Latitudinal patterns in stabilizing density dependence of forest communities.

Numerous studies have shown reduced performance in plants that are surrounded by neighbours of the same species1,2, a phenomenon known as conspecific negative density dependence (CNDD)3. A long-held ecological hypothesis posits that CNDD is more pronounced in tropical than in temperate forests4,5, which increases community stabilization, species coexistence and the diversity of local tree species6,7. Previous analyses supporting such a latitudinal gradient in CNDD8,9 have suffered from methodological limitations related to the use of static data10-12. Here we present a comprehensive assessment of latitudinal CNDD patterns using dynamic mortality data to estimate species-site-specific CNDD across 23 sites. Averaged across species, we found that stabilizing CNDD was present at all except one site, but that average stabilizing CNDD was not stronger toward the tropics. However, in tropical tree communities, rare and intermediate abundant species experienced stronger stabilizing CNDD than did common species. This pattern was absent in temperate forests, which suggests that CNDD influences species abundances more strongly in tropical forests than it does in temperate ones13. We also found that interspecific variation in CNDD, which might attenuate its stabilizing effect on species diversity14,15, was high but not significantly different across latitudes. Although the consequences of these patterns for latitudinal diversity gradients are difficult to evaluate, we speculate that a more effective regulation of population abundances could translate into greater stabilization of tropical tree communities and thus contribute to the high local diversity of tropical forests.

Climate change determines the sign of productivity trends in US forests.

Forests are integral to the global land carbon sink, which has sequestered ~30% of anthropogenic carbon emissions over recent decades. The persistence of this sink depends on the balance of positive drivers that increase ecosystem carbon storage-e.g., CO2 fertilization-and negative drivers that decrease it-e.g., intensifying disturbances. The net response of forest productivity to these drivers is uncertain due to the challenge of separating their effects from background disturbance-regrowth dynamics. We fit non-linear models to US forest inventory data (113,806 plot remeasurements in non-plantation forests from ~1999 to 2020) to quantify productivity trends while accounting for stand age, tree mortality, and harvest. Productivity trends were generally positive in the eastern United States, where climate change has been mild, and negative in the western United States, where climate change has been more severe. Productivity declines in the western United States cannot be explained by increased mortality or harvest; these declines likely reflect adverse climate-change impacts on tree growth. In the eastern United States, where data were available to partition biomass change into age-dependent and age-independent components, forest maturation and increasing productivity (likely due, at least in part, to CO2 fertilization) contributed roughly equally to biomass carbon sinks. Thus, adverse effects of climate change appear to overwhelm any positive drivers in the water-limited forests of the western United States, whereas forest maturation and positive responses to age-independent drivers contribute to eastern US carbon sinks. The future land carbon balance of forests will likely depend on the geographic extent of drought and heat stress.

The unexpected influence of legacy conspecific density dependence.

When plants die, neighbours escape competition. Living conspecifics could disproportionately benefit because they are freed from negative intraspecific processes; however, if the negative effects of past conspecific neighbours persist, other species might be advantaged, and diversity might be maintained through legacy effects. We examined legacy effects in a mapped forest by modelling the survival of 37,212 trees of 23 species using four neighbourhood properties: living conspecific, living heterospecific, legacy conspecific (dead conspecifics) and legacy heterospecific densities. Legacy conspecific effects proved nearly four times stronger than living conspecific effects; changes in annual survival associated with legacy conspecific density were 1.5% greater than living conspecific effects. Over 90% of species were negatively impacted by legacy conspecific density, compared to 47% by living conspecific density. Our results emphasize that legacies of trees alter community dynamics, revealing that prior research may have underestimated the strength of density dependent interactions by not considering legacy effects.

Oaks enhance early life stage longleaf pine growth and density in a subtropical xeric savanna.

The interplay of positive and negative species interactions controls species assembly in communities. Dryland plant communities, such as savannas, are important to global biodiversity and ecosystem functioning. Sandhill oaks in xeric savannas of the southeastern United States can facilitate longleaf pine by enhancing seedling survival, but the effects of oaks on recruitment and growth of longleaf pine have not been examined. We censused, mapped, and monitored nine contiguous hectares of longleaf pine in a xeric savanna to quantify oak-pine facilitation, and to examine other factors impacting recruitment, such as vegetation cover and longleaf pine tree density. We found that newly recruited seedlings and grass stage longleaf pines were more abundant in oak-dominated areas where densities were 230% (newly recruited seedlings) and 360% (grass stage) greater from lowest to highest oak neighborhood densities. Longleaf pine also grew faster under higher oak density. Longleaf pine recruitment was lowest under longleaf pine canopies. Mortality of grass stage and bolt stage longleaf pine was low (~1.0% yr-1) in the census interval without fire. Overall, our findings highlight the complex interactions between pines and oaks-two economically and ecologically important genera globally. Xeric oaks should be incorporated as a management option for conservation and restoration of longleaf pine ecosystems.

Outcomes of Iliac Wing Fractures: A Systematic Review of the Literature.

To review the literature on iliac wing fractures to assess outcomes of operative and nonoperative treatment. A search of PubMed, MEDLINE, and Cochrane Database of Systematic Reviews was performed. Articles reporting on iliac wing fractures without pelvic ring destabilization or intraarticular extension were included. Study information and patient data were collected, and a Methodological Index for Non-randomized Studies (MINORS) score was assigned to each article. In total, 19,363 articles were identified with 32 qualifying for inclusion. The articles included 131 patients with 133 fractures. The mean age was 43.6, and mean follow-up time was 41.9 months. Forty-eight (36%) fractures were treated operatively, and 85 (64%) were treated nonoperatively. Associated injuries included bowel injuries, other pelvic fractures, gunshot wounds, and arterial injuries. There is an absence of comparative studies between operative and nonoperative management of iliac wing fractures. Indications for operative management appear to depend on comminution, open fractures, and associated injuries. (Journal of Surgical Orthopaedic Advances 32(3):139-147, 2023).

Synthesis and characterisation of new antimalarial fluorinated triazolopyrazine compounds.

Nine new fluorinated analogues were synthesised by late-stage functionalisation using Diversinate™ chemistry on the Open Source Malaria (OSM) triazolopyrazine scaffold (Series 4). The structures of all analogues were fully characterised by NMR, UV and MS data analysis; three triazolopyrazines were confirmed by X-ray crystal structure analysis. The inhibitory activity of all compounds against the growth of the malaria parasite Plasmodium falciparum (3D7 and Dd2 strains) and the cytotoxicity against a human embryonic kidney (HEK293) cell line were tested. Some of the compounds demonstrated moderate antimalarial activity with IC50 values ranging from 0.2 to >80 µM; none of the compounds displayed any cytotoxicity against HEK293 cells at 80 µM. Antimalarial activity was significantly reduced when C-8 of the triazolopyrazine scaffold was substituted with CF3 and CF2H moieties, whereas incorporation of a CF2Me group at the same position completely abolished antiplasmodial effects.

Demographic composition, not demographic diversity, predicts biomass and turnover across temperate and tropical forests.

The growth and survival of individual trees determine the physical structure of a forest with important consequences for forest function. However, given the diversity of tree species and forest biomes, quantifying the multitude of demographic strategies within and across forests and the way that they translate into forest structure and function remains a significant challenge. Here, we quantify the demographic rates of 1961 tree species from temperate and tropical forests and evaluate how demographic diversity (DD) and demographic composition (DC) differ across forests, and how these differences in demography relate to species richness, aboveground biomass (AGB), and carbon residence time. We find wide variation in DD and DC across forest plots, patterns that are not explained by species richness or climate variables alone. There is no evidence that DD has an effect on either AGB or carbon residence time. Rather, the DC of forests, specifically the relative abundance of large statured species, predicted both biomass and carbon residence time. Our results demonstrate the distinct DCs of globally distributed forests, reflecting biogeography, recent history, and current plot conditions. Linking the DC of forests to resilience or vulnerability to climate change, will improve the precision and accuracy of predictions of future forest composition, structure, and function.

Determining the Impact of the COVID-19 Pandemic on Hand Surgery Fellowship Education.

The purpose of this study is to report the impact of COVID-19 on hand surgery fellow learning and preparedness for practice. A multi-dimensional questionnaire was distributed to current hand fellows and fellowship directors across the United States. Survey questions included fellowship location, institutional response, impact on practice, education and job search. Thirty-two hand surgery fellows and 14 fellowship directors completed the survey. Of fellows, 59% reported a greater than 75% decrease in case volume. Mean hours worked per week per fellow decreased by 52%. All fellowship directors and 94% of fellows did not expect COVID-19 to impact their ability to graduate, and nearly all fellows felt prepared to start practice after fellowship training. However, many fellows expressed concern about job opportunities. The work hours and exposure of hand surgery fellows to elective surgical cases have been adversely impacted by COVID-19. Nevertheless, current hand fellows feel prepared to enter practice. (Journal of Surgical Orthopaedic Advances 31(1):048-052, 2022).

Wildlife disturbances as a source of conspecific negative density-dependent mortality in tropical trees.

Large vertebrates are rarely considered important drivers of conspecific negative density-dependent mortality (CNDD) in plants because they are generalist consumers. However, disturbances like trampling and nesting also cause plant mortality, and their impact on plant diversity depends on the spatial overlap between wildlife habitat preferences and plant species composition. We studied the impact of native wildlife on a hyperdiverse tree community in Malaysia. Pigs (Sus scrofa) are abnormally abundant at the site due to food subsidies in nearby farmland and they construct birthing nests using hundreds of tree saplings. We tagged 34 950 tree saplings in a 25 ha plot during an initial census and assessed the source mortality by recovering tree tags from pig nests (n = 1672 pig-induced deaths). At the stand scale, pigs nested in flat dry habitats, and at the local neighbourhood scale, they nested within clumps of saplings, both of which are intuitive for safe and efficient nest building. At the stand scale, flat dry habitats contained higher sapling densities and higher proportions of common species, so pig nesting increased the weighted average species evenness across habitats. At the neighbourhood scale, pig-induced sapling mortality was associated with higher heterospecific and especially conspecific sapling densities. Tree species have clumped distributions due to dispersal limitation and habitat filtering, so pig disturbances in sapling clumps indirectly caused CNDD. As a result, Pielou species evenness in 400 m2 quadrats increased 105% more in areas with pig-induced deaths than areas without disturbances. Wildlife induced CNDD and this supported tree species evenness, but they also drove a 62% decline in sapling densities from 1996 to 2010, which is unsustainable. We suspect pig nesting is an important feature shaping tree composition throughout the region.

COVID-19 and the rise of virtual medicine in spine surgery: a worldwide study.

PURPOSE: The COVID-19 pandemic forced many surgeons to adopt "virtual medicine" practices, defined as telehealth services for patient care and online platforms for continuing medical education. The purpose of this study was to assess spine surgeon reliance on virtual medicine during the pandemic and to discuss the future of virtual medicine in spine surgery. METHODS: A comprehensive survey addressing demographic data and virtual medicine practices was distributed to spine surgeons worldwide between March 27, 2020, and April 4, 2020. RESULTS: 902 spine surgeons representing seven global regions responded. 35.6% of surgeons were identified as "high telehealth users," conducting more than half of clinic visits virtually. Predictors of high telehealth utilization included working in an academic practice (OR = 1.68, p = 0.0015) and practicing in Europe/North America (OR 3.42, p < 0.0001). 80.1% of all surgeons were interested in online education. Dedicating more than 25% of one's practice to teaching (OR = 1.89, p = 0.037) predicted increased interest in online education. 26.2% of respondents were identified as "virtual medicine surgeons," defined as surgeons with both high telehealth usage and increased interest in online education. Living in Europe/North America and practicing in an academic practice increased odds of being a virtual medicine surgeon by 2.28 (p = 0.002) and 1.15 (p = 0.0082), respectively. 93.8% of surgeons reported interest in a centralized platform facilitating surgeon-to-surgeon communication. CONCLUSION: COVID-19 has changed spine surgery by triggering rapid adoption of virtual medicine practices. The demonstrated global interest in virtual medicine suggests that it may become part of the "new normal" for surgeons in the post-pandemic era.

Risk of Infection in Thumb Carpometacarpal Surgery After Corticosteroid Injection.

PURPOSE: The purpose of this study was to determine whether patients who had an intra-articular corticosteroid injection into the thumb carpometacarpal (CMC) joint for the treatment of arthritis within the 3 months before CMC joint arthroplasty or arthrodesis were at increased risk for wound complication/infection and/or repeat surgery for wound complication/infection in comparison with patients who did not receive an injection within 6 months or who received an injection between 3 and 6 months before surgery. METHODS: We identified 5,046 patients in the Humana claims database who underwent surgery for CMC joint arthritis. The patients were stratified into 3 groups: (1) no thumb injection within 6 months of CMC joint surgery, (2) thumb injection between 3 and 6 months before CMC joint surgery, and (3) thumb injection within 3 months before CMC joint surgery. The primary outcome was wound complication/infection within 90 days after surgery. The secondary outcome was repeat surgery for wound complication/infection within 90 days after surgery. Multivariable logistic regression was performed to assess the associations between the timing of injection and wound complication/infection and repeat surgery for wound complication/infection. RESULTS: The rates of wound complication/infection within 90 days after surgery were similar among the 3 study groups. However, patients who received an intra-articular corticosteroid injection within 3 months before surgery had a 2.2 times greater likelihood of repeat surgery for a wound complication/infection compared with patients who did not have an injection within 6 months before surgery. CONCLUSIONS: Patients who receive an intra-articular corticosteroid injection within the 3 months before surgery for CMC joint arthritis may be at increased risk of repeat surgery to treat a wound complication/infection in the 90-day postoperative period. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic II.

The Potential Value of Performing Preoperative Urinalysis Prior to Total Knee Arthroplasty.

BACKGROUND: Although the practice of checking a urinalysis prior to elective total knee arthroplasty (TKA) is relatively common, very little has been reported on the association between a preoperative urinary tract infection (UTI) and adverse events in primary TKA. The goal of this study is to investigate the risk of postoperative complication following TKA as it relates to preoperative UTI. METHODS: Patients undergoing TKA were queried in the National Surgical Quality Improvement Program. Morbid events were classified as minor (transfusion, pneumonia, wound dehiscence, UTI, and renal insufficiency) and serious (wound infection, thromboembolic event, renal failure, myocardial infarction, prolonged ventilation, unplanned intubation, sepsis, and death). Risk factors for adverse events were analyzed in both univariate and multivariate fashion. RESULTS: A total of 203,851 patients undergoing TKA met inclusion criteria and 507 patients had a UTI present at time of surgery (UTI PATOS). A propensity matched analysis controlling for age, gender, body mass index, operative year, and American Society of Anesthesiologists score identified 507 patients without a UTI PATOS to serve as the control group. Following adjustment for baseline characteristics, operative year, and American Society of Anesthesiologists score, UTI PATOS was associated with increased risk for serious adverse events (odds ratio [OR] 2.746, 95% confidence interval [CI] 1.546-4.878, P = .0006), occurrence of any morbid event (OR 1.894, 95% CI 1.299-2.761, P = .0009), and reoperation (OR 4, 95% CI 2.592-6.169, P < .0001). CONCLUSION: This study suggests that a UTI present at time of TKA increases the risk of multiple postoperative complications and reoperation.

Synthesis of New Triazolopyrazine Antimalarial Compounds.

A radical approach to late-stage functionalization using photoredox and Diversinate™ chemistry on the Open Source Malaria (OSM) triazolopyrazine scaffold (Series 4) resulted in the synthesis of 12 new analogues, which were characterized by NMR, UV, and MS data analysis. The structures of four triazolopyrazines were confirmed by X-ray crystal structure analysis. Several minor and unexpected side products were generated during these studies, including two resulting from a possible disproportionation reaction. All compounds were tested for their ability to inhibit the growth of the malaria parasite Plasmodium falciparum (3D7 and Dd2 strains) and for cytotoxicity against a human embryonic kidney (HEK293) cell line. Moderate antimalarial activity was observed for some of the compounds, with IC50 values ranging from 0.3 to >20 µM; none of the compounds displayed any toxicity against HEK293 at 80 µM.

Conspecific negative density dependence in rainy season enhanced seedling diversity across habitats in a tropical forest.

Conspecific negative density dependence (CNDD) could be one of the most important local-scale mechanisms shaping plant species coexistence. However, the spatial and temporal changes in the strength CNDD and the implications for the plant diversity remain unknown. We used 10 years of seedling data, in a seasonal tropical rainforest, to discover how CNDD influences tree seedling survival across habitats and seasons. We also evaluated the relation between CNDD and species diversity. We found the strength of CNDD in the valley habitat was significantly stronger than in ridge habitat in rainy season, but not significantly different in dry season. Corresponding to expectations of CNDD as mechanism of diversity maintenance, seedling species diversity was significantly higher in valley habitat than in ridge habitat and significantly correlated with CNDD. Additionally, conspecific and heterospecific seedling neighbour densities positively affected the survival of tree seedlings, but heterospecific adult neighbour density had a weak effect. Our study finds that CNDD varied significantly across habitats and was correlated with local seedling diversity. Our results highlight the importance of CNDD in driving species diversity at the local scale. Recognizing the spatial and temporal variation in the strength of CNDD will aid efforts to model and understand species coexistence.

Learning from the past: did experience with previous epidemics help mitigate the impact of COVID-19 among spine surgeons worldwide?

PURPOSE: Spine surgeons around the world have been universally impacted by COVID-19. The current study addressed whether prior experience with disease epidemics among the spine surgeon community had an impact on preparedness and response toward COVID-19. METHODS: A 73-item survey was distributed to spine surgeons worldwide via AO Spine. Questions focused on: demographics, COVID-19 preparedness, response, and impact. Respondents with and without prior epidemic experience (e.g., SARS, H1NI, MERS) were assessed on preparedness and response via univariate and multivariate modeling. Results of the survey were compared against the Global Health Security Index. RESULTS: Totally, 902 surgeons from 7 global regions completed the survey. 24.2% of respondents had prior experience with global health crises. Only 49.6% reported adequate access to personal protective equipment. There were no differences in preparedness reported by respondents with prior epidemic exposure. Government and hospital responses were fairly consistent around the world. Prior epidemic experience did not impact the presence of preparedness guidelines. There were subtle differences in sources of stress, coping strategies, performance of elective surgeries, and impact on income driven by prior epidemic exposure. 94.7% expressed a need for formal, international guidelines to help mitigate the impact of the current and future pandemics. CONCLUSIONS: This is the first study to note that prior experience with infectious disease crises did not appear to help spine surgeons prepare for the current COVID-19 pandemic. Based on survey results, the GHSI was not an effective measure of COVID-19 preparedness. Formal international guidelines for crisis preparedness are needed to mitigate future pandemics.

Correction to: Learning from the past: did experience with previous epidemics help mitigate the impact of COVID-19 among spine surgeons worldwide?

Unfortunately, the 13th author name has been incorrectly published in the original publication. The complete correct name is given below.

Assessment of Flexion Strength Following Single- Versus Double-Hamstring Tendon Harvest for Anterior Cruciate Ligament Reconstruction.

PURPOSE: To compare isometric hamstring strength deficits, knee laxity, functional outcomes, and patient-reported outcomes between patients who underwent anterior cruciate ligament (ACL) reconstruction with doubled semitendinosus and gracilis tendon autograft (ST/G) versus quadrupled semitendinosus autograft (ST), at a minimum follow-up of 1-year postoperatively. METHODS: Patients who underwent ACL reconstruction with ST/G or ST hamstring autografts were retrospectively identified. Isometric hamstring strength was tested with a hand-held dynamometer at 30, 60, and 90° of knee flexion. Anterior knee laxity was assessed using a KT-1000 arthrometer. Functional outcomes were collected using the single-leg hop test and single-leg squat test. Side-to-side differences were determined and compared between the ST/G and ST groups. Patient-reported outcomes were collected on all patients. RESULTS: Eighty-four patients who underwent ST/G (n = 34) or ST (n = 50) autograft ACL reconstruction were recruited to participate in this study. There was no difference in knee laxity between the groups. Side-to-side hamstring strength deficits increased with increased flexion angles. At 90° of flexion, the ST/G group had a significantly greater flexion strength deficit compared with the ST group (37.8 ± 15.1% vs 24.7 ± 12.5%, P < .001). Aside from a significant difference in the KOOS pain Score (P .045), no other significant differences in functional or patient reported outcomes between the groups were identified. CONCLUSIONS: Patients who underwent ACL reconstruction with ST/G compared with ST autograft have a significantly greater isometric flexion strength deficit at 90° of flexion. Future investigations are required to determine the clinical relevance of this difference and whether specialized therapy protocols can mitigate this deficit. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Risk factors for 30-day readmission following hip arthroscopy.

PURPOSE: Hip arthroscopy is known to be safe with low rates of postoperative complications. The purpose of this study is to evaluate hip arthroscopy cases in a national surgical database to identify risk factors associated with readmission. METHODS: The American College of Surgeons National Surgical Quality Improvement Program database was queried from 2012 to 2016 for current procedural terminology billing codes related to hip arthroscopy. International Classification of Diseases diagnostic codes were used to exclude cases involving infection, fracture, or open procedures. Univariate and multivariate analyses were performed to identify risk factors associated with 30-day readmission. RESULTS: 1493 patients were identified who had undergone hip arthroscopy. The most common procedures were labral resection or chondroplasty (n = 589, 39.5%) and femoroplasty (n = 527, 35.3%). The 30-day complication rate was 1.7% and the most common complications following the procedure were bleeding (n = 12, 0.8%) superficial infections (n = 5, 0.3%), and returning to the operating room (n = 4, 0.3%). The 30-day readmission rate was 1.3%. On multivariate analysis, hypertension requiring anti-hypertensive medication (odds ratio [OR], 3.5; 95% confidence interval [CI], 1.4-8.7) and chronic corticosteroid or immunosuppressant use (OR 7.2; 95% CI 1.9-26.7) were identified as independent risk factors for readmission. There was no difference in complication rates when hip arthroscopy was performed with isolated femoroplasty (n = 340), isolated acetabuloplasty (n = 103), both (n = 187) or neither (n = 863). CONCLUSION: These findings confirm that the 30-day readmission (1.3%) and complication rate (1.7%) are low for isolated hip arthroscopy procedures; however, hypertension and chronic steroid use are independent risk factors for readmission. LEVEL OF EVIDENCE: Retrospective comparative study, Level III.

Partial rupture of the distal biceps brachii tendon: a magnetic resonance imaging analysis.

BACKGROUND: This study is the largest cohort of partial distal biceps brachii tendon ruptures in the literature that was analyzed according to rupture morphology of the long and short tendon heads. METHODS: Patients with partial distal biceps tendon ruptures were identified using an institutional enterprise data warehouse query at a single institution. A retrospective chart review was performed to record patient demographics, past medical history, and injury mechanism for each patient. Each patient's magnetic resonance images were reviewed to determine injury patterns, specifically the extent of long head (LH) and short head (SH) tendon involvement, and associated injuries. Rupture morphologies were correlated with mechanism of injury, diabetes status, and smoking history. RESULTS: Seventy-seven patients were included in the study. The average age was 52 years (±11.9, range: 23-90 years); 67% were male, with an average body mass index of 28.3 (±4.3). A smoking history was reported in 31.2% of patients and 5.2% were diabetic. The partial ruptures were caused by a traumatic mechanism in 57.1% of cases, 23.4% were atraumatic, and 19.5% had an unknown mechanism. The most common injury morphology was a partial LH rupture with an intact SH tendon (33.8%). Isolated complete ruptures of the LH represented the least common injury morphology. Injury morphology was significantly related to mechanism (P < .01). Traumatic ruptures had a higher percentage of SH involvement compared with the atraumatic group (77.3% vs. 37.7%, respectively). In contrast, atraumatic ruptures involved the LH tendon in 89% of cases, with only 37.7% of cases involving the SH tendon. Patients with a history of smoking were more likely to have an atraumatic mechanism (P = .01). A history of diabetes was unrelated to mechanism (P = .20). CONCLUSION: Partial ruptures of the distal biceps brachii tendon represent a spectrum of patterns with varying involvement of the LH and SH tendons. Injury morphology was significantly related to mechanism (P < .01). LH tendon involvement was seen in 88.9% of atraumatic cases, whereas SH tendon involvement was seen in 77.3% of traumatic cases. A more comprehensive understanding of partial rupture patterns is critical to further understand the risk factors that may preclude to worse clinical outcomes, and aid in deciding which patients would benefit from operative vs. nonoperative management.

Risk Factors for Greater Than 24-Hour Length of Stay After Primary Total Knee Arthroplasty.

BACKGROUND: Recently, the Center for Medicare Services removed total knee arthroplasty (TKA) from the inpatient-only procedure list. The purpose of this study is to assess the role of demographics, medical comorbidities, and postsurgical complications in predicting safe discharge to home within 24 hours after TKA. METHODS: Patients undergoing primary TKA between 2011 and 2016 were identified in the American College of Surgeons National Surgical Quality Improvement Program. Patients were grouped into those whose length of stay (LOS) was less than 24 hours after surgery vs those greater than 24 hours. Demographics, preoperative comorbidities, operative variables, and postoperative adverse events were studied as risk factors for LOS greater than 24 hours. RESULTS: A total of 210,075 patients undergoing primary TKA met the inclusion criteria, and of those, 18,134 (8.6%) patients were discharged within 24 hours postoperatively. In a risk-adjusted multivariate analysis, patients with increasing age, obesity, preoperative comorbidities of smoking, diabetes, dyspnea, chronic obstructive pulmonary disease, hypertension, bleeding disorder, corticosteroid use preoperatively, and dependent functional status conferred a greater risk for discharge greater than 24 hours. Male gender, spinal anesthesia, and monitored anesthesia care were protective against LOS greater than 24 hours. CONCLUSION: This study suggests that dependent functional status, preoperative comorbidities, and postoperative complications are all associated with a LOS greater than 24 hours after TKA. Surgeons and patients should be aware of the clinical and demographic variables associated with risk for LOS greater than 24 hours when considering outpatient status for patients undergoing TKA.