A practical guide to imaging of cartilage repair with emphasis on bone marrow changes

Orthopedic surgeons have multiple options available to treat articular cartilage lesions, including microfracture, osteochondral autografting, and autologous chondrocyte implantation. By having basic knowledge of these surgical procedures, radiologists can more accurately interpret imaging studies obtained after surgery. In this article, we briefly review the different types of cartilage repair procedures, their appearance on magnetic resonance imaging (MRI), and pathologic MRI findings associated with postoperative complications. We also briefly discuss advanced MRI techniques (T2 mapping, delayed gadolinium-enhanced MRI of cartilage, sodium MRI) that have been recently used to assess the biochemical composition of repair tissue matrix. MRI can accurately assess the status and health of cartilage repair tissue. By providing this information to orthopedic surgeons, radiologists can play a valuable role in the management of patients who undergo cartilage repair surgery.     

Magnetization transfer contrast and T2 mapping in the evaluation of cartilage repair tissue with 3T MRI

PURPOSE: To use magnetization transfer (MT) imaging in the visualization of healthy articular cartilage and cartilage repair tissue after different cartilage repair procedures, and to assess global as well as zonal values and compare the results to T2-relaxation. MATERIALS AND METHODS: Thirty-four patients (17 after microfracture [MFX] and 17 after matrix-associated autologous cartilage transplantation [MACT]) were examined with 3T MRI. The MT ratio (MTR) was calculated from measurements with and without MT contrast. T2-values were evaluated using a multiecho, spin-echo approach. Global (full thickness of cartilage) and zonal (deep and superficial aspect) region-of-interest assessment of cartilage repair tissue and normal-appearing cartilage was performed. RESULTS: In patients after MFX and MACT, the global MTR of cartilage repair tissue was significantly lower compared to healthy cartilage. In contrast, using T2, cartilage repair tissue showed significantly lower T2 values only after MFX, whereas after MACT, global T2 values were comparable to healthy cartilage. For zonal evaluation, MTR and T2 showed a significant stratification within healthy cartilage, and T2 additionally within cartilage repair tissue after MACT. CONCLUSION: MT imaging is capable and sensitive in the detection of differences between healthy cartilage and areas of cartilage repair and might be an additional tool in biochemical cartilage imaging. For both MTR and T2 mapping, zonal assessment is desirable.     

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.     

Magnetic resonance imaging of cartilage and cartilage repair

Magnetic resonance (MR) imaging of articular cartilage has assumed increased importance because of the prevalence of cartilage injury and degeneration, as well as the development of new surgical and pharmacological techniques to treat damaged cartilage. This article will review relevant aspects of the structure and biochemistry of cartilage that are important for understanding MR imaging of cartilage, describe optimal MR pulse sequences for its evaluation, and review the role of experimental quantitative MR techniques. These MR aspects are applied to clinical scenarios, including traumatic chondral injury, osteoarthritis, inflammatory arthritis, and cartilage repair procedures.     

MR imaging of autologous chondrocyte implantation of the knee

Autologous chondrocyte implantation (ACI) is a surgical technique that is increasingly being used in the treatment of full-thickness defects of articular cartilage in the knee. It involves the arthroscopic harvesting and in vitro culture of chondrocytes that are subsequently implanted into a previously identified chondral defect. The aim is to produce a repair tissue that closely resembles hyaline articular cartilage that gradually becomes incorporated, restoring joint congruity. Over the long term, it is hoped that this will prevent the progression of full-thickness articular cartilage defects to osteoarthritis. This article reviews the indications and operative procedure performed in ACI. Magnetic resonance imaging (MRI) sequences that provide optimal visualization of articular cartilage in the post-operative period are discussed. Normal appearances of ACI on MRI are presented along with common complications that are encountered with this technique.     

Magnetic resonance imaging of articular cartilage: trauma, degeneration, and repair

The assessment of articular cartilage using magnetic resonance imaging has seen considerable advances in recent years. Cartilage morphologic characteristics can now be evaluated with a high degree of accuracy and reproducibility using dedicated pulse sequences, which are becoming standard at many institutions. These techniques detect clinically unsuspected traumatic cartilage lesions, allowing the physician to study their natural history with longitudinal evaluation and also to assess disease status in degenerative osteoarthritis. Magnetic resonance imaging also provides a more objective assessment of cartilage repair to augment the information obtained from more subjective clinical outcome instruments. Newly developed methods that provide detail at an ultrastructural level offer an important addition to cartilage evaluation, particularly in the detection of early alterations in the extracellular matrix. These methods have created an undeniably important role for magnetic resonance imaging in the reproducible, noninvasive, and objective evaluation and monitoring of cartilage. An overview of the advances, current techniques, and impact of magnetic resonance imaging in the setting of trauma, degenerative arthritides, and surgical treatment for cartilage injury is presented.     

MR示踪技术在干细胞移植治疗软骨缺损中的研究进展

关节软骨缺损临床十分常见, 但目前的治疗方法均存在修复不完全的缺陷。间充质干细胞移植治疗的发展为再生修复关节软骨缺损提供了新的治疗策略, 但是作为组织修复执行者的干细胞移植后的在体迁徙分布、增殖及转归过程, 目前尚无安全无创、实时动态的监测手段, 因此难以明确外源性干细胞在关节软骨缺损再生修复中所扮演的角色。而MR在体示踪细胞技术为解决上述问题提供了新思路。MRI具有无创、无电离辐射、时间空间分辨率高、对比度好等优点, 协同MRI对比剂, 既可无创提供关节软骨的详细解剖结构信息, 还可动态评估移植干细胞的归宿。笔者就MR示踪技术在干细胞移植治疗软骨缺损中的最新研究进展进行综述, 探讨其优势、局限性及未来前景。     

Matrix-based autologous chondrocyte implantation for cartilage repair with HyalograftC: two-year follow-up by magnetic resonance imaging

OBJECTIVE: Monitoring of articular cartilage repair after matrix-associated autologous chondrocyte implantation with HyalograftC by a new grading system based on non-invasive high-resolution magnetic resonance imaging. PATIENTS AND METHODS: In 23 patients, postoperative magnetic resonance imaging (MRI) was performed between 76 and 120 weeks. In nine of these patients, five MRI examinations were performed at 4, 12, 24, 52 and 104 weeks after HyalograftC implant. The repair tissue was described with separate variables: degree of defect repair in width and length, signal intensity of the repair tissue and status of the subchondral bone. For these variables a grading system with point scale evaluation was applied. RESULTS: CONCLUSION: High-resolution MRI provides a non-invasive tool for monitoring the development of cartilage repair tissue following HyalograftC technology, shows a good correlation with clinical outcome and may help to differentiate abnormal repair tissue from a normal maturation process.     

Application of MR imaging for internal derangement of the knee (orthopedic surgeon' view)

Magnetic resonance imaging is a noninvasive imaging modality with clear contrast and superior spatial resolution. These characteristics are especially useful for detecting pathology of the soft tissue of the knee joint, such as the menisci, ligaments and articular cartilage, which are difficult to diagnose using plain X-ray examination. MRI has become one of the first choice diagnostic modalities for the internal derangement of the knee joint, and is generally replacing some invasive arthrographic or arthroscopic examination. Pathology of the articular cartilage cannot yet be depicted clearly by MRI. We expect further development of the spatial resolution of MRI to make possible the detection of chondral lesions more clearly and precisely in the near future.     

Effects of calcified cartilage on healing of chondral defects treated with microfracture in horses

BACKGROUND: Microfracture of full-thickness articular defects has been shown to significantly enhance the amount of repair tissue. However, there is a suggestion that leaving calcified cartilage inhibits this repair response. HYPOTHESIS: Removal of the calcified cartilage with retention of subchondral bone enhances the amount of attachment of the repair tissue compared with retention of the calcified cartilage layer. STUDY DESIGN: Controlled laboratory study. METHODS: There were 1-cm(2) articular cartilage defects made in 12 skeletally mature horses on the axial weightbearing portion of both medial femoral condyles. Using a custom measuring device and direct arthroscopic observation of the subchondral bone beneath the calcified cartilage layer, the authors removed the calcified cartilage from 1 defect of each horse. The repair was assessed with arthroscopy, clinical examination, radiographic and magnetic resonance imaging examinations, biopsy at 4 months, gross and histopathologic examinations at 12 months, as well as mRNA and immunohistochemical evaluations. RESULTS: Removal of calcified cartilage with retention of the subchondral bone plate increased the overall repair tissue as assessed by arthroscopic (4 months) and gross evaluation (12 months). An increase in the level of the subchondral bone was also observed with removal of the calcified cartilage layer. The clinical pain, radiographic examinations, magnetic resonance imaging evaluations, histologic character, matrix proteins, or mRNA expression do not appear to differ based on level of defect debridement. CLINICAL RELEVANCE: Removal of the calcified cartilage layer appears to provide optimal amount and attachment of repair tissue. Therefore, close arthroscopic visualization is recommended for debridement of clinical lesions to ensure removal of the calcified cartilage layer.     

MR imaging of osteochondral grafts and autologous chondrocyte implantation

Surgical articular cartilage repair therapies for cartilage defects such as osteochondral autograft transfer, autologous chondrocyte implantation (ACI) or matrix associated autologous chondrocyte transplantation (MACT) are becoming more common. MRI has become the method of choice for non-invasive follow-up of patients after cartilage repair surgery. It should be performed with cartilage sensitive sequences, including fat-suppressed proton density-weighted T2 fast spin-echo (PD/T2-FSE) and three-dimensional gradient-echo (3D GRE) sequences, which provide good signal-to-noise and contrast-to-noise ratios. A thorough magnetic resonance (MR)-based assessment of cartilage repair tissue includes evaluations of defect filling, the surface and structure of repair tissue, the signal intensity of repair tissue and the subchondral bone status. Furthermore, in osteochondral autografts surface congruity, osseous incorporation and the donor site should be assessed. High spatial resolution is mandatory and can be achieved either by using a surface coil with a 1.5-T scanner or with a knee coil at 3 T; it is particularly important for assessing graft morphology and integration. Moreover, MR imaging facilitates assessment of complications including periosteal hypertrophy, delamination, adhesions, surface incongruence and reactive changes such as effusions and synovitis. Ongoing developments include isotropic 3D sequences, for improved morphological analysis, and in vivo biochemical imaging such as dGEMRIC, T2 mapping and diffusion-weighted imaging, which make functional analysis of cartilage possible.     

Reversed laminar appearance of articular cartilage by T1‐weighting in 3D fat‐suppressed spoiled gradient recalled echo (SPGR) imaging

Purpose:

To investigate the reversed intensity pattern in the laminar appearance of articular cartilage by 3D fat‐suppressed spoiled gradient recalled echo (FS‐SPGR) imaging in magnetic resonance imaging (MRI).

Materials and Methods:

The 3D SPGR experiments were carried out on canine articular cartilage with an echo time (TE) of 2.12 msec, a repetition time (TR) of 60 msec, and various flip angles (5° to 80°). In addition, T1, T2, and T2* in cartilage were imaged and used to explain the laminar appearance in SPGR imaging.

Results:

The profiles of T2 and T2* in cartilage were similar in shape. However, the T2 values from the multigradient‐echo imaging sequence were about 1/3 of those from single spin‐echo sequences at a pixel resolution of 26 μm. While the laminar appearance of cartilage in spin‐echo imaging is caused mostly by T2‐weighting, the laminar appearance of cartilage in fast imaging (ie, short TR) at the magic angle can have a reversed intensity pattern, which is caused mostly by T1‐weighting.

Conclusion:

The laminar appearance of articular cartilage can have opposite intensity patterns in the deep part of the tissue, depending on whether the image is T1‐weighted or T2‐weighted. The underlying molecular structure and experimental protocols should both be considered when one examines cartilage images in MRI. J. Magn. Reson. Imaging 2010;32:733–737. © 2010 Wiley‐Liss, Inc.     

Advanced morphological and biochemical magnetic resonance imaging of cartilage repair procedures in the knee joint at 3 Tesla

Morphological and biochemical magnetic resonance imaging (MRI) is due to high field MR systems, advanced coil technology, and sophisticated sequence protocols capable of visualizing articular cartilage in vivo with high resolution in clinical applicable scan time. Several conventional two-dimensional (2D) and three-dimensional (3D) approaches show changes in cartilage structure. Furthermore newer isotropic 3D sequences show great promise in improving cartilage imaging and additionally in diagnosing surrounding pathologies within the knee joint. Functional MR approaches are additionally able to provide a specific measure of the composition of cartilage. Cartilage physiology and ultra-structure can be determined, changes in cartilage macromolecules can be detected, and cartilage repair tissue can thus be assessed and potentially differentiated. In cartilage defects and following nonsurgical and surgical cartilage repair, morphological MRI provides the basis for diagnosis and follow-up evaluation, whereas biochemical MRI provides a deeper insight into the composition of cartilage and cartilage repair tissue. A combination of both, together with clinical evaluation, may represent a desirable multimodal approach in the future, also available in routine clinical use.     

Imaging of acute injuries of the articular surfaces (chondral, osteochondral and subchondral fractures)

Fractures involving the articulating surfaces of bone are a common cause of chronic disability after joint injury. Acute fractures of the articular surface typically run parallel to the surface and are confined to the cartilage and/or the immediate subchondral cancellous bone. They should be distinguished from vertical or oblique bone fractures with intra-articular extension. This article reviews the mechanism of acute articular surface injuries, as well as their incidence, clinical presentation, radiologic appearance and treatment. A classification is presented based on direct inspection (arthroscopy) and imaging (especially MRI), emphasizing the distinction between lesions with intact (subchondral impaction and subchondral bone bruises) and disrupted (chondral, osteochondral lesions) cartilage. Hyaline cartilage, subchondral bone plate and subchondral cancellous bone are to be considered an anatomic unit. Subchondral articular surface lesions, osteochondral fractures and solely chondral fractures are different manifestations of impaction injuries that affect the articulating surface. Of the noninvasive imaging modalities, conventional radiography and MRI provide the most relevant information. The appropriate use of short tau inversion recovery, T1-weighted and T2-weighted (turbo) spin-echo as well as gradient-echo sequences, enables MRI to classify the various acute articular surface lesions with great accuracy and provides therapeutic guidance. Received: 5 April 1999 Revision requested: 6 May 1999 Revision received: 21 June 1999 Accepted: 12 July 1999     

Evaluation of chondral injuriesby magnetic resonance imaging: Repair assessments

Magnetic resonance (MR) is a versatile imaging modality that can be tailored to address many of the clinical andresearch questions encountered in musculoskeletal diseases. Developments in MR techniques for cartilage imaging have paralleled the advances in clinical approaches to cartilage injury assessment and repair. This article reviews the current state-of-the-art clinical MR imaging methods designed for noninvasive evaluation of cartilage. Basic technical considerations are discussed, including selection of an imaging site for patient referral, interpretation of MR images, and the limitations of each acquisition technique. Clinical examples are used to illustrate the appearance of chondral lesions. Finally, the unique issues arising from cartilage assessment after surgical repair are examined.     

MR imaging of articular cartilage

With the advent of new treatments for articular cartilage disorders, accurate noninvasive assessment of articular cartilage, particularly with MR imaging, has become important. Understanding the MR imaging features of articular cartilage has led to the development of two types of routinely available MR imaging techniques which have demonstrated clinical accuracy and interobserver reliability. Received: 25 January 2000 Revision requested: 21 March 2000 Revision received: 31 March 2000 Accepted: 3 April 2000     

Radiologische Bildgebung der Kniegelenkarthrose

Clinical/methodical issue

Osteoarthritis is the most common degenerative age-related joint disease leading to typical degradation of articular cartilage with severe pain and limitation of joint motion.

Standard radiological methods

Although knee radiographs are widely considered as the gold standard for the assessment of knee osteoarthritis in clinical and scientific settings they increasingly have significant limitations in situations when resolution and assessment of cartilage is required.

Methodical innovations

Analysis of osteoarthritis of the knee with conventional x-ray is associated with many technical limitations and is increasingly being replaced by high-quality assessment using magnetic resonance imaging (MRI) or sonography both in the clinical routine and scientific studies.

Performance

Novel imaging modalities such as MRI or ultrasound enable in vivo visualization of the quality of the cartilaginous structure and bone as well as all articular and periarticular tissue. Therefore, the limitations of radiographs in assessment of knee osteoarthritis could be overcome by these techniques. This review article aims to provide insights into the most important radiological features of knee osteoarthritis and systematic visualization with different imaging approaches.

Practical recommendations

The demographic development in western industrialized countries predicts an increase of ageing-related osteoarthritis of the knee for the next decades. A systematic radiological evaluation of patients with knee osteoarthritis includes the assessment of the periarticular soft tissue, cartilaginous thickness, cartilage volume, possible cartilage defects, the macromodular network of hyaline cartilage, bone marrow edema, menisci and articular ligaments. Modern imaging modalities, such as MRI and sonography allow the limitations of conventional radiography to be overcome and to visualize the knee structures in great detail to quantitatively assess the severity of knee osteoarthritis.