Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association

DOJ 10.5005/jp-journals-10017-1007 Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association ORIGINAL RESEARCH Tibial Plateau ...
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DOJ 10.5005/jp-journals-10017-1007 Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association

ORIGINAL RESEARCH

Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association 1

Manjiri M Didolkar MD, 2Emily N Vinson MD

1

Instructor in Radiology, Musculoskeletal Radiology BIDMC, Harvard Medical School, Boston, MA, USA

2

Department of Radiology, Division of Musculoskeletal Radiology, Duke University Medical Center, Durham, NC, USA

Correspondence: Emily N Vinson, Department of Radiology, Division of Musculoskeletal Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USA, Phone: (919) 684-7272, Fax: (919) 684-7129, e-mail: [email protected]

ABSTRACT Background: The purpose of this study is to identify a possible relationship between high T2-signal cyst-like foci in the tibial plateau at the meniscal root insertions and meniscal pathology. Methods: Institutional review board approval was obtained for this retrospective study. HIPAA compliance was maintained throughout this study. Two radiologists reviewed 200 knee MRI examinations for tibial plateau cysts at the meniscal root insertion sites; meniscal tears and intrameniscal cysts were also noted. The knee MRI examinations were also evaluated for articular cartilage abnormalities of the medial and lateral tibial plateaus. Results: Of the 200 knee examinations, 83(41.5%) demonstrated medial meniscal pathology and 47(23.5%) demonstrated lateral meniscal pathology. Twenty (10%) demonstrated cysts in at least one of the described locations; two knees had cysts in two separate locations. four (2%) examinations had cysts at the anterior horn medial meniscal insertion, and all four (100%) had medial meniscal pathology (p = 0.028). Eleven (5.5%) examinations demonstrated cysts at the posterior horn medial meniscal insertion, and eight (72.7%) had medial meniscal pathology (p = 0.031). five (2.5%) examinations demonstrated cysts at the anterior horn lateral meniscal insertion, and one (20%) had lateral meniscal pathology (p = 0.374). Two (1%) examinations demonstrated cysts at the posterior horn lateral meniscal insertion, and one (50%) had lateral meniscal pathology (p = 0.852). Conclusions: Cysts at the meniscal insertions are often seen on knee MRI. Cysts located at the insertions of the medial meniscus have a statistically significant association with meniscal pathology. Level of evidence: Level II, retrospective study with development of diagnostic criteria on the basis of consecutive patients. Keywords: Tibial plateau cysts, Meniscal root.

INTRODUCTION The use of fat-suppression with T2-weighted sequences has greatly improved the sensitivity of magnetic resonance (MR) imaging for detecting subtle bone marrow abnormalities.1,2 Small high T2-signal intensity foci in the bone marrow of the tibial plateau are often seen on knee MR imaging examinations, and often occur at the meniscal root insertions. These “cysts” may be incidental, degenerative, age-related or developmental.1,3,4 We have noted that these cysts are often seen in the presence of an abnormality in the adjacent meniscus, including meniscal tears and intrameniscal cysts, raising the possibility that the finding of a tibial cyst at the meniscal root insertion may indicate an increased incidence of meniscal abnormality. The purpose of this study is to evaluate the incidence of tibial plateau cysts on routine knee MR examinations obtained for clinical purposes, and to evaluate for a correlation between the presence of a cyst and the presence of an abnormality in the adjacent meniscus. MATERIALS AND METHODS Institutional review board approval was obtained for this retrospective study. One musculoskeletal-trained radiologist and The Duke Orthopaedic Journal, July 2010-June 2011;1(1):45-49

a 4th-year radiology resident retrospectively reviewed 212 consecutive knee MRI examinations obtained in patients 18 years or older at a single institution over a 2-month period from 4 June, 2007 to 9 July, 2007. Twelve examinations were excluded due to significant obscuration of the tibial plateau bone marrow: 11 due to extensive postoperative changes and one due to extensive bone infarction. Of the remaining 200 knee examinations, 107 were obtained in female patients and 93 were obtained in male patients, with a mean age of 32.5 years (range 18 to 83 years). A total of 153 knees were scanned on a General Electric 1.5 Tesla MR scanner; 36 knees were scanned on a Siemens 1.5 Tesla MR scanner; three knees were scanned on a General Electric 3 Tesla scanner; and eight knees were scanned on a Siemens 3 Tesla MR scanner. All of the knee MRI examinations utilized our standard knee MRI protocol, consisting of axial, sagittal, and coronal fat-suppressed fast spin echo T2-weighted images and sagittal fat-suppressed proton density weighted images. All images were obtained with a dedicated send-receive knee coil. The 200 knee MRI studies were examined for the presence or absence of tibial plateau cysts at each of the four meniscal root insertion sites, corresponding to the anterior and posterior horns of the medial and lateral menisci. A cyst was defined as a

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Manjiri M Didolkar, Emily N Vinson

was cartilage surface irregularity, grade 3 was partial thickness cartilage defect and grade 4 was full thickness cartilage defect. This data was also evaluated for any statistically significant relationship between the presence of tibial plateau cysts and ipsilateral cartilage abnormalities. A Chi-square test was used to evaluate for statistical significance, and a p-value of less than 0.05 was considered statistically significant. RESULTS Figs 1A and B: A 42-year-old male with atraumatic left knee pain. Fatsuppressed T2-weighted axial (A) and coronal (B) images demonstrating a rounded, well-circumscribed, high T2-signal intensity structure (white arrows) at the posterior horn lateral meniscus insertion, representing a tibial plateau cyst at a meniscal root insertion, with surrounding high T2-signal intensity bone marrow signal abnormality. No meniscal pathology identified on the examination.

Of the 200 knee examinations, 83(41.5%) demonstrated medial meniscal pathology and 47(23.5%) demonstrated lateral meniscal pathology. Twenty (10.0%) of the 200 knee MRI examinations demonstrated cysts in at least one of the four root insertion locations; two knees had cysts in two separate locations. Four (2%) of the examinations had cysts at the anterior horn medial meniscal root insertion (Fig. 3A), and all four (100%) of these had medial meniscal pathology (Table 1); one intrameniscal cyst, one complex tear (Fig. 3B), one peripheral vertical tear and one small radial tear. This was statistically significant by the Fisher’s exact test (p = 0.028). Eleven (5.5%) of the examinations demonstrated cysts at the posterior horn medial meniscal root insertion (Fig. 4A), and eight (72.7%) of these had associated medial meniscal pathology (Table 1); one intrameniscal cyst with a small radial tear, one small radial tear and six complex tears (Fig. 4B). This was statistically significant

Figs 2A and B: A 52-year-old female with traumatic left knee pain after twisting injury. Fat-suppressed FSE T2-weighted coronal (A) and sagittal (B) images demonstrating a rounded, well-circumscribed, high T2-signal intensity structure (white arrows) at the posterior horn medial meniscus insertion, representing a tibial plateau cyst at a meniscal root insertion. No meniscal pathology identified on the examination.

rounded, well-circumscribed, high T2-signal intensity structure, with three measureable dimensions (Figs 1A to 2B); linear and/ or branching signal abnormalities were not included. The examinations were also evaluated for medial and lateral meniscal pathology, including meniscal tears and intrameniscal cysts. A meniscal tear was defined as signal abnormality within the meniscus extending to an articular surface.5 An intrameniscal cyst was defined as abnormal signal within the meniscus in an area of abnormal expansion of the meniscus,1 with or without a parameniscal component of the cyst. A parameniscal component was defined as a high T2-signal intensity cyst-like structure emanating from the meniscus.1,2,6 The data was evaluated for any statistically significant relationship between the presence of tibial plateau cysts at meniscal root insertions and ipsilateral meniscal pathology using a chi-square test, except for those tables in which there was a cell with a zero value; in those tables, a Fisher’s exact test was used to evaluate for statistical significance. A p-value of less than 0.05 was considered statistically significant. The knee MRI examinations were also evaluated for articular cartilage abnormalities of the medial and lateral tibial plateaus. These were graded on a scale of 1 through 4; where grade 1 was focal signal alteration within the cartilage, grade 2

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Figs 3A and B: A 48-year-old male with right knee pain. (A) Axial fatsuppressed FSE T2-weighed image with tibial cyst at the anterior horn medial meniscus insertion (white arrow) and (B) sagittal proton density demonstrates a complex tear of the body and posterior horn of the medial meniscus (black arrow).

Figs 4A and B: 58-year-old female with right knee pain. (A) Coronal fat-suppressed FSE T2-weighed image with tibial cyst at the posterior horn medial meniscus insertion (white arrow) and (B) sagittal proton density image demonstrates a complex tear of the body and posterior horn of the medial meniscus (black arrow).

JAYPEE

DOJ Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association

Table 1: Presence of tibial cysts at the medial meniscus root insertions and correlation with meniscal pathology Medial meniscus

Abnormal medial meniscus

Positive for tibial cyst Anterior horn root insertion Posterior horn root insertion

4 (p = 0.028) 8 (p = 0.031)

Negative for tibial cyst Anterior horn root insertion Posterior horn root insertion

79 75

Normal medial meniscus 0 3 117 114

Table 2: Presence of tibial cysts at the lateral meniscus root insertions and correlation with meniscal pathology Lateral meniscus

Abnormal lateral meniscus

Positive for tibial cyst Anterior horn root insertion Posterior horn root insertion

1 (p = 0.374) 1 (p = 0.852)

Negative for tibial cyst Anterior horn root insertion Posterior horn root insertion

46 46

Normal lateral meniscus 4 1 149 152

Table 3: Presence of tibial cysts at the medial meniscus root insertions and correlation with articular cartilage abnormality Medial meniscus

Abnormal medial tibial plateau articular cartilage

Positive for tibial cyst Anterior horn root insertion Posterior horn root insertion

1 (p = 0.312) 3 (p = 0.148)

Negative for tibial cyst Anterior horn root insertion Posterior horn root insertion

19 17

Normal medial tibial plateau articular cartilage 3 8 177 172

Table 4: Presence of tibial cysts at the lateral meniscus root insertions and correlation with articular cartilage abnormality Lateral meniscus

Abnormal lateral tibial plateau articular cartilage

Positive for tibial cyst Anterior horn root insertion Posterior horn root insertion

1 (p = 0.954) 1 (p = 0.261)

Negative for tibial cyst Anterior horn root insertion Posterior horn root insertion

37 37

by the chi-square test (p = 0.031). Five (2.5%) of the studies demonstrated cysts at the anterior horn lateral meniscal root insertion, and one (20%) of these had associated lateral meniscal pathology (Table 2), an intrameniscal cyst. This was not statistically significant by the chi-square test (p = 0.374). Two (1%) of the studies demonstrated cysts at the posterior horn lateral meniscal root insertion, and one (50%) of these had associated lateral meniscal pathology (Table 2), a small radial tear. This was not statistically significant by the Chi-square test (p = 0.852). The Duke Orthopaedic Journal, July 2010-June 2011;1(1):45-49

Normal lateral tibial plateau articular cartilage 4 1 158 161

Of the 200 knee examinations, 48 (24%) demonstrated articular cartilage abnormalities of the tibial plateau; 20 (10%) of the medial tibial plateau and 38 (19%) of the lateral tibial plateau (10 knees had both medial and lateral tibial articular cartilage abnormalities). Of the four knees with a tibial plateau cyst at the anterior horn medial meniscus root insertion, one (25%) had medial tibial plateau articular cartilage abnormality (Table 3), consisting of cartilage surface irregularity. This was not statistically significant by the chi-square test (p = 0.312). Of the 11 knees with a tibial plateau cyst at the posterior horn

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Manjiri M Didolkar, Emily N Vinson

medial meniscus root insertion, three (27.3%) had medial tibial plateau articular cartilage abnormalities (Table 3); two with full thickness cartilage defects and one with a partial thickness defect. This was not statistically significant by the Chi-square test (p = 0.148). Of the five knees with a tibial plateau cyst at the anterior horn lateral meniscus root insertion, one (20%) had lateral tibial plateau articular cartilage abnormality (Table 4), consisting of cartilage surface irregularity. This was not statistically significant by the Chi-square test (p = 0.954). Of the two knees with a tibial plateau cyst at the posterior horn lateral meniscus root insertion, one (50%) had lateral tibial plateau articular cartilage abnormality (Table 4), consisting of a partial thickness defect. This was not statistically significant by the chi-square test (p = 0.261). DISCUSSION The menisci of the knee have certain biomechanical functions, including load transmission and shock absorption.7 The central attachments, or roots, of the menisci to the tibia are essential for the correct positioning of the menisci during knee motion as well as correct biomechanical functioning of the knee.7 The anatomic locations of the meniscal root insertions have been well-described.7 The medial meniscus anterior root insertion has the largest attachment of the four meniscal roots, and inserts onto the anterior intercondylar crest, just anterior to the transverse genu ligament, which is anterior to the lateral meniscus anterior root insertion. The medial meniscus posterior root insertion has a small attachment site on the posterior slope of the medial tibial tubercle, just posterior to the lateral meniscus posterior root insertion. The lateral meniscus anterior root insertion attaches just posterior to or onto the anterior intercondylar crest, anterior to the lateral tibial tubercle. The lateral meniscus posterior root inserts on the horizontal portion of the posterior intercondylar region with a small portion attaching to the posterior slope of the lateral tibial tubercle.7 The root attachments are also associated with the cruciate ligament insertions, with the lateral meniscus anterior root inserting just lateral to the ACL insertion, the medial meniscus posterior root abutting the PCL insertion site, and the PCL insertion just posterior to both posterior roots.7 The etiology of tibial plateau bone marrow cysts is not well known. There have been many types of tibial cysts described, including intraosseous ganglia, subchondral cysts (geodes), mucoid cysts and cysts due to synovial herniation.8 The type most similar to the tibial cysts that we studied is the intraosseous cyst/ganglion at insertion sites. These have been reported to occur at or near the insertions of the cruciate ligaments or meniscotibial attachments. 1,3,4 McLauren et al in 1992 performed a study to determine the prevalence of tibial plateau cysts, which they described as similar to intraosseous ganglia, at the cruciate ligament insertion sites, and to evaluate for a significant association with cruciate ligament pathology.3 While no significant relationship was found, it is interesting to note that ten of the fifteen patients in the study did have findings of

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meniscal pathology, including tears and intrameniscal degeneration. They defined intraosseous ganglia as cyst-like structures in the epiphyseal-metaphyseal region of long bones adjacent to a joint or ligamentous insertions, with the femur and tibia as the most common locations.1,3 They proposed that these cysts may be due to abnormal stress on the bone, causing focal necrosis with liquefaction and ganglion formation.1,3,4 Given the close proximity of the cruciate ligament insertions and the meniscal root insertions, it may be that these cysts were very similar to those at the meniscal insertions described in our study, which do appear to be associated with meniscal pathology. To our knowledge, this association has not been previously reported. Similar intraosseous cysts in other regions of the body have been described to be associated with soft tissue injury, particularly humeral head cysts related to rotator cuff pathology. Several studies have shown that humeral head cysts in the greater tuberosity were associated with rotator cuff tears.9,10 Needell et al concluded that humeral head cysts correlated well with the severity of rotator cuff pathology in asymptomatic patients, regardless of age.9 Sano et al demonstrated that humeral head cysts located in the posterior half of the middle facet near the bare area were more commonly related to degeneration due to aging, while those located anteriorly and at the lesser tuberosity were associated with tears of the supraspinatus and subscapularis tendons respectively. 10 The etiology of these cysts was postulated to be due to direct contact of the bone at the torn rotator cuff attachment with the coracoacromial arch with possible additional causes including disruption of the tensile force on the bony architecture after tendon tear.10 Just as in the humeral head cyst studies, in the present study we illustrate that there is a relationship between tibial cysts at the meniscal root insertion sites and ipsilateral meniscal pathology. In particular, there is a statistically significant correlation between cysts at the medial meniscus root insertions and medial meniscus pathology. There was not a statistically significant correlation between lateral meniscus insertional cysts and meniscal abnormalities. Though there appeared to be an association, the fact that the lateral meniscus is torn less frequently than the medial meniscus may have contributed to this finding.5,6 Also, there are important anatomic and functional differences between the medial and lateral menisci and their attachments that may explain differences in both meniscal pathology and in marrow cystic changes, including the firmness of the medial meniscal attachment compared with the greater excursion of the lateral meniscus during flexion, and differences in the femoral condylar radii of curvature.11 Some previous studies have noted an increased incidence of tibial plateau cysts in osteoarthritic knees,1,8,12 and some have suggested a causative relationship.12 These cysts may be characterized as degenerative subchondral cysts or geodes.1,12 In our study, we did not find a statistically significant correlation between ipsilateral articular cartilage abnormalities and the presence of tibial plateau cysts at the meniscus root insertions. JAYPEE

DOJ Tibial Plateau Cysts at the Meniscal Root Insertions: Incidence and Association

A previous study by Pouders et al determined the prevalence of cysts in the weight-bearing areas and interspinous bone cysts in tibial plateau specimens derived from knees with advanced osteoarthritis and performed MRI-anatomic correlation, and defined their histologic characteristics.8 This study found that most of the cysts located in the weight-bearing areas were adjacent to intact cartilage.9 Also, this study hypothesized that the weight-bearing area cysts and interspinous cysts may form because of repetitive mechanical stresses on the bone.8 This study as well as our own results supports the hypothesis that tibial plateau cysts at the meniscal root insertions are more likely to be associated with ipsilateral meniscal pathology than with articular cartilage abnormalities, and that their formation may be due to abnormal stresses on the bone at these insertion sites. MR imaging has become very important in the diagnosis of meniscal pathology. Direct as well as indirect signs are readily seen on MR imaging to allow for a diagnosis.13 For instance, the presence of a parameniscal cyst has been well-demonstrated as a sign of meniscal tear.1,2,6,13 Other indirect signs include meniscal extrusion, edema around the ipsilateral collateral ligament, subchondral bone marrow edema and focal cartilage loss.13 Our study shows that tibial plateau cysts at the medial meniscal root insertions may be another indirect sign of meniscal injury. Our study is limited by its retrospective non-blinded format. All studies were obtained in symptomatic patients. The same readers who evaluated the studies for tibial cysts also evaluated the studies for meniscal pathology, and observer bias may thus have been introduced. Also, we did not evaluate for other possible confounding variables, such as ligamentous abnormalities. Our criteria for tibial cysts may have excluded some tibial plateau cysts that did exist, for instance if they were not fluid bright on T2-weighted images or if they were of a linear or branching nature. We did not attempt to correlate our MR findings with any available operative findings, and the histologic nature of the tibial plateau cysts was not elucidated. However, our findings do suggest that cysts in the bone marrow at the meniscal root insertions are a common finding on knee MRI examinations, and were seen in 10% of knee MRI examinations in this study. In addition, there was a statistically significant association between the presence of tibial plateau cysts at the anterior and posterior horn medial meniscus insertions and medial meniscal pathology.

The Duke Orthopaedic Journal, July 2010-June 2011;1(1):45-49

ACKNOWLEDGMENT The authors thank Dr Craig Beam for assistance with statistical analyses. REFERENCES 1. McCarthy CL, McNally EG. The MRI appearance of cystic lesions around the knee. Skeletal Radiol 2004;33:187-209. 2. Burk DL, Dalinka MK, Kanal E, et al. Meniscal and ganglion cysts of the knee: MR evaluation. Am J Roentgenol 1988;150:331-36. 3. McLaren DB, Buckwalter KA, Vahey TN. The prevalence and significance of cyst-like changes at the cruciate ligament attachments in the knee. Skeletal Radiol 1992;21:365-69. 4. Janzen DL, Peterfy CG, Forbes JR, Tirman PF, Genant HK. Cystic lesions around the knee joint: MR imaging findings. Am J Roentgenol 1994;163:155-61. 5. DeSmet AAD, Norris MA, Yandow DR, Quintana FA, Graf BK, Keene JS. MR diagnosis of meniscal tears of the knee: Importance of high signal in the meniscus that extends to the surface. Am J Roentgenol 1993;161:101-07. 6. Campbell SE, Sanders TG, Morrison WB. MR imaging of meniscal cysts: Incidence, location, and clinical significance. Am J Roentgenol 2001;177:409-13. 7. Brody JM, Hulstyn MJ, Fleming BC, Tung GA. The meniscal roots: Gross anatomic correlation with 3-T MRI findings. Am J Roentgenol 2007;188:W446-50. 8. Pouders C, Maeseneer MD, Van Roy P, Gielen J, Goossens A, Shahabpour M. Prevalence and MRI-anatomic correlation of bone cysts in osteoarthritic knees. Am J Roentgenol 2008;190:17-21. 9. Needell SD, Zlatkin MB, Sher JS, Murphy BJ, Uribe JW. MR imaging of the rotator cuff: Peritendinous and bone abnormalities in an asymptomatic population. Am J Roentgenol 1996;166: 863-67. 10. Sano A, Itoi E, Konno N, Kido T, Urayama M, Sato K. Cystic changes of the humeral head on MR imaging, relation to age and cuff-tears. Acta Orthop Scand 1998;69(4):397-400. 11. Benjamin M, Evans EJ, Rao RD, Findlay JA, Pemberton DJ. Quantitative differences in the histology of the attachment zones of the meniscal horns in the knee joint of man. J Anat 1991;177:127-34. 12. Ostlere SJ, Seeger LL, Eckardt JJ. Subchondral cysts of the tibia secondary to osteoarthritis of the knee. Skelet Radiol 1990;19:287-89. 13. Bergin D, Hochberg H, Zoga AC, Qazi N, Parker L, Morrison WB. Indirect soft-tissue and osseous signs on knee MRI of surgically proven meniscal tears. Am J Roentgenol 2008;191: 86-92.

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