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MR Arthrography of Postoperative Knee: For Which Patients Is It Useful?¹

¹ From the Neuroimaging Institute, 27 E Hibiscus Blvd, Melbourne, FL 32901. Received August 7, 2002; revision requested September 24; final revision received January 23, 2003; accepted February 24. Address correspondence to T.M. (e-mail: tmageerad@cfl.rr.com).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To assess which postoperative patients benefit most from MR arthrography of the knee.

MATERIALS AND METHODS: One hundred consecutive MR arthrograms obtained in patients who had previous knee surgery underwent retrospective review in consensus by three radiologists after prospective reading by one of the three radiologists. Criterion on MR arthrograms for a retear was abnormal tracking of an intraarticular dilute gadolinium-based contrast material and saline mixture into the substance of a meniscus. Patients were separated into three groups: those with more than 25% meniscal resection, those with less than 25% meniscal resection, and those with meniscal repair. All 100 patients had preoperative MR images to review directly in conjunction with the postoperative MR images. Fifty-seven of these 100 patients underwent second-look arthroscopy.

RESULTS: Nine patients had MR findings consistent with avascular necrosis. Nineteen patients had marked degenerative arthrosis in the area of previous surgery. Seven patients had chondral defects or injuries. Twenty-nine patients had clear MR evidence of a meniscal retear without any contrast material injected into the joint. In 32 of the 100 patients, intraarticular contrast material was useful in demonstrating a retear. Of these 32 patients, 22 had MR arthrographic evidence of a retear, while 10 had no clear MR arthrographic finding to explain postoperative pain. Four additional patients had no clear MR imaging or MR arthrographic abnormality. All patients with meniscal repair (n = 16) needed MR arthrography to diagnose a residual or recurrent meniscal tear. No patient with less than 25% meniscal resection (n = 23) needed MR arthrography to demonstrate a residual or recurrent meniscal tear. Sixteen of 61 patients with more than 25% meniscal resection needed MR arthrography to demonstrate a residual or recurrent meniscal tear.

CONCLUSION: All patients with meniscal repair required MR arthrography. All patients with meniscal resection of more than 25%, who did not have severe degenerative arthrosis, chondral injuries, or avascular necrosis required MR arthrography. Patients with less than 25% meniscal resection did not need MR arthrography.

© RSNA, 2003

Index terms: Knee, ligaments, menisci, and cartilage, 4524.4852, 4525.4852 • Knee, MR, 4524.121411, 4524.121415, 4525.121411, 4525.121415 • Magnetic resonance (MR), arthrography, 4524.121411, 4524.121415, 4525.121411, 4525.121415

	INTRODUCTION

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Accurate diagnosis of meniscal retear as opposed to residual abnormal signal intensity at magnetic resonance (MR) imaging after surgery can be difficult in postoperative patients after more than 25% meniscal resection or meniscal repair (1,2). Abnormal signal intensity within the meniscus may persist after surgery. This makes the classic criterion (ie, high signal intensity in a meniscus that contacts an articular surface on proton-density or T1-weighted MR images) in the untreated knee unreliable at conventional MR imaging (1–5).

In a previous study (4), the reliability of MR arthrography of the postoperative knee was compared with that of conventional MR imaging. Diagnostic accuracy in patients with more than 25% resection of the meniscus increased from 65% with conventional MR imaging to 87% with MR arthrography.

In our practice, orders from orthopedic surgeons have increased for MR arthrography in the postoperative knee. Although MR arthrography is a simple minimally invasive procedure, most patients prefer to avoid an injection if possible (6). The purpose of our study was to assess which patients benefit most from MR arthrography of the postoperative knee.

	MATERIALS AND METHODS

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Patients
We retrospectively reviewed postoperative knee MR arthrograms obtained between June 2000 and December 2001 in 100 consecutive patients (62 male and 38 female patients; mean age, 38 years; age range, 14–68 years) who were referred by three orthopedic surgeons. The patients were experiencing new or persistent pain after knee surgery. All 100 patients had preoperative knee MR images that could be compared with postoperative MR images and MR arthrograms. All 100 patients had evidence of meniscal tears on preoperative knee MR images, and all had undergone either partial menisectomy or meniscal repair. All postoperative MR images were obtained within 2 years after initial arthroscopy.

MR imaging and MR arthrography had been performed with the informed consent of the patients. Our investigational review board did not require its approval or informed consent for this retrospective study.

MR Imaging Protocol
All patients underwent MR imaging of the postoperative knee in coronal, transverse, and sagittal planes with 1.5-T MR systems (Symphony, Siemens Medical Systems, Erlangen, Germany, or Signa, GE Medical Systems, Milwaukee, Wis). Ninety-eight examinations were performed with the Symphony imager, and two examinations were performed with the Signa imager. Symphony protocols were the following: coronal turbo spin-echo T1-weighted (repetition time msec/echo time msec of 749/10, echo train length of three), coronal fat-saturated turbo spin-echo T2-weighted (3,950/51, echo train length of five), transverse fat-saturated turbo spin-echo T2-weighted (2,590/61, echo train length of 11), sagittal fat-saturated turbo spin-echo T2-weighted (3,830/76, echo train length of seven), and sagittal fat-saturated intermediate-weighted (1,800/12). The field of view was 15 cm for coronal and sagittal imaging and 16 cm for transverse imaging. Signa protocols were the following: coronal spin-echo T1-weighted (700/12), transverse fast spin-echo T2-weighted with fat saturation (4,650/85), coronal fast spin-echo T2-weighted with fat saturation (2,750/102), sagittal fast spin-echo T2-weighted with fat saturation (2,750/102), and sagittal intermediate-weighted with fat saturation (2,500/34). The field of view was 16 cm, and two signals were acquired for all but T1-weighted sequences, where one and a half signals were acquired. All postoperative patients underwent a full conventional MR imaging knee examination before MR arthrography. Section thickness was 4 mm, except with the fat-saturated intermediate-weighted sequence, when section thickness was 3 mm. An extremity coil was used.

MR Arthrography
MR arthrography was performed with approximately 25 mL of a dilute gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ) and saline mixture (hereafter, contrast mixture), with a concentration of 0.15 mL of gadopentetate dimeglumine per 20 mL of normal saline. A 22-gauge needle was placed beneath the center of the articular surface of the patella. This procedure was performed without fluoroscopy with the patient lying supine on the MR imaging table. MR arthrography was performed in all patients immediately after conventional MR imaging, at the request of the orthopedic surgeon. One of three musculoskeletal radiologists (T.M., M.S., D.W.) performed the injection. All injections were placed successfully within the joint space. After injection of the contrast mixture into the knee joint, the knee was exercised. All patients exercised the knee by extending and bending the knee continuously for 5 minutes before repeat imaging. After exercise, T1-weighted (684/9.5) fat-saturated coronal and sagittal MR images were obtained before MR arthrography for comparison. The same section thickness, gap, field of view, and coil were used at MR arthrography that were used in the conventional MR imaging examination.

Image Interpretation
All pre- and postoperative MR images were interpreted prospectively by one of the three musculoskeletal radiologists. The postoperative MR images were separated into three groups on the basis of the work of Applegate et al (4): those who had undergone meniscal repair, less than 25% meniscal resection, or more than 25% meniscal resection. These images were then reviewed retrospectively by the three musculoskeletal radiologists with consensus. Postoperative conventional MR images were reviewed separately from postoperative MR arthrograms and then in conjunction with them. Prospective and retrospective findings were then compared. Assessment was made as to whether the MR arthrographic examination at the request of the referring orthopedic surgeon was useful for accurate interpretation. MR arthrography was considered useful when it provided additional information (ie, definitive presence or absence of a retear) that could not be determined on the conventional MR images. All MR images in patients who subsequently underwent second-look arthroscopy (n = 57) were compared with results at arthroscopy.

Postoperative MR images and MR arthrograms were compared with preoperative MR images. Abnormalities assessed on MR images were the presence or absence of findings consistent with avascular necrosis, marked degenerative joint disease, chondral defects or injuries, or indications of a new tear. The indications included extension of native joint fluid into a site of linear signal intensity abnormality, a tear in a new area, a displaced fragment, or an irregularly truncated meniscus. An estimate was made on the prospective MR images of the width of the chondral defect and the percentage of the articular cartilage thickness affected by the defect. Criteria for MR imaging findings consistent with avascular necrosis were a well-defined geographic area of decreased signal intensity on T1-weighted MR images and an area of decreased signal intensity on T2-weighted MR images that was surrounded by high signal intensity. Criteria for MR imaging findings consistent with severe degenerative joint disease were loss of articular cartilage, sclerosis (decreased signal intensity on T1- and T2-weighted MR images), osteophyte formation, and subchondral fibrocystic change. The criterion for MR arthrographic findings of a meniscal tear was abnormal communication of the contrast mixture from the joint into the substance of the meniscus (4).

	RESULTS

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Nine patients had MR imaging findings of avascular necrosis. The nine lesions corresponded to the area of previous surgery. Nineteen patients had marked degenerative joint disease in the area of previous surgery, and seven had chondral defects or injuries. Chondral defects ranged in width from 4 mm to 1.5 cm and involved 75% or more of the articular cartilage thickness. Twenty-nine patients had clear MR imaging evidence of a retear without the contrast mixture. These 29 patients had fluid that extended into a tear, a tear in a new area, a displaced fragment, and/or an irregularly truncated meniscus. Thirty-two of the 100 patients required injection of the contrast mixture to determine whether there was a retear. Among these 32 patients, 22 had MR arthrographic evidence of a retear. Fourteen patients did not have clear MR imaging or MR arthrographic findings to explain new or persistent pain after surgery.

On conventional MR images, 19 of the patients with more than 25% meniscal resection had severe degenerative joint disease, eight had avascular necrosis, five had chondral defects, and 13 had a retear. In four patients, there was no clear explanation on MR images or MR arthrograms for new or persistent pain after surgery (Table 1). In the group of patients with less than 25% meniscal resection, 16 had clear evidence of a retear, two had chondral defects, and one had avascular necrosis on conventional MR images; four patients had no clear explanation on MR images or MR arthrograms for new or persistent pain after surgery (Table 2). Among the patients who underwent meniscal repair, six had no clear explanation on MR images or MR arthrograms for new or persistent pain after surgery (Table 3).

In this study, the 16 patients with meniscal repair required MR arthrography to delineate whether there was a residual or recurrent meniscal tear. All meniscal repairs had the same appearance on postoperative and preoperative MR images. In 10 patients, MR arthrograms demonstrated abnormal communication of the mixture into a meniscal repair, which indicates a residual or recurrent meniscal tear. Nine of the 10 patients underwent second-look arthroscopy to confirm the meniscal tear (Figs 1, 2; Table 3).

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 1a. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 42-year-old man with knee pain after meniscal repair. (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 1b. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 42-year-old man with knee pain after meniscal repair. (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 34-year-old woman with knee pain after meniscal repair. (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into joint space, no abnormal communication is seen from joint space into meniscus, which indicates absence of meniscal tear (arrow).

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 34-year-old woman with knee pain after meniscal repair. (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into joint space, no abnormal communication is seen from joint space into meniscus, which indicates absence of meniscal tear (arrow).

View larger version (182K): [in this window] [in a new window] [Download PPT slide]   Figure 3a. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 28-year-old man with knee pain after meniscal resection (<25%). (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into the joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy. MR arthrography was not needed in this patient because meniscal tear could be diagnosed reliably on MR images.

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 3b. Sagittal fat-saturated T1-weighted MR images (684/9.5) in a 28-year-old man with knee pain after meniscal resection (<25%). (a) Linear area of increased signal intensity (arrow) contacts inferior articular surface. (b) After instillation of contrast mixture into the joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy. MR arthrography was not needed in this patient because meniscal tear could be diagnosed reliably on MR images.

View larger version (170K): [in this window] [in a new window] [Download PPT slide]   Figure 4. Coronal T2-weighted MR image (3,950/51) in a 39-year-old man with knee pain after meniscal resection (>25%). Severe degenerative arthrosis is seen in area of previous meniscal resection, as well as marked loss of articular cartilage, osteophyte formation, and subchondral edema (arrow). MR arthrography (not shown) was performed in this patient at the request of the referring orthopedic surgeon, but no further information was added.

Sixteen of the patients with more than 25% meniscal resection required MR arthrography to demonstrate a residual or recurrent meniscal tear. Meniscal tears could not be demonstrated on postoperative conventional MR images in these patients. Twelve of them had MR arthrographic findings that indicated a tear. All 12 patients underwent arthroscopy, and all were found to have tears (Fig 5). The four patients without evidence of a meniscal tear at MR arthrography did not undergo second-look arthroscopy (Table 1).

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 5a. Sagittal T1-weighted MR images (684/9.5) in a 32-year-old man with knee pain after meniscal resection (>25%). (a) Linear area of increased signal intensity (arrow) extends near the inferior articular surface. (b) After instillation of contrast mixture into joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy.

View larger version (171K): [in this window] [in a new window] [Download PPT slide]   Figure 5b. Sagittal T1-weighted MR images (684/9.5) in a 32-year-old man with knee pain after meniscal resection (>25%). (a) Linear area of increased signal intensity (arrow) extends near the inferior articular surface. (b) After instillation of contrast mixture into joint space, abnormal communication is seen from joint space into meniscus, which is consistent with meniscal tear (arrow). This was confirmed at arthroscopy.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
It was established previously with short-echo-time MR images of the untreated knee that an area of high signal intensity that contacts an articular surface represents a meniscal tear at arthroscopy in more than 90% of patients. This criterion was found to be less accurate in patients after meniscal resection or repair. This finding persists after surgery whether or not a tear was present (1,2).

It was demonstrated that increased T2-weighted signal intensity within a meniscus that extends to two articular surfaces is a reliable indicator of a retear in the postoperative knee. This was a specific finding, but the sensitivity was only 60% (2). Applegate et al (4) found that T2-weighted MR imaging had an accuracy of 41% for detection of a recurrent meniscal tear, and that with MR arthrography was 88%. In their study, meniscal resections were divided into those less than 25% versus those more than 25%. Meniscal repairs were not addressed specifically. Also, other findings that most likely account for pain, such as degenerative joint disease, chondral injuries, or avascular necrosis, were not addressed specifically (1).

White et al (7) prospectively evaluated conventional MR imaging, indirect MR arthrography, and direct MR arthrography in the postoperative knee. They concluded that there is a small increase in accuracy with direct MR arthrography versus that with conventional MR imaging or indirect MR arthrography. The design of their study is different from that of our study. Theirs is a prospective randomized study in which each patient underwent imaging with one of the three modalities. Findings at MR arthrography were not compared directly with those at conventional MR imaging in the same patient. Also, meniscal resection procedures were not divided into less than 25% or more than 25%. Also, their studies were performed at several institutions.

In our study, postoperative patients were divided into three groups. The 16 patients who underwent meniscal repair required MR arthrography to determine if there was a tear. In the 23 patients who underwent meniscal resection of less than 25%, the criteria established previously for the untreated knee were accurate in the diagnosis of retear. MR arthrography was not necessary in this group.

The most complicated group to assess comprised the 61 patients who underwent meniscal resection of more than 25%. MR arthrography was not useful in the patients with native joint fluid that extended into the meniscus, a tear in a new area, severe degenerative joint disease, chondral injury, or MR imaging evidence of avascular necrosis. The other patients in the group benefitted from MR arthrography.

A limitation of this study is that the false-negative rate of MR arthrography for retear could not be assessed. A second limitation is that the three readers were from the same institution, and retrospective review was performed by consensus. These individuals may read MR images in a more uniform fashion than those from different institutions.

In conclusion, previously established MR arthrographic criteria for meniscal retear in the postoperative knee are useful. However, most patients do not need to undergo MR arthrography in the postoperative knee because the findings were useful in making a diagnosis in a minority of the patients. In patients with meniscal resection of less than 25%, MR arthrography is not necessary. In patients with meniscal resection of more than 25% who do not have severe degenerative arthrosis, avascular necrosis, chondral injuries, native joint fluid that extends into a meniscus, or a tear in a new area, MR arthrography is useful in the diagnosis of residual or recurrent tear. The diagnosis of a meniscal tear in a new area in a postoperative knee requires that the preoperative MR images or operative report is available for comparison. For all patients who underwent meniscal repair, MR arthrography was required to diagnose a residual or recurrent tear. On the basis of results in this study, we currently forego conventional MR imaging and perform MR arthrography in all patients after meniscal repair.

	FOOTNOTES

 
Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, T.M.; literature research, T.M.; clinical studies, all authors; data acquisition and analysis/interpretation, all authors; statistical analysis, T.M.; manuscript preparation, definition of intellectual content, editing, and revision/review, T.M.; manuscript final version approval, all authors

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Totty WG, Matava MJ. Imaging the postoperative meniscus. Magn Reson Imaging Clin N Am 2000; 8:271-284.[Medline]
2. Haims AH, Katz LD, Ruwe PA. MR arthrography of the knee. Semin Musculoskel Radiol 1998; 2:385-395.
3. Trattnig S, Rand T, Czerny C, et al. Magnetic resonance imaging of the postoperative knee. Top Magn Reson Imaging 1999; 10:221-236.[CrossRef][Medline]
4. Applegate GR, Flannigan BD, Tolin BS, et al. MR diagnosis of recurrent tears in the knee: value of intraarticular contrast material. AJR Am J Roentgenol 1993; 161:821-825.[Abstract/Free Full Text]
5. Sciulli RL, Boutin RD, Brown RR, et al. Evaluation of the postoperative meniscus of the knee: a study comparing conventional arthrography, conventional MR imaging, MR arthrography with iodinated contrast material, and MR arthrography with gadolinium-based contrast material. Skeletal Radiol 1999; 28:508-514.[CrossRef][Medline]
6. Robbins MI, Anzilotti KF, Katz LD, et al. Patient perception of magnetic resonance arthrography. Skeletal Radiol 2000; 29:265-269.[CrossRef][Medline]
7. White LM, Schweitzer ME, Weishaupt D, et al. Diagnosis of recurrent meniscal tears: prospective evaluation of conventional MR imaging, indirect MR arthrography, and direct MR arthrography. Radiology 2002; 222:421-429.[Abstract/Free Full Text]

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This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2291020988v1 229/1/159    most recent 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 Magee, T. Articles by Williams, D. Search for Related Content PubMed PubMed Citation Articles by Magee, T. Articles by Williams, D.