Intravenous tranexamic acid reduces complications following surgical treatment of pathologic fractures of the lower extremity

BACKGROUND AND OBJECTIVES

This study aimed to evaluate the postoperative complications associated with administering intravenous (IV) tranexamic acid (TXA) in patients undergoing surgical fixation for neoplastic pathologic fractures of the lower extremities.

METHODS

Patients ≥18 years old who underwent surgical intervention for neoplastic pathologic lower extremity fractures from 2015 to 2021 were identified using the Premier Healthcare Database. This cohort was divided by TXA receipt on the index surgery day. Patient demographics, hospital factors, patient comorbidities, and 90-day complications were assessed and compared between the cohorts.

RESULTS

From 2015 to 2021, 4497 patients met inclusion criteria (769 TXA[+] and 3728 TXA[-]). Following propensity score matching, patients who received TXA had a significantly shorter length of stay than those who did not (7.6 ± 7.3 days vs. 9.0 ± 15.2, p = 0.036). Between the two cohorts, there were no significant differences in comorbidities. Regarding differences in postoperative complications, TXA(+) patients had significantly decreased odds of deep vein thrombosis (DVT) (1.87% vs. 5.46%; odds ratio [OR]:0.33; 95% confidence interval: 0.17-0.62; p = 0.001).

CONCLUSION

Administration of IV TXA may be associated with a decreased risk of postoperative DVT without an increased risk of other complications. Orthopedic surgeons should consider the utilization of IV TXA in patients treated surgically for neoplastic pathologic fractures of the lower extremity.

Risk Factors Associated with Thromboembolic Complications After total Hip Arthroplasty: An Analysis of 1,129 Pulmonary Emboli

INTRODUCTION

Venous thromboembolism (VTE) remains a dangerous complication after total hip arthroplasty (THA), despite advances in chemoprophylactic measures. This study aimed to identify risk factors of developing pulmonary embolism (PE) and deep vein thrombosis (DVT) after THA using a modern cohort of patients reflecting contemporary practices.

METHODS

The Premier Healthcare Database was queried for primary, elective THAs from January 1st, 2015, to December 31st, 2021. Patients who developed PE or DVT within 90 days of THA were compared with patients who did not develop any postoperative VTE. Differences in patient demographics, comorbidities, hospital factors, perioperative medications, chemoprophylactic agents, and allogeneic blood transfusion were compared between cohorts. Multivariable logistic regression models were used to identify independent risk factors of PE and DVT. In total, 544,298 THAs were identified, of which 1,129 (0.21%) developed a PE and 1,799 (0.33%) developed a DVT.

RESULTS

Patients diagnosed with a PE had significantly higher rates of in-hospital death (2.6% vs 0.1%, P < 0.001) compared with those without a PE. Age (adjusted odds ratio: 1.02 per year, 95% confidence interval [CI]: 1.01 to 1.03) and Black race (aOR: 1.52, 95% CI: 1.24 to 1.87) were associated with an increased risk of PE. Comorbidities associated with increased risk of PE included chronic pulmonary disease (aOR: 1.58, 95% CI: 1.36 to 1.84), pulmonary hypertension (aOR: 2.06, 95% CI: 1.39 to 3.04), and history of VTE (aOR: 2.38, 95% CI: 1.98 to 2.86). Allogeneic blood transfusion (aOR: 2.40, 95% CI: 1.88 to 3.06) was also associated with an increased risk of PE while dexamethasone utilization was associated with a reduced risk (aOR: 0.83, 95% CI: 0.73 to 0.95).

DISCUSSION

Increasing age; Black race; allogeneic blood transfusion; and comorbidities, including chronic pulmonary disease, pulmonary hypertension, and history of VTE, were independent risk factors of PE after THA. Given the increased mortality associated with PE, patients should be carefully evaluated for these factors and managed with an appropriate chemoprophylactic regimen.

Same-Day Total Joint Arthroplasty in the United States From 2016 to 2020: The Impact of the Medicare Inpatient Only List and the COVID-19 Pandemic

BACKGROUND

Same-day total hip arthroplasty (THA) and total knee arthroplasty (TKA) continue to gain popularity in the United States. The present study sought to quantify recent same-day outpatient trends taking into consideration the COVID-19 pandemic as well as the removal of these procedures from the Medicare inpatient only (IPO) list.

METHODS

Patients undergoing primary elective TKA and THA were identified using the Nationwide Ambulatory Surgery Sample and the National Inpatient Sample from January 1, 2016, to December 31, 2020. The same-day cohort included Nationwide Ambulatory Surgery Sample and National Inpatient Sample patients with a length of stay = 0 days. The inpatient cohort included patients with length of stay ≥1 day. National estimates were extrapolated using weight functions.

RESULTS

From January 2016 to December 2020, the proportion of same-day TKA increased from 1.2 (719) to 62.4% (31,293) and the proportion of same-day THA increased from 2.0 (599) to 54.5% (18,252). Following removal from the Medicare IPO list, same-day TKAs increased from 3.2% (1,895) in December 2017 to 13.8% (9,269) in January 2018, and same-day THAs increased from 10.7% (4,295) in December 2019 to 22.5% (8,708) in January 2020. Between February and March 2020, same-day TKAs increased from 42.4 (26,148) to 44.4% (16,972) and same-day THAs increased from 28.5 (10,729) to 30.2% (7,409).

CONCLUSIONS

The proportion of same-day TKA and THA dramatically increased following removal from the Medicare IPO list and in response to the COVID-19 pandemic. By December 2020, same-day TKA and THA accounted for >50% of all cases performed in the United States.

Robotic-Assisted Total Knee Arthroplasty in Obese Patients

Background

Robotic-assisted systems have gained popularity in total knee arthroplasty (TKA). The purpose of this study was to evaluate operative characteristics and radiographic outcomes of obese patients undergoing robotic-assisted TKA.

Methods

A retrospective review of consecutive cases performed by a single surgeon was performed from January 1, 2016, to January 31, 2022. Adult patients with body mass index ≥35 kg/m2 who underwent primary TKA using a computed tomography-assisted robotic system were compared to patients who underwent primary TKA using conventional instrumentation. Demographics, preoperative and postoperative radiographic measurements, and intraoperative outcomes were compared between cohorts. In total, 119 patients were identified, 60 in the robotic-assisted cohort and 59 in the conventional instrumentation cohort.

Results

Age, body mass index, and estimated blood loss were not significantly different between the cohorts. The robotic-assisted cohort experienced longer tourniquet times (93.3 vs 75.5 minutes, P < .001). Preoperative hip-knee-ankle angle (HKA) was similar between the robotic-assisted and conventional cohorts (8.4° ± 4.9° vs 9.3° ± 5.3°, P = .335). Postoperative HKA was 2.0° ± 1.4° in the robotic-assisted group and 3.1° ± 3.23° in the conventional group (P = .040). The proportion of patients with postoperative HKA > 3° of varus or valgus was 9 of 60 (15.0%) in the robotic-assisted cohort compared to 18 of 59 (30.5%) using conventional instrumentation (P = .043).

Conclusions

Obese patients treated with robotic-assisted TKA had postoperative alignment closer to neutral and fewer postoperative radiographic outliers than patients treated with conventional instrumentation. The results of this study support use of robotic-assisted technologies in TKA, particularly in obese patients.

An Updated Estimate of Total Hip and Total Knee Arthroplasty Inpatient Case Volume During the 2020 COVID-19 Pandemic in the United States

Background

Inpatient total hip arthroplasty (THA) and total knee arthroplasty (TKA) practices were dramatically affected in the United States in 2020 as elective surgeries were paused in response to the COVID-19 pandemic. This study sought to provide an updated estimate of inpatient total joint arthroplasty (TJA) case volumes in the United States in 2020.

Methods

A retrospective cohort study was performed by identifying all adult patients who underwent primary, elective TJA from January 1st, 2017 to December 31st, 2020, using the National Inpatient Sample. Monthly and annual case volumes were reported with descriptive statistics. Baseline case volumes were established by taking the average number of monthly cases performed in 2017, 2018, and 2019. These monthly averages were compared to 2020 values.

Results

From 2017 to 2019, the average case volume was 1,056,669 cases per year (41.0% THA, 59.0% TKA) and 88,055 cases per month. In 2020, 535,441 cases were identified (45.4% THA, 54.6% TKA), corresponding to a 49.3% reduction from the 2017-2019 annual average. Monthly cases decreased to 4515 in April during the "first wave" of COVID-19, corresponding to a 94.8% decrease from prior years. In June, cases rebounded to 55,520 before decreasing again in July to 50,100 during the "second wave" of COVID-19. During the "third wave," COVID-19 cases decreased month-over-month from October through December (56.5% decrease).

Conclusions

This updated estimate identified a 49.3% decrease in inpatient TJA cases in 2020 compared to prior years. This is similar to the 46.5-47.7% decrease in case volume previously reported.

Limited Durability of Extensor Mechanism Reconstruction Following Total Knee Arthroplasty: Mesh and Allograft Show Equivalent Outcomes at Five-Year Follow-Up

BACKGROUND

Extensor mechanism disruption is a challenging complication following total knee arthroplasty. The purpose of this study was to compare outcomes between patients who received mesh versus allograft extensor mechanism reconstruction.

METHODS

All patients who underwent extensor mechanism reconstruction at a single institution were screened. Demographic and surgical variables were recorded, including technique (ie, synthetic mesh versus allograft reconstruction). Patients were assessed for preoperative and postoperative extensor lag, revision, and duration of follow-up. Analyses, including Kaplan-Meier survivorships, were performed to compare mesh to allograft reconstruction. In total, 50 extensor mechanism reconstructions (30 mesh and 20 allograft) were conducted between January 1st, 2001, and December 31st, 2022.

RESULTS

There were no differences between the cohorts with respect to revision (26.7 [8 of 30] versus 35.0% [7 of 20], P = .680) or failure defined as above knee amputation or fusion (6.7 [2 of 30] versus 5.0% [1 of 20], P = .808). There were also no differences in time to reoperation (average 27 months [range, 6.7 to 58.8] versus 29 months [range, 1.2 to 84.9], P = .910) or in postoperative extensor lag among patients who did not undergo a reoperation (13 [0 to 50] versus 11° [0 to 30], P = .921). The estimated 5-year Kaplan-Meier survival with extensor mechanism revision as the endpoint was similar between the 2 groups (52.1, 95% confidence interval [CI] = 25.4 to 73.3 versus 55.0%, 95% CI = 23.0 to 78.4%, P = .990).

CONCLUSIONS

The purpose of this study was to present the findings of a large cohort of patients who required extensor mechanism reconstruction. Regardless of the reconstruction type, the 5-year outcomes of patients requiring extensor mechanism reconstruction are suboptimal.

Higher Blood Glucose Levels on the Day of Surgery Are Associated with an Increased Risk of Periprosthetic Joint Infection After Total Hip Arthroplasty

BACKGROUND

Hyperglycemia has been identified as a risk factor for periprosthetic joint infection (PJI) after total hip arthroplasty (THA). However, there is no consensus with regard to the preoperative blood glucose level (BGL) on the day of the surgical procedure associated with increased risk. We sought to identify preoperative BGL thresholds associated with an increased risk of PJI.

METHODS

The Premier Healthcare Database was retrospectively queried for adult patients who underwent primary, elective THA and had a measurement of the preoperative BGL recorded on the day of the surgical procedure (preoperative BGL) from January 1, 2016, to December 31, 2021. The association between preoperative BGL and 90-day PJI risk was modeled using multivariable logistic regression with restricted cubic splines. Patients with and without diabetes with a preoperative BGL associated with 1.5 times greater odds of PJI (high preoperative BGL) were then compared with patients with a normal preoperative BGL.

RESULTS

In this study, 90,830 patients who underwent THA and had a recorded preoperative BGL were identified. The preoperative BGL associated with 1.5 times greater odds of PJI was found to be 277 mg/dL in patients with diabetes and 193 mg/dL in patients without diabetes. Compared with the normal preoperative BGL cohort, those with high preoperative BGL had increased odds of PJI (adjusted odds ratio [OR], 2.60 [95% confidence interval (CI), 1.45 to 4.67] for patients with diabetes and 1.66 [95% CI, 1.10 to 2.51] for patients without diabetes) and 90-day readmissions (adjusted OR, 1.92 [95% CI, 1.45 to 2.53] for patients with diabetes and 1.66 [95% CI, 1.37 to 2.00] for patients without diabetes).

CONCLUSIONS

Increased preoperative BGL was found to be associated with an increased risk of PJI following primary THA. Surgeons should be aware of patients with diabetes and a preoperative BGL of >277 mg/dL and patients without diabetes but with a preoperative BGL of >193 mg/dL.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Dexamethasone-Associated Hyperglycemia is Not Associated With Infectious Complications After Total Joint Arthroplasty in Diabetic Patients

BACKGROUND

Postoperative infection is a devastating complication of total joint arthroplasty (TJA). Perioperative use of dexamethasone in patients who have diabetes mellitus (DM) remains controversial due to concern for increased infection risk. This study aimed to evaluate the association between dexamethasone and infection risk among patients who have DM undergoing TJA.

METHODS

This was a retrospective cohort study conducted on adult patients who underwent primary, elective total knee arthroplasty (TKA) or total hip arthroplasty (THA) between January 2016 and December 2021 using a large national database. We identified 110,568 TJA patients (TKA: 66.6%; THA: 33.4%), 31.0% (34,298) of which had DM. Patients who received perioperative dexamethasone were compared to those who did not. The primary end points were the 90-day risk of postoperative periprosthetic joint infection, surgical site infection (SSI), and other non-SSI (urinary tract infection, pneumonia, sepsis).

RESULTS

When modeling the association between dexamethasone exposure and study outcomes while accounting for the interaction between dexamethasone and morning blood glucose levels, dexamethasone administration conferred no increased odds of postoperative periprosthetic joint infection nor SSI in diabetics. However, dexamethasone significantly lowered the adjusted odds of other postoperative infections in diabetic patients (TKA: adjusted odds ratio = 09, 95% confidence interval = 0.8 to 1.0, P = .030; THA: adjusted odds ratio = 0.7, 95% confidence interval = 0.6 to 0.9, P = .001); specifically in patients with morning blood glucose levels between 110 to 248 mg/dL in TKA and ≤ 172 mg/dL in THA.

CONCLUSIONS

This study provides strong evidence against withholding dexamethasone in diabetic patients undergoing TJA based on concern for infection. Instead, short-course perioperative dexamethasone reduced infection risk in select patients. The narrative surrounding dexamethasone should shift away from questions about whether dexamethasone is appropriate for diabetic patients, and instead focus on how best to optimize its use.

Total Hip and Total Knee Arthroplasty Outpatient Case Volume During the 2020 COVID-19 Pandemic in New York and California

BACKGROUND

Inpatient total hip and total knee arthroplasty were substantially impacted by the SARS-CoV-2 (COVID-19) pandemic. We sought to characterize the transition of total joint arthroplasty (TJA) to the outpatient setting in 2 large state health systems during this pandemic.

METHODS

Adult patients who underwent primary elective TJA between January 1, 2016 and December 31, 2020 were retrospectively reviewed using the New York Statewide Planning and Research Cooperative System and California Department of Health Care Access and Information datasets. Yearly inpatient and outpatient case volumes and patient demographics, including age, sex, race, and payer coverage, were recorded. Continuous and categorical variables were compared using descriptive statistics. Significance was set at P < .05.

RESULTS

In New York during 2020, TJA volume decreased 16% because 22,742 fewer inpatient TJAs were performed. Much of this lost volume (46.6%) was offset by a 166% increase in outpatient TJA. In California during 2020, TJA volume decreased 20% because 34,114 fewer inpatient TJAs were performed. Much of this lost volume (37%) was offset by a 47% increase in outpatient TJA.

CONCLUSIONS

This present study demonstrates a marked increase in the proportion of TJA being performed on an outpatient basis in both California and New York. In both states, despite a decrease in overall TJA volume in 2020, outpatient TJA volume increased markedly.

LEVEL OF EVIDENCE

Therapeutic Level IV, Retrospective Cohort Study.

Tranexamic Acid Is Safe in Patients with a History of Venous Thromboembolism Undergoing Total Joint Arthroplasty

BACKGROUND

Tranexamic acid (TXA) is increasingly utilized during total knee arthroplasty (TKA) and total hip arthroplasty (THA) to decrease blood loss; however, there are concerns with regard to potential thromboembolic complications, particularly in high-risk patients. This study sought to define a subset of patients at elevated risk for thromboembolic complications following total joint arthroplasty (TJA) and to compare postoperative outcomes between patients who received TXA and those who did not.

METHODS

Patients who underwent primary, elective TJA from 2015 to 2021 were identified in the Premier Healthcare Database. Patients with a history of venous thromboembolism, defined as a history of pulmonary embolism or deep vein thrombosis, were identified and formed the high-risk cohort. Patient demographic characteristics, hospital factors, patient comorbidities, antithrombotic medication use, perioperative blood transfusion, and 90-day complications were assessed and compared between patients who received TXA and those who did not. Univariate regression and multivariable regression were performed to account for potential confounders.

RESULTS

The high-risk cohort comprised 70,759 patients who underwent TJA, of whom 46,074 (65.1%) received TXA and 24,685 (34.9%) did not. After controlling for confounding factors, patients in the TXA cohort had similar risks of pulmonary embolism (adjusted odds ratio [OR], 0.90 [95% confidence interval (CI), 0.79 to 1.02]; p = 0.097), stroke (adjusted OR, 0.97 [95% CI, 0.69 to 1.37]; p = 0.867), and myocardial infarction (adjusted OR, 0.93 [95% CI, 0.69 to 1.24]; p = 0.614) compared with patients who did not receive TXA. Patients who received TXA demonstrated decreased risks of transfusion (adjusted OR, 0.42 [95% CI, 0.38 to 0.46]; p < 0.001) and 90-day readmission (adjusted OR, 0.87 [95% CI, 0.80 to 0.94]; p < 0.001).

CONCLUSIONS

TXA utilization was not associated with an increased risk of postoperative pulmonary embolism, stroke, or myocardial infarction in patients with a history of venous thromboembolism. Furthermore, patients who received TXA had a decreased risk of transfusion and readmission. This evidence suggests that TXA may be safely utilized among select high-risk patients.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Increased Complication Risk Associated With Simultaneous Bilateral Total Hip Arthroplasty: A Contemporary, Matched Cohort Analysis

BACKGROUND

Simultaneous bilateral total hip arthroplasty (sbTHA) continues to be performed in patients who have bilateral end-stage osteoarthritis. However, few studies have evaluated the risk associated with this practice compared to unilateral total hip arthroplasty (THA).

METHODS

Using a large national database, primary, elective sbTHAs, and unilateral THAs were identified from January 1, 2015 to December 31, 2021. The sbTHAs were matched to unilateral THAs at a 1:5 ratio on age, sex, and pertinent comorbidities. Patient characteristics and comorbidities, and hospital factors were compared between both cohorts. Additionally, 90-day risk of postoperative complications, readmissions, and in-hospital deaths were assessed. After matching, 2,913 sbTHAs were compared to 14,565 unilateral THAs with an average age of 58.5 ± 10.0 years.

RESULTS

Compared to unilateral patients, sbTHA patients demonstrated higher rates of pulmonary embolism (PE) (0.4 versus 0.2%, P = .002), acute renal failure (1.2 versus 0.7%, P = .007), acute blood loss anemia (30.4 versus 16.7%, P < .001), and need for transfusion (6.6 versus 1.8%, P < .001). After accounting for confounders, sbTHA patients demonstrated increased risk of PE (adjusted odds ratio [aOR]: 3.76, 95% CI: 1.84 to 7.70, P < .001), acute renal failure (aOR: 1.83, 95% CI: 1.23 to 2.72, P = .003), acute blood loss anemia (aOR: 2.3, 95% CI: 2.10 to 2.53, P < .001), and transfusion (aOR: 4.08, 95% CI: 3.35 to 4.98, P < .001) compared to unilateral THA patients.

CONCLUSION

The practice of performing sbTHA was associated with an increased risk of PE, acute renal failure, and risk of transfusion. Careful evaluation of patient-specific risk factors is warranted when considering these bilateral procedures.

Complications of cryoprobe cryoablation as a surgical adjuvant for the treatment of metastatic carcinoma to bone, benign bone tumors, and soft tissue tumors: A series of 148 patients

BACKGROUND AND OBJECTIVE

This study describes the complication profile of modern cryoablation utilizing probes as an adjuvant during open surgical treatment of orthopedic tumors.

METHODS

A retrospective, single-surgeon study was performed for patients receiving cryoprobe cryoablation. Demographic information, malignancy-related and operative details, and clinical courses were collected. Outcomes assessed included rates of complications, recurrence, and correlations between the number of probes or cryoablation cycles performed.

RESULTS

In this 148-patient study, 67.6% had metastatic carcinoma to bone, 27.7% had benign bone tumors, and 4.7% had soft tissue tumors. An average of 3.4 ± 1.7 cryoablation probes were utilized and 1.7 ± 0.6 freezing cycles were performed. The overall cohort aggregate complication rate was 16.9%. These complications included postoperative fracture (3.4%), nerve palsy (2.7%), wound complications (7.4%), and infection (3.4%). The number of cycles and probes was significantly correlated with the incidence of aggregate complications in the overall cohort (Pearson = 0.162, p = 0.049) and metastatic bone cohort (Pearson = 0.222, p = 0.027). There were 13 recurrences.

CONCLUSION

This study describes the complication rates involving cryoablation probes used as surgical adjuvants. Greater probe number usage was correlated with increased aggregate complications in patients with metastatic disease to bone; meanwhile, more treatment cycles were associated with increased aggregate complications in the overall cohort.

Perioperative Dexamethasone Associated With Decreased Length of Stay After Total Hip and Knee Arthroplasty

INTRODUCTION

Dexamethasone is increasingly used after total joint arthroplasty (TJA) to reduce postoperative nausea and vomiting (PONV) and pain. The primary aim of this study was to examine the relationship between perioperative intravenous (IV) dexamethasone and length of stay (LOS) in patients undergoing primary, elective TJA.

METHODS

All patients who underwent TJA from 2015 to 2020 and received perioperative IV dexamethasone were queried from the Premier Healthcare Database. The cohort of patients who received dexamethasone was randomly truncated by a power of 10 and matched in a 1:2 ratio based on age and sex to patients who did not receive dexamethasone. Patient characteristics, hospital factors, comorbidities, 90-day postoperative complications, LOS, and postoperative morphine milligram equivalents were recorded for each cohort. Univariate and multivariate analyses were conducted to assess differences.

RESULTS

Overall, 190,974 matched patients were included, 63,658 (33.3%) of whom received dexamethasone and 127,316 (66.7%) did not. The dexamethasone cohort was composed of fewer patients with uncomplicated diabetes (11.6% vs. 17.5%, P < 0.001). Patients who received dexamethasone had significantly decreased mean LOS compared with patients who did not receive dexamethasone (1.66 vs. 2.03 days, P < 0.001). After controlling for confounding variables, dexamethasone was associated with significantly lower risk of pulmonary embolism (adjusted odds ratio [aOR]: 0.74, 95% CI: 0.61 to 0.90, P = 0.003), deep vein thrombosis (aOR: 0.78, 95% CI: 0.68 to 0.89, P < 0.001), PONV (aOR: 0.75, 95% CI: 0.70 to 0.80, P < 0.001), acute kidney injury (aOR: 0.82, 95% CI: 0.75 to 0.89, P < 0.001), and urinary tract infection (aOR: 0.77, 95% CI: 0.70 to 0.80, P < 0.001). In aggregate, dexamethasone was associated with similar postoperative opioid utilization between cohorts ( P = 0.061).

CONCLUSION

Perioperative dexamethasone was associated with reduced LOS and decreased postoperative complications including PONV, pulmonary embolism, deep vein thrombosis, acute kidney injury, and urinary tract infection after TJA. Although perioperative dexamethasone was not associated with notable reductions in postoperative opioid utilization, this study supports the use of dexamethasone to decrease LOS through multifactorial mechanisms beyond decreased pain.

Increased Risk of Venous Thromboembolism in Patients with Postoperative Anemia After Total Joint Arthroplasty: Are Transfusions to Blame?

BACKGROUND

The relationship between anemia and the risk of venous thromboembolism (VTE) following total knee arthroplasty (TKA) and total hip arthroplasty (THA) remains unclear. Red blood cell (RBC) transfusions, which have been shown to have thrombogenic effects, may explain conflicting data. This study sought to elucidate the relationship between anemia, RBC transfusions, and VTE following total joint arthroplasty (TJA).

METHODS

Using the International Classification of Diseases, Tenth Revision (ICD-10) and Current Procedural Terminology (CPT) codes, the Premier Healthcare Database was queried for all adults who underwent primary elective THA or TKA from January 2015 to December 2020. Patients were classified into 3 cohorts: those who did not have a diagnosis of anemia and did not receive an RBC transfusion (the control group), those with acute blood loss anemia who did not receive a transfusion (the anemia without transfusion group), and those with acute blood loss anemia who did receive a transfusion (the anemia with transfusion group). The primary outcomes assessed were the 90-day rate and risk of deep vein thrombosis (DVT), pulmonary embolism (PE), and aggregate VTE. Analysis of variance and pairwise comparisons were used to compare groups. Multivariable analyses were performed to account for confounding factors.

RESULTS

The 1,290,815 patients identified as having undergone TJA included 1,078,507 control patients (83.6%), 198,233 patients who had anemia without transfusion (15.4%), and 14,075 patients who had anemia and transfusion (1.1%). Age, sex, race, length of hospital stay, and hospital costs were significantly different between the 3 groups. After adjusting for confounding factors, there was no difference between the anemia without transfusion group and the control group with regard to DVT (adjusted odds ratio [OR], 0.97 [95% confidence interval (CI), 0.89 to 1.06]; p = 0.500), PE (adjusted OR, 1.04 [95% CI, 0.92 to 1.18]; p = 0.543), and VTE (adjusted OR, 0.99 [95% CI, 0.92 to 1.06]; p = 0.697). However, patients with anemia and transfusion had an increased risk of PE (adjusted OR, 1.83 [95% CI, 1.34 to 2.51]; p < 0.001) and VTE (adjusted OR, 1.39 [95% CI, 1.14 to 1.70]; p = 0.001) compared with patients in the control group.

CONCLUSIONS

Patients with acute blood loss anemia who received a transfusion were at increased risk for developing VTE following TJA, whereas patients with anemia who did not receive a transfusion were not. Orthopaedic surgeons need to be aware of the risks of transfusion and individualize the use of transfusions in their patients.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Complications and Safety of Simultaneous Bilateral Total Knee Arthroplasty: A Patient Characteristic and Comorbidity-Matched Analysis

BACKGROUND

Total knee arthroplasty (TKA) is a highly successful surgical procedure that decreases pain and improves function. Many patients who undergo TKA may require surgical intervention on both extremities because of bilateral osteoarthritis. The purpose of this study was to evaluate the safety of simultaneous bilateral TKA compared with that of unilateral TKA.

METHODS

Patients who underwent unilateral or simultaneous bilateral primary, elective TKA from 2015 to 2020 were identified using the Premier Healthcare Database. Subsequently, the simultaneous bilateral TKA cohort was matched to the unilateral TKA cohort in a 1:6 ratio by age, sex, race, and presence of pertinent comorbidities. Patient characteristics, hospital factors, and comorbidities were compared between the cohorts. The 90-day risks of postoperative complications, readmission, and in-hospital death were assessed. Differences were assessed using univariable regression, and multivariable regression analyses were performed to account for potential confounders.

RESULTS

Overall, 21,044 patients who underwent simultaneous bilateral TKA and 126,264 matched patients who underwent unilateral TKA were included. After accounting for confounding factors, patients who underwent simultaneous bilateral TKA demonstrated a significantly increased risk of postoperative complications, including pulmonary embolism (adjusted odds ratio [OR], 2.13 [95% confidence interval (CI), 1.57 to 2.89]; p < 0.001), stroke (adjusted OR, 2.21 [95% CI, 1.42 to 3.42]; p < 0.001), acute blood loss anemia (adjusted OR, 2.06 [95% CI, 1.99 to 2.13]; p < 0.001), and transfusion (adjusted OR, 7.84 [95% CI, 7.16 to 8.59]; p < 0.001). Patients who underwent simultaneous bilateral TKA were at increased risk of 90-day readmission (adjusted OR, 1.35 [95% CI, 1.24 to 1.48]; p < 0.001).

CONCLUSIONS

Simultaneous bilateral TKA was associated with increased rates of complications including pulmonary embolism, stroke, and transfusion. Orthopaedic surgeons and patients should consider these potential complications when contemplating simultaneous bilateral TKA. When simultaneous bilateral TKA is pursued, patient counseling and thorough medical optimization should be performed.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Medicaid Patients Undergo Total Joint Arthroplasty at Lower-Volume Hospitals by Lower-Volume Surgeons and Have Poorer Outcomes

BACKGROUND

Medicaid insurance coverage among patients undergoing total hip arthroplasty (THA) or those undergoing total knee arthroplasty (TKA) has been associated with worse postoperative outcomes compared with patients without Medicaid. Surgeons and hospitals with lower annual total joint arthroplasty (TJA) volume have also been associated with worse outcomes. This study sought to characterize the associations between Medicaid insurance status, surgeon case volume, and hospital case volume and to assess the rates of postoperative complications compared with other payer types.

METHODS

The Premier Healthcare Database was queried for all adult patients who underwent primary TJA from 2016 to 2019. Patients were divided on the basis of their insurance status: Medicaid compared with non-Medicaid. The distribution of annual hospital and surgeon case volume was assessed for each cohort. Multivariable analyses were performed accounting for patient demographic characteristics, comorbidities, surgeon volume, and hospital volume to assess the 90-day risk of postoperative complications by insurance status.

RESULTS

Overall, 986,230 patients who underwent TJA were identified. Of these, 44,370 (4.5%) had Medicaid. Of the patients undergoing TJA, 46.4% of those with Medicaid were treated by surgeons performing ≤100 TJA cases annually compared with 34.3% of those without Medicaid. Furthermore, a higher percentage of patients with Medicaid underwent TJA at lower-volume hospitals performing ≤500 cases annually, 50.8% compared with 35.5% for patients without Medicaid. After accounting for differences among the 2 cohorts, patients with Medicaid remained at increased risk for postoperative deep vein thrombosis (adjusted odds ratio [OR], 1.16; p = 0.031), pulmonary embolism (adjusted OR, 1.39; p < 0.001), periprosthetic joint infection (adjusted OR, 1.35; p < 0.001), and 90-day readmission (adjusted OR, 1.25; p < 0.001).

CONCLUSIONS

Patients with Medicaid were more likely to undergo TJA performed by lower-volume surgeons at lower-volume hospitals and had higher rates of postoperative complications compared with patients without Medicaid. Future research should assess socioeconomic status, insurance, and postoperative outcomes in this vulnerable patient population seeking arthroplasty care.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Aspirin for Venous Thromboembolic Prophylaxis Following Total Hip and Total Knee Arthroplasty: An Analysis of Safety and Efficacy Accounting for Surgeon Selection Bias

BACKGROUND

Aspirin may be effective at preventing venous thromboembolism following total knee arthroplasty (TKA) or total hip arthroplasty (THA). Current evidence is limited by bias as many surgeons who use aspirin prescribe for high-risk patients alternative chemoprophylactic agents. Therefore, this study aimed to evaluate the risk of pulmonary embolism (PE) and deep vein thrombosis (DVT) in patients who received aspirin and warfarin while accounting for surgeon selection bias.

METHODS

A national database was queried for patients undergoing primary elective TKA or THA from 2015 to 2020. Patients whose surgeon used aspirin in >90% of their patients were compared to patients whose surgeon used warfarin in >90% of cases. Instrumental variable analyses were performed to assess for PE, DVT, and transfusion while accounting for selection bias. Among TKA patients, 26,657 (18.8%) were in the warfarin cohort and 115,005 (81.2%) were in the aspirin cohort. Among THA patients, 13,035 (17.7%) were in the warfarin cohort and 60,726 (82.3%) were in the aspirin cohort.

RESULTS

Analyses were unable to identify a difference in the risk of PE (TKA: adjusted odds ratio [aOR]: 0.98, P = .659; THA: aOR = 0.93, P = .310) and DVT (TKA: aOR = 1.05, P = .188; THA: aOR = 0.96, P = .493) between the aspirin and warfarin cohorts. However, the aspirin cohort was associated with a lower risk of transfusion (TKA: aOR = 0.58, P < .001, THA: 0.84, P < .001).

DISCUSSION

After accounting for surgeon selection bias, aspirin was as effective as warfarin at preventing PE and DVT following TKA and THA. Furthermore, aspirin was associated with a lower risk of transfusion compared to warfarin.

The Persistent Effects of the COVID-19 Pandemic on Total Joint Arthroplasty Changes in Practice Patterns in the United States From 2020 to 2021

BACKGROUND

The SARS-CoV-2 (COVID-19) pandemic has dramatically disrupted orthopaedic surgery practice patterns. This study aimed to examine differences between patients who underwent total joint arthroplasty (TJA) before the pandemic compared to 2020 and 2021.

METHODS

A retrospective cohort study was performed on all patients who underwent elective inpatient TJA from January 2017 to December 2021 using a national large database. Descriptive statistics were utilized to trend length of stay (LOS) and patient age. Patient demographics, discharge destinations, and rates of medical comorbidities were assessed for patients undergoing TJA in 2020 and 2021 compared to patients from prepandemic years (2017 to 2019). Overall, 1,173,366 TJAs were identified (2017 to 2019: 810,268 TJAs, average 270,089 cases/year; 2020: 175,185 TJAs; 2021: 187,627 TJAs). There was a 35.3% and 30.5% decrease in 2020 and 2021, respectively, when compared to the prepandemic annual average.

RESULTS

Average LOS decreased from 1.6 days in January 2020 to 0.9 days by December 2021. Same-day discharges increased from 6.2% of cases in 2019 to 30.5% in 2021. Discharge to skilled nursing facilities (SNF) reduced from 11.3% in 2017 to 2019 to 4.3% and 4.5% in 2020 and 2021, respectively. Patients ≥70 years old undergoing elective TJA decreased from 39.6% in 2017 to 2019 to 29.2% in April 2020.

CONCLUSION

In response to the COVID-19 pandemic, same-day discharges following primary elective TJA increased markedly, the average LOS decreased, discharges to SNFs decreased, and a preferential shift toward younger patients was observed.

LEVEL OF EVIDENCE

Therapeutic Level III.

Convergent evolution of pain-inducing defensive venom components in spitting cobras

Convergent evolution provides insights into the selective drivers underlying evolutionary change. Snake venoms, with a direct genetic basis and clearly defined functional phenotype, provide a model system for exploring the repeated evolution of adaptations. While snakes use venom primarily for predation, and venom composition often reflects diet specificity, three lineages of cobras have independently evolved the ability to spit venom at adversaries. Using gene, protein, and functional analyses, we show that the three spitting lineages possess venoms characterized by an up-regulation of phospholipase A2 (PLA2) toxins, which potentiate the action of preexisting venom cytotoxins to activate mammalian sensory neurons and cause enhanced pain. These repeated independent changes provide a fascinating example of convergent evolution across multiple phenotypic levels driven by selection for defense.

Analysis of cardiac development in the turtle Emys orbicularis (Testudines: Emidydae) using 3-D computer modeling from histological sections

In this article we present a 3-D modeling study of cardiac development in the European pond turtle, Emys orbicularis (of the reptilian order Testudines). The study is aimed at elucidating the embryonic development of the horizontal septum in the ventricle and underscoring the importance of 3-D reconstructions in studying morphogenesis. Turtles possess one common ventricle, partly divided into three cava by a vertical and a horizontal septum, of which the embryonic origins have so far not been described. We used serial sectioning and computerized high-resolution 3-D reconstructions of different developmental stages to create a chronological overview of cardiogenesis, in order to study this process. This has yielded a new understanding of the development of the horizontal septum and (directly related) the looping of the heart tube. This looping is found to be markedly different from that in the human heart, with the turtle having two clear bends in the part of the heart tube leaving the primitive ventricle, as opposed to one in humans. It is this particular looping that is responsible for the formation of the horizontal septum. In addition to our findings on the ventricular septation this study has also yielded new insights into the developmental origins of the pulmonary vein. The 3-D reconstructions were built using our platform TDR-3-D base and enabled us to study the developmental processes in specific parts of the turtle heart separately and in three dimensions, over time. The complete 3-D reconstructions have been made available to the reader via internet using our 3-D model browser application, which allows interactive viewing of the models. The browser application can be found on bio-imaging.liacs.nl/galleries/emysorbicularis/TurtleGallery.html, along with additional images of both models and histological sections and animation sequences of the models. By allowing the reader to view the material in such an interactive way, we hope to make optimal use of the new 3-D reconstruction techniques and to engage the reader in a more direct manner.

Sequencing and genomic annotation of the chicken (Gallus gallus) Hox clusters, and mapping of evolutionarily conserved regions

Hox genes encode transcription factors that are involved in the regulation of normal development and are mutated in some diseases and malformations. Chicken HOX genes have been extensively studied in the chick limb and other developmental models. To date while the chicken HOXA cluster has been completely sequenced many other chicken HOX genes are known only from partial mRNAs or unfinished genome assemblies. Furthermore, although a finished sequence of the HOXA cluster is available, the sequence has not yet been annotated. We have therefore manually annotated the available HOX sequences and improved the sequences by sequencing PCR fragments that bridge existing gaps in the genome sequences. These sequences complement the published sequences, including the currently incomplete WashUC Gallus_gallus-2.1 build, to give an improved coverage of the cluster. We used phylogenetic footprinting to map the genomic location of 398 Ultra Conserved Regions in the HOX complex 248 of which do not overlap with any known annotated coding exon. These included the hox-related microRNAs miR-10 and miR-196. The chicken HOX clusters appear to be broadly comparable to their human counterparts. A few human orthologues were not recovered from the chicken, presumably because of incomplete sequence.

Symposium on neural crest development

The following review articles are based on presentations given at a Symposium on Neural Crest Development, held in December 1996 at St George's Hospital Medical School, London. The Symposium formed part of the Winter Meeting of the Anatomical Society of Great Britain and Ireland. There were 6 invited speakers, 5 selected short presentations, and posters. The topics ranged widely, from autocrine regulation of Schwann cell development through clinical and animal disorders involving the melanocyte lineage, the heart and other organs, to the regulation of neural crest cell differentiation by cytokines.

Comparative methods in developmental biology

The need for a phylogenetic framework is becoming appreciated in many areas of biology. Such a framework has found limited use in developmental studies. Our current research program is therefore directed to applying comparative and phylogenetic methods to developmental data. In this paper, we examine the concepts underlying this work, discuss potential difficulties, and identify some solutions. While developmental biologists frequently make cross-species comparisons, they usually adopt a phenetic approach, whereby degrees of overall similarity in development are sought. Little emphasis is placed on reconstructing the evolutionary divergence in developmental characters. Indeed, developmental biologists have historically concentrated on apparently 'conserved' or 'universal' developmental mechanisms. Thus, there has been little need for phylogenetic methodologies which analyse specialised features shared only within a subset of species (i.e., synapomorphies). We discuss the potential value of such methodologies, and argue that difficulties in adapting them to developmental studies fall into three interlinked areas: One concerns the nature and definition of developmental characters. Another is the difficulty of identifying equivalent developmental stages in different species. Finally the phylogenetic non-independence of developmental characters presents real problems under some protocols. These problems are not resolved. However, it is clear that the application of phylogenetic methodology to developmental data is both necessary and fundamental to research into the relationship between evolution and development.

Genomic annotation and transcriptome analysis of the zebrafish (Danio rerio) hox complex with description of a novel member, hoxb13a

The zebrafish (Danio rerio) is an important model in evolutionary developmental biology, and its study is being revolutionized by the zebrafish genome project. Sequencing is at an advanced stage, but annotation is largely the result of in silico analyses. We have performed genomic annotation, comparative genomics, and transcriptional analysis using microarrays of the hox homeobox-containing transcription factors. These genes have important roles in specifying the body plan. Candidate sequences were located in version Z v 4 of the Ensembl genome database by TBLASTN searching with Danio and other vertebrate published Hox protein sequences. Homologies were confirmed by alignment with reference sequences, and by the relative position of genes along each cluster. RT-PCR using adult Tübingen cDNA was used to confirm annotations, to check the genomic sequence and to confirm expression in vivo. Our RT-PCR and microarray data show that all 49 hox genes are expressed in adult zebrafish. Significant expression for all known hox genes could be detected in our microarray analysis. We also find significant expression of hox 8 paralogs and hox b 7 a in the anti-sense direction. A novel gene, D. rerio hox b 13 a, was identified, and a preliminary characterization by in situ hybridization showed expression at 24 hpf at the tip of the developing tail. We are currently characterizing this gene at the functional level. We argue that the oligo design for microarrays can be greatly enhanced by the availability of genomic sequences.

Limb development in a "nonmodel" vertebrate, the direct-developing frog Eleutherodactylus coqui

Mechanisms that mediate limb development are regarded as highly conserved among vertebrates, especially tetrapods. Yet, this assumption is based on the study of relatively few species, and virtually none of those that display any of a large number of specialized life-history or reproductive modes, which might be expected to affect developmental pattern or process. Direct development is an alternative life history found in many anuran amphibians. Many adult features that form after hatching in metamorphic frogs, such as limbs, appear during embryogenesis in direct-developing species. Limb development in the direct-developing frog Eleutherodactylus coqui presents a mosaic of apparently conserved and novel features. The former include the basic sequence and pattern of limb chondrogenesis, which are typical of anurans generally and appear largely unaffected by the gross shift in developmental timing; expression of Distal-less protein (Dlx) in the distal ectoderm; expression of the gene Sonic hedgehog (Shh) in the zone of polarizing activity (ZPA); and the ability of the ZPA to induce supernumerary digits when transplanted to the anterior region of an early host limb bud. Novel features include the absence of a morphologically distinct apical ectodermal ridge, the ability of the limb to continue distal outgrowth and differentiation following removal of the distal ectoderm, and earlier cessation of the inductive ability of the ZPA. Attempts to represent tetrapod limb development as a developmental "module" must allow for this kind of evolutionary variation among species.

Development of the human pulmonary vein and its incorporation in the morphologically left atrium

OBJECTIVE

Using a newly acquired archive of previously prepared material, we sought to re-examine the origin of the pulmonary vein in the human heart, aiming to determine whether it originates from the systemic venous sinus ("sinus venosus"), or appears as a new structure draining to the left atrium. In addition, we examined the temporal sequence of incorporation of the initially solitary pulmonary vein to the stage at which four venous orifices opened to the left atrium.

METHODS

We studied 26 normal human embryos, ranging from 3.8 mm to 112 mm crown-rump length, and representing the period from the 12th Carnegie stage to 15 weeks of gestation.

RESULTS

The pulmonary vein canalised as a solitary vessel within the mediastinal tissues so as to connect the intraparenchymal pulmonary venous networks to the heart, using the regressing dorsal mesocardium as its portal of cardiac entry. The vein was always distinct from the tributaries of the embryonic systemic venous sinus. The orifice of the solitary vein became committed to the left atrium by growth of the vestibular spine. During development, a marked disparity was seen between the temporal and morphological patterns of incorporation of the left-sided and right-sided veins into the left atrium. The pattern of the primary bifurcation was asymmetrical, a much longer tributary being formed on the left than on the right. Contact between the atrial wall and the venous tributary on the left initially produced a shelf, which became effaced with incorporation of the two left-sided veins into the atrium.

CONCLUSIONS

The initial process of formation of the human pulmonary vein is very similar to that seen in animal models. The walls of the initially solitary vein in humans become incorporated by a morphologically asymmetric process so that four pulmonary veins eventually drain independently into the left atrium. Failure of incorporation on the left side may provide the substrate for congenital division of the left atrium.

Septation and valvar formation in the outflow tract of the embryonic chick heart

There is no agreement, in the chick, about the number of the endocardial cushions within the outflow tract or their pattern of fusion. Also, little is known of their relative contributions to the formation of the arterial valves, the subpulmonary infundibulum, and the arterial valvar sinuses. As the chick heart is an important model for studying septation of the outflow tract, our objective was to clarify these issues. Normal septation of the outflow tract was studied in a series of 60 staged chick hearts, by using stained whole-mount preparations, serial sections, and scanning electron microscopy. A further six hearts were examined subsequent to hatching. At stage 21, two pairs of endocardial cushions were seen within the developing outflow tract. One pair was positioned proximally, with the other pair located distally. By stage 25, a third distal cushion had developed. This finding was before the appearance of two further, intercalated, endocardial cushions, also distally positioned, which were first seen at stage 29. In the arterial segment, the aortic and pulmonary channels were separated by the structure known as the aortopulmonary septum. The dorsal limb of this septum penetrated the distal dorsal cushion, whereas the ventral limb grew between the remaining two distal cushions, both of which were positioned ventrally. The three distal endocardial cushions, and the two intercalated endocardial cushions, contributed to the formation of the leaflets and sinuses of the arterial roots. The two proximal cushions gave rise to a transient septum, which later became transformed into the muscular component of the subpulmonary infundibulum. Concomitant with these changes, an extracardiac tissue plane was formed which separated this newly formed structure from the sinuses of the aortic root. Our study confirms that three endocardial cushions are positioned distally, and two proximally, within the developing outflow tract of the chick. The pattern of the distal cushions, and the position of the ventral limb of the aortopulmonary septum, differs significantly from that seen in mammals.

Misexpression of noggin leads to septal defects in the outflow tract of the chick heart

BMP-2 and BMP-4 are known to be involved in the early events which specify the cardiac lineage. Their later patterns of expression in the developing mouse and chick heart, in the myocardium overlying the atrioventricular canal (AV) and outflow tract (OFT) cushions, also suggest that they may play a role in valvoseptal development. In this study, we have used a recombinant retrovirus expressing noggin to inhibit the function of BMP-2/4 in the developing chick heart. This procedure resulted in abnormal development of the OFT and the ventricular septum. A spectrum of abnormalities was seen ranging from common arterial trunk to double outlet right ventricle. In hearts infected with noggin virus, where the neural crest cells have been labelled, the results show that BMP-2/4 function is required for the migration of neural crest cells into the developing OFT to form the aortopulmonary septum. Prior to septation, misexpression of noggin also leads to a decrease in the number of proliferating mesenchymal cells within the proximal cushions of the outflow tract. These results suggest that BMP-2/4 function may mediate several key events during cardiac development.

Generation and characterization of monoclonal antibodies to the neural crest

The generation of monoclonal antibodies (MAbs) specific for quail neural crest may provide valuable tools for studying the differentiation of embryonic precursor cells. Unfortunately, relatively few antibodies are available because of the difficulty in obtaining sufficient cells for in vivo immunization strategies. We have overcome this problem by using intrasplenic immunization with formaldehyde-fixed cells harvested from neural crest cultures. In addition, booster injections of cultured whole-embryo cells were administered intraperitoneally. Following two fusions, a total of 18 hybridomas were generated with antibody reactivity to the cytoplasm of neural crest cells. Furthermore, 32 were reactive against both somite (a noncrest mesodermal control) and crest cultures, whilst 15 were not reactive. Out of those hybridomas reactive with neural crest, six designated 160D, 164D, OE, 12E, 120E and 124E were further characterized. Interestingly MAb supernatants OE, 12E, 120E, and 124E exhibited reactivity against some but not all neural crest cells suggesting that they might recognise subpopulations. Immunoglobulin isotyping of supernatants revealed that 4 (160D, 164D, OE, and 120E) were IgM and 2 (12E and 124E) were IgG(2b). On assessing their reactivity against human tissue sections, all six hybridoma supernatants cross-reacted with neuroendocrine cells within appendix, colon and rectum. These MAbs could provide novel reagents for the understanding of neural crest development.

Relationship in the chick of the developing pulmonary vein to the embryonic systemic venous sinus

Previous studies have shown that the relationship of the systemic venous sinus (sinus venosus) to the developing pulmonary vein are very similar in mice, rats, and man, with the pulmonary vein gaining access to the heart through a persisting segment of the dorsal mesocardium. It has been suggested that this process differs in avian development, with the pulmonary vein being connected to the systemic venous sinus with subsequent transfer to the left atrium. Here we have investigated the anatomical sequence of events in the chick, using serial histological sections and microdissection followed by scanning electron microscopy. We examined a temporal series of chick embryos, ranging from Hamburger and Hamilton stage 15 to stage 30. Although there are some differences in detail, the development of the pulmonary venous connections in the chick was found to be directly comparable to that already described in eutherian mammals. In both mammals and the chick, the dorsal mesocardial connection, which connects the primitive atrium to the posterior thoracic wall, forms a fixed point through which the pulmonary vein gains access to the atrial compartment of the heart, only varying if the connection itself is anomalous. The tributaries of the systemic venous sinus and the primary atrial septal structures develop around the dorsal connection.

A treasure house of comparative embryology

The Embryo Collection of the Hubrecht Laboratory is a treasure house of comparative embryology. It is the largest and most important collection of its kind in the world, and consists of thousands of vertebrate embryos stored in alcohol, or prepared as histological sections. Many elusive species are included in the collection, some represented by complete developmental series. The accompanying archives offer a remarkable insight into the methods used to collect embryos form wild animals, as well as the motives behind the founders of the collection. Carefully maintained, documented and catalogued, the collection is available for study by all interested scientists. We argue that this collection is one of the greatest biodiversity resources in existence.

Vertebrate evolution: the developmental origins of adult variation

Many biologists assume, as Darwin did, that natural selection acts mainly on late embryonic or postnatal development. This view is consistent with von Baer's observations of morphological divergence at late stages. It is also suggested by the conserved morphology and common molecular genetic mechanisms of pattern formation seen in embryos. I argue here, however, that differences in adult morphology may be generated at a variety of stages. Natural selection may have a major action on developmental mechanisms during the organogenetic period, because this is when many adult traits are specified. Evolutionary changes in these early developmental mechanisms probably include subtle shifts in the timing of gene expression. Changes of this kind have little or no gross effect on the anatomy of the embryo; they are only phenotypically expressed, or readily detected, when amplified at later stages. The phylotypic stage, the developmental hourglass, modularity, and von Baerian divergence are reassessed in terms of these arguments.

Morphology of the distal tip of the upper mandible of the ostrich (Struthio camelus) embryo during hatching

1. The morphology of the distal part of the upper mandible in ostrich embryos was investigated using scanning electron microscopy just prior to and during hatching. 2. Although a keel-like structure on the tip of the upper mandible superficially resembles an egg tooth it appears to play no role during hatching. 3. The distal tip of the upper mandible is covered by an amorphous layer, the right side of which disappears during the hatching process. This layer acts to protect the beak during the rubbing process which creates a hole in the inner shell membrane during hatching.

Limb development and evolution: a frog embryo with no apical ectodermal ridge (AER)

The treefrog Eleutherodactylus coqui is a direct developer--it has no tadpole stage. The limb buds develop earlier than in metamorphosing species (indirect developers, such as Xenopus laevis). Previous molecular studies suggest that at least some mechanisms of limb development in E. coqui are similar to those of other vertebrates and we wished to see how limb morphogenesis in this species compares with that in other vertebrates. We found that the hind limb buds are larger and more advanced than the forelimbs at all stages examined, thus differing from the typical amniote pattern. The limb buds were also small compared to those in the chick. Scanning and transmission electron microscopy showed that although the apical ectoderm is thickened, there was no apical ectodermal ridge (AER). In addition, the limb buds lacked the dorsoventral flattening seen in many amniotes. These findings could suggest a mechanical function for the AER in maintaining dorsoventral flattening, although not all data are consistent with this view. Removal of distal ectoderm from E. coqui hindlimb buds does not stop outgrowth, although it does produce anterior defects in the skeletal pattern. The defects are less severe when the excisions are performed earlier. These results contrast with the chick, in which AER excision leads to loss of distal structures. We suggest that an AER was present in the common ancestor of anurans and amniotes and has been lost in at least some direct developers including E. coqui.

Somite number and vertebrate evolution

Variation in segment number is an important but neglected feature of vertebrate evolution. Some vertebrates have as few as six trunk vertebrae, while others have hundreds. We examine this phenomenon in relation to recent models of evolution and development. Surprisingly, differences in vertebral number are foreshadowed by different somite counts at the tailbud stage, thought to be a highly conserved (phylotypic) stage. Somite number therefore violates the ‘developmental hourglass’ model. We argue that this is because somitogenesis shows uncoupling or dissociation from the conserved positional field encoded by genes of the zootype. Several other systems show this kind of dissociation, including limbs and feathers. Bmp-7 expression patterns demonstrate dissociation in the chick pharyngeal arches. This makes it difficult to recognise a common stage of pharyngeal development or ‘pharyngula’ in all species. Rhombomere number is more stable during evolution than somite number, possibly because segmentation and positional specification in the hindbrain are relatively interdependent. Although developmental mechanisms are strongly conserved, dissociation allows at least some major evolutionary changes to be generated in phylotypic stages.

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development

Embryos of different species of vertebrate share a common organisation and often look similar. Adult differences among species become more apparent through divergence at later stages. Some authors have suggested that members of most or all vertebrate clades pass through a virtually identical, conserved stage. This idea was promoted by Haeckel, and has recently been revived in the context of claims regarding the universality of developmental mechanisms. Thus embryonic resemblance at the tailbud stage has been linked with a conserved pattern of developmental gene expression - the zootype. Haeckel's drawings of the external morphology of various vertebrates remain the most comprehensive comparative data purporting to show a conserved stage. However, their accuracy has been questioned and only a narrow range of species was illustrated. In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage - thought to correspond to a conserved stage - show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel's drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species.

The neural crest population responding to endothelin-3 in vitro includes multipotent cells

The peptide endothelin 3 (EDN3) is essential for normal neural crest development in vivo, and is a potent mitogen for quail truncal crest cells in vitro. It is not known which subpopulations of crest cells are targets for this response, although it has been suggested that EDN3 is selective for melanoblasts. In the absence of cell markers for different precursor types in the quail crest, we have characterised EDN3-responsive cell types using in vitro colony assay and clonal analysis. Colonies were analysed for the presence of Schwann cells, melanocytes, adrenergic cells or sensory-like cells. We provide for the first time a description of the temporal pattern of lineage segregation in neural crest cultures. In the absence of exogenous EDN3, crest cells proliferate and then differentiate. Colony assay indicates that in these differentiated cultures few undifferentiated precursors remain and there is a low replating efficiency. By contrast, in the presence of 100 ng/ml EDN3 differentiation is inhibited and most of the cells maintain the ability to give rise to mixed colonies and clones containing neural crest derivatives. A high replating efficiency is maintained. In secondary culture there was a progressive decline in the number of cell types per colony in control medium. This loss of developmental potential was not seen when exogenous EDN3 was present. Cell type analysis suggests two novel cellular targets for EDN3 under these conditions. Contrary to expectations, one is a multipotent precursor whose descendants include melanocytes, adrenergic cells and sensory-like cells; the other can give rise to melanocytes and Schwann cells. Our data do not support previous claims that the action of EDN3 in neural crest culture is selective for cells in the melanocyte lineage.

Overexpression of BMP-2 and BMP-4 alters the size and shape of developing skeletal elements in the chick limb

Bone morphogenetic proteins are members of the transforming growth factor beta (TGF beta) superfamily which are involved in a range of developmental processes including modelling of the skeleton. We show here that Bmp-2 is expressed in mesenchyme surrounding early cartilage condensations in the developing chick limb, and that Bmp-4 is expressed in the perichondrium of developing cartilage elements. To investigate their roles during cartilage development, BMP-2 and BMP-4 were expressed ectopically in developing chick limbs using retroviral vectors. Over-expression of BMP-2 or BMP-4 led to a dramatic increase in the volume of cartilage elements, altered their shapes and led to joint fusions. This increase in volume appeared to result from an increase in the amount of matrix and in the number of chondrocytes. The latter did not appear to be due to increased proliferation of chondrocytes, suggesting that it may result from increased recruitment of precursors. BMP-2 and BMP-4 also delayed hypertrophy of chondrocytes and formation of the osteogenic periosteum. These data provide insights into how BMP-2 and BMP-4 may model and control the growth of skeletal elements during normal embryonic development, suggesting roles for both molecules in recruiting non-chondrogenic precursors to chondrogenic fate.

Gene expression, polarising activity and skeletal patterning in reaggregated hind limb mesenchyme

The developing chick limb has two major signalling centres; the apical ectodermal ridge maintains expression of several important genes and outgrowth of the limb, and the polarising region specifies the pattern of skeletal elements along the anteroposterior axis. We have used reaggregated leg grafts (mesenchyme dissociated into single cells, placed in an ectodermal jacket and grafted to a host) to study patterning in a system where the developmental axes are severely disrupted. Reaggregates from different regions of leg mesenchyme developed correspondingly different digits, giving a system in which skeletal phenotype could be compared with the expression of genes thought to be important in patterning. We found that posterior third and whole leg reaggregates gave rise to different digits, yet expressed the same combination of HoxD, Bmp-2 and shh genes throughout their development. Anterior thirds initially only express the 3′ end of the HoxD cluster but activate the more 5′ members of the cluster sequentially over a period of 48 hours, a period during which Bmp-2 is activated but no shh or Fgf-4 expression could be detected. Our results suggest that there are two independent mechanisms for activating the HoxD complex, one polarising region-dependent and one independent, and that shh expression may not be necessary to maintain outgrowth and patterning once a ridge has been established.

Heterochrony and the phylotypic period

There has been a resurgence of interest in comparative embryology. It is now important to be able to compare gene expression in different species at similar developmental stages. One phenomenon which may make it difficult to compare embryos in this way is heterochrony--a change in developmental timing during evolution. It is not clear whether heterochrony can affect the intermediate stages of embryonic development, when many important genes involved in pattern formation are expressed. A prevalent view is that these so-called phylotypic stages are resistant to evolutionary change because they are when the body plan is laid down. Haeckel's famous drawings, which show different vertebrates developing from virtually identical somite-stage embryos, are still used to support this idea. I have reexamined the morphological data relating to developmental timing in somite-stage embryos. The data reveal striking patterns of heterochrony during vertebrate evolution. These shifts in developmental timing have strongly affected the phylotypic stage, which is therefore poorly conserved and is more appropriately described as the phylotypic period. This is contrary to the impression created by Haeckel's drawings, which I show to be inaccurate and misleading. The study of gene expression in embryos which show heterochrony could give important insights into evolutionary and developmental mechanisms.

Bone morphogenetic proteins and a signalling pathway that controls patterning in the developing chick limb

We show here that bone morphogenetic protein 2 (BMP-2) is involved in patterning the developing chick limb. During early stages of limb development, mesenchymal expression of the Bmp-2 gene is restricted to the posterior part of the bud, in a domain that colocalizes with the polarizing region. The polarizing region is a group of cells at the posterior margin of the limb bud that can respecify the anteroposterior axis of the limb when grafted anteriorly and can activate expression of genes of the HoxD complex. We dissect possible roles of BMP-2 in the polarizing region signalling pathway by manipulating the developing wing bud. Retinoic acid application, which mimics the effects of polarizing region grafts, activates Bmp-2 gene expression in anterior cells. This shows that changes in anteroposterior pattern are correlated with changes in Bmp-2 expression. When polarizing region grafts are placed at the anterior margin of the wing bud, the grafts continue to express the Bmp-2 gene and also activate Bmp-2 expression in the adjacent anterior host mesenchyme. These data suggest that BMP-2 is part of the response pathway to the polarizing signal, rather than being the signal itself. In support of this, BMP-2 protein does not appear to have any detectable polarizing activity when applied to the wing bud. The pattern of Bmp-4 gene expression in the developing wing bud raises the possibility that BMP-2 and BMP-4 could act in concert. There is a close relationship, both temporal and spatial, between the activation of the Bmp-2 and Hoxd-13 genes in response to retinoic acid and polarizing region grafts, suggesting that expression of the two genes might be linked.