Biomechanical Design Optimization of Distal Humerus Fracture Plates: A Review.

The goal of this article was to review studies on distal humerus fracture plates (DHFPs) to understand the biomechanical influence of systematically changing the plate or screw variables. The problem is that DHFPs are commonly used surgically, although complications can still occur, and it is unclear if implant configurations are always optimized using biomechanical criteria. A systematic search of the PubMed database was conducted to identify English-language biomechanical optimization studies of DHFPs that parametrically altered plate and/or screw variables to analyze their influence on engineering performance. Intraarticular and extraarticular fracture (EAF) data were separated and organized under commonly used biomechanical outcome metrics. The results identified 52 eligible DHFP studies, which evaluated various plate and screw variables. The most common plate variables evaluated were geometry, hole type, number, and position. Fewer studies assessed screw variables, with number and angle being the most common. However, no studies examined nonmetallic materials for plates or screws, which may be of interest in future research. Also, articles used various combinations of biomechanical outcome metrics, such as interfragmentary fracture motion, bone, plate, or screw stress, number of loading cycles to failure, and overall stiffness (Os) or failure strength (Fs). However, no study evaluated the bone stress under the plate to examine bone "stress shielding," which may impact bone health clinically. Surgeons treating intraarticular and extraarticular distal humerus fractures should seriously consider two precontoured, long, thick, locked, and parallel plates that are secured by long, thick, and plate-to-plate screws that are located at staggered levels along the proximal parts of the plates, as well as an extra transfracture plate screw. Also, research engineers could improve new studies by perusing recommendations in future work (e.g., studying alternative nonmetallic materials or "stress shielding"), clinical ramifications (e.g., benefits of locked plates), and study quality (e.g., experimental validation of computational studies).

Biomechanical testing of a computationally optimized far cortical locking plate versus traditional implants for distal femur fracture repair.

BACKGROUND: This study experimentally validated a computationally optimized screw number and screw distribution far cortical locking distal femur fracture plate and compared the results to traditional implants. METHODS: 24 artificial femurs were osteotomized with a 10 mm fracture gap 60 mm proximal to the intercondylar notch. Three fixation constructs were used. (i) Standard locking plates secured with three far cortical locking screws inserted according to a previously optimized distribution in the femur shaft (n = 8). (ii) Standard locking plates secured with four standard locking screws inserted in alternating plate holes in the femur shaft (n = 8). (iii) Retrograde intramedullary nail secured proximally with one anterior-posterior screw and distally with two oblique screws (n = 8). Axial hip forces (700 and 2800 N) were applied while measuring axial interfragmentary motion, shear interfragmentary motion, and overall stiffness. FINDINGS: Experimental far cortical locking plate results compared well to published computational findings. Far cortical locking femurs contained the highest axial motion within the potential ideal range of 0.2-1 mm and a sheer-to-axial motion ratio < 1.6 at toe-touch weight-bearing (700 N). At full weight-bearing (2800 N), Standard locking-plated femurs had the only axial motion within 0.2-1 mm but had an excess shear-to-axial motion ratio. Nail-implanted femurs underperformed at both forces. INTERPRETATION: For toe-touch weight-bearing, the far cortical locking construct provided optimal biomechanics to allow moderate motion, which has been suggested to encourage early callus formation. Conversely, at full weight-bearing, the standard locking construct offered the biomechanical advantage on fracture motion.

Cytotoxicity of novel hybrid composite materials for making bone fracture plates.

Bone fracture plates are usually made from steel or titanium, which are much stiffer than cortical bone. This may cause bone 'stress shielding' (i.e. bone resorption leading to plate loosening) and delayed fracture healing (i.e. fracture motion is less than needed to stimulate callus formation at the fracture). Thus, the authors previously designed, fabricated, and mechanically tested novel 'hybrid' composites made from inorganic and organic materials as potential bone fracture plates that are more flexible to reduce these negative effects. This is the first study to measure the cytotoxicity of these composites via the survival of rat cells. Cubes of carbon fiber/flax fiber/epoxy and glass fiber/flax fiber/epoxy had better cell survival vs. Kevlar fiber/flax fiber/epoxy (57% and 58% vs. 50%). Layers and powders made of carbon fiber/epoxy and glass fiber/epoxy had higher cell survival than Kevlar fiber/epoxy (96%-100% and 100% vs. 39%-90%). The presence of flax fibers usually decreased cell survival. Thus, carbon and glass fiber composites (with or without flax fibers), but not Kevlar fiber composites (with or without flax fibers), may potentially be used for bone fracture plates.

Biomechanical design optimization of proximal humerus locked plates: A review.

BACKGROUND: Proximal humerus locked plates (PHLPs) are widely used for fracture surgery. Yet, non-union, malunion, infection, avascular necrosis, screw cut-out (i.e., perforation), fixation failure, and re-operation occur. Most biomechanical investigators compare a specific PHLP configuration to other implants like non-locked plates, nails, wires, and arthroplasties. However, it is unknown whether the PHLP configuration is biomechanically optimal according to some well-known biomechanical criteria. Therefore, this is the first review of the systematic optimization of plate and/or screw design variables for improved PHLP biomechanical performance. METHODS: The PubMed website was searched for papers using the terms "proximal humerus" or "shoulder" plus "biomechanics/biomechanical" plus "locked/locking plates". PHLP papers were included if they were (a) optimization studies that systematically varied plate and screw variables to determine their influence on PHLP's biomechanical performance; (b) focused on plate and screw variables rather than augmentation techniques (i.e., extra implants, bone struts, or cement); (c) published after the year 2000 signaling the commercial availability of locked plate technology; and (d) written in English. RESULTS: The 41 eligible papers involved experimental testing and/or finite element modeling. Plate variables investigated by these papers were geometry, material, and/or position, while screw variables studied were number, distribution, angle, size, and/or threads. Numerical outcomes given by these papers included stiffness, strength, fracture motion, bone and implant stress, and/or the number of loading cycles to failure. But, no paper fully optimized any plate or screw variable for a PHLP by simultaneously applying four well-established biomechanical criteria: (a) allow controlled fracture motion for early callus generation; (b) reduce bone and implant stress below the material's ultimate stress to prevent failure; (c) maintain sufficient bone-plate interface stress to reduce bone resorption (i.e., stress shielding); and (d) increase the number of loading cycles before failure for a clinically beneficial lifespan (i.e., fatigue life). Finally, this review made suggestions for future work, identified clinical implications, and assessed the quality of the papers reviewed. CONCLUSIONS: Applying biomechanical optimization criteria can assist biomedical engineers in designing or evaluating PHLPs, so orthopaedic surgeons can have superior PHLP constructs for clinical use.

Optimal delivery of endothelial progenitor cells in a rat model of critical-size bone defects.

Nonunion and segmental bone defects are complex issues in orthopedic trauma. The use of endothelial progenitor cells (EPCs), as part of a cell-based therapy for bone healing is a promising approach. In preclinical studies, culture medium (CM) is commonly used to deliver EPCs to the defect site, which has the potential for immunogenicity in humans. The goal of this study was to find an effective and clinically translatable delivery medium for EPCs. Accordingly, this study compared EPCs delivered in CM, phosphate-buffered saline (PBS), platelet-poor plasma (PPP), and platelet-rich plasma (PRP) in a rat model of femoral critical-size defects. Fischer 344 rats (n = 35) were divided into six groups: EPC+CM, EPC+PBS, EPC+PPP, EPC+PRP, PPP alone, and PRP alone. A 5 mm mid-diaphyseal defect was created in the right femur and stabilized with a miniplate. The defect was filled with a gelatin scaffold impregnated with the corresponding treatment. Radiographic, microcomputed tomography and biomechanical analyses were performed. Overall, regardless of the delivery medium, groups that received EPCs had higher radiographic scores and union rates, higher bone volume, and superior biomechanical properties compared to groups treated with PPP or PRP alone. There were no significant differences in any outcomes between EPC subgroups or between PPP and PRP alone. These results suggest that EPCs are effective in treating segmental defects in a rat model of critical-size defects regardless of the delivery medium used. Consequently, PBS could be the optimal medium for delivering EPCs, given its low cost, ease of preparation, accessibility, noninvasiveness, and nonimmunogenic properties.

Reducing the Burden of Disease Associated With Periprosthetic Fractures: Prevention and the Need for Improved Perioperative Care.

The management of periprosthetic fractures remains challenging and controversial. There continues to be a significant burden of disease and substantial resource implications associated with fractures following total joint arthroplasty. Achieving consensus opinions regarding the prevention and treatment of this problem has important implications given the profound effect on patient outcomes. Multidisciplinary care in the preoperative and postoperative settings is critical, with a specific focus on bone health.

Fixation Strategies for Periprosthetic Fractures With Stable Implants.

The fixation of periprosthetic fractures remains challenging and controversial. It is important to achieve consensus opinions regarding the management of stable periprosthetic fractures with internal fixation. Key strategies to optimize surgical decision making and fixation and manage complications following these difficult injuries are addressed.

The Role of Revision Total Joint Arthroplasty for Periprosthetic Fractures With Unstable Implants.

The management of periprosthetic fractures with unstable prosthetic implants is a challenging and commonly encountered problem. It is important to address the many current issues and controversies regarding the treatment of periprosthetic fractures with revision total joint arthroplasty. Key strategies to optimize surgical decision making around the use of arthroplasty and management of complications following these complex injuries will be addressed.

Biomechanical effects of different loads and constraints on finite element modeling of the humerus.

Currently, there is no established finite element (FE) method to apply physiologically realistic loads and constraints to the humerus. This FE study showed that 2 'simple' methods involving direct head loads, no head constraints, and rigid elbow or mid-length constraints created excessive stresses and bending. However, 2 'intermediate' methods involving direct head loads, but flexible head and elbow constraints, produced lower stresses and bending. Also, 2 'complex' methods involving muscles to generate head loads, plus flexible head and elbow constraints, generated the lowest stresses and moderate bending. This has implications for FE modeling research on intact and implanted humeri.

Experimental Methods for Studying the Contact Mechanics of Joints.

Biomechanics researchers often experimentally measure static or fluctuating dynamic contact forces, areas, and stresses at the interface of natural and artificial joints, including the shoulders, elbows, hips, and knees. This information helps explain joint contact mechanics, as well as mechanisms that may contribute to disease, damage, and degradation. Currently, the most common in vitro experimental technique involves a thin pressure-sensitive film inserted into the joint space; but, the film's finite thickness disturbs the joint's ordinary articulation. Similarly, the most common in vivo experimental technique uses video recording of 3D limb motion combined with dynamic analysis of a 3D link-segment model to calculate joint contact force, but this does not provide joint contact area or stress distribution. Moreover, many researchers may be unaware of older or newer alternative techniques that may be more suitable for their particular research application. Thus, this article surveys over 50 years of English-language scientific literature in order to (a) describe the basic working principles, advantages, and disadvantages of each technique, (b) examine the trends among the studies and methods, and (c) make recommendations for future directions. This article will hopefully inform biomechanics investigators about various in vitro and in vivo experimental methods for studying the contact mechanics of joints.

Biomechanical stress analysis using thermography: A review.

Biomechanics investigators are interested in experimentally measuring stresses experienced by dental structures, whole bones, joint replacements, soft tissues, normal limbs, etc. To do so, various experimental methods have been used that are based on acoustic, optical, piezo-resistive, or other principles, like digital image correlation, fiber optic sensors, photo-elasticity, strain gages, ultrasound, etc. Several biomechanical review papers have surveyed these research technologies, but they do not mention thermography. Thermography can identify temperature anomalies indicating low- or high-stress areas on a bone, implant, prosthesis, etc., which may need to be repaired, replaced, or redesigned to avoid damage, degradation, or failure. In addition, thermography can accurately predict a structure's cyclic fatigue strength. Consequently, this article gives an up-to-date survey of the scientific literature on thermography for biomechanical stress analysis. This review (i) describes the basic physics of thermography, thermo-elastic properties of biomaterials, experimental protocols for thermography, advantages, and disadvantages, (ii) surveys published studies on various applications that used thermography for biomechanical stress measurements, and (iii) discusses general findings and future work. This article is intended to inform biomechanics investigators about the potential of thermography for stress analysis.

Biomechanical properties of artificial bones made by Sawbones: A review.

Biomedical engineers and physicists frequently use human or animal bone for orthopaedic biomechanics research because they are excellent approximations of living bone. But, there are drawbacks to biological bone, like degradation over time, ethical concerns, high financial costs, inter-specimen variability, storage requirements, supplier sourcing, transportation rules, etc. Consequently, since the late 1980s, the Sawbones® company has been one of the world's largest suppliers of artificial bones for biomechanical testing that counteract many disadvantages of biological bone. There have been many published reports using these bone analogs for research on joint replacement, bone fracture fixation, spine surgery, etc. But, there exists no prior review paper on these artificial bones that gives a comprehensive and in-depth look at the numerical data of interest to biomedical engineers and physicists. Thus, this paper critically reviews 25 years of English-language studies on the biomechanical properties of these artificial bones that (a) characterized unknown or unreported values, (b) validated them against biological bone, and/or (c) optimized different design parameters. This survey of data, advantages, disadvantages, and knowledge gaps will hopefully be useful to biomedical engineers and physicists in developing mechanical testing protocols and computational finite element models.

Open fractures: Current treatment perspective.

Severe open fractures present challenges to orthopaedic surgeons worldwide, with increased risks of significant complications. Although different global regions have different resources and systems, there continue to be many consistent approaches to open fracture care. Management of these complex injures continues to evolve in areas ranging from timing of initial operative debridement to the management of critical-sized bone defects. This review, compiled by representative members of the International Orthopaedic Trauma Association, focuses on several critical areas of open fracture management, including antibiotic administration, timing of debridement, bone loss, soft tissue management, and areas of need for future investigation.

Mechanical Properties of Synthetic Bones Made by Synbone: A Review.

Biomechanical engineers and physicists commonly employ biological bone for biomechanics studies, since they are good representations of living bone. Yet, there are challenges to using biological bone, such as cost, degradation, disease, ethics, shipping, sourcing, storage, variability, etc. Therefore, the Synbone® company has developed a series of synthetic bones that have been used by biomechanical investigators to offset some drawbacks of biological bone. There have been a number of published biomechanical reports using these bone surrogates for dental, injury, orthopedic, and other applications. But, there is no prior review paper that has summarized the mechanical properties of these synthetic bones in order to understand their general performance or how well they represent biological bone. Thus, the goal of this article was to survey the English-language literature on the mechanical properties of these synthetic bones. Studies were included if they quantitatively (a) characterized previously unknown values for synthetic bone, (b) validated synthetic versus biological bone, and/or (c) optimized synthetic bone performance by varying geometric or material parameters. This review of data, pros, cons, and future work will hopefully assist biomechanical engineers and physicists that use these synthetic bones as they develop experimental testing regimes and computational models.

Biomechanics of plate fixation following traditional olecranon osteotomy versus novel proximal ulna osteotomy for visualizing a distal humerus injury.

After a distal humeral injury, olecranon osteotomy (OO) is a traditional way to visualize the distal humerus for performing fracture fixation. In contrast, the current authors previously showed that novel proximal ulna osteotomy (PUO) allows better access to the distal humerus without ligamentous compromise. Therefore, this study biomechanically compared plating repair following OO versus PUO. The left or right ulna from eight matched pairs of human cadaveric elbows were randomly assigned to receive OO or PUO and repaired using pre-contoured titanium plates. Destructive and non-destructive mechanical tests were performed to assess stability. Mechanical tests on OO versus PUO groups yielded average results for ulna cantilever bending stiffness at a 90° elbow angle (29.6 vs 30.5 N/mm, p = 0.742), triceps tendon pull stiffness at a 90° elbow angle (28.2 vs 24.4 N/mm, p = 0.051), triceps tendon pull stiffness at a 110° elbow angle (61.9 vs 59.5 N/mm, p = 0.640), and triceps tendon pull failure load at a 110° elbow angle (1070.1 vs 1359.7 N, p = 0.078). OO and PUO elbows had similar failure mechanisms, namely, tendon tear or avulsion from the ulna with or without some fracture of the proximal bone fragment, or complete avulsion of the proximal bone fragment from the plate. The similar biomechanical stability (i.e., no statistical difference for 4 of 4 mechanical measurements) and failure mechanisms of OO and PUO plated elbows support the clinical use of PUO as a possible alternative to OO for visualizing the distal humerus.

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.

Intramedullary Nailing vs Sliding Hip Screw in Trochanteric Fracture Management: The INSITE Randomized Clinical Trial.

Importance: Fractures of the hip have devastating effects on function and quality of life. Intramedullary nails (IMN) are the dominant implant choice for the treatment of trochanteric fractures of the hip. Higher costs of IMNs and inconclusive benefit in comparison with sliding hip screws (SHSs) convey the need for definitive evidence. Objective: To compare 1-year outcomes of patients with trochanteric fractures treated with the IMN vs an SHS. Design, Setting, and Participants: This randomized clinical trial was conducted at 25 international sites across 12 countries. Participants included ambulatory patients aged 18 years and older with low-energy trochanteric (AO Foundation and Orthopaedic Trauma Association [AO/OTA] type 31-A1 or 31-A2) fractures. Patient recruitment occurred between January 2012 and January 2016, and patients were followed up for 52 weeks (primary end point). Follow-up was completed in January 2017. The analysis was performed in July 2018 and confirmed in January 2022. Interventions: Surgical fixation with a Gamma3 IMN or an SHS. Main Outcomes and Measures: The primary outcome was health-related quality of life (HRQOL), measured by the EuroQol-5 Dimension (EQ5D) at 1-year postsurgery. Secondary outcomes included revision surgical procedure, fracture healing, adverse events, patient mobility (measured by the Parker mobility score), and hip function (measured by the Harris hip score). Results: In this randomized clinical trial, 850 patients were randomized (mean [range] age, 78.5 [18-102] years; 549 [64.6% female) with trochanteric fractures to undergo fixation with either the IMN (n = 423) or an SHS (n = 427). A total of 621 patients completed follow-up at 1 year postsurgery (304 treated with the IMN [71.9%], 317 treated with an SHS [74.2%]). There were no significant differences between groups in EQ5D scores (mean difference, 0.02 points; 95% CI, -0.03 to 0.07 points; P = .42). Furthermore, after adjusting for relevant covariables, there were no between-group differences in EQ5D scores (regression coefficient, 0.00; 95% CI, -0.04 to 0.05; P = .81). There were no between-group differences for any secondary outcomes. There were also no significant interactions for fracture stability (ß [SE] , 0.01 [0.05]; P = .82) or previous fracture (ß [SE], 0.01 [0.10]; P = .88) and treatment group. Conclusions and Relevance: This randomized clinical trial found that IMNs for the treatment of trochanteric fractures had similar 1-year outcomes compared with SHSs. These results suggest that the SHS is an acceptable lower-cost alternative for trochanteric fractures of the hip. Trial Registration: ClinicalTrials.gov Identifier: NCT01380444.

Biomechanical design optimization of distal femur locked plates: A review.

Clinical findings, manufacturer instructions, and surgeon's preferences often dictate the implantation of distal femur locked plates (DFLPs), but healing problems and implant failures still persist. Also, most biomechanical researchers compare a particular DFLP configuration to implants like plates and nails. However, this begs the question: Is this specific DFLP configuration biomechanically optimal to encourage early callus formation, reduce bone and implant failure, and minimize bone "stress shielding"? Consequently, it is crucial to optimize, or characterize, the biomechanical performance (stiffness, strength, fracture micro-motion, bone stress, plate stress) of DFLPs influenced by plate variables (geometry, position, material) and screw variables (distribution, size, number, angle, material). Thus, this article reviews 20 years of biomechanical design optimization studies on DFLPs. As such, Google Scholar and PubMed websites were searched for articles in English published since 2000 using the terms "distal femur plates" or "supracondylar femur plates" plus "biomechanics/biomechanical" and "locked/locking," followed by searching article reference lists. Key numerical outcomes and common trends were identified, such as: (a) plate cross-sectional area moment of inertia can be enlarged to lower plate stress at the fracture; (b) plate material has a larger influence on plate stress than plate thickness, buttress screws, and inserts for empty plate holes; (c) screw distribution has a major influence on fracture micro-motion, etc. Recommendations for future work and clinical implications are then provided, such as: (a) simultaneously optimizing fracture micro-motion for early healing, reducing bone and implant stresses to prevent re-injury, lowering "stress shielding" to avoid bone resorption, and ensuring adequate fatigue life; (b) examining alternate non-metallic materials for plates and screws; (c) assessing the influence of condylar screw number, distribution, and angulation, etc. This information can benefit biomedical engineers in designing or evaluating DFLPs, as well as orthopedic surgeons in choosing the best DFLPs for their patients.

Development of machine-learning algorithms for 90-day and one-year mortality prediction in the elderly with femoral neck fractures based on the HEALTH and FAITH trials.

To develop prediction models using machine-learning (ML) algorithms for 90-day and one-year mortality prediction in femoral neck fracture (FNF) patients aged 50 years or older based on the Hip fracture Evaluation with Alternatives of Total Hip arthroplasty versus Hemiarthroplasty (HEALTH) and Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trials. This study included 2,388 patients from the HEALTH and FAITH trials, with 90-day and one-year mortality proportions of 3.0% (71/2,388) and 6.4% (153/2,388), respectively. The mean age was 75.9 years (SD 10.8) and 65.9% of patients (1,574/2,388) were female. The algorithms included patient and injury characteristics. Six algorithms were developed, internally validated and evaluated across discrimination (c-statistic; discriminative ability between those with risk of mortality and those without), calibration (observed outcome compared to the predicted probability), and the Brier score (composite of discrimination and calibration). The developed algorithms distinguished between patients at high and low risk for 90-day and one-year mortality. The penalized logistic regression algorithm had the best performance metrics for both 90-day (c-statistic 0.80, calibration slope 0.95, calibration intercept -0.06, and Brier score 0.039) and one-year (c-statistic 0.76, calibration slope 0.86, calibration intercept -0.20, and Brier score 0.074) mortality prediction in the hold-out set. Using high-quality data, the ML-based prediction models accurately predicted 90-day and one-year mortality in patients aged 50 years or older with a FNF. The final models must be externally validated to assess generalizability to other populations, and prospectively evaluated in the process of shared decision-making.

Trends in Outpatient Total Knee Arthroplasty From 2012 to 2020.

BACKGROUND: Trends over the past decade suggest a steady increase in the proportion of total knee arthroplasty (TKA) performed on an outpatient basis. However, the optimal patient selection criteria for outpatient TKA remain unclear. We aimed to describe longitudinal trends in patients selected for outpatient TKA and identify risk factors for 30-day morbidity following inpatient and outpatient TKA. METHODS: We identified 379,959 primary TKA patients, 17,170 (4.5%) of whom underwent outpatient surgery from 2012 to 2020 within a large national database. We used regression models to evaluate trends in outpatient TKA, factors associated with undergoing outpatient (versus inpatient) TKA and 30-day morbidity following outpatient and inpatient TKA. We used receiver operating curves to examine cutoff points for continuous risk factors. RESULTS: The proportion of patients undergoing outpatient TKA increased from 0.4% in 2012 to 14.1% in 2020. Younger age, male sex, lower body mass index (BMI), higher hematocrit, and fewer comorbidities were associated with receiving outpatient (versus inpatient) TKA. Variables associated with 30-day morbidity in the outpatient group included older age, chronic dyspnea, chronic obstructive pulmonary disease, and higher BMI. The receiver operating curves indicated outpatients aged 68 years and older, or with a BMI of 31.4 or higher were more likely to experience 30-day complications. CONCLUSION: The proportion of patients undergoing outpatient TKA has been increasing since 2012. Older age (≥68 years), a higher BMI (≥31.4), and comorbidities such as chronic dyspnea, chronic obstructive pulmonary disease, diabetes, and hypertension were associated with an increased odd of 30-day morbidity following outpatient TKA.