Evaluation of patellar cartilage in cadavers with a low-field-strength extremity-only magnet: comparison of MR imaging sequences, with macroscopic findings as the standard

Magnetic resonance tomography of the knee joint

OBJECTIVES

To compare the diagnostic performance of magnetic resonance imaging (MRI) in terms of sensitivity and specificity using a field strength of <1.0 T (T) versus ≥1.5 T for diagnosing or ruling out knee injuries or knee pathologies.

METHODS

The systematic literature research revealed more than 10,000 references, of which 1598 abstracts were reviewed and 87 full-text articles were retrieved. The further selection process resulted in the inclusion of four systematic reviews and six primary studies.

RESULTS

No differences could be identified in the diagnostic performance of low- versus high-field MRI for the detection or exclusion of meniscal or cruciate ligament tears. Regarding the detection or grading of cartilage defects and osteoarthritis of the knee, the existing evidence suggests that high-field MRI is tolerably specific but not very sensitive, while there is literally no evidence for low-field MRI because only a few studies with small sample sizes and equivocal findings have been performed.

CONCLUSIONS

We can recommend the use of low-field strength MRI systems in suspected meniscal or cruciate ligament injuries. This does, however, not apply to the diagnosis and grading of knee cartilage defects and osteoarthritis because of insufficient evidence.

Quantitative evaluation in combination with nonquantitative evaluation in early patellar cartilage osteoarthritis at 3.0 T

Purpose

To evaluate quantitative T1 and T2 relaxation times and magnetization transfer ratios (MTRs) in the early diagnosis of patellar cartilage osteoarthritis (OA) and to quantify and possibly refine the current Kellgren-Lawrence score criteria.

Materials and methods

A total of 92 cases of knee joints with 40 normal volunteers and 30 patients with OA were prospectively evaluated. The knee joints with OA were divided into mild and moderate groups according to the Kellgren-Lawrence score criteria. The discriminative analysis method was used to analyze the accuracy of the original grouped cases correctly classified by age, sex, T1 relaxation times, T2 relaxation times, and MTR values. Linear regression analysis was used between T1 relaxation time, T2 relaxation time, and MTR values.

Results

The mean T1 relaxation times decreased with the severity of OA, and a significant difference was only found between the normal and moderate OA groups (P<0.05). The mean T2 relaxation times increased, and significant differences were found between the normal and mild OA groups and the normal and moderate OA groups (P<0.001). The MTR values were 35.8%±4.2%, 36.1%±3.2%, and 35.4%±3.8%, respectively. There were no significant differences between the normal and OA groups. In addition, T1 relaxation times were positively correlated with MTR values (P<0.01). A discriminative analysis using a synthesis of all the influential factors indicated a high accuracy rate (93.9%) for the correct classification of the original grouped cases.

Conclusion

Quantitative T1 and T2 relaxation times were useful in the diagnosis of early OA; T2 relaxation times were more relatively sensitive. The functional usefulness of MTR values may be limited. T1 relaxation times positively correlated with MTR values. Multiple quantitative parameters, combined with some relative nonquantitative clinical parameters and Kellgren-Lawrence scores, may be useful in the early stage of OA and provide better information for clinical treatment and follow-up.

Anterior cruciate ligament reconstruction using patellar tendon versus hamstring tendon: a prospective comparative study with 9-year follow-up

PURPOSE

To analyze the long-term evaluation of clinical, functional, and magnetic resonance imaging (MRI) results after implant-free press-fit anterior cruciate ligament (ACL) reconstruction with bone-patella tendon (BPT) versus quadrupled hamstring tendon (HT) grafts.

METHODS

Sixty-two ACL-insufficient patients were included in a prospective, randomized study (31 BPT and 31 HT). Both surgical procedures were performed without any implants by a press-fit technique by the senior author. The femoral tunnel was drilled through the anteromedial portal for anatomic placement. At 8.8 years after reconstruction, 53 patients (28 BPT and 25 HT) were examined by different clinical and functional tests. Bilateral MRI scans were performed and interpreted by an independent radiologist.

RESULTS

On follow-up, the score on the International Knee Documentation Committee evaluation form was significantly better in the HT group. The clinical examination including range of motion, KT-1000 test (MEDmetric, San Diego, CA), and pivot-shift test showed no significant differences. On isokinetic testing, the mean quadriceps strength was close to normal (96%) in both groups, but the hamstring strength was lower in the HT group (100.3%/95.1%). Kneeling (1.5/1.1, P = .002), knee walking (1.72/1.14, P = .002), and single-leg hop test (95.8%/99.1%, P = .057) were better in the HT group. The MRI findings about the mean degree of cartilage lesion (International Cartilage Repair Society protocol) of the operated (2.1/2.1) and nonoperated (1.4/1.8) knee showed no significant differences. No significant difference was found in the grade of medial or lateral meniscal lesion or the number of patients having meniscal lesions when the operated and nonoperated knees were compared. Tunnel measurements, Caton-Deschamps Index, and the sagittal ACL angle were similar.

CONCLUSIONS

The implant-free press-fit technique for anterior cruciate ligament reconstruction by use of bone-patellar tendon and hamstring grafts with anatomic graft placement is an innovative technique to preserve the cartilage and meniscal status without significant differences between the operated and nonoperated knees in the long term. Significantly less anterior knee pain was noted in the hamstring group, when testing for kneeling and knee walking.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

MR imaging in osteoarthritis: hardware, coils, and sequences

Whole-organ assessment of a joint with osteoarthritis (OA) requires tailored MR imaging hardware and imaging protocols to diagnose and monitor degenerative disease of the cartilage, menisci, bone marrow, ligaments, and tendons. Image quality benefits from increased field strength, and 3.0-T MR imaging is used increasingly for assessing joints with OA. Dedicated surface coils are required for best visualization of joints affected by OA, and the use of multichannel phased-array coils with parallel imaging improves image quality and/or shortens acquisition times. Sequences that best show morphologic abnormalities of the whole joint include intermediate-weighted fast-spin echo sequences. Also quantitative sequences have been developed to assess cartilage volume and thickness and to analyze cartilage biochemical composition.

Magnetic resonance imaging of the femoral trochlea: evaluation of anatomical landmarks and grading articular cartilage in cadaveric knees

PURPOSE

The purpose of the study was to define magnetic resonance imaging (MRI) findings before and after contrast medium opacification of the knee joint in cadaveric specimens to demonstrate anatomical landmarks of the trochlear surface in relation to the neighboring structures, and to evaluate different MRI sequences in the detection of cartilage defects of the trochlear and patellar surface of the knee.

MATERIALS AND METHODS

The morphology and relationship of the proximal trochlear surface to the prefemoral fat of the distal femur were investigated by use of different MR sequences before and after intra-articular gadolinium administration into the knee joint in ten cadaveric knees. Anatomic sections were subsequently obtained. In addition, evaluation of the articular surface of the trochlea was performed by two independent observers. The cartilage surfaces were graded using a 2-point system, and results were compared with macroscopic findings.

RESULTS

Of 40 cartilage surfaces evaluated, histopathologic findings showed 9 normal surfaces, 20 containing partial-thickness defects, and 11 containing full-thickness defects. Compared with macroscopic data, sensitivity of MR sequences for the two reviewers was between 17 and 90%; specificity, 75 and 100%; positive predictive value, 75 and 100%; negative predictive value, 20 and 100%, depending on patellar or trochlea lesions. Interobserver variability for the presence of disease, which was measured using the kappa statistic, was dependent on the MR sequence used between 0.243 and 0.851.

CONCLUSION

Magnetic resonance imaging sequences can be used to evaluate the cartilage of the trochlear surface with less accuracy when compared with the results of grading the articular cartilage of the patella.

MRI of osteochondral defects of the lateral femoral condyle: incidence and pattern of injury after transient lateral dislocation of the patella

OBJECTIVE

The typical bone bruise pattern involving the anterolateral femoral condyle and inferomedial patella after transient lateral dislocation of the patella is a well-described MRI finding. In our study, however, we sought to determine the incidence and location of lateral femoral condyle osteochondral injuries after transient lateral dislocation of the patella.

CONCLUSION

Osteochondral defects of the lateral femoral condyle are a common sequela after transient lateral patellar dislocation. A significant number of osteochondral injuries involve the midlateral weight-bearing portion of the lateral femoral condyle and are more posterior than would be expected after transient dislocation of the patella.

Condromalácia de patela: comparação entre os achados em aparelhos de RM de alto e baixo campo magnético

OBJETIVO: Comparar os aparelhos de ressonância magnética de baixo campo e de alto campo para estudo da cartilagem articular da patela. MATERIAIS E MÉTODOS: Foi realizado estudo usando as seqüências GRE 2D, GRE 3D, FSE T2 e STIR (baixo campo) e TSE T2 SPIR. Cada seqüência foi analisada separadamente para o estudo da cartilagem, sem o conhecimento dos dados do paciente e do resultado das outras seqüências, sendo atribuído grau de lesão de 0 a 3 e descrita a sua localização. Os resultados de concordância e discordância foram analisados pelos testes de Kappa e McNemar. RESULTADOS: Na faceta medial houve baixas concordâncias e as discordâncias mostraram significativa superestimação. Na faceta lateral houve boas concordâncias e as discordâncias não foram significativas. No ápice houve boas concordâncias e as discordâncias mostraram significativa subestimação. CONCLUSÃO: A seqüência STIR teve a melhor concordância com a seqüência TSE T2 SPIR. Lesões de alto grau são mais bem caracterizadas pelas seqüências do aparelho de baixo campo. Áreas de aumento de sinal dificultam o estudo da cartilagem da faceta medial da patela no aparelho de baixo campo.

Musculoskeletal Imaging at 3T: Current Techniques and Future Applications

MSK MR imaging applications are making the transition rapidly from 1.5T to 3T. Initial experience in the knee suggests that the higher SNR provides technical improvement in routine clinical imaging with the potential for greater accuracy in the diagnosis of articular cartilage injury. Similarly, initial experience with 3T MR imaging in the evaluation of the hip and small joints of the hand and wrist has been positive. In other joints, clinical development has been limited by the lack of availability of dedicated surface coils, and sensitivity of 3TMR imaging to artifact. The clinical impact of this technology remains uncertain because no published controlled clinical trial has evaluated the impact of 3T MR imaging on diagnostic outcomes. In addition to clinical application, 3T MR imaging has an important role for furthering translational research in MSK diseases through the development of new molecular and functional MR imaging techniques.

High- Versus Low-Field MR Imaging

The role of MR imaging as a noninvasive technique in the detection and evaluation of musculoskeletal diseases is unquestionable. Most of the studies reported in the literature are based on high-field MR imaging. Initial studies performed with low-field-strength have reported unsatisfactory results in the assessment of the musculoskeletal system. Recent improvements, however, have generated a renewed interest in low-field-strength MR imaging. This article presents the principal applications and results published in the literature.

Biomechanical, histologic and macroscopic assessment of articular cartilage in a sheep model of osteoarthritis

OBJECTIVES

Our primary objective was to explore the full potential of the ovine medial meniscectomy (MMx) model of early osteoarthritis (OA) for studies to validate non-destructive articular cartilage (AC) assessments and therapeutic interventions. Our secondary objective was to re-evaluate the relationships between the different types of AC assessment after MMx in sheep.

METHODS

Macroscopic assessments, dynamic shear modulus (G*), phase lag and AC thickness measurements were performed at a total of 5437 reference points on all six articular surfaces in four normal joints and 16 MMx ovine stifle (knee) joints. Comparisons with histologic assessments of gross structural damage, collagen organisation (birefringence) and proteoglycan content were possible at 702 of these points.

RESULTS

Histologic gross structural damage and proteoglycan loss were seen throughout the joint with greatest severity (fibrillation) in closest proximity to the MMx site. Increases in AC (30-50%) thickness, reductions in G* (30-40%) and collagen birefringence intensity (15-30%) occurred more evenly throughout the joint. Macroscopic softening was evident only when G* declined by 80%. G* correlated with AC thickness (rho=-0.47), collagen organisation rho=0.44), gross structural damage (rho=-0.44) and proteoglycan content (rho=0.42). Multivariate analysis showed that collagen organisation contributed twice as much to dynamic shear modulus (t=6.66 as proteoglycan content (t=3.21). Collagen organisation (rho=0.11) and proteoglycan content (rho=0.09) correlated only weakly to phase lag.

CONCLUSIONS

Macroscopic assessments were insensitive to AC softening suggesting that arthroscopic assessments of AC status might also perform poorly. Collagen integrity was more important for the maintenance of AC stiffness (G*) than proteoglycan content. The development of major AC softening and thickening throughout the joint following MMx suggested involvement of non-mechanical (e.g., protein and biochemical) chemical and cytokine mediated processes in addition to the disturbance in biomechanical loading. The ovine MMx model provides a setting in which the spectrum of AC changes associated with the initiation and progression of OA may be evaluated.

MR appearance of cartilage defects of the knee: preliminary results of a spiral CT arthrography-guided analysis

The aim of this study was to determine signal intensity patterns of cartilage defects at MR imaging. The MR imaging (3-mm-thick fat-suppressed intermediate-weighted fast spin-echo images) was obtained in 31 knees (21 male and 10 female patients; mean age 45.5 years) blindly selected from a series of 252 consecutive knees investigated by dual-detector spiral CT arthrography. Two radiologists determined in consensus the MR signal intensity of the cartilage areas where cartilage defects had been demonstrated on the corresponding reformatted CT arthrographic images. There were 83 cartilage defects at spiral CT arthrography. In 52 (63%) lesion areas, the MR signal intensity was higher than that of adjacent normal cartilage with signal intensity equivalent to (n=31) or lower than (n=21) that of articular fluid. The MR signal intensity was equivalent to that of adjacent normal cartilage in 17 (20%) lesion areas and lower than that of adjacent cartilage in 8 (10%) lesion areas. In 6 (7%) lesion areas, mixed low and high signal intensity was observed. The MR signal intensity of cartilage defects demonstrated on spiral CT arthrographic images varies from low to high on fat-suppressed intermediate-weighted fast spin-echo MR images obtained with our equipment and MR parameters.

A critical appraisal of quantitative arthroscopy as an outcome measure in osteoarthritis of the knee

BACKGROUND AND OBJECTIVES

To review the performance of arthroscopic assessment of articular cartilage damage in osteoarthritis.

METHODS

The literature was reviewed for publications containing data regarding validity and reliability of arthroscopic systems of cartilage evaluation in knee osteoarthritis.

RESULTS

Fifty-two distinct measurement systems were identified in 60 publications. There were 30 simple severity-scoring systems, 3 global visual analogue scale systems, and 19 composite systems. No systems consisted solely of measurements of lesion size or site, although 13 systems used either or both of these for the calculation of composite scores. Only 6 publications (10%) undertook any reliability evaluation and these generally used inappropriate methods of statistical analysis. Thirty-five publications (58%) evaluated validity. Construct validity was tested using several constructs (clinical in 2, magnetic resonance imaging in 10, radiographs in 10, or other arthroscopic assessments in 5 publications). Criterion validity was ascertained by using several methods including cartilage histology, histochemistry, or biomechanics in 10 publications. Responsiveness was determined in 1 publication.

DISCUSSION

Many publications evaluated composite systems but only a few evaluated fundamental aspects of arthroscopic measurement. Conceptually, composite scoring systems have the best validity; however, at present, there is only enough evidence to support the use of simple chondropathy severity scores and there are little data on the responsiveness of these methods. A proposed program for comprehensive evaluation and development of valid and responsive arthroscopic assessments of articular cartilage is outlined.

Fat suppression gradient-echo magnetic resonance imaging of experimental articular cartilage lesions: comparison between phase-contrast method at 0.23T and chemical shift selective method at 1.5T

PURPOSE

To evaluate the diagnostic performance of a newly developed single-scan phase-contrast water-fat imaging technique for fat suppression at 0.23T open magnet, compared to the conventional chemical shift selective fat suppression method at 1.5T, in the detection of experimental articular cartilage lesions.

MATERIALS AND METHODS

Sixty regions of 20 knee joint specimens of pigs with artificially created articular cartilage lesions were examined with 0.23T and 1.5T MR scanners. Sagittal fat-suppressed three-dimensional gradient-echo (3D GRE) images, obtained with the phase-contrast method at 0.23T, and fat-suppressed three-dimensional spoiled gradient recalled echo (3D SPGR) images, obtained with a chemical shift selective method at 1.5T, were evaluated. Diagnostic performance was analyzed. The conspicuity of the lesions, the amount of artifacts, and the uniformity of fat suppression were evaluated. The contrast-to-noise (CNR) values of cartilage-to-bone marrow, and cartilage-to-infrapatellar fat were calculated.

RESULTS

At 0.23T, sensitivity and specificity were 80% and 95% for partial cartilage lesions (grade 2), and 91% and 100% for full-thickness lesions (grade 3). At 1.5T, sensitivity and specificity were 85% and 95% for grade 2 lesions, and 96% and 97% for grade 3 lesions. No significant difference was detected in the conspicuity of lesions. The uniformity of fat suppression was more constant with 3D SPGR images compared to 3D GRE images. More susceptibility artifacts, derived from the procedure of creating lesions, were detected at 1.5T. The cartilage-to-fat CNRs were significantly higher with high-field images.

CONCLUSION

Phase-contrast method for fat suppression at 0.23T is a useful technique in detecting articular cartilage lesions.

The value of water-excitation 3D FLASH and fat-saturated PDw TSE MR imaging for detecting and grading articular cartilage lesions of the knee

OBJECTIVE

To evaluate the diagnostic accuracy of water-excitation (WE) 3D FLASH and fat-saturated (FS) proton density-weighted (PDw) TSE MR imaging for detecting, grading, and sizing articular cartilage lesions of the knee.

DESIGN AND PATIENTS

A total of 26 patients underwent MR imaging prior to arthroscopy with the following sequences: (1) WE 3D FLASH: 28/11 ms, scan time: 4 min 58 s, flip angle: 40 degrees; (2) FS PDw TSE: 3433/15 ms, scan time: 6 min 15 s, flip angle: 180 degrees. Grade and size of the detected lesions were quantified and compared with the results of arthroscopy for each compartment.

RESULTS

The sensitivity, specificity, positive and negative predictive values, and accuracy for detecting cartilage lesions were 46%, 92%, 81%, 71% and 74% for WE 3D FLASH and 91%, 98%, 96%, 94% and 95% for FS PDw TSE MR imaging. WE 3D FLASH correlated significantly with arthroscopy for grading on the patella ( P<0.0001) and the femoral trochlea ( P=0.02) and for sizing on the femoral trochlea ( P=0.03). FS PDw correlated significantly ( P<0.0001) with arthroscopy for grading and sizing on all compartments.

CONCLUSION

FS PDw TSE is an accurate method for detecting, grading and sizing articular cartilage lesions of the knee and yielded superior results relative to WE 3D FLASH MR imaging.

MR arthrography in chondromalacia patellae diagnosis on a low-field open magnet system

OBJECTIVE

The purpose of this study was to compare the diagnostic efficacy conventional MRI and MR arthrography (MRA) in the diagnosis of chondromalacia patella (CP) on a low-field open magnet system (LFOMS), correlated with arthroscopy.

SUBJECTS AND METHODS

Forty-two patients (50 knees) with pain in the anterior part of the knee were prospectively examined with LFOMS, including T1-weighted, proton density-weighted and T2-weighted sequences. All were also examined T1-weighted MRI after intraarticular injection of dilue gadopentetate dimeglumine. Two observers, who reached a consensus interpretation, evaluated each imaging technique independently. Thirty-six of the 50 facets examined had chondromalacia shown by arthroscopy, which was used as the standard of reference. The sensitivity, specificity and accuracy of each imaging technique in the diagnosis of each stage of CP were determined and compared by using the McNemar two-tailed analysis.

RESULTS

Arthroscopy showed that 16 facets were normal. Four (30%) of 13 grade 1 lesions were detected with T1. Four lesions (30%) with T2 and three lesions (23%) with proton-weighted images were detected. Seven (53%) of 13 grade 1 lesions were detected with MRA. Grade 2 abnormalities were diagnosed in two (33%) of six facets with proton density-weighted pulse sequences, two (33%) of six facets with T1-weighted pulse sequences, in three (50%) of six facets with T2-weighted pulse sequences, in five (83%) of six facets with MRA sequences. Grade 3 abnormalities were diagnosed in three (71%) of seven facets with proton density- and T1-weighted images, five (71%) of seven facets with T2-weighted pulse sequences, six (85%) of seven facets with MRA sequences. Grade 4 CP was detected with equal sensitivity with T1-, proton density- and T2-weighted pulse sequences, all showing seven (87%) of the eight lesions. MRA again showed these findings in all eight patients. All imaging techniques were insensitive to grade 1 lesions and highly sensitive to grade 4 lesion, so that no significant difference among the techniques could be shown.

CONCLUSION

All imaging technique studied had high specificity and accuracy in the detection and grading of CP; however, MRA was more sensitive than T1-weighted and proton density-weighted MR imaging on a LFOMS. Although the arthrographic techniques were not significantly better than T2-weighted imaging, the number of false-positive diagnosis was greatest with T2-weighted MRI.

Assessment of progression in knee osteoarthritis: results of a 1 year study comparing arthroscopy and MRI

OBJECTIVE

The objectives of this study were to determine the sensitivity to change of magnetic resonance imaging (MRI) quantification of chondropathy after 1 year in osteoarthritis of the medial tibiofemoral compartment and to assess the predictive value of subchondral bone marrow edema and bone abnormalities on progression of chondropathy.

DESIGN

Twenty patients with symptomatic knee osteoarthritis of the medial compartment underwent a prospective, longitudinal study. All patients were evaluated the same day at entry and after 1 year by plain weight-bearing radiographs, MRI with a three-dimensional gradient-echo sequence, using a 0.2-T dedicated MR unit, and arthroscopy. The medial tibiofemoral chondropathy was quantified blindly with MRI and arthroscopy using the French Society of Arthroscopy (SFA) score. Presence of subchondral bone marrow edema and bone abnormalities on initial MRI was recorded in order to evaluate their influence on both unchanged and worsened chondropathy after 1 year.

RESULTS

After 1 year, no statistically significant changes were observed with plain radiographs and arthroscopy. At variance, a statistically significant worsening of chondropathy was found with MRI using the SFA-MR score (P=0.01). SFA-MR score was the most responsive outcome. Absence of subchondral bone abnormalities and bone marrow edema on initial MR assessment predicted absence of worsening of chondropathy after 1 year.

CONCLUSION

MRI appears promising for evaluating progression of knee osteoarthritis.

Protocols in sports magnetic resonance imaging

Magnetic resonance imaging, with its multiplanar imaging capability and superior soft-tissue contrast, has become the preferred method for imaging sports-related injuries. Advances in gradient technology, receiver coils, and imaging software have allowed the imaging of the injured athlete to take place quickly and at high resolution. Understanding the tissues being imaged, the underlying anatomy, and the capabilities of today's scanners is crucial to the design of intelligent and efficient protocols.

Assessment of knee cartilage in cadavers with dual-detector spiral CT arthrography and MR imaging

PURPOSE

To assess dual-detector spiral CT arthrography in the evaluation of the entire knee cartilage obtained from cadavers.

MATERIALS AND METHODS

Two independent observers characterized articular cartilage in 12 cadaver knees in which MR imaging and dual-detector spiral CT arthrography were performed and compared their findings to those found during macroscopic assessment. The sensitivity and specificity of MR imaging and spiral CT arthrography for detecting grade 2A or higher and grade 2B or higher cartilage lesions, the Spearman correlation coefficient between arthrographic and macroscopic grading, and kappa statistics for assessing interobserver reproducibility were determined.

RESULTS

At spiral CT arthrography, sensitivities and specificities ranged between 80% and 88% for the detection of grade 2A or higher cartilage lesions and ranged between 85% and 94% for the detection of grade 2B or higher cartilage lesions. At MR imaging, sensitivities and specificities ranged between 78% and 86% and between 76% and 91% for the detection of grade 2A or higher and grade 2B or higher cartilage lesions, respectively. Spearman correlation coefficients between spiral CT arthrography or MR imaging and macroscopic grading of articular surfaces were 0.797 and 0.702, respectively.

CONCLUSION

Dual-detector spiral CT arthrography of the knee is a valuable method for the assessment of open cartilage lesions of the entire knee.

Three-point Dixon chemical-shift imaging for evaluating articular cartilage defects in the knee joint on a low-field-strength open magnet

OBJECTIVE

The purpose of our study was to assess the value of a modified three-point Dixon MR technique for evaluating articular cartilage defects in the knee joint on a low-field-strength open magnet, correlated with arthroscopy.

SUBJECTS AND METHODS

Twenty consecutive patients who underwent both MR imaging and arthroscopy of the knee joint for suspected internal derangement were examined. A modified three-point Dixon MR sequence with a single radiofrequency echo single-scan method for water and fat separation with correction of the static field inhomogeneities was performed on a 0.35-T open magnet to obtain fat suppression. The MR images were prospectively evaluated for the presence and grade of articular cartilage defects.

RESULTS

Uniform fat suppression was obtained in all patients using the modified three-point Dixon technique. Fifty-nine cartilage abnormalities were identified in 19 patients on the basis of arthroscopy. Forty-seven of 59 arthroscopically proven abnormalities were prospectively detected on MR imaging. Compared with arthroscopy, the overall sensitivity of the modified three-point Dixon technique in detecting cartilage lesions was 80% and the specificity was 73%. Sixty-five percent of the cartilage abnormalities were graded identically on MR imaging and arthroscopy.

CONCLUSION

The modified three-point Dixon sequence is a useful technique for achieving fat suppression in the knee joint on a 0.35-T open magnet. It is a sensitive and specific technique for the assessment of cartilage abnormalities in the knee.

Magnetic resonance imaging of articular cartilage of the knee

Recently developed magnetic resonance (MR) imaging techniques allow accurate detection of moderate- and high-grade articular cartilage defects. There has been increased interest in MR imaging of articular cartilage in part because it is useful in identifying patients who may benefit from new articular cartilage replacement therapies, including chondrocyte transplantation, improved techniques for osteochondral transplantation, chondroprotective agents, and cartilage growth stimulation factors. The modality also has the potential to play an important role in the follow-up of patients during and after treatment. Detection of articular cartilage defects is beneficial for patients undergoing arthroscopy for other injuries, such as meniscal tears, because the presence of articular cartilage injury worsens prognosis and may modify therapy options.

Detection of articular cartilage lesions: experimental evaluation of low- and high-field-strength MR imaging at 0.18 and 1.0 T

The objective of this study was to compare the diagnostic performance of a dedicated orthopedic magnetic resonance (MR) imaging system (0.18 T) and a conventional MR imaging system (1.0 T) in the detection of articular cartilage lesions. Fifty knee joint specimens of pigs with artificially created articular cartilage lesions of different diameters, grades (2-3), and localizations, as well as 50 joints with intact articular cartilage, were imaged at 0. 18 and 1.0 T. Diagnostic performance was determined by means of receiver operating characteristics (ROC) analysis with three independent observers. For none of the pulse sequences used at 0.18 T or 1.0 T areas under ROC curves (A(z)) showed significant differences between the three observers. A(z) values from averaged data were as follows: a) 0.18 T: T1-weighted spin echo (SE): 0.70, proton-density-weighted SE: 0.59, T2-weighted SE: 0.61, two-dimensional (2D) gradient-echo (GRE): 0.73, 3D GRE: 0.75; and b) 1.0 T: T1-weighted SE: 0.73, fat-suppressed T2-weighted turbo-SE: 0. 79, 2D fast low-angle shot (FLASH): 0.79, fat-suppressed 3D FLASH: 0. 96, and water-excited 3D double-echo steady state (DESS): 0.96. With the use of 3D pulse sequences, the high-field system demonstrated a significantly better diagnostic performance than the low-field system in the detection of grades 2 and 3 articular cartilage lesions (P < 0.001).

Magnetic resonance imaging of superficial cartilage lesions: role of contrast in lesion detection

Excised patellar cartilage phantoms with artificial surface lesions were imaged in a 2 g/dl albumin solution to determine the effect of cartilage/fluid contrast on detection of early degenerative change. Surface lesions consisted of full-thickness holes, superficial grooves, and coarse abrasion. Phantoms were imaged with a T1-weighted fast low-angle shot (FLASH) and T2*-weighted dual-echo in the steady state (DESS) sequence. Although both sequences were able to identify full-thickness holes, they underestimated the presence of superficial grooves and extent of fibrillation. Despite greater bulk tissue contrast between cartilage and fluid for the FLASH sequence, detection of fibrillation was poorer compared with the DESS images. The results of this study suggest that surface properties of fibrillated cartilage contribute significantly to the insensitivity of magnetic resonance imaging in detecting superficial lesions. In contrast to previous papers suggesting that T1-weighted spoiled gradient-echo imaging provides the greatest accuracy for lesion detection, our results indicate that, in the presence of joint fluid, T2*-weighted imaging increases detection of superficial lesions. J. Magn. Reson. Imaging 1999;10:178-182.