Radiographic Measurement of Joint Space Width Using the Fixed Flexion View in 1,102 Knees of Japanese Patients with Osteoarthritis in Comparison with the Standing Extended View

Assessment of validity, reliability, and feasibility of OMERACT ultrasound knee osteoarthritis scores in Egyptian patients with primary knee osteoarthritis

BACKGROUND

Ultrasound (US) can evaluate all joint components affected by knee osteoarthritis (KOA); however, standardized scoring of US-detected pathology is needed to improve its diagnostic and monitoring capabilities.

OBJECTIVES

To examine the validity, reliability, and feasibility of the Outcome Measures in Rheumatology (OMERACT) ultrasound scoring for KOA, comparing with clinical and radiography measures, using predefined cutoff values.

METHODS

This cross-sectional study included 75 Egyptian patients with primary KOA. All patients had Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, bilateral knee radiography, and ultrasonography. Inter-observer reliability of ultrasound was evaluated in 30 knees by another newly trained operator.

RESULTS

Most of the OMERACT-US KOA scores showed significant associations with WOMAC clinical scores, except for femoral cartilage damage and effusion. The synovitis score was significantly associated with WOMAC-pain score (p-value 0.046), while medial meniscus extrusion (MME) and medial osteophytes were significantly associated with WOMAC-stiffness score (p-value 0.009 and 0.023, respectively). MME and synovitis were significantly associated with WOMAC-physical score (p-value 0.035 and 0.020, respectively). The ultrasound scores also showed a strong correlation with radiographic scoring. Inter-observer reliability ranged from moderate to excellent agreement (k = 0.58 to k = 0.83); it was highest for lateral osteophytes (k = 0.83), good agreement for synovitis (k = 0.72), any osteophytes (k = 0.71), damage of femoral cartilage (k = 0.70), and moderate agreement for medial osteophytes (k = 0.58) and MME (k = 0.59).

CONCLUSION

OMERACT-US scoring system for KOA demonstrated validity, reliability, and feasibility for evaluating both structural and inflammatory components. Using cutoff values improved the scoring reliability for osteophytes and MME. Key Points • OMERACT-US scores provide a valid assessment of inflammatory and structural components of knee osteoarthritis. • The following changes may improve the performance of the OMERACT-US scores. a. The binary score for effusion and synovial hypertrophy can be omitted, as they have no added value. b. A semi-quantitative grading for effusion may capture the impact of effusion on clinical outcomes. c. Added cutoff values to score medial meniscal extrusion, osteophytes, and pathological effusion improved the respective scores' reliability. d. Applying the updated OMERACT definition of synovitis. • OMERACT-US scores are reliable to be used with a newly trained operator, particularly when cutoff values are included, and proper training time is provided. • The OMERACT-US score is feasible to be used in clinical practice, as the time taken to perform was short, even for a newly trained operator.

Comparative evaluation of knee osteoarthritis: radiography vs. ultrasonography in Nepalese population: a cross-sectional study

Background and objectives

Osteoarthritis (OA) is a degenerative and long-term debilitating disease with rising prevalence, predominantly involving larger joints including the knee joint. While radiography has traditionally been the primary modality for joint evaluation, there is a growing trend towards using ultrasonography (USG) for musculoskeletal disorders, including joint assessment. This study aimed to find the role of USG in the evaluation of OA of knee joints with comparison to the radiographs.

Methods

This was a cross-sectional study done on patients with signs and symptoms of OA of the knee who visited the radiology department for knee radiographs. Kellgren and Lawrence system was used for grading OA in radiographs. USG of knee joints was done with high-frequency probes and searched for joint space width, articular cartilage thickness, marginal osteophytes, meniscal extrusion, and other articular/ extra-articular abnormalities. The USG findings were correlated with findings in anteroposterior and lateral radiographs.

Results

The mean number of osteophytes was higher in USG compared to the radiographs (P<0.001). Mean joint spaces were comparable in both modalities. Meniscal extrusion was seen with USG, which significantly correlated with joint space width and cartilage thickness (P<0.005). USG also detected synovial changes, effusion, and Baker's cyst.

Conclusion

Although radiography is the standard first-line radiological investigation for the diagnosis of OA of the knee joint, USG can be an adjunct as it well correlates with the radiograph findings and can provide more useful information.

Radiographic Thigh Muscle Measurements Are a Reliable Predictor of Psoas Area and Sarcopenia

BACKGROUND

Sarcopenia is associated with falls, fractures, postoperative complications such as periprosthetic joint infections and dislocations, and early mortality. Although cross-sectional imaging is currently used to diagnose sarcopenia, inexpensive and widely available screening tests are needed. The goal of this study was to investigate whether measurements of thigh muscles made on radiographs can predict psoas muscle area and the presence of sarcopenia as determined on computed tomography (CT) scans.

METHODS

A retrospective radiographic review was performed to measure thigh muscle area in the coronal and sagittal planes using the differential in soft-tissue attenuation. Psoas muscle area on CT at L3 and L4 served as the gold standard for the diagnosis of sarcopenia. The correlation between thigh muscle and psoas muscle areas was determined, and multivariable models were developed to identify predictors of psoas muscle area and sarcopenia.

RESULTS

Four hundred and fourteen patients (252 male, 162 female) were identified. Seventy-six (18.4%) of the patients had an L4 psoas muscle area below the sex-specific cutoff value for sarcopenia. Patients with sarcopenia on abdominal CT had significantly smaller thigh muscle measurements on all radiographic views. The mean and standard deviation of the thigh muscle measurements were determined for the entire cohort and for patients with sarcopenia, as well as for adults aged 18 to 40 years without sarcopenia to provide normative reference values. The intraclass correlation coefficients were >0.8 for all radiographic measurements. The anteroposterior-view measurement of thigh muscle width and lateral-view measurement of quadriceps height were identified as independent predictors of both psoas muscle area and sarcopenia.

CONCLUSIONS

Measurements of thigh muscle size made on radiographs can predict both psoas muscle area and sarcopenia. These measurements are a reliable and readily available screening tool to aid in the diagnosis and treatment of sarcopenia in the orthopaedic population.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Statistical modeling: Assessing the anatomic variability of knee joint space width

Population-based knee joint space width (JSW) assessments are promising for the prevention and early diagnosis of osteoarthritis. This study aimed to establish the statistical shape and alignment model (SSAM) of knee joints for assessing anatomic variation in knee JSW in the healthy Chinese male population. CT scans of asymptomatic knee joints of healthy male participants (n = 107) were collected for manual segmentation to create mesh samples. The as-scanned positional error was reduced by a standard processing flow of deformable mesh registration. Principal component analysis (PCA) was performed to create a tibiofemoral SSAM that was trained on all mesh samples. The anatomic variability of the JSW in the healthy Chinese male population was then assessed using the SSAM with regression analysis and 3D analysis by color-coded mapping. Almost all PCA modes had a linear influence on the anatomic variation of the medial and lateral JSW. The JSW variability within the SSAM was mainly explained by mode 1 (45.1 % of variation), demonstrating that this mode had the greatest influence on JSW variation. 3D assessment of the JSW showed that the minimum medial JSW varied from 2.76 to 3.23 mm, and its site shifted a short distance on the medial tibial plateau. The root-mean-square fitting and generalization errors of the SSAM were below 1 mm. This study will benefit the design and optimization of prosthetic devices, and may be applicable to the prevention and early diagnosis of osteoarthritis.

Advances in osteoarthritis imaging

PURPOSE OF REVIEW

Imaging plays a pivotal role for diagnosis, follow-up and stratification of osteoarthritis patients in clinical trials and research. We aim to present an overview of currently available and emerging imaging techniques for osteoarthritis assessment and provide insight into relevant benefits and pitfalls of the different modalities.

RECENT FINDINGS

Although radiography is considered sufficient for a structural diagnosis of osteoarthritis and is commonly used to define eligibility of patients for participation in clinical trials, it has inherent limitations based on the projectional nature of the technique and inherent challenges regarding reproducibility in longitudinal assessment. MRI has changed our understanding of the disease from 'wear and tear' of cartilage to a whole organ disorder. MRI assessment of structural changes of osteoarthritis includes semi-quantitative, quantitative and compositional evaluation. Ultrasound is helpful in evaluating the degree of synovitis and has value in the assessment particularly of the patella-femoral joint. Recent development of computed tomography technology including weight-bearing systems has led to broader application of this technology in a research context.

SUMMARY

Advances in MRI technology have resulted in a significant improvement in understanding osteoarthritis as a multitissue disease.

Changes in joint space width over time and risk factors for deterioration of joint space width after medial opening-wedge high tibial osteotomy

PURPOSE

The purpose of this study was to evaluate the changes in joint space width (JSW) over time after medial opening-wedge high tibial osteotomy (MOWHTO) and identify risk factors for deterioration of JSW using anteroposterior (AP) and Rosenberg views.

METHODS

We retrospectively analyzed changes in JSW of 104 MOWHTO patients whose preoperative osteoarthritis (OA) grade was K-L grade 3 or less on AP and Rosenberg views. Serial changes in JSW were assessed from preoperatively to at least 3 years postoperatively. Patients were divided into two groups according to JSW change patterns on each of AP and Rosenberg views: non-deterioration group had either unchanged or increased JSW, and deterioration group had decreased JSW. Clinical outcomes were compared using Western Ontario and McMaster Universities OA Index (WOMAC) score between groups. Multivariate logistic regression analysis was performed to identify risk factors for deterioration of JSW.

RESULTS

JSW on average for all patients increased 0.5 mm and 0.8 mm on AP and Rosenberg views, respectively (p < 0.05). Non-deterioration group showed significant improvement based on patient-reported outcomes (WOMAC) than deterioration group (all p < 0.05). Undercorrection was an independent risk factor for failure to achieve maintained or increased JSW on both AP (OR 6.885, 95% CI 1.976-23.986, p = 0.002) and Rosenberg (OR 12.756, 95% CI 2.952-55.129, p = 0.001) views.

CONCLUSION

JSW increased gradually and continuously on standing AP and Rosenberg views until postoperative 3 years after MOWHTO. Deterioration of JSW following MOWHTO was closely related to the undercorrection and affected clinical outcomes.

LEVEL OF EVIDENCE

Level III, case control study.

Radiological and clinical outcomes of concurrent hamstring stretching with quadriceps strengthening in patients with knee osteoarthritis: A randomized clinical trial

BACKGROUND: Hamstring shortening altered joint reaction forces during activities of daily living (ADL), causing knee pain. Moreover, weak quadriceps may negatively distribute the compressive and shear forces at the knee joint. PURPOSE: The study examined the effect of adding hamstring stretching to quadriceps strengthening exercises on joint space narrowing (JSN), medial joint space width (mJSW), and physical abilities in patients with knee osteoarthritis (KOA). METHODS: A total of 42 osteoarthritis patients, aged from 50 to 65 years, were randomized and assigned into 2 groups: the study and the control groups. Quadriceps strengthening exercises were given to both groups, while static hamstring stretching was applied to only the study group. Patients of both groups were screened with a weight-bearing x-ray beam to investigate the JSN, mJSW, and functional abilities measured in the WOMAC scale. The Outcomes were evaluated at the baseline and immediately after 6 weeks of treatment. RESULTS: The mJSW improved in the study group (p< 0.001) compared to the control group (p= 0.07). The OARSI JSN was enhanced significantly in both groups, but in favor of the study group (p< 0.001) over the control group (p= 0.046). Both MVIC and total score of WOMAC were significantly improved in both groups (p< 0.001). CONCLUSION: Adding static hamstring stretching to quadriceps strengthening exercises provided a substantial effect on mJSW, JSN, and functional abilities in KOA patients.

Gravidity, parity and knee breadth at midlife: a population-based cohort study

Gestation increases the biomechanical loading of lower extremities. Gestational loading may influence anthropometrics of articular surfaces in similar means as bone diaphyseal properties. This study aimed to investigate whether gravidity (i.e. number of pregnancies) and parity (i.e. number of deliveries) is associated with knee breadth among middle-aged women. The study sample comprised 815 women from the Northern Finland Birth Cohort 1966. The median parity count of our sample was 2 and the median gravidity count 3. At the age of 46, questionnaires were used to enquire gravidity and parity, and posteroanterior knee radiographs were used to obtain two knee breadth parameters (tibial plateau mediolateral breadth (TPML) and femoral condylar mediolateral breadth (FCML)) as representatives of articular size. The associations of gravidity and parity with knee breadth were analyzed using general linear models with adjustments for height, weight, leisure-time physical activity, smoking, and education years. Individuals with osteoarthritic changes were excluded from our sample. The mean TPML in our sample was 70.3 mm and the mean FCML 71.6 mm respectively. In the fully adjusted models, gravidity and parity showed positive associations with knee breadth. Each pregnancy was associated with 0.11–0.14% larger knee breath (p < 0.05), and each delivery accounted for an increase of 0.20% in knee breadth (p < 0.01). Between-group comparisons showed that multiparous women had 0.68–1.01% larger knee breath than nulli- and primiparous women (p < 0.05). Pregnancies and deliveries seem to increase the mediolateral breadth of the knee. This increase is potentially associated with increased biomechanical loadings during gestation.

Imaging in Osteoarthritis

Osteoarthritis (OA) is the most frequent form of arthritis with major implications on both individual and public health care levels. The field of joint imaging, and particularly magnetic resonance imaging (MRI), has evolved rapidly due to the application of technical advances to the field of clinical research. This narrative review will provide an introduction to the different aspects of OA imaging aimed at an audience of scientists, clinicians, students, industry employees, and others who are interested in OA but who do not necessarily focus on OA. The current role of radiography and recent advances in measuring joint space width will be discussed. The status of cartilage morphology assessment and evaluation of cartilage biochemical composition will be presented. Advances in quantitative three-dimensional morphologic cartilage assessment and semi-quantitative whole-organ assessment of OA will be reviewed. Although MRI has evolved as the most important imaging method used in OA research, other modalities such as ultrasound, computed tomography, and metabolic imaging play a complementary role and will also be discussed.

Accelerometer-measured physical activity is associated with knee breadth in middle-aged Finns - a population-based study

Background

Articular surface size is traditionally considered to be a relatively stable trait throughout adulthood. Increased joint size reduces bone and cartilage tissue strains. Although physical activity (PA) has a clear association with diaphyseal morphology, the association between PA and articular surface size is yet to be confirmed. This cross-sectional study aimed to clarify the role of moderate-to-vigorous PA (MVPA) in knee morphology in terms of tibiofemoral joint size.

Methods

A sample of 1508 individuals from the population-based Northern Finland Birth Cohort 1966 was used. At the age of 46, wrist-worn accelerometers were used to monitor MVPA (≥3.5 METs) during a period of two weeks, and knee radiographs were used to obtain three knee breadth measurements (femoral biepicondylar breadth, mediolateral breadth of femoral condyles, mediolateral breadth of the tibial plateau). The association between MVPA and knee breadth was analyzed using general linear models with adjustments for body mass index, smoking, education years, and accelerometer weartime.

Results

Of the sample, 54.8% were women. Most individuals were non-smokers (54.6%) and had 9—12 years of education (69.6%). Mean body mass index was 26.2 (standard deviation 4.3) kg/m². MVPA was uniformly associated with all three knee breadth measurements among both women and men. For each 60 minutes/day of MVPA, the knee breadth dimensions were 1.8—2.0% (or 1.26—1.42 mm) larger among women (p < 0.001) and 1.4—1.6% (or 1.21—1.28 mm) larger among men (p < 0.001).

Conclusions

Higher MVPA is associated with larger tibiofemoral joint size. Our findings indicate that MVPA could potentially increase knee dimensions through similar biomechanical mechanisms it affects diaphyseal morphology, thus offering a potential target in reducing tissue strains and preventing knee problems. Further studies are needed to confirm and investigate the association between articulation area and musculoskeletal health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05475-7.

Correlation of tibiofemoral joint-space width with the clinico-radiological scoring of knee osteoarthritis – a comparison between anteroposterior and lyon-schuss radiographic views

Background

The degree of joint space narrowing measured on radiographs provide a reliable estimate of the extent and severity of Osteoarthritis (OA) of the knee. While the standing antero-posterior (AP) view radiographs have been used traditionally, recent studies suggest that the Lyon-Schuss (LS) view is able to detect early OA changes better. The present study was, therefore, conducted to make an objective comparison between the two views with respect to their corelation with the patient's clinical and radiological scores.

Methods

Forty patients (80 knees) were included in this cross-sectional study. Medial as well as lateral tibiofemoral joint space widths (JSW) were measured using vernier callipers on printed, calibrated radiographic images. Knee Society Score (Function) (KSS-F) was used as the clinical outcome measure while Ahlbäck grade was used for determining radiological severity. JSW was correlated with KSS-F and the Ahlbäck grade using Spearman's rho correlation coefficient. Reproducibility of the method was assessed using the intra-class correlation coefficient (ICC).

Results

Average age of the participants was 60 ± 7.65 (range 50–78) years, with 18 males and 22 females. ICC for intraobserver reliability was 0.97 and for inter-observer reliability, was 0.91 (AP view) and 0.92 (LS view), respectively. Medial JSW measurements taken on the AP view were found to have a significantly higher degree of correlation with both KSS-F and Ahlbäck grade ( p  < 0.05) than those obtained from the LS view.

Conclusion

Although the LS view may be more sensitive for detecting early OA changes in knee, particularly in the lateral tibiofemoral compartment, the present study shows that AP view correlates better with the patient's overall clinical and radiological profile.

Alignment changes after open-wedge high tibial osteotomy result in offloading in the patellofemoral joint: a SPECT/CT analysis

PURPOSE

The patellofemoral (PF) joint may be adversely affected by medial open-wedge high tibial osteotomy (OWHTO). This study aimed to evaluate the PF compartmental changes using combined single-photon emission computed tomography (SPECT) and conventional computed tomography (CT) after OWHTO to provide clinical guidance regarding the PF joint pressure and force.

METHODS

Patients with medial osteoarthritis and varus malalignment > 5° were treated using OWHTO. Patients with a minimum 2-year follow-up were included in the study. The patellar positions were evaluated based on the radiographic parameters. The changes in chondral lesions during second-look arthroscopic examination were evaluated, and the PF joint arthritis grade was recorded on patellar Merchant radiographs using Kellgren-Lawrence classification. The PF compartmental changes according to SPECT/CT analysis after OWHTO were evaluated in all patients. The scintigraphic uptake was graded on four scales. Patients were divided into improved and unimproved groups according to the PF compartmental grade using the SPECT/CT uptake grading system.

RESULTS

At a mean follow-up period of 47.0 months (range 25-74 months), the mean mechanical femorotibial angle changed significantly from varus 6.3° (range 5-12°) to valgus 2.6° (range 0-8°); p < 0.001) postoperatively. The radiological parameters presenting patellar positions, including the tibial slope, patellar convergence angle, and lateral tilt angle, did not change significantly between the preoperative values and the 2-year follow-up values. The mean patellar height significantly decreased (0.07 ± 0.14, p = 0.001 according to the Blackburn-Peel index and 0.32 ± 0.23, p < 0.001 using the modified Insall-Salvati ratio). The average tibial tubercle to trochlear groove (TT-TG) distance significantly decreased from 14.1 to 12.2 mm (p < 0.001). The Q angle also significantly decreased from 9.8^o to 7.7^o (p = 0.008). Chondral lesions of the patella and trochlear groove revealed significant deterioration; at 2 years after OWHTO, the arthritic grades of the PF joints worsened significantly, as determined by radiography (p = 0.007). Scintigraphic uptake in the PF joint was significantly lower (from 2 to 1) at 2 years postoperatively compared to that immediately after the index operation (p < 0.001). Only 4 of 56 (7.1%) patients showed increased uptake. Comparison between the improved and unimproved groups according to scintigraphic uptake changes revealed that the changes in the cartilage status on the patellar undersurface and TT-TG distance were the most significant predictive factors of increased scintigraphic uptake in the PF joint after OWHTO.

CONCLUSION

Alignment correction by OWHTO result in PF compartment offloading and should be considered when identifying the surgical indications for OWHTO.

LEVEL OF EVIDENCE

Therapeutic, Level IV.

Sex estimation from knee breadth dimensions in a Finnish population

Sex estimation is an important part of osteological analysis of skeletons and forensic identification process. Traditionally cranial and pelvic traits are utilized for accurate sex estimation. However, post-cranial measurements have also been proven to accurately estimate sex especially from robust bones such as the femur. In this study, we investigated the potential of knee breadth dimensions in sex estimation in a Finnish population. To conduct this study we utilized a study sample (n = 1654) belonging to the Northern Finland Birth Cohort 1966. All individuals were 46 years of age at the time of the examination. Three knee breadth dimensions were measured from subjects' knee posteroanterior radiographs: femoral biepicondylar breadth (FBEB), mediolateral breadth of the femoral condyles (FCML), and mediolateral breadth of the tibial plateau (TPML). Sex estimation was performed using logistic regression. The study clearly demonstrated that all three measurements were different between males and females. Sectioning points for individual knee breadth measurements were 82.9 mm for FBEB, 76.6 mm for FCML and 75.4 mm for TPML. The classification rates ranged from 90.9% to 93.6%. The less commonly used measurements of FCML and TPML showed higher accuracy than FBEB in sex estimation. Our study confirmed that knee breadths can be successfully utilized to improve sex estimation in cases where the skeleton is only partially preserved and other major components of sex estimation are absent. We can also provide new standards for sex estimation from the knee joint in a Finnish population.

Validation of joint space narrowing on plain radiographs and its relevance to partial knee arthroplasty

AIMS

To explore the clinical relevance of joint space width (JSW) narrowing on standardized-flexion (SF) radiographs in the assessment of cartilage degeneration in specific subregions seen on MRI sequences in knee osteoarthritis (OA) with neutral, valgus, and varus alignments, and potential planning of partial knee arthroplasty.

METHODS

We retrospectively reviewed 639 subjects, aged 45 to 79 years, in the Osteoarthritis Initiative (OAI) study, who had symptomatic knees with Kellgren and Lawrence grade 2 to 4. Knees were categorized as neutral, valgus, and varus knees by measuring hip-knee-angles on hip-knee-ankle radiographs. Femorotibial JSW was measured on posteroanterior SF radiographs using a special software. The femorotibial compartment was divided into 16 subregions, and MR-tomographic measurements of cartilage volume, thickness, and subchondral bone area were documented. Linear regression with adjustment for age, sex, body mass index, and Kellgren and Lawrence grade was used.

RESULTS

We studied 345 neutral, 87 valgus, and 207 varus knees. Radiological JSW narrowing was significantly (p < 0.01) associated with cartilage volume and thickness in medial femorotibial compartment in neutral (r = 0.78, odds ratio (OR) 2.33) and varus knees (r = 0.86, OR 1.92), and in lateral tibial subregions in valgus knees (r = 0.87, OR 3.71). A significant negative correlation was found between JSW narrowing and area of subchondral bone in external lateral tibial subregion in valgus knees (r = -0.65, p < 0.01) and in external medial tibial subregion in varus knees (r = -0.77, p < 0.01). No statistically significant correlation was found in anterior and posterior subregions.

CONCLUSION

SF radiographs can be potentially used for initial detection of cartilage degeneration as assessed by MRI in medial and lateral but not in anterior or posterior subregions. Cite this article: Bone Joint Res 2021;10(3):173-187.

Fixed-flexion view X-ray of the knee superior in detection and follow-up of knee osteoarthritis

A fixed flexion view (FFV) is useful for evaluating joint space when assessing the severity of osteoarthritis (OA) of the knee. We analyzed changes in joint space revealed by standing extended view (SEV) and FFV over a mean 4 years, to compare both views on their capacity to measure joint space width accurately at particular time points during follow-up.SEV and FFV images were acquired in patients with knee OA. The 81 patients (157 knees) followed up for ≥24 months were selected as study subjects. Medial joint space widths (MJSW), Kellgren-Lawrence (KL) grades, and reductions in MJSW on SEV (ΔSEV) and FFV (ΔFFV) were compared in knees evaluated by SEV and FFV.At both time-points, mean MJSW was significantly lower by FFV than by SEV. Mean MJSW was significantly lower at follow-up than at first examination by both SEV and FFV. At both time-points, the KL grade was higher by FFV than by SEV group. The ΔFFV was significantly greater than the ΔSEV. ΔSEV did not differ significantly among KL grades, but ΔFFV was significantly greater in patients with KL grade II than in patients with other KL grades.FFV is not only useful for evaluating joint space in knees with OA, but also for accurately evaluating the progression of OA. The risk of rapid progression of knee OA may be higher in patients with KL grade II, as determined by FFV. FFV may be superior to SEV in determining appropriate treatment strategies for knee OA.