➢ The emergence of newer pharmacotherapeutic agents and surgical cartilage resurfacing techniques is driving the need for imaging modalities capable of early, accurate, and reproducible lesion detection.
➢ Magnetic resonance imaging (MRI) has emerged as a noninvasive tool for direct 2-dimensional (2D) and 3-dimensional (3D) assessment of the articular cartilage in both clinical and research settings. MRI has largely overcome the shortcomings of the current gold standard, radiography, by allowing for the detection of preclinical disease and subtle early abnormalities prior to the onset of radiographic disease, when damage is still reversible.
➢ Current MRI techniques are either morphological (2D/3D qualitative and quantitative techniques) or compositional (matrix-assessment techniques that detect macromolecular changes prior to morphological changes).
➢ MRI is evolving as a complete answer to our cartilage-imaging requirements of lesion description, treatment planning, and outcome measurement as well as in various research settings.
Hyaline articular cartilage, an essential component of diarthrodial joints, is composed predominantly of water, chondrocytes, and an extracellular matrix of macromolecules, including collagen and proteoglycans (protein core, negatively-charged glycosaminoglycans [GAGs], hyaluronic acid). It is organized into a trilaminar appearance, with superficial, intermediate, and deep layers, depending on the distribution of chondrocytes and the orientation of the collagen fibrils.
Broadly, the pathological conditions affecting articular cartilage can be focal (e.g., trauma) or diffuse (e.g., degeneration). The depth of cartilage involvement is classified according to the modified Outerbridge/Noyes (arthroscopy/magnetic resonance imaging [MRI]) scale1-3 (Table I).
Today, MRI is the modality of choice for imaging of the articular cartilage4-9 because it allows multiplanar, high-resolution, direct visualization of the cartilage and provides excellent soft-tissue contrast, which can be manipulated. Unlike radiographs, MRI also allows simultaneous evaluation of the rest of the joint structures, such as ligaments and menisci. Unlike computed tomography (CT) and radiographs, MRI is not associated with radiation-related hazards, and, unlike arthroscopy, MRI is noninvasive.
The roles of MRI in cartilage imaging include the detection of radiographic occult chondral lesions that can predispose to osteoarthritis (OA) if left untreated, the detection of degeneration when it is still reversible, and the description of lesion morphology and the quantification of disease involvement for the purpose of treatment planning. MRI has high reproducibility for longitudinal follow-up of disease progression and treatment outcome and serves as an outcome measure in various research settings10,11.
The advanced application of MRI as stated above has been made possible by the availability of high field strengths, improved gradients, and dedicated phased coils. Both open and closed-bore MRI systems are compatible with cartilage imaging. Dynamic open interventional scanners with their so-called double-doughnut design have taken cartilage imaging to a new realm in which imaging is possible in multiple postures as well as during motion. Scanners with a field strength of 0.18 to 0.2 T are largely inadequate for morphological assessment and are not recommended for the evaluation of knee OA or cartilage repair. A field strength of at least 1.0 T is necessary for morphological assessment, and 1.5 T is adequate for morphological and compositional assessments. A field strength of 3 T provides a twofold increase in signal-to-noise ratio (SNR) at the same spatial resolution and time, a twofold increase in spatial resolution at the same SNR and imaging time, and a fourfold reduction in imaging time at the same SNR and spatial resolution. Higher reproducibility for cartilage volume measurement12 and higher sensitivity (66% to 80% at 3 T, compared with 40% to 94% at 1.5 T) for cartilage defect measurement have been reported13,14. However, no significant difference in cartilage thickness measurements has been found12,15. The limitations of 3-T scanners include higher energy deposition, vulnerability to flow artifact, linear increase in chemical shift effects, and magnetic susceptibility. 7-T scanners are still predominantly used as a research tool.
Current MRI techniques are either morphological or compositional (Table II).
Qualitative 2D/3D Techniques
Among conventional 2D spin-echo sequences, proton-density-weighted (PD) images and T2-weighted images (Figs. 1-A through 1-C) most clearly depict the cartilage as an intermediate-signal-intensity structure in the backdrop of the hyperintense synovial fluid16. At an intermediate echo time (TE) of 33 to 60 msec, even the internal trilaminar stratification can be demonstrated17-19. A high in-plane resolution (0.3 to 0.6 mm) and high SNR make these images sensitive for surface defects, intrinsic cartilage lesions, and joint structures such as menisci and ligaments. Imaging is possible even in the presence of instrumentation without an increase in imaging time (4 to 5 minutes). Contrast between the marrow signal and cartilage as well as the conspicuity of marrow abnormalities such as edema or subchondral cysts is further improved by various fat-suppression techniques (Figs. 2-A and 2-B). Chemical fat saturation also reduces the chemical shift artifacts at the marrow fat and cartilage fluid interface while adding dynamic range; however, acquisition time and susceptibility to magnetic field inhomogeneities are increased. Chemical fat saturation has taken precedence over short tau inversion recovery (STIR) sequences, which have a low SNR and a low CNR (contrast-to-noise ratio). Newer techniques include water excitation imaging, in which non-fat-bound protons are excited with use of a short repetition time (TR) (18 msec) and a small flip angle (Fig. 2-C), and iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL), in which multipoint fat-water excitation allows the generation of separate fat and water images.
Moderately T2-weighted spin-echo images with fat suppression and wider receiver bandwidth can achieve high sensitivity (94%), specificity (99%), and accuracy (98%)16 in comparison with the lower sensitivity (73% to 87%), specificity (79% to 94%), and accuracy (92%) associated with T2-weighted non-fat-suppressed images20. The only limitation of these T2-weighted spin-echo sequences is their 2D nature. Voxel anisotropy leads to partial volume averaging, which reduces sensitivity, and hence imaging in multiple planes is necessary for adequate lesion detection. Simply converting 2D fast-spin-echo (FSE) images into 3D FSE images with small voxel sizes would yield poor-resolution images with long imaging times5. The solution was provided by 3D gradient-recalled echo (GRE) techniques, in which small flip angles are used to produce 3D data sets from which 2D reformations can be generated21,22. Standard GRE techniques produce images with both T1 and T2 contrast with bright synovial fluid. These techniques have been further modified over the years to suit our cartilage-imaging needs. For simplicity, the GRE sequences can be either T1-weighted (dark fluid) or T2*-weighted (bright fluid), although most of these yield relative T1/T2 contrast.
T1-weighted GRE sequences, including spoiled gradient-recalled echo (SPGR), fast low-angle shot (FLASH), and volumetric interpolated breath-hold examination (VIBE) (Fig. 3-A) sequences, depict cartilage with an intermediate to high signal and joint fluid with a hypointense signal. Along with lipid suppression, these sequences attain sensitivity as high as 93% in correlation with arthroscopy and provide better depiction of the deep cartilage layers21. T2*-weighted sequences, including the driven equilibrium Fourier transform (DEFT)23-26 and balanced steady-state free precision imaging (bSSFP) sequences, depict cartilage with low to intermediate signal and joint fluid with a hyperintense signal27-29 (Fig. 3-B). These sequences enhance the synovial fluid signal while preserving the cartilage signal. This phenomenon is called the arthrographic effect as it is similar to the increase in synovial fluid signal after intra-articular contrast injection in MR arthrography. Newer techniques include the dual-echo steady-state (DESS)30-32 (Figs. 3-C and 3-D) and multi-echo data image combination (MEDIC) (Fig. 3-E) sequences. One variant is fluctuating equilibrium MRI (FMRI), in which 2 complete data sets are reconstructed into fat and water images33 and this sequence is possible at very short acquisition times (acquisition time is 2 minutes using a TR of 6.6 msec). Vastly interpolated projection reconstruction imaging (VIPR) uses a combination of bSSFP imaging and 3D radial k-space acquisitions at short acquisition times to produce 3D data sets34,35. All of these cartilage-specific 3D GRE sequences suffer from the common limitations of relatively long acquisition times, high extrinsic but low intrinsic cartilage contrast, insensitivity to bone marrow abnormalities, and lower sensitivity for the evaluation of structures other than cartilage. In the study by Chalkias et al., 3D GRE sequences had higher rates of several image artifacts than FSE sequences36, including ambiguity of surface defects in the posterior femoral condyle (71% compared with 0%), linear high signal intensity in the deep zone adjacent to the subchondral bone in the femoral condyle (93% compared with 0%), pseudolaminar appearance in the posterior region of the femoral condyle (86% compared with 21%), truncation artifact in the patellofemoral compartment (96% compared with 25%), and susceptibility artifacts from air and metal in patients who had prior arthroscopy (59% compared with 10%). However, FSE sequences had higher rates of the artifacts of cartilage thinning in the central portion of the lateral femoral condyle adjacent to the anterior horn of the lateral meniscus and cartilage flattening in the posterior region of the femoral condyle as compared with the GRE sequences (75% compared with 67.9% and 32.1% compared with 57%, respectively).
Hence, an ideal pulse sequence that has the high resolution of FSE and the high sensitivity of 3D GRE is still sought. Few attempts have been made to develop 3D FSE sequences, such as sampling perfection with application-optimized contrast with use of different flip angle evolutions (SPACE). These techniques involve the use of flip angle modulation to reduce blurring and parallel imaging to reduce acquisition time37-41 (Fig. 4). In the future, a single-acquisition 3D FSE technique with multiplanar reformatting could replace standard 2D FSE sequences.
Quantitative Techniques: Cartilage Segmentation Analysis
The qualitative techniques discussed above do not provide measurable outcome points for disease quantification and treatment follow-up. Quantitative MRI techniques provide measurement parameters such as the cartilage thickness, cartilage volume, or size of focal defects42-48. 3D measurements of total cartilage volume and thickness require segmentation of the cartilage from the underlying bone with manual or semi-automated techniques. Semi-automated techniques include signal intensity-based thresholding, seed-growing algorithms, filtering techniques, watershed and live-wire approaches, or model-based segmentation to create volume or thickness maps. 3D thickness maps are generated using a 3D Euclidean distance transformation that determines at each point the minimum distance from the articular surface to the bone-cartilage interface49. Dynamic quantitation is used to measure cartilage volume during movement and different postures.
Intra-articular injection of gadolinium chelate solution (e.g., 20 mL of contrast medium with a gadolinium content of 2.5 mmol/L) and subsequent MRI scanning has lost much of its usefulness for the evaluation of large joints such as the knee, with the resolution of cartilage-sensitive sequences reaching as high as that of MR arthrography. However, it is still used for the evaluation of smaller joints such as the hip and shoulder. The recent study by Sutter et al.50 demonstrated a significant difference in sensitivity between morphological MRI (58% [reader 1] and 83% [reader 2]) and MR arthrography (71% [reader 1] and 92% [reader 2]) for the detection of acetabular cartilage lesions. However, no significant difference in the sensitivity for the detection of femoral cartilage lesions was found between the 2 modalities by either reader (reader 1 found a sensitivity of 50% for both modalities, and reader 2 found a sensitivity of 83% for both modalities).
Matrix-Assessment Techniques (Physiological/Biochemical Analysis)
All matrix-assessment techniques measure the macromolecular changes within the cartilage well before morphological changes have appeared. These techniques measure either collagen or proteoglycan content (Table II).
Collagen Assessment (T2 Mapping)
Cartilage T2 relaxation time is low because of anisotropic motion of water molecules in a fibrous collagen network (accounting for normal radial zone hypointense signal). Degeneration causes an increase in water content and damage to collagen, allowing increased water motion. T2 mapping measures this degeneration as an increase in the T2 relaxation times of cartilage49,51-54. T2-weighted multi-echo, spin echo images with different TEs and identical TRs are acquired, and T2 maps are computed, assuming exponential signal decay. T2 is defined as the time at which the signal decays to 37% of the maximum signal. Maps depict either the distribution of T2 values in each voxel or Z scores (Fig. 5).
The Z score in each voxel is calculated as (VoxelI – Meannormal, compartment)/SDnormal, compartment, where VoxelI is the T2 in the voxel of interest, Meannormal, compartment is the mean T2 for all voxels of the normal knees in that compartment, and the SDnormal, compartment is the standard deviation of the same normal T2 distribution.
The rationale behind proteoglycan assessment techniques is that proteoglycans are highly negatively charged protein aggregates because of their GAG-side chains termed as the fixed charge density (FCD). These techniques detect the changes in this fixed charge density55-57. Sodium (Na) MRI is based on the fact that positively charged Na ions are attracted by this negative fixed charge. Loss of proteoglycans leads to loss of Na signal58-62. The limitations of this technique include the need for special equipment (transmit and receive coils), an inherently low sensitivity because of the naturally lower abundance of 23Na, a long scan time for adequate SNR (21 minutes), and more applications at higher field strengths (7 T). T1ρ (rho)-weighted imaging measures T1ρ relaxation time (the duration of spin-lattice relaxation in a rotating frame), similar to the measurement of T2 relaxation time63-65. It probes the slow-motion interaction between motionally restricted water molecules and their local macromolecular environment. Increased water or loss of proteoglycans in degeneration is seen as an increase in T1ρ relaxation time. Spatial variation of the T1ρ values is represented as a color map. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) relies on the diffusion of negatively charged gadolinium ions across joint fluid into cartilage. Gadolinium ions replace the charge deficit created by the loss of negatively charged proteoglycans in degenerated cartilage66-68. Increased gadolinium ion concentration within the cartilage shortens the T1 relaxation time of the cartilage, which is seen as an increased MR signal on T1-weighted images (3D SPGR with a variable flip angle). Color maps varying from green to red that depict the dGEMRIC index within each voxel are highly sensitive to even miniscule macromolecular changes in both large joints and small joints (e.g., metacarpophalangeal joints). The limitation of dGEMRIC is the requirement for intravenous injection of a gadolinium contrast medium such as gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA2–) followed by exercise (10 minutes) and a delay to allow penetration of Gd-DTPA2− through the full cartilage thickness (90 minutes). The dGEMRIC index is also affected by physiological factors such as exercise and body mass index. Attempts were made to use diffusion-weighted imaging (DWI) to assess increased apparent diffusion coefficient (ADC) in degeneration. Disruption of the cartilage matrix in degeneration results in enhanced water mobility, which increases the ADC of cartilage. The variations in ADC values within cartilage can be mapped; however, this technique has been put to better use in meniscal tear evaluation.
Newer matrix-assessment techniques that have been attempted in research settings include chemical exchange saturation transfer (CEST) and the use of new contrast agents such as dendrimer-linked nitroxides and liposome-containing compounds. In CEST, hydroxyl residues on GAGs are selectively excited to provide contrast between regions of high and low GAG content. Dendrimer-linked nitroxides are positively charged dendrimers such as polypropylenimine and polyamidoamine (PAMAM) linked to stable nitroxides. These dendrimers, after intra-articular injection, are preferentially taken up by cartilage. MRI is performed immediately after injection and at 20-minute intervals through 3.5 hours. Paramagnetic liposomes incorporating MRI contrast agents are excluded from intact articular cartilage and selectively release contrast medium in damaged articular cartilage degraded by collagenase, resulting in an increased T1 signal. However, these newer techniques have not yet been validated in the clinical setting.
Imaging of Specific Chondral Lesions
Focal Chondral Lesions
Focal chondral lesions are due to either trauma or ischemic necrosis. Traumatic lesions include isolated chondral lesions and osteochondral lesions. Cartilage, because of its avascular nature, has limited ability for repair. Partial-thickness chondral lesions have little or no tendency to spontaneously repair, whereas full-thickness lesions may heal with fibrocartilage formation; hence the need for accurate diagnosis for treatment planning. MRI is the modality of choice as radiographs largely fail to detect focal chondral lesions. The MRI description should include location, size, depth, and the presence or absence of displacement. 2D intermediate-weighted FSE sequences have very high specificity for Grade-I and II lesions (according to the modified Outerbridge/Noyes scale), with sensitivity reaching 100% for Grade-III and IV lesions42,69. The sensitivity for Grade-III and IV lesions is higher for 3D GRE (SPGR FS [fat saturated], DESS WE [water excitation]) (85% to 100%) compared with 2D FSE PD/T2 FS imaging in at least 2 planes (80% to 95%). The sensitivity for Grade-I and II lesions is <70% for all pulse sequences3,16,42,69. The spectrum of chondral injuries varies from superficial blistering and fibrillation/fraying to partial-thickness Grade-III lesions or full-thickness Grade-IV lesions. Grade-IV lesions can be linear fissures, focal ulcerations, or large defects. Traumatic focal lesions can be distinguished from degenerative lesions by their acutely angled margins, often solitary nature, and accompanying underlying subchondral marrow edema or trabecular microfractures. More severe trauma may lead to ulceration with flap formation or delamination of large portions of cartilage. Fragments may remain attached or get displaced into the joint space. The subchondral marrow edema can be either diffuse or linearly branching in pattern. In either case, it should serve as an indication of a possible overlying chondral lesion, warranting a thorough evaluation.
Osteochondral injury can manifest as a contusion (with predominant subchondral marrow edema, bowing, and focal impaction) or as an osteochondral fracture. The osteochondral fragment bears the signature hyperintense fatty marrow signal of the osseous part and a hypointense subchondral plate separating it from the intermediate signal of the articular cartilage. Fragments can be undisplaced or displaced; in either case, they are amenable to repair and hence should not be missed. Biochemical assessment techniques detect cartilage matrix changes in cases of morphologically occult trauma. T1ρ mapping can demonstrate the traumatic effects of an anterior cruciate ligament (ACL) tear on cartilage biochemistry as compared with the findings in healthy controls. Increased heterogeneity of T1ρ relaxation times within cartilage have been observed within weeks after an ACL injury, suggesting that early changes within the cartilage structure are initiated at the time of injury70. Na imaging can also reveal the impact of an ACL tear on GAG content. The same is true for T2 relaxation mapping.
MRI is the modality of choice for detecting radiographically occult Grade-I and II lesions as well as Grade-III and IV stable and unstable lesions in patients with osteochondritis dissecans, aiding the orthopaedic surgeon in making the early diagnosis and in treatment planning.
Diffuse Chondral Lesions
Degeneration (i.e., OA), which is the second-most-common cause of permanent disability among subjects over the age of 50 years, is the most important diffuse chondral lesion. The goals of imaging in cases of OA have been largely redefined, with the emphasis now being on the detection of early disease when it is still reversible and amenable to treatment with drugs, exercise, and lifestyle modification. Among the current MRI methods, biochemical assessment techniques are capable of detecting the macromolecular changes within the cartilage that occur very early on in the buildup to actual morphological changes of cartilage thinning and focal defects (Fig. 6-A).
dGEMRIC detects internal macromolecular changes in normal-thickness cartilage as well as in obviously thinned-out cartilage. T2 relaxation maps show focally increased T2 signal in damaged articular cartilage52 that can be distinguished from the diffusely increased T2 signal in senescent cartilage. Dunn et al.71 and Stahl et al.72 found that T2 relaxation time differs between patients with and without OA; however, it is not a sensitive marker of radiographic severity. No significant difference in T2 relaxation times was found between patients with mild OA and those with severe OA. Stahl et al.72 found T1ρ maps to be more sensitive for the detection of degeneration. They also found a significant difference in the T1ρ values of cartilage in patients with mild and severe OA. Low cartilage Na signal and heterogeneous distribution is seen in patients with OA. Biochemical assessment is feasible not only for the evaluation of joints with primary OA but also for the evaluation of joints that are at risk for secondary OA because of conditions such as hip dysplasia or femoroacetabular impingement. Nevertheless, we still cannot disregard the ability of morphological MRI to elucidate features of advanced OA such as diffuse chondral thinning; alteration in contour; fibrillation; surface irregularity; obtuse margined focal defects; subchondral changes (edema, cysts, and sclerosis); osteophytes; loose bodies; synovial thickening; joint effusion; integrity of the cruciate ligaments, collateral ligaments, and menisci; and alterations in alignment (varus/valgus) (Figs. 6-B and 6-C). Quantitative values such as cartilage volume, cartilage thickness, and even focal lesion depth are instrumental for the assessment of disease load prior to treatment as well as for longitudinal follow-up. Volume measurements detect cartilage loss in the absence of joint-space narrowing73 with high reproducibility (interobserver variability, 0.4% to 7.8%; intraobserver variability, 0.3% to 6.4%)52,53. Cartilage thickness, a one-dimensional (1D) estimate of a 3D structure, is more prone to repositioning errors than cartilage volume is; hence, it has lower reproducibility in terms of both intraobserver variability (coefficient of variation [CV], 3.2% to 10.5%) and interobserver variability (CV, 5.4% to 29.7%)69. In clinical trials involving patients with OA, the use of MRI as an outcome measure reduces the number of participants and the length and cost of the trials as it provides a sensitive, accurate, and reliable assessment of articular cartilage change. MRI has facilitated the assessment of risk-related factors such as obesity74, physical activity75, smoking76, and vitamin D77 for the prevention of OA. MRI has been used to evaluate the efficacy of various disease-modifying OA drugs (DMOADS) such as licofelone and naproxen. In the study by Raynauld et al., the mean loss of cartilage thickness was significantly less in the licofelone group than in the naproxen group at 12 and 24 months (p < 0.001)78. In the study by Wildi et al., the loss of cartilage volume was significantly less in the chondroitin sulfate group than in the placebo group (p = 0.030 for global knee, p = 0.015 for the lateral compartment, and p = 0.002 for the tibial plateau)79. In the study by Wang et al., intra-articular injection of hyaluronic acid (Hylan G-F 20) reduced cartilage volume loss over 2 years80. In the study by McAlindon et al., collagen hydrolysate increased the dGEMRIC score81. In other studies, no effect was observed in association with vitamin E82 and celecoxib83. The effects of intervention could be established earlier with MRI as compared with radiographs14.
Cartilage Imaging in Repair
With the advent of numerous cartilage-resurfacing techniques and with MRI gradually replacing arthroscopy for postoperative evaluation, it has become incumbent on orthopaedic surgeons to be aware of the normal appearance of cartilage on MRI and the expected complications following cartilage repair. For this purpose, a simple method has been devised: the MR observation of cartilage repair tissue (MOCART).
Cartilage-repair techniques can involve either stimulation (e.g., simple debridement, microfractures, subchondral drilling, abrasion chondroplasty) or transplantation or implantation (e.g., insertion of autologous or allogeneic osteochondral grafts, autologous chondrocytes, carbon fiber rods, or synthetic scaffolds). Stimulation releases pluripotent stem cells from the subchondral bone into the fibrin clot. These stem cells produce repair tissue, which is a hybrid of hyaline cartilage and fibrocartilage. Osteochondral transplantation involves the use of either autologous or allogeneic osteochondral plugs or the use of synthetic scaffolds to replace focal cartilage defects. Autologous chondrocyte implantation (ACI) is a two-stage procedure involving chondrocyte harvest and culture followed by injection under a periosteal flap at the site of the defect. Selection and planning of the procedure required can be done better by assessing the lesion for size, depth, and grade with MRI. The MOCART method involves the use of a 9-point evaluation postoperatively to assess the repair tissue, subchondral bone, and complications (Table III).
Following the use of stimulation techniques, the repair fibrocartilage is hyperintense, with prolongation of T2 relaxation time (T2 mapping) in the early postoperative period, with accompanying subchondral bone marrow edema. Signal intensity is reduced in the late postoperative period. Following osteochondral transplantation, there is a cartilage cap with native articular cartilage signal and an intervening fibrocartilaginous grout with increased T2 signal and decreased signal on the 3D FS SPGR. The osseous part of the plug has fat-like marrow at 2 weeks, graft and perigraft marrow edema with contrast enhancement at 4 to 6 weeks, fatty marrow with reduced enhancement at 6 to 9 months, and decreased perigraft edema at 1 to 2 years. In cases of autologous transplantation, additional assessment is needed for the evaluation of donor-site morbidity. The donor site may be either empty or filled with cancellous bone and/or fibrocartilage-like material, which has low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Fatty marrow with overlying fibrocartilage repair tissue develops at 6 to 9 months. Following ACI, the repair tissue is hyaline cartilage-like. It has intermediate signal intensity on T1 and PD-weighted images and hyperintense signal on T2-weighted images (almost like joint fluid) with enhancement in the proliferative phase (1 to 6 weeks). Signal intensity is reduced in the transitional phase (7 to 26 weeks) and is similar to that of hyaline articular cartilage in the remodeling phase. The changes can also be demonstrated at the macromolecular level on T2 mapping. Peripheral integration is seen as physical continuity as well as similarity of the contents on the biochemical assessment. In cases of rejection or poor integration, edema persists after 6 to 12 months, with subchondral cysts, graft collapse, and fluid signal at the graft-host interface. Restoration of contour is mandatory in all techniques. Osteochondral plugs should be neither depressed nor proud. Complications specific to ACI include graft hypertrophy and variable degrees of delamination. It is important to distinguish the immature ACI repair tissue from joint fluid at the base of the delaminated graft. An MR arthrogram helps in such a situation as the contrast medium is seen insinuating underneath a flap but not through the immature repair cartilage. Last, MRI is very sensitive for detecting other complications such as effusion or adhesions.
The emergence of newer pharmacotherapeutic agents and surgical cartilage-resurfacing techniques is driving the need for imaging modalities capable of early, accurate, and reproducible lesion detection. MRI compositional measures and morphological imaging are evolving as a complete answer to our cartilage-imaging requirements of lesion description, treatment planning, and outcome measurement as well as in various research settings.
Investigation performed at the Government Medical College Srinagar, Jammu and Kashmir, India
Disclosure: No external funds were received in support of this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
- Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated