Factors predicting change in pelvic posterior tilt after THA

What Changes in Pelvic Sagittal Tilt Occur 20 Years After THA?

BACKGROUND

Cup orientation in THA in the supine, standing, and sitting positions is affected by pelvic sagittal tilt (PT). Patterns of PT shift between these positions may increase the risk of dislocation and edge loading. The PT has also been reported to change during the aging process; however, there is limited research regarding long-term changes in PT and PT shifts after THA.

QUESTIONS/PURPOSES

(1) What changes occur in PT in the supine, standing, and sitting positions during 20 years of follow-up after THA in patients who have not had revision or dislocation? (2) What factors are associated with the differences between preoperative supine PT and postoperative sitting or standing PT (Δ sitting and Δ standing, respectively) 20 years postoperatively?

METHODS

Between January 1998 and December 1999, 101 consecutive patients underwent THA for appropriate indications. AP radiographs of the pelvis in the supine, standing, and sitting positions preoperatively and at 1, 10, and 20 years after THA were longitudinally performed to evaluate changes in PT. Fifty-nine percent (60 of 101) of patients were lost before 20 years of follow-up or had incomplete sets of imaging tests, leaving 41% (41 of 101) eligible for analysis here. There were no patients who had recurrent dislocation or underwent revision arthroplasty in the cohort; therefore, this analysis regarding postoperative changes in PT indicates the natural course of the change in PT during follow-up of THA. PT was measured based on the anterior pelvic plane. PT shifts with positional changes, Δ standing, and Δ sitting during the follow-up period were calculated. Posterior changes and shifts are represented by negative values. To analyze the factors associated with Δ standing and Δ sitting after 20 years, the correlations between these parameters and preoperative factors (including sex, age, pelvic incidence [PI], lumbar lordosis [LL], preoperative PT, and preoperative PT shift) and postoperative factors (including the occurrence of new lumbar vertebral fractures, lumbar spondylolisthesis, contralateral THA performed during follow-up, and PI-LL 20 years after THA) were determined.

RESULTS

Median (IQR) supine and standing PTs changed (moved posteriorly) by -5° (-11° to -2°; p < 0.01) and -10° (-15° to -7°; p < 0.01), respectively. Sitting PT did not change during the 20-year follow-up period. Median (IQR) PT shift from standing to sitting changed from -34° preoperatively (-40° to -28°) to -23° after 20 years (-28° to -20°). There were posterior changes in median (range) Δ standing (median -12° at 20 years [-19° to -7°]); Δ sitting did not change during the follow-up period (median -36° at 20 years [-40° to -29°]). Patients with a large preoperative posterior PT shift from supine to standing demonstrated larger posterior tilt of Δ standing at 20 years. Patients with lumbar vertebral fractures during follow-up demonstrated larger posterior tilt of Δ standing at 20 years.

CONCLUSION

Patients who demonstrate a large preoperative posterior shift from supine to standing deserve special consideration when undergoing THA. In such circumstances, we recommend that the anteversion of the cup not be excessive, given that there is a relatively high risk of further posterior tilt in PT, which may lead to anterior dislocation and edge loading. Further longitudinal study in a larger cohort of patients with complications including postoperative dislocation and revision, as well as older patients, is needed to verify these assumptions on the potential risk for dislocation and edge loading after THA.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Implications of the uncertainty of postoperative functional parameters for the preoperative planning of total hip arthroplasty

The functional parameters pelvic tilt (PT) and hip joint force (HJF) are required to calculate patient-specific target zones based on the range of motion (ROM) and implant loading for preoperative planning of total hip arthroplasty (THA). Both functional parameters may change after THA. The preoperative prediction of the postoperative PT and HJF is associated with a specific amount of uncertainty. The prediction uncertainty has to be considered in the preoperative planning process to avoid a suboptimal implantation. So far, very little attention has been paid to the necessary reduction of patient-specific target zones by the prediction uncertainties of postoperative functional parameters. Prediction models for the postoperative PT in standing position and for the HJF during one-leg stance as a surrogate for the peak force phase during level walking were used to quantify the reduction of the ROM- and load-based target zones of 196 Japanese THA patients. The prediction uncertainty was about 14° for the postoperative standing PT and ranged from 17% body weight to 37% body weight for the components of the HJF. On average, the prosthetic ROM-based target zone had to be significantly reduced by 43% and the load-based target zone by 39%. This led to a median reduction of the combined prosthetic ROM- and load-based target zone of 96%. The study sharpens the awareness for the substantial reduction of ROM- and load-based target zones by prediction uncertainties of the postoperative PT and HJF and highlights the importance of further research to improve prediction models for both functional parameters.

Is the Rate of Change in Posterior Pelvic Tilt After Total Hip Arthroplasty Constant?

Background

The purpose of this study was to evaluate the age-related change in pelvic sagittal inclination in the standing position after total hip arthroplasty (THA). This study hypothesized that the rate of progression of posterior tilt is not constant.

Material and methods

We measured sacral slope and pelvic tilt in 36 patients who were followed up for more than 10 years after unilateral primary THA.

Results

The posterior pelvic tilt in the standing position progressed significantly in the first year after THA and then progressed slowly. However, there was a tendency to accelerate again for those older than 75 years. Posterior pelvic tilt tended to progress rapidly after surgery in patients with femoral neck fractures and subchondral fractures of the femoral head.

Conclusions

In patients older than 75 years and those with fragility fractures, postoperative pelvic tilt in the standing position tends to be greater, suggesting that the use of a large head or dual mobility system should be considered.

Clinical Impact of Pelvic Malrotation on Radiograph-Based Preoperative Planning for Total Hip Arthroplasty: A Proof-of-Concept and Prudent Prediction of Acceptable Rotation

Introduction

Pelvic rotation (PR) on preoperative radiograph templating can affect various critical measured acetabular angles and potentially outcomes of successful total hip arthroplasty (THA). Optimising anatomical reconstruction of the joint is essential to achieve function, longevity and prevention of complications following surgery. There is limited literature that standardises the degree of acceptable PR on radiograph or its effects on the fitting of acetabular prostheses.

Objective

This study aimed to develop a proof-of-concept that quantifies how PR can affect various acetabular angles used in pre-operative THA templating and to formulate a practicable method of determining if the preoperative PR is acceptable.

Materials and methods

Computerised tomography (CT) models from three control and two THA patients were generated and manipulated in various degrees of PR. CT slices were thickened to simulate radiographs and acetabular angles measured.

Results

The acetabular anteversion distance (AAD) and lateral opening angle (LOA) demonstrated a linear and quadratic relationship with good correlation (R 2 = 0.923, R 2 = 0.710 respectively, p < 0.0001) in relation to PR. Change in area of prosthesis (AOP) demonstrated a good linear correlation (r 2 = 0.774 and r 2 = 0.875, p < 0.0001) with PR. Two novel measurements were used to estimate the degree of PR from a pelvic radiograph; the horizontal distance between pubic symphysis and middle of sacrococcygeal joint (PSSC) and the simplified pelvic rotation ratio (SPRR). A strong correlation between PSSC and SPRR with change in PR was observed (R 2 = 0.970, R 2 = 0.953, p < 0.001).

Conclusion

Preliminary result suggests that an SPRR > 2.0 correlates to PR > 20° with potential to have a clinical impact on preoperative measurements.

Pelvic position, lying on a traction table, during THA by direct anterior approach. Comparison with the standing position and influence on the acetabular cup anteversion

INTRODUCTION

The placement of prostheses for a total hip arthroplasty (THA) is essential to limit complications and optimize functional results. In a recent study of more than 100 THA placed through a direct anterior approach using a traction table, we found that the mean anteversion of the cup was greater (30°) than recommended (20°). To explain this phenomenon, we considered that the anterior pelvic plane (APP), defined by the plane passing through the anterior-superior iliac spines and the pubic symphysis, which serves as a landmark for the placement and calculation of the anteversion of the cup, was not horizontal when the patient was lying on the traction table. This concept has not been evaluated so we conducted a prospective study to: 1) measure the position of the pelvis on a traction table; 2) compare to the standing position, 3) assess its impact on the anteversion of the cup.

HYPOTHESIS

The standing pelvic version is identical to the supine pelvic version on the traction table.

MATERIAL AND METHODS

A prospective 3-month monocentric study was conducted. All patients operated on for a THA by a direct anterior approach, on a traction table, were included. The position of the pelvis was assessed by measuring the tilt of the APP on lateral pelvic X-rays, while on the traction table and while standing. The impact of the position of the pelvis on the positioning of the cup, as well as the anteversion, were measured using the EOS imaging system. The anatomic anteversion of the cup was measured in relation to the APP.

RESULTS

Fifty-eight patients were included (32 women, 26 men) with an average age of 67 years. The tilt of the supine APP was 6°±8.3 [range of -10.5 to 31.0] (indicating a retroverted pelvis on the traction table). The difference between the tilt of the standing and lying APP (within 90°) was not significant (standing was on average 4.5° [range of -11.0 to 27.0] versus lying on the table, was on average 6° [range of -10.5 to 31.0] (p=0.75). A strong correlation was observed between the tilt of the supine APP and the anatomic anteversion of the cup (p<0.001). Thus, the more retroverted the pelvis was on the traction table, the lower the anatomic anteversion of the acetabular cup.

CONCLUSION

The supine pelvis on the traction table is not always horizontal and its position on the traction table is similar to its standing position, within 90 degrees. The analysis of the positioning of the preoperative pelvis appears to be essential in the planning of a THA through direct anterior approach using a traction table.

LEVEL OF EVIDENCE

IV; Prospective Cohort Study.

Anterior pelvic plane tilt poorly estimates the sagittal body alignment due to internal rotation of innominate bone

This study investigated the influence of the rotation of innominate bone on anterior pelvic plane (APP) tilt, the angle formed by the APP, and coronal plane of the body to determine whether the provision of proper information about the sagittal balance of the body by the value of the APP tilt (APPT). In total, 244 patients (171 females, 73 males) who were candidates for total hip or knee arthroplasty, periacetabular osteotomy, or shelf arthroplasty were included. The rotational angle of the innominate bone was quantified using computed tomography images at the level of the anterior superior, and anterior inferior iliac spine, and ischiopubic portion. Clustering analysis was performed to identify subtypes of innominate bone rotation. High, intermediate, and low internal rotational alignment groups were identified in females, characterized by rotational angles. Males were treated as one group, and no intergroup differences were observed in sacral slope (SS) and pelvic incidence. However, intergroup differences in APPT were found, indicating a variation in APPT irrespective of sagittal body balance. A negligible relationship between SS and APPT was observed in the high-internal-rotation group, intermediate-internal-rotation group, and male group, whereas a moderate correlation found in the low-internal-rotation group (r = .59). The results could suggest surgeons that the value of the APPT provides no information on the sagittal balance; therefore, it may be ignored for acetabular component positioning during preoperative planning for total hip arthroplasty.

Preoperative factors improving the prediction of the postoperative sagittal orientation of the pelvis in standing position after total hip arthroplasty

The aims of this study were to investigate if the sagittal orientation of the pelvis (SOP) in the standing position changes after total hip arthroplasty (THA) and evaluate what preoperative factors may improve the prediction of the postoperative standing SOP in the context of a patient-specific functional cup orientation. 196 primary THA patients from Japan were retrospectively selected for this study. Computed tomography imaging of the pelvis, EOS imaging of the lower body and lateral radiographs of the lumbar spine in the standing position were taken preoperatively. Common biometrics and preoperative Harris Hip Score were recorded. The EOS imaging in the standing position was repeated three months following THA. A 3D/2.5D registration process was used to determine the standing SOP. Thirty-three preoperative biometric, morphological and functional parameters were measured. Important preoperative parameters were identified that significantly improve the prediction of the postoperative standing SOP by using multiple linear LASSO regression. On average, the SOP changed significantly (p < 0.001) between the preoperative and postoperative standing position three months after THA by 3° ± 4° in the posterior direction. The age, standing lumbar lordosis angle (LLA) and preoperative supine and standing SOP significantly (p < 0.001) improve the prediction of the postoperative standing SOP. The linear regression model for the prediction of the postoperative standing SOP is significantly (p < 0.001) improved by adding the parameters preoperative standing SOP and LLA, in addition to the preoperative supine SOP, reducing the root mean square error derived from a leave-one-out cross-validation by more than 1°. The mean standing SOP in Japanese patients changes already three months after THA in comparison to the preoperative value. The preoperative factors age, LLA, supine and standing SOP can significantly improve the prediction of the postoperative standing SOP and should be considered within the preoperative planning process of a patient-specific functional cup orientation.

The Impingement-free, Prosthesis-specific, and Anatomy-adjusted Combined Target Zone for Component Positioning in THA Depends on Design and Implantation Parameters of both Components

BACKGROUND

Lewinnek's recommendation for orienting the cup in THA is criticized because it involves a static assessment of the safe zone and because it does not consider stem geometry. A revised concept of the safe zone should consider those factors, but to our knowledge, this has not been assessed.

QUESTIONS/PURPOSES

(1) To determine the shape, size, and location of target zones for combined cup and stem orientation for a straight stem/hemispheric cup THA to maximize the impingement-free ROM and (2) To determine whether and how these implant positions change as stem anteversion, neck-shaft angle, prosthetic head size and target range of movements are varied.

METHODS

A three-dimensional computer-assisted design model, in which design geometry was expressed in terms of parameters, of a straight stem/hemispheric cup hip prosthesis was designed, its design parameters modified systematically, and each prosthesis model was implanted virtually at predefined component orientations. Functional component orientation referencing to body planes was used: cups were abducted from 20° to 70°, and anteverted from -10° to 40°. Stems were rotated from -10° to 40° anteversion, neck-shaft angles varied from 115° to 143°, and head sizes varied from 28 to 40 mm. Hip movements up to the point of prosthetic impingement were tested, including simple flexion/extension, internal/external rotation, ab/adduction, combinations of these, and activities of daily living that were known to trigger dislocation. For each combination of parameters, the impingement-free combined target zone was determined. Maximizing the size of the combined target zone was the optimization criterion.

RESULTS

The combined target zones for impingement-free cup orientation had polygonal boundaries. Their size and position in the diagram changed with stem anteversion, neck-shaft angle, head size, and target ROM. The largest target zones were at neck-shaft angles from 125° to 127°, at stem anteversions from 10° to 20°, and at radiographic cup anteversions between 17° and 25°. Cup anteversion and stem anteversion were inverse-linearly correlated supporting the combined-anteversion concept. The range of impingement-free cup inclinations depended on head size, stem anteversion, and neck-shaft angle. For a 127°-neck-shaft angle, the lowest cup inclinations that fell within the target zone were 42° for the 28-mm and 35° for the 40-mm head. Cup anteversion and combined version depended on neck-shaft angle. For head size 32-mm cup, anteversion was 6° for a 115° neck-shaft angle and 25° for a 135°-neck-shaft angle, and combined version was 15° and 34° respectively.

CONCLUSIONS

The shape, size, and location of the combined target zones were dependent on design and implantation parameters of both components. Changing the prosthesis design or changing implantation parameters also changed the combined target zone. A maximized combined target zone was found. It is mandatory to consider both components to determine the accurate impingement-free prosthetic ROM in THA.

CLINICAL RELEVANCE

This study accurately defines the hypothetical impingement-free, design-specific component orientation in THA. Transforming it into clinical precision may be the case for navigation and/or robotics, but this is speculative, and as of now, unproven.

Surgical implications of the hip-spine relationship in total hip arthroplasty

Total hip arthroplasty (THA) is considered the most successful orthopedic surgical procedure of the last century with excellent survivorship up to 20-years. However, instability remains a major issue representing the most common reason for revision after THA. Hip-spine relationship has gained progressive interest between arthroplasty surgeons and its understanding is crucial in order to identify high-risk patients for postoperative dislocation. Spinal deformity and abnormal spinopelvic mobility have been associated with increased risk for instability, dislocation and revision THA. Preoperative workup begins with standing anteroposterior pelvis x-ray and lateral spinopelvic radiographs in the standing and sitting position. Hip-spine stiffness needs to be addressed before THA in consideration of adapting the preoperative planning to the patient's characteristics. Acetabular component should be implanted with different anteversion and inclination angles according to the pattern of hip-spine motion in order to reduce the risk of impingement and consequent dislocation. Different algorithmic approaches have been proposed in case of concomitant hip-spine disease and in case of altered sagittal balance and pelvic mobility. The aim of this review is to investigate and clarify the hip-spine relationships and evaluate the impact on modern total hip arthroplasty.

Influence of pelvic sagittal tilt on 3-dimensional bone coverage in total hip arthroplasty: a simulation analysis

BACKGROUND

In total hip arthroplasty with computer navigation assistance, cup orientation is generally determined according to the coordinate system relative to the functional pelvic plane (FPP). However, there is a large difference in the cup anteversion between a posterior pelvic tilt relative to the computed tomography (CT) table in the sagittal plane and anterior pelvic tilt, even when the cup is set at the same orientation angle according to each FPP. The present study analysed this difference from the viewpoint of 3-dimensional (3D) coverage of the acetabular component (3D coverage) to determine how the 3D acetabular coverage is altered with changes in pelvic sagittal tilt.

METHODS

We analysed 3D-simulated acetabular coverage measured in 3D pelvic models reconstructed from the preoperative CT data of 50 patients. In each patient, we created 5 pelvic models with a sagittal tilt of 10° increments between 20° anterior tilt and 20° posterior tilt relative to the CT table.

RESULTS

We found that 3D coverage decreased as the pelvis tilted posteriorly. Particularly, there were significant differences between the pelvis with 20° anterior tilt and that with neutral tilt (p < 0.001). There was also a difference between the pelvis with neutral tilt and that with a 20° posterior tilt (p < 0.01). The mean decrease in 3D coverage between the pelvis with neutral tilt and that with 20° posterior tilt was 7.2 ± 1.6%.

CONCLUSIONS

We found that 3D coverage differed among pelvis with different sagittal tilts when the cup orientation angle was determined according to FPP.

Reproducibility of pelvic sagittal inclination while acquiring radiographs in supine and standing postures

PURPOSE

Pelvic position on the sagittal plane is usually evaluated with the pelvic sagittal inclination (PSI) angle from a single radiograph. However, the reproducibility of pelvic positioning has not been investigated, and thus, the validity of measuring the PSI from a single film/time point is not understood. Herein, the reproducibility of a patient's pelvic positions in supine and standing postures was analyzed.

METHODS

A total of 34 patients who underwent either a pelvic osteotomy or total hip arthroplasty were enrolled in this study. Preoperative radiographs in both supine and standing postures were acquired twice (first X-ray and second X-ray) within 6 months; preoperative computed tomography (CT) images of the full pelvis were also acquired in a supine posture (preop-CT). To eliminate measurement variability, each PSI was automatically measured from radiographs and CT images through the use of CT segmentation and landmark localization followed by intensity-based 2D-3D registration. The absolute difference of PSI among each image was calculated and the intra-class correlation coefficient (ICC) in each posture was also analyzed.

RESULTS

The median absolute differences of PSI in the supine posture were 1.3° between the first and second X-rays, 1.2° between the first X-ray and preop-CT, and 1.3° between the second X-ray and preop-CT. The median absolute difference of PSI in the standing posture was 1.5°. The ICC was 0.965 (95% CI: 0.939-0.981) in supine and 0.977 (95% CI: 0.954-0.988) during standing.

CONCLUSIONS

Pelvic positions in supine and standing postures are reproducible. Thus, measuring the PSI from a single radiograph is reliable.

The Influence of Pelvic Tilt on the Anteversion Angle of the Acetabular Prosthesis

The concept of the "safe area" of the acetabular prosthesis has a long history and has been recognized by many scholars. It is generally believed that postoperative hip dislocation rate is low, when the acetabular anteversion angle is placed in the range of 15° ± 10°. Despite this, hip dislocation is a common complication after total hip arthroplasty. In recent years, more and more scholars have paid attention to the influence of pelvic tilt on the acetabular anteversion angle. The concept of acetabular anteversion changes as the pelvic tilt changes, and is challenging the traditional acetabular prosthesis "safe area." This study summarized the potential influencing factors of pelvic tilt and discussed the influence of the phenomenon on the anteversion angle of total hip arthroplasty (THA) acetabular prosthesis based on the literature review. We conclude that from the supine position to standing, followed by sitting, the pelvis tends to move backward. Pelvic sagittal activity, lumbar disease (ankylosing spondylitis), lumbar fusion (lumbar fusion, spine-pelvic fusion), and other factors related to the tilt are THA risk factors for postoperative dislocation and revision. With the change of body position, the degree of acetabular anteversion is directly related to the degree of pelvic tilt. The acetabular anteversion varies greatly, which leads to increased hip prosthesis wear and even hip dislocation. The lateral X-ray of the spine and pelvis is recommended in supine, standing, and sitting positions before THA. In addition, the pelvic tilt should be regarded as a reference of the acetabular prosthesis in the preoperative planning of THA.

Tilt-adjusted Cup Anteversion in Patients with Severe Backward Pelvic Tilt is Associated with the Risk of Iliopsoas Impingement: A Three-dimensional Implantation Simulation

BACKGROUND

Anterior overhang of the acetabular component is associated with iliopsoas impingement, which may cause groin pain and functional limitations after THA. However, little is known about the relationship between component overhang and functional alignment of the acetabular component. CT-based image simulation may be illuminating in learning more about this because CT images are more effective than radiographs for evaluating the component's overhang and position.

QUESTIONS/PURPOSES

Using CT simulations based on preoperative data of nondysplastic and dysplastic hips, we asked: (1) What are the differences in the amount of component overhang, defined as the mediolateral distance from the component's edge to the native acetabular bony boundary on axial images (axial overhang), and as the AP distance on sagittal images (sagittal overhang) among pelvises with neutral and posterior tilt (in which the cephalad portion of the pelvis is more posterior than the caudad portion in the sagittal plane) in patients with dysplastic hips and those with nondysplastic hips? (2) Are increments in the amount of component overhang associated with a difference in the likelihood that the iliopsoas tendon will impinge against the edge of the acetabular component, after controlling for native acetabular abduction and anteversion and the presence of dysplasia?

METHODS

A total of 128 hips (dysplastic group: 73 hips; nondysplastic group: 55 hips) were evaluated. We defined a dysplastic hip as one with a lateral center-edge angle of less than 20° on AP radiographs. Pelvic models with neutral (0°) and 10° and 20° of posterior tilt were created from CT data. In simulations, acetabular component models were implanted into the true acetabulum with a tilt-adjusted orientation angle that was defined as the component's angle based on a reference for the functional pelvic plane (coronal plane of the body) in each pelvic model. Axial and sagittal component overhang were measured on CT images. Axial overhang of at least 12 mm and sagittal overhang of at least 4 mm were defined as thresholds increasing the likelihood of iliopsoas impingement according to previous studies. When determining the amount of overhang of the acetabular component, we controlled for abduction and anteversion of the native acetabulum and the presence of dysplasia by performing a multivariable logistic regression analysis.

RESULTS

In dysplastic hips, axial overhang increased by a mean ± SD of 5 ± 1 mm (Bonferroni adjusted p < 0.001; 95% CI, 4.7-5.1) from 0° to 10° of posterior tilt and by 5 ± 1 mm (p < 0.001; 95% CI, 4.9-5.3) from 10° to 20° of posterior tilt. Sagittal overhang increased by 1 ± 0 mm (p < 0.001; 95% CI, 1.0-1.0) from 0° to 10° of posterior tilt and by 1 ± 0 mm (p < 0.001; 95% CI, 1.0-1.0) from 10° to 20° of posterior tilt. In nondysplastic hips, axial overhang increased by a mean of 5 ± 0 mm (p < 0.001; 95% CI, 4.7-5.0) from 0° to 10° of posterior tilt and by 5 ± 1 mm (p < 0.001; 95% CI, 4.6-5.0) from 10° to 20° of posterior tilt. Sagittal overhang increased by 1 ± 0 mm (p < 0.001; 95% CI, 1.0-1.1) from 0° to 10° of posterior tilt and by 1 ± 0 mm (p < 0.001; 95% CI, 1.0-1.1) from 10° to 20° of posterior tilt. After controlling for the presence of dysplasia, we found that native acetabular abduction and anteversion and posterior pelvic tilt, presence of dysplasia (p = 0.030; adjusted odds ratio [OR], 2.2; 95% CI, 1.1-4.6), native acetabular anteversion (p < 0.001; adjusted OR, 1.4; 95% CI, 1.3-1.5), and 10° and 20° of backward tilt compared with 0° of tilt (10° of posterior tilt: p < 0.001; adjusted OR, 15; 95% CI, 5.5-41; 20° of posterior tilt: p < 0.001; adjusted OR, 333; 95% CI, 96-1157) were independently associated with axial overhang of at least 12 mm; the model showed high goodness of fit (Nagelkerke's r = 0.68). In contrast, native acetabular anteversion (p < 0.001; adjusted OR, 1.2; 95% CI, 1.1-1.2) and 20° of backward tilt compared with 0° of tilt (p = 0.015; adjusted OR, 2.2; 95% CI, 1.2-4.0) were independently associated with sagittal overhang of at least 4 mm; the model had low goodness of fit (Nagelkerke's r = 0.20).

CONCLUSIONS

Acetabular component overhang is more severe when the pelvis tilts posteriorly. Moreover, posterior pelvic tilt, the presence of dysplasia, and higher native acetabular anteversion were independently associated with an increased risk of component overhang. When 20° of posterior tilt was adjusted, the risk of severe overhang was especially increased.

CLINICAL RELEVANCE

Based on these results, surgeons can attempt to prevent severe overhang in patients with posterior pelvic tilt by increasing component anteversion and abduction; when component anteversion is increased by 8° and abduction is increased by 2° from the target angle of 15° of anteversion and 40° of abduction in patients with posterior tilt of 20°, the risk of severe overhang is reduced to by approximately one-twentieth. However, it is still unclear how much the degree of component anteversion should be increased when surgeons attempt to prevent anterior prosthetic dislocation at the same time. Future studies such as prospective clinical trials evaluating both prosthetic dislocation and iliopsoas impingement in patients with posterior tilt might clarify this issue.

Influence of Spinopelvic Alignment on Pelvic Tilt after Total Hip Arthroplasty

Objective

To evaluate the impact of spinopelvic parameters and hip contracture on change in the pelvic tilt (PT) after Total hip arthroplasty (THA).

Methods

One hundred patients (15 male and 85 female) who underwent THA were included in this prospective study. Radiographic data were obtained preoperatively and 1 year after THA. Radiographic parameters included sagittal anterior pelvic plane (APP), sagittal vertical axis (SVA), sacral slope (SS), pelvic inclination (PI), and lumbar lordosis angle (LL). The APP was defined as the angle between the anterior pelvic plane and the vertical plane. A positive value indicates pelvic retroversion. Postoperative changes in PT were divided into three groups: the PA group (pelvic anteversion, ΔAPP < −5°), the PR group (pelvic retroversion, ΔAPP > 5°), and the PT group (minimal change, ΔAPP ≤ ± 5°). The Kruskal–Wallis test and the Steel–Dwass test were used to compare the preoperative and postoperative spinopelvic parameters among the three groups. The Spearman's rank correlation coefficient was used to evaluate the correlation between ΔAPP and spinopelvic parameters.

Results

Minimal change in pelvic tilt was observed in 59% of patients, while pelvic anteversion was observed in 16% of patients and pelvic retroversion was observed in 25% of patients. There were no significant changes in the spinopelvic parameters, including TK, LL, SVA, LL, SS, and APP after THA. The Femoral angle (FA) was significantly decreased after THA (P < 0.001). Preoperative APP was significantly more retroverted in the PA group than the PR group, and the PT group (6.8 ± 12.2, 0.2 ± 9.9, −8.3 ± 8.3, P < 0.001). Preoperative SS, PI‐LL, and PI were significantly smaller in the PA group than the PT group and the PR group. A significant negative correlation was identified between preoperative APP and ΔAPP (r = −0.418, P < 0.001).

Conclusion

Approximately 60% of the patients did not have any marked change in PT after THA. Preoperative APP was the only predictive factor associated with marked anterior or posterior change in PT.

Non-equivalent Results from Different Anteversion Measurements Methods for the Evaluation of the Acetabular Cup Orientation in Total Hip Arthroplasty

Objective

To determine the comparability among 10 radiographic anteversion methods for acetabular cup orientation in total hip arthroplasty (THA) found in the literature and the “gold” standard of assessing the anteversion with CT.

Methods

This is a retrospective study that blindly compares 10 different conventional radiographic anteversion measurements with the “gold” standard, the measurement of anteversion on the transverse plane of the 3‐D images made with CT. The patient archiving and communications system (PACS) was systematically searched for subjects that had undergone a CT angiogram of the abdomen and lower extremities, including the pelvis, had at least one THA in situ and had undergone anterior‐posterior (AP) and cross‐lateral pelvic radiography between January 2013 and August 2016 in the Diakonessenhuis Hospital Utrecht/Zeist, a non‐academic institution. CT scans of patients (n = 16) were systematically collected. Three observers independently measured cup anteversion from radiographs, using a total of 10 different methods, and measured the “gold” standard on CT images. The outcomes of the 10 radiographic anteversion were compared in terms of linear correlation with the “gold” standard on CT images.

Results

The correlations of the radiographic measured anteversions with the “gold” standard measured on CT images were 0.528 for the method of Liaw, 0.556 for Wan, 0.562 for the cross‐lateral method, 0.586 for Hassan, 0.594 for Dorr, 0.602 for Lewinnek, 0.624 for Widmer, 0.671 for the lateral CT, 0.747 for Ackland, and 0.771 for the method of Riten Pradham.

Conclusion

Anteversion measurement methods represent different projectional angles of the acetabular cup in different planes around different axes. Therefore, they differ from the “gold” standard and are not interchangeable, as is shown by this study. We consider the anatomical anteversion in the transverse plane rotating around the longitudinal axis as the “gold” standard and recommend avoiding using the term anteversion for other projectional angles in different planes.

Hip-Spine Syndrome: Acetabular Anteversion Angle Is Associated with Anterior Pelvic Tilt and Lumbar Hyperlordosis in Patients with Acetabular Dysplasia: A Retrospective Study

Background:

Hip-spine syndrome was originally described by Offierski and MacNab, who argued that the flexion deformity of the hip rotated the pelvis forward, causing the spine symptoms. We additionally hypothesized that in patients who have osteoarthritis (OA) of the hip, the pelvis is tilted anteriorly to compensate for the anterior acetabular coverage defect. We investigated the hip factors associated with anterior pelvic tilt (PT) in patients who had OA of the hip due to acetabular dysplasia.

Methods:

We retrospectively reviewed the medical records of patients who had undergone total hip arthroplasty between January 2009 and December 2017 to identify those who had unilateral secondary OA due to acetabular dysplasia. Patients who had spinal imbalance, a history of spinal or lower limb fracture or surgery, bilateral OA of the hip, or a severely subluxated hip were excluded, leaving 100 eligible patients. We defined the indicators of an anterior acetabular coverage defect, flexion deformity of the hip, and anterior PT as the acetabular anteversion angle (AAA), extension range of motion (ROM), and anterior tilt of the pelvis, respectively. We measured hip factors and spinal parameters on radiographs and the standardized axial and coronal planes on 3-dimensional computed tomography with reference to the anterior pelvic plane. Hip factors associated with PT were investigated.

Results:

Univariate analysis showed a significant correlation between PT and both AAA (r = –0.389, p < 0.001) and combined anteversion angle (r = –0.272, p = 0.03). Multivariate regression analysis identified AAA (β = –0.385, p < 0.001) and extension ROM (β = 0.212, p = 0.0496) as independent factors associated with PT. Lumbar lordosis and pelvic incidence minus lumbar lordosis were significantly correlated with AAA, but sagittal vertical axis was not.

Conclusions:

When treating patients who have acetabular dysplasia, surgeons should recognize the relationship between the anterior acetabular coverage and anterior PT. Correcting hyperlordosis of the lumbar spine can induce progression of hip OA because it may decrease the acetabular anterior coverage.

Trigonometric Algorithm Defining the True Three-Dimensional Acetabular Cup Orientation: Correlation Between Measured and Calculated Cup Orientation Angles

BACKGROUND

Acetabular cup orientation plays a key role in implant stability and the success of total hip arthroplasty. To date, the orientation has been measured with different imaging modalities and definitions, leading to lack of consensus on optimal cup placement. A 3-dimensional (3D) concept involving a trigonometric description enables unambiguous definitions. Our objective was to test the validity and reliability of a 3D trigonometric description of cup orientation.

METHODS

Computed tomographic scans of the pelvis, performed for vascular assessment of 20 patients with 22 primary total hip replacements in situ, were systematically collected. On multiplanar reconstructions, 3 observers independently measured cup orientation retrospectively in terms of coronal inclination, sagittal tilt, and transverse version. The angles measured in 2 planes were used to calculate the angle in the third plane via a trigonometric algorithm. For correlation and reliability analyses, intraobserver and interobserver differences between measured and calculated angles were evaluated with use of the intraclass correlation coefficient (ICC).

RESULTS

Measured and calculated angles had ICCs of 0.953 for coronal inclination, 0.985 for sagittal tilt, and 0.982 for transverse version. Intraobserver and interobserver reliability had ICCs of 0.987 and 0.987, respectively, for coronal inclination; 0.979 and 0.981, respectively, for sagittal tilt; and 0.992 and 0.978, respectively, for transverse version.

CONCLUSIONS

The 3D concept with its trigonometric algorithm is a valid and reliable tool for the measurement of cup orientation.

CLINICAL RELEVANCE

By calculating the transverse version of cups from coronal inclination and sagittal tilt measurements, the trigonometric algorithm enables a 3D definition of cup orientation, regardless of the imaging modality used. In addition, it introduces sagittal tilt that, like pelvic tilt, rotates around the transverse axis.

Effect of Pelvic Tilt and Rotation on Cup Orientation in Both Supine and Standing Positions

BACKGROUND

The purpose of this study is to analyze the effect of pelvic tilt and rotation on radiographic measurement of cup orientation.

METHODS

A total of 68 patients (79 hips) were included in this study. The patients had a computed tomography study and approximately 3 months of postoperative standing anteroposterior pelvic radiographs in both supine and standing positions. We used 2-dimensional (2D)/3-dimensional (3D) matching to measure pelvic tilt and rotation, and cup orientation.

RESULTS

There was a wide range of pelvic tilt between individuals in both supine and standing positions. Supine pelvic tilt was different from standing pelvic tilt (P < .05). There were differences in cup anteversion before and after 2D/3D matching in both supine and standing positions (P < .05). Supine and standing pelvic tilt correlated with differences in cup anteversion before and after 2D/3D matching. When all 79 hips were separated into right and left side, pelvic rotation inversely correlated with the pelvic tilt-adjusted difference in anteversion before and after 2D/3D matching of the right side but directly correlated with that of the left side in both supine and standing positions.

CONCLUSION

This study demonstrated that the measurement of cup anteversion on anteroposterior radiographs is significantly affected by both pelvic tilt and pelvic rotation (depending on the side). Improved understanding of pelvic orientation and improved ability to measure pelvic orientation may eventually allow for desired cup positioning to potentially protect against complications associated with malposition of the cup.

Pelvic Tilt Displacement Before and After Artificial Hip Joint Replacement Surgery

BACKGROUND

Prediction of pelvic displacement before total hip arthroplasty (THA) is important for accurate acetabular implant placement. This study aimed to evaluate the effect of contralateral joint conditions on pelvic displacement after THA.

METHODS

A total of 355 cases that underwent computed tomography before and after THA for osteoarthritis due to developmental dysplasia were assessed. The pelvic plane was based on preoperative and postoperative day 1 computed tomography images. The displacement in the anteversion direction was expressed as +. Subjects with a minimal joint space <2 mm in the contralateral hip joint were in group N; subjects with ≥2 mm were in group W; subjects with THA were in group P; and subjects who underwent THA simultaneously on both sides were in group B. The Bartlett test was used when conducting the equal variance test among the groups. The F test was used for pairwise comparison. A P value <.01 was considered statistically significant.

RESULTS

Groups N, W, P, and B had 49, 227, 55, and 24 cases, respectively, and their displacements were -0.2° ± 2.7°, 0.8° ± 3.9°, 0.5° ± 2.6°, and 1.1° ± 4.0°, respectively; the variance between the groups was significantly different (P = .0001). The differences between groups W and N (P = .0020), between groups W and P (P = .0003), and between groups P and B (P = .0086) were statistically significant.

CONCLUSION

When the contralateral joint space is wide, the variance of the displacement is high. The contralateral joint affects pelvic displacement.

The Association of Tibia Femur Ratio and Degenerative Disease of the Spine, Hips, and Knees

BACKGROUND

When individuals with asymmetric lower extremities present for evaluation of limb-length inequality, correction can occur at the tibia, femur, or in both bones; however, there are limited data available to justify either technique. The aim of this study is to examine the normal ratio of tibia length/femur length (T/F), and to explore the relationship between T/F ratio and osteoarthritis of the spine, hips, and knees.

METHODS

Bone lengths of 1152 cadaveric femora and tibiae from the Hamann-Todd osteological collection were measured. Degenerative joint disease was graded in the hip, knee, and spine. Correlations between the ratio of T/F and osteoarthritis were evaluated with multiple regression analysis.

RESULTS

The average ratio of T/F was 0.80±0.03. There was a strong correlation between age and arthritis at all sites, with standardized β ranging from 0.44 to 0.57 (P<0.0005 for all). There was a significant correlation between increasing T/F and hip arthritis (standardized β=0.08, P=0.006), and knee arthritis (standardized β=0.08, P=0.008).

DISCUSSION

Increasing tibia length relative to femur length was found to be a significant predictor of ipsilateral hip and knee arthritis. Therefore, we recommend that when performing limb lengthening, surgical planning should lean toward recreating the normal ratio of 0.80. In circumstances where one bone is to be overlengthened relative to the other, bias should be toward overlengthening the femur. This same principle can be applied to limb-reduction surgery, where in certain circumstances, one may choose to preferentially shorten the tibia.

CLINICAL RELEVANCE

This is the first study to report long-term consequences of lower extremity segment disproportion.

Change in Pelvic Sagittal Inclination From Supine to Standing Position Before Hip Arthroplasty

BACKGROUND

Cup anteversion and inclination are important for avoiding implant impingement and dislocation in total hip arthroplasty. However, functional cup anteversion and cup inclination also change as the pelvic sagittal inclination (PSI) changes. Therefore, PSI in both supine and standing positions was measured in a large cohort in this study.

METHODS

A total of 422 patients (median age, 61; range, 15-87) who underwent total hip arthroplasty were the subjects of this study. There were 83 patients with primary osteoarthritis (OA), 274 patients with developmental dysplasia-derived secondary OA, 48 patients with osteonecrosis, and 17 patients with rapidly destructive coxopathy (RDC). Preoperative PSI in supine and standing positions was measured by automated computed topography segmentation and landmark localization of the pelvis followed by intensity-based 2D-3D registration, and the number of cases in which PSI changed more than 10° posteriorly was calculated. Hip disease, sex, and age were analyzed if they were related to a PSI change of more than 10°.

RESULTS

The median PSI was 5.1° (interquartile range, 0.4°-9.4°) in supine and -1.3° (interquartile range, -6.5° to 4.2°) in standing position. There were 79 cases (19%) in which the PSI changed more than 10° posteriorly from supine to standing. Elder age and patients with primary OA and RDC were revealed to be the related factors.

CONCLUSION

PSI changed more than 10° posteriorly from supine to standing in 19% of cases. Age and diagnosis of primary OA and RDC were the significant factors for the posterior rotation.

Sagittal spinopelvic alignment predicts hip function after total hip arthroplasty

The aim of this study was to investigate the association between preoperative sagittal spinopelvic alignment and postoperative clinical outcomes after total hip arthroplasty (THA). This retrospective study included 92 patients with hip osteoarthritis who underwent primary THA between May 2013 and October 2015. Patients' characteristics, radiographic sagittal spinopelvic parameters and modified Harris Hip Scores, including function scores (gait scores and functional activities scores), were investigated. Multivariate linear regression analysis was performed to determine the associations between each preoperative sagittal spinopelvic parameter and postoperative hip function The preoperative sagittal spinopelvic parameters that were associated with postoperative gait scores were sagittal vertical axis (adjusted β-coefficient=-0.28, P=0.02), lumbar lordosis angle (adjusted β-coefficient=0.29, P=0.0089), pelvic tilt (adjusted β-coefficient=-0.25, P=0.045), sacral slope (adjusted β-coefficient=0.27, P=0.017) and pelvic incidence minus lumbar lordosis angle (adjusted β-coefficient=-0.31, P=0.01). The preoperative sagittal spinopelvic parameters that were related to the postoperative functional activities scores were sagittal vertical axis (adjusted β-coefficient=-0.38, P=0.0051) and pelvic incidence minus lumbar lordosis angle (adjusted β-coefficient=-0.39, P=0.0033). Patients with preoperative imbalanced sagittal alignment such as larger sagittal vertical axis, larger pelvic incidence minus lumbar lordosis and retroversion of pelvis had poorer clinical outcomes than others after THA. While, those preoperative imbalanced patients with anteversion of pelvis may have a compensatory ability which could correct the abnormal sagittal alignment after THA. Preoperative sagittal spinopelvic alignment affected postoperative clinical outcomes after THA.

The Validity of Using the Posterior Condylar Line as a Rotational Reference for the Femur

Rotation of the femur is usually measured by the posterior condylar line (PCL). However, the functional position of the PCL has not been studied well. The angles between the PCL and the horizontal body line (HBL) were measured on preoperative computed tomographic (CT) images of 324 hips with osteoarthritis and compared with the CT images taken after hip arthroplasty. The PCL rotated 0.4° (±10.9° SD) internally from the HBL on preoperative CT images and was significantly correlated with femoral anteversion, Kellgren-Lawrence grade, and sex. On postoperative CT images, the PCL rotated 10.1° (interquartile range, 1.7°-15.5°) internally from the HBL. There was individual variance in the position of the PCL, and caution may be needed when using it as a rotational reference.

What is the Fate of Total Hip Arthroplasty (THA) Acetabular Component Orientation When Evaluated in the Standing Position?

This retrospective study measured the change of the acetabular component orientation between supine and standing radiographs in 113 THA patients and identified the associated anatomical parameters that may help direct pre-operative planning. The mean change of the acetabular component inclination and version from supine to standing was 4.6° and 5.9° respectively (P<0.0001), with 49 (43%) hips showing inclination change >5° and 69 (53%) hips showing version change >5°. Twelve (43%) of 28 'malpositioned' cups became 'well-positioned' and 26 (31%) of 85 'well-positioned' cups became 'malpositioned' upon standing. Changes in inclination were associated with leg length discrepancy and pelvic obliquity; and changes in version were associated with pelvic tilt and pelvic incidence. Standing position and patient factors should be considered when defining "optimal" acetabular orientation.

Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter?

Pelvic tilt (PT) affects the functional anteversion and inclination of acetabular components in total hip arthroplasty (THA). One-hundred and thirty-eight consecutive patients who underwent unilateral primary THA were reviewed. Most cases had some degree of pre-operative PT, with 17% having greater than 10° of PT on standing pre-operative radiographs. There was no significant change in PT following THA. A computer model of a hemispheric acetabular component implanted in a range of anatomic positions in a pelvis with varying PT was created to determine the effects of PT on functional anteversion and inclination. Based on the study results, tilt-adjustment of the acetabular component position based on standing pre-operative imaging will likely improve functional component position in most patients undergoing THA.

Rapid hip osteoarthritis development in a patient with anterior acetabular cyst with sagittal alignment change

Rapidly destructive coxarthrosis (RDC) is rare and develops unusual clinical course. Recent studies suggest multiple possible mechanisms of the development of RDC. However the exact mechanism of RDC is still not clear. The difficulty of the study on RDC is attributed to its rareness and the fact that the data before the onset of RDC is normally unavailable. In this report, we presented the patient having the radiographic data before the onset who had rapid osteoarthritis (OA) development after contralateral THA, which meets the current criteria of RDC. We thought that the increased posterior tilt of the pelvis after THA reinforced the stress concentration at pre-existed anterior acetabular cyst, thereby the destruction of the cyst was occurred. As a result the rapid OA was developed. We think that there is the case of rapid osteoarthritis developing due to alternating load concentration by posterior pelvic tilt on preexisting anterior acetabular cyst such as our patient among the cases diagnosed as RDC without any identifiable etiology. The recognition of sagittal alignment changes and anterior acetabular cyst may play important role in prediction and prevention of the rapid hip osteoarthritis development similar to RDC.

Risk of edge-loading and prosthesis impingement due to posterior pelvic tilting after total hip arthroplasty

BACKGROUND

Proper implant orientation is essential for avoiding edge-loading and prosthesis impingement in total hip arthroplasty. Although cup orientation is affected by a change in pelvic tilt after surgery, it has been unclear whether surgeons can prevent impingement and edge-loading by proper positioning by taking into account any change in pelvic alignment associated with alteration of hip range of motion.

METHODS

We simulated implant orientation without edge-loading and prosthesis impingement, even with a change in pelvic tilt and associated change in hip range of motion after surgery, by collision detection using implant models created with computer-aided design.

FINDINGS

If posterior pelvic tilting with a corresponding hyperextension change in hip range of motion after surgery remains within 10°, as occurs in 90% of cases, surgeons can avoid edge-loading and impingement by correctly orienting the implant, even when using a conventional prosthesis. However, if a 20° change occurs after surgery, it may be difficult to avoid those risks.

INTERPRETATION

Although edge-loading and impingement can be prevented by performing appropriate surgery in most cases, even when taking into account postoperative changes in pelvic tilt, it may also be important to pay attention to spinal conditions to ensure that pelvic tilting is not extreme because of increasing kyphosis.