MRI Is Better Than CT Scan for Detection of Structural Pathologies After Traumatic Posterior Hip Dislocations in Children and Adolescents

MRI as a viable alternative to CT for 3D surgical planning of cavitary bone tumors

Cavitary bone defects, defined as a volumetric loss of native bone tissue, require accurate preoperative imaging for treatment planning. While CT (computed tomography) has traditionally been the gold standard for segmentation due to its superior resolution of cortical bone, MRI (magnetic resonance imaging) offers unique advantages, particularly in visualizing the soft tissue-bone interface. Furthermore, MRI eliminates the ionizing radiation associated with CT, making it an advantageous alternative, especially in the management of benign and low-grade malignant bone tumors. Despite these advantages, MRI's inherently lower spatial resolution may introduce artifacts, which can complicate segmentation accuracy. This study evaluates the feasibility of MRI as a viable alternative to CT in the preoperative planning of cavitary bone defect treatment. We analyzed CT and MRI scans from 80 patients with benign and locally aggressive primary bone tumors, generating three-dimensional (3D) models through manual segmentation in Mimics, validated using Geomagic Control X. Volumetric differences between the CT- and MRI-derived models were assessed using the Wilcoxon signed-rank test and paired t-test. The mean volumetric difference between MRI and CT scans was 2.68 ± 1.44 %, which was not statistically significant (p = 0.15). Additionally, multiple regression analysis examining sex, age, and diagnosis revealed no significant differences in the 3D model volumes derived from the two imaging modalities (sex: p = 0.51, age: p = 0.98, and diagnosis: p = 0.50). These results support MRI-based segmentation as a reliable, radiation-free alternative to CT, particularly when precise delineation of soft tissue boundaries is critical for surgical planning.

Acetabular labral entrapment following spontaneous nonconcentric reduction of posterior hip dislocation in a child

Traumatic pediatric hip dislocations are uncommon and can occur following minor trauma. This injury may be overlooked, as pediatric hip dislocations can reduce spontaneously prior to medical attention. In this scenario, the presenting hip radiographs may provide evidence of a prior transient hip dislocation episode by demonstrating signs of a nonconcentric hip reduction, and prompt further evaluation with advanced imaging. We present a rare case of a traumatic posterior hip dislocation with spontaneous nonconcentric reduction in a child. CT and MRI revealed a block in concentric reduction by the avulsed and entrapped posterior acetabular labrum and contiguous epiphyseal fragment. This case highlights the imaging characteristics of this rare injury, and the importance of early diagnosis to guide surgical management.

Clinical treatment of traumatic hip dislocation in children: a single-centre retrospective study

This study aimed to analyse the treatment and outcomes of traumatic hip dislocation (THD) in children. Clinical data of children with THD were collected at our clinical centre from 1 June 2012 to 1 January 2023. Demographic data, injury mechanism, type of dislocation, combined injuries, reduction time, reduction method, and radiographs were analysed. The Merle d'Aubigné-Postel hip score was used to evaluate hip function and complications at the final follow-up. A total of 19 children with THD were enrolled, including 12 male and seven female patients, with an average age of 8.28 ± 0.99 years. Posterior dislocation was the main type of dislocation (89.47%). Fifteen patients (78.95%) had experienced high-energy injuries and traffic accidents were the main causes of injury (47.37%). Closed reduction was performed as soon as possible, and open reduction was performed if necessary. The hip scores of 18 patients (94.74%) were excellent. One patient had osteonecrosis of the femoral head, with a hip function score of 10 (moderate). High-energy injuries, such as traffic accidents, have gradually become the main cause of injury. The prognosis for THD in children is generally good.

Acetabular "Fleck" Sign: Outcomes of Surgical Repair

BACKGROUND

Traumatic, posterior hip dislocations in the pediatric population are typically managed by closed reduction to achieve a concentric hip joint. The presence of an acetabular "fleck" sign, despite concentric reduction, has been shown to signify significant hip pathology. The purpose of this study was to evaluate the outcomes of open labral repair through a surgical hip dislocation (SHD) in a consecutive series of patients with an acetabular "fleck" sign associated with a traumatic hip dislocation/subluxation.

METHODS

A retrospective review of patients between 2008 and 2022 who presented to a single, level 1 pediatric trauma center with a traumatic posterior hip dislocation/subluxation was performed. Patients were included if they had an acetabular "fleck" sign on advanced imaging and underwent open labral repair through SHD. Medical records were reviewed for sex, age, laterality, mechanism of injury (MOI), and associated orthopaedic injuries. The modified Harris hip score (mHHS) was utilized as the primary clinical outcomes measure. Patients were assessed for the presence of heterotopic ossification (HO) and complications, including implant issues, infection, avascular necrosis (AVN), and post-traumatic dysplasia.

RESULTS

Twenty-nine patients (23 male, average age: 13.0±2.7 y; range: 5.2 to 17.3) were identified. Eighteen injuries were sports related, 9 caused by motor vehicle accidents, and 1 pedestrian struck. All patients were found to have an acetabular "fleck" sign on CT (26 patients) or MRI (5 patients). Associated injuries included: femoral head fracture (n=6), pelvic ring injury (n=3), ipsilateral femur fracture (n=2), and ipsilateral PCL avulsion (n=1). At the latest follow-up (2.2±1.4 y), all patients had returned to preinjury activity/sport. Three patients developed asymptomatic, grade 1 HO in the greater trochanter region. There was no incidence of AVN. One patient developed post-traumatic acetabular dysplasia due to early triradiate closure. mHHS scores showed excellent outcomes (n=21, 94.9±7.4, range: 81 to 100.1).

CONCLUSIONS

The acetabular "fleck" sign indicates a consistent pattern of osteochondral avulsion of the posterior/superior labrum. Restoring native hip anatomy and stability is likely to improve outcomes. SHD with open labral repair in these patients produces excellent clinical outcomes, with no reported cases of AVN.

LEVEL OF EVIDENCE

Level IV-therapeutic.

Clinical Outcomes and Associated Pathologies Following Pediatric Traumatic Hip Dislocations: A Systematic Review of the Literature

INTRODUCTION

Pediatric traumatic hip dislocations are a rare condition that can have devastating short and/or long-term outcomes and associated pathologies (APs), including associated injuries (AIs) and long-term adverse events (LTAEs), with negative long-term sequelae. Currently, there are little data that exist on the rate of APs, with the most notable being avascular necrosis (AVN), for pediatric traumatic hip dislocations. The purpose of this systematic review is to evaluate the outcome relative frequency of dislocation direction, reduction type, and rate of APs for traumatic hip dislocations in the pediatric population.

METHODS

A systematic review on the topic of traumatic hip dislocations in the pediatric population was performed using PubMed, ScienceDirect, Web of Science, CINAHL, and MEDLINE databases from database inception to March 30, 2023. Inclusion criteria was full-text English articles, addressed traumatic hip dislocations, and pediatric patients (<18 y old).

RESULTS

A total of 24 articles (n=575 patients) met final inclusion criteria from a total of 219 articles retrieved from the initial search. For the average age of the included patients with reported age (n=433 patients), the frequency weighted mean was 9.50 years±1.75 years with a frequency weighted mean follow-up time of 74.05 months ±45.97 months (n=399 patients). The most common dislocation direction was posterior (86.4%), the most common treatment type was closed reduction (84.5%), AVN was the most common type of LTAEs (15.5% of APs), and labral/capsular injuries and acetabular fractures were the most common type of AIs (14.0% and 9.4% of APs, respectively). There were a combined total of 414 APs (72%) out of 575 total patients.

CONCLUSION

Pediatric traumatic hip dislocations are associated with a high rate of AIs and LTAEs (72%, 414 APs out of 575 patients). AVN, labral/capsular injuries, and acetabular fractures are the most common APs after pediatric traumatic hip dislocations. Pediatric hip dislocations are usually posterior and commonly managed through closed reduction.

LEVEL OF EVIDENCE

III, Systematic Review.

Application of Medical Image Navigation Technology in Minimally Invasive Puncture Robot

Microneedle puncture is a standard minimally invasive treatment and surgical method, which is widely used in extracting blood, tissues, and their secretions for pathological examination, needle-puncture-directed drug therapy, local anaesthesia, microwave ablation needle therapy, radiotherapy, and other procedures. The use of robots for microneedle puncture has become a worldwide research hotspot, and medical imaging navigation technology plays an essential role in preoperative robotic puncture path planning, intraoperative assisted puncture, and surgical efficacy detection. This paper introduces medical imaging technology and minimally invasive puncture robots, reviews the current status of research on the application of medical imaging navigation technology in minimally invasive puncture robots, and points out its future development trends and challenges.

Epidemiology and injury morphology of traumatic hip dislocations in children and adolescents in Germany: a multi-centre study

OBJECTIVE

Traumatic hip dislocations are very rare in childhood and adolescence. The aim of this multi-centre study is to analyse the current epidemiology and injury morphology of a large number of traumatic hip dislocations in children. This can provide a better understanding of childhood hip dislocations and contribute to the development of a therapeutic approach in order to prevent long-term impacts.

METHODOLOGY

This retrospective, anonymised multi-centre study included patients, aged up to 17 years, with acute traumatic hip dislocations and open growth plates. The patients came from 16 German hospitals. Exclusion criteria included insufficient data, a positive history of hip dysplasia, or an association with syndromal, neurological or connective tissue diseases predisposing to hip dislocation. An analysis was carried out on the patients' anthropometric data and scans (X-ray, MRI, CT), which were collected between 1979 and 2021. Gender, age at the time of dislocation, associated fractures, mechanism of injury, initial treatment including time between dislocation and reduction, method of reduction, treatment algorithm following reduction and all documented complications and concomitant injuries were evaluated.

RESULTS

Seventy-six patients met the inclusion criteria. There were two age peaks at 4-8 years and 11-15 years. There was an increased incidence of girls in the under-eight age group, who had mild trauma, and in the group of over-eights there were more boys, who had moderate and severe trauma. Dorsal dislocation occurred in 89.9% of cases. Mono-injuries dominated across all age groups. Concomitant injuries rarely occurred before the age of eight; however, they increased with increasing ossification of the acetabulum and appeared as avulsion injuries in 32% of 11-15-year-olds. Of the 76 patients, 4 underwent a spontaneous, 67 a closed and 5 a primary open reduction. A reduction was performed within 6 h on 84% of the children; however, in around 10% of cases a reduction was not performed until after 24 h. Concomitant injuries needing intervention were identified in 34 children following reduction. Complications included nerve irritation in the form of sensitivity disorders (n = 6) as well as avascular necrosis (AVN) of the femoral head in 15.8% of the patients (n = 12).

CONCLUSIONS

Traumatic hip dislocations are rare in childhood and adolescence and have high complication rates. The most severe complication, femoral head necrosis, occurred in 16% of cases. Minor injuries, especially in younger children, are enough to cause a dislocation. Posterior dislocation was more frequent and primarily occurred as a mono-injury; however, concomitant injuries must be considered with increasing age. Children continue to experience delayed reductions. The length of time until reduction, age and the severity of the concomitant injury play a role in the development of femoral head necrosis; however, this topic requires additional investigation.

Traumatic hip dislocations in a pediatric cohort: The importance of advanced imaging

Purpose

Given that pediatric traumatic hip dislocations are relatively rare, the purpose of the current study is twofold: first, to contribute a significant cohort to the existing corpus, and second, to provide evidence toward the role that computed tomography and magnetic resonance imaging could play in identification and management of this type of injury.

Methods

A retrospective review was conducted of all patients with traumatic hip dislocation who presented from 2012 to 2022 at a tertiary-level pediatric trauma center. Data regarding demographics, mechanism of injury, imaging, and treatment were tabulated. Outcomes of interest included immobilization length, concomitant injuries, imaging performed and findings, and rates of avascular necrosis, pain, and stiffness. Concomitant injuries were identified using imaging, clinical, and operative notes. Differences between categorical variables were compared using chi-square analysis or Fischer-exact testing, while continuous variables were compared using Student t tests or Wilcoxon rank sum tests when appropriate.

Results

Thirty-four patients were identified. Postreduction, 28 patients had a cumulative 17 magnetic resonance imaging, 19 computed tomographies, and 1 intraoperative arthrogram. Of these, 16 patients had 19 injuries identified on advanced imaging that were missed on initial radiographs. Eleven of these patients went on to operative treatment. In eight of these, postreduction advanced imaging helped guide the decision for surgery. In four patients, magnetic resonance imaging was necessary to fully characterize injury to the posterior acetabular rim after initial identification on computed tomography. Magnetic resonance imaging was also used to rule out one computed tomography-diagnosed acetabular fracture.

Conclusion

Magnetic resonance imaging is valuable to fully define associated rim and intra-articular injuries following initial treatment of pediatric traumatic hip dislocations.

Level of evidence

Level IV diagnostic study.

Traumatic Hip Dislocation in Pediatric Patients: Clinical Case Series and a Narrative Review of the Literature with an Emphasis on Primary and Long-Term Complications

Traumatic hip dislocation is a rare injury in pediatric populations. Dislocation may be associated with low-energy trauma, such as a minor fall. Traumatic hip dislocation is associated with severe complications, such as avascular necrosis of the femoral head. Timely diagnosis and reposition decrease the rate of complications. In this study we retrospectively assessed traumatic hip dislocations in pediatric patients during a 10-year timespan in a university hospital. There were eight cases of traumatic hip dislocations. All patients had a minimum follow-up of two years and were followed with MRI scans. One patient developed avascular necrosis during the follow-up which resolved conservatively. There were no other significant complications. In conclusion, traumatic hip dislocation is a rare injury which is associated with severe complications. Patients in our case series underwent a timely reposition. The complication rate was similar to previous reports.

Acetabular Labral Tear with a Missed Posterior Wall Fracture in an Adolescent Athlete: A Case Report

CASE

We present an adolescent contact-sport athlete presenting with hip pain after a traumatic in-play event. After delayed clinical improvement, a magnetic resonance arthrogram (MRA) revealed a posterior acetabular labral tear and the patient was referred for arthroscopic repair. However, subsequent critical interpretation of the MRA demonstrated a missed concomitant posterior acetabular wall fracture, which was later confirmed with computed tomography.

CONCLUSION

Despite the low incidence of acetabular fractures in adolescents, this case report highlights the importance of maintaining clinical suspicion in young athletes after a traumatic injury, recognizing the association with labral tears, and acknowledging the limitations of certain imaging modalities.

Magnetic Resonance Imaging Versus Computed Tomography for Three-Dimensional Bone Imaging of Musculoskeletal Pathologies: A Review

Magnetic resonance imaging (MRI) is increasingly utilized as a radiation‐free alternative to computed tomography (CT) for the diagnosis and treatment planning of musculoskeletal pathologies. MR imaging of hard tissues such as cortical bone remains challenging due to their low proton density and short transverse relaxation times, rendering bone tissues as nonspecific low signal structures on MR images obtained from most sequences. Developments in MR image acquisition and post‐processing have opened the path for enhanced MR‐based bone visualization aiming to provide a CT‐like contrast and, as such, ease clinical interpretation. The purpose of this review is to provide an overview of studies comparing MR and CT imaging for diagnostic and treatment planning purposes in orthopedic care, with a special focus on selective bone visualization, bone segmentation, and three‐dimensional (3D) modeling. This review discusses conventional gradient‐echo derived techniques as well as dedicated short echo time acquisition techniques and post‐processing techniques, including the generation of synthetic CT, in the context of 3D and specific bone visualization. Based on the reviewed literature, it may be concluded that the recent developments in MRI‐based bone visualization are promising. MRI alone provides valuable information on both bone and soft tissues for a broad range of applications including diagnostics, 3D modeling, and treatment planning in multiple anatomical regions, including the skull, spine, shoulder, pelvis, and long bones.

Traumatic hip dislocation in the paediatric population: A case series from a specialist centre

INTRODUCTION

Traumatic hip dislocation is a rare injury in the paediatric population. It can occur after high energy trauma, but also after lower energy injuries especially in younger children. Posterior dislocation is the most common pattern of hip dislocation. In most cases, closed reduction is successful, but occasionally open reduction is required to achieve concentric reduction. The aim of our study was to present the 10-year experience from a Level-1 Trauma Paediatric Hospital and to comment on how our experience correlates with the current literature.

PATIENTS AND METHODS

This is a retrospective case series of all paediatric patients (< 16 years old) with a traumatic hip dislocation presented and/or treated at our institution, between the 1^st of January 2010 and 31^st August 2020.

RESULTS

Thirteen cases of traumatic hip dislocation were identified. There were 7 females. The mean age was 9.8 years. Typically, younger patients were involved in lower energy injuries. The direction of hip dislocation was posterior in ten cases. Associated injuries were seen in eight patients. All cases underwent closed reduction, which was successful in nine cases. Mean time to reduction was 6.8 hours. Post reduction imaging with CT and/or MRI was performed in all cases. There was residual subluxation in three cases, requiring open reduction. In one case with unrecognised undisplaced physeal injury, closed reduction resulted in a Delbet type 1 hip fracture. Two cases developed avascular necrosis (AVN).

CONCLUSIONS

Traumatic paediatric hip dislocation is a rare injury. A target of 6 hours for reduction should be employed as this will reduce the risk of AVN in those who have not permanently damaged the vessels at the time of injury. We advocate all attempts for closed reduction to be performed in an operating theatre with the use of an image intensifier to help identifying associated injuries and confirm concentric reduction. If closed reduction fails, open reduction is required. Post-reduction MRI is an important adjunct to recognise associated soft tissue injuries. Follow up of patients should continue for 2 years as a minimum to help detect AVN.

Traumatic Hip Dislocations in Patients Younger Than 16 Years Old: A Single Center Experience with Mean Follow-Up of 10.4 Years

INTRODUCTION

Traumatic hip dislocation in childhood is a rare injury. The aim of this study was to present the experience of a single center for traumatic hip dislocation in the pediatric and adolescent age group.

MATERIALS AND METHODS

The orthopedic trauma database of a single center was retrospectively searched for patients who had sustained a traumatic hip dislocation between 2004 and 2019. Data related to age, mechanism of injury, additional fractures, presence of any open fracture or neurovascular injury, and dislocation side were retrieved from the patient files. Functional outcome was evaluated using the Harris Hip Scoring system.

RESULTS

The mean age of 13 patients at the time of injury was 7.7 years and the mean follow-up time was 124.5 months (10.4 years). All traumatic hip dislocations were posterior dislocations. The mean Harris Hip score was 95.7 points (range 55-100 points) with 12 patients scored as excellent and 1 as poor results. Ten complications including limb length inequality, avascular necrosis and hip arthritis were determined in seven patients.

CONCLUSION

Traumatic hip dislocation is a rare injury in the pediatric age group. Early diagnosis and concentric reduction of the femoral head is essential for better functional results and to avoid complications. Limb length inequality is a frequently seen complication, which has not been reported in previous studies.

Recurrent traumatic hip dislocation in an 8-year-old boy

Pediatric traumatic hip dislocations (PTHD) are rare and represent around 5% of all pediatric dislocations. Associated bony or soft tissue injury can occur as often as 17%–25% of the time. We report a case of an 8-year-old boy presenting a posterior hip dislocation after a low-energy trauma, which was initially managed with closed reduction and bed rest for 1 week. Two days after hospital discharge, he suffered a recurrent posterior hip dislocation. He was now managed with 4 weeks of bed rest and lower limb skin traction followed by 1 week of no weight-bearing on crutches. With 6 months of follow-up, he is asymptomatic, walking autonomously, with complete and painless range of motion of the affected hip and no major radiographic changes. Pediatric traumatic hip dislocation is a rare and challenging injury that should be managed promptly. Currently, there is no protocol concerning treatment in the literature and its largely dependent of patient and parents' cooperation.

A Rare Case of a Traumatic Posterior Hip Dislocation in a 3-Year-Old Boy: A Case Report and Review of the Literature

We present a rare case of neglected hip dislocation in a 3-year-old boy. Hip dislocations in childhood represent less than 6% of all injuries. The boy presented to the ED with ongoing hip pain after his leg got stuck in a carousel. The physical and radiologic examination revealed a posterior right hip dislocation. The closed reduction failed, so open reduction during surgery was performed. The postoperative protocol included 3 days of immobilization with early mobilization and pain-adapted weight bearing. No signs of femoral head malperfusion occurred 2 months after the injury. The patient did not complain of any limitations such as weight bearing problems or loss of range of motion. In comparison to adults, there are several specialties such as the fact that minor trauma can lead to hip dislocations due to the laxity of the ligaments, and due to the limited direct anamnestic options, neglected hip dislocations can occur. The treatment should focus on immediate proper reduction. The main complications after traumatic hip dislocation are avascular necrosis of the femoral head, redislocation, and early osteoarthritis.

Acetabular Retroversion and Decreased Posterior Coverage Are Associated With Sports-related Posterior Hip Dislocation in Adolescents

BACKGROUND

Leverage of the femoral head against the acetabular rim may lead to posterior hip dislocation during sports activities in hips with femoroacetabular impingement (FAI) deformity. Abnormal concavity of the femoral head and neck junction has been well described in association with posterior hip dislocation. However, acetabular morphology variations are not fully understood.

QUESTIONS/PURPOSES

The purpose of this study was to compare the acetabular morphology in terms of acetabular version and coverage of the femoral head in adolescents who sustained a posterior hip dislocation during sports and recreational activities with a control group of patients without a history of hip disease matched by age and sex.

METHODS

In this case-control study, we identified 27 adolescents with posterior hip dislocation sustained during sports or recreational activities who underwent a CT scan of the hips (study group) and matched them to patients without a history of hip disease being evaluated with CT for possible appendicitis (control group). Between 2001 and 2017, we treated 71 adolescents (aged 10-19 years old) for posterior hip dislocations. During the period in question, we obtained CT scans or MR images after closed reduction of a posterior hip dislocation. One patient was excluded because of a diagnosis of Down syndrome. Twenty-one patients who were in motor vehicle-related accidents were also excluded. Twelve patients were excluded because MRI was obtained instead of CT. Finally, three patients with no imaging after reduction and seven patients with inadequate CT reformatting were excluded. Twenty-seven patients (38%) had CT scans of suitable quality for analysis, and these 27 patients constituted the study group. We compared those hips with 27 age- and sex-matched adolescents who had CT scans for appendicitis and who had no history of hip pain or symptoms (control group). One orthopaedic surgeon and one pediatric musculoskeletal radiologist, not invoved in the care of the patients included in the study, measured the lateral center-edge angle, acetabular index, acetabular depth/width ratio, acetabular anteversion angle (10 mm from the dome and at the level of the center of the femoral heads), and the anterior and posterior sector angles in the dislocated hip; the contralateral uninvolved hip of the patients with hip dislocations; and both hips in the matched control patients. Both the study and control groups had 25 (93%) males with a mean age of 13 (± 1.7) years. Inter- and intrarater reliability of measurements was assessed with intraclass correlation coefficient (ICC). There was excellent reliability (ICC > 0.90) for the acetabular anteversion angle measured at the center of the femoral head, the acetabular version 10 mm from the dome, and the posterior acetabular sector angle.

RESULTS

The mean acetabular anteversion angle (± SD) was lower in the study group at 10 mm from the acetabular dome (-0.4° ± 9° versus 4° ± 4°; mean difference -5°; 95% confidence interval [CI], -9 to -0.3; p = 0.015) and at the center of the femoral heads (10° ± 5° versus 14° ± 4°; mean difference -3°; 95% CI, -6 to -0.9; p = 0.003). A higher proportion of acetabula was severely retroverted in the study group (14 of 27 [52%]; 95% CI, 33%-71% versus four of 27 [15%]; 95% CI, 1%-28%; p = 0.006). The mean posterior acetabular sector angle was lower in the study group (82° ± 8° versus 90° ± 6°; mean difference -8°; 95% CI, -11 to -4; p < 0.001), whereas no difference was found for the anterior acetabular sector angle (65° ± 6° versus 65° ± 7°; mean difference 0.3°; 95% CI, -3 to 4; p = 0.944). There was no difference for the lateral center-edge angle (27° ± 6° versus 26° ± 5°; p = 0.299), acetabular index (5° ± 3° versus 6 ± 4°; p = 0.761), or acetabular depth/width ration (305 ± 30 versus 304 ± 31; p = 0.944) between groups. Acetabular anteversion angle at the center of the femoral heads (11° ± 4° versus 14° ± 4°; p = 0.006) and the posterior acetabular sector angle (86° ± 7 ° versus 91° ± 6°; p = 0.007) were lower in the contralateral uninvolved hips compared with control hips.

CONCLUSIONS

Decreased acetabular anteversion angle and posterior acetabular coverage of the femoral head were associated with posterior dislocation of the hip in adolescents with sports-related injury even in the absence of a high-energy mechanism. Further studies are necessary to clarify whether a causative effect exists between acetabular and femoral morphology and the dislocation of the hip in patients with sports-related injuries.

LEVEL OF EVIDENCE

Level III, prognostic study.