The influence of sagittal spinal deformity on anteversion of the acetabular component in 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.

Outcomes and complications of Total Hip Arthroplasty in patients with a pre-existing pathologic spine-hip relation. A systematic review of the literature

BACKGROUND

There has been a growing interest in pathologic spine-hip relations (PSHR) in current literature, with the aim of reducing the risk of prosthetic impingement, dislocation, and edge loading in total hip arthroplasty (THA). The primary objective of this review is to determine the effect of different PSHR on primary THA outcomes and complication profile. The secondary objective is to stratify the risk of different subgroups of PSHR patients.

METHODS

A systematic review of the literature was performed in accordance with PRISMA guidelines. Randomised controlled trials, comparative cohort studies and case-control studies comparing outcomes and complication rates of primary THA in patients with and without a PSHR (spinal fusion; degenerative spinal conditions determining stiff spine and/or spinal misalignment) were included. The quality of the included studies and the risk of bias were assessed. The revision rate, complications, and clinical and radiological data were analysed. Complications included: aseptic loosening (AL), periprosthetic joint infections (PJI), hip dislocations and periprosthetic fractures (PF).

RESULTS

Fifteen articles were included with 3.306.342 THAs. The mean follow-up (FU) was 31.4 ± 21.7 months. The population was divided into three subgroups: spinal fusion patients (48.315 THAs); non-fused patients with spinal stiffness (106.110 THAs); non-fused patients with normal spines (3.151.917 THAs). A statistically significant risk stratification was observed about dislocation rate (5.98 ± 6.9% SF, 3.0 ± 1.9% non-SF Stiff and 2.26 ± 1.4% non-SF; p = 0.028). Similarly, about THA revision rate, a statistically significant risk stratification was also observed (7.3 ± 6.8% SF, 6.4 ± 3.1% non-SF Stiff and 2.7 ± 1.7% non-SF; p = 0.020). No statistically significant difference was observed when analysing AL, PJI and PF.

CONCLUSION

A statistically significant risk stratification of dislocation and revision rate was observed in the different PHSR, as theorised by the Bordeaux classification. Fused patients present a higher risk, degenerated and/or stiff spine an intermediate risk and mobile spines a lower risk profile. A standardised approach to THA candidate patients must consider the possible PSHR to improve clinical outcomes and reduce adverse events of THA.

Hip-spine relationship: clinical evidence and biomechanical issues

The hip-spine relationship is a critical consideration in total hip arthroplasty (THA) procedures. While THA is generally successful in patient, complications such as instability and dislocation can arise. These issues are significantly influenced by the alignment of implant components and the overall balance of the spine and pelvis, known as spinopelvic balance. Patients with alteration of those parameters, in particular rigid spines, often due to fusion surgery, face a higher risk of THA complications, with an emphasis on complications in instability, impingement and dislocation. For these reasons, over the years, computer modelling and simulation techniques have been developed to support clinicians in the different steps of surgery. The aim of the current review is to present current knowledge on hip-spine relationship to serve as a common platform of discussion among clinicians and engineers. The offered overview aims to update the reader on the main critical aspects of the issue, from both a theoretical and practical perspective, and to be a valuable introductory tool for those approaching this problem for the first time.

Fluoroscopy Versus Imageless Optical Navigation in Direct Anterior Approach Total Hip Arthroplasty

BACKGROUND

Utilization of the direct anterior approach (DAA) for total hip arthroplasty (THA) has risen in popularity. Accurate implant placement is a critical factor that influences patient outcomes. The goal of this study was to compare the accuracy and precision of fluoroscopy with imageless optical navigation in DAA THA.

METHODS

This was a cohort study of 640 consecutive primary DAA THAs performed with intraoperative fluoroscopy (n = 300 patients) or imageless optical navigation (n = 304 patients). Accuracy was compared by measuring acetabular cup inclination, anteversion, and leg-length discrepancy (LLD). The proportion of implants placed within the Lewinnek safe zone and those placed within a more precise target of 40 ± 5° inclination and 20 ± 5° anteversion was evaluated.

RESULTS

According to the Lewinnek criteria, there was no difference in the percentage of implants placed within both inclination and anteversion targets (fluoroscopy: 90.3%; navigation: 88.8%, P = 0.519). Using the more precise targets, navigation increased the implants positioned correctly for both inclination and anteversion (fluoroscopy: 50.3%; navigation: 65.6%, P < 0.001). Navigation increased the proportion of implants positioned within the target anteversion zone (fluoroscopy: 71.3%; navigation: 83.8%, P < 0.001) but not inclination (fluoroscopy: 71.9%; navigation: 76.9%, P = 0.147). The mean LLD was higher with the use of fluoroscopy compared with navigation (5.5 mm, standard deviation: 4.1; 4.6 mm, SD: 3.4, P < 0.005). No difference in dislocation rate was observed ( P = 0.643).

CONCLUSION

Both fluoroscopy and imageless optical navigation demonstrated accurate acetabular implant positioning during DAA THA. Navigation was more precise and associated with improved acetabular anteversion placement and restoration of LLD. Navigation is an accurate alternative to fluoroscopy with decreased radiation exposure.

"Stuck in the middle": the missing lumbosacral link in total hip arthroplasty

INTRODUCTION

Spinopelvic mobility drives functional acetabular position, influencing dislocation risk after total hip arthroplasty (THA). Patients have been described as "stuck sitting" or "stuck standing" based on pelvic tilt (PT). We hypothesised that some patients are "stuck in the middle," meaning their PT changes minimally from sitting to standing - increasing their risk of dislocation.

METHODS

We reviewed 195 patients with standing and sitting whole body radiographs prior to THA. Standing anterior pelvic plane tilt (APPT) and standing and sitting sacral slope (SS) were measured and used to calculate sitting APPT. Normal standing and sitting were defined as APPT >-10° and <-20°, respectively. Spinal stiffness was classified as <10° change in sacral slope between sitting and standing. Patients were categorised as: (A) able to fully sit and stand; (B) "stuck sitting" - able to fully sit; unable to fully stand; (C) "stuck standing" - able to fully stand; unable to fully sit; or (D) "stuck in the middle" - unable to sit or stand fully.

RESULTS

84 patients could sit and stand normally (A), 22 patients were stuck sitting (B), 76 patients were stuck standing (C), and 13 patients were stuck in the middle (D). While 111 patients (56.9%) were considered stuck, only 58 patients (29.7%) met criteria for spinal stiffness.

DISCUSSION

We identified a subset of patients with stiff spines and abnormal PT in both sitting and standing, including 37.1% of patients who would be classified as "stuck sitting" based only on standing radiographs. Placing acetabular components in less than anatomic anteversion in these patients may increase posterior dislocation risk.

How Do Spinopelvic Characteristics Change Post-Total Hip Arthroplasty? A Longitudinal Assessment Raising Awareness of the Postoperative Period

BACKGROUND

Spinopelvic characteristics, including sacral slope (SS), are commonly evaluated in different positions pre-total hip arthroplasty (THA). This study aimed to: 1) investigate the change in spinopelvic parameters at 7 days (early) and 1-year post-THA; and 2) identify patient characteristics associated with a change in SS of more than 7° post-THA.

METHODS

We prospectively studied 250 patients who underwent unilateral THA [132 women, age 66 years (range, 32 to 88)] and underwent biplanar images preoperatively and at 7 days and 1-year post-THA. Parameters measured included pelvic incidence, standing lumbar lordosis, SS, and proximal femoral angle (PFA). A SS change ≥ 7° was considered the threshold as it would result in more than a 5° change in cup orientation.

RESULTS

Early post-THA SSstanding remained within ± 6º from preoperative measurements in 75% of patients, reduced by ≥ 7° in 9%, and increased by ≥ 7° in 16%. Those that showed a reduction in SS had the lowest PFA and the highest SS pre-THA (P = .028, .107, and < 0.001, respectively). From 7 days until the 1-year mark, pelvic tilt increased, SS reduced (mean: -4º, range: -29 to 17º, P < .001), and patients stood with greater hip extension ΔPFAstanding (mean 7°, range: -34 to 37°, P < .001). At 1 year, SSseated had remained within ± 6º, relative to the pre-THA value, in 49% of patients.

CONCLUSIONS

Standing spinopelvic characteristics, especially SSstanding, remain within ±6° in three-quarters of patients both early- and at 1-year post-THA. In the remaining cases, pelvic tilt changes significantly. In 9% of cases, SS reduces ≥ 7° early THA, probably due to the alleviation of fixed-flexion contractures. The SSseated changes by ≥ ± 7° in almost 50% of cases in this study, and its clinical value as a preoperative planning tool should be questioned.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Spinal fusion and total hip arthroplasty: why timing is important

BACKGROUND

There is increasing debate among orthopaedic surgeons over the temporal relationship between lumbar spinal fusion (LSF) and total hip arthroplasty (THA) for patients with hip-spine syndrome. Few large studies have directly compared the results of patients who undergo LSF prior to THA (LSF-THA) to those who undergo LSF after THA (THA-LSF). The current study matched THA patients with a prior LSF to patients who underwent LSF after THA to assess: 90-day and 1-year (1) medical/surgical complications; and (2) revisions.

METHODS

We queried a national, all-payer database to identify all patients undergoing THA between 2010 and 2018 (n = 716,084). The LSF-THA patients and THA-LSF patients were then matched 1:1 on age, sex, Charleson Comorbidity Index, and obesity. Medical/surgical complications and revisions at 90 days and 1 year were recorded. Categorical and continuous variables were analysed utilising t-tests and chi-square, respectively.

RESULTS

LSF-THA patients experienced significantly more postoperative dislocations at 90 days and 1 year compared to THA-LSF patients (p = 0.048 and p < 0.001). There were a similar number of revisions performed for LSF-THA and THA-LSF patients at both 90 days and 1 year (p = 0.183 and p = 0.426). Furthermore, at 1 year, LSF-THA patients experienced more pneumonia (p = 0.005) and joint infection (p = 0.020).

CONCLUSIONS

Prior LSF has been demonstrated to increase the risk of postoperative dislocation in patients undergoing THA. The results of the present study demonstrate increased dislocations with LSF-THA compared to THA-LSF. For "hip spine syndrome" patients requiring both LSF and THA, it may be more beneficial to undergo THA prior to LSF. Arthroplasty surgeons may wish to collaborate with spinal surgeons to ensure optimal outcomes for this group of patients.

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.

Association of radiological severity of hip involvement with clinical characteristics and sagittal spinopelvic balance in patients with ankylosing spondylitis

INTRODUCTION

This is the first study to analyze the associations between the radiological severity of hip involvement with clinical characteristics and sagittal spinopelvic balance in patients with ankylosing spondylitis (AS).

METHOD

We evaluated 182 patients with AS who were referred to outpatient clinics. Patient demographic data and clinical and radiographic parameters were collected. Patients were divided into three groups based on the Bath Ankylosing Spondylitis Radiology Hip Index. Clinical characteristics and spinopelvic parameters acquired by a low-dose biplanar imaging system were evaluated among these groups.

RESULTS

Patients with more severe hip involvement were older and had longer disease duration and diagnostic delay, with lower Harris Hip Score (p < 0.001) and 12-item Short Form Health Survey Physical Component Score (p < 0.001) and higher Bath Ankylosing Spondylitis Disease Activity Index (p = 0.030) and Functional Index (p < 0.001). Patients with more severe hip involvement had significantly higher sacroiliac grade (p < 0.001) and higher modified Stoke Ankylosing Spondylitis Spinal Score (p < 0.001). Patients with moderate and severe hip involvement had similar lumbar lordosis and spino-sacral angle, whereas patients with severe hip involvement had lower pelvic tilt, pelvic femoral angle, higher sacral slope, and sagittal vertical axis.

CONCLUSIONS

The severity of hip involvement is associated with physical function and is not consistent with the severity of spinal involvement. Severe hip involvement impairs the ability to retrovert the pelvis to accommodate the sagittal deformity, and spinopelvic parameters should be concretely evaluated in preoperative counseling of patients with AS waiting for total hip arthroplasty. Key Points • The severity of hip involvement in patients with AS is associated with physical function. • Severe hip involvement impairs the ability to retrovert the pelvis to accommodate the sagittal deformity.

A patient-specific algorithm for predicting the standing sagittal pelvic tilt one year after total hip arthroplasty

Aims

The aim of this study was to evaluate the reliability and validity of a patient-specific algorithm which we developed for predicting changes in sagittal pelvic tilt after total hip arthroplasty (THA).

Methods

This retrospective study included 143 patients who underwent 171 THAs between April 2019 and October 2020 and had full-body lateral radiographs preoperatively and at one year postoperatively. We measured the pelvic incidence (PI), the sagittal vertical axis (SVA), pelvic tilt, sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis to classify patients into types A, B1, B2, B3, and C. The change of pelvic tilt was predicted according to the normal range of SVA (0 mm to 50 mm) for types A, B1, B2, and B3, and based on the absolute value of one-third of the PI-LL mismatch for type C patients. The reliability of the classification of the patients and the prediction of the change of pelvic tilt were assessed using kappa values and intraclass correlation coefficients (ICCs), respectively. Validity was assessed using the overall mean error and mean absolute error (MAE) for the prediction of the change of pelvic tilt.

Results

The kappa values were 0.927 (95% confidence interval (CI) 0.861 to 0.992) and 0.945 (95% CI 0.903 to 0.988) for the inter- and intraobserver reliabilities, respectively, and the ICCs ranged from 0.919 to 0.997. The overall mean error and MAE for the prediction of the change of pelvic tilt were -0.3° (SD 3.6°) and 2.8° (SD 2.4°), respectively. The overall absolute change of pelvic tilt was 5.0° (SD 4.1°). Pre- and postoperative values and changes in pelvic tilt, SVA, SS, and LL varied significantly among the five types of patient.

Conclusion

We found that the proposed algorithm was reliable and valid for predicting the standing pelvic tilt after THA.

Accuracy comparison of cup positioning during total hip arthroplasty using Hip Align and AR-Hip in the supine position

INTRODUCTION

The aim of this study is to compare the accuracy of acetabular cup positioning between the accelerometer-based navigation system and the augmented reality-based navigation system during THA in the supine position.

MATERIALS AND METHODS

This retrospective study included 66 patients (70 hips) who underwent THA using two types of portable navigation system, Hip Align or AR-Hip, in the spine position. The absolute difference between the intraoperative navigation record and postoperative measurement using computed tomography data was evaluated. Preoperative clinical factors that decreased the accuracy of cup positioning by ≥ 3° were analyzed via multiple logistic regression analyses.

RESULTS

The average absolute error of inclination was 2.8 ± 2.6° in Hip Align and 2.7 ± 1.8° in AR-Hip, and absolute anteversion error was 2.5 ± 2.0° in Hip Align and 2.6 ± 2.2° in AR-Hip, and there was no significantly different between the two navigation systems. There was a significant association between the absolute measurement error (≥ 3°) of cup inclination and patients' BMI in the Hip Align group [odds ratio (OR) 1.350; 95% confidence interval (CI) 1.035-1.760; p = 0.027], but not in the AR-Hip group.

CONCLUSIONS

The accuracy of the acetabular cup positioning between the Hip Align and AR-Hip showed no difference during THA in the spine position. The high BMI could have negative influence on the accuracy of cup positioning in THA using Hip Align, thus AR-Hip could be designable for obesity patients.

Radiological signs of femoroacetabular impingement are linked to pelvic version in asymptomatic subjects

INTRODUCTION

With the recent interest in hip-spine relationship, the link between femoroacetabular impingement (FAI) and the lumbar-pelvic-femoral complex (LPFC) appears decisive. The objectives of this study were (1) to compare the pelvic version, as well as (2) all the parameters of the LPFC between two populations of healthy subjects, comparing those with radiological signs of FAI to those without and finally, (3) to evaluate the LPFC parameters according to the type of FAI.

HYPOTHESIS

Asymptomatic subjects with radiological signs of FAI had superior pelvic anteversion.

MATERIALS AND METHOD

This retrospective study was based on a prospective cohort of 118 voluntary asymptomatic patients including 62 men (52.5%) with a mean age of 25.6 years±4.4 (19-39). The following parameters: pelvic version (PV), pelvic incidence (PI), lumbar lordosis (LL), sacral slope (SS), hip flexion, intrinsic (IER) and extrinsic (EER) extension reserve were measured using EOS imaging™ in the reference standing position and the lunge position. The radiological signs of FAI (cam, pincer, mixed) were identified on these acquisitions then separated into 2 groups. The first was the group presenting with one or more images of FAI (FAI+) and the second group with no images of FAI (FAI-).

RESULTS

There were 143 hips in the FAI+ group compared to 93 hips in the FAI- group. There were 36.4% cams and 45% pincers. With an average of 9.08°±7.81 (-11.0; 27.0) versus 12.33°±8.94 (-5.0; 55.0), the PV was significantly lower (p=0.022) in the FAI+ group compared to the FAI- group. A post-hoc power analysis on the primary outcome (PV) confirmed sufficient power (1-β=0.809). Compared to the FAI- group, the cam group presented a significantly lower IER and EER (respectively p=0.014 and p=0.047). The comparative analysis between the FAI- and pincer groups found a significant difference in PI (p=0.001), PV (p<0.001), IER (p=0.017) and hip flexion (p<0.001), SS in lunge position (p=0.031) and EER (p=0.039).

CONCLUSION

Asymptomatic subjects with radiographic signs of FAI present with weak pelvic version when standing. This pelvic hyper-anteversion is mainly found in the event of a radiological pincer sign.

LEVEL OF EVIDENCE

III, retrospective comparative study.

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.

Current Concepts in Diagnosis and Management of Patients Undergoing Total Hip Replacement with Concurrent Disorders of Spinopelvic Anatomy: A Narrative Review

Despite the high success rate of primary total hip replacement (THR), a significant early revision rate remains, which is largely attributed to instability and dislocations. Despite the implants being placed according to the safe zone philosophy of Lewinnek, occurrence of THR dislocation is not an uncommon complication. Large diagnostic and computational model studies have shown variability in patients' mobility based on the individual anatomic and functional relationship of the hip-pelvis-spine complex. The absolute and relative position of hip replacement components changes throughout motion of the patient's body. In the case of spinopelvic pathology such as spine stiffness, the system reaches abnormal positional states, as shown with computerized models. The clinical result of such pathologic hip positioning is edge loading, implant impingement, or even joint dislocation. To prevent such complications, surgeons must change the dogma of single correct implant positioning and take into account patients' individualized anatomy and function. It is essential to broaden the standard diagnostics and their anatomical interpretation, and correct the pre-operative surgical planning. The need for correct and personalized implant placement pushes forward the development and adaptation of novel technologies in THR, such as robotics. In this current concepts narrative review, we simplify the spinopelvic biomechanics and pathoanatomy, the relevant anatomical terminology, and the diagnosis and management algorithms most commonly used today.

Patient-Specific Safe Zones for Acetabular Component Positioning in Total Hip Arthroplasty: Mathematically Accounting for Spinopelvic Biomechanics

BACKGROUND

Despite a growing understanding of spinopelvic biomechanics in total hip arthroplasty (THA), there is no validated approach for executing patient-specific acetabular component positioning. The purpose of this study was to (1) validate quantitative, patient-specific acetabular "safe zone" component positioning from spinopelvic parameters and (2) characterize differences between quantitative patient-specific acetabular targets and qualitative hip-spine classification targets.

METHODS

From 2,457 consecutive primary THA patients, 22 (0.88%) underwent revision for instability. Spinopelvic parameters were measured prior to index THA. Acetabular position was measured following index and revision arthroplasty. Using a mathematical proof, we developed an open-source tool translating a surgeon-selected, preoperative standing acetabular target to a patient-specific safe zone intraoperative acetabular target. Difference between the patient-specific safe zone and the actual component position was compared before and after revision. Hip-spine classification targets were compared to patient-specific safe zone targets.

RESULTS

Of the 22 who underwent revision, none dislocated at follow-up (4.6 [range, 1 to 6.9]). Patient-specific safe zone targets differed from prerevision acetabular component position by 9.1 ± 4.2° inclination/13.3 ± 6.7° version; after revision, the mean difference was 3.2 ± 3.0° inclination/5.3 ± 2.7° version. Differences between patient-specific safe zones and the median and extremes of recommended hip-spine classification targets were 2.2 ± 1.9° inclination/5.6 ± 3.7° version and 3.0 ± 2.3° inclination/7.9 ± 3.5° version, respectively.

CONCLUSION

A mathematically derived, patient-specific approach accommodating spinopelvic biomechanics for acetabular component positioning was validated by approximating revised, now-stable hips within 5° version and 3° inclination. These patient-specific safe zones augment the hip-spine classification with prescriptive quantitative targets for nuanced preoperative planning.

An Analysis of the Preoperative Factors, Spinopelvic Mobility and Sagittal Spinal Alignment in Pre-THA Patients

Hip arthroplasty is a very effective medical procedure. The optimal positioning of the components and the functioning of the endoprosthesis are influenced, among other things, by the mobility and balance of the spine. The aim of the study was to analyze the factors influencing the mobility of the lumbar-pelvic-iliac complex (spinopelvic mobility) together with the assessment of sagittal spinal alignment in patients prior to THA (total hip arthroplasty). Patients who underwent hip replacement surgery due to advanced osteoarthritis of the hip were enrolled in the study (n = 103). The sociodemographic characteristics, BMI, radiological advancement of the degenerative disease, quality of life, and range of joint mobility were completed using a proprietary questionnaire, the EQ-5D-5L questionnaire, and a clinical examination. X-ray images were analyzed: AP of the pelvis standing up, lateral of the spine standing and sitting. Key parameters were measured as ∆SS-change in sacrum angle value when changing from standing to sitting position and pelvic incidence (PI)-lumbar lordosis (LL) mismatch-sagittal lumbar pelvic balance measured in standing position. The patients were assigned to the appropriate groups according to the Hip-Spine Classification: normal group: 1A (n = 65; 63.1%), abnormal groups: 1B (n = 17; 16.5%), 2A (n = 16; 15.5%), 2B (n = 5; 4.9%). A correlation was shown between the abnormal groups and the individual components of PROMs in the scope of the self-service and normal activities categories (EQ-5D and EQ-VAS). However, the strength of the relationship turned out to be moderate, and the remaining components of the survey were statistically insignificant. The remaining factors analyzed, i.e., age, BMI, the range of hip motion, the presence of contracture in the joint in a clinical examination, and the radiological advancement of osteoarthritis on the Tonnis scale, do not predict abnormal relationships between the spine and the pelvis in our patients waiting for THA. Therefore, further investigations are needed to evaluate the correlation between preoperative factors and the lumbar-pelvic-iliac complex in patients prior to planned hip arthroplasty.

Error of intraoperative measurement of stem anteversion is decreased by measuring in neutral hip position during total hip arthroplasty

BACKGROUND

Intraoperative stem anteversion, which is the angle between the lower leg axis and the trial-stem axis with hip flexion and adduction, is generally evaluated by the surgeon's visual estimation during total hip arthroplasty (THA). However, the conventional approach can be influenced by knee osteoarthritis or uncertain surgeon's observation point. Therefore, we developed a new method for measuring the stem anteversion angle in the neutral hip position using an original rod attached to the trial-stem perpendicular to the long axis and parallel to the stem neck. This study aimed to assess the accuracy of our method in comparison with the conventional method of measuring intraoperative stem anteversion angle.

METHODS

We measured the intraoperative stem anteversion angle in consecutive 106 hips of 106 patients who underwent cementless primary THA with a tapered wedge stem. Absolute error in the stem anteversion angle was expressed as the difference between intraoperative (common vs. neutral hip positions) and postoperative computed tomography measurements, i.e., true stem anteversion. Additionally, we investigated the factors affecting these errors.

RESULTS

The absolute error of measurement was significantly smaller in the neutral hip position than in the common position (3.0° ± 2.5° vs. 8.0° ± 3.9°; p < 0.0001). The factor associated with the error was advanced knee osteoarthritis in the common position, whereas it was not statistically significant in the neutral hip position.

CONCLUSIONS

This study suggests that the error in the intraoperative measurement of stem anteversion is decreased by measuring in the neutral hip position during THA.

Bibliometric Analysis of Spinopelvic Alignment in Total Hip Arthroplasty

INTRODUCTION

Postoperative dislocation of unclear etiology remains a concern after total hip arthroplasty (THA). Interest is growing in the importance of spinopelvic alignment on stability in THA. The purpose of this study was to analyze publication trends, areas of interest, and future research direction of spinopelvic alignment in THA.

METHODS

Articles on the topic of spinopelvic alignment in THA published between 1990 and 2022 were obtained through Web of Science Core Collection of Clarivate Analytics (WSCCA). Results were screened by title, abstract, and full text. The inclusion criterion was English-language peer-reviewed journal publications on the clinical topic of spinopelvic alignment in THA. Bibliometric software was used to characterize publication trends.

RESULTS

We screened 1,211 articles, yielding 132 meeting the inclusion criterion. From 1990 to 2022, published articles have steadily increased, peaking in 2021. Countries that have been the most productive in contributions to research are those in which THA is the most prevalent. Our analysis of keyword frequency showed increasing interest in "pelvic tilt," "anteversion," and "acetabular component" position.

CONCLUSION

Our study identified that increasing attention is being given to spinopelvic mobility and PT in the setting of THA. The United States and France produced the most studies related to spinopelvic alignment.

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

BACKGROUND

Several 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.

METHODS

A 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.

RESULTS

A 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%.

CONCLUSION

In 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.

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.

Functional Component Positioning in Total Hip Arthroplasty and the Role of Robotic-Arm Assistance in Addressing Spinopelvic Pathology

Hip, spine, and pelvis function as a unified kinetic chain. Any spinal pathology, results in compensatory changes in the other components to accommodate for the reduced spinopelvic motion. The complex relationship between spinopelvic mobility and component positioning in total hip arthroplasty presents a challenge in achieving functional implant positioning. Patients with spinal pathology, especially those with stiff spines and little change in sacral slope, are at high instability risk. In this challenging subgroup, robotic-arm assistance enables the execution of a patient specific plan, avoiding impingement and maximizing range of motion; especially utilizing virtual range of motion to dynamically assess impingement.

The Top Three Burning Questions in Total Hip Arthroplasty

Total hip arthroplasty (THA) for end-stage osteoarthritis is one of the most effective surgical treatments in medicine. Impressive outcomes have been well documented in the literature with patients gaining ambulation and recovery of hip joint function. Nevertheless, there are still debatable issues and controversies that the orthopedic community has not been able to provide a definitive answer for. This review is focused on the current three most debatable issues surrounding the THA procedure: (1) new cutting-edge technology, (2) spinopelvic mobility, and (3) fast-track protocols. The scope of the herein narrative review is to analyze the debatable issues surrounding the three aforementioned topics and conclude the best contemporary clinical approaches regarding each issue.

Dislocation Rates of Primary Total Hip Arthroplasty in Patients With Prior Lumbar Spine Fusion and Lumbar Degenerative Disk Disease With and Without Utilization of Dual Mobility Cups: An American Joint Replacement Registry Study

INTRODUCTION

Patients undergoing primary total hip arthroplasty (THA) with a previous history of lumbar spine fusion (LSF) are at increased risk of dislocation. The purpose of this study was to compare the 90-day and 1-year dislocation rates of patients with LSF or lumbar degenerative disk disease who underwent primary THA with and without dual mobility (DM) constructs.

METHODS

An American Joint Replacement Registry data set of patients aged 65 years and older undergoing primary THA with minimum 1-year follow-up with a history of prior LSF or a diagnosis of lumbar degenerative disk disease was created. DM status was identified, and dislocation and all-cause revision at 90 days and 1 year were assessed.

RESULTS

A total of 15,572 patients met study criteria. The overall dislocation rates for the non-DM and DM groups were 1.17% and 0.68%, respectively, at 90 days, and 1.68% and 0.91%, respectively, at 1 year ( P = 0.005). The odds of 90-day (OR = 0.578, [ P = 0.0328]) and 1-year (OR = 0.534, [ P = 0.0044]) dislocation were significantly less with DM constructs, compared with non-DM constructs. No statistically significant difference was observed in revision rates between groups.

DISCUSSION

This large registry-based study identified a reduced risk of dislocation in patients at risk for spinal stiffness when a DM compared with non-DM construct was used in primary THA at 90-day and 1-year follow-up intervals. Our data support the use of DM constructs in high-risk patients with stiff spines and altered spinopelvic mobility as a promising option to mitigate the risk of postoperative hip instability after primary THA.

LEVELS OF EVIDENCE

Level III. Therapeutic retrospective cohort.

Association of age and spinopelvic function in patients receiving a total hip arthroplasty

Restricted spinopelvic mobility received attention as a contributing factor for total hip arthroplasty (THA) instability. However, it is still unknown, how the spinopelvic function is influenced by age. In identifying the patients at highest risk for altered spinopelvic mechanics the study aimed to determine the association of age on the individual segments of the spinopelvic complex and global spinal sagittal alignment in patients undergoing THA. 197 patients were included in the prospective observational study conducting biplanar stereoradiography (EOS) in standing and sitting position pre-and postoperatively. Two independent investigators assessed C7-sagittal vertical axis (C7-SVA), cervical lordosis (CL), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA). Key segments of the spinopelvic complex are defined as lumbar flexibility (∆ LL = LL_standing - LL_sitting), pelvic mobility (∆ SS = SS_standing - SS_sitting) and hip motion (∆ PFA = PFA_standing - PFA_sitting). Pelvic mobility was further defined based on ∆ SS = SS_standing - SS_sitting as stiff (∆ SS < 10°), normal (∆ SS ≥ 10°-30°) and hypermobile (∆ SS > 30°). The patient collective was classified into three groups: (1) < 60 years (n = 56), (2) ≥ 60-79 years (n = 112) and (3) ≥ 80 years (n = 29). Lumbar flexibility (∆ LL) was decreased with increasing age between all groups (36.1° vs. 23.1° vs. 17.2°/p₁₊₂ < 0.000, p₂₊₃ = 0.020, p₁₊₃ < 0.000) postoperatively. Pelvic mobility (∆ SS) was decreased in the groups 2 and 3 compared to group 1 (21.0° and 17.9° vs. 27.8°/p₁₊₂ < 0.000, p₂₊₃ = 0.371, p₁₊₃ = 0.001). Pelvic retroversion in standing position (APPT) was higher in group 2 and 3 compared to group 1 (1.9° and - 0.5° vs 6.9°/p₁₊₂ < 0.000, p₂₊₃ = 0.330, p₁₊₃ < 0.000). Global sagittal spinal balance (C7-SVA) showed more imbalance in groups 2 and 3 compared to group 1 (60.4 mm and 71.2 mm vs. 34.5 mm/p₁₊₂ < 0.000, p₂₊₃ = 0.376, p₁₊₃ < 0.000) postoperatively. The preoperative proportion of patients with stiff pelvic mobility in group 1 was distinctly lower than in group 3 (23.2% vs. 35.7%) and declined in group 1 to 1.8% compared to 20.7% in group 3 after THA. Changes after THA were reported for groups 1 and 2 representing spinopelvic complex key parameter lumbar flexibility (∆ LL), pelvic mobility (∆ SS) and hip motion (∆ PFA), but not for group 3. This is the first study to present age-adjusted normative values for spinopelvic mobility. The subgroups with increased age were identified as risk cohort for altered spinopelvic mechanics and enhanced sagittal spinal imbalance and limited capacity for improvement of mobility after THA. This valuable information serves to focus in the preoperative screening on the THA candidates with the highest risk for abnormal spinopelvic function.

Functional implant positioning in total hip arthroplasty and the role of robotic-arm assistance

INTRODUCTION

Accurate implant positioning, tailored to the phenotype and unique biomechanics of each patient is the single most important objective in achieving stability in THA and maximise range of motion. The spine-pelvis-hip construct functions as a single unit adapting to postural changes. It is widely accepted in the literature that no universaltarget exists and variations in spinopelvic mobility mandate adjustments to the surgical plan; thus bringing to the fore the concept of personalised, functional component positioning.

METHODS

This manuscript aims to outline the challenges posed by spinopelvic imbalance and present a reproducible, stepwise approach to achieve functional-component positioning. We also present the one-year functional outcomes and Patient Reported Outcome Measures of a prospective cohort operated with this technique.

RESULTS AND CONCLUSION

Robotic-arm assisted Total Hip Arthroplasty has facilitated enhanced planning based on the patient's phenotype and evidence suggests it results in more reproducible and accurate implant positioning. Preservation of offset, avoiding leg-length discrepancy, accurate restoration of the centre of rotation and accomplishing the combinedversion target are very important parameters in Total Hip Arthroplasty that affect post-operative implant longevity, patient satisfaction and clinical outcomes.

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

PURPOSE

Hip 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.

METHODS

Asymptomatic 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.

RESULTS

Among 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.

CONCLUSION

Spinopelvic parameters as measured in the supine position on MRI, do not correlate with hip osteoarthritis or lateral center edge angle.

Measurement of spinopelvic sagittal alignment in the relaxed seated position rather than in the straight seated position is suitable for assessing spinopelvic mobility in patients before total hip arthroplasty

PURPOSE

The relationship between spinopelvic mobility and dislocation in total hip arthroplasty (THA) has recently attracted attention. This study aimed to investigate the differences in sacral slope (SS) between two types of upright seated positions and to determine which seated position was appropriate for assessing spinopelvic mobility (change in SS from standing to sitting) before THA.

MATERIALS AND METHODS

This prospective cohort study included 75 hips from 75 patients who had undergone primary THA. Each patient underwent preoperative lateral spinopelvic radiography in standing (st) and two seated positions: relaxed (rs) and straight (ss). The change in SS between each position (Δ) was measured.

RESULTS

Differences in all spinopelvic sagittal alignment parameters between the two seated positions were statistically significant (p < 0.001). The range, median, and mean values of ΔSS_ss-rs were -2.0° to 26.5°, 6.8°, and 8.3°, respectively. ΔSS_ss-rs was significantly correlated with SS, LLA, and PFA in the relaxed seated position (r = -0.52, -0.39, and 0.37; p < 0.001, p < 0.001, and p = 0.001, respectively), but was not correlated to these parameters in the straight seated position. Of the 52 patients with normal spinopelvic mobility in the relaxed seated position (ΔSS_st-rs > 10°), 24 (46%) patients were misrepresented as having a stiff spine in the straight seated position (ΔSS_st-ss < 10°).

CONCLUSION

The change in SS from the straight to the relaxed seated position widely varied in patients before THA. The spinopelvic radiograph in the relaxed seated position is appropriate when evaluating spinopelvic mobility for preoperative planning.

The Impact of Hip Mobility on Lumbar and Pelvic Mobility before and after Total Hip Arthroplasty

Hip arthrosis and total hip arthroplasty (THA) can alter a patient's balance and spinopelvic mobility. In this study, we hypothesized that lumbar, pelvic, and hip mobility and their inter-relations are affected by THA and that their study could give an insight in our understanding of postoperative balance and mobility. A total of 165 patients with hip arthrosis and with an indication for THA were included in this single-center prospective cohort. Sagittal radiographs were acquired in four positions: free-standing, standing extension, relaxed-seating and flexed-seating preoperatively and at 6 and 12 months. Spinopelvic parameters were measured (pelvic tilt and incidence, sacral slope, lumbar lordosis, pelvic-femoral angle). Standing spinopelvic parameters did not significantly change postoperatively. However, the postural changes occurring between positions were significantly altered after THA. In particular, pelvic and lumbar mobility was significantly reduced postoperatively, while hip mobility was increased. Correlations were observed between the changes in lumbar, pelvic and hip mobility before and after THA. This study confirmed that there is a relationship between lumbar, pelvic and hip mobility in osteoarthritis, and that this relationship is modified by the postoperative compensation mechanisms deployed by the patient in dynamic postures. Hence, surgeons should consider these relationships when planning surgery, in order to obtain a physiological pelvic tilt postoperatively and to account for the potential increased risk of impingement and dislocation with hip hypermobility.

Variations in lower limb alignments indicate pelvic tilt after total hip arthroplasty

OBJECTIVE

We sought to correlate various spinopelvic and lower limb alignments, and to examine the current spinopelvic theories on a Chinese cohort.

METHODS

We retrospectively reviewed 166 patients undergoing THA. Among them, 138 patients with unilateral THA met the inclusion criteria. Sagittal alignments and cup orientations were measured on standing and sitting lateral EOS images. Patients were categorized into two groups with a scoring system for lumbar spine degeneration. Patients' demographics including age, sex, lumbar spine degeneration and radiographic measurements were studied.

RESULTS

PT, SS, LL and TK differed significantly between standing and sitting within each group except for TK in degenerative group (32.8 ± 13.9 vs. 32.9 ± 14.2, p = 0.905). Compared with degenerative spine group, non-degenerative spine patients have great pelvic mobility (ΔPT, -24.4 ± 12.5° vs. -17.6 ± 10.7, p = 0.0008), greater lumbar mobility (ΔLL, -34.8 ± 15.2 vs. -21.7 ± 12.2, p = < 0.0001) and compensatory cup orientation changes (ΔRA, -15.5 ± 11.1 vs. -12.0 ± 8.4, p = 0.00920; ΔRI, -10.8 ± 11.5 vs. -5.6 ± 7.5, p = 0.0055). Standing PT and ankle dorsiflexion angle correlated positively (R² = 0.236, p = 0.005).

CONCLUSION

THA patients in this cohort showed a spinopelvic motion paradigm similar to that from previous studies on Caucasians. Ankle dorsiflexion indicate greater posterior pelvic tilt on standing. Surgeons should beware of risks of instability in patients with lower limb compensations.

ADVANCES IN KNOWLEDGE

This study provides new insights into the clinical relevance of lower limb alignments to spinopelvic motion after THA in a relatively young Chinese population.

The Functional Mechanics of the Acetabular Component in Total Hip Arthroplasty

BACKGROUND

Total 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.

METHODS

Theoretical 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.

RESULTS

A 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.

CONCLUSION

This 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.

Spinal pathology and outcome post-THA: does segment of arthrodesis matter?

INTRODUCTION

The presence of lumbar spine arthrodesis (SA) is associated with abnormal spinopelvic characteristics and inferior outcome post total hip arthroplasty (THA). However, whether patients with upper segment SA are also at increased risk of complications is unknown. This study aims to (1) determine if upper segment SA is associated with inferior THA outcomes; (2) assess spino-pelvic characteristics; and (3) test whether static or dynamic spinopelvic characteristics correlate with outcome post-THA.

MATERIALS AND METHODS

In this retrospective, case-matched, cohort study from a tertiary referral centre, 40 patients (59 hips) that had undergone both THA and any level of spinal arthrodesis (49 THA-Lumb and 10 THA-Cerv) were compared with 41 patients (59 hips) who had THA-only without known spinal pathology. Spino-pelvic characteristics [including severity of Degenerative-Disc-Disease (DDD); spinal balance and stiffness] and outcome, including patient reported outcome measures (PROMs), at minimum of 1-year post-THA were assessed.

RESULTS

THA-Lumb and THA-Cerv groups had greater number of complications and inferior hip and spinal PROMs compared to THA-Only (p < 0.001). Similar spinopelvic characteristics were seen between the THA-Cerv and THA-Lumb, which were significantly different to the THA-only group. The presence of DDD and unbalanced or stiff spine was associated with increased dislocation and inferior PROMs in the whole cohort.

CONCLUSIONS

THA in the presence of SA, regardless of level, is associated with inferior outcomes and an increased risk for dislocation. The presence of a SA is associated with increased risk of adverse spinopelvic characteristics. Such characteristics were strongly associated with increased dislocation-risk and inferior PROMs. It is likely that these adverse characteristics are the most important adverse predictor, rather than segment of SA per se.

Spinopelvic Relationship and Its Impact on Total Hip Arthroplasty

The dynamic, complex interaction among the spine, pelvis, and hip is often underappreciated, yet understanding it is vital for both arthroplasty and spinal surgeons. There is an increasing incidence of degenerative hip and spinal pathologies as a result of the ageing population. Furthermore, hip pathology can cause spine pathology and vice versa through “hip-spine” and “spine-hip syndrome.” Consequently, total hip arthroplasty (THA) and spinal fusion surgery, which both affect spinopelvic mobility, are also on the rise. Alteration in spinopelvic motion can affect the orientation of the acetabulum and, therefore, implant positioning in THA, leading to complications such as dislocation, impingement, aseptic loosening, and wear of components. This makes it imperative to assess spinopelvic motion and pelvic tilt prior to patients undergoing THA. In this paper, we explore how the surgeon should proceed to reduce risk of component malalignment, as well as the role of navigation systems in acetabular cup positioning.

Does spinopelvic motion change after total hip arthroplasty?

PURPOSE

Spinopelvic motion plays an important role in functional acetabular cup position after total hip arthroplasty (THA). Sacral slope (SS) has been a useful surrogate for spinopelvic motion. The present study aimed to investigate statistical characteristics of spinopelvic motion before and after THA using changes in SS in supine, standing, and sitting positions.

METHODS

A total of 76 patients (88 hips) were assessed. To classify spinopelvic mobility, defined as a change in SS from standing to sitting position (ΔSS_stand/sit), 10° ≤ ΔSS_stand/sit ≤ 30°, ΔSS_stand/sit < 10°, and ΔSS_stand/sit > 30° were considered normal, stiff, and hypermobile, respectively.

RESULTS

Over ± 7° changes in SS between before and one year after THA were observed in 39 (44.3%) hips in the sitting position, 19 (21.6%) hips in the supine position, seven (7.9%) in the standing position. Percentages of hips with stiff spinopelvic mobility (11.4% vs. 22.7%) and hypermobile spinopelvic mobility (23.9% vs. 12.5%) between before THA and one year after THA were significantly different (p = 0.034 and p = 0.016, McNemar's test). At one year after THA, 40.0% (4/10) of hips with stiff spinopelvic mobility and 57.1% (12/21) of hips with hypermobile spinopelvic mobility shifted to normal spinopelvic mobility.

CONCLUSIONS

Change in SS between before THA and one year after THA had a high inter-subject variability especially in the sitting position. In addition, there was a distinct shift to normal spinopelvic mobility postoperatively in hips with stiff and hypermobile spinopelvic mobility pre-operatively.

Spinopelvic Mobility Pattern and Acetabular Anteversion in Stiff Hips With Ankylosing Spondylitis After Total Hip Arthroplasty

BACKGROUND

Fused hips with spine stiffness in ankylosing spondylitis (AS) reduce spinopelvic mobility. We aimed to assess spinopelvic mobility pattern and acetabular anteversion in AS after total hip arthroplasty (THA).

MATERIAL AND METHODS

Ninety-four stiff hips in 58 AS individuals (mean age: 37.05) who underwent THA between 2012 and 2018 with a modified lateral approach were included. Twenty-three hips were fused, and 71 hips had mean flexion of 37.67°. Pelvic tilt, pelvic inclination, sacral slope (SS), and lumbar lordosis were correlated with THA, and functional outcomes were assessed at 34.6-month mean follow-up.

RESULTS

Thirty-seven had a stuck sitting pattern with stuck standing seen in 4 individuals. SS standing before and after THA were 25.08° and 27.30°. SS sitting was 8.99° compared to 16.80°. SS from sitting to standing was reduced (17.7°) in 17 individuals. Spine stiffness in extension was seen in 4 out of 37. Mean acetabular inclination after THA was 42.67°, and acetabular anteversion was 17.48°. Flexion after THA improved to mean 98.47°. Changes in SS from sitting to standing were correlated with THA (r-value: 0.93, P-value: .0001). The Harris Hip Score improved from 25.31 to 82.39 (P-value <.05), and the mean 12-item Short Form Survey at review was 52.18 and 59.55 (physical and mental components). The mean Western Ontario and Mc Master Universities Arthritis Index score was 17.56.

CONCLUSIONS

Spinopelvic mobility change was <10° after THA in AS, stuck sitting was seen in 37 of 58 (63.8%), and stuck standing was seen in 4 of 58 (6.9%), including spine stiffness in flexion or extension. Acetabular anteversion assessed was 17.48° (standard deviation: 4.41), with significant functional improvement.

LEVEL OF EVIDENCE

Level 4.

Imaging in Hip Arthroplasty Management Part 2: Postoperative Diagnostic Imaging Strategy

Hip arthroplasty (HA) is a frequently used procedure with high success rates, but 7% to 27% of the patients complain of persistent postsurgical pain 1 to 4 years post-operation. HA complications depend on the post-operative delay, the type of material used, the patient’s characteristics, and the surgical approach. Radiographs are still the first imaging modality used for routine follow-up, in asymptomatic and painful cases. CT and MRI used to suffer from metallic artifacts but are nowadays central in HA complications diagnosis, both having their advantages and drawbacks. Additionally, there is no consensus on the optimal imaging workup for HA complication diagnosis, which may have an impact on patient management. After a brief reminder about the different types of prostheses, this article reviews their normal and pathologic appearance, according to each imaging modality, keeping in mind that few abnormalities might be present, not anyone requiring treatment, depending on the clinical scenario. A diagnostic imaging workup is also discussed, to aid the therapist in his imaging studies prescription and the radiologist in their practical aspects.

Effect of Coronal and Sagittal Spinal Malalignment on Spinopelvic Mobility in Patients Undergoing Total Hip Replacement: A Prospective Observational Study

STUDY DESIGN

This was a prospective observational study.

OBJECTIVE

This investigation aimed (1) to determine the impact of sagittal spinal alignment with C7-sagittal vertical axis (SVA), pelvic incidence-lumbar lordosis (PI-LL) mismatch and Roussouly classification on individual segments of spinopelvic mobility represented by lumbar flexibility [∆lumbar lordosis (LL)], pelvic mobility [∆pelvic tilt (PT)], and hip motion [∆pelvic femoral angle (PFA)] and (2) to assess the influence of coronal spinal balance on the spinopelvic complex in patients undergoing total hip arthroplasty (THA) preoperatively and postoperatively.

SUMMARY OF BACKGROUND DATA

Restricted spinopelvic mobility gained attention as a contributing factor for THA instability. However, it remains unclear what influence the coronal and sagittal spinal alignment has on spinopelvic mobility.

MATERIALS AND METHODS

A total of 197 THA patients were included in the investigation conducting biplanar stereoradiography in standing and sitting position preoperatively and postoperatively. Two independent investigators assessed C7-SVA (≤50 mm balanced, >50 mm imbalanced), PI-LL (≤10 degrees balanced, >10 degrees imbalanced), refounded Roussouly classification, coronal spinal balance with C7-central sacral vertical line, LL, pelvic incidence (PI), PT, PFA. Individual segments of spinopelvic mobility based on the change from standing to sitting were defined as ∆LL, ∆PT, and ∆PFA. Unpaired t test or Welch t test for comparison between groups of 2 was applied. Analysis of variance and post hoc analysis according to Bonferroni or Games-Howell was used to determine differences between groups of >2. The Spearman rank correlation coefficient was used to determine the interrater reliability of the radiographic measurements.

RESULTS

Significant differences were demonstrated for ∆LL (SVA balanced/imbalanced: 24.7 degrees/19.1 degrees, P =0.001; PI-LL balanced/imbalanced: 24.4 degrees/16.4 degrees, P <0.000), PT (SVA balanced/imbalanced: 12.5 degrees/15.2 degrees, P =0.029; PI-LL balanced/imbalanced: 10.8 degrees/20.5 degrees, P <0.000), PI (SVA balanced/imbalanced: 52.9 degrees/56.9 degrees, P =0.001; PI-LL balanced/imbalanced: 52.1 degrees/61.0 degrees, P <0.000), LL (SVA balanced/imbalanced: 54.8 degrees/47.8 degrees, P =0.029; PI-LL balanced/imbalanced: 55.3 degrees/42.6 degrees, P <0.000). The coronal spinal balance (central sacral vertical line) indicated no significant differences regarding spinopelvic mobility between positive, neutral, or negative balanced groups. Significant differences with decreased pelvic mobility (∆PT) and lumbar flexibility (∆LL) in low-grade PI types 1 and 2 compared with high-grade PI type 4 according to the Roussouly classification were observed.

CONCLUSIONS

This is the first study to investigate spinal sagittal alignment using 3 different classifications in association to the spinopelvic complex in THA patients preoperatively and postoperatively. The significantly altered spinopelvic mechanics with decreased lumbar flexibility and increased pelvic retroversion in sagittal imbalanced patients clearly indicate the need for a separate consideration of the global spinal sagittal alignment. Our findings emphasize the importance of risk stratification for THA candidates in terms of sagittal imbalance attempting to mitigate the THA instability risk with accurate preoperative planning.

LEVEL OF EVIDENCE

Level III.

Two-Level Pedicle Subtraction Osteotomy in Lateral Position for an Ankylosing Spondylitis Patient With Severe Thoracolumbar Kyphosis and Hip Flexion Contracture: A Case Report

BACKGROUND AND IMPORTANCE

Spinal osteotomy and total hip replacement (THR) are the most common surgical interventions for ankylosing spondylitis (AS). It is recommended that patients with AS with severe thoracolumbar kyphotic deformity (TLKD) and flexed hips receive spinal osteotomy before THR to reduce the risk of hip prosthesis dislocation after THR. Standardly, spinal osteotomy is performed in the prone position; however, it is impractical to place patients with AS with kyphosis and closed hips in a prone position. In this report, we present an AS case with severe TLKD and closed hips who underwent spinal osteotomy in a lateral position first, then THR in the second stage.

CLINICAL PRESENTATION

The patient with AS was a 40-year-old woamn with severe TLKD and a closed hip. Back pain, difficulty walking, and gaze loss are the chief complaints. In consideration of the infeasibility of adopting the prone position, the patient was placed in a lateral position and underwent 2-level pedicle subtraction osteotomy at L1 and L3 with a long instrumentation from T10 to S1 at the first stage. Then, THR was performed at the second stage. The patient achieved pain relief, horizontal gaze, and nearly normal ambulation after spinal deformity correction and THR. After 2-year follow-up, the spinal alignment remains good and hip function was satisfactory.

DISCUSSION

The sequence of spinal osteotomy and THR performed for AS patients with TLKD and hip flexion contracture remains inconclusive. According to previous studies, patients treated with THR under a sagittal malaligned spine may require revision of the acetabular component to accommodate to the re-orientated acetabula resulting from the subsequent spinal osteotomy and realignment. Thus, we believe it is more reasonable to perform spinal osteotomy first. For osteotomy in lateral position, one of the key points is that the operation table should be tilted away from the surgeon side at a certain angle. Another point is that contralateral cancellous bone should be removed as much as possible when performing osteotomy at the side of vertebral away from the table. The satisfactory outcomes of this case revealed the feasibility of osteotomy in a lateral position for such severe AS with closed hip.

CONCLUSION

Performing double-level spinal osteotomy in a lateral position first could be an alternative for patients with AS who cannot be placed in the prone position because of the severe deformity of the spine and hips.

The effect of lumbar spinal fusion on native acetabular anteinclination in standing position

PURPOSE

The complex and dynamic spinopelvic interplay is not well understood. The aims of the present study were to investigate the following: (1) whether native acetabular anteinclination (AI) in standing position changes following lumbar spinal fusion (LSF); (2) potential correlations between AI change (ΔAI) and several spinopelvic parameters such as the change in lumbar lordosis (ΔLL), pelvic tilt (ΔPT), and anterior pelvic plane angle (ΔaPP).

METHODS

A total of 485 patients (Males: 262, Females: 223) with an average age of 64 ± 13 years who underwent a primary LSF were identified from our institutional database. The difference (Δ) between pre-and postoperative acetabular anteinclination (AI), lumbar lordosis (LL), anterior pelvic plane angle (aPP), sacral slope (SS), and pelvic tilt (PT) were measured on a standing lateral radiograph (EOS®) and compared to find the effect of LSF on the lumbopelvic geometry.

RESULTS

Following LSF, the average absolute ΔAI was 5.4 ± 4 (0 to 26)°, ΔLL: 5.5 ± 4 (0 to 27)°, ΔaPP: 5.4 ± 4 (0 to 38)°, ΔPT: 7 ± 5 (0 to 33)° and ΔSS: 5.3 ± 4 (0 to 33)°. No significant differences were observed between LSF levels. A ΔAI ≥ 10° was observed in 66 (13.6%) and ΔAI ≥ 20° in 5 (1%) patients. The Pearson correlation demonstrated a strong negative correlation of ΔAI with ΔLL (r = 0.72, p < .001).

CONCLUSION

Clinical decision-making should consider the relationship between native anteinclination and lumbar lordosis to reduce the risk of functional acetabular component malalignment in patients with concomitant hip and spine pathology.

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Hip-spine relationship in total hip arthroplasty - Simplifying the concepts

Total hip arthroplasty (THA) has been described as the operation of the century. Despite significant advancement in the field of technology, hip instability remains second most common cause of revision hip surgery after infection. There is garning interest to identify role of hip-spine relationship in order to identify high-risk patients for instability after THA. Acetabular component position varies according to spinal alignment and mobility in order to decrease risk of impingement and instability. Preoperative work up includes standing pelvis anteroposterior radiograph and lateral spino-pelvic radiograph in standing and sitting position. The focus of this review is to develop an algorithm to address the spino-pelvic pathology and guide the treatment on the basis of sagittal movement of the spine-pelvis-hip complex and to minimise the rate of dislocation following THA.

Spinopelvic Characteristics Normalize 1 Year After Total Hip Arthroplasty: A Prospective, Longitudinal, Case-Controlled Study

BACKGROUND

The presence of hip osteoarthritis is associated with abnormal spinopelvic characteristics. This study aimed to determine whether the preoperative, pathological spinopelvic characteristics normalize at 1 year after total hip arthroplasty (THA).

METHODS

This was a prospective, longitudinal, case-control, matched cohort study. Forty-seven patients undergoing THA underwent preoperative and 1-year postoperative assessments. This group was matched with regard to age, sex, and body mass index with 47 controls (volunteers) with well-functioning hips. All participants underwent clinical and radiographic assessments including lateral radiographs in standing, relaxed-seated, and deep-flexed-seated positions. Spinopelvic characteristics included change in lumbar lordosis (ΔLL), change in pelvic tilt (ΔPT), and hip flexion (change in pelvic-femoral angle, ΔPFA) when moving from a standing position to either of the seated positions. Spinopelvic hypermobility was defined as ΔPT > 30° between the standing and upright-seated positions.

RESULTS

Patients who underwent THA, compared with the control group, preoperatively demonstrated less mean change in hip flexion (ΔPFA, -54.8° ± 17.1° compared with -68.5° ± 9.5°; p < 0.001), greater mean change in pelvic tilt (ΔPT, 22.0° ± 13.5° compared with 12.7° ± 8.1°; p < 0.001), and greater mean lumbar movement (ΔLL, -22.7° ± 15.5° compared with -15.4° ± 10.9°; p = 0.015) transitioning from a standing position to an upright-seated position. After THA, these differences were no longer present between the THA group and the control group: the mean postoperative changes were -65.8° ± 12.5° (p = 0.256) for ΔPFA, 14.3° ± 9.5° (p = 0.429) for ΔPT, and -15.3° ± 10.6° (p = 0.966) for ΔLL. The higher prevalence of spinopelvic hypermobility in the THA group compared with the control group that was observed preoperatively (21% compared with 0%; p = 0.009) was no longer present after THA (6% compared with 0%; p = 0.194). Similar results were found moving from a standing position to a deep-seated position after THA.

CONCLUSIONS

Preoperative spinopelvic characteristics that contribute to abnormal mechanics can normalize after THA following improvement in hip flexion. This leads to patients having the expected hip, pelvic, and spinal flexion as demographically matched controls, thus potentially eliminating abnormal mechanics that contribute to the development or exacerbation of hip-spine syndrome.

LEVEL OF EVIDENCE

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

Conversion of the Sagittal Functional Safe Zone to the Coronal Plane Using a Mathematical Algorithm: The Reason for Failure of the Lewinnek Safe Zone

BACKGROUND

Ante-inclination (AI) of the cup is a key component of the combined sagittal index (CSI) for predicting joint stability after total hip arthroplasty (THA). We aimed to (1) validate a mathematical algorithm relating AI to radiographic anteversion (RA), radiographic inclination (RI), and pelvic tilt (PT); (2) convert the AI criterion of the CSI into the coronal functional safe zone (CFSZ) and explore the influences of standing-to-sitting pelvic motion (PM) and pelvic incidence (PI) on the CFSZ; and (3) attempt to locate a universal cup orientation that always fulfills the AI criterion of the CSI for all patients.

METHODS

In the first phase, a phantom pelvis was designed to simulate a range of PT values, and an acetabular cup was implanted with different RA, RI, and PT settings using a robot-assisted technique and scanned using the EOS imaging system. The second phase involved patient radiographs. We enrolled 100 patients who underwent robot-assisted THA from April 2019 to December 2019, and EOS images before THA and at the 12-month follow-up were recorded. The AI was measured on a lateral radiograph; this angle was used as the reference and compared with the calculated AI to assess the accuracy of the algorithm. Linear regression was conducted to explore the relationship between the size of the CFSZ and the values of PM and PI. We calculated the intersection of the CFSZs of the patients to find a universal cup orientation (RA and RI) for the CSI.

RESULTS

The algorithm was accurate according to both the phantom study and patient radiographs using PT at the time of follow-up, with mean absolute errors (MAEs) of 1.5° (width of 95% confidence interval [CI], 2.2°) and 2.8° (width of 95% CI, 3.0°), respectively. However, the preoperatively predicted AI had an MAE of 9.0° (width of 95% CI, 10.5°). In patient subgroups with lower PM or PI, the sizes of the CFSZ and of its intersection with the Lewinnek safe zone were significantly smaller (p < 0.017). No universal cup orientation existed to fulfill the CSI criteria for all patients or for any of the PM or PI subgroups.

CONCLUSIONS

The target orientation for the cup in THA should be individualized. Our validated algorithm may serve as a quantitative tool for the patient-specific optimization of cup AI on the basis of the functional safe zone.

CLINICAL RELEVANCE

The Lewinnek safe zone fails because it cannot predict the functional orientation of the cup. The concept of a universal safe zone of cup orientation should be abandoned and replaced by a patient-specific surgical target.

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.

Integrating the Combined Sagittal Index Reduces the Risk of Dislocation Following Total Hip Replacement

BACKGROUND

The aims of this matched cohort study were to (1) assess differences in spinopelvic characteristics between patients who sustained a dislocation after total hip arthroplasty (THA) and a control group without a dislocation, (2) identify spinopelvic characteristics associated with the risk of dislocation, and (3) propose an algorithm including individual spinopelvic characteristics to define an optimized cup orientation target to minimize dislocation risk.

METHODS

Fifty patients with a history of THA dislocation (29 posterior and 21 anterior dislocations) were matched for age, sex, body mass index (BMI), index diagnosis, surgical approach, and femoral head size with 200 controls. All patients underwent detailed quasi-static radiographic evaluations of the coronal (offset, center of rotation, and cup inclination/anteversion) and sagittal (pelvic tilt [PT], sacral slope [SS], pelvic incidence [PI], lumbar lordosis [LL], pelvic-femoral angle [PFA], and cup anteinclination [AI]) reconstructions. The spinopelvic balance (PI - LL), combined sagittal index (CSI = PFA + cup AI), and Hip-User Index were determined. Parameters were compared between the control and dislocation groups (2-group analysis) and between the controls and 2 dislocation groups identified according to the direction of the dislocation (3-group analysis). Important thresholds were determined from receiver operating characteristic (ROC) curve analyses and the mean values of the control group; thresholds were expanded incrementally in conjunction with running-hypothesis tests.

RESULTS

There were no coronal differences, other than cup anteversion, between groups. However, most sagittal parameters (LL, PT, CSI, PI - LL, and Hip-User Index) differed significantly. The 3 strongest predictors of instability were PI - LL >10° (sensitivity of 70% and specificity of 65% for instability regardless of direction), CSIstanding of <216° (posterior instability), and CSIstanding of >244° (anterior instability). A CSI that was not between 205° and 245° on the standing radiograph (CSIstanding) was associated with a significantly increased dislocation risk (odds ratio [OR]: 4.2; 95% confidence interval [CI]: 2.2 to 8.2; p < 0.001). In patients with an unbalanced and/or rigid lumbar spine, a CSIstanding that was not 215° to 235° was associated with a significantly increased dislocation risk (OR: 5.1; 95% CI: 1.8 to 14.9; p = 0.001).

CONCLUSIONS

Spinopelvic imbalance (PI - LL >10°) determined from a preoperative standing lateral spinopelvic radiograph can be a useful screening tool, alerting surgeons that a patient is at increased dislocation risk. Measurement of the PFA preoperatively provides valuable information to determine the optimum cup orientation to aim for a CSIstanding of 205° to 245°, which is associated with a reduced dislocation risk. For patients at increased dislocation risk due to spinopelvic imbalance (PI - LL >10°), the range for the optimum CSI is narrower.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Can Abnormal Spinopelvic Relationships be Identified by Anteroposterior Pelvic Radiographs?

BACKGROUND

Abnormal spinopelvic relationships may place patients at an increased risk for instability after primary total hip arthroplasty. The purpose of this study was to determine if radiographic markers on a standing anteroposterior (AP) pelvis radiograph could identify patients with sagittal spinopelvic imbalance or spinal stiffness.

METHODS

Patients undergoing primary total hip arthroplasty at a single institution from 2017 to 2020 with standing AP pelvis radiographs and sitting/standing lateral radiographs were identified. AP pelvis radiographs were assessed for the following: lumbosacral hardware, spine osteophytes, disc space narrowing, scoliosis>5°, pelvic obliquity>5°, and overlap of the sacrococcygeal junction/pubic symphysis. Patients with spinopelvic imbalance and/or spinopelvic stiffness were identified. Univariate and multivariate analyses were performed. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

Four hundred eighty-six patients were included. Prevalence of isolated sagittal spinopelvic imbalance and isolated spinopelvic stiffness was 12% and 21%, respectively; 11% of patients had sagittal imbalance and stiffness. Overlap of the sacrococcygeal junction/pubic symphysis (OR = 10.2, 95% CI = 5.3-19.8) and presence of lumbosacral hardware (OR = 4.4, 95% CI = 2.0-9.4) were markers of an increased risk of combined sagittal imbalance and stiffness. Seventy-nine percent of patients with overlap of the sacrococcygeal junction and pubic symphysis and 82% of patients with lumbosacral hardware had an abnormal spinopelvic relationship.

CONCLUSION

Isolated sagittal imbalance and stiffness were difficult to predict on standing AP pelvis radiographs. Overlap of the sacrococcygeal junction/pubic symphysis and presence of lumbosacral hardware associated with a higher risk of combined sagittal imbalance/stiffness and were present in ≥79% of patients with an abnormal spinopelvic relationship.

LEVEL OF EVIDENCE

IV; retrospective cohort study.

Pelvic incidence significance relative to spinopelvic risk factors for total hip arthroplasty instability

AIMS

Pelvic incidence (PI) is a position-independent spinopelvic parameter traditionally used by spinal surgeons to determine spinal alignment. Its relevance to the arthroplasty surgeon in assessing patient risk for total hip arthroplasty (THA) instability preoperatively is unclear. This study was undertaken to investigate the significance of PI relative to other spinopelvic parameter risk factors for instability to help guide its clinical application.

METHODS

Retrospective analysis was performed of a multicentre THA database of 9,414 patients with preoperative imaging (dynamic spinopelvic radiographs and pelvic CT scans). Several spinopelvic parameter measurements were made by engineers using advanced software including sacral slope (SS), standing anterior pelvic plane tilt (APPT), spinopelvic tilt (SPT), lumbar lordosis (LL), and PI. Lumbar flexion (LF) was determined by change in LL between standing and flexed-seated lateral radiographs. Abnormal pelvic mobility was defined as ∆SPT ≥ 20° between standing and flexed-forward positions. Sagittal spinal deformity (SSD) was defined as PI-LL mismatch > 10°.

RESULTS

PI showed a positive correlation with parameters of SS, SPT, and LL (r-value range 0.468 to 0.661). Patients with a higher PI value showed higher degrees of standing LL, likely as a compensatory measure to maintain sagittal spine balance. There was a positive correlation between LL and LF such that patients with less standing LL had decreased LF (r = 0.49). Similarly, there was a positive correlation between increased SSD and decreased LF (r = 0.54). PI in isolation did not show any significant correlation with lumbar (r = 0.04) or pelvic mobility (r = 0.02). The majority of patients (range 89.4% to 94.2%) had normal lumbar and pelvic mobility regardless of the PI value.

CONCLUSION

The PI value alone is not indicative of either spinal or pelvic mobility, and thus in isolation may not be a risk factor for THA instability. Patients with SSD had higher rates of spinopelvic stiffness, which may be the mechanism by which PI relates to THA instability risk, but further clinical studies are required. Cite this article: Bone Joint J 2022;104-B(3):352-358.

Augmented Reality- vs Accelerometer-Based Portable Navigation System to Improve the Accuracy of Acetabular Cup Placement During Total Hip Arthroplasty in the Lateral Decubitus Position

BACKGROUND

There have been no studies regarding the effectiveness of augmented reality (AR)-based portable navigation systems compared with accelerometer-based portable navigation systems in total hip arthroplasty (THA).

METHODS

We retrospectively compared THAs performed using an AR-based portable navigation system (n = 45) and those performed using an accelerometer-based portable navigation system (n = 42). All THAs were performed with the patient in the lateral decubitus position. The primary outcome was the absolute difference between cup placement angles displayed on the navigation screen and those measured on postoperative X-ray.

RESULTS

The mean absolute differences were significantly smaller in the AR-based portable navigation system group than the accelerometer-based portable navigation system group in radiographic inclination (2.5° ± 1.7° vs 4.6° ± 3.1°; 95% confidence interval 1.1°-3.2°, P < .0001). Similarly, the mean absolute differences were significantly better in the AR-based portable navigation system group in radiographic anteversion (2.1° ± 1.8° vs 6.4° ± 4.2°; 95% confidence interval 3.0°-5.7°, P < .0001). Neither hip dislocation, surgical site infection, nor other complications associated with use of the navigation system occurred in either group.

CONCLUSION

The AR-based portable navigation system may provide more precise acetabular cup placement compared with the accelerometer-based portable navigation system in THA.

Total Hip Replacement Influences Spinopelvic Mobility: A Prospective Observational Study

BACKGROUND

Abnormal 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.

METHODS

A 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.

RESULTS

Spinopelvic 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).

CONCLUSION

Definition 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.