The Current Knowledge on Spinopelvic Mobility

Recent studies may suggest that our conventional knowledge of risk factors for dislocation may need rethinking. Previous studies have demonstrated a large majority of total hip arthroplasty instability with acetabular cups implanted in safe zones. Recently discovered spinopelvic motion is a coordinated biomechanical relationship among acetabular anteversion, pelvic tilt, and lumbar lordosis. Classification includes normal, hypermobile, stiff, stuck standing, stuck sitting, and fused. Normal spinopelvic motion from standing to sitting occurs with hip flexion, posterior sacral tilt, and decreased lumbar lordosis to accommodate a flexed femur and prevent impingement and dislocation. Acetabular cup implantation ideally is adapted based on spinopelvic interactions. This may lower the rate of impingement and subsequent dislocation. These new biomechanical interactions may provide a better understanding of the safe zones of anteversion and inclination.     

Total Hip Arthroplasty Patients With Fixed Spinopelvic Alignment Are at Higher Risk of Hip Dislocation

Background

Sitting radiographs have been used as a pre-operative tool to plan patient-specific total hip arthroplasty (THA) component position that would improve hip stability. Previous work has demonstrated that spinal mobility may impact functional acetabular position when seated. We sought to determine whether patients who dislocate following THA have different sitting spinopelvic alignment or acetabular component orientation compared to patients who did not dislocate.

Total hip arthroplasty in fused hips with spine stiffness in ankylosing spondylitis

Ankylosing spondylitis (AS) is characterized by involvement of the spine and hip joints with progressive stiffness and loss of function. Functional impairment is significant, with spine and hip involvement, and is predominantly seen in the younger age group. Total hip arthroplasty (THA) for fused hips with stiff spines in AS results in considerable improvement of mobility and function. Spine stiffness associated with AS needs evaluation before THA. Preoperative assessment with lateral spine radiographs shows loss of lumbar lordosis. Spinopelvic mobility is reduced with change in sacral slope from sitting to standing less than 10 degrees conforming to the stiff pattern. Care should be taken to reduce acetabular component anteversion at THA in these fused hips, as the posterior pelvic tilt would increase the risk of posterior impingement and anterior dislocation. Fused hips require femoral neck osteotomy, true acetabular floor identification and restoration of the hip center with horizontal and vertical offset to achieve a good functional outcome. Cementless and cemented fixation have shown comparable long-term results with the choice dependent on bone stock at THA. Risks at THA in AS include intraoperative fractures, dislocation, heterotopic ossification, among others. There is significant improvement of functional scores and quality of life following THA in these deserving young individuals with fused hips and spine stiffness.     

Total Hip Arthroplasty in the Spinal Deformity Population: Does Degree of Sagittal Deformity Affect Rates of Safe Zone Placement,Instability, or Revision?

Background

Changes in spinal alignment and pelvic tilt alter acetabular orientation in predictable ways, which may have implications on stability of total hip arthroplasty (THA). Patients with sagittal spinal deformity represent a subset of patients who may be at particularly high risk of THA instability because of postural compensation for abnormal spinal alignment.

Can pelvic tilting be ignored in total hip arthroplasty?

INTRODUCTION

The orientation of acetabular component is influenced by pelvic tilt, body position and individual variation in pelvic parameters. Most post-operative adverse events may be attributed to malposition of the component in the functional position. There is evidence that orientation of the pelvis changes from the supine to standing position. Authors report a case of recurrent dislocation after total hip arthroplasty due to excessive pelvic tilting.PRESENTATION OF CASE A 69-year old female with coxarthrosis had undergone total hip replacement with recurrent dislocation of the hip on bearing weight in spite of using constrained acetabular component.

DISCUSSION

Our case report substantiates the influence of pelvic tilt, incurred by a sagittal deformity of spine, on dynamic orientation of the acetabular cup which was positioned in accordance with the anatomic landmarks alone. If the reference is only bony architecture and dynamic positions of the pelvis are not taken into account, improper functional orientation of the acetabular cup can result in sitting and standing positions. These can induce instability even in anatomically appropriately oriented acetabular component.

CONCLUSION

The sagittal position of pelvis is a key factor in impingement and dislocation after total hip arthroplasty. Pelvic tilting affects the position of acetabular component in the sagittal plane of the body as compared with its anatomic position in the pelvis. We suggest a preoperative lateral view of spine-pelvis, in upright and supine position for evaluation of a corrective adaptation of the acetabular cup accordingly with pelvic balance.     

Acetabular component orientation in intra- and postoperative positions in total hip arthroplasty

Introduction  In total hip arthroplasty (THA), acetabular component orientation has critically important effects on dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. The differences in the pelvic orientation in the intraoperative lateral position for insertion of acetabular component during operation and that in the postoperative supine position for evaluation of acetabular component orientation will be one of the factors, which make outliers in acetabular component orientation. We compared acetabular component orientation between intraoperative lateral position and postoperative supine position in 100 consecutive primary THAs. Materials and methods  A total of 100 consecutive primary THAs (between October 2004 and December 2005) in 100 patients performed by a single surgical team were investigated. Intraoperative anteroposterior radiographs of pelvis in the lateral position and postoperative anteroposterior radiographs of pelvis in the supine position were taken. Acetabular component orientation (vertical tilt and anteversion) were measured using computer software. Results  The absolute values of difference between measurements in the two positions were 5.3° ± 4.5° (mean ± SD) for vertical tilt and 5.1° ± 3.7° for anteversion. The difference in the vertical tilt between the two positions was significant (P < 0.0001). Conclusion  The difference in the acetabular component orientation between the two positions, which might be caused by the difference between intra- and postoperative pelvic orientation, should be considered during THA.     

Variability in Acetabular Component Position in Patients Undergoing Direct Anterior Approach Total Hip Arthroplasty Who Have Concomitant Spine Pathology

BackgroundHip instability following total hip arthroplasty (THA) can be a major cause of revision surgery. Physiological patient position impacts acetabular anteversion and abduction, and influences the functional component positioning. Osteoarthritis of the spine leads to abnormal spinopelvic biomechanics and motion, but there is no consensus on the degree of component variability for THAs performed by anterior approach. Therefore, we sought to present guidelines for changes in acetabular component positioning between supine and standing positions for patients undergoing primary THA by a uniform anterior approach.MethodsPerioperative patient radiographs of the pelvis and lumbar spine were collected. Images were used to determine acetabular component positioning and degree of coexisting spinal pathology, categorized as a Lane Grade (LG). Final analysis of variance was performed on a sample size of 643 anterior primary THAs.ResultsFrom supine to standing position, as the severity of lumbar pathology increased the change in anteversion also increased (LG:0 = ?0.11° ± 4.65°, LG:1 = 2.02° ± 4.09°, LG:2-3 = 5.78° ± 5.72°, P < .001). The mean supine anteversion in patients with absent lumbar pathology was 19.72° ± 5.05° and was lower in patients with worsening lumbar pathology (LG:1 = 18.25° ± 4.81°, LG:2-3 = 16.73° ± 5.28°, P < .001).ConclusionPatients undergoing primary THA by anterior approach with worsening spinal pathology have larger increases in component anteversion when transitioning from supine to standing positions. Consideration should be given to this expected variability when placing the patient’s acetabular component.     

伴腰椎退变性后凸畸形的人工全髋关节置换安放髋臼假体前倾角的策略

目的：探讨伴腰椎退变性后凸畸形患者行人工全髋关节置换时如何更合理地安放髋臼假体的前倾角。方法：纳入2017年12月至2019年10月行人工全髋关节置换术的患者122例,均伴腰椎退变性后凸畸形,分为试验组和对照组,各61例。试验组男25例,女36例;年龄中位数67.0岁;病程中位数46.0个月;术中根据骨盆前平面支架,按不同类型,设置安装髋臼前倾角的功能性骨盆平面。对照组男27例,女34例;年龄中位数67.0岁;病程中位数42.0个月;对照组以传统的方法设定前倾角。术后随访3个月,记录两组患者手术时间、术中出血量,统计3个月内感染脱位发生,记录手术前和术后3个月Harris评分,测量术后3个月患者站立位功能性前倾角。结果：试验组和对照组手术时间、术中出血量比较差异无统计学意义（P=0.918,0.381）;术后3个月内两组均无感染;对照组1例髋关节脱位,试验组无脱位。手术前后Harris评分比较差异无统计学意义（P>0.05）。3个月后复查骨盆站立位X线片示：髋臼假体功能性前倾角在安全区外的患者数量试验组比对照组少（P=0.048）;并且试验组在15°~20°范围内更集中（P<0.001）。。结论：伴有腰椎退变性后凸畸形的人工髋关节置换,根据术前对患者的评估分类,可以借助骨盆前平面参考支架,获得更佳的髋臼假体功能性前倾角。     

Acetabular and Femoral Anteversions in Standing Position are Outside the Proposed Safe Zone After Total Hip Arthroplasty

Background

Although most hip dislocations occur in either standing or sitting position, the safe zone for implant position is defined for the supine position. Our goal was to determine preoperative and postoperative pelvis and hip orientations and whether the safe zone defined in supine position can be used to assess standing radiographs.

Measurements of pelvic flexion angle using three-dimensional computed tomography

The purpose of the current study was to evaluate whether safe acetabular component position depends on differences in pelvic location between the supine, standing, and sitting positions. The subjects of the current study were 101 patients who had total hip arthroplasty. Anteroposterior radiographs of the pelvis with the patients in the supine, standing, and sitting positions were obtained preoperatively and 1 year after total hip arthroplasty. Computed tomography images of the pelvis were obtained preoperatively. Using image matching between the three-dimensional computed tomography model and anteroposterior radiograph, pelvic flexion angles with the patient in the supine, standing, and sitting positions were calculated. The mean preoperative pelvic flexion angle was 5 degrees +/- 9 degrees (range, -37 degrees -30 degrees ) in the supine position, 3 degrees +/- 12 degrees (range, -46 degrees -33 degrees ) in the standing position, and -29 degrees +/- 12 degrees (range, -62 degrees -10 degrees ) in the sitting position. Because there was much intersubject variability in pelvic flexion angle, it is not appropriate to determine orientation of the acetabular component from anatomic landmarks. In 90% of the cases, the difference in pelvic flexion angle between the supine and standing positions preoperatively was 10 degrees or less. In 90% of the cases, there was 20 degrees or greater extension of the pelvis from the supine position to the sitting position preoperatively, and the safe range of flexion of the hip from anterior prosthetic impingement in the sitting position was 20 degrees or greater than that in the supine position. Preoperative pelvic position in each case was almost completely maintained 1 year after total hip arthroplasty. It is reasonable to regard the pelvic position in the supine position as the functional pelvic position and proper pelvic reference frame in determining optimal orientation of the acetabular component in 90% of cases before and 1 year after total hip arthroplasty, although an adjustment of orientation of the acetabular component was needed for the remaining cases.     

Spinal Factors Influencing Change in Pelvic Sagittal Inclination From Supine Position to Standing Position in Patients Before Total Hip Arthroplasty

In some atypical patients, pelvic sagittal inclination (PSI) changes posteriorly by > 10° from supine to standing position before total hip arthroplasty (THA). Several studies have suggested PSI in standing position is related to lumbar degeneration. The purpose of this study was to investigate spinal factors influencing changes in PSI from supine to standing position before THA. Participants comprised 163 consecutive patients who had undergone THA. Presence of compression fractures, presence of lumbar spondylolisthesis, thoracic kyphosis angle, lumbar lordosis angle, S1 anterior tilt angle and T4 plumb line position were investigated as spinal factors. Presence of compression fractures, age, presence of lumbar spondylolisthesis and small S1 anterior tilt angle were independently associated with posterior change in PSI from supine to standing position in patients before THA.     

脊柱矢状面平衡与否对于指导髋臼假体定位的重要意义

自Lewinnek提出的"安全区"概念以来便得到了大家的广泛认同,但近年来许多学者发现即使髋臼假体摆放在"安全区内"仍有很多人工髋关节置换术发生不明原因的假体脱位.并开始质疑"安全区"是否真的适合所有患者.脊柱退变、畸形,腰椎融合等会导致脊柱矢状面不平衡及骨盆活动的改变,进而导致髋臼方向的改变,最终导致人工全髋关节置换...     

Pelvic tilt between supine and standing after total hip arthroplasty an RSA up to seven years after the operation

The pose of the prosthetic components after total hip arthroplasty (THA) is commonly evaluated on conventional radiographs. Any change of the pelvic position after the operation in supine and between supine and standing position with time will influence validity of the measurements. We evaluated the changed pelvic tilt angle (PTA) in supine and standing position up to 7 years after operation. The aims of our study were (a) to evaluate if the PTA change over time after THA, (b) to assess any difference in PTA between supine and standing positions, and (c) to investigate whether factors such as gender, the condition of the opposite hip or low‐back pain have any influence on PTA after THA. Repeated radiostereophotogrammetric radiographs of 106 patients were studied. Patients had been examined in the supine position postoperatively, and in both supine and standing positions at 6 months and 7‐year follow‐up. Measurements of supine patients showed an increasing mean posterior pelvic tilt over time. From supine to standing, the pelvis tilted in the opposite direction. At 6 months, the mean anterior tilt was 3.6° ± 3.8° (confidence interval [CI]: 2.8° to 4.3°) which increased to 6.4° ± 3.9° (CI: 5.7° to 7.2°) at 7 years. The mean changes in pelvic rotations around the longitudinal and sagittal axis were less than 1 degree, in both positions. In individual patients, this change reached about 11.0 degrees in supine and 18.0 degrees when standing.     

The Use of Fluoroscopy During Direct Anterior Hip Arthroplasty: Powerful or Misleading?

Background

Direct anterior approach total hip arthroplasty (THA) with fluoroscopic assistance is growing in popularity. Variables such as pelvic tilt, c-arm technique, and patient positioning can affect the perceived fluoroscopic view. This study evaluates the effect of these variables on the position of the acetabular component.

Lumbar Spine Degeneration and Flatback Deformity Alter Sitting-Standing Spinopelvic Mechanics—Implications for Total Hip Arthroplasty

BackgroundSpinal degeneration and lumbar flatback deformity can decrease recruitment of protective posterior pelvic tilt when sitting, leading to anterior impingement and increased instability. We aim at analyzing regional and global spinal alignment between sitting and standing to better understand the implications of spinal degeneration and flatback deformity for hip arthroplasty.MethodsSpinopelvic parameters of patients with full-body sitting-standing stereoradiographs were assessed: lumbar lordosis (LL), spinopelvic tilt (SPT), pelvic incidence minus LL (PI-LL), sagittal vertical axis (SVA), and T1 pelvic angle (TPA). Lumbar spines were classified as normal, degenerative (disc height loss >50%, facet arthropathy, or spondylolisthesis), or flatback (degenerative criteria and PI-LL >10°). Independent t-tests and analysis of variance were used to analyze alignment differences between groups.ResultsAfter propensity matching for age, sex, and hip osteoarthritis grade, 57 patients per group were included (62 ± 11 years, 58% female). Mean standing and sitting SPT, PI-LL, SVA, and TPA increased along the spectrum of disease severity. Increasing severity of disease was associated with decreasing standing and sitting LL. The flatback group demonstrated the greatest sitting SPT, PI-LL, SVA, and TPA. The amount of sitting-to-standing change in SPT, LL, PI-LL, SVA, and TPA decreased along the spectrum of disease severity.ConclusionSpinal degeneration and lumbar flatback deformity both significantly decrease lower lumbar spine mobility and posterior SPT from standing to sitting in a stepwise fashion. The demonstrated hypomobility in flatback patients likely serves as a pathomechanism for the previously observed increased risk of dislocation in total hip arthroplasty.     

The acetabulum: The elusive home run of THR

The objective is to describe the current factors for optimizing positioning of the acetabular component in THR. The emphasis in cup placement today is personalizing the component position for each patientʼs anatomy rather than a “one size fits all” (always put the cup in the same position such as 45° inclination and 15° anteversion). To individualize, the arthroplasty requires remembering the operation is on both sides of the joint (combined anteversion) and implanting the cup in the functional plane of that patient, which requires knowledge of the pelvic tilt at surgery and the changes in the spine−pelvic−hip construct between standing and sitting for that patient. To individualize, the cup position will demand higher precision than has been accepted in the past, such as computer navigation, to augment the experience and instinct of the surgeon in performing total hip replacement. In conclusion, acetabular cup placement is an elusive home run because the complexity of its positioning for each patient requires new preoperative planning, and more precise intraoperative positioning.     

What is the Impact of a Spinal Fusion on Acetabular Implant Orientation in Functional Standing and Sitting Positions?

Background

This study used EOS imaging of primary total hip arthroplasty (THA) patients, with and without predating spinal fusion, to investigate (1) the impact of spinal fusion on acetabular implant anteversion and inclination, and (2) whether more extensive spinal fusion (fusion starting above the thoracolumbar junction or extension of fusion to the sacrum) affects acetabular implant orientation differently than lumbar only spinal fusion.

Does Functional Cup Orientation Change at Minimum of 10 Years After Primary Total Hip Arthroplasty?

BackgroundCup orientation has been shown to influence the postoperative risk of impingement and dislocation following total hip arthroplasty (THA) and may change over time due to changes in pelvic tilt that occur with aging. The purpose of this study is to determine if there is a significant change in acetabular cup inclination and anteversion over a 10-year period following THA.MethodsA retrospective, multisurgeon, single-center cohort study was conducted of 46 patients that underwent THA between 1995 and 2002. A total of 46 patients were included, with a median age at surgery of 56 years, and a median time between initial postoperative radiograph and the most recent one being 13.5 years (minimum 10 years). Cup orientation was measured from postoperative and follow-up supine anterior-posterior pelvic radiographs. Using a validated software, inclination and anteversion were calculated at each interval and the change in cup anteversion and inclination angle was determined. Furthermore, the difference in the sacro-femoral-pubic angle was measured, reflecting the difference in pelvic tilt between intervals.ResultsNo significant difference was detected between measurements taken from initial postoperative radiograph and measurements a minimum of 10 years later (P > .45), with the median (interquartile range) change in anteversion, inclination, and sacro-femoral-pubic being 0° (−1° to 3°), 1° (−3° to 2°), and 0° (−2° to 3°), respectively.ConclusionOur study found no significant change in functional cup orientation a minimum of 10 years after THA. No shifts in functional cup orientation as a result of altering spinopelvic alignment seemed to be present over a 10-year period.     

Anteversion of the acetabular component aligned with the transverse acetabular ligament in total hip arthroplasty

In total hip arthroplasty (THA), accurately positioning the cup is crucial for achieving an adequate postoperative range of motion and stability. For 47 THA cases in which the inferomedial rim of the cup had been positioned parallel to the transverse acetabular ligament, we retrospectively performed the measurements of the radiographic cup anteversion angle relative to the anterior pelvic plane using 3-dimensional reconstruction computed tomography. The mean anteversion angle was 21.2°, with no significant difference detected in mean cup anteversion between the dysplastic hip group (15 hips) and the control group (15 hips). We suggest that the transverse acetabular ligament is a practical anatomical landmark for determining cup anteversion in THA for both dysplastic and nondysplastic hip cases.     

联合前倾角技术在成人发育性髋关节发育不良全髋关节置换术中的应用

目的探讨联合前倾角技术在成人发育性髋关节发育不良全髋关节置换术中应用的可行性及临床价值。方法回顾性分析自2016-09—2018-06采用联合前倾角技术行全髋关节置换术治疗的31例(36髋)成人发育性髋关节发育不良,比较手术前后髋臼前倾角、股骨前倾角、联合前倾角及髋关节功能Harris评分。结果31例均获得12个月以上随访。术后骨盆正位及髋关节侧位X线片显示假体位置及对应关系良好,无假体松动、下沉,无脱位表现。末次随访时所有患者步态均明显改善,髋部疼痛均消失,仅2例轻度跛行。术后髋臼前倾角、股骨前倾角、联合前倾角较术前明显减小,末次随访时髋关节功能Harris评分较术前明显增加,差异有统计学意义(P<0.05)。结论联合前倾角技术应用于成人发育性髋关节发育不良全髋关节置换术对于指导合适假体的选择、设计以及确定合适的髋臼前倾角、股骨柄前倾角具有重要意义,良好的联合前倾角能够有效预防术后假体脱位的发生。