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.

Extended Fixation for Paprosky Type III Acetabular Defects in Revision Total Hip Arthroplasty with a Minimum Follow-Up of 2 Years.

OBJECTIVE: Revision of total hip arthroplasty for patients with severe acetabular bone defects is challenging. This study aims to report the minimum 2 years outcome of the iliac extended fixation technique in patients with Paprosky type III acetabular defects. METHODS: Fifty-seven revision total hip arthroplasty patients were retrospectively reviewed who underwent reconstruction with the concept of iliac extended fixation from 2014 to 2017 in our hospital. We proposed a new concept of "iliac extended fixation" in revision total hip arthroplasty as fixation extending superiorly 2 cm beyond the original acetabular rim with porous metal augments, which was further classified into intracavitary and extracavitary fixation. Patients were assessed using the Harris Hip Score and the Western Ontario and McMaster Universities Osteoarthritis Index Score. Radiographs and patient-reported satisfaction were assessed. RESULTS: At an average follow-up of 63 months (range 25-88 months), the postoperative Harris Hip Score and Western Ontario and McMaster Universities Osteoarthritis Index scores were significantly improved at the last follow-up (p < 0.001). The center of rotation was significantly improved (p < 0.05). Fifty-three (93.0%) patients were satisfied with the outcome. The extracavitary iliac extended fixation group had higher rate of osteointegration in zone 1A (the superior lateral zone) than the intracavitary iliac extended fixation group (82.3% vs 55.0%, p = 0.015), and significantly more horizontal screws fixation (5.1 ± 24.7° vs 42.3 ± 36.8°, p < 0.001). CONCLUSION: Intracavitary and extracavitary iliac extended fixation with porous metal augments and cementless cups are effective in reconstructing severe superior acetabular bone defects. The difference in screw direction might reflect the different biomechanics of augment fixation.

Clinical and Radiological Outcomes of Revision Total Hip Arthroplasty for Patients with Prior Hartofilakidis Type C Hip Dysplasia.

OBJECTIVE: To investigate the clinical and radiological results of revision total hip arthroplasty (THA) for patients with previously diagnosed Hartofilakidis type C hip dysplasia, which is technically challenging and lacks literature. METHODS: We enrolled 20 patients with previously diagnosed Hartofilakidis type C hip dysplasia who underwent revision THA between November 2008 and July 2015 at our hospital. Patients were followed up for an average of 87 months. Data pertaining to the Harris hip score (HHS), modified Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), general satisfaction, and the level of satisfaction related to 16 hip functions or issues experienced after revision THA were collected. The vertical and horizontal center of rotation (COR) of the hips were measured bilaterally based on preoperative and postoperative anteroposterior radiographs. Categorical variables were analyzed by the chi-square test. Continuous variables were analyzed using the student's t test or non-parametric Wilcoxon Rank Sum test. RESULTS: There were significant postoperative improvements in the HHS (47.4 ± 31.6 vs 70.1 ± 39.0), modified WOMAC (48.5 ± 27.9 vs 75.7 ± 36.8), and the vertical (45.7 ± 33.7 mm vs 21.6 ± 21.8 mm) and horizontal (41.8 ± 17.0 mm vs 31.4 ± 14.7 mm) offset of the COR after revision THA (P < 0.05). Fifteen (75.0%) patients were satisfied with the procedure. The satisfaction rate for each of the 16 items ranged from 45% to 100%. The top three dissatisfactory items were squatting, getting into/out of cars, and leg-length discrepancy. Postoperatively, dissatisfied patients had a significantly higher visual analogue scale pain score and lower WOMAC pain, HHS pain, WOMAC total, and HHS total scores, a lower satisfaction rate for pain relief, and a higher vertical COR. CONCLUSION: There is a high rate (25%) of dissatisfaction with the outcome after revision THA for patients with prior Hartofilakidis type C hip dysplasia. The most likely reasons for dissatisfaction were inadequate pain relief and a higher vertical COR measured on radiography.

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.

Patient-reported adherence to physical exercises of patients with ankylosing spondylitis.

INTRODUCTION: Studies on adherence to exercise therapy of patients with ankylosing spondylitis (AS) are rare, and the criteria for adherence to exercise are inconsistent. This study aimed to quantify patient-reported adherence to exercise therapy of Chinese outpatients with AS and investigate the factors related to poor adherence. METHODS: The subjects' sociodemographic, disease-related, radiographic, and laboratory parameters were collected. Patients' adherence to exercise therapy was assessed using the Exercise Attitude Questionnaire (EAQ) with a 4-point Likert scale. All cases were grouped as good adherence and poor adherence using a cutoff score of 60, according to a previous study. Univariate analysis was conducted to assess the intergroup differences. Then, we built a multivariate logistic regression model to identify possible significant factors related to poor adherence to exercise therapy. RESULTS: A total of 185 outpatients completed the questionnaire. The mean EAQ score was 49.4 (IQR, 40.7-59.3) and 146 patients (78.9%) were considered to have poor adherence, and 39 patients (21.1%) were considered to have good adherence. The rates of current nonsteroidal anti-inflammatory drugs (NSAIDs), conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), and tumor necrosis factor-α inhibitor (TNF-i) use were significantly higher in the poor adherence group (p=0.001, p=0.027, p=0.018, respectively). Our multivariate logistic regression model revealed that the only significant associated factor was current use of NSAIDs (OR=3.517; p=0.016; 95% CI, 1.259-9.827). CONCLUSIONS: Outpatients with AS had an unacceptable level of adherence to exercise therapy, and current use of NSAIDs was a significantly associated factor. Key Points • Outpatients with AS had an unacceptable level of adherence to exercise therapy. • Current use of NSAIDs exerted a negative impact on patients' adherence to exercise therapy.

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

BACKGROUND: Ante-inclination (AI) of the cup is a key component of the combined sagittal index (CSI) for predicting joint stability after total hip arthroplasty (THA). We aimed to (1) validate a mathematical algorithm relating AI to radiographic anteversion (RA), radiographic inclination (RI), and pelvic tilt (PT); (2) convert the AI criterion of the CSI into the coronal functional safe zone (CFSZ) and explore the influences of standing-to-sitting pelvic motion (PM) and pelvic incidence (PI) on the CFSZ; and (3) attempt to locate a universal cup orientation that always fulfills the AI criterion of the CSI for all patients. METHODS: In the first phase, a phantom pelvis was designed to simulate a range of PT values, and an acetabular cup was implanted with different RA, RI, and PT settings using a robot-assisted technique and scanned using the EOS imaging system. The second phase involved patient radiographs. We enrolled 100 patients who underwent robot-assisted THA from April 2019 to December 2019, and EOS images before THA and at the 12-month follow-up were recorded. The AI was measured on a lateral radiograph; this angle was used as the reference and compared with the calculated AI to assess the accuracy of the algorithm. Linear regression was conducted to explore the relationship between the size of the CFSZ and the values of PM and PI. We calculated the intersection of the CFSZs of the patients to find a universal cup orientation (RA and RI) for the CSI. RESULTS: The algorithm was accurate according to both the phantom study and patient radiographs using PT at the time of follow-up, with mean absolute errors (MAEs) of 1.5° (width of 95% confidence interval [CI], 2.2°) and 2.8° (width of 95% CI, 3.0°), respectively. However, the preoperatively predicted AI had an MAE of 9.0° (width of 95% CI, 10.5°). In patient subgroups with lower PM or PI, the sizes of the CFSZ and of its intersection with the Lewinnek safe zone were significantly smaller (p < 0.017). No universal cup orientation existed to fulfill the CSI criteria for all patients or for any of the PM or PI subgroups. CONCLUSIONS: The target orientation for the cup in THA should be individualized. Our validated algorithm may serve as a quantitative tool for the patient-specific optimization of cup AI on the basis of the functional safe zone. CLINICAL RELEVANCE: The Lewinnek safe zone fails because it cannot predict the functional orientation of the cup. The concept of a universal safe zone of cup orientation should be abandoned and replaced by a patient-specific surgical target.

A Modeling Study of a Patient-specific Safe Zone for THA: Calculation, Validation, and Key Factors Based on Standing and Sitting Sagittal Pelvic Tilt.

BACKGROUND: Lumbar-pelvic stiffness and sagittal imbalance have been reported to increase the risk of dislocation and wear after THA. One potential way to approach this concern is by identifying patient-specific safe zones for THA components based on the standing and sitting sagittal pelvic tilt. However, there is no algorithm to integrate the standing and sitting pelvic tilt into the surgical plan of component orientations. QUESTIONS/PURPOSES: We established a new mathematical algorithm for determining a patient-specific safe zone for THA by integrating the impingement-free ROM requirements of standing and sitting while preventing edge loading while standing. We aimed to determine (1) the accuracy of this new method for predicting the impingement-free ROM for a given component orientation, (2) the sensitivity and specificity of detecting an impingement-free acetabular cup position for standing and sitting, and (3) the influences of key factors including pelvic tilt while standing and pelvic tilt while sitting and implant parameters on patient-specific safe zones. METHODS: A strategy for calculating the intersection of standing and sitting impingement-free safe zones and the zone of a standing radiographic inclination of ≤ 45° was used to develop patient-specific safe zones. We conducted a computer simulation study including the pelvis and THA prosthesis to answer the three study questions. We enrolled 10 patients who underwent robot-assisted THA for avascular necrosis of the femoral head (mean age 49 ± 19 years; five were women) from October 2019 to December 2019. We used a prosthesis model with a conical stem neck and a non-hooded liner, with the femoral head diameter ranging between 28 mm and 40 mm, and the corresponding head-neck ratio ranging between 2.33 and 3.33. We tested 1680 movements for the accuracy of impingement-free ROM (Question 1), and 80 marginal points and 120 non-marginal points of the comprehensive impingement-free safe zone, which combines the standing and sitting postures (Question 2). For Question 3, we explored the influences of standing and sitting pelvic tilt, femoral head diameter, and ROM criteria on the size of the patient-specific safe zone. RESULTS: With the simulation method as a reference for detecting impingement, the mean absolute error (arithmetic mean of all the absolute errors) of the calculated impingement-free ROM was 1.4° ± 2.3°, and the limit of agreement of errors was between -3.6° and 3.7°. The sensitivity of detecting a safe cup orientation within the comprehensive impingement-free safe zone for a given ROM criterion was 98.9% (95% CI 93.6% to 99.9%), and specificity was 97.1% (95% CI 91.0% to 99.2%). There were no impingement-free safe zones for 29% (pelvic tilt combinations without an impingement-free safe zone and all tested combinations) and no patient-specific safe zones for 46% (pelvic tilt combinations without a patient-specific safe zone and all tested combinations) of the tested combinations of standing and sitting pelvic tilt. The patient-specific safe zone was sensitive to changes in standing and sitting pelvic tilt, femoral head diameter, stem version, and ROM criteria. Stem anteversions beyond 10° to 20° dramatically reduced the size of the patient-specific safe zone to 0 within a change of 10° to 20°. CONCLUSION: The patient-specific safe zone algorithm can be an accurate method for determining the optimal orientation for acetabular cups and femoral stems in THA. The patient-specific safe zone is sensitive to changes in standing and sitting pelvic tilt, stem version, ROM criteria, and the femoral head diameter. A narrow zone of 10° to 20° for stem anteversion is recommended to maximize the size of the patient-specific safe zone. CLINICAL RELEVANCE: This study suggests the potential of a mathematical algorithm to optimize the orientation of THA components and illustrates how key parameters affect the patient-specific safe zone.

Assessment of hip involvement in patients with ankylosing spondylitis: reliability and validity of the Hip Inflammation MRI Scoring System.

BACKGROUND: This study aimed to test the reliability and validity of the Hip Inflammation MRI Scoring System (HIMRISS) in assessing hip involvement of AS patients with AS at different stages of the bath ankylosing spondylitis radiology index (BASRI-hip) scoring system. METHODS: Fifty-two outpatients with ankylosing spondylitis (AS) were included in this study. The subjects' data includes demographics, clinical characteristics, disease activity score, and functional index. Based on the Harris hip scoring (HHS) of involved hip and BASRI-hip score, we devided these patients into no hip involvement group((HHS ≥ 80 and BASRI ≤ 1) (Group A), mild hip involvement subgroup (BASRI = 2 or BASRI ≤ 1 and HHS ≤ 79) (Group B), and moderate to advanced hip involvement subgroup (BASRI ≥ 3) (Group C). Data was analyzed statistically by SPSS software. RESULTS: In total of 44 patients (88 hips), group A consisted of 21 hips, group B consisted of 42 hips and group C consisted of 25 hips. The test-retest intraclass correlation coefficients (ICCs) in four raters were 0.955 ~ 0.977 and interrater ICC was 0.993. HIMRISS correlated moderately with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (r = 0.540, p < 0.001), the Bath ankylosing spondylitis functional index (BASFI) (r = 0.540, p < 0.001), the Bath Ankylosing Spondylitis Functional Index (BASFI) (r = 0.581, p < 0.001), ASDAS-ESR (r = 0.604, p < 0.001), and Ankylosing Spondylitis Disease Activity Score (ASDAS)-C reactive protein (CRP) (r = 0.575, p < 0.001). HIMRISS in groups B and C was significantly higher than that in group A: 29.38 (17.00, 40.94) vs. 14.50 (11.38, 22.25), p = 0.009; 38 (31.13, 64.38) vs 14.50 (11.38, 22.25), p < 0.001. CONCLUSIONS: HIMRISS applied to patients with AS demonstrated a satisfactory reliability, meaning it is a reliable quantitive assessment tool for evaluating early hip involvement in patients with AS.