dr. gonzalo delgado p articular cartilage: evaluation by ... · dr. gonzalo delgado p. figure 8. t2...

Revista Chilena de Radiología. Vol. 19 Nº 3, año 2013; 134-139.

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Dr. Gonzalo Delgado P.

Articular cartilage lesions are common in various joints and their multifactorial etiologies, including traumatic causes, inflammatory and infectious (septic arthritis) arthropathies and degenerative causes. Lesions of degenerative origin are the most frequent, being an important public health problem due to the high economic and social costs that re-present the direct or indirect spending in relation to treatment and absence from work. It is estimated that approximately 75% of the population over 75 years of age have osteoarthritis(1).

Articular cartilage or hyaline cartilage is of vital importance in diarthrosis type joints (joints with a wide range of movement) and its main function is to distribute and transmit forces over joint surfa-ces, cushioning loads and providing an adequate sliding surface between the articular surfaces. As a main feature, the hyaline cartilage is an avascular tissue (nourished from the synovial fluid), it has no innervation and no capacity to regenerate with the

same tissue, only a limited reparative capacity with fibrocartilage, which is less resistant.

Articular cartilage consists of (Figure 1):A. Water (65-80 %): it is present in greater quantity

in the superficial portions of the cartilage and its content increases with the aging process and with degenerative changes.

B. Collagen (10-20%): the predominant collagen is type II (95%), corresponding to the support matrix of the cartilage and provides resistan-ce to tension forces. Collagen is the primary component in dehydrated cartilage.

C. Proteoglycans (10-15%): are produced by chon-drocytes, glycosaminoglycans (GAG) being its subunits. They provide resistance to compres-sion forces and have elastic resistance.

D. Chondrocytes (5%): are the only cells found in the cartilage and are responsible for producing proteoglycans, collagen, proteins and some enzymes.

Articular cartilage: Evaluation by magnetic resonance


Radiologist. Radiology Department, Clinica Alemana de Santiago.Medical Faculty Clinica Alemana – Universidad de Desarrollo. Santiago, Chile.

Delgado G. Cartílago articular: Evaluación por resonancia magnética. Rev Chil 2013; 19(3): 134-139.Correspondence: Dr. Gonzalo Delgado P. / [email protected] previously published at http://www.alemana.cl/contactocientifico/1/ediciones_anteriores.html 2012; 2(5). Reproduction authorized by both editors.

Abstract: This article reviews the radiographic evaluation of articular cartilage lesions with emphasis on its magnetic resonance imaging study, we will discuss the usefulness of conventional sequences and advanced MRI studies which allow detection of incipient intrasubstance chondral lesions, prior to the ulceration of its surface.Keywords: Articular cartilage, Magnetic resonance.

Resumen: El presente artículo revisa la evaluación imagenologica de las lesiones del cartílago articular con énfasis en su estudio por resonancia magnética, discutiendo la utilidad de las secuencias conven-cionales y los estudios avanzados de RM que permiten detectar lesiones condrales incipientes intrasus-tancia, previo a la ulceración de su superficie.Palabras clave: Cartílago articular, Resonancia magnética.

CIR-GDelgado.indd 134 31-10-13 21:40


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its water content increases. Together these alterations determine loss of the characteristics and functions of the cartilage, making it less resistant and prone to injury from fissures and ulcerations.

It is possible to find various classifications of chondral lesions, not only from an imagenological but also an arthroscopical viewpoint. Therefore communication with clinicians is important, especially orthopedists, as radiologists must use classifications that are known and used by clinicians who interact with us and if necessary adjust the basic arthroscopic classifications to our imaging reports. One of the key classifications most used by clinicians dedicated to the issue of chondral lesions, is the classification by the ICRS (International Cartilage Repair Society) (Table I). This arthroscopic classification is easy to compare to our imaging studies, as it based primarily on the depth of the lesion.

Figure 1. Diagram showing the various components of articular cartilage.

In the articular cartilage different zones are identified depending on the depth and collagen fiber orientation (Figure 2). Thus, a surface or superficial zone that covers about 10 to 20% of the thickness of cartilage is recognized where the collagen fibers are arranged parallel to the cartilage surface. The transi-tional zone corresponds to 40 - 60%, where collagen fibers are randomly arranged. In the deep or radial zone, corresponding to approximately 30%, the colla-gen fibers are arranged perpendicular to the surface and it is the zone where the interlaced framework of collagen fibrils is more compact. Finally, the calcified sheet (zone), corresponding to the zone where the cartilage is fused to the articular cortical bone.

Figure 2. Diagram showing the different zones of the articular cartilage, depending on the orientation of the collagen fibers.

Table I. ICRS (International Cartilage Repair Society) classification of chondral lesions.

0 Normal1A Superficial fibrillation or softening1B Superficial fissures and lacerations 2 Defects <50% 3A Defects >50% without extending down to the

calcified layer3B Defects >50% extending down to the calcified

layer4A Total defects involving subchondral plate4B Total defects with deep involvement of

subchondral plate

The aging processes and degeneration of the articular cartilage are associated with loss of repro-ductive capacity of the chondrocytes and the reduction of proteoglycans. Cartilage becomes more rigid and

Magnetic resonance imaging (MRI) is the method of choice for evaluating articular cartilage lesions as it is non-invasive, has high contrast resolution and multi-plane capability.

MRI performance in the detection of chondral lesions will depend on the equipment used, high field 1.5 or 3 Tesla resonators being necessary for the eva-luation of articular cartilage lesions. It is important to use appropriate protocols and sequences to identify subtle lesions (Figure 3). The sensitivity of the MRI is directly proportional to the magnitude in terms of the involved chondral surface and the depth of the lesion(2). Furthermore, thicker cartilage such as that of the knee, is easier to evaluate than the cartilage of smaller joints. It is important, always and in all articular MRI studies, to conduct a directed search for chondral lesions, as it is usual when reviewing retrospectively and comparing with surgical findings, to see lesions that were not apparent during the first reading. The



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chondral lesion characteristics, especially when focal and unique, which we must specify in the MRI report, are summarized in Table II.

Much has been published regarding the most useful sequences in the evaluation of articular car-tilage. Sequences with good contrast between the cartilage and fluid, and with good contrast between cartilage and subchondral bone, are appropriate for the evaluation of chondral pathology. Sequences that best meet these contrast conditions are specifically fast spin echo proton density enhanced (FSE PD) with fat suppression and T1 gradient sequences (T1 SPGR) with fat saturation. In FSE PD with fat saturation, cartilage is seen with intermediate signal intensity, the fluid with high signal and subchondral bone with low signal (Figure 4). In T1 SPGR with fat-suppression, the cartilage is seen with high signal, and the fluid and subchondral bone have low signal intensity (Figure 5). This last sequence performed with 3D technique, allows thin slicing.

Figure 3. High-resolution coronal T2 slice image using 1.5 Tesla unit, shows small superficial lesions (arrows) in cartilage of the medial compartment of the knee. Sagittal T2 slice image on 3 Tesla unit shows thin traumatic lesion of the tibial plateau cartilage (arrow).

Table II. Important characteristics to report in a focal chondral lesion.

1. Surface area measuring AP and transversal area.

2. Lesion depth (percentage of thickness of involved cartilage).

3. Location on the articular surface (involvement of weight-bearing zone).

4. Subchondral bone alterations (edema, cysts).5. Intra-articular chondral or osteochondral

bodies.

Figure 4. Proton density enhanced axial slice with fat suppression, showing the patella cartilage. The cartilage has an intermediate signal in contrast to the articular fluid high signal.

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Figure 5. Gradient sequential T1-weighted SPGR axial image showing the patellar cartilage and femoral trochlea. Cartilage signal is high in contrast to the articular fluid with a low signal.



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T2 sequences have good contrast between car-tilage (low signal) and fluid (high signal), however, the contrast between cartilage and subchondral cortical bone is not suitable, since both have a low signal. Although this sequence is not very sensi-tive to subtle changes, it is important in traumatic chondral lesions.

There is considerable consensus that the most useful sequences are FSE PD with fat suppression and T1 SPGR with fat saturation(3). These sequences have good contrast and are sensitive to pathological changes of the articular cartilage, which makes them the best sequences. As mentioned previously, it is important to conduct a directed search for cartilage lesions, independent of the protocol used for the study.

Chondral lesions of traumatic origin are typically solitary and with well defined contours. They often involve the whole cartilage thickness (Figura 6) and can be associated with intra-articular chondral or osteochondral bodies, which can cause joint locking. Lesions of degenerative origin begin with intrasubs-tance biochemical alterations, followed by fibrillation, fissures, full-thickness ulcerations and finally total loss of the complete cartilage thickness. Usually the degenerative lesions have irregular contours and often involve more than one area of the articular surfaces with lesions of variable thickness. Depending on the stage of involvement, secondary osteoarthritic changes such as marginal osteophytes, cysts and alterations of the subchondral bone signal can be observed (Figure 7).

The MRI is important in evaluating surgically treated chondral lesions. In this sense the two most frequently used surgical techniques are microfracture and autologous osteochondral grafts. Microfracture involves drilling in the area of the chondral lesion, which induces bleeding of the subchondral bone with the formation of undifferentiated bone marrow mesenchymal cell clusters that will produce the repa-rative fibrocartilage, which is of lower resistance than hyaline cartilage. Autologous osteochondral grafts are used mainly in chondral lesions on weight-bearing surfaces of the knee, which consists in taking an osteochondral fragment from a non-weight-bearing area (usually femoral trochlea) to be placed in the area of the original chondral lesion. This procedure, although more demanding technically, has the ad-vantage of repairing the lesion with hyaline cartilage.

MRI advanced studiesSpecial methods of MRI have been developed

for the evaluation of articular cartilage. The majority of these are studies that remain mainly in research, without important clinical application, the exception being the T2 mapping study, which has been deve-loped mainly in daily practice and will be reviewed in more detail.

Figure 6. Sagittal slice images of the external Tibiofemoral compartment of the knee, PD enhanced with fat saturation (a) and T2 (b). A full thickness focal chondral lesion of traumatic origin can be seen.

Figure 7. Axial PD enhanced fat saturated image, showing advanced degenerative chondropathy of the patella.

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Figure 8. T2 color scale map of normal patella cartilage, where the deepest part is colored red, indicating low levels of T2 relaxation times, the central part is colored yellow and the green colored more superficial zone indicates higher levels of T2.

Figure 9. T2 color map in two separate patients, showing altered areas (arrows) with increased T2 levels in the articular cartilage thickness.

The articular cartilage T2 mapping, is a quantita-tive method for evaluating the internal structure of the cartilage. With this technique it is possible to measure the T2 relaxation time of the cartilage.

T2 relaxation times in normal cartilage are lower in the deeper layers where interlacing of cartilage fibers is more compact and there is less amount of water. T2 relaxation times increase toward the more superficial areas of cartilage.

This method is based mainly on the fact that degenerative changes produce disorganization of the collagen matrix, which becomes more relaxed allowing higher content of H2O protons which are also freer, producing an increase in T2 relaxation values, over normal levels.

With the right program, at the work station it is possible to measure the T2 relaxation time in milli-seconds, placing the area of interest where deemed necessary, allowing objective measurement of altera-tions. Furthermore this can be represented morpho-logically in color image, using a predefined scale to make it visually detectable (Figure 8). As this is not a morphological study, but more so quantitative, its main use is to detect initial intrasubstance alterations of the cartilage, before ulcerations or fissures on its surface (Figure 9). This capability enables this method to evaluate the evolution of emerging chon-dral alterations after pharmacological treatments or others. Of the more advances techniques for cartilage evaluation, this is the one which is being most used in clinical practice(4-6).

Delayed gadolinium reinforcementThis method involves intravenously injecting

ionic gadolinium, which has negative charges, and undertaking active movements and exercising the articulation under study to allow the contrast to pass into the synovial fluid. This method allows evaluation of the proteoglycans concentration in the articular cartilage(7).

This study is based on the negative charges that the glycosaminoglycans have, which are subunits of the proteoglycans. It is known that the degenerative and aging processes of articular cartilage decreases the amount of proteoglycans. If there is a normal amount of glycosaminoglycans (negative charge), the contrast (negative charge) will be repelled and will not diffuse into the cartilage. When the amount of glycosaminoglycans is reduced, it allows the contrast to penetrate and permeate the cartilage in the affected areas. This increased uptake can be represented in color image.

Among other advanced study methods and used mainly in research more so than in clinical application, we can mention specific techniques such as short echo time projection reconstruction and cartilage spectroscopy.

SummaryThe articular cartilage is a highly resistant tissue.

However, lesions are frequent and MRI is the method

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of choice for image evaluation of these. Conventional sequences are useful for this, although some other specialized MRI techniques exist that can allow a more objective, quantitative evaluation of the emer-ging degenerative chondral alterations. Several of these special techniques are still in the process of development and investigation and have not yet been applied to clinical practice. An exception to this is the T2 mapping of articular cartilage, which it is being used more routinely.

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nance findings. Arthroscopy 2007; 23(3): 312-315.3. Recht M, Goodwin D, Winalski C, White L.MRI of ar-

ticular cartilage: Revisiting current status and future directions. AJR 2005; 185: 899-914.

4. Dunn T, Lu Y, Jin H, Ries M, Majumdar S. T2 relaxation times of cartilage at MR Imaging: comparison with severity of knee osteoarthritis. Radiology 2004; 232: 592-598.

5. Mosher T, Dardzinski B, Smith M, et al. Human articular cartilage influence of aging and early symptomatic degeneration on the spatial variation of T2-Preliminary findings at 3T. Radiology 2000; 214: 259-266.

6. Watrin A, Ruaud JP, Olivier P, Guingamp N, et al. T2 mapping of rat patellar cartilage. Radiology 2001; 219: 395-402.

7. Young A, Stanwell P, Williams A, Rohrsheim J, Parker D, Giuffre B, et al. Glycosaminoglycan content of knee cartilage following posterior cruciate ligament rupture demonstrated by delayed gadolinium-enhanced mag-netic resonance imaging of cartilage (dGEMRIC). Bone and Joint Surg 2005; 87(12): 2763-2767.


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