HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Boxheimer, L. Articles by Weishaupt, D. Search for Related Content PubMed PubMed Citation Articles by Boxheimer, L. Articles by Weishaupt, D.

Characteristics of Displaceable and Nondisplaceable Meniscal Tears at Kinematic MR Imaging of the Knee¹

¹ From the Institute of Diagnostic Radiology (L.B., A.M.L., K.T., B.M., D.W.) and Department of Trauma Surgery (L.L.), University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland; and Department of Radiology, Orthopedic University Hospital Balgrist, Zurich, Switzerland (M.Z.). Received July 19, 2004; revision requested September 27; revision received December 22; accepted February 1, 2005; final version accepted, February 28. Address correspondence to D.W. (e-mail: dominik.weishaupt{at}usz.ch).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Purpose: To prospectively determine if kinematic magnetic resonance (MR) imaging of the knee may demonstrate displacement of menisci with tears and, if so, to characterize displaceable and nondisplaceable meniscal tears.

Materials and Methods: The study was approved by the hospital's review board, and informed consent was obtained. Forty-two patients (30 men, 12 women; mean age, 36.9 years) with 43 arthroscopically documented meniscal tears visible at 1.5-T MR imaging underwent kinematic MR imaging with an open-configuration 0.5-T MR imager with their knees in supine neutral, supine with 90° flexion and external or internal rotation, and upright weight-bearing positions. Analysis of meniscal movement was performed in different knee positions in the coronal MR imaging plane. Meniscal displacement—that is, meniscal movement of 3 mm or more (in the medial direction for the medial meniscus, in the lateral direction for the lateral meniscus)—was compared with the patient's pain level as assessed with a visual analog scale by using analysis of variance.

Results: Between the different knee positions, meniscal displacement of 3 mm or more (displaceable meniscal tears) was noted in 18 (42%) of 43 menisci with tears. Simultaneous occurrence of grade II or III ipsilateral collateral ligament lesions was present in all 18 displaceable meniscal tears, whereas a normal-appearing collateral ligament or collateral ligament lesion (grade I) was present in 22 of 25 nondisplaceable tears (P < .05). Displaced menisci most commonly had complex, radial, or longitudinal tear configurations (16 of 18, 89%). Patients with displaceable meniscal tears had significantly more pain than did patients with nondisplaceable meniscal tears (P < .001), independent of the concomitant knee abnormalities.

Conclusion: Displaceable meniscal tears usually have longitudinal, radial, or complex configurations; such tears are associated with substantial ipsilateral collateral ligament lesions and pain.

© RSNA, 2006

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Magnetic resonance (MR) imaging of the knee has been shown to accurately demonstrate meniscal tears (1). Results of a metaanalysis have demonstrated pooled weighted sensitivity and specificity values of 93% and 88%, respectively, for medial meniscal tears and 79% and 95%, respectively, for lateral meniscal tears (1). Although MR imaging has been shown to help in clinical decision making in treating patients with internal knee derangement (2,3), in our experience, it may be difficult to assess the clinical relevance of abnormal MR imaging findings of the knee when correlating the imaging findings with the patient's complaints. This is particularly true for meniscal tears where, with use of MR imaging, results of several studies have demonstrated that meniscal tears may occur in up to 63% of asymptomatic knees (4–7). In clinical practice, different approaches have been used to distinguish between symptomatic and asymptomatic meniscal tears. An important concept is that of meniscal stability. Clinical data indicate that physical activities or rotational stress may increase the symptoms of meniscal injuries, probably as result of insufficient meniscal stability.

With arthroscopy, meniscal tears can be classified as stable or unstable (8–10). Lesion stability is usually assessed by means of direct visualization and direct probing during arthroscopy. In an unstable lesion, the meniscus or a meniscal fragment can be inappropriately displaced by a probe in the femorotibial joint. For some orthopedic surgeons, meniscal lesion stability is an important criterion in deciding whether to resect or repair a meniscal tear or to leave it alone (9,11,12).

The concept of meniscal stability has stimulated our interest in the dynamic characteristics of meniscal tears, in particular, to evaluate whether meniscal displacement in patients with meniscal tears (ie, change of the anatomic position of torn menisci or fragments during stress positions) can be visualized by using kinematic MR imaging. The feasibility and the dynamic characteristics of menisci in normal volunteers at kinematic MR imaging in different knee positions has been studied by using an open-configuration MR system (13,14).

Thus, the purpose of our study was to prospectively determine if kinematic MR imaging of the knee may demonstrate displacement of menisci with tears and, if so, to characterize displaceable and nondisplaceable meniscal tears.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Subjects and Initial MR Evaluation
Between June 2002 and July 2003, 279 patients suspected of having a meniscal tear were referred to our institution (University Hospital Zurich) for MR imaging of the knee for clinical purposes. All patients were referred by experienced orthopedic or trauma surgeons working at our institution. The study was approved by the hospital's review board, and informed consent was obtained from all participating patients.

All patients underwent MR imaging of the knee on one of three 1.5-T systems (241 patients: Signa CV/i or Signa Horizon LX, GE Medical Systems, Milwaukee, Wis; 38 patients: Gyroscan Intera, Philips Medical Systems, Eindhoven, the Netherlands). With all 1.5-T MR systems, imaging was performed with the patient in a conventional supine position, with a dedicated phased-array quadrature knee coil (hereafter, referred to as standard MR imaging). The following imaging protocol was applied with all 1.5-T MR systems: a sagittal intermediate-weighted spin-echo (SE) sequence (repetition time msec/echo time msec, 1200/20; 3-mm section thickness with 1-mm spacing; matrix, 256 x 256; field of view, 14 x 14 cm; one signal acquired); sagittal, transverse, and coronal T2-weighted fast SE sequences with fat saturation (4000/60–75; echo train length of eight; 3-mm section thickness with 1-mm spacing; matrix, 256 x 256; field of view, 14 x 14 cm; two signals acquired); and a coronal T1-weighted SE sequence (350/16; 3-mm section thickness with 1-mm spacing; matrix, 256 x 256; field of view, 16 x 16 cm; two signals acquired).

After completion of standard MR imaging and subsequent clinical evaluation by the referring clinician, the patients were asked to undergo MR imaging in an open-configuration MR system with the knee in a supine neutral position, in a supine with 90° flexion position with external or internal rotation, and in an upright weight-bearing position if all of the following criteria were fulfilled: history of trauma that occurred 2 weeks or less prior to standard MR imaging, no history of previous knee surgery of the affected knee, evidence of a unilateral meniscal tear at 1.5-T MR imaging, absence of cartilage lesions grade 2B or 3 (according to a commonly used arthroscopic classification [15] adapted for MR imaging [16]), and arthroscopy or open surgery planned on the basis of clinical findings, as well as on findings at MR imaging. For this purpose, standard MR images were reviewed prior to inclusion of the patient in the study for the presence of meniscal tears and cartilage loss by one of two experienced radiologists (D.W., 10 years of experience in reading musculoskeletal MR images). A meniscal tear was diagnosed if there was an abnormal intrameniscal signal intensity extending to the articular surface of the meniscus on more than two T1-weighted or intermediate-weighted MR images or if there was increased intrameniscal signal intensity similar to that of water on T2-weighted images (17–20). In addition, abnormal meniscal shape (contour defect or fragmentation) was also considered a meniscal tear sign.

Cartilage loss was graded by using intermediate-weighted SE images, as well as T2-weighted images, in the sagittal and coronal MR imaging planes according to the Noyes classification adapted for MR imaging (16). Noyes grade 2B cartilage lesions were defined as substance loss of more than half but less than full thickness of cartilage, whereas grade 3 cartilage lesions included exposed bone with or without bone surface irregularity. Only patients with homogeneous signal intensity of the cartilage without surface irregularities (grade 0), those with focal superficial signal intensity changes without cartilage surface irregularity (grade 1), or those with substance loss of less than half of the cartilage thickness (grade 2A) were included in the study. Patients with grade 2B or 3 cartilage loss were excluded, because they are expected to have a greatly increased probability of degenerative meniscal tears.

A total of 50 patients (37 men, 13 women; mean age, 32.9 years; age range, 18–65 years) were eligible for the study. Five patients were excluded because arthroscopy had not been performed. Another three patients were excluded because no meniscal tear was found at arthroscopy. Hence, a total of 42 patients (30 men, 12 women; mean age, 36.9 years; age range, 18–60 years) with 43 arthroscopically documented meniscal tears in 42 knees joints (17 right knees, 25 left knees) were included in the study. All these patients underwent kinematic MR imaging of the knee in the open-configuration MR system, as will be described in the next section. The delay between standard MR imaging and kinematic MR imaging was 4.8 days (range, 0–13 days). Clinically indicated arthroscopy was performed in all 42 patients. None of the patients underwent arthroscopy for explicit study purposes. The mean delay between standard MR imaging and arthroscopy was 22.9 days (range, 1–74 days).

Kinematic MR Imaging
Kinematic MR imaging was performed with a vertically opened superconducting 0.5-T MR system (Signa SP; GE Medical Systems). After meniscal tears were diagnosed at standard MR imaging, kinematic MR imaging was first performed with the patients supine and the knee in neutral position by using a circular flexible transmit-receive surface coil (loop coil) placed around the knee joint. The patients were subsequently imaged in the supine position with the knee in 90° flexion, with external or internal rotation (Fig 1a). For this purpose, the patient remained supine and the knee was placed in a specially constructed device that consisted of nonferromagnetic material. This device allowed the maintenance of 90° knee flexion in the supine position.

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: Different knee positions for kinematic MR imaging. (a) Patient is placed in supine position with knee in 90° flexion on a positioning device designed for kinematic MR imaging of the knee. A circular flexible transmit-receive surface coil (loop coil) is placed around the knee joint. (b) Within the MR imager, examiner applies additional external or internal rotation stress and compression to 90° flexed knee. (c) Positioning device designed for MR imaging in upright weight-bearing position consists of a nonferromagnetic knee brace, which allows fixation of the knee and calf.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: Different knee positions for kinematic MR imaging. (a) Patient is placed in supine position with knee in 90° flexion on a positioning device designed for kinematic MR imaging of the knee. A circular flexible transmit-receive surface coil (loop coil) is placed around the knee joint. (b) Within the MR imager, examiner applies additional external or internal rotation stress and compression to 90° flexed knee. (c) Positioning device designed for MR imaging in upright weight-bearing position consists of a nonferromagnetic knee brace, which allows fixation of the knee and calf.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 1c: Different knee positions for kinematic MR imaging. (a) Patient is placed in supine position with knee in 90° flexion on a positioning device designed for kinematic MR imaging of the knee. A circular flexible transmit-receive surface coil (loop coil) is placed around the knee joint. (b) Within the MR imager, examiner applies additional external or internal rotation stress and compression to 90° flexed knee. (c) Positioning device designed for MR imaging in upright weight-bearing position consists of a nonferromagnetic knee brace, which allows fixation of the knee and calf.

Image Analysis
All MR images obtained in each patient were analyzed independently by two radiologists (D.W. and L.B., with 10 and 3 years of experience, respectively, in reading musculoskeletal MR images) on separate workstations (Advantage Windowing Workstation; GE Medical Systems Europe, Buc, France). In cases of disagreement, a consensus was reached. The numeric measurements were also obtained by the readers separately.

The readers first evaluated the standard MR images, and, after a delay of 6 weeks, they evaluated the kinematic MR images in random order. On standard MR images, the menisci, collateral ligaments, cruciate ligaments, bone marrow, and cartilage were analyzed. Meniscal tears were classified by using a previously described classification system as follows: horizontal or oblique tear (a horizontal tear indicates a tear parallel to the tibial plateau separating the meniscus into an upper and a lower part; an oblique tear indicates a tear propagating obliquely to the main axis of the meniscus), longitudinal tear (a vertical tear perpendicular to the tibial plateau propagating parallel to the main axis of the meniscus), radial tear (a vertical tear propagating perpendicular to the free edge of the meniscus), and displaced meniscal tear (1,22–25). A complex tear was diagnosed if the meniscal tear consisted of more than one lesion pattern or more than one cleavage plane orientation lacking continuity (1,22).

Collateral ligament injuries were graded according to the grading system proposed by Stoller et al (24): grade 0, normal collateral ligament; grade I, periligamentous injury with a superficial fluid collection and absence of displacement, thickening, or discontinuity of the collateral ligament; grade II, thickening of the ligament with intraligamentous hyperintense signal intensity on T2-weighted fat-suppressed images but with the ligament still in continuity; and grade III, discontinuity of the collateral ligament. Cartilage loss was graded by using the same classification system as described previously in this text for standard MR imaging. The anterior and posterior cruciate ligaments were assessed as intact or torn by using previously described criteria (24). The bone marrow was assessed by using the following classifications: normal, edema-like zones (zones with ill-defined high signal intensity on T2-weighted fat-suppressed images compared with the normal fatty bone marrow, low signal intensity on T1-weighted images); edema-like zones plus well-defined zones (low signal intensity on T1- and T2-weighted images) indicating possible necrosis; and edema-like zones plus linear changes indicating possible fractures (26).

Six weeks after evaluation of the standard MR images, the same readers evaluated the kinematic MR images independently in random order. Both readers reviewed the MR images for the anatomic position of the torn meniscus in the coronal plane. In cases of disagreement, a consensus was reached. The reviewers were blinded to any clinical data; however, the standard MR images were available for identification of the meniscal tear configuration, because the kinematic MR sequence was not suitable for determination of meniscal tear configuration.

In the coronal plane, meniscal position of the meniscus with the tear was measured at the level of the meniscal body. The meniscal body is usually located at the level of the collateral ligaments, and these ligaments are considered additional stabilizers in preventing lateral displacement of the menisci (27). By using a section thickness of 4 mm, the medial collateral ligament was usually visible on three contiguous sections; measurements were obtained on the middle section of these three. Measurements for the lateral meniscus were obtained on a section where the collateral ligament was clearly visible. Usually the lateral collateral ligament was present on two sections by using a section thickness of 4 mm. During knee flexion, both collateral ligaments move dorsally. Therefore, to avoid false measurement of meniscal position in the supine position in 90° knee flexion and internal or external rotation, the measurements were obtained on that section where the same bony appearance of the tibial plateau was visible as in the supine neutral and the upright weight-bearing positions.

To determine the position of the torn meniscus at the level of the meniscal body in the coronal plane, a line that paralleled the outermost cortical surface of the tibial plateau (horizontal tibial reference line) was set perpendicular to a line that paralleled the outermost edge of the articular cartilage at the medial or lateral border of the tibia (ie, medial or lateral tibial reference line) (Fig 2). The distance between the medial or lateral tibial reference lines and the outer inferior edge of the medial or lateral menisci was measured.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Diagram shows measurement of position of the medial meniscus at level of meniscal body in the coronal plane, with knee in supine neutral position. A line paralleling the cortical surface of the tibial plateau (horizontal tibial reference line, HTRL) was set perpendicular to a line paralleling the medial outermost edge of the articular cartilage of the tibial surface (medial tibial reference line, MTRL). The distance between the outer inferior edge of the meniscus (arrow) and the medial tibial reference line was measured. In this case, distance between the outer inferior edge of the meniscus and the medial tibial reference line is 0 mm. Meniscal movement was calculated as the difference of these distances between the different knee positions. MCL = medial collateral ligament.

Because the outer inferior edge of the meniscus is usually intersecting or immediately adjacent to the vertical tibial reference line in healthy knees of normal volunteers, meniscal displacement is visible as meniscal protrusion. Meniscal protrusion (also called meniscal subluxation) (28,29) is defined as any extension of the outer inferior edge of the meniscus beyond the tibial plateau. In healthy knees of asymptomatic volunteers, meniscal protrusion for the medial and lateral meniscus is less than 3 mm in the coronal plane for the medial and the lateral meniscus (14,29).

Assessment of Pain Intensity
After performing kinematic MR imaging, each patient's knee pain in all different knee positions was assessed by using a visual analog scale. The visual analog scale is an established, validated, self-reporting measure of pain intensity that usually consists of a 100-mm line on paper with vertical anchors to label the ends. The patients were instructed to grade the sensation by placing a mark between the two anchors, without being told about the precise distance between them. The left anchor was defined as indicating no pain at all, and the right anchor was defined as indicating unbearable pain. The distance between one of these anchors and the patient's mark was then measured, and the patient's level of pain was expressed in millimeters (30,31).

Statistical Analysis
Continuous variables were expressed as mean ± standard deviation. The Fisher exact test was used to determine whether the imaging findings between displaceable and nondisplaceable menisci were significantly different. Pain intensities, as assessed by means of the visual analog scale, between the knees with displaceable and those with nondisplaceable meniscal tears were compared by using the Mann-Whitney U test. The correlation between the pain intensity as assessed by means of the visual analog scale and the different knee abnormalities, including displaceable menisci with tear, nondisplaceable menisci with tear, bone marrow abnormalities, anterior cruciate ligament rupture, and collateral ligament injuries, were analyzed by using analysis of variance. A P value of less than .05 was considered to indicate statistical significance. Statistical analysis was performed with StatView (version 5.0.1; SAS Institute, Cary, NC) and SPSS (version 10.0; SPSS, Chicago, Ill) software.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
At standard MR imaging, 43 meniscal tears were found among the 42 patients included in this study. All meniscal tears seen at MR imaging were confirmed at arthroscopy.

The distribution of meniscal tears with regard to lesion type and the concomitant knee abnormalities are shown in Table 1. There were 37 (86%) medial and six (14%) lateral meniscal tears. Twenty-two (51%) of the 43 meniscal tears were associated with a normal ipsilateral collateral ligament (grade 0) or a grade I ipsilateral collateral ligament injury (Table 2). The remaining 21 (49%) meniscal tears were associated with grade II or III ipsilateral collateral ligament injuries (Table 2).

Supine Neutral versus Upright Weight-bearing Position
Between these two positions, meniscal movement of 3 mm or less (mean, 0.7 mm; range, 1.4–1.5 mm) was present in 30 instances of meniscal tears. Meniscal movement of more than 3 mm (ie, meniscal displacement) was observed in 13 instances in the coronal plane (mean, 3.9 mm; range, 3.2–6.8 mm) when changing from the supine neutral to the upright weight-bearing position.

Supine 90° Flexion with Rotation versus Upright Weight-bearing Position
Between the supine position with 90° flexion and internal or external rotation and the upright weight-bearing position, meniscal movement of 3 mm or less (mean, 0.6 mm; range, 6.2–2.9 mm) was present in 37 instances. Meniscal movement of more than 3 mm (mean, 5.1 mm; range, 4.5–6.0 mm) was observed in six instances.

Displaceable versus Nondisplaceable Tears
Overall, meniscal displacement between (a) the supine neutral and the supine 90° flexed with internal or external rotation positions and (b) the supine neutral or the supine 90° flexed position with internal or external rotation and the upright weight-bearing position was observed in 18 (42%) of 43 instances.

Among these 18 cases of displaceable meniscal tears at kinematic MR imaging, the tear configuration was complex in seven instances (39%), radial in six instances (33%), and longitudinal in three instances (17%), whereas a meniscal tear with a displaced fragment was present in two instances (11%) (Table 3). Twenty-five (58%) of 43 menisci with tears did not reveal any displacement between the different knee positions (Fig 3). There was a statistically significant difference in the distribution of displaceable and nondisplaceable tears with regard to meniscal tear configuration; the group with displaceable meniscal tears contained more longitudinal, radial, and complex meniscal tear configurations (16 of 18 tears, 89%) than did the group with nondisplaceable menisci (11 of 25, 44%). In the group with the nondisplaceable meniscal tears, most tears (13 of 25, 52%) were horizontal or oblique. This difference was statistically significant (P < .05).

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

View larger version (189K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

View larger version (187K): [in this window] [in a new window] [Download PPT slide]   Figure 3c: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 3d: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 3e: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 3f: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with normal ipsilateral collateral ligament (grade 0) in a 39-year-old man. (a) Sagittal intermediate-weighted SE (4700/17), (b) coronal T1-weighted (420/14), and (c) coronal T2-weighted fat-suppressed fast SE (4580/86) images obtained with a 1.5-T closed-configuration MR system and knee in supine neutral position. A horizontal tear component (thin arrow), as well as radial tear component (thick arrow), are noted in a. The ipsilateral collateral ligament (arrowheads) is normal (grade 0). (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0; flip angle, 30°) obtained at 0.5 T with knee in (d) supine neutral, (e) 90° flexion with external rotation, and (f) upright weight-bearing positions. Meniscal movement is 0 mm between supine neutral and supine 90° flexed positions and is also 0 mm between supine 90° flexed and upright weight-bearing positions. Because meniscal movement is less than 3 mm between positions, no meniscal displacement was judged to be present. HTRL = horizontal tibial reference line, MTRL = medial tibial reference line.

Ipsilateral collateral ligament injuries of grade II or III were found in all 18 instances of displaceable meniscal tears (Table 3) (Fig 4). In contrast, in 22 of 25 instances of nondisplaceable meniscal tears, the ipsilateral collateral ligaments were intact (grade 0) or showed an ipsilateral collateral ligament injury of grade I. The remaining three nondisplaceable meniscal tears were associated with a collateral ligament injury of grade II. Two of these three nondisplaceable meniscal tears with concomitant ipsilateral collateral grade II lesion were complex tears of the medial meniscus and showed medial protrusion of 2.6 mm in all knee positions (Fig 4). In the remaining instance of a nondisplaceable tear and an ipsilateral grade II collateral ligament injury, the tear configuration was horizontal. The difference with regard to the frequency of ipsilateral collateral ligament injuries was statistically significant (P = .002), whereas all other frequencies of knee abnormalities between these groups were not statistically significant (P = .08–.95).

View larger version (185K): [in this window] [in a new window] [Download PPT slide]   Figure 4a: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

View larger version (183K): [in this window] [in a new window] [Download PPT slide]   Figure 4b: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 4c: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 4d: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 4e: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 4f: MR images show positional dependence of arthroscopically confirmed complex tear of medial meniscus with an ipsilateral grade II collateral ligament injury in a 24-year-old man. (a, b) Consecutive sagittal 1.5-T intermediate-weighted SE images (4700/18) show a complex tear (arrow, longitudinal component; arrowhead, horizontal component). (c) Coronal 1.5-T T2-weighted fat-suppressed image (4580/86) shows ipsilateral grade II injury (arrowheads). In addition, a small area of edema-like bone marrow changes (arrow) is visible in the medial femoral condyle. (d–f) Coronal T1-weighted fast spoiled gradient-echo images (20/9.0) obtained at 0.5 T with the knee in (d) supine neutral, (e) supine neutral in 90° flexion and external rotation, and (f) upright weight-bearing positions. The outer inferior meniscal border, which served as a landmark for meniscal distance, is outlined by arrowheads. Meniscal movement between supine neutral and supine 90° flexed position with external rotation measures 4.5 mm and movement between supine neutral and upright weight-bearing position measures 5.1 mm. On the basis of these measurements, no meniscal displacement was judged to be present in the supine 90° flexed position with external rotation or in the upright weight-bearing position.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Several authors have investigated the dynamic characteristics of the normal menisci during knee joint motion (13,32). On the basis of results of cadaveric studies, there is clear evidence that the menisci are mobile and allow movement in either an anterior-posterior direction (ie, translational movement) or in a lateral-medial direction (ie, radial movement) during flexion and extension (14). Authors of two in vivo studies (13,14) have examined the dynamic range of motion of normal menisci at MR imaging in asymptomatic volunteers. Both of these studies were performed in an open-configuration MR system, which allows MR imaging of the knee in positions other than the neutral position, a position that is usually used for imaging in conventional closed-configuration MR systems. Vedi and coworkers (13) have demonstrated differences in meniscal position between sitting non–weight-bearing and sitting weight-bearing body positions reflecting the dynamic properties of the menisci.

In a recent study (14), it has been shown that the radial movement of both menisci in general is relatively small between the different positions, ranging between 0.6 and 1.6 mm as measured in the coronal MR imaging plane. As a result of this limited range of radial movement of the meniscus, meniscal protrusion (ie, the extension of any part of the meniscus beyond the tibial plateau [medially for the medial meniscus and laterally for the lateral meniscus]) is unusual in healthy knees and, if present, measures less than 3 mm for the medial and lateral meniscus (in the supine neutral position and in the supine 90° flexed position with internal or external rotation, as well as in the upright weight-bearing position) (14).

The dynamic characteristics of the knee menisci are maintained by the anatomic stabilizers of the knee, which, for the medial meniscus, include the medial collateral ligament (the deep fibers are attached to the peripheral margin of the medial meniscus) (33). The lateral meniscus is stabilized by the coronary ligament, the meniscofemoral ligaments, the arcuate ligament, and probably the meniscotibial ligament (25,33). Both menisci are additionally stabilized by the transverse ligament (23). If one of these supporting structures or the meniscus itself degenerates or is torn, the meniscus may become unstable.

The question of stability in a torn meniscus is important in deciding whether to resect or repair a meniscal lesion or to leave it alone (9,11,12). Lesion stability is assessed intraoperatively by means of palpation with a probe. If the meniscus or a fragment can be inappropriately displaced into the femorotibial joint, the meniscal tear is regarded as unstable. The concept of meniscal tear stability and the fact that orthopedic surgeons use stress tests, such as the grinding and reversed grinding test (21), for examination of patients suspected of having meniscal tears of the knee prompted our interest in evaluating patients with meniscal tears of the knee by using kinematic MR imaging and different body positions. In fact, our study has shown that by using kinematic MR imaging, movement of the entire meniscus or part of it more than 3 mm (as measured in the coronal plane at the level of the collateral ligaments; ie, meniscal displacement) was noted in 18 (42%) of 43 meniscal tears. In our study, meniscal displacement was slightly more frequent between the supine neutral and the 90° flexed position with external (for the medial meniscus) or internal rotation (for the lateral meniscus) (15 instances) than it was between the supine neutral and the upright weight-bearing body position (13 instances).

Notably, all 18 meniscal tears that showed displacement in our study were associated with an ipsilateral collateral ligament injury of grade II or III, whereas 22 of 25 remaining menisci with tears without displacement were associated with a normal collateral ligament or a grade I injury. Among the three nondisplaced meniscal tears with ipsilateral grade II collateral ligament injuries, protrusion was noted in two of these three instances, with meniscal tears observed in all three positions. Therefore, if protrusion of a meniscus with a tear is already visible in supine neutral position, additional displacement between other knee positions is unlikely.

The fact that only meniscal tears with an ipsilateral collateral ligament injury may displace underlines the importance of the collateral ligaments as key stabilizers for the knee menisci (34). The stabilizing function of the medial collateral ligament is of particular importance for the medial meniscus, where the deep fibers of the collateral ligament (the meniscofemoral and meniscotibial attachments and the coronary ligament) are firmly attached to the peripheral margin of the medial meniscus (24,25,33). The meniscotibial ligament is thought to stabilize the lateral meniscus at weight bearing in extension (25). Tissakht et al (27) have shown that the attachments of the medial meniscus and the medial collateral ligament are also important in limiting the motion of the medial meniscus. Another interesting aspect of our study results is the observation that patients with displaceable meniscal tears had significantly more pain than did patients with nondisplaceable meniscal tears, independent of associated injuries.

A study by Zanetti (7) has also shown that there is a striking variation in the frequency of certain meniscal tear configurations. Whereas horizontal and oblique meniscal tears were the most frequent type of tear in asymptomatic knees, complex and longitudinal tears were more frequently found in symptomatic knees. Similarly, the results of our study have also shown that horizontal and oblique meniscal tears were present only in the nondisplaceable menisci, whereas longitudinal tear configurations were exclusively noted among the displaceable meniscal tears. Hence, it may be hypothesized that horizontal and oblique meniscal tears are probably not painful because they are stable and are not associated with collateral ligament injuries.

Zanetti (7) also showed striking differences in MR imaging findings of the collateral ligament between the symptomatic and the asymptomatic knees. Collateral ligament injuries at the site of the meniscal tear were far more frequent in the symptomatic knees than in the contralateral asymptomatic knees (53% vs 6%). This result underlines the importance of associated collateral ligament injuries and meniscal tears and is in agreement with the results of our study, which have shown that patients with displaceable meniscal tears with ipsilateral collateral ligament injuries have significantly more pain than do patients with nondisplaceable meniscal tears without collateral ligament injuries.

We acknowledge the following limitations. A potential limitation is the measurement of meniscal movements under weight-bearing conditions, since the applied body position does not entirely reflect normal conditions under weight bearing. Another limitation may be the fact that it is unclear to what extent an injury of the anterior cruciate ligament may have influenced meniscal movement. However, since there was no statistical difference with regard to the frequency of anterior cruciate ligament injuries in patients with nondisplaceable and those with displaceable meniscal tears, this influence does not seem to be important. Another limitation may be the fact that multiple hypothesis tests were performed for comparing the data, because multiple testing increases the likelihood of being unable to detect differences. Finally, the number of the investigated knees was limited.

In conclusion, results of our study have demonstrated that displacement of meniscal tears of the knee can be demonstrated at kinematic MR imaging. Displaceable meniscal tears usually have longitudinal, radial, or complex configurations; such tears are associated with substantial ipsilateral collateral ligament lesions and pain.

	FOOTNOTES

 

Abbreviations: SE = spin echo

Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, D.W.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, L.B., A.M.L., K.T., L.L.; clinical studies, L.B., A.M.L., K.T., L.L.; and manuscript editing, L.B., A.M.L., M.Z., B.M., D.W.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 

1. Anderson MW. MR imaging of the meniscus. Radiol Clin North Am 2002;40:1081–1094.[CrossRef][Medline]
2. Maurer EJ, Kaplan PA, Dussault RG, et al. Acutely injured knee: effect of MR imaging on diagnostic and therapeutic decisions. Radiology 1997;204:799–805.[Abstract/Free Full Text]
3. Mackenzie R, Dixon AK. Clinical value of magnetic resonance imaging of the knee [abstr]. Acad Radiol 1996;3(suppl 1):S32.
4. Kornick J, Trefelner E, McCarthy S, Lange R, Lynch K, Jokl P. Meniscal abnormalities in the asymptomatic population at MR imaging. Radiology 1990;177:463–465.[Abstract/Free Full Text]
5. Boden SD, Davis DO, Dina TS, et al. A prospective and blinded investigation of magnetic resonance imaging of the knee: abnormal findings in asymptomatic subjects. Clin Orthop Relat Res 1992;282:177–185.
6. LaPrade RF, Burnett QM 2nd, Veenstra MA, Hodgman CG. The prevalence of abnormal magnetic resonance imaging findings in asymptomatic knees: with correlation of magnetic resonance imaging to arthroscopic findings in symptomatic knees. Am J Sports Med 1994;22:739–745.[Abstract/Free Full Text]
7. Zanetti M. Patients with suspected meniscal tears: prevalence of abnormalities seen on MR imaging of 100 symptomatic and 100 contralateral asymptomatic knees. AJR Am J Roentgenol 2003;181:635–641.[Abstract/Free Full Text]
8. Dandy DJ. The arthroscopic anatomy of symptomatic meniscal lesions. J Bone Joint Surg Br 1990;72:628–633.
9. Newman AP, Daniels AU, Burks RT. Principles and decision making in meniscal surgery. Arthroscopy 1993;9:33–51.[Medline]
10. Metcalf R. Arthroscopic meniscectomy. In: McGinty J, ed. Operative arthroscopy. 2nd ed. Philadelphia, Pa: Lippincott-Raven, 1996; 263–297.
11. DeHaven KE. Decision-making factors in the treatment of meniscus lesions. Clin Orthop Relat Res 1990;252:49–54.
12. Weiss CB, Lundberg M, Hamberg P, DeHaven KE, Gillquist J. Non-operative treatment of meniscal tears. J Bone Joint Surg Am 1989;71:811–822.[Abstract/Free Full Text]
13. Vedi V, Williams A, Tennant SJ, Spouse E, Hunt DM, Gedroyc WM. Meniscal movement: an in-vivo study using dynamic MRI. J Bone Joint Surg Br 1999;81:37–41.
14. Boxheimer L, Lutz AM, Treiber K, et al. MR imaging of the knee: position related changes of the menisci in asymptomatic volunteers. Invest Radiol 2004;39:254–263.[CrossRef][Medline]
15. Noyes FR, Stabler CL. A system for grading articular cartilage lesions at arthroscopy. Am J Sports Med 1989;17:505–513.[Abstract/Free Full Text]
16. Vande Berg BC. Assessment of knee cartilage in cadavers with dual-detector spiral CT arthrography and MR imaging. Radiology 2002;222:430–436.[Abstract/Free Full Text]
17. Rubin DA, Paletta GA Jr. Current concepts and controversies in meniscal imaging. Magn Reson Imaging Clin N Am 2000;8:243–270.[Medline]
18. De Smet AA, 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. AJR Am J Roentgenol 1993;161:101–107.[Abstract/Free Full Text]
19. Resnick D, Kang H. The knee. In: Resnick D, Kang HS, eds. Internal derangements of joints: emphasis on MR imaging. Philadelphia, Pa: Saunders, 1997; 595–662.
20. Vande Berg BC, Poilvache P, Duchateau F, et al. Lesions of the menisci of the knee: value of MR imaging criteria for recognition of unstable lesions. AJR Am J Roentgenol 2001;176:771–776.[Abstract/Free Full Text]
21. Apley G. The diagnosis of meniscus injuries. J Bone Joint Surg 1947;29:78–84.[Abstract/Free Full Text]
22. Jee WH, McCauley TR, Kim JM, et al. Meniscal tear configurations: categorization with MR imaging. AJR Am J Roentgenol 2003;180:93–97.[Abstract/Free Full Text]
23. Rubin DA. MR imaging of the knee menisci. Radiol Clin North Am 1997;35:21–44.[Medline]
24. Stoller D, Cannon W, Anderson L. The knee. In: Stoller DW, ed. Magnetic resonance imaging in orthopaedics and sports medicine. 2nd ed. Philadelphia, Pa: Lippincott-Raven, 1997; 203–442.
25. Crues JV, Stoller DW. The menisci. In: Mink JH, Reicher MA, Crues JV, Deutsch AL, eds. MRI of the knee. 2nd ed. New York, NY: Raven, 1993; 91–140.
26. Zanetti M, Steiner CL, Seifert B, Hodler J. Clinical outcome of edema-like bone marrow abnormalities of the foot. Radiology 2002;222:184–188.[Abstract/Free Full Text]
27. Tissakht M, Farinaccio R, Ahmed A. Effect of ligament attachments on the response of the knee menisci in compression and torsion: a final element study. Rosemont, Ill: Orthopedic Research Society, 1989; 313–314.
28. Breitenseher MJ, Trattnig S, Dobrocky I, et al. MR imaging of meniscal subluxation in the knee. Acta Radiol 1997;38:876–879.[Medline]
29. Gale DR, Chaisson CE, Totterman SM, Schwartz RK, Gale ME, Felson D. Meniscal subluxation: association with osteoarthritis and joint space narrowing. Osteoarthritis Cartilage 1999;7:526–532.[CrossRef][Medline]
30. Jamison RN, Gracely RH, Raymond SA, et al. Comparative study of electronic vs. paper VAS ratings: a randomized, crossover trial using healthy volunteers. Pain 2002;99:341–347.
31. Ohnhaus EE, Adler R. Methodological problems in the measurement of pain: a comparison between the verbal rating scale and the visual analogue scale. Pain 1975;1:379–384.[CrossRef][Medline]
32. Kawahara Y, Uetani M, Fuchi K, Eguchi H, Hayashi K. MR assessment of movement and morphologic change in the menisci during knee flexion. Acta Radiol 1999;40:610–614.[Medline]
33. Mow VC, Ratcliffe A, Chern K, Kelly MA. Structure and function relationships of the menisci of the knee. In: Mow VC, Arnoczky SP, Jackson DW, eds. Knee meniscus: basic and clinical foundations. New York, NY: Raven, 1992.
34. Brantigan O. The mechanics of the ligaments and menisci of the knee joint. J Bone Joint Surg 1941;23:44–66.[Abstract/Free Full Text]

This article has been cited by other articles:

				A. O. T. Mustonen, M. P. Koivikko, J. Lindahl, and S. K. Koskinen MRI of Acute Meniscal Injury Associated with Tibial Plateau Fractures: Prevalence, Type, and Location Am. J. Roentgenol., October 1, 2008; 191(4): 1002 - 1009. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services