Dust Settling and Clumping in MRI-turbulent Outer Protoplanetary Disks

Planetesimal formation is a crucial yet poorly understood process in planet formation. It is widely believed that planetesimal formation is the outcome of dust clumping by the streaming instability (SI). However, recent analytical and numerical studies have shown that the SI can be damped or suppressed by external turbulence, and at least the outer regions of protoplanetary disks are likely weakly turbulent due to magneto-rotational instability (MRI). We conduct high-resolution local shearing-box simulations of hybrid particle-gas magnetohydrodynamics (MHD), incorporating ambipolar diffusion as the dominant nonideal MHD effect, applicable to outer disk regions. We first show that dust backreaction enhances dust settling toward the midplane by reducing turbulence correlation time. Under modest level of MRI turbulence, we find that dust clumping is in fact easier than the conventional SI case, in the sense that the threshold of solid abundance for clumping is lower. The key to dust clumping includes dust backreaction and the presence of local pressure maxima, which in our work is formed by the MRI zonal flows overcoming background pressure gradient. Overall, our results support planetesimal formation in the MRI-turbulent outer protoplanetary disks, especially in ring-like substructures.

Morphology, Development and Deformation of the Spine in Mild and Moderate Scoliosis: Are Changes in the Spine Primary or Secondary?

Introduction and aim of the study: We aim to determine whether the changes in the spine in scoliogenesis of idiopathic scoliosis (IS), are primary/inherent or secondary. There is limited information on this issue in the literature. We studied the sagittal profile of the spine in IS using surface topography. Material and methods: After approval of the ethics committee of the hospital, we studied 45 children, 4 boys and 41 girls, with an average age of 12.5 years (range 7.5–16.4 years), referred to the scoliosis clinic by our school screening program. These children were divided in two groups: A and B. Group A included 17 children with IS, 15 girls and 2 boys. All of them had a trunk asymmetry, measured with a scoliometer, greater than or equal to 5 degrees. Group B, (control group) included 26 children, 15 girls and 11 boys, with no trunk asymmetry and scoliometer measurement less than 2 degrees. The height and weight of children were measured. The Prujis scoliometer was used in standing Adam test in the thoracic (T), thoraco-lumbar (TL) and lumbar (L) regions. All IS children had an ATR greater than or equal to 5 degrees. The Cobb angle was assessed in the postero-anterior radiographs in Group A. A posterior truncal surface topogram, using the “Formetric 4” apparatus, was also performed and the distance from the vertebra prominence (VP) to the apex of the kyphosis (KA), and similarly to the apex of the lumbar lordosis (LA) was calculated. The ratio of the distances (VP-KA) for (PV-LA) was calculated. The averages of the parameters were studied, and the correlation of the ratio of distances (VP-KA) to (VP-KA) with the scoliometer and Cobb angle measurements were assessed, respectively (Pearson corr. Coeff. r), in both groups and between them. Results: Regarding group A (IS), the average height was 1.55 m (range 1.37, 1.71), weight 47.76 kg (range 33, 65). The IS children had right (Rt) T or TL curves. The mean T Cobb angle was 24 degrees and 26 in L. In the same group, the kyphotic apex (KA (VPDM)) distance was −125.82 mm (range −26, −184) and the lordotic apex (LA (VPDM)) distance was −321.65 mm (range −237, −417). The correlations of the ratio of distances (KA (VPDM))/(LA (VPDM)) with the Major Curve Cobb angle measurement and scoliometer findings were non-statistically significant (Pearson r = 0.077, −0.211, p: 0.768, 0.416, respectively. Similarly, in the control group, KA (VPDM))/(LA (VPDM) was not significantly correlated with scoliometer findings (Pearson r = −0.016, −p: 0.939). Discussion and conclusions: The lateral profile of the spine was commonly considered to be a primary aetiological factor of IS due to the fact that the kyphotic thoracic apex in IS is located in a higher thoracic vertebra (more vertebrae are posteriorly inclined), thus creating conditions of greater rotational instability and therefore greater vulnerability for IS development. Our findings do not confirm this hypothesis, since the correlation of the (VP-KA) to (VP-KA) ratio with the truncal asymmetry, assessed with the scoliometer and Cobb angle measurements, is non-statistically significant, in both groups A and B. In addition, the aforementioned ratio did not differ significantly between the two groups in our sample (0.39 ± 0.11 vs. 0.44 ± 0.08, p: 0.134). It is clear that hypokyphosis is not a primary causal factor for the commencing, mild or moderate scoliotic curve, as published elsewhere. We consider that the small thoracic hypokyphosis in developing scoliosis adds to the view that the reduced kyphosis, facilitating the axial rotation, could be considered as a permissive factor rather than a causal one, in the pathogenesis of IS. This view is consistent with previously published views and it is obviously the result of gravity, growth and muscle tone.

Variables affecting complication rates in type III paediatric supracondylar humerus fractures

Purpose Unstable supracondylar humerus (SCH) fractures may have different outcomes as a result of direction of displacement and pin configuration. This study evaluates the impact of fracture displacement, pin configuration and fellowship training on clinical and radiographic outcomes in unstable fractures. Methods A total of 99 patients with completely displaced type III fractures were identified at an academic centre and a local community hospital. Patient characteristics and the fellowship training of the treating surgeon were recorded, and injury films documented the direction of displacement. Pin configuration, coronal and sagittal alignment were recorded from postoperative radiographs and at healing. Radiographic outcomes including coronal, sagittal and rotational malunion as well as clinical complications were analyzed. Results Fractures with direct posterior displacement had a lower composite malunion rate compared with those with posterolateral (PL) or posteromedial (PM) displacement (6.9%, 36.4%, 29.2% respectively; p = 0.019). PM displacement had a higher rate of coronal malunion compared with PL (18.2% versus 0%; post hoc p = 0.024). All-lateral constructs resulted in more rotational malunions (20.9% versus 1.8%; p = 0.002) compared with crossed pinning. PL fractures treated with all-lateral fixation showed a trend toward increased rotational instability or malunion (23.8% versus 1.3%; p = 0.073). Higher composite complication rates were noted in patients treated by surgeons with non-paediatric, non-trauma fellowship training. Conclusion For displaced SCH fractures, all-lateral fixation is associated with higher rates of rotational instability and malunion. Posteromedially and posterolaterally displaced fractures have higher rates of malunion compared with fractures with straight posterior displacement. Fellowship training other than paediatric or trauma was associated with increased complications. Level of Evidence Level III

Fragmenting Active Asteroid 331P/Gibbs

We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space Telescope (HST) data taken between 2015 and 2018. 331P is an outer main belt active asteroid with a long-lived debris trail that formed in 2011. Embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1% of the mass of the primary nucleus. The largest shows a photometric range (∼1.5 mag), a V-shaped minimum, and a two-peaked lightcurve period near 9 hr, consistent with a symmetric contact binary. Less convincing explanations are that 331P-A is a monolithic, elongated splinter or that its surface shows hemispheric 4:1 albedo variations. The debris trail is composed of centimeter-sized and larger particles ejected with characteristic 10 cm s−1 speeds following a size distribution with index q = 3.7 ± 0.1 to 4.1 ± 0.2. The HST data show that earlier, ground-based measurements of the nucleus were contaminated by near-nucleus debris, which cleared by 2015. We find that the primary nucleus has effective radius 0.8 ± 0.1 km and is in rapid rotation (3.26 ± 0.01 hr), with a lightcurve range of 0.25 mag and a minimum density of 1600 kg m−3 if strengthless. The properties of 331P are consistent with (1) formation about 1.5 Myr ago by impact shattering of a precursor body, (2) spin-up by radiation torques to critical rotation, (3) ejection of about 1% of the nucleus mass in mid 2011 by rotational instability, and (4) subsequent evolution of the fragments and dispersal of the debris by radiation pressure.

Tactics of Two-Stage IOL Implantation in Difficult Refractive Cases

In a number of complex refractive cases, the achievement of an accurate refractive result cannot be guaranteed. Simultaneous implantation of a toric or multifocal IOL for the correction of complex ametropias may be accompanied by a significant deviation from the target refraction. The tactics of two-stage implantation with the usage of an additional Sulcoflex IOL for the final correction of astigmatism and possible residual spherical ametropia allows achieving emmetropia. In our study, this method was used in 15 patients with difficult refractive cases. Toric, multifocal, and multifocal toric Sulcoflex IOL were used. Implantation of all Sulcoflex modifications was performed through a 2.4 mm temporal incision using wound assisted technology. In cases of high degree hypermetropia, preventive iridectomy was performed using a 23G vitrectome. The target refraction was achieved in the entire observation group. In the postoperative period, no significant level of ophthalmic hypertension was registered. No cases of introlens opacification, iridocyclitis, or rotational instability were registered either.The method of two-stage IOL implantation allows achieving the target refraction in difficult refractive situations with almost guaranteed accuracy. The calculation method provides good predictability of the refractive result. This technology significantly expands the indications for intraocular correction using toric and multifocal IOL, as well as the limits of correction of high degree astigmatism. Our Sulcoflex IOL implantation experience has shown their high efficiency and safety.

Intraoperative pivot-shift accelerometry combined with anesthesia improves the measure of rotatory knee instability in anterior cruciate ligament injury

Purpose The knee stiffness acquired following an Anterior Cruciate Ligament (ACL) injury might affect clinical knee tests, i.e., the pivot-shift maneuver. In contrast, the motor effects of spinal anesthesia could favor the identification of rotatory knee deficiencies prior to ACL reconstruction. Hence, we hypothesized that the intra-operative pivot-shift maneuver under spinal anesthesia generates more acceleration in the lateral tibial plateau of patients with an injured ACL than without. Methods Seventy patients with unilateral and acute ACL rupture (62 men and 8 women, IKDC of 55.1 ± 13.8 pts) were assessed using the pivot-shift maneuver before and after receiving spinal anesthesia. A triaxial accelerometer was attached to the skin between Gerdys’ tubercle and the anterior tuberosity to measure the subluxation and reduction phases. Mixed ANOVA and multiple comparisons were performed considering the anesthesia and leg as factors (alpha = 5%). Results We found a higher acceleration in the injured leg measured under anesthesia compared to without anesthesia (5.12 ± 1.56 m.s− 2 vs. 2.73 ± 1.19 m.s− 2, p < 0.001), and compared to the non-injured leg (5.12 ± 1.56 m.s− 2 vs. 3.45 ± 1.35 m.s− 2, p < 0.001). There was a presence of significant interaction between leg and anesthesia conditions (p < 0.001). Conclusions The pivot-shift maneuver performed under anesthesia identifies better rotatory instability than without anesthesia because testing the pivot-shift without anesthesia underestimates the rotatory subluxation of the knee by an increased knee stiffness. Thus, testing under anesthesia provides a unique opportunity to determine the rotational instability prior to ACL reconstruction.

Clinical Outcomes of Anterolateral Ligament Reconstruction or Lateral Extra-articular Tenodesis Combined With Primary ACL Reconstruction: A Systematic Review With Meta-analysis

Background: Residual rotational instability after isolated anterior cruciate ligament reconstruction (ACLR) has been a challenge for many years. Anterolateral extra-articular procedures (AEAPs), including anterolateral ligament reconstruction (ALLR) or lateral extra-articular tenodesis (LET), are performed as a surgical option for additional rotational stability, but clear evidence for their usefulness is lacking. Purpose: To conduct a systematic review and meta-analysis of the literature regarding the efficacy of AEAP in primary ACLR. Study Design: Systematic review; Level of evidence, 3. Methods: A literature search, data extraction, and quality assessment were conducted by 2 independent reviewers. MEDLINE, EMBASE, and the Cochrane Library were searched in April 2020, following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. A total of 3444 studies were screened, and 20 studies (11 randomized controlled trials and 9 nonrandomized studies) were evaluated. Functional outcomes, stability, and complications were compared between patients who underwent primary ACLR with AEAP and those who underwent isolated primary ACLR. For subgroup analysis, outcomes were compared according to AEAP technique (ALLR vs LET) and time from injury to surgery (≤12 vs >12 months). The methodological quality of the included studies was assessed using the Cochrane risk-of-bias tool, Jadad scale, and Newcastle-Ottawa Scale. Results: Compared with isolated ACLR, combined ACLR with AEAP led to improved pivot-shift grades and graft failure rates, regardless of the AEAP technique or of time from injury to surgery. A limited, marginal improvement in subjective function score was observed in patients who underwent AEAP combined with ACLR. In contrast to ALLR, patients who underwent LET combined with ACLR had an increased risk of knee stiffness and adverse events. Conclusion: Our review suggests that when there is a need to improve rotational stability and subjective function, AEAP combined with primary ACLR can be considered regardless of time from injury. ALLR appeared to be a better option for improving rotational stability compared with LET.

Bent or broken: analysis of set screw fracture in the TFNa implant

Objectives To evaluate set screw fracture in the Trochanteric Femoral Nail Advanced implant (TFNa, Synthes, West Chester, PA) and to identify additional mechanisms of set screw failure in the TFNa. Materials and methods Patients who had experienced failure after open reduction and internal fixation (ORIF) with the TFNa were identified. TFNa implants were explanted and inspected following revision surgery. Medical device reports (MDRs) and manufacturer’s inspection reports describing similar failures for the TFNa in the United States Food and Drug Administration (FDA) Manufacturer and User Facility Device Experience (MAUDE) database were also reviewed. Results Four set screw fractures that occurred at a level II trauma center were observed. Sixty-seven reported failures were identified in the MAUDE database for review. Twenty-eight failed implants were returned to the manufacturer for inspection with a published inspection report available for analysis. Set screw fractures can occur in the TFNa when the set screw is deployed prematurely into the proximal screw aperture prior to blade/screw insertion. The set screw can also bend and deform if it is advanced against a helical blade/lag screw that is not fully seated into position, thereby potentially compromising its function. Conclusion The TFNa set screw allows for potential fracture during implant insertion leading to uncontrolled collapse, early excessive proximal femoral shortening, and rotational instability of the helical blade/lag screw. Similar failures in the TFNa can be prevented by having the surgeon inspect the proximal screw aperture after attachment of the proximal aiming aim to ensure the set screw has not been deployed prematurely. Level of evidence Therapeutic Level III.

A Surgical Algorithm According to Pivot-Shift Grade in Patients With ACL Injury: A Prospective Clinical and Radiological Evaluation

Background: Some patients have a positive pivot-shift finding and rotational instability after anterior cruciate ligament (ACL) reconstruction (ACLR). Three major pathologies known to affect the pivot-shift examination include ACL tear, anterolateral ligament injury, and loss of posterior lateral meniscus root function. Purpose: To describe a surgical algorithm determining indications for lateral extra-articular tenodesis (LET) based on intraoperative pivot-shift examination to prevent postoperative pivot shift and rotational instability and to evaluate the 2-year clinical and functional outcomes. Study Design: Case series; Level of evidence, 4. Methods: The study included 47 consecutive patients (39 men and 8 women) who underwent operative treatment for ACL injury between 2016 and 2017. Pivot-shift examination was performed under anesthesia, and the pivot shift was graded as grade 1 (glide), grade 2 (clunk), or grade 3 (gross). According to the surgical algorithm, single-bundle ACLR was performed in patients with grade 1 pivot shift. In patients with grade 2 with loss of posterior lateral meniscus root function, concurrent lateral meniscal repair was performed, and in patients with grade 2 with an intact lateral meniscus posterior root, concurrent extra-articular iliotibial band tenodesis was performed. Patients with grade 3 underwent ACLR, lateral meniscal repair, and LET. Clinical and radiographic evaluations were performed. Results: The mean age was 27.2 years (range, 16-56 years). In total, 26 (55.3%) patients were evaluated as having pivot-shift grade 1; 16 (34%) patients, grade 2; and 5 (10.6%) patients, grade 3. A total of 7 (14.9%) patients underwent LET in addition to ACLR. Two of these patients had pivot-shift grade 2, and LET was performed since the lateral meniscus posterior root was intact. In 14 of 16 patients with grade 2, lateral meniscus root disruption was detected, and lateral meniscal repair was performed. One patient was excluded from the further follow-up because of graft failure. At a mean postoperative follow-up of 29 months in 46 patients, the pivot-shift examination was negative in all patients. The mean Lysholm and International Knee Documentation Committee subjective scores were 95.35 ± 4.40 and 82.87 ± 9.36, respectively. Radiographic evidence of osteoarthritis was not detected. Conclusion: Only 14.9% of patients needed LET. With proper ACL, lateral meniscal, and anterolateral ligament surgery, it was possible to prevent positive pivot-shift findings postoperatively.

Proximal Overresection During Femoral Osteochondroplasty Negatively Affects the Distractive Stability of the Hip Joint: A Cadaver Study

Background: Contact between the acetabular labrum and articular cartilage of the femoral head creates a suction seal that helps maintain stability of the femoral head in the acetabulum. A femoral osteochodroplasty may occasionally extend proximally into the femoral head, diminishing the articular surface area available for sealing contact. Purpose: To determine whether proximal overresection decreases the rotational and distractive stability of the hip joint. Study Design: Controlled laboratory study. Methods: Six hemipelvises in the following conditions were tested: intact, T-capsulotomy, osteochondroplasty to the physeal scar, and 5- and 10-mm proximal extension. The pelvis was secured to a metal plate, and the femur was potted and attached to a multiaxial hip jig. Specimens were axially distracted using a load from 0 to 150 N. For rotational stability testing, 5 N·m of internal and external torque was applied. Both tests were performed at different angles of flexion (0°, 15°, 30°, 60°, 90°). Displacement and rotation were recorded using a 3-dimensional motion tracking system. Results: The T-capsulotomy decreased the distractive stability of the hip joint. A femoral osteochondroplasty up to the physeal scar did not seem to affect the distractive stability. However, a proximal extension of the resection by 5 and 10 mm increased axial instability at every angle of flexion tested, with the greatest increase observed at larger angles of flexion ( P < .01). External rotation increased significantly after T-capsulotomy in smaller angles of flexion (0°, P = .01; 15°, P = .01; 30°, P = .03). Femoral osteochondroplasty did not create further external rotational instability, except when the resection was extended 10 mm proximally and the hip was in 90° of flexion ( P = .04). Conclusion: This cadaveric study demonstrated that proximal extension of osteochondroplasty into the femoral head compromises the distractive stability of the hip joint but does not affect hip rotational stability. Clinical Relevance: Clinically, this study highlights the importance of accuracy when performing femoral osteochondroplasty to minimize proximal extension that may increase iatrogenic instability of the hip joint.