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  Received: 7 April 1999Revision requested: 26 May 1999Revision received: 17 June 1999Accepted: 18 June 1999 Abstract Objective. To comparefour imaging methods in the evalua-tion of the postoperative meniscus:conventional arthrography, conven-tional MR imaging, MR arthrogra-phy with iodinated contrast material,and MR arthrography with gadolini-um-based contrast material.  Design and patients. Thirty-three pa-tients referred for knee MR examina-tions with a history of meniscal sur-gery were studied prospectively. Atthe first patient visit, conventionalMR examination was followed by anMR arthrogram with gadolinium-based contrast material. At the sec-ond visit, a conventional arthrogramwith iodinated contrast material wasfollowed immediately by an MR ex-amination. Imaging examinationswere interpreted by a masked reader,and then compared with the resultsof repeat arthroscopic surgery in 12patients.  Results. The correct evaluation of the status of postoperative menisciwas allowed in 12 of 13 patients(92%) by MR arthrography using ga-dolinium-based contrast agent, 10 of 13 patients (77%) by conventionalMR examination, 9 of 12 patients(75%) by MR arthrography, and 7 of 12 patients (58%) by conventionalarthrography. Conclusion. Intra-articular fluid isadvantageous in the evaluation of patients with a suspected meniscalretear. MR arthrography with gado-linium-based contrast material is themost accurate imaging method forthe diagnosis of meniscal retears. Key words Arthrography, knee · Arthroscopic surgery, knee · Meniscus · MR imaging, knee · MR arthrography, knee Skeletal Radiol (1999) 28:508–514©International Skeletal Society 1999 ARTICLE Robert L. SciulliRobert D. BoutinRobert. R. BrownKhanh D. NguyenClaus MuhleNittaya LektrakulMini N. PathriaRobert PedowitzDonald Resnick Evaluation of the postoperative meniscus of the knee: a study comparing conventionalarthrography, conventional MR imaging, MR arthrography with iodinated contrast material, and MR arthrography  with gadolinium-based contrast material Introduction Meniscal tears are commonplace and are a well-recog-nized source of knee pain and disability. Meniscal tearscurrently can be treated with several meniscal conserv-ing techniques, including partial meniscectomy [1], me-niscal repair with suture [2], and meniscal repair withbioabsorbable arrows [3].Conventional MR imaging of the postoperative menis-cus has been reported to have unreliable results [4], with ac-curacies generally ranging between 38% [5] and 82% [6] R.L. Sciulli, M.D. · N. Lektrakul, M.D.M.N. Pathria, M.D. · D. Resnick, M.D.Department of Radiology, Veterans Affairs Medical Center, San Diego, California, USAR.D. Boutin, M.D.National Orthopedic Imaging Associates,Marin Radiology Medical Group,San Mateo, California, USAR.R. Brown, M.D.Department of Radiology, Hospital for Joint Diseases, New York, New York, USAK.D. Nguyen, M.D.Department of Radiology, Via Christi Regional Medical Center, Wichita, Kansas, USAR. Pedowitz, M.D.Department of Orthopedics, UCSD School of Medicine, San Diego, California, USAC. Muhle, M.D.Department of Diagnostic Radiology, University of Kiel, GermanyD. Resnick, M.D. (  )Osteoradiology-114, Veterans Affairs Medical Center, 3350 La Jolla Village Drive, San Diego, CA 92161, USA  509 (Fig. 1). The conventional diagnostic criteria used to diag-nose meniscal tears cannot necessarily be applied to thepostoperative meniscus for two reasons. First, when a par-tial meniscectomy is performed, hyperintense intrasub-stance (grade 1 or 2) signal intensity can be converted intograde 3 signal intensity, thus simulating a meniscal tear. Inaddition, a healing tear (e.g., after meniscal repair) also maybe seen as hyperintense signal intensity in meniscal sub-stance owing to the presence of granulation tissue. Conse-quently, MR arthrography with gadolinium-based contrastmaterial has been suggested as a means of improving diag-nostic accuracy in patients who have had more than 25% of the meniscus resected [7]. However, no study has comparedthe effectiveness of conventional MR imaging and MR ar-thrography using gadolinium-based contrast material versusless expensive alternative imaging techniques: conventionalarthrography and MR arthrography using saline or iodina-ted contrast material. Given our cost-conscious environmentand the increasing number of patients with prior meniscalsurgery who present with suspected meniscal retears, wesought to assess the usefulness of these imaging techniques.The purpose of this study was to compare the accuracyof four imaging techniques – conventional arthrography,conventional MR imaging, MR arthrography using iodi-nated contrast material, and MR arthrography using gado-linium-based contrast material – in the evaluation of thepostoperative meniscus for a recurrent or residual tear. Materials and methods Patient population and imaging protocolPatients were eligible for inclusion in this study if they had hadprior meniscal surgery and presented with new knee symptomssuggesting a meniscal retear. Using these inclusion criteria, 33 pa-tients were prospectively enrolled in the study. There were 31 menand two women with an average age of 42 years and an age rangeof 22–66 years. Following clinical examination and informed pa-tient consent, an extensive imaging protocol was implementedwhich had been approved by the Human Subjects Committee atour institution. The imaging protocol, involving two different ar-thrographic procedures and three different MR imaging studies,was accomplished during two patient visits.During the first patient visit, a conventional MR examinationof the knee was performed. This examination included sagittalproton density (PD) (TR/TE 2300/30) and T2-weighted (TR/TE2300/80) spin-echo, and coronal T1-weighted (TR/TE 600/13)spin-echo and fat-suppressed PD fast spin-echo (FSE) (TR/TE3000/21) pulse sequences. In addition, fat-suppressed sagittal andcoronal T1-weighted (TR/TE 500–700/13–16) spin-echo sequenc-es were acquired as a reference for the MR arthrogram with gado-linium-based contrast material which followed later that same day.This MR arthrogram was performed by first diluting 1 ml of gado-pentetate dimeglumine (Magnevist, Schering, Berlin, Germany) in250 ml of sterile saline. After confirming the intra-articular posi-tioning of a 21-guage needle with less than 1 ml of iodinated con-trast material (iothalamate meglumine 202 mg/ml, Conray 43,Mallinckrodt, St. Louis, Mo.; or iohexol 240 mg/ml, Omnipaque,Nycomed, Princeton, N.J.), 20–40 ml of diluted gadolinium-basedcontrast material was injected. No epinephrine was administered.MR imaging in the sagittal and coronal planes using fat-sup-pressed T1-weighted (TR/TE 500–700/13–16) spin-echo sequenc-es was initiated within 30 min of intra-articular injection withoutany intervening exercise or manipulation of the knee. Prior to eachMR imaging examination, an elastic bandage was wrapped aroundthe suprapatellar region in an attempt to increase intra-articularpressure.During a second patient visit, a conventional arthrogram of theknee was performed by injecting 20–40 ml of iodinated contrastmaterial intra-articularly. The iodinated contrast material was usedas a surrogate for saline, both of which display intermediate T1-weighted and high T2-weighted signal intensity. During fluor-oscopic monitoring, multiple radiographs were obtained in variousobliquities, both with and without stress maneuvers applied to theknee. Within 30 min of the conventional arthrogram, the patientunderwent a third and final MR imaging examination. This MRarthrogram utilized iodinated contrast material and employed PD(TR/TE 2216/30) and T2-weighted (TR/TE 2300/80) spin-echosequences in the sagittal and coronal planes. For each of the MRexaminations the slice thickness was 3–4 mm with a 0.5–1.0 mminterslice gap, the matrix was 256 × 256, and the field of view was14 cm.Of the 33 patients initially enrolled in the study, the entire pro-tocol was completed in 16 patients. In the remaining 17 patients,two ( n =3) or three ( n =5) of the four imaging techniques were ac-complished. The entire imaging protocol was completed within a3-week period with only three exceptions; the longest delay be-tween the two patient visits was 12 weeks (in one case).Image analysis and second-look arthroscopyOn all MR imaging examinations, the criteria used to diagnose arecurrent meniscal tear were: (1) fluid entering the meniscal sub- Fig. 1A, B Normal postopera-tive meniscus mimicking a tear.When a partial meniscectomy( dotted lines ) is performed, hy-perintense intrasubstance(grade 1 or 2) signal intensity( A , curved arrow ) can be con-verted into grade 3 signal inten-sity ( B , curved arrow ), thussimulating a meniscal tear  510stance, (2) separation or displacement of the meniscus, (3) agrossly irregular meniscal contour, or (4) a combination of thesefindings. On the conventional MR images, a linear or wedge-shaped area of intermediate or high signal intensity that extendedto an articular surface was also interpreted as a meniscal tear.Menisci that appeared small, blunted, or had grade 1 or 2 signalintensity [8] were not interpreted as torn. On the conventional ar-thrograms, the sole diagnostic criterion for meniscal retear wasiodinated contrast material extending into the substance of themeniscus.Each imaging study was assessed in a randomized, retrospec-tive fashion by a masked observer experienced in both MR imag-ing and conventional arthrography of the knee. The MR arthro-grams were interpreted with the benefit of the precontrast fat-sup-pressed T1-weighted images described previously. In order to as-sess diagnostic accuracy and identify causes of misinterpretationby the masked observer, a second experienced observer subse-quently reviewed the masked interpretations and all imaging stud-ies, using second-look arthroscopic findings as the gold standard.Errors in imaging interpretation by the masked observer were cat-egorized according to DeSmet et al. [9] as unavoidable errors, in-terpretation errors, or errors related to equivocal imaging findingsof a meniscal tear.Of the 33 patients entered in the study, 12 underwent second-look arthroscopy; these patients formed the basis for our compara-tive analysis. Of these 12 patients, 10 underwent the entire imag-ing protocol and two did not. A total of 13 postoperative menisciwere evaluated in these patients. Surgery was accomplished within2 months following completion of the imaging protocol, with oneexception in which there was a delay of 5 months between imag-ing and surgery. Arthroscopic surgery was performed by three dif-ferent experienced orthopedic surgeons who were not masked tothe imaging findings. In five patients, the imaging studies showedno meniscal retear, and no surgery was performed. In the remain-ing 16 patients, surgery was deferred or the patient was lost to fol-low-up evaluation. A chi-square statistical analysis was performedthat compared the results of each of the imaging techniques withone another. Results At second-look arthroscopy, 11 of 12 patients had menis-cal tears (Table 1). A total of 12 meniscal tears were ob-served at surgery: nine medial and three lateral. The cor-responding imaging results are displayed in Table 2.Conventional arthrography correctly demonstrated 7(58%) of 12 meniscal tears (Fig. 2). However, this ex-amination yielded one false-positive and four false-neg-ative results. Conventional MR imaging allowed cor-rect diagnosis of 10 (77%) of 13 meniscal retears (Figs.3, 4) with one false-positive and two false-negativecases. MR arthrography with iodinated contrast materi-al yielded the correct diagnosis in 9 (75%) of 12 cases(Fig. 5), with one false-positive and two false-negativeresults. MR arthrography with gadolinium-based con-trast material correctly demonstrated 12 (92%) of 13postoperative menisci (Fig. 6), with only one false-neg-ative case. Re-review of the data by the second observ-er found that the incorrect imaging interpretations re-sulted either from unavoidable errors or from equivocalarthrographic findings, rather than errors in interpreta-tion per se.Using chi-square statistical analysis, the only signifi-cant difference was between conventional arthrographyand MR arthrography using gadolinium contrast material( P <0.05). No statistically significant difference wasfound when comparing any of the other imaging tech-niques. Table 1 Comparison of imag-ing examinations with surgicalresults (  M  male, F  female,  MM  medial meniscus tear,  LM  later-al meniscus tear, dash (–) ex-amination not performed)Patient no. Conventional Conventional IodinatedGadolinium Surgical Age/SexarthrographyMR imagingMR arthrographyMR arthrographyfindings1. 32/MLMLMLMLMLM2. 33/MNo tearLMLMLMLM3. 30/MMMMMMMMMMM4. 62/MMMMMMMMMMM5. 47/MMMMMMMNo tearNo tear 6. 53/M–No tear–No tearMM7. 60/MNo tearMMNo tearMMMM8. 41/MNo tearMMMMMMMM9. 49/MMMMMMMMMMM10. 43/MMMNo tearNo tearMMMM11. 46/MMMMMMMMMMMNo LM tearLMLMLMLM12. 27/MMMMMMMMMMM Table 2 Imaging results ( n isthe number of menisci exam-ined with this imaging method,with subsequent second-look arthroscopy used as the goldstandard)Imaging True False True False Accuracy methodpositivepositivenegativenegative(%)Conventional arthrography ( n =12)*710458Conventional MR imaging ( n =13)1010277Iodinated MR arthrography ( n =12)910275Gadolinium MR arthrography ( n =13)1101192  511 Discussion Knee arthroscopy has become an increasingly commonprocedure and now is the seventh most frequent opera-tion performed in the United States (632,000 proceduresannually) [10]. In these patients with postoperative kneepain, the possibility of a recurrent or residual meniscaltear often is a chief clinical concern [11]. Since repeatarthroscopy is both invasive and expensive, imaging iscommonly considered an alternative method of noninva-sive diagnosis. This research project was initiated to ad-dress the controversy over the single most effective im- Fig. 2A,B Medial meniscus retear in a 27-year-old man. A Con-ventional arthrogram demonstrates iodinated contrast materialwithin the medial meniscus retear ( arrow ). B Sagittal proton den-sity (TR/TE 2216/30) MR arthrogram with iodinated contrast ma-terial demonstrates increased signal intensity within the medialmeniscal retear ( arrow ) Fig. 3 Lateral meniscus retear in a 32-year-old man. Coronal T2-weighted (TR/TE 3000/80) MR image demonstrates the lateralmeniscus retear ( arrow ) with sizeable joint effusion and fluidwithin the tear Fig. 4 Medial meniscus retear in a 62-year-old man. Sagittal T2-weighted (TR/TE 2300/80) MR image demonstrates a diminutiveposterior horn of the medial meniscus ( white arrow ) owing to par-tial meniscectomy. Note the presence of joint fluid extending intothe medial meniscus retear ( curved arrow ) in this patient who hada large joint effusion Fig. 5A,B Medial and lateral meniscus retears in a 46-year-oldman. Sagittal T2-weighted (TR/TE 2300/80) MR arthrogram withiodinated contrast material demonstrates retears ( arrows ) of themedial meniscus ( A ) and lateral meniscus ( B ) aging technique for evaluation of the postoperative me-niscus.Diagnostic accuracies and considerations Conventional arthrography Conventional arthrography was once a widely used tech-nique for the evaluation of meniscal tears, with a report-ed accuracy of between 73% and 97% in unoperatedknees [12–15]. Conventional arthrography of the postop-
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