The Journal of Arthroplasty xxx (2014) xxx–xxx

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An Increase in Cranial Acetabular Version With Age: Implications for Femoroacetabular Impingement Nathan J. Kopydlowski, BA a, Eric P. Tannenbaum, MD b, Asheesh Bedi, MD b, Matthew V. Smith, MD c, Jon K. Sekiya, MD b a b c

University of Michigan Medical School, Ann Arbor, Michigan MedSport, Department of Orthopedic Surgery, University of Michigan, Ann Arbor, Michigan Department of Orthopaedic Surgery, Washington University in St. Louis, Chesterfield, Missouri

a r t i c l e

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Article history: Received 18 November 2013 Accepted 31 March 2014 Available online xxxx Keywords: femoroacetabular impingement hip impingement acetabular retroversion pincer impingement hip pain

a b s t r a c t This cadaveric study aimed to determine if acetabular retroversion demonstrates predictable changes with age that could inform understanding of factors that may contribute to the pathophysiology of femoroacetabular impingement. Two-hundred forty pelves were divided into young and old groups. Version was measured at the cranial (5 mm below superior rim), central (transverse of acetabulum), and caudal (5 mm above inferior rim) locations. The data showed a significant difference between young (10 ± 10°) and old (13 ± 9°) cranial version (P = .02). Cranial retroversion increases with age and may reflect a developmental component in the etiology of the focal rim impingement lesion or ossification of the damaged labrum. Global acetabular retroversion does not appear to change with age and may reflect a congenital etiology. © 2014 Elsevier Inc. All rights reserved.

During infancy, the development of the acetabulum is a product of lateral growth from acetabular cartilage and medial growth from the triradiate cartilage [1,2]. The balanced growth of these two structures and its interaction with the femoral head determine the overall structure and orientation of the acetabulum [3]. The height and width of the acetabulum are controlled by the interstitial growth of the triradiate cartilage [4]. An uncoordinated growth by these two regions can result in morphological abnormalities of the skeletally mature acetabulum. One of the many pathologies resulting from an uncoordinated growth of these two cartilage regions is focal or global change in the abduction and version of the acetabulum. Cranial retroversion can result in repetitive contact stresses of a normal femoral neck against an abnormal area of focal acetabular “overcoverage.” On an anteroposterior (AP) radiograph, this focal anterosuperior overcoverage is manifest as a "cross-over" sign, which is seen when the anterior rim line extends lateral to the posterior rim in the cranial part of the acetabulum and then crosses over the posterior line to become more medial in the central and caudal acetabulum [5]. This situation results in degeneration and tearing of the anterosuperior labrum and a posteroinferior “contre-coup” pattern of chondral injury to the femoral head and acetabulum.

The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.03.042. Reprint requests: Jon K. Sekiya, MD, Larry S. Matthews Collegiate Professor, Sports Medicine, MedSport, Department of Orthopaedic Surgery, University of Michigan, 24 Frank Lloyd Wright Drive, Lobby A, Ann Arbor, MI 48106.

With focal rim impingement, the labrum is primarily injured, resulting in progressive bone apposition on the osseous rim adjacent to the labrum and ultimately ossification of the labrum itself [6]. In contrast, global acetabular retroversion is an often misdiagnosed variety of hip dysplasia that does not present until the second or third decade of life [7]. While it may present with clinical symptoms similar to those of a focal rim lesion, the mechanical problem is distinct and reflects “overcoverage” anteriorly combined with “undercoverage” posteriorly. The diagnosis is preoperatively suspected on plain radiographs by the “posterior wall sign,” or medial passage of the posterior wall relative to the center of the femoral head on an AP view. Computed tomography (CT) scan with axial views clearly demonstrates retroversion of the acetabulum at the cranial (5 mm inferior to the superior border of the acetabulum), central (through the longitudinal center of the acetabulum), and caudal (5 mm superior to inferior border of the acetabulum) locations. Some orthopedists refer to cranial retroversion as simply “retroversion” when in fact that term should be reserved for global retroversion. The posterior femoral head is the site of the highest joint pressure, and any deficiency in support of this area results in large contact stresses and later pathologies [8]. Furthermore, loss of offset anteriorly at the femoral head–neck junction in combination with acetabular retroversion and posterior “undercoverage” may result in posterior instability or dislocation. In certain circumstances, pain with associated symptoms of posterior instability symptoms could be better addressed with a reverse, “anteverting” periacetabular osteotomy to correct the anteversion of the acetabulum and improve mechanics

http://dx.doi.org/10.1016/j.arth.2014.03.042 0883-5403/© 2014 Elsevier Inc. All rights reserved.

Please cite this article as: Kopydlowski NJ, et al, An Increase in Cranial Acetabular Version With Age: Implications for Femoroacetabular Impingement, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.03.042

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N.J. Kopydlowski et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx

between the acetabular rim and the femoral head–neck junction [9]. Therefore, research studies examining the complexity of the pathoanatomy are essential to further understand the appropriate treatment necessary to achieve the best patient outcome. Studies have suggested a correlation between hip retroversion and a predisposition to develop osteoarthritis in the hip [10,11]. The repetitive impact caused by the decrease in clearance between the femoral head/neck junctions may lead to local cartilage damage and hip pain. This contact may lead to degenerative changes to the acetabular rim and adjacent structures [12–15]. The criterion for a diagnosis of acetabular retroversion was the presence of a so-called crossover sign on the AP radiograph of the pelvis. It has been found that patients with osteoarthritis, developmental dysplasia, or Legg– Calvé–Perthes disease were significantly more likely to have acetabular retroversion than normal subjects (P b .05) [16]. Understanding the relationship between changes in focal and global acetabular retroversion and femoroacetabular impingement (FAI) is of paramount importance to the clinical treatment of symptomatic patients. Furthermore, this information could offer novel insight into the developmental or congenital factors that may contribute to the pathophysiology of FAI. The purpose of this study is to measure focal and global acetabular version and to identify potential differences between age groups and racial groups. The hypothesis of our study is that focal (cranial) acetabular retroversion increases with age and may reflect a developmental component in the etiology of rim impingement lesion, potentially secondary to progressive ossification of the damaged labrum. Methods Populations The Hamann–Todd Human Osteological Collection at the Cleveland Museum of Natural History has 2967 skeletal specimens. Measurements were made on 240 randomly chosen pelves between the ages of 14 and 60 years. Specimens younger than 14 years were excluded secondary to skeletal immaturity and specimens over the age of 60 years were excluded due to degenerative changes resulting in osteophyte formation and dysmorphic acetabuli. The specimens were divided into two groups based on specimen age (young: 14–24 years, old: 25–60 years). Cut off ages were chosen to have an equal number of specimens in each group. The groups were normalized by having equal numbers of males and females, as well as equal distribution between Caucasians and African Americans, within each group. All of the specimens were representative of a population from Northern Ohio during the early twentieth century.

Fig. 1. The pelvis was placed on a flat surface with the anterior superior iliac spine and pubic symphysis in contact with the table. The table served as the frontal plane and the version of the acetabulum was measured at the three acetabular regions (cranial, central, and caudal).

the global version. Since most acetabular chondral damage in FAI occurs anterosuperiorly near the anterior inferior iliac spine, the distance of 5 mm cranially was used. Statistics All data are presented as the mean plus/minus the standard deviation, and all statistical analyses were done on SPSS (IBM Corp, Armonk, New York). Significant differences were determined by using two-tailed t-tests and one-way ANOVA tests with an α value of 0.05. Student Newman Keuls post hoc tests were also performed with an α value of 0.05. Data from a pilot cadaveric study of acetabular

Anatomic Measurements Anatomic measurement techniques were adopted from Jamali et al [11]. Each disarticulated pelvis and sacrum were reconnected using rubber bands and a 5-cm thick foam piece that was compressed to 2 cm in place of the pubis symphysis. The plane formed between the anterior superior iliac spines (ASIS) and the pubic symphysis was used to define the anatomic frontal plane of reference of the pelvis. During normal upright standing and walking, this plane is positioned vertically [17,18]. To stabilize the pelvic specimens while taking measurements, the specimens were set on a flat table with the ASIS and the pubic symphysis rested against the table. Thus, the table represented the anatomic frontal plane (Fig. 1). The acetabular version was measured using a goniometer at three separate transverse sections: cranial (5 mm distal to the acetabular roof), central (through the longitudinal center of the acetabulum), and caudal (5 mm proximal from the most inferior edge of the acetabular cavity) (Fig. 2). The average of the three distinct measurement locations was determined and will be referred to as

Fig. 2. (A) Cranial version was measured 5 mm distal to the acetabular roof. (B) Central version was measured through the longitudinal center of the acetabulum. (C) Caudal version was measured 5 mm proximal to the most inferior edge of the acetabulum.

Please cite this article as: Kopydlowski NJ, et al, An Increase in Cranial Acetabular Version With Age: Implications for Femoroacetabular Impingement, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.03.042

N.J. Kopydlowski et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx

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retroversion of 50 specimens demonstrated a mean global acetabular version difference of 2.45° ± 6.68° between young and old groups. Power analysis determined that a minimum of n = 117 would be able to detect a significant difference between groups with a power of 0.80 and a significance of P b .05. Based on these data we chose a sample size of n = 120 specimens for this study. Results The version at each of the defined acetabular regions was measured and averaged to determine the global version of each specimen. The global version of the entire population was 17° ± 9°. The cranial, central, and caudal versions were 12° ± 9°, 20° ± 8°, and 21° ± 8°, respectively. The cranial version was found to be significantly less anteverted than the central and caudal versions in both age groups. Global retroversion, defined by the average version of each specimen, was observed in 10% (24/240) of the population (24 specimens). There was no significant difference in the incidence of globally retroverted acetabuli between age groups (63% in the young group versus 37% in the old group, P N .05) (Table 1). Focal acetabular version, however, demonstrated some significant differences between the young and old groups. Cranial version was significantly less anteverted in the younger group (10° ± 10°) than in the older group (13° ± 9°; P b .02) (Fig. 3). The central (19° ± 8°), caudal (21° ± 8°), and global (17° ± 8°) versions of the young group were not significantly different from the central (21° ± 8°), caudal (21° ± 8°), and global (18° ± 8°) versions of the older group (P N .05) (Fig. 3). When grouped by both age and race, the ages within each group were not significantly different (Table 2). The version did not vary between the races at any of the anatomic positions. The only significant variations were seen with age within the Caucasian group, with the young being less anteverted than the old population. Discussion This study measured the acetabular version of ex vivo cadaveric specimens in an attempt to better understand how acetabular version changes with age and whether race played a role in any developmental changes noted in the acetabular morphology. While no significant differences in acetabular version were observed between races within each age group, cranial version differences were observed when comparing younger specimens to older specimens. This study demonstrated a significant decrease in cranial retroversion with age that may reflect a developmental, compensatory component in the etiology of the focal rim impingement lesion. In other words, younger patients with cranial retroversion initially at risk for developing a cam-type FAI may possibly have the potential to remodel their cranial acetabular morphology thereby decreasing the likelihood of progressing to symptomatic FAI as they age. In contrast, global acetabular version and focal version centrally and caudally did not significantly change with age. In this regard, global acetabular retroversion may reflect a more congenital and stable finding rather than a dynamic pattern seen in the cranial acetabulum. Cranial retroversion has been thought to be associated with pincer-type femoroacetabular impingement. This study demonstrates significantly more focal cranial retroversion in younger specimens compared to older specimens. The explanation for this finding may be multifactorial. The data suggest that a developmental factor may Table 1 Age Differences in Mean Acetabular Version ± SD Reported in Degrees. Group

Cranial Version

Central Version

Caudal Version

Global Version

Young Old

11° ± 10° 13° ± 9°

19° ± 8° 21° ± 8°

21° ± 8° 21° ± 8°

17° ± 8° 18° ± 8°

Fig. 3. Mean young and old acetabular versions.

influence acetabular growth and morphology, thereby resulting in a significant change in acetabular cranial version over time. It is certainly plausible that altered mechanical stresses may be responsible for alterations in the growth and ossification of the proximal femoral physis and triradiate cartilage that result in anatomic changes that could possibly be potentially protective against the development of FAI after skeletal maturity or altered activity levels. The global acetabular retroversion did not show a significant difference between the young and the old age groups. These findings suggest that global retroversion may reflect a more fundamental, congenital etiology and is similar to other forms of developmental dysplasia of the hip. However, given that cam-type FAI impingement typically occurs in the anterosuperior acetabulum, the absence of any statistically significant difference noted in the central, caudal, and global acetabular versions likely has minimal clinical impact in terms of patients who go on to develop symptomatic FAI. Numerous previous studies have measured acetabular version from radiographs and compared between genders. The measurement of acetabular version can be uniformly altered due to pelvic tilt, the inability to standardize AP radiographs, and the inability to determine the exact location of the pelvic rim. The results obtained from our ex vivo measurements show an average version of 17° ± 9° and are consistent with the results of many other studies done with CT scans or radiographs in which the acetabular version ranges from 15° to 20° [8,11,13,19–21]. This study was unique, however, in its focal assessment of version at three different axial planes of the acetabulum to define focal rim impingement overcoverage and to further identify differences between age groups in a pre-arthritic population. The nature of the sample population and the lack of information available for each specimen are limitations of this study. The sample size was powered to determine how many samples were needed to show if a significant difference was present. The clinical relevance of a difference of only 2.5° in absolute numbers for cranial retroversion between young and old means is unknown, but clinical relevance may be defined in later studies. The differences seen in our data could be truly developmental or may show subtle degenerative changes over time, but due to the cross-sectional design of this study, the results of this study cannot predict changes in individual patients over time. The study was limited in that patients with greater retroversion may have Table 2 Age and Versions at the Three Acetabular Regions and the Global Version, by Both Age and Race.

Group

Age (Y)

African American, Young Caucasian, Young African American, Old Caucasian, Old

21 22 42 43

± ± ± ±

3 3 10 10

Cranial Version 12° 9° 13° 14

± ± ± ±

11° 7° 9° 9°

Central Version 21° 18° 21° 21°

± ± ± ±

9° 6° 8° 8°

Caudal Version 21° 21° 22° 21°

± ± ± ±

9° 6° 8° 8°

Global Version 18° 16° 19° 18

± ± ± ±

9° 6° 8° 8°

Please cite this article as: Kopydlowski NJ, et al, An Increase in Cranial Acetabular Version With Age: Implications for Femoroacetabular Impingement, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.03.042

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N.J. Kopydlowski et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx

corresponding changes on the femoral head or neck to compensate and mitigate the risk of FAI. Further studies are needed to determine the relationship between acetabular and femoral version. Conclusions Acetabular retroversion (and more specifically cranial retroversion) has been thought to be a good determinant for the potential of developing cam-type femoroacetabular impingement. One of the direct results of retroverted hips is a disturbance in the support and movement of the femoral head in the acetabulum. This disruption in movement can lead to pincer-type femoroacetabular impingement. The results of our study have shown that it may be possible for the superior rim of the acetabulum to remodel over time and decrease a patient's risk for FAI. Understanding how acetabular version may change and develop over time can give treating surgeons an advantage in evaluating patients with pre-arthritic hip pain, and ultimately help to prevent the development of osteoarthritis of the hip joint. Acknowledgments We thank Lyman M. Jellema from the Hamann–Todd Human Osteological Collection at the Cleveland Museum of Natural History, for providing access to the skeletal specimens. We would also like to thank the Howard Hughes Medical Institute and the University of Michigan Student Biomedical Research Project for grants that helped to make this project possible. References 1. Ponseti IV. Growth and development of the acetabulum in the normal child. Anatomical, histological, and roentgenographic studies. J Bone Joint Surg Am 1978;60(5):575. 2. Giori NJ. Offset acetabular components introduce torsion on the implant and may increase the risk of fixation failure. J Arthroplasty 2003;18(1):89.

3. Harrison TJ. The influence of the femoral head on pelvic growth and acetabular form in the rat. J Anat 1961;95:12. 4. Sankar WN, Flynn JM. The development of acetabular retroversion in children with Legg–Calve–Perthes disease. J Pediatr Orthop 2008;28(4):440. 5. Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis—what the radiologist should know. AJR Am J Roentgenol 2007;188(6):1540. 6. Beall DP, Sweet CF, Martin HD, et al. Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiol 2005;34(11):691. 7. Banks KP, Grayson DE. Acetabular retroversion as a rare cause of chronic hip pain: recognition of the "figure-eight" sign. Skeletal Radiol 2007;36(Suppl. 1):S108. 8. Kim WY, Hutchinson CE, Andrew JG, et al. The relationship between acetabular retroversion and osteoarthritis of the hip. J Bone Joint Surg (Br) 2006;88(6):727. 9. Bedi A, Dolan M, Leunig M, et al. Static and dynamic mechanical causes of hip pain. Arthroscopy 2011;27(2):235. 10. Giori NJ, Trousdale RT. Acetabular retroversion is associated with osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:263. 11. Jamali AA, Mladenov K, Meyer DC, et al. Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the "cross-over-sign". J Orthop Res 2007;25(6):758. 12. Menke W, Schmitz B, Schild H, et al. Transverse skeletal axes of the lower extremity in coxarthrosis. Z Orthop Ihre Grenzgeb 1991;129(3):255. 13. Tonnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am 1999;81(12):1747. 14. Beck M, Leunig M, Parvizi J, et al. Anterior femoroacetabular impingement: part II. Midterm results of surgical treatment. Clin Orthop Relat Res 2004;418:67. 15. Wenger DE, Kendell KR, Miner MR, et al. Acetabular labral tears rarely occur in the absence of bony abnormalities. Clin Orthop Relat Res 2004;426:145. 16. Ezoe M, Naito M, Inoue T. The prevalence of acetabular retroversion among various disorders of the hip. J Bone Joint Surg Am 2006;88(2):372. 17. McKibbin B. Anatomical factors in the stability of the hip joint in the newborn. J Bone Joint Surg (Br) 1970;52(1):148. 18. Visser JD, Jonkers A, Hillen B. Hip joint measurements with computerized tomography. J Pediatr Orthop 1982;2(2):143. 19. Reikeras O, Bjerkreim I, Kolbenstvedt A. Anteversion of the acetabulum and femoral neck in normals and in patients with osteoarthritis of the hip. Acta Orthop Scand 1983;54(1):18. 20. Maruyama M, Feinberg JR, Capello WN, et al. The Frank Stinchfield Award: morphologic features of the acetabulum and femur: anteversion angle and implant positioning. Clin Orthop Relat Res 2001;393:52. 21. Hoiseth A, Reikeras O, Fonstelien E. Lack of correlation between femoral neck anteversion and acetabular orientation. Radiography and computed tomography in cadavers and in vivo. Acta Orthop Scand 1989;60(1):93.

Please cite this article as: Kopydlowski NJ, et al, An Increase in Cranial Acetabular Version With Age: Implications for Femoroacetabular Impingement, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.03.042

An increase in cranial acetabular version with age: implications for femoroacetabular impingement.

This cadaveric study aimed to determine if acetabular retroversion demonstrates predictable changes with age that could inform understanding of factor...
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