusing on meniscal tear in middle aged and older individuals, in the setting of OA. Additional references were included when they were considered of importance. The literature was sorted and analyzed and is presented here according to technical
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considerations, anatomy, and meniscal tears, with an emphasis on the effects of different types of meniscal tears in the pathogenesis and progression of knee OA. Anatomy: The meniscus is a wedge-shaped, semilunar, fibrocartilaginous structure, with a thicker peripheral portion and tapered central free edge, as well as a superior concave surface conforming to the femoral condyle and a flat base attached to the tibia via a central root ligament. The attachment is essential for normal meniscal function and distribution of axial compressive loads across the tibial plateau. Circumferentially-oriented type I collagen fibers provide the meniscus with hoop strength, and are critical to resisting axial load and preventing meniscal extrusion [35]. When exposed layer by layer with electron microscopy, the meniscus reveal three distinct layers: A superficial meshwork of thin fibrils covering the tibial and femoral sides, with lamella-like collagen fibril bundles beneath, and a main central portion of collagen fibrils oriented in a circular manner, which explains the circumferential orientation of the majority of tears in the meniscal tissue [36]. A capillary network originating within the synovium supplies the meniscus and capsular tissues of the knee along the meniscal periphery, only part receiving a direct blood supply. As a result the meniscus is usually divided into three zones based on their vascular supply, and the location of the tear within one of those areas plays a determining role in the prognosis of spontaneous or surgical healing. The peripheral vascular portion called the “red-red” zone, has an excellent prognosis. An intermediate portion at the border of the vascular supply-– the “red-white” zone– has a generally positive prognosis. However the inner portion – the “white-white zone” – is relatively avascular and has a poor prognosis for healing [37-39].
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Technical Considerations: The diagnosis of meniscal tears by MRI requires high spatial resolution and an optimized signalto-noise ratio [40], achieved by the use of a dedicated knee coil, a slice thickness no more than 3 mm, a field-of-view of 16cm or less, and a matrix size of at least 288x288 [41]. While sagittal and coronal images are essential [1], axial images can help in characterizing meniscal injuries, particularly in regard to radial tear detection [35; 42]. Reported sensitivity and specificity for detection of medial meniscal tears are 93% and 90% at 1.5T, and 96% and 88% at 3.0T, suggesting similar accuracy [43]. Other studies reported slightly better results with 3.0T [44; 45]. Most common sequences include spin-echo or fast spin echo (FSE) proton density with or without fat saturation, T1, and gradient echo [46]. These sequences usually share short echo times, i.e, 3~6 ms [47], which has the advantage of decreasing susceptibility and flow artifacts, improving noise-to-signal ratio, and reducing scan time, [46; 48]. With shorter echo times (<1ms) the entire meniscus can be seen with high signal intensity, which limits detection of pathology [47]. The “magic angle” artifact, however, has to be considered when using short echo times. It results in artifactual abnormal meniscal signal, usually in the upsloping portion of the posterior horn of the lateral meniscus, and can be mistaken for a tear by inexperienced readers [49]. Meniscal Intra-substance Signal Abnormality: Meniscal intra-substance signal abnormalities are defined as an increased signal that does not fulfill the criteria for a meniscal tear according the “two-slice-touch” rule (i.e it does not reach the meniscal surface on two consecutive views) and is a common finding on routine MRI of the knee (figure 1) [50-52]. Its reported prevalence in middle aged (45-55 years) individuals with or without OA, is between 26% and 43% [50; 52]. Histologically, intra-meniscal signal intensity may represent foci or bands of mucoid degeneration or microcyst formation and separation of
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collagen bundles [53; 54]. These changes may weaken the meniscal structure and may serve as a risk factor for degenerative meniscal tears [52]. The natural history of intra-substance signal abnormalities is still not fully understood. Initial studies failed to show an association between intrameniscal signal intensity and incident meniscal tears [50; 55]. These studies may have been biased by short follow-up interval (12 months) [50], or subject selection (younger subjects after knee trauma) [55]. More recently a six-year longitudinal study that included 269 middle-aged participants without radiographic knee OA from the Osteoarthritis Initiative, reported by Kumm et al. showed intrameniscal signal changes at baseline to be highly unlikely to regress (only one of 130 showed regression). Indeed, it was associated with an increased risk of developing a degenerative meniscal tear in the same segment, typically a horizontal cleavage or a flap tear [52]. Meniscal Tears: In one population-based study that included 991 randomly selected adults regardless of knee symptoms. Englund et al. reported an overall prevalence of meniscal tears of 31%, increasing with age and consistently higher in men, ranging from 19% in women aged 50-59 years to 56% among men between 70 and 90 years[34]. Regardless of pain status, the prevalence of meniscal tears was markedly higher in subjects with established radiographic OA [34]. When present, meniscal tears involved the medial meniscus and/or the posterior horn in two thirds of the cases, with horizontal and complex tears the most common. In another cohort sample from the same study, Guermazi et al. reported a prevalence of meniscal tears of 24% of the knees, regardless of pain status [56]. It should be mentioned that most subjects with a meniscal tear are asymptomatic [34]. Meniscal tears in the context of osteoarthritis usually occur without predisposing trauma. The American College of Radiology’s appropriateness criteria show that non-contrast enhanced MRI is “usually appropriate” for non-traumatic knee pain with a negative initial x ray (or x-ray
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with joint effusion). Meniscal tears are among the MR findings in this case, along with ligamentous injury, cartilage damage, bone marrow edema, joint effusion. Regardless of morphologic type, meniscal tears are strongly associated with OA cross-sectionally and predict OA longitudinally and are considered to be part of the spectrum of early or preradiographic disease [15-17]. Furthermore, any type of meniscal tear is associated with, and is a risk factor for, meniscal body extrusion commonly measured in the coronal plane on MRI [57; 58]. Often enough meniscal tear types are categorized into varying groups for comparison rather than separately compared to each other. For example horizontal tears are sometimes combined with complex tears, or with flap and radial tears, which prevents comparison of tear type characteristics [59; 60]. In the following sections we will highlight the different types of tears and discuss their role in the context of OA incidence and progression based on the published literature. Horizontal Tear: A horizontal tear runs parallel to the tibial plateau, involves either one of the articular surfaces and/or the periphery, dividing the meniscus into superior and inferior halves. Commonly, in the radiologic community, a horizontal-oblique tear only differs by a slight difference in direction of meniscal cleavage (figure 2). In semiquantitative MRI scoring systems of knee OA, a horizontaloblique tear is scored as horizontal [61]. Table 1 provides a comparison between the different semiquantitative MRI scoring systems for the evaluation of meniscal damage. Experimental studies have shown that horizontal cleavage of the medial meniscus results in a statistically significant increase in peak contact pressure, compared with an intact meniscus [62; 63], which may be one explanation for associated cartilage damage. In the Framingham cohort, horizontal tears were found in 40% of all knees with meniscal tears [34]. In a cross-sectional arthroscopic study including 103 patients with isolated medial meniscal tears, and investigating the relationship between tear morphology and cartilage degeneration,
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Henry et al. reported a prevalence of isolated horizontal tears of 24% [32]. The study showed similar findings for horizontal and complex tears in regard to severity of chondral degeneration in the ipsilateral compartment [32]. Other arthroscopic studies reported conflicting results regarding overall prevalence and severity of associated cartilage degeneration in horizontal tears compared to other tears. The conflicts are mainly due to inconsistent categorization of tear morphology [59; 60]. There is no longitudinal data comparing horizontal meniscal tears to other morphologic types in regard to structural joint outcomes, such as cartilage loss and bone marrow changes. Complex Tear: Complex tears include any combination of radial, horizontal, and longitudinal components. The meniscus often appears fragmented with the tear extending into more than one plane (figure 3) [35]. Complex tears were present in 37% of the subjects with meniscal tears in the Framingham cohort [34], and in 22% in the arthroscopic study by Henry et al. [32]. Unfortunately, as for horizontal tears, there is no longitudinal data on OA progression of complex tears as compared with other morphologic types. Flap Tear: Flap tears are commonly regarded as within the spectrum of degenerative tears [1; 33], caused by either horizontal or oblique fissures of the meniscus with superior or inferior displacement of the fragment into the meniscal recess or the intercondylar space (figure 4)[64; 65]. Usually flap tears involve the body and posterior horn of the medial meniscus and displacement occurs inferiorly adjacent to the tibial plateau [64]. However, flap tears of the lateral meniscus more likely involve the posterior horn [64]. Radial Tear: Radial meniscal tears are oriented perpendicularly to the meniscal axis and tibial plateau, transecting the longitudinal collagen bundles extending from the free edge toward the periphery
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(figure 5). This pattern disrupts the meniscal hoop strength resulting in a dramatic loss of function and may result in meniscal extrusion. Complete radial tears impair the ability of the medial meniscus to withstand loading, and have been described as equivalent to total meniscectomy [66]. Radial tears were present in 15% of subjects with meniscal tears in the Framingham study [34], while Bergkvist et al reported radial tears in 7% of arthroscopy-detected meniscal tears in patients with a preoperative diagnosis of knee OA and/or chronic meniscal tears [33]. In other clinical cohorts, radial tears were identified by arthroscopy in 15-25 % of the cases [67; 68]. Bergkvist et al. reported that medial meniscus radial tears predominantly affect the posterior horn, and had the highest association with ipsilateral cartilage damage compared to all other morphologic types (although there is no mention of statistical significance). The mean age of affected individuals (51 years) was no different from subjects with degenerative horizontal or flap tears. In addition arthroscopic findings of medial radial tears were consistent with degenerative tears [33]. It is worth noting however that the study made no distinction between radial and root tears. Furthermore, in a study including 407 patients who underwent knee arthroscopy for tears of the medial meniscus, Wu et al. reported that higher grade cartilage damage was found in radial tears than in horizontal tears [69]. In a retrospective series of 102 patients with medial posterior horn tears, meniscal extrusion was greater and more severe in patients with a radial tear component than in those without a radial component [70]. Taken together, these studies suggest the significance of radial tears of the medial posterior horn in the natural history of knee OA. Unfortunately, there is no longitudinal data in the literature to confirm this significance. In contrast with medial meniscus radial tears, lateral radial tears are encountered in younger patients (mean age 32 years) and have a higher association with ACL injuries (36%) than medial meniscus radial tears (8%) [33]. They are thus considered to be of traumatic origin.
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The location of the tear relative to the imaging plane may affect the MRI findings. For example a radial tear of the posterior horn may appear as “cleft” on coronal view, and “ghost/truncated” on sagittal view [35]. Another example, a radial tear involving the junction of the meniscal body and posterior horn results in a “marching cleft” appearance, progressing away from the free edge on contiguous sagittal images [35]. This variability may explain, at least in part, the reported underdiagnosis of radial tears by MRI, when compared to arthroscopy [67; 68; 71]. Harper et al. reported only 37% of radial tears were diagnosed correctly. Sometimes, radial tears may be seen in only one view, such as coronal or axial [42; 45]. Because of the possibly more deleterious consequences resulting from radial tears compared with other morphological types, we suggest that MRI-detected complex tears with radial component should be classified as radial tears. While biomechanical studies have reported on the importance of meniscal repair in restoring the meniscal function [72; 73], treatment of radial tears in individuals with OA usually consists of partial meniscectomy [70; 74]. Root Tear: Meniscal root tear is an avulsion injury or radial tear occurring within 1 cm of the bony tibial attachment (figure 6) [75; 76]. Biomechanically, it compromises the loading profile with subsequent increased tibiofemoral contact pressure [77-82]. Clinically, posterior medial meniscus root tears result in severe instability of the knee joint [83]. The prevalence of meniscal root tears varies between 1% in the middle aged and elderly among the general population [34] to 6% in adults with radiographic OA [84], and was up to 27.8% in a group of Korean patients with medial meniscal tears treated arthroscopically [68]. The latter high prevalence was attributed to local cultural factors, such as squatting and sitting on the floor with folded legs [68]. Henry et al. reported more ipsilateral cartilage damage of the femoral condyle in medial posterior root tears than in all other types [32]. A retrospective arthroscopic study further showed that medial meniscus posterior root tears were associated with a greater degree of meniscal extrusion
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and more cases of osteonecrosis in comparison with horizontal tears [85]. However, in a retrospective series of 102 patients with medial posterior horn tears, Lee et al. reported a similar incidence of major meniscal extrusion in knees with root tear and non-root tears [70]. Biomechanical studies showed that alteration of the loading profile secondary to posterior medial meniscus root tears can be almost totally reversed with anatomic repair [77]. This is consistent with clinical studies reporting refixation to be more effective than partial meniscectomy in regard to clinical and radiologic outcomes [86; 87]. Vertical (Longitudinal And Bucket-Handle) Tear: Vertical tears run perpendicular to the tibial plateau and parallel to the long axis of the meniscus, dividing the meniscus into central and peripheral halves. Unlike horizontal or radial tears, pure longitudinal tears do not involve the free edge of the meniscus (figure 7). Bergkvist et al. reported longitudinal and bucket handle tears in 25% of patients [33]. Regardless of the compartment, vertical tears were encountered in a younger age group (mean age 35 to 37 years) compared to degenerative (horizontal or flap) meniscal tears (mean age 49 to 50 years). Longitudinal and bucket handle tears were twice as common in the medial as the lateral compartment, and ACL injuries were present in almost half of the cases [33]. Shelbourne and Carr reported in a retrospective study involving 155 patients with bucket handle tears and ACL injuries that the white-white zone was involved in 80% [88]. On MRI images, a bucket handle tear represents a longitudinal separation with central migration of the inner handle fragment in the intercondylar notch, resulting in a “double PCL” sign, or “double anterior horn” with flipped meniscus. The non-displaced fragment (usually the posterior horn) appears disproportionally small [35]. Displaced lateral meniscal fragments are commonly found along the posterior joint line or within the lateral recess [89]. In a retrospective comparative study between MRI and arthroscopy, MRI was shown to be highly specific (78%), but only moderately sensitive (65%)
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for the detection of displaced meniscal fragments [89]. Identification of free meniscal fragments on MRI is paramount as they often result in persistent pain and potential knee locking. Distinguishing longitudinal or bucket handle tears from other types of meniscal tears on MRI is essential as the preferred treatment in this case is suturing (if the tear is located peripherally), rather than resection as for other types of meniscal tears, besides root tears [33]. Meniscal Substance Loss: Meniscal substance loss can result from previous surgical resection or from degenerative processes of the meniscus, and is termed partial/complete maceration. Although not classified as a tear, meniscal maceration is typically associated with radiographic evidence of knee OA (figure 8) [1], and has been shown to be a predictor of knee replacement within the following year [90]. Its incidence is reported as up to 10% in the general population aged 50 years and older in the Framingham cohort [34]. Crema et al. showed a significant association between high-grade medial meniscus maceration and increased cartilage loss, longitudinally [20]. A detailed discussion of meniscal maceration is beyond the scope of this paper but there are ongoing research efforts focusing on 3D volume approaches, which should shed further light on the relevance of the loss of meniscal volume in knee OA [8; 9; 11]. Summary: There is a striking lack of data on the relevance of different morphologic types of meniscal tears in OA, both cross-sectionally and, more importantly, longitudinally. Horizontal and complex tears are common findings in knees with OA with similar characteristics in regard to associated cartilage damage. Posterior radial tears of the medial meniscus are associated with a high degree of cartilage loss and meniscal extrusion, and appear to be a highly relevant event in the progression of OA in the knee. On the other hand, lateral meniscus radial tears affect younger individuals and are considered post-traumatic. Despite their suggested high relevance, radial tears
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are more commonly misdiagnosed on MRI than any other type of tear. We recommend that complex tears with radial components should be classified as radial tears. While medial meniscus posterior root tears are of “radial” morphology, there is growing interest in regarding them as a separate entity. Longitudinal and bucket handle tears – whether of the medial or lateral menisci – affect younger individuals and are highly associated with ACL injuries, favoring a traumatic etiology. MRI is paramount in detecting and locating a possible displaced tear. Further epidemiologic studies should focus on the morphology of specific meniscal tears to better understand their relevance in the genesis and progression of knee OA. In addition further studies should focus on increasing the accuracy of MRI with regard to the diagnosis of radial tears, which may be underestimated in large MRI-based epidemiologic studies on knee OA. Authors Contributions: (1) All authors were involved in the conception and design of the study, or acquisition of data, or analysis and interpretation of data. (2) All authors contributed to drafting the article or revising it critically for important intellectual content. (3) All authors gave their final approval of the manuscript to be submitted. Competing Interest Statement: A. Guermazi: President of Boston Imaging Core Lab (BICL) LLC., Consultant for Astra Zeneca, Genzyme, Novartis, Stryker, and Merck Serono. Research grant by General Electric; F. Roemer: CMO BICL LLC. None of the other authors declare any conflict of interest. Funding and role of the funding source: No funding was received.
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Trauma-Related Symptomatic Medial Meniscal Tear in Patients More Than 60 Years of Age. Arthroscopy. 10.1016/j.arthro.2015.11.040 Koenig JH, Ranawat AS, Umans HR, Difelice GS (2009) Meniscal root tears: diagnosis and treatment. Arthroscopy 25:1025-1032 Smigielski R, Becker R, Zdanowicz U, Ciszek B (2015) Medial meniscus anatomy-from basic science to treatment. Knee Surg Sports Traumatol Arthrosc 23:8-14 Allaire R, Muriuki M, Gilbertson L, Harner CD (2008) Biomechanical consequences of a tear of the posterior root of the medial meniscus. Similar to total meniscectomy. J Bone Joint Surg Am 90:1922-1931 Hein CN, Deperio JG, Ehrensberger MT, Marzo JM (2011) Effects of medial meniscal posterior horn avulsion and repair on meniscal displacement. Knee 18:189-192 LaPrade CM, Jansson KS, Dornan G, Smith SD, Wijdicks CA, LaPrade RF (2014) Altered tibiofemoral contact mechanics due to lateral meniscus posterior horn root avulsions and radial tears can be restored with in situ pull-out suture repairs. J Bone Joint Surg Am 96:471-479 Marzo JM, Gurske-DePerio J (2009) Effects of medial meniscus posterior horn avulsion and repair on tibiofemoral contact area and peak contact pressure with clinical implications. Am J Sports Med 37:124-129 Schillhammer CK, Werner FW, Scuderi MG, Cannizzaro JP (2012) Repair of lateral meniscus posterior horn detachment lesions: a biomechanical evaluation. Am J Sports Med 40:2604-2609 LaPrade CM, James EW, Cram TR, Feagin JA, Engebretsen L, LaPrade RF (2015) Meniscal root tears: a classification system based on tear morphology. Am J Sports Med 43:363-369 Ra HJ, Ha JK, Jang HS, Kim JG (2015) Traumatic posterior root tear of the medial meniscus in patients with severe medial instability of the knee. Knee Surg Sports Traumatol Arthrosc 23:3121-3126 Guermazi A, Hayashi D, Jarraya M et al (2013) Medial posterior meniscal root tears are associated with development or worsening of medial tibiofemoral cartilage damage: the multicenter osteoarthritis study. Radiology 268:814821 Sung JH, Ha JK, Lee DW, Seo WY, Kim JG (2013) Meniscal extrusion and spontaneous osteonecrosis with root tear of medial meniscus: comparison with horizontal tear. Arthroscopy 29:726-732 Chung KS, Ha JK, Yeom CH et al (2015) Comparison of Clinical and Radiologic Results Between Partial Meniscectomy and Refixation of Medial Meniscus Posterior Root Tears: A Minimum 5-Year Follow-up. Arthroscopy 31:19411950 Chung KS, Ha JK, Ra HJ, Kim JG (2015) A meta-analysis of clinical and radiographic outcomes of posterior horn medial meniscus root repairs. Knee Surg Sports Traumatol Arthrosc. 10.1007/s00167-015-3832-0 Shelbourne KD, Carr DR (2003) Meniscal repair compared with meniscectomy for bucket-handle medial meniscal tears in anterior cruciate ligament-reconstructed knees. Am J Sports Med 31:718-723 20
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Vande Berg BC, Malghem J, Poilvache P, Maldague B, Lecouvet FE (2005) Meniscal tears with fragments displaced in notch and recesses of knee: MR imaging with arthroscopic comparison. Radiology 234:842-850 Roemer FW, Kwoh CK, Hannon MJ et al (2015) Can structural joint damage measured with MR imaging be used to predict knee replacement in the following year? Radiology 274:810-820
Table 1: Comparison of different semiquantitative systems of knee osteoarthritis for the evaluation of meniscal damage [61]. WORMS
KOSS
BLOKS
MOAKS
Subregional Division
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
No subregional division
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
Anterior horn, body and posterior horn scored separately in the medial and lateral meniscus
Meniscal tears / changes
1. Minor radial or parrot beak tear
1. Horizontal
1.Intrameniscal signal
1. Intrameniscal signal
2. Vertical tear
2. Vertical tear
3. Horizontal tear
3. Horizontal tear
2. Vertical 2. Nondisplaced tear or prior surgical tear 3. Displaced tear or partial resection 4. Complete maceration or destruction or complete resection
3. Radial 4. Complex
4. Complex tear 5. BucketHandle
4. Complex tear 5. Root tear 5. Root tear
6. Meniscal Intrasubstance degeneration (scored from 0 to 3)
6. Maceration 7. Meniscal cyst
6. Partial Maceration 7. Progressive partial maceration 8. Meniscal cyst 9. Hypertrophy
Other meniscal
-
Meniscal
21
Meniscal
Meniscal extrusion
features
extrusion (from 0 to 3)
extrusion (from 0 to 3)
(from 0 to 3)
Figure 1. Meniscal intra-substance signal abnormality. A and B. Drawings showing (A) 3D and (B) sagittal views of the meniscal posterior horn with intra-substance abnormality not reaching the articular surface (arrows). C. Coronal intermediateweighted image shows punctate intrameniscal hyperintense signal changes in the body of the medial and lateral meniscus that do not reach the meniscal surface (arrows). Note marked extrusion medially. D. Sagittal intermediate-weighted fatsuppressed image shows intrameniscal linear hyperintense signal not reaching the meniscal surface and thus not qualifying for the diagnosis of meniscal tear. It has been shown that intrameniscal signal changes are a risk factor for subsequent tear development. Figure 2. Horizontal oblique tear. A and B. Drawings showing (A) 3D and (B) sagittal views of the meniscal posterior horn with a horizontal tear. C and D. Drawings showing (C) 3D and (D) sagittal views of the meniscal posterior horn with an oblique tear. E. Sagittal intermediate-weighted fat-suppressed image shows a horizontal oblique tear of the posterior horn of the medial meniscus reaching the inferior meniscal surface (arrow). Note that the tear only reaches one surface but not the superior or posterior meniscal margins. These tears are also referred to as “parrot beak” tears based on their shape. F. Sagittal intermediate-weighted fatsuppressed image depicts another horizontal oblique tear of the medial posterior
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horn (long arrow). In this case the tear reaches the inferior and posterior meniscal surfaces. There is also meniscal intra-substance signal abnormality of the anterior horn not reaching any meniscal surface (short arrow). Figure 3. Complex Tear. A and B. Drawings showing 3D (A) and sagittal (B) views of a posterior meniscal horn with a complex tear. C. Sagittal intermediate-weighted fat-suppressed image of the lateral tibio-femoral compartment shows a complex tear of the lateral posterior horn characterized by tear components that reach the superior and inferior meniscal surface and an oblique component reaching the posterior meniscal margin (arrows). Figure 4. Flap tear. Coronal intermediate-weighted fat-suppressed image shows a small dislocated meniscal flap component next to the tibial margin (arrow). Note the adjacent tibial bone marrow edema (small arrows) and synovitis (arrowhead). Figure 5. Radial tear. A and B. Drawings showing (A) superior and (B) sagittal views of the meniscal posterior horn with a radial tear (arrows). C. Sagittal intermediate-weighted fat-suppressed image shows the amputated free edge of the medial posterior horn (arrow). D. Corresponding axially reformatted dual echo at steady state (DESS) image confirms small radial tear of the posterior horn (arrow). Figure 6. Root tear. A and B. Drawings showing (A) superior and (B) coronal views of a medial posterior meniscal horn with a root tear. C. Coronal intermediateweighted image shows a tear of the ligamentous attachment of the posterior horn of the medial meniscus consistent with meniscal root tear. D. Axially reformatted dual echo a steady state (DESS) image confirms complete disruption of the meniscal root
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(arrow). E. Another case of medial posterior root tear is shown in this axially reformatted DESS image (arrow). F. Corresponding coronal intermediate-weighted image shows consequent marked extrusion of the medial meniscal body leading to a status of functional total meniscectomy (double-headed arrow). Note diffuse cartilage thinning in the central weight-bearing region of the medial femur and tibia. Figure 7. Bucket handle tear. A and B. Drawings showing (A) superior and (B) sagittal views of the posterior meniscal horn with a bucket handle tear, making a “double PCL” sign in the sagittal image, resulting from a displaced meniscal fragment lying under the PCL. C. Coronal proton density-weighted fat-suppressed image shows a dislocated bucket-handle fragment in the intercondylar notch (long arrow). The fragment originates from the body of the medial meniscus, which clearly shows substance loss. Note the anterior cruciate ligament directly adjacent to the meniscal fragment (short arrow). D. Sagittal proton density-weighted image shows meniscal bucket handle component anteriorly to the PCL resulting in the socalled “double PCL sign”. Figure 8. Development of meniscal damage over time. A. Baseline coronal intermediate-weighted fat-suppressed image shows intrameniscal signal change of the meniscal body and discrete meniscal extrusion in regard to tibial margin. B. Follow-up image one year later shows increase in extrusion and deformation of the meniscal body without apparent tear component and without meniscal substance loss. C. Another year later a flap tear has developed with fragment dislocated adjacent to the medial femoral margin (short arrow). Note substance loss at the
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medial free edge consistent with partial meniscal maceration as a consequence of the flap tear (long arrow).
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26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54