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Hyaline Cartilage Thickness in Radiographically Normal Cadaveric Hips: Comparison of Spiral CT Arthrographic and Macroscopic Measurements¹

¹ From the Departments of Skeletal Radiology (A.W., V.B., J.D.L.) and Pathology (M.P.), Lariboisière Teaching Hospital, 2 rue Ambroise Paré, 75475 Paris Cedex 10, France; Paris VII University UFR Lariboisière-Saint Louis, Paris, France (C.B.); Centre Médico-chirurgical, Paris V University, Paris, France (E.L.); and Department of Statistics, Fernand-Widal Teaching Hospital, Paris, France (E.V.). Received August 18, 2005; revision requested October 27; revision received January 26, 2006; accepted February 14; final version accepted May 1. Address correspondence to A.W. (e-mail: annabelle.wyler{at}lrb.aphp.fr).

	ABSTRACT

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Purpose: To assess spiral multidetector computed tomographic (CT) arthrography for the depiction of cartilage thickness in hips without cartilage loss, with evaluation of anatomic slices as the reference standard.

Materials and Methods: Permission to perform imaging studies in cadaveric specimens of individuals who had willed their bodies to science was obtained from the institutional review board. Two independent observers measured the femoral and acetabular hyaline cartilage thickness of 12 radiographically normal cadaveric hips (from six women and five men; age range at death, 52–98 years; mean, 76.5 years) on spiral multidetector CT arthrographic reformations and on coronal anatomic slices. Regions of cartilage loss at gross or histologic examination were excluded. CT arthrographic and anatomic measurements in the coronal plane were compared by using Bland-Altman representation and a paired t test. Differences between mean cartilage thicknesses at the points of measurement were tested by means of analysis of variance. Interobserver and intraobserver reproducibilities were determined.

Results: At CT arthrography, mean cartilage thickness ranged from 0.32 to 2.53 mm on the femoral head and from 0.95 to 3.13 mm on the acetabulum. Observers underestimated cartilage thickness in the coronal plane by 0.30 mm ± 0.52 (mean ± standard error) at CT arthrography (P < .001) compared with the anatomic reference standard. Ninety-five percent of the differences between CT arthrography and anatomic values ranged from –1.34 to 0.74 mm. The difference between mean cartilage thicknesses at the different measurement points was significant for coronal spiral multidetector CT arthrography and anatomic measurement of the femoral head and acetabulum and for sagittal and transverse CT arthrography of the femoral head (P < .001). Changes in cartilage thickness from the periphery to the center of the joint ("gradients") were found by means of spiral multidetector CT arthrography and anatomic measurement.

Conclusion: Spiral multidetector CT arthrography depicts cartilage thickness gradients in radiographically normal cadaveric hips.

© RSNA, 2007

	INTRODUCTION

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The diagnosis of early hip osteoarthritis responsible for chronic mechanical pain may be challenging (1,2) since, in some patients, conventional radiographs and magnetic resonance (MR) images of the hip may demonstrate normal findings or nonspecific changes. In such patients, computed tomographic (CT) arthrography or MR arthrography may enable visualization of early lesions (ie, lesions not detected at conventional radiography or MR imaging) in the hyaline cartilage (3). Developments in spiral CT technology, including the introduction of multidetector arrays that provide submillimeter spatial resolution, have considerably improved the performance of CT arthrography in the assessment of normal and abnormal hyaline cartilage in joints (4–8). To our knowledge, one study (3) has been performed to evaluate the use of CT arthrography for the detection of early hip osteoarthritis in patients with normal radiographs. However, that study was performed without an anatomic reference standard.

Normal cartilage thickness at the hip has been measured by using cartilage specimens (9), needle probe techniques (10), radiography (11), ultrasonography (US) (12–14), and three-dimensional MR imaging (15,16). The results have shown large variations across joint sites, and authors have described the distribution of hyaline cartilage thickness in the normal hip. However, to our knowledge, the presence of cartilage thickness gradients (ie, gradual changes in acetabular and femoral cartilage thickness from the periphery to the center of the joint [16–18]) has not been reported with use of CT arthrography and has not been investigated by using statistical tests to identify significant thickness differences across joint sites of CT arthrographic measurement.

Thus, the purpose of our study was to assess spiral multidetector CT arthrography for the depiction of cartilage thickness in hips without cartilage loss, with measurement of anatomic slices as the reference standard.

	MATERIALS AND METHODS

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Permission to perform imaging studies of the cadaveric hip specimens was obtained from the institutional review board (Institut d'Anatomie UFR Biomédicale des Saints-Pères, Paris V University). We used the nonembalmed cadavers of 11 individuals who had willed their bodies to science. CT arthrography was performed in radiographically normal cadaveric hips, which were sliced coronally. Areas with cartilage loss at macroscopic and microscopic evaluation, despite normal radiographs, were excluded. Cartilage thickness was measured on CT arthrographic reformations and on anatomic slices.

Cadaveric Hips
There were cadavers of six women and five men, with a mean age of 76.5 years (range, 52–98 years) at death. Slices were made through the sacroiliac joint and the proximal third of the femur to excise 12 hips from these 11 cadavers. The inclusion criterion was a normal anteroposterior radiograph of the excised hip (determined in consensus by A.W. [2 years of experience] and another physician [30 years of experience]). Congenital or acquired dysplasia, evidence of degenerative disease, and previous hip surgery or fracture were exclusion criteria.

CT Arthrography
The hips, conserved at –20°C, were thawed at room temperature and were placed in a mold of paperboard and plaster in the neutral position. A volume of 15 mL of nonionic contrast material (300 mg of iodine per milliliter) (iohexol, Omnipaque 300; Nycomed, Roskilde, Denmark) diluted in 5 mL of isotonic saline was injected into the joint cavity by using fluoroscopic guidance (A.W. and J.D.L., with 1 year and 25 years of experience, respectively, with hip injections). A two–detector row CT scanner (Siemens, Erlangen, Germany) was used for transverse spiral imaging from the upper part of the acetabulum to the femoral neck. The following standardized protocol was used: 140 kV, 150 mA, collimation of 0.5 mm, table speed of 1 mm/sec (effective pitch of 1), and rotation time of 1 second. Reconstructions were performed by using 0.5-mm sections, 0.5-mm increments, high-resolution B70s filter, 130-mm field of view, and 512 x 512 matrix. Multiplanar reconstructions with 0.5-mm sections and no gap were performed in three planes: the coronal plane parallel to the femoral neck, the sagittal plane perpendicular to the femoral neck, and the transverse plane.

Anatomic Evaluation
After hip dissection, the gross appearance of the cartilage surfaces was recorded, and the hips were then cut into coronal slices. Cartilage at the measurement points (see below) on the coronal slices was examined histologically.

Gross appearance of hip hyaline cartilage.—Superficial tissues were removed to expose the joint, which was then disarticulated. To improve visualization of cartilage damage, the joint surfaces were rinsed with saline, stained with waterproof green India ink (Sanford Rotring, Hamburg, Germany), dried for 10 minutes, and rinsed again to remove the ink from the normal cartilage surfaces so that only the cartilage lesions were green (4,19). All joint surfaces were photographed alongside a ruler. Femoral head and acetabular joint surfaces were examined (A.W.) without knowledge of CT arthrographic findings. The joint surfaces of the femoral head and acetabulum were each divided into six regions (3), which yielded 12 regions per hip (144 regions total): on the femoral head, there were the superolateral, superomedial, anterosuperior, anteroinferior, posterosuperior, and posteroinferior regions; on the acetabulum, there were the anterior horn, posterior horn, anteromedial, anterolateral, posteromedial, and posterolateral regions.

In each cartilage region, the cartilage was considered to have no substance loss when its surface was smooth or presented some fibrillation with no visible cartilage loss (4,20).

Preparation of the anatomic slices.—The 12 cadaveric hips were fixed for 10 days in a 10% formaldehyde solution, rinsed, and decalcified for 10 days in a 5% hydrochloric acid solution. This did not alter cartilage staining. On each hip, the femoral head cartilage that was not covered by the acetabulum was measured on CT arthrographic sections through the center of the femoral head in the three planes: coronal, sagittal, and transverse. Before slicing, the acetabulum was placed relative to the femoral head in the position that replicated the position used for CT arthrographic measurements of femoral head cartilage not covered by the acetabulum in the three planes through the center of the femoral head—that is, through the part of the femoral head with the largest diameter. The hips were then cut in 0.5-mm slices in the coronal plane relative to the femoral neck (as for the CT arthrographic coronal reformations) by using a commercially available rotating saw (MAS 9101; Bosch, Munich, Germany) (4). Each anatomic slice was numbered and photographed alongside a ruler, with the same orientation as on the CT sections.

Histologic evaluation of hip hyaline cartilage.—We selected the anatomic slice through the central part of the femoral head (through the part with largest diameter); when this slice showed cartilage loss, the adjacent slice was selected (Fig 1). The measurement points of cartilage thickness on the femoral head and acetabulum were marked on the selected slice with black ink (Fig 2a). The cartilage at and around each ink mark was embedded in paraffin and examined histologically. Regions with cartilage loss at gross and/or histologic examination were excluded from the analysis (4,20); thus, 47 of the 144 cartilage regions were excluded (these 47 regions contained 11 among the total 228 measurement points [4.8% of all measurement points]).

View larger version (188K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Anatomic coronal slice through the center of the femoral head. In the upper part of the joint, cartilage thickness gradients are found on the femoral head and acetabulum, in opposite directions: Cartilage thickness increases from the periphery to the center of the femoral head and from the medial to the lateral edge of the acetabulum.

View larger version (10K): [in this window] [in a new window] [Download PPT slide]   Figure 2a: Diagrams show measurement points used in each plane through the center of the femoral head (C). (a) Coronal plane. C' = center of femoral neck; E = superolateral point, on the ray starting from C, passing through the most lateral part of the acetabular roof subchondral sclerosis; If = central point on femoral head just above the fovea; T = superomedial point, on the ray starting from C, passing through the most medial part of the acetabular roof subchondral sclerosis; and V = apical point with C'CV = 130°. (b) Sagittal plane. 90 = 90° point vertical to C, A = anterosuperior point, and P = posteroinferior point. (c) Transverse plane. AH = middle of anterior acetabular horn, PH = middle of posterior acetabular horn, Pre = prefoveal point on femoral head just anterior to the fovea, and Ret = retrofoveal point on femoral head just posterior to the fovea.

View larger version (10K): [in this window] [in a new window] [Download PPT slide]   Figure 2b: Diagrams show measurement points used in each plane through the center of the femoral head (C). (a) Coronal plane. C' = center of femoral neck; E = superolateral point, on the ray starting from C, passing through the most lateral part of the acetabular roof subchondral sclerosis; If = central point on femoral head just above the fovea; T = superomedial point, on the ray starting from C, passing through the most medial part of the acetabular roof subchondral sclerosis; and V = apical point with C'CV = 130°. (b) Sagittal plane. 90 = 90° point vertical to C, A = anterosuperior point, and P = posteroinferior point. (c) Transverse plane. AH = middle of anterior acetabular horn, PH = middle of posterior acetabular horn, Pre = prefoveal point on femoral head just anterior to the fovea, and Ret = retrofoveal point on femoral head just posterior to the fovea.

View larger version (10K): [in this window] [in a new window] [Download PPT slide]   Figure 2c: Diagrams show measurement points used in each plane through the center of the femoral head (C). (a) Coronal plane. C' = center of femoral neck; E = superolateral point, on the ray starting from C, passing through the most lateral part of the acetabular roof subchondral sclerosis; If = central point on femoral head just above the fovea; T = superomedial point, on the ray starting from C, passing through the most medial part of the acetabular roof subchondral sclerosis; and V = apical point with C'CV = 130°. (b) Sagittal plane. 90 = 90° point vertical to C, A = anterosuperior point, and P = posteroinferior point. (c) Transverse plane. AH = middle of anterior acetabular horn, PH = middle of posterior acetabular horn, Pre = prefoveal point on femoral head just anterior to the fovea, and Ret = retrofoveal point on femoral head just posterior to the fovea.

CT arthrograms were printed out on film with a zoom factor of one. Measurements were taken at selected points that were marked on the film images with a fine-pointed HB pencil, by using a x10 magnifying glass, with a scale marked in increments of 0.1 mm (Fig 2a–2c). On coronal sections, there were seven measurement points as follows: the superolateral point, which was on the ray starting from the center of the femoral head, passing through the most lateral part of the acetabular roof subchondral sclerosis; the apical point, which was on a 130° angle from the neck shaft (ie, the line formed between the center of the femoral head and the center of the femoral neck); the superomedial point, which was on the ray starting from the center of the femoral head, passing through the most medial part of the acetabular roof subchondral sclerosis; and the central point, located on the femoral head just above the fovea (Fig 2a). The first three points were measured on both the femoral head and the acetabulum, and the central point was measured only on the femoral head.

The six measurement points on sagittal sections were the posteroinferior point; the 90° point, which was the point vertical to the center of the femoral head; and the anterosuperior point. All three points were measured on both the femoral head and the acetabulum (Fig 2b).

On the transverse sections, the six measurement points were as follows: the anterior horn and the posterior horn, which were measured at a point in the middle of the anterior and posterior acetabular horns, respectively, on both the femoral head and the acetabulum; and the prefoveal point and the retrofoveal point, which were points measured on the femoral head, located just anterior and just posterior to the fovea, respectively (Fig 2c).

Cartilage thickness at anatomic evaluation.—Cartilage thickness at both the femoral head and the acetabulum was measured twice, at an interval of 2 weeks apart, by a musculoskeletal radiologist (A.W.) who was blinded to CT arthrographic measurements. Measurements were made on the anatomic slice through the center of the femoral head, at the points used for CT arthrography, by using a x10 magnifying glass (Fig 2a). The order of the slices was different at the second evaluation 2 weeks later.

Statistical Analysis
Inter- and intraobserver variabilities were assessed by using the mean difference between the measurements and by using the intraclass correlation coefficients.

Descriptive statistics were computed for cartilage thickness data obtained at CT arthrography and anatomic evaluation. Because anatomic evaluation was our reference standard, we used the mean of the two anatomic measurements in order to minimize errors.

Thickness measurements at CT arthrography in the coronal plane were compared with anatomic measurements by using the Bland-Altman representation to show the magnitude of the differences between the two methods (21) and by using a paired t test to detect a systematic bias. Analysis of variance (ANOVA) of the mean difference between the CT arthrographic value and the anatomic value at each measurement point was performed to look for a significant difference in measurement error across points.

The hypothesis was that differences would be found across the mean cartilage thickness values at the various measurement points (minimum of three points, maximum of four points) in our sample of hips without cartilage loss. The hypothesis was tested by means of one-way ANOVA for repeated measurement, on the femoral head and on the acetabulum, in each CT arthrographic reformation plane and in the coronal plane at anatomic evaluation. For example, for the femoral head assessment on the coronal CT arthrographic reformation, we looked for a difference among the mean cartilage thicknesses at the superolateral, apical, superomedial, and central points. On the basis of the ANOVA, in our sample of 12 hips the difference was statistically significant. Therefore, we rejected the null hypothesis of equality of the cartilage thickness at the various points on the femoral head. For the transverse CT arthrographic reformation, although we compared only the mean cartilage thicknesses of the two acetabular horns, for simplicity, since a paired t test yielded the same result as ANOVA, we also used ANOVA in this case.

When there was a significant difference in a particular plane, we described the change in mean cartilage thickness at the measurement points used in that plane. A gradient of cartilage thickness was considered to exist when the mean cartilage thickness increased or decreased from the periphery to the center of the joint.

We also evaluated the number of hips for which the difference in cartilage thickness at the two extreme points in a plane was greater than twice the intraobserver standard error. We used this criterion to define radiologically relevant variation in cartilage thickness.

All tests were two sided, with a significance level fixed at .05.

	RESULTS

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Intraobserver reproducibilities for anatomic and CT arthrographic evaluation were good, but interobserver agreement for CT arthrography was poor: 95% of the interobserver measurement differences ranged from –0.73 to 0.91 mm (Table 1).

View larger version (15K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Bland-Altman representation of differences between cartilage thickness measurements on anatomic slices and CT arthrograms in the coronal plane, related to the mean of those measurements. The mean cartilage thickness difference between the anatomic slices and the CT reformations was 0.30 mm ± 0.52. Ninety-five percent of the differences between CT arthrography and anatomic values ranged from –1.34 to 0.74 mm. SE = standard error.

In the coronal plane, the gradual changes in cartilage thickness in a given plane, which we called "gradients," were in opposite directions: mean femoral cartilage thickness increased gradually from the periphery to the center, whereas acetabular cartilage thickness increased gradually from the medial to the lateral edge (Fig 4, Table 3).

View larger version (161K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Coronal CT arthrographic reformation of a cadaveric hip. Cartilage thickness gradients are seen on the femoral head and acetabulum. Femoral cartilage (thin arrows) is thinnest at the periphery and gradually increases in thickness toward the center of the femoral head, whereas acetabular cartilage (thick arrows) thickness increases gradually from the medial to the lateral edge.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Sagittal CT arthrographic reformation of a cadaveric hip. No cartilage thickness gradient is seen between the anterosuperior and posterosuperior parts of the acetabulum (thick arrows). In contrast, on the femoral head, the cartilage (thin arrows) increases in thickness from the periphery to the upper and anterior part of the femoral head.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Transverse CT arthrographic reformation of a cadaveric hip. On the femoral head, the cartilage (thin arrows) is thin peripherally and increases in thickness toward the central part of the head. The cartilage is thicker around the fovea. The cartilage at the two acetabular horns (thick arrows) is very thin, about 1 mm.

	DISCUSSION

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Our data indicated that spiral multidetector CT arthrography can be used for measuring cartilage thickness in radiographically normal hips. The mean difference in measurement between the CT arthrography values and the anatomic values was 0.30 mm. Significant differences (P < .001) in mean cartilage thickness at the measurement points were found on the coronal CT arthrographic reformations of both the femoral head and the acetabulum and on the sagittal and transverse reformations of the femoral head, as well as on the anatomic slices in the coronal plane. In each of the 12 hips, on both the coronal CT arthrographic reformations and the anatomic slices, cartilage thickness increased from the periphery to the center of the femoral head and from the medial to the lateral edge of the acetabular cartilage. We used the term cartilage thickness gradients to designate the changes in acetabular and femoral cartilage thickness from the periphery to the center of the joint.

To our knowledge, this was the first study performed to compare thickness measurements of the hip hyaline cartilage without substance loss on CT arthrograms and anatomic slices. Other groups have measured hip cartilage thickness by using punch biopsy (9) or US (12,14) of normal cadaveric hips or three-dimensional MR imaging of femoral heads in healthy volunteers (15).

In our study, on the coronal anatomic slices, femoral head cartilage was thickest at the center, with values ranging from 1.5 to 3.8 mm (mean, 2.83 mm). These results agree with those of earlier studies, in which maximal thicknesses between 3.1 and 4.4 mm (9) or 2.4 and 5.3 mm (12) and mean values of 2.41 mm (14), 2.8 mm (13), 2.84 mm (15), and 3.5 mm (12) were shown.

Acetabular cartilage was thickest near the labrum, with values ranging from 1.4 to 4.8 mm (mean, 2.97 mm); similarly, authors of previous studies found maximal thickness values ranging from 3.1 to 3.26 mm (9) or 2.6 to 4.3 mm (12) and mean values of 1.97 mm (16), 2.3 mm (14), 3.3 mm (12), and 3.6 mm (13).

The thinnest cartilage values in our study were 0.8 mm at the femoral head and 1.3 mm at the acetabulum; these values are in agreement with findings in previous studies that showed values of 0.7 and 0.8 mm at these two sites, respectively, by means of US (13) and 1.14 mm (15) and 1.12 mm (16), respectively, by means of three-dimensional MR imaging.

On sagittal CT arthrographic reformations in our study, mean cartilage thickness at the femoral head was 0.95 mm anteriorly, 1.36 mm apically, and 0.87 mm posteriorly. Similarly, by using lateral radiographs of femoral heads, Armstrong and Gardner (11) found values of 1 mm anteriorly, of more than 2 mm apically, and of less than 1 mm posteriorly. In keeping with the findings of Armstrong and Gardner (11), we found that mean cartilage thickness was greater over the anterior than over the posterior aspect of the femoral head, but the difference was not statistically significant.

When findings at CT arthrography were compared with those at anatomic evaluation, the mean difference in cartilage thickness was 0.30 mm. One likely explanation for this small discrepancy is the difficulty in matching measurement points on CT arthrograms to those on anatomic slices: Identification must be achieved regarding the coronal plane, section through the femoral head center, position of the acetabulum relative to the femoral head, and location of the measurement points on CT sections and anatomic slices. Because the hip cartilage thicknesses were small, the small difference translated into a large percentage. Differences in positioning of the measurement points across observers possibly contributed to the poor interobserver agreement, which was evaluated on the basis of both measurement point positioning and cartilage thickness measurement. The same measurement points were used in previous studies on anteroposterior radiographs of the hip or on three-dimensional MR images (15,17,18,22,23). The 130° neck shaft angle that determines the position of the apical point varies somewhat across individuals but was used for all measurements in each hip and, therefore, did not affect comparisons within a given hip.

In our study, observers underestimated cartilage thickness on CT arthrograms in the coronal plane (P < .001). This systematic bias is probably ascribable to the partial volume effect, which is an artifact to which hip cartilage imaging is particularly sensitive. Hip cartilage is very thin, and, because the joint surfaces are curved, the imaging plane is rarely perpendicular to the cartilage surface. Spatial resolution is also limited by pixel size. In this study, the section thickness was close to the mean difference between anatomic and CT arthrography values. In addition, owing to the anisotropy of CT scan acquisition, spatial resolution was not as good in the studied coronal plane as in the acquisition plane.

In each plane that exhibited significant differences in mean cartilage thicknesses at the different measurement points, we described cartilage thickness gradients on the femoral head and acetabulum by using CT arthrograms and anatomic slices: Cartilage thickness increased steadily from the periphery to the center of the femoral head and from the medial to the lateral edge of the acetabulum. Authors of previous studies have found considerable variation in cartilage thickness across measurement sites on normal hips (12,14) and have described the same distribution of hyaline cartilage thickness in the normal hip (9,12–16). However, to our knowledge, the presence of cartilage thickness gradients have not been reported by using CT arthrography, and none of the previous studies involved statistical tests to look for significant differences in mean cartilage thickness at different points in each reformation plane. The cartilage thickness gradient found on the femoral head on sagittal CT arthrographic sections in our study is in keeping with previous data that were obtained by Armstrong and Gardner (11) by using lateral radiographs of femoral heads.

Cartilage thickness gradients possibly represent an adaptation to local differences in weight-bearing forces. Carter et al (24) hypothesized that joint cartilage thickness is determined by the position where the subchondral growth front stabilizes so that, in mature joints, cartilage is thickest where pressure from weight bearing is greatest.

Our study had several limitations. First, we examined only 12 hips, which limits the value of our conclusions. However, the differences in cartilage thickness across the measurement points were statistically significant despite the small number of hips evaluated. Moreover, this number is within the range usually examined in cadaver studies, which are technically demanding. Second, a few measurement points had to be excluded because they contained cartilage loss, although the radiographs were normal. However, all measurements were performed at sites without cartilage loss. Third, the use of hips from elderly subjects may have influenced the results. However, Lequesne et al (18) found no variation in the hip joint space width with age on normal hip radiographs. Last, we compared cartilage thickness by using CT arthrograms of nonembalmed cadavers and by examining anatomic slices after formaldehyde fixation, which may modify the cartilage. Adam et al (25), however, found no effect of fixation on knee cartilage thickness measured at US. No cartilage alteration caused by hydrochloric acid decalcification has been identified by means of histologic examination. Because of the radiation dose, CT arthrography should be performed only when necessary and with the application of two fundamental principles: justification of the use of CT and optimization of CT settings to reduce the exposure to as low as reasonably achievable (the ALARA principle).

In summary, spiral multidetector CT arthrography provides useful data on hip cartilage with no substance loss, and observers underestimate cartilage thickness by 0.30 mm, on average, with CT arthrograms in comparison with anatomic slices. CT arthrography depicts the cartilage thickness gradients that characterize the hip without cartilage loss.

Practical application: When one considers the high interobserver variability and the small number of hips studied, the presence of cartilage thickness gradients is a more important finding than are the cartilage thickness values. In clinical practice, cartilage thickness gradients are more useful than are the thickness measurements themselves. The finding of cartilage thickness gradients is especially important for the diagnosis of early hip osteoarthritis, which may manifest with uniform loss of cartilage thickness across the maximal weight-bearing area and result in loss of the cartilage thickness gradient. However, the study of a larger series of cases is necessary to determine whether these cartilage thickness gradients are constant findings in the population without osteoarthritis, congenital or acquired dysplasia, previous surgery, or fracture of the hip.

	ADVANCES IN KNOWLEDGE

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• We noted a mean difference between spiral multidetector CT arthrographic and anatomic measurements of 0.30 mm (underestimation at CT) for cartilage thickness in hips without cartilage loss.
  
• Femoral and acetabular cartilage thickness gradients were consistently found on the anatomic coronal slices and on spiral multidetector CT arthrographic coronal reformations from all 12 cadaveric hips (P < .001).
  
• On CT arthrographic sagittal and transverse reformations of cadaveric hips, a cartilage thickness gradient was found for the femoral head (P < .001).
  

	ACKNOWLEDGMENTS

 
We are grateful to J. Hodler, MD, MBA, B. Vande Berg, MD, PhD, and C. Alvarez, MD, for their contribution to the study design. We also express our gratitude to J. P. Lassau, PhD, J. Chrétien, MD, M. Harasse, and M. Sisnaki for their contribution to the data acquisition.

	FOOTNOTES

 

Abbreviations: ANOVA = analysis of variance

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, A.W., V.B., J.D.L.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, A.W., V.B., M.P., J.D.L.; experimental studies, A.W., V.B., C.B., M.P., E.L., J.D.L.; statistical analysis, A.W., E.V., J.D.L.; and manuscript editing, all authors

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