Abnormalities of articular cartilage in the knee: analysis of available MR techniques

MR Imaging of Articular Cartilage: Current State and Recent Developments

Osteoarthritis is the most common type of arthritis and a frequent cause of pain and disability. A number of exciting surgical treatment modalities have been introduced recently, including autologous chondrocyte transplantation and osteochondral allografting or autografting. MR imaging offers the distinct advantage of visualizing the articular cartilage directly. MR imaging can detect signal and morphologic changes in the cartilage and has been used to detect cartilage surface fraying, fissuring, and varying degrees of cartilage thinning.

Imaging of Patellar Cartilage with a 2D Multiple-Echo Data Image Combination Sequence

OBJECTIVE

We sought to evaluate the diagnostic value of a 2D multiple-echo data image combination (MEDIC) MRI sequence in the detection of patellar cartilage defects.

MATERIALS AND METHODS

Our study included 52 consecutive patients who had knee surgery within 4 months of undergoing an MRI examination including an axial 2D MEDIC (TR/TE, 884/26; flip angle, 30 degrees ) sequence. Cartilage was surgically graded on a 5-point scale: 0, normal; 1, softening or swelling; 2, partial thickness defect; 3, fissuring to the level of the subchondral bone; or 4, exposed subchondral bone. Cartilage was graded on MRI according to a scale that was almost identical to the surgical scale except that grade 1 lesions were defined as signal alteration or swelling of cartilage. Two blinded reviewers independently analyzed patellar cartilage. Sensitivity, specificity, accuracy, and weighted kappa values for interobserver variability were calculated.

RESULTS

Low-grade cartilage lesions predominated in our study group. When grade 2 or higher was considered the threshold for relevance, the sensitivity, specificity, and accuracy for the MEDIC sequence was as high as 79%, 82%, and 81%, respectively. Increasing the threshold of relevance to grade 3 increased the sensitivity, specificity, and accuracy to as high as 83%, 91%, and 90%, respectively. Interobserver agreement for the MEDIC sequence was good (weighted kappa = 0.68).

CONCLUSION

The 2D MEDIC sequence performs comparably to previously described sequences optimized for cartilage imaging such as the 3D double-echo steady-state or 3D spoiled gradient-recalled sequences with good interobserver agreement, high sensitivity, and excellent specificity for revealing low- to intermediate-degree cartilage defects.

Postoperative MR evaluation of chondral repair in the knee

Articular cartilage abnormalities of the knee are a cause of significant patient morbidity. Several surgical techniques have been developed to treat these lesions to improve patient symptoms and to delay or prevent the development of osteoarthritis. MRI has been shown to be an accurate non-invasive test for the evaluation of articular cartilage injuries and for evaluating the postoperative knee following chondral repair. As these surgical repair techniques become more commonly performed, is important for radiologists to be familiar with the surgical techniques and the MRI appearance of the postoperative knee including both normal and abnormal findings. In this article, these chondral repair techniques will be reviewed as well those normal and abnormal MRI findings following these surgeries.

Arthroscopic meniscus repair in the ACL-deficient knee

Between 1985 and 1995, 45 patients underwent closed meniscus repair. There were 30 men and 15 women with a mean age of 32.5 years. In 23 patients, the anterior cruciate ligament was intact (group 1) whereas it was deficient in 22 patients (group 2). All patients were managed with the same postoperative program of partial weight bearing, immediate motion and rehabilitation of the knee. Five patients had a failed meniscal repair and underwent a repeat arthroscopy and a partial meniscectomy. These patients were considered as failures and excluded from the final scoring. After a mean follow-up of more than 9 years, all patients were subjected to a clinical examination using the Hospital for Special Surgery (HSS) knee rating system. Seven patients in group 2 had episodes of frequent giving way and had their anterior cruciate ligament (ACL) reconstructed 6 and 7 years after the initial meniscus repair. None of the other patients had any clinical symptoms or signs of a meniscal tear. In group 1, 20 patients and in group 2, 14 patients, all had a satisfactory knee score. Even though the failure rate of meniscus repair may be greater in an unstable knee, it is concluded that meniscal repair is not contraindicated in a knee with a deficient ACL.

MR arthrography of the hip: diagnostic performance of a dedicated water-excitation 3D double-echo steady-state sequence to detect cartilage lesions

OBJECTIVE

The objective of our study was to compare the diagnostic performance of a dedicated cartilage MR sequence (water-excitation 3D double-echo steady-state) with a standard MR sequence (T1-weighted spin-echo) in detecting articular cartilage lesions of the hip after intraarticular injection of gadopentetate dimeglumine.

MATERIALS AND METHODS

In 50 MR arthrograms of the hip joint obtained in 47 consecutive patients, a sagittal 3D double-echo steady-state sequence (TR/TE, 24/6.5; flip angle, 25 degrees ) was compared with a sagittal T1-weighted spin-echo sequence (350/14). Two musculoskeletal radiologists independently evaluated articular cartilage. Sensitivity and specificity for detecting cartilage defects were calculated for those hips that underwent open surgery (n = 21). Lesion conspicuity was retrospectively reviewed and graded between 1 (not visible) and 5 (well defined).

RESULTS

At surgery, a total of 26 lesions of the acetabular (n = 20) and femoral (n = 6) cartilage were found. For the 3D double-echo steady-state and T1-weighted spin-echo sequences, sensitivities and specificities for cartilage lesion detection were 58% and 88% and 81% and 81% for reviewer 1 and 62% and 94% and 62% and 100% for reviewer 2, respectively. Lesion conspicuity was significantly superior (p = 0.036) for the 3D double-echo steady-state sequence (mean grade, 3.4) compared with the T1-weighted spin-echo sequence (mean grade, 3.0). The kappa value was fair for the 3D double-echo steady-state sequence (kappa = 0.40) and moderate for the T1-weighted spin-echo sequence (kappa = 0.55).

CONCLUSION

The 3D double-echo steady-state sequence optimized for cartilage imaging improves lesion conspicuity but does not improve diagnostic performance.

Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2-weighted fast spin echo, T1-weighted two-dimensional and three-dimensional gradient echo pulse sequences

PURPOSE

To evaluate and compare the diagnostic accuracy of appropriate magnetic resonance (MR) sequences in the detection of cartilage lesions at 1.5T and 3.0T.

MATERIAL AND METHODS

Twelve chondral defects of varying depths, widths, and locations were created in the retropatellar hyaline cartilage in six sheep cadaver limbs. Axial images employing three fat-suppressed imaging sequences--(1) a T2-weighted fast spin-echo (FSE) sequence, (2) a two-dimensional (2D) and (3) three-dimensional (3D) gradient-echo (GE) sequence at 1.5T and 3.0T using an extremity quadrature coil--were evaluated by three experienced radiologists. Statistical analysis of the results consisted of receiver operating characteristics (ROC) and significant testing using the bivariate chi-square test. In addition, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were evaluated with significance testing using the Wilcoxon test.

RESULTS

The 3D GE sequence compared favorably with other sequences at 3.0T and 1.5T (Az=0.88 at 3.0T and Az=0.85 at 1.5T) missing only one small grade 2 lesion. 2D GE imaging was inferior to 3D imaging at both field strengths (P<0.05) in general. However, compared to 1.5T, lesion detectability was improved at the higher magnetic field of 3.0T (Az=0.81 and 0.73 at 3.0T and 1.5T, respectively). FSE images showed significantly inferior sensitivity and less anatomical detail compared to the GE sequences at both field strengths (Az=0.64 and 0.72 at 3.0T and 1.5T, respectively; P<0.05). However, compared to 1.5T, lesion detectability SNR and CNR values were superior in all sequences tested at 3.0T.

CONCLUSION

MRI at 3.0T improves SNR and CNR significantly in the most common sequences for cartilage MRI, resulting in an improvement in chondral lesion detection. GE imaging therefore allows resolution to be increased in an acceptable time manner for patient comfort, and the 3D GE fat-suppressed sequence at 3.0T appears to be best suited for cartilage imaging in a clinical setting.

Short tau inversion recovery and proton density-weighted fat suppressed sequences for the evaluation of osteoarthritis of the knee with a 1.0 T dedicated extremity MRI: development of a time-efficient sequence protocol

Aim of this study was to develop a time-efficient sequence protocol for a 1.0 T dedicated MR system to be used for whole-organ scoring of osteoarthritis (OA). Thirty-four knees were examined using a protocol that included fat suppressed fast spin echo proton density weighted sequences (PDFS) in three planes plus a coronal STIR sequence. Two radiologists scored each knee by consensus for five OA features. In separate sessions, all knees were scored using three different combinations of sequences: (1) all four sequences (reference protocol, 16 min 31 s scanning time), (2) three PDFS sequences without STIR ("No STIR", 12 min 25 s scanning time) and (3) sagittal and axial PDFS sequences plus a coronal STIR sequence ("No PDFS", 11 min 49 s scanning time). Agreement of the readings using both subsets of sequences compared to the reference protocol was evaluated using weighted kappa statistics. kappa-coefficients showed good or excellent agreement for both sequence subsets in comparison to the reference protocol for all assessed features. kappa-coefficients for No PDFS/No STIR: bone marrow abnormalities (0.74/0.67), subarticular cysts (0.84/0.63), marginal osteophytes (0.77/0.71), menisci (0.75/0.79), tibial cartilage (0.71/0.78). Optimization of sequence protocols consisting of three sequences results in time savings and cost efficiency in imaging of knee OA without loss of information over a more time consuming protocol.

Hylan G-F 20 efficacy on articular cartilage quality in patients with knee osteoarthritis: clinical and MRI assessment

The aim of this study was to investigate the effects of intra-articular hyaluronic acid (HA) on symptoms, functional outcome, and changes in articular cartilage assessed by magnetic resonance imaging (MRI) in patients with knee osteoarthritis. Thirty patients were randomly assigned to treatment with HA (hylan G-F 20, Synvisc) or saline. The treatment group consisted of 20 patients receiving three weekly injections of HA into one or both knees (30 knees). The control group consisted of ten patients receiving three intra-articular injections of 2 ml saline at the same intervals (ten knees). To determine the effectiveness of the HA therapy, all patients were assessed prior to the injections (baseline) and after the 1st, 2nd, 3rd, and 8th weeks. Assessment comprised the following: pain at rest, at night, and on walking using a visual analogue scale (VAS); Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain, stiffness, and function scores; 15-m walking time; need for analgesics; and evaluation of treatment by the patients. MRI of patellofemoral (PF) articular cartilage was also examined before and after the course of injections at the 8th week. When compared to placebo, a significant statistical difference was found in all clinical parameters. On MRI, although the difference in the PF joint cartilage quality in the HA group before and after the treatment was statistically significant (p < 0.05), this significance was not detected between the groups after the treatment (p > 0.05). After the HA injections, a significant analgesic effect was seen as early as the 3rd week continuing up to the 8th week and functional improvement was seen at the 8th week. In conclusion, intra-articular injections of HA is an effective choice of treatment in patients with knee osteoarthritis.

Impact of high field (3.0 T) magnetic resonance imaging on diagnosis of osteochondral defects in the ankle joint

OBJECTIVE

To evaluate high field magnetic resonance (MR) imaging for imaging of osteochondral defects.

MATERIALS AND METHODS

Nine osteochondral defects were simulated in three cadaveric talus specimens using a diamond drill. All specimens were examined on a 1.0 T MR unit and a 3.0 T MR unit. A T2-weighted turbo spin-echo (TSE) sequence with a 2 mm slice thickness and a 256 x 256 matrix size was used on both scanners. The visibility of the osteochondral separation and the presence of susceptibility artifacts at the drilling bores were scored on all images.

RESULTS

Compared to the 1.0 T MR unit, the protocol on the 3.0 T MR unit allowed a better delineation of the disruption of the articular cartilage and a better demarcation of the subchondral defect. Differences regarding the visualization of the subchondral defect were found to be statistically significant (P<0.05). Differences with regard to susceptibility artifacts at the drilling bores were not statistically significant (P>0.05). The average SNR was higher using 3.0 T MRI (SNR=12), compared to 1.0 T MRI (SNR=7).

CONCLUSION

High field MRI enables the acquisition of images with sufficient resolution and higher SNR and has therefore the potential to improve the staging of osteochondral defects.

Cartilage Thickness in Cadaveric Ankles: Measurement with Double-Contrast Multi–Detector Row CT Arthrography versus MR Imaging

PURPOSE

To test the accuracy of double-contrast multi-detector row computed tomographic (CT) arthrography for measurement of cartilage thickness in cadaveric ankles and to compare this technique with three-dimensional (3D) fat-suppressed spoiled gradient-echo in the steady state (FS-SPGR) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Five cadaveric ankles were used. In the ankle specimens, five to nine 1.5-mm-diameter holes were drilled across the joint traversing the tibial subchondral bone, tibial articular cartilage, talar dome cartilage, and talar subchondral bone. The ankle specimens were obtained and used according to institutional policies. Each ankle specimen was imaged first by using 3D FS-SPGR MR imaging with a 1.5-T magnet and then by using double-contrast arthrography followed by CT with a four-detector row scanner (ie, double-contrast multi-detector row CT arthrography). The section thickness used for CT scanning was 1.0 mm reconstructed in 0.5-mm intervals. The MR and CT images obtained in the five specimens were then downloaded to a workstation, where a measurement tool was used to measure the cartilage thickness at each hole. The physical measurement of cartilage thickness at each hole was used as the reference standard with which the MR imaging and CT measurements were compared. Linear regression and correlation analyses were performed by using a statistical computer program.

RESULTS

Double-contrast arthrography followed by multi-detector row CT, as compared with 3D FS-SPGR MR imaging, enabled more accurate measurement of the physical cartilage thickness in the ankle (P < .001).

CONCLUSION

In this study of five cadaveric ankles, multi-detector row CT arthrography was more accurate than 3D FS-SPGR MR imaging for measurement of articular cartilage thickness in the ankle.

Toward imaging biomarkers for osteoarthritis

Many new therapeutic strategies have been and are being developed to correct, prevent, or slow the progression of osteoarthritis. Our ability to evaluate the efficacy of these techniques, or to determine the situations for which they might provide the most benefit, critically depends on diagnostic measures that can serve as proxies for the present or predicted state of the cartilage. Many of the magnetic resonance imaging techniques that have been emerging over the past decades appear promising in that they have shown technical validity in measuring the morphologic and molecular state of cartilage. With continued development and added insight from pilot clinical studies, these or related methods may soon be in customary use. These techniques are part of a paradigm shift where therapeutic strategies are developed hand-in-hand with diagnostic approaches-a shift that offers the promise of speeding development of effective therapies, and focusing their use in areas where they can be most successful.

Imaging of patellofemoral disorders

Anterior knee pain is a common symptom, which may have a large variety of causes including patellofemoral pathologies. Patellofemoral maltracking refers to dynamic abnormality of patellofemoral alignment and has been measured using plain film, computed tomography (CT) and magnetic resonance imaging (MRI) using static and kinematic techniques. Patellar dislocation is usually transient, but specific conventional radiographic and MRI features may provide evidence of prior acute or chronic dislocation. In addition, chondromalacia patellae, osteochondritis dissecans, patellofemoral osteoarthritis, excessive lateral pressure syndrome, and bipartite patella have all been implicated in causing patellofemoral pain. The imaging and clinical features of these processes are reviewed, highlighting the specific diagnostic features of each condition.

High-resolution MRI and micro-CT in an ex vivo rabbit anterior cruciate ligament transection model of osteoarthritis

OBJECTIVE

The aim of this study was to investigate the potential of using non-invasive, multi-modality imaging techniques to quantify disease progression in a rabbit model of experimentally induced osteoarthritis (OA).

METHODS

High-resolution 4-T magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) techniques were implemented and validated in an ex vivo rabbit anterior cruciate ligament transection (ACLT) model of OA. A three-dimensional (3-D) rigid body registration technique was executed and evaluated to allow combined MR-CT analysis in co-registered image volumes of the knee.

RESULTS

The 3-D MRI and micro-CT data formats made it possible to quantify cartilage damage, joint-space, and osseous changes in the rabbit ACLT model of OA. Spoiled gradient-recalled echo and fast-spin echo (FSE) sequences were jointly used to evaluate femorotibial cartilage and determine the sensitivity (78.3%) and specificity (95.3%) of 4-T MRI to detect clinically significant cartilage lesions. Overall precision error of the micro-CT technique for analysis of joint-space, volumetric bone mineral density (vBMD), and bone volume fraction (BV/TV) was 1.8%, 1.2%, and 2.0%, respectively. Co-registration of the 3-D data sets was achieved to within 0.36 mm for completed intermodality registrations, 0.22 mm for extrapolated intramodality registrations, and 0.50mm for extrapolated intermodality registrations.

CONCLUSIONS

These results indicate that high-resolution 4-T MRI and micro-CT can be used to accurately quantify cartilage damage and calcified tissue changes in the rabbit ACLT model of OA. In addition, image volumes can be successfully co-registered to facilitate a comprehensive multi-modality examination of localized changes in both soft tissue and bone within the rabbit femorotibial joint.

Articular cartilage of knee: normal patterns at MR imaging that mimic disease in healthy subjects and patients with osteoarthritis

PURPOSE

To evaluate normal magnetic resonance (MR) imaging findings that may mimic articular cartilage diseases in healthy subjects and patients with osteoarthritis of the knee.

MATERIALS AND METHODS

Sagittal fat-suppressed intermediate-weighted fast spin-echo (FSE) (repetition time msec/echo time [TE] msec, 4,000/13), sagittal T2-weighted FSE (4,000/39), and sagittal fat-suppressed three-dimensional (3D) spoiled gradient-echo (SPGR) (60/5, 40 degrees flip angle) MR images were acquired in 28 patients and four volunteers. FSE images with a TE of 13 msec were considered "short-TE images"; those with a TE of 39 msec were considered "long-TE images." Presence of normal MR imaging appearance of articular cartilage was determined by one author. Contrast between cartilage and adjacent structures (meniscus, joint capsule, synovial fluid, muscle) was calculated in posterior regions of the femoral condyle on images obtained with each sequence; Wilcoxon signed rank testing was performed.

RESULTS

The following appearances were observed in patients with knee osteoarthritis (on short-TE FSE, long-TE FSE, and SPGR MR images, respectively): (a) ambiguity of surface contour in posterior region of the femoral condylar cartilage (in zero, zero, and 20 patients), (b) linear area of high signal intensity in deep zone adjacent to subchondral bone of femoral condyle (in zero, zero, and 26 patients), (c) pseudolaminar appearance in posterior region of femoral condylar cartilage (in seven, nine, and 24 patients), (d) truncation artifact in patellofemoral compartment (in seven, six, and 27 patients), (e) susceptibility artifact on cartilage surface caused by air or metal (in three, three, and 11 patients), (f) decreased signal intensity in distal part of trochlear cartilage (in 28, 28, and 28 patients), (g) cartilage thinning adjacent to the anterior horn of the lateral meniscus (in 19, 19, and 21 patients), and (h) focal cartilage flattening in posterior region of femoral condyle (in 16, 16, and nine patients). Cartilage-meniscus and cartilage-synovial fluid contrast was significantly higher on fat-suppressed FSE than on fat-suppressed 3D SPGR MR images (P <.001).

CONCLUSION

Fat-suppressed FSE and 3D SPGR MR images showed nonuniform signal intensity arising from articular cartilage and cartilage thinning, both of which could mimic disease.

MR imaging for surgical planning and postoperative assessment in early osteoarthritis

Chondral lesions in young active patients are a common problem encountered by orthopedic surgeons. Owing to the lack of vascularity, isolated chondral lesions do not heal spontaneously and may lead to osteoarthritis, creating a difficult treatment conundrum. Arthroscopic lavage and debridement provide temporary symptomatic relief without addressing the underlying pathology. Marrow stimulation techniques fill the defects with fibrocartilage that is believed to be biomechanically inferior. Osteoarticular autografts are useful for small lesions but are technically demanding. ACI can provide durable hyaline cartilage even in salvage reconstruction scenarios; however, complications such as periosteal overgrowth, arthrofibrosis, and failure of graft incorporation may occur and require reoperation. Arthroplasty remains the ultimate salvage for the arthritic joint, but biomechanical limitations preclude its use in young athletic adults. MR imaging has a crucial role in the diagnosis and treatment planning of chondral lesions and continues to remain valuable in followup of cartilage reconstructions longitudinally. MR imaging shows promise in reducing the need for more costly and invasive diagnostic arthroscopy.

Radiography, computed tomography and magnetic resonance imaging at 0.5 Tesla of mechanically inducedosteoarthritis in rabbit knees

In the present experimental study we assessed induced osteoarthritis data in rabbits, compared three diagnostic methods, i.e., radiography (XR), computed tomography (CT) and magnetic resonance imaging (MRI), and correlated the imaging findings with those obtained by macroscopic evaluation. Ten young female rabbits of the Norfolk breed were used. Seven rabbits had the right knee immobilized in extension for a period of 12 weeks (immobilized group), and three others did not have a limb immobilized and were maintained under the same conditions (control group). Alterations observed by XR, CT and MRI after the period of immobilization were osteophytes, osteochondral lesions, increase and decrease of joint space, all of them present both in the immobilized and non-immobilized contralateral limbs. However, a significantly higher score was obtained for the immobilized limbs (XT: P = 0.016, CT: P = 0.031, MRI: P = 0.0156). All imaging methods were able to detect osteoarthritis changes after the 12 weeks of immobilization. Macroscopic evaluation identified increased thickening of joint capsule, proliferative and connective tissue in the femoropatellar joint, and irregularities of articular cartilage, especially in immobilized knees. The differences among XR, CT and MRI were not statistically significant for the immobilized knees. However, MRI using a 0.5 Tesla scanner was statistically different from CT and XR for the non-immobilized contralateral knees. We conclude that the three methods detected osteoarthritis lesions in rabbit knees, but MRI was less sensitive than XR and CT in detecting lesions compatible with initial osteoarthritis. Since none of the techniques revealed all the lesions, it is important to use all methods to establish an accurate diagnosis.

Osteoarthritis: symptoms, signs and source of pain

Osteoarthritis is the most common form of arthritis. The condition is characterised by loss or failure of the functional and/or biochemical integrity of the joint. The clinical symptoms include joint stiffness, pain and dysfunction, but the principal problem for the majority of patients is the pain. Although there are no pain receptors in the cartilage, the origin of the pain is thought to be due to stimulation of the A delta mechanoreceptors and the C polymodal nerve endings in the synovium and surrounding tissues. However, some of the pain experienced in and around the joints is referred pain or sympathetic efferent pain. In addition, there is a poor correlation of clinical symptoms with radiological or imaging appearance. This lack of correlation of clinical evaluation and imaging makes attempts at treatment difficult and compromises attempts to design studies and to evaluate the outcome of osteoarthritis in clinical trials.

Magnetic resonance imaging of articular cartilage of the knee: Comparison between fat-suppressed three-dimensional SPGR imaging, fat-suppressed FSE imaging, and fat-suppressed three-dimensional DEFT imaging, and correlation with arthroscopy

PURPOSE

To compare signal-to-noise ratios (S/N) and contrast-to-noise ratios (C/N) in various MR sequences, including fat-suppressed three-dimensional spoiled gradient-echo (SPGR) imaging, fat-suppressed fast spin echo (FSE) imaging, and fat-suppressed three-dimensional driven equilibrium Fourier transform (DEFT) imaging, and to determine the diagnostic accuracy of these imaging sequences for detecting cartilage lesions in osteoarthritic knees, as compared with arthroscopy.

MATERIALS AND METHODS

Two sagittal fat-suppressed FSE images (repetition time [TR] / echo time [TE], 4000/13 [FSE short TE] and 4000/39 [FSE long TE]), sagittal fat-suppressed three-dimensional SPGR images (60/5, 40 degrees flip angle), and sagittal fat-suppressed echo-planar three-dimensional DEFT images (400/21.2) were acquired in 35 knees from 28 patients with osteoarthritis of the knee. The S/N efficiencies (S/Neffs) of cartilage, synovial fluid, muscle, meniscus, bone marrow, and fat tissue, and the C/N efficiencies (C/Neffs) of these structures were calculated. Kappa values, exact agreement, sensitivity, specificity, positive predictive value, and negative predictive value were determined by comparison of MR grading with arthroscopic results.

RESULTS

The synovial fluid S/Neff on fat-suppressed FSE short TE images, fat-suppressed FSE long TE images, and fat-suppressed three-dimensional DEFT images showed similar values. Fat-suppressed three-dimensional DEFT images showed the highest fluid-cartilage C/Neff of all sequences. All images showed fair to good agreement with arthroscopy (kappa, 0.615 in FSE short TE, 0.601 in FSE long TE, 0.583 in three-dimensional SPGR, and 0.561 in three-dimensional DEFT). Although the sensitivity of all sequences was high (100% in FSE short TE, FSE long TE, and DEFT; 96.7% in SPGR), specificity was relatively low (67.6% in FSE short TE and FSE long TE; 85.3% in SPGR; 58.3% in DEFT). The peripheral area of bone marrow edema or whole area of bone marrow edema on fat-suppressed FSE images was demonstrated as low or iso-signal intensity on fat-suppressed three-dimensional DEFT images.

CONCLUSION

Fat-suppressed three-dimensional SPGR imaging and fat-suppressed FSE imaging showed high sensitivity and high negative predictive values, but relatively low specificity. The Kappa value and exact agreement was the highest on fat-suppressed FSE short TE images. Fat-suppressed three-dimensional DEFT images showed results similar to the conventional sequences.

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.

Templates of the cartilage layers of the patellofemoral joint and their use in the assessment of osteoarthritic cartilage damage

OBJECTIVE

To develop a methodology for generating templates that represent the normal human patellofemoral joint (PFJ) topography and cartilage thickness, based on a statistical average of healthy joints. Also, to determine the cartilage thickness in the PFJs of patients with osteoarthritis (OA) and develop a methodology for comparing an individual patient's thickness maps to the normal templates in order to identify regions that are most likely to represent loss of cartilage thickness.

DESIGN

The patella and femur surfaces of 14 non-arthritic human knee joints were quantified using either stereophotogrammetry or magnetic resonance imaging. The surfaces were aligned, scaled, and averaged to create articular topography templates. Cartilage thicknesses were measured across the surfaces and averaged to create maps of normal cartilage thickness distribution. In vivo thickness maps of articular layers from 33 joints with OA were also generated, and difference maps were created depicting discrepancies between the patients' cartilage thickness maps and the normative template.

RESULTS

In the normative template, the surface-wide mean+/-SD (maximum) of the cartilage thickness was 2.2+/-0.4mm (3.7mm) and 3.3+/-0.6mm (4.6mm) for the femur and patella, respectively. It was demonstrated that difference maps could be used to identify regions of thinner-than-normal cartilage in patients with OA. Patients were shown to have statistically greater regions of thin cartilage over their articular layers than the normal joints. On average, patients showed deficits in cartilage thickness in the lateral facet of the patella, in the anterior medial and lateral condyles, and in the lateral trochlea of the femur.

CONCLUSIONS

This technique can be useful for in vivo clinical evaluation of cartilage thinning in the osteoarthritic patellofemoral joint.

Kinematics of the patella in deep flexion. Analysis with magnetic resonance imaging

BACKGROUND

Little information is available on the kinematics of the normal knee in deep flexion. The purpose of this study was to use magnetic resonance imaging to analyze the patellofemoral articulation in deep flexion.

METHODS

Axial scans were made of the patellofemoral joint of twenty healthy Japanese volunteers with the knee in approximately 90 degrees of flexion, in maximum active flexion (mean [and standard deviation], 140 degrees +/- 10 degrees ), and in maximum passive flexion (mean, 156 degrees +/- 5 degrees ). A fat-suppressed, three-dimensional, fast low-angle shot sequence was used to visualize the articular cartilage. The patellofemoral contact area was determined on sequential images and was reconstructed three-dimensionally.

RESULTS

At 90 degrees of flexion, the contact area on the patella was continuous over the medial and lateral facets in fourteen knees and was located in the proximal half of the articular surface. At maximum active and passive flexion, the odd facet engaged in fifteen and eighteen knees, respectively. At maximum passive flexion, the contact area of the lateral facet moved distally and decreased significantly (p = 0.0002). From 90 degrees of flexion to maximum active flexion, the mean total contact area remained constant (3.43 +/- 0.70 and 3.62 +/- 0.72 cm (2), respectively); it then decreased significantly in maximum passive flexion (2.96 +/- 0.78 cm (2), p = 0.04).

CONCLUSIONS

The contact area on the patella was divided into two parts (the odd and lateral facets) and moved distally in deep knee flexion. The size of the contact area on the lateral facet significantly decreased in maximum passive flexion.

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.

Measurement accuracy of focal cartilage defects from MRI and correlation of MRI graded lesions with histology: a preliminary study

OBJECTIVES

Although accurate spatial measurement of cartilage thickness from MRI is possible, no studies have assessed the accuracy of measuring cartilage defect dimensions from MRI. In addition, current MR grading scales for assessing cartilage lesions have limited categories, and little is known about how well these scales correlate with histological assessment of the lesion. The objective of this preliminary study is to address both these issues.

METHODS

We performed two experiments on four cadaver knee joints from elderly donors: Experiment 1 assessed the accuracy of measuring controlled defects in cartilage, and Experiment 2 compared MRI grading (Noyes scale) of natural cartilage lesions to histological grading (Mankin scale) of the sectioned cartilage tissue. MRI was performed on 1.5 T clinical scanner (fat-suppressed 3D-SPGR at TR/TE/alpha=55/13.5/45 and 256 x 256 matrix).

RESULTS

The mean difference between defect diameters measured and introduced was less than 0.1mm, which was statistically insignificant (P=0.754). Defect depth was less accurate at >0.4mm, significantly under predicting actual defect depth (P=0.004). Correlation between Noyes grading scores and Mankin grading scores of natural lesions was moderately high (r=0.7) and statistically significant (P=0.001).

CONCLUSIONS

Three-dimensional mapping of cartilage thickness shows great promise for the accurate measurement of focal cartilage defects, though improvement is needed. The Noyes grading scale is consistent with histological Mankin grading of cartilage lesions, though enhancement of MR grading scales is needed, and warranted, based on the signal intensity information available from clinical MRI. Integration of these two analyses-focal defect measurement and signal intensity analysis-could potentially result in a valuable clinical tool for early osteoarthritis diagnosis and longitudinal tracking.

Validation of cartilage volume and thickness measurements in the human shoulder with quantitative magnetic resonance imaging

OBJECTIVE

To validate quantitative magnetic resonance imaging (qMRI) for the assessment of cartilage volume and thickness in thin and curved cartilage layers, such as the shoulder.

METHODS

Eight shoulder specimens from healthy individuals (aged 31-69 years) were investigated using a 3D gradient echo sequence with selective water excitation. After segmentation with a B-spline Snake algorithm, the cartilage volume and thickness were determined three dimensionally. The cartilage volume data were compared with water displacement of surgically removed tissue, and the thickness with A-mode ultrasound.

RESULTS

The glenoid and humeral head cartilage volume from qMRI agreed highly with that from water displacement (systematic difference, +/-1 to +/-3%; absolute difference, 4 to 7%). For the cartilage thickness, the mean systematic difference ranged from -17% (mean cartilage thickness of the glenoid) to +7% (maximal cartilage thickness of the glenoid); the standard error of the estimate was 3.7% for the humeral head, and 6.4% for the glenoid.

CONCLUSIONS

The applied technique can be used for accurate determination of cartilage volume and thickness in human joints with highly curved and thin cartilage layers, such as the shoulder. In vivo application of this method will depend on the development of efficient surface coils that allow high resolution imaging under in situ conditions.

Accuracy of cartilage and subchondral bone spatial thickness distribution from MRI

PURPOSE

To assess three-dimensional measurement accuracy of articular cartilage (AC) and subchondral bone (SB) thickness from MRI.

MATERIALS AND METHODS

A computer program was used to calculate AC and SB thickness from MRI (three-dimensional spoiled gradient echo (SPGR),.31-mm resolution, 1-mm slice thickness) of six adult femoral heads. Specimens were imaged in five anatomical planes ranging between +30 degrees to -30 degrees from neutral and cut into 2-mm thick sections along the five anatomical planes. Faxitron x-ray was used to produce microradiographic (.05-mm resolution) images of the sections.

RESULTS

In-plane measurement accuracy was.165 +/-.108 mm for AC thickness and.387 +/-.174 mm for SB thickness. Taking into account chemical-shift misregistration in SB thickness, accuracy of measurements improved to.213 +/- 128 mm. Out-of-plane (three-dimensional) thickness accuracy of the model, assessed by numerical simulation, was.015 mm. However, three-dimensional thickness errors in specimens were.319 +/-.256 mm for AC and.253 +/-.183 mm for SB thickness.

CONCLUSION

Errors in three-dimensional AC thickness were attributed to volume-averaging effects caused by oblique intersection of the image plane with the joint surface. Errors in three-dimensional SB thickness were attributed to chemical-shift artifact. We conclude that accuracy of AC thickness is within clinically acceptable standards but that more sophisticated pulse sequences are needed to improve the measurement of SB thickness.

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.

MR imaging of cartilage repair procedures

It is becoming increasingly important for the radiologist to evaluate the appearance and outcome of cartilage repair procedures. MR imaging is currently the best method for such evaluation but it is necessary to use cartilage-specific sequences and to modify those sequences when necessary to minimize artifacts from retained metal within the joint. This article reviews the surgical technique of the more commonly performed cartilage repair procedures, currently recommended techniques for the MR imaging evaluation of articular cartilage and cartilage repair procedures, and the MR imaging appearance of cartilage repair procedures and of the most frequently encountered complications following such procedures.

Correlation of knee-joint cartilage morphology with muscle cross-sectional areas vs. anthropometric variables

We tested the hypothesis that muscle cross-sectional areas (MCSAs) are more highly (and independently) correlated with cartilage morphology than are body height and weight, and that the physiological reduction of cartilage thickness with aging is associated with a proportional, age-dependent decrease in MCSAs. In 59 asymptomatic individuals (23-75 years old), morphological parameters of the knee cartilages (volume, thickness, and bone-cartilage interface area), and MCSAs were determined from magnetic resonance imaging (MRI) data. Multiple regression models were used to calculate which proportion of the variability of the normal cartilage morphology can be predicted based on independent variables. MCSAs and body height and weight showed correlation coefficients of +0.66, +0.60, and +0.25, respectively, with knee-joint cartilage volume. The correlation coefficients with cartilage thickness were +0.44, +0.35, and +0.24, respectively. Age accounted for a significant (P<0.01) reduction in cartilage thickness, but there was no proportional change of MCSAs. Approximately 76% of the variability of the knee cartilage volume could be predicted from independent variables in a multiple regression model with MCSAs contributing significant, independent information. In conclusion, we find that MCSAs are more highly correlated with cartilage morphology than are body height and weight. The significant decrease in cartilage volume and thickness with age is not associated with a proportional decrease in MCSAs.

Articular cartilage lesions of the glenohumeral joint: diagnostic effectiveness of MR arthrography and prevalence in patients with subacromial impingement syndrome

PURPOSE

To determine the prevalence of articular cartilage lesions in patients with subacromial impingement syndrome and to assess the diagnostic effectiveness of magnetic resonance (MR) arthrography in detecting such cartilage abnormalities.

MATERIALS AND METHODS

MR arthrographic images obtained in 52 consecutive patients (mean age, 45.8 years; age range, 17-73 years; 26 male and 26 female patients) were retrospectively evaluated for glenohumeral cartilage lesions. Two experienced musculoskeletal radiologists who were blinded to the arthroscopy report independently analyzed the articular cartilage. Humeral and glenoidal cartilage were assessed separately. The lesions were graded as either subtle or marked. Arthroscopic findings were the standard of reference. Sensitivity, specificity, accuracy, and interobserver agreement were calculated.

RESULTS

At arthroscopy, humeral cartilage lesions were found in 15 patients (frequency, 29%). Four lesions were subtle, and 11 were marked. Cartilage lesions of the glenoid were less frequent (eight patients; frequency, 15%): Three were subtle, and five were marked. For reader 1 and reader 2, respectively, sensitivity of MR arthrography for humeral cartilage lesions was 53% and 100%, specificity was 87% and 51%, and accuracy was 77% and 65%; sensitivity for glenoidal cartilage lesions was 75% and 75%, specificity was 66% and 63%, and accuracy was 67% and 65%. Interobserver agreement for the grading of cartilage lesions with MR arthrography was fair (humeral lesions, kappa = 0.20; glenoidal lesions, kappa = 0.27).

CONCLUSION

Glenohumeral cartilage lesions are found in up to one third of patients referred for MR arthrography for subacromial impingement syndrome. The performance of MR arthrography in the detection of glenohumeral cartilage lesions is moderate.

Magnetic resonance relaxivity of dendrimer-linked nitroxides

The relaxivity and bioreduction rates of eight dendrimer-linked nitroxides varying in the number of nitroxides per molecule were measured and the potential use of these compounds as MR contrast agents was demonstrated. The T(1) and T(2) relaxivities, measured at room temperature and 1.5 T, varied linearly with the number of nitroxides per molecule for compounds with up to 16 nitroxides per molecule. Fourth-generation polypropylenimide- (DAB) and third-generation polyamidoamine- (PAMAM) dendrimer-linked nitroxides were found to have greater relaxivity than gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA). The greater number of nitroxides per dendrimer increased relaxivity over that of a single nitroxide, allowing a decreased dose to achieve differential contrast with MR evaluations. Rates of nitroxide bioreduction were below detection threshold using EPR spectroscopy for generation 2 dendrimers and higher. A pilot assessment of in vivo cartilage uptake that compared intraarticular injection of three structurally different dendrimer-linked nitroxides with Gd-DTPA and with saline demonstrated high affinity of the DAB-dendrimer-linked nitroxides for normal rabbit articular cartilage. From these results, it is evident that target-specific dendrimer-linked nitroxides can be designed.

Long-term and resegmentation precision of quantitative cartilage MR imaging (qMRI)

OBJECTIVE

Follow up of osteoarthritis (OA) and evaluation of structure modifying OA drugs require longitudinal data on cartilage structure. The aim of this study was to analyse the long term and resegmentation precision of quantitative cartilage analysis with magnetic resonance imaging (qMRI) in vivo, and to relate precision errors to the estimated cartilage loss in OA.

METHOD

Sagittal MR images of the knee were obtained in 14 individuals, four datasets being acquired in a first imaging session. In 12 subjects, two further datasets were acquired over the next months. Image analysis was performed in the same session for image data obtained under short-term and long-term imaging conditions, and in three different sessions (months apart) for the first data set (resegmentation precision).

RESULTS

Long-term precision errors ranged from 1.4% (total knee) to 3.9% (total femur) for cartilage volume and thickness and were only marginally higher than those under short term conditions. In the medial tibia, the error was 84 mm(3) compared with an estimated loss of >1,200 mm(3) in varus OA. Precision errors for resegmentation were somewhat higher, but considerably smaller than the intersubject variability.

CONCLUSIONS

Scanner drift and changes in imaging or patient conditions appear not to represent a critical problem in quantitative cartilage analysis with magnetic resonance imaging (qMRI). In longitudinal studies, image analysis of sequential data should be performed within the same post-processing session. Under these conditions, qMRI promises to be a very powerful method to assess structural change of cartilage in OA.

Grading articular cartilage of the knee using fast spin-echo proton density-weighted MR imaging without fat suppression

OBJECTIVE

The objective of this work was to determine the accuracy of fast spin-echo proton density-weighted MR imaging in the evaluation of the articular cartilage of the knee using arthroscopy as a gold standard.

MATERIALS AND METHODS

We retrospectively reviewed MR images of the knee in 54 patients for whom arthroscopic results were available. All MR imaging studies included fast spin-echo proton density-weighted coronal and axial sequences as part of our routine protocol. Evaluation of the articular surfaces was performed by three independent observers who were unaware of the arthroscopic results. The cartilage surfaces were graded using a 3-point system, and results were compared with arthroscopic findings.

RESULTS

Of 324 cartilage surfaces evaluated, arthroscopy showed 241 surfaces as normal, 56 as containing partial-thickness defects, and 27 as containing full-thickness defects. Compared with arthroscopic data, sensitivity of MR imaging for the three reviewers was 59-73.5%; specificity, 86.7-90.5%; positive predictive value, 60.5-72.6%; negative predictive value, 86.0-90.8%; and accuracy, 79.6-86.1%. Interobserver variability for the presence of disease, which was measured using the kappa statistic, was 0.63.

CONCLUSION

Fast spin-echo proton density-weighted MR imaging sequences can be used to evaluate the cartilage of the knee with accuracy comparable to that of previously reported cartilage-specific sequences.

Cartilaginous endplates of the spine: MRI with anatomic correlation in cadavers

PURPOSE

The purpose of this work was to describe the MR appearance of cartilaginous endplates (CEPs) with close anatomic correlation in cadavers derived from elderly subjects.

METHOD

High-resolution MRI was performed on five cadaveric lumbar spines, and a total of 48 CEPs were studied with T1-weighted spin echo, T2-weighted fast spin echo, and fat-suppressed 3D spoiled GRASS gradient echo (SPGR) MR images. All specimens underwent anatomic sectioning, and gross anatomic findings were correlated with those of MRI.

RESULTS

Conventional MR images allowed gross morphologic evaluation of the integrity of the CEPs and demonstrated cartilaginous nodes. In all specimens, fat-suppressed 3D-SPGR images invariably improved visualization of the fine anatomic structures at the diskovertebral junction (p < 0.01). Various morphologic abnormalities of the CEPs demonstrated on MR images, including thinning, irregularity, erosions, cartilaginous defects, and Schmorl nodes, were confirmed on anatomic inspection.

CONCLUSION

Results in our study indicate that MRI may delineate the normal anatomy of CEPs and demonstrate morphologic changes occurring at the diskovertebral junction. Dedicated high-resolution technique and fat-suppressed 3D-SPGR images may significantly improve the diagnostic capabilities of MRI of this particular anatomic region.

Long-term assessment of arthroscopic meniscus repair: a 13-year follow-up study

A prospective study was set up to evaluate meniscal suturing using an inside-out technique. Of an initial group of 20 patients who underwent closed meniscus repair between 1985 and 1988 using an inside-out technique, 13 were studied. All patients were subjected to a clinical examination and a magnetic resonance imaging (MRI) investigation. The findings were compared with those of their previous follow-up examination (1994). The Hospital for Special Surgery (HSS) knee rating system (R.G. Stone et al. Athroscopy 1990; 73-78) was used. The study included seven men and six women, ranging in age from 29 years to 50 years (mean age: 35 years 6 months). The mean follow-up was 13 years 2 months (11 years 11 months-15 years 4 months). Six left and seven right knees were involved. Seven patients also had an anterior cruciate ligament (ACL) injury of which one was repaired 6 years after meniscal repair. All patients obtained an HSS score of more than 75%. In all patients, the site of the previous suture was still visible on MRI mainly by small metal artefacts in the meniscus. Patients with an unrepaired ACL lesion had an early onset of arthrosis and cartilage degeneration. Meniscal suturing gives good clinical long-term results. Magnetic resonance imaging, however, showed signs of mucoid degeneration or scar tissue in 46% of the patients.

Imaging articular cartilage defects in the ankle joint with 3D fat-suppressed echo planar imaging: comparison with conventional 3D fat-suppressed gradient echo imaging

PURPOSE

To shorten the examination time for articular cartilage imaging, using a recently developed three-dimensional (3D) multishot echo planar imaging (EPI) sequence with fat saturated (FS), compared to a conventional 3D fat-saturated spoiled gradient echo sequence (3D FS GRE).

MATERIAL AND METHODS

There were 32 consecutive patients with ankle joint disorders who underwent magnetic resonance imaging (MRI) in a 1.0-T unit. Hyaline cartilage was imaged with a 3D FS EPI sequence and a 3D FS GRE sequence. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, contrast-to-noise ratios (CNRs) of cartilage vs. joint fluid and bone marrow were measured.

RESULTS

The 3D FS EPI sequence provided a high CNR between cartilage and subchondral bone, similar to that of the 3D FS GRE sequence. The CNR between cartilage and effusion was significantly lower on the 3D EPI sequence due to the higher signal intensity of fluid. Both sequences were equal in lesion detection ability. The image quality of the 3D FS GRE sequence was slightly higher than that of the 3D FS EPI, but the difference was not statistically significant.

CONCLUSION

We conclude that the 3D FS EPI sequence is comparable to the 3D FS GRE sequence in the detection of cartilage lesions, with the additional advantage of reduction in scan time by a factor of 4.

Effectiveness of MR imaging in selection of patients for arthroscopy of the knee

PURPOSE

To determine the effectiveness of magnetic resonance (MR) imaging in the appropriate identification of those patients with a high clinical suspicion of internal derangements of the knee who require arthroscopic therapy.

MATERIALS AND METHODS

In a prospective multicenter study, MR imaging was performed at 0.5 T in 430 consecutive patients. The sensitivity and specificity of MR imaging in the patients who underwent arthroscopy and the corrected sensitivity and specificity of MR in all the study patients were calculated. For this correction, patients with negative MR and arthroscopic results were considered representative of the patients with negative MR results who were conservatively treated, and the number of the former was doubled. The standard errors of the corrected values were adjusted with the delta method.

RESULTS

At MR imaging, arthroscopy was indicated in 221 patients, 200 of whom underwent arthroscopy. Two hundred nine patients with negative MR imaging results were randomized for arthroscopic (105 patients) or for conservative treatment (104 patients). Of the 105 patients randomized for arthroscopy, 93 actually underwent arthroscopy. Arthroscopic treatment was necessary in 13 of 93 patients with a negative diagnosis at MR imaging. Arthroscopic treatment was necessary in 179 of 200 patients with a positive diagnosis at MR (sensitivity, 93.2%; specificity, 79.2%). Sensitivity and specificity corrected for randomization were 87.3% and 88.4%. Sensitivity and specificity corrected for randomization, respectively, were 84.1% and 94.2% for the diagnosis of medial meniscal tears and 69.5% and 94.5% for the diagnosis of lateral meniscal tears at MR.

CONCLUSION

MR imaging is an effective tool in the selection of patients for arthroscopy from among a general population.

The effects of immobilization on the characteristics of articular cartilage: current concepts and future directions

OBJECTIVE

The purpose of this paper is to review current data and concepts concerning the effect of immobilization on articular cartilage in animal models. We also evaluate the methods to measure articular cartilage changes in humans.

METHODS

Studies looking at the effects of immobilization on morphological, biochemical, and biomechanical characteristics of articular cartilage are reviewed.

RESULTS

Articular cartilage changes in immobilized animals include altered proteoglycan synthesis, as well as thinning and softening of the tissue. The overall thickness of articular cartilage in the knee decreases up to 9% after 11 weeks of immobilization and the deformation rate under test load increases up to 42%. Quantitative data about changes in human articular cartilage following immobilization are not available. This is mainly due to the lack of an accurate, reproducible, and non-invasive method to characterize articular cartilage.

DISCUSSION

An understanding of the alterations in articular cartilage following short and long term immobilization in humans is essential for the optimization of rehabilitation programs. Refined imaging techniques combined with state-of-the-art visualization tools could allow the systematical monitoring of articular cartilage morphology changes in immobilized humans.

Fat-suppressed 3D-T1-weighted-echo planar imaging: comparison with fat-suppressed 3D-T1-weighted-gradient echo in imaging the cartilage of the knee

This study was conducted to compare a three-dimensional (3D) multi-shot echo-planar imaging (EPI) sequence with fat-suppression (FS) with the 3D-fat-suppressed gradient echo (GRE-FS) sequence in imaging the cartilage of the knee. One hundred sixty-nine patients were studied prospectively. The cartilage was imaged in the sagittal plane with: (a) 3D-T1-EPI-FS and (b) 3D-T1-GRE-FS sequences using a 1T MR scanner. The signal-to-noise ratio (SNR) of bone (b) and cartilage (c), and relative contrast (ReCon) between bone and cartilage and meniscus and cartilage were measured in 60 patients with arthroscopically normal cartilage. The imaging accuracy was assessed by comparing with linear regression analysis (length and depth) 32 defects in the cartilage of cadaveric (human and bovine) knees. The 3D-T1-EPI-FS provided better bone marrow signal suppression, better SNRc and better ReCon(bc) and ReCon(cm) (p<0.01). The 3D-T1-EPI-FS showed better accuracy concerning the depth of the defects and the 3D-T1-GRE-FS better accuracy concerning the length of the defects. In conclusion, the 3D-T1-EPI-FS pulse sequence could be included in the routine protocol in imaging the cartilage of the knee because it achieves high SNR of the cartilage and high ReCon compared to the surrounding structures, at a reduced scan time.

Quantitative cartilage imaging of the human hind foot: precision and inter-subject variability

Alterations of ankle cartilage are observed in degenerative and inflammatory joint disease, but cartilage cannot be directly visualized by radiography. The purpose of this study was therefore to analyze the feasibility and precision of quantitative cartilage imaging in the human hind foot (talocrural, talotarsal, and intertarsal joints), and to report the inter-subject variability for cartilage volume, thickness and surface areas. The feet of 16 healthy volunteers were imaged using a 3D gradient-echo magnetic resonance imaging sequence with water-excitation. After interpolation to a resolution of 1 x 0.125 x 0.125 mm3 the cartilage plates were segmented, and the cartilage volume, thickness, and surface areas determined. The precision (four repeated measurements) was examined in eight volunteers, the RMS average CV% being 2.1% to 10.9% in single joint surfaces, and < or = 3% for the cumulative values of all joints. The mean cartilage thickness ranged from 0.57+/-0.08 (navicular surface) to 0.89+/-0.19 mm (trochlear surface for tibia). In conclusion this study shows that it is feasible to quantify thin cartilage layers in the hind foot under in vivo imaging conditions, and that the precision errors are substantially smaller than the inter-subject variability in healthy subjects.

Automated techniques for visualization and mapping of articular cartilage in MR images of the osteoarthritic knee: a base technique for the assessment of microdamage and submicro damage

The purpose of this paper is to describe automated techniques for the visualization and mapping of articular cartilage in magnetic resonance (MR) images of the osteoarthritic knee. The MR sequences and analysis software which will be described allow the assessment of cartilage damage using a range of standard scanners. With high field strength systems it would be possible, using these techniques, to assess micro-damage. The specific aim of the paper is to develop and validate software for automated segmentation and thickness mapping of articular cartilage from three-dimensional (3-D) gradient-echo MR images of the knee. The method can also be used for MR-based assessment of tissue engineered grafts. Typical values of cartilage thickness over seven defined regions can be obtained in patients with osteoarthritis (OA) and control subjects without OA. Three groups of patients were studied. The first group comprised patients with moderate OA in the age range 45-73 years. The second group comprised asymptomatic volunteers of 50-65 years; the third group, younger volunteers selected by clinical interview, history and X-ray. In this paper, sagittal 3-D spoiled-gradient steady-state acquisition images were obtained using a 1.5-T GE whole-body scanner with a specialist knee coil. For validation bovine and porcine cadaveric knees were given artificial cartilage lesions and then imaged. The animal validations showed close agreement between direct lesion measurements and those obtained from the MR images. The feasibility of semi-automated segmentation is demonstrated. Regional cartilage thickness values are seen as having practical application for fully automated detection of OA lesions even down to the submicrometer level.

Functional adaptation of human joints to mechanical stimuli

OBJECTIVE

This study tests the hypothesis that functional adaptation occurs in human joints, and that substantial differences in joint 'loading history' explain the phenotypic variability observed in human cartilage morphology.

METHOD

We examined 18 triathletes (nine men and nine women) who had been physically active throughout life (training for >10 h per week for the last 3 years), and 18 volunteers that had never been physically active on a regular basis. The right knee joints were imaged with a previously validated fat-suppressed gradient-echo MR sequence. Cartilage volume, thickness, joint surface areas, and normalized cartilage signal intensity were determined with post-processing software, specifically designed for these applications.

RESULTS

The knee joint cartilage thickness, and signal intensity were not significantly different between athletes and inactive volunteers, but male athletes displayed significantly larger knee joint surfaces (P< 0.01; +8.8%). Female athletes displayed a significantly larger medial tibia (P< 0.05; +18.9%), the difference in the total knee surface area reaching borderline significance (P=0.08; +7.0%).

CONCLUSIONS

The results suggest that joint size can be modulated during growth, but that (opposite to muscle and bone) the thickness of the cartilage does not adapt to mechanical stimulation. This finding may reveal a general principle in the development and functional adaptation of diarthrodial joints, elucidating an important mechanism for reducing mechanical stress in biphasic cartilage layers.

Magnetic resonance imaging-based assessment of cartilage loss in severe osteoarthritis: accuracy, precision, and diagnostic value

OBJECTIVE

To examine the in vivo accuracy and precision of magnetic resonance imaging (MRI)-based assessment of cartilage loss in patients with severe osteoarthritis (OA) of the knee.

METHODS

High-resolution MRI images of the tibial cartilage were obtained in 8 patients prior to total knee arthroplasty, using a water-excitation gradient-echo MRI sequence (acquisition time 6 minutes 19 seconds; spatial resolution 1.2 x 0.31 x 0.31 mm3). The MRI measurements were repeated after joint repositioning. The precision of the cartilage volume and thickness computations was determined after 3-dimensional reconstruction. During surgery, the tibial plateaus were resected, and the MRI data were compared with water displacement of surgically retrieved cartilage.

RESULTS

The standard deviation (coefficient of variation) of repeated tibial cartilage volume measurements was 56 mm3 (5.5%) medially and 59 mm3 (3.8%) laterally. The deviation from surgically removed tissue was -13%, on average, with a high linear correlation between both methods (r = 0.98). In patients with varus OA, the tissue loss was estimated to be 1,290 mm3 in the medial tibia and 1,150 mm3 in the lateral tibia, compared with the data in healthy volunteers.

CONCLUSION

Noninvasive quantitative MRI-based analysis of cartilage morphometry in severe OA is accurate, precise, and displays high potential diagnostic value.

High-resolution MRI detects cartilage swelling at the early stages of experimental osteoarthritis

OBJECTIVE

The progressive early changes in cartilage and subchondral bone in an experimental model of osteoarthritis (OA) were investigated with high-resolution magnetic resonance imaging (MRI) and microradiography.

METHODS

Partial medial meniscectomy was performed in the left knee of 16 rabbits. Four normal and four sham-operated additional rabbits were used as controls. Changes in cartilage and subchondral bone were sequentially assessed after surgery with MRI at 0, 2, 4, 6, 8 and 10 weeks, subchondral bone variations quantified postoperatively on microradiographs of sagittal sections at 6 and 10 weeks and the macroscopic alterations graded according to the severity of joint changes.

RESULTS

MRI demonstrated a progressive increase in the articular cartilage thickness in the weight-bearing area of the femur at weeks 4, 6 and 8 vs basal. Tibial cartilage thickness only showed a significant increment at week 6. No significant abnormalities were detected on X-rays in subchondral bone when compared to controls. Macroscopically, 4 weeks after the operation OA rabbits had only slight cartilage discoloration. Cartilage eburnation, pitting, superficial erosions and osteophytes were detected at week 6. These abnormalities were more evident at 8 and 10 weeks after meniscectomy.

CONCLUSION

The focal increase in cartilage thickness is one of the earliest measurable changes in OA and preceeds subchondral bone remodeling. The measurement of cartilage thickness variations with MRI can be used to follow the course of OA and to evaluate the potential beneficial effect of novel therapies.

Magnetic resonance imaging of rheumatoid arthritis: the evolution of clinical applications through clinical trials

Powerful techniques are being developed for evaluating rheumatoid arthritis with magnetic resonance imaging (MRI). Much of this development is being driven by the pharmaceutical and biotechnology industries searching for novel therapies for this disease. Accordingly, the imaging tools that ultimately will be used to direct patients to specific therapies and then to monitor treatment effectiveness and safety are currently being refined and validated in rigorous multicenter and multinational clinical trials aimed at gaining regulatory approval of these new therapies. As these trials approach completion, rheumatologists can anticipate an increased demand for expertise and experience in evaluating disease progression and treatment response with these techniques and the emergence of MRI systems specifically designed for this market. The following discussion reviews this novel pathway for evolving imaging techniques for clinical use through clinical drug trials, lists the most promising MRI markers available today for evaluating joint destruction in rheumatoid arthritis, and speculates on how these techniques will find their way into clinical practice.

Evaluation of chondromalacia of the patella with axial inversion recovery-fast spin-echo imaging

The purpose of our study was to assess the accuracy of inversion recovery-fast spin-echo (IR-FSE) imaging for the evaluation of chondromalacia of the patella. Eighty-six patients were included, they underwent magnetic resonance (MR) examination and subsequent knee arthroscopy. Medial and lateral facets of the patella were evaluated separately. Axial images were obtained by using IR-FSE (TR/TE/TI = 3000/25/150 msec; echo train length, 8; 4-mm thickness; 12-cm field of view; 512 x 256 matrix; two, number of excitations) with a 1.5-T MR machine. MR interpretation of chondromalacia was made on the basis of the arthroscopic grading system. Of a total of 172 facets graded, arthroscopy revealed chondromalacia in 14 facets with various grades (G0, 158; G1, 1; G2, 3; G3, 6; G4, 4). Sensitivity, specificity, and accuracy in the chondromalacia grades were 57.1%, 93.0%, and 90.1%, respectively. There was one false-negative case (G4) and 11 false-positive cases (G1, eight; G2, two; G3, one). Sensitivity and specificity corrected by one grade difference were improved to 85.7% and 98.1%, respectively. When cartilage changes were grouped into early (corresponding to grade 1 and 2) and advanced (grade 3 and 4) diseases, sensitivity and specificity of the early and advanced diseases were 75% and 94% and 80% and 99%, respectively. IR-FSE imaging of the knee revealed high specificity but low sensitivity for the evaluation of chondromalacia of the patella.