How Does Spinopelvic Mobility and Sagittal Functional Cup Orientation Affect Patient-Reported Outcome 1 Year after THA?—A Prospective Diagnostic Cohort Study

BackgroundThis prospective cohort study aimed to characterize how spinopelvic characteristics change post-total hip arthroplasty (THA) and determine how patient-reported outcome measures are associated with 1) individual spinopelvic mobility and 2) functional sagittal cup orientation post-THA.MethodsOne hundred consecutive patients who received unilateral THAs for end-stage hip osteoarthritis, without spinal pathology were studied. Preoperatively and postoperatively, patients underwent clinical and radiographic evaluations. Patient-reported outcomes were collected using the hip disability and osteoarthritis outcome score - physical function shortform (HOOS-PS). Radiographic parameters measured from standing and relaxed-seated radiographs, included the lumbar lordosis angle, pelvic tilt, pelvic femoral angle and cup orientation in the coronal (inclination/anteversion) and sagittal (anteinclination) planes. Spinopelvic mobility was characterized (ΔPT: “stiff” [<10°], “normal” [10°-30°], and “hypermobile” [>30°]).ResultsPreoperative spinopelvic characteristics were not associated with HOOS-PS. Post-THA, the spinopelvic characteristics changed, with less patients having spinopelvic hypermobility (7%) compared with preop (14%). Postoperatively, patients with spinopelvic hypermobility showed significantly worse HOOS-PS scores (21 ± 17 vs 21 ± 22 vs 41 ± 23; ANOVA P = .037). Sagittal but not coronal cup orientation was associated with postoperative spinopelvic characteristics. Cup anteinclination was less in the patients with postoperative spinopelvic hypermobility (27 ± 7° vs 36 ± 8° vs 36 ± 10°; ANOVA: P = .035).ConclusionWe hypothesize that spinopelvic hypermobility is secondary to impingement and reduced hip flexion; to achieve a seated position, impinging hips require more posterior pelvic tilt. Patients with spinopelvic hypermobility are likely impinging secondary to the low cup anteinclination (sagittal malorientation despite optimum coronal orientation) and thus have lower HOOS-PS compared. Sagittal assessments are thus important to adequately study hip mechanics.Level of EvidenceLevel II, diagnostic study.     

Effects of Sagittal Spinal Alignment on Postural Pelvic Mobility in Total Hip Arthroplasty Candidates

BackgroundRecent research has demonstrated that patients with reduced pelvic mobility from standing to sitting have higher rates of dislocation after total hip arthroplasty (THA). This study evaluates the effect of sagittal spinal deformity, defined by pelvic incidence–lumbar lordosis mismatch (PI-LL), on postural changes in pelvic tilt (PT).MethodsA multicenter database of 1100 preoperative THA patients was queried. Anterior-pelvic-plane tilt (APPt), spinopelvic tilt (SPT), and LL were measured from radiographs of patients in supine, standing, flexed-seated, and stepping-up postures; PI was measured from computed tomography. Patients were separated into 3 groups based on PI-LL (<?10°, ?10° to 10°, >10°) and propensity-score matched by PI. Lumbar flatback-deformity was defined as PI-LL > 10°, hyperlordosis: PI-LL < ?10°. SPT/APPt, including changes between each posture were compared across PI-LL groups using analysis of variance, with post-hoc Tukey tests. Pearson correlations were reported when testing associations between SPT/APPt change and PI-LL.ResultsAfter propensity-score matching, 288 patients were analyzed (mean 65 y; 49% F). SPT and APPt change differed across all PI-LL categories from standing to seated, supine, and stepping-up with less SPT/APPt recruitment among hyperlordotic vs flatback patients (all P < .001). Greater PI-LL correlated with greater SPT recruitment from standing to seated (R = 0.294), supine (R = 0.292), and stepping-up (R = 0.207) (all P < .001). Smaller LL changes from standing to seated were associated with greater SPT recruitment (R = 0.372, P < .001).ConclusionsPostural changes in SPT/APPt are associated with spinopelvic measures in THA candidates. Hyperlordotic patients tend to utilize their spines more compared with flatback patients who were more likely to recruit PT. Increased focus on patients with lumbar flatback and hyperlordosis may help in reducing prosthetic dislocation prevalence following THA.     

Total Hip Replacement Influences Spinopelvic Mobility: A Prospective Observational Study

BackgroundAbnormal spinopelvic mobility is identified as a contributing element of total hip arthroplasty (THA) instability. Preoperative identification of THA patients at risk is still a remaining challenge. We therefore conducted this study to (1) evaluate if preoperative and postoperative spinopelvic mobility differs, (2) determine the interactions between the elements of the spinopelvic complex, and (3) identify preoperative parameters for predicting spinopelvic mobility.MethodsA prospective observational study assessing 197 THA patients was conducted with biplanar stereoradiography in standing and relaxed sitting positions preoperatively and postoperatively. Two independent investigators determined spinopelvic mobility based on 2 different classifications (Δ sacral slope [SS] and Δ pelvic tilt [PT]; Δ from standing to sitting; Δ < 10° stiff, Δ ≥ 10°-30° normal, Δ > 30° hypermobile). Multiple regression analysis and receiver operating characteristic analysis were used to identify predictors for postoperative spinopelvic mobility.ResultsSpinopelvic mobility significantly increased after THA based on ΔPT (Pre/Post: 18.5°/22.8°; P < .000) and ΔSS (Pre/Post 17.9°/22.4°; P < .000). A distinct shift in the ratio from stiff (Pre/Post: 24%/9.7%) to hypermobile (Pre/Post: 10.2%/22.1%) mobility postoperatively was observed. Receiver operating characteristic analysis predicted postoperative stiffness using preoperative PT_Standing ≥ 13.0° with a sensitivity of 90% and a specificity of 51% and hypermobility with preoperative SS_Standing ≥ 35.2° with a sensitivity of 81% and a specificity of 34%. Age at surgery, preoperative PT_Standing, and pelvic incidence were independent predictors of spinopelvic mobility (R² = 0.24).ConclusionDefinition of preoperative stiffness should be interpreted with caution by arthroplasty surgeons as mobility itself is influenced by THA. For the first time thresholds for standing preoperative parameters for predicting postoperative spinopelvic mobility could be provided. For preoperative standing only lateral assessment could serve as a screening tool for spinopelvic mobility.     

Can Flexed-Seated and Single-Leg Standing Radiographs Be Useful in Preoperative Evaluation of Lumbar Mobility in Total Hip Arthroplasty?

BackgroundThe purpose of this study is to determine whether simulated radiographs in the “flexed-seated” or “step-up” positions better demonstrate a patient’s range of spinopelvic motion between standing and sitting positions than relaxed sitting and standing radiographs.MethodsAn institutional review board approved cohort of 43 patients with hip osteoarthritis whom underwent full body sitting-standing radiographs from August 2016 to December 2017 at a single institution was reviewed. Subjects underwent single-leg step-up standing and flexed-seated radiographs, and relaxed standing and sitting radiographs. Sacral slope, spinopelvic tilt (SPT), and lumbar lordosis were measured in all radiographs. Alignment parameters were compared between both sets of imaging, and the change in SPT between the imaging modalities was plotted and stratified by pre-existing lumbar pathology.ResultsThere were significant differences between the relaxed standing and step-up radiographs and the relaxed and flexed-seated radiographs for sacral slope, SPT, and lumbar lordosis (P < .002 for all), with the exception of SPT in the relaxed and step-up standing postures (P = .110). When transitioning from the standing to sitting position, the mean changes in SPT differed significantly between both sets of radiographs. Most importantly, when plotting changes in SPT between flexed and relaxed sitting postures, patients with fusions and flatback deformity trended toward greater anterior pelvic tilting, a position of greater risk of posterior dislocation.ConclusionFlexed sitting and single-leg standing imaging may emphasize the compensatory mechanisms of patients with concomitant hip and spine pathology more than relaxed imaging using our measurements. Our method may provide insight into high dislocation risk patients compared to the previously published hip measurement method.Level of EvidenceIII.     

High Prevalence of Spinopelvic Risk Factors in Patients With Post-Operative Hip Dislocations

BackgroundExcessive standing posterior pelvic tilt (PT), lumbar spine stiffness, low pelvic incidence (PI), and severe sagittal spinal deformity (SSD) have been linked to increased dislocation rates. We aimed to determine the prevalence of these 4 parameters in a cohort of unstable total hip arthroplasty (THA) patients and compare these to a large representative control population of primary THA patients.MethodsForty-eight patients with instability following primary THA were compared to a control cohort of 9414 THA patients. Lateral X-rays in standing and flexed-seated positions were used to assess PT and lumbar lordosis (LL). Computed tomography scans were used to measure PI and acetabular cup orientation. Thresholds for “at risk” spinopelvic parameters were standing posterior PT ≤ −15°, lumbar flexion (LL_stand–LL_seated) ≤ 20°, PI ≤ 41°, PI ≥ 70°, and SSD (PI–LL_stand mismatch ≥ 20°).ResultsThere were significant differences in mean spinopelvic parameters between the dislocating and control cohorts (P < .001). There were no differences in mean PI (58° versus 56°, respectively, P = .29) or prevalence of high and low PI between groups. 67% of the dislocating patients had one or more significant risk factors, compared to only 11% of the control. A total of 71% of the dislocating patients had cup orientations within the traditional safe zone.ConclusionExcessive standing posterior PT, low lumbar flexion, and a severe SSD are more prevalent in unstable THAs. Pre-op screening for these parameters combined with appropriate planning and implant selection may help identify at risk patients and reduce the prevalence of dislocation.     

Prevalence of Sagittal Spinal Deformity Among Patients Undergoing Total Hip Arthroplasty

BackgroundThe important relationship between sagittal spinal alignment and total hip arthroplasty (THA) is becoming well recognized. Prior research has shown a significant relationship between sagittal spinal deformity (SSD) and THA instability. This study aims at determining the prevalence of SSD among preoperative THA patients.MethodsA multicenter database of preoperative THA patients was analyzed. Radiographic parameters measured from standing radiographs included anterior pelvic plane tilt, spinopelvic tilt, and lumbar lordosis (LL); pelvic incidence (PI) was measured from computed tomography scans. Lumbar flatback was defined as PI-LL mismatch >10°, balanced as PI-LL of −10° to 10°, and hyperlordosis as PI-LL <−10°.ResultsA total of 1088 patients were analyzed (mean, 64 years; 48% female). And 59% (n = 644) of patients had balanced alignment, 16% (n = 174) had a PI-LL > 10°, and 4% (n = 46) had a PI-LL > 20° (severe flatback deformity). The prevalence of hyperlordosis was 25% (n = 270). Flatback patients tended to be older than balanced and hyperlordotic patients (69.5 vs 64.0 vs 60.8 years, P < .001). Spinopelvic tilt was more posterior in flatback compared to balanced and hyperlordotic patients (24.7° vs 15.4° vs 7.0°) as was anterior pelvic plane tilt (−7.1° vs −2.0° vs 2.5°) and PI (64.1° vs 56.8° vs 49.0°), all P < .001.ConclusionOnly 59% of patients undergoing THA have normally aligned lumbar spines. Flatback SSD was observed in 16% (4% with severe flatback deformity) and there was a 25% prevalence of hyperlordosis. Lumbar flatback was associated with increasing age, posterior pelvic tilt, and larger PI. The relatively high prevalence of spinal deformity in this population reinforces the importance of considering spinopelvic alignment in THA planning and risk stratification.     

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

Background

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

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

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

Analysis of hip dysplasia and spinopelvic alignment in cerebral palsy

Background contextKnowledge of sagittal spinopelvic parameters and hip dysplasia is important in cerebral palsy (CP) patients because these parameters differ from those found in the general population and can be related to symptoms.PurposeThe purpose of this study was to analyze sagittal spinopelvic alignment and determine its relation to hip dysplasia in CP patients.Study designRadiological analysis was conducted on patients with CP.Patient sampleFifty-four patients with CP and 24 normal controls were included in this study.Outcome measuresParticipants underwent radiographs of the whole spine.MethodsThe patient and control groups comprised 54 CP patients and 24 volunteers, respectively. All underwent lateral radiography of the whole spine and hip joint anteroposterior radiography. The radiographic parameters examined were sacral slope, pelvic tilt, pelvic incidence, S1 overhang, thoracic kyphosis, thoracolumbar kyphosis, lumbar lordosis, sagittal balance, center edge angle, acetabular angle, and migration index. Statistical analysis was performed to identify significant differences and correlations between the two groups.ResultsSacral slope, thoracolumbar kyphosis, lumbar lordosis, sagittal balance, acetabular angle, and migration index were significantly higher in CP patients, whereas pelvic tilt, S1 overhang, and center edge angle were significantly lower (p<.05). Correlation analysis revealed that pelvic incidence, sacral slope, pelvic tilt, and S1 overhang were related to each other and that thoracolumbar kyphosis was related to the thoracic kyphosis and lumbar lordosis (p<.05). For spinal and pelvic parameters, lumbar lordosis was related to sacral slope, pelvic incidence, pelvic tilt, and S1 overhang; for hip dysplasia parameters, center edge angle and acetabular angle were found to be interrelated (p<.05). Regarding symptoms, pelvic tilt, S1 overhang, and thoracolumbar kyphosis were found to be correlated with symptom severity in patients. However, no hip dysplasia parameters were found to be related to hip or spinal symptoms.ConclusionsThis study found significant differences between CP patients and normal controls in terms of spinopelvic alignment and hip dysplasia. Furthermore, relationships were found between the sagittal spinopelvic parameters and hip dysplasia, and correlations were found between sagittal spinopelvic parameters and pain.     

The Functional Mechanics of the Acetabular Component in Total Hip Arthroplasty

BackgroundTotal hip arthroplasty functional safe zones match postural hip changes to dynamic positioning of the acetabular component. We studied integrating the Anteinclination (AI) cup angle into the spinopelvic environment, defining normative values for all parameters and calculating adjustments to AI for each degree of altered standing pelvic position and postural mobility from these values. A sagittal geometric model was employed to determine these values using established spinopelvic parameter angles.MethodsTheoretical normative Pelvic Incidence (PI) specific values were calculated using a triangular construct employing a linear equation describing the functional relationship between the pelvic parameters at a mobility producing an isosceles solution for normative acetabular angles. Individual optimal AI cup values for altered Sacral Slope (SS)/pelvic tilt (sPT) and mobility (dSS) were calculated using specific ratios of angular change between parameters correcting from these normative values.ResultsA PI:SS:sPT ratio of angular change of 3:2:1 at dSS = 25° mobility creates an isosceles condition solving for PI specific theoretical normative values for all construct parameters. Individualized tilt correction applies to each posture a +0.25° AI alteration for each +1° sPT increase from this architectural value. Mobility correction applies a +0.5° standing AI and ?0.5° sitting AI alteration for each ?1° dSS < 25°, the opposite for each +1° dSS > 25°. The Sacroacetabular angle/Pelvic acetabular angle (SAA/PAA) index describes the underlying spinopelvic environment the cup functions within.ConclusionThis model quantitatively integrates an implanted acetabular component into the host spinopelvic environment. Theoretical normative and individual optimal cup orientations are passively determined by these conditions of standing pelvic position and mobility.     

In vivo kinematics,component alignment and hardware variables influence on the liner-to-neck clearance during chair-rising after total hip arthroplasty

BackgroundThere is an interest in quantifying dynamic hip kinematics before and after total hip arthroplasty (THA) during chair-rising: one of daily life activities.MethodsThe study consisted of 21 patients who underwent unilateral total hip arthroplasty for symptomatic osteoarthritis. We obtained continuous radiographs using a flat-panel X-ray detector while the participants rose from chair. We assessed the pre and postoperative hip joint's movements using three-dimensional-to-two-dimensional model-to-image registration techniques. We also measured minimum liner-to-neck distances at maximum hip flexion and extension as anterior and posterior liner-to-neck distances, respectively. Multivariate analyses were applied to determine which factors were associated with liner-to-neck distances.ResultsThe cup inclination, cup anteversion, and stem anteversion averaged 37.4°, 23.1°, and 30.1°, respectively. Significantly larger maximum hip flexion angle (72°) was found during chair-rising after THA compared to that before THA (63°, P < 0.01). The anterior pelvic tilt at the maximum hip flexion after THA (3° of anterior tilt) was significantly (P < 0.05) anterior compared to that before THA (1° of posterior tilt). The anterior and posterior liner-to-neck distances averaged 12.3 mm and 8.1 mm, respectively, with a significant difference (P < 0.01). No liner-to-neck contact was found in any hips. In multivariate analysis, the hip flexion angle, cup inclination, stem anteversion and head diameter were significantly associated with the anterior liner-to-neck distance (P < 0.05), the hip extension angle, cup anteversion, neck length and with or without elevated rim were significantly associated with the posterior liner-to-neck distance (P < 0.05, 0.01, 0.05, 0.01, respectively).ConclusionThis study indicates that well-positioned THA provide increased range of hip flexion with sufficient anterior liner-to-neck clearance during chair-rising. Dynamic hip kinematics, component position, and hardware variables significantly influenced on the liner-to-neck clearance under weight-bearing conditions.     

Lack of correlation between hip osteoarthritis and anatomical spinopelvic parameters obtained in supine position on MRI

PurposeHip osteoarthritis (HOA) is known to have a multifactorial pathogenesis. Recent studies suggest that spinopelvic alignment may represent an important additional pathogenic abnormality resulting in HOA. This study aims to assess the correlation between spinopelvic parameters (pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS) and lumbar lordosis (LL)) obtained in the supine position on MRI and HOA, lateral center edge (LCE) angle, and patient reported back pain.MethodsAsymptomatic participants from the whole-body MRI cohort (FF4) from the cross-sectional case-control “Cooperative Health Research in the Region of Augsburg” study (KORA) were included. Whole-body MRI was performed in a standardized fashion in each case, on which hip osteoarthritis (HOA), anatomical spinopelvic parameters and lateral center edge angle were measured. Presence of back pain was assessed using a standardized questionnaire. Correlations were estimated by logistic regression models providing odds ratio.ResultsAmong 340 subjects (mean age 56.3 ± 9.3 years; 56.5% male), HOA was present in 89.1% (male: 87.0%, female: 91.7%, p = 0.17). The LCE angle was 30.0° ± 5.5 (men: 29.8° ± 5.9; women: 30.1° ± 5.1; p = 0.696). Mean PI was 54.0° ± 11.3°, PT was 13.7° ± 5.9°, SS was 40.3° ± 8.8° (significantly smaller in women p<0.05) and LL was 36.4° ± 9.6° (significantly greater in women p<0.05). None of the spinopelvic parameters correlated significantly with hip osteoarthritis or LCE angle. HOA was not correlated with back pain.ConclusionSpinopelvic parameters as measured in the supine position on MRI, do not correlate with hip osteoarthritis or lateral center edge angle.     

The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations

BackgroundAnterior and posterior pelvic tilt appears to play a role in total hip arthroplasty (THA) stability. When changing from the standing to the sitting position, the pelvis typically rotates posteriorly while the hips flex and this affects the femoro-acetabular positions. This case-control study compares changes in 3-D acetabular cup orientation during functional pelvic tilt between posterior THA dislocations vs stable THAs.MethodsStanding and sitting 3-D cup orientation was compared between fifteen posterior dislocations vs 233 prospectively followed stable THAs. 3-D cup orientation was calculated using previously validated trigonometric algorithms on biplanar radiographs. Those algorithms combine the angles in the three anatomical planes (coronal inclination, transverse version, and sagittal ante-inclination) in the standing position with the change in sagittal pelvic tilt from standing to sitting to calculate the 3-D orientation in the sitting position.ResultsThe standing cup orientation of the dislocated THAs was only characterized by a lower coronal inclination (P = .039). Compared with the controls, from standing to sitting, they showed less posterior pelvic tilt (P < .001). This led to a significant lower coronal inclination (P < .001) and sagittal ante-inclination (P < .001) in the sitting position but similar transverse version (P = .366).ConclusionsComparing posterior THA dislocations to stable THAs, there is a lower increase of all three orientation angles from standing to sitting. This leads to a decreased sitting coronal inclination and sagittal ante-inclination which may lead to an increased risk of impingement ensued by THA instability. By contrast, the transverse version was not significantly different in both positions. This confirms the importance of biplanar data on functional cup orientation.Level of EvidenceDiagnostic, Level III.     

Sagittal lumbar and pelvic alignment in the standing and sitting positions

BackgroundThe sitting position has become the most common posture in today’s workplace. In relation to this position, kinematic analysis of the lumbar spine is helpful in understanding the causes of low back pain and its prevention.MethodsIn this study, we investigated the relationship between sagittal lumbar alignment and pelvic alignment in the standing and sitting positions for 50 healthy adults. Lumbar lordotic angle (LLA), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI) were measured on lateral lumbar spine standing and sitting radiographs.ResultsRegarding changes from the standing to sitting positions, averageLLA, SS, and PT were ?16.6° (?49.8 %), ?18.7° (?50.3 %), and 18.3° (284.8 %), respectively (P < 0.01). In the sitting position, lumbar lordosis was reduced and pelvic rotation became posterior.ConclusionsThis study showed that LLA decreased by approximately 50 % and PT increased by approximately 25 % in the sitting position compared with the standing position. No significant gender differences were observed for LLA, SS, and PT in the standing position. In the sitting position, however, LLA and SS were markedly larger for women.     

Prevalence of Risk Factors for Adverse Spinopelvic Mobility Among Patients Undergoing Total Hip Arthroplasty

BackgroundPatients with adverse spinopelvic mobility have higher complication rates following total hip arthroplasty (THA). Risk factors include a stiff lumbar spine, standing posterior pelvic tilt ≤ ?10°, and a severe sagittal spinal deformity (pelvic incidence minus lumbar lordosis mismatch ≥20°). The purpose of this study is to define the spinopelvic risk factors and quantify the prevalence of risk factors for pathologic spinopelvic mobility.MethodsA retrospective cohort analysis from January 2014 to February 2020 was performed on a multicenter series of 9414 primary THAs by 168 surgeons, all with preoperative spinopelvic measurements in the supine, standing, and flex-seated positions. All patients were included. The prevalence of adverse spinopelvic mobility and frequency of each spinopelvic risk factor was calculated.ResultsThe cohort was 52% female, 48% male, with an average age of 65 years. Thirteen percent of patients exhibited adverse spinopelvic mobility and 17% had one or more of the 3 risk factors. Adverse mobility was found in 35% of patients with at least 1 risk factor, 47% with at least 2 risk factors, and 57% with all 3 risk factors.ConclusionForty-six percent of patients had spinopelvic pathology driven by one or more of the risk factors. Number of risk factors present and risk of adverse spinopelvic mobility were positively correlated, with 57% of patients with all 3 risk factors exhibiting adverse spinopelvic mobility. Although this study defines the prevalence of these risk factors in this highly selected cohort, it does not report incidence in a general THA population.Level of EvidencePrognostic Level IV.     

Does It Matter: Total Hip Arthroplasty or Lumbar Spinal Fusion First? Preoperative Sagittal Spinopelvic Measurements Guide Patient-Specific Surgical Strategies in Patients Requiring Both

BackgroundIn patients requiring both total hip arthroplasty (THA) and lumbar spinal fusion (LSF), consideration of preoperative sagittal spinopelvic measurements can aid in the prediction of postfusion compensatory changes in pelvic tilt (PT) and inform adjustments to traditional THA cup anteversion. This study aims to identify relationships between spinopelvic measurements and post-THA hip instability and to determine if procedure order reveals a difference in hip dislocation rate.MethodsPatients at a single practice site who received both THA and LSF between 2005 and 2015 (292: 158 = LSF prior to THA, 134 = THA prior to LSF) were retrospectively reviewed for incidents of THA instability. Those with complete radiograph series (89) had their sagittal (standing) spinopelvic profiles measured preoperatively, immediately postoperatively, and 3 months, 6 months, 1 year, 1.5 years, and 2 years postoperatively. Measured parameters included lumbar lordosis (LL), pelvic incidence (PI), PT, and sacral slope (SS).ResultsNo significant differences in dislocation rates between operative order groups were elicited (7/73 LSF first, 4/62 THA first; Z = 0.664, P = .509). Compared to nondislocators, dislocators had lower LL (−10.9) and SS (−7.8), and higher PT (+4.3) and PI-LL (+7.3). Additional risk factors for dislocation included sacral fusion (relative risk [RR] = 3.0) and revision fusion (RR = 2.7) . Predictive power of the model generated through multiple regression to characterize individual profiles of post-LSF PT compensation based on perioperative measurements was most significant at 1 year (R² = 0.565, F = 0.000456, P = .028) and 2 years (R² = 0.741, F = 0.031, P = .001) postoperatively.ConclusionIn performing THA after LSF, it is theoretically ideal to proceed with THA at a postfusion interval of at least 1 year, beyond which further compensatory PT change is minimal. However, the order of surgical procedure revealed no statistical difference in hip instability rates. In cases characterized by large PI-LL mismatch (larger or less predictable compensation profiles) or large SS or LL loss (considerably atypical muscle recruitment), consideration of full functional anteversion range between sitting and standing positions to account for abnormalities not appreciated with standing radiographic assessment alone may be warranted.     

Prediction of sagittal balance in patients with osteoporosis using spinopelvic parameters

Purpose

Little data is available on the relationships between sagittal balance and spinopelvic parameters in osteoporosis. We analyzed sagittal spinopelvic parameters in osteoporotic patients.

Methods

In this prospective study, the patient and control groups comprised 124 osteoporotic patients and 40 controls. Average age was 72.4 ± 6.8 in the osteoporosis group and 42.7 ± 12.5 in the control group, which was significantly different (P < 0.001). Osteoporotic patients were allocated to two groups by sagittal vertical axis, namely, a sagittal balance group (n = 56) and a sagittal imbalance group (n = 68). All 164 study subjects underwent whole spine lateral radiography, which included hip joints. The radiographic parameters investigated were sacral slope, pelvic tilt, pelvic incidence, thoracic kyphosis, lumbar lordosis, and sagittal vertical axis. Statistical analysis was performed to identify significant differences between the two groups.

Results

Osteoporotic patients and controls were found to be significantly different in terms of sagittal vertical axis, sacral slope, pelvic tilt, lumbar lordosis, and thoracic kyphosis. However, no significant difference was observed between patients and controls in terms of pelvic incidence (P > 0.05). Significant differences were found between the balance and imbalance groups in terms of age, lumbar spine bone mineral density (LSBMD), femoral neck BMD (FNBMD), visual analogue scale (VAS) score, sacral slope, and pelvic incidence. Correlation analysis revealed significant relationships between sagittal parameters and osteoporosis. Stepwise logistic regression analysis revealed that FNBMD and pelvic incidence contributed significantly to sagittal balance.

Conclusion

Sagittal spinopelvic parameters were found to be significantly different in patients and normal controls. Significant relationships were found between sagittal spinopelvic parameters in osteoporotic patients. In particular, low FNBMD and high pelvic incidence were significant parameters in determination of sagittal balance in osteoporotic patients.     

Sacral Slope Change From Standing to Relaxed-Seated Grossly Overpredicts the Presence of a Stiff Spine

BackgroundSeveral authors propose that a change in sacral slope of ≤10° between the standing and relaxed-seated positions (ΔSS_{standing→relaxed-seated}) identifies a patient with a stiff lumbar spine and has suggested the use of dual-mobility bearings for such patients undergoing a total hip arthroplasty (THA). The aim of this study was to assess how accurately ΔSS_{standing→relaxed-seated} can identify patients with a stiff spine.MethodsA prospective, multicentre, consecutive cohort series of 312 patients had standing, relaxed-seated, and flexed-seated lateral radiographs prior to THA. ΔSS_{standing→relaxed-seated} was determined by the change in sacral slope between the standing and relaxed-seated positions. Lumbar flexion (LF) was defined as the difference in lumbar lordotic angle between standing and flexed-seated. LF ≤20° was considered a stiff spine. The predictive value of ΔSS_{standing→relaxed-seated} for characterizing a stiff spine was assessed.ResultsA weak correlation between ΔSS_{standing→relaxed-seated} and LF was identified (r² = 0.13). Eighty six patients (28%) had ΔSS_{standing→relaxed-seated} ≤10° and 19 patients (6%) had a stiff spine. Of the 86 patients with ΔSS_{standing→relaxed-seated} ≤10°, 13 had a stiff spine. The positive predictive value of ΔSS_{standing→relaxed-seated} ≤10° for identifying a stiff spine was 15%.ConclusionIn this cohort, ΔSS_{standing→relaxed-seated} ≤10° was not correlated with a stiff spine. Using this simplified approach could lead to a 7-fold overprediction of patients with a stiff lumbar spine and abnormal spinopelvic mobility, unnecessary use of dual-mobility bearings, and incorrect component alignment targets. Referring to patients with ΔSS_{standing→relaxed-seated} ≤10° as being stiff is misleading. The flexed-seated position should be used to effectively assess a patient’s spine mobility prior to THA.     

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

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

The Current Knowledge on Spinopelvic Mobility

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