Is Fluoroquinolone Exposure after Primary Tendon Repair Associated with Higher Rates of Reoperations? A Matched Cohort Study.

Background: The association between tendon damage and fluoroquinolone (FQ) antibiotics has been well documented. However, there is limited data evaluating the impact of postoperative FQ use on outcomes of primary tendon repairs. The purpose of this study was to compare rates of reoperation for patients with FQ exposure after primary tendon repair versus controls. Methods: A retrospective cohort study was conducted using the PearlDiver database. All patients who underwent primary repair of distal biceps ruptures, Achilles tendon ruptures, and rotator cuff tears were identified. For each tendon, patients who were prescribed FQs within 90 days postoperatively were propensity score matched at a 1:3 ratio with controls without postoperative FQ prescriptions across age, sex, and several comorbidities. Rates of reoperation were compared at two years postoperatively with multivariable logistic regression. Results: A total of 124,322 patients who underwent primary tendon procedures were identified, including 3,982 (3.2%) patients with FQ prescriptions within 90 days postoperatively: 448 with distal biceps repair, 2,538 with rotator cuff repair, and 996 with Achilles tendon repair. These cohorts were matched with 1,344, 7,614, and 2,988 controls, respectively. Patients with postoperative FQ prescriptions exhibited significantly higher rates of revision surgery after primary repair of distal biceps ruptures (3.6% vs. 1.7%; OR 2.13; 95% CI, 1.09-4.04), rotator cuff tears (7.1% vs. 4.1%; OR 1.77; 95% CI, 1.48-2.15), and Achilles tendon ruptures (3.8% vs. 1.8%; OR 2.15; 95% CI, 1.40-3.27). Conclusion: Patients with FQ prescriptions within 90 days after primary tendon repair demonstrated significantly higher rates of reoperations for distal biceps, rotator cuff, and Achilles tendon repair at two years postoperatively. To achieve optimal outcomes and avoid complications in patients following primary tendon repair procedures, physicians should consider prescribing alternative non-FQ antibiotics and counsel patients on the risk of reoperation associated with postoperative FQ use.

The Effects of Gout Following total Knee Arthroplasty: A Retrospective Analysis.

BACKGROUND: The prevalence of gout is increasing along with the number of total knee arthroplasties (TKA) performed annually. The purpose of this study was to evaluate the incidence of gout following TKA in patients who had a previous history of gout and to determine if it is associated with an increased rate of postoperative joint complications. METHODS: Patients who did and did not have a preoperative diagnosis of gout and underwent a primary TKA were identified from a national database. The gout patients were matched 1:1 to patients who did not have gout and rates of postoperative gout diagnoses within 2 years of surgery were compared. Complication rates at mean 1 and 2 years were then compared for both patient cohorts using multivariable logistic regressions. A total of 17,463 patients with a prior diagnosis of gout were matched with 17,463 controls. RESULTS: There were 53.8% of patients who had previous gout and had a recurrence of gout within 2 years versus 3.6% of controls (Odds Ratios [OR]: 30.86). At mean 1-year, patients who had gout were significantly more likely to experience prosthetic joint infections (PJIs) and revision procedures. At mean 2 years, gout patients were at increased risk of prosthetic loosening, PJI, revision, and incision and debridement procedures. CONCLUSION: This study suggests that patients who had a prior diagnosis of gout are significantly more likely to experience recurrent episodes of gout after TKA. Gout attacks after TKA are associated with an increase in the rate of joint complications. LEVEL OF EVIDENCE: Level III.

Rates of Operative Management for Achilles Tendon Rupture Over the Last Decade and the Influence of Gender and Age.

BACKGROUND: With emerging evidence supporting functional rehabilitation for Achilles tendon ruptures (ATRs), this study sought to evaluate the treatment trends for patients sustaining an acute ATR and whether gender and age may influence the rates of operative repair. METHODS: A retrospective database review identified ATRs from 2010 through 2019. Patients were then stratified into three cohorts based on age (18-30, 30-45, and 46 and older), separated by gender, and then assessed whether patients were treated operatively or not. Cochran-Armitage Trend test was performed to analyze the trends of operative management. Chi-square analyses were performed to assess whether the proportion of patients who received operative management in each age cohort differed from 2010 to 2019. Logistic regression analyses were performed to assess whether gender influenced treatment. RESULTS: Over the previous decade, the total rates of operative treatment for ATR significantly decreased (18.3%-12.3%, P < .0001). Each individual age cohort experienced a proportional decrease in operative management when comparing 2010 with 2019 (all P < .0001). Within all age cohorts, males were significantly more likely to receive operative treatment for an ATR over the previous decade (odds ratios: 2.63-3.22). Conclusion. Overall rates of operative management for ATR decreased across all cohorts likely due to previous studies providing evidence of similar results between operative and nonoperative managements. Over the previous decade, males were demonstrated to be far more likely than females to undergo operative management. Why females are less likely to receive an operation for ATR is likely multi-factorial and requires further exploration. LEVEL OF EVIDENCE: Level III: Retrospective comparative study.

Trends in Surgical Approach for Single-Level Lumbar Fusion Over the Past Decade.

STUDY DESIGN: Retrospective Comparative Study. OBJECTIVE: The purpose of this study was to characterize trends in surgical approach for single-level lumbar fusion over the past decade. SUMMARY OF BACKGROUND DATA: The number of elective lumbar fusion cases performed is increasing annually. Several different surgical approaches exist for lumbar spinal fusion including novel anterior approaches developed in recent years. With ongoing innovation, trends in the utilization of common surgical approaches in recent years are unclear. MATERIALS AND METHODS: A retrospective cohort study was conducted using the PearlDiver database (Fort Wayne, IN). Patients undergoing single-level lumbar fusion between 2010 and 2019 were identified using Current Procedural Technology codes and divided into 4 mutually exclusive cohorts based on surgical approach: (1) anterior-only, (2) anterior approach with posterior instrumentation, (3) posterolateral, and (4) posterior-only interbody. Trend analyses of surgical approach utilization over the last decade were performed with the Cochran-Armitage test to evaluate the 2-tailed null hypothesis that utilization of each surgical approach for single-level lumbar fusion remained constant. RESULTS: A total of 53,234 patients met inclusion criteria and were stratified into 4 cohorts: anterior-only (n=5104), anterior with posterior instrumentation (n=23,515), posterolateral (n=5525), and posterior-only interbody (n=19,090). Trend analysis revealed the utilization of a posterior-only interbody approach significantly decreased from 36.7% to 29.2% ( P <0.001), whereas the utilization of a combined anterior and posterior approach significantly increased from 45.8% to 50.4% ( P <0.001). The utilization of an anterior-only approach also significantly increased from 7.9% to 10.5% ( P <0.001). CONCLUSIONS: Utilization of anterior-only and anterior with posterior instrumentation approaches for single-level lumbar fusion have been significantly increasing over the past decade while use of posterior-only interbody approach trended significantly downward. These data may be particularly useful for trainees and spine surgeons as new techniques and technology become available. LEVEL OF EVIDENCE: Level III-retrospective cohort study.

Trends in Total Joint Arthroplasty Among Patients With Rheumatoid Arthritis: The Effect of Recent Disease Modifying Antirheumatic Drug Utilization Guidelines.

INTRODUCTION: The 2015 change in the American College of Rheumatology (ACR) guidelines narrowed indications for initiating treatment with biologic disease-modifying antirheumatic drugs (bDMARDs) in patients with rheumatoid arthritis (RA). This study sought to evaluate trends in total joint arthroplasty (TJA) in patients with RA and to characterize the effect of bDMARDs on arthroplasty risk in this population after the change in ACR treatment guidelines. METHODS: A retrospective review was conducted using the PearlDiver database. TJA procedures included total shoulder arthroplasty, total elbow arthroplasty, total hip arthroplasty, and total knee arthroplasty. The Cochran-Armitage Trend Test was used to evaluate trends in the volume of TJA procedures conducted in patients with RA between 2010 and 2019. Logistic regression was used to compare 2-year arthroplasty risk after an initial joint-specific RA International Classification of Diseases 10th Revision diagnosis for RA patients with versus without bDMARD exposure. RESULTS: A total of 2,942,360 patients with RA were identified, and 80,744 (2.74%) underwent TJA between 2010 and 2019. Rates of TJA procedures trended significantly upward over the decade (2.6% versus 5.1%, P < 0.001) with a sharp increase between 2015 and 2016 (2.1% versus 4.9%, P < 0.001). Among the 16,736 identified patients with an initial International Classification of Diseases 10th Revision joint-specific RA diagnosis, 3362 patients (20.09%) were treated with bDMARDs and 13,374 (79.91%) were not. Untreated patients exhibited significantly lower risk of any TJA (5.92% versus 7.73%; odds ratio [OR]: 0.72; 95% confidence interval [CI]: 0.64 to 0.82), total hip arthroplasty (OR: 0.69, 95% CI: 0.50 to 0.95), and total knee arthroplasty (OR: 0.63, 95% CI: 0.52 to 0.75) compared with treated patients. DISCUSSION: The volume of TJA procedures conducted in patients with RA has trended markedly upward over the past decade, with a sharp increase after 2015. bDMARD treatment was associated with markedly increased risk of TJA, likely because of initiation of bDMARDs in only those patients with advanced disease per ACR guidelines.

Local and Systemic Complications of Knee and Hip Arthroscopy: A Matched-Cohort Study.

Background: Surgeons are familiar with the complication rates and risks of knee arthroscopy, but comparative data between hip arthroscopy and knee arthroscopy are lacking. Purpose: To compare complications in knee arthroscopy, the most common arthroscopic procedure, with those in hip arthroscopy. Study Design: Cohort study; Level of evidence, 3. Methods: A retrospective matched-cohort study analyzing patients who received a primary hip or knee arthroscopy was performed using the PearlDiver database. A total of 19,735 patients were identified for each cohort. Systemic complications and readmissions were assessed at 3 months postoperatively. Local complications and reoperations were assessed at 6 months, 12 months, and 24 months postoperatively. All categorical variables were compared using chi-square analysis. Results: Hip arthroscopy had significantly higher rates of nerve injury, stiffness, heterotopic ossification, and avascular necrosis (all P < .001) than knee arthroscopy at all observed time periods postoperatively. Hip arthroscopy also had a greater rate of all local joint complications than knee arthroscopy (16.79% vs 11.80%; P < .001). Knee arthroscopy was found to have higher incidences of deep vein thrombosis (0.98% vs 0.66%; P < .001) and myocardial infarction (0.06% vs 0.00%; P < .001) as well as a higher overall systemic complication rate (3.93% vs 3.44%; P = .013). Hip arthroscopy was found to have higher rates of subsequent arthroscopy, arthroplasty, and overall reoperation when compared with knee arthroscopy (11.99% vs 14.99%; P < .001) at all time periods up to 24 months postoperatively. Conclusion: Although the systemic complication rate was higher in knee arthroscopy, local joint complications, reoperation, and total complication rates were higher for hip arthroscopy. Surgeons should be aware of these potential differences to best discuss and mitigate risks with this expanding patient population.

Femur Strength is Similar Before and After Iatrogenic Fracture During Total Hip Arthroplasty: A Biomechanical Analysis.

Background: The purpose of this study was to compare the biomechanical strength of femurs before an iatrogenic periprosthetic fracture vs after an initial fracture with supporting cerclage fixation during cementless total hip arthroplasty. Material and methods: Nineteen composite femurs and 5 matched pairs of cadaveric femurs were implanted with a single-wedge or dual-wedge tapered femoral stem and tested for ultimate load to failure producing a periprosthetic fracture. Following initial fracture, each femur was cerclaged with Vitallium cables and retested for ultimate load to failure. The mean force eliciting iatrogenic fracture before cabling and that after cabling were compared with a two-sided paired Student's t-test. Results: All composite femurs developed periprosthetic fractures with an average length extension from the calcar of 75.17 mm. For the 19 composite femurs, the mean ultimate load to failure before cabling and that after cabling were not significantly different (2422.95 N vs 2505.14 N, P = .678). For the 10 cadaveric femurs, the mean ultimate load to failure for the initial fracture vs that after cabling was statistically comparable (5828.62 N vs 7002.63 N, P = .126). Subanalysis of the 5 cadaveric femurs with a double-wedge stem revealed a significantly higher mean load to failure following cabling (5007.38 N vs 7811.17 N, P = .011). Conclusion: Biomechanical strength was similar for femurs that sustained an initial iatrogenic periprosthetic fracture and the same femurs cabled with cerclage wires after being fractured. These data may assist in operative decision-making for treating iatrogenic fractures during total hip arthroplasty.

Patella Strength Characteristics in Cemented vs Press-fit Implants: A Biomechanical Analysis of Initial Stability.

Background: Patellar resurfacing is routinely performed during total knee arthroplasty to reduce pain associated with patellofemoral osteoarthritis. With 3-dimensional ingrowth materials readily available, the present study aimed to evaluate if cemented polyethylene (CP) patellar buttons conferred higher ultimate load to failure than press-fit metal-backed (PF) buttons in axial compression. Material and methods: Ten matched cadaveric and 20 composite patellae were resurfaced and implanted with either a PF or CP button. Biomechanical testing using an MTS machine was performed to measure the force required to generate a periprosthetic patella fracture. Mean load to failure and load to failure per 1-mm patellar thickness were compared with a paired and independent samples Students' t-test for the cadaveric and composite patellae, respectively. Results: The average load to failure for the matched cadaveric patellae with PF implants was significantly lower than that for patellae with CP buttons (4082.05 N vs 5898.37 N, P = .045). The average load to failure for composite patella with PF implants was significantly higher than that for composite patellae with CP implants (6004.09 N vs 4551.40 N, P = .001). The mean load to failure per 1-mm patellar thickness was also significantly higher for composite patellae with PF implants (263.80 N/mm vs 200.37 N/mm, P = .001). Conclusion: Cadaveric patellae with cemented implants had a significantly higher ultimate load to failure in axial compression than press-fit patella. However, this result was reversed in the composite model. Exploration of biological and composite model properties could provide further insight into patellar implant selection during total knee arthroplasty.

How age and gender influence proximal humerus fracture management in patients older than fifty years.

BACKGROUND: As the aging population expands, proximal humerus fractures have become more prevalent. This study aimed to evaluate acute management of proximal humerus fractures in women and men older than the age of 50 years to determine how gender and age have affected definitive treatment selection over the last decade. METHODS: Patient records were retrospectively reviewed from a commercially available database, PearlDiver, to identify treatments for proximal humerus fractures between 2010 and 2019. Data were separated by age into two cohorts, patients aged 50-64 years and those aged 65 years and older before stratification by gender. Within each cohort, groups were matched with respect to age, region, and Elixhauser comorbidity index. Logistic regression analyses were performed to determine which gender was associated with a higher risk of undergoing operative treatment, which gender was associated with a higher risk of receiving arthroplasty, and which of the individual surgical operations were more likely given the patient's gender and age. RESULTS: In the 50- to 64-year-old cohort, men were less likely to be treated operatively than women (odds ratio [OR]: 0.90). However, men in this cohort had a 31% higher likelihood of receiving an arthroplasty procedure than women when given operative treatment. Specifically, men aged 50 to 64 years were more likely to receive hemiarthroplasty (OR: 1.48) and intramedullary nailing (OR: 1.19) and were less likely to have open reduction internal fixation (ORIF) (OR: 0.71). In the 65 years and older cohort, there was no relationship between gender and the likelihood of operative treatment for a proximal humerus fracture. Men older than 65 years had a 29% lower likelihood of receiving an arthroplasty type procedure than women older than 65 years. In addition, men older than 65 years were more likely to receive ORIF (OR: 1.14) and intramedullary nailing (OR: 1.43) and less likely to receive hemiarthroplasty (OR: 0.86) and reverse total shoulder arthroplasty (OR: 0.66) than similarly aged women. CONCLUSION: Both age and gender have an association with the definitive treatment patients received for proximal humerus fractures over the last decade. Women younger than 65 years of age were more likely to undergo operative treatment, although once older than 65 years, there was no influence of gender on operative treatment. Men younger than 65 years were more likely to receive arthroplasty and women, more likely to undergo ORIF; however, as patients reached the age of 65 years and older, this finding was reversed such that women were more likely to receive arthroplasty and men, ORIF. Further exploration into these differences could improve decision-making between surgeons and patients.

Examining the Relationship Between Mild Traumatic Brain Injuries and Development of Mental Illness Disorders in a Mid-Term Follow-up Period.

OBJECTIVE: The sequalae of mild concussions continue to emerge with increased awareness in sports-related injuries. This study aimed to quantify the number of patients who are affected by a mental illness within 3 yrs of a concussion and identify whether demographic differences exist that may influence a mental illness diagnosis. DESIGN: Using a nationwide database, data were queried for a diagnosis of concussion, capturing patients aged 18-45 yrs with no previous mental illness, and then identified if these patients were diagnosed with a mental illness within 3 yrs of their concussion. The mental illnesses specifically chosen for this study included depression, anxiety, panic disorder, posttraumatic stress disorder, bipolar, and schizophrenia. RESULTS: Within 3 yrs after a concussion, 48% of patients were later diagnosed with a mental illness. All of the mental illnesses this study chose to evaluate were present in a higher proportion of patients after a concussion than the general population. CONCLUSIONS: The mechanism between concussions and mental illness remains unclear. A large proportion of patients who experience a concussion are later diagnosed with a mental illness within 3 yrs. Patients with a history of a previous concussion may benefit from screening for the development of a mental illness.

Trending a decade of proximal humerus fracture management in older adults.

BACKGROUND: Proximal humerus fractures are the third most common fracture in older adults. Because of the aging population, the incidence of these fractures and their impact will continue to grow. With advancement in treatment options for proximal humeral fractures, the aim of this study was to evaluate the trends in acute management of proximal humerus fractures to determine how definitive treatment has changed over the past decade in patients older than 65 years. METHODS: Using a commercially available database, patient records were queried from 2010 to 2019 for the incidence of proximal humerus fractures. For each individual year, data were queried to identify the incidence of closed reduction percutaneous pinning (CRPP), hemiarthroplasty (HA), intramedullary nailing (IMN), open reduction internal fixation (ORIF), total shoulder arthroplasty (TSA), reverse total shoulder arthroplasty (RSA), or nonoperative treatment for acute proximal humeral fractures. A Cochran-Armitage trend test was used to determine significant changes in the trends of proximal humerus fracture management. Logistic regression analyses were performed to generate odds ratios (OR) with associated 95% confidence intervals comparing each individual procedure performed in 2019 to 2010. RESULTS: A total of 160,836 patients at least 65 years of age and older were diagnosed with a proximal humerus fracture. Of this total, 28,503 (17.72%) patients received operative treatment and 132,333 (82.28%) received nonoperative treatment. From 2010 to 2019, operative treatment trends of proximal humerus fractures changed such that CRPP decreased by 60.0%, HA decreased by 81.4%, IMN decreased by 81.9%, ORIF decreased by 25.7%, TSA decreased by 80.5%, and RSA increased by 1841.4% (all P < .0001). Overall, nonsurgical management increased from 80% to 85% during the examined study period (P < .0001). Patients in 2019 were significantly more likely to receive an RSA (OR 22.65) and were significantly less likely to receive CRPP (OR 0.45), HA (OR 0.20), IMN (OR 0.20), ORIF (OR 0.82), and TSA (OR 0.22) than patients in 2010. In addition, patients in 2019 were significantly more likely to receive nonoperative treatment than patients in 2010 (OR 1.10). CONCLUSION: Over the past decade, most of older adults who sustain proximal humerus fractures continue to receive nonoperative treatment. Although CRPP, IMN, HA, ORIF, and TSA have decreased, RSA has recently become more widely utilized, which is consistent with what has been noted in other countries. Continued examination of the mid- and long-term outcomes of the increasing percentages in RSA should be performed in this population.

A Review of Proximal Tibia Entry Points for Intramedullary Nailing and Validation of The Lateral Parapatellar Approach as Extra-articular.

Tibial shaft fractures are the most common long bone injury and are often treated surgically in an attempt to minimize complications. Although treatment options for tibial shaft fractures vary based on factors including open injury, severity of fracture, and soft tissue status, intramedullary nailing in adults has emerged as the preferred definitive option for stabilization. Therefore, the primary purposes of this review and cadaveric study were to evaluate the entry points for reamed tibial nails and the risks, benefits, and advantages of each approach. Due to concerns of violating the joint capsule and the generalized applicability to everyday practice of the extra-articular lateral parapatellar semi-extended technique, the secondary goal of this manuscript was to evaluate whether an intramedullary tibial nail can be consistently placed extra-articularly using the lateral parapatellar technique described by Kubiak et al. and generalizability to surgeons of varying experience.

Fracture Risk With Patella Resurfacing During Total Knee Arthroplasty After Anterior Cruciate Ligament Reconstruction Using Bone-Patella-Bone Autograft: A Biomechanical Analysis.

BACKGROUND: Anterior cruciate ligament (ACL) tears are common injuries. Ipsilateral bone patellar tendon bone (BPTB) autograft has been frequently used for ACL reconstructions. A large percentage of patients who sustain ACL ruptures develop early osteoarthritis and require total knee arthroplasty (TKA). When patients with previous BPTB autograft for an ACL tear undergo TKA, there may be an increased risk of fracture after patellar resurfacing. METHODS: There were 20 artificial Sawbones and 10 cadaveric patellae resurfaced. To simulate the presence of a previous BPTB autograft, a bone plug was removed from the anterior surface of the patellae and was resurfaced with a cemented patellar button. Biomechanical testing was performed to determine the compressive load to fracture of patellae with and without previous BPTB autograft. RESULTS: The average maximum load to failure for the artificial Sawbones patellae without a previous BPTB autograft was 4551.40 N ± 753.12 compared with 2855.39 N ± 531.46 with a previous BPTB autograft (P < .001). The average maximum load to failure for the cadaveric patellae without a previous BPTB autograft was 7256.37 N ± 1473.97 compared with 5232.22 N ± 475.04 with a previous BPTB autograft (P = .021). CONCLUSIONS: The results demonstrate a significantly lower maximum load to failure of a resurfaced patella in the presence of a previous BPTB autograft. This can be used to aid in the decision of whether to resurface the patellae in these patients and to educate patients that the presence of a previous BPTB autograft may be an increased risk factor for patella fracture after TKA.

Effect of Sickle Cell Trait on Total Hip Arthroplasty in a Matched Cohort.

BACKGROUND: It is unclear if sickle cell trait (SCT) carrier status conveys an increased risk for poor outcomes following total hip arthroplasty (THA). The purpose of this study is to compare short-term clinical outcomes of THA for patients with SCT vs matched controls. METHODS: Patient records were queried from the PearlDiver database using International Classification of Diseases, Ninth and Tenth Revision and Current Procedural Terminology codes. Patients with SCT who underwent THA were matched 1:1 with controls across age, gender, Elixhauser Comorbidity Index, obesity, and US region. Thirty-day and 90-day rates of systemic complications and 1-year and 2-year rates of joint complications were compared with logistic regression. RESULTS: In total, 1646 patients were assigned to each cohort. In the 30-day and 90-day postoperative periods, SCT carriers had a higher likelihood of cerebrovascular accident, anemia, acute renal failure, pneumonia, sepsis, deep vein thrombosis, pulmonary embolism, and respiratory failure (all P < .05). SCT carriers exhibited significantly higher risk of periprosthetic joint infection at both 1 (3.5% vs 2.1%; odds ratio [OR] 1.91, 95% confidence interval [CI] 1.22-2.99) and 2 years (3.7% vs 2.6%; OR 1.63, 95% CI 1.07-2.49) postoperatively. Prosthetic loosening was also significantly more likely for SCT carriers within 1 year (1.3% vs 0.3%; OR 4.49, 95% CI 1.75-13.86). CONCLUSION: Patients with SCT exhibited significantly higher risk for systemic complications, periprosthetic joint infection, and prosthetic loosening after THA. Increased perioperative efforts should be made to prevent hypoxia, acidosis, and dehydration, as these states increase red blood cell sickling, which may reduce complication rates and improve outcomes in patients with SCT.

Total Knee Arthroplasty in Freestanding Ambulatory Surgery Centers: 5-Year Retrospective Chart Review of 90-Day Postsurgical Outcomes and Health Care Resource Utilization.

INTRODUCTION: Migration of total knee arthroplasty (TKA) procedures from the inpatient setting to outpatient venues, especially freestanding ambulatory surgery centers (ASCs), requires the use of reliable patient selection algorithms and standardized perioperative pathways to facilitate favorable outcomes for patients. METHODS: This retrospective chart review included consecutive TKA procedures performed over a 5-year period between January 2014 and January 2019 at 2 freestanding ASCs. The patient selection algorithm was developed on the basis of patient comorbidities to minimize the potential for adverse events. All procedures were performed by one of eight orthopedic surgeons who were identified a priori as adhering to similar multimodal pain management regimens, including the use of spinal anesthesia, general or monitored-care anesthesia, adductor canal blocks, pericapsular injection of liposomal bupivacaine, nonsteroidal anti-inflammatory drugs, gabapentin, tramadol, acetaminophen, and oxycodone on an as-needed basis. Outcomes, including surgical complications, healthcare resource utilization (HCRU), and patient satisfaction, were measured before discharge and at a 90-day follow-up visit. RESULTS: Four hundred thirty-nine TKA procedures in 386 patients were identified for inclusion. Of these patients, 115 (29.8%) were performed in patients with the American Society of Anesthesiologists physical status IIIa. Mean (standard deviation) length of stay at the ASC was 500 (107) minutes, including 136 (47) minutes of surgery and 201 (78) minutes to ambulation. The overall rates of surgical complications and 90-day hospital admissions were low (1.4% and 0.7%, respectively), as was the need for additional HCRU, including additional surgical procedures related to index surgery, emergency department visits, and unplanned clinic visits or calls. At the 90-day follow-up visit, 96% of patients reported being pleased with their outcomes. DISCUSSION: With careful patient selection, standardized perioperative pathways, and multimodal analgesia protocols, TKA procedures can be performed in the ASC setting with low complication rates, minimal postdischarge HCRU, and high rates of patient satisfaction. LEVEL OF EVIDENCE: III.

The Promiscuity of Allosteric Regulation of Nuclear Receptors by Retinoid X Receptor.

The promiscuous protein retinoid X receptor (RXR) displays essential allosteric regulation of several members in the nuclear hormone receptor superfamily via heterodimerization and (anti)cooperative binding of cognate ligands. Here, the structural basis of the positive allostery of RXR and constitutive androstane receptor (CAR) is revealed. In contrast, a similar computational approach had previously revealed the mechanism for negative allostery in the complex of RXR and thyroid receptor (TR). By comparing the positive and negative allostery of RXR complexed with CAR and TR respectively, we reported the promiscuous allosteric control involving RXR. We characterize the allosteric mechanism by expressing the correlated dynamics of selected residue-residue contacts which was extracted from atomistic molecular dynamics simulation and statistical analysis. While the same set of residues in the binding pocket of RXR may initiate the residue-residue interaction network, RXR uses largely different sets of contacts (only about one-third identical) and allosteric modes to regulate TR and CAR. The promiscuity of RXR control may originate from multiple factors, including (1) the frustrated fit of cognate ligand 9c to the RXR binding pocket and (2) the different ligand-binding features of TR (loose) versus CAR (tight) to their corresponding cognate ligands.