Impact of spinopelvic parameters on acetabular cup positioning and patient-reported outcomes following total hip arthroplasty

Jonathan Liu; Sarah Criddle; Noah Gilreath; Jeremy Heard; Mohammad Daher; Tucker Callanan; Edward Testa; Alan H. Daniels; Valentin Antoci

doi:10.1016/j.jor.2025.05.005

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69 (); 186-190

doi:

10.1016/j.jor.2025.05.005

Impact of spinopelvic parameters on acetabular cup positioning and patient-reported outcomes following total hip arthroplasty

Jonathan Liu^a,, Sarah Criddle^a, Noah Gilreath^b,c, Jeremy Heard^a, Mohammad Daher^a, Tucker Callanan^a, Edward Testa^a,d, Alan H. Daniels^a,d, Valentin Antoci^a,d

a Brown University, Department of Orthopaedics, Providence, RI, USA

b University Orthopaedics, Inc, East Providence, RI, USA

c Umass Chan Medical School, Worcester, MA, USA

d University Orthopaedics Inc, East Providence, RI, USA

⁎Corresponding author: Jonathan Liu. jliu@uoi.com

Received: 2025-4-10, Accepted: 2025-5-3, Published: 2025-5-5

Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Hip instability is one of the most common complications after total hip arthroplasty (THA). While prior research has explored patient factors, surgical technique, soft tissue dynamics, implant design, and spinopelvic parameters. In particular, the relationship between spinopelvic alignment and acetabular cup positioning is not yet fully understood. Therefore, we aim to evaluate the association between spinopelvic parameters, acetabular cup positioning, and 12-month postoperative PROMs.

This study included 90 patients undergoing primary THA at a single institution from March 2019 to May 2023. Pelvic parameters (acetabular inclination, acetabular version, pelvic incidence, pelvic tilt, sacral slope, flexion, and obliquity) were assessed using EOS imaging and radiographs. Additional data were obtained from the Veterans RAND-12 survey and the FORCE-TJR database. PROMs were collected preoperatively, at 3 months, and at 12 months postoperatively, along with postoperative hospital metrics. Statistical analysis included Pearson's correlation to evaluate associations between pelvic parameters and PROMs.

Postoperatively, 1.1 % of patients required reoperation, 2.2 % experienced dislocation, 5.5 % were readmitted within 90 days, and 12.1 % had complications, though none were associated with spinopelvic parameters or cup positioning. Acetabular cup inclination was significantly correlated with pelvic tilt (R = 0.30, p = 0.003), while acetabular version showed negative correlations with pelvic incidence (R = −0.23, p = 0.02) and sacral slope (R = −0.31, p = 0.002). At 12 months, acetabular inclination predicted improvement in MCS (R = 0.28, p = 0.02), and obliquity predicted improvements in activities of daily living (R = 0.29, p = 0.02), pain (R = 0.28, p = 0.03), and quality of life (R = 0.30, p = 0.002).

In the first year after THA, acetabular inclination was linked to improved patient-reported outcomes, while greater pelvic obliquity was associated with better scores in activities of daily living, pain, and quality of life. Post-operative acetabular cup version had weak correlations with pelvic incidence, sacral slope, and pelvic tilt. No other associations were found between spinopelvic parameters, cup positioning, and instability or complications.

Keywords

Total hip arthroplasty

Hip instability

Spinopelvic parameters

Acetabular cup positioning

Patient-reported outcome measures

Postoperative complications

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1 Introduction

Total hip arthroplasty (THA) is one of the most common and successful orthopedic surgeries, with the American College of Rheumatology reporting an annual rate of over 544,000 THAs performed in 2023.¹ Moreover, the rate of THA is expected to further increase over the coming years.² While there are relatively low rates of complications associated with THA, the procedure's prevalence results in a significant number of patients affected by complications.^3–5 Therefore, understanding factors associated with complications after THA is critical to help optimize patient outcomes.

Hip instability is a relatively common complication after THA, with rates cited around 2–3 % at 2 years follow-up, and it often leads to revision surgery.^6–8 While research on the patient, surgeon, soft tissue, and implant factors has been the topic of significant attention, we still lack a comprehensive understanding of all factors leading to instability after THA.⁹^,¹⁰ One critical factor is acetabular component (cup) positioning. While there is literature assessing instability concerning coronal cup inclination and anteversion, the position of the pelvis during daily activities changes due to individual spinopelvic alignment.^11–15 Researchers have demonstrated increased rates of dislocation associated with THA in patients with spinal arthrodesis.^16–18 This has lead surgeons to consider patient specific spinopelvic parameters in order to optimize cup positioning and prevent episodes of instability. There are various direct measurements used to assess spinopelvic balance, including pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), sacral slope (SS), and sagittal vertical axis (SVA) in addition to derived parameters such as the PI-LL and Roussouly classification.¹⁹^,²⁰ Authors have begun to assess the relationship between these parameters and instability after THA.¹⁶^,^21–24 However, there is minimal data on the impact of spinopelvic parameters and cup positioning on patient reported outcomes (PROs) after surgery.²⁵

While researchers have begun to define the relationship between spinopelvic parameters and instability after THA, additional research with broad inclusion of spinopelvic parameters is needed to develop a more complete understanding of the relationship between these parameters and cup positioning after THA. In addition, there is a lack of data regarding patient-reported outcomes measures (PROMs) concerning acetabular cup positioning in the context of spinopelvic alignment. Therefore, the primary goal of our study was to identify specific spinopelvic parameters that may impact acetabular cup positioning in THA. Secondarily, we aimed to assess the impact of spinopelvic parameters on post-operative complications and PROMS after THA.

2 Methods

2.1

2.1 Study design and participants

Following approval from the institutional review board, patient charts and records were retrospectively reviewed, focusing on individuals who underwent primary THA at a single institution between March 2019 to May 2023. All surgeries were performed by a single board-certified surgeon.

Patients were excluded if they did not have preoperative standing stereoradiography (EOS) imaging completed or if PROs data were missing from any of the preoperative, 3-month or 12-month postoperative time frames. Demographic data, including age, gender, and body mass index (BMI) were collected from electronic medical records. Clinical outcomes assessed included dislocation, 90-day readmission, reoperation, and any postoperative complication. Additional data from the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) registry were included in the analysis.

2.2

2.2 Postoperative outcome measures

Through the FORCE-TJR database, perceived quality of life (QoL), activities of daily living (ADL) and pain were evaluated at preoperative, 3-month, and 12-month time points following THA. These outcomes were assessed using the Hip Disability Osteoarthritis Outcome Score (HOOS), which is a validated instrument commonly utilized in orthopedic research to measure pain and functional outcomes in hip arthroplasty.²⁶ Additionally, the mental component score (MCS) and physical component score (PCS) were measured using the Veterans RAND-12 form (VR-12) and retrospectively extracted from the FORCE-TJR database. Lower scores indicate lower perceived QOL, reduced ability to perform ADLs, lower functional status (PCS), and worse emotional health (MCS). Whereas a lower pain score signifies greater knee pain. Postoperative clinical data including dislocation, 90-day readmission, reoperation and any other complications were obtained from electronic medical records.

2.3

2.3 Radiographic measurements

Preoperative EOS imaging performed at the time of indication for THA was reviewed to evaluate the pelvic parameters. A consistent protocol was utilized, with two orthopedic staff performing these measurements. Acetabular cup inclination and anteversion were measured on standing anterior posterior X-rays using Brainlab TraumaCad (Westchester, IL) software, following a reliable and established method. The following pelvic measurements were conducted in reference to Murtagh et al.²⁷ Pelvic obliquity, pelvic incidence, pelvic tilt, sacral slope, pelvic flexion were all measured using the standing long-leg, two-view EOS images (Fig. 1a–b).

Methods for measuring pelvic parameters on a lateral (a) and anterior (b) view of EOS imaging. Pelvic incidence (PI) is measured as the angle between a line perpendicular to the superior plate of S1 and a line passing through the axis of the femoral head. Pelvic tilt (PT) is defined as the angle between the line connecting the midpoint of the sacral plate to the femoral head axis (C) and a vertical reference line (V). Sacral slope (SS) is the angle between the horizontal plane (H) and the superior endplate of S1. The anterior pelvic plane (APP) angle is calculated as the angle between a vertical line and a line connecting the bilateral anterior superior iliac spines (ASIS) to the pubic symphysis. Pelvic obliquity, defined as the angle between a horizontal line parallel to the floor and a line connecting the superior aspects of the bilateral iliac wings.

2.4

2.4 Statistical analysis

Data was captured on an excel spreadsheet, and SPSS (IBM SPSS Statistics, Version 25.0. Armonk, NY: IBM Corp.) was used to perform statistical analysis. Continuous variables were described as means ± standard deviations and categorical variables as numbers and percentages. A Pearsons’ correlation was used to assess which pelvic parameters correlated with PROMS pre-operatively and their improvement at 3 and 12 months post-operatively. The cutoff point for statistical significance was set at p = 0.05.

3 Results

3.1

3.1 Patient characteristics

90 patients who had undergone a primary THA were included in this study. This cohort had a mean age of 67.9 ± 10.2 years and a mean BMI of 29.0 ± 6.2 with 56 being females (62 %) and 34 being males (38 %). Pelvic parameters had a mean of 43.6 ± 6.2° for acetabular inclination, 25.3 ± 8.8° for acetabular version, 54.5 ± 12.0° for pelvic incidence, 15.7 ± 8.3° for pelvic tilt, 38.4 ± 11.7° for sacral slope, 4.9 ± 8.8° for flexion, and 2.3 ± 2.0° for obliquity. Post-operatively, only 1 (1.1 %) patient had a reoperation, 2 (2.2 %) had a dislocation, 5 (5.5 %) were readmitted within 90 days post-operatively, and 11 (12.1 %) had complications. None of these adverse events were found to be associated with spinopelvic parameters or cup position.

3.2

3.2 Correlation of spinopelvic parameters with cup position

When evaluating acetabular version, there were weak, negative correlations with both sacral slope (R = −0.31, p = 0.002)(Fig. 2a) and pelvic incidence (R = −0.23, p = 0.02)(Fig. 2b). As for acetabular cup inclination, there was a weak, positive correlation with pelvic tilt (R = 0.30, p = 0.003)(Fig. 2c). The remaining correlations can be found in Table 1.

Correlation of spinopelvic parameters with acetabular cup position. (a) Sacral slope demonstrated a negative correlation with acetabular version. (b) Pelvic incidence showed a similar negative correlation with acetabular version. (c) Pelvic tilt demonstrated a positive correlation with acetabular cup inclination.

Table 1 Associations between pelvic parameters and cup positioning.

Variables	Inclination		Version
Variables	R	p-value	R	p-value
Flexion	−0.13	0.2	−0.08	0.43
Pelvic Incidence	0.17	0.1	−0.23	0.02
Sacral Slope	−0.1	0.33	−0.31	0.02
Pelvic Tilt	0.3	0.003	0.06	0.54

3.3

3.3 Correlation with PROMs

At 3 months postoperatively, none of the pelvic parameters correlated with any of the PROMs. However, at 12 months postoperatively, acetabular inclination was shown to predict the improvement in MCS (R = 0.28, p = 0.02), and obliquity was shown to predict the improvement in activities of daily living (R = 0.29, p = 0.02), pain (R = 0.28, p = 0.03) and quality of life (R = 0.30, p = 0.002) (Table 2).

Table 2 Correlation between pelvic parameters and 12-month postoperative patient-reported outcome measures.

Variable	R	p-value
PCS
Flexion	−0.02	0.91
Obliquity	0.09	0.49
Pelvic Incidence	0.12	0.33
Sacral Slope	0.14	0.26
Pelvic tilt	−0.05	0.7
Inclination	−0.08	0.52
Version	0.12	0.36
MCS
Flexion	−0.05	0.69
Obliquity	0.004	0.98
Pelvic Incidence	−0.17	0.18
Sacral Slope	−0.2	0.11
Pelvic tilt	0.001	1
Inclination	0.28	0.02
Version	0.04	0.77
ADL
Flexion	−0.1	0.45
Obliquity	0.29	0.02
Pelvic Incidence	−0.06	0.67
Sacral Slope	−0.01	0.93
Pelvic tilt	−0.09	0.51
Inclination	−0.03	0.83
Version	0.2288	0.08
PAIN
Flexion	−0.07	0.6
Obliquity	0.23	0.03
Pelvic Incidence	−0.07	0.59
Sacral Slope	−0.05	0.7
Pelvic tilt	−0.04	0.78
Inclination	0.06	0.65
Version	0.23	0.07
QoL
Flexion	0.11	0.4
Obliquity	0.3	0.02
Pelvic Incidence	−0.2	0.11
Sacral Slope	−0.09	0.48
Pelvic tilt	−0.16	0.2
Inclination	−0.004	0.98
Version	0.13	0.33

4 Discussion

With a continued emphasis on optimizing the quality of surgical care, it is imperative to understand all factors that affect PROMs following common orthopaedic procedures such as THA. The results of the current study provide a unique perspective on the evaluation of PROMs after THA, with a focus on the effect of cup positioning and spinopelvic parameters on PROMs. One year postoperatively, acetabular inclination was found to have a positive association with PROMs, while increasing pelvic obliquity predicted improvements in scores related to ADLs, pain, and QOL. There were several weak correlations between cup position and spinopelvic parameters, in which acetabular version had a negative correlation with PI and SS, and a positive correlation to PT. In our series, spinopelvic parameters and cup position based upon static EOS imaging was not associated with instability or other complications, which is important given certain cup positions in the context of spinopelvic parameters have been shown to be associated with increased instability.²⁴

Attention to spinopelvic parameters has been a focus of THA literature in recent years. Grammatopoulos et al. found that spinopelvic imbalance (PI-LL>10°) and combined sagittal index (CSI) outside of 205–245° were associated with increased dislocation risk.¹⁶ Additionally, Vigdorchick highlighted that posterior pelvic tilt (PT < −15°) on standing radiographs predicted instability.²¹ Heckmann et al. demonstrated that decreased spinopelvic motion is associated with increased femoral motion, leading to impingement and dislocation.²² Esposito et al. found that fixed spinopelvic alignment from standing to sitting portends a higher risk of dislocation.²³ The results of the current study demonstrate that cup anteversion is negatively, albeit weakly, correlated with pelvic incidence and sacral slope. Pelvic incidence is an anatomically fixed angle made by a line connecting the acetabular centroid to the center of the superior endplate of S1 and a line perpendicular to the superior endplate of S1.²⁸

Given that pelvic incidence is the summation of sacral slope and pelvic tilt, it is possible that the sacral slope is driving this correlation, especially since PT was not correlated with anteversion.²⁹ Importantly, we acknowledge that patients were not evaluated for spinal mobility as there were not preoperative sitting EOS films obtained which limits the application of this association. It is possible that patients included in the study with stiff spines who are “stuck standing” have cups that were placed with too little anteversion, although we did not see an increase in adverse events associated with this. Patients with a high pelvic incidence have been shown to have signs of decreased femoral head coverage.³⁰ This would suggest the need for increased cup version in THA to adjust for the relative uncovering which could potentially result in a cup position that is in a less anatomic position, given that PI is a fixed measurement. Our study found patients with high PI have low anteversion on postoperative imaging, which is perhaps related to efforts intraoperatively to match the patient's native anatomy.

PROMs have yet to be studied extensively in the context of spinopelvic parameters and THA. Fontalis et al. demonstrated that considering spinopelvic parameters to help determine cup positioning was associated with significant improvements in PROMs.²⁵ An interesting finding in the present study is the positive correlation between preoperative pelvic obliquity and improvement in various PROMs after surgery. Other authors have demonstrated that pelvic obliquity is associated with more advanced osteoarthritis.³¹ As a result, these patients may be starting at a lower function baseline and thus have more room for improvement after THA. This is an important consideration for surgeons when considering preoperative factors associated with improved patient reported outcomes after THA. Additionally, while spinopelvic parameters were not significantly associated with adverse events, there was a positive correlation between pelvic tilt and acetabular inclination; as such, the lack of significant association should be interpreted with caution given the overall low rate of adverse events in the study population and the relatively small patient population studied.

4.1

4.1 Limitations

Despite the various clinically important findings of the current study, this work is not without limitation. Firstly, there are various well understood limitations inherent to retrospective review. In particular, unknown relationships between those included in this study cohort and their personal characteristics may exist which could confound the results. In addition, as mentioned previously, the rate of adverse events was likely too low for statistically significant associations with cup positioning or spinopelvic parameters to be established. The study had a relatively low sample size, which could also affect statistical significance of the relationships as a greater sample size may produce or reduce significant findings. Importantly, dynamic radiographic analysis of spinopelvic parameters during sitting and standing may be more important than one static EOS imaging for determining the best cup placement during THA for reduction of dislocation rates, producing a notable limitation in our radiographic analysis.²²

5 Conclusion

In the first year following THA, acetabular inclination was found to have a positive association with patient-reported outcome measures, while increasing pelvic obliquity predicted improvements in scores related to activities of daily living, pain, and quality of life. Acetabular version was found to have a weak, negative correlation with pelvic incidence and sacral slope, and a weak positive correlation to pelvic tilt. Spinopelvic parameters and cup position based upon static EOS imaging was not associated with instability or other complications.

Credit author statment

JL, SC, and MD: Writing – original draft, NG, TC, JH, ET: Collecting data, AHD, VA: Writing – review & editing.

Ethical statement

All patients signed an informed consent form and procedures were conducted according to the Declaration of Helsinki.

Funding

None.

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