Cartilage imaging: motivation, techniques, current and future significance

Articular cartilage and labral lesions of the glenohumeral joint: diagnostic performance of 3D water-excitation true FISP MR arthrography

OBJECTIVE

To evaluate the diagnostic performance of MR arthrography in the detection of articular cartilage and labral lesions of the glenohumeral joint using a transverse 3D water-excitation true fast imaging with steady-state precession (FISP) sequence.

MATERIALS AND METHODS

Seventy-five shoulders were included retrospectively. Shoulder arthroscopy was performed within 6 months of MR arthrography. MR images were evaluated separately by two radiologists. They were blinded to clinical and arthroscopic information. Arthroscopy served as the reference standard.

RESULTS

For the detection of humeral cartilage lesions, sensitivities and specificities were 86% (12/14)/89% (50/56) for observer 1 and 93%/86% for observer 2) for the transverse true FISP sequence and 64%/86% (50%/82% for observer 2) for the coronal intermediate-weighted spin-echo images. The corresponding values for the glenoidal cartilage were 60% (6/10)/88% (51/58) (80%/76% for observer 2) and 70%/86% (60%/74% for observer 2) respectively. For the detection of abnormalities of the anterior labrum (only assessed on true FISP images) the values were 94% (15/16)/84% (36/43) (88%/79% for observer 2). The corresponding values for the posterior labrum were 67% (8/12)/77% (36/47) (observer 2: 25%/74%). The kappa values for the grading of the humeral and glenoidal cartilage lesions were 0.81 and 0.55 for true FISP images compared with 0.49 and 0.43 for intermediate-weighted fast spin-echo images. Kappa values for true FISP evaluation of the anterior and posterior part of the labrum were 0.81 and 0.70.

CONCLUSION

Transverse 3D true FISP MR arthrography images are useful for the difficult diagnosis of glenohumeral cartilage lesions and suitable for detecting labral abnormalities.

Improved identification of the palmar fibrocartilage of the navicular bone with saline magnetic resonance bursography

Fibrocartilage degeneration is the earliest pathologic finding in navicular disease but remains difficult to detect, even with magnetic resonance (MR) imaging. We hypothesized that injection of the navicular bursa with saline would improve accuracy of MR imaging evaluation of palmar fibrocartilage. Thoracic limbs were collected from 11 horses within 6 h of death. Imaging was performed with a 1.5 T magnet using sagittal 2D proton density and transverse 3D FLASH sequences with fat saturation. For the purpose of determining sensitivity and specificity of the MR images, fibrocartilage was classified as normal or abnormal, based on combination of the findings of gross and microscopic pathology. Thickness of fibrocartilage was measured on histologic sections and corresponding transverse FLASH MR images before and after injection of saline. A paired Student's t-test was used for comparison of measurements. Partial thickness fibrocartilage loss was present in 6 of 22 limbs. Sensitivity of precontrast MR images for detection of lesions was 100% while specificity was 6%. Saline MR arthrography resulted in both sensitivity and specificity of 100% based on consensus review. Mean histologic fibrocartilage thickness was 0.75 +/- 0.12 mm. Mean fibrocartilage thickness on precontrast transverse FLASH images was 0.93 +/- 0.065 and 0.73 +/- 0.09 mm on postsaline images. The histologic cartilage thickness was signficantly different from that in precontrast images (P<0.001) but not in images acquired after saline injection (P = 0.716). Based on our results, and using pulse sequences as described herein, navicular fibrocartilage can only be evaluated reliably for the presence of partial thickness lesions after intrabursal injection of saline.

Imaging of lower limb cartilage

The cartilage of the lower limb joints is exposed to high levels of mechanical stress and therefore is a frequent site of degenerative and traumatic lesions. Magnetic resonance imaging (MRI) is the modality of choice for the assessment of these cartilage lesions. To date, clinically available sequences have focused on morphological defects and cartilage loss. Efforts have been made in recent years to depict cartilage lesions at an earlier stage, with new quantitative sequences focusing on the biochemical assessment of tissue.After a brief review of the hyaline cartilage structure, we review the current morphological imaging methods and the biochemical MRI techniques to assess the cartilage. We then illustrate the application of these MRI sequences for the most common degenerative and traumatic disorders affecting lower limb cartilage.

Non-invasive MRI assessment of the articular cartilage in clinical studies and experimental settings

Attrition and eventual loss of articular cartilage are important elements in the pathophysiology of osteoarthritis (OA). Preventing the breakdown of cartilage is believed to be critical to preserve the functional integrity of a joint. Chondral injuries are also common in the knee joint, and many patients benefit from cartilage repair. Magnetic resonance imaging (MRI) and advanced digital post-processing techniques have opened possibilities for in vivo analysis of cartilage morphology, structure, and function in healthy and diseased knee joints. Techniques of semi-quantitative scoring of human knee cartilage pathology and quantitative assessment of human cartilage have been developed. Cartilage thickness and volume have been quantified in humans as well as in small animals. MRI detected cartilage loss has been shown to be more sensitive than radiographs detecting joint space narrowing. It is possible to longitudinally study knee cartilage morphology with enough accuracy to follow the disease-caused changes and also evaluate the therapeutic effects of chondro-protective drugs. There are also several MRI methods that may allow evaluation of the glycosaminoglycan matrix or collagen network of articular cartilage, and may be more sensitive for the detection of early changes. The clinical relevance of these methods is being validated. With the development of new therapies for OA and cartilage injury, MR images will play an important role in the diagnosis, staging, and evaluation of the effectiveness of these therapies.

Patellar cartilage: T2 values and morphologic abnormalities at 3.0-T MR imaging in relation to physical activity in asymptomatic subjects from the osteoarthritis initiative

PURPOSE

To study the interrelationship between patella cartilage T2 relaxation time, other knee abnormalities, and physical activity levels in asymptomatic subjects from the Osteoarthritis Initiative (OAI) incidence cohort.

MATERIALS AND METHODS

The study had institutional review board approval and was HIPAA compliant. One hundred twenty subjects from the OAI without knee pain (age, 45-55 years) and with risk factors for knee osteoarthritis (OA) were studied by using knee radiographs, 3.0-T knee magnetic resonance (MR) images (including intermediate-weighted fast spin-echo and T2 mapping sequences), and the Physical Activity Scale for the Elderly. MR images of the right knee were assessed by two musculoskeletal radiologists for the presence and grade of abnormalities. Segmentation of the patella cartilage was performed, and T2 maps were generated. Statistical significance was determined by using analysis of variance, chi(2) analysis, correlation coefficient tests, the Cohen kappa, and a multiple linear regression model.

RESULTS

Cartilage lesions were found in 95 (79.0%) of 120 knees, and meniscal lesions were found in 54 (45%) of 120 knees. A significant correlation between patella cartilage T2 values and the severity and grade of cartilage (P = .0025) and meniscus (P = .0067) lesions was demonstrated. Subjects with high activity levels had significantly higher prevalence and grade of abnormalities and higher T2 values (48.7 msec +/-4.35 vs 45.8 msec +/-3.93; P < .001) than did subjects with low activity levels.

CONCLUSION

Middle-aged asymptomatic individuals with risk factors for knee OA had a high prevalence of cartilage and meniscus knee lesions. Physically active individuals had more knee abnormalities and higher patellar T2 values. Additional studies will be needed to determine causality.

T2 measurements of cartilage in osteoarthritis patients with meniscal tears

OBJECTIVE

The objective of this study was to quantitatively assess cartilage degeneration via T2 mapping to compare patients with and those without meniscal tears.

SUBJECTS AND METHODS

Thirty-seven patients (18 men, mean age +/- SD, 65.7 +/- 7.8 years; 19 women, mean age, 63.8 +/- 12.0 years) with clinical symptoms of osteoarthritis were studied on 3-T MRI using a 2D multiecho spin-echo sequence for T2 mapping. Meniscal signal and morphology were qualitatively graded and correlated to the T2 values of cartilage. Analysis of covariance, Bonferroni multiple comparison correction, and Spearman's correlation coefficients were used for statistical analysis.

RESULTS

Patients with meniscal tears (median +/- interquartile range, 50.1 +/- 6.1 milliseconds) had significantly (p = 0.021) higher T2 values of cartilage than those without meniscal tears (45.7 +/- 4.8 milliseconds). T2 values of cartilage were significantly higher in the medial compartment than in the lateral compartment in patients with medial meniscal tears (p = 0.018).

CONCLUSION

T2 measurements are increased in patients with meniscal tears; this finding adds support to the theory of an association of osteoarthritis with damage to both the menisci and hyaline cartilage.

T2 assessment and clinical outcome following autologous matrix-assisted chondrocyte and osteochondral autograft transplantation

OBJECTIVE

Both, matrix-assisted chondrocyte transplantation (MACT) and osteochondral autograft transplantation (OCT), are applied for treatment of articular cartilage defects. While previous clinical studies have compared the respective outcome, there is no such information investigating the ultrastructural composition using T2 mapping comparing cartilage T2 values of the repair tissue (RT).

METHODS

Eighteen patients that underwent MACT or OCT for treatment of cartilage defects at the knee joint (nine MACT, nine OCT) were matched for gender (one female, eight male pairs), age (33.8), body mass index (BMI) (28.3), defect localization, and postoperative interval (41.6 months). T2 assessment was accomplished by T2 maps, while the clinical evaluation included the Lysholm and Cincinnati knee scores, a visual analogue scale (VAS) for pain, the Tegner activity scale, and the Short Form-36.

RESULTS

Global T2 values of healthy femoral cartilage (HC) were similar among groups, while T2 values of the RT following MACT (46.8ms, SD 8.6) were significantly lower when compared to RT T2 values after OCT (55.5ms, SD 6.7) (P=0.048). MACT values were also significantly lower in comparison to HC (52.5ms, SD 7.9) within MACT patients (P=0.046), while OCT values were significantly higher compared to HC (49.9ms, SD 5.1) within OCT patients (P=0.041). The clinical outcome following MACT was consistently superior to that after OCT while only the Lysholm score reached the level of significance (MACT 77.0, OCT 66.8; P=0.04).

CONCLUSION

These findings indicate that MACT and OCT result in a different ultrastructural outcome, which is only partially represented by the clinical picture.

[New imaging techniques in the evaluation of joint cartilage]

Magnetic resonance (MR) imaging provides an excellent spatial resolution to visualize cartilage and define its main properties. Both 1.5 and especially 3 Tesla equipments have become very efficient in showing the whole articular cartilage and classifying the degenerative damage by analyzing morphological, structural and physical properties. MR evaluation of articular cartilage is of great clinical importance due to the prevalence of degenerative lesions and the development of new drugs and surgery-based treatments. In this work we explain the advances in the MR quantitation of the articular cartilage properties, particularly focusing on T2 and T1 relaxation times, the distribution of first-pass contrast agent (pharmacokinetic study) and late enhancement percentage. By using specific sequences and adequate measuring techniques, MR allows the evaluation of important parameters such as cartilage surface, thickness and volume; signal intensity and the physical properties related to collagen integrity and edema; cartilage perfusion and endothelial permeability related to neovascularization; and the presence of late enhancement areas, related to proteoglycan concentrations. This information will aid early diagnosis, establishment of the degree of degeneration, assessment of prognosis, definition of therapeutic options and evaluation of treatment effectiveness. The study of the cartilage structural and functional alterations by MR imaging is an excellent biomarker of tissue degeneration.

The in vivo effects of unloading and compression on T1-Gd (dGEMRIC) relaxation times in healthy articular knee cartilage at 3.0 Tesla

PURPOSE

The purpose was to investigate the in vivo effects of unloading and compression on T1-Gd relaxation times in healthy articular knee cartilage.

MATERIALS AND METHODS

Ten volunteers were enrolled, and dGEMRIC images of their right knee joints were obtained using 3.0-T MR at three timepoints: directly following exercise ("baseline"), approximately 15 min after unloading ("unloading") and during application of a compressive force (50% of the body weight) generated by a loading device via a footplate ("compression").

RESULTS

Our analysis of variance of pooled data from all cartilage zones demonstrated a significant mean T1-Gd decrease of 56.6 ms between baseline and compression (p < 0.001), and a significant mean decrease of 42.1 ms between unloading and compression (p < 0.001). No significant difference was found between baseline and unloading. Higher mean T1-Gd values were observed in the cartilage contact zone (central femoral and tibial zones; 698.3 +/- 162.2 ms) than in the non-contact zone (anterior and posterior femoral and tibial zones, and dorsal femoral zone; 662.9 +/- 149.3 ms; p < 0.01).

CONCLUSION

T1-Gd times appear to be sensitive to mechanical cartilage stress, and thus, further studies are warranted that investigate the relationship between the biochemical load response and the biomechanical properties of articular cartilage.

Spatial distribution and relationship of T1rho and T2 relaxation times in knee cartilage with osteoarthritis

T(1rho) and T(2) relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T(1rho) and T(2) values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T(1rho) and T(2) values was investigated using Z-scores. The spatial variation of T(1rho) and T(2) values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray-level co-occurrence matrices (GLCM). The mean Z-scores for T(1rho) and T(2) values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T(1rho) and T(2) Z-scores showed a large range in both controls and OA patients (0.2-0.7). OA patients had significantly greater GLCM contrast and entropy of T(1rho) values than controls (P < 0.05). In summary, T(1rho) and T(2) values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T(1rho) and T(2) values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA.

CT arthrography, MR arthrography, PET, and scintigraphy in osteoarthritis

CT arthrography and MR arthrography are accurate methods for the study of surface cartilage lesions and cartilage loss. They also provide information on subchondral bone and marrow changes, and ligaments and meniscal lesions that can be associated with osteoarthritis. Nuclear medicine also offers new insights in the assessment of the disease. This article discusses the strengths and limitations of CT arthrography and MR arthrography. It also highlights nuclear medicine methods that may be relevant to the study of osteoarthritis in research and clinical practice.

Assessement of rheumatic diseases with computational radiology: current status and future potential

In recent years, several computational image analysis methods to assess disease progression in rheumatic diseases were presented. This review article explains the basics of these methods as well as their potential application in rheumatic disease monitoring, it covers radiography, sonography as well as magnetic resonance imaging in quantitative analysis frameworks.

MRI in degenerative arthritides: structural and clinical aspects

Owing to the potential to image not only bone but also cartilage, bone marrow, and the surrounding internal soft tissue structures, MRI is particularly useful for the assessment of degenerative arthritides. Cartilage-sensitive MRI techniques have been shown to have a significant correlation with arthroscopic grading scores. MRI is also helpful in differentiating osteoarthritis from avascular necrosis, labral pathology, and pigmented villonodular synovitis. This chapter describes advanced imaging techniques, including driven equilibrium Fourier transform (DEFT) and steady-state free precision (SSFP) imaging, direct MRI arthrography, and 3D-T1rho-relaxation mapping.

T2 mapping of articular cartilage of glenohumeral joint with routine MRI correlation--initial experience

The evaluation of articular cartilage currently relies primarily on the identification of morphological alterations of the articular cartilage. Unlike anatomic imaging, T2 mapping is sensitive to changes in the chemical composition and structure of the cartilage. Clinical evaluation of T2 mapping of the glenohumeral joint has not been previously reported. The objectives of this study were to evaluate the feasibility of magnetic resonance T2 mapping of the glenohumeral joint in routine clinical imaging, to assess the normal T2 mapping appearance of the glenohumeral joint, and to compare the findings on T2 maps to conventional MR pulse sequences. Magnetic resonance imaging (MRI) examinations of 27 shoulders were performed in a routine clinical setting. All studies included acquisition of T2 mapping using a dedicated software. The T2 maps were analyzed along with the routine MR exam and correlation of cartilage appearance on T2 map and on conventional MR sequences. T2 imaging maps were obtained successfully in all patients. T2 maps and routine MRI correlated in cases of normal cartilage and prolonged T2 values and cartilage defects. In four cases, increased T2 relaxation times in the cartilage and cartilage defects were more apparent on T2 maps. Acquisition of T2 maps at the time of routine MRI scanning is feasible and not time-consuming.

Isotropic 3D fast spin-echo imaging versus standard 2D imaging at 3.0 T of the knee--image quality and diagnostic performance

The objective of this study was to compare a newly developed fat-saturated intermediate-weighted (IM-w) 3D fast spin-echo (FSE) sequence with standard 2D IM-w FSE sequences regarding image quality and diagnostic performance in assessing abnormal findings of the knee. MR imaging was performed at 3.0 T in 50 patients. Images were assessed independently by three radiologists. Image quality was rated significantly higher (p < 0.05) for the 2D versus the 3D FSE sequences. Sensitivity for cartilage lesions was slightly higher for the 3D sequence, but specificity was lower. Low contrast objects were better visualized with 2D sequences, while high contrast objects were better shown with the 3D sequence. Confidence scores were higher for 2D than for 3D sequences, but differences were not significant. In conclusion, isotropic 3D FSE IM-w imaging may enhance standard knee MRI by increased visualization of high contrast lesions; however, 3D FSE image quality was lower.

Assessment of cartilage-dedicated sequences at ultra-high-field MRI: comparison of imaging performance and diagnostic confidence between 3.0 and 7.0 T with respect to osteoarthritis-induced changes at the knee joint

OBJECTIVE

The objectives of the study were to optimize three cartilage-dedicated sequences for in vivo knee imaging at 7.0 T ultra-high-field (UHF) magnetic resonance imaging (MRI) and to compare imaging performance and diagnostic confidence concerning osteoarthritis (OA)-induced changes at 7.0 and 3.0 T MRI.

MATERIALS AND METHODS

Optimized MRI sequences for cartilage imaging at 3.0 T were tailored for 7.0 T: an intermediate-weighted fast spin-echo (IM-w FSE), a fast imaging employing steady-state acquisition (FIESTA) and a T1-weighted 3D high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) sequence. Three healthy subjects and seven patients with mild OA were examined. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), diagnostic confidence in assessing cartilage abnormalities, and image quality were determined. Abnormalities were assessed with the whole organ magnetic resonance imaging score (WORMS). Focal cartilage lesions and bone marrow edema pattern (BMEP) were also quantified.

RESULTS

At 7.0 T, SNR was increased (p < 0.05) for all sequences. For the IM-w FSE sequence, limitations with the specific absorption rate (SAR) required modifications of the scan parameters yielding an incomplete coverage of the knee joint, extensive artifacts, and a less effective fat saturation. CNR and image quality were increased (p < 0.05) for SPGR and FIESTA and decreased for IM-w FSE. Diagnostic confidence for cartilage lesions was highest (p < 0.05) for FIESTA at 7.0 T. Evaluation of BMEP was decreased (p < 0.05) at 7.0 T due to limited performance of IM-w FSE.

CONCLUSION

Gradient echo-based pulse sequences like SPGR and FIESTA are well suited for imaging at UHF which may improve early detection of cartilage lesions. However, UHF IM-w FSE sequences are less feasible for clinical use.

Comparative study of imaging at 3.0 T versus 1.5 T of the knee

PURPOSE

The objectives of the study were to compare MR imaging at 1.5 and 3.0 T in the same patients concerning image quality and visualization of cartilage pathology and to assess diagnostic performance using arthroscopy as a standard of reference.

MATERIALS AND METHODS

Twenty-six patients were identified retrospectively as having comparative 1.5 and 3.0 T MR studies of the knee within an average of 102 days. Standard protocols included T1-weighted and fat-saturated intermediate-weighted fast spin-echo sequences in three planes; sequence parameters had been adjusted to account for differences in relaxation at 3.0 T. Arthroscopy was performed in 19 patients. Four radiologists reviewed each study independently, scored image quality, and analyzed pathological findings. Sensitivities, specificities, and accuracies in diagnosing cartilage lesions were calculated in the 19 patients with arthroscopy, and differences between 1.5 and 3.0 T exams were compared using paired Student's t tests with a significance threshold of p < 0.05.

RESULTS

Each radiologist scored the 3.0 T studies higher than those obtained at 1.5 T in visualizing anatomical structures and abnormalities (p < 0.05). Using arthroscopy as a standard of reference, diagnosis of cartilage abnormalities was improved at 3.0 T with higher sensitivity (75.7% versus 70.6%), accuracy (88.2% versus 86.4%), and correct grading of cartilage lesions (51.3% versus 42.9%). Diagnostic confidence scores were higher at 3.0 than 1.5 T (p < 0.05) and signal-to-noise ratio at 3.0 T was approximately twofold higher than at 1.5 T.

CONCLUSION

MRI at 3.0 T improved visualization of anatomical structures and improved diagnostic confidence compared to 1.5 T. This resulted in significantly better sensitivity and grading of cartilage lesions at the knee.

Meniscal measurements of T1rho and T2 at MR imaging in healthy subjects and patients with osteoarthritis

PURPOSE

To prospectively evaluate differences in T1(rho) (T1 relaxation time in the rotating frame) and T2 values in the meniscus at magnetic resonance (MR) imaging in both patients with varying degrees of osteoarthritis (OA) and healthy control subjects.

MATERIALS AND METHODS

The study was institutional review board approved and HIPAA compliant. Written informed consent was obtained from all subjects. T1(rho) and T2 measurements were performed at 3.0-T MR imaging in 60 subjects deemed to be healthy (n = 23; mean age, 34.1 years +/- 10.0 [standard deviation]; age range, 23-59 years), having mild OA (n = 27; mean age, 52.5 years +/- 10.9; age range, 32-69 years), or having severe OA (n = 10; mean age, 61.6 years +/- 11.6; age range, 50-86 years). Semiautomatic segmentation was performed to generate T1(rho) and T2 maps of the menisci. Clinical findings were assessed by using Western Ontario and McMaster Osteoarthritis (WOMAC) questionnaires. Differences in T1(rho) and T2 values between the three subject groups were calculated by using two-tailed t tests (with P < .05 indicating significance), and receiver operating characteristic analyses were performed. Correlations of meniscal T1(rho) and T2 values with age, cartilage-derived T1(rho) and T2 parameters, and WOMAC scores were calculated.

RESULTS

Significant differences between the three subject groups were found: Mean T1(rho) values were 14.7 msec +/- 5.5, 16.1 msec +/- 6.6, and 19.3 msec +/- 7.6 for the healthy, mild OA, and severe OA groups, respectively. Mean T2 values were 11.4 msec +/- 3.9, 13.5 msec +/- 4.7, and 16.6 msec +/- 8.2 for the healthy, mild OA, and severe OA groups, respectively. Correlations of meniscal T1(rho) and T2 values with subject age (R(2) = 0.18, for correlation with T2 only), cartilage-derived parameters (R(2) = 0.14-0.29), and WOMAC scores (R(2) = 0.11-0.45) were significant.

CONCLUSION

Meniscal T1(rho) and T2 values correlate with clinical findings of OA and can be used to differentiate healthy subjects from patients with mild or severe OA.

Novel contrast mechanisms at 3 Tesla and 7 Tesla

Osteoarthritis (OA) is the most common musculoskeletal degenerative disease, affecting millions of people. Although OA has been considered primarily a cartilage disorder associated with focal cartilage degeneration, it is accompanied by well-known changes in subchondral and trabecular bone, including sclerosis and osteophyte formation. The exact cause of OA initiation and progression remains under debate, but OA typically first affects weightbearing joints such as the knee. Magnetic resonance imaging (MRI) has been recognized as a potential tool for quantitative assessment of cartilage abnormalities due to its excellent soft tissue contrast. Over the last two decades, several new MR biochemical imaging methods have been developed to characterize the disease process and possibly predict the progression of knee OA. These new MR biochemical methods play an important role not only for diagnosis of disease at an early stage, but also for their potential use in monitoring outcome of various drug therapies (success or failure). Recent advances in multicoil radiofrequency technology and high field systems (3 T and above) significantly improve the sensitivity and specificity of imaging studies for the diagnosis of musculoskeletal disorders. The current state-of-the-art MR imaging methods are briefly reviewed for the quantitative biochemical and functional imaging assessment of musculoskeletal systems.

Quantitative imaging of musculoskeletal tissue

Quantitative imaging of musculoskeletal tissue, including radiography, computed tomography (CT), and magnetic resonance imaging (MRI), has become the essential methodology in clinical practice for diagnosis and monitoring of various musculoskeletal conditions. Furthermore, quantitative imaging technologies have become indispensable for research and development in diseases of the human skeleton. Standardized methods of image analysis have been developed through the years to quantify measurements on bone and cartilage with high precision and accuracy. Key areas of musculoskeletal disease where quantitative imaging is currently employed are osteoporosis and arthritis.

Micro-computed tomography of early lesions of osteochondrosis in the tarsus of foals

INTRODUCTION

Osteochondrosis (OC) is an important developmental orthopedic disease of human and equine patients. The disease is defined as a focal disturbance in enchondral ossification. In horses, the disturbance can occur secondary to failure of the blood supply to growth cartilage. Diagnosis of the early, subclinical stages that can clarify the etiology is currently confined to cross-sectional histological examination. The potential for micro-computed tomography (micro-CT) with angiography to detect early lesions of OC has not yet been investigated.

MATERIALS AND METHODS

Nine Standardbred foals bred from parents with OC of the tarso-crural joint were sacrificed at weekly intervals from birth to 7 weeks of age. Permanent barium angiograms were created within one hind limb post mortem, and samples collected from two predilection sites for OC within the tarso-crural joint of the perfused hind limb. The resulting 18 sample blocks were scanned with a custom-built micro-CT equipment set-up, and analyzed as 2D slices and 3D volume rendered models before sectioning for conventional histological examination.

RESULTS

Histological examination identified eight early lesions in seven locations within six joints from the nine foals. Micro-CT with angiography was able to detect seven lesions in the same sites as histological examination. Lesions consisted of non-perfused foci within growth cartilage. No perfused vessels exited from subchondral bone deep to any lesion. Six of the seven lesions were associated with focal defects in the subchondral bone plate. Evidence of ongoing ossification was seen in three out of the seven lesions and included one separate center of ossification.

CONCLUSION

Micro-CT was a useful technique for examination of early lesions of OC. The results of micro-CT were compatible with failure of cartilage canal vessels at the point where they cross the ossification front. Resultant areas of ischemic chondronecrosis were associated with focal delay in enchondral ossification as visualized in 3D volume rendered models. Micro-CT combined with histology clarified the role of different forms of ossification in the secondary repair responses to lesions.

Prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects-a 3.0 T magnetic resonance imaging study

PURPOSE

To determine the prevalence of pathologic findings in asymptomatic knees of marathon runners before and after a competition in comparison with physically active subjects. To compare the diagnostic performance of cartilage-dedicated magnetic resonance imaging (MRI) sequences at 3.0 T.

MATERIALS AND METHODS

Ten marathon runners underwent 3.0 T MRI 2-3 days before and after competition. Twelve physically active asymptomatic subjects not performing long-distance running were examined as controls. Pathologic condition was assessed with the whole-organ magnetic resonance imaging score (WORMS). Cartilage abnormalities and bone marrow edema pattern (BMEP) were quantified. Visualization of cartilage pathology was assessed with intermediate-weighted fast spin-echo (IM-w FSE), fast imaging employing steady-state acquisition (FIESTA) and T1-weighted three-dimensional (3D) high-spatial-resolution volumetric fat-suppressed spoiled gradient-echo (SPGR) MRI sequences.

RESULTS

Eight of ten marathon runners and 7/12 controls showed knee abnormality. Slightly more and larger cartilage abnormalities, and BMEP, in marathon runners yielded higher but not significantly different WORMS (P > 0.05) than in controls. Running a single marathon did not alter MR findings substantially. Cartilage abnormalities were best visualized with IM-w FSE images (P < 0.05).

CONCLUSION

A high prevalence of knee abnormalities was found in marathon runners and also in active subjects participating in other recreational sports. IM-w FSE sequences delineated more cartilage MR imaging abnormalities than did FIESTA and SPGR sequences.

The 5.5-year results of MegaOATS--autologous transfer of the posterior femoral condyle: a case-series study

INTRODUCTION

Large osteochondral defects of the weight-bearing zones of femoral condyles in young and active patients were treated by autologous transfer of the posterior femoral condyle (large osteochondral autogenous transplantation system (MegaOATS)). The technique presented is a sound and feasible salvage procedure to address large osteochondral defects in weight-bearing zones.

METHODS

Thirty-six patients between July 1996 and December 2000 were included. Thirty-three patients (10 females, 23 males) were evaluated by the Lysholm score and X-ray scans. A random sample of 16 individuals underwent magnetic resonance imaging analysis. The average age at the date of surgery was 34.3 (15 to 59) years, and the mean follow up was 66.4 (46 to 98) months. The mean defect size was 6.2 (2 to 10.5) cm2, in 27 patients affecting the medial femoral condyle and in six patients affecting the lateral femoral condyle. Trauma or osteochondrosis dissecans were pathogenetic in 82%.

RESULTS

The Lysholm score in all 33 individuals showed a highly significant increase from a preoperative median 49.0 points to a median 86.0 points (P < or = 0.001). Twenty-seven patients returned to recreational sports. X-ray scans showed a rounding of the osteotomy edge in 24 patients, interpreted as a partial remodelling of the posterior femoral condyle. Preoperative osteoarthritis in 17 individuals was related to significant lower Lysholm scores (P = 0.014), but progression in 17 patients did not significantly influence the score results (P = 0.143). All 16 magnetic resonance imaging examinations showed vital and congruent grafts.

CONCLUSION

Patients significantly improve in the Lysholm score, in daily-life activity levels and in return to recreational sports. Thirty-one out of 33 patients were comfortable with the results and would undergo the procedure again. The MegaOATS technique is therefore recommended as a salvage procedure for young individuals with large osteochondral defects in the weight-bearing zone of the femoral condyle.

High-resolution morphological and biochemical imaging of articular cartilage of the ankle joint at 3.0 T using a new dedicated phased array coil: in vivo reproducibility study

OBJECTIVE

The objective of this study was to evaluate the feasibility and reproducibility of high-resolution magnetic resonance imaging (MRI) and quantitative T2 mapping of the talocrural cartilage within a clinically applicable scan time using a new dedicated ankle coil and high-field MRI.

MATERIALS AND METHODS

Ten healthy volunteers (mean age 32.4 years) underwent MRI of the ankle. As morphological sequences, proton density fat-suppressed turbo spin echo (PD-FS-TSE), as a reference, was compared with 3D true fast imaging with steady-state precession (TrueFISP). Furthermore, biochemical quantitative T2 imaging was prepared using a multi-echo spin-echo T2 approach. Data analysis was performed three times each by three different observers on sagittal slices, planned on the isotropic 3D-TrueFISP; as a morphological parameter, cartilage thickness was assessed and for T2 relaxation times, region-of-interest (ROI) evaluation was done. Reproducibility was determined as a coefficient of variation (CV) for each volunteer; averaged as root mean square (RMSA) given as a percentage; statistical evaluation was done using analysis of variance.

RESULTS

Cartilage thickness of the talocrural joint showed significantly higher values for the 3D-TrueFISP (ranging from 1.07 to 1.14 mm) compared with the PD-FS-TSE (ranging from 0.74 to 0.99 mm); however, both morphological sequences showed comparable good results with RMSA of 7.1 to 8.5%. Regarding quantitative T2 mapping, measurements showed T2 relaxation times of about 54 ms with an excellent reproducibility (RMSA) ranging from 3.2 to 4.7%.

CONCLUSION

In our study the assessment of cartilage thickness and T2 relaxation times could be performed with high reproducibility in a clinically realizable scan time, demonstrating new possibilities for further investigations into patient groups.

Diagnostic performance of in vivo 3-T MRI for articular cartilage abnormalities in human osteoarthritic knees using histology as standard of reference

The purpose of this study was (1) to evaluate the sensitivity, specificity and accuracy of sagittal in vivo 3-T intermediate-weighted fast spin-echo (iwFSE) sequences in the assessment of knee cartilage pathologies using histology as the reference standard in patients undergoing total knee replacement, and (2) to correlate MR imaging findings typically associated with osteoarthritis such as bone marrow edema pattern (BMEP) and cartilage swelling with histological findings. Tibial plateaus and femoral condyles of eight knees of seven patients were resected during surgery, and sagittal histological sections were prepared for histology. Preoperative MRI findings were compared to the corresponding region in histological sections for thickness, surface integrity and signal pattern of cartilage, and histological findings in areas of BMEP and swelling were documented. The overall sensitivity, specificity and accuracy were 72%, 69% and 70% for thickness, 69%, 74% and 73% for surface and 36%, 62% and 45% for intracartilaginous signal pattern. For all cases of BMEP on MRI subchondral ingrowth of fibrovascular tissue and increased bone remodeling were observed. MRI using fat-saturated iwFSE sequences showed good performance in assessing cartilage thickness and surface lesions, while signal changes of cartilage were not suited to characterize the severity of cartilage degeneration as validated by histology.

Noninvasive quantification of human nucleus pulposus pressure with use of T1rho-weighted magnetic resonance imaging

BACKGROUND

Early diagnosis is a challenge in the treatment of degenerative disc disease. A noninvasive biomarker detecting functional mechanics of the disc is needed. T1rho-weighted imaging, a spin-lock magnetic resonance imaging technique, has shown promise for meeting this need in in vivo studies demonstrating the clinical feasibility of evaluating both intervertebral discs and articular cartilage. The objectives of the present study were (1) to quantitatively determine the relationship between T1rho relaxation time and measures of nucleus pulposus mechanics, and (2) to evaluate whether the quantitative relationship of T1rho relaxation time with the degenerative grade and glycosaminoglycan content extend to more severe degeneration. It was hypothesized that the isometric swelling pressure and compressive modulus would be directly correlated with the T1rho relaxation time and the apparent permeability would be inversely correlated with the T1rho relaxation time.

METHODS

Eight cadaver human lumbar spines were imaged to measure T1rho relaxation times. The nucleus pulposus tissue from the L1 disc through the S1 disc was tested in confined compression to determine the swelling pressure, compressive modulus, and permeability. The glycosaminoglycan and water contents were measured in adjacent tissue. Linear regression analyses were performed to examine the correlation between the T1rho relaxation time and the other measured variables. Mechanical properties and biochemical content were evaluated for differences associated with degeneration.

RESULTS

A positive linear correlation was observed between the T1rho relaxation time on the images of the nucleus pulposus and the swelling pressure (r = 0.59), glycosaminoglycan content per dry weight (r = 0.69), glycosaminoglycan per wet weight (r = 0.49), and water content (r = 0.53). No significant correlations were observed between the T1rho relaxation time and the modulus or permeability. Similarly, the T1rho relaxation time, swelling pressure, glycosaminoglycan content per dry weight, and water content were significantly altered with degeneration, whereas the modulus and permeability were not.

CONCLUSIONS

T1rho-weighted magnetic resonance imaging has a strong potential as a quantitative biomarker of the mechanical function of the nucleus pulposus and of disc degeneration.

Imaging of knee osteoarthritis: data beyond the beauty

PURPOSE OF REVIEW

MRI has revolutionized osteoarthritis research by providing semi-quantitative and quantitative imaging endpoints on most articular tissues. With the first image data of the Osteoarthritis Initiative now becoming publicly available, this article reviews recent developments in quantitative imaging of osteoarthritis.

RECENT FINDINGS

Although radiography remains the standard for regulatory studies on disease modifying osteoarthritis drugs, there is no consensus on the optimal positioning and acquisition protocol. With MRI, semi-quantitative scoring systems for evaluation of multiple articular tissue changes have been developed and are currently investigated in the context of correlation with symptoms and of predicting structural progression of osteoarthritis. Most efforts on quantitative measurement of imaging endpoints have focused on cartilage morphology and composition, with higher field strength (3T), newer sequences, and new measurement endpoints being a driver of current innovation.

SUMMARY

The semi-quantitative and quantitative tools for analysis of articular structure are now available and permit comprehensive analysis of morphological and compositional tissue changes in osteoarthritis. These changes will need to be related to clinical outcomes (e.g. how a patient feels or functions) with current epidemiological studies, such as the Osteoarthritis Initiatives, providing the opportunity for clinical validation of these imaging biomarkers.

Stadiengerechte operative Knorpeltherapie

Chondral or osteochondral lesions are typical injuries in orthopaedics and traumatology. Since there is no regeneration of damaged articular cartilage, these lesions can lead to premature osteoarthritis. Therefore, an adequate therapy for these injuries is an important goal. Nowadays, common methods in cartilage therapy are procedures for the recruitment of mesenchymal stem cells: autologous osteochondral transplantation and autologous chondrocyte transplantation. Currently, autologous osteochondral transplantation is the only procedure that allows the replacement of the defect with hyaline cartilage. However, this procedure has the problem of donor-site morbidity and limited availability of transplants. Stem cell recruiting procedures and autologous chondrocyte transplantation normally achieve a regeneration of the defect with only fibrocartilage tissue, but both can achieve good medium-term clinical results. Each of these therapeutic principles has certain major indications. In order to select an adequate therapy, the classification of chondral or osteochondral lesion is needed. From a multiplicity of classification systems, those of the ICRS are of particular clinical relevance.