High Energy Transsyndesmotic Ankle Fracture Dislocation - Does Deltoid Ligament Repair Influence the Progression of Posttraumatic Arthritis in Logsplitter Injuries?

OBJECTIVE: To determine the effect of deltoid ligament repair on the development of posttraumatic arthritis in logsplitter ankle injuries. METHODS: Design: Retrospective cohort. SETTING: Academic, Level I trauma center. PATIENT SELECTION CRITERIA: Patients ≥18 years of age with logsplitter injuries (OTA/AO 44B, 44C) treated with open reduction internal fixation with or without deltoid ligament repair from January 2008 to October 2021. OUTCOME MEASURES AND COMPARISON: The rate of posttraumatic arthritis (PTOA) development at final follow-up (minimum 6 months) after open reduction internal fixation was evaluated using the Kellgren-Lawrence scale. The achievement of acceptable reduction indicated by articular reduction <2mm, and a medial clear space ≤4mm was assessed at 6 weeks postoperatively with weightbearing radiographs. The effect of deltoid ligament repair on the development of PTOA was investigated. RESULTS: Fifty-nine patients aged 49.1 ± 17.2 years met inclusion criteria with a mean follow up of 16.6 months (range = 6 to 96). Twenty-six of 59 patients (44%) had developed PTOA at final follow-up. Acceptable reduction was achieved in 83.1% (49/59) of fractures. The acceptable reduction rate in fractures undergoing deltoid ligament repair was 100% versus 78% in those without deltoid ligament repair (13/13 vs. 36/46, p=0.017). The rate of PTOA development was significantly lower in patients who underwent deltoid ligament repair (15%) compared to those who did not (52%), p=0.026. Patients who underwent deltoid ligament repair had a significantly reduced rate of PTOA development leading to arthrodesis compared to those who did not (0% vs. 17%, p=0.013). CONCLUSIONS: Logsplitter injuries resulted in a high rate of development of posttraumatic arthritis. An acceptable reduction is required to minimize risk of development of PTOA and progression to arthrodesis. Deltoid ligament repair during open reduction internal fixation may facilitate acceptable reduction, decrease the rate of PTOA and progression to arthrodesis in these injuries. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Condensate interfaces can accelerate protein aggregation.

Protein aggregates, formed from the assembly of aberrant, misfolded proteins, are a hallmark of neurodegenerative diseases. Disease-associated aggregates such as mutant Huntingtin polyQ inclusions, are typically enriched in p62/SQSTM1, an oligomeric protein that binds to and sequesters aberrant proteins. p62 has been suggested to sequester proteins through formation of liquid-like biomolecular condensates, but the physical mechanisms by which p62 condensates may regulate pathological protein aggregation remain unclear. Here, we use a light-inducible biomimetic condensate system to show that p62 condensates enhance coarsening of mutant polyQ aggregates through interface-mediated sequestration, which accelerates polyQ accumulation into larger aggregates. However, the resulting large aggregates accumulate polyubiquitinated proteins, which depletes free p62, ultimately suppressing further p62 condensation. This dynamic interplay between interface-mediated coarsening of solid aggregates and downstream consequences on the phase behavior of associated regulatory proteins could contribute to the onset and progression of protein aggregation diseases.

Poly(GR) interacts with key stress granule factors promoting its assembly into cytoplasmic inclusions.

C9orf72 repeat expansions are the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Poly(GR) proteins are toxic to neurons by forming cytoplasmic inclusions that sequester RNA-binding proteins including stress granule (SG) proteins. However, little is known of the factors governing poly(GR) inclusion formation. Here, we show that poly(GR) infiltrates a finely tuned network of protein-RNA interactions underpinning SG formation. It interacts with G3BP1, the key driver of SG assembly and a protein we found is critical for poly(GR) inclusion formation. Moreover, we discovered that N6-methyladenosine (m6A)-modified mRNAs and m6A-binding YTHDF proteins not only co-localize with poly(GR) inclusions in brains of c9FTD/ALS mouse models and patients with c9FTD, they promote poly(GR) inclusion formation via the incorporation of RNA into the inclusions. Our findings thus suggest that interrupting interactions between poly(GR) and G3BP1 or YTHDF1 proteins or decreasing poly(GR) altogether represent promising therapeutic strategies to combat c9FTD/ALS pathogenesis.

Reamed compared with unreamed nailing of tibial shaft fractures: Does the initial method of nail insertion influence outcome in patients requiring reoperations?

BACKGROUND: Patients with a tibial shaft fracture experiencing their first postoperative complication following treatment with intramedullary nails may be at greater risk of subsequent complications than the whole population. We aimed to determine whether the initial method of nail insertion influences outcome in patients with a tibial shaft fracture requiring multiple reoperations. METHODS: Using the Study to Prospectively Evaluate Reamed Intramedullary Nails in Tibial Shaft Fractures trial data, we categorized patients as those not requiring reoperation, those requiring a single reoperation and those requiring multiple reoperations, and we compared them by nail insertion technique (reamed v. unreamed) and fracture type (open v. closed). We then determined the number of patients whose first reoperation was in response to infection, and we compared other clinical outcomes between the reamed and unreamed groups. RESULTS: Among 1226 patients included in this analysis, 175 (14.27%) experienced a single reoperation and 44 patients (3.59%) underwent multiple reoperations. Nail insertion techniques (reamed v. unreamed) did not play a role in the need to perform multiple reoperations. Seventy-five percent of patients requiring multiple reoperations had open tibial shaft fractures. An equal number of these were reamed and unreamed insertions. The majority of patients had their course complicated by infection and almost 50% of patients whose first reoperation was for infection required more than 2 reoperations for management. The rest required multiple procedures for nonunion or bone loss. CONCLUSION: Our findings corroborate those of other studies, in which open fracture type rather than nail insertion technique was found to be the cause of morbidity following intramedullary nailing of tibial fractures. CLINICAL TRIAL REGISTRATION: www. CLINICALTRIALS: gov, no. NCT00038129.

Postfasciotomy Classification System for Acute Compartment Syndrome of the Leg.

OBJECTIVE: Acute compartment syndrome (ACS) is a true emergency. Even with urgent fasciotomy, there is often muscle damage and need for further surgery. Although ACS is not uncommon, no validated classification system exists to aid in efficient and clear communication. The aim of this study was to establish and validate a classification system for the consequences of ACS treated with fasciotomy. METHODS: Using a modified Delphi method, an international panel of ACS experts was assembled to establish a grading scheme for the disease and then validate the classification system. The goal was to articulate discrete grades of ACS related to fasciotomy findings and associated costs. A pilot analysis was used to determine questions that were clear to the respondents. Discussion of this analysis resulted in another round of cases used for 24 other raters. The 24 individuals implemented the classification system 2 separate times to compare outcomes for 32 clinical cases. The accuracy and reproducibility of the classification system were subsequently calculated based on the providers' responses. RESULTS: The Fleiss Kappa of all raters was at 0.711, showing a strong agreement between the 24 raters. Secondary validation was performed for paired 276 raters and correlation was tested using the Kendall coefficient. The median correlation coefficient was 0.855. All 276 pairs had statistically significant correlation. Correlation coefficient between the first and second rating sessions was strong with the median pair scoring at 0.867. All surgeons had statistically significant internal consistency. CONCLUSION: This new ACS classification system may be applied to better understand the impact of ACS on patient outcomes and economic costs for leg ACS.

DnaJC7 specifically regulates tau seeding.

Neurodegenerative tauopathies are caused by accumulation of toxic tau protein assemblies. This appears to involve template-based seeding events, whereby tau monomer changes conformation and is recruited to a growing aggregate. Several large families of chaperone proteins, including Hsp70s and J domain proteins (JDPs), cooperate to regulate the folding of intracellular proteins such as tau, but the factors that coordinate this activity are not well known. The JDP DnaJC7 binds tau and reduces its intracellular aggregation. However, it is unknown whether this is specific to DnaJC7 or if other JDPs might be similarly involved. We used proteomics within a cell model to determine that DnaJC7 co-purified with insoluble tau and colocalized with intracellular aggregates. We individually knocked out every possible JDP and tested the effect on intracellular aggregation and seeding. DnaJC7 knockout decreased aggregate clearance and increased intracellular tau seeding. This depended on the ability of the J domain (JD) of DnaJC7 to stimulate Hsp70 ATPase activity, as JD mutations that block this interaction abrogated the protective activity. Disease-associated mutations in the JD and substrate binding site of DnaJC7 also abolished its protective activity. DnaJC7 thus specifically regulates tau aggregation in cooperation with Hsp70.

Size distributions of intracellular condensates reflect competition between coalescence and nucleation.

Phase separation of biomolecules into condensates has emerged as a mechanism for intracellular organization and affects many intracellular processes, including reaction pathways through the clustering of enzymes and pathway intermediates. Precise and rapid spatiotemporal control of reactions by condensates requires tuning of their sizes. However, the physical processes that govern the distribution of condensate sizes remain unclear. Here we show that both native and synthetic condensates display an exponential size distribution, which is captured by Monte Carlo simulations of fast nucleation followed by coalescence. In contrast, pathological aggregates exhibit a power-law size distribution. These distinct behaviours reflect the relative importance of nucleation and coalescence kinetics. We demonstrate this by utilizing a combination of synthetic and native condensates to probe the underlying physical mechanisms determining condensate size. The appearance of exponential distributions for abrupt nucleation versus power-law distributions under continuous nucleation may reflect a general principle that determines condensate size distributions.

DnaJC7 specifically regulates tau seeding.

Neurodegenerative tauopathies are caused by accumulation of toxic tau protein assemblies. This appears to involve template-based seeding events, whereby tau monomer changes conformation and is recruited to a growing aggregate. Several large families of chaperone proteins, including Hsp70s and J domain proteins (JDPs) cooperate to regulate the folding of intracellular proteins such as tau, but the factors that coordinate this activity are not well known. The JDP DnaJC7 binds tau and reduces its intracellular aggregation. However, it is unknown whether this is specific to DnaJC7 or if other JDPs might be similarly involved. We used proteomics within a cell model to determine that DnaJC7 co-purified with insoluble tau and colocalized with intracellular aggregates. We individually knocked out every possible JDP and tested the effect on intracellular aggregation and seeding. DnaJC7 knockout decreased aggregate clearance and increased intracellular tau seeding. This depended on the ability of the J domain (JD) of DnaJC7 to bind to Hsp70, as JD mutations that block binding to Hsp70 abrogated the protective activity. Disease-associated mutations in the JD and substrate binding site of DnaJC7 also abrogated its protective activity. DnaJC7 thus specifically regulates tau aggregation in cooperation with Hsp70.

The AAA+ chaperone VCP disaggregates Tau fibrils and generates aggregate seeds in a cellular system.

Amyloid-like aggregates of the microtubule-associated protein Tau are associated with several neurodegenerative disorders including Alzheimer's disease. The existence of cellular machinery for the removal of such aggregates has remained unclear, as specialized disaggregase chaperones are thought to be absent in mammalian cells. Here we show in cell culture and in neurons that the hexameric ATPase valosin-containing protein (VCP) is recruited to ubiquitylated Tau fibrils, resulting in their efficient disaggregation. Aggregate clearance depends on the functional cooperation of VCP with heat shock 70 kDa protein (Hsp70) and the ubiquitin-proteasome machinery. While inhibition of VCP activity stabilizes large Tau aggregates, disaggregation by VCP generates seeding-active Tau species as byproduct. These findings identify VCP as a core component of the machinery for the removal of neurodegenerative disease aggregates and suggest that its activity can be associated with enhanced aggregate spreading in tauopathies.

Factors Predictive of Early Complications Following Total Ankle Arthroplasty.

Background: The safety of outpatient total ankle arthroplasty (TAA), and factors predictive of early complications are poorly understood. The objective of this study was to determine the frequency of early complications in patients undergoing outpatient TAA compared to a matched inpatient TAA cohort. Factors predictive of early complications following TAA are elucidated. Methods: A retrospective review of prospectively collected data from the 2011-2018 American College of Surgeons-National Surgical Quality Improvement Program (ACS-NSQIP) database was performed. An unadjusted analysis comparing complication rates in outpatient, and inpatient TAA was performed followed by a propensity score-matched cohort analysis. A multivariate logistic regression model was then used to identify significant independent predictors for complications, reoperation, and readmission following TAA. Results: A total of 1487 patients (198 outpatient, 1289 inpatient) undergoing TAA were included in the study. Inpatient TAA was associated with increased 30-day readmission compared with outpatient TAA (3.54% vs 0.51%, P = .032) in a matched cohort analysis. Thirty-eight (2.6%) patients had a minor complication, with 16 (1.1%) patients having a major complication after TAR. Nineteen (1.3%) patients underwent reoperation, and 42 (2.8%) patients were readmitted within 30 days of the index TAR. Multivariate analysis identified factors predictive of early complications to include length of stay (LOS) >2 days, smoking, hypertension, bleeding disorders, and diabetes mellitus. Conclusion: From this relatively limited data set, outpatient TAA appears to be safe for management of end-stage ankle arthritis in select patients. Inpatient status was associated with an increased rate of 30-day readmission following TAA. Postoperative length of stay >2 days, smoking, hypertension, bleeding disorders, and diabetes mellitus were identified to be associated with early postoperative complications following TAA in this cohort. Level of Evidence: Level III, retrospective cohort study.

Preoperative photography improves patient satisfaction following hallux valgus surgery.

BACKGROUND: Patient satisfaction is variable following hallux valgus (HV) surgery. This prospective, blinded, randomized trial endeavored to determine whether showing patients a preoperative photograph would improve satisfaction following HV corrective surgery. METHODS: Adult patients undergoing HV surgery were randomized to a picture group (P) or a no picture group (NP). P-group patients were shown their preoperative photograph for 5 min at each postoperative visit. Outcome measures included the Foot Function Index (FFI), the Foot Ankle Outcome Score (FAOS), and a patient satisfaction questionnaire. RESULTS: Twenty-nine patients were enrolled in the study (15P, 14 NP). At 3, and 6 months postoperatively, patients in the P-group were more likely to be completely satisfied with the appearance of their foot. There were no differences between groups with respect to postoperative HVA, IMA, or FFI, and FAOS scores. CONCLUSION: Patient satisfaction is increased following hallux valgus corrective surgery by reminding patients of the preoperative appearance of their foot through the use of photographs. LEVEL OF EVIDENCE: Level I, randomized control trial.

High-Energy Transsyndesmotic Ankle Fracture Dislocation-Injury Characteristics, Radiographic Outcomes, and Factors Affecting the Rate of Posttraumatic Arthritis in Logsplitter Injuries.

OBJECTIVES: To investigate patient demographics, injury characteristics, radiographic outcomes, and identify risk factors for developing posttraumatic arthritis in high-energy transsyndesmotic ankle fracture dislocations or "logsplitter" injuries. DESIGN: Retrospective cohort study. SETTING: Academic level one trauma center. PATIENTS/PARTICIPANTS: Twenty-seven adult patients with logsplitter injuries. INTERVENTION: All patients were treated with open reduction internal fixation, with possible addition of syndesmosis screw(s) and deltoid repair. MAIN OUTCOME MEASUREMENTS: The rate of posttraumatic arthritis at one year along with rate and reasons for reoperation. RESULTS: Twenty-seven patients were included with a mean follow-up of 14.5 ± 12.5 months. At one-year postoperative, 14 of the 20 patients (70%) demonstrated posttraumatic arthritis. Two patients (7.4%) went onto fusion. The reoperation rate was 51.9%. There was no significant difference in the arthritis rate with the number of syndesmosis screws used, quality of reduction, or addition of deltoid repair. CONCLUSIONS: The logsplitter injury is one with devastating outcomes and high rates of arthritis; it should be considered separately from conventional ankle fractures. The role of deltoid repair remains unclear. Further study of this injury pattern is required. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Early radiographic outcomes following deltoid ligament repair in bimalleolar equivalent ankle fractures.

BACKGROUND: Indications for deltoid ligament repair in bimalleolar equivalent ankle fractures are unclear. This study compared radiographic outcomes in bimalleolar equivalent ankle fractures undergoing open reduction internal fixation (ORIF) +/- deltoid ligament repair. METHODS: A retrospective review of 1024 ankle fractures was performed. Bimalleolar equivalent injuries treated with ORIF +/- deltoid ligament repair were included. Radiographic assessment was performed preoperatively, and at three months postoperatively. RESULTS: One hundred and forty-seven ankle fractures met inclusion criteria with 46 undergoing deltoid ligament repairs. There was a significant decrease in medial clear space (1.93 ± 0.65 mm vs. 2.26 ± 0.64 mm, p = 0.01), and tibiofibular clear space (3.89 ± 1.20 mm vs. 4.87 ± 1.37 mm, p = 0.0001) at 3 months postoperative in the deltoid repair group compared to the no repair group. When syndesmotic fixation was performed, there were no differences between groups. CONCLUSION: Deltoid ligament repair in bimalleolar equivalent ankle fractures resulted in reduced medial clear space, and tibiofibular clear space in the early postoperative period. These differences were small and remained within established normal limits. LEVEL OF CLINICAL EVIDENCE: Level III, retrospective cohort study.

Nucleation landscape of biomolecular condensates.

All structures within living cells must form at the right time and place. This includes condensates such as the nucleolus, Cajal bodies and stress granules, which form via liquid-liquid phase separation of biomolecules, particularly proteins enriched in intrinsically disordered regions (IDRs)1,2. In non-living systems, the initial stages of nucleated phase separation arise when thermal fluctuations overcome an energy barrier due to surface tension. This phenomenon can be modelled by classical nucleation theory (CNT), which describes how the rate of droplet nucleation depends on the degree of supersaturation, whereas the location at which droplets appear is controlled by interfacial heterogeneities3,4. However, it remains unknown whether this framework applies in living cells, owing to the multicomponent and highly complex nature of the intracellular environment, including the presence of diverse IDRs, whose specificity of biomolecular interactions is unclear5-8. Here we show that despite this complexity, nucleation in living cells occurs through a physical process similar to that in inanimate materials, but the efficacy of nucleation sites can be tuned by their biomolecular features. By quantitatively characterizing the nucleation kinetics of endogenous and biomimetic condensates in living cells, we find that key features of condensate nucleation can be quantitatively understood through a CNT-like theoretical framework. Nucleation rates can be substantially enhanced by compatible biomolecular (IDR) seeds, and the kinetics of cellular processes can impact condensate nucleation rates and specificity of location. This quantitative framework sheds light on the intracellular nucleation landscape, and paves the way for engineering synthetic condensates precisely positioned in space and time.

Impact of centre volume, surgeon volume, surgeon experience and geographic location on reoperation after intramedullary nailing of tibial shaft fractures

Background: Tibial shaft fractures are the most common long-bone injury, with a reported annual incidence of more than 75 000 in the United States. This study aimed to determine whether patients with tibial fractures managed with intramedullary nails experience a lower rate of reoperation if treated at higher-volume hospitals, or by higher-volume or more experienced surgeons. Methods: The Study to Prospectively Evaluate Reamed Intramedullary Nails in Patients with Tibial Fractures (SPRINT) was a multicentre randomized clinical trial comparing reamed and nonreamed intramedullary nailing on rates of reoperation to promote fracture union, treat infection or preserve the limb in patients with open and closed fractures of the tibial shaft. Using data from SPRINT, we quantified centre and surgeon volumes into quintiles. We performed analyses adjusted for type of fracture (open v. closed), type of injury (isolated v. multitrauma), gender and age for the primary outcome of reoperation using multivariable logistic regression. Results: There were no significant differences in the odds of reoperation between high- and low-volume centres (p = 0.9). Overall, surgeon volume significantly affected the odds of reoperation (p = 0.03). The odds of reoperation among patients treated by moderate-volume surgeons were 50% less than those among patients treated by verylow-volume surgeons (odds ratio [OR] 0.50, 95% confidence interval [CI] 0.28­0.88), and the odds of reoperation among patients treated by high-volume surgeons were 47% less than those among patients treated by very-low-volume surgeons (OR 0.53, 95% CI 0.30­0.93). Conclusion: There appears to be no significant additional patient benefit in treatment by a higher-volume centre for intramedullary fixation of tibial shaft fractures. Additional research on the effects of surgical and clinical site volume in tibial shaft fracture management is needed to confirm this finding. The odds of reoperation were higher in patients treated by very-low-volume surgeons; this finding may be used to optimize the results of tibial shaft fracture management. Clinical trial registration: ClinicalTrials.gov, NCT00038129

Contexte: La fracture de la diaphyse tibiale est la plus commune des fractures des os longs, avec une incidence annuelle déclarée de plus 75 000 cas aux États-Unis. Cette étude visait à déterminer si les patients traités par enclouage intramédullaire pour une fracture du tibia sont moins souvent réopérés quand l'intervention est effectuée dans des établissements qui traitent de plus forts volumes de cas ou par des chirurgiens opérant un plus fort volume de cas ou plus expérimentés. Méthodes: L'étude SPRINT (Study to Prospectively Evaluate Reamed Intramedullary Nails in Patients with Tibial Fractures) est un essai clinique multicentrique randomisé qui a comparé l'effet de l'enclouage alésé c. non alésé sur le taux des réinterventions visant à promouvoir la consolidation osseuse de la fracture, à traiter une infection ou à préserver le membre chez des patients victimes de fractures fermées ou ouvertes de la diaphyse tibiale. À partir des données de l'étude SPRINT, nous avons classé les établissements et les chirurgiens en quintiles selon les volumes de cas traités. Nous avons effectué des analyses ajustées en fonction du type de fracture (ouverte c. fermée), du type de blessure (isolée c. polytraumatisme), du sexe et de l'âge, pour établir le taux de réintervention (paramètre principal), en utilisant la régression logistique multivariée. Résultats: On n'a noté aucune différence significative quant au risque de réintervention entre les centres qui traitaient des volumes élevés c. bas (p = 0,9). Dans l'ensemble le volume d'opérations des chirurgiens a significativement influé sur le risque de réintervention (p = 0,03). Le risque de réintervention chez les patients traités par des chirurgiens dont le volume d'interventions était moyen était de 50 % de moins que chez les patients traités par des chirurgiens dont le volume était très bas (risque relatif [RR] 0,50, intervalle de confiance [IC] à 95 % 0,28­0,88) et le risque de réintervention chez les patients traités par des chirurgiens dont le volume était très élevé était de 47 % de moins que chez les patients traités par des chirurgiens dont le volume était très bas (RR 0,53, IC à 95 % 0,30­0,93). Conclusion: Il ne semble y avoir aucun bienfait additionnel significatif au fait d'être opéré dans un centre où le volume d'interventions pour enclouage intramédullaire des fractures de la diaphyse tibiale est élevé. Il faudra approfondir la recherche sur les effets du volume chirurgical et de l'expérience clinique des établissements pour confirmer cette observation. Le risque de réintervention a été plus élevé chez les patients traités par des chirurgiens dont le volume d'interventions était très bas; cette observation pourrait être utilisée pour optimiser l'issue du traitement des fractures de la diaphyse tibiale. Enregistrement de l'essai clinique : ClinicalTrials. gov, NCT00038129.

SARS-CoV-2 requires cholesterol for viral entry and pathological syncytia formation.

Many enveloped viruses induce multinucleated cells (syncytia), reflective of membrane fusion events caused by the same machinery that underlies viral entry. These syncytia are thought to facilitate replication and evasion of the host immune response. Here, we report that co-culture of human cells expressing the receptor ACE2 with cells expressing SARS-CoV-2 spike, results in synapse-like intercellular contacts that initiate cell-cell fusion, producing syncytia resembling those we identify in lungs of COVID-19 patients. To assess the mechanism of spike/ACE2-driven membrane fusion, we developed a microscopy-based, cell-cell fusion assay to screen ~6000 drugs and >30 spike variants. Together with quantitative cell biology approaches, the screen reveals an essential role for biophysical aspects of the membrane, particularly cholesterol-rich regions, in spike-mediated fusion, which extends to replication-competent SARS-CoV-2 isolates. Our findings potentially provide a molecular basis for positive outcomes reported in COVID-19 patients taking statins and suggest new strategies for therapeutics targeting the membrane of SARS-CoV-2 and other fusogenic viruses.

Composition-dependent thermodynamics of intracellular phase separation.

Intracellular bodies such as nucleoli, Cajal bodies and various signalling assemblies represent membraneless organelles, or condensates, that form via liquid-liquid phase separation (LLPS)1,2. Biomolecular interactions-particularly homotypic interactions mediated by self-associating intrinsically disordered protein regions-are thought to underlie the thermodynamic driving forces for LLPS, forming condensates that can facilitate the assembly and processing of biochemically active complexes, such as ribosomal subunits within the nucleolus. Simplified model systems3-6 have led to the concept that a single fixed saturation concentration is a defining feature of endogenous LLPS7-9, and has been suggested as a mechanism for intracellular concentration buffering2,7,8,10. However, the assumption of a fixed saturation concentration remains largely untested within living cells, in which the richly multicomponent nature of condensates could complicate this simple picture. Here we show that heterotypic multicomponent interactions dominate endogenous LLPS, and give rise to nucleoli and other condensates that do not exhibit a fixed saturation concentration. As the concentration of individual components is varied, their partition coefficients change in a manner that can be used to determine the thermodynamic free energies that underlie LLPS. We find that heterotypic interactions among protein and RNA components stabilize various archetypal intracellular condensates-including the nucleolus, Cajal bodies, stress granules and P-bodies-implying that the composition of condensates is finely tuned by the thermodynamics of the underlying biomolecular interaction network. In the context of RNA-processing condensates such as the nucleolus, this manifests in the selective exclusion of fully assembled ribonucleoprotein complexes, providing a thermodynamic basis for vectorial ribosomal RNA flux out of the nucleolus. This methodology is conceptually straightforward and readily implemented, and can be broadly used to extract thermodynamic parameters from microscopy images. These approaches pave the way for a deeper understanding of the thermodynamics of multicomponent intracellular phase behaviour and its interplay with the nonequilibrium activity that is characteristic of endogenous condensates.

Competing Protein-RNA Interaction Networks Control Multiphase Intracellular Organization.

Liquid-liquid phase separation (LLPS) mediates formation of membraneless condensates such as those associated with RNA processing, but the rules that dictate their assembly, substructure, and coexistence with other liquid-like compartments remain elusive. Here, we address the biophysical mechanism of this multiphase organization using quantitative reconstitution of cytoplasmic stress granules (SGs) with attached P-bodies in human cells. Protein-interaction networks can be viewed as interconnected complexes (nodes) of RNA-binding domains (RBDs), whose integrated RNA-binding capacity determines whether LLPS occurs upon RNA influx. Surprisingly, both RBD-RNA specificity and disordered segments of key proteins are non-essential, but modulate multiphase condensation. Instead, stoichiometry-dependent competition between protein networks for connecting nodes determines SG and P-body composition and miscibility, while competitive binding of unconnected proteins disengages networks and prevents LLPS. Inspired by patchy colloid theory, we propose a general framework by which competing networks give rise to compositionally specific and tunable condensates, while relative linkage between nodes underlies multiphase organization.

Impaction fractures of the anterior tibial plafond: Outcomes after fractures around the ankle: Is the anterior impaction plafond fracture a problem?

OBJECTIVES: To determine whether patients with AO/OTA 43-B anterior impaction tibial plafond fractures have worse clinical outcomes, and an increased risk of progression to ankle arthrodesis. DESIGN: Retrospective cohort study. SETTING: Level 1 academic trauma center. PATIENTS: One hundred sixty-eight patients were included in the study, all of whom had tibial plafond fractures. INTERVENTION: Study patients underwent external fixation and/or open reduction internal fixation (ORIF) as indicated by fracture/injury pattern. MAIN OUTCOME MEASUREMENTS: Arthrodesis rate. RESULTS: AO 43-B Anterior impaction tibial plafond fractures have an increased risk of progression to arthrodesis when compared to AO 43-B nonanterior impaction type fractures (19.4% vs 8%). CONCLUSIONS: AO 43-B anterior impaction tibial plafond fractures have a worse clinical outcome compared to AO 43-B nonanterior impaction fractures. These fractures also confer increased risk of progression to arthrodesis. CONFLICTS OF INTEREST: The authors have no conflict of interests to declare.