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Change in Pelvic Tilt Angle 2 to 4 Years After Total Hip Arthroplasty
The Journal of Arthroplasty Vol. 27 No. 6 2012
Change in Pelvic Tilt Angle 2 to 4 Years After Total Hip Arthroplasty Naoya Taki, MD,* Naoto Mitsugi, MD, PhD,* Yuichi Mochida, MD, PhD,y Yasushi Akamatsu, MD, PhD,* and Tomoyuki Saito, MD, PhDz
Abstract: The purpose of this study was to evaluate the change in pelvic tilt angle (PA) in the sagittal plane in the standing and supine positions for 2 to 4 years after total hip arthroplasty (THA). Anteroposterior pelvic radiographs of 21 male and 65 female patients were investigated before and after THA yearly over 2 to 4 years. Both the standing and supine PA significantly posteriorly tilted after THA. The difference in PA between the standing and supine positions (dPA) significantly increased after THA. Although the PA in the standing and supine positions plateaued 1 year after THA, the dPA gradually increased. In addition, the percentage of patients who showed a difference of more than 10° in dPA tended to increase yearly. In particular, elderly female patients who showed posterior tilt in PA in the standing or supine positions or a large dPA before THA tended to show a dPA of more than 10° after THA. Keywords: total hip arthroplasty (THA), pelvic tilt, sagittal alignment, cup anteversion, standing position, cup orientation. © 2012 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) is an established and excellent treatment for patients with osteoarthritis (OA) of the hip. In this aging society, the number of patients with hip OA is increasing, in particular, the number of elderly patients. Generally, pelvic posterior tilt increases when people become old [1-5] because of the loss of lumbar lordosis, flexion contracture of the knee, and weakness of the back muscle and others. Among these patients, some show different radiographic pelvic tilt in the sagittal plane between the standing and supine positions. This difference alters the relationship between the cup and stem with different posture after THA. Lembeck et al [6] demonstrated that pelvic reclination of 1° will lead to functional anteversion of the cup of approximately 0.7°, which may cause impingement between the cup and stem. In addition, it may cause excessive wear due to edge loading of the
From the *Department of Orthopaedic Surgery, Yokohama City University Medical Center, Yokohama, Japan; yCenter for Rheumatoid Disease, Yokohama City University Medical Center, Yokohama, Japan; and zDepartment of Orthopaedic Surgery, Yokohama City University, Graduate School of Medicine, Yokohama, Japan. Submitted September 14, 2010; accepted October 6, 2011. The Conflict of Interest associated with this article can be found at doi:10.1016/j.arth.2011.10.003. Reprint requests: Naoya Taki, MD, Department of Orthopaedic Surgery, Yokohama City University Medical Center, 4-57 Urafunecho Minami-ku, Yokohama, 232-0024, Japan. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2706-0019$36.00/0 doi:10.1016/j.arth.2011.10.003
joint. Thus, the change in pelvic tilt warrants further study. Nishihara et al [7] observed the pelvic tilt angle (PA) of 101 patients who had undergone THA before and 1 year after THA. They reported that the difference in the standing and supine PA before and 1 year after surgery was less than 10° in 90% of the patients. However, there are no reports concerning the difference in PA between the standing and supine positions (dPA) more than 1 year after THA. The purposes of this study were to evaluate the change in PA in the sagittal plane in the standing and supine positions for 2 to 4 years after THA and to investigate the factors that may contribute to the dPA.
Materials and Methods This retrospective study was approved by our institutional review board. Between November 2004 and December 2007, 178 primary THAs were performed by 5 surgeons in the same surgery team in our institution. One patient (2 joints) died because of cancer. Fourteen joints were excluded because of contralateral THA within 2 years. Fourteen rheumatoid patients were excluded. Sixteen patients have not returned within 2 years. Forty-six patients had not taken suitable radiographs for this study. Finally, the remaining 86 patients were enrolled in this study. There were 21 males and 65 females. Sixty-nine patients had developmental dysplasia of the hip, 2 patients had primary OA of the hip, 1 patient had posttraumatic OA, and 14 had osteonecrosis of the femoral head. Mean age at surgery was 64 ±
940
Change in Pelvic Tilt After THA Taki et al
Results Mean PA before THA was 22.6° ± 10.4° in the standing position and 18.5° ± 8.0° in the supine position. Mean PA 1 year after THA was 26.5° ± 10.5° in the standing position and 21.2° ± 7.3° in the supine position. Pelvic tilt angle gradually increased (posteriorly tilted) after surgery. The mean PA in the standing and supine positions at each time point was significantly higher than that before THA. The PA at each time point, except supine PA 4 years after surgery, showed a positive correlation to age at THA. The change in PA was the largest 1 year after THA. The change in PA appears to plateau after 1 year (Table 1).
T
Table 1. Pelvic Tilt Angle and Change in PA in the Standing and Supine Positions
N Standing PA Supine PA Change in standing PA Change in supine PA
Before THA
1 y after THA
2 y after THA
3 y after THA
4 y after THA
86 22.6 ± 10.4 18.5 ± 8.0 0
86 26.5 ± 10.5* 21.2 ± 7.3* 3.9 ± 6.2 *
86 27.9 ± 10.6* 21.1 ± 7.1* 5.3 ± 7.1 *
55 26.7 ± 10.9* 20.8 ± 7.8* 5.1 ± 5.7 *
32 29.1 ± 11.7* 22.3 ± 7.4* 5.2 ± 6.2 *
0
2.7 ± 4.4 * 2.6 ± 3.9 * 3.0 ± 4.2 * 2.6 ± 3.2 *
* P b .05, paired t test (mean ± SD).
There were only 5 patients (6%) who showed a change of more than 10° in the supine PA at the final follow-up point compared with the supine PA before surgery. However, with PA in the standing position, 12 patients (14%) showed a change of more than 10° 1 year after THA compared with that before surgery. At 2 years, 21 patients (24%); at 3 years, 14 patients (25%); and at 4 years, 5 patients (16%) showed a change of more than 10° in the standing PA. The older aged patients tended to show a greater PA than the younger aged patients. In addition, the dPA seemed to be larger in the older aged patients than in the younger aged patients (Fig. 2). Although the change in PA seemed to plateau 1 year after THA, dPA seemed to increase yearly. The percentage of patients who showed a difference of more than 10° in dPA was 9.3% before THA, 16.3% at 1 year, and 28.1% at 4 years after THA (Fig. 3). The factors that may contribute to the larger dPA 2 to 4 years after surgery are female sex, age at THA, supine PA, standing PA, and dPA before THA (Table 2). For 40 35 30
PA (degree)
9 years (mean ± SD) with a range of 39 to 85 years. Mean body mass index was 24.6 ± 3.8 kg/m 2 with a range of 17.5 to 46.7 kg/m 2. Standardized anteroposterior radiographs of the pelvis were obtained in the supine and standing positions before surgery and every year after. Fifty-five patients were evaluated for 3 years and 32 patients for 4 years after surgery. Pelvic tilt angle was calculated from these radiographs in accordance with the method of Doiguchi et al [8]. Briefly, the transverse diameter (T) and longitudinal diameter (L) of the pelvis were measured from a digital image (Fig. 1A). Pelvic tilt angle was calculated using the following formula: −67 × L/T + 55.7 for males and −69 × L/T + 61.6 for females. Reported mean PA was 20° (Fig. 1B). Measurements were taken 3 times (before surgery, 1 year after surgery, and 2 years after surgery) in 31 patients, 4 times (3 times plus 3 years after surgery) in 23 patients, and 5 times (4 times plus 4 years after surgery) in 32 patients. All measurements were taken in the standing and supine radiographs at each time point. Statistical analysis was performed using Stat Mate III (ATMS, Tokyo, Japan). The mean values of all the subgroups were compared using Mann-Whitney U test or χ 2 test. The mean values of each time point were compared using paired t test. Correlations were analyzed with Pearson correlation analysis.
941
25 20 15 10
L
PA
group 1 (standing) group 2 (standing) group 3 (standing)
5
group 1 (supine) group 2 (supine) group 3 (supine)
0 Before THA
A
B
Fig. 1. Calculation of PA. Anteroposterior image (A) and lateral image (B) PA was calculated using the following formula: −67 × L/T + 55.7 for males and −69 × L/T + 61.6 for females. Reported mean PA was 20° [8].
1Y
2Y
3Y
4Y
after THA
Fig. 2. Change in PA with different generation. Graph shows mean PA in the standing (solid line) and supine (broken line) positions of 3 different generations. Group 1, age at THA was less than 60 years; group 2, age at THA was between 60 and 74 years; group 3, age at THA was 75 years or older. The number of the patients in groups 1, 2, and 3 are 29, 41, and 16, respectively.
942 The Journal of Arthroplasty Vol. 27 No. 6 June 2012 100
10
6.7±7.2
6.7±6.9
dPA (degree)
5.2±5.8
dPA
4.0±5.0
50
5 29.1
28.1
Percentage (%)
5.9±6.0
23.6 16.3 9.3
0 Before THA
1Y
2Y
3Y
4Y
0
after THA
Fig. 3. Change in dPA and percentage of patients who showed more than 10° difference in dPA.
17 female patients, either the age at surgery was 72 years or older, the supine PA before THA was more than 22°, the standing PA before THA was more than 30°, or dPA before THA was more than 7°, and 10 of these 17 patients (59%) showed dPA of more than 10° at final follow-up.
Discussion In this study, we demonstrated that PA changes after THA. Recently, several reports have included concerns that radiographic measurement of cup position after THA is inaccurate because of pelvic tilt [6,9-16]. Therefore, it is important to evaluate PA after THA. There are several reports comparing the PA before and after THA [7,10,14,17,18]. Most of them compare the PA within 1 year. Nishihara et al [7] compared the standing PA before and 1 year after THA and reported that 13% of the patients in their study showed a change of more than 10° in PA compared with that before surgery. This percentage is almost the same as that in our study. Blondel et al [17] measured the standing PA before and 3 years after THA and reported that there was no significant difference in PA between the 2 time points. In addition, they reported that no patient showed a difference of more than 10° between the 2 time points. In our study, 25% of the patients who underwent THA showed a change of more than 10° in the standing PA 3 years after surgery. Four years after surgery, 16% of the patients showed a change of more than 10° in the standing PA. The difference in our findings might be due to the difference in the study criteria for the patients of each study. Our study included all of the patients who underwent THA. Blondel et al excluded the patients with spinal deformity or bilateral arthritis. Our result showed that the patients who showed a large change in PA after surgery tended to have increased posterior tilt in PA. One of the causes of increased posterior tilt in PA is a loss of lumbar lordosis. Therefore, the patients who showed a large change in PA might have a spinal deformity. Of course, the patients who had OA of the hip
may have a spinal deformity; it is dangerous to conclude that PA does not change 3 years after THA. Both the standing and supine PA showed the largest change 1 year after surgery. After 1 year, the changes in both the standing and supine PA tended to plateau. The standing and supine alignments of the pelvis are improved after surgery because of elimination of the contracture from the hip joint, relief of pain of the hip, and recovery of the strength of the gluteal and back muscles. It seems that most of this improvement is achieved within 1 year. In this study, we investigated the change in the dPA after THA. The reason for this was that when we see patients for follow-up after THA, some show a great dPA. Generally, PA increases from supine to standing position. If the PA increases, cup anteversion also increases. This may cause neck impingement. Because the cup anteversion increases in the standing position, excessive wear may occur due to edge loading. Some patients show so much anteversion of the cup due to extensively increased posterior tilt of the pelvis, that anterior dislocation of the hip might occur [19,20]. Therefore, we wanted to clarify the change in dPA after THA. As described by Babisch et al [10], we also considered that less than 10° difference in dPA may not increase the risk of hip dislocation. In addition, we wanted to clarify the factors that contribute to the change in dPA. The mean dPA before surgery was 4.0° ± 5.0°, which is similar to those in the report of Nishihara et al [7] and the report of Babisch et al [10] (2.0° ± 6.4° and 5.4° ± 4.6°, respectively). The percentage of patients who showed a difference of more than 10° in dPA before THA was almost the same as that in the report of Nishihara et al. Although the changes in mean PA in both the standing and supine positions tended to plateau from 1 year after THA, our result showed that dPA tended to increase yearly. Moreover, the percentage of the patients who showed a dPA of more than 10° tended to increase Table 2. Correlations Between dPA after THA and Preoperative Patient Factors dPA n Female sex * Age at THA † Supine PA before THA † Standing PA before THA † dPA before THA †
2 y after THA
3 y after THA
4 y after THA
86 P = .027 P b .001, r = 0.36 P = .002, r = 0.34 P b .001, r = 0.38 P = .024, r = 0.24
55 P = .27 P = .006, r = 0.37 P = .002, r = 0.40 P b .001, r = 0.52 P b .001, r = 0.48
32 P = .24 P = .21
* χ2 Test. † Pearson correlation analysis.
P = .02, r = 0.40 P = .005, r = 0.49 P = .054
Change in Pelvic Tilt After THA Taki et al
yearly. This demonstrated that, in some cases, dPA increases after THA within a few years. Mayr et al [3] measured the pelvic inclination in the standing and supine positions of 120 volunteers (60 healthy controls, 30 patients who had undergone THA, and 30 patients with coxarthrosis). They found relationships between age and standing PA and between age and dPA. These relationships are also found at most of the time points in our study. However, they concluded that the mean difference between standing and supine positions in all 120 patients was only 1.1°, which is clinically irrelevant. Their subjects are different from those in our study. In addition, their study is cross-sectional, whereas our study investigated longitudinal change after THA. Therefore, we think that it is clinically important for surgeons to be aware that dPA changes, in some cases, within a few years after THA. Then, we investigated the factors that may contribute to the change in dPA after surgery. The factors that might contribute to dPA change after THA were female sex, the age at surgery, the supine PA, the standing PA, and the dPA before THA. One of the limitations of this study was that we measured PA from anteroposterior radiographs in accordance with the method described in a previous report. Pelvic tilt angle was calculated from the transverse diameter and longitudinal diameter of the pelvis measured from the digital image. Tannast et al [21] reported that the correlation between actual PA and the PA measured from the transverse diameter and longitudinal diameter of the pelvis was moderately strong. As the PA calculated from anteroposterior radiograph was not precise, we compared PA in the same patient. There is less accidental error in calculating the change in PA in the same patient than comparing PA among different patients. Anteroposterior radiograph is a standard method to evaluate the preoperative and postoperative status of the hip joint. It is useful for surgeons to have information of the change in PA obtained from anteroposterior radiograph. Sagittal pelvic alignment not only is determined by the hip joint but also is affected by spinal alignment, contracture of the knees, and strength of the muscles. In this study, we did not evaluate these other factors. We only checked whether the patients had undergone surgery during the follow-up period. No patients had knee arthroplasty or spinal surgery during the follow-up period. Therefore, such external factors may or may not have influenced sagittal pelvic alignment during followup. Kobayashi et al [22] investigated a change of sagittal spinal alignment in 100 adult volunteers for more than 10 years. Sacral inclination angle significantly decreased (posteriorly tilted) in 10 years, but the mean difference in sacral inclination angle was only 7.5° for 10 years. Mendoza-Lattes et al [23] investigated the natural history of spinopelvic alignment with a cross-sectional
943
study and systematic review of the literature. In their study, the average sacral slope of asymptomatic subjects tended to be unaffected by advancing age. These studies indicated that aging alone does not change PA so much. Pelvic tilt angle changes were noted after THA. In addition, in some patients, dPA changes were noted after THA. These changes may be related to the hip arthroplasty or other contributing factors. We believe that other contributing factors already affect the standing and supine PA before THA and, also, that these factors affect the PA after THA as they did before THA. Therefore, when evaluating the 2- to 4-year longitudinal change in PA in the same patients, we think that the effect of THA might be much higher than those of other contributing factors. This study does not have a control group. In this study, our interests were focused on the change in PA after THA in the standing and supine positions in patients with OA. A number of patients with OA have knee contracture or lumbar degeneration because of hip OA. If we were to try and investigate only the effect of THA on the change in PA, the control group must be patients with OA, who should undergo THA. Because we considered it difficult to have such a control group, we studied the longitudinal change in PA after THA. To the best of our knowledge, this is the first report to evaluate the longitudinal change in PA in the standing and supine positions before and after THA for more than 2 years. If surgeons can predict postsurgical change in PA before THA from standard radiographs without any other special examination such as computed tomography or motion analysis, it will be very useful because they can plan the anteversion of the cup with reference to the postoperative standing PA or with reference to the postoperative change in dPA. From this study, we recommend that surgeons take into consideration the standing and supine radiographs of the pelvis before THA, especially with aged female patients. If the pelvis shows increased tilt in PA, the patient has a risk to show a large dPA after THA. In addition, if the radiograph shows a large dPA (N10°; approximately N1.5 cm of difference in the longitudinal diameter of the pelvis between the standing and supine radiographs) before THA, the patient has a risk to show a large dPA after THA (Table 2). For these patients, we recommend surgeons to align the cup with less anteversion. For these patients, we usually aim to place the cup with 10° of anteversion in the supine position. Thus, if the PA of the patient increases in the standing position, the cup anteversion angle stays inside the safe zone advocated by Lewinneck et al [24]. In addition, a surgeon can choose the implants that have a wider oscillation angle. Using these implants, the surgeon may avoid the impingement if PA shows a large increase after THA. Moreover, this study demonstrated that the aged patients showed a large dPA after THA. Considering this aging society and the long lifetime
944 The Journal of Arthroplasty Vol. 27 No. 6 June 2012 of modern prostheses, it might be better to align the cup with low anteversion considering the change in PA with aging. Not only before THA but also at the follow-up after THA, we suggest obtaining both standing and supine pelvic radiographs to check dPA. Even patients who show ideal implant position in the supine radiograph might experience dislocation due to large dPA. In summary, there were several cases in which sagittal pelvic tilt changed over 2 to 4 years after THA. The older patients showed a larger change in PA after THA. In particular, elderly female patients who showed increased posterior tilt in the standing or supine PA before THA or a large difference in dPA before THA, tended to show a large dPA a few years after THA. A large dPA may cause impingement, dislocation of the joint, or excessive wear due to edge loading. During surgery, surgeons should pay attention to the cup anteversion with reference to the change in PA after THA.
10.
11.
12.
13.
14.
15.
References 1. Hammerberg EM, Wood KB. Sagittal profile of the elderly. J Spinal Disord Tech 2003;16:44. 2. Jackson RP, McManus AC. Radiographic analysis of sagittal plane alignment and balance in standing volunteers and patients with low back pain matched for age, sex, and size: a prospective controlled clinical study. Spine 1994;19:1611. 3. Mayr E, Kessler O, Prassl A, et al. The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: spatial orientation of the pelvis in different positions. Acta Orthop 2005;76:848. 4. Schwab F, Lafage V, Patel A, et al. Sagittal plane considerations and pelvis in the adult patients. Spine 2009;34:1828. 5. Yoshimoto H, Sato S, Masuda T, et al. Spinopelvic alignment in patients with osteoarthrosis of the hip: a radiographic comparison to patients with low back pain. Spine 2005;30:1650. 6. Lembeck B, Mueller O, Reize P, et al. Pelvic tilt makes acetabular cup navigation inaccurate. Acta Orthop 2005; 76:517. 7. Nishihara S, Sugano N, Nishii T, et al. Measurements of pelvic flexion angle using three-dimensional computed tomography. Clin Orthop Relat Res 2003;411:140. 8. Doiguchi Y, Iwasaki K, Yamada K, et al. Correlation between pelvic inclination and radiological shape of the pelvic cavity. Seikei geka to saigai geka (Orthop Traumatology) 1992;41:641. 9. Ala Eddine T, Migaud H, Chantelot C, et al. Variations of pelvic anteversion in the lying and standing positions
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analysis of 24 control subjects and implications for CT measurement of position of a prosthetic cup. Surg Radiol Anat 2001;23:105. Babisch JW, Layher F, Amiot LP. The rationale for tiltadjusted acetabular cup navigation. J Bone Joint Surg Am 2008;90:357. Beckmann J, Luring C, Tingart M, et al. Cup positioning in THA: current status and pitfalls. A systematic evaluation of the literature. Arch Orthop Trauma Surg 2009;129:863. Haenle M, Heinter A, Mittelmeier W, et al. Assessment of cup position from plain radiographs: impact of pelvic tilting. Surg Radiol Anat 2007;29:29. Lazennec JY, Charlot N, Gorin M, et al. Hip-spine relationship: a radio-anatomical study for optimization in acetabular cup positioning. Surg Radiol Anat 2004;26:136. Paratte S, Pagnano MW, Coleman-Wood K, et al. Variation in postoperative pelvic tilt may confound the accuracy of hip navigation system. Clin Orthop Relat Res 2009;467:43. Shon WY, Gupta S, Biswal S, et al. Validation of a simple radiographic method to determine variations in pelvic and acetabular cup sagittal plane alignment after total hip arthroplasty. Skeletal Radiol 2008;37:1119. Steppacher SD, Tannast M, Zheng G, et al. Validation of a new method for determination of cup orientation in THA. J Orthop Res 2009;27:1583. Blondel B, Parratte S, Tropiano P, et al. Pelvic tilt measurement before and after total hip arthroplasty. Orthop Trauma Surg Res 2009;95:568. DiGioia III AM, Hafez MA, Jaramaz B, et al. Functional pelvic orientation measured from lateral standing and sitting radiographs. Clin Orthop Relat Res 2006;453:272. Di Schino M, Baudart F, Zilber S, et al. Anterior dislocation of a total hip replacement. Radiographic and CT-scan assessment. Behavior following conservative management. Orthop Trauma Surg Res 2009;95:573. Biedermann R, Tonin A, Krismer M, et al. Reducing the risk of dislocation after total hip arthroplasty: the effect of the acetabular component. J Bone Joint Surg Br 2005; 87:762. Tannast M, Murphy SB, Langlotz F, et al. Estimation of pelvic tilt on anteroposterior X-rays a comparison of six parameters. Skeletal Radiol 2006;35:14. Kobayashi T, Atsuta Y, Matsuno T, et al. A longitudinal study of congruent sagittal spinal alignment in an adult cohort. Spine 2004;29:671. Mendoza-Lattes S, Ries Z, Gao Y, et al. Natural history of spinopelvic alignment differs from symptomatic deformity of the spine. Spine 2010;35:E792. Lewinneck GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217.
Change in Pelvic Tilt Angle 2 to 4 Years After Total Hip Arthroplasty Naoya Taki, MD,* Naoto Mitsugi, MD, PhD,* Yuichi Mochida, MD, PhD,y Yasushi Akamatsu, MD, PhD,* and Tomoyuki Saito, MD, PhDz
Abstract: The purpose of this study was to evaluate the change in pelvic tilt angle (PA) in the sagittal plane in the standing and supine positions for 2 to 4 years after total hip arthroplasty (THA). Anteroposterior pelvic radiographs of 21 male and 65 female patients were investigated before and after THA yearly over 2 to 4 years. Both the standing and supine PA significantly posteriorly tilted after THA. The difference in PA between the standing and supine positions (dPA) significantly increased after THA. Although the PA in the standing and supine positions plateaued 1 year after THA, the dPA gradually increased. In addition, the percentage of patients who showed a difference of more than 10° in dPA tended to increase yearly. In particular, elderly female patients who showed posterior tilt in PA in the standing or supine positions or a large dPA before THA tended to show a dPA of more than 10° after THA. Keywords: total hip arthroplasty (THA), pelvic tilt, sagittal alignment, cup anteversion, standing position, cup orientation. © 2012 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) is an established and excellent treatment for patients with osteoarthritis (OA) of the hip. In this aging society, the number of patients with hip OA is increasing, in particular, the number of elderly patients. Generally, pelvic posterior tilt increases when people become old [1-5] because of the loss of lumbar lordosis, flexion contracture of the knee, and weakness of the back muscle and others. Among these patients, some show different radiographic pelvic tilt in the sagittal plane between the standing and supine positions. This difference alters the relationship between the cup and stem with different posture after THA. Lembeck et al [6] demonstrated that pelvic reclination of 1° will lead to functional anteversion of the cup of approximately 0.7°, which may cause impingement between the cup and stem. In addition, it may cause excessive wear due to edge loading of the
From the *Department of Orthopaedic Surgery, Yokohama City University Medical Center, Yokohama, Japan; yCenter for Rheumatoid Disease, Yokohama City University Medical Center, Yokohama, Japan; and zDepartment of Orthopaedic Surgery, Yokohama City University, Graduate School of Medicine, Yokohama, Japan. Submitted September 14, 2010; accepted October 6, 2011. The Conflict of Interest associated with this article can be found at doi:10.1016/j.arth.2011.10.003. Reprint requests: Naoya Taki, MD, Department of Orthopaedic Surgery, Yokohama City University Medical Center, 4-57 Urafunecho Minami-ku, Yokohama, 232-0024, Japan. © 2012 Elsevier Inc. All rights reserved. 0883-5403/2706-0019$36.00/0 doi:10.1016/j.arth.2011.10.003
joint. Thus, the change in pelvic tilt warrants further study. Nishihara et al [7] observed the pelvic tilt angle (PA) of 101 patients who had undergone THA before and 1 year after THA. They reported that the difference in the standing and supine PA before and 1 year after surgery was less than 10° in 90% of the patients. However, there are no reports concerning the difference in PA between the standing and supine positions (dPA) more than 1 year after THA. The purposes of this study were to evaluate the change in PA in the sagittal plane in the standing and supine positions for 2 to 4 years after THA and to investigate the factors that may contribute to the dPA.
Materials and Methods This retrospective study was approved by our institutional review board. Between November 2004 and December 2007, 178 primary THAs were performed by 5 surgeons in the same surgery team in our institution. One patient (2 joints) died because of cancer. Fourteen joints were excluded because of contralateral THA within 2 years. Fourteen rheumatoid patients were excluded. Sixteen patients have not returned within 2 years. Forty-six patients had not taken suitable radiographs for this study. Finally, the remaining 86 patients were enrolled in this study. There were 21 males and 65 females. Sixty-nine patients had developmental dysplasia of the hip, 2 patients had primary OA of the hip, 1 patient had posttraumatic OA, and 14 had osteonecrosis of the femoral head. Mean age at surgery was 64 ±
940
Change in Pelvic Tilt After THA Taki et al
Results Mean PA before THA was 22.6° ± 10.4° in the standing position and 18.5° ± 8.0° in the supine position. Mean PA 1 year after THA was 26.5° ± 10.5° in the standing position and 21.2° ± 7.3° in the supine position. Pelvic tilt angle gradually increased (posteriorly tilted) after surgery. The mean PA in the standing and supine positions at each time point was significantly higher than that before THA. The PA at each time point, except supine PA 4 years after surgery, showed a positive correlation to age at THA. The change in PA was the largest 1 year after THA. The change in PA appears to plateau after 1 year (Table 1).
T
Table 1. Pelvic Tilt Angle and Change in PA in the Standing and Supine Positions
N Standing PA Supine PA Change in standing PA Change in supine PA
Before THA
1 y after THA
2 y after THA
3 y after THA
4 y after THA
86 22.6 ± 10.4 18.5 ± 8.0 0
86 26.5 ± 10.5* 21.2 ± 7.3* 3.9 ± 6.2 *
86 27.9 ± 10.6* 21.1 ± 7.1* 5.3 ± 7.1 *
55 26.7 ± 10.9* 20.8 ± 7.8* 5.1 ± 5.7 *
32 29.1 ± 11.7* 22.3 ± 7.4* 5.2 ± 6.2 *
0
2.7 ± 4.4 * 2.6 ± 3.9 * 3.0 ± 4.2 * 2.6 ± 3.2 *
* P b .05, paired t test (mean ± SD).
There were only 5 patients (6%) who showed a change of more than 10° in the supine PA at the final follow-up point compared with the supine PA before surgery. However, with PA in the standing position, 12 patients (14%) showed a change of more than 10° 1 year after THA compared with that before surgery. At 2 years, 21 patients (24%); at 3 years, 14 patients (25%); and at 4 years, 5 patients (16%) showed a change of more than 10° in the standing PA. The older aged patients tended to show a greater PA than the younger aged patients. In addition, the dPA seemed to be larger in the older aged patients than in the younger aged patients (Fig. 2). Although the change in PA seemed to plateau 1 year after THA, dPA seemed to increase yearly. The percentage of patients who showed a difference of more than 10° in dPA was 9.3% before THA, 16.3% at 1 year, and 28.1% at 4 years after THA (Fig. 3). The factors that may contribute to the larger dPA 2 to 4 years after surgery are female sex, age at THA, supine PA, standing PA, and dPA before THA (Table 2). For 40 35 30
PA (degree)
9 years (mean ± SD) with a range of 39 to 85 years. Mean body mass index was 24.6 ± 3.8 kg/m 2 with a range of 17.5 to 46.7 kg/m 2. Standardized anteroposterior radiographs of the pelvis were obtained in the supine and standing positions before surgery and every year after. Fifty-five patients were evaluated for 3 years and 32 patients for 4 years after surgery. Pelvic tilt angle was calculated from these radiographs in accordance with the method of Doiguchi et al [8]. Briefly, the transverse diameter (T) and longitudinal diameter (L) of the pelvis were measured from a digital image (Fig. 1A). Pelvic tilt angle was calculated using the following formula: −67 × L/T + 55.7 for males and −69 × L/T + 61.6 for females. Reported mean PA was 20° (Fig. 1B). Measurements were taken 3 times (before surgery, 1 year after surgery, and 2 years after surgery) in 31 patients, 4 times (3 times plus 3 years after surgery) in 23 patients, and 5 times (4 times plus 4 years after surgery) in 32 patients. All measurements were taken in the standing and supine radiographs at each time point. Statistical analysis was performed using Stat Mate III (ATMS, Tokyo, Japan). The mean values of all the subgroups were compared using Mann-Whitney U test or χ 2 test. The mean values of each time point were compared using paired t test. Correlations were analyzed with Pearson correlation analysis.
941
25 20 15 10
L
PA
group 1 (standing) group 2 (standing) group 3 (standing)
5
group 1 (supine) group 2 (supine) group 3 (supine)
0 Before THA
A
B
Fig. 1. Calculation of PA. Anteroposterior image (A) and lateral image (B) PA was calculated using the following formula: −67 × L/T + 55.7 for males and −69 × L/T + 61.6 for females. Reported mean PA was 20° [8].
1Y
2Y
3Y
4Y
after THA
Fig. 2. Change in PA with different generation. Graph shows mean PA in the standing (solid line) and supine (broken line) positions of 3 different generations. Group 1, age at THA was less than 60 years; group 2, age at THA was between 60 and 74 years; group 3, age at THA was 75 years or older. The number of the patients in groups 1, 2, and 3 are 29, 41, and 16, respectively.
942 The Journal of Arthroplasty Vol. 27 No. 6 June 2012 100
10
6.7±7.2
6.7±6.9
dPA (degree)
5.2±5.8
dPA
4.0±5.0
50
5 29.1
28.1
Percentage (%)
5.9±6.0
23.6 16.3 9.3
0 Before THA
1Y
2Y
3Y
4Y
0
after THA
Fig. 3. Change in dPA and percentage of patients who showed more than 10° difference in dPA.
17 female patients, either the age at surgery was 72 years or older, the supine PA before THA was more than 22°, the standing PA before THA was more than 30°, or dPA before THA was more than 7°, and 10 of these 17 patients (59%) showed dPA of more than 10° at final follow-up.
Discussion In this study, we demonstrated that PA changes after THA. Recently, several reports have included concerns that radiographic measurement of cup position after THA is inaccurate because of pelvic tilt [6,9-16]. Therefore, it is important to evaluate PA after THA. There are several reports comparing the PA before and after THA [7,10,14,17,18]. Most of them compare the PA within 1 year. Nishihara et al [7] compared the standing PA before and 1 year after THA and reported that 13% of the patients in their study showed a change of more than 10° in PA compared with that before surgery. This percentage is almost the same as that in our study. Blondel et al [17] measured the standing PA before and 3 years after THA and reported that there was no significant difference in PA between the 2 time points. In addition, they reported that no patient showed a difference of more than 10° between the 2 time points. In our study, 25% of the patients who underwent THA showed a change of more than 10° in the standing PA 3 years after surgery. Four years after surgery, 16% of the patients showed a change of more than 10° in the standing PA. The difference in our findings might be due to the difference in the study criteria for the patients of each study. Our study included all of the patients who underwent THA. Blondel et al excluded the patients with spinal deformity or bilateral arthritis. Our result showed that the patients who showed a large change in PA after surgery tended to have increased posterior tilt in PA. One of the causes of increased posterior tilt in PA is a loss of lumbar lordosis. Therefore, the patients who showed a large change in PA might have a spinal deformity. Of course, the patients who had OA of the hip
may have a spinal deformity; it is dangerous to conclude that PA does not change 3 years after THA. Both the standing and supine PA showed the largest change 1 year after surgery. After 1 year, the changes in both the standing and supine PA tended to plateau. The standing and supine alignments of the pelvis are improved after surgery because of elimination of the contracture from the hip joint, relief of pain of the hip, and recovery of the strength of the gluteal and back muscles. It seems that most of this improvement is achieved within 1 year. In this study, we investigated the change in the dPA after THA. The reason for this was that when we see patients for follow-up after THA, some show a great dPA. Generally, PA increases from supine to standing position. If the PA increases, cup anteversion also increases. This may cause neck impingement. Because the cup anteversion increases in the standing position, excessive wear may occur due to edge loading. Some patients show so much anteversion of the cup due to extensively increased posterior tilt of the pelvis, that anterior dislocation of the hip might occur [19,20]. Therefore, we wanted to clarify the change in dPA after THA. As described by Babisch et al [10], we also considered that less than 10° difference in dPA may not increase the risk of hip dislocation. In addition, we wanted to clarify the factors that contribute to the change in dPA. The mean dPA before surgery was 4.0° ± 5.0°, which is similar to those in the report of Nishihara et al [7] and the report of Babisch et al [10] (2.0° ± 6.4° and 5.4° ± 4.6°, respectively). The percentage of patients who showed a difference of more than 10° in dPA before THA was almost the same as that in the report of Nishihara et al. Although the changes in mean PA in both the standing and supine positions tended to plateau from 1 year after THA, our result showed that dPA tended to increase yearly. Moreover, the percentage of the patients who showed a dPA of more than 10° tended to increase Table 2. Correlations Between dPA after THA and Preoperative Patient Factors dPA n Female sex * Age at THA † Supine PA before THA † Standing PA before THA † dPA before THA †
2 y after THA
3 y after THA
4 y after THA
86 P = .027 P b .001, r = 0.36 P = .002, r = 0.34 P b .001, r = 0.38 P = .024, r = 0.24
55 P = .27 P = .006, r = 0.37 P = .002, r = 0.40 P b .001, r = 0.52 P b .001, r = 0.48
32 P = .24 P = .21
* χ2 Test. † Pearson correlation analysis.
P = .02, r = 0.40 P = .005, r = 0.49 P = .054
Change in Pelvic Tilt After THA Taki et al
yearly. This demonstrated that, in some cases, dPA increases after THA within a few years. Mayr et al [3] measured the pelvic inclination in the standing and supine positions of 120 volunteers (60 healthy controls, 30 patients who had undergone THA, and 30 patients with coxarthrosis). They found relationships between age and standing PA and between age and dPA. These relationships are also found at most of the time points in our study. However, they concluded that the mean difference between standing and supine positions in all 120 patients was only 1.1°, which is clinically irrelevant. Their subjects are different from those in our study. In addition, their study is cross-sectional, whereas our study investigated longitudinal change after THA. Therefore, we think that it is clinically important for surgeons to be aware that dPA changes, in some cases, within a few years after THA. Then, we investigated the factors that may contribute to the change in dPA after surgery. The factors that might contribute to dPA change after THA were female sex, the age at surgery, the supine PA, the standing PA, and the dPA before THA. One of the limitations of this study was that we measured PA from anteroposterior radiographs in accordance with the method described in a previous report. Pelvic tilt angle was calculated from the transverse diameter and longitudinal diameter of the pelvis measured from the digital image. Tannast et al [21] reported that the correlation between actual PA and the PA measured from the transverse diameter and longitudinal diameter of the pelvis was moderately strong. As the PA calculated from anteroposterior radiograph was not precise, we compared PA in the same patient. There is less accidental error in calculating the change in PA in the same patient than comparing PA among different patients. Anteroposterior radiograph is a standard method to evaluate the preoperative and postoperative status of the hip joint. It is useful for surgeons to have information of the change in PA obtained from anteroposterior radiograph. Sagittal pelvic alignment not only is determined by the hip joint but also is affected by spinal alignment, contracture of the knees, and strength of the muscles. In this study, we did not evaluate these other factors. We only checked whether the patients had undergone surgery during the follow-up period. No patients had knee arthroplasty or spinal surgery during the follow-up period. Therefore, such external factors may or may not have influenced sagittal pelvic alignment during followup. Kobayashi et al [22] investigated a change of sagittal spinal alignment in 100 adult volunteers for more than 10 years. Sacral inclination angle significantly decreased (posteriorly tilted) in 10 years, but the mean difference in sacral inclination angle was only 7.5° for 10 years. Mendoza-Lattes et al [23] investigated the natural history of spinopelvic alignment with a cross-sectional
943
study and systematic review of the literature. In their study, the average sacral slope of asymptomatic subjects tended to be unaffected by advancing age. These studies indicated that aging alone does not change PA so much. Pelvic tilt angle changes were noted after THA. In addition, in some patients, dPA changes were noted after THA. These changes may be related to the hip arthroplasty or other contributing factors. We believe that other contributing factors already affect the standing and supine PA before THA and, also, that these factors affect the PA after THA as they did before THA. Therefore, when evaluating the 2- to 4-year longitudinal change in PA in the same patients, we think that the effect of THA might be much higher than those of other contributing factors. This study does not have a control group. In this study, our interests were focused on the change in PA after THA in the standing and supine positions in patients with OA. A number of patients with OA have knee contracture or lumbar degeneration because of hip OA. If we were to try and investigate only the effect of THA on the change in PA, the control group must be patients with OA, who should undergo THA. Because we considered it difficult to have such a control group, we studied the longitudinal change in PA after THA. To the best of our knowledge, this is the first report to evaluate the longitudinal change in PA in the standing and supine positions before and after THA for more than 2 years. If surgeons can predict postsurgical change in PA before THA from standard radiographs without any other special examination such as computed tomography or motion analysis, it will be very useful because they can plan the anteversion of the cup with reference to the postoperative standing PA or with reference to the postoperative change in dPA. From this study, we recommend that surgeons take into consideration the standing and supine radiographs of the pelvis before THA, especially with aged female patients. If the pelvis shows increased tilt in PA, the patient has a risk to show a large dPA after THA. In addition, if the radiograph shows a large dPA (N10°; approximately N1.5 cm of difference in the longitudinal diameter of the pelvis between the standing and supine radiographs) before THA, the patient has a risk to show a large dPA after THA (Table 2). For these patients, we recommend surgeons to align the cup with less anteversion. For these patients, we usually aim to place the cup with 10° of anteversion in the supine position. Thus, if the PA of the patient increases in the standing position, the cup anteversion angle stays inside the safe zone advocated by Lewinneck et al [24]. In addition, a surgeon can choose the implants that have a wider oscillation angle. Using these implants, the surgeon may avoid the impingement if PA shows a large increase after THA. Moreover, this study demonstrated that the aged patients showed a large dPA after THA. Considering this aging society and the long lifetime
944 The Journal of Arthroplasty Vol. 27 No. 6 June 2012 of modern prostheses, it might be better to align the cup with low anteversion considering the change in PA with aging. Not only before THA but also at the follow-up after THA, we suggest obtaining both standing and supine pelvic radiographs to check dPA. Even patients who show ideal implant position in the supine radiograph might experience dislocation due to large dPA. In summary, there were several cases in which sagittal pelvic tilt changed over 2 to 4 years after THA. The older patients showed a larger change in PA after THA. In particular, elderly female patients who showed increased posterior tilt in the standing or supine PA before THA or a large difference in dPA before THA, tended to show a large dPA a few years after THA. A large dPA may cause impingement, dislocation of the joint, or excessive wear due to edge loading. During surgery, surgeons should pay attention to the cup anteversion with reference to the change in PA after THA.
10.
11.
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13.
14.
15.
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