Modular dual-mobility articulations in patients with adverse spinopelvic mobility

Adverse spinopelvic mobility in patients undergoing total hip arthroplasty is associated with high mobility of the hip in a flexed seated position

PURPOSE

Adverse spinopelvic mobility from a standing to a flexed seated position of more than 20° of the spinopelvic tilt (∆SPT) has been shown to have a high risk of dislocation. If hypermobility of the hip analysed with the pelvic femoral angle (∆PFA) has a high risk of impingement, the correlation between the range of motion of the hip from a standing to a flexed seated position and its implication in adverse spinopelvic mobility has not been described.

METHODS

A series of 337 patients treated with primary THA underwent lateral x-ray in standing and flexed seated positions to analyse ∆SPT, ∆PFA and spinopelvic parameters. The objectives were to establish a ∆PFA threshold associated with a ∆SPT ⩾20° and to subsequently investigate its influence in conjunction with spinopelvic risk factors on the occurrence of adverse spinopelvic mobility.

RESULTS

The area under the curve was 0.904 (95%CI, 0.864-0.945) for ∆PFA to predict ∆SPT ⩾ 20°; it was predicted by ∆PFA ⩾ 95° with a sensitivity of 91.7% and a specificity of 74.4% at the Youden optimal threshold. Patients with a ∆SPT < 20° (277 patients) had a mean ∆PFA of 83° compared to 110° if ∆SPT ⩾ 20° (60 patients) (p < 0.001). Patients with a ∆PFA < 95° (203 patients) had a mean ∆SPT of -6° compared to 18° if ∆PFA ⩾ 95° (134 patients) (p < 0.001). ∆PFA ⩾ 95° rates were 95% (57/60) and 27.8% (77/200) in patients with ∆SPT ⩾ 20° and ∆SPT < 20°, respectively (OR 49.35; CI, 15.01-162.28; p < 0.001).

CONCLUSIONS

High mobility of the hip (∆PFA ⩾ 95°) seems to be a necessary condition for adverse spinopelvic mobility. A preoperative analysis of patients with lower hip mobility, associated with spinopelvic risk factors, might identify patients with abnormal spinopelvic mobility after the restoration of femoral flexion.

TRIAL REGISTRATION

IDRCB 2023-A01390, CNIL MR004 2225508 (07/06/2023), retrospectively registered.

Archetype analysis of the spine-hip relationship identifies distinct spinopelvic profiles

INTRODUCTION

The position of the pelvis in the sagittal plane can vary considerably between different functional positions. Adapting the position of the acetabular cup in relation to the alignment between the spine and the hip of each individual, prior to prosthesis placement, can prevent the risk of prosthetic impingement. Taken individually, risk factors for unfavorable spinopelvic kinematics can be difficult to interpret when trying to precisely predict which patients are at risk. Furthermore, the use of classifications or algorithms can be complex, most often associated with limited values and often difficult to apply in current practices of risk assessment.

HYPOTHESIS

We hypothesized that the deconstruction of the data matrix including age and spinopelvic parameters (SPT, LL, PI, LF and PI-LL) correlated with the analysis of spinopelvic kinematics could be used to define an individualized hip-spine relationship.

MATERIAL AND METHOD

We applied archetypal analysis, which is a probabilistic, data-driven and unsupervised approach, to a complete phenotype cohort of 330 patients before total hip arthroplasty to define the spinopelvic profile of each individual using the spinopelvic parameters without threshold value. For each archetype, we analyzed the spinopelvic kinematics, not implemented in the creation of the archetypes.

RESULTS

An unsupervised learning method revealed seven archetypes with distinct spinopelvic kinematic profiles ranging from -8.9 ° to 13.15 ° (p = 0.0001) from standing to sitting and -5. 35 ° to -10.81 ° (p = 0.0001) from supine to standing. Archetype 1 represents the "ideal" patient (A1); young patients without spinopelvic anomaly and the least at risk of mobility anomaly. Followed by 3 archetypes without sagittal imbalance according to their lumbar lordosis and pelvic incidence, from the highest to the lowest (archetypes 2-4), archetype 4 exposing a greater risk of spinopelvic kinematic anomaly compared to others. Then 2 archetypes with sagittal imbalance: archetype 5, with an immobile pelvis in the horizontal plane from standing to sitting position in anterior tilt and archetype A6, with significant posterior pelvic tilt standing, likely compensating for the imbalance and associated with the greatest anomaly of spinopelvic kinematics. Finally, archetype 7 with the stiffest lumbar spine without sagittal imbalance and significant unfavorable kinematics from standing to sitting.

CONCLUSION

An archetypal approach to patients before hip replacement can refine diagnostic and prognostic features associated with the hip-spine relationship and reduced heterogeneity, thereby improving spinopelvic characterization. This risk stratification of spinopelvic kinematic abnormalities could make it possible to target patients who require adapted positioning or types of implants before prosthetic surgery.

LEVEL OF EVIDENCE

IV retrospective study.

In silico analysis of the patient-specific acetabular cup anteversion safe zone

INTRODUCTION

Various computer-assisted surgical systems claim to improve the accuracy of cup placement in total hip arthroplasties after assessing spinopelvic mobility to prevent prosthetic impingement. However, no study has yet analyzed the extent of the patient-specific cup anteversion safe zones.

HYPOTHESIS

We hypothesized that most patients have a safe zone >10 °, except those with abnormal spinopelvic mobility, who have a much narrower safe zone.

MATERIALS AND METHODS

We simulated the risks of prosthetic impingement using the planned cup anteversion. The consecutive cohort included 341 patients who underwent total hip arthroplasty. Our primary endpoint was the patient-specific impingement-free zone for cup anteversion, which was then divided into four subgroups: 0 °, 1 ° to 5 °, 6 ° to 10 °, and >10 °. This data was then secondarily analyzed for abnormal spinopelvic mobility (the difference in the spinopelvic tilt [ΔSPT] from a standing to a flexed seated position >20 °).

RESULTS

The mean anteversion safe zone was 22.8 ° with 82.4% (281/341) of patients with a zone strictly >10 °. The mean safe zone was 8.9 ° (+/- 9 °) in patients with an ΔSPT ≥20 ° (18.2%), with 37.1% of these patients having a zone of 0 °, 16.13% a zone between 1 ° and 5 °, 8.06% a zone between 6 ° and 10 ° and 38.71% a zone >10 °. The mean safe zone was 25.9 ° (+/- 9 °) in patients with an ΔSPT <20 ° (81.8%), and the proportion of cases in each zone was 2.51%, 1.08%, 4.3%, and 92.11%, respectively (p < 0.001).

CONCLUSION

The safe zone for anteversion appears to be fairly wide in most patients. However, identifying patients at risk of abnormal spinopelvic mobility seems necessary to identify the two-thirds of patients with a narrow safe zone.

LEVEL OF EVIDENCE

IV; retrospective study.

Spinal alignment and surgical correction in the aging spine and osteoporotic patient

Background

The aging spine often presents multifaceted surgical challenges for the surgeon because it can directly and indirectly impact a patient's spinal alignment and quality of life. Elderly and osteoporotic patients are predisposed to progressive spinal deformities and potential neurologic compromise and surgical management can be difficult because these patients often present with greater frailty.

Methods

This was a literature review of spinal alignment changes, preoperative considerations, and spinal alignment considerations for surgical strategies.

Results

Many factors impact spinal alignment as we age including lumbar lordosis flexibility, hip flexion, deformity, and osteoporosis. Preoperative considerations are required to assess the patient's overall health, bone mineral density, and osteoporosis medications. Careful radiographic assessment of the spinopelvic parameters using various classification/scoring systems provide the surgeon with goals for surgical treatment. An individualized surgical strategy can be planned for the patient including extent of surgery, surgical approach, extent of the constructs, fixation techniques, vertebral augmentation, ligamentous augmentation, and staging surgery.

Conclusions

Surgical treatment should only be considered after a thorough assessment of the patient's health, deformity, bone quality and corresponding age matched alignment goals. An individualized treatment approach is often required to tackle the deformity and minimize the risk of hardware related complications and pseudarthrosis. Anabolic agents offer a promising benefit in this patient population by directly addressing and improving their bone quality and mineral density preoperatively and postoperatively.

Is it feasible to develop a supervised learning algorithm incorporating spinopelvic mobility to predict impingement in patients undergoing total hip arthroplasty?

Aims

Precise implant positioning, tailored to individual spinopelvic biomechanics and phenotype, is paramount for stability in total hip arthroplasty (THA). Despite a few studies on instability prediction, there is a notable gap in research utilizing artificial intelligence (AI). The objective of our pilot study was to evaluate the feasibility of developing an AI algorithm tailored to individual spinopelvic mechanics and patient phenotype for predicting impingement.

Methods

This international, multicentre prospective cohort study across two centres encompassed 157 adults undergoing primary robotic arm-assisted THA. Impingement during specific flexion and extension stances was identified using the virtual range of motion (ROM) tool of the robotic software. The primary AI model, the Light Gradient-Boosting Machine (LGBM), used tabular data to predict impingement presence, direction (flexion or extension), and type. A secondary model integrating tabular data with plain anteroposterior pelvis radiographs was evaluated to assess for any potential enhancement in prediction accuracy.

Results

We identified nine predictors from an analysis of baseline spinopelvic characteristics and surgical planning parameters. Using fivefold cross-validation, the LGBM achieved 70.2% impingement prediction accuracy. With impingement data, the LGBM estimated direction with 85% accuracy, while the support vector machine (SVM) determined impingement type with 72.9% accuracy. After integrating imaging data with a multilayer perceptron (tabular) and a convolutional neural network (radiograph), the LGBM's prediction was 68.1%. Both combined and LGBM-only had similar impingement direction prediction rates (around 84.5%).

Conclusion

This study is a pioneering effort in leveraging AI for impingement prediction in THA, utilizing a comprehensive, real-world clinical dataset. Our machine-learning algorithm demonstrated promising accuracy in predicting impingement, its type, and direction. While the addition of imaging data to our deep-learning algorithm did not boost accuracy, the potential for refined annotations, such as landmark markings, offers avenues for future enhancement. Prior to clinical integration, external validation and larger-scale testing of this algorithm are essential.

Monobloc dual-mobility acetabular component versus a standard single-mobility acetabular component

Aims

The benefit of a dual-mobility acetabular component (DMC) for primary total hip arthroplasties (THAs) is controversial. This study aimed to compare the dislocation and complication rates when using a DMC compared to single-mobility (SM) acetabular component in primary elective THA using data collected at a single centre, and compare the revision rates and survival outcomes in these two groups.

Methods

Between 2010 and 2019, 2,075 primary THAs using either a cementless DM or SM acetabular component were included. Indications for DMC were patients aged older than 70 years or with high risk of dislocation. All other patients received a SM acetabular component. Exclusion criteria were cemented implants, patients treated for femoral neck fracture, and follow-up of less than one year. In total, 1,940 THAs were analyzed: 1,149 DMC (59.2%) and 791 SM (40.8%). The mean age was 73 years (SD 9.2) in the DMC group and 57 years (SD 12) in the SM group. Complications and revisions have been analyzed retrospectively.

Results

The mean follow-up was 41.9 months (SD 14; 12 to 134). There were significantly fewer dislocations in the DMC group (n = 2; 0.17%) compared to the SM group (n = 8; 1%) (p = 0.019). The femoral head size did not influence the dislocation rate in the SM group (p = 0.702). The overall complication rate in the DMC group was 5.1% (n = 59) and in the SM group was 6.7% (n = 53); these were not statistically different (p = 0.214). No specific complications were attributed to the use of DMCs. In the DMC group, 18 THAs (1.6%) were revised versus 15 THAs in the SM group (1.9%) (p = 0.709). There was no statistical difference for any cause of revisions in both groups. The acetabular component aseptic revision-free survival rates at five years were 98% in the DMC group and 97.3% in the SM group (p = 0.780).

Conclusion

The use of a monobloc DMC had a lower risk of dislocation in a high-risk population than SM component in a low-risk population at the mid-term follow-up. There was no significant risk of component-specific complications or revisions with DMCs in this large cohort.

Metal artifact reduction sequence-MRI abnormalities in asymptomatic patients with dual-mobility hip prostheses

Aims

Modular dual-mobility (DM) articulations are increasingly used during total hip arthroplasty (THA). However, concerns remain regarding the metal liner modularity. This study aims to correlate metal artifact reduction sequence (MARS)-MRI abnormalities with serum metal ion levels in patients with DM articulations.

Methods

A total of 45 patients (50 hips) with a modular DM articulation were included with mean follow-up of 3.7 years (SD 1.2). Enrolled patients with an asymptomatic, primary THA and DM articulation with over two years' follow-up underwent MARS-MRI. Each patient had serum cobalt, chromium, and titanium levels drawn. Patient satisfaction, Oxford Hip Score, and Forgotten Joint Score-12 (FJS-12) were collected. Each MARS-MRI was independently reviewed by fellowship-trained musculoskeletal radiologists blinded to serum ion levels.

Results

Overall, two patients (4.4%) had abnormal periprosthetic fluid collections on MARS-MRI with cobalt levels > 3.0 μg/l. Four patients (8.9%) had MARS-MRI findings consistent with greater trochanteric bursitis, all with cobalt levels < 1.0 μg/l. A seventh patient had a periprosthetic fluid collection with normal ion levels. Of the 38 patients without MARS-MRI abnormalities, 37 (97.4%) had cobalt levels < 1.0 μg/l, while one (2.6%) had a cobalt level of 1.4 μg/l. One patient (2.2%) had a chromium level > 3.0 μg/l and a periprosthetic fluid collection. Of the 41 patients with titanium levels, five (12.2%) had titanium levels > 5.0 μg/l without associated MARS-MRI abnormalities.

Conclusion

Periprosthetic fluid collections associated with elevated serum cobalt levels in patients with asymptomatic DM articulations occur infrequently (4.4%), but further assessment is necessary due to implant heterogeneity.

Excessive posterior pelvic tilt from preoperative supine to postoperative standing after total hip arthroplasty

Aims

Excessive posterior pelvic tilt (PT) may increase the risk of anterior instability after total hip arthroplasty (THA). The aim of this study was to investigate the changes in PT occurring from the preoperative supine to postoperative standing position following THA, and identify factors associated with significant changes in PT.

Methods

Supine PT was measured on preoperative CT scans and standing PT was measured on preoperative and one-year postoperative standing lateral radiographs in 933 patients who underwent primary THA. Negative values indicate posterior PT. Patients with > 13° of posterior PT from preoperative supine to postoperative standing (ΔPT ≤ -13°) radiographs, which corresponds to approximately a 10° increase in functional anteversion of the acetabular component, were compared with patients with less change (ΔPT > -13°). Logistic regression analysis was used to assess preoperative demographic and spinopelvic parameters predictive of PT changes of ≤ -13°. The area under receiver operating characteristic curve (AUC) determined the diagnostic accuracy of the predictive factors.

Results

PT changed from a mean of 3.8° (SD 6.0°)) preoperatively to -3.5° (SD 6.9°) postoperatively, a mean change of -7.4 (SD 4.5°; p < 0.001). A total of 95 patients (10.2%) had ≤ -13° change in PT from preoperative supine to postoperative standing. The strongest predictive preoperative factors of large changes in PT (≤ -13°) from preoperative supine to postoperative standing were a large posterior change in PT from supine to standing, increased supine PT, and decreased standing PT (p < 0.001). Flexed-seated PT (p = 0.006) and female sex (p = 0.045) were weaker significant predictive factors. When including all predictive factors, the accuracy of the AUC prediction was 84.9%, with 83.5% sensitivity and 71.2% specificity.

Conclusion

A total of 10% of patients had > 13° of posterior PT postoperatively compared with their supine pelvic position, resulting in an increased functional anteversion of > 10°. The strongest predictive factors of changes in postoperative PT were the preoperative supine-to-standing differences, the anterior supine PT, and the posterior standing PT. Surgeons who introduce the acetabular component with the patient supine using an anterior approach should be aware of the potentially large increase in functional anteversion occurring in these patients.

How to Screen for Lumbar Spine Stiffness in Patients Awaiting Total Hip Arthroplasty

BACKGROUND

This study aimed to (1) define the prevalence of spinopelvic abnormalities among patients who have hip osteoarthritis (OA) and controls (asymptomatic volunteers) and (2) identify factors that reliably predict the presence of lumbar spine stiffness.

METHODS

This is a prospective, cross-sectional, case-cohort study of patients who have end-stage primary hip OA, who underwent primary total hip arthroplasty (THA). Patients were compared with a cohort of asymptomatic volunteers, matched for age, sex, and body mass index (BMI), serving as a control group. Spinopelvic pathologies were defined as: lumbar spine flatback deformity (difference of 10 or more degrees for pelvic incidence minus lumbar lordosis angle), a standing sagittal pelvic tilt of 19° or more and lumbar spine stiffness (lumbar flexion of less than 20° between both postures).

RESULTS

The prevalence of spinopelvic pathologies was similar between patients and controls (flatback deformity: 16% versus 10%, P = .209; standing pelvic tilt >19°: 17% versus 24%, P = .218; lumbar spine stiffness: 6% versus 5%, P = .827). Age over 65 years-old and standing lumbar lordosis angle less than 45° were associated with high sensitivity and specificity for identifying lumbar spine stiffness (age >65 years: 82% and 66%; standing lumbar lordosis angle <45°: 85% and 73%).

CONCLUSION

The presence of end-stage hip osteoarthritis was not associated with increased prevalence of adverse spinopelvic characteristics compared to matched, asymptomatic volunteers. Age and LLstanding are the strongest predictors of lumbar spine flexion and can guide clinical practice on when to obtain additional radiographs for patients who have hip OA before arthroplasty to identify at-risk patients.

LEVEL OF EVIDENCE

II (prospective, cohort study).

Increased Cup Anteversion May Not Prevent Posterior Dislocation in Patients With Abnormal Spinopelvic Characteristics in Total Hip Arthroplasty

Background

The aims of this study were to (1) assess the degree of variation in acetabular component placement and combined anteversion in a large cohort of dislocating total hip arthroplasties; (2) assess the spinopelvic characteristics of the cohort; and (3) examine the association between cup anteversion and reported direction of instability.

Methods

A commercial database of 245 dislocating total hip arthroplasties referred for postoperative computed tomography and functional radiographic imaging and analysis were reviewed. Spinopelvic parameters and cup and stem positions were measured in the supine, standing, flex-seated, and anterior pelvic plane (APP) positions. Spinopelvic characteristics were stratified by high, neutral, and low cup anteversion using thresholds of >35° and <15° anteversion in standing, respectively.

Results

In the dislocation cohort, 62%, 45%, and 42% of cups were within the safe zone in supine, standing, and the APP, respectively (P < .001). Patients with high vs neutral or low cup anteversion had significantly stiffer spines, more posterior pelvic tilt in standing, greater changes in pelvic tilt, and higher sagittal imbalance. Of the 45 patients with high cup anteversion and reported instability direction, 60% and 40% were reported to have posterior and anterior instability, respectively, with no differences in spinopelvic characteristics.

Conclusions

In this dislocating cohort, there is a decreased percentage of cups within the safe zone in the APP and standing position compared to the supine reference. In addition, we found that patients having poor spinopelvic characteristics and high cup anteversion can still dislocate, suggesting that adjusting cup anteversion alone may not be sufficient for preventing instability.

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

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

Comparing dislocation rates by approach following elective primary dual mobility total hip arthroplasty: a systematic review

BACKGROUND

Dual mobility components can be implanted during total hip arthroplasty (THA) for primary osteoarthritis via a direct anterior approach (DAA), anterolateral approach (ALA), direct lateral approach (DLA), or posterior/posterolateral approach (PLA). This review compares dual mobility hip dislocation rates using these approaches for elective primary THA.

METHODS

PubMed, Embase, and Cochrane databases were systematically searched for articles published after January 1, 2006 that reported dislocation rates for adult patients after primary THA with dual mobility implants. Articles were excluded if they reported revision procedures, nonelective THA for femoral neck fractures, acetabular defects requiring supplemental implants, prior surgery, or ≤ 5 patients. The primary outcome was hip dislocation rate. Secondary outcomes included infection, Harris Hip Score (HHS), and Postel-Merle d'Aubigné (PMA) score.

RESULTS

After screening 542 articles, 63 met inclusion criteria. Due to study heterogeneity, we did not perform a meta-analysis. Eight studies reported DAA, 5 reported ALA, 6 reported the DLA, and 56 reported PLA. Study size ranged from 41 to 2,601 patients. Mean follow-up time ranged from 6 months to 25 years. Rates of infection and dislocation were low; 80% of ALA, 87.5% of DAA, 100% of DLA, and 82.1% of PLA studies reported zero postoperative dislocations. Studies reporting postoperative HHS and PMA scores showed considerable improvement for all approaches.

CONCLUSIONS

Patients undergoing primary THA with dual mobility implants rarely experience postoperative dislocation, regardless of surgical approach. Additional studies directly comparing DAA, ALA, DLA, and PLA are needed to confirm these findings.

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

INTRODUCTION

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

METHODS

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

RESULTS AND CONCLUSION

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

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.