What preoperative factors predict postoperative sitting pelvic position one year following 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.

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.

Creating Consensus in the Definition of Spinopelvic Mobility

INTRODUCTION

The term "spinopelvic mobility" is most often applied to motion within the spinopelvic segment. It has also been used to describe changes in pelvic tilt between various functional positions, which is influenced by motion at the hip, knee, ankle and spinopelvic segment. In the interest of establishing a consistent language for spinopelvic mobility, we sought to clarify and simplify its definition to create consensus, improve communication, and increase consistency with research into the hip-spine relationship.

METHODS

A literature search was performed using the Medline (PubMed) library to identify all existing articles pertaining to spinopelvic mobility. We reported on the varying definitions of spinopelvic mobility including how different radiographic imaging techniques are used to define mobility.

RESULTS

The search term "spinopelvic mobility" returned a total of 72 articles. The frequency and context for the varying definitions of mobility were reported. 41 papers used standing and upright relaxed-seated radiographs without the use of extreme positioning, and 17 papers discussed the use of extreme positioning to define spinopelvic mobility.

DISCUSSION

Our review suggests that the definitions of spinopelvic mobility is not consistent in the majority of published literature. We suggest descriptions of spinopelvic mobility independently consider spinal motion, hip motion, and pelvic position, while recognizing and describing their interdependence.

Validation of a preoperative formula to estimate postoperative pelvic sagittal alignment and mobility before performing total hip arthroplasty for patients with hip osteoarthritis

BACKGROUND

Although it is important to consider pelvic alignment and mobility in the standing and sitting positions before THA, it is not known how to preoperatively predict individual postoperative pelvic alignment and mobility. The purpose of this study was to investigate the pelvic alignment and mobility before and after THA, and to develop a predictive formula using preoperative factors to calculate postoperative sagittal alignment and mobility.

METHODS

One hundred seventy patients were assessed. The 170 patients were randomly divided into a prediction model analysis group (n = 85) and an external validation group (n = 85). In the prediction model analysis group, preoperative spinopelvic parameters were used to develop the predictive formulas to predict the postoperative sacral slope (SS) in standing and sitting positions and ΔSS. These were applied to the external validation group and assessed.

RESULTS

R² in multiple linear regression models for postoperative SS in standing, SS in sitting and ΔSS were 0.810, 0.672, and 0.423, respectively. The values of predicted and postoperative parameters were very close with no significant difference: SS in standing (33.87 vs. 34.23, P = 0.834), SS in sitting (18.86 vs. 19.51, P = 0.228), and ΔSS (15.38 vs. 14.72, P = 0.619).

CONCLUSION

The present study showed that the pelvic alignment and mobility after THA can be predicted using preoperative factors. Although a model with higher accuracy is needed, it is important to use a predictive formula to estimate the postoperative condition before performing THA.

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.

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

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

Association between sagittal spinal alignment and mechanical complications after primary total hip arthroplasty: a systematic review

Objective

Total hip arthroplasty (THA) affects pelvic posture and spinal alignment. These postural changes may further predispose patients to mechanical complications (MCs) after THA. The aim of this study was to conduct a systematic review to investigate whether any high-quality studies have assessed the association between sagittal spinal alignment and MCs after primary THA.

Methods

Inclusion criteria for studies were adult patients (age ≥18 years), primary THA, pre- and postoperative spinopelvic standing sagittal radiographs acquired preoperatively and at a minimum of 6-month follow-up, measurements of spinopelvic parameters, and reporting of possible MCs after THA. The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

Results

Six articles met the inclusion criteria. Although several studies confirmed the importance of spinal alignment when planning THA, these mainly investigated pelvic mobility as a risk factor for THA dislocation. Radiological follow-up imaging practices varied, and studies focused on different individual spinopelvic parameters.

Conclusion

Based on our study findings, no conclusions can be drawn regarding the association between sagittal spinal alignment and MCs after primary THA. Further research is needed to improve our knowledge of the connection between MCs after THA and sagittal spinal alignment.

Association of the Psoas Muscle Index and Sagittal Spinal Alignment With Patient-Reported Outcomes After Total Hip Arthroplasty: A Minimum 5-Year Follow-Up

BACKGROUND

The aim of this study is to assess the association between a spinopelvic malalignment and patient-reported perception of the hip as being "artificial" after total hip arthroplasty (THA). This is a critical issue as an age-related spinopelvic mismatch has been postulated to be associated with the risk of poor outcomes after THA.

METHODS

This is a retrospective case-control study of 274 THAs (244 of whom were women), with a mean follow-up of 6.2 (range 5.0-8.2) years. Hip perception was assessed by asking subjects whether their joint felt "natural" or "artificial." The association between an artificial perception and the following factors was evaluated: age, gender, psoas muscle index (PMI, cross-sectional area of bilateral psoas at L3 divided by height squared), and spinopelvic measures using logistic regression analysis.

RESULTS

An artificial hip perception (130 hips, 47.4%) was associated with a lower PMI (P = .016), Hip Disability and Osteoarthritis Outcome Score Joint Replacement score (P = .035), EuroQol 5-Dimension score (P = .041), and a higher incidence of a pelvic incidence-minus-lumbar lordosis (PI-LL) mismatch >10° (P < .001). A flatback deformity (odds ratio 2.24, 95% confidence interval 1.22-6.31, P = .001) and PMI (odds ratio 0.61, 95% confidence interval 0.34-0.82, P = .012) were predictive of an artificial perception. With the threshold of PI-LL set to 10°, PMI (P = .034), Hip Disability and Osteoarthritis Outcome Score Joint Replacement score (P < .001), joint perception (P = .020), EuroQol 5-Dimension score (P = .028), pain (P = .031), and satisfaction (P < .001) differed between the 2 groups.

CONCLUSION

A flatback deformity is associated with the risk of an artificial perception post-THA, especially in patients with sarcopenia. PMI and PI-LL measurements may help predict THA outcomes.

The accuracy in determining pelvic tilt from anteroposterior pelvic radiographs in patients awaiting hip arthroplasty

Spinopelvic mobility affects outcome after THA. Whether the sacro-femoral-pubic (SFP) angle, measured on AP radiographs, can be reliably used to estimate pelvic tilt (PT) in hip osteoarthritis patients is unknown. This study aimed to (1) validate the use of the SFP angle in the calculation of PT from AP radiographs, and (2) identify individual patient factors affecting the estimation of PT. A cohort of 100 patients awaiting THA for end-stage hip osteoarthritis was prospectively studied. AP and lateral radiographs, taken in the standing and relaxed-seated positions were evaluated for spinopelvic measurements (SFP, PT, and pelvic incidence [PI]). To validate the SFP angle, estimated PT values using the formula [PT = 75°-SFP] were compared to the true, measured values from the lateral radiographs. Despite good agreement for the estimated and true PT (16.2 ± 5.9° vs. 15.5 ± 8.6°; p = .315), a significantly poorer agreement could be found between the two methods at high or low values of PT. Patient-specific PI correlated with the difference between the two measurement methods (Pearson's r = -0.644; p < .001). However, the change in SFP angle equaled approximately the change in pelvic tilt (∆PT = 2°-∆SFP; Pearson's r = -0.934; p < .001). Absolute values for the sagittal PT should not be estimated from AP pelvic radiographs in patients awaiting total hip arthroplasty. However, the relative change in PT between different positions equals approximately the change in SFP angle. This may allow functional cup orientation after THA to be determined between different postures from an AP radiograph of the pelvis. The SFP angle has moderate accuracy in determining a patient's pelvic tilt; however, it can accurately determine a patient's change in pelvic tilt in different positions.

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.

Timing of Total Hip Arthroplasty Affects Lumbar Spinal Fusion Outcomes

STUDY DESIGN

This is a retrospective cohort study of consecutive patients undergoing lumbar spinal fusion (LSF) within the PearlDiver Humana research database from 2010 to 2018.

OBJECTIVE

The aim of this study was to determine if timing of total hip arthroplasty (THA) affects LSF outcomes.

SUMMARY OF BACKGROUND DATA

In patients with both spine and hip pathology, outcomes of THA have been shown to be affected by the timing of THA relative to LSF. However, few studies have assessed postoperative outcomes following LSF in this clinical scenario.

MATERIALS AND METHODS

A national database was queried for patients undergoing lumbar fusion and divided into 4 groups: (1) those who underwent LSF without THA (No THA); (2) those who underwent THA at least 2 years before LSF (>2 Prior THA); (3) those who underwent THA in the 2 years before LSF (0-2 Prior THA); and (4) those who underwent THA after LSF (THA After). We assessed lumbar-specific outcomes, including pseudarthrosis, revision, mechanical failure, and adjacent segment disease (ASD); as well as systemic complications. Controlling for age, sex, and Charlson comorbidity index, complication rates between all groups were assessed using univariate and multivariate logistic regression analysis. Post hoc comparisons were performed using the Fisher exact test with Bonferroni correction to account for multiple pairwise comparisons, resulting in an adjusted threshold for statistical significance of P<0.007.

RESULTS

When compared with the no THA group, those in the THA After group had a higher rate of ASD on multivariate analysis [adjusted odds ratio: 1.53, 95% confidence interval: 1.20-1.94, P<0.001]. When compared with all patients who underwent THA before LSF, patients who underwent THA after LSF had an increased risk of ASD (adjusted odds ratio: 3.80, 95% confidence interval: 2.21-6.98, P<0.001).

CONCLUSIONS

Patients who undergo THA after LSF have an increased rate of lumbar-related complications both when compared with patients who do not undergo THA and when compared with patients who undergo THA before LSF.

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.

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.

SPINOPELVIC MOBILITY IN PATIENTS WITH HIP OSTEOARTHRITIS AND TOTAL HIP ARTHROPLASTY INDICATION

ABSTRACT Introduction: Reduction of spinopelvic mobility is associated with an increased dislocation of total hip arthroplasty (THA). Objective: To assess 1) spinopelvic mobility in patients with primary hip osteoarthritis and THA indication and 2) the influence of hip flexion contracture on spinopelvic mobility. Methods: Thirty adult patients with primary hip osteoarthritis and THA indication were evaluated using radiographic parameters (pelvic incidence, pelvic tilt, sacral slope, lumbar flexibility, and spinopelvic mobility). Results: Spinopelvic mobility ranged from 6.90 a 54.50° (mean 32.79 ± 11.42) and the group of patients with hip flexion contracture had higher mobility. Spinopelvic mobility was correlated with pelvic tilt as well as with lumbar flexibility. Conclusion: Around 13.4% of patients had spinopelvic mobility under 20° , indicating reduced spinopelvic mobility and risk of THA dislocation. Level of Evidence III, Retrospective Comparative Study.

Does obesity affect acetabular cup position, spinopelvic function and sagittal spinal alignment? A prospective investigation with standing and sitting assessment of primary hip arthroplasty patients

Background

Total hip arthroplasty (THA) instability is influenced by acetabular component positioning, spinopelvic function and sagittal spinal alignment. Obesity is considered as a risk factor of THA instability, but the causal relationship remains unknown. This study aimed to investigate the influence of BMI on (1) spinopelvic function (lumbar flexibility, pelvic mobility and hip motion), (2) sagittal spinal alignment pre- and postoperatively and (3) acetabular cup position postoperatively in primary THA patients in a prospective setting.

Methods

One hundred ninety patients receiving primary total hip arthroplasty were enrolled in a prospective cohort study and retrospectively analysed. All patients received stereoradiography (EOS) in standing and relaxed sitting position pre-and postoperatively. C7-sagittal vertical axis (C7-SVA), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA) were assessed. Key parameters of the spinopelvic function were defined as lumbar flexibility (∆ LL = LL_standing − LL_sitting), pelvic mobility (∆ PT = PT_standing − PT_sitting) and hip motion (∆ PFA = PFA_standing − PFA_sitting). Pelvic mobility was further defined based on ∆ PT as stiff, normal and hypermobile (∆ PT < 10°; 10°–30°; > 30°). The patients were stratified to BMI according to WHO definition: normal BMI ≥ 18.5–24.9 kg/m² (n = 68), overweight ≥ 25.0–29.9 kg/m² (n = 81) and obese ≥ 30–39.9 kg/m² (n = 41). Post-hoc analysis according to Hochberg's GT2 was applied to determine differences between BMI groups.

Results

Standing cup inclination was significant higher in the obese group compared to the normal BMI group (45.3° vs. 40.1°; p = 0.015) whereas standing cup anteversion was significantly decreased (22.0° vs. 25.3°; p = 0.011). There were no significant differences for spinopelvic function key parameter lumbar flexibility (∆ LL), pelvic mobility (∆ PT) and hip motion (∆ PFA) in relation to BMI stratified groups. The obese group demonstrated significant enhanced pelvic retroversion compared to the normal BMI group (APPT − 1.8° vs. 2.4°; p = 0.028). The preoperative proportion of stiff pelvic mobility was decreased in the obese group (12.2%) compared to normal (25.0%) and overweight (27.2%) groups. Spinal sagittal alignment in C7-SVA and PI-LL mismatch demonstrated significantly greater imbalance in the obese group compared to the normal BMI group (68.6 mm vs. 42.6 mm, p = 0.002 and 7.7° vs. 1.2°, p = 0.032, respectively) The proportion of patients with imbalanced C7-SVA was higher in the obese (58.5%) than in the normal BMI group (44.1%).

Conclusions

The significantly increased spinal sagittal imbalance with altered pelvic mechanics is a potential cause for the reported increased risk of THA dislocations in obese patients. Consequently, the increased spinal sagittal imbalance in combination with normal pelvic mobility need to be taken into account when performing THA in obese patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02716-8.

The impact of functional combined anteversion on hip range of motion: a new optimal zone to reduce risk of impingement in total hip arthroplasty

AIMS

Pelvic tilt (PT) can significantly change the functional orientation of the acetabular component and may differ markedly between patients undergoing total hip arthroplasty (THA). Patients with stiff spines who have little change in PT are considered at high risk for instability following THA. Femoral component position also contributes to the limits of impingement-free range of motion (ROM), but has been less studied. Little is known about the impact of combined anteversion on risk of impingement with changing pelvic position.

METHODS

We used a virtual hip ROM (vROM) tool to investigate whether there is an ideal functional combined anteversion for reduced risk of hip impingement. We collected PT information from functional lateral radiographs (standing and sitting) and a supine CT scan, which was then input into the vROM tool. We developed a novel vROM scoring system, considering both seated flexion and standing extension manoeuvres, to quantify whether hips had limited ROM and then correlated the vROM score to component position.

RESULTS

The vast majority of THA planned with standing combined anteversion between 30° to 50° and sitting combined anteversion between 45° to 65° had a vROM score > 99%, while the majority of vROM scores less than 99% were outside of this zone. The range of PT in supine, standing, and sitting positions varied widely between patients. Patients who had little change in PT from standing to sitting positions had decreased hip vROM.

CONCLUSION

It has been shown previously that an individual's unique spinopelvic alignment influences functional cup anteversion. But functional combined anteversion, which also considers stem position, should be used to identify an ideal THA position for impingement-free ROM. We found a functional combined anteversion zone for THA that may be used moving forward to place total hip components. Cite this article: Bone Jt Open 2021;2(10):834-841.

Prediction of pelvic mobility using whole-spinal and pelvic alignment in standing and sitting position in total hip arthroplasty patients

PURPOSE

Dislocation is a major complication after total hip arthroplasty (THA), and pelvic stiffness is reportedly a significant risk factor for dislocation. This study aimed to investigate spinopelvic alignment, and identify preoperative factors associated with postoperative pelvic mobility.

METHODS

We enrolled 78 THA patients with unilateral osteoarthritis. The sagittal spinopelvic alignment in the standing and sitting position was measured using an EOS imaging system before and 3 months after THA. We evaluated postoperative pelvic mobility, and defined cases with less than 10° of sacral slope change as pelvic stiff type. The preoperative characteristics of those with postoperative stiff type, and preoperative factors associated with risk of postoperative stiff type were evaluated.

RESULTS

Sagittal spinopelvic alignment except for lumbar alignment were significantly changed after THA.A total of 13 patients (17%) were identified as postoperative pelvic stiff type. Preoperative lower pelvic and lumbar mobility were determined as significant factors for prediction of postoperative pelvic stiff type. Among these patients, nine patients (69%) did not have pelvic stiffness before THA. Preoperative factor associated with the risk of postoperative pelvic stiff type in those without preoperative stiffness was lower lumbar lordosis in standing position by multivariate regression analysis.

CONCLUSION

Spinopelvic alignments except lumber alignment was significantly changed after THA. The lower pelvic mobility and lumbar alignment were identified as the preoperative predictive factors for postoperative pelvic mobility. Evaluation of preoperative lumbar alignment may be especially useful for the prediction in patients with hip contractures, for these patients may possibly experience the extensive perioperative change in pelvic mobility.

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

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

Differences in Spinopelvic Characteristics Between Hip Osteoarthritis Patients and Controls

BACKGROUND

This study of patients with hip primary osteoarthritis and a matched, asymptomatic, volunteers (controls) group aimed to determine spinopelvic differences between the two groups and their consequences for total hip arthroplasty.

METHODS

104 patients (52 in each group) had their sagittal spinopelvic parameters (lumbar lordosis angle, sacral slope, pelvic tilt, pelvic incidence, and the pelvic-femoral angle) measured in the standing, relaxed-seated, and deep-flexed seated positions. Spinopelvic movement was calculated as the change between the different positions, and individual spinopelvic mobility was classified in accordance with the change in pelvic tilt as previously described (ΔPT: stiff (<10°), normal (10-30°), and hypermobile (>30°)).

RESULTS

Transitioning from the standing to relaxed-seated position, patients demonstrated 13˚ less hip flexion (P < .001), 12˚ more posterior pelvic tilt (P = .006), and 6˚ more lumbar flexion (P = .038) compared with controls. Transitioning from the standing to deep-flexed seated position, patients demonstrated 18˚ less hip flexion (P < .001), accompanied by a posterior and not an anterior pelvic tilt as in the controls (7˚ ± 14 vs -6˚ ± 17; P < .001). Patients showed a higher percentage of spinopelvic hypermobility (19% vs 2%; P = .008).

CONCLUSION

The reduced ability of flexion in the arthritic hip, leads to posterior pelvic tilt in the relaxed-seated position. This is associated with a likely compensatory increased lumbar flexion to keep an upright position. Therefore, spinopelvic hypermobility has to be defined as pathologic. When moving to the deep-flexed seated position, decreased flexion of the arthritic hip prevents the pelvis from tilting anteriorly while the lumbar spine performs a compensatory flexion by approximately the same amount compared with controls.

LEVEL OF EVIDENCE

Level II, diagnostic study.

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

BACKGROUND

This prospective cohort study aimed to characterize how spinopelvic characteristics change post-total hip arthroplasty (THA) and determine how patient-reported outcome measures are associated with 1) individual spinopelvic mobility and 2) functional sagittal cup orientation post-THA.

METHODS

One hundred consecutive patients who received unilateral THAs for end-stage hip osteoarthritis, without spinal pathology were studied. Preoperatively and postoperatively, patients underwent clinical and radiographic evaluations. Patient-reported outcomes were collected using the hip disability and osteoarthritis outcome score - physical function shortform (HOOS-PS). Radiographic parameters measured from standing and relaxed-seated radiographs, included the lumbar lordosis angle, pelvic tilt, pelvic femoral angle and cup orientation in the coronal (inclination/anteversion) and sagittal (anteinclination) planes. Spinopelvic mobility was characterized (ΔPT: "stiff" [<10°], "normal" [10°-30°], and "hypermobile" [>30°]).

RESULTS

Preoperative spinopelvic characteristics were not associated with HOOS-PS. Post-THA, the spinopelvic characteristics changed, with less patients having spinopelvic hypermobility (7%) compared with preop (14%). Postoperatively, patients with spinopelvic hypermobility showed significantly worse HOOS-PS scores (21 ± 17 vs 21 ± 22 vs 41 ± 23; ANOVA P = .037). Sagittal but not coronal cup orientation was associated with postoperative spinopelvic characteristics. Cup anteinclination was less in the patients with postoperative spinopelvic hypermobility (27 ± 7° vs 36 ± 8° vs 36 ± 10°; ANOVA: P = .035).

CONCLUSION

We hypothesize that spinopelvic hypermobility is secondary to impingement and reduced hip flexion; to achieve a seated position, impinging hips require more posterior pelvic tilt. Patients with spinopelvic hypermobility are likely impinging secondary to the low cup anteinclination (sagittal malorientation despite optimum coronal orientation) and thus have lower HOOS-PS compared. Sagittal assessments are thus important to adequately study hip mechanics.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Applying the hip-spine relationship in total hip arthroplasty

Total hip arthroplasty dislocations that occur inside Lewinnek's anatomical safe zone represent a need to better understand the hip-spine relationship. Unfortunately, the use of obtuse and redundant terminology to describe the hip-spine relationship has made it a relatively inaccessible topic in orthopaedics. However, with a few basic definitions and principles, the hip-spine relationship can be simplified and understood to prevent unnecessary dislocations following total hip arthroplasty.In the following text, we use common language to define a normal and abnormal hip-spine relationship, present an algorithm for recognising and treating a high-risk hip-spine patient, and discuss several common, high-risk hip-spine pathologies to apply these concepts. Simply, high-risk hip-spine patients often require subtle adjustments to acetabular anteversion based on radiographic evaluations and should also be considered for a high-offset stem, dual-mobility articulation, or large femoral head for additional protection against instability and dislocation.

Influence of sagittal degenerative spondylolisthesis on anteversion of the acetabular component in total hip arthroplasty

BACKGROUND

Degenerative lumbar spondylolisthesis (DSPL), as opposed to other degenerative spinal conditions, is disregarded in the assessment of hip stability after total hip arthroplasty (THA). This study aimed to determine whether patients with DSPL have different acetabular anteversion compared to patients with normal spine before and following THA.

METHODS

Preoperative and postoperative 6‑month lateral pelvic radiographs in standing and sitting positions from 91 patients who underwent primary THA were retrospectively compared for spinopelvic parameters between patients with DSPL (n = 31) and with normal spine (n = 34).

RESULTS

Compared to control patients in the standing position, patients with DSPL had significantly increased preoperative pelvic tilt (24° in DSPL vs. 8° in controls; p < 0.01), pelvic-femoral angle (194° in DSPL vs. 174° in controls; p < 0.05), decreased lumbar lordosis (35° in DSPL vs. 43° in controls; p < 0.05), increased postoperative pelvic tilt (22° in DSPL vs. 7° in controls; p < 0.01), pelvic-femoral angle (187° in DSPL vs. 179° in controls; p < 0.05), and acetabular anteversion (31° in DSPL vs. 23° in controls; p < 0.05). Preoperative (p = 0.181) and postoperative (p = 0.201) sitting pelvic tilt did not differ. There were positive correlations between preoperative standing pelvic tilt and postoperative standing acetabular anteversion, pelvic-femoral angle, and combined sagittal index (CSI) in DSPL (R² = 0.8416; R² = 0.9180; R² = 0.9459, respectively, p < 0.01) and in controls (R² = 0.6872; R² = 0.6176; R² = 0.7129, respectively, p < 0.01).

CONCLUSION

While the imbalance of seated sagittal plane is usually insignificant and compensable, the mechanism by which DSPL patients achieve a standing posture is different from control patients, with more hip extension and posterior tilt of the pelvis. Special attention should be paid to the risk of impingement caused by the increase of acetabular anteversion in the postoperative standing position.

Pathologic spinopelvic balance in patients with hip osteoarthritis : Preoperative screening and therapeutic implications

Recently spinopelvic balance and mobility, i.e. the dynamic interaction of the spine, pelvis and the femur in the sagittal plane between different postures, has been identified as a relevant factor influencing the outcome of primary total hip arthroplasty (THA). Individual spinopelvic balance and mobility seem to affect patient reported outcome and the risk of impingement and dislocation following THA. The aim of this article is to provide a concise overview of normal and pathologic spinopelvic alignment, to characterize relevant spinopelvic parameters and the diagnostic assessment in patients with hip OA and to discuss potential implications for THA with respect to implant selection and component orientation.Spinopelvic characteristics are highly variable. Patients with stiff lumbar spines and mobile hips seem to be at an increased risk of impingement and dislocation and can be screened with single lateral standing radiographs of the spinopelvic complex before THA. In patients with hip and spine pathology, particular attention should be paid to evaluate the individual pathoanatomy of the hip and established clinical measurements should be diligently taken with respect to the reconstruction of the center of rotation, hip offset, leg length and soft tissue tension in order to minimize the risk of impingement and dislocation. No evidence-based recommendations for novel target zones concerning implant position can currently be made. In patients at risk 36 mm heads should be used whenever possible. In high risk patients, such as the combination of a stiff unbalanced lumbar spine ("flatback") and a mobile hip or in the presence of long spinal fusions or fusions involving the sacrum, dual mobility cups offer additional stability.

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

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

How Can Patients With Mobile Hips and Stiff Lumbar Spines Be Identified Prior to Total Hip Arthroplasty? A Prospective, Diagnostic Cohort Study

BACKGROUND

Patients with reduced lumbar spine mobility are at higher risk of dislocation following total hip arthroplasty (THA). Therefore our study aimed to (1) define the optimal protocol for identifying patients with mobile hips and stiff lumbar spines and (2) determine clinical and standing radiographic parameters predicting these patients.

METHODS

A cohort of 113 patients with end-stage hip osteoarthritis awaiting THA was prospectively studied. Clinical data, patient-reported outcome measures, and spinopelvic radiographs were assessed with the patient in the standing, "relaxed-seated," and "deep-flexed seated" position. A "hip user index" was calculated quantifying the percentage of sagittal hip movement compared to overall movement between the standing and deep-flexed seated position.

RESULTS

Radiographs in the relaxed-seated position had an accuracy of 56% (95% confidence interval 46-65) to detect patients with stiff lumbar spines, compared to a detected rate of 100% in the deep-flexed seated position. A standing pelvic tilt of ≥19° was the only predictor for being a hip user with a sensitivity of 90% and specificity of 71% (area under the curve 0.83). Patients with a standing pelvic tilt ≥19° and an unbalanced spine with a flatback deformity had a 30× fold relative risk (95% confidence interval 4-226, P < .001) of being a hip user.

CONCLUSION

Patients awaiting THA and having combined high hip and reduced lumbar spine mobility can be screened for with lateral standing radiographs of the spinopelvic complex. Hip user verification should be done utilizing radiographs in the deep-flexed seated position due to a higher accuracy compared to relaxed-seated radiographs.

LEVEL OF EVIDENCE

Level II, diagnostic study.

The Influence of Lumbosacral Spine Pathology on Minimum 2-Year Outcome After Hip Arthroscopy: A Nested Case-Control Analysis

BACKGROUND

Previous literature has examined the association between lumbosacral pathology and hip pathomechanics. However, the effect of lumbosacral pathologies and previous lumbosacral surgery on achieving meaningful outcomes after hip arthroscopy for femoroacetabular impingement syndrome (FAIS) has yet to be studied conclusively.

PURPOSE

To determine whether a history of lumbosacral spine pathology has an influence on achieving minimal clinically important differences (MCIDs) after hip arthroscopy for FAIS.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Patients undergoing hip arthroscopy for FAIS by a single, fellowship-trained orthopaedic surgeon between January 2012 and April 2017 with minimum 2-year follow-up were retrospectively reviewed. Patients with a history of lumbosacral spine pathology (eg, lumbosacral fusion, disc or vertebral pathology, or history of lumbosacral fractures) were matched 1:2 by age, body mass index, and sex to patients without spine pathology. Clinical outcomes including the Hip Outcome Score-activities of daily living subscale (HOS-ADL), HOS-sports subscale (HOS-SS), modified Harris Hip Score (mHHS), international Hip Outcome Tool-12 (iHOT-12), visual analog scale (VAS) pain, and VAS satisfaction were compared between the groups using an independent t test. The threshold of every outcome score for achieving MCID was calculated separately for each group and frequencies were compared.

RESULTS

A total of 83 of 108 eligible patients with lumbosacral pathology were identified and matched to 166 patients without any spine pathology. When compared with the non-spine pathology group, the lumbosacral pathology group had significantly lower 2-year postoperative outcome score averages across all reported outcome tools (all P < .001). There were significant differences in the proportion achieving the threshold for HOS-ADL (60.6% vs 80.0%; P = .004), HOS-SS (57.6% vs 82.1%; P < .001), mHHS (66.7% vs 81.7%; P = .025), and iHOT-12 (54.8% vs 87.6%; P < .001) scores for MCID when comparing the lumbosacral and nonlumbosacral pathology groups.

CONCLUSION

Patients with a history of lumbosacral pathology achieved significantly lower short-term meaningful clinical outcomes after undergoing hip arthroscopy for FAIS when compared with patients without spine pathology. The present study findings have implications for preoperative patient screening, shared decision-making processes/expectation management, and rehabilitation strategies.

Kinematic alignment versus conventional techniques for total hip arthroplasty: A retrospective case control study

BACKGROUND

Residual complications of conventionally implanted hip components have only been partially reduced by improved implant design and higher surgical precision, and their occurrence is poorly predicted by the radiographic standing/supine cup orientation. This has raised awareness that conventional techniques may not aim for the correct component orientation target, and the lumbo-pelvic kinematics, which influences the functional acetabular orientation, may be of interest to further improve THA clinical outcomes. This has led to the development of the Lumbo-Pelvic kinematic alignment (KA) technique for THA that aims to anatomically position and kinematically align hip implants (acetabular and femoral, total and resurfacing components), in order to optimise prosthetic hip biomechanics and hopefully improve prosthetic function, patient satisfaction, and components' lifespan. Therefore, we conducted a case control investigation to assess the early-term safety and efficacy of this new technique by answering the following questions: does the KA technique for THA: (1) better restore the native hip anatomy, (2) generate a different radiographic supine cup position, and (3) improve clinical outcomes in comparison to the conventional mechanical alignment technique?

HYPOTHESES

Using KA technique allows there is no statistically significant difference between the pre to postoperative differential for acetabular medial and vertical offsets, femoral offset, and leg length.

METHODS

We led a case control retrospective study with prospectively collected clinical data. Forty-one consecutive unselected KA-THAs performed with manual instrumentation were paired with 41 mechanically aligned THAs. The 1-year clinical outcomes and radiographical measurements were compared.

RESULTS

Compared to the mechanical alignment technique, the KA technique resulted in a more anatomical restoration of the prosthetic hip centre of rotation with a lower delta pre- to post-operative horizontal acetabular offset (1.47mm for KA versus -5.1mm for MA, p=0.001), and with 74% of KA versus 50% of MA cups (p=0.044) being within 15% of native anatomy for the horizontal acetabular offset. In addition, the KA technique resulted in a higher cup anteversion (22°±7° vs 15°±8°, p<0.001) but similar cup inclination (41°±6° vs. 42°±7°, p=0.25), a similar proportion of cups within the Lewinnek zone (65% vs. 70%, p=0.8), similar excellent functional outcomes (delta Oxford score pre- to follow-up of 24.3 and 23.5 points for KA and MA groups, respectively, p=0.88), similar patient satisfaction scores of 95.4/100 and 89.5/100 for KA and MA groups, respectively, and the same absence of aseptic complications.

CONCLUSION

The KA technique for THA has been demonstrated to be safe, efficacious, and not inferior to the conventional MA technique at early-term. As the concept of the KA technique for THA is only at an early stage, its influence on mid to long-term clinical outcomes remains to be determined and further refinements of the concept are yet to be made.

LEVEL OF EVIDENCE

III; case-control retrospective study.

Can spinopelvic mobility be predicted in patients awaiting total hip arthroplasty? A prospective, diagnostic study of patients with end-stage hip osteoarthritis

AIMS

This study of patients with osteoarthritis (OA) of the hip aimed to: 1) characterize the contribution of the hip, spinopelvic complex, and lumbar spine when moving from the standing to the sitting position; 2) assess whether abnormal spinopelvic mobility is associated with worse symptoms; and 3) identify whether spinopelvic mobility can be predicted from static anatomical radiological parameters.

PATIENTS AND METHODS

A total of 122 patients with end-stage OA of the hip awaiting total hip arthroplasty (THA) were prospectively studied. Patient-reported outcome measures (PROMs; Oxford Hip Score, Oswestry Disability Index, and Veterans RAND 12-Item Health Survey Score) and clinical data were collected. Sagittal spinopelvic mobility was calculated as the change from the standing to sitting position using the lumbar lordosis angle (LL), sacral slope (SS), pelvic tilt (PT), pelvic-femoral angle (PFA), and acetabular anteinclination (AI) from lateral radiographs. The interaction of the different parameters was assessed. PROMs were compared between patients with normal spinopelvic mobility (10° ≤ ∆PT ≤ 30°) or abnormal spinopelvic mobility (stiff: ∆PT < ± 10°; hypermobile: ∆PT > ± 30°). Multiple regression and receiver operating characteristic (ROC) curve analyses were used to test for possible predictors of spinopelvic mobility.

RESULTS

Standing to sitting, the hip flexed by a mean of 57° (sd 17°), the pelvis tilted backwards by a mean of 20° (sd 12°), and the lumbar spine flexed by a mean of 20° (sd 14°); strong correlations were detected. There was no difference in PROMs between patients in the different spinopelvic mobility groups. Maximum hip flexion, standing PT, and standing AI were independent predictors of spinopelvic mobility (R² = 0.42). The combined thresholds for standing was PT ≥ 13° and hip flexion ≥ 88° in the clinical examination, and had 90% sensitivity and 63% specificity of predicting spinopelvic stiffness, while SS ≥ 42° had 84% sensitivity and 67% specificity of predicting spinopelvic hypermobility.

CONCLUSION

The hip, on average, accounts for three-quarters of the standing-to-sitting movement, but there is great variation. Abnormal spinopelvic mobility cannot be screened with PROMs. However, clinical and standing radiological features can predict spinopelvic mobility with good enough accuracy, allowing them to be used as reliable screening tools. Cite this article: Bone Joint J 2019;101-B:902-909.

Functional Safe Zone Is Superior to the Lewinnek Safe Zone for Total Hip Arthroplasty: Why the Lewinnek Safe Zone Is Not Always Predictive of Stability

BACKGROUND

The Lewinnek "safe zone" is not always predictive of stability after total hip arthroplasty (THA). Recent studies have focused on functional hip motion as observed on lateral spine-pelvis-hip x-rays. The purpose of this study was to assess the correlation between the Lewinnek safe zone and the functional safe zone based on hip and pelvic motion in the sagittal plane.

METHODS

Three hundred twenty hips (291 patients) underwent primary THA using computer navigation. Two hundred ninety-six of these hips (92.5%) were within the Lewinnek safe zone as determined by inclination of 40° ± 10° and anteversion of 15° ± 10°. All patients had preoperative and postoperative standing and sitting lateral spinopelvic x-rays. The combined sagittal index (CSI), a combination of sagittal acetabular and femoral position, was measured for each patient and used to assess the functional safe zone. Data analysis was performed to identify hips in the Lewinnek safe zone inside and outside the sagittal functional safe zone. Predictive factors for hips outside the functional safe zone were identified.

RESULTS

Of the 296 hips within the Lewinnek safe zone, 254 (85.8%) were also in the functional safe zone. Forty-two patients were outside the functional safe zone based on CSI; 19 had an increased standing CSI and 23 had a decreased sitting CSI, all were considered at risk for dislocation. Predictive factors for falling outside the functional safe zone were increased femoral mobility (P < .001, r = 0.632), decreased spinopelvic mobility (P < .001, r = 0.455), and pelvic incidence (P < .001, r = 0.400).

CONCLUSION

In this study, 14.2% of hips within the Lewinnek safe zone were outside the functional safe zone, identifying a potential reason hips dislocate despite having "normal" cup angles. The best predictor for falling outside the functional safe zone, both preoperatively and postoperatively, was femoral mobility, not the sagittal cup position (ie, cup anteinclination).

LEVEL OF EVIDENCE

Level III, retrospective review.