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Musculoskeletal Imaging |
1 From the Department of Orthopedic Surgery, University of Berne, Inselspital, CH-3010 Berne, Switzerland (M.L., M.B., M.K., Y.J.K., R.G.); and Department of Radiology, Clinic Sonnenhof, Berne, Switzerland (S.W.). Received January 25, 2004; revision requested April 2; final revision received August 30; accepted September 29. M.K. supported by a grant from the University of Teheran. Y.J.K. supported by a fellowship from AO-International. Address correspondence to M.L. (e-mail: michael.leunig{at}balgrist.ch).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: The institutional review board approved this study and did not require informed patient consent. An orthopedic surgeon and a radiologist in consensus retrospectively reviewed the anteroposterior (AP) pelvic radiographs of 117 hips with FAI and compared these images with the AP radiographs of a control group of 132 hips with developmental dysplasia (DD) to determine the prevalence of juxtaarticular fibrocystic changes at the anterosuperior femoral neck. Criteria for juxtaarticular fibrocystic changes at the anterosuperior femoral neck were location close to the physis and a diameter (of the fibrocystic change) of greater than 3 mm. The sensitivity and specificity of AP pelvic radiography in the detection of these fibrocystic changes were calculated by using an additional 61 hips with FAI and on the basis of findings at magnetic resonance (MR) arthrography, which was routinely performed for assessment of FAI. In 24 patients who underwent joint-preserving surgery for FAI, the fibrocystic changes were localized intraoperatively and the spatial relation of the region of these changes to the area of FAI was identified. Joint-preserving surgery consisted of anterior surgical dislocation of the hip with osteochondroplasty of the proximal femur and/or the acetabular rim to improve the impingement-free range of hip motion. For statistical comparisons, nonparametric tests were performed.
RESULTS: Fibrocystic changes were identified on the AP radiographs of 39 (33%) of the 117 FAI-affected hips and on none of the radiographs of the 132 DD-affected hips. According to MR arthrogram findings, the sensitivity, specificity, and positive and negative predictive values of AP pelvic radiography were 64%, 93%, 91%, and 71%, respectively. The mean diameter of the juxtaarticular fibrocystic changes was 5 mm (range, 3–15 mm); smaller lesions were more prevalent. Dynamic MR imaging with the hip flexed and intraoperative observations revealed a close spatial relationship between the region of the fibrocystic changes at the anterosuperior femoral neck and the acetabular rim.
CONCLUSION: The high prevalence of juxtaarticular fibrocystic changes at the anterosuperior femoral neck and their spatial relation to the impingement site suggest an association and possible causal relationship between these alterations and FAI.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The presence of abnormalities at the femoral head-neck junction is a constant alteration seen in hips with associated femoroacetabular impingement (FAI) (11,12). FAI recently has been proposed as a potential cause of hip osteoarthritis (OA) (13). It has been suggested that owing to morphologic alterations affecting the proximal femur and/or the acetabulum, repetitive mechanical contusions occur during hip motion, particularly flexion and internal rotation. These contusions can lead to acetabular rim lesions that involve the labrum and, even more seriously, the adjacent acetabular cartilage.
On the basis of observed skeletal morphologic features, two distinct types of FAI have been identified: Femoral FAI is caused by an abnormally shaped femoral head that has a peripherally increasing radius causing acetabular rim damage as it enters the acetabulum during motion, especially flexion with internal rotation (14,15). Acetabular FAI is the result of a linear contact between the acetabular rim and the femoral head-neck junction. The femoral head may have normal morphologic features but an indentation (ie, fossa) due to an acetabular abnormality. This acetabular morphologic deviation may be characterized as a generalized overcoverage, which has been identified in patients with a deep acetabular socket, or a localized anterior overcoverage, which is seen in patients with acetabular retroversion. However, in most cases of FAI, combined femoral and acetabular abnormalities can be found (13).
The concept of nondysplastic deviations of the hip leading to OA is not novel. Stulberg et al (16) reported identifying abnormal head-neck configurations on the anteroposterior (AP) radiographs obtained in patients with idiopathic OA. They introduced the term pistol grip deformity to describe the radiologic appearance of this morphologic abnormality but did not elucidate any underlying mechanisms that result in early OA. Other authors (17–20) have suggested an abnormal anatomic relationship between the femoral head and the femoral neck as a possible cause of OA. Several investigators have suggested subclinical displacement of the femoral epiphysis as a risk factor for OA and have used the term head tilt (17) or post slip (16) to describe the deformity that results from a mildly slipped capital femoral epiphysis (14,16,17,21). Similarly, acetabular alterations including a deep (22,23) or retroverted acetabular socket (24) have been related to OA. For the majority of patients with hip FAI, however, a history of predisposing factors is lacking.
On the basis of the morphologic abnormalities seen with FAI (13) and the published reports on herniation pits (2,5), we hypothesized that these alterations at the anterosuperior femoral head-neck junction are not incidental. We proposed that they are instead caused by repetitive mechanical contact between the femoral head-neck and the acetabular rim. Thus, the purpose of our study was to retrospectively evaluate if there is an association between juxtaarticular fibrocystic changes of the anterosuperior femoral neck and FAI.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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2 test).
To assess the sensitivity and specificity of AP pelvic radiography in the detection of these fibrocystic lesions, an additional 61 hips in 54 consecutive patients who had hips with FAI (24 men, 30 women; mean age, 34 years ± 9; range, 12–51 years) and were treated between January 2002 and June 2002 were reviewed. The patients in this additional group had age (difference of 0.1 year; 95% confidence interval: –3.2, 3.2; P > .99, t test) and sex (55.6% vs 44.6%; P = .19, 2 test) distributions similar to those of the patients in the FAI group who were treated between 1992 and 2000. AP pelvic radiography and MR arthrography were part of the routine preoperative examination of these patients with FAI-affected hips, who included a subset of 24 patients who underwent joint-preserving surgery. All patients with FAI-affected hips whose imaging data were analyzed in this study had hip pain combined with clinical symptoms and radiographic signs (described below). Our retrospective study was approved by the institutional review board of Inselspital, University of Berne, which did not require informed patient consent.
FAI usually presents in association with a slow onset of groin pain in young active adults. During the initial stages of the disease, the pain is intermittent and may be exacerbated by excessive demands on the hip during activities such as athletic exercises. Affected individuals often experience the pain after sitting for a prolonged period. Examination of the hip frequently reveals limited motion, particularly internal rotation and abduction with hip flexion. Results of the impingement test, which is performed with the patient supine (25), are almost always positive. The FAI-affected hip is internally rotated when it is passively flexed to 90° and adducted. The combination of flexion and adduction leads to the approximation of the femoral neck and the acetabular rim. It is hypothesized that additional forceful internal rotation induces shearing forces at the labrum and consequently a sharp pain.
Symptoms of DD-affected hips range from early fatigue to clear abductor weakness with irritation at the greater trochanter. However, the primary complaint is a sharp knifelike pain in the groin that subsides as acutely as it begins. Prolonged sitting or walking can exacerbate the pain. Activities that involve forced hip flexion, adduction, and internal rotation can cause another onset of pain. As the occurrences of symptoms increase, residual pain may cause a slight but noticeable limp. The suspicion of an acetabular rim abnormality (25,26), like the suspicion of FAI, is best confirmed by performing the impingement test (25). Patients with hip FAI generally have a decreased range of hip motion, while patients with DD-affected hips frequently have hypermobility.
Commonly observed radiographic and morphologic abnormalities in patients with hip FAI include a bone prominence in the anterosuperior region of the femoral head-neck junction (27), as well as acetabular retroversion, coxa profunda, protrusio acetabuli, and acetabular rim ossification. The crossover sign has been previously identified as a radiographic indicator of acetabular retroversion and is present if the radiographically depicted anterior acetabular rim is projected laterally relative to the same point of the posterior rim at the most proximal aspect of the acetabulum (28,29). Projection of the acetabular fossa (with coxa profunda) or the femoral head (with protrusio acetabuli) medial to the ilioischial line is considered to be radiographic evidence of increased acetabular socket depth.
According to the criteria used by Severin (30), acetabular dysplasia—ranging from acetabular dysplasia without subluxation (group 3) to dysplasia with subluxation (group 4)—was present in all of the DD-affected hips for which data were analyzed in the current study. In some patients, a secondary acetabulum (group 5) was present. In an attempt to eliminate additional cases of FAI among the DD-affected hips, we excluded hips showing a positive crossover sign on radiographs (28,29), which is indicative of acetabular retroversion, from the DD group.
All patients in both the group with FAI-affected hips and the group with DD-affected hips who underwent hip-preserving surgery had positive clinical and/or radiographic signs of either FAI or DD, as described above. Exclusion criteria for both groups were previous hip surgery and/or advanced hip OA (grade 
1) according to the grading system of Tonnis (31). Pelvic radiography and MR arthrography were performed for the assessment of hip abnormalities with the informed consent of the patients.
AP Pelvic Radiography
Standardized conventional AP pelvic radiographs were obtained while the patient was supine by using a tube-to-film distance of 120 cm and a tube orientation perpendicular to the table (29). Both legs were internally rotated by approximately 15° to adjust for femoral neck antetorsion. The central beam was directed toward the midpoint between the upper border of the symphysis and a horizontal line connecting the anterosuperior iliac spines on both sides. Pelvic rotation was assessed on the basis of the alignment of the tip of the coccyx with the middle of the pubic symphysis and the symmetric appearance of the radiographically depicted "teardrops," the obturator foramina, and the iliac wings. Close adherence to these criteria is required for the conclusive assessment of femoral abnormalities and acetabular coverage (29). Fewer than 10% (n = 32) of the available radiographs did not meet these criteria and had to be excluded from the study.
MR Arthrography
All MR arthrograms were obtained by using sequences specifically designed for the detection of FAI. With use of this protocol, no special sequences for the detection of juxtaarticular fibrocystic changes were included. All MR arthrography examinations were performed by using a high-field-strength imaging system (Vision 1.5 T; Siemens, Erlangen, Germany) and a flexible surface coil for high spatial resolution and a high signal-to-noise ratio. Patients were placed in a supine position, and 10–20 mL of saline-diluted gadoterate meglumine (Dotarem 1:200; Guerbet, Aulnay-sous-Bois, France) was injected intraarticularly into the hip with fluoroscopic guidance. The lower extremities were fixed to prevent motion during imaging. Imaging began with a short localizer MR image acquisition followed by a transverse T1-weighted image acquisition to assess the shape of the anterosuperior femoral neck. The MR arthrography imaging parameters were as follows: 650/20 (repetition time msec/echo time msec), 200 x 200-mm field of view, 224 x 512 matrix, 4-mm section thickness with a 0.2-mm intersection gap, and 17 acquired sections.
The depiction of the acetabulum was assessed with transverse fast low-angle shot MR arthrography by using the following parameters: 550/10, 90° flip angle, 120 x 120-mm field of view, 256 x 256 matrix, 2-mm section thickness with a 0.1-mm intersection gap, and 11 acquired sections. MR arthrography continued with the acquisition of sagittal and coronal intermediate-weighted images and three-dimensional (3D) two-echo steady-state images for evaluation of the cartilage surfaces of the acetabulum and the femoral head. These sequences were also used to assess the water content of the fibrocystic changes. The following parameters were used to perform the coronal and sagittal examinations: 3200/15, 120 x 120-mm field of view, 256 x 256 matrix, 2-mm section thickness with a 0.1-mm (coronal images) or 0.2-mm (sagittal images) intersection gap, and 23 acquired sections. The following parameters were used to perform the 3D two-echo steady-state examinations: 26.8/9.0, 40° flip angle, 1 48-mm-diameter voxel, 48 partitions, 160 x 160-mm field of view, and 256 x 256 matrix.
To visualize acetabular rim abnormalities, a radial intermediate-weighted sequence was used, with the section orientation orthogonal to the acetabular rim and the labrum. This sequence is based on a double oblique localizer sequence that originates from a transverse sequence that serves as a localizer for the sagittal oblique sequence. The sagittal oblique section is needed to serve as a second oblique localizer for the coronal oblique sequence with which the radial sections that serve as true orthogonal sections in the acetabular plane are generated. The following MR arthrography parameters were used to perform these examinations: 2000/15, 260 x 260-mm field of view, 266 x 512 matrix, 4-mm section thickness, and 16 acquired sections.
Dynamic MR Imaging
Two patients from the group of patients with FAI who had juxtaarticular cysts at the femoral neck were randomly selected to undergo dynamic MR imaging with an open-magnet-bore configuration (Magnetom Open 0.2 T; Siemens) to allow flexion of the hip during imaging. With these patients supine, sagittal and coronal oblique intermediate-weighted MR images (3000/24, 180 x 180-mm field of view, 256 x 256 matrix, 4-mm section thickness, 20 acquired sections) were obtained with the hip in full extension and in full flexion. Because of the inferior image quality yielded at low-field-strength open-configuration MR imaging, this part of the study was limited to two patients.
Radiograph and MR Arthrogram Analyses
The AP pelvic radiographs and MR arthrograms were obtained within 6 months prior to surgery and were retrospectively reviewed. An orthopedic surgeon (M.L.) and a musculoskeletal radiologist (S.W.), each with more than 10 years of experience, reviewed the AP pelvic radiographs or MR arthrograms separately. The two investigators determined the presence or absence of juxtaarticular fibrocystic changes in consensus and without knowledge of the clinical or surgical data; however, they were aware of the purpose of this study.
Juxtaarticular fibrocystic changes on radiographs were defined on the basis of the presence of an area of radiolucency at the anterosuperior femoral neck, a surrounding sclerotic margin, a diameter (of the fibrocystic change) of greater than 3 mm, and a location distal to the physis. The lower size limit was based on the known diameters of the nutrient arteries at the femoral head-neck junction, which range from 0.100 to 1.550 mm in adults (32). MR arthrography was used to determine the sensitivity of conventional radiography, the cyst size, and the presence or absence of fluid within the juxtaarticular cysts. The sizes of the cysts were determined by measuring the maximum diameter of the sclerotic ring on the intermediate-weighted images. An area of increased signal intensity surrounded by an area of decreased signal intensity on the 3D two-echo steady-state image was indicative of high water content of the fibrocystic change. In cases of decreased signal intensity centrally, the cyst was considered to be filled with a dense fibrous tissue of low water content.
Surgical Technique
For joint-preserving surgery, the patients were placed in the lateral decubitus position and a Kocher-Langenbeck (33) or Gibson-type (34) approach was combined with a trochanteric osteotomy (35). Surgery was performed by the same three surgeons (M.L., M.B., and R.G.) in all cases. The surgeons exposed the hip anteriorly and dislocated it in the same direction while respecting the integrity of the external rotator muscles, including the piriformis muscle. This technique allows full protection of the vascular supply of the femoral head (36). It also enables a full 360° view of the femoral head and the acetabulum for inspection. The site of FAI was identified, and the femoral head-neck junction, labrum, and acetabular cartilage were evaluated for the presence of any lesions.
The surgical treatment for FAI secondary to a femoral abnormality involved the removal of any nonspherical portions of the femoral head and neck to facilitate improved hip range of motion (37). By performing this femoral osteochondroplasty, the impingement-inducing excessive bone and cartilage tissue was resected, and this resection allowed the identification of juxtaarticular cysts. The aim of this treatment was not the removal of the fibrocystic alteration but rather the optimization of femoral head sphericity by means of removal of the osteochondral tissue that overlaid the lesion. For acetabular causes of FAI, treatment included reducing the regional (retroversion) or global (coxa profunda, protrusio acetabuli) overcoverage by reducing the acetabular rim (37) or reorienting the entire acetabulum by means of periacetabular osteotomy (38). In the majority of cases, combined femoral and acetabular FAIs were present, and both required treatment.
Intraoperative Analysis
During surgery, the spatial relationship between any abnormalities of the anterosuperior femoral head-neck junction and the acetabular rim in the position of maximal FAI was evaluated by each surgeon (M.L., M.B., and R.G.). The femoral head was dislocated anteriorly for inspection of the labrum and the adjacent cartilage. After femoral osteochondroplasty, the femoral head-neck junction was assessed for the presence of fibrocystic alterations. The type and extent of degenerative lesions of the labrum and the adjacent cartilage were recorded on standardized documentation sheets and in the surgical report. A clock-face system in which 12 o'clock was the position pointed toward the head of the patient was used. The presence or absence of juxtaarticular fibrocystic lesions was recorded.
Statistical Analyses
Data are expressed as means ± standard deviations. The size distribution of the fibrocystic changes and the location of the labral lesions are depicted on histograms. P < .05 was considered to indicate significance. The sensitivity (TP/[TP + FN]), specificity (TN/[TN + FP]), positive predictive value (TP/[TP + FP]), and negative predictive value (TN/[TN + FN]) were calculated on the basis of data obtained at MR arthrography, where TP is the number of true-positive findings; TN, the number of true-negative findings; FP, the number of false-positive findings; and FN, the number of false-negative findings. On the basis of preliminary clinical observations, we expected a prevalence of herniation pits of at least 20% among the patients who had hip FAI. With the assumption of a prevalence of herniation pits of 5% or lower (in the general population) for the DD-affected hips and a significance level of 5%, the chosen sample sizes of 132 DD-affected hips and 117 FAI-affected hips provided a power of at least 93%. To examine the effects of clustering on the standard error, we calculated a design factor—that is, a robust standard error assuming clustering divided by the crude standard error assuming independency of observations. All analyses were performed by using STATA 8.2 software (Stata, College Station, Tex).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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2 test). The design factor (robust standard error assuming clustering divided by crude standard error assuming independency of observations) was 1.01, which indicated that the correlation of the characteristics of the patients' hips had negligible effects on standard errors.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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FAI may develop as a result of morphologic abnormalities, or it may occur in patients whose hips are subjected to an extreme and supraphysiologic range of motion. The concept of FAI is focused more on dynamic hip motion than on axial loading as a cause of the hip pain and the associated degenerative conditions. According to observed patterns of chondral and labral injury, two distinct types of FAI have been distinguished: Femoral FAI is caused by the jamming of an abnormally shaped femoral head that has an increasing peripheral radius into the acetabulum during forceful motion, especially hip flexion (14,15,40). Acetabular FAI is the result of linear contact between the acetabular rim and the femoral head-neck junction.
In some instances, the femoral head has normal morphologic features and the abutment is the result of an acetabular abnormality. Often, this abnormality is either a typical overcoverage from a deep socket or a local overcoverage from a retroverted acetabulum (38,41). Because both abnormalities frequently manifest together, it is difficult to clearly attribute the formation of juxtaarticular fibrocysts to either femoral FAI or acetabular FAI. Peak loading occurs with both femoral FAI and acetabular FAI when individuals are in frequently used positions, such as flexion during sitting or flexion and/or internal rotation with sports activities, and explains the relatively localized occurrence of impingement-associated lesions.
On the basis of the different mechanism of motion failure in the DD-affected hips, these patients served as FAI-free control subjects. DD-affected hips have deficient anterosuperior acetabular coverage and a tendency toward migration of the femoral head in the direction of this insufficiency. This static instability of the hip causes chronic shear forces that are most pronounced during full extension and external rotation of the hip. As a result, the anterolateral migratory tendency of the femoral head in DD-affected hips should further increase the pressure induced by the anterior joint capsule. Although this could lead to an increased number of herniation pits, the opposite was observed in the current study. In fact, no juxtaarticular cysts were found in the DD-affected hips; this observation supports our hypothesis that herniation pits are caused by a mechanism different from that previously suggested.
In contrast, juxtaarticular fibrocysts were diagnosed in 39 (33%) of the hips with FAI on the basis of findings seen at interpretation of the conventional radiographs. This datum indicates a five- to sevenfold increase in the prevalence of juxtaarticular cysts compared with the previously reported prevalence of 5% in healthy populations (5,10). Although more than 100 hips were reviewed in the first part of this study, this retrospective assessment involving the use of conventional radiographs was limited by the absence of a second method to confirm that the alterations were actually fibrocysts.
Therefore, a subset of patients with hip FAI who underwent both conventional AP pelvic radiography and MR arthrography was used to compare these two methods for their capability to depict these fibrocysts. MR imaging has been suggested as a highly sensitive method (42) in the differential diagnosis of cystic lesions (43). Additionally, the typical morphologic features of the underlying process can be demonstrated on MR arthrograms. For those hips treated with joint-preserving surgery, the positive MR arthrography result was confirmed intraoperatively. Although no specific MR imaging sequences for the diagnosis of cysts were used in the routine work-up of FAI-affected hips, the use of 3D two-echo steady-state sequences enabled assessment of the fluid content of these fibrocystic alterations. Additionally, no marrow edema surrounded these fibrocysts; this finding potentially indicated a slow repetitive process as opposed to forceful impacts as the mechanism of fibrocyst formation in these patients.
What causes these fibrocystic lesions, which formerly were termed herniation pits? Since the first description of these abnormalities by Pitt et al (5), herniation pits of the femoral neck have been attributed to the commonly acquired degenerative changes that develop at the surface of the femoral neck after repetitive low-degree traumas. It has been suggested that the synovium invaginates through cortical defects at this location (cervical fossa of Allen) (44) to form a subcortical pit or cavity (5). It has been postulated that this herniation is mediated by pressure from the iliofemoral ligament of the anteromedial hip capsule. With certain activities such as running—and specifically hurdling—movement of the iliopsoas muscle relative to the joint capsule with the hip in extension has been suggested as the cause of the observed progressive soft-tissue herniation (2). The anatomic study by Daenen et al (2) revealed that ligaments of the hip are tightened with extension and internal rotation. It was further suggested that the overlying iliopsoas muscle, which is tightly applied to the hip, may contribute to the abrasive effect of the capsule on the reaction area.
On the basis of work during the first 3 decades of the past century by Fick (45), Poirier and Charpy (46), and Meyer (47), a different theory about the origin of these herniation pits might be proposed. These authors suggested that morphologic alterations at the femoral neck that had an appearance similar to that of herniation pits were secondary to pressure from the ilium or the labrum. Furthermore, they believed that not hip extension but rather positions of extreme hip flexion with internal rotation were primarily responsible. The results of the current study indicate that there is a close spatial relationship between these lesions and the site of impingement, favoring this latter theory that flexion-induced pressure causes the production of these fibrocystic changes.
On the basis of the radiographically depicted location of the fibrocystic alterations at the anterosuperior femoral neck and the reported location of herniation pits (1–3,5–7,10), it is very likely that herniation pits and FAI-induced fibrocysts are the same entity. This theory is further supported by the histologic appearances identified in this study and the original description of herniation pits (5), which are similar to the appearances and description reported by Schajowicz et al (48). Combining our experience with those described in previous reports, we believe that these lesions are intraosseous ganglia rather than synovial invaginations occurring through cortical defects. The differences in the signal intensities of the fibrocystic changes at MR arthrography are probably the result of differences in the water content of the fibrous tissue within the cysts. It is proposed that these juxtaarticular fibrocystic changes are caused by the same morphologic alterations that lead to the labral and adjacent cartilage disorders observed with FAI. Therefore, these lesions may represent a radiographic indicator of FAI rather than an incidental finding in patients with hip pain, as previously suggested (5).
Our study was observational in that we used a retrospective design to assess abnormal (FAI- and DD-affected) hips and thereby investigate the potential association between juxtaarticular fibrocysts of the anterosuperior femoral neck and FAI. Potential bias in the assessment of radiographs could be reduced by omitting the rest of the pelvis-hip region. On the basis of our study data, however, one can speculate about the prevalence of these fibrocystic changes in populations. At present, there is, to our knowledge, only one study—that conducted by Notzli et al (15)—in which nonsymptomatic volunteers were compared with clinically symptomatic patients with hip FAI. In that series, 12.5% of nonsymptomatic control subjects had limited internal rotation of the hip that was characteristic of FAI. The 33% of patients with morphologic features of FAI in our study who had fibrocystic changes at the femoral neck is close to the prevalence of these changes reported by Pitt et al (5), given a 5% prevalence (one of 20 hips) of these findings in the general population. The level of evidence generated by our findings could be strengthened in the future with intraobserver comparisons and the use of a prospective study design.
Nevertheless, on the basis of the results of this study, we have several recommendations for the examination of patients with unexplained hip pain. In patients with symptomatic hips and associated juxtaarticular fibrocysts at the anterosuperior femoral head-neck junction, we suggest performing a thorough investigation for the potential presence of femoral and/or acetabular impingement. This can be accomplished with several methods, including clinical examination, conventional radiography, and MR arthrography. Although MR arthrograms are not specifically obtained for the primary identification of juxtaarticular fibrocystic changes, they are useful for assessing early damage to the labrum and the adjacent cartilage, which frequently is not detectable on conventional radiographs (49). If no morphologic features of FAI can be identified, metastatic bone disease or lymphoma, osteoid osteoma (50), cartilaginous rests (51), fibromas (52), and conversion defects (53) have to be ruled out.
Currently, there are few reliable radiographic markers that predict early hip OA. Juxtaarticular fibrocysts, when present in a patient with associated clinical symptoms of hip abnormality, may suggest the presence of FAI as a prearthritic condition. Therefore, juxtaarticular fibrocystic changes at the femoral head-neck junction may represent a radiographic indicator of FAI rather than an incidental finding in patients with hip pain.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Abbreviations: AP = anteroposterior • DD = developmental dysplasia • FAI = femoroacetabular impingement • OA = osteoarthritis • 3D = three-dimensional
2 Current address: Department of Orthopaedics, Balgrist University Hospital, University of Zürich, Zürich, Switzerland 
3 Current address: Firouzgar Medical Center, University of Medical Sciences, Teheran, Iran
4 Current address: Department of Orthopaedic Surgery, Children's Hospital, Harvard Medical School, Boston, Mass
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, all authors; study concepts, M.L., R.G.; study design, all authors; literature research, M.L.; data acquisition and analysis/interpretation, all authors; statistical analysis, M.L.; manuscript preparation, editing, and revision/review, M.L.; manuscript definition of intellectual content and final version approval, all authors
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