A new proposal for the radiographic evaluation of cartilage wasting in osteoarthritic hip joints

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1 DOI /s ORIGINAL ARTICLE A new proposal for the radiographic evaluation of cartilage wasting in osteoarthritic hip joints A. Amaro H. J. Appell F. Amado J. A. Duarte Received: 16 April 2007 / Accepted: 10 September 2007 Springer-Verlag 2007 Abstract The aim of the present study was to analyze the distinct locations of minimum joint space width (mjsw) across the articular surface among osteoarthritic (OA) hip joints and to correlate the radiographic signs of cartilage wasting with clinical measures of hip function. Forty patients (mean age 67.6 years, range years) with 80 hips showing varying degrees of OA were included in this study. For each hip, the Index and the passive range of hip motion were evaluated and the mjsw was localized and measured in a.p. radiographs. Independent of the mjsw localization, the lateral, superior, and axial joint space width (JSW) were additionally measured in radiographs. Radiographic and clinical data were analysed and correlated with each other. mjsw was found in the superiolateral and axial parts of the OA hip joint in 90% of the cases. A signiwcant correlation was found among almost all variables; however, the highest correlation (P < 0.01) existed between all functional variables and the sum of lateral, superior, and axial JSW (lsajsw). As compared to the traditional mjsw, the results strongly recommend the measurement of lsajsw, since this radiographic parameter represents well the weightbearing areas of cartilage and shows a superior correlation with clinical evidences of hip disability. A. Amaro F. Amado Health School, University of Aveiro, Aveiro, Portugal H. J. Appell Department of Physiology and Anatomy, German Sport University, DSHS Cologne, Cologne, Germany J. A. Duarte (&) CIAFEL, FADE, University of Porto, Rua Dr. Plácido Costa 91, Porto, Portugal jarduarte@fade.up.pt Keywords Pain measurement Hip joint Cartilage Articular range of motion Evaluation radiographique des débris cartilagineux dans la coxarthrose Résumé Le but de la présente étude a été d analyser les endroits distincts du pincement de l interligne articulaire (mjsw) à travers la surface articulaire dans les hanches arthrosiques et de corréler les signes radiographiques de détérioration cartilagineuses avec les données chivrées de la fonction de l articulation. Quarante patients (l âge moyen 67.6 ans, extrêmes ans) avec 80 hanches atteintes à des degrés variables de coxarthrose ont été inclus dans cette étude. Pour chaque hanche, l index de et l amplitude passive des mouvements de la hanche ont été évalués et le mjsw a été localisé et mesuré radiologiquement. Une corrélation signiwcative a été trouvée parmi presque toutes les variables. Mots clés Evaluation de la douleur Articulation coxo-fémorale Hanche Cartilage Amplitude articulaire Introduction Joint space narrowing, subchondral sclerosis, subchondral cysts, and the formation of osteophytes are the most frequent radiological features of osteoarthritis (OA); they are useful to assess the severity of hip OA in a global radiological classiwcation such as the widely used Kellgren and Lawrence`s grading system [11]. Especially, the measurement of joint space width (JSW) has been found to well

2 rexect the clinical status and the progression of hip OA [4,8 10], since it is most closely associated with reported hip pain [7,16]. Despite its obvious importance, apparently a well-dewned critical threshold of JSW for OA does not exist unequivocally, since it has been reported to range from 1.5 to 4.0 mm [6,19]. The radiographic pattern of cartilage loss in hip OA has been classiwed into three subtypes according to its location, i.e. superolateral, concentric, and medial [14,17]; but it remains uncertain whether they represent a common pathophysiological entity. Nevertheless, biomechanical studies have shown that the cranial part of the acetabulum is the main area of femoral contact for weight-bearing, which is in agreement with the greater frequency of superolateral narrowing of the JSW in OA hips [17]. Common knowledge suggests that the extent of joint space narrowing is correlated with hip disability, but most studies sought to identify the location of the narrowest JSW. However, a reduced JSW at an isolated location should not necessarily allow for the prediction of hip dysfunction related to OA, if other parts of the hip joint are well covered with cartilage. Therefore, not only the smallest JWS might be of interest, but also, especially its localization considering the biomechanical situation and the JSW across larger weight-bearing areas of the hip joint. The aim of the present study was to analyze the distinct locations of minimum JSW (mjsw) across the articular surface among hip joints in patients with OA of diverent severity. Based on local predilections of mjsw, joint space width was assessed at three points across the weight-bearing area. Clinical measures related to hip function and to pain, were correlated with JSW. The special objective was to propose a more global measurement across well-dewned larger weight-bearing areas of the hip joint. Materials and methods This work was approved by the local Ethical Board and all patients gave their informed consent to the objective and protocol of the study. Forty patients (25 males and 15 females, with a mean age of years, ranging years and a BMI of , ranging ) were referred to the Orthopedic Department because of hip OA symptoms. History of hip surgery or fractures, noticeable pelvic asymmetries, neurological or muscular disturbances that might interfere with hip joint function, hip disorders during childhood, or rheumatoid arthritis of any joint constituted exclusion criteria. From all patients, both hip joints were evaluated according to the clinical criteria of the American College of Rheumatology [1] based on the presence of pain in the articular region during the last month and on radiological alterations. None of the patients showed a Xexion contracture that would bias the radiological assessment. Clinical examination Hip pain and function were assessed using the Index [15]; the function was also evaluated by the measurement of the passive range of motion with a standard goniometer using well-established methods [2]. All tests were done by the same examiner who was not aware of the respective radiographic Wndings. Radiographic evaluation A pelvic radiograph was taken from each patient in the standard anteroposterior (AP) view, with the patients in supine position, legs in neutral position, and the X ray tube centered to the pubic symphysis 100 cm above the table. The distance of the femoral trochanters (identiwed by palpation) to the table was controlled to be equal at both sides, the height of the trochanters above the table varied interindividually between 9.5 and 16 cm. The severity of OA was graded using the Kellgren and Lawrence grading scale. The location of mjsw was registered and the width was measured. JSW was furthermore assessed across the joint at three locations (lateral, superior, and axial); the lateral JSW was measured at the lateral margin of the acetabular subchondral sclerotic line; the superior JSW was measured at the apical transection of a vertical line through the center of the femoral head; the axial JSW was measured just superior from the fovea (Fig. 1). All quantitative measurements were standardized and corrected for magniwcation, and were performed by the same observer using a 0.1-mm graded ruler. The sums of the lateral, superior and axial (L + S + A) JSW and of the L + S JSW were calculated as an overall estimate of the available cartilage to resist to weight-bearing activities. Statistical analysis All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS for Windows Version13.0, Chicago, IL). The respective data for the radiographic and functional parameters were correlated for each hip using the Pearson correlation coeycient with a signiwcance level of Results The population studied had a Kellgren and Lawrence grade between score 0 and score 4 (n = 9 score 0 1, n =17 score 2, n = 31 score 3, n = 23 score 4). The severity of radiological

3 Fig. 2 Example of a patient (male, 62 years) with a marked OA of the right hip, while the left shows less degenerative signs. The lateral, superior, and axial JSW are marked with black arrowheads and the location of mjsw is marked with white arrows. The left hip was completely asymptomatic, while the right hip was symptomatic with regard to pain ( score 7/8) and to a restricted range of motion Fig. 1 Radiograph of a hip joint with a histogram included to show the local distribution of the minimum JSW in n = 80 hips. The points measured for JSW in the lateral, superior, and axial weight-bearing areas are shown by dotted lines from the center of the femoral head toward joint space Table 1 Radiographic characteristics of the sample (JSW joint space width in mm) Minimum Maximum Mean Std. deviation JSW lateral (L) JSW superior (S) JSW axial (A) JSW L + S JSW L + S + A Minimum JSW Table 2 Clinical characteristics of the sample characteristics with regard to JSW varied considerably among the sample (Table 1) and within subjects (Fig. 2), as did clinical symptoms assessed by the index and range of motion (Table 2). With regard to the mjsw determined on the radiographs, only eight hips (10%) showed the mjsw in the medial compartment of the joint, i.e. outside the major weight-bearing region. The histogram of the localizations of the mjsw (Fig. 1) shows accumulations at the lateral, superior and axial sites, especially superiolateral. Even in those hips where a very small mjsw was found in the medial compartment, the joint space showed a considerable overall narrowing. Body mass index of the patients did not show correlations with any of the radiographical or clinical parameters, while some correlations were found between age and superior JSW ( 0.24; P < 0.05), axial JSW ( 0.25; P <0.05), L+S+A JSW ( 0.26; P < 0.05), and mjsw ( 0.28; P < 0.05) as well as for abduction ( 0.35; P < 0.05) and internal rotation ( 0.25; P <0.05). In cases where a small mjsw was found, the whole joint showed an overall narrowing of the joint space, which is supported by a high correlation between mjsw and L+S+M JSW (0.90, P < 0.001). A signiwcant correlation was found between the radiographic and functional parameters for almost all variables (Table 3). The highest correlations with each of the clinical parameters were found for the sum of the three (L + S + A) JSW measurements, which were even higher than for L + S JSW or mjsw, respectively. Discussion Minimum Maximum Mean Std. deviation total pain function Flexion ( ) Abduction ( ) Adduction ( ) External Rotation ( ) Internal Rotation ( ) Some precautions have been taken in this study to obtain as unbiased radiographs as possible. The equal height of

4 Table 3 Pearson correlation coeycients between radiographic and clinical hip joint parameters (JSW joint space width) total pain function Flexion Abduction Adduction External rotation Internal rotation JSW lateral (L) 0.52** 0.50** 0.39** 0.40** 0.56** 0.38** 0.53** 0.39** JSW superior (S) 0.52** 0.57** 0.33** 0.37** 0.57** 0.40** 0.47** 0.30* JSW axial (A) 0.39** 0.42** 0.25* ** 0.37** * JSW L + S 0.56** 0.57** 0.39** 0.42** 0.61** 0.42** 0.54** 0.38** JSW L + S + A 0.62** 0.64** 0.43** 0.44** 0.66** 0.50** 0.57** 0.44** Minimum JSW 0.56** 0.60** 0.26* 0.34** 0.63** 0.45** 0.50** 0.42** * P <0.05 ** P <0.01 both femoral trochanters above the table had been controlled before the radiographs were taken. Considering the diverences in trochanter height among the patients, which could be taken as a rough measure of hip joint height above the table, the calculated error for magniwcation was below the measuring precision of the ruler. If aiming to evaluate articular cartilage thickness in weight-bearing areas of the hip joint, one might expect to take radiographs in standing position. Previous studies, however, have demonstrated that radiographs taken in standing or supine positions virtually show identical results with regard to JSW [3]. Although some studies were not able to show strong correlations between hip pain and OA radiographic signs [12,13,19], such correlations appear to become stronger with increasing severity of OA [4,5,18]. Sixty-seven percent of the hips examined in the present study were considered to show severe OA with a Kellgren index of 3 or more. Not surprisingly, signiwcant correlations existed between radiographic signs of interarticular space narrowing and functional parameters for almost all of the variables studied. Age was only slightly correlated to some of the functional and radiographical parameters, which may be interpreted as a normal but not necessarily consistent degenerative process during aging. It appeared surprising that BMI index did not show correlations with the parameters assessed, since overweight is assumed a risk factor for the development of hip OA [9]. However, the fact that BMI was only evaluated at the moment the patients visited the hospital and does not provide information about the history of the patients BMI over the past years has to be considered. The diagnosis and grading of OA is mainly based on narrowing of the articular space width or on global scales [7,11]. When determining the minimal JSW, one might be faced with some diyculties to select the exact point to be measured. This may account for the wide variations in dewning the threshold of JSW, at which a hip joint is considered to have OA [6,19]. It appears obvious that a decision based on a single point measurement might not guarantee for great conwdence. In accordance with biomechanical considerations [17], mjsw was found to be located superiolaterally in the majority of cases, but also toward the axial part of the joint (cf. Fig. 1). We therefore had opted to make additional measurements of JSW at three distinct points and to calculate the sum of L + S JSW and of L + S + A JSW for further correlation with clinical parameters. The results showed that the correlations of mjsw and of L + S JSW, respectively, were similar, but those for L + S + A JSW were always the highest. Although the axial compartment has received less attention than the superiolateral one, these data appear to emphasize the importance of its inclusion to judge the overall situation of the hip joint. It is therefore suggested that three measurements as done in this study give a more global picture of articular cartilage wasting and allows for a more systematic evaluation. The strong correlation (0.90) between mjsw and L + S + A JSW may raise some doubt about the benewt of additional three measurements; this argument seems to be weak considering the higher correlations of L + S + A JSW with the clinical parameters than that of mjsw. The sum of the three measurements might therefore be considered a valid diagnostic tool in radiographic assessment of hip OA. Since it is strongly correlated with functional impairment and pain that usually forces a patient to seek for the advice of a physician, this measure might also be helpful for the detection of developing yet asymptomatic OA. Future longitudinal research may prove to be meaningful, by taking repeated measurements over longer periods of time and by following a potential evolution leading to severe symptomatic hip OA or by predicting hip disability, especially in middle-aged populations. Such forthcoming studies using large number of subjects of diverent ages should also allow for the determination of L + S + A JSW range for asymptomatic, presymptomatic, and symptomatic OA hip joints.

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