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(Radiology. 2000;216:851-857.)
© RSNA, 2000

Musculoskeletal Imaging

Dual-Detector Spiral CT Arthrography of the Knee: Accuracy for Detection of Meniscal Abnormalities and Unstable Meniscal Tears1

Bruno C. Vande Berg, MD, PhD, Frederic E. Lecouvet, MD, PhD, Pascal Poilvache, MD, Jean-Emile Dubuc, MD, Bernard Bedat, MD, Baudouin Maldague, MD, Jean-Jacques Rombouts, MD and Jacques Malghem, MD

1 From the Departments of Radiology (B.C.V.B., F.E.L., B.M., J.M.) and Orthopaedic Surgery (P.P., J.E.D., B.B., J.J.R.), Cliniques Universitaires St Luc, Université Catholique de Louvain, 10 av Hippocrate, 1200 Brussels, Belgium. Received June 14, 1999; revision requested August 3; final revision received November 15; accepted December 6. Address correspondence to B.C.V.B. (e-mail: vandeberg@rdgn.ucl.ac.be).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To determine the sensitivity and specificity of dual-detector spiral computed tomographic (CT) arthrography of the knee in the detection of meniscal abnormalities and unstable meniscal tears.

MATERIALS AND METHODS: The meniscal changes in 50 consecutive patients who underwent dual-detector spiral CT of the knee after intraarticular injection of iodinated contrast material (0.55-mm effective section thickness, 0.75 pitch value, 0.3-mm increment reconstruction, 0.43-mm in-plane resolution, 0.3-mm longitudinal resolution) were determined by two observers and were compared with arthroscopic findings. The sensitivity and specificity of CT arthrography for the detection of meniscal abnormalities and unstable meniscal tears and the {kappa} statistics for assessing interobserver reproducibility were determined.

RESULTS: The sensitivity and specificity for the detection of meniscal abnormalities were 98% and 94%, respectively. The sensitivity and specificity for the detection of unstable meniscal tears were 97% and 90%, respectively. Interobserver agreement was excellent for the detection of meniscal abnormalities ({kappa} = 0.899) and of unstable meniscal tears ({kappa} = 0.885).

CONCLUSION: Dual-detector spiral CT arthrography of the knee is an accurate and reproducible method for detecting meniscal abnormalities and unstable meniscal tears.

Index terms: Knee, abnormalities, 4524.4852, 4524.4853, 4525.4852, 4525.4853 • Knee, CT, 4524.12112, 4524.12115, 4525.12112, 4525.12115 • Knee, ligaments, menisci, and cartilage, 4524.4852, 4524.4853, 4525.4852, 4525.4853


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Magnetic resonance (MR) imaging is the dominant imaging technique for evaluating internal derangements of the knee. Because MR imaging is noninvasive and has a clinically acceptable accuracy in the detection of meniscal and ligamentous lesions, it has largely replaced conventional knee arthrography (1–3). Developments in spiral computed tomographic (CT) technology with dual-detector arrays that enable submillimeter spatial resolution (4,5) raised the question of the potential use of dual-detector spiral CT arthrography of the knee for the assessment of meniscus lesions. We undertook this study to determine the sensitivity and specificity of dual-detector spiral CT scanning of the knee as a single imaging procedure performed after intraarticular injection of iodinated contrast material to detect meniscal abnormalities and unstable meniscal tears.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Patients
At our institution, MR imaging and spiral CT arthrography with iodinated contrast material are routinely performed to investigate internal derangement of the knee. The choice of the imaging technique mainly depends on the clinical findings. MR imaging is performed in patients with a history of recent major knee trauma, in patients with clinical suspicion of cruciate ligament tears, in patients with known allergic reaction to iodinated products, and in children. Spiral CT arthrography is performed in patients suspected to have meniscal or hyaline cartilage lesions. The waiting list for MR imaging is 5 weeks, and that for spiral CT arthrography is 1 week. Between February 1 and December 30, 1998, 450 MR imaging studies and 251 spiral CT arthrographic examinations of the knee were performed in our institution.

We reviewed the charts of 251 patients who underwent dual-detector spiral CT arthrography of the knee. The study population consisted of 50 consecutive patients who underwent spiral CT arthrography and subsequent arthroscopy at our institution but not prior arthroscopy in that knee. The other 201 patients included 12 who had undergone prior knee arthroscopy and subsequent arthroscopy, 69 who were referred by physicians outside of the institution, and 120 who did not undergo arthroscopy. The 40 men and the 10 women in the study group had a mean age ± SD of 44.9 years ± 14 (range, 23–77 years; median, 40 years).

All patients were referred by four orthopaedic surgeons (P.P., J.E.D., B.B., and J.J.R.) from our institution for right (n = 31) or left (n = 19) knee spiral CT arthrography because of clinical suspicion of a meniscal lesion. Patients with clinically obvious meniscal lesions were operated on without further investigations. Thirty-one patients had a history of knee trauma that had occurred 3 weeks to 5 years before CT arthrography (median delay, 9 weeks; mean delay, 45 weeks). The informed consent of patients was obtained before the arthrographic procedure. Ethical committee approval from our institution was not solicited since CT arthrography is routinely performed to assess internal derangement of the knee (6,7).

Arthrography
A volume of 10 mL of ionic contrast material (Hexabrix 320 [ioxaglate meglumine and ioxaglate sodium; 320 mg of iodine per milliliter]; Guerbet, Aulnay-sous-Bois, France) mixed with 1 mL of a 0.1% solution of epinephrine was injected under fluoroscopic control through a 20-gauge needle placed in the suprapatellar pouch of the knee joint after sterile skin preparation (8). Knee effusion, if present, was drained before injecting the contrast material. After intraarticular injection, patients were asked to walk about the room and to perform full-range knee flexions. The radiologist performing the procedure used fluoroscopy to evaluate for homogeneous coating of the menisci and articular surfaces by contrast material. No complications were encountered. Patients walked to the nearby CT scanner.

Spiral CT Scanning
CT studies were performed with a dual-detector helical unit (Twin RTS [real time scanning], Elscint-Picker, Haifa, Israel) with the spiral scanning mode. All patients were supine with 15° knee flexion. After a frontal projection scout image was obtained, 65 to 85 seconds of scanning was performed to image the area between the upper pole of the patella and the tibial plateaus. Spiral scanning was performed at 140 kVp and 135 mAs, with a focus of 0.75 mm. A dynamic oscillating focus was used (9). The field of view at acquisition was 430 mm. The table speed was 0.75 mm/sec (effective pitch of 0.75), and the effective section thickness was 0.55 mm.

For reconstruction, a 360° linear interpolation algorithm, a high-frequency kernel, an increment of 0.3 mm (40% section overlap), and a zoom factor of 1.94 were used. With the 360° linear interpolation algorithm, raw data from four contiguous sections were used to generate reconstructed images at 0.3-mm intervals, which provided a higher signal-to-noise ratio than for conventional CT images or images reconstructed with a 180° linear interpolation algorithm (10). A 180° linear interpolation algorithm would have provided thinner section sensitivity profiles but was not available with pitch values lower than 1 (11). The high-frequency kernel used for reconstruction enabled a spatial definition of 14 line pairs per centimeter with a theoretic in-plane resolution of 0.36 mm at the cutoff frequency of modulation and 6.5 line pairs per centimeter at 50% of the frequency of modulation. Images were reconstructed on a 512 x 512 matrix, and in-plane resolution was 0.43 mm. Longitudinal resolution was 0.3 mm because, with a pitch value of 0.75 and a reconstruction increment of 60% of the nominal section width, longitudinal resolution equaled the reconstruction increment of 0.3 mm (12,13). The procedure duration was 10 minutes for patient positioning and image acquisition and 10 minutes for reconstruction. All reconstructed images were prospectively stored on erasable optical disks.

Image Analysis
A meniscal abnormality was defined by the presence of contour irregularity, peripheral separation, or tear of a meniscus. Contour irregularity was defined by altered meniscal shape with truncation, blunting, flattening, and/or rounding of the inner borders. Peripheral meniscal separation was defined by the presence of contrast material between the substance of the meniscus and the capsule, after the exclusion of normal anatomic variations (14). Meniscal tear was defined by the presence of contrast material tracking into the substance of the meniscus.

Meniscal abnormalities were classified as stable or unstable according to the pattern and extent of the lesions and the presence of a meniscal fragment, which was defined as a piece of meniscus that was partially separated from the meniscus (15,16). A meniscal lesion was considered to be stable if it consisted of a contour abnormality, partial horizontal or vertical tear, radial tear, or a complete vertical tear or peripheral separation involving less than one-third of the meniscus length (Fig 1,A). A meniscal lesion was considered to be unstable if it consisted of a complete vertical tear or a meniscal separation involving more than one-third of the meniscus length or a tear with meniscal fragments, which included radial, oblique, or horizontal tears, in continuity with a vertical tear (Fig 1,B).



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  		Figure 1. A, Schematic drawing of a meniscal segment with stable meniscal lesions, which include a short vertical tear or separation (large thick solid arrow), a partial vertical tear (large thin solid arrow), a horizontal tear (arrowheads), a radial tear (small solid arrows), and a contour irregularity (open arrow). B, Schematic drawing of a meniscal segment with unstable meniscal lesions, which include a vertical tear or separation (solid arrows) or complex lesions with a radial tear associated with a horizontal tear (arrowheads) or with a vertical tear (open arrow) (parrot-beak tear).

 
Fragment size and location were determined. Small or large fragments were smaller than one-third or larger than two-thirds of the meniscus, respectively. Other fragments were medium-sized. Fragments separated from the meniscus by less than 3 mm were considered to be undisplaced. Displaced meniscal fragments consisted of fragments that had lost their anatomic location and that were found in the intercondylar notch, the superior meniscal recess, the inferior meniscal recess, or the femorotibial articular space.

A musculoskeletal radiologist (B.C.V.B.) with 10 years of experience (observer 1) reviewed images from 150 CT arthrographic examinations performed during the study that included the 50 procedures from the study population. This observer ignored which patients subsequently underwent arthroscopy. A musculoskeletal radiologist (F.E.L.) with 4 years of experience (observer 2) reviewed the 50 knee CT arthrographic images from the study population.

The two observers, blinded to the arthroscopic findings, separately reviewed the images from all of the examinations on a workstation (Omnipro; Silicon Graphics, Mountain View, Calif). Sagittal and coronal reformations with 0.45 mm thickness and a 2-mm interval were viewed at bone settings (window width, 1,900 HU; window level, 450 HU) with a zoom factor of 2 to 4.5. Curvilinear transverse reformations planned on sagittal images of each femorotibial compartment with 0.45 mm thickness and a 0.2-mm interval were obtained separately for both menisci with window settings and zoom factors identical to those used for sagittal and coronal reformations. The time necessary to evaluate the status of the meniscus and to determine the stability of the meniscal lesions was 2–5 minutes.

Arthroscopy
All knee arthroscopic examinations were performed by three orthopaedic surgeons (P.P., J.E.D., B.B.) at a mean delay of 8.2 weeks (median delay, 7 weeks; range, 1–24 weeks) after spiral CT arthrography. Sagittal, coronal, and transverse reconstructed spiral CT arthrographic images were available to surgeons on film. Original reports made by the three radiologists (B.C.V.B., F.E.L., J.M.) included meniscal lesion description, with notation of the presence or absence of displaced fragments. Reports made by the three radiologists did not mention whether the lesions were considered to be stable or unstable.

At the time of arthroscopy, meniscal lesion patterns, including tear, peripheral separation, and contour irregularities, were noted on charts. Drawings that showed the locations and configurations of all meniscal abnormalities were made. Meniscal lesions were considered to be unstable if displaced or mobile meniscal fragments were found at inspection and palpation during arthroscopy, according to standard criteria (15). Meniscal lesions without meniscal flaps or displaced fragments were considered to be stable.

Statistical Analysis
Surgical notes and drawings were used as the standard of reference for determining meniscal integrity and meniscal lesion stability. Sensitivity, specificity, and positive and negative predictive values with 95% CIs for the detection of meniscal abnormalities and unstable meniscal tears among abnormal menisci were calculated for both observers. Interobserver reproducibility for the detection of meniscal abnormalities and of unstable meniscal tears and for the locations and sizes of fragments was assessed by using the {kappa} statistic for categoric parameters. A {kappa} statistic of 0.41–0.60 represented a poor level of interobserver agreement; a {kappa} statistic of 0.61–0.80, good agreement; and a {kappa} statistic of 0.81–1.00, excellent agreement.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Meniscal Abnormalities
Thirty-five of 36 medial and 17 of 17 lateral menisci that were found to be abnormal at arthroscopy were also found to be abnormal at spiral CT arthrography by observer 1. Among the 14 medial and 33 lateral menisci that were normal at arthroscopy, 14 medial and 30 lateral menisci were normal at spiral CT arthrography per observer 1. One medial meniscal abnormality at arthroscopy was overlooked at spiral CT arthrography by observer 1. Three normal lateral menisci at arthroscopy were considered to be abnormal at spiral CT arthrography by observer 1. For observer 1, the sensitivity and specificity of spiral CT arthrography for the detection of a meniscal abnormality were 98% and 94%, respectively (Table 1). For observer 2, the sensitivity and specificity for the detection of a meniscal abnormality were 98% and 96%, respectively.


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  		TABLE 1. Sensitivity, Specificity, and Positive and Negative Predictive Values for the Detection of Meniscal Abnormalities at CT Arthrography of the Knee with Knee Arthroscopy as the Standard
 
Meniscal Tear Stability
All 24 medial and seven of eight lateral meniscal tears that were found to be unstable at arthroscopy were also found to be unstable at spiral CT arthrography by observer 1 (Table 2). Among the 12 medial and nine lateral menisci with a stable tear at arthroscopy, 11 medial and eight lateral menisci with a stable tear were found at spiral CT arthrography by observer 1 (Fig 2). One lateral meniscal tear that was unstable at arthroscopy was considered to be stable at spiral CT arthrography by observer 1. One medial meniscal lesion and one lateral meniscal lesion that were abnormal and stable at arthroscopy were considered unstable at spiral CT arthrography by observer 1. For observer 1, the sensitivity and specificity of spiral CT arthrography for the detection of unstable meniscal tears were 97% and 90%, respectively (Table 3). For observer 2, the sensitivity and specificity for the detection of unstable meniscal tears were 94% and 81%, respectively.


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  		TABLE 2. Distribution of Stable and Unstable Meniscal Tears at Arthroscopy and Spiral CT Arthrography as Determined by Observers 1 and 2
 


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  		Figure 2a. (a) Sagittal reformation reconstructed after spiral CT arthrography of the left knee of a 35-year-old man shows a tear (arrow) of the posterior horn of the medial meniscus. (b) Coronal and (c) curvilinear transverse reformations show the extent of the lesion (arrowheads) in its transverse plane. The tear was considered to be stable at CT arthrography. At arthroscopy, a stable longitudinal tear of the posterior horn of the medial meniscus was found.

 


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  		Figure 2b. (a) Sagittal reformation reconstructed after spiral CT arthrography of the left knee of a 35-year-old man shows a tear (arrow) of the posterior horn of the medial meniscus. (b) Coronal and (c) curvilinear transverse reformations show the extent of the lesion (arrowheads) in its transverse plane. The tear was considered to be stable at CT arthrography. At arthroscopy, a stable longitudinal tear of the posterior horn of the medial meniscus was found.

 


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  		Figure 2c. (a) Sagittal reformation reconstructed after spiral CT arthrography of the left knee of a 35-year-old man shows a tear (arrow) of the posterior horn of the medial meniscus. (b) Coronal and (c) curvilinear transverse reformations show the extent of the lesion (arrowheads) in its transverse plane. The tear was considered to be stable at CT arthrography. At arthroscopy, a stable longitudinal tear of the posterior horn of the medial meniscus was found.

 

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  		TABLE 3. Sensitivity, Specificity, and Positive and Negative Predictive Values for the Detection of Unstable Meniscal Tears among Meniscal Lesions at Spiral CT Arthrography of the Knee with Knee Arthroscopy as the Standard
 
At spiral CT arthrography, 16 small, seven medium, and 10 large fragments were found by observer 1. Sixteen undisplaced and 17 displaced meniscal fragments were found. Displaced fragments were located in the intercondylar notch (n = 12) (Fig 3), in the superior meniscal recess (n = 1) (Fig 4), in the inferior meniscal recess (n = 2), and in the femorotibial articular space (n = 2) (Fig 5).



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  		Figure 3a. (a) Coronal reformation obtained after spiral CT arthrography of the right knee of a 36-year-old man shows a horizontal tear (arrow) in a small medial meniscus. A meniscal fragment (arrowheads) is found in the intercondylar notch and indicates an unstable meniscal tear. (b) Sagittal reformations show a meniscal fragment (arrow) flipped anteriorly and laterally in the intercondylar notch (double posterior cruciate ligament sign [arrowheads]). At arthroscopy, a large bucket-handle tear with a meniscal fragment displaced in the intercondylar notch was found.

 


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  		Figure 3b. (a) Coronal reformation obtained after spiral CT arthrography of the right knee of a 36-year-old man shows a horizontal tear (arrow) in a small medial meniscus. A meniscal fragment (arrowheads) is found in the intercondylar notch and indicates an unstable meniscal tear. (b) Sagittal reformations show a meniscal fragment (arrow) flipped anteriorly and laterally in the intercondylar notch (double posterior cruciate ligament sign [arrowheads]). At arthroscopy, a large bucket-handle tear with a meniscal fragment displaced in the intercondylar notch was found.

 


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  		Figure 4. Anterior (top) to posterior (bottom) coronal reformations obtained after spiral CT arthrography of the left knee of a 56-year-old man. Anteriorly, a meniscal fragment (thick arrows) is observed in the superior meniscal recess. The attachment of the meniscal fragment to the body of the meniscus (arrowhead) is found below the displaced fragment. More posteriorly, the meniscal tear with substance loss (thin arrow) is clearly visible. Unstable meniscal tear was found at arthroscopy.

 


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  		Figure 5a. (a) Sagittal reformations obtained after CT arthrography of the right knee of a 45-year-old man show a complex tear (large arrows) of the posterior horn of the medial meniscus, with a fragment displaced into the articular space (arrowheads). Focal cartilage ulceration (small arrows) is found in the mid third of the femoral condyle. (b) Transverse reformation of the medial meniscus best demonstrates the complex tear (black arrows) of the posterior horn, the displaced meniscal fragment (arrowheads), and a more anterior longitudinal tear (white arrow). An unstable tear of the medial meniscus was found at arthroscopy.

 


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  		Figure 5b. (a) Sagittal reformations obtained after CT arthrography of the right knee of a 45-year-old man show a complex tear (large arrows) of the posterior horn of the medial meniscus, with a fragment displaced into the articular space (arrowheads). Focal cartilage ulceration (small arrows) is found in the mid third of the femoral condyle. (b) Transverse reformation of the medial meniscus best demonstrates the complex tear (black arrows) of the posterior horn, the displaced meniscal fragment (arrowheads), and a more anterior longitudinal tear (white arrow). An unstable tear of the medial meniscus was found at arthroscopy.

 
Reproducibility
Interobserver reproducibility was excellent for the detection of meniscal abnormality and unstable meniscal tear and for determining the location of displaced fragments (Table 4). Interobserver reproducibility for the estimation of meniscal fragment size was excellent for the lateral meniscus, poor for the medial meniscus, and good for both menisci (Table 4).


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  		TABLE 4. Interobserver Reproducibility as {kappa} Statistics for the Detection of Meniscal Abnormalities and Unstable Meniscal Tears and for the Determination of the Locations and Sizes of Meniscal Fragments
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Findings of this study demonstrated that dual-detector spiral CT arthrography of the knee enabled accurate detection of meniscal abnormalities and of unstable meniscal tears. First, meniscal abnormalities were detected with sensitivities and specificities of 98% and 94%, respectively, for observer 1 and of 98% and 96%, respectively, for observer 2. These values were equivalent to those in most studies with MR imaging (1,2,16,17) and were superior to those in studies with conventional arthrography (18,19).

Second, spiral CT arthrography of the knee enabled recognition of unstable meniscal tears with sensitivities and specificities of 97% and 90%, respectively, for observer 1 and of 94% and 81%, respectively, for observer 2. Meniscal tear stability is an essential criterion for deciding whether to resect, repair, or leave alone a meniscal lesion (20,21) and is best determined with direct depiction and palpation at arthroscopy (15,22).

Poor performance of MR imaging in the recognition of peripheral meniscal separation (23) and of displaced meniscal fragments smaller than one-third of the meniscus (16,24) has been reported. MR criteria for meniscal tear instability have been proposed (25) but to our knowledge have not been validated. Findings of previous studies (3,26,27) with conventional CT performed with 1-mm-thick sections after arthrography showed that conventional CT enables the detection of displaced meniscal fragments. The finding that spiral CT arthrography enabled recognition of stable meniscal tears and unstable meniscal tears represents a step further in the assessment of meniscal lesions. The potential value of the preoperative determination of meniscal tear stability that would enable the selection of an unstable meniscal tear for resection remains to be assessed in large clinical studies.

We can only postulate as to why spiral CT arthrography of the knee enabled accurate assessment of meniscal integrity and meniscal tear stability. Most likely, the value of spiral CT arthrography derives from its spatial resolution and multiplanar capacity. Developments in CT technology of two parallel arcs of detectors doubled the speed of data acquisition, which could be traded for increased volume of coverage, improved image quality, and high temporal or high spatial resolution (4). In this study, parameters used for image acquisition and reconstruction were balanced toward high spatial resolution with 0.43-mm in-plane resolution and 0.3-mm longitudinal resolution. Stair-step artifacts that can be observed on reconstructed images on surfaces inclined with respect to the longitudinal axis were not observed because the detector collimation and table increment were much lower than the longitudinal dimensions of the menisci (28).

The multiplanar capacity largely contributed to the value of spiral CT arthrography. Sagittal and coronal images reconstructed after spiral CT arthrography depicted meniscal lesions in a manner similar to conventional MR imaging, with alterations of the normal triangular meniscal shape or the appearance of abnormal attenuation within the meniscal substance. Furthermore, submillimeter-thick transverse curvilinear sections reconstructed in the meniscal plane provided excellent delineation of radial and oblique components of meniscal tears, with subsequent accurate detection of undisplaced meniscal fragments. The importance of thin transverse images in the detection and anatomic delineation of complex meniscal tears has already been emphasized at MR imaging (16, 29–31).

Single- and not double-contrast arthrography was performed because both menisci can be scanned simultaneously after single-contrast arthrography. At double-contrast arthrography, the two menisci must be scanned successively, and different patient positions are needed for articular space distention and air repletion (26,32). Conventional fluoroscopy was used to control the injection and to evaluate for the successful coating of menisci by contrast material to limit the procedure duration at the CT unit. Alternatively, the procedure could be controlled by using CT fluoroscopy if no conventional room were available.

The imaging technique, number and selection of patients, and lesion definitions used in the current study limited our results. First, results obtained with dual-detector spiral CT arthrography and submillimeter spatial resolution may not be extrapolated to CT arthrography with standard spatial resolution. Second, the small number of patients implies cautious interpretation of the results, although 95% CIs for sensitivity and specificity remain within the range of clinically acceptable values. A larger series of patients in a multicentric study is needed to validate our results.

Third, patients were selected by the orthopaedic surgeons (P.P., J.E.D., B.B., J.J.R.) who decided first that spiral CT arthrography should be performed and second that surgery should be performed. The fact that patients with major acute knee trauma or suspected cruciate ligament lesions were investigated by using MR imaging rather than spiral CT arthrography could have influenced the meniscal lesion patterns that were observed at spiral CT arthrography (33). However, 31 of 50 patients had a history of knee trauma, and trauma-related lesion patterns were observed.

Finally, the criteria for unstable meniscal tears at arthrography require in-depth evaluation. Assessment of the longitudinal extent of a vertical tear or peripheral separation and of the presence of displaced or undisplaced meniscal fragments appeared sufficient to enable accurate and reproducible detection of unstable tears. It is likely that the excellent interobserver reproducibility was biased by the fact that both observers routinely work conjointly. The fact that interobserver reproducibility in the estimation of meniscal fragment size was poor in the medial compartment and excellent in the lateral compartment should be addressed in a study based on more numerous cases with more precise arthroscopic description of the lesions.

The clinical value of MR imaging in the assessment of internal derangement of the knee derives from its ability to depict not only meniscal lesions but also soft-tissue and bone marrow lesions. The current study was focused on meniscal lesions not only for the sake of clarity but also because of the selection criteria used by the orthopaedic surgeons at our institution who use MR imaging to examine patients suspected to have anterior cruciate tears. In the current series of 50 patients who underwent surgery, four of five anterior cruciate ligament tears that were found at arthroscopy were also recognized at CT arthrography by using criteria similar to those used to analyze MR images. The limited number of observations does not allow us to draw any conclusion. To our knowledge, the ability of spiral CT arthrography to depict cartilage, ligament, and soft-tissue lesions adjacent to the articular space remains to be determined.

Spiral CT arthrography is definitely more invasive than conventional MR imaging. It uses ionizing radiation and has the potential complications inherent to intraarticular injection of iodinated contrast material (34). Comparative studies between spiral CT arthrography and MR imaging of the knee are needed to define conditions in which spiral CT arthrography could benefit patients in spite of its increased invasiveness.

Dual-detector spiral CT of the knee performed after intraarticular injection of iodinated contrast material enabled accurate and reproducible detection of meniscal abnormalities and of unstable meniscal tears.


   ACKNOWLEDGMENTS
 
The authors thank Alain Vlassenbroek, PhysD, of Elscint-Picker, Brussels, Belgium, for optimizing the technical parameters for image acquisition and reconstruction, Françoise Martin for secretarial assistance, and Eric Ligot for photography. This study is dedicated to the memory of Franz Vande Berg, MD (1901–1961), who contributed to the development of knee arthrography in Belgium.


   FOOTNOTES
 
Author contributions: Guarantor of integrity of entire study, B.C.V.B.; study concepts and design, B.C.V.B., F.E.L.; definition of intellectual content, B.C.V.B., F.E.L., J.M.; literature research, B.C.V.B.; clinical studies, B.C.V.B., F.E.L., J.M.; data acquisition, B.C.V.B., F.E.L., P.P., J.E.D., B.B.; data analysis, B.C.V.B., F.E.L.; statistical analysis, B.C.V.B.; manuscript preparation, editing, and review, all authors.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Crues JV, III, Mink J, Levy TL, Lotysch M, Stoller DW. Meniscal tears of the knee: accuracy of MR imaging. Radiology 1987; 164:445-448.[Abstract/Free Full Text]
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