Acetabular Cup Orientation Research Articles

Measurement of the Acetabular Cup Orientation After Total Hip Arthroplasty Based on 3-Dimensional Reconstruction From a Single X-Ray Image Using Generative Adversarial Networks

BackgroundThe purpose of this study was to reconstruct 3-dimensional (3D) computed tomography (CT) images from single anteroposterior (AP) postoperative total hip arthroplasty (THA) X-ray images using a deep learning algorithm known as generative adversarial networks (GANs) and to validate the accuracy of cup angle measurement on GAN-generated CT. MethodsWe used 2 GAN-based models, CycleGAN and X2CT-GAN, to generate 3D CT images from X-ray images of 386 patients who underwent primary THAs using a cementless cup. The training dataset consisted of 522 CT images and 2,282 X-ray images. The image quality was validated using the peak signal-to-noise ratio and the structural similarity index measure. The cup anteversion and inclination measurements on the GAN-generated CT images were compared with the actual CT measurements. Statistical analyses of absolute measurement errors were performed using Mann–Whitney U tests and nonlinear regression analyses. ResultsThe study successfully achieved 3D reconstruction from single AP postoperative THA X-ray images using GANs, exhibiting excellent peak signal-to-noise ratio (37.40) and structural similarity index measure (0.74). The median absolute difference in radiographic anteversion was 3.45° and the median absolute difference in radiographic inclination was 3.25°, respectively. Absolute measurement errors tended to be larger in cases with cup malposition than in those with optimal cup orientation. ConclusionsThis study demonstrates the potential of GANs for 3D reconstruction from single AP postoperative THA X-ray images to evaluate cup orientation. Further investigation and refinement of this model are required to improve its performance.

Dynamic Acetabular Cup Orientation during Gait: A Study of Fast- and Slow-Walking Total Hip Replacement Patients.

The dynamic orientation of total hip replacement acetabular cups during walking may vary substantially from their assumed position at surgical implantation and may vary between individuals. The scale of this effect is of interest for both pre-clinical device testing and for pre-operative surgical planning. This work aimed to evaluate (1) patient variation in dynamic cup orientation; (2) whether walking speed was a candidate proxy measure for the dynamic cup orientation; and (3) the relationships between dynamic cup orientation angles and planar pelvic angles. Pelvic movement data for patients with fast (20 patients) and slow (19 patients) self-selected walking speeds were used to calculate acetabular cup inclination and version angles through gait. For aim 1, the range and extremes of acetabular cup orientation angles were analysed for all patients. A large patient-to-patient variation was found in the ranges of both inclination angle (1° to 11°) and version angle (4° to 18°). The version angle was typically retroverted in comparison to the implantation position (greatest deviation 27°). This orientation is substantially different to the static, 0° version, simplifying assumptions in pre-clinical 'edge loading' testing. For aim 2, the cup orientation angles were compared between the fast- and slow-walking groups using statistical parametric mapping. The only significant differences observed were for cup version angle, during ~12% of the gait cycle before toe-off (p < 0.05). Therefore, self-selected walking speed, in isolation, is not a sufficient proxy measure for dynamic acetabular orientation. For aim 3, correlations were recorded between the acetabular cup orientation angles and the planar pelvic angles. The cup inclination angle during gait was strongly correlated (Spearman's coefficient -1) with pelvic obliquity alone, indicating that simple planar assessment could be used to anticipate inclination angle range. The cup version angle was correlated with both pelvic rotation and tilt (Spearman's coefficient 0.8-1), indicating that cup version cannot be predicted directly from any single pelvic movement. This complexity, along with the interaction between inclination angle and range of version angle, supports the use of computational tools to aid clinical understanding.

Is the Acetabular Cup Orientation Different in Robot-Assisted and Conventional Total Hip Arthroplasty With Right-Handed Surgeons Using an Anterolateral Approach?

Introduction Total hip arthroplasty (THA) is one of the most successful orthopaedic procedures. Survival rates from 90% at 10 years to 93% at 20 years have been reported in different studies. Differences in implant and patient characteristics can undoubtedly explain some of this variability observed in prosthesis durability, but the effect of surgical technique and implant orientation cannot be ignored. Therefore, many intraoperative methods (anatomic landmarks, intraoperative x-ray, fluoroscopy, navigation, and robotic surgery) have been attempted to avoid acetabular component malpositioning.Although postoperative computed tomography (CT) is accepted as the gold standard for the measurement of acetabular anteversion, it remains controversial in respect of costs and radiation exposure. The aim of this study was to examine how acetabular component orientation was affected in robotic and conventional THA operations performed by two surgeons with right-hand dominance. Material and methods The study included 113 primary THA operations performed on 113 patients between 2017 and 2022 in two groups: (i) robotic THA (Mako, Stryker Corporation, Kalamazoo, Michigan, United States) (55 patients) and (ii) conventional THA (58 patients). The patients comprised 51 males and 62 females. THA was performed on 54 right-side hips and 59 left-side hips. The operations were performed by two orthopaedic surgeons, each with 20 years of arthroplasty experience, on all the patients in the lateral decubitus position with an anterolateral approach. In all the cases, the orientation of the acetabular component was 40° inclination and 20° anteversion. Difficult THA procedures (patients with developmental dysplasia of the hip (DDH), a history of hip surgery, revision THA, defect or deformity of the acetabulum, a history of scoliosis or lumbar posterior surgery, or those requiring proximal femoral osteotomy) were excluded from the study. Using the Liaw and Lewinnek methods, the acetabular component anteversion was measured on the radiographs taken in the optimal position postoperatively and the acetabular cup inclination angles were measured on the pelvis radiographs. The groups were compared using the Kolmogorov-Smirnov, Pearson Chi-square and Mann-Whitney U statistical tests. The limits were accepted as 40±5° for inclination and 20±5° for anteversion. Results No statistically significant difference was determined between the groups in respect of age, gender, or operated side. No statistically significant difference was determined between the optimal acetabular cup inclination angles of the robotic and conventional THA groups (p = 0.79). No statistically significant difference was determined between the optimal acetabular cup anteversion angles of the left and right conventional THA groups. Statistically significantly better results were determined in the robotic group in respect of acetabular cup anteversion (p<0,001). Conclusion The optimal orientation of the acetabular component is a key factor for successful THA. Otherwise, revision surgery is inevitable for reasons such as instability, impingement, or increased wear. The results of this study demonstrated that robotic surgery was superior to the conventional method in the placement of the acetabular component in the desired orientation.

The accuracy and precision of acetabular implant measurements from CT imaging.

The placement of acetabular implant components determines the short- and long-term outcomes of total hip replacement (THR) and a number of tools have been developed to assist the surgeon in achieving cup orientation to match the surgical plan. However, the accuracy and precision of 3D-CT for the measurement of acetabular component position and orientation is yet to be established. To investigate this, we compared measurements of cobalt chrome acetabular components implanted into 2 different bony pelvic models between a coordinate measuring Faro arm and 3 different low dose CT images, including 3D-CT, 2D anterior pelvic plane (APP) referenced CT and 2D scanner referenced (SR) CT. Intra-observer differences were assessed using the Intraclass correlation coefficient (ICC). The effect of imaging the pelvis positioned in 3 different orientations within the CT scanner was also assessed. The measured parameters were the angles of inclination and version. 3D-CT measurements were found to closely match the "true values" of the component position measurements, compared with the 2D-CT methods. ICC analysis also showed good agreement between the coordinate measuring arm (CMA) and 3D-CT but poor agreement between the 2D SR method, in the results from two observers. When using the coordinate system of the CT scanner, the measurements consistently produced the greatest error; this method yielded values up to 34° different from the reference digitising arm. However, the difference between the true inclination and version angles and those measured from 3D APP CT was below half a degree in all cases. We concluded that low radiation dose 3D-CT is a validated reference standard for the measurement of acetabular cup orientation.

Surgeon Estimations of Acetabular Cup Orientation Using Intraoperative Fluoroscopic Imagining Are Unreliable

Accurate acetabular cup orientation is associated with decreased revision rates and improved outcomes of primary total hip arthroplasty. This study assesses surgeon's ability to estimate both the acetabular component inclination and anteversion angles via intraoperative fluoroscopy (IF) images. We surveyed orthopedic surgeons to estimate acetabular component inclination and anteversion based on 20 IF images of total hip arthroplasty through a direct anterior approach. Postoperative computed-tomography scans were used to calculate the true inclination and anteversion component angles. The absolute difference between the true and estimated values was calculated to determine the mean and standard deviation of the survey results. Interrater reliability was determined through interclass correlation coefficients. A majority of surgeons preferred the direct anterior approach (83.3%) and utilized IF during surgery (70%). Surgeons surveyed were on average 5.9° away from the true value of inclination (standard deviation= 4.7) and 8.8° away from the true value of anteversion (standard deviation= 6.0). Respondents were within 5° of both inclination and anteversion in 19.7% of cases, and within 10° in 57.3% of cases. All surgeons were determined to have poor reliability in estimating anteversion (interclass correlation coefficient < 0.5). Only 2 surgeons were determined to have moderate reliability when estimating inclination. Surgeons, when solely relying on IF for the estimation of anteversion and inclination, are unreliable. Utilization of other techniques in conjunction with IF would improve observer reliability.

Model-Based Acetabular Cup Orientation Optimization Based on Minimizing the Risk of Edge-Loading and Implant Impingement Following Total Hip Arthroplasty.

In this paper, a computationally efficient model-based method for determining patient-specific optimal acetabular cup alignment for total hip arthroplasty (THA) is presented. The proposed algorithm minimizes the risk of implant impingement and edge-loading, which are reported as the major causes of hip dislocation following THA. First, by using motion capture data recorded from the patient performing different daily activities, the hip contact force and the relative orientation of the femur and pelvis are calculated by a musculoskeletal model. Then, by defining two quantitative indices, i.e., angular impingement distance and angular edge-loading distance (AED), the risk of impingement and edge-loading are assessed for a wide range of cup alignments. Finally, three optimization criteria are introduced to estimate the optimal cup alignment with a tradeoff between the risk of impingement and edge loading. The results show that patient-specific characteristics such as pelvic tilt could significantly change the optimal cup alignment, especially the value of cup anteversion. Therefore, in some cases, the well-known Lewinnek safe zone may not be optimal, or even safe. Unlike other dynamic model-based methods, in this work, the need for force plate measurements is eliminated by estimating the ground reaction forces and moments, which makes this method more practical and cost-efficient. Furthermore, the low computational complexity due to analytical formulas makes this method suitable for both pre-operative and intra-operative planning.

High Prevalence of Spinopelvic Risk Factors in Patients With Post-Operative Hip Dislocations

BackgroundExcessive standing posterior pelvic tilt (PT), lumbar spine stiffness, low pelvic incidence (PI), and severe sagittal spinal deformity (SSD) have been linked to increased dislocation rates. We aimed to determine the prevalence of these 4 parameters in a cohort of unstable total hip arthroplasty (THA) patients and compare these to a large representative control population of primary THA patients. MethodsForty-eight patients with instability following primary THA were compared to a control cohort of 9414 THA patients. Lateral X-rays in standing and flexed-seated positions were used to assess PT and lumbar lordosis (LL). Computed tomography scans were used to measure PI and acetabular cup orientation. Thresholds for “at risk” spinopelvic parameters were standing posterior PT ≤ −15°, lumbar flexion (LLstand–LLseated) ≤ 20°, PI ≤ 41°, PI ≥ 70°, and SSD (PI–LLstand mismatch ≥ 20°). ResultsThere were significant differences in mean spinopelvic parameters between the dislocating and control cohorts (P < .001). There were no differences in mean PI (58° versus 56°, respectively, P = .29) or prevalence of high and low PI between groups. 67% of the dislocating patients had one or more significant risk factors, compared to only 11% of the control. A total of 71% of the dislocating patients had cup orientations within the traditional safe zone. ConclusionExcessive standing posterior PT, low lumbar flexion, and a severe SSD are more prevalent in unstable THAs. Pre-op screening for these parameters combined with appropriate planning and implant selection may help identify at risk patients and reduce the prevalence of dislocation.

Radiographic results on acetabular cup placement with the SuperPath technique: a retrospective study of 756 cases

BackgroundThe Supercapsular percutaneously assisted total hip (SuperPath) technique is a relatively new minimally invasive approach for total hip arthroplasty (THA). Good clinical outcomes related to its use are reported in the literature. Nonetheless, there are still uncertainties about its validity in terms of radiographic outcomes.Main purpose of the study is to evaluate the effectiveness of the SuperPath in acetabular cup positioning through radiographic evaluation of acetabular inclination angle (IA) and acetabular anteversion (AA) angle within the safe zone described by Lewinnek. The leg length discrepancy (LLD), femoral offset (FO), and acetabular offset (AO) were also measured to ascertain the radiographic effectiveness of SuperPath in the acetabular cup placement.MethodsBetween January 2016 and December 2019, all SuperPath cases eligible for the study were included. They were operated by three orthopaedic surgeons with long-standing experience in THA via conventional posterolateral approach and who have performed SuperPath training fellowship. The Mann-Whitney U test was used for statistical assessments (p-value < 0.05). Means ± standard deviation (SD) of the radiographic IA and AA were calculated for each year.ResultsA retrospective analysis of 756 THAs was performed. The average percentage of IA within the Lewinnek’s safe zone was from 80 to 85%, while the average percentage of AA was from 76 to 79%. Both IA and AA showed no statistically significant difference between two consecutive years. Good results, in the ranges of normal values, were also obtained for LLD, FO and AO, with homogeneous outcomes between 1 year and the following one.ConclusionIt is possible to achieve good radiographic values of acetabular cup orientation through the SuperPath within the Lewinnek’s safe zone. These results are similar to those reported in the literature by authors using SuperPath. Low rate (0,3%) of hip dislocations were reported. Therefore, the SuperPath technique represents a good alternative THA approach. Nevertheless, there is not a statistically significant improvement in these radiographic parameters over a four-year time.Level of evidenceLevel IV, retrospective study.

Novel lateral support system increases stability and reduces angular error in total hip arthroplasty: A case control study

Background/Aim: Intraoperative changes in patient position or other changes that would disrupt the decisive position during preoperative preparation would directly have a negative impact on acetabular cup orientation in patients undergoing total hip arthroplasty. This study aimed to compare the standard support system and a novel lateral support system (Maltepe), which ensures stable lateral decubitus positioning during the perioperative period, in patients undergoing total hip arthroplasty with the posterolateral approach. Methods: Patients operated in our department for osteoarthritis of the hip between 2012 - 2019 were included in this case-control study retrospectively. 46 and 41 patients were prepared for surgery in lateral decubitus position using the classical (Group 1) and novel (Group 2) lateral support systems, respectively. The groups were compared in terms of demographic characteristics, duration of preparation, anteversion and inclination, and Harris Hip scores. Results: Mean patient age was 66.89 (7.53). There was no significant difference between the two groups in terms of age (P=0.546), gender (P=1.00), body mass index (P=0.302) and the operative side (P=0.724). Duration of preparation and absolute deviation values from 15 degrees and 45 degrees were significantly better in group 2 compared to group 1 (P

Design of custom acetabular components: influence of the type of defects on the design

Options for treatment of massive acetabular defects are very diverse and continue to be a challenge for the surgeon. Although custom implants do not perform well over other reconstruction methods, design variability offers wide option for reliable primary fixation. There were performed 115 acetabular reconstructions with custom implants in Russian Scientific Research Institute of Traumatology and Orthopedics named after R.R. Vreden of the Ministry of Health of the Russian Federation from 2015 to 2019 years. The aim of our study was to clarify and define main types of custom implants which were used for reconstruction of extensive acetabular defects. Despite the most defects refers to such categories as 3A, 3B according to Paprosky and pelvic ring discontinuity, the type of custom implants was determined to a greater extent by the geometry of the defect. Custom implants were used as augmentation of posterior, anterior or superior wall in the cases when the medial wall was saved. When medial support was absent, custom implants had bridge-like fixation and antiprotrusion properties. In the most severe cases, in the absence of support and connection with the axial skeleton, custom acetabular component had iliac flange and a stem that was fixed in the posterior parts of the iliac body. The main design types of the presented constructions are represented by augments, threeflange and flanged constructions with a stem. Along with patient-specific acetabular reconstruction various design types wided primary screw fixation options, allowed us to find optimal hip rotational center position and acetabular cup orientation yet at planning stage. Custom designing of acetabular implants lets combine different fixation options of various acetabular implant types.

Fretting Corrosion, Third-Body Polyethylene Damage, and Cup Positioning in Primary vs Revision Dual Mobility Total Hip Arthroplasty

BackgroundDual mobility (DM) articulations were introduced for total hip arthroplasty to reduce the risk of instability for patients who have a high risk of dislocation. The use of DM constructs in both primary and revision total hip arthroplasty has been steadily increasing, leading to concerns regarding potential risks of fretting corrosion, polyethylene wear, metal release, and failure due to component positioning. MethodsA total of 56 retrieved DM constructs were collected. The inner and outer polyethylene liner surfaces were assessed for 7 damage mechanisms, and fretting corrosion was evaluated for the femoral stem, head, and modular liner. Three polyethylene liners with the greatest amounts of embedded debris were examined using scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to determine the elemental content of the debris. Acetabular cup orientation was analyzed radiographically using the EBRA (Einzel-Bild-Roentgen-Analyse) method. ResultsThe devices were revised most frequently for infection (36%), loosening (21%), and instability/dislocation (18%). The most common polyethylene damage mechanisms were scratching, pitting, burnishing, and embedded debris, and no difference in total damage was found between primary and revision cases. Scanning electron microscopy/energy-dispersive X-ray spectroscopy revealed that debris morphology and composition were consistent with porous titanium coating, resulting from cup loosening or broken screws and augments. A total of 71% and 50% of the constructs were determined to be within the Lewinnek safe zone for inclination and anteversion, respectively. ConclusionThe most notable mechanisms of surface damage were due to third-body debris, especially for the polyethylene surfaces which articulate against cobalt-chromium femoral heads and acetabular liners. Scratching of the femoral head and the metal liner from this debris may support the clinical use of ceramic for DM bearing surfaces in the future.

The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations

BackgroundAnterior and posterior pelvic tilt appears to play a role in total hip arthroplasty (THA) stability. When changing from the standing to the sitting position, the pelvis typically rotates posteriorly while the hips flex and this affects the femoro-acetabular positions. This case-control study compares changes in 3-D acetabular cup orientation during functional pelvic tilt between posterior THA dislocations vs stable THAs. MethodsStanding and sitting 3-D cup orientation was compared between fifteen posterior dislocations vs 233 prospectively followed stable THAs. 3-D cup orientation was calculated using previously validated trigonometric algorithms on biplanar radiographs. Those algorithms combine the angles in the three anatomical planes (coronal inclination, transverse version, and sagittal ante-inclination) in the standing position with the change in sagittal pelvic tilt from standing to sitting to calculate the 3-D orientation in the sitting position. ResultsThe standing cup orientation of the dislocated THAs was only characterized by a lower coronal inclination (P = .039). Compared with the controls, from standing to sitting, they showed less posterior pelvic tilt (P < .001). This led to a significant lower coronal inclination (P < .001) and sagittal ante-inclination (P < .001) in the sitting position but similar transverse version (P = .366). ConclusionsComparing posterior THA dislocations to stable THAs, there is a lower increase of all three orientation angles from standing to sitting. This leads to a decreased sitting coronal inclination and sagittal ante-inclination which may lead to an increased risk of impingement ensued by THA instability. By contrast, the transverse version was not significantly different in both positions. This confirms the importance of biplanar data on functional cup orientation. Level of EvidenceDiagnostic, Level III.

Case series on the effectiveness of preoperative radiological templating on acetabular cup orientation in total hip arthroplasty of developmental dysplasia of the hip

Total hip arthroplasty becomes the challenging treatment in cases of neglected developmental dysplasia of the hip but requires elaborate preoperative planning, especially for the restoration of the normal hip center, correction of shortening, and achieve normal biomechanics to avoid limb and early failures. To determine the morphological changes resulting from the dysplasia, the anatomic acetabular position, the height of the femur head dislocation and the combined anteversion must all be established. Preoperative planning was done using 100% zoom digital X-rays of the pelvis with both hips in 15° of internal rotation. This included identification of true acetabulum and centre of hip rotation using Ranawat's triangle. Templating was done to determine the position of acetabulum and size of the cup and required length of subtrochanteric osteotomy. The length of subtrochantric osteotomy was determined so that it would not lengthen the leg more than 3 cm to prevent sciatic nerve stretching. The postoperative X-rays were compared with the template of X-rays for the effectiveness of preoperative planning in restoring the near-normal biomechanics of the hip joint.

A novel mechanical inclinometer device to measure acetabular cup inclination in total hip arthroplasty

It is well recognised that acetabular cup orientation influences patient function and implant survival post-THR. Reliable intra-operative determination of cup orientation remains a challenge. We describe the design and testing of a novel mechanical inclinometer to measure intra-operative acetabular cup inclination. The aim was to design a generic inclinometer to measure acetabular inclination to within + 5° without requiring modification to existing instrumentation while remaining easy to handle, robust/reusable, and sterilizable. The device was drafted using CAD software, prototyped using a 3D printer and constructed using stainless steel. Two experiments were undertaken to test accuracy: (1) the absolute accuracy was tested; (2) placement of an acetabular component using the device was compared to a freehand technique using a sawbone pelvis. 18 surgeons were asked to place an uncemented acetabular cup in a saw bone pelvis to a target of 40°. The average root-mean-square error was 1.1° (SD: 0.9°). Comparison showed that with the freehand component placement 50% of the surgeons were outside the specified range (35°–45°) where all participants achieved placement within range when using the inclinometer. This work demonstrates that the design and initial testing of a mechanical inclinometer which is suitable for use in determining the acetabular cup inclination in THR.

The Effect of Postural Pelvic Dynamics on the Three-dimensional Orientation of the Acetabular Cup in THA Is Patient Specific.

Sagittal pelvic dynamics mainly consist of the pelvis rotating anteriorly or posteriorly while the hips flexes, and this affects the femoroacetabular or THA configuration. Thus far, it is unknown how the acetabular cup of the THA in the individual patient reorients with changing sagittal pelvic dynamics. The aim of this study was to validate a method that establishes the three-dimensional (3-D) acetabular cup orientation with changing sagittal pelvic dynamics and describe these changes during functional pelvic dynamics. A novel trigonometric mathematical model, which was incorporated into an easy-to-use tool, was tested. The model connected sagittal tilt, transverse version, and coronal inclination of the acetabular cup during sagittal pelvic tilt. Furthermore, the effect of sagittal pelvic tilt on the 3-D reorientation of acetabular cups was simulated for cups with different initial positions. Twelve pelvic CT images of patients who underwent THA were taken and rotated around the hip axis to different degrees of anterior and posterior sagittal pelvic tilt (± 30°) to simulate functional pelvic tilt in various body positions. For each simulated pelvic tilt, the transverse version and coronal inclination of the cup were manually measured and compared with those measured in a mathematical model in which the 3-D cup positions were calculated. Next, this model was applied to different acetabular cup positions to simulate the effect of sagittal pelvic dynamics on the 3-D orientation of the acetabular cup in the coronal and transverse plane. After pelvic tilt was applied, the intraclass correlation coefficients of 108 measured and calculated coronal and transverse cup orientation angles were 0.963 and 0.990, respectively, validating the clinical use of the mathematical model. The changes in 3-D acetabular cup orientation by functional pelvic tilt differed substantially between cups with different initial positions; the change in transverse version was much more pronounced in cups with low coronal inclination (from 50° to -29°) during functional pelvic tilt than in cups with a normal coronal inclination (from 39° to -11°) or high coronal inclination (from 31° to 2°). However, changes in coronal inclination were more pronounced in acetabular cups with high transverse version. Using a simple algorithm to determine the dynamic 3-D reorientation of the acetabular cup during functional sagittal pelvic tilt, we demonstrated that the 3-D effect of functional pelvic tilt is specific to the initial acetabular cup orientation and thus per THA patient. Future studies concerning THA (in)stability should not only include the initial acetabular cup orientation, but also they need to incorporate the effect of sagittal pelvic dynamics on the individual 3-D acetabular cup orientation. Clinicians can also use the developed tool, www.3d-hip.com, to calculate the acetabular cup's orientation in other instances, such as for patients with spinopelvic imbalance.

Characterising acetabular component orientation with pelvic motion during total hip arthroplasty.

Suboptimal acetabular component position can result in impingement, dislocation, and accelerated wear. Intraoperative pelvic motion has led to surgeon error and acetabular cup malposition. This study characterises the relationship between pelvic rotation and postoperative acetabular cup orientation. A device was constructed to allow cadaveric pelvis rotation along three axes about an acetabular cup in fixed orientation. The acetabular cup was fixed in space at 40° of radiographic inclination and 15° of anteversion relative to the anterior pelvic plane to represent consistent surgeon intraoperative placement. Active marker clusters were fixed to surgical equipment while the cadaveric pelvis was cemented with passive reflective markers, both identified with the Optotrak Certus motion capture system. The reamed cadaveric pelvis was rotated along three axes from -45° to 45° of roll, -30° to 30° of tilt, and -35° to 35° of pitch. The change in component inclination and anteversion was recorded at each 5° interval. Using computed tomography 3D reconstruction, the experimental setup was duplicated computationally to assess against a greater range of pelvis and implant sizes. Radiographic anteversion and inclination showed a non-linear relationship dependent on pelvic roll, tilt, and pitch. Radiographic anteversion changed -0.59°, 0.76° and 0.01° while radiographic inclination changed 0.23°, 0.18° and 1.00° for every 1° of pelvic roll, tilt and pitch, respectively. Computationally, anteversion changed -0.61°, 0.75° and 0.00° while inclination changed 0.22°, 0.19° and 1.00° for every 1° of pelvic roll, tilt and pitch, respectively. These results were independent of cup and pelvis size. Intraoperative pelvic motion can significantly affect final cup position, and this should be accounted for when placing acetabular components during total hip arthroplasty. Based on this study, intraoperative adjustment of the acetabular component position based on pelvis motion may be implemented to improve postoperative component position.

Impact of surgeon handedness in manual and robot-assisted total hip arthroplasty

BackgroundThe purpose of this study was to examine whether surgeon handedness could affect cup positioning in manual total hip arthroplasty (THA), and whether robot could diminish or eliminate the impact of surgeon handedness on cup positioning in robot-assisted THA.MethodsFifty-three patients who underwent bilateral robot-assisted THA and sixty-two patients who underwent bilateral manual THA between August 2018 and July 2019 in our institute were respectively analyzed in this study. When the difference between the bilateral anteversion and inclination was greater than 5°, the patient was regarded as having different cup positioning between bilateral THA. Their demographics, orientation of acetabular cup, and postoperative 3 month Harris hip score (HHS) were recorded for analysis.ResultsThere were no significant differences in the gender, age, BMI, diagnosis’s composition, and preoperative and postoperative HHS between the robotic and manual group. Two left hips dislocated in the manual group. The anteversion of left hip was significantly larger than that of right hip (24.77 ± 10.44 vs 22.44 ± 8.67, p = 0.043) in the manual group. There were no significant differences of cup positioning between bilateral robot-assisted THA. The patients in manual group were significantly more likely to have different cup positioning between bilateral hips than those in robotic group (77% vs 45%, p = 0.000). More manual THA were located out of the target zone than robot-assisted THA (70% vs 48%, p = 0.001).ConclusionsSurgeon’s handedness showed a trend towards an impact on cup positioning in manual THA and robot might help surgeon eliminate the adverse impact. However, the impact of handedness on the clinical outcomes still needs further observation.

An accelerometer-based navigation system provides acetabular cup orientation accuracy comparable to that of computed tomography-based navigation during total hip arthroplasty in the supine position

BackgroundInadequate acetabular component orientation is associated with postoperative impingement, dislocation, and accelerated polyethylene wear. Computed tomography (CT)-based navigation systems provide accuracy for total hip arthroplasty (THA) but are not available in all facilities. Accelerometer-based navigation systems are inexpensive, but their accuracy remains undetermined. This study compares the accuracy of cup orientation in THA using CT-based and accelerometer-based navigation systems.MethodsThis retrospective study included 35 consecutive patients (11 males, 24 females; mean age, 65 years) who underwent primary cementless THA via an anterolateral approach in the supine position. Both CT-based and accelerometer-based navigation systems were used simultaneously. The accuracy of cup orientation was compared between the two systems using postoperative CT.ResultsThe accuracy of cup inclination was 2.7° ± 2.0° in the CT-based group and 3.3° ± 2.4° in the accelerometer-based group. The accuracy of cup anteversion was 2.8° ± 2.6° in the CT-based group and 3.4° ± 2.2° in the accelerometer-based group. No significant difference was observed in cup inclination (p = 0.29) or cup anteversion (p = 0.34) between CT-based and accelerometer-based navigation.ConclusionsThe accuracy of cup positioning did not differ significantly between CT-based and accelerometer-based navigation systems.

Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review.

Optimal acetabular cup orientation is of substantial importance to good long-term function and low complication rates after total hip arthroplasty (THA). The radiographic anteversion (RA) and inclination (RI) angles of the cup are typically studied due to the practicability, simplicity, and ease of interpretation of their measurements. A great number of methods have been developed to date, most of which have been performed on pelvic or hip anteroposterior radiographs. However, there are primarily two influencing factors for these methods: X-ray offset and pelvic rotation. In addition, there are three types of pelvic rotations about the transverse, longitudinal, and anteroposterior axes of the body. Their effects on the RA and RI angles of the cup are interactively correlated with the position and true orientation of the cup. To date, various fitted or analytical models have been established to disclose the correlations between the X-ray offset and pelvic rotation and the RA and RI angles of the cup. Most of these models do not incorporate all the potential influencing parameters. Advanced methods for performing X-ray offset and pelvic rotation corrections are mainly performed on a single pelvic AP radiograph, two synchronized radiographs, or a two-dimensional/three-dimensional (2D-3D) registration system. Some measurement systems, originally developed for evaluating implant migration or wear, could also be used for correcting the X-ray offset and pelvic rotation simultaneously, but some drawbacks still exist with these systems. Above all, the 2D-3D registration technique might be an alternative and powerful tool for accurately measuring cup orientation. In addition to the current methods used for postoperative assessment, navigation systems and augmented reality are also used for the preoperative planning and intraoperative guidance of cup placement. With the continuing development of artificial intelligence and machine learning, these techniques could be incorporated into robot-assisted orthopaedic surgery in the future.

The influence of spinal sagittal balance on acetabular component orientation and its clinical relevance

Total hip arthroplasty (THA) is a well developed technique to which the spatial orientation of acetabular component is crucial. Since the idea of safe zone being proposed, such idea has long been obeyed by hip surgeons but has also been challenged in recent years. This is because post-operative instability could happen even if acetabular components are placed within safe zone . The latest researches have demonstrated that sagittal spinal balance and spino-pelvic mobility can affect the spatial orientation of acetabular components. Factors including spinal degenerative changes, long lumbosacral changes and spinal ankyloses can lead to sagittal spinal imbalance and/or influence spino-pelvic mobility, which subsequently affect pelvic retroversion. Proper pelvic retroversion is a way to compensate for sagittal spinal imbalance and is beneficial to post-operative stability. It is necessary for hip surgeons to rethink safe zone before performing THA and understand spinal balance as well as spinopelvic mobility. The goal is to reduce the rate of dislocation. This review started by introducing the related spinopelvic parameters frequently seen in papers published recently and the definitions of acetabular cup orientations. After the spinal sagittal balance and its compensatory mechanisms session, discussed its clinical relevance, as well as the significance of spinal mobility, in spinopelvic motion under three different postures.