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Prevalence of radiological femoroacetabular impingement in Japanese hip joints: detailed investigation with computed tomography
J Orthop Sci DOI 10.1007/s00776-015-0733-5
ORIGINAL ARTICLE
Prevalence of radiological femoroacetabular impingement in Japanese hip joints: detailed investigation with computed tomography Tomohiro Mimura1 · Taku Kawasaki1 · Shin Itakura2 · Tomohiro Hirata1 · Hitomi Fuzikawa1 · Kanji Mori1 · Shinji Imai1
Received: 6 October 2014 / Accepted: 21 April 2015 © The Japanese Orthopaedic Association 2015
Abstract Background Femoroacetabular impingement (FAI) has been highlighted as a new etiology for osteoarthritis of the hip, and its prevalence has been reported in the past decade. In the present study, we performed a detailed investigation of the anatomical parameters related to FAI and calculated the prevalence of FAI-related findings in asymptomatic Japanese hip joints using computed tomography. Methods We evaluated high-resolution reconstructed multislice computed tomography images in patients who had undergone computed tomography imaging in our institution for conditions unrelated to hip disorders. The examined parameters were as follows: center-edge (CE) angle; acetabular index; acetabular anteversion (five slices in the axial plane); and asphericity angle of the femoral head (AAFH) (six slices in multiple radial planes). The AAFH in the oblique axial slice through the center of the femoral neck is the so-called α-angle. We then examined the accurate prevalence of FAI-related findings in Japan. Results We investigated a total of 103 hips. The mean age of the subjects was 59.4 years. The mean CE angle was 31.1° and the mean acetabular index was 7.0°. The mean acetabular anteversion was 20.3° at the level of the hip center, and decreased as the slice level neared the superior margin of the femoral head. The mean AAFH ranged from 40.6° to 49.2° in the radial planes. The AAFH was largest
* Tomohiro Mimura [email protected]‑med.ac.jp 1
Department of Orthopedic Surgery, Shiga University of Medical Science, Tsukinowa‑cho, Seta, Otsu, Shiga 520‑2192, Japan
2
Department of Orthopedic Surgery, Shiga Medical Center for Children, Shiga 524‑0022, Japan
at 60° rotated slice from the oblique axial slice through the center of the femoral neck. The prevalence of FAIrelated findings in these Japanese hip joints was assessed as follows. An AAFH of >50° in any slice was detected in 51.5 % of the hips, and acetabular anteversion was negative for all images in 16.5 % of the hips, meaning that a total of 56.3 % of the images met the criteria for radiological FAI. Conclusions With consideration of our results, we emphasize that “anatomical or radiological FAI” is not uncommon in Japanese hips. Therefore, the diagnosis of FAI should be performed with the clinical findings taken into account.
Introduction Femoroacetabular impingement (FAI) has recently been reported as a cause of osteoarthritis (OA) of the hip. It was first described by Myers et al. [1] and then in detail by Ganz et al. [2]. The etiology of FAI is abnormal contact between the acetabulum and femoral head-neck junction that leads to labral tearing and subsequent osteochondral disorders. FAI is divided into two subcategories: cam deformity and pincer deformity [2, 3]. A cam deformity is defined as an abnormal morphological finding of the femoral side of FAI, and is characterized by a bony bump of the anterior femoral head-neck junction or non-spherical femoral head. A pincer deformity is defined as a morphological abnormality of the acetabular side of FAI, and is characterized by excessive anterior coverage at the superior acetabulum or acetabular retroversion. Many studies have described these radiographic deformities and the prevalence of FAI [3–9]. However, many of the reports were roentgenogram image investigations, which run the risk of being affected by the patient’s position and posture [10, 11]. Therefore,
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several studies involving anatomical investigations related to FAI using computed tomography (CT) have recently been reported in Western countries [12–15]. In the present study, we aimed to perform a detailed investigation of the anatomical parameters related to FAI in asymptomatic hips using high-resolution reconstructed multislice CT images and to examine the accurate prevalence of FAI-related findings in Japan.
This study was approved by our institutional review board. We conducted a patient-based study on patients who had undergone CT imaging from the chest to the abdomen. As other departments in our institution had ordered these scans, the CT scans were undertaken for conditions unrelated to hip disorders. The inclusion criteria for investigations were as follows: (1) whole pelvis and both hip joints were involved; (2) reconstructed axial slice thickness was ≤1 mm; (3) pelvic rotations and tilt were normal (described below in the section for standardization of CT images). The
exclusion criteria were as follows: (1) age under 20 years; (2) evident pathology of hip OA, such as joint space narrowing, osteophytes, or subchondral bone changes including cysts and sclerosis [16]. We retrospectively examined consecutive patients fulfilling the above criteria from 1 July 2013 to 31 July 2013. The parameters examined were as follows: age; sex; center-edge (CE) angle [17]; acetabular index [18]; and acetabular anteversion in the axial plane (five slices; first slice at the level of the superior margin of the femoral head, followed by four slices at 5, 10, and 15 mm below the superior margin of the femoral head, and at the level of the hip center) (Fig. 1). In addition, we measured the asphericity angle of the femoral head (AAFH) in multiple radial slices using previously described methods [19, 20]. For this, six radial slices were generated at 15° intervals, including slices with 0°, 15°, 30°, 45°, 60°, and 75° rotation from the oblique axial slice through the center of the femoral neck (hereafter referred to as S1, S2, S3, S4, S5, and S6, respectively) (Fig. 2). The AAFH of each slice was measured as previously described [21]: the S1 slice angle is the so-called α-angle [2, 3]. Negative acetabular anteversion in any slice was defined as pincer deformity, while an AAFH of >50° in any slice was defined as cam deformity.
Fig. 1 Measurement of the acetabular anteversion angles in five axial slices. a Reference plane for the acetabular anteversion angle measurements. Each line represents one of the five slice lines. The axial views of lines b, c, d, e, and f are shown in b, c, d, e, and f, respectively. b Axial view of the superior margin of the femoral head (line b). Angle ø is the acetabular anteversion angle at the superior margin of the femoral head. The angle is measured between the line joining the anterior and posterior edges of the acetabulum and the line per-
pendicular to the line joining the posterior edges at both acetabula. c Acetabular anteversion angle in the axial view at 5 mm below the superior margin of the femoral head (line c). d Acetabular anteversion angle in the axial view at 10 mm below the superior margin of the femoral head (line d). e Acetabular anteversion angle in the axial view at 15 mm below the superior margin of the femoral head (line e). f Acetabular anteversion angle in the axial view at the level of the center of the femoral head (line f)
Materials and methods Patients and parameters
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Prevalence of radiological femoroacetabular impingement in Japanese…
Fig. 2 Measurement of the asphericity angles of the femoral head (AAFHs) in multiple radial slices. a The dotted line is the axis through the center of the femoral neck, adjusted to be parallel to the femoral neck-shaft angle. The solid line is the reference plane for radial angle reconstruction. b The reconstructed plane demonstrates superimposed radial reference lines at 15° intervals. S1 is the oblique axial slice (dotted line in a), S2 is a plane rotated 15° from S1, S3 is a plane rotated 30° from S1, S4 is a plane rotated 45° from S1, S5 is a plane rotated 60° from S1, and S6 is a plane rotated 75° from S1. c
Reconstructed slice of the S1 plane. Angle ø is the AAFH; namely the α-angle. The angle is measured between the line joining the femoral head and the center of the neck and the line drawn from the center of the femoral head to the point where the spherical image of the femoral head is lost. d Reconstructed radial slice of the S2 plane. e Reconstructed radial slice of the S3 plane. f Reconstructed radial slice of the S4 plane. g Reconstructed radial slice of the S5 plane. h Reconstructed radial slice of the S6 plane
Radiological examination and standardization of CT images
Cary, NC). One-way analysis of variance (ANOVA) with a Scheffé post hoc test was used to determine the significance of differences among five or six groups. Student’s t-test was used to determine the significance of differences between two groups. Values of P < 0.05 were considered to indicate statistical significance.
All CT images were axial, sequential, and obtained in the supine position without gantry tilt (120 kV, 160 mA, 0.5 s) using a Toshiba Aquilion CX (Toshiba Medical Systems Corporation, Tokyo, Japan). The data were reconstructed under conditions suitable for bone evaluation using AquariasNet Viewer software (TeraRecon Inc., San Francisco, CA). This software allowed the reconstruction of optimal sagittal, coronal, and axial views, as well as threedimensional reconstructed CT (3DCT) views. We used the 3DCT images to confirm the pelvic rotations and tilt. We confirmed the rotation of the coronal plane to investigate whether the teardrop line was horizontal and confirmed the rotation of the axial plane to examine whether there was any horizontal distance between the tip of the coccyx and the pubic symphysis [3]. We also confirmed the neutral pelvic tilt to investigate the distance between the upper border of the symphysis and the midportion of the sacrococcygeal joint, as previously described [3, 10]. Statistical analysis Data were expressed as mean ± SD. All statistical analyses were performed using StatView version 5.0 (SAS Institute,
Results A total of 103 hips (males 57 hips; females 46 hips) were recruited for the analysis. Table 1 shows the mean age and data for each parameter in the subjects. The mean age of the subjects was 59.4 ± 14.8 years. The mean CE angle was 31.1° ± 7.1°, and the mean acetabular index was 7.0° ± 9.8°. The mean acetabular anteversion was 8.6° ± 8.7° at the superior margin of the femoral head, 11.5° ± 9.5° at 5 mm below the superior margin, 16.3° ± 9.3° at 10 mm below the superior margin, and 19.1° ± 8.4° at 15 mm below the superior margin. The acetabular anteversion at the level of the hip center was 20.3° ± 14.1°. The anteversion angle decreased as the slice height neared the superior margin of the femoral head with a significant difference (Fig. 3). Negative acetabular anteversion (pincer deformity) in any images was observed in 17 hips (16.5 %).
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The findings for the AAFH were as follows. The mean AAFH was 40.6° ± 5.0° in the oblique axial slice through the center of the neck (slice S1), and 43.1° ± 6.0°, 46.0° ± 5.9°, 48.2° ± 5.7°, 49.2° ± 7.1°, and 47.1° ± 7.9° in slices S2, S3, S4, S5, and S6, respectively. The AAFH in S1 was smaller than the other AAFHs, and the AAFH increased from S1 to S5 in a stepwise manner (Fig. 4). The AAFH in S1 was significantly smaller than those in S3–S6. The AAFH in S5 was the largest, and significantly larger than those in S1, S2, and S3. In addition, the AAFHs in men were significantly larger than those in women for all Table 1 Mean age and data for each parameter in the subjects Mean ± SD (95 % confidence interval) Age (years) CE angle (°) Acetabular index (°) Acetabular anteversion angle (°) Superior margin of the femoral head
59.4 ± 14.8 (56.6–62.3) 31.1 ± 7.1 (29.7–32.5) 7.0 ± 9.8 (5.1–8.9)
5 mm below 10 mm below 15 mm below Hip center AAFH (°) S1 S2 S3 S4 S5
11.5 ± 9.5 (9.7–13.4) 16.3 ± 9.3 (13.6–17.4) 19.1 ± 8.4 (17.6–20.8) 20.3 ± 14.1 (17.6–23.0)
S6
8.6 ± 8.7 (6.9–10.4)
40.6 ± 5.0 (39.6–41.6) 43.1 ± 6.0 (41.9–44.2) 46.0 ± 5.9 (44.9–47.2) 48.2 ± 5.7 (47.1–49.3) 49.2 ± 7.1 (47.8–50.6) 47.1 ± 7.9 (45.6–48.7)
CE center-edge angle; AAFH asphericity angle of the femoral head, namely α-angle; S1 oblique axial slice through the center of the femoral neck, parallel to the femoral neck-shaft angle; S2 slice rotated 15° from S1; S3 slice rotated 30° from S1; S4 slice rotated 45° from S1; S5 slice rotated 60° from S1; S6 slice rotated 75° from S1 Fig. 3 Acetabular anteversion angles in the individual slices. The acetabular anteversion angle decreases as the slice height nears the superior margin of the femoral head. The anteversion decreases in a stepwise manner with significant differences between “superior margin” and the other slices, “5 mm below” and the other slices, and “10 mm below” and “hip center”. Data are expressed as mean ± SD. *P < 0.0001, # P = 0.004, †P = 0.037
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slices (Fig. 5). An AAFH of >50° (cam deformity) in any images was detected for 53 hips (51.5 %). Assuming that these two values reflected pincer-type and cam-type FAI, a total of 58 hips (56.3 %) had images that met the criteria for radiological FAI. We also examined the possible correlations between the acetabular anteversion and other parameters, and between the AAFH and other parameters. A moderate correlation was defined as a correlation coefficient of ≥0.4. No correlations with any parameters were observed for the acetabular anteversion and the AAFH (data not shown). Furthermore, when patients were classified according to sex, no correlations with any parameters were detected (data not shown).
Discussion In the present study, we used high-resolution CT images to perform a detailed investigation of the parameters associated with FAI, and then examined the accurate prevalence of FAI-related findings in Japanese asymptomatic hips. To the best of our knowledge, this is the first study to provide a detailed discussion about the anatomical parameters of cam-type and pincer-type deformities with multislice imaging and to report the prevalence of FAI-related findings in asymptomatic Japanese hip joints using CT. In total, 56.3 % of the images met the criteria for radiological FAI. Pincer deformity was detected in 16.5 % of the hips. The acetabular anteversion angle decreased as the slice height neared the superior margin of the femoral head with a significant difference. These results were consistent with a previous report by Perreira et al. [14], who reported that the mean upper level and midlevel acetabular anteversion was 14.4° and 21.3°, respectively, and found that the angle increased as the slice height neared the femoral head using multislice CT examination in the United States. In the present study, there was no significant difference between the
Prevalence of radiological femoroacetabular impingement in Japanese… Fig. 4 Mean asphericity angles of the femoral head (AAFHs) in the radial slices. The AAFH in S1, namely the α-angle, is smaller than the other AAFHs, and the AAFH increases from S1 to S5 in a stepwise manner. The AAFH in S1 is significantly smaller than those in S3–S6. The AAFH in S2 is significantly smaller than those in S4–S6. There is a significant difference between S3 and S5. Data are expressed as mean ± SD. *P < 0.0001, #P = 0.038
Fig. 5 Mean asphericity angles of the femoral head (AAFHs) classified according to sex. The AAFHs for men and women in S1, namely the α-angles for men and women, are 42.0° ± 4.9° and 38.9° ± 4.5°, respectively. Similarly, the angles for men and women in S2, S3, S4, S5, and S6 are 44.5° ± 6.3° and 41.4° ± 5.0°, 47.2° ± 6.3°
and 44.7° ± 5.1°, 49.4° ± 6.6° and 46.9° ± 3.9°, 51.3° ± 7.4° and 46.2° ± 5.7°, and 49.8° ± 8.9° and 44.0° ± 5.0°, respectively. The AAFHs in men are significantly larger than those in women for all slices. Data are expressed as mean ± SD. *P < 0.002, **P < 0.01, # P = 0.03, †P < 0.001
slice 15 mm below the superior margin of the femoral head and the hip center. Furthermore, only two hips showed retroversion of the acetabulum at 15 mm below the superior margin of the femoral head. These results suggest that the lower level for detailed evaluation of pincer deformity is sufficient at 15 mm below the superior margin of the femoral head. In the present study, we employed an abnormal cut-off of the AAFH of >50°; namely an α-angle of >50° [3, 6, 8]. According to this criterion, cam deformity was detected in 51.5 % of the hips. The mean AAFH ranged from 40.6° to 49.2°, which was consistent with the value of 43.8° in 20 asymptomatic hips in a previous study using threedimensional CT in the United States [12]. Similarly, Kang et al. [15] reported that the mean α-angle was 45.6° in the center slice at the femoral neck using CT in asymptomatic
individuals in New Zealand. In the present study, the α-angles in S4 and S5 were larger than those in the other slices. From these findings, the prevalence of FAI is likely to be underestimated if cam deformity is investigated by lateral radiographs only. Chakraverty et al. [13] reported that an α-angle of >55° was detected in 49 % of asymptomatic patients by investigating multiple radial slice-reconstructed CT images, while just 3 % of cases were detected by investigating the simple axial oblique plane only. They also reported that the α-angle in the 1-o’clock slice (same slice as S5 in our study) was larger than those in other slices examined. In addition, Ergen et al. [22] compared the α-angle at the center of the femoral neck in a simple axial oblique view and several α-angles in the radial-formatted view reconstructed from CT images. They showed that the angles obtained from the radial-formatted images were
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higher than those obtained from the simple axial oblique view. When considering these findings about the α-angle and the concept of FAI, we emphasize that evaluation of a bony bump (cam deformity) at the more superior part from the neck center should be performed and must be important. Moreover, the α-angles were smaller in women than in men. This result agrees with previous reports describing that the prevalence of FAI was lower in women than in men. Specifically, Jung et al. [4] reported that cam-type deformity was seen in 13.9 % of men and 5.56 % of women among 838 hips in asymptomatic patients in the United States, based on CT scout images. Our investigations revealed that FAI-related findings were observed in 56.3 % of asymptomatic Japanese hips, which is consistent with previous reports outside of Japan. Chakraverty et al. [13] described that 60 % of asymptomatic hips in men were detected as cam-type FAI by investigating multiple radial CT images in the United Kingdom. Hack et al. [19] also described that 53 % of volunteers had an α-angle of >50.5° at the 1:30 position in radial slices (same slice as S4 in our study). Wenger et al. [5] used arthro-magnetic resonance imaging and arthro-CT to retrospectively investigate radiographic images from 31 patients with acetabular labral tears. They reported that the crossover sign (radiographic sign of pincer deformity [3]) was present in 36 % of patients, and that 41 % of patients had a femoral head–neck offset of <7.2 mm. In addition, Ochoa et al. [6] described that 87 % of patients with hip pain showed signs of FAI on radiographic images. Furthermore, Laborie et al. [7] investigated a population-based cohort comprising 2081 patients with a mean age of 18.6 years. They observed the crossover sign in 47.9 % of these patients, the posterior wall sign (radiographic sign of acetabular retroversion [3]) in 16.2 %, and the pistol grip deformity (radiographic sign of cam deformity [3]) in 10.9 %. They also reported that FAI was a common finding on radiographic images. Among Japanese reports, the review by Nakamura et al. [23] found that 88 % of patients had secondary OA with developmental dysplasia of the hip in 1989. In Japan and other Asian countries, it appears that the etiology of hip OA may differ from that in Western populations. However, several authors have recently reported the prevalence of FAI in Japanese populations using radiography. Mori et al. [8] identified radiographic evidence of FAI in 29.7 % of patients during an investigation of OA patients with hip pain corresponding to grade 0 or 1 in the Tönnis classification. Meanwhile, Fukushima et al. [9] presented radiographic evidence of radiographic FAI in 27.6 % of 87 patients who had undergone total hip arthroplasty, with no pain on the contralateral side, during the procedure in a retrospective examination. Additionally, Takeyama et al. [24] reported on the causes of hip OA in Japan. They investigated 817 patients who underwent surgery with the diagnosis of
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OA, and found that the percentage of OA development associated with FAI was only 0.6 %. In the present study, 56.3 % of the total images met the criteria for radiological FAI. If a CE angle of >39° and acetabular index of ≤0° were also employed as criteria for FAI [3], 12.6 % of all images showed a CE angle of >39° and 19.4 % showed an acetabular index of ≤0°, meaning that 71.8 % (74/103) of the total images met the criteria for radiological FAI. The prevalence in our results is higher than those in previous investigations in Japan. The differences between the present study and the previous studies may arise from whether the investigations were performed using CT or radiography. Our study involved multislice CT scans, with cam deformity investigated in six slices and pincer deformity investigated in five slices. Lepage-Saucier et al. [25] reported normal α-angles in asymptomatic Belgian populations using CT. They showed that the upper limit of the 95 % reference interval limit for the α-angle was 83° at the 1:30 position in radial slices (same slice as S4 in our study), which was far beyond the abnormal thresholds found in the previous literature (α-angle of >50° [3, 6, 8] or >60° [24, 26]). They concluded that the current morphological parameters needed to be redefined for the diagnosis of FAI. We also believe that the previously reported prevalences of radiological FAI in Japan may change to larger numbers if the parameters were investigated in detail using multislice imaging. This study has several limitations. The first is that the study was patient-based. The CT scans were ordered by other departments in our institution, such as cardiology and endocrinology, and therefore we could not know whether the hips were really asymptomatic; there is the possibility that some patients had been receiving treatment for hip problems at other institutions. The second limitation is that the only available information was the patient’s age, sex, and CT images. Because this study was permitted by our institutional review board under the stipulation that we could not check the clinical records or personal information, we could not know the patients’ symptoms, roentgenogram, past history, underlying disease, body mass index, and activity or occupation. The third limitation is that the sample size was relatively small. Some authors have shown that FAI is one of the major causes of hip OA in young patients and active patients [2, 27, 28], and that cam deformity in particular is a special risk for OA [29, 30]. Meanwhile, other authors have reported that radiological FAI findings do not lead to the development of significant OA [31–33]. Paliobeis et al. [34] emphasized that the presence of coexisting developmental dysplasia of the hip should be taken into account for the treatment of patients with FAI. The issue of whether FAI is a risk factor for the development of hip OA remains controversial. Moreover, accurate criteria for FAI are still unknown. For example, various cutoff values for the α-angle are used for the diagnosis of FAI,
Prevalence of radiological femoroacetabular impingement in Japanese…
with some authors reporting that angles of >50° are pathological [3, 6, 8] and others reporting that angles of >55° [13– 15] or >60° [24, 26] are pathological. In fact, if an α-angle of >55° was employed as the criterion for cam deformity, 34.0 % (35/103) of all images showed cam deformity, meaning that 40.7 % (42/103) of all images met the criteria for radiological FAI. If an α-angle of >60° was employed as the criterion for cam deformity, 18.4 % (19/103) of all images showed cam deformity, meaning that 29.1 % (30/103) of all images met the criteria for radiological FAI. We conclude that FAI-related findings were common in Japanese hips, similar to the case for Western countries, upon detailed investigation with CT. However, we also recognize that it may be incorrect to generalize our results to regions throughout Japan. Nevertheless, our results show the important fact that findings of “anatomical or radiological FAI” are not uncommon in Japanese asymptomatic hips. The diagnosis of FAI should be performed with the clinical findings taken into account. As the next step, our concern is to investigate these parameters in FAI patients diagnosed by their clinical symptoms. Investigations of these parameters in hips with “clinical FAI” and comparisons with the data generated from the present study are warranted. Conflict of interest The authors declare that they have no conflicts of interest.
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T. Mimura et al. 28. Murphy SB, Tannast M, Kim YJ, Buly R, Millis MB. Debridement of adult hip for femoroacetabular impingement: indications and preliminary clinical results. Clin Orthop Relat Res. 2004;429:178–81. 29. Jäger M, Wild A, Westhoff B, Krauspe R. Femoroacetabular impingement caused by a femoral osseous head-neck bump deformity: clinical, radiological, and experimental results. J Orthop Sci. 2004;9(3):256–63. 30. Agricola R, Waarsing JH, Arden NK, Carr AJ, Bierma-Zeinstra SM, Thomas GE, Weinans H, Glyn-Jones S. Cam impingement of the hip: a risk for hip osteoarthritis. Nat Rev Rheumatol. 2013;9(10):630–4. 31. Agricola R, Heijboer MP, Roze RH, Reijman M, Bierma-Zeinstra SM, Verhaar JA, Weinans H, Waarsing JH. Pincer deformity does not lead to osteoarthritis of the hip whereas acetabular dysplasia does: acetabular coverage and development of osteoarthritis in a
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nationwide prospective cohort study (CHECK). Osteoarthr Cartil. 2013;21(10):1514–21. 32. Hartofilakidis G, Bardakos NV, Badis GC, Geirgiades G. An examination of the association between different morphotypes of femoroacetabular impingement in asymptomatic subjects and the development of osteoarthritis of the hip. J Bone Joint Surg Br. 2011;93(5):580–6. 33. Bardakos NV, Villar RN. Predictors of progression of osteoarthritis in femoroacetabular impingement: a radiological study with a minimum of ten years follow-up. J Bone Joint Surg Br. 2009;91(2):162–9. 34. Paliobeis CP, Villar RN. The presence of dysplasia in femoroacetabular impingement. Hip Int. 2011;21(2):141–5.
ORIGINAL ARTICLE
Prevalence of radiological femoroacetabular impingement in Japanese hip joints: detailed investigation with computed tomography Tomohiro Mimura1 · Taku Kawasaki1 · Shin Itakura2 · Tomohiro Hirata1 · Hitomi Fuzikawa1 · Kanji Mori1 · Shinji Imai1
Received: 6 October 2014 / Accepted: 21 April 2015 © The Japanese Orthopaedic Association 2015
Abstract Background Femoroacetabular impingement (FAI) has been highlighted as a new etiology for osteoarthritis of the hip, and its prevalence has been reported in the past decade. In the present study, we performed a detailed investigation of the anatomical parameters related to FAI and calculated the prevalence of FAI-related findings in asymptomatic Japanese hip joints using computed tomography. Methods We evaluated high-resolution reconstructed multislice computed tomography images in patients who had undergone computed tomography imaging in our institution for conditions unrelated to hip disorders. The examined parameters were as follows: center-edge (CE) angle; acetabular index; acetabular anteversion (five slices in the axial plane); and asphericity angle of the femoral head (AAFH) (six slices in multiple radial planes). The AAFH in the oblique axial slice through the center of the femoral neck is the so-called α-angle. We then examined the accurate prevalence of FAI-related findings in Japan. Results We investigated a total of 103 hips. The mean age of the subjects was 59.4 years. The mean CE angle was 31.1° and the mean acetabular index was 7.0°. The mean acetabular anteversion was 20.3° at the level of the hip center, and decreased as the slice level neared the superior margin of the femoral head. The mean AAFH ranged from 40.6° to 49.2° in the radial planes. The AAFH was largest
* Tomohiro Mimura [email protected]‑med.ac.jp 1
Department of Orthopedic Surgery, Shiga University of Medical Science, Tsukinowa‑cho, Seta, Otsu, Shiga 520‑2192, Japan
2
Department of Orthopedic Surgery, Shiga Medical Center for Children, Shiga 524‑0022, Japan
at 60° rotated slice from the oblique axial slice through the center of the femoral neck. The prevalence of FAIrelated findings in these Japanese hip joints was assessed as follows. An AAFH of >50° in any slice was detected in 51.5 % of the hips, and acetabular anteversion was negative for all images in 16.5 % of the hips, meaning that a total of 56.3 % of the images met the criteria for radiological FAI. Conclusions With consideration of our results, we emphasize that “anatomical or radiological FAI” is not uncommon in Japanese hips. Therefore, the diagnosis of FAI should be performed with the clinical findings taken into account.
Introduction Femoroacetabular impingement (FAI) has recently been reported as a cause of osteoarthritis (OA) of the hip. It was first described by Myers et al. [1] and then in detail by Ganz et al. [2]. The etiology of FAI is abnormal contact between the acetabulum and femoral head-neck junction that leads to labral tearing and subsequent osteochondral disorders. FAI is divided into two subcategories: cam deformity and pincer deformity [2, 3]. A cam deformity is defined as an abnormal morphological finding of the femoral side of FAI, and is characterized by a bony bump of the anterior femoral head-neck junction or non-spherical femoral head. A pincer deformity is defined as a morphological abnormality of the acetabular side of FAI, and is characterized by excessive anterior coverage at the superior acetabulum or acetabular retroversion. Many studies have described these radiographic deformities and the prevalence of FAI [3–9]. However, many of the reports were roentgenogram image investigations, which run the risk of being affected by the patient’s position and posture [10, 11]. Therefore,
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several studies involving anatomical investigations related to FAI using computed tomography (CT) have recently been reported in Western countries [12–15]. In the present study, we aimed to perform a detailed investigation of the anatomical parameters related to FAI in asymptomatic hips using high-resolution reconstructed multislice CT images and to examine the accurate prevalence of FAI-related findings in Japan.
This study was approved by our institutional review board. We conducted a patient-based study on patients who had undergone CT imaging from the chest to the abdomen. As other departments in our institution had ordered these scans, the CT scans were undertaken for conditions unrelated to hip disorders. The inclusion criteria for investigations were as follows: (1) whole pelvis and both hip joints were involved; (2) reconstructed axial slice thickness was ≤1 mm; (3) pelvic rotations and tilt were normal (described below in the section for standardization of CT images). The
exclusion criteria were as follows: (1) age under 20 years; (2) evident pathology of hip OA, such as joint space narrowing, osteophytes, or subchondral bone changes including cysts and sclerosis [16]. We retrospectively examined consecutive patients fulfilling the above criteria from 1 July 2013 to 31 July 2013. The parameters examined were as follows: age; sex; center-edge (CE) angle [17]; acetabular index [18]; and acetabular anteversion in the axial plane (five slices; first slice at the level of the superior margin of the femoral head, followed by four slices at 5, 10, and 15 mm below the superior margin of the femoral head, and at the level of the hip center) (Fig. 1). In addition, we measured the asphericity angle of the femoral head (AAFH) in multiple radial slices using previously described methods [19, 20]. For this, six radial slices were generated at 15° intervals, including slices with 0°, 15°, 30°, 45°, 60°, and 75° rotation from the oblique axial slice through the center of the femoral neck (hereafter referred to as S1, S2, S3, S4, S5, and S6, respectively) (Fig. 2). The AAFH of each slice was measured as previously described [21]: the S1 slice angle is the so-called α-angle [2, 3]. Negative acetabular anteversion in any slice was defined as pincer deformity, while an AAFH of >50° in any slice was defined as cam deformity.
Fig. 1 Measurement of the acetabular anteversion angles in five axial slices. a Reference plane for the acetabular anteversion angle measurements. Each line represents one of the five slice lines. The axial views of lines b, c, d, e, and f are shown in b, c, d, e, and f, respectively. b Axial view of the superior margin of the femoral head (line b). Angle ø is the acetabular anteversion angle at the superior margin of the femoral head. The angle is measured between the line joining the anterior and posterior edges of the acetabulum and the line per-
pendicular to the line joining the posterior edges at both acetabula. c Acetabular anteversion angle in the axial view at 5 mm below the superior margin of the femoral head (line c). d Acetabular anteversion angle in the axial view at 10 mm below the superior margin of the femoral head (line d). e Acetabular anteversion angle in the axial view at 15 mm below the superior margin of the femoral head (line e). f Acetabular anteversion angle in the axial view at the level of the center of the femoral head (line f)
Materials and methods Patients and parameters
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Prevalence of radiological femoroacetabular impingement in Japanese…
Fig. 2 Measurement of the asphericity angles of the femoral head (AAFHs) in multiple radial slices. a The dotted line is the axis through the center of the femoral neck, adjusted to be parallel to the femoral neck-shaft angle. The solid line is the reference plane for radial angle reconstruction. b The reconstructed plane demonstrates superimposed radial reference lines at 15° intervals. S1 is the oblique axial slice (dotted line in a), S2 is a plane rotated 15° from S1, S3 is a plane rotated 30° from S1, S4 is a plane rotated 45° from S1, S5 is a plane rotated 60° from S1, and S6 is a plane rotated 75° from S1. c
Reconstructed slice of the S1 plane. Angle ø is the AAFH; namely the α-angle. The angle is measured between the line joining the femoral head and the center of the neck and the line drawn from the center of the femoral head to the point where the spherical image of the femoral head is lost. d Reconstructed radial slice of the S2 plane. e Reconstructed radial slice of the S3 plane. f Reconstructed radial slice of the S4 plane. g Reconstructed radial slice of the S5 plane. h Reconstructed radial slice of the S6 plane
Radiological examination and standardization of CT images
Cary, NC). One-way analysis of variance (ANOVA) with a Scheffé post hoc test was used to determine the significance of differences among five or six groups. Student’s t-test was used to determine the significance of differences between two groups. Values of P < 0.05 were considered to indicate statistical significance.
All CT images were axial, sequential, and obtained in the supine position without gantry tilt (120 kV, 160 mA, 0.5 s) using a Toshiba Aquilion CX (Toshiba Medical Systems Corporation, Tokyo, Japan). The data were reconstructed under conditions suitable for bone evaluation using AquariasNet Viewer software (TeraRecon Inc., San Francisco, CA). This software allowed the reconstruction of optimal sagittal, coronal, and axial views, as well as threedimensional reconstructed CT (3DCT) views. We used the 3DCT images to confirm the pelvic rotations and tilt. We confirmed the rotation of the coronal plane to investigate whether the teardrop line was horizontal and confirmed the rotation of the axial plane to examine whether there was any horizontal distance between the tip of the coccyx and the pubic symphysis [3]. We also confirmed the neutral pelvic tilt to investigate the distance between the upper border of the symphysis and the midportion of the sacrococcygeal joint, as previously described [3, 10]. Statistical analysis Data were expressed as mean ± SD. All statistical analyses were performed using StatView version 5.0 (SAS Institute,
Results A total of 103 hips (males 57 hips; females 46 hips) were recruited for the analysis. Table 1 shows the mean age and data for each parameter in the subjects. The mean age of the subjects was 59.4 ± 14.8 years. The mean CE angle was 31.1° ± 7.1°, and the mean acetabular index was 7.0° ± 9.8°. The mean acetabular anteversion was 8.6° ± 8.7° at the superior margin of the femoral head, 11.5° ± 9.5° at 5 mm below the superior margin, 16.3° ± 9.3° at 10 mm below the superior margin, and 19.1° ± 8.4° at 15 mm below the superior margin. The acetabular anteversion at the level of the hip center was 20.3° ± 14.1°. The anteversion angle decreased as the slice height neared the superior margin of the femoral head with a significant difference (Fig. 3). Negative acetabular anteversion (pincer deformity) in any images was observed in 17 hips (16.5 %).
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The findings for the AAFH were as follows. The mean AAFH was 40.6° ± 5.0° in the oblique axial slice through the center of the neck (slice S1), and 43.1° ± 6.0°, 46.0° ± 5.9°, 48.2° ± 5.7°, 49.2° ± 7.1°, and 47.1° ± 7.9° in slices S2, S3, S4, S5, and S6, respectively. The AAFH in S1 was smaller than the other AAFHs, and the AAFH increased from S1 to S5 in a stepwise manner (Fig. 4). The AAFH in S1 was significantly smaller than those in S3–S6. The AAFH in S5 was the largest, and significantly larger than those in S1, S2, and S3. In addition, the AAFHs in men were significantly larger than those in women for all Table 1 Mean age and data for each parameter in the subjects Mean ± SD (95 % confidence interval) Age (years) CE angle (°) Acetabular index (°) Acetabular anteversion angle (°) Superior margin of the femoral head
59.4 ± 14.8 (56.6–62.3) 31.1 ± 7.1 (29.7–32.5) 7.0 ± 9.8 (5.1–8.9)
5 mm below 10 mm below 15 mm below Hip center AAFH (°) S1 S2 S3 S4 S5
11.5 ± 9.5 (9.7–13.4) 16.3 ± 9.3 (13.6–17.4) 19.1 ± 8.4 (17.6–20.8) 20.3 ± 14.1 (17.6–23.0)
S6
8.6 ± 8.7 (6.9–10.4)
40.6 ± 5.0 (39.6–41.6) 43.1 ± 6.0 (41.9–44.2) 46.0 ± 5.9 (44.9–47.2) 48.2 ± 5.7 (47.1–49.3) 49.2 ± 7.1 (47.8–50.6) 47.1 ± 7.9 (45.6–48.7)
CE center-edge angle; AAFH asphericity angle of the femoral head, namely α-angle; S1 oblique axial slice through the center of the femoral neck, parallel to the femoral neck-shaft angle; S2 slice rotated 15° from S1; S3 slice rotated 30° from S1; S4 slice rotated 45° from S1; S5 slice rotated 60° from S1; S6 slice rotated 75° from S1 Fig. 3 Acetabular anteversion angles in the individual slices. The acetabular anteversion angle decreases as the slice height nears the superior margin of the femoral head. The anteversion decreases in a stepwise manner with significant differences between “superior margin” and the other slices, “5 mm below” and the other slices, and “10 mm below” and “hip center”. Data are expressed as mean ± SD. *P < 0.0001, # P = 0.004, †P = 0.037
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slices (Fig. 5). An AAFH of >50° (cam deformity) in any images was detected for 53 hips (51.5 %). Assuming that these two values reflected pincer-type and cam-type FAI, a total of 58 hips (56.3 %) had images that met the criteria for radiological FAI. We also examined the possible correlations between the acetabular anteversion and other parameters, and between the AAFH and other parameters. A moderate correlation was defined as a correlation coefficient of ≥0.4. No correlations with any parameters were observed for the acetabular anteversion and the AAFH (data not shown). Furthermore, when patients were classified according to sex, no correlations with any parameters were detected (data not shown).
Discussion In the present study, we used high-resolution CT images to perform a detailed investigation of the parameters associated with FAI, and then examined the accurate prevalence of FAI-related findings in Japanese asymptomatic hips. To the best of our knowledge, this is the first study to provide a detailed discussion about the anatomical parameters of cam-type and pincer-type deformities with multislice imaging and to report the prevalence of FAI-related findings in asymptomatic Japanese hip joints using CT. In total, 56.3 % of the images met the criteria for radiological FAI. Pincer deformity was detected in 16.5 % of the hips. The acetabular anteversion angle decreased as the slice height neared the superior margin of the femoral head with a significant difference. These results were consistent with a previous report by Perreira et al. [14], who reported that the mean upper level and midlevel acetabular anteversion was 14.4° and 21.3°, respectively, and found that the angle increased as the slice height neared the femoral head using multislice CT examination in the United States. In the present study, there was no significant difference between the
Prevalence of radiological femoroacetabular impingement in Japanese… Fig. 4 Mean asphericity angles of the femoral head (AAFHs) in the radial slices. The AAFH in S1, namely the α-angle, is smaller than the other AAFHs, and the AAFH increases from S1 to S5 in a stepwise manner. The AAFH in S1 is significantly smaller than those in S3–S6. The AAFH in S2 is significantly smaller than those in S4–S6. There is a significant difference between S3 and S5. Data are expressed as mean ± SD. *P < 0.0001, #P = 0.038
Fig. 5 Mean asphericity angles of the femoral head (AAFHs) classified according to sex. The AAFHs for men and women in S1, namely the α-angles for men and women, are 42.0° ± 4.9° and 38.9° ± 4.5°, respectively. Similarly, the angles for men and women in S2, S3, S4, S5, and S6 are 44.5° ± 6.3° and 41.4° ± 5.0°, 47.2° ± 6.3°
and 44.7° ± 5.1°, 49.4° ± 6.6° and 46.9° ± 3.9°, 51.3° ± 7.4° and 46.2° ± 5.7°, and 49.8° ± 8.9° and 44.0° ± 5.0°, respectively. The AAFHs in men are significantly larger than those in women for all slices. Data are expressed as mean ± SD. *P < 0.002, **P < 0.01, # P = 0.03, †P < 0.001
slice 15 mm below the superior margin of the femoral head and the hip center. Furthermore, only two hips showed retroversion of the acetabulum at 15 mm below the superior margin of the femoral head. These results suggest that the lower level for detailed evaluation of pincer deformity is sufficient at 15 mm below the superior margin of the femoral head. In the present study, we employed an abnormal cut-off of the AAFH of >50°; namely an α-angle of >50° [3, 6, 8]. According to this criterion, cam deformity was detected in 51.5 % of the hips. The mean AAFH ranged from 40.6° to 49.2°, which was consistent with the value of 43.8° in 20 asymptomatic hips in a previous study using threedimensional CT in the United States [12]. Similarly, Kang et al. [15] reported that the mean α-angle was 45.6° in the center slice at the femoral neck using CT in asymptomatic
individuals in New Zealand. In the present study, the α-angles in S4 and S5 were larger than those in the other slices. From these findings, the prevalence of FAI is likely to be underestimated if cam deformity is investigated by lateral radiographs only. Chakraverty et al. [13] reported that an α-angle of >55° was detected in 49 % of asymptomatic patients by investigating multiple radial slice-reconstructed CT images, while just 3 % of cases were detected by investigating the simple axial oblique plane only. They also reported that the α-angle in the 1-o’clock slice (same slice as S5 in our study) was larger than those in other slices examined. In addition, Ergen et al. [22] compared the α-angle at the center of the femoral neck in a simple axial oblique view and several α-angles in the radial-formatted view reconstructed from CT images. They showed that the angles obtained from the radial-formatted images were
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higher than those obtained from the simple axial oblique view. When considering these findings about the α-angle and the concept of FAI, we emphasize that evaluation of a bony bump (cam deformity) at the more superior part from the neck center should be performed and must be important. Moreover, the α-angles were smaller in women than in men. This result agrees with previous reports describing that the prevalence of FAI was lower in women than in men. Specifically, Jung et al. [4] reported that cam-type deformity was seen in 13.9 % of men and 5.56 % of women among 838 hips in asymptomatic patients in the United States, based on CT scout images. Our investigations revealed that FAI-related findings were observed in 56.3 % of asymptomatic Japanese hips, which is consistent with previous reports outside of Japan. Chakraverty et al. [13] described that 60 % of asymptomatic hips in men were detected as cam-type FAI by investigating multiple radial CT images in the United Kingdom. Hack et al. [19] also described that 53 % of volunteers had an α-angle of >50.5° at the 1:30 position in radial slices (same slice as S4 in our study). Wenger et al. [5] used arthro-magnetic resonance imaging and arthro-CT to retrospectively investigate radiographic images from 31 patients with acetabular labral tears. They reported that the crossover sign (radiographic sign of pincer deformity [3]) was present in 36 % of patients, and that 41 % of patients had a femoral head–neck offset of <7.2 mm. In addition, Ochoa et al. [6] described that 87 % of patients with hip pain showed signs of FAI on radiographic images. Furthermore, Laborie et al. [7] investigated a population-based cohort comprising 2081 patients with a mean age of 18.6 years. They observed the crossover sign in 47.9 % of these patients, the posterior wall sign (radiographic sign of acetabular retroversion [3]) in 16.2 %, and the pistol grip deformity (radiographic sign of cam deformity [3]) in 10.9 %. They also reported that FAI was a common finding on radiographic images. Among Japanese reports, the review by Nakamura et al. [23] found that 88 % of patients had secondary OA with developmental dysplasia of the hip in 1989. In Japan and other Asian countries, it appears that the etiology of hip OA may differ from that in Western populations. However, several authors have recently reported the prevalence of FAI in Japanese populations using radiography. Mori et al. [8] identified radiographic evidence of FAI in 29.7 % of patients during an investigation of OA patients with hip pain corresponding to grade 0 or 1 in the Tönnis classification. Meanwhile, Fukushima et al. [9] presented radiographic evidence of radiographic FAI in 27.6 % of 87 patients who had undergone total hip arthroplasty, with no pain on the contralateral side, during the procedure in a retrospective examination. Additionally, Takeyama et al. [24] reported on the causes of hip OA in Japan. They investigated 817 patients who underwent surgery with the diagnosis of
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OA, and found that the percentage of OA development associated with FAI was only 0.6 %. In the present study, 56.3 % of the total images met the criteria for radiological FAI. If a CE angle of >39° and acetabular index of ≤0° were also employed as criteria for FAI [3], 12.6 % of all images showed a CE angle of >39° and 19.4 % showed an acetabular index of ≤0°, meaning that 71.8 % (74/103) of the total images met the criteria for radiological FAI. The prevalence in our results is higher than those in previous investigations in Japan. The differences between the present study and the previous studies may arise from whether the investigations were performed using CT or radiography. Our study involved multislice CT scans, with cam deformity investigated in six slices and pincer deformity investigated in five slices. Lepage-Saucier et al. [25] reported normal α-angles in asymptomatic Belgian populations using CT. They showed that the upper limit of the 95 % reference interval limit for the α-angle was 83° at the 1:30 position in radial slices (same slice as S4 in our study), which was far beyond the abnormal thresholds found in the previous literature (α-angle of >50° [3, 6, 8] or >60° [24, 26]). They concluded that the current morphological parameters needed to be redefined for the diagnosis of FAI. We also believe that the previously reported prevalences of radiological FAI in Japan may change to larger numbers if the parameters were investigated in detail using multislice imaging. This study has several limitations. The first is that the study was patient-based. The CT scans were ordered by other departments in our institution, such as cardiology and endocrinology, and therefore we could not know whether the hips were really asymptomatic; there is the possibility that some patients had been receiving treatment for hip problems at other institutions. The second limitation is that the only available information was the patient’s age, sex, and CT images. Because this study was permitted by our institutional review board under the stipulation that we could not check the clinical records or personal information, we could not know the patients’ symptoms, roentgenogram, past history, underlying disease, body mass index, and activity or occupation. The third limitation is that the sample size was relatively small. Some authors have shown that FAI is one of the major causes of hip OA in young patients and active patients [2, 27, 28], and that cam deformity in particular is a special risk for OA [29, 30]. Meanwhile, other authors have reported that radiological FAI findings do not lead to the development of significant OA [31–33]. Paliobeis et al. [34] emphasized that the presence of coexisting developmental dysplasia of the hip should be taken into account for the treatment of patients with FAI. The issue of whether FAI is a risk factor for the development of hip OA remains controversial. Moreover, accurate criteria for FAI are still unknown. For example, various cutoff values for the α-angle are used for the diagnosis of FAI,
Prevalence of radiological femoroacetabular impingement in Japanese…
with some authors reporting that angles of >50° are pathological [3, 6, 8] and others reporting that angles of >55° [13– 15] or >60° [24, 26] are pathological. In fact, if an α-angle of >55° was employed as the criterion for cam deformity, 34.0 % (35/103) of all images showed cam deformity, meaning that 40.7 % (42/103) of all images met the criteria for radiological FAI. If an α-angle of >60° was employed as the criterion for cam deformity, 18.4 % (19/103) of all images showed cam deformity, meaning that 29.1 % (30/103) of all images met the criteria for radiological FAI. We conclude that FAI-related findings were common in Japanese hips, similar to the case for Western countries, upon detailed investigation with CT. However, we also recognize that it may be incorrect to generalize our results to regions throughout Japan. Nevertheless, our results show the important fact that findings of “anatomical or radiological FAI” are not uncommon in Japanese asymptomatic hips. The diagnosis of FAI should be performed with the clinical findings taken into account. As the next step, our concern is to investigate these parameters in FAI patients diagnosed by their clinical symptoms. Investigations of these parameters in hips with “clinical FAI” and comparisons with the data generated from the present study are warranted. Conflict of interest The authors declare that they have no conflicts of interest.
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