A Bayesian model of the disambiguation of gravitoinertial force by visual cues

The otoliths are stimulated in the same fashion by gravitational and inertial forces, so otolith signals are ambiguous indicators of self-orientation. The ambiguity can be resolved with added visual information indicating orientation and acceleration with respect to the earth. Here we present a Bayesian model of the statistically optimal combination of noisy vestibular and visual signals. Likelihoods associated with sensory measurements are represented in an orientation/acceleration space. The likelihood function associated with the otolith signal illustrates the ambiguity; there is no unique solution for self-orientation or acceleration. Likelihood functions associated with other sensory signals can resolve this ambiguity. In addition, we propose two priors, each acting on a dimension in the orientation/acceleration space: the idiotropic prior and the no-acceleration prior. We conducted experiments using a motion platform and attached visual display to examine the influence of visual signals on the interpretation of the otolith signal. Subjects made pitch and acceleration judgments as the vestibular and visual signals were manipulated independently. Predictions of the model were confirmed: (1) visual signals affected the interpretation of the otolith signal, (2) less variable signals had more influence on perceived orientation and acceleration than more variable ones, and (3) combined estimates were more precise than single-cue estimates. We also show that the model can explain some well-known phenomena including the perception of upright in zero gravity, the Aubert effect, and the somatogravic illusion.     

Household food insecurity and future orientation of Ghanaian youth and their parents

Food insecurity heightens risk for poor mental health and psychosocial functioning. Higher levels of future orientation influence numerous desirable behaviors. However, limited evidence exists on the association between food insecurity and future orientation, particularly in low-resource settings. The objective of this study was to examine the association between food insecurity and future orientation of Ghanaian youth and their parents. The study included a cross-sectional sample of 2656 youth and 2656 parents from 8 of Ghana’s 10 regions. Food insecurity was measured using the Household Food Insecurity Access Scale. Future orientation in the Ghanaian context was measured using three distinct factors adapted from the School Success Profile and the Consideration of Future Consequences scale. We analyzed our data using hierarchical linear modeling, with a three-level linear random-intercept model with covariates. Results suggest an inverse relationship between food insecurity and future orientation of youth and their parents. Food insecurity was consistently and significantly associated with lower orientation toward success (β = ?0.18, 95% confidence interval [CI] = ?0.22, ?0.14) and higher uncertainty of the future (β = 0.22, 95% CI = 0.17, 0.28) among youth, as well as lower consideration of future consequences (β = ?0.15, 95% CI = ?0.23, ?0.06) among parents. Additionally, severe food insecurity was associated with the lowest future orientation scores for youth and their parents. Our findings indicate that, under conditions of food insecurity, youth and their parents lose sight of the future, which may come at a great cost. Encouraging individuals to engage in thinking about the future or to create future images of their selves may not be meaningful if their basic needs, including access to food, are not met. Programs that provide opportunities to generate income and accumulate assets may have a twofold effect of increasing access to food and improving future orientation.     

The Association between Intentional Overdose and Same-Sex Sexual Intercourse in a Cohort of People who Inject Drugs in Melbourne,Australia

Background: People who inject drugs (PWID) are at disproportionately high risk of suicidal behaviors, as are individuals who report same-sex attraction or experience. However, there is little evidence of compounded risk of suicide for individuals who report same-sex sexual intercourse (SSI) and are PWID. Objectives: To explore the associations of lifetime intentional overdose amongst a cohort of PWID, with particular attention to those reporting SSI. Methods: The sample included 529 participants, from an ongoing cohort of 757 PWID. An “ever” SSI variable was created for participants who reported sexual intercourse with a same-sex partner at any longitudinal interview. We explored the adjusted associations between SSI and lifetime intentional overdose using logistic regression. Results: Ninety-one (17%) participants reported ever experiencing an intentional overdose. Forty-one (8%) participants reported SSI at any interview. Three hundred and sixty (68%) participants reported diagnosis of a mental health condition. Diagnosis of a mental health condition (AOR = 2.02, 95% CIs: 1.14, 3.59) and SSI (AOR = 2.58, 95% CIs: 1.22, 5.48) significantly increased the odds of lifetime intentional overdose. Conclusions/Importance: We found a heightened risk of intentional overdose amongst PWID reporting SSI, after controlling for diagnosis of a mental health condition. Services need to be aware of this heightened risk and target interventions appropriately.     

Variability in Acetabular Component Position in Patients Undergoing Direct Anterior Approach Total Hip Arthroplasty Who Have Concomitant Spine Pathology

BackgroundHip instability following total hip arthroplasty (THA) can be a major cause of revision surgery. Physiological patient position impacts acetabular anteversion and abduction, and influences the functional component positioning. Osteoarthritis of the spine leads to abnormal spinopelvic biomechanics and motion, but there is no consensus on the degree of component variability for THAs performed by anterior approach. Therefore, we sought to present guidelines for changes in acetabular component positioning between supine and standing positions for patients undergoing primary THA by a uniform anterior approach.MethodsPerioperative patient radiographs of the pelvis and lumbar spine were collected. Images were used to determine acetabular component positioning and degree of coexisting spinal pathology, categorized as a Lane Grade (LG). Final analysis of variance was performed on a sample size of 643 anterior primary THAs.ResultsFrom supine to standing position, as the severity of lumbar pathology increased the change in anteversion also increased (LG:0 = ?0.11° ± 4.65°, LG:1 = 2.02° ± 4.09°, LG:2-3 = 5.78° ± 5.72°, P < .001). The mean supine anteversion in patients with absent lumbar pathology was 19.72° ± 5.05° and was lower in patients with worsening lumbar pathology (LG:1 = 18.25° ± 4.81°, LG:2-3 = 16.73° ± 5.28°, P < .001).ConclusionPatients undergoing primary THA by anterior approach with worsening spinal pathology have larger increases in component anteversion when transitioning from supine to standing positions. Consideration should be given to this expected variability when placing the patient’s acetabular component.     

The Functional Mechanics of the Acetabular Component in Total Hip Arthroplasty

BackgroundTotal hip arthroplasty functional safe zones match postural hip changes to dynamic positioning of the acetabular component. We studied integrating the Anteinclination (AI) cup angle into the spinopelvic environment, defining normative values for all parameters and calculating adjustments to AI for each degree of altered standing pelvic position and postural mobility from these values. A sagittal geometric model was employed to determine these values using established spinopelvic parameter angles.MethodsTheoretical normative Pelvic Incidence (PI) specific values were calculated using a triangular construct employing a linear equation describing the functional relationship between the pelvic parameters at a mobility producing an isosceles solution for normative acetabular angles. Individual optimal AI cup values for altered Sacral Slope (SS)/pelvic tilt (sPT) and mobility (dSS) were calculated using specific ratios of angular change between parameters correcting from these normative values.ResultsA PI:SS:sPT ratio of angular change of 3:2:1 at dSS = 25° mobility creates an isosceles condition solving for PI specific theoretical normative values for all construct parameters. Individualized tilt correction applies to each posture a +0.25° AI alteration for each +1° sPT increase from this architectural value. Mobility correction applies a +0.5° standing AI and ?0.5° sitting AI alteration for each ?1° dSS < 25°, the opposite for each +1° dSS > 25°. The Sacroacetabular angle/Pelvic acetabular angle (SAA/PAA) index describes the underlying spinopelvic environment the cup functions within.ConclusionThis model quantitatively integrates an implanted acetabular component into the host spinopelvic environment. Theoretical normative and individual optimal cup orientations are passively determined by these conditions of standing pelvic position and mobility.     

The lateral edge and sourcil acetabular indices for surgical decision-making in developmental dysplasia of the hip

PurposeThe acetabular index (AI) is a radiographic measure that guides surgical decision-making in developmental dysplasia of the hip (DDH). Two AI measurement methods are described; to the lateral edge of the acetabulum (AI-L) and to the lateral edge of the sourcil (AI-S). The purpose of this study was to determine the level of agreement between AI-L and AI-S on the diagnosis and degree of acetabular dysplasia in DDH.MethodsA total of 35 patients treated for DDH with Pavlik harness were identified. The AI-L and AI-S were measured on radiographs (70 hips) at two and five years of age. AI-L and AI-S were then transformed relative to published normative data (tAI-L and tAI-S). Bland-Altman plots, linear regression and heat mapping were used to evaluate the agreement between tAI-L and tAI-S.ResultsThere was poor agreement between tAI-S and tAI-L on the Bland-Altman plots with wide limits of agreement and no proportional bias. The two AI measurements were in agreement as to the presence and severity of dysplasia in only 63% of hips at two years of age and 81% at five years of age, leaving the remaining hips classified as various combinations of normal, mildly and severely dysplastic.ConclusionAI-L and AI-S have poor agreement on the presence or degree of acetabular dysplasia in DDH and cannot be used interchangeably. Clinicians are cautioned to prudently evaluate both measures of AI in surgical decision-making.Level of evidenceI     

Fixation Stability of Uncemented Acetabular Cups With Respect to Different Bone Defect Sizes

BackgroundIn total hip arthroplasty, acetabular press-fit cups require a proper bone stock for sufficient primary implant fixation. The presence of acetabular bone defects compromises the primary fixation stability of acetabular press-fit cups. The aim of the present study is to determine the fixation stability of a cementless acetabular cup regarding standardized bone defects in an experimental setup.MethodsAn acetabular defect model was developed and transferred to a biomechanical cup-block model. The lack of superior cup coverage was divided into 4 stages of superior rim loss (33%, 50%, 67%, and 83%) in the anterior-posterior direction and into 4 stages of mediolateral wall absence (11%, 22%, 33%, and 50%). This resulted in 11 different defect cavities, which were compared to the intact cavity in push-in and lever-out tests of one press-fit cup design (56 mm outer diameter). Thereby, push-in force, lever-out moment, lever-out angle, and interface stiffness were determined.ResultsThe determined lever-out moments range from 15.53 ± 1.38 Nm (intact cavity) to 1.37 ± 0.54 Nm (83%/50% defect). Smaller defects (33%/11%, 33%/22%, and 50%/11%) reduce the lever-out moments by an average of 33.9% ± 2.8%.ConclusionThe lack of mediolateral acetabular coverage of 50% was assessed as critical for cementless cup fixation, whereby the contact zone between implant and bone in the defect is lost. A lack of 20% to 30% mediolateral coverage appears to be acceptable for press-fit cup fixation in the presence of primary stability. A defect of 50%/50% was identified as the threshold for using additional fixation methods.     

Selective age-related changes in orientation perception

Orientation perception is a fundamental property of the visual system and an important basic processing stage for visual scene perception. Neurophysiological studies have found broader tuning curves and increased noise in orientation-selective neurons of senescent monkeys and cats, results that suggest an age-related decline in orientation perception. However, behavioral studies in humans have found no evidence for such decline, with performance being comparable for younger and older participants in orientation detection and discrimination tasks. Crucially, previous behavioral studies assessed performance for cardinal orientation only, and it is well known that the human visual system prefers cardinal over oblique orientations, a phenomenon called the oblique effect. We hypothesized that age-related changes depend on the orientation tested. In two experiments, we investigated orientation discrimination and reproduction for a large range of cardinal and oblique orientations in younger and older adults. We found substantial age-related decline for oblique but not for cardinal orientations, thus demonstrating that orientation perception selectively declines for oblique orientations. Taken together, our results serve as the missing link between previous neurophysiological and human behavioral studies on orientation perception in healthy aging.     

Positron emission tomography–computed tomography in the assessment of viability of femoral head in acetabular fractures

Purpose

The aim of this study was to use positron emission tomography–computed tomography (PET-CT) imaging as a tool for assessment of viability of femoral head in acetabular fractures and help in early detection of complications like avascular necrosis (AVN) of the femoral head.

Methods

In our study PET-CT was done pre-operatively and six weeks postoperatively in 31 patients who underwent open reduction and internal fixation (ORIF) of acetabular fractures and fracture–dislocations. There were 26 male and five female patients who were treated in our institute between January 2009 and July 2010. Patients were subsequently followed up with plain radiographs for a mean period of 3.8 years and minimum of two years.

Results

Although seven out of 31 patients showed avascularity of the femoral head on PET-CT in the pre-operative period, only two patients progressed to AVN at final follow up, whereas the other five patients regained the vascularity at the end of six weeks. There was no statistically significant correlation between vascular status on pre-operative scan and the presence of AVN on final follow-up radiograph. There was a significant correlation between avascularity of the femoral head on the sixth week PET-CT and AVN in the final radiograph.

Conclusion

PET-CT seems to be useful as a prognostic investigation in the assessment of the vascular status of the femoral head following injuries around the hip. Both pre-operative and postoperative imaging are necessary to understand the time-dependent changes in blood flow following injury.     

Total Hip Arthroplasty after Acetabular Fracture: Incidence of Complications,Reoperation Rates and Functional Outcomes: Evidence Today

The outcome of THA following acetabular fracture was analyzed on 654 patients with a systematic review approach. An uncemented acetabular and femoral component was used in 80.1% and 59.8% of the cases respectively. The median Harris hip score was 88 points. In the early THA group, Kaplan–Meier survivorship analysis with any loosening, osteolysis or revision as the end point revealed that the 10-year cup survival was 81% whereas in the late THA group was 76% (P = 0.287). The 10-year survival was 95% for the early stems and 85% for the late ones (P = 0.001). Due to their complexity these fractures should be managed in highly specializing units where the expertise of arthroplasty and trauma reconstruction is available.