Repeated posterior dislocation of total hip arthroplasty after spinal corrective long fusion with pelvic fixation

Challenges in Total Hip Arthroplasty with Prior Spinal Arthrodesis: A Comprehensive Review of Biomechanics, Complications, and Surgical Strategies

Total hip arthroplasty (THA) has revolutionized patients' lives with hip osteoarthritis. However, the increasing prevalence of THA in individuals with prior lumbar arthrodesis (LA) poses unique challenges. This review delves into the biomechanical alterations, complications, and surgical strategies specific to this patient subset, highlighting the need for tailored preoperative assessments and planning. Due to altered pelvic and spinal biomechanics, patients with LA undergoing THA face a higher risk of dislocation and revision. The complex interplay between spinal and hip biomechanics underscores the need for meticulous preoperative planning. Comprehensive clinical examination and radiographic evaluation are vital for understanding patient-specific challenges. Various radiographic techniques, including computed tomography (CT)/X-ray matching and standing/seated studies, provide insights into postural changes affecting pelvic and spinal alignment. Complications following THA in patients with LA highlight the necessity for personalized surgical strategies. Careful consideration of implant selection, the surgical approach, and component positioning are essential to prevent complications. In summary, THA in patients with prior LA demands individualized preoperative assessments and planning. This approach is crucial to optimize outcomes and mitigate the heightened risks of complications, underlining the importance of tailored surgical strategies.

Correlation between Acetabular Anteversion with a False-Profile View and Spinopelvic Parameters in Adult Spinal Deformity after Long-Segment Corrective Spinal Surgery

Introduction

Studies describing the relationship between the hip and spine have reported that corrective spinal surgery for adult spinal deformity (ASD) affects the orientation of the acetabulum. However, the extent to which spinal correction in ASD affects acetabular anteversion in the standing position is unclear, especially after total hip arthroplasty, for which dislocation is a concern. The purpose of this study was to evaluate changes in anterior acetabular coverage in the upright position due to extensive correction surgery for ASD.

Methods

Thirty-six consecutive patients who had undergone spinal corrective surgery from the thoracolumbar region to the pelvis were enrolled and evaluated. The ventral-central-acetabular (VCA) angle and anterior acetabular head index (AAHI) were measured with a false-profile view to evaluate the relationship between acetabular anteversion in the standing position and spinopelvic parameters before and after surgery. The spinopelvic parameters measured included thoracic kyphosis, pelvic incidence, pelvic tilt (PT), sacral slope, lumbar lordosis (LL), sagittal vertical axis, and global tilt.

Results

The VCA angle and AAHI were significantly increased after spinal deformity correction (p<0.001). The changes in LL and PT were correlated with the VCA angle (LL: right, ρ=0.56; left, ρ=0.55, p<0.001; PT: right, ρ=-0.59; left, ρ=-0.64, p<0.001) and AAHI (LL: right, ρ=0.51; left, ρ=0.58, p<0.01; PT: right, ρ=-0.52; left, ρ=-0.59, p<0.01), respectively. Linear regression analysis revealed that a 10° increase in LL results in 1.4°-1.9° and 1.6%-2% increases in the VCA angle and AAHI, respectively.

Conclusions

Surgical correction for ASD significantly affects sagittal spinopelvic parameters, resulting in increased acetabular anteversion. The anterior coverage of the acetabulum in the postoperative standing position could be predicted with the intraoperatively measured LL, and evaluation using a false-profile was considered useful for treating ASD, particularly in patients after total hip arthroplasty.

Mobility of the lumbo-pelvic-hip complex (spinopelvic mobility) and sagittal spinal alignment - implications for surgeons performing hip arthroplasty

INTRODUCTION

The optimal positioning of the hip prosthesis components is influenced by the mobility and balance of the spine. The present study classifies patients with pathology of the spino-pelvic-hip complex, showing possible methods of preventing hip dislocations after arthroplasty.

HYPOTHESIS

Hip-Spine Classification helps arthroplasty surgeons to implant components in more patient-specific position.

MATERIALS AND METHODS

The group of 100 patients treated with total hip arthroplasty. Antero-posterior (AP) X-rays of the pelvis in a standing position, lateral spine (standing and sitting) and AP of the pelvis (supine after the procedure) were analyzed. We analyzed a change in sacral tilt value when changing from standing to sitting (∆SS), Pelvic Incidence (PI), Lumbar Lordosis (LL) Mismatch, sagittal lumbar pelvic balance (standing position). Patients were classified according to the Hip-Spine Classification. Postoperatively, the inclination and anteversion of the implanted acetabular component were measured.

RESULTS

In our study 1 A was diagnosed in 61% of all cases, 1B in 18%, 2 A in 16%, 2B in 5%. 50 out of 61 (82%) in group 1 A were placed within the Levinnek "safe zone". In 1B, 2 A, 2B, the position of the acetabular component was influenced by both the spinopelvic mobility and sagittal spinal balance. The mean inclination was 43.35° and the anteversion was 17.4°.

CONCLUSIONS

Categorizing patients according to Hip-Spine Classification one can identify possible consequences the patients at risk. Pathology of the spino-pelvic-hipcomplex can lead to destabilization or dislocation of hip after surgery even though implanted according to Lewinnek's indications. Our findings suggest that Lewinnek safe zone should be abandoned in favor of the concept of functional safe zones.

Superior outcomes of total hip arthroplasty without prior lumbar arthrodesis: a systematic review and meta-analysis

PURPOSE

The number of patients undergoing total hip arthroplasty (THA) surgery after previous lumbar arthrodesis (LA) is rising. Literature suggests that LA may significantly impact pelvic biomechanics and potentially compromise the success of prosthetic hip replacement. This study aims to evaluate complication rates, dislocation rates, and revision rates in patients with prior LA undergoing THA surgery compared to those undergoing THA surgery without prior LA.

METHODS

A systematic review and meta-analysis were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A PICOS template was developed to ensure a structured approach. The search for relevant studies was performed across five databases, including Pubmed, Scopus, Embase, Medline, and Cochrane. The selected articles were evaluated based on the Levels of Evidence (LoE) criteria. The Coleman Methodology Score (mCMS) was employed to analyze the retrospective studies. This systematic review and meta-analysis were registered in the International Prospective Register of Systematic Reviews (PROSPERO). For the outcomes that allowed for a meta-analysis performed using R software, a p < 0.05 was considered statistically significant.

RESULTS

The final analysis included seventeen studies comprising a total of 3,139,164 cases of THA. Among these cases, 3,081,137 underwent THA surgery alone, while 58,027 patients underwent THA with a previous LA. The study investigated various factors, including dislocation rates, revision rates, and complication, as well as the surgical approach and type of implant used, for both the THA-only group and the group of patients who underwent THA with prior LA. The analysis revealed a statistically significant difference (p < 0.05) for all variables studied, favoring the group of patients who underwent THA alone without prior LA.

CONCLUSIONS

This systematic review and meta-analysis demonstrated a statistically significant superiority in all analyzed outcomes for patients who underwent THA-only without prior LA. Specifically, patients with isolated THA implants experienced significantly lower incidences of THA dislocation, wound complications, periprosthetic joint infection, revision, and mechanical complications.

LEVEL OF EVIDENCE

Level IV.

Increased dislocation rates following total hip arthroplasty in patients with ankylosing spondylitis

BACKGROUND

Patients with ankylosing spondylitis (AS) experience abnormal spinopelvic motion due to chronic inflammation of the axial skeleton, predisposing them to impingement and dislocation. The purpose of this study was to evaluate total hip arthroplasty (THA) dislocation rates in AS patients and evaluate the effects of age and gender on dislocation risk.

METHODS

Patients who underwent primary THA from 2005 to 2014 were identified using the PearlDiver database. AS patients were compared to age- and gender-matched controls without AS. Patients with a history of spine pathology or spine surgery were excluded. Univariate analyses were performed based on age and sex to evaluate dislocation rates at 90 days, 6 months, 1 year, and 5 years postoperatively.

RESULTS

A total of 2792 THA patients (59.6% male) with AS were identified and compared to an age- and gender-matched control group of 5582 THA patients (59.5% male) without AS or known spine pathology. At final follow-up, there were 96 dislocations (3.4%) in the AS group and 138 (2.5%) dislocations in the control group (OR 1.40; 95% CI, 1.08-1.83; p = 0.0118). AS patients ⩾70 years old had higher dislocation rates at all time points (OR range, 1.75-2.09; p < 0.05) compared to controls. At 5-year follow-up, dislocation-free survivorship was 95.7% (95% CI, 94.5-96.9%) for AS patients ⩾70 years old compared to 97.3% (95% CI, 96.6-98.0%) for patients ⩾70 years old without AS.

CONCLUSIONS

Older AS patients have higher dislocation rates following THA. This effect is likely related to decreased spinopelvic motion in the sagittal plane, predisposing patients to impinge and dislocate.

Risk of Dislocation and Revision Following Primary Total Hip Arthroplasty in Patients With Prior Lumbar Fusion With Spinopelvic Fixation

BACKGROUND

The effect of spinopelvic fixation in addition to lumbar spinal fusion (LSF) on dislocation/instability and revision in patients undergoing primary total hip arthroplasty (THA) has not been reported previously.

METHODS

The PearlDiver Research Program was used to identify patients aged 30 and above undergoing primary THA who received (1) THA only, (2) THA with prior single-level LSF, (3) THA with prior 2-5 level LSF, or (4) THA with prior LSF with spinopelvic fixation. The incidence of THA revision and dislocation/instability was compared through logistic regression and Chi-squared analysis. All regressions were controlled for age, gender, and Elixhauser Comorbidity Index (ECI).

RESULTS

Between 2010 and 2018, 465,558 patients without history of LSF undergoing THA were examined and compared to 180 THA patients with prior spinopelvic fixation, 5,299 with prior single-level LSF, and 1,465 with prior 2-5 level LSF. At 2 years, 7.8% of THA patients with prior spinopelvic fixation, 4.7% of THA patients with prior 2-5 level LSF, 4.2% of THA patients with prior single-level LSF, and 2.2% of THA patients undergoing only THA had a dislocation event or instability (P < .0001). After controlling for length of fusion, pelvic fixation itself was associated with higher independent risk of revision (at 2 years: 2-5 level LSF + spinopelvic fixation: aHR = 3.15, 95% CI 1.77-5.61, P < .0001 vs 2-5 level LSF with no spinopelvic fixation: aOR = 1.39, 95% CI 1.10-1.76, P < .0001).

CONCLUSION

At 2 years, spinopelvic fixation in THA patients were associated with a greater than 3.5-fold increase in hip dislocation risk compared to those without LSF, and an over 2-fold increase in THA revision risk compared to those with LSF without spinopelvic fixation.

LEVEL OF EVIDENCE

III.

Does the Change of Acetabular Anteversion Result From Lumbar Pedicle Subtraction Osteotomy in Ankylosing Spondylitis-Related Kyphosis After Primary Total Hip Arthroplasty?

STUDY DESIGN

Retrospective study.

OBJECTIVES

To analyze the change in acetabular anteversion (AA) after lumbar pedicle subtraction osteotomy (PSO) in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis who have already undergone total hip arthroplasty (THA).

METHODS

AS patients with thoracolumbar kyphosis following lumbar PSO from January 2005 to January 2020 were retrospectively reviewed. Only the patients performed with THA prior to the PSO were included. AA was measured on the full-length standing posterior-anterior radiographs using the ellipse method.

RESULTS

Twenty patients (34 hips) with a mean age of 36.8 years (range, 22 to 63 years) were included. After lumbar PSO, AA was reduced from 18.59° to 5.85° (P < 0.001). Postoperative change in AA was correlated with the spinal deformity correction. Additionally, the change in AA postoperatively was correlated with pelvic incidence (PI) (R = 0.346, P = 0.045). Although the postoperative change in sagittal vertical axis (SVA) was larger in the patients after L2 or L3 PSO (153.97 mm vs 70.03 mm, P = 0.006), no difference was found in the postoperative change in AA (12.83° vs 10.96°, P = 0.540) compared with the patients following L1 PSO.

CONCLUSIONS

AA was significantly decreased following lumbar PSO and the postoperative change in AA was correlated with the magnitude of spinal deformity correction. Notably, the effect of osteotomy level on the postoperative change in AA was limited in the AS patients underwent 1-level PSO.

How does corrective fusion surgery for adult spinal deformities affect pelvic inclination in the supine position as the reference plane for THA?

PURPOSE

To determine the changes in pelvic inclination in the supine and standing positions after spinal corrective surgery, and to identify the most predictive factor for changes in pelvic inclination with the supine position as the reference plane for total hip arthroplasty.

METHODS

We retrospectively analysed the data of 124 patients who underwent spinal corrective fusion surgery for adult spinal deformity between 2012 and 2016 at our institution. Spinal parameters were assessed preoperatively and postoperatively using whole spine radiographs in the standing position. The sacral slope (SS) was measured using spine and pelvis computed tomography. Differences between the preoperative and postoperative SS values in each position were calculated as Δsupine SS_{pre post} and Δstanding SS_{pre post}, respectively. We statistically analysed the correlations between Δsupine SS _{pre post} and preoperative spinal parameters to determine the most useful predictor of Δ supine SS_{pre post}.

RESULTS

The mean Δsupine SS_{pre post} of 10.5°(-13°-50°) was significantly smaller than the mean Δstanding SS_{pre post} of 13.2° (-19°-44°) (p = 0.02). Moreover, 21 patients (17%) had Δsupine SS_{pre post} > 20°. The Δsupine SS _{pre post} was correlated with preoperative LL (r = -0.34 p < 0.01), PT (r = 0.42 p < 0.01), and SVA (r = 0.37 p < 0.01). Preoperative supine SS (r = -0.54, p < 0.01) had the highest correlation with Δsupine SS_{pre post}, whereas preoperative standing SS showed no correlation (r = -0.14 p = 0.12).

CONCLUSION

Preoperative supine SS is the most useful predictive factor for changes in supine pelvic inclination, and low preoperative values should be noted. This information should be considered for the management of patients with hip-spine syndrome.

Improvement of Coxarthrosis Due to Realignment of Pelvic Retroversion Following Spinal Corrective Surgery: A Case Report

CASE

A 70-year-old woman presented with severe trunk deformity, gait disturbance, and bilateral hip pain. Radiography and magnetic resonance imaging revealed severe spinal kyphosis, bilateral osteoarthritis of the hip joints, and lumbar canal stenosis. A 2-stage corrective surgery for the treatment of spinal kyphosis was performed. Subsequently, the spinopelvic alignment changed remarkably. The spinal symptoms and radiographic parameters improved postoperatively, and bilateral hip pain and range of motion also showed improvement.

CONCLUSION

Corrective surgery for the treatment of degenerative spinal kyphosis affected the spinopelvic alignment, and the symptoms of simultaneous coxarthrosis also improved after the corrective surgery.

Risk Factors for Progressive Spinal Sagittal Imbalance in the Short-Term Course after Total Hip Arthroplasty: A 3 Year Follow-Up Study of Female Patients

Total hip arthroplasty (THA) for patients with hip osteoarthritis improves hip flexion contracture, subsequently improving spinal sagittal balance. However, in some cases, spinal sagittal imbalance develops in the course after THA, and its risk factors remain unknown. We aimed to investigate the risk factors of progressive spinal sagittal imbalance after THA. This retrospective cohort study of a prospectively maintained database included female patients aged ≥50 years who underwent THA. Before performing THA, we obtained each patient’s anthropometric and muscle strength measurements and whole-spine radiographs. Three years postoperatively, patients underwent whole-spine radiography to examine changes in the spinal sagittal balance. Patients were assigned into groups on the basis of their preoperative and 3 year postoperative sagittal vertical axis (SVA) values. Patients with 3 year postoperative SVA values ≥40 mm with an increase ≥30 mm were categorized into the imbalance group; the other patients were categorized into the non-imbalance group. Of 103 patients, 11 (10.7%) were in the imbalance group. In multiple logistic regression analysis, preoperative weak abdominal trunk muscle strength (ATMS) (p = 0.007) and small sacral slope (SS) (p = 0.005) were significant risk factors for progressive spinal sagittal imbalance. In conclusion, risk factors for progressive spinal sagittal imbalance after THA were weak preoperative ATMS and small SS.

The Effect of Hip Offset and Spinopelvic Abnormalities on the Risk of Dislocation Following Total Hip Arthroplasty

BACKGROUND

Previous studies have demonstrated that patients with abnormal spinopelvic motion are at increased risk of dislocation. However, little is known about the effect of hip offset on dislocation risk following total hip arthroplasty (THA) in patients with abnormal spinopelvic motion. The purpose of this study is to investigate the prevalence of under-restored hip offset and spinopelvic abnormalities in a series of THA patients treated for recurrent instability.

METHODS

This is a retrospective review of consecutive patients treated for hip instability following primary THA (THA+I) from 2012 to 2020. Patient demographics, surgical variables, and radiographic parameters were recorded. THA+I patients were compared to an age-matched and gender-matched control THA population without hip instability (THA). Univariate analyses were performed to compare differences between groups.

RESULTS

Thirty-three THA+I patients (44 hips) were compared to 44 THA patients (44 hips). THA+I patients had a higher prevalence of spinopelvic pathology (odds ratio [OR] 7.80, 95% confidence interval [CI] 2.59-23.50, P < .001). The majority of acetabular components were placed within the Lewinnek safe zone (86.4% THA+I vs 72.7% THA; P = .119). THA+I patients were at greater risk of markedly under-restored hip offset (Δoffset ≤ 3 mm; OR 6.34, 95% CI 2.20-18.30, P = .001) and small (<32 mm) femoral head diameter (OR 4.38, 95% CI 1.53-12.53, P = .006) compared to THA patients.

CONCLUSION

Lumbar degenerative disease and under-restoration of hip offset were present in a high proportion of patients with hip instability. Although multiple factors may contribute to THA instability, these data suggest that restoration of offset is essential, particularly in patients with spinopelvic pathology, and may be more important than historically described acetabular targets.

LEVEL OF EVIDENCE

Level III.

Impact of the hip joint mobility on whole-body sagittal alignment: prospective analysis in case with hip arthroplasty

PURPOSE

To clarify the impact of restriction of hip extension on radiographic whole-body sagittal alignment with using postoperative changes of radiographical parameters for hip osteoarthritis.

METHODS

We prospectively enrolled 68 patients with hip osteoarthritis scheduled for arthroplasty. Variables included manual examination of hip range of motion (H-ROM) and radiographic whole-body sagittal alignment parameters including sagittal vertical axis (SVA), center of acoustic meatus and femoral head offset (CAM-HA), thoracic kyphosis (TK), lumbar lordosis, sacral slope (SS), and knee flexion angle (KF). We divided patients with preoperative hip extension angle < 0 into the extension restriction (ER) + group and ≥ 0 into the ER- group. Differences in H-ROM, radiographic parameters between groups and postoperative changes were comparatively analyzed.

RESULTS

Fifty-seven patients (The ER + group included 28 patients and the ER- group included 29 patients.) were available for the analysis. Pre-/postoperative H-ROM were 99.7 ± 24.9/118.1 ± 16.0 degrees (p < .01). Greater increases in SVA (5.4 ± 3.4 vs 3.4 ± 2.8 cm, p = .02) and in CAM-HA (3.9 ± 3.9 vs 2.8 ± 3.4 cm, p =  013) were found in the ER + group versus ER- group. Postoperatively, the ER + group showed an increase in TK (pre-/postoperative: 35.2 ± 9.7/37.4 ± 8.8 degrees, p = .04) and decreases in SS (36.5 ± 9.6/33.7 ± 9.9 degrees, p < .01) and KF (9.5 ± 7.0/6.9 ± 6.0 degrees, p = .02). Postoperative changes in radiographic parameters in the ER- group were not significant.

CONCLUSION

Patients with restriction of hip extension showed global spine imbalance, and significant changes in TK, SS, and KF were observed after arthroplasty. The presence of hip joint disorder and H-ROM restriction must be considered when evaluating spinopelvic alignment and whole-body sagittal alignment.

Influence of lumbar sagittal profile on pelvic orientation and pelvic motion during postural changes in patients with ankylosing spondylitis-related thoracolumbar kyphosis following pedicle subtraction osteotomy

OBJECTIVE

The objective of this study was to investigate the impact of the lumbar sagittal profile on pelvic orientation and pelvic motion during postural changes in patients with ankylosing spondylitis (AS) and thoracolumbar kyphosis and to evaluate the potential risk of prosthetic dislocation after total hip arthroplasty (THA) following pedicle subtraction osteotomy (PSO).

METHODS

Seventy-two patients with AS-related thoracolumbar kyphosis following spinal osteotomy were retrospectively reviewed, and 21 healthy volunteers were recruited as a control group. Pre- and postoperative 2D full-body images in standing and sitting positions were obtained to evaluate the anterior pelvic plane angle (APPA), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), proximal femur angle (PFA), and femoroacetabular flexion during postural changes. Patients with AS were categorized in either a lordotic or kyphotic group based on the lumbar sagittal profile.

RESULTS

Significant increases in the SS and decreases in the APPA, PT, and LL were observed postoperatively in both the standing and sitting positions (p < 0.001 for all). Significantly higher APPA, PT, LL, and ΔPT, and lower SS, ΔSS, and ΔSS+ΔPFA were observed in the kyphotic group (p < 0.05). After undergoing PSO, ΔPT and ΔSS significantly decreased while femoroacetabular flexion significantly increased in both AS groups (p < 0.05), and no significant difference was present between the two groups (p > 0.05). Bath Ankylosing Spondylitis Radiology Hip Index scores in the kyphotic group were significantly worse than those in the lordotic group pre- and postoperatively (p < 0.05). No significant difference in parameters concerning pelvic motion (ΔAPPA, ΔPT, and ΔSS) was found when PSO was performed in the thoracolumbar or lumbar spine.

CONCLUSIONS

Lumbar sagittal profiles greatly affect pelvic orientation and pelvic motion in AS. When THA is performed before PSO, AS patients with lumbar kyphosis are at higher risk of anterior prosthetic dislocation, while those with lordotic lumbar sagittal profiles are at higher risk of posterior dislocation. PSO should be performed prior to THA. After PSO, further decreased pelvic motion indicated a potential risk of posterior prosthetic dislocation after sequential THA, whereas theoretically patients with preoperative lumbar kyphosis are at higher risk of THA dislocation. The site where PSO was performed (thoracolumbar or lumbar spine) does not influence the risk of THA dislocation.

Kinematic pelvic tilt during gait alters functional cup position in total hip arthroplasty

Static pelvic tilt impacts functional cup position in total hip arthroplasty (THA). In the current study we investigated the effect of kinematic pelvic changes on cup position. In the course of a prospective controlled trial postoperative 3D-computed tomography (CT) and gait analysis before and 6 and 12 months after THA were obtained in 60 patients. Kinematic pelvic motion during gait was measured using Anybody Modeling System. By fusion with 3D-CT, the impact of kinematic pelvic tilt alterations on cup anteversion and inclination was calculated. Furthermore, risk factors correlating with high pelvic mobility were evaluated. During gait a high pelvic range of motion up to 15.6° exceeding 5° in 61.7% (37/60) of patients before THA was found. After surgery, the pelvis tilted posteriorly by a mean of 4.0 ± 6.6° (p < .001). The pelvic anteflexion led to a mean decrease of -1.9 ± 2.2° (p < .001) for cup inclination and -15.1 ± 6.1° (p < .001) for anteversion in relation to the anterior pelvic plane (APP). Kinematic pelvic changes resulted in a further change up to 2.3° for inclination and up to 12.3° for anteversion. In relation to the preoperative situation differences in postoperative cup position ranged from -4.4 to 4.6° for inclination and from -7.8 to 17.9° for anteversion, respectively. Female sex (p < .001) and normal body weight (p < .001) correlated with high alterations in pelvic tilt. Kinematic pelvic changes highly impact cup anteversion in THA. Surgeons using the APP as reference should aim for a higher anteversion of about 15° due to the functional anteflexion of the pelvis during gait.

Adjunct pelvic fixation in short-to-medium segment degenerative fusion constructs independently predicts readmission and morbidity

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Surgical correction for adult spinal deformity increases acetabular lateral coverage of femoral heads

BACKGROUND

Studies explaining the relationship between hip and spine reported that spinal corrective surgery affected acetabular orientation and changes in pelvic tilt were capable of influencing radiographic measures of acetabular coverage. This study aimed to assess the change in coronal parameters for acetabular coverage as a result of adult spinal deformity (ASD) correction and to analyze the relationship between the postoperative changes in sagittal spinopelvic parameters and coronal acetabular coverage parameters.

METHODS

Fifty-two consecutive patients who had undergone multilevel spinal surgical correction were enrolled and evaluated. Coronal acetabular coverage parameters included Tönnis angle (TA), lateral center edge angle (LCEA), and the angle of Sharp (SA). All radiographic parameters were evaluated at the preoperative and the postoperative 1 year. Paired t test was used to determine whether there were significant changes between the time points. Bivariate correlation and linear regression analysis were used to assess the relationship between the postoperative changes of spinal alignment and acetabular orientation.

RESULTS

The surgical correction resulted in significant decrease of TA, increase of LCEA and SA, respectively (p < 0.001). The changes in pelvic tilt (PT) demonstrated weak correlation on TA (β = 0.117, p < 0.001 for right; β = 0.111, p < 0.001 for left).

CONCLUSIONS

Although the surgical correction of ASD significantly changed PT resulting in increased acetabular lateral coverage parameters, the correlation between the changes of PT following sagittal correction of ASD and acetabular coverage parameters was low.

TRIAL REGISTRATION

This study was retrospectively registered with approval by the institutional review board (IRB) of our institution (approval number: KHNMC-2020-10-010).

Pelvic incidence affects postoperative dislocation rate in total hip arthropalsty patients with spinal fusion

PURPOSE

The purpose of this study was to compare the clinical outcome of total hip arthroplasty (THA) with and without spinal fusion (SF), and to evaluate the radiographic characteristics of patients with dislocation after THA.

METHODS

A case-controlled study of 53 patients (67 hips) who underwent both THA and SF was performed. The control group was matched to the SF group by age, gender and body mass index, and 106 patients (134 hips) were selected. Hip function was evaluated using the Japanese Orthopaedic Association (JOA) hip score. In addition, the incidence rates of postoperative complications were determined. Radiograph evaluation included lateral inclination and anteversion of the acetabular component. We also analysed sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI).

RESULTS

The JOA hip score at final follow up was significantly poorer in the SF group compared to the control group. There were 5 cases of dislocations in the SF group and none in the control group. The anteversion of acetabular cup, PT, and PI were significantly higher in the SF group compare to the control group. In particular, the PI of patients with anterior dislocation were significantly higher compare to those of patients without dislocation.

CONCLUSIONS

Our study showed that SF is a risk factor for a poorer clinical outcome and postoperative dislocation of THA. In addition, the abnormal value of PI may be a risk factor to predict dislocation after THA with SF.

Spinopelvic Biomechanics and Total Hip Arthroplasty: A Primer for Clinical Practice

Abnormal spinopelvic motion from spine pathology is associated with inferior outcomes after total hip arthroplasty, including inferior patient-reported outcomes, increased rates of instability, and higher revision rates. Identifying these high-risk patients preoperatively is important to conduct the appropriate workup and formulate a surgical plan. Standing and sitting lateral spinopelvic radiographs are able to identify and quantify abnormal spinopelvic motion. Depending on the type of spinopelvic deformity, some patients may require increased anteversion, increased offset, and large diameter heads or dual mobility articulations to prevent dislocation. This review article will provide the reader with practical information that can be applied to patients regarding the terminology, pathophysiology, evaluation, and management of total hip arthroplasty patients with spinopelvic pathology.

Managing Hip-Spine Concepts in the Direct Anterior Approach With Use of Fluoroscopy

BACKGROUND

The spinopelvic relationship in regard to total hip arthroplasty has become a topic of increasing interest in recent years. Hip arthritis and a stiff lumbar spine create a situation where the spinopelvic junction has decreased mobility, which in turn increases the risk of instability after total hip arthroplasty as the femoral acetabular joint must undergo increased motion. Regardless of the approach, surgeons should be aware of the risk of instability in patients with a stiff spinopelvic junction and the necessary modifications to component positioning to avoid postoperative instability. As many direct anterior approach surgeons use fluoroscopy for intraoperative navigation, anterior approach surgeons must also understand how to best use this technology to improve component positioning.

METHODS

In this article, we address the basic concepts surrounding spinopelvic stiffness, the intraoperative component adjustments necessary for optimizing stability, and how to appropriately use fluoroscopy for navigation in the direct anterior approach.

CONCLUSIONS

Appropriate use of intraoperative fluoroscopy includes understanding the impact of parallax and distortion, properly recreating the patient's standing functional pelvic plane intraoperatively and adjusting the cup's target position based on a preoperative understanding of the patient's spinopelvic motion.

No linear correlation between pelvic incidence and acetabular orientation: Retrospective observational study

Links between sagittal spinal alignment and acetabular orientation attract considerable research attention with the goal of understanding “hip-spine syndrome.” However, whether pelvic incidence (PI) is related to acetabular orientation remains debatable. The purpose of the present study was to determine: 1. whether the correlation between PI and acetabular orientation is present in pelvises of young healthy adults, and 2. whether the correlation is present in subgroups of sex, or between the left and right pelvis. We analyzed 100 abdominopelvic computed tomography (CT) scans of skeletally healthy young adults. We measured PI and acetabular orientation with three-dimensional (3D) measurements. The orientation of 200 acetabula was measured using 3D reconstructed models of 100 pelvises in the coordinate system based on the anterior pelvic plane (APP). To quantify the acetabular orientation, the radiographic definitions of anteversion and inclination were used. To examine the correlation between acetabular orientation and PI, Pearson's correlation was used. The mean PI was 46.9° ± 10.2°, and the mean acetabular orientation 15.3° ± 5.7° anteverted and 37.5° ± 3.9° inclined. While no significant difference in the PI was observed, the average acetabular orientation of female pelvises (anteversion, 17.5° ± 5.6°; inclination, 36.7° ± 3.7°) was more anteverted and less inclined compared to that of male pelvises (anteversion, 13.2° ± 4.9°; inclination, 38.3° ± 3.9°, respectively; P values < .05). The correlation between PI and acetabular orientation was statistically not significant. After division of study group by sex, the linear correlation between PI and acetabular orientation was not statistically supported. The asymmetry of the acetabular orientation between the left and right sides was not significant. The linear relationship between anatomical acetabular orientation and PI was not evident in the normal population. Our finding thus proves the absence of a linear relationship between the upper and lower articular orientation of the pelvic segment and deepens the understanding of the characteristics of acetabular orientation and PI.

Simulation of Implant Impingement After Spinal Corrective Fusion Surgery in Patients with Previous Total Hip Arthroplasty: A Retrospective Case Series

STUDY DESIGN

A retrospective case series.

OBJECTIVE

The aim of this study was to introduce the prevention of total hip arthroplasty (THA) dislocation using an implant impingement simulation after spinal corrective fusion and to verify the outcomes.

SUMMARY OF BACKGROUND DATA

A high dislocation rate was found among patients who underwent spinal deformity corrective fusion with previous THA. To avoid dislocation, an appropriate position of the stem and cup is important, but the pelvic inclination may change after corrective fusion for spinal deformity.

METHODS

Twelve consecutive patients (two men, 10 women; average age, 72.1 [range, 55-81] years during spine surgery) with previous THA were included. Data were retrospectively retrieved from a single-center's prospectively collected database of adult spinal deformity operation. Before surgery, anterior implant impingement simulation in THA was performed using computed tomography-based software. The tolerable pelvic tilt (PT) in which the anterior implant impingement occurred in the hip at the 120° flexion position was measured. The lumbar lordosis angle was deliberately reduced during spinal surgery according to the tolerable PT. The effect of the implant impingement simulation was verified by comparison with patients who underwent surgery before simulation (before 2014).

RESULTS

THA dislocation occurred in six patients: four of five (80%) in the non-simulation, and two of seven (28.6%) in the simulation group. The difference between the preoperative and tolerable PT angles was-25° to 33°, and three patients had negative angles. In these three patients, the risk of anterior impingement and THA dislocation significantly increased with correction of lumbar lordosis if the PT was anterior. Two patients experienced repeated THA dislocation with postoperative and tolerable PT angle differences of 2° and -23°.

CONCLUSION

Our simulation of anterior implant impingement and subsequent adjustment of the degree of spinal correction was useful to prevent dislocation. However, this method did not prevent dislocation in some patients.Level of Evidence: 4.

Anatomic Total Hip Component Position Is More Reproducible With the Direct Anterior Approach Using Intraoperative Fluoroscopy

Background

Total hip arthroplasty (THA) has demonstrated excellent results regardless of the surgical approach. However, the approach used may be a factor in final positioning of implants. We hypothesized that the direct anterior approach (DAA) with fluoroscopy would be associated with more anatomic implant positioning than the posterior approach (PA).

Methods

A retrospective review of 200 patients was performed. One hundred patients underwent THA utilizing the PA, and 100 patients, with the DAA. All patients had an anterior-posterior pelvis radiograph preoperatively and postoperatively with a magnification marker present to standardize each radiograph. Exclusion criteria included contralateral THA or any pelvic or femoral deformity.

Results

Preoperative radiographs demonstrated identical cohorts with respect to leg length, femoral offset, and total offset. Postoperatively, the DAA achieved more accurate anatomic restoration of leg length (1.6 mm vs 5.5 mm; P < .0001), femoral offset (4.8 mm vs 9.3 mm; P < .0001), and total offset (0.5 mm vs 4.7 mm; P < .0001) compared with the PA. Ideal cup abduction and anteversion were significantly superior to the DAA (96% vs 78%, P = .0002, and 69% vs 24%, P < .0001, respectively).

Conclusions

This study is the first to compare anatomic implant positioning between patients undergoing THA with these 2 approaches. All parameters were significantly closer to anatomic implant positioning with the DAA. There are at least 2 potential explanations for this: (1) The DAA implant positioning was performed under fluoroscopic guidance, whereas the PA was not. (2) The PA disrupts the posterior capsule and external rotators, and therefore, increased offset or leg length may be necessary to achieve comparable hip stability with the DAA.

Sagittal Spinopelvic Translation Is Combined With Pelvic Tilt During the Standing to Sitting Position: Pelvic Incidence Is a Key Factor in Patients Who Underwent THA

Background

Sagittal spinopelvic translation (SSPT) is the horizontal distance from the hip center to the C7 plumb line (C7PL). SSPT is an important variable showing the overall patient balance in different functional positions which could affect the rate of hip instability. This study investigates the SSPT modification in patients who underwent total hip arthroplasty (THA).

Methods

A total of 120 patients were assessed preoperatively and postoperatively on standing and sitting acquisitions (primary unilateral THA without complication). SSPT is zero when the C7PL goes through the center of the femoral heads and positive when the C7PL is posterior to the hips’ center (negative if anterior). Three subgroups were defined based on the pelvic incidence (PI): low PI <45°, 45°< normal PI <65°, or high PI >65°.

Results

The overall mean preoperative SSPT change from standing to sitting was 2.2 cm ([-7.2 to 17.4]) (P < .05). The overall mean postoperative SSPT change from standing to sitting was 1.2 cm ([-14.2 to 22.4]) (P < .05). In low- and normal-PI groups, standing to sitting SSPT and preoperative to postoperative changes in standing SSPT were increased significantly after surgery with the C7PL behind the hips’ center (P < .05). In the high-PI group, standing to sitting SSPT was increased postoperatively (P = .034) (no significant changes from preoperative to postoperative status in standing and sitting).

Conclusions

Adaptation from standing to sitting positions combines pelvic tilt and anteroposterior pelvic translation. THA implantation induces significant changes in SSPT mainly for low- and standard-PI patients. This is an important variable to consider when investigating the causes of THA subluxation or dislocation.

Prediction of Pelvic Inclination in the Sitting Position after Corrective Surgery for Adult Spinal Deformity

Introduction

Hip dislocation rates in patients with combined total hip arthroplasty (THA) and spinal deformity fixation are significantly higher than those of THA alone. Nevertheless, there are no treatment recommendations for patients who undergo THA and require a spine deformity correction later.

Methods

Twenty-eight patients underwent spinal fixation surgery for adult spinal deformity. Sagittal spinopelvic alignment was analyzed on lateral radiographs taken preoperatively and postoperatively in the sitting and standing positions. Univariate linear regression analysis was conducted to identify the factors affecting the pelvic inclination in the sitting position after spinal fixation. Multiple regression analysis was conducted to determine the most efficient combination of radiographic parameters for predicting postoperative pelvic inclination while sitting.

Results

There were significantly weak associations between postoperative sacral slope (SS) in the sitting position and the following factors: the number of vertebral levels fused (β = 0.30, p = 0.003); the presence of sacral fixation (β = 0.22, p = 0.01); the presence of sacroiliac joint fixation (β = 0.24, p = 0.008); and preoperative SS while standing and sitting (β = 0.21, p = 0.01 and β = 0.34, p = 0.001). Postoperative lumbar lordosis (LL) while standing was strongly associated with postoperative SS in the sitting position (β = 0.67, p <.0001). The combination of postoperative LL in the standing position and preoperative SS in the sitting position was the best fit, and the adjusted R-squared was 0.82.

Conclusions

We devised a prediction formula for pelvic inclination while sitting after spinal fixation that has high predictability: postoperative SS while sitting = 11.7+ (0.4 × postoperative planned LL while standing) + (0.16 × preoperative SS while sitting). This study could be the basis for treatment recommendations for patients who have undergone THA and require a spine deformity correction later.

Dislocation rate and its risk factors in total hip arthroplasty with concurrent extensive spinal corrective fusion with pelvic fixation for adult spinal deformity

BACKGROUND

Though there are several reports on the high dislocation rates following total hip arthroplasty (THA) before or after spinal surgery, the literature specific to extensive spinal corrective fusion with pelvic fixation for adult spinal deformity is limited. This study determined the rate and risk of hip dislocation after THA and extensive spinal corrective fusion.

METHODS

We retrospectively analyzed the data of 23 adults (27 hips) who underwent both extensive spinal corrective fusion with pelvic fixation and THA between 2010 and 2018. Surgery-related characteristics were investigated from medical records, while standing anteroposterior pelvic radiographs and lateral spinal radiographs were used to measure spinal alignment parameters and THA acetabular orientation. Patients were grouped based on the occurrence of dislocation, and the rate and risk of dislocation were compared.

RESULTS

The rate of THA dislocations was extremely high-22% (6 of 27 hips) of patients. All dislocations occurred posteriorly in patients with prior THAs that were performed using the posterior approach. The pelvic tilt was significantly greater in patients with THA dislocations (p = 0.02) than in those without. Cup radiographic anteversion in the supine (p = 0.02) and standing (p = 0.05) positions was significantly smaller in patients with dislocations than in those without.

CONCLUSION

Total hip arthroplasty concurrent with extensive spinal corrective fusion with pelvic fixation for adult spinal deformity has an extremely high rate of posterior hip dislocation. The posterior surgical approach and prior THA were high risk factors for dislocation. Hip and spine surgeons need focused pre-surgical planning to account for this risk.

The Impact of Spinopelvic Mobility on Arthroplasty: Implications for Hip and Spine Surgeons

Spinopelvic mobility represents the complex interaction of hip, pelvis, and spine. Understanding this interaction is relevant for both arthroplasty and spine surgeons, as a predicted increasing number of patients will suffer from hip and spinal pathologies simultaneously. We conducted a comprehensive literature review, defined the nomenclature, summarized the various classifications of spinopelvic mobility, and outlined the corresponding treatment algorithms. In addition, we developed a step-by-step workup for spinopelvic mobility and total hip arthroplasty (THA). Normal spinopelvic mobility changes from standing to sitting; the hip flexes, and the posterior pelvic tilt increases with a concomitant increase in acetabular anteversion and decreasing lumbar lordosis. Most classifications are based on a division of spinopelvic mobility based on ΔSS (sacral slope) into stiff, normal, and hypermobile, and a categorization of the sagittal spinal balance regarding pelvic incidence (PI) and lumbar lordosis (LL) mismatch (PI–LL = ± 10° balanced versus PI–LL > 10° unbalanced) and corresponding adjustment of the acetabular component implantation. When performing THA, patients with suspected pathologic spinopelvic mobility should be identified by medical history and examination, and a radiological evaluation (a.p. pelvis standing and lateral femur to L1 or C7 (if EOS (EOS imaging, Paris, France) is available), respectively, for standing and sitting radiographs) of spinopelvic parameters should be conducted in order to classify the patient and determine the appropriate treatment strategy. Spine surgeons, before planned spinal fusion in the presence of osteoarthritis of the hip, should consider a hip flexion contracture and inform the patient of an increased risk of complications with existing or planned THA.

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.

A systematic approach to the hip-spine relationship and its applications to total hip arthroplasty

There remains confusion in the literature with regard to the spinopelvic relationship, and its contribution to ideal acetabular component position. Critical assessment of the literature has been limited by use of conflicting terminology and definitions of new concepts that further confuse the topic. In 2017, the concept of a Hip-Spine Workgroup was created with the first meeting held at the American Academy of Orthopedic Surgeons Annual Meeting in 2018. The goal of this workgroup was to first help standardize terminology across the literature so that as a topic, multiple groups could produce literature that is immediately understandable and applicable. This consensus review from the Hip-Spine Workgroup aims to simplify the spinopelvic relationship, offer hip surgeons a concise summary of available literature, and select common terminology approved by both hip surgeons and spine surgeons for future research.

Cite this article: Bone Joint J 2019;101-B:808–816.

Knee-Hip-Spine Syndrome: Improvement in Preoperative Abnormal Posture following Total Knee Arthroplasty

An ergonomic upright body posture is maintained by the alignment of the spine, pelvis, and lower extremities, and the muscle strength of body trunk and lower extremities. The posture varies with age because of the degenerative changes in the involved structures and the weakening of the muscles. The compensatory mechanisms underlying these changes have recently been evaluated, and the loss of lumbar lordosis results in spinal kyphosis, pelvic retroversion, hip extension, knee flexion, and ankle dorsiflexion. These mechanisms are referred to as the hip–spine and knee–spine syndromes. The spine, hip, and knee are anatomically connected, and the pain and discomfort of the lower back, hip, and knee frequently arise due to degenerative changes of these structures. Thus, these mechanisms are considered as the knee–hip–spine syndrome. Spinal fusion, total hip arthroplasty, and total knee arthroplasty are the surgical procedures for severe degeneration, and their clinical outcomes for the affected sites are promising. However, despite surgeries, other structures may degenerate and result in complications, such as proximal junctional kyphosis and hip dislocation, following spinal fusion. Therefore, it is necessary to evaluate each patient under specific conditions and to treat each section while considering associations between the target structure and entire body. The purpose of this article is to introduce postural maintenance, variations with age, and improvements with surgical interventions of spine, hip, and knee as the knee–hip–spine syndrome.

Late Dislocation Following Total Hip Arthroplasty: Spinopelvic Imbalance as a Causative Factor

BACKGROUND

Late dislocations after total hip arthroplasty (THA) are challenging for the hip surgeon because the cause is often not evident and recurrence is common. Recently, decreased spinopelvic motion has been implicated as a cause of dislocation. The purpose of this study was to assess the mechanical causes of late dislocation, including the influence of spinopelvic motion.

METHODS

Twenty consecutive patients were studied to identify the cause of their late dislocation. Cup inclination and anteversion were measured on standard pelvic radiographs. Lateral standing and sitting spine-pelvis-hip radiographs were used to measure pelvic motion, femoral mobility, and sagittal cup position by assessing sacral slope, pelvic-femoral angle, and cup ante-inclination. Spinopelvic motion was defined as the difference between the standing and sitting sacral slopes (Δsacral slope). A new measurement, the combined sagittal index, which measures the sagittal acetabular and femoral positions, was used to assess the functional motion of the hip joint and risk of impingement.

RESULTS

There were 9 anterior dislocations (45%) and 11 posterior dislocations (55%) at a mean of 8.3 years after a primary THA. Eight of the 9 patients with an anterior dislocation had spinopelvic abnormalities such as fixed posterior pelvic tilt when standing, increased standing femoral extension, and an increased standing combined sagittal index. Ten of the 11 patients with a posterior dislocation had abnormal spinopelvic measurements such as decreased spinopelvic motion (average Δsacral slope [and standard error] = 9.0° ± 2.4°), increased femoral flexion, and a decreased sitting combined sagittal index. For every 1° decrease in spinopelvic motion, there was an associated 0.9° increase in femoral motion and, in some patients, this resulted in osseous impingement and dislocation.

CONCLUSIONS

Patients with a late dislocation have abnormal spinopelvic motion that precipitates the dislocation, especially when combined with cup malposition or soft-tissue abnormalities. Spinopelvic stiffness is associated with increased age and increased femoral motion, which may lead to impingement and dislocation. Lateral spine-pelvis-hip radiographs may predict the risk and direction of dislocation.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Investigation of the Unstable Total Hip Arthroplasty

The investigation of recurrent instability after total hip arthroplasty requires a thorough history and physical examination focused on characterizing the dislocation events and the patient factors that contribute to instability. Radiographic studies include plain radiographs, in particular a cross-table lateral, and computed tomography to accurately assess the implant orientation relative to the patient's native anatomy. More advanced imaging such as magnetic resonance imaging may be useful to assess abductor tendon integrity. A classification system, based on etiology of recurrent instability, is available and helpful to guide treatment strategy. Finally, emerging research has debunked the previous characterization of an acetabular "safe zone" and further identified lumbar spine disease and surgical fusion as a significant risk factor for recurrent instability. Current and future research efforts target radiographic assessment of lumbopelvic alignment in diagnosis, treatment, and prevention of recurrent total hip arthroplasty instability.

Spine-hip relations in patients with hip osteoarthritis

Patients with hip osteoarthritis often have an abnormal spine-hip relation (SHR), meaning the presence of a clinically deleterious spine-hip and/or hip-spine syndrome.

Definition of the individual SHR is ideally done using the EOS® imaging system or, if not available, with conventional lumbopelvic lateral radiographs.

By pre-operatively screening patients with abnormal SHR, it is possible to refine total hip replacement (THR) surgical planning, which may improve outcomes.

An important component of the concept of kinematically aligned total hip arthroplasty (KA THA) consists of defining the optimal acetabular cup design and orientation based on the assessment of an individual’s SHR, and use of the transverse acetabular ligament to adjust the cup positioning.

The Bordeaux classification might advance the understanding of SHR and hopefully help improve THR outcomes.

Cite this article: EFORT Open Rev 2018;3:39-44. DOI: 10.1302/2058-5241.3.170020