Dislocation of a primary total hip arthroplasty is more common in patients with a lumbar spinal fusion

Patients With Low-Grade Lumbosacral Transitional Vertebrae Demonstrate No Difference in Achievement of Clinical Thresholds After Hip Arthroscopy for Femoroacetabular Impingement Syndrome

PURPOSE

To compare clinical outcomes at 2 years following primary hip arthroscopy (HA) for femoroacetabular impingement syndrome (FAIS) between patients with and without low-grade lumbosacral transitional vertebra (LSTV).

METHODS

We performed a retrospective matched-cohort analysis of patients who underwent primary HA for FAIS from 2011 to 2018 with minimum 2-year follow-up. LSTV was graded on preoperative radiographs using the Castellvi classification. Patients with grades I and II LSTV were matched 1:1 with controls on age, sex, and body mass index. Radiographic markers of FAIS morphology were measured. Pre- to postoperative improvement in the modified Harris Hip Score (mHHS) and Non-Arthritic Hip Score (NAHS) as well as 2-year achievement rates for the minimum clinically-important difference, substantial clinical benefit, and patient acceptable symptom state were compared between patients with versus without LSTV. The Wilcoxon signed-rank test was used for intergroup mean comparisons and the Cochran-Mantel-Haenszel test for categorical variables.

RESULTS

In total, 58 patients with LSTV were matched to 58 controls. Among LSTV patients, 48 were Castellvi type 1 (82.8%) and 32 (55.2%) had bilateral findings. No significant differences were found between groups with respect to radiographic markers of FAIS, including alpha angle (P = .88), lateral center edge angle (P = .42), or crossover sign (P = .71). Although patients with LSTV had greater improvement in NAHS at 2-year follow-up compared with control patients (P = .04), there were no significant differences in modified Harris Hip Score improvement (P = .31) or achievement of the minimum clinically-important difference (P = .73), substantial clinical benefit (P = .61), or patient acceptable symptom state (P = .16).

CONCLUSIONS

Patients with low-grade LSTV had greater 2-year improvement in NAHS than controls, whereas no significant differences were observed in achievement of clinical thresholds at 2-year follow-up. There were no differences between groups with respect to any measured radiographic markers of FAIS morphology. Importantly, the findings of this study are underpowered and should be viewed with caution in the greater context of the LSTV literature.

LEVEL OF EVIDENCE

III; retrospective comparative study.

Hip arthroplasty dislocation risk calculator: evaluation of one million primary implants and twenty-five thousand dislocations with deep learning artificial intelligence in a systematic review of reviews

PURPOSE

This paper aims to provide an overview of the possibility regarding the artificial intelligence application in orthopaedics to predict dislocation with a calculator according to the type of implant (hemiarthroplasty, standard total hip arthroplasty, dual mobility, constrained cups) after primary arthroplasty.

MATERIAL AND METHODS

Among 75 results for primary arthroplasties, 26 articles were reviews on dislocation after hemiarthroplasty, 40 after standard total hip arthroplasty, seven about primary dual-mobility arthroplasty (DM THA), and two reviews about constrained implants. Although our search method for systematic reviews covers ten years (2012-2022), none for dual mobility was published before 2016, showing a recent explosion of original articles on this subject. A total of 1,069,565 implants and 26,488 dislocations in primary arthroplasties are included in these 75 reviews. We used a supervised learning model in which models assign objects to groups as input and artificial neural network (ANN) with nodes, hidden layers, and output layers. We considered only four implant types as the input layer. We considered the patient's factors (indication for THA, demographics, spine surgery, and neurologic disease) as the second input values (hidden layer). We considered the implant position as the third input (hidden layer) property including head size, combined anteversion, or spinopelvic alignment. Surgery-related factors, approach, capsule repair, etc. were the fourth input values (hidden layer). The output was a post-operative dislocation or not within three months.

RESULTS

The accuracy for predicting dislocation with this systematic review was 95%. Dislocation risk, based on the type of implant, was wide-ranging, from 0 to 3.9% (mean 0.31%) for the 3045 DM THA, from 0.2 to 1.2% (overall 0.91%) for the 457 constrained liners, from 1.76 to 4.2% (mean 2.1%) for 895,734 conventional total hip arthroplasties, and from 0.76 to 12.2% (mean 4.5%) for 170,329 hemiarthroplasties. In the conventional THA group, many factors increase the risk of dislocation according to the calculator, and only a few (big head, anterior approach) decrease the risk, but not very significantly. In the hemiarthroplasty group, many factors can increase the risk of dislocation until 30%, but none could decrease the risk. According to the calculator, the DM THA and the constrained liner markedly decreased the risk and were not affected by implant position, spine surgery, and spinopelvic position.

CONCLUSION

To our knowledge, this study is the first to yield an implant-specific dislocation risk calculator that incorporates the patient's comorbidities, the position of components, and surgery factors affecting instability risk.

Complications following total hip arthroplasty and hemiarthroplasty for femoral neck fractures in patients with a history of lumbar spinal fusion

INTRODUCTION

The purpose of this study was to examine whether previous lumbar spinal fusion (LSF) was an independent risk factor for complications in patients undergoing total hip arthroplasty (THA) or hemiarthroplasty for displaced femoral neck fractures.

METHODS AND MATERIALS

An administrative database was queried from 2010 to Q2 of 2019 to analyze and compare complications in patients undergoing either THA or hemiarthroplasty for femoral neck fracture with a history of LSF versus no history of LSF. Joint complications including periprosthetic fracture, prosthetic joint infection (PJI), prosthetic joint dislocation (PJD), aseptic loosening, and prosthetic revision were examined at 90 days and 1 year post-operatively.

RESULTS

In the THA cohort, patients with prior LSF had significantly higher likelihood of aseptic loosening at 90 days and 1 year post-operatively in comparison to those without prior LSF (90-day: OR 2.22; 1-year: OR 1.95). Patients in the hemiarthroplasty cohort with prior LSF had significantly higher likelihood of PJI (90-day: OR 2.18; 1-year: OR 2.37), aseptic loosening (90-day: OR 3.42; 1-year: OR 4.68), and prosthetic revision (90-day: OR 2.27; 1-year: OR 2.25) in both the 90-day and 1-year postoperative period in comparison to those without prior LSF. Additionally, for the same cohort, periprosthetic fracture (1-year: OR 2.32) and PJD (1-year: OR 2.31) were significantly higher at 1-year postoperative.

CONCLUSION

Presence of LSF was found to be an independent risk factor for increased joint complications in patients undergoing either a THA or hemiarthroplasty for displaced femoral neck fractures.

Influence of kinematics of the lumbopelvic complex in hip arthroplasty dislocation: from assessment to recommendations

INTRODUCTION

In total hip arthroplasty (THA), misplacement of the implant can provide instability. Adequate orientation of the acetabular cup is a challenge due to variations in inter-individual anatomy and kinematics of the pelvis in everyday life. The aim of this study was to characterize the kinematic factors influencing the risk of dislocation in order to give recommendations for optimal placement of the cup. We hypothesized that the lack of pelvic adaptation would influence the risk of prosthetic instability and motivate adapted.

MATERIALS AND METHODS

Eighty patients with primary unilateral THA were included in a matched case-control study. Seventy-four patients were divided into two groups: group 1 (G1) consisting of patients with postoperative THA dislocation (37 patients) and group 2 (G2), without episodes of dislocation within two years postoperatively (37 patients). In both groups, spino-pelvic parameters and cup orientation were measured in standing and sitting positions with EOS^® X-ray imaging and compared to each other between 12 and 24 months post-operatively.

RESULTS

No significant difference between the two groups was found for static parameters. In a sitting position, a lack of pelvic retroversion with a significant lower variation in sacral slope was observed in group 1 (8.0° ± 9.3 for G1 versus 14.7° ± 6.2 for G2, p < 0.01). Twenty-two (59%) patients with THA instability had sacral slope variations of less than 10° versus eight (21% of patients) with stable THA (p < 0.01). Cup orientation in the Lewinnek safe zone was not significantly different (59% vs 67%, p = 0.62), and the spino-pelvic parameters and cup orientation measured did not change between the standing and sitting positions. However, only 14 (37%) cups in G1 were in the functional safe zone versus 24 (67%) in G2 (p = 0.03).

CONCLUSION

Static parameters of the sagittal spinopelvic balance have a low predictive value for prosthetic instability. Dynamic analysis is essential. Kinematic parameters must be taken into account in determining the ideal position of the cup or stem. Stiffness with locked standing or sitting pelvis must be integrated in order to determine a personalized safe zone.

LEVEL OF EVIDENCE

Level III (matched case-control study).

Evaluating Outcomes of Spinopelvic Fixation for Patients Undergoing Long Segment Thoracolumbar Fusion with a Prior Total Hip Arthroplasty

INTRODUCTION

Understanding the relationship between spinal fusion and its effects on relative spinopelvic alignment in patients with prior total hip arthroplasty (THA) is critical. However, limited data exist on the effects of long spinal fusions on hip alignment in patients with a prior THA. Our objective was to compare clinical outcomes and changes in hip alignment between patients undergoing long fusion to the sacrum versus to the pelvis in the setting of prior THA.

METHODS

Patients with a prior THA who underwent elective thoracolumbar spinal fusion starting at L2 or above were retrospectively identified. Patients were placed into one of two groups: fusion to the sacrum or pelvis. Preoperative, six-month postoperative, one-year postoperative, and delta spinopelvic and acetabular measurements were measured from standing lumbar radiographs.

RESULTS

A total of 112 patients (55 sacral fusions, 57 pelvic fusions) were included. Patients who underwent fusion to the pelvis experienced longer length of stay (LOS) (8.31 vs. 4.21, P < 0.001) and less frequent home discharges (30.8% vs. 61.9%, P = 0.010), but fewer spinal revisions (12.3% vs. 30.9%, P = 0.030). No difference was observed in hip dislocation rates (3.51% vs. 1.82%, P = 1.000) or hip revisions (5.26% vs. 3.64%, P = 1.000) based on fusion construct. Fusion to the sacrum alone was an independent predictor of an increased spine revision rate (odds ratio: 3.56, P = 0.023). Patients in the pelvic fusion group had lower baseline lumbar lordosis (LL) (29.2 vs. 42.9, P < 0.001), six-month postoperative LL (38.7 vs. 47.3, P = 0.038), and greater 1-year ∆ pelvic incidence-lumbar lordosis (-7.98 vs. 0.21, P = 0.032).

CONCLUSION

Patients with prior THA undergoing long fusion to the pelvis experienced longer LOS, more surgical complications, and lower rate of spinal revisions. Patients with instrumentation to the pelvis had lower LL preoperatively with greater changes in LL and pelvic incidence-lumbar lordosis postoperatively. No differences were observed in acetabular positioning, hip dislocations, or THA revision rates between groups.

Does fusion length matter? Total hip arthroplasty dislocation after extension of lumbosacral fusion: a case report

CASE

Hip-spine syndrome is a complex challenge for orthopedic surgeons. We present a 60-year-old female with a history of spinal fusion and total hip arthroplasty. The patient underwent extension of the previous fusion with sacropelvic fixation, and 5 months later she presented with left posterior prosthetic hip dislocation which required sedation and closed reduction.

CONCLUSION

Even with no change in lumbar lordosis or pelvic tilt and adequate acetabular cup position, extension of the fusion construct may predispose patients to dislocation. This may be the result of an increased lever arm acting at the hip joint, thereby leading to instability.

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.

Lumbar spinal fusion does not increase early dislocation risk in primary total hip arthroplasty through the direct anterior approach

INTRODUCTION

Patients with total hip arthroplasty (THA) and a concomitant lumbar spinal fusion (LSF) might have an increased incidence of revision surgery and postoperative complications such as early THA dislocation. The direct anterior approach (DAA) has gained popularity in THA due to its soft tissue-preserving nature and the relatively low dislocation risk. The purpose of the present study was to examine whether LSF patients undergoing minimally invasive THA through the DAA might have an increased risk of prosthetic-related complications compared to matched-control patients without a LSF.

MATERIALS AND METHODS

Patients who underwent THA through the DAA in our institution from January 2014 to December 2018 were identified. A total of 30 primary THA also underwent LSF within 3 months from the initial operation. These patients were randomly matched (1:3) for sex, age, and body mass index with patients who underwent primary THA in our institution without a history of LSF (control group). Peri and postoperative complications, revisions, radiographic and clinical outcomes were assessed retrospectively.

RESULTS

LSF patients who underwent THA through the DAA did not have an increased risk of prosthetic-related complications compared to matched-control subjects without a LSF (6.6% versus 4.4%, P < 0.05). The functional and radiological outcomes were similar between groups.

CONCLUSION

LSF patients undergoing THA could benefit from the DAA similarly to patients without LSF and without increased rate of early THA dislocation. Although the complex interplay between the lumbar spine and hip in THA patients warrants further investigation, the outcomes of THA through the DAA in LSF patients appear promising.

LEVEL OF EVIDENCE

Retrospective case-control study, III.

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.

Hip replacement improves lumbar flexibility and intervertebral disc height - a prospective observational investigation with standing and sitting assessment of patients undergoing total hip arthroplasty

PURPOSE

The pathogenic mechanism of the hip-spine syndrome is still poorly elucidated. Some studies have reported a reduction in low back pain after total hip arthroplasty (THA). However, the biomechanical mechanisms of THA acting on the lumbar spine are not well understood. The aim of the study is to evaluate the influence of THA on (1) the lumbar lordosis and the lumbar flexibility and (2) the lumbar intervertebral disc height.

METHODS

A total of 197 primary THA patients were prospectively enrolled. Pre- and post-operative biplanar stereoradiography was performed in standing and sitting positions. Spinopelvic parameters (lumbar lordosis (LL), pelvic tilt, sacral slope, pelvic incidence), sagittal spinal alignment (sagittal vertical axis, PI-LL mismatch (PI-LL)) and lumbar disc height index (DHI) for each segment (L1/2 to L5/S1) were evaluated. The difference between standing and sitting LL (∆LL = LL_standing - LL_sitting) was determined as lumbar flexibility. Osteochondrosis intervertebralis was graded according to Kellgren and Lawrence (0-4), and patients were assigned to subgroups (mild: 0-2; severe: 3-4).

RESULTS

Lumbar flexibility increased significantly after THA (pre: 22.04 ± 12.26°; post: 25.87 ± 12.26°; p < 0.001), due to significant alterations in LL in standing (pre: 51.3 ± 14.3°; post: 52.4 ± 13.8°; p < 0.001) and sitting (pre: 29.4 ± 15.4°; post: 26.7 ± 15.4°; p = 0.01). ∆LL increased significantly in both subgroups stratified by osteochondrosis (pre/post: ΔLL_mild: 25.4 (± 11.8)/29.4 ± 12.0°; p < 0.001; ΔLL_severe: 17.5 (± 11.4)/21.0 ± 10.9°; p = 0.003). The DHI increased significantly from pre-operatively to post-operatively in each lumbar segment. PI-LL mismatch decreased significantly after THA (pre: 3.5°; post: 1.4°; p < 0.001).

CONCLUSION

The impact of THA on the spinopelvic complex was demonstrated by significantly improved lumbar flexibility and a gain in post-operative disc height. These results illustrate the close interaction between the pelvis and the vertebral column. The investigation provides new insights into the biomechanical patterns influencing the hip-spine syndrome.

An artificial neural network model based on standing lateral radiographs for predicting sitting pelvic tilt in healthy adults

Background

Spinopelvic motion, the cornerstone of the sagittal balance of the human body, is pivotal in patient-specific total hip arthroplasty.

Purpose

This study aims to develop a novel model using back propagation neural network (BPNN) to predict pelvic changes when one sits down, based on standing lateral spinopelvic radiographs.

Methods

Young healthy volunteers were included in the study, 18 spinopelvic parameters were taken, such as pelvic incidence (PI) and so on. First, standing parameters correlated with sitting pelvic tilt (PT) and sacral slope (SS) were identified via Pearson correlation. Then, with these parameters as inputs and sitting PT and SS as outputs, the BPNN prediction network was established. Finally, the prediction results were evaluated by relative error (RE), prediction accuracy (PA), and normalized root mean squared error (NRMSE).

Results

The study included 145 volunteers of 23.1 ± 2.3 years old (M:F = 51:94). Pearson analysis revealed sitting PT was correlated with six standing measurements and sitting SS with five. The best BPNN model achieved 78.48% and 77.54% accuracy in predicting PT and SS, respectively; As for PI, a constant for pelvic morphology, it was 95.99%.

Discussion

In this study, the BPNN model yielded desirable accuracy in predicting sitting spinopelvic parameters, which provides new insights and tools for characterizing spinopelvic changes throughout the motion cycle.

Ankylosing Spondylitis Patients Have Lower Risk of Dislocation Following Total Hip Arthroplasty Compared with Patients Undergoing Lumbar Spinal Fusion Surgery

Purpose

Patients undergoing lumbar spinal fusion (LSF) surgery and patients with ankylosing spondylitis (AS) have concomitant pathology of hip and lumbosacral spine. The purpose of our study is to compare the dislocation rate following total hip arthroplasty (THA) between patients with LSF and AS and reveal the differences of lumbar fusion secondary to LSF and AS.

Patients and methods

Fifty-nine patients (73 hips) were included in Group LSF and every patient was matched with two patients in Group AS. Follow-ups were conducted for information of surgical prognosis and dislocation events following THA. Multiple anatomic parameters were measured on preoperative and postoperative radiological images.

Results

The dislocation rate of patients in Group AS (0.68%) was obviously lower than that of patients in Group LSF (4.11%) and the hazard ratio of dislocation events following THA reached 6.1. Considering the low calculated power (1-β, 0.24), we supposed insufficient statistical evidence (p=0.118) could be attributed to small sample size. Postoperative hip flexion range of motion (ROM) in Group AS (102.1°±24.5°) was significantly lower than that in Group LSF (117.4°±14.2°) (p<0.0005). Postoperative flexion ROM of lumbar was also significantly lower in Group AS (p<0.001). There was no significant difference between two groups concerning postoperative acetabular inclination (p=0.988) and anteversion (p=0.25). However, patients in Group AS had a significantly lower sacral slope (p=0.025) and higher pelvic tilt (p<0.0005) than patients in Group LSF after THA.

Conclusion

Patients with AS have a lower risk of dislocation after THA compared with patients undergoing LSF. The lower risk is significantly relevant to severer stiffness and lower mobility along the spine-pelvis--hip axis in AS patients after THA. Acetabular orientation has no significant effect on the difference of dislocation rate between patients with LSF and AS.

Total hip arthroplasty has higher complication rates in stiff spine patients: a systematic review and network meta-analysis

BACKGROUND

Ankylosing spondylitis (AS) and spinal fusion (SF) classified as stiff spines have been associated with the increased rate of complications following total hip arthroplasty (THA). However, the differences between the two cohorts have inconsistent evidence.

METHODS

We searched for studies comparing complications among stiff spine patients, including SF and AS, who underwent THA in PubMed/MEDLINE, Embase, Cochrane CENTRAL, Web of Science, and Scopus until March 2021. Studies detailing rates of mechanical complications, aseptic loosening, dislocation, infection, and revisions were included. We performed network meta-analyses using frequentist random-effects models to compare differences between cohorts. We used P-score to rank the better exposure with the lowest complications.

RESULTS

Fourteen studies were included in the final analysis. A total of 740,042 patients were included in the systematic review and network meta-analysis. Mechanical complications were highest among SF patients (OR 2.33, 95% CI 1.86, 2.92, p < 0.05), followed by AS patients (OR 1.18, 95% CI 0.87, 1.61, p = 0.82) compared to controls. Long Spinal Fusions had the highest aseptic loosening (OR 2.33, 95% CI 1.83, 2.95, p < 0.05), dislocations (OR 3.25, 95% CI 2.58, 4.10, p < 0.05), infections (OR 2.14, 95% CI 1.73, 2.65, p < 0.05), and revisions (OR 5.25, 95% CI 2.23, 12.32, p < 0.05) compared to AS and controls. Our results suggested that SF with longer constructs may be associated with higher complications in THA patients.

CONCLUSIONS

THAs following SFs have higher mechanical complications, aseptic loosening, dislocations, and infections, especially with longer constructs. AS patients may have fewer complications compared to this cohort.

Instability After Primary Total Hip Arthroplasty: Dual Mobility Versus Jumbo Femoral Heads

BACKGROUND

The use of dual mobility (DM) articulations has grown substantially over the last decade to help minimize dislocation risk. The purpose of this study is to compare the results of DM articulations to jumbo femoral heads of equivalent sizes as they relate to postoperative dislocation.

METHODS

This is a retrospective cohort study of primary total hip arthroplasties (THAs) performed at a single institution between 2005 and 2018. DM articulations and large-diameter metal-on-metal femoral heads were included. Patients were followed with Harris Hip Scores and standard radiographs. Complications were prospectively recorded. Statistical analyses included chi-squared and Brown-Forsythe tests.

RESULTS

In total, 1,288 Magnum femoral head THAs and 365 Active Articulation DM THAs were included for analysis. The same monoblock cup was implanted via a posterior approach in all cases. Age, gender, body mass index, and diagnosis were similar between groups. Average follow-up in the DM group was 49 months, and 126 months in the jumbo head group. The average head sizes in the DM and jumbo head groups were 50 mm. There were no dislocations in the DM hips and only 2 (0.2%) in the jumbo femoral head group. Both groups had significant improvements in Harris Hip Score from their preoperative baseline.

CONCLUSION

Our study found similarly low dislocation rates in DM and jumbo femoral heads in primary THA. No evidence currently exists showing a benefit of the DM articulation beyond that of the large effective head size, and we recommend making every attempt at maximizing head size prior to using DM articulations.

Intraoperative Technology Use Improves Accuracy of Functional Safe Zone Targeting in Total Hip Arthroplasty

BACKGROUND

Targets of acetabular inclination and anteversion have been suggested based on a patient's spinopelvic mobility. Current methods in total hip arthroplasty (THA) include manual instrumentation, computer-assisted navigation, and robotic-assisted surgery. This study aims to compare the accuracy of these 3 methods in targeting the functional safe zone.

METHODS

This is a prospective multicenter study including a series of 251 consecutive primary posterior THA patients from April 2019 to January 2021. Preoperative lateral standing and sitting spinopelvic radiographs were obtained. Each patient was classified using the Hip-Spine Classification. A functional safe zone plan was determined. Surgeons used their preferred method (manual instrumentation, computer-assisted, or robotic-assisted). Postoperative anteversion and inclination was measured and compared to the preoperative plan. Mean differences between preoperative and postoperative values were calculated. Welch's t-test was used to assess significant between-group differences with P < .05 considered significant.

RESULTS

Of the 249 patients, there were 63 manual instrumentation, 68 computer-assisted navigation, and 118 robotic-assisted surgery. Robotic-assisted surgery (rTHA) was significantly more accurate in targeting anteversion (1 ± 2) compared to manual instrumentation (mTHA; 7 ± 6, P < .001) and computer-assisted navigation (cTHA; 6 ± 6, P < .001). rTHA was also significantly more accurate in targeting inclination (1 ± 1) compared to mTHA (8 ± 7, P < .001) and cTHA (6 ± 7, P < .001). Although cTHA had greater accuracy in targeting both inclination and anteversion compared to mTHA, these differences were not statistically significant.

CONCLUSION

Robotic-assisted surgery was more accurate than both computer-assisted navigation and manual instrumentation in targeting the functional safe zone in primary THA. Further research is needed to evaluate the effect of improved accuracy on dislocation rates.

Creation of a Total Hip Arthroplasty Patient-Specific Dislocation Risk Calculator

BACKGROUND

Many risk factors have been described for dislocation following total hip arthroplasty (THA), yet a patient-specific risk assessment tool remains elusive. The purpose of this study was to develop a high-dimensional, patient-specific risk-stratification nomogram that allows dynamic risk modification based on operative decisions.

METHODS

In this study, 29,349 THAs, including 21,978 primary and 7371 revision cases, performed between 1998 and 2018 were evaluated. During a mean 6-year follow-up, 1521 THAs were followed by a dislocation. Patients were characterized, through individual-chart review, according to non-modifiable factors (demographics, indication for THA, spine disease, prior spine surgery, and neurologic disease) and modifiable operative decisions (operative approach, femoral head diameter, and type of acetabular liner [standard, elevated, constrained, or dual-mobility]). Multivariable regression models and nomograms were developed with dislocation as a binary outcome at 1 year and 5 years postoperatively.

RESULTS

Dislocation risk, based on patient-specific comorbidities and operative decisions, was wide-ranging-from 0.3% to 13% at 1 year and from 0.4% to 19% at 5 years after primary THA, and from 2% to 32% at 1 year and from 3% to 42% at 5 years after revision THA. In the primary-THA group, the direct anterior approach (hazard ratio [HR] = 0.27) and lateral approach (HR = 0.58) decreased the dislocation risk compared with the posterior approach. After adjusting for the approach in that group, the combination of a ≥36-mm-diameter femoral head and an elevated liner yielded the largest decrease in dislocation risk (HR = 0.28), followed by dual-mobility constructs (HR = 0.48). In the patients who underwent revision THA, the adjusted risk of dislocation was most markedly decreased by the use of a dual-mobility construct (HR = 0.40), followed by a ≥36-mm femoral head and an elevated liner (HR = 0.88). The adjusted risk of dislocation after revision THA was decreased by acetabular revision (HR = 0.58), irrespective of whether other components were revised.

CONCLUSIONS

Our patient-specific dislocation risk calculator, which was strengthened by our use of a robust multivariable model that accounted for comorbidities associated with instability, demonstrated wide-ranging patient-specific risks based on comorbidity profiles. The resultant nomograms can be used as a screening tool to identify patients at high risk for dislocation following THA and to individualize operative decisions for evidence-based risk mitigation.

LEVEL OF EVIDENCE

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

Robotic Assistance for Posterior Approach Total Hip Arthroplasty Is Associated With Lower Risk of Revision for Dislocation When Compared to Manual Techniques

BACKGROUND

Robotic-assistance total hip arthroplasty (RA-THA) and computer navigation THA (CN-THA) have been shown to improve accuracy of component positioning compared to manual techniques; however, controversy exists regarding clinical benefit. Moreover, these technologies may expose patients to risks. The purpose of this study is to compare rates of intraoperative fracture and complications requiring reoperation within 1 year for posterior approach RA-THA, CN-THA, and THA with no technology (Manual-THA).

METHODS

In total, 13,802 primary, unilateral, elective, posterior approach THAs (1770 RA-THAs, 3155 CN-THAs, and 8877 Manual-THAs) were performed at a single institution between 2016 and 2020. Intraoperative fractures and reoperations within 1 year of the index procedure were identified. Cohorts were balanced using inverse probability of treatment weight based on age, gender, body mass index, femoral cementation, history of spine fusion, and Charlson Comorbidity Index. Logistic regression was performed to create odds ratios for complications. Additional regression analysis for dislocation was performed, adjusting for dual mobility and femoral head size.

RESULTS

There were no differences in intraoperative fracture and postoperative complication rates between the groups (P = .521). RA-THA had a 0.3 odds ratio (95% confidence interval 0.1-0.9, P = .046) compared to Manual-THA for reoperation due to dislocation. CN-THA had an odds ratio of 3.0 for reoperation due to dislocation (95% confidence interval 0.8-11.3, P = .114) compared to RA-THA. The remaining complication odds ratios, including those for infection, loosening, dehiscence, and "other" were similar between the groups.

CONCLUSION

RA-THA is associated with lower risk of revision for dislocation within 1 year of index surgery, when compared to Manual-THA performed through the posterior approach.

Scientometric Analysis of the Top 50 Most-Cited Joint Arthroplasty Papers: Traditional vs Altmetric Measures

Background

Material and methods

Results

Conclusion

In Revision THA, Is the Re-revision Risk for Dislocation and Aseptic Causes Greater in Dual-mobility Constructs or Large Femoral Head Bearings? A Study from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

Dislocation is one of the most common causes of a re-revision after a revision THA. Dual-mobility constructs and large femoral head bearings (≥ 36 mm) are known options for mitigating this risk. However, it is unknown which of these choices is better for reducing the risk of dislocation and all-cause re-revision surgery. It is also unknown whether there is a difference between dual-mobility constructs and large femoral head bearings according to the size of the acetabular component.

QUESTIONS/PURPOSES

We used data from a large national registry to ask: In patients undergoing revision THA for aseptic causes after a primary THA performed for osteoarthritis, (1) Does the proportion of re-revision surgery for prosthesis dislocation differ between revision THAs performed with dual-mobility constructs and those performed with large femoral head bearings? (2) Does the proportion of re-revision surgery for all aseptic causes differ between revision THAs performed with dual-mobility constructs and those performed with large femoral head bearings? (3) Is there a difference when the results are stratified by acetabular component size?

METHODS

Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) were analyzed for 1295 first-revision THAs for aseptic causes after a primary THA performed for osteoarthritis. The study period was from January 2008-when the first dual-mobility prosthesis was recorded-to December 2019. There were 502 dual-mobility constructs and 793 large femoral head bearings. There was a larger percentage of women in the dual-mobility construct group (67% [334 of 502]) compared with the large femoral head bearing group (51% [402 of 793]), but this was adjusted for in the statistical analysis. Patient ages were similar for the dual-mobility construct group (67 ± 11 years) and the large femoral head group (65 ± 12 years). American Society of Anesthesiologists (ASA) class and BMI distributions were similar. The mean follow-up was shorter for dual-mobility constructs at 2 ± 1.8 years compared with 4 ± 2.9 years for large femoral head bearings. The cumulative percent revision (CPR) was determined for a diagnosis of prosthesis dislocation as well as for all aseptic causes (excluding infection). Procedures using metal-on-metal bearings were excluded. The time to the re-revision was described using Kaplan-Meier estimates of survivorship, with right censoring for death or database closure at the time of analysis. The unadjusted CPR was estimated each year of the first 5 years for dual-mobility constructs and for each of the first 9 years for large femoral head bearings, with 95% confidence intervals using unadjusted pointwise Greenwood estimates. The apparent shorter follow-up of the dual-mobility construct group relates to the more recent increase in dual-mobility numbers recorded in the registry. The results were adjusted for age, gender, and femoral fixation. Results were subanalyzed for acetabular component sizes < 58 mm and ≥ 58 mm, set a priori on the basis of biomechanical and other registry data.

RESULTS

There was no difference in the proportion of re-revision for prosthesis dislocation between dual-mobility constructs and large femoral head bearings (hazard ratio 1.22 [95% CI 0.70 to 2.12]; p = 0.49). At 5 years, the CPR of the re-revision for prosthesis dislocation was 4.0% for dual mobility constructs (95% CI 2.3% to 6.8%) and 4.1% for large femoral head bearings (95% CI 2.7% to 6.1%). There was no difference in the proportion of all aseptic-cause second revisions between dual-mobility constructs and large femoral head bearings (HR 1.02 [95% CI 0.76 to 1.37]; p = 0.89). At 5 years, the CPR of dual-mobility constructs was 17.6% for all aseptic-cause second revision (95% CI 12.6% to 24.3%) and 17.8% for large femoral head bearings (95% CI 14.9% to 21.2%). When stratified by acetabular component sizes less than 58 mm and at least 58 mm, there was no difference in the re-revision CPR for dislocation or for all aseptic causes between dual-mobility constructs and large femoral head bearings.

CONCLUSION

Either dual-mobility constructs or large femoral head bearings can be used in revision THA, regardless of acetabular component size, as they did not differ in terms of re-revision rates for dislocation and all aseptic causes in this registry study. Longer term follow-up is required to assess whether complications develop with either implant or whether a difference in revision rates becomes apparent. Ongoing follow-up and comparison in a registry format would seem the best way to compare long-term complications and revision rates. Future studies should also compare surgeon factors and whether they influence decision-making between prosthesis options and second revision rates. Nested randomized controlled trials in national registries would seem a viable option for future research.

LEVEL OF EVIDENCE

Level III, therapeutic study.

The role of the femoral component orientation on dislocations in THA: a systematic review

INTRODUCTION

Dislocation remains a major complication in total hip arthroplasty (THA), in which femoral component orientation is considered a key parameter. New imaging modalities and definitions on femoral component orientation have been introduced, describing orientation in different planes. This study aims to systematically review the relevance of the different orientation parameters on implant stability.

METHODS

A systematic review was performed according to the PRISMA guidelines to identify articles in the PubMed and EMBASE databases that study the relation between any femoral component orientation parameters and implant stability in primary THA.

RESULTS

After screening for inclusion and exclusion criteria and quality assessment, nine articles were included. Definitions to describe the femoral component orientation and methodologies to assess its relevance for implant stability differed greatly, with lack of consensus. Seven retrospective case-control studies reported on the relevance of the transversal plane orientation: Low femoral- or low combined femoral and acetabular anteversion was statistical significantly related with more posterior dislocations, and high femoral- or combined femoral and acetabular anteversion with anterior dislocations in two studies. There were insufficient data on sagittal and coronal component orientation in relation to implant stability.

CONCLUSION

Because of incomparable definitions, limited quality and heterogeneity in methodology of the included studies, there is only weak evidence that the degree of transverse component version is related with implant stability in primary THA. Recommendations about the optimal orientation of the femoral component in all three anatomical planes cannot be provided. Future studies should uniformly define the three-dimensional orientation of the femoral component and systematically describe implant stability.

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.

Stability in Direct Lateral vs Direct Anterior Total Hip Arthroplasty in the Context of Lumbar Spinal Fusion

INTRODUCTION

Lumbar spinal fusion (LSF) may increase the risk of dislocation in patients who have undergone total hip arthroplasty (THA), especially when the LSF was done before the THA. Most publications evaluated patients who had undergone THA using a posterior approach to the hip, yet there are little data on the influence of other surgical approaches. The goal of this study was to evaluate the risk of THA dislocation with anterior supine-based surgical approaches to the hip in patients who have undergone surgical management of concurrent hip and spine pathology.

METHODS

Patients older than 18 years who underwent an LSF and THA using a supine approach-either direct anterior (DA) or direct lateral (DL)-between 2000 and 2018 were identified. Only standard bearings (28-32-36-40 mm) were used. The dislocation rate was determined in this cohort. A subsequent analysis was conducted, stratifying patients based on the order in which they received the LSF or THA.

RESULTS

A total of 582 surgical hip-spine patients were retrospectively identified and included in the cohort. Of total, 332 patients (57.0%) received an LSF before the THA; 250 (43.0%) had the fusion after a primary hip replacement. There were 143 patients (24.6%) in the DA group and 439 (75.4%) in the DL group. Overall, there were five dislocations (0.9%) in the entire cohort.

CONCLUSIONS

In patients with simultaneous degenerative hip and lumbar spine pathology, anterior supine-based approaches demonstrate a low (<1%) risk of instability. Given the small number of total dislocation events (n = 5), additional analysis is warranted to assess the effect of different anterior approaches (DA versus DL) or timing of lumbar spinal surgery (before or after THA).

LEVEL OF EVIDENCE

Level III.

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

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

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.

Inpatient dislocation after primary total hip arthroplasty: incidence and associated patient and hospital factors

INTRODUCTION

Inpatient dislocation following total hip arthroplasty (THA) may incur substantial financial penalties for hospitals in the United States. However, limited studies report on current incidence and variability of dislocations. We utilised a large national database to evaluate inpatient hip dislocation trends regarding: (1) yearly incidences; (2) lengths of stay (LOS); (3) demographic factors; and (4) hospital metrics.

METHODS

The National Inpatient Sample was queried from 2012 to2016 for primary THA patients (n = 1,610,155), identifying 2490 inpatient dislocations. Various patient demographics and hospital characteristics were assessed. Multivariate regression analyses were conducted to identify dislocation risk factors.

RESULTS

Dislocation rates increased from 0.11% in 2012 to 0.18% in 2016 (p < 0.001). Dislocated patients experienced significantly longer LOS (p < 0.001). Patient demographic factors associated with dislocation were sex, race, Medicaid insurance, alcohol use disorder, psychosis, hemiparesis/hemiplegia, chronic renal failure, and obesity. Spinal fusion was not associated with inpatient dislocation. Dislocations were likeliest in the South and least likely in teaching hospitals.

CONCLUSION

Inpatient dislocation has increased in recent years. Optimised management and recognition of the patient and hospital factors outlined in this study may help decrease inpatient dislocation risks following THA, thus avoiding hospital reimbursement penalties for this preventable complication.

Does Prior Lumbar Fusion Influence Dislocation Risk in Hip Arthroplasty Performed for Femoral Neck Fracture?

BACKGROUND

Immobility of the lumbar spine predicts instability following elective total hip arthroplasty (THA). The purpose of this study is to determine how prior lumbar fusion (LF) influenced dislocation rates and revision rates for patients undergoing THA or hemiarthroplasty (HA) for femoral neck fracture (FNF).

METHODS

A retrospective cohort analysis was conducted utilizing the PearlDiver database from 2010 to 2018. Patients who underwent arthroplasty for FNF were identified based on history of LF and whether they underwent THA or HA. Univariate and multivariate analyses were performed.

RESULTS

A total of 328 patients with prior LF and FNF who underwent THA were at increased risk for 1-year dislocation (odds ratio [OR] 2.19, P < .001) and 2-year revision (OR 2.22, P < .001) compared to 14,217 patients without LF. The 461 patients with prior LF and FNF who underwent HA were at increased risk for dislocation (OR 2.22, P < .001) compared to 42,327 patients without LF. Patients with prior LF and FNF who underwent THA had higher rates of revision than patients with prior LF who underwent HA for FNF (OR 2.11, P < .001). In patients with prior LF and FNF, THA was associated with significantly increased risk for dislocation (OR 3.07, P < .001) and revision (OR 2.53, P < .001) compared to THA performed for osteoarthritis.

CONCLUSION

Patients with prior LF who sustained an FNF and underwent THA or HA were at increased risk for early dislocation and revision compared to those without prior LF. This risk of dislocation and revision is even greater than that observed in patients with prior LF who underwent THA for osteoarthritis.

LEVEL OF EVIDENCE

Level III.

The journey to preventing dislocation after total hip arthroplasty : how did we get here?

Dislocation following total hip arthroplasty (THA) is a well-known and potentially devastating complication. Clinicians have used many strategies in attempts to prevent dislocation since the introduction of THA. While the importance of postoperative care cannot be ignored, particular emphasis has been placed on preoperative planning in the prevention of dislocation. The strategies have progressed from more traditional approaches, including modular implants, the size of the femoral head, and augmentation of the offset, to newer concepts, including patient-specific component positioning combined with computer navigation, robotics, and the use of dual-mobility implants. As clinicians continue to pursue improved outcomes and reduced complications, these concepts will lay the foundation for future innovation in THA and ultimately improved outcomes. Cite this article: Bone Joint J 2022;104-B(1):8-11.

Cost-Effectiveness of Preoperative Spinal Imaging Before Total Hip Arthroplasty

BACKGROUND

The risk of instability, dislocation, and revision following total hip arthroplasty (THA) is increased in patients with abnormal spinopelvic mobility. Seated and standing lateral lumbar spine imaging can identify patients with stiff/hypermobile spine (SHS) to guide interventions such as changes in acetabular cup placement or use of a dual-mobility hip construct aimed at reducing dislocation risk.

METHODS

A Markov decision model was created to compare routine preoperative spinal imaging (PSI) to no screening in patients with and without SHS. Screened patients with SHS were assumed to receive dual-mobility hardware while those without SHS and nonscreened patients were assumed to receive conventional THA. Cost-effectiveness was determined by estimating the incremental cost-effectiveness ratio. Effectiveness measured as quality-adjusted life years (QALYs), with $100,000 per additional QALY as the threshold for cost-effectiveness. Sensitivity analyses were performed to determine the robustness of the base-case result.

RESULTS

The screening strategy with PSI had a lifetime cost of $12,515 and QALY gains of 16.91 compared with no-screening ($13,331 and 16.77). The PSI strategy reached cost-effectiveness at 5 years and was dominant (ie, less costly and more effective) at 11 years following THA. In sensitivity analyses, PSI remained the dominant strategy if prevalence of SHS was >1.9%, the cost of PSI was <$925, and the cost of dual-mobility hardware exceeded the cost of conventional hardware by <$2850.

CONCLUSION

Screening patients for SHS prior to THA with PSI is both less costly and more effective and should be considered as part of standard presurgical workup.

A Multivariate Analysis to Predict Total Hip Arthroplasty Dislocation With Preoperative Diagnosis, Surgical Approach, Spinal Pathology, Cup Orientation, and Head Size

BACKGROUND

There are several risk factors for dislocation after total hip arthroplasty (THA), but few studies include radiographic assessment of implants, with spine pathology and patient characteristics. This study estimates the rate of dislocation by patient gender, age, race/ethnicity, body mass index, Charlson Comorbidity Index, spine pathology, prior spine fusion, levels affected, radiographic Kellgren-Lawrence score of spine osteoarthritis, THA indication, surgical approach, and femoral head size.

METHODS

Seventy-six primary THA patients between January 2007 and 2020 with a dislocation were matched on age and gender to subjects without a known history of dislocation using a 2:1 allocation. Univariable and multivariable survival models that account for matched strata were used to estimate the rate of dislocation.

RESULTS

Median follow-up of patients at risk for dislocation was 26.48 months (95% confidence interval [CI] 23.75-36.40). On multivariable analysis, patients with an indication other than primary osteoarthritis were 3.69 (95% CI 2.22-6.13, P < .001) times more likely to dislocate than those with osteoarthritis. Patients with a spine pathology were also nominally more likely to dislocate (hazard ratio 1.76, 95% CI 0.97-3.18, P = .06), and patients receiving a posterior surgical approach were 2.74 (95% CI 1.11-6.76, P = .03) times more likely than those receiving a non-posterior approach to dislocate.

CONCLUSION

Patients with THA indication other than primary osteoarthritis and receiving a posterior surgical approach, and to a lesser degree spinal pathology, were identified as affecting the rate of dislocation. After correcting for other variables, femoral head size, cup orientation, and patient factors were not predictive.

LEVEL OF EVIDENCE

Level IV, case-control study.

Paradoxical spinopelvic motion: does global balance influence spinopelvic motion in total hip arthroplasty?

Background

Recent research has proposed a classification of spinopelvic stiffness according to pelvic spatial orientation for risk stratification in patients who undergo total hip arthroplasty (THA). However, the influence of global alignment was not investigated, and this study evaluated the effect of global balance (sagittal vertical axis [SVA]) on spinopelvic motion.

Methods

We conducted a retrospective review of consecutive primary THA patients. We measured SVA, spinopelvic parameters (pelvic tilt [PT], pelvic incidence, and sacral slope), thoracic kyphosis (TK), lumbar lordosis (LL), proximal femur angle (PFA), and cup version using functional radiographs of patients in the standing and upright sitting positions. Linear regression was performed to identify parameters related to global trunk alignment change (∆SVA). Spinopelvic stiffness was defined as PT position change < 10°, and a subset of patients with PT change < 0° was categorized into a paradoxical spinopelvic motion group.

Results

One hundred twenty-four patients were analyzed (mean age: 65 years, 61% female). In univariate regression analysis, ∆TK, ∆LL, and ∆PFA were correlated to ∆SVA. In multivariate regression analysis, ΔLL (p < 0.001) and ΔPFA (p < 0.001) were found to be correlated to ΔSVA (ΔSVA = − 11.97 + 0.05ΔTK – 0.23ΔLL – 0.17ΔPFA; adjusted R² = 0.558). Spinopelvic stiffness was observed in 40 patients (32%), including five (4%) with paradoxical motion (∆PT = − 3° ± 1°, p < 0.001) with characteristics of balanced standing global trunk alignment (standing SVA = − 1.0 ± 5.1 cm), similar stiffness of the lumbosacral spine (∆LL = − 7° ± 5°), higher hip motion (∆PFA = − 78° ± 6°, p = 0.017), and higher anterior trunk shift (∆SVA = 6.2 ± 2.0 cm, p = 0.003) from standing to sitting as compared to the stiffness group. Two of these five patients experienced dislocation events after THA.

Conclusions

The lumbosacral and hip motions were the major contributors to global alignment postural change. Paradoxical motion is a rare but dangerous clinical condition in THA that might be related to a disproportionally large trunk shift in the stiff lumbosacral spine causing excessive hip motion. In paradoxical motion, diminishing functional acetabular clearance during position change might pose the prosthesis at higher risk of impingement and instability than spinopelvic stiffness.

Does lumbar spine fusion predispose patients to future total hip replacement?

OBJECTIVE

Hip-spine syndrome has been well studied since it was first described by Offierski and MacNab in 1983. Today, strong evidence links symptoms of hip and spine pathology to postsurgical outcomes. Recent studies have reported increased rates of hip dislocation in patients previously treated with total hip arthroplasty (THA) who had undergone lumbar fusion procedures. However, the effect of this link on native hip-joint degeneration remains an area of ongoing research. The purpose of this study was to characterize the relationship between use of lumbar fusion procedures and acceleration of hip pathology by analyzing the rate of future THA in patients with preexisting hip osteoarthritis.

METHODS

This population-level, retrospective cohort study was conducted by using the PearlDiver research program. The initial patient cohort was defined by the presence of diagnosis codes for hip osteoarthritis. Patients were categorized according to use of lumbar fusion after diagnosis of hip pathology. Survival curves with respect to THA were generated by comparison of the no lumbar fusion cohort with the lumbar fusion cohort. To assess the impact of fusion construct length, the lumbar fusion cohort was then stratified according to the number of levels treated (1-2, 3-7, or ≥ 8 levels). Hazard ratios (HRs) were then calculated for the risk factors of number of levels treated, patient age, and sex.

RESULTS

A total of 2,275,683 patients matched the authors' inclusion criteria. Log-rank analysis showed no significant difference in the rates of THA over time between the no lumbar fusion cohort (2,239,946 patients) and lumbar fusion cohort (35,737 patients; p = 0.40). When patients were stratified according to number of levels treated, again no differences in the incidence rates of THA over the study period were determined (p = 0.30). Patients aged 70-74 years (HR 0.871, p < 0.001), 75-79 years (HR 0.733, p < 0.001), 80-84 years (HR 0.557, p < 0.001), and ≥ 85 years (HR = 0.275, p < 0.001) were less likely to undergo THA relative to the reference group (patients aged 65-69 years).

CONCLUSIONS

Although lumbar fusion was initially hypothesized to have a significant effect on rate of THA, lumbar fusion was not associated with increased need for future THA in patients with preexisting hip osteoarthritis. Additionally, there was no relationship between fusion construct length and rate of THA. Although lumbar fusion reportedly increases the risk of hip dislocation in patients with prior THA, these data suggest that lumbar fusion may not clinically accelerate native hip degeneration.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Usefulness of intraoperative C-arm image intensifier in reducing errors of acetabular component during primary total hip arthroplasty: an application of Widmer's method

Background

Acetabular prosthesis positioning in total hip arthroplasty (THA) is crucial in reducing the risk of dislocation. There has been minimal research on the proper way to put the acetabular components into the safe zone intraoperatively. Assessment of version by intraoperative imaging intensifier is very valuable. The value of Widmer’s method, using the intraoperative C-arm available to determine cup anteversion was assessed.

Methods

One hundred one hips in 91 patients who underwent primary THA were eligible for inclusion. Utilizing intraoperative C-arm images, measurement was performed using the technique described by Widmer. The values obtained using 3D computed tomography postoperatively, which determined the anteversion of the acetabular component, were regarded as the reference standard.

Results

The method of Widmer obtained values similar to those obtained using 3D computed tomography and was considered accurate (n.s.). All 101 hips were positioned in the set target zone. Among the 101 hips, the cup position in nine hips (8.9%) was changed. The dislocation rate in our study was 1.0% with all dislocations occurring in hips placed in the target zone. The mean Harris hip score after THA in 1 year was 94.2 (82-98).

Conclusions

The method of Widmer was accurate using intraoperative imaging intensifier for the measurement of the anteversion of the acetabular component during THA, with reference to the anteversion obtained from the 3D computed tomography. Also, utilizing intraoperative C-arm imaging was very useful because it allowed for correction of the position of the acetabular cup.

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.

Does timing of lumbar fusion affect dislocation rate after total hip arthroplasty?

Introduction

The impact of lumbar spinal fusion (LSF) on pelvic mobility and increased risk for THA dislocation are recognized. However, there is still controversy on whether THA should be performed prior or following LSF. This study aims to compare the rates of hip dislocation in patients undergoing THA prior to or following LSF.

Methods

We retrospectively reviewed 109 primary THA and LSF. There were 34 men and 75 women with a mean age of 66.9. The cohort was divided into 2 groups: 1) THA prior to lumbar fusion (n = 42) and 2) THA following lumbar fusion (n = 67). Radiographic parameters including acetabular component abduction, anteversion, pelvic incidence (PI), sacral slope, standing lumbar lordosis (LL) and PI-LL mismatch were determined for each patient. The surgical approach and THA parameters were also recorded and compared between the 2 groups. Patients with fracture, malignant disease, and prior hip hardware were excluded.

Results

The mean follow up was 14.7 months. Overall, 8 patients (7.3%) had a postoperative hip dislocation (0 in group 1 (0%), and 8 in group 2 (11.9%) (p = 0.022). The mean cup abduction and anteversion in patients that dislocated was 37.7° and 23.4° respectively while patients who did not dislocate had an average cup abduction of 37.6° (p = 0.970) and anteversion of 25.9° (p = 0.367). Patients who dislocated had decreased lumbar lordosis (p = 0.022) and higher PI-LL mismatch (p = 0.0004) compared to that did not dislocate. There were no other significant differences in the spinopelvic parameters between the 2 groups. Neither surgical approach nor dual mobility articulations use had a significant impact on postoperative dislocations.

Conclusion

Higher rates of hip dislocation were observed in patients undergoing primary THA following LSF. Dislocators had decreased lumbar lordosis and increased PI-LL mismatch. Patients who require both spinal fusion and THA should undergo hip arthroplasty first to minimize the risk of postoperative instability.

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.

The Hip-Spine Challenge

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The proper diagnosis and treatment of patients with concurrent hip and spine pathological processes can be challenging because of the substantial overlap in symptomatology.

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There is no consensus on which pathological condition should be addressed first.

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Factors such as advanced spinal degeneration, deformity, and prior fusion alter the biomechanics of the spinopelvic unit. Attention should be paid to recognizing these issues during the work-up for a total hip arthroplasty as they can result in an increased risk of dislocation.

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In patients with concurrent spine and hip degeneration, the surgeon must pay close attention to appropriate implant positioning and have consideration for implants with enhanced stability to minimize the risk of dislocation.

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A proper understanding of sagittal balance and restoration of this balance is integral to improving patient outcomes following spinal surgery.

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The advent of new imaging modalities, increased awareness of spinopelvic mobility, as well as a better understanding of sagittal alignment will hopefully improve our treatment of patients with hip-spine syndrome.

Importance of Hip-Spine Syndrome in Hip Arthroplasty: Influence on the Outcome and Therapeutic Consequences

Correct interaction between the spine, pelvis, and hip is an essential condition for successful progress after total hip replacement. Spinal pathologies, such as degeneration, fractures, and spinopelvic imbalance with and without lumbar fusions, are closely associated with an increased risk of impingement or even dislocation of the prosthesis. To significantly reduce this risk, various parameters are required to quantify the risk groups. Knowledge on the presence of stiffness of the spine (change in pelvic tilt between standing and sitting at < 10°) and sagittal spinal deformity (pelvic incidence-lumbar lordosis mismatch > 10° or 20°) is essential in identifying patients with corresponding risk. The individual risk profile can be assessed through a specific history and examination. Before total hip arthroplasty, a routine preoperative workup is recommended for high-risk patients: using information from standardised preoperative radiographs while sitting and standing (pelvis, anteroposterior view, lying and standing; spine and pelvis, lateral view, standing and sitting). Important changes can be made during the surgery. If the spine is stiff, attention should be paid to the position of the cup, with increased anteversion, sufficient offset, and larger head that is secure to dislocation - to reduce the risk of dislocation. In the case of a sagittal spinal deformity, the functional coronary pelvic level must be carefully controlled so that it is better to use double mobility cups. Digital systems, such as navigation and robotics, can optimise component positioning although, so far, there is little evidence that the complication rate decreased. Therefore, further studies are warranted.

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.

A Comparison of Revision Rates for Dislocation and Aseptic Causes Between Dual Mobility and Large Femoral Head Bearings in Primary Total Hip Arthroplasty With Subanalysis by Acetabular Component Size: An Analysis of 106,163 Primary Total Hip Arthroplasties

BACKGROUND

Dual mobility (DM) and large femoral head bearings (≥36 mm) both decrease the risk of dislocation in total hip arthroplasty (THA). There is limited comparable data in primary THA. This study compared the revision rates for dislocation and aseptic causes between DM and large femoral heads and subanalyzed by acetabular component size.

METHODS

Data from the Australian Orthopedic Association National Joint Replacement Registry were analyzed for patients undergoing primary THA for osteoarthritis from January 2008 (the year of first recorded DM use) to December 2019. All DM and large femoral head bearings were identified. The primary outcome measure was the cumulative percent revision (CPR) for dislocation and for all aseptic causes. The results were adjusted by age, sex, and femoral fixation. A subanalysis was performed stratifying acetabular component diameter <58 m and ≥58 mm.

RESULTS

There were 4942 DM and 101,221 large femoral head bearings recorded. There was no difference in the CPR for dislocation (HR = 0.69 (95% CI 0.42, 1.13), P = .138) or aseptic causes (HR = 0.91 (95% CI 0.70, 1.18), P = .457). When stratified by acetabular component size, DM reduced the CPR for dislocation in acetabular component diameter <58 mm (HR = 0.55 (95% CI 0.30, 1.00), P = .049). There was no difference for diameter ≥58 mm. There was no difference in aseptic revision when stratified by acetabular component diameter.

CONCLUSION

There is no difference in revision rates for dislocation or aseptic causes between DM and large femoral heads in primary THA. When stratified by acetabular component size, DM reduces dislocation for acetabular component diameter <58 mm.

LEVEL OF EVIDENCE

Level III.

Lumbar Spine Fusion and Symptoms of Leg Length Discrepancy After Hip Arthroplasty

BACKGROUND

Hip length discrepancy (HLD) is common after total hip arthroplasty (THA); however, the effect of spinal fusion on perceived leg length discrepancy (LLD) symptoms after THA has not been examined. This study tested the hypothesis that LLD symptoms are increased in patients who underwent lumbar spinal fusion and THA, compared with patients with THA only.

METHODS

This retrospective cohort study included 67 patients who underwent lumbar spinal fusion and THA, along with 78 matched control patients who underwent THA only. Hip and spine measurements were taken on postoperative, standing anterior-posterior pelvic, lateral lumbar, and anterior-posterior lumbar spinal radiographs. Perceived LLD symptoms were assessed via telephone survey.

RESULTS

Between the spinal fusion and control groups, there was no significant difference in HLD (M = 7.10 mm, SE = 0.70 and M = 5.60 mm, SE = 0.49) (P = .403). The spinal fusion patients reported more frequently noticing a difference in the length of their legs than the control group (P = .046) and reported limping "all the time" compared with the control group (P = .001). Among all patients with an HLD ≤10 mm, those in the spinal fusion group reported limping at a higher frequency than patients in the control group (P = .008). Patients in the spinal fusion group were also more likely to report worsened back pain after THA (P = .011) than the control group.

CONCLUSION

Frequencies of a perceived LLD, limping, and worsened back pain after THA were increased in patients with THA and a spinal fusion compared with patients who had THA only, even in a population with HLD traditionally considered to be subclinical. The results indicate that in patients with prior spinal fusion, precautions should be taken to avoid even minor LLD in the setting of THA.

Systematic review of the top 10 ranked spine articles in the last 10 years [2011-2021]

Background

Spine-related research continues to evolve rapidly and in the paradigm of increasing data, evidence-based practice becomes imperative. Citation-based rankings are thus critical in allowing clinicians to quickly ascertain the importance and value of a study. The purpose of this article is to report on the 10 most cited articles in the field of spine surgery over the last 10 years to provide an insight into the direction of research and clinical endeavors.

Methods

Google Scholar was searched (1st April 2021) using an algorithm that sorts all cited spine surgery publications based on the number of citations per year. The top 10 most cited articles were identified. Information including journal, publication title, published year, subspecialty, and purpose of the study were compiled.

Results

The top 10 publications ranged from 471 to 66 citations, with yearly citations ranging from 67 to 14. Eight articles directly related to lumbar fusion, 2 related to 3D Printing in spinal surgery, and one article on robotic surgery. There were 4 retrospective studies, 1 randomized controlled trial (RCT), and 2 systematic reviews. 3 of the papers related to decision making in surgery, 4 on outcomes of surgery, and 3 on innovations in surgery. The journal that appeared most frequently in the top 10 list was the Journal of Spine Surgery.

Discussion

Novel surgical approaches or management strategies are almost always a manifestation of advancements in clinical and basic science research. Algorithm-based identification of highly cited articles provides an effective and prompt avenue for evidence-based medicine. Our ranking found a predominance of publications related to lumbar spinal fusion. Several articles in the top 10 provide an in-depth discussion on novel surgical techniques and technologies that define the current epoch of innovations in spine surgery.

Pelvic incidence and pelvic tilt can be calculated using either the femoral heads or acetabular domes in patients with hip osteoarthritis

AIMS

The aim of the study was to compare two methods of calculating pelvic incidence (PI) and pelvic tilt (PT), either by using the femoral heads or acetabular domes to determine the bicoxofemoral axis, in patients with unilateral or bilateral primary hip osteoarthritis (OA).

METHODS

PI and PT were measured on standing lateral radiographs of the spine in two groups: 50 patients with unilateral (Group I) and 50 patients with bilateral hip OA (Group II), using the femoral heads or acetabular domes to define the bicoxofemoral axis. Agreement between the methods was determined by intraclass correlation coefficient (ICC) and the standard error of measurement (SEm). The intraobserver reproducibility and interobserver reliability of the two methods were analyzed on 31 radiographs in both groups to calculate ICC and SEm.

RESULTS

In both groups, excellent agreement between the two methods was obtained, with ICC of 0.99 and SEm 0.3° for Group I, and ICC 0.99 and SEm 0.4° for Group II. The intraobserver reproducibility was excellent for both methods in both groups, with an ICC of at least 0.97 and SEm not exceeding 0.8°. The study also revealed excellent interobserver reliability for both methods in both groups, with ICC 0.99 and SEm 0.5° or less.

CONCLUSION

Either the femoral heads or acetabular domes can be used to define the bicoxofemoral axis on the lateral standing radiographs of the spine for measuring PI and PT in patients with idiopathic unilateral or bilateral hip OA. Cite this article: Bone Joint J 2021;103-B(8):1345-1350.

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.

Spinopelvic mobility affects accuracy of acetabular anteversion measurements on cross-table lateral radiographs

AIMS

Cross-table lateral (CTL) radiographs are commonly used to measure acetabular component anteversion after total hip arthroplasty (THA). The CTL measurements may differ by > 10° from CT scan measurements but the reasons for this discrepancy are poorly understood. Anteversion measurements from CTL radiographs and CT scans are compared to identify spinopelvic parameters predictive of inaccuracy.

METHODS

THA patients (n = 47; 27 males, 20 females; mean age 62.9 years (SD 6.95)) with preoperative spinopelvic mobility, radiological analysis, and postoperative CT scans were retrospectively reviewed. Acetabular component anteversion was measured on postoperative CTL radiographs and CT scans using 3D reconstructions of the pelvis. Two cohorts were identified based on a CTL-CT error of ≥ 10° (n = 11) or < 10° (n = 36). Spinopelvic mobility parameters were compared using independent-samples t-tests. Correlation between error and mobility parameters were assessed with Pearson's coefficient.

RESULTS

Patients with CTL error > 10° (10° to 14°) had stiffer lumbar spines with less mean lumbar flexion (38.9°(SD 11.6°) vs 47.4° (SD 13.1°); p = 0.030), different sagittal balance measured by pelvic incidence-lumbar lordosis mismatch (5.9° (SD 18.8°) vs -1.7° (SD 9.8°); p = 0.042), more pelvic extension when seated (pelvic tilt -9.7° (SD 14.1°) vs -2.2° (SD 13.2°); p = 0.050), and greater change in pelvic tilt between supine and seated positions (12.6° (SD 12.1°) vs 4.7° (SD 12.5°); p = 0.036). The CTL measurement error showed a positive correlation with increased CTL anteversion (r = 0.5; p = 0.001), standing lordosis (r = 0.23; p = 0.050), seated lordosis (r = 0.4; p = 0.009), and pelvic tilt change between supine and step-up positions (r = 0.34; p = 0.010).

CONCLUSION

Differences in spinopelvic mobility may explain the variability of acetabular anteversion measurements made on CTL radiographs. Patients with stiff spines and increased compensatory pelvic movement have less accurate measurements on CTL radiographs. Flexion of the contralateral hip is required to obtain clear CTL radiographs. In patients with lumbar stiffness, this movement may extend the pelvis and increase anteversion of the acetabulum on CTL views. Reliable analysis of acetabular component anteversion in this patient population may require advanced imaging with a CT scan. Cite this article: Bone Joint J 2021;103-B(7 Supple B):59-65.