261 © 2013 Chinese Orthopaedic Association and Wiley Publishing Asia Pty Ltd
Change in Spinal Alignment after Total Hip Arthroplasty Kristen E Radcliff, MD, Fabio Orozco, MD, Nicholas Molby, BS, Lawrence Delasotta, MD, Eric Chen, BS, Zachary Post, MD, Alvin Ong, MD Department of Orthopaedic Surgery, Rothman Institute, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, USA
Objective: The study hypotheses were that: (i) there would be a difference in sagittal plane alignment between patients with symptomatic osteoarthritis of the hip and those with lumbar degenerative disk disease; and (ii) that sagittal plane lumbar alignment would change following total hip arthroplasty (THA). Methods: In this prospective study, a series of patients without back pain or lumbar complaints who were scheduled to undergo THA underwent lateral lumbar radiography prior to and nine months after elective THA. Radiographic measurements of lumbar alignment included sacral slope, lumbar lordosis, and L1 axis S1 distance (L1 ASD). All measurements were performed on upright, standing, lateral radiographs. A control group of patients underwent serial radiography over the same period for evaluation of lumbar degenerative disease. The independent sample t-test was used to compare the mean sacral slope, lumbar lordosis, and L1 ASD in the THA and control groups. Results: There were 12 patients in the THA group and 34 in the control group. Mean follow-up was 9 months. Average age in the control group was 63 years and in the THA group 64.2 years. The sacral slope was greater in the THA group (mean, 23°) than in the lumbar patients (control group) and this difference was statistically significant (mean, 11°, P = 0.001). There were no statistically significant differences between THA and control patients in lumbar lordosis or L1 ASD. Change before and after THA was measured. There were no statistically significant differences in assessed radiographic variables preoperatively versus postoperatively. Conclusion: There is no significant change in spinal alignment after unilateral THA. At baseline, patients with symptomatic spine complaints have less sacral slope than their hip arthroplasty counterparts. Key words: Hip arthroplasty; Hip spine syndrome; Lumbar alignment; Sagittal balance lumbar
Introduction ip spine syndrome (HSS) is a symptomatic pain syndrome in the spine that develops following hip reconstruction1. HSS commonly occurs in patients in whom total hip arthroplasty (THA) has induced new, or exacerbated preexisting, lumbar degenerative disease2–4. The precise cause of HSS is unknown. It has been postulated that change in the mechanics of the pelvis may increase spinal joint loading5, particularly in the setting of underlying spinal abnormalities6. Thus, hip deformity correction7,8, contracture release9,10 or reconstruction11,12 may alter kinematics and contribute to symptomatic spinal joint degeneration.
Change in sagittal plane alignment is a major predictor of the outcome of lumbar reconstruction13. Kyphotic lumbar alignment (due to loss of lumbar lordosis secondary to degenerative disk disease [DDD]) increases the gravitational moment arm, thus increasing the work of the paraspinous muscles14. To maintain upright posture, patients compensate for sagittal plane lumbar deformities by sagittal plane pelvic retroversion through the hips15, resulting in an increased pelvic tilt16–18. The purpose of this study was to assess the relationship between sagittal plane lumbopelvic alignment and HSS19,20. The study hypotheses were that: (i) there would be a
Address for correspondence Kristen E Radcliff, MD, Department of Orthopaedic Surgery, Rothman Institute, Thomas Jefferson University, Philadelphia, PA, USA 19107 Tel: 001-609-5733301; Fax: 001-215-9554322; Email: [email protected]
, [email protected]
Disclosure: The authors of this manuscript do not have any conflicts of interest to report. Received 19 June 2013; accepted 23 September 2013
Orthopaedic Surgery 2013;5:261–265 • DOI: 10.1111/os.12076
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Change in Spinal Alignment after THA
statistically significant difference in sagittal plane alignment between patients with symptomatic osteoarthritis of the hip and those with lumbar degenerative disc disease; and (ii) that sagittal plane variables would change following total hip arthroplasty. This information may be useful both for identifying risk factors for degenerative disk disease and identifying aspects of reconstruction that may predispose toward the development of HSS. Materials and Methods nstitutional review board approval was obtained prior to study onset. Inclusion criteria were consecutive patients without history of back pain or lumbar spine complaints who were scheduled to undergo THA for symptomatic, unilateral hip osteoarthritis due to degenerative joint disease. Fifty-five such patients were screened. However, of these only twelve were eligible for enrollment because the remainder had either current or past spine complaints. The patients underwent elective THA via an anterolateral approach. During the same period, a control group of patients with symptomatic lumbar degenerative disease was selected. Exclusion criteria were patients who had previously undergone total hip arthroplasty, spinal surgery, infection, fractures, avascular necrosis and neoplastic conditions. Lumbar radiographic measurements were performed immediately before the THA and radiographic follow-up was performed at soon as possible after patients had achieved normal gait and kinematics and pain free motion without an assistive device following hip arthroplasty, which was an average of 9 months postoperatively. The control (lumbar DDD) group underwent initial and final radiographs at an average of 9 months apart. Measurements included the sacral slope (SS)21, lumbar lordosis (LL) and L1 axis to S1 distance (L1ASD)22. All measurements were performed on upright, standing, lateral radiographs (Figs 1 and 2). SS was measured as the angle between the S1 endplate and an idealized horizontal reference line. LL was the angle subtended by the S1 superior endplate and the L1 superior endplate. L1ASD reflects lumbar sagittal balance by measuring the forward position of a reference line from the anterior superior endplate of the L1 vertebral body to the posterior superior S1 endplate. To account for differences in patient height when assessing L1ASD, the angle between the S1 endplate and a line from the posterosuperior corner of S1 to the anterior corner of the L1 vertebral body was termed the L1 inclination and this was also measured. To assess differences between patients with THA and DDD, the independent sample t-test was used to compare the mean SS, LL and L1ASD in the THA and control groups. To assess changes in sagittal alignment after THA, the paired samples t-test was used to compare pre- and post-arthroplasty measurements in each patient.
Results here were 12 patients in the THA cohort and 34 in the lumbar DDD group. Mean follow-up was 9 months. Average age in the DDD group was 63 years and in the THA
Fig. 1 Preoperative sagittal spinal measurements. (A) Sacral slope. Angle between the S1 endplate and the horizontal. (B) Lumbar lordosis. Angle between S1 superior endplate and L1 superior endplate. (C) L1 axis S1 distance. Distance between the posterior superior corner S1 endplate and a vertical line from L1. (D) L1 inclination. Angle between S1 endplate and a vertical line from L1.
group 64.2 years (P > 0.05). There was no difference between groups in the sex distribution (55% women in both groups, P = 1). The mean values in the THA and DDD populations were calculated. The SS was significantly greater in the THA than in the DDD group (Table 1). Both before and after hip replacement, the SS was greater in the THA patients (mean, 23°) than in the DDD patients (mean, 11°, P = 0.001). There were no statistically significant differences between THA and control patients in pre- or postoperative LL, L1 ASD or L1 inclination (P > 0.05). Changes in assessed radiographic variables were compared before and after THA in the THA population to
>0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 0.05
P value* *Paired samples t-test
development of subsequent symptomatic spinal disease3,23 based on the observation that some patients develop symptomatic DDD following THA. However, no previous study has identified quantifiable changes in spinal radiographic measurements following THA. We failed to identify a change in assessed radiographic variables following THA. We therefore postulate that HSS is caused by soft tissue factors, such as release of the hip joint capsule or changes in musculature. Alternatively, HSS may be a consequence of increased physical demand on adjacent joints following THA. Interestingly, this study identified that patients with symptomatic hip osteoarthritis have a different baseline pelvic alignment than patients with symptomatic lumbar DDD. The greater SS in the former group corresponds with a more vertical sacral orientation caused by pelvic flexion (anterior rotation of the sacrum over the centers of the femoral heads). Such pelvic flexion may create acetabular over-coverage, thereby resulting in femoroacetabular impingement and early development of hip osteoarthritis. The measurements in both of our groups were similar to those of asymptomatic patients in published reports21. We chose a case control study design to test our hypothesis because little is known about the relationship between THA and HSS. Limitations of this study design are that it is observational, and confounding factors may have confused the relationship between THA and spinal alignment. It may be inaccurate to extrapolate these data from patients with endstage degenerative joint disease requiring THA to patients with mild degenerative joint disease. In addition, the duration of follow-up was short compared with many other clinical outcome studies. We deliberately selected a short duration of follow-up to isolate changes in alignment following hip arthroplasty before any other confounding factors (such as onset of lumbar DDD) could cause secondary sagittal alignment changes. Because patients may temporarily have a limp or altered kinematics immediately after hip arthroplasty, we attempted to select the earliest time by which their gaits would
have normalized but secondary changes would not have occurred. Another limitation is that the small number of patients in both groups may have produced a type II error. Although 55 patients were screened for the study (THA) cohort, the majority had to be excluded because of historical or current lumbar spine complaints. In addition, because of concern about the radiation dosage of lumbar radiographs, we limited the number of patients in the study. We intended this to be a pilot study that provided preliminary information to support a larger study. The purpose of this study was to identify change in pelvic variables in patients who were completely asymptomatic for spinal complaints. Future studies may be able to increase enrollment by including patients with simultaneous complaints or historical lumbar complaints, although these would be different study populations. Finally, since we observed a statistically significant difference between cohorts and therefore rejected the null hypothesis of “no difference”, we believe that there is less likely to be a type II error in our analysis. Another limitation is the lack of clinical data to supplement the radiographic analysis. Ideally, we would have included pelvic tilt and pelvic incidence measurements among the radiographic measurements. However such measurements rely upon precise localization of the center of the femoral head and may be confounded by the THA, both because the metallic implant may overlie the native hip and obscure precise localization of the midpoint of the centers of the femoral head and because the position of the center of the femoral head may change after THA. This prospective case control study was designed to be an economical and low-radiation exposure means of assessing the need for a future cohort or randomized study to explain HSS. In conclusion, these results indicate that there is no significant change in spinal alignment after unilateral THA. At baseline, patients with symptomatic spine complaints have less SS than their hip arthroplasty counterparts. HSS may be caused by factors other than change in spinal posture and alignment after arthroplasty.
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