Redefining the 3D Topography of the Acetabular Safe Zone: A Multivariable Study Evaluating Prosthetic Hip Stability

Spinopelvic interactions in total hip arthroplasty: 295 patients followed for a minimum follow-up of 10 years

BACKGROUND

Concurrent spinal pathology is frequent in patients undergoing total hip arthroplasty (THA). In this study we examined whether spinopelvic interactions affect THA outcomes at a minimum follow-up of 10 years.

PATIENTS AND METHODS

295 patients with a mean age of 63.3 (range 56‒80) years receiving a THA between 2006 and 2009 were assessed. Of these, 195 had mild lumbar disc degeneration and 100 had advanced lumbar spondylosis. We analysed the changes in the Harris Hip Score (HHS) and the survival rate for postoperative low back pain (LBP) and dislocation. Changes in acetabular component position, sacro-femoral-pubic (SFP) and pelvic obliquity (PO) angles were assessed with radiological images.

RESULTS

The mean HHS was lower in female patients (p = 0.009), patients >65 years of age (p < 0.001) and those with advanced lumbar spondylosis (p = 0.002). 52 (71.2%) of the patients reporting preoperative LBP experienced improvement after THA while 47 (21.1%) of those without preoperative LBP postoperatively reported new onset LBP. Female patients (p = 0.025; hazard ratio [HR]: 1.831; 95% CI, 1.081-3.101) and those with preoperative LBP (p = 0.007; HR 2.068; 95% CI, 1.221-3.504) were at a higher risk of developing postoperative LBP at 10 years. 4 out of 9 THA dislocations were late and had shown decreasing SFP angle values over time. Acetabular component inclination and anteversion angles increased over time, whereas the SFP angle was associated with sex and age and the PO angle with age and the severity of any preoperative lumbar degeneration.

CONCLUSIONS

Concurrent spinal pathology influences THA outcomes at a minimum follow-up of 10 years. Sex, age, and associated lumbar degeneration can affect clinical and radiological changes over time. A decrease in SFP angle values over time was found in patients sustaining late dislocation.

A multicentre prospective assessment of the utility of robotic assisted total hip arthroplasty with virtual range of motion on intraoperative implant positioning

BACKGROUND

The growing adoption of robotic-assistance during total hip arthroplasty (THA) has provided novel means through which a patient's anatomy and dynamic spinopelvic relationship can be incorporated into surgical planning. However, the impact of enhanced technologies on intraoperative decision-making and changes to component positioning has not yet been described.

METHODS

A multicentre, prospective study included 105 patients (52% women) patients who underwent robotic-assisted THA with the integration of software that incorporates a patient's pelvic tilt (PT) and virtual range-of-motion (VROM) for impingement modeling. The primary outcome of the study was the percentage of patients who underwent changes to the preoperative plan for cup position after incorporating the data from the software.

RESULTS

Utilising the intraoperative VROM information, the preoperative plan for cup position was changed from the default (40° inclination and 20° anteversion) in 82/105 (78%) cases. When stratifying by spinopelvic mobility, 64% were considered normal (change ⩾ 10° and ⩽30°), 27% were stiff (change < 10°), and 9% were hypermobile (change > 30°). For all cohorts, the majority of cases (78%) deviated from the 40° inclination and 20° version target. When evaluating the proportion of cases within the Lewinnek and Callanan safe zones based on spinopelvic mobility, 19% of cases within the normal group were planned outside of both zones compared to 39% of stiff cases and 10% of hypermobile cases.

CONCLUSIONS

Utilising the latest version of robotic-assisted THA software, the preoperative plan for cup position was changed in the vast majority (78%) of patients, causing substantial deviations from traditional, generic cup targets.

Cup safe zone and optimal stem anteversion in total hip arthroplasty for patients with highly required range of motion

To avoid dislocation after total hip arthroplasty, it is desirable to avoid implant impingement during activities of daily living. Numerous simulation studies have been performed at 30° of internal rotation (IR) with 90° of flexion. However, these studies may not reflect the impingement that occurs during activities such as floor sitting, which require a larger IR during flexion. The purpose of this study was to assess the impact of varying IR angles during flexion on the impingement-free safe zone and optimal stem anteversion. In this study, implant impingement simulation was evaluated in computer simulation. The prosthesis used a flat liner, and a 32- or 40-mm femoral head and stem. Three patterns of required IR angle (30° IR/40° IR/50° IR with 90° flexion) combined with 13 directions of the required range of motion were simulated. The optimal stem anteversion to maximize the safe zone was analyzed. Increasing the required IR at 90° flexion decreased the safe zone, particularly with small stem anteversion angles. With a 32-mm head, the desirable stem anteversion at 40° of cup inclination was 15°/25°/35° in required 30° IR/40° IR/50° IR with 90° flexion, respectively. The safe zone area of the 32-mm head was smaller than that of the 40-mm head. For patients who require a larger IR with 90° flexion, the stem and cup target anteversion should be adjusted according to the implant design, head diameter, and patient's required IR at flexion in their lifestyle.

Combining inertial navigation with transacetabular ligament in total hip arthroplasty via direct anterior approach results in excellent accuracy compared to standard manual technique - A retrospective cohort study

BACKGROUND

Correct acetabular component placement plays a critical role in reducing early revisions after dislocations in total hip arthroplasty (THA). Although the transverse acetabular ligament (TAL) guides anteversion, inclination can only be accurately guided by navigation. In order to overcome the initial disadvantages with navigation, an imageless, easy-to-use inertial navigation system has been recently introduced. This study aims to analyze the accuracy of inclination with this navigation system compared to the standard manual technique.

METHODS

Two cohorts, manual technique (MT) and navigation (NAV) cohorts, consisted of 83 and 95 patients, respectively, after exclusion criteria were applied. Inclination target was 38° and anteversion was guided by TAL. Demographic data were collected, and anteroposterior (AP) pelvic and cross-table lateral radiographs were obtained 6 weeks post-operatively. Inclination and anteversion were determined on the AP pelvic and cross-table lateral radiograph, respectively.

RESULTS

A mean inclination of 41.8° (±6.8°) and 38.9° (±4.4°) was found in the MT and NAV cohorts, respectively. There was no statistical difference in gender, age, and BMI. If the inclination was set within 10° of the target (i.e., 38°), 88% of the MT cohort and 97% of the NAV cohort were within the target zone. Accuracy decreased to 53% and 83%, respectively, if the target zone range was narrowed down to ± 5°.

CONCLUSION

Combining inertial imageless navigation for inclination and TAL as a landmark for anteversion is significantly more accurate compared to the manual technique, without having the limitations and disadvantages of current standard navigational techniques.

THA-Net: A Deep Learning Solution for Next-Generation Templating and Patient-specific Surgical Execution

BACKGROUND

This study introduces THA-Net, a deep learning inpainting algorithm for simulating postoperative total hip arthroplasty (THA) radiographs from a single preoperative pelvis radiograph input, while being able to generate predictions either unconditionally (algorithm chooses implants) or conditionally (surgeon chooses implants).

METHODS

The THA-Net is a deep learning algorithm which receives an input preoperative radiograph and subsequently replaces the target hip joint with THA implants to generate a synthetic yet realistic postoperative radiograph. We trained THA-Net on 356,305 pairs of radiographs from 14,357 patients from a single institution's total joint registry and evaluated the validity (quality of surgical execution) and realism (ability to differentiate real and synthetic radiographs) of its outputs against both human-based and software-based criteria.

RESULTS

The surgical validity of synthetic postoperative radiographs was significantly higher than their real counterparts (mean difference: 0.8 to 1.1 points on 10-point Likert scale, P < .001), but they were not able to be differentiated in terms of realism in blinded expert review. Synthetic images showed excellent validity and realism when analyzed with already validated deep learning models.

CONCLUSION

We developed a THA next-generation templating tool that can generate synthetic radiographs graded higher on ultimate surgical execution than real radiographs from training data. Further refinement of this tool may potentiate patient-specific surgical planning and enable technologies such as robotics, navigation, and augmented reality (an online demo of THA-Net is available at: https://demo.osail.ai/tha_net).

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Femoral Head Length Impact on Outcomes Following Total Hip Arthroplasty in 36 Millimeter Cobalt Chrome-on-Highly Crosslinked Polyethylene Articulations

BACKGROUND

Despite concerns for corrosion, dislocation, and periprosthetic femur fractures, minimal literature has investigated the effect of adjusting femoral head length on outcomes after primary total hip arthroplasty (THA). Therefore, we aimed to investigate the effect of femoral head length on the risk of any revision and reoperation following cobalt chromium (CoCr)-on-highly crosslinked polyethylene (HXLPE) THAs.

METHODS

Between 2004 and 2018, we identified 1,187 primary THAs with CoCr-on-HXLPE articulations using our institutional total joint registry. The mean age at THA was 71 years (range, 19-97), 40% were women, and mean body mass index was 30 (range, 10-68). All THAs using 36 mm diameter femoral heads were included. Neutral (0 mm), positive, or negative femoral head lengths were used in 42, 31, and 27% of the THAs, respectively. Kaplan-Meier survivorship was assessed. The mean follow-up was 7 years (range, 2-16).

RESULTS

The 10-year survivorships free of any revision or reoperation were 94 and 92%, respectively. A total of 47 revisions were performed, including periprosthetic femur fracture (17), periprosthetic joint infection (8), dislocation (7), aseptic loosening of either component (6), corrosion (4), and other (5). Nonrevision reoperations included wound revision (11), open reduction and internal fixation of periprosthetic femur fracture (4), and abductor repair (2). Multivariable analyses found no significant associations between femoral head length and revision or reoperation.

CONCLUSION

Altering femoral head lengths in 36 mm CoCr-on-HXLPE THAs did not affect outcomes. Surgeons should select femoral head lengths that optimize hip stability and center of rotation.

LEVEL OF EVIDENCE

III.

Radiographic findings involved in knee osteoarthritis progression are associated with pain symptom frequency and baseline disease severity: a population-level analysis using deep learning

PURPOSE

To (1) develop a deep-learning (DL) algorithm capable of producing limb-length and knee-alignment measurements, and (2) determine the association between limb-length discrepancy (LLD), coronal-plane alignment, osteoarthritis (OA) severity, and patient-reported knee pain.

METHODS

A multicenter, prospective patient cohort from the Osteoarthritis Initiative between 2004 and 2015 with full-limb standing radiographs at 12 month follow-up was included. A convolutional neural network was developed to automate measurements of the hip-knee-ankle (HKA) angle, femur, and tibia lengths, and LLD. At 12 month follow-up, patients reported their frequency of knee pain since enrollment and current level of knee pain.

RESULTS

A total of 1011 patients (2022 knees, 52.3% female) with an average age of 61.2 ± 9.0 years were included. The algorithm performed 12,312 measurements in 5.4 h. ICC values of HKA and LLD ranged between 0.87 and 1.00 when compared against trained radiologist measurements. Knees producing pain most days of the month were significantly more varus (mean HKA:- 3.9° ± 2.8°) or valgus (mean HKA:2.8° ± 2.3°) compared to knees that did not produce any pain (p < 0.05). In varus knees, those producing pain on most days were part of the shorter limb compared to nonpainful knees (p < 0.05). Baseline Kellgren-Lawrence grade was significantly associated with HKA magnitude, LLD, and pain frequency at 12 month follow-up (p < 0.05 all).

CONCLUSION

A higher frequency of knee pain was associated with more severe coronal plane deformity, with valgus deviation being one degree less than varus on average, suggesting that the knee tolerates less valgus deformation before symptoms become more consistent. Knee pain frequency was also associated with greater LLD and baseline KL grade, suggesting an association between radiographically apparent joint degeneration and pain frequency.

LEVEL OF EVIDENCE

IV case series.

Applying Deep Learning to Establish a Total Hip Arthroplasty Radiography Registry: A Stepwise Approach

BACKGROUND

Establishing imaging registries for large patient cohorts is challenging because manual labeling is tedious and relying solely on DICOM (digital imaging and communications in medicine) metadata can result in errors. We endeavored to establish an automated hip and pelvic radiography registry of total hip arthroplasty (THA) patients by utilizing deep-learning pipelines. The aims of the study were (1) to utilize these automated pipelines to identify all pelvic and hip radiographs with appropriate annotation of laterality and presence or absence of implants, and (2) to automatically measure acetabular component inclination and version for THA images.

METHODS

We retrospectively retrieved 846,988 hip and pelvic radiography DICOM files from 20,378 patients who underwent primary or revision THA performed at our institution from 2000 to 2020. Metadata for the files were screened followed by extraction of imaging data. Two deep-learning algorithms (an EfficientNetB3 classifier and a YOLOv5 object detector) were developed to automatically determine the radiographic appearance of all files. Additional deep-learning algorithms were utilized to automatically measure the acetabular angles on anteroposterior pelvic and lateral hip radiographs. Algorithm performance was compared with that of human annotators on a random test sample of 5,000 radiographs.

RESULTS

Deep-learning algorithms enabled appropriate exclusion of 209,332 DICOM files (24.7%) as misclassified non-hip/pelvic radiographs or having corrupted pixel data. The final registry was automatically curated and annotated in <8 hours and included 168,551 anteroposterior pelvic, 176,890 anteroposterior hip, 174,637 lateral hip, and 117,578 oblique hip radiographs. The algorithms achieved 99.9% accuracy, 99.6% precision, 99.5% recall, and a 99.6% F1 score in determining the radiograph appearance.

CONCLUSIONS

We developed a highly accurate series of deep-learning algorithms to rapidly curate and annotate THA patient radiographs. This efficient pipeline can be utilized by other institutions or registries to construct radiography databases for patient care, longitudinal surveillance, and large-scale research. The stepwise approach for establishing a radiography registry can further be utilized as a workflow guide for other anatomic areas.

LEVEL OF EVIDENCE

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

Lumbosacral Transitional Vertebrae Influence on Acetabular Orientation and Pelvic Tilt

Lumbosacral transitional vertebrae (LSTV) are common congenital variances with a prevalence found in the population up to 35.6%. The literature demonstrates an influence of LSTV on bony pelvic anatomy. The influence on the anatomical acetabular orientation, which is important for cup positioning in total hip arthroplasty, has not yet been described for patients with LSTV. A total of 53 patients with LSTV were identified from a CT Database including 819 subjects. Fifty patients with LSTV could be included and were matched for age and sex against a control group. We examined the influence of LSTV, classified according to Castellvi, on acetabular orientation and pelvic tilt in the supine position. Functional acetabular anteversion and inclination, assessed against the table plane, were compared against anatomical acetabular anteversion and inclination, assessed against the anterior pelvic plane. The anatomical acetabular inclination correlated with the pelvic tilt (r = 0.363, p < 0.001). The anatomical acetabular inclination was significantly larger than the functional acetabular inclination in the supine position (p < 0.001). Castellvi grading of LSTV correlated negatively with pelvic tilt (ρ = −0.387, p = 0.006). Castellvi grading correlated significantly with functional acetabular anteversion (ρ = 0.324, p = 0.022) and anatomical acetabular anteversion (ρ = 0.306, p = 0.022). A higher Castellvi grading was accompanied by a reduced pelvic tilt in the supine position. The functional acetabular anteversion and anatomical acetabular anteversion increased in parallel to the higher Castellvi grading. Therefore, LSTV and Castellvi grading might be assessed on pre-operative X-rays prior to hip arthroplasty and surgeons might consider adjusting cup positioning accordingly.

John Charnley Award: Deep Learning Prediction of Hip Joint Center on Standard Pelvis Radiographs

BACKGROUND

Accurate hip joint center (HJC) determination is critical for preoperative planning, intraoperative execution, clinical outcomes after total hip arthroplasty, and commonly used classification systems in primary and revision hip replacement. However, current methods of preoperative HJC estimation are prone to subjectivity and human error. The purpose of the study was to leverage deep learning (DL) to develop a rapid and objective HJC estimation tool on anteroposterior (AP) pelvis radiographs.

METHODS

Radiographs from 3,965 patients (7,930 hips) were included. A DL model workflow was created to detect bony landmarks and estimate HJC based on a pelvic height ratio method. The workflow was utilized to conduct a grid-search for optimal nonspecific, sex-specific, and patient-specific (using contralateral hip) pelvic height ratios on the training/validation cohort (6,344 hips). Algorithm performance was assessed on an independent testing cohort for HJC estimation comparison.

RESULTS

The algorithm estimated HJC for the testing cohort at a rate of 0.65 seconds/hip based on features in AP radiographs alone. The model predicted HJC within 5 mm of error for 80% of hips using nonspecific ratios, which increased to 83% with sex-specific and 91% with patient-specific pelvic height ratio models. Mean error decreased utilizing the patient-specific model (3.09 ± 1.69 mm, P < .001).

CONCLUSION

Using DL, we developed nonspecific, sex-specific, and patient-specific models capable of estimating native HJC on AP pelvis radiographs. This tool may provide clinical value when considering preoperative component position in patients planned to undergo THA and in reducing the subjective variability in HJC estimation.

LEVEL OF EVIDENCE

Diagnostic, level IV.

Reliability and Validity of Standing Lateral Radiograph Method for Measuring Acetabular Component Version: A Modified Cross-table Lateral Radiograph Method

OBJECTIVES

To investigate the effect of the X-ray incidence angle on cup version measurements and the reliability and validity of standing lateral (SL) radiography for measuring cup versions.

METHODS

Cup versions under different X-ray incidence angles were investigated by the 3D simulation analysis. Ninety-three patients, who underwent primary total hip arthroplasty (THA) with postoperative SL radiographs and CT scans between April 2020 and December 2021, were retrospectively analyzed. SL radiography was taken under naturally standing position, correcting for the measurement error of pelvic tilt in cross-table lateral (CL) radiography. Cup versions were measured on SL radiographs and CT images by two qualified orthopedic physicians. The intra- and inter-observer reliabilities were assessed by intra-class correlation coefficient. The consistency between radiographic and CT measurements was evaluated using Pearson correlation coefficient.

RESULTS

No significant differences in cup version measurements were observed between groups of different X-ray incidence angles (P = 0.663) in the 3D simulation analysis. All measurements had excellent intra- and inter-observer reliabilities, with an intraclass correlation coefficient of >0.95. Mean cup version measurements from SL radiographs correlated well with those from CT scans (r = 0.853, P < 0.001). The mean difference between radiographic and CT measurements was -0.49° (range -12.62° to 10.37°, SD 3.95°), and the majority of differences were within the 95% limits of agreement.

CONCLUSION

The cup versions measured with SL radiography were close to the CT measurements. SL radiograph method is reliable and valid for measuring acetabular component version after THA.