MRI Characteristics of Healed and Unhealed Peripheral Vertical Meniscal Tears

Transcription

1 Musculoskeletal Imaging Original Research Kijowski et al. MRI of Peripheral Meniscal Tears Musculoskeletal Imaging Original Research Richard Kijowski 1 Humberto G. Rosas 1 Kenneth S. Lee 1 rnold Cheung 1 lejandro Munoz del Rio 1,2 en K. Graf 3 Kijowski R, Rosas HG, Lee KL, Cheung, Munoz del Rio, Graf K Keywords: knee, meniscus, MRI, sports medicine, trauma DOI: /JR Received July 2, 2013; accepted after revision ugust 15, Department of Radiology, University of Wisconsin, 600 Highland ve, Clinical Science Center E3/311, Madison, WI ddress correspondence to R. Kijowski (rkijowski@uwhealth.org). 2 Department of Statistics, University of Wisconsin, Madison, WI. 3 Department of Orthopedic Surgery, University of Wisconsin, Madison, WI. JR 2014; 202: X/14/ merican Roentgen Ray Society MRI Characteristics of Healed and Unhealed Peripheral Vertical Meniscal Tears OJECTIVE. The objective of our study was to retrospectively compare the MRI characteristics of surgically confirmed healed and unhealed peripheral vertical meniscal tears. MTERILS ND METHODS. The study group consisted of 64 patients with 86 peripheral vertical meniscal tears diagnosed on MRI who subsequently underwent knee surgery. The MRI examinations were retrospectively reviewed to assess the following tear characteristics: tear location relative to the meniscocapsular junction, tear width, tear length, tear extension through one or both surfaces, sequences on which tear was visualized, signal intensity of tear on T2-weighted imaging, and presence of low-signal-intensity strands bridging the tear on T2-weighted imaging. Multivariate logistic regression models were used to determine whether MRI characteristics could be used to distinguish between healed and unhealed tears at surgery. RESULTS. Tear location was the most significant characteristic (p < 0.001) for distinguishing between healed and unhealed tears: 17 of 18 (94.4%) tears located at the meniscocapsular junction of the medial meniscus were healed and 15 of 68 (22.1%) tears not located at the meniscocapsular junction were healed. For tears not located at the meniscocapsular junction, MRI characteristics significantly associated with healed tears included a tear width of less than 2 mm (p = 0.01), tear visualized only on intermediate-weighted imaging (p = 0.01), tear showing intermediate or bright signal intensity on T2-weighted imaging (p = 0.06), and low-signal-intensity strands bridging the tear on T2-weighted imaging (p < 0.001). CONCLUSION. Most peripheral vertical tears at the meniscocapsular junction of the medial meniscus spontaneously heal. The MRI characteristics of tears not located at the meniscocapsular junction can help distinguish between healed and unhealed tears. M eniscal tears are the most common treated knee injury [1]. Meniscal tears have been classified into multiple types on the basis of morphology including vertical, horizontal, oblique, radial, complex, buckle-handle, and flap tears [2, 3]. Vertical tears are caused by compressive forces applied to the meniscus during trauma and are typically located in the periphery of the posterior horn of the meniscus where they extend parallel to the course of the circumferentially oriented collagen fibers [2 4]. Peripheral vertical meniscal tears are common in patients with an anterior cruciate ligament (CL) injury [2, 5 7]. However, they also comprise between 23% and 39% of meniscal tears identified in individuals with stable knees [3, 8]. Peripheral vertical meniscal tears occur near the meniscocapsular junction in an area of increased vascularity and thus have potential for spontaneously healing [9, 10]. Many authors have reported excellent long-term clinical results after nonoperative treatment of peripheral vertical meniscal tears especially in patients with an CL injury [11 13]. However, a recent meta-analysis has shown that orthopedic surgeons repair or partially resect most meniscal tears identified at CL reconstruction surgery including peripheral vertical tears [14]. MRI is commonly used for the preoperative diagnosis of meniscal tears [15 17]. Identifying findings on MRI indicating that a peripheral vertical meniscal tear has a high likelihood of spontaneously healing could help determine whether conservative therapy or surgical intervention is the best treatment option for the patient. Despite the ability of MRI to provide important prognostic information, few previous studies have investigated the use of MRI for assessing the healing potential of peripheral vertical meniscal tears [18, 19]. Thus, this study was performed to JR:202, March

2 Kijowski et al. retrospectively compare the MRI characteristics of surgically confirmed healed and unhealed peripheral vertical meniscal tears. Materials and Methods Subjects The retrospective study was performed in compliance with HIP regulations with approval from our institutional review board and a waiver of informed consent. musculoskeletal radiology database was used to identify 276 patients with a peripheral vertical meniscal tear diagnosed on an MRI examination of the knee performed at our institution between July 1, 2005, and July 1, The inclusion criteria of the study were a history of acute knee injury, a peripheral vertical meniscal tear prospectively diagnosed on MRI by a fellowship-trained musculoskeletal radiologist at our institution and retrospectively confirmed independently by two additional fellowship-trained musculoskeletal radiologists, arthroscopic knee surgery performed by an orthopedic sports medicine specialist at our institution, MRI examination and knee surgery performed within 6 months of the knee injury, and no recurrent episodes of knee injury or knee instability between the time of the MRI examination and knee surgery. The study group consisted of 64 patients (40 male and 24 female; age range, years; average age, 25.2 years) with 86 peripheral vertical meniscal tears who met these inclusion criteria. MR Examinations ll 64 patients in the study group were imaged on the same 1.5-T (n = 44 patients) or 3-T (n = 20) MRI scanner (Signa HDx, GE Healthcare) using an 8-channel phased-array extremity coil (Precision Eight TX/TR High Resolution Knee rray, Invivo). ll MRI examinations consisted of an axial frequency-selective fat-suppressed T2-weighted fast spin-echo (FSE) sequence (TR/TE, 3800/88 at 1.5 T and 4050/85 at 3 T), a coronal intermediate-weighted FSE sequence (TR/TE, 1800/20 at 1.5 and 3 T), a coronal frequency-selective fat-suppressed intermediate-weighted FSE sequence (TR/ TE, 2400/40 at 1.5 and 3 T), a sagittal intermediate-weighted FSE sequence (TR/TE, 1800/20 at 1.5 and 3 T), and a sagittal frequency-selective fatsuppressed T2-weighted FSE sequence (TR/TE, 4200/80 at 1.5 T and 4000/80 at 3 T). ll sequences were performed with a 14-cm FOV, a matrix of at 1.5 T and at 3 T, a slice thickness of 2 3 mm with an interslice gap of mm, a bandwidth of khz, an echo-train length of 3 15, and 2 or 3 signal averages. Review of Medical Records The clinical notes of all 64 patients in the study group were reviewed by a radiology research assistant to determine the age and sex of the patient, the knee injured, the time interval between the knee injury and MRI examination, the time interval between the MRI examination and knee surgery, and the time interval between the knee injury and knee surgery. The surgical reports of all 64 patients were reviewed to determine whether the peripheral vertical meniscal tears identified on MRI were found to be healed or unhealed at arthroscopy. healed peripheral vertical meniscus tear was defined as either a normal meniscus or a meniscal tear completely filled in with reparative tissue that required no further treatment. partially healed meniscal tear was considered to be unhealed because all partially healed tears in our patient population were treated with surgical intervention including repair, débridement, or trephination. The location of the meniscal tears at surgery was also determined and classified as being at the meniscocapsular junction or within the substance of the ll arthroscopic knee surgeries were performed by one of three orthopedic sports medicine specialists at our institution who had years of clinical experience and were aware of the findings of the MRI examination at the time of surgeries. The orthopedic surgeons routinely inspect all areas of the meniscus determined to be abnormal on the preoperative MRI examination both visually and with a surgical probe to assess the exact extent of meniscal injury. Review of MRI Examinations ll MRI examinations were retrospectively reviewed independently by two fellowship-trained musculoskeletal radiologists with 8 and 10 years of clinical experience who were blinded to the clinical and surgical findings. The readers reviewed the MR studies to determine the following characteristics of each peripheral vertical meniscal tear: the location of the tear within the medial or lateral meniscus, the location of the tear relative to the meniscocapsular junction, the width of the tear, the length of the tear, the extension of the tear, the sequences on which the tear was visualized, the signal intensity of the tear on T2-weighted imaging (intermediate, bright, or fluid), and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging. For medial meniscal tears, the location of the tear relative to the meniscocapsular junction was described as at the meniscocapsular junction, 1 3 mm from the meniscocapsular junction, or more than 3 mm from the meniscocapsular junction. For lateral meniscal tears, the location was described as 1 3 mm from the meniscocapsular junction or more than 3 mm from the meniscocapsular junction; a peripheral vertical tear within the lateral meniscus was not classified as being at the meniscocapsular junction because of the looser attachment of the lateral meniscus to the joint capsule when compared with the medial meniscus [9, 10, 20, 21]. The maximal width of the tear on sagittal intermediate-weighted images was classified as < 2 mm or as 2 mm. The length of the tear was determined as the number of consecutive sagittal intermediate-weighted images on which the tear was visualized. The extension of the tear was noted to be through one or both articular surfaces of the meniscus on sagittal intermediate-weighted images. The sequences on which the tear was visualized were either sagittal intermediate-weighted images only or both sagittal intermediate-weighted and fat-suppressed T2-weighted images. When the two radiologists had discordant interpretations for a particular characteristic of the peripheral vertical meniscal tear, a third fellowship-trained musculoskeletal radiologist with 8 years of clinical experience who was blinded to the clinical and surgical findings of all patients reviewed the MRI examination to help make the final interpretation. Statistical nalysis Statistical analysis was performed using the R programming environment (version 2.3.1, R Foundation of Statistical Imaging). For all statistical tests, differences were considered to be statistically significant if the p value was < 0.05 and to be marginally significant if the p value was < The kappa statistic was used to determine interobserver agreement between radiologists for assessing the MRI characteristics of peripheral vertical meniscal tears. Interobserver agreement was assessed according to the recommendations of Landis and Koch [22] in which a kappa value of indicates slight agreement; , fair agreement; , moderate agreement; , substantial agreement; 0.81 to less than 1.00, near perfect agreement; and 1.00, perfect agreement. Univariate logistic regression models for continuous variables and Fisher exact tests for categoric variables were used to compare demographic and clinical variables between healed and unhealed peripheral vertical meniscal tears including the age and sex of the patient, the knee injured, the time interval between the knee injury and MRI examination, the time interval between the MRI examination and knee surgery, the time interval between the knee injury and knee surgery, and the type of scanner used in the MRI examination. Univariate logistic regression models and Fisher exact tests were also used to compare MRI characteristics between healed and unhealed peripheral vertical meniscal tears. nalyses were performed for all meniscal tears combined and for meniscal tears not located at the meniscocapsular junction of the medial Multivariate logistic regression models were used to determine whether MRI characteristics found to be at least marginally significant in the univariate analysis maintained their significance when adjusting 586 JR:202, March 2014

3 MRI of Peripheral Meniscal Tears 26 Tears were 1 3 mm from the meniscocapsular junction for confounding factors that could potentially influence the likelihood that a peripheral vertical meniscal tear spontaneously healed. These confounding factors included the age and sex of the patient, the time interval between the knee injury and MRI examination, the time interval between the MRI examination and knee surgery, and the time interval between the knee injury and knee surgery. Positive predictive values and negative predictive values of the MRI characteristics for detecting surgically confirmed healed peripheral vertical meniscal tears not located at the meniscocapsular junction of the medial meniscus were also calculated. Results Surgical Findings of Peripheral Vertical Meniscal Tears Identified on MRI ll peripheral vertical tears were located in the posterior horn of the medial or lateral Forty-five of the 64 patients (70.3%) in the study group were found to have an unhealed peripheral vertical meniscal tear. Forty-seven patients (73.4%) were also found to have a torn CL and underwent ligament reconstruction surgery. Of the 86 peripheral vertical meniscal tears identified on MRI, 32 tears (37.2%) were healed and 54 tears (62.8%) were unhealed. Of the 55 tears in the medial meniscus, 25 tears (45.5%) were healed and 30 tears (54.5%) were unhealed. Of the 31 tears in Medial meniscus: 55 peripheral vertical meniscal tears 18 Tears were at the meniscocapsular junction 11 Tears were > 3 mm from the meniscocapsular junction 5 Healed 21 Unhealed 17 Healed 1 Unhealed 3 Healed 8 Unhealed Fig. 1 Chart shows distribution of healed and unhealed peripheral vertical tears within medial meniscus according to their location relative to meniscocapsular junction on MRI. 30 Tears were 1 3 mm from the meniscocapsular junction Lateral meniscus: 31 peripheral vertical meniscal tears 1 Tear was > 3 mm from the meniscocapsular junction 7 Healed 23 Unhealed 0 Healed 1 Unhealed Fig. 2 Chart shows distribution of healed and unhealed peripheral vertical tears within lateral meniscus according to their location relative to meniscocapsular junction on MRI. the lateral meniscus, seven tears (22.6%) were healed and 24 tears (77.4%) were unhealed. Of the 54 unhealed tears, 39 tears (72.2%) were repaired, 10 tears (18.5%) were partially resected, and five tears (9.3%) underwent trephination. Figures 1 3 show the distribution of healed and unhealed peripheral vertical tears within the medial and lateral meniscus according to their location relative to the meniscocapsular junction on MRI. Seventeen of 18 tears (94.4%) located at the meniscocapsular junction of the medial meniscus were healed, whereas only 15 of 68 tears (22.1%) not located at the meniscocapsular junction of the medial meniscus were healed. Of the 18 peripheral vertical tears located at the meniscocapsular junction on MRI, one tear corresponded to an unhealed tear within the peripheral substance of the meniscus, six tears corresponded to healed tears within the peripheral substance of the meniscus, four tears corresponded to healed tears at the meniscocapsular junction, and seven tears corresponded to normal menisci at surgery. Of the 68 peripheral vertical tears not located at the meniscocapsular junction of the medial meniscus on MRI, 53 tears corresponded to unhealed tears and 15 tears corresponded to healed tears within the peripheral substance of the Characteristics of Healed and Unhealed Peripheral Vertical Meniscal Tears The average time interval between the knee injury and MRI examination, between the MRI examination and knee surgery, and between the knee injury and knee surgery was 22 days (range, 2 37 days; SD, 22 days), 48 days (range, days; SD, 27 days), and 70 days (range, days; SD, 40 days), respectively. There was no statistically significant difference between healed and unhealed peripheral vertical meniscal tears in the age (p = 0.31) and sex (p = 0.36) of the patient, the knee injured (p = 0.70), the time interval between the knee injury and MRI examination (p = 0.58), the time interval between the MRI examination and knee surgery (p = 0.24), the time interval between the knee injury and knee surgery (p = 0.28), and the type of scanner used in the MRI examination (p = 0.46). There was near perfect agreement between radiologists for assessing the MRI characteristics of the peripheral vertical meniscal tears: Kappa values ranged from 0.81 to For all tears combined, there was a statistically differ- Fig. 3 Three-dimensional illustrations of posterior horn of medial and lateral menisci show rate of spontaneous healing of peripheral vertical meniscus tears according to their location relative to meniscocapsular junction on MRI. JR:202, March

4 Kijowski et al. TLE 1: Difference in MRI Characteristics etween Healed and Unhealed Peripheral Vertical Meniscal Tears for ll Tears Combined Using Univariate and Multivariate nalyses p MRI Characteristic Univariate nalysis Multivariate nalysis Tear location In medial or lateral meniscus Relative to meniscocapsular junction < < Tear width 0.13 Tear length 0.88 Sequence on which tear was visualized 0.28 Tear extension 0.75 Tear signal intensity on T2-weighted imaging 0.15 Presence of low-signal-intensity strands bridging the tear on T2-weighted imaging < < Note Dash ( ) indicates that MRI characteristic was not tested because only the MRI characteristics that were found to be at least marginally significant using the univariate analysis were tested using the multivariate analysis. TLE 2: Difference in MRI Characteristics etween Healed and Unhealed Peripheral Vertical Meniscus Tears for Tears Not Located at the Meniscocapsular Junction of the Medial Meniscus Using Univariate and Multivariate nalyses p MRI Characteristic Univariate nalysis Multivariate nalysis Tear location In medial or lateral meniscus 1.00 Relative to meniscocapsular junction 0.71 Tear width Tear length 0.71 Sequence on which tear was visualized Tear extension 0.40 Tear signal intensity on T2-weighted imaging Presence of low-signal-intensity strands bridging the tear on T2-weighted imaging < < Note Dash ( ) indicates that MRI characteristic was not tested because only the MRI characteristics that were found to be at least marginally significant using the univariate analysis were tested using the multivariate analysis. ence (p < 0.05) between healed and unhealed peripheral vertical meniscal tears in the location of the tear in the medial or lateral meniscus, the location of the tear relative to the meniscocapsular junction, and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging (Table 1). When tears at the meniscocapsular junction were removed from the analysis, there was a statistically significant difference (p < 0.05) between healed and unhealed peripheral vertical meniscal tears in the sequence on which the tear was visualized and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging and a marginally significant difference (p < 0.10) between healed and unhealed peripheral vertical meniscal tears in the width of the tear and the signal intensity of the tear on T2-weighted imaging (Table 2). These MRI characteristics maintained their significance when a multivariate analysis model was used to account for confounding factors. The presence of low-signal-intensity strands bridging the tear on T2-weighted imaging had the best combined positive and negative predictive values for detecting a healed peripheral vertical meniscus tear not located at the meniscocapsular junction of the medial meniscus (Table 3 and Figs. 4 9). Discussion The results of our study have shown that MRI can be used to provide prognostic information regarding the likelihood that a peripheral vertical meniscal tear will spontaneously heal. The most important MRI characteristic for distinguishing between healed and unhealed peripheral vertical meniscal tears was the location of the tear relative to the meniscocapsular junction. In our study, 94.4% of tears located at the meniscocapsular junction of the medial meniscus were found to be healed at surgery. This result corresponds well to the results of previous studies that have shown that between 66.7% and 87.9% of tears located at the meniscocapsular junction of the medial meniscus on MRI corresponded to normal menisci or healed tears at arthroscopy [18, 19]. Tears at the meniscocapsular junction may be difficult to differentiate from tears within the far periphery of the meniscus because many peripheral vertical tears of the medial meniscus classified as being at the meniscocapsular junction on MRI in our study were found to be located within the substance of the meniscus at surgery. However, if increased signal intensity on T2-weighted 588 JR:202, March 2014

5 MRI of Peripheral Meniscal Tears TLE 3: Positive Predictive Values (PPVs) and Negative Predictive Values (NPVs) of MRI Characteristics for Detecting Surgically Confirmed Healed Peripheral Vertical Meniscus Tears Value (95% CI) MRI Characteristic PPV NPV Tear width < 2 mm 0.29 ( ) 0.95 ( ) Tear visualized on intermediate-weighted imaging only 1.00 ( ) 0.80 ( ) Tear shows intermediate or bright signal intensity on T2-weighted imaging 0.28 ( ) 0.93 ( ) Presence of low-signal-intensity strands bridging the tear on T2-weighted imaging 0.72 ( ) 0.91 ( ) imaging is identified at the meniscocapsular junction of the medial meniscus on MRI with no discrete piece of meniscal tissue remaining attached to the joint capsule, the meniscal injury should be considered to have a high likelihood of healing spontaneously. Our study found a healing rate of only 22.1% for peripheral vertical tears not located at the meniscocapsular junction of the medial De Smet and associates [19] also reported that only 16% of peripheral vertical tears within the medial meniscus not located at the meniscocapsular junction on MRI corresponded to normal menisci or to healed tears at arthroscopy. Weiss and associates [11] found that 61.3% of surgically confirmed peripheral vertical tears of the medial and lateral meniscus were healed at repeat arthroscopy. However, their study did not classify medial meniscal tears as being located at the meniscocapsular junction or within the substance of the meniscus, which may account for the higher rate of spontaneous healing. The lower healing rate of tears not located at the meniscocapsular junction of the medial meniscus may be because of a diminished vascular supply to these regions. The medial meniscus is firmly attached to the joint capsule; thus, the meniscocapsular junction of the medial meniscus has a more robust blood supply from the capillary plexus, which originates from the capsule and supplies the outer 10 25% of the meniscus [9, 10]. The results of our study have shown that MRI characteristics including the width of the tear, the sequences on which the tear is visualized, the signal intensity of the tear on T2-weighted imaging, and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging can be used to assess the healing potential of peripheral vertical meniscal tears not located at the menisco- Fig year-old girl with surgically confirmed medial rthroscopic knee surgery was performed 42 days after knee injury. (FSE) image of knee shows tear (arrow) that is more than 2 mm wide located at meniscocapsular junction of posterior horn of medial weighted FSE image of knee shows fluid signal intensity between margins of meniscal tear (arrow). Fig year-old man with surgically confirmed medial rthroscopic knee surgery was performed 62 days after knee injury. (FSE) image of knee shows tear (arrow) that is less than 2 mm wide located more than 3 mm from meniscocapsular junction of posterior horn of medial weighted FSE image of knee shows normal-appearing meniscus (arrow). JR:202, March

6 Kijowski et al. capsular junction of the medial The presence of low-signal-intensity strands bridging the tear on T2-weighted imaging most likely represents reparative tissue or residual intact fibers connecting the edges of the torn meniscus and had the best combined positive and negative predictive values for detecting a healed tear. tear visualized only on intermediate-weighted images had a very high positive predictive value, which indicates that the presence of this finding on MRI strongly suggests that the tear will spontaneously heal. tear width of less than 2 mm and intermediate or bright signal intensity of the tear on T2-weighted imaging had very high negative predictive values for detecting a healed tear. Thus, a peripheral vertical meniscal tear that is 2 mm wide or wider and shows fluid signal intensity on T2-weighted imaging strongly suggests that the tear will not heal with conservative therapy. wide gap between the torn edges of the meniscus indicating meniscal displacement and fluid signal intensity of the tear on T2-weighted imaging have also been described as MRI findings of an unstable meniscal tear [19]. The chronic micromotion at the edges of an unstable peripheral vertical meniscal tear would presumably reduce the likelihood that the tear would spontaneously heal. Only one previous study to date has compared the MRI characteristics of healed and unhealed peripheral vertical meniscal tears. De Smet and associates [19] described the MRI characteristics of 50 peripheral vertical tears of the medial meniscus in patients with surgical correlation and reported findings similar to the results of this study. They found that tears located at the meniscocapsular junction of the medial meniscus were significantly more likely to correspond to normal menisci or healed tears at arthroscopy than tears in the peripheral third of the Furthermore, there was no statistically significant difference between healed and unhealed tears in the length of the tear, the extension of the tear into one or both articular surfaces of the meniscus, or the time interval between the MRI examination and Fig year-old man with surgically confirmed lateral rthroscopic knee surgery was performed 71 days after knee injury. (FSE) image of knee shows tear (arrow) that is less than 2 mm wide located between 1 and 3 mm from meniscocapsular junction of posterior horn of lateral weighted FSE image of knee shows intermediate signal intensity between margins of meniscal tear (thin arrow) with thin horizontal strands of low signal intensity bridging tear (thick arrow). Fig year-old girl with surgically confirmed medial rthroscopic knee surgery was performed 63 days after knee injury. (FSE) image of knee shows tear (arrow) that is less than 2 mm wide located between 1 and 3 mm from meniscocapsular junction of posterior horn of medial weighted FSE image of knee shows intermediate signal intensity between margins of meniscal tear (thin arrow) with thin horizontal strands of low signal intensity bridging tear (thick arrow). knee surgery [19]. However, in that study, De Smet and associates did not investigate other MRI characteristics including the width of the tear, the sequences on which the tear was visualized, the signal intensity of the tear on T2-weighted imaging, and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging. In our study, these additional MRI characteristics were found to be significantly different for healed and unhealed peripheral vertical meniscal tears. Our study has several limitations. One limitation was its retrospective study design. second limitation was the presence of selection bias because the study group was composed of patients with peripheral vertical meniscal tears diagnosed on MRI. Thus, the study could not assess the sensitivity of MRI for detecting this tear type because patients with surgically confirmed peripheral vertical meniscal tears not detected on the MRI examination were not included in the study group. nother limitation of the study was that a normal meniscus at arthroscopy was considered to be a healed 590 JR:202, March 2014

7 MRI of Peripheral Meniscal Tears meniscal tear. lthough only patients with peripheral vertical meniscal tears diagnosed prospectively by a musculoskeletal radiologist and confirmed retrospectively by two additional musculoskeletal radiologists were included in the study group, it is possible that all three radiologists made an incorrect interpretation of the MRI examination. final limitation of our study was that arthroscopic knee surgery is an imperfect reference standard for determining the presence or absence of meniscal tears [23]. In particular, evaluating the meniscocapsular junction of the medial meniscus at arthroscopy is technically challenging, and it is often difficult to differentiate a healed or partially healed meniscocapsular tear from a deep meniscocapsular sulcus [24]. In conclusion, the results of our study have shown that MRI can be used to assess the healing potential of peripheral vertical meniscal tears. The most important MRI characteristic for distinguishing between healed and unhealed tears was their location relative to the meniscocapsular junction. lmost all tears at the meniscocapsular junction of the medial meniscus spontaneously healed, whereas most tears not located at the meniscocapsular junction of the medial meniscus did not heal. For tears not located at the meniscocapsular junction, MRI characteristics that were significantly associated with healed tears included a tear width of less than 2 mm, the tear visualized only on intermediate-weighted imaging, intermediate or bright signal intensity of the tear on T2-weighted imaging, and the presence of low-signal-intensity strands bridging the tear on T2-weighted imaging. Using these characteristics to assess a peripheral vertical meniscal tear on MRI can provide prognostic information regarding the likelihood that the tear will spontaneously heal. References 1. Kim S, osque J, Meehan JP, Jamali, Marder R. Increase in outpatient knee arthroscopy in the United States: a comparison of National Surveys of mbulatory Surgery, 1996 and J one Joint Surg m 2011; 93: Fig year-old man with surgically confirmed medial rthroscopic knee surgery was performed 33 days after knee injury. (FSE) image of knee shows tear (arrow) that is less than 2 mm wide located between 1 and 3 mm from meniscocapsular junction of posterior horn of medial weighted FSE image of knee shows fluid signal intensity between margins of meniscal tear (thin arrow) with thin horizontal strands of low signal intensity bridging tear (thick arrow). Fig year-old man with surgically confirmed unhealed peripheral vertical tear of posterior horn of medial rthroscopic knee surgery was performed 140 days after knee injury. (FSE) image of knee shows tear (arrow) that is less than 2 mm wide located more than 3 mm from meniscocapsular junction of posterior horn of medial weighted FSE image of knee shows fluid signal intensity between margins of meniscus tear (arrow). 2. Slauterbeck JR, Kousa P, Clifton C, et al. Geographic mapping of meniscus and cartilage lesions associated with anterior cruciate ligament injuries. J one Joint Surg m 2009; 91: Metcalf MH, arrett GR. Prospective evaluation of 1485 meniscal tear patterns in patients with stable knees. m J Sports Med 2004; 32: Petersen W, Tillmann. Collagenous fibril texture of the human knee joint menisci. nat Embryol (erl) 1998; 197: Smith JP 3rd, arrett GR. Medial and lateral meniscal tear patterns in anterior cruciate ligament deficient knees: a prospective analysis of 575 tears. m J Sports Med 2001; 29: Vinson EN, Gage J, Lacy JN. ssociation of peripheral vertical meniscal tears with anterior cruciate ligament tears. Skeletal Radiol 2008; 37: De Smet, Graf K. Meniscal tears missed on MR imaging: relationship to meniscal tear patterns and anterior cruciate ligament tears. JR 1994; 162: Terzidis IP, Christodoulou, Ploumis, Givissis P, Natsis K, Koimtzis M. Meniscal tear characteristics in young athletes with a stable knee: ar- JR:202, March

8 Kijowski et al. throscopic evaluation. m J Sports Med 2006; construction. rthroscopy 2012; 28: false-positive knee MR diagnoses of medial menis- 34: Cheung LP, Li KC, Hollett MD, ergman G, cal tears. JR 2008; 191: rnoczky SP, Warren RF. Microvasculature of the Herfkens RJ. Meniscal tears of the knee: accuracy 20. Robinson JR, Sanchez-allester J, ull M, Thom- human m J Sports Med 1982; 10:90 95 of detection with fast spin-echo MR imaging and as Rde W, mis. The posteromedial corner 10. Day, Mackenzie WG, Shim SS, Leung G. The arthroscopic correlation in 293 patients. Radiology revisited: an anatomical description of the passive vascular and nerve supply of the human 1997; 203: restraining structures of the medial aspect of the hu- rthroscopy 1985; 1: Weiss C, Lundberg M, Hamberg P, DeHaven KE, Gillquist J. Non-operative treatment of meniscal tears. J one Joint Surg m 1989; 71: Shelbourne KD, Heinrich J. The long-term evaluation of lateral meniscus tears left in situ at the time of anterior cruciate ligament reconstruction. rthroscopy 2004; 20: Shelbourne KD, Gray T. Meniscus tears that can be left in situ, with or without trephination or synovial abrasion to stimulate healing. Sports Med rthrosc 2012; 20: Noyes FR, arber-westin SD. Treatment of meniscus tears during anterior cruciate ligament re- 16. Escobedo EM, Hunter JC, Zink-rody GC, Wilson J, Harrison SD, Fisher DJ. Usefulness of turbo spin-echo MR imaging in the evaluation of meniscal tears: comparison with a conventional spinecho sequence. JR 1996; 167: Oei EH, Nikken JJ, Verstijnen C, Ginai Z, Myriam Hunink MG. MR imaging of the menisci and cruciate ligaments: a systematic review. Radiology 2003; 226: Rubin D, ritton C, Towers JD, Harner CD. re MR imaging signs of meniscocapsular separation valid? Radiology 1996; 201: De Smet, Nathan DH, Graf K, Haaland, Fine JP. Clinical and MRI findings associated with man knee. J one Joint Surg r 2004; 86: Seebacher JR, Inglis E, Marshall JL, Warren RF. The structure of the posterolateral aspect of the knee. J one Joint Surg m 1982; 64: Landis JR, Koch GG. The measurement of observer agreement for categorical data. iometrics 1977; 33: Quinn SF, rown TF. Meniscal tears diagnosed with MR imaging versus arthroscopy: how reliable a standard is arthroscopy? Radiology 1991; 181: Morin WD, Steadman JR. rthroscopic assessment of the posterior compartments of the knee via the intercondylar notch: the arthroscopist s field of view. rthroscopy 1993; 9: JR:202, March 2014