Initial versus Staged Thyroidectomy for Differentiated Thyroid Cancer: A Retrospective Multi-Dimensional Cohort Analysis of Effectiveness and Safety.

The optimal surgical approach for differentiated thyroid cancer remains controversial, with debate regarding the comparative risks of upfront total thyroidectomy versus staged completion thyroidectomy following the initial lobectomy. This study aimed to assess the complication rates associated with these two strategies and identify the optimal timing for completion thyroidectomy using a multi-dimensional analysis of four cohorts: an institutional series (n = 148), the National Surgical Quality Improvement Program (NSQIP) database (n = 39,992), the TriNetX repository (n > 30,000), and a pooled literature review (10 studies, n = 6015). Institutional data revealed higher overall complication rates with total thyroidectomy (18.3%) compared to completion thyroidectomy (6.8%), primarily due to increased temporary hypocalcemia (10% vs. 0%, p = 0.004). The NSQIP analysis demonstrated that total thyroidectomy was associated with a 72% increased risk of transient hypocalcemia (p < 0.001) and a 25% increased risk of permanent hypocalcemia (p < 0.001). TriNetX data confirmed these findings and identified obesity and concurrent neck dissection as risk factors for complications. A meta-analysis showed that total thyroidectomy increased the rates of transient (RR = 1.63) and permanent (RR = 1.23) hypocalcemia (p < 0.001). Institutional and TriNetX data suggested that performing completion thyroidectomy between 1 and 6 months after the initial lobectomy minimized permanent complication rates compared to delays beyond 6 months. In conclusion, for differentiated thyroid cancer, total thyroidectomy is associated with higher risks of transient and permanent hypocalcemia compared to staged completion thyroidectomy. However, performing completion thyroidectomy within 1-6 months of the initial lobectomy may mitigate the risk of permanent complications. These findings can inform personalized surgical decision-making for patients with differentiated thyroid cancer.

Proximal radiolucent lines around fully hydroxyapatite-coated tapered femoral stems: should we be concerned?

INTRODUCTION: Radiolucent lines occasionally develop around the proximal aspect of fully hydroxyapatite (HA)-coated tapered femoral stems after total hip arthroplasty (THA). It was hypothesised that distal wedging of stems may predispose to proximal radiolucent line formation, which may negatively impact clinical outcome. METHODS: All primary THA performed with a collarless fully HA-coated stem that had a minimum of 1 year of radiographic follow-up were identified in a surgical database (n = 244). Radiographic measures of proximal femoral morphology and femoral canal fill at the middle and distal thirds of the stem were analysed for association with the presence of proximal radiolucent lines. Linear regression was used to explore any association between radiolucent lines and patient reported outcome measures (PROMs), available in 61% of patients. RESULTS: Proximal radiolucent lines developed in 31 cases (12.7%) at final follow-up. Dorr A femoral morphology and increased canal-fill at the distal ⅓ of the stem correlated with the development of radiolucent lines (p < 0.001). No correlation was observed between pain or PROMs and the presence of proximal radiolucent lines. DISCUSSION: We observed an unexpectedly high incidence of proximal femoral radiolucent lines about collarless fully HA coated stems. Distal-only implant wedging in Dorr A bone may compromise proximal fixation. Although this finding did not correlate with short-term outcomes, the long-term clinical impact requires further study.

Females Are More Likely Than Males to Fill an Opioid Prescription in the Year After Anterior Cruciate Ligament Reconstruction.

Purpose: To report rates of preoperative and postoperative opioid use between male and female patients and to identify risk factors for extended opioid use following anterior cruciate ligament reconstruction (ACLR). Methods: Patients undergoing ACLR between 2011 and 2018 were identified from the PearlDiver database. The opioid refill rates for males vs females were compared at monthly intervals for 1 year after ACLR. Patients who filled an opioid prescription <3 months before surgery were classified as opioid users, while those who had never filled one were classified as nonopioid users. Results: Of 106,995 ACLR patients, 37,890 (35.4%) were opioid users <3 months before surgery, and 37,554 (35.1%) had never filled an opioid prescription. Of the preoperative opioid users, 20,413 (53.9%) were female and 17,477 (46.1%) were male (P < .001). Postoperatively, females were at higher risk of filling an opioid prescription at each monthly interval, except for the first month after surgery. The refill rate for opioid users was also higher than that for nonopioid users at each monthly interval after ACLR. In addition to patient sex, a preoperative diagnosis of anxiety/depression, low back pain, myalgia, a history of drug dependence, alcohol abuse, and tobacco use increased a patient's risk of filling an opioid prescription postoperatively. Conclusions: This study demonstrated that females are significantly more likely to be opioid users than males prior to ACLR and are more likely to continue to refill an opioid prescription in the year following surgery. Multiple risk factors were associated with prolonged postoperative opioid utilization, including female sex, anxiety/depression, low back pain, myalgia, a history of drug dependence, alcohol abuse, and tobacco use. Level of Evidence: Level III, retrospective cohort study.

A CIRCULATION-FIRST APPROACH FOR RESUSCITATION OF TRAUMA PATIENTS WITH HEMORRHAGIC SHOCK.

ABSTRACT: The original guidelines of cardiopulmonary resuscitation focused on the establishment of an airway and rescue breathing before restoration of circulation through cardiopulmonary resuscitation. As a result, the airway-breathing-circulation approach became the central guiding principle of resuscitation. Despite new guidelines by the American Heart Association for a circulation-first approach, Advanced Trauma Life Support guidelines continue to advocate for the airway-breathing-circulation sequence. Although definitive airway management is often necessary for severely injured patients, endotracheal intubation (ETI) before resuscitation in patients with hemorrhagic shock may worsen hypotension and precipitate cardiac arrest. In severely injured patients, a paradigm shift should be considered, which prioritizes restoration of circulation before ETI and positive pressure ventilation while maintaining a focus on basic airway assessment and noninvasive airway interventions. For this patient population, the most reasonable current strategy may be to target a simultaneous resuscitation approach, with immediate efforts to control hemorrhage and provide basic airway interventions while prioritizing volume resuscitation with blood products and deferring ETI until adequate systemic perfusion has been attained. We believe that a circulation-first sequence will improve both survival and neurologic outcomes for a traumatically injured patient and will continue to advocate this approach, as additional clinical evidence is generated to inform how to best tailor circulation-first resuscitation for varied injury patterns and patient populations.

Consideration of pelvic tilt at the time of preoperative planning improves standing acetabular position after robotic-arm assisted total hip arthroplasty.

INTRODUCTION: Approximately half of dislocating total hip arthroplasties (THAs) demonstrate acetabular component position within traditional safe zones. It is unclear if postoperative functional acetabular position can be reliably improved by considering preoperative pelvic tilt. We investigated whether standing cup position targets could be more accurately achieved by considering preoperative standing pelvic tilt in addition to bone landmarks when planning for robot-assisted THA. METHODS: We reviewed 146 THAs performed by a single surgeon using computed tomography-based 3-dimensional planning and robotic technology to guide acetabular reaming and component insertion. Planning for 73 consecutive cases started at 40° of inclination and 22° of anteversion relative to the supine functional plane and was adjusted to better match native hip anatomy. Planning for the next 73 cases was modified to consider standing pelvic position based on standing preoperative radiographs. We compared groups to determine the rate when cups were placed outside our standing targets of 15-30° anteversion and 35-50° inclination. RESULTS: Cup position proved to be reliable in both groups, with 83% of cups in the anatomic planning cohort and 90% of cups in the functional planning cohort achieving standing targets for both anteversion and inclination (p = 0.227). Variances were lower in the functional planning group: 9.4° versus 15.8° of inclination (p = 0.079) and 18.3° versus 26.1° of anteversion (p = 0.352). The range of functional positions was narrower in the functional planning group: 35.7-47.5° versus 31.8-54.9° of inclination and 16.7-35.0° versus 10.1-35.9° of anteversion. DISCUSSION: Our results suggest enhanced planning that considers pelvic tilt, when coupled to a precision tool to achieve the plan, can reliably achieve target standing component positions. Considering preoperative functional pelvic position may improve postoperative functional acetabular component placement in THA, but the clinical benefit of this has yet to be confirmed.

Quality Assessment of YouTube Content on SLAP Tears.

OBJECTIVES: Superior labrum anterior posterior (SLAP) tears can cause shoulder pain, disability, instability, and humeral head translation. YouTube has become an increasingly popular source of medical information, but little is currently known in terms of quality control of the uploaded content. The purpose of this study was to assess the quality of YouTube videos related to the diagnosis and treatment of Superior Labrum Anterior Posterior (SLAP) tears. METHODS: YouTube was queried in August 2021 using the two predetermined keywords: 'SLAP tear' and 'superior labral tear.' The first 50 videos were analyzed by two independent reviewers and scored using 3 scoring systems: Global Quality Scale (GQS), the Journal of the American Medical Association (JAMA), and the Shoulder-Specific Score (SSS) to determine video accuracy and reliability. Title, number of views, video duration, video source, content type, views/day, number of likes, number of dislikes, days since upload, like ratio (Like × 100/ [Like + Dislike]) and Video Power Index (VPI) (Like ratio × View ratio/100) were all recorded and analyzed. RESULTS: The scores of most videos were low, with a mean JAMA score of 2.5 (1-4, SD 0.73), a mean GQS of 2.66 (0.5-4.5, SD 0.99) and a mean SSS of 7.13 (0-18, SD 4.39). There were significantly higher mean scores for JAMA, GQS, and SSS in the academic and independent physician categories, with a mean JAMA score of 3.11, GQS score of 3.39, and SSS score of 11 for academic sources and a mean JAMA score of 2.83, GQS score of 3.23, and SSS score of 9.23 for independent physician sources. JAMA score was significantly and positively correlated with video duration (r = 0.405, p = 0.006). Views, likes, dislikes, publication dates, and VPI were not significantly correlated with any scoring scale. CONCLUSION: YouTube videos on the diagnosis and management of SLAP tears have low overall quality and reliability scores. Independent physician and academic institution sources received higher mean scores for JAMA, GQS, and SSS. Video quality was not correlated with number of views.

Adoption of Robotic-Arm-Assisted Total Knee Arthroplasty Is Associated with Decreased Use of Articular Constraint and Manipulation under Anesthesia Compared to a Manual Approach.

Haptic robotic-arm-assisted total knee arthroplasty (RATKA) seeks to leverage three-dimensional planning, intraoperative assessment of ligament laxity, and guided bone preparation to establish and achieve patient-specific targets for implant position. We sought to compare (1) operative details, (2) knee alignment, (3) recovery of knee function, and (4) complications during adoption of this technique to our experience with manual TKA. We compared 120 RATKAs performed between December 2016 and July 2018 to 120 consecutive manual TKAs performed between May 2015 and January 2017. Operative details, lengths of stay (LOS), and discharge dispositions were collected. Tibiofemoral angles, Knee Society Scores (KSS), and ranges of motion were assessed until 3 months postoperatively. Manipulations under anesthesia, complications, and reoperations were tabulated. Mean operative times were 22 minutes longer in RATKA (p < 0.001) for this early cohort, but decreased by 27 minutes (p < 0.001) from the first 25 RATKA cases to the last 25 RATKA cases. Less articular constraint was used to achieve stability in RATKA (93 vs. 55% cruciate-retaining, p < 0.001; 3 vs. 35% posterior stabilized (PS), p < 0.001; and 4 vs. 10% varus-valgus constrained, p_ = _0.127). RATKA had lower LOS (2.7 vs. 3.4 days, p < 0.001). Discharge dispositions, tibiofemoral angles, KSS, and knee flexion angles did not differ, but manipulations were less common in RATKAs (4 vs. 17%, p = 0.013). We observed less use of constraint, shorter LOS, and fewer manipulations under anesthesia in RATKA, with no increase in complications. Operative times were longer, particularly early in the learning curve, but improved with experience. All measured patient-centered outcomes were equivalent or favored the newer technique, suggesting that RATKA with patient-specific alignment targets does not compromise initial quality. Observed differences may relate to improved ligament balance or diminished need for ligament release.

Thrombin spatial distribution determines protein C activation during hemostasis and thrombosis.

Rebalancing the hemostatic system by targeting endogenous anticoagulant pathways, like the protein C (PC) system, is being tested as a means of improving hemostasis in patients with hemophilia. Recent intravital studies of hemostasis demonstrated that, in some vascular contexts, thrombin activity is sequestered in the extravascular compartment. These findings raise important questions about the context-dependent contribution of activated PC (APC) to the hemostatic response, because PC activation occurs on the surface of endothelial cells. We used a combination of pharmacologic, genetic, imaging, and computational approaches to examine the relationships among thrombin spatial distribution, PC activation, and APC anticoagulant function. We found that inhibition of APC activity, in mice either harboring the factor V Leiden mutation or infused with an APC-blocking antibody, significantly enhanced fibrin formation and platelet activation in a microvascular injury model, consistent with the role of APC as an anticoagulant. In contrast, inhibition of APC activity had no effect on hemostasis after penetrating injury of the mouse jugular vein. Computational studies showed that differences in blood velocity, injury size, and vessel geometry determine the localization of thrombin generation and, consequently, the extent of PC activation. Computational predictions were tested in vivo and showed that when thrombin generation occurred intravascularly, without penetration of the vessel wall, inhibition of APC significantly increased fibrin formation in the jugular vein. Together, these studies show the importance of thrombin spatial distribution in determining PC activation during hemostasis and thrombosis.

Conservative Treatment of Avulsion Injuries of the Lesser Trochanter in Adolescent Athletes.

BACKGROUND:  Avulsion injuries of the lesser trochanter apophysis are relatively uncommon injuries and there have been no peer-reviewed case series dedicated to the evaluation and treatment of this injury. The purpose of this study is to characterize avulsion injuries of the lesser trochanter apophysis, review treatment protocols, and time to return to sport.  Methods: We reviewed 30 confirmed avulsion fractures of the lesser trochanter. Clinical data were reviewed to evaluate treatment protocols, duration, and time to return to sport. Radiographs were reviewed to confirm lesser trochanter avulsion and fracture displacement. RESULTS: There were 26 males and 4 females, with the average age at the time of injury being 14.2 years. Treatment modalities consisted of protective weight-bearing, discontinuation of the patient's sport in all cases, and formal physical therapy in 18 cases. The average treatment duration was 30.7 days. The mean follow-up time was 102 days. The radiographic assessment demonstrated an average fracture displacement of 5.1 mm. The average return to sport was 11 weeks. CONCLUSION: This is the first large case series studying avulsion injuries of the lesser trochanter. We have shown that these athletes can be managed non-surgically and can successfully return back to sport within three months.

Adoption of Robotic Arm-Assisted Total Hip Arthroplasty Results in Reliable Clinical and Radiographic Outcomes at Minimum Two-Year Follow Up.

INTRODUCTION: Longevity and success of total hip arthroplasty (THA) is largely dependent on component positioning. While use of robotic platforms can improve this positioning, published evidence on its clinical benefits is limited. Therefore, the aim of this study was to assess the clinical outcomes of THA with robotic surgical assistance. MATERIALS AND METHODS: We conducted an analysis of robotic arm-assisted primary THAs performed by a single surgeon utilizing a posterior approach. A total of 99 patients (107 cases) who had a minimum two-year follow up were identified. Their mean age was 61 years (range, 33 to 84 years), and their mean body mass index was 30.5 kg/m2 (range, 18.5 to 49.1 kg/m2). There were 56% female patients and primary osteoarthritis was the principal hip diagnosis in 88.8%. Operative times, lengths of hospital stay, and discharge dispositions were recorded, along with any complications. Modified Harris Hip Scores (HHS) were calculated to quantify clinical outcomes. RESULTS: Mean postoperative increases in HHS at 2- to 5.7-year follow up was 33 points (range, 6 to 77 points). There were no complications attributable to the use of robotic assistance. Surgical-site complications were rare; one case underwent a revision for prosthetic joint infection (0.93%) but there were no dislocations, periprosthetic fractures, or cases of mechanical implant loosening. There was no evidence of progressive radiolucencies or radiographic failure. DISCUSSION: Robotic arm-assisted THA resulted in low complication rates at minimum two-year follow up, with clinical outcomes comparable to those reported with manual surgery.1-4 The haptically-guided acetabular bone preparation enabled reliable cementless acetabular fixation and there were no adverse events related to the use of the robot. Dislocations were avoided in this case series. Randomized controlled clinical trials are needed to compare manual to robotic surgery and to investigate whether the precision found with this functional planning will reliably reduce the incidence of dislocations.

Femoral Neck Notching in Dual Mobility Implants: Is This a Reason for Concern?

BACKGROUND: Dual mobility (DM) total hip arthroplasty (THA) implants have been advocated for patients at risk for impingement due to abnormal spinopelvic mobility. Impingement against cobalt-chromium acetabular bearings, however, can result in notching of titanium femoral stems. This study investigated the incidence of femoral stem notching associated with DM implants and sought to identify risk factors. METHODS: A multicenter retrospective study reviewed 256 modular and 32 monoblock DM components with minimum 1-year clinical and radiographic follow-up, including 112 revisions, 4 conversion THAs, and 172 primary THAs. Radiographs were inspected for evidence of femoral notching and to calculate acetabular inclination and anteversion. Revisions and dislocations were recorded. RESULTS: Ten cases of femoral notching were discovered (3.5%), all associated with modular cylindrospheric cobalt-chromium DM implants (P = .049). Notches were first observed radiographically at mean 1.3 years after surgery (range 0.5-2.7 years). Notch location was anterior (20%), superior (60%), or posterior (20%) on the prosthetic femoral neck. Notch depth ranged from 1.7% to 20% of the prosthetic neck diameter. Eight cases with notching had lumbar pathology that can affect spinopelvic mobility. None of these notches resulted in stem fracture, at mean 2.7-year follow-up (range 1-7.6 years). There were no dislocations or revisions in patients with notching. CONCLUSION: Femoral notching was identified in 3.5% of DM cases, slightly surpassing the dislocation rate in a cohort selected for risk of impingement and instability. Although these cases of notching have not resulted in catastrophic failures thus far, further study of clinical sequelae is warranted. Component position, spinopelvic mobility, and implant design may influence risk.

Impact of Acetabular Implant Design on Aseptic Failure in Total Hip Arthroplasty.

BACKGROUND: Failure of cementless acetabular osseointegration is rare in total hip arthroplasty. Nevertheless, new fixation surfaces continue to be introduced. Novel implants may lack large diameter, constrained bearings, or dual mobility (DM) bearings to address instability. We compared clinical and radiographic outcomes for acetabular components with differing fixation surfaces and bearing options, focusing on the relationship between fixation surface and osseointegration and the relationship between bearing options and dislocation rate. METHODS: We retrospectively reviewed 463 total hip arthroplasties implanted with 3 different acetabular components between 2012 and 2016. Records were reviewed for demographics, clinical scores, and complications. Radiographs were examined for evidence of acetabular osteointegration. Analysis of variance and chi-square tests were used to compare cohorts. RESULTS: All cohorts had 100% survivorship free of acetabular fixation failure with no differences in clinical scores. Dislocation occurred in 1.3% of cases (n = 6). Analysis of the "transition" sizes, for which brand determined the maximum bearing diameter, revealed a significantly higher dislocation rate (3/50, 6%) in implants with limited bearing options. All 4 revisions for recurrent dislocation involved well-positioned components that did not accept large diameter, constrained bearings, or DM bearings, resulting in 3 shell revisions to expand bearing options. Femoral revisions were associated with dislocation risk but did not vary between cohorts. CONCLUSION: Dislocation was the primary mechanical cause for acetabular revision, while acetabular fixation failure was not encountered. We caution against selecting "new and improved" acetabular components without options for large diameter, constrained bearings, or DM bearings, even when enabling technology makes component positioning reliable.

Equivalent VTE rates after total joint arthroplasty using thromboprophylaxis with aspirin versus potent anticoagulants: retrospective analysis of 4562 cases across a diverse healthcare system.

BACKGROUND: Guidelines support aspirin thromboprophylaxis for primary total hip and knee arthroplasty (THA and TKA) but supporting evidence has come from high volume centers and the practice remains controversial. METHODS: We studied 4562 Medicare patients who underwent elective primary THA (1736, 38.1%) or TKA (2826, 61.9%) at 9 diverse hospitals. Thirty-day claims data were combined with data from the health system's electronic medical records to compare rates of venous thromboembolism (VTE) between patients who received prophylaxis with: (1) aspirin alone (47.3%), (2) a single, potent anticoagulant (29%), (3) antiplatelet agents other than aspirin or multiple anticoagulants (21.5%), or (4) low-dose subcutaneous unfractionated heparin or no anticoagulation (2.2%). Sub-analyses separately evaluating THA, TKA and cases from lower volume hospitals (n = 975) were performed. RESULTS: The 30-day VTE incidence was 0.6% (29/4562). VTE rates were equal in patients receiving aspirin and those receiving a single potent anticoagulant (0.5% in both groups). Patients with VTE were significantly older than patients without VTE (mean 76.5 vs. 73.1 years, P = 0.04). VTE rate did not associate with sex or hospital case volume. On bivariate analysis considering age, aspirin did not associate with greater VTE risk compared to a single potent anticoagulant (OR = 2.1, CI = 0.7-6.3) with the numbers available. Odds of VTE were increased with use of subcutaneous heparin or no anticoagulant (OR = 6.4, CI = 1.2-35.6) and with multiple anticoagulants (OR = 3.6, CI = 1.1-11.2). THA and TKA demonstrated similar rates of VTE (0.5% vs. 0.7%, respectively, P = 0.43). Of 975 cases done at lower volume hospitals, 387 received aspirin, none of whom developed VTE. CONCLUSIONS: This study provides further support for aspirin as an effective form of pharmacological VTE prophylaxis after total joint arthroplasty in the setting of a multi-modal regimen using 30-day outcomes. VTE occurred in 0.7% of primary joint arthroplasties. Aspirin prophylaxis did not associate with greater VTE risk compared to potent anticoagulants in the total population or at lower volume hospitals.

Benefits of CT Scanning for the Management of Hip Arthritis and Arthroplasty.

INTRODUCTION: Imaging studies for preoperative planning of total hip arthroplasty (THA) are typically obtained by two-dimensional (2D) anteroposterior radiographs. However, CT imaging has proven to be a valuable tool that may be more accurate than standard radiographs. The purpose of this review was to report on the current literature to assess the utility of CT imaging for preoperative planning of THA. Specifically, we assessed its utility in the evaluation of: 1) hip arthritis; 2) femoral head osteonecrosis; 3) implant size prediction; 4) component alignment; 5) limb length evaluation; and 6) radiation exposure. MATERIALS AND METHODS: A literature search was performed using search terms "computed tomography", "radiograph", "joint" "alignment", "hip," and "arthroplasty". Our initial search returned a total of 562 results. After applying our criteria, 26 studies were included. RESULTS: CT scans were found to be more accurate than radiographs in predicting implant size and alignment preoperatively and provide improved visualization of extraarticular deformities that may be essential to consider when planning a THA. Although radiation is a potential concern, newer imaging protocols have minimized the radiation to levels comparable to x-ray. CONCLUSION: The current literature suggests that CT has several advantages over radiographs for preoperative planning of THA including more accurate planning of implant size, component alignment, and postoperative leg length. It is also superior to x-ray in identifying extraarticular hip deformities using the minimum effective dose for CT and the minimum scan length required by templating software. The radiation can be reduced to values similar to radiography.

Impingement Resulting in Femoral Notching and Elevated Metal-Ion Levels After Dual-Mobility Total Hip Arthroplasty.

A 60-year-old woman underwent revision total hip arthroplasty with a modular dual-mobility articulation for recurrent dislocation. At 1-year follow-up, the patient reported no dislocations but had occasional clicking and discomfort with extreme motion. A Dunn radiograph identified notching of the femoral stem, attributed to impingement. Metal ions were elevated without adverse local-tissue reaction. After 4.5 years of observation, the notch size remained stable. She denied pain. Neither stem fracture nor prosthetic dislocation occurred. Impingement against cobalt-chromium acetabular bearing surfaces can result in notching of titanium femoral components after total hip arthroplasty. Increased anteversion intended to protect against posterior dislocation may be a risk factor. Posterior notching is best visualized on Dunn views, so incidence may be underestimated. No associated femoral implant fractures were identified on literature review.

Interrelationships between structure and function during the hemostatic response to injury.

Extensive studies have detailed the molecular regulation of individual components of the hemostatic system, including platelets, coagulation factors, and regulatory proteins. Questions remain, however, about how these elements are integrated at the systems level within a rapidly changing physical environment. To answer some of these questions, we developed a puncture injury model in mouse jugular veins that combines high-resolution, multimodal imaging with functional readouts in vivo. The results reveal striking spatial regulation of platelet activation and fibrin formation that could not be inferred from studies performed ex vivo. As in the microcirculation, where previous studies have been performed, gradients of platelet activation are readily apparent, as is an asymmetrical distribution of fibrin deposition and thrombin activity. Both are oriented from the outer to the inner surface of the damaged vessel wall, with a greater extent of platelet activation and fibrin accumulation on the outside than the inside. Further, we show that the importance of P2Y12 signaling in establishing a competent hemostatic plug is related to the size of the injury, thus limiting its contribution to hemostasis to specific physiologic contexts. Taken together, these studies offer insights into the organization of hemostatic plugs, provide a detailed understanding of the adverse bleeding associated with a widely prescribed class of antiplatelet agents, and highlight differences between hemostasis and thrombosis that may suggest alternative therapeutic approaches.

Coordination of platelet agonist signaling during the hemostatic response in vivo.

The local microenvironment within an evolving hemostatic plug shapes the distribution of soluble platelet agonists, resulting in a gradient of platelet activation. We previously showed that thrombin activity at a site of vascular injury is spatially restricted, resulting in robust activation of a subpopulation of platelets in the hemostatic plug core. In contrast, adenosine 5'-diphosphate (ADP)/P2Y12 signaling contributes to the accumulation of partially activated, loosely packed platelets in a shell overlying the core. The contribution of the additional platelet agonists thromboxane A2 (TxA2) and epinephrine to this hierarchical organization was not previously shown. Using a combination of genetic and pharmacologic approaches coupled with real-time intravital imaging, we show that TxA2 signaling is critical and nonredundant with ADP/P2Y12 for platelet accumulation in the shell region but not required for full platelet activation in the hemostatic plug core, where thrombin activity is highest. In contrast, epinephrine signaling is dispensable even in the presence of a P2Y12 antagonist. Finally, dual P2Y12 and thrombin inhibition does not substantially inhibit hemostatic plug core formation any more than thrombin inhibition alone, providing further evidence that thrombin is the primary driver of platelet activation in this region. Taken together, these studies show for the first time how thrombin, P2Y12, and TxA2 signaling are coordinated during development of a hierarchical organization of hemostatic plugs in vivo and provide novel insights into the impact of dual antiplatelet therapy on hemostasis and thrombosis.