The Prevalence of Acetabular Retroversion Among Various Disorders of the Hip

Ezoe, Masamitsu MD; Naito, Masatoshi MD; Inoue, Toshio MD

Journal of Bone & Joint Surgery - American Volume: February 2006 - Volume 88 - Issue 2 - p 372–379
doi: 10.2106/JBJS.D.02385
Scientific Articles

Background: Acetabular retroversion can result from posterior wall deficiency in an otherwise normally oriented acetabulum or from excessive anterior coverage secondary to a malpositioned acetabulum, or both. Theoretically, a retroverted acetabulum, which adversely affects load transmission across the hip, may occur more frequently in hips with degenerative arthritis. The aim of this study was to assess the prevalence of acetabular retroversion in normal hips and in hips with osteoarthritis, developmental dysplasia, osteonecrosis, and Legg-Calvé-Perthes disease.

Methods: We retrospectively examined anteroposterior radiographs of the pelvis of 250 patients (342 hips). Fifty-six patients (112 hips) had normal findings; sixty-six patients (seventy hips) had osteoarthritis; sixty-four (seventy-four hips), developmental dysplasia; thirty (thirty-six hips), osteonecrosis of the femoral head; and thirty-four (fifty hips), Legg-Calvé-Perthes disease. The sole criterion for a diagnosis of acetabular retroversion was the presence of a so-called cross-over sign on the anteroposterior radiograph of the pelvis.

Results: The prevalence of acetabular retroversion was 6% (seven of 112 hips) in the normal group, 20% (fourteen of seventy hips) in the osteoarthritis group, 18% (thirteen of seventy-four hips) in the developmental dysplasia group, 6% (two of thirty-six hips) in the group with osteonecrosis of the femoral head, and 42% (twenty-one of fifty hips) in the group with Legg-Calvé-Perthes disease. In patients with Legg-Calvé-Perthes disease, the prevalence of acetabular retroversion was 68% in twenty-five hips with Stulberg class-III, IV, or V involvement. In contrast, only four (16%) of twenty-five hips with Stulberg class-I or II involvement had acetabular retroversion. The difference was significant (p = 0.0002). Patients with osteoarthritis, developmental dysplasia, or Legg-Calvé-Perthes disease are significantly more likely to have acetabular retroversion than are normal subjects (p < 0.05).

Conclusions: Acetabular retroversion occurs more commonly in association with a variety of hip diseases, in which the prevalence of subsequent degenerative arthritis is increased, than has been previously noted.

Level of Evidence: Diagnostic Level III. See Instructions to Authors for a complete description of levels of evidence.

1 Department of Orthopaedic Surgery, Fukuoka University School of Medicine, 7-45-1, Nanakuma, Jyonan-ku, Fukuoka 814-0180, Japan. E-mail address for M. Ezoe: md010001@mms.bbiq.jp

Article Outline

Developmental dysplasia of the hip is often associated with deficient anterior or global coverage of the femoral head1 and is associated with an increased prevalence of osteoarthritis2-4. Recently, acetabular retroversion, which can result from posterior wall deficiency or excessive anterior coverage, or both, has been described as a possible etiologic factor in osteoarthritis5-10. The diagnosis of acetabular retroversion is made when the cross-over sign, which was described by Reynolds et al., can be seen on standard anteroposterior radiographs of the pelvis8. Giori and Trousdale compared the presence of the cross-over sign in patients with osteoarthritis of the hip and in subjects with normal hips and found that the prevalence of acetabular retroversion was 20% in patients with osteoarthritis of the hip and 5% in normal subjects11.

In Legg-Calvé-Perthes disease, femoral head deformity is often accompanied by deformity of the acetabulum12. In such hips, we have observed that the cross-over sign appears frequently on standard anteroposterior radiographs of the pelvis (unpublished data).

The purposes of the present study were to investigate the prevalence of acetabular retroversion in diseases associated with an increased rate of subsequent osteoarthritis of the hip, such as developmental dysplasia, osteonecrosis of the femoral head, and Legg-Calvé-Perthes disease, and to compare the prevalence of acetabular retroversion in hips with these diseases and that in normal, asymptomatic hips.

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Materials and Methods

We retrospectively selected 449 anteroposterior radiographs of the pelvis from 449 patients and normal subjects during a period from December 10, 2001 to June 3, 2004. All of these individuals were Asian. The patients had a diagnosis of osteoarthritis, developmental dysplasia, osteonecrosis, or Legg-Calvé-Perthes disease. From each group, we selected radiographs using a table of random numbers to avoid selection bias. Of the initial 449 patients, 185 were excluded because of excessive pelvic tilt or pelvic asymmetry, which can obscure accurate interpretation of the radiographs, and fourteen hips were excluded because the diagnosis was unclear as a result of acetabular rim degeneration. The remaining study cohort consisted of 250 patients (342 hips). Institutional review board approval and informed consent were obtained from all subjects and patients.

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Normal Subjects and Patients

Normal group: We originally reviewed 240 radiographs (240 subjects) and, using a table of random numbers, selected 120 subjects (240 hips). From these initial 120 subjects, sixty-four were excluded because of excessive pelvic tilt or pelvic asymmetry. The resulting group comprised 112 hips in fifty-six subjects (twenty-six subjects were doctors, nurses, and physiotherapists who had volunteered, and thirty were patients who had had standard anteroposterior radiographs of the hips for evaluation of symptoms that did not involve the hip). There were twenty-two male and thirty-four female subjects, with a mean age of 34.9 years (range, fifteen to fifty-four years). None of these subjects had a history of lumbar osteoarthritis, osteoarthritis of the hip, developmental dysplasia, trauma, osteonecrosis of the femoral head, or metabolic bone disease.

Osteoarthritis group: We originally reviewed 274 preoperative radiographs of patients who had undergone total hip arthroplasty for a diagnosis of osteoarthritis. Using a table of random numbers, we selected 137 patients (142 hips). Fifty-seven patients were excluded because of excessive pelvic tilt or pelvic asymmetry, and fourteen were excluded because the diagnosis was unclear as a result of acetabular rim degeneration. The remaining sixty-six patients (seventy hips) included eight men and fifty-eight women, with a mean age of 68.6 years (range, fifty-four to seventy-nine years).

Dysplasia group: We originally reviewed 198 patients with a diagnosis of developmental dysplasia (defined by us as a center-edge angle of <20°) who subsequently underwent a periacetabular osteotomy. Using a random-numbers table, we selected ninety-nine patients (111 hips). Thirty-five patients (thirty-seven hips) were excluded because of excessive pelvic tilt or pelvic asymmetry, leaving sixty-four patients (seventy-four hips). There were eight male and fifty-six female patients, with a mean age of 36.1 years (range, fourteen to fifty-four years).

Osteonecrosis group: We originally reviewed ninety radiographs and, using a random-numbers table, selected forty-five patients (fifty-three hips). Fifteen patients were excluded because of excessive pelvic tilt or pelvic asymmetry, leaving thirty patients (thirty-six hips) with osteonecrosis of the femoral head but without radiographic signs of developmental dysplasia, trauma, or metabolic bone disease. There were sixteen male and fourteen female patients, with a mean age of 45.9 years (range, twenty to eighty-one years). The etiology of the femoral head osteonecrosis was idiopathic in three patients and was attributed to steroid use in seventeen patients and to alcohol use in ten patients. In all patients, the femoral head osteonecrosis had occurred subsequent to skeletal maturity.

Legg-Calvé-Perthes group: We originally reviewed ninety-six radiographs and, using a random-numbers table, selected forty-eight patients (sixty-two hips). Fourteen of them were excluded because of excessive pelvic tilt or pelvic asymmetry, leaving thirty-four patients (fifty hips) who were treated nonoperatively until epiphyseal closure. There were seventeen men and seventeen women, with a mean age of forty-three years (range, twenty-one to sixty-four years). The alignment of the anterior and posterior walls of the proximal part of the acetabulum was confirmed on transectional computed tomography images of six of these patients.

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Radiographic Technique

Anteroposterior radiographs of the pelvis were made with the patient in the supine position. The tube-to-film distance was 120 cm, and the tube was oriented perpendicular to the table. The central beam was directed to the midpoint between the upper border of the symphysis and a horizontal line connecting both anterior superior iliac spines. To judge the extent of pelvic inclination, we used the method described by Siebenrock et al.9,13. The distance between the pubic symphysis and the sacrococcygeal joint was measured on each standard anteroposterior radiograph for comparison with the reported control values of 25 to 40 mm for men and 40 to 55 mm for women.

For all groups, if the distance between the pubic symphysis and the sacrococcygeal joint did not lie within the range of the control values, the patient was considered to have excessive pelvic inclination and was therefore excluded from the evaluation of acetabular retroversion. Pelvic symmetry was evaluated in terms of the comparative radiographic appearance of the obturator foramina and the positions of the sacral midpoint and the pubic symphysis. In addition, transectional computed tomography images were made at 2-mm intervals with the patient in the supine position to verify the alignment of the anterior and posterior walls of the acetabulum. The Tönnis classification14 was used to grade the extent of osteoarthritis in the hips of the normal volunteers and patients (Table I).

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The Cross-over Sign and the Posterior Wall Sign

In an anteverted acetabulum (Fig. 1), a line can be drawn from the superolateral edge of the acetabulum that represents the anterior rim of the acetabulum. It runs medially and distally. A second line representing the posterior rim of the acetabulum can be drawn, and it runs more vertically. In contrast, in a retroverted acetabulum (Fig. 2), the superior part of the anterior line is actually lateral to the posterior line. As these lines progress medially and distally, the anterior line crosses the posterior line. This finding is termed the cross-over sign (Fig. 2)8. The posterior line lies at or just lateral to the center of the femoral head8. If the line of the edge of the posterior wall is located well medial to the center of the femoral head, this finding is termed the posterior wall sign (Fig. 2)8. The posterior wall sign indicates relatively less posterior coverage9.

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Statistical Analysis

Statistical analyses were performed with StatView software (version 5.0; SAS Institute, Cary, North Carolina). We used the chi-square test to compare the frequency rate of acetabular retroversion between each pair of groups. A difference was considered to be significant when the p value was <0.05.

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Results

In the normal group, all fifty-six subjects (112 hips) had Grade-0 osteoarthritis according to the Tönnis classification system (Table II). The prevalence of acetabular retroversion was 6% (seven hips). Acetabular retroversion was slightly more frequent among male subjects, occurring in three (7%) of the forty-four hips in male subjects and four (6%) of the sixty-eight hips in the female subjects. The difference was not significant. The posterior wall sign was present in five of the seven hips with acetabular retroversion.

In the osteoarthritis group (sixty-six patients; seventy hips), no hip had Grade-0 osteoarthritis; two had Grade-1, thirty-four had Grade-2, and thirty-four had Grade-3 osteoarthritis according to the Tönnis classification system. The prevalence of acetabular retroversion was 20% (fourteen hips), a significantly higher prevalence than that in the normal group (p = 0.0047) (Table III). Two of the nine hips in the male patients and twelve (20%) of the sixty-one hips in the female patients demonstrated acetabular retroversion; the difference was not significant. The posterior wall sign was noted in ten of the fourteen hips with acetabular retroversion. Of the fourteen hips with acetabular retroversion, six had Grade-2 osteoarthritis and eight had Grade-3 osteoarthritis according to the Tönnis classification system. No significant association was detected between the prevalence of acetabular retroversion and the Tönnis classification.

In the dysplasia group (sixty-four patients; seventy-four hips), thirty-five hips had Grade-0 osteoarthritis according to the Tönnis classification system, thirty-three had Grade 1, six had Grade 2, and no hip had Grade 3. The prevalence of acetabular retroversion was 18% (thirteen hips), which was significantly higher than that in the normal group (6%; p = 0.0147) (Fig. 3). The prevalence of acetabular retroversion was higher for male patients (two of eight hips) than for female patients (17%; eleven of sixty-six hips) (p = 0.559). The posterior wall sign was seen in all thirteen hips with acetabular retroversion.

The prevalence of acetabular retroversion in the osteonecrosis group was 6% (two of thirty-six hips). No significant difference was detected between this group and the normal group or between male and female patients. Acetabular retroversion occurred in one (5%) of the twenty hips in male patients and in one of the sixteen hips in the female patients. The posterior wall sign was present in one of these two hips. A collapsed femoral head was seen in twenty-four hips in twenty patients.

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In the Legg-Calvé-Perthes group (thirty-four patients; fifty hips), thirteen hips had Grade-0 osteoarthritis according to the Tönnis classification system, twenty-three had Grade 1, fourteen had Grade 2, and no hip had Grade 3. The prevalence of acetabular retroversion was 42% (twenty-one hips), a significantly higher frequency than in the normal group (p < 0.0001). Acetabular retroversion was more frequent among male patients; it occurred in eleven (46%) of twenty-four hips in male patients and in ten (38%) of the twenty-six hips in female patients (p = 0.598). The posterior wall sign was observed in nineteen of the twenty-one hips with acetabular retroversion.

The Legg-Calvé-Perthes group was divided according to the Stulberg classification of femoral head and acetabular deformities12. The acetabular retroversion occurred in one of eight class-I hips, three of seventeen class-II hips, nine of thirteen class-III hips, six of nine class-IV hips, and two of three class-V hips.

In the Legg-Calvé-Perthes group, we also compared the prevalence of acetabular retroversion in the hips with spherical femoral heads (Stulberg classes I and II [the spherical group]) and the hips with Stulberg class-III, IV, and V involvement (the nonspherical group). Seventeen (68%) of twenty-five hips in the nonspherical group had acetabular retroversion compared with only four (16%) of twenty-five hips in the spherical group (p = 0.0002) (Fig. 4).

No significant association was seen in the Legg-Calvé-Perthes group between the prevalence of acetabular retroversion and the Tönnis classification.

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Discussion

The posterior aspect of the acetabulum is subjected to high loads during the activities of daily living15-17. With acetabular retroversion, theoretically greater unit loads are imposed on the available posterior cartilage. These increased unit loads may be responsible for the development of osteoarthritis of the hip.

A proper determination of acetabular retroversion requires that the orientation of the pelvis be taken into consideration. The cross-over sign can be easily influenced by the inclination or rotation of the pelvis9,14,18,19. Siebenrock et al.9 suggested that the cross-over sign is influenced by the inclination of the pelvis. They measured the distance between the pubic symphysis and the sacrococcygeal joint in healthy subjects and reported a mean value of 32.3 mm for males and 47.3 mm for females. The values we obtained were slightly larger than those, although the difference might reflect lifestyle and skeletal differences between Asian and white populations. If pelvic inclination and rotation are overlooked, some normal images may be misdiagnosed as acetabular retroversion.

In a review of the literature, Li and Ganz reported that acetabular retroversion was found in forty (17.2%) of 232 hips with developmental dysplasia20. This prevalence is almost identical to our findings (18%). In contrast, Mast et al. reported that acetabular retroversion was found in eighty-seven (37%) of 235 hips with developmental dysplasia21. However, they used different criteria to evaluate pelvic tilt. Their study excluded patients in whom the tip of the coccyx was >2 cm from the superior border of the pubic symphysis, which they considered excessive inclination of the pelvis, whereas we used the pelvic tilt evaluation criteria of Siebenrock et al.9,13. Mast et al. also reported that a smaller lateral center-edge angle is closely related not only to acetabular anteversion but also to acetabular retroversion21.

Malformations of the acetabulum, such as those seen in developmental dysplasia, slipped capital femoral epiphysis, and Legg-Calvé-Perthes disease are thought to be of etiologic importance to the development of osteoarthritis of the hip2,22,23. The dysplasia group in our study had a higher prevalence of acetabular retroversion than the normal group, and the posterior wall sign was recognized in all dysplastic hips with retroversion. These results indicate that retroversion in developmental dysplasia is more common than previously thought. Murphy et al. found heterogeneous patterns of developmental dysplasia1. Of twenty dysplastic hips, seven had anterolateral deficiency, six had posterolateral deficiency, and seven had symmetric, global deficiency. This heterogeneity has important implications for corrective surgery because the type of acetabular insufficiency must be evaluated preoperatively so that appropriate reorientation of the acetabulum is performed.

Adult-onset osteonecrosis and the resulting collapse and deformity of the femoral head generally occur after the completion of acetabular growth. The prevalence of acetabular retroversion in the osteonecrosis group was 6%, and no significant difference was observed between this group and the normal group. Therefore, it appears that osteonecrosis is a problem exclusively of the femoral head, and acetabular retroversion is not a contributing factor to the osteoarthritis that ensues.

In contrast, the prevalence of acetabular retroversion in patients with so-called idiopathic osteoarthritis was 20%. Harris postulated that most instances of so-called idiopathic osteoarthritis were secondary to preexisting developmental deformities2. While we did not examine these patients or hips to elucidate possible developmental abnormalities, we believe that this group of patients deserves further study to determine why the prevalence of retroversion is so high.

Recent reports have examined the relationship between femoroacetabular impingement attributable to acetabular retroversion and osteoarthritis of the hip5-7,9. For hips with acetabular retroversion but without the posterior wall sign, it is possible that acetabular retroversion might have resulted from excessive coverage of the anterior wall. We suspect that, in the four hips with acetabular retroversion but without the posterior wall sign in the osteoarthritis group, the deformity might have been caused by excessive coverage of the anterior acetabular wall rather than by deficiency of the posterior wall. We further presume that excessive coverage of the anterior acetabular wall might lead to femoroacetabular impingement5-7,9.

Legg-Calvé-Perthes disease is an idiopathic osteonecrosis of the femoral head in children. Although the age at onset ranges from two to thirteen years, the majority of our patients were between four and seven years of age when it developed. The prevalence of acetabular retroversion in the Legg-Calvé-Perthes group was 42%, which was significantly higher than that in the normal group. In addition, within the Legg-Calvé-Perthes group, the frequency of acetabular retroversion was significantly higher in the nonspherical group than in the spherical group. It is unclear whether acetabular retroversion is a cause or effect of the femoral head deformities in these patients. The significantly higher frequency of acetabular retroversion in the nonspherical group compared with the spherical group suggests that the magnitude of femoral head deformity during growth is related to the development of acetabular retroversion in patients with Legg-Calvé-Perthes disease.

We perform periacetabular osteotomy as surgical treatment for developmental dysplasia24. The presence of acetabular retroversion influences the reorientation of the acetabulum during surgery. When dysplasia of the lateral and anterior aspect of the acetabulum is found, we transfer the osteotomized acetabulum anterolaterally to obtain sufficient coverage of the femoral head. However, when we perform a periacetabular osteotomy for a patient with lateral developmental dysplasia and acetabular retroversion, we transfer the osteotomized acetabulum only in a lateral direction while simultaneously moving the femoral head medially, to avoid transferring the acetabulum anteriorly and thus cause an insufficiency in the posterior wall and a possible exacerbation of femoroacetabular impingement25,26.

When we perform a total hip arthroplasty on a patient with acetabular retroversion, we pay careful attention not to align the acetabular component with an insufficient posterior wall and thereby orient the cup in retroversion.

In conclusion, we investigated the prevalence of acetabular retroversion in normal subjects and in patients with osteoarthritis of the hip, developmental dysplasia, osteonecrosis of the femoral head, and residual deformity resulting from Legg-Calvé-Perthes disease, by examining standard anteroposterior radiographs of the pelvis. Acetabular retroversion occurred at a significantly higher rate in patients with osteoarthritis of the hip, developmental dysplasia, and Legg-Calvé-Perthes disease compared with that in subjects in the normal group. Within the Legg-Calvé-Perthes group, the frequency of acetabular retroversion was significantly higher in the nonspherical group than in the spherical group. Acetabular retroversion is more common than has been previously noted, and it appears in a variety of diseases of the hip. Its relationship to the subsequent development of degenerative arthritis in these entities deserves further study. ▪

The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Department of Orthopaedic Surgery, Fukuoka University School of Medicine, Fukuoka, Japan

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