Conversion of the Sagittal Functional Safe Zone to the Coronal Plane Using a Mathematical Algorithm: The Reason for Failure of the Lewinnek Safe Zone

Robotic arm-assisted acetabular reconstruction in revision total hip arthroplasty : a clinical study with minimum two-year follow-up

Aims

This study aimed to report the surgical techniques and early clinical results of robotic arm-assisted acetabular reconstruction in revision total hip arthroplasty (THA).

Methods

Between October 2019 and May 2021, we used the Mako robotic system to perform 62 revision THAs at our hospital. This study included 54 patients who underwent robotic arm-assisted revision THA for acetabular reconstruction. Surgical techniques using the robotic system to reconstruct the acetabulum, including preoperative planning, intraoperative registration, and the accuracy of different registration methods, are reported. The accuracy between the target acetabular component orientation and final orientation was evaluated. The latest follow-up Harris Hip Score (HHS) and radiographs were analyzed.

Results

Among the 54 hips included, four types of intraoperative registration methods with different surfaces were developed and registered 65 times. The overall success rate of the registration process was 98.5%. The mean accuracy of successful registration was 0.38 mm (0.2 to 0.5). The median difference between the target and final acetabular component orientations assessed by Mako was 1.0° (-2.0° to 0.0°) for inclination and 0.0° (-1.0° to 1.0°) for anteversion. Four hips were classified as outliers for acetabular component orientation. The reconstructed centres of rotation (CORs) were slightly lower than the anatomical CORs by a mean 4.72 mm (SD 4.71), and shifted laterally by 3.92 mm (SD 4.62) on postoperative radiographs. The median HHS improved significantly from 46.0 (IQR 33.0 to 58.3) preoperatively to 89.0 (IQR 78.3 to 93.0) postoperatively (p < 0.001). The overall satisfaction rate was 86.0% (n = 50). There were no radiological failures at the latest follow-up.

Conclusion

Robotic arm-assisted revision THA provides valuable information for the analysis of bone defects to guide reconstructive strategies. Robotic arm-assisted reaming and acetabular component or augment positioning facilitates accurate component position and orientation. The radiological and preliminary clinical results of this cohort were satisfactory.

Does Replicating Native Hip Biomechanics Improve Patient-Reported Outcome Measures After Total Hip Arthroplasty?

BACKGROUND

Enabling technology, such as computer navigation and robotics, provides more precise implant position, which allows surgeons the ability for personalized alignment in total hip arthroplasty (THA). To date, THA implant position studies have focused on dislocation rates, rather than on patient-reported outcome measures (PROMs). This study evaluated the impact of the THA component position on clinically significant differences in PROMs.

METHODS

A total of 1,682 consecutive primary THAs were retrospectively reviewed. Acetabular and femoral component position as well as femoral offset and leg-length discrepancy (LLD) were measured on all preoperative and postoperative radiographs. Modern PROM scores were evaluated. Minimal clinically important difference (MCID), substantial clinical benefit, and patient-acceptable symptom state values were assessed for applicable PROMs. Univariate and multivariate statistical analyses were performed with P < 0.05 as significant. The mean clinical follow-up was 21.9 months (range, one to 128).

RESULTS

In multivariate analysis, the acetabular component position closer to the native hip center of rotation was associated with a greater probability of achieving the Hip disability and Osteoarthritis Outcome Score for Joint Replacement MCID, substantial clinical benefit, and patient-acceptable symptom state thresholds (P ≤ 0.008). An increase in postoperative femoral offset was associated with achieving the MCID for the University of California Los Angeles activity level and patients being 'very satisfied or satisfied' (P ≤ 0.004). The mean postoperative LLD was 3.8 mm (range, 24.5 mm short to 36.6 mm long); however, postoperative LLD was not a predictor of PROMs (P ≥ 0.167) with statistical power ≥ 87%.

CONCLUSIONS

Study results demonstrated that replicating the native center of rotation and optimizing femoral offset was associated with clinically relevant improvements in PROMs. Interestingly, in this large cohort, leg length inequality was not associated with PROMs. Further research is warranted on THA component position, including spino-pelvic parameters and PROMs.

LEVEL OF EVIDENCE

III.

Application and exploration of total hip arthroplasty for developmental dysplasia of the hip assisted by full-process robotics

OBJECTIVE

This study aimed to explore whether total hip arthroplasty (THA) aided by full-process robotics was effective in patients undergoing developmental dysplasia of the hip (DDH).

METHODS

Totally 112 patients were enrolled and classified into robotic-assisted group (n = 56) and the conventional group (n = 56). In addition, retrospective analysis was used for comparing the difference in therapeutic efficacy.

RESULTS

A total of 112 patients received THA, and were followed up for (12.78 ± 0.76) months on average, with no occurrence of associated complications. For patients in robot-assisted group, their abduction and anteversion angles of acetabular cup placement were in the safe zone, while those in 8 patients of the conventional group were outside the safe zone. Compared to the conventional group, the robot-assisted group had higher postoperative Harris Hip Score and FJS, whereas lower VAS score.

CONCLUSION

Robot-assisted THA is advantageous in terms of both intraoperative precision and postoperative effect on the treatment of patients with DDH.

Evaluating the Accuracy of a Computed Tomography-Based Mixed-Reality Navigation Tool for Acetabular Component Positioning in Total Hip Arthroplasty

BACKGROUND

Robotics and navigation systems have improved the accuracy and precision of acetabular component placement in total hip arthroplasty (THA). The purpose of this study was to determine if the intraoperative use of a novel mixed-reality (MR) navigation system resulted in accurate acetabular component placement with minimal outliers.

METHODS

A series of 79 patients who underwent THA performed by a single surgeon using a novel MR navigation system were retrospectively reviewed. The preoperative planned acetabular component operative inclination (OI) and tilt-adjusted operative anteversion (OA) were collected for each case. At the six-week follow-up, each patient underwent three-dimensional EOS imaging, which was used to measure the acetabular component placement via validated measuring software. Patients who had bilateral THAs or three-dimensional images that did not have critical bony landmarks visible for measurement were excluded from the study. Absolute error was calculated for both inclination and anteversion. Outliers were defined as any cup position that was outside a range of ± 10 degrees from the preoperatively planned target. A total of 39 patients met the inclusion criteria.

RESULTS

The mean planned OI for each patient was 40.8 (range, 40 to 41) degrees, and the mean measured postoperative OI was 40.4 (range, 37 to 46) degrees (P = 0.40), resulting in a mean absolute error of 1.8 (range, zero to five) degrees. The mean planned OA was 30.2 (range, 25 to 35) degrees, and the mean measured postoperative OA was 31.1 (range, 27 to 42) degrees (P = 0.11), resulting in a mean absolute error of 2.0 (range, zero to six) degrees. There were no outliers in either OI or OA.

CONCLUSIONS

The results of this study suggest that the use of MR navigation during THA results in accurate postoperative acetabular component inclination and anteversion relative to the preoperative plan without outliers.

Spinopelvic alignment and precise cup placement in total hip arthroplasty - A systematic review

Study Design

A systematic literature review and meta- analysis.

Objective

To extract and combine the available literature focused on normal and abnormal biomechanical principles of spine-pelvis-hip complex and to sum up the data in the application of THA both in the setting with and without spinal disorders.

Methods

An extensive search and analysis of the articles was done by 3 authors independently in 7 platforms based on PRISMA and MOOSE guidelines. Selection criteria 1. Articles that assessed spinopelvic parameters (SS, SPT, PI, and acetabular cup orientation) in patients undergoing THA, Articles that assessed balance in spinopelvic complex after THA, Randomized control studies, Systematic literature reviews, Meta-analyses, Clinical trials / original research studies, Review articles and Articles after 2015 were included. Cochrane's GRADE method was used to define the level of evidence. 2.Participants: Patients who underwent THA only (in asymptomatic spine), those who had ankylosing spondylitis and underwent THA and those who underwent THA with prior spinal arthrodesis. 3.Study parameters: Ante Inclination (AI), sacral slope (SS), pelvic Incidence (PI) and spinopelvic tilt (SPT) in both positions of standing and sitting. ΔAI, ΔSS and ΔSPT. Data were collected and analyzed, the means of the study parameters with SD were calculated and a meta-analysis is performed to evaluate the pooled means with optimal value range.

Results

From 218 abstracts extracted and after eligibility assessment and exclusion, 4 articles involving 439 patients were enrolled. The mean SS in standing and sitting calculated were 35.53±10.52 and 33.13±12.38. The mean of AI and SPT in standing /sitting positions are 29.7±12.29/34.69±12.96 (n = 242) and 19.56±8.9/21.22±12.53 (n=439) respectively. The ΔAI, ΔSS, and ΔSPT were 4.99,2.4 and 1.66 respectively.

Conclusion

There is a proportionate change between the spinopelvic tilt and the acetabular orientation in postural variations. Evaluation of spine, pelvis and hip becomes more critical in identifying these changes and thereby prompting the acetabular cup position in the functional safe zone.

The Association of Jumbo Femoral Heads and Acetabular Cup Position on Patient Outcomes After Modern Posterior Approach Total Hip Arthroplasty

BACKGROUND

Use of jumbo femoral heads (≥ 40 mm) in total hip arthroplasty decreases postoperative dislocation; however, may leave patients more susceptible to groin pain. Limited data exist for the effect of jumbo femoral heads and acetabular cup position on modern patient-reported outcome measures (PROMs). This study evaluated the effect of jumbo femoral heads and acetabular cup position on PROMs after primary total hip arthroplasty.

METHODS

A total of 328 consecutive primary THAs of a single implant system with various femoral head sizes (36% ≥ 40 mm) were retrospectively reviewed. Acetabular cup inclination and anteversion were radiographically measured. Demographics, comorbidities, and implant sizes were documented. Prospectively collected University of California Los Angeles Activity Level, Hip Disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS JR), and satisfaction were evaluated. The mean follow-up was 1.2 years (range, one to five). A P-value of 0.05 was considered statistically significant.

RESULTS

Femoral head size was not associated with University of California Los AngelesActivity Level scores at any time point (P ≥ 0.209). Independent of patient sex, the mean HOOS JR score was significantly higher in the ≥ 40 mm femoral head group compared to the < 40 mm head group at 4 months although not reaching a clinically significant threshold (mean difference 4.4, 95% CI [confidence interval]: 0.5 to 8.3, P = 0.027); however, mean scores at the latest follow-up were not different (P = 0.956). The HOOS JR scores ≥ 90 and being "very satisfied or satisfied" were associated with a wide range and several combinations of acetabular cup inclination and anteversion. A total of 88.9% of patients reported being "very satisfied or satisfied" at the latest follow-up.

CONCLUSIONS

Patients achieved comparable PROMs regardless of femoral head size, suggesting large femoral heads may not leave patients susceptible to groin pain in addition to reducing the risk of postoperative dislocation. Excellent patient outcomes correlated with wide ranges of acetabular cup positions.

LEVEL OF EVIDENCE

III.

Kinematic-kinetic compliant acetabular cup positioning based on preoperative motion tracking and musculoskeletal modeling for total hip arthroplasty

The invention of the surgical robot enabled accurate component implantation during total hip arthroplasty (THA). However, a preoperative surgical planning methodology is still lacking to determine the acetabular cup alignment considering the patient-specific hip functions during daily activities such as walking. To simultaneously avoid implant edgeloading and impingement, this study established a kinematic-kinetic compliant (KKC) acetabular cup positioning method based on preoperative gait kinematics measurement and musculoskeletal modeling. Computed tomography images around the hip joint and their biomechanical data during gait, including motion tracking and foot-ground reaction forces, were collected. Using the reconstructed pelvic and femur geometries, the patient-specific hip muscle insertions were located in the lower limb musculoskeletal model via point cloud registration. The designed cup orientation has to be within the patient-specific safe zone to prevent implant impingement, and the optimized value selected based on the time-dependent hip joint reaction force to minimize the risk of edgeloading. As a validation of the proposed musculoskeletal model, the predicted lower limb muscle activations for seven patients were correlated with their surface electromyographic measurements, and the computed hip contact force was also in quantitative agreement with data from the literature. However, the designed cup orientations were not always within the well-known Lewinnek safe zone, highlighting the importance of KKC surgical planning based on patient-specific biomechanical evaluations.

The Relationship of Cup Inclination and Anteversion in the Coronal Plane with Ante-Inclination in the Sagittal Plane: Exposing the Fallacy of Cup Safe Zones

Background

This study aimed to establish an equation for calculating cup ante-inclination (AI) from radiographic cup inclination and anteversion, to validate this equation in a total hip arthroplasty (THA) cohort, and to test whether achieving previously described radiographic cup inclination and anteversion targets would also satisfy sagittal cup AI targets.

Methods

A mathematical equation linking cup AI, radiographic inclination (RI), and anteversion (RA) was determined: tan(AI) = tan(RA)/cos(RI). Supine and standing anteroposterior and lateral radiographs of 440 consecutive THAs were assessed to measure cup RI and RA and spinopelvic parameters, including cup AI, using a validated software tool. Whether orientation within previously defined RI and RA targets was associated with achieving the AI target and satisfying the sagittal component orientation (combined sagittal index, 205° to 245°) was tested.

Results

The cups in the THA cohort had a measured mean inclination (and standard deviation) of 43° ± 7°, anteversion of 26° ± 9°, and AI of 34° ± 10°. The calculated cup AI was 34° ± 12°. A strong correlation existed between measured and calculated AI (r = 0.75; p < 0.001), with a mean error of 0° ± 8°. The inclination and anteversion targets were both satisfied in 194 (44.1%) to 330 (75.0%) of the cases, depending on the safe zone targets that were used, and 311 cases (70.7%) satisfied the AI target. Only 125 (28.4%) to 233 (53.0%) of the cases satisfied the AI target as well as the inclination and anteversion targets. Satisfying inclination and anteversion targets was not associated with increased chances of satisfying the AI target.

Conclusions

Achieving optimal cup inclination and anteversion does not ensure optimal orientation in the sagittal plane. The equation and nomograms provided can be used to determine and visualize how the 2 planes used for evaluating the cup orientation and the pertinent angles relate, potentially aiding in preoperative planning.

Radiographic study of direct anterior approach hip arthroplasty: a 10-15 year follow-up of Chinese patients

BACKGROUND

Controversy remains over whether different surgical approaches exert an impact on the component positioning in total hip arthroplasty. We conducted a retrospective study to reveal the long-term position of prostheses in the first group of patients in China who underwent direct anterior hip arthroplasty.

METHODS

Collected were data from 350 patients who underwent direct anterior hip arthroplasty between 2008 and 2013, including demographic information, imaging data, Harris hip scores, and surgical complications. Variables, measured radiographically or by CT, included hip offset, leg length discrepancy, component position, and stability within one week after surgery and at the last follow-up. The data were subjected to statistical analysis by using paired t-tests and Pearson chi-square tests.

RESULTS

Data were harvested by follow-up and self-reported questionnaires. The postoperative follow-up lasted for 13.1 years on average (minimum, 10 years; maximum, 15 years), and the overall survival rate of hip prostheses was 96.3%. The mean Harris score at the final follow-up was 91.8 points. After excluding patients with significant preoperative hip deformities, the incidence of postoperative limb inequality (> 5 mm) was 4.9% at the last follow-up, and the incidence of hip offset discrepancy (> 5 mm) was 14.6%. The overall proportion of the acetabular components located in the Lewinnek safe zone was 77.7%, whereas the proportion of femoral prostheses in the safe zone (< 3° inclination) was 94.0%. Based on the revised data and the last follow-up imaging, the total proportion of acetabular and femoral prostheses with a radiolucence of > 2 mm was 5.1%.

CONCLUSION

Direct anterior approach hip arthroplasty could achieve excellent component positioning and long-term prosthesis survival in patients without severe hip deformities.

Quantification of soft tissue artifacts using CT registration and subject-specific multibody modeling

The potential use of gait analysis for quantitative preoperative planning in total hip arthroplasty (THA) has previously been demonstrated. However, the joint kinematic data measured through this process tend to be unreliable for surgical planning due to distortions caused by soft tissue artifacts (STAs). In this study, we developed a novel motion capture framework by combining computed tomography (CT)-based postural calibration and subject-specific multibody dynamics modeling to prevent the effect of STAs in measuring hip kinematics. Three subjects with femoroacetabular impingement syndrome were recruited, and CT data for each patient were collected by attaching marker clusters near the hip. A subject-specific multibody hip joint model was developed based on reconstructed CT data. Spring-dashpot network calculations were performed to minimize the distance between the anatomical landmark and its corresponding infrared reflective marker. The STAs of the thigh was described as six degrees of freedom viscoelastic bushing elements, and their parameter values were identified via smooth orthogonal decomposition. Least squares optimization was used to modify the pelvic rotations to compensate for the rigid components of STAs. The results showed that CT-assisted motion tracking enabled the successful identification of STA influences in gait and squat positions. Furthermore, STA effects were found to alter maximal pelvis tilt and hip rotations during a squat. Compared to other techniques, such as dual fluoroscopic imaging, the adopted framework does not require additional medical imaging for patients undergoing robot-assisted THA surgery and is thus a practical way of evaluating hip joint kinematics for preoperative surgical planning.

A patient-specific algorithm for predicting the standing sagittal pelvic tilt one year after total hip arthroplasty

Aims

The aim of this study was to evaluate the reliability and validity of a patient-specific algorithm which we developed for predicting changes in sagittal pelvic tilt after total hip arthroplasty (THA).

Methods

This retrospective study included 143 patients who underwent 171 THAs between April 2019 and October 2020 and had full-body lateral radiographs preoperatively and at one year postoperatively. We measured the pelvic incidence (PI), the sagittal vertical axis (SVA), pelvic tilt, sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis to classify patients into types A, B1, B2, B3, and C. The change of pelvic tilt was predicted according to the normal range of SVA (0 mm to 50 mm) for types A, B1, B2, and B3, and based on the absolute value of one-third of the PI-LL mismatch for type C patients. The reliability of the classification of the patients and the prediction of the change of pelvic tilt were assessed using kappa values and intraclass correlation coefficients (ICCs), respectively. Validity was assessed using the overall mean error and mean absolute error (MAE) for the prediction of the change of pelvic tilt.

Results

The kappa values were 0.927 (95% confidence interval (CI) 0.861 to 0.992) and 0.945 (95% CI 0.903 to 0.988) for the inter- and intraobserver reliabilities, respectively, and the ICCs ranged from 0.919 to 0.997. The overall mean error and MAE for the prediction of the change of pelvic tilt were -0.3° (SD 3.6°) and 2.8° (SD 2.4°), respectively. The overall absolute change of pelvic tilt was 5.0° (SD 4.1°). Pre- and postoperative values and changes in pelvic tilt, SVA, SS, and LL varied significantly among the five types of patient.

Conclusion

We found that the proposed algorithm was reliable and valid for predicting the standing pelvic tilt after THA.

Prospective randomized controlled trial on the accuracy of prosthesis positioning in total hip arthroplasty assisted by a newly designed whole-process robotic arm

INTRODUCTION

The purpose of this article is to study whether the newly designed whole-process total hip arthroplasty (THA) robotic arm can improve the accuracy of prosthesis placement in THA.

METHOD

In this study, 72 patients undergoing THA were prospectively included and randomly divided into two groups. The experimental group was treated with THA assisted by a newly designed robotic arm. The control group received THA with conventional surgical methods. The imaging data were compared after operation.

RESULT

Compared with the conventional operation, the whole-process robotic arm can more accurately place the acetabular prosthesis in the anteversion safe zone of 5 ~ 25°, but in terms of the inclination angle, whether the reference is the safe zone of 30 ~ 50° or 30 ~ 45°, there is no statistical difference between the two groups. The average lower limb length discrepancy (LLLD) in the experimental group was 3.77 ± 8.31 mm longer than contralateral side, while the counterpart in the control group was 8.39 ± 9.11 mm, with significant difference (P = 0.029). The femoral prosthesis was fixed in neutral position in 35 (100%) cases in the experimental group and only 30 (83.3%) in the control group (P = 0.036). There was no significant difference in the recovery of hip offset, femoral anteversion, and canal fill ratio (CFR) between the two groups.

CONCLUSION

Robotic arm can improve the accuracy of anteversion of acetabular cup, restore the consistency of the length of lower limbs, and more accurately implant the femoral prosthesis to the neutral position in the coronal position.

CLINICAL TRIAL REGISTRATION NUMBER

ChiCTR2100044124 (date of registration: 2021-3-11).

Effectiveness and Accuracy of a Patient-Specific Instrumentation System for Total Hip Arthroplasty

OBJECTIVE

Traditional total hip arthroplasty (THA) is often performed by visual inspection due to the lack of reliable reference, which results in inappropriate position of prosthesis and poor outcomes. This study attempts to introduce a novel patient-specific instrumentation (PSI) system and assess its effectiveness and accuracy compared with freehand operation and robot system through bone model experiments.

METHODS

Equally divide 30 sawbone models into the freehand group, PSI group, and robot group. Ten sets of prosthesis parameters were randomly generated as planning, and the three groups underwent simulated THA depending on these parameters. After the placement of the femoral prosthesis, the acetabular anteversion plan was adjusted in the PSI and robot groups so that the combined anteversion was maintained before and after adjustment. After the surgery, the actual prosthesis parameters of all bone models were measured and analyzed statistically.

RESULTS

No statistically significant difference was found in femoral anteversion error among the three groups (p = 0.951). The errors of acetabular cup anteversion, acetabular cup abduction, and combined anteversion in PSI group were 3.92° (2.94°, 4.62°), 5.65° (4.63°, 6.70°), and 3.93° (2.94°, 4.62°), respectively, which were significantly smaller than those in the freehand group [11.84° (9.92°, 13.87°), 13.54° (9.81°, 15.21°), 16.04° (8.18°, 19.25°), respectively, p < 0.05], but significantly larger than those in the robot group [1.34° (0.98°, 1.70°), 1.80° (1°, 2.02°), 1.34° (0.98°, 1.70°), respectively, p < 0.05].

CONCLUSION

Compared with the traditional freehand operation, the patient-specific instrumentation system is feasible in total hip arthroplasty because it improves the accuracy of prosthesis placement. In addition, the rapid measurement of intraoperative femoral prosthesis parameters can help surgeons optimize preoperative planning.

Is Robotic-Assisted Technology Still Accurate in Total Hip Arthroplasty for Fibrous-Fused Hips?

BACKGROUND

Total hip arthroplasty (THA) for fibrous-fused hips is technically demanding. This study aimed to evaluate the precision and accuracy, as well as the rate of conversion of robotic-assisted THA in such difficult patients.

METHODS

We retrospectively analyzed 67 patients (84 hips) who underwent THA with fibrous-fused hips between August 2018 and June 2021 at our institution. Demographics, acetabular cup positioning, leg-length discrepancies, and postoperative Harris hip scores were recorded for all patients. Thirty-six patients (44 hips) who underwent robotic-assisted THA and 31 patients (40 hips) who underwent manual THA were enrolled in this study.

RESULTS

The robot accurately executed the preoperative plan, and there were no statistically significant differences between the preoperative planned anteversion, inclination, and postoperative measurements. In the robotic group, the percentage of acetabular cups in the safe zone was significantly higher than in the manual group (87.2 versus 55%, respectively, P = .042). The rate of conversion to manual THA for various reasons in the robotic-assisted THA group was 11.4% (5/44). Compared with manual THA, the mean increase in operative time for conversion from robotic-assisted to manual THA was 24 min (P < .001).

CONCLUSION

In patients who have fibrous-fused hips, preoperative planning can be accurately executed by robotic-assisted technology. Compared with manual THA, robotic-assisted THA had a remarkable advantage in improving the frequency of achieving cup positioning within the target zone. Overall, robotic-assisted technology was helpful in such difficult cases, and the approximately 11.4% of cases converted to manual THA are reminders that surgeons should be thoroughly prepared preoperatively.

Functional outcome of conversion total hip arthroplasty (CTHA) using uncemented distally loading femoral stem for failed fixation of proximal femoral nail - A case series

Introduction and aims

There is paucity of prospective studies on conversion total hip arthroplasty (CTHA) for failed proximal femoral nailing. The objective of this study is to evaluate the functional outcome of CTHA using extensively porous coated distal loading stem for failed proximal femoral nailing.

Patients and methods

Fifteen consecutively operated patients for failed proximal femoral nail treated with single stage procedure of nail extraction and CTHA were included in this prospective observational study. All patients received metal-on-polyethylene bearing with uncemented press-fit acetabular cup (Pinnacle cup; DePuy, Warsaw [IN], USA) and extensively porous coated distally loading revision stem (Solution stem; DePuy, Warsaw [IN], USA). All patients were assessed preoperatively and postoperatively at one, three, six and more than twelve months using the Harris Hip Score (HHS). The responsiveness of HHS was assessed using Effect Size (ES) and Standardised Response Mean (SRM). ES and SRM >0.8 indicates adequate responsiveness.

Results

The mean duration of follow-up was 16.9 months for the overall cohort (SD: 7.9; range: 6-28 months). The mean preoperative HHS was 32 ± 6.1, the mean HHS at six months follow-up was 89.7 ± 4.0 and the mean HHS at final follow-up of atleast one year was 93.7 ± 3.0. There was a statistically and clinically significant improvement in the HHS from preoperatively to final follow-up postoperatively (p < 0.0001). At the final follow-up, twelve patients (80%) had an excellent outcome and three patients (20%) had a good outcome as per HHS grading. The ES was 9.87 and the SRM was 8.86 thereby suggesting adequate responsiveness. One patient developed surgical site infection and another patient developed dislocation. Both were successfully treated and subsequently the patients made uneventful recovery. None of the patients required revision surgery.

Conclusion

HHS has adequate responsiveness for assessing the functional outcome of CTHA. We recommend the use of an uncemented cup and uncemented extensively porous coated, distal loading stem for failed PFN fixation in intertrochanteric hip fractures.

Assessing component orientation of total hip arthroplasty using the low-dose bi-planar radiographs

Background

Three-dimensional computed tomography (3D CT) reconstruction is the reference standard for measuring component orientation. However, functional cup orientation in standing position is preferable compared with supine position. The low-dose bi-planar radiographs can be used to analyze standing cup component orientation. We aimed to assess the validity and reliability of the component orientation using the low-dose bi-planar radiographs compared with the 3D CT reconstruction, and explore the differences between the functional cup orientation in standing radiographs and supine CT scans.

Methods

A retrospective study, including 44 patients (50 hips) with total hip arthroplasty (THA), was conducted. CT scans were taken 1 week after surgery and the low-dose bi-planar radiographs were taken in the follow-up 6 weeks later. Component orientation measurement was performed using the anterior pelvic plane and the radiographic coronal plane as reference, respectively.

Results

The study showed no significant difference in cup anteversion (p = 0.160), cup inclination (p = 0.486), and stem anteversion (p = 0.219) measured by the low-dose bi-planar radiographs and 3D reconstruction. The differences calculated by the Bland–Altman analysis ranged from − 0.4° to 0.6° for the three measured angles. However, the mean absolute error was 4.76 ± 1.07° for functional anteversion (p = 0.035) and 4.02 ± 1.08° for functional inclination (p = 0.030) measured by the bi-planar radiographs and supine CT scans.

Conclusions

The low-dose bi-planar radiographs are the same reliable and accurate as 3D CT reconstruction to assess post-THA patients’ component orientation, while providing more valuable functional component orientation than supine CT scans.