Low energy gunshot injuries: Does removal of retained bullet fragmentation at the time of internal fixation reduce the risk of fracture related infection?

OBJECTIVE: To examine the effects of RBF (Retained Bullet Fragment) removal at the time of long bone fixation on FRI (fracture related infection) rates in low energy GSI (Gunshot Injury) related fractures. DESIGN: Retrospective Cohort Study SETTING: Level 1 Academic Trauma Center INTERVENTION: Retrospective review of the impact of RBFs on the risk of FRI when employing internal fixation in low energy GSI (Gunshot Injury) related fractures. In situations where the injury pattern requires surgical fixation, the question arises as to whether or not the RBFs need to be removed to prevent FRI. MAIN OUTCOME MEASURES: Whether or not the RBFs removed in our patient population prevented short- and long-term fracture related infection after low-energy gunshot injury (FRI-LGI). RESULTS: Of the 2,136 GSI related fractures, 131 patients met inclusion criteria, 81 patients underwent removal (R) of RBFs at the time of internal fixation while 50 patients did not undergo any removal (NR) at time of internal fixation. Among the patients who underwent surgical intervention, (Open Reduction Internal Fixation) ORIF was performed in 55 cases (R: 39; NR: 16), and (Intramedullary Nail) IMN was performed in 76 cases (R: 42; NR: 34). The overall rate of deep FRI-LGI was 6.9 % of the 131-patient cohort. We found that removal of RBFs had a statistically significant impact on the rate of deep FRI-LGI when compared to the NR group (p = 0.031). In the RBF removal group, only two patients (2.4 %) developed deep FRI-LGIs, whereas in the NR group, seven patients (14.0 %) developed deep FRI-LGIs. The incidence of early FRI-LGI was higher in the NR group (median 0.6 months) compared to the R group, which was associated with late FRI-LGIs (median 10.1 months) when they occurred. DISCUSSION: In our study population, we found a statistically significantly increased incidence of deep and early FRI-LGI when RBFs are not removed at the time of extra-articular long bone internal fixation. The presence of retained bullet fragments following internal fixation may pose a risk factor for future development of deep FRI-LGI. We believe a surgeon should use their best judgment as to whether a RBF can safely be removed at the time of long bone fixation. Based on our findings, if safely permitted, RBF removal should be considered at the time of GSI long bone fixation resulting from low energy hand gun injuries.

Increasing radial growth in old-growth high-elevation conifers in Southern California, USA, during the exceptional "hot drought" of 2000-2020.

Hot droughts, droughts attributed to below-average precipitation and exceptional warmth, are increasingly common in the twenty-first century, yet little is known about their effect on coniferous tree growth because of their historical rarity. In much of the American West, including California, radial tree growth is principally driven by precipitation, and narrow ring widths are typically associated with either drier or drought conditions. However, for species growing at high elevations (e.g., Larix lyalli, Pinus albicaulis), growth can be closely aligned with above-average temperatures with maximum growth coinciding with meteorological drought, suggesting that the growth effects of drought span from adverse to beneficial depending on location. Here, we compare radial growth responses of three high-elevation old-growth pines (Pinus jeffreyi, P. lambertiana, and P. contorta) growing in the San Jacinto Mountains, California, during a twenty-first-century hot drought (2000-2020) largely caused by exceptional warmth and a twentieth-century drought (1959-1966) principally driven by precipitation deficits. Mean radial growth during the hot drought was 12% above average while 18% below average during the mid-century drought illustrating that the consequences of environmental stress exhibit spatiotemporal variability. We conclude that the effects of hot droughts on tree growth in high-elevation forests may produce responses different than what is commonly associated with extended dry periods for much of western North America's forested lands at lower elevational ranges and likely applies to other mountainous regions (e.g., Mediterranean Europe) defined by summer-dry conditions. Thus, the climatological/biological interactions discovered in Southern California may offer clues to the unique nature of high-elevation forested ecosystems globally.

Anatomic Referencing Restores the Anatomy of the Distal Femur with Less Compromise.

Historically, anterior referencing and posterior referencing are two specific techniques that surgeons can use for proper sizing of the femoral component in total knee arthroplasty (TKA). In this review, we introduce the concept of "anatomic referencing" which has become useful with more incremental sizes of the femoral component to more perfectly match the native anatomy of each patient and reduce overstuffing of the patellofemoral joint and medial-lateral (ML) overhang. Fifty consecutive TKA cases were reviewed where the novel anatomic referencing technique was used. Lateral radiographic projections were obtained preoperatively and postoperatively. The posterior condylar offset (PCO) was evaluated on the lateral radiographs by measuring the distance between the tangent line of the femoral diaphysis posterior cortex and the posterior condylar margin. PCO ratio (PCOR) was calculated by dividing the PCO by the distance between the posterior condylar border and a tangent line along the anterior cortex of the femoral diaphysis. Forty-five patients (50 TKAs) were reviewed. Average age of the patients was 70.34, range: 47-91. There were 19 males and 26 females reviewed in this series. On average, the delta PCOR was 0.022 (standard deviation = 0.032; min: -0.049, max: 0.082). When grouping our results into three main groups: < -0.03, -0.03 to 0.03, and > 0.03, we found that 62% fell within the -0.03 to 0.03 range. There was no statistically significant difference in delta PCOR between standard and narrow implants (p = 0.418). The proposed novel anatomic referencing technique has allowed for proper sizing of patients' femurs in the anteroposterior and ML direction while avoiding component overhang or the need for component downsizing to obtain a proper ML fit. This radiographic review confirmed this to be a highly accurate and reproducible technique.

Accuracy of Leg Length and Hip Offset Measurements Using a Fluoroscopic Grid During Anterior Approach Total Hip Arthroplasty.

Background: Minimizing leg length (LLD) and hip offset (OD) discrepancies is critical for tissue tension and implant longevity in total hip arthroplasty (THA). The direct anterior approach (DAA) helps surgeons recreate these values under fluoroscopy. Several methods to accomplish this have been described, with no consensus on which is superior. This study evaluated the ability to minimize LLD and OD using a surgeon-controlled, adjustable fluoroscopic grid. We hypothesized that this tool would recreate parameters to within 10 mm of the contralateral side. Methods: One hundred eleven primary THAs performed with an adjustable radiopaque grid to equalize leg length and hip offset were retrospectively reviewed. These values were measured on postoperative radiographs and compared to the contralateral hip. Patients were excluded if they had inadequate imaging, revision arthroplasty, preexisting deformities, or underwent approaches other than DAA. Results: Mean age was 59.1 ± 11.1 years, 63.1% of patients were female, and average body mass index was 27.8 ± 7.0. Mean LLD was 3.7 ± 3.0 mm, while mean OD was 4.6 ± 3.6 mm. 95.5% of hips showed LLD < 10 mm, while 93.7% of hips had OD < 10 mm. Furthermore, 76.6% of hips had LLD < 5 mm, while 62.2% of hips had OD < 5 mm. Conclusions: The described technique restored limb length and hip offset during DAA THA. This technique yields consistent results and offers an inexpensive alternative to costly digital software and more cumbersome fixed grid systems.

Does Hip Fracture Admitting Service Affect Proper Deep Venous Thrombosis Prophylaxis? An Investigation at a Level 1 Trauma Center.

OBJECTIVE: To examine if rates of appropriate thromboprophylaxis prescribing at the time of discharge would be higher in patients admitted to the orthopaedic service. Second, to see if improvements could be made in the rates of these missed events after a structured intervention. DESIGN: Retrospective Cohort Study, Prospective Interventional. SETTING: Level 1 Academic Hospital. PATIENTS: Two hundred forty-six patients undergoing a hip hemiarthroplasty for femoral neck fracture discharged to an extended care facility. INTERVENTION: A letter was sent to the internal quality control committee detailing our preintervention study. MAIN OUTCOME MEASURE: We looked at the differences among admitting services for missed thromboembolic prophylaxis (TPx) at the time of hospital discharge and rates of appropriate TPx after a structured intervention. RESULTS: No statistically significant differences existed in relation to patient age, gender, body mass index, or postoperative discharge day in the preintervention group. Orthopaedic surgery prescribed adequate TPx at discharge for 76 of 77 patients (98.7%), general trauma surgery for 26 of 30 patients (86.7%), and internal medicine for 85 of 96 patients (86.7%) in the preintervention group. There was a statistically significant difference when comparing adequate TPx between orthopaedic surgery and other services (P < 0.013 and <0.021, respectively). Our postintervention data found a significant decrease in the rates of missed TPx on discharge. In our preintervention sample group compared with our postintervention sample group, we saw a decrease in missed TPx of 5/39 versus 0/43 events (P = 0.021). CONCLUSIONS: We found that a letter sent to all members of a hospital internal quality committee decreased incidences of missed TPx. Specifically, this letter explained the details of our study that kept track of rates of missed TPx among different admitting services. We found that after our intervention, which consisted of a letter and a multidisciplinary discussion, the rate of missed thromboembolic prophylaxis events improved from 5/39 (12%) to 0/43 (0%) (P = 0.021). LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Review of a Novel Antimicrobial Wound Gel System Used in Total Knee Arthroplasty Including a Protocol for a Randomized Controlled Trial at Our Institutions.

INTRODUCTION: Surgical-site infections (SSIs) remain a challenging complication following total knee arthroplasty (TKA) with estimates nearing 2%. Current antimicrobial dressing options have gained popularity despite reported bacterial resistance and ineffectiveness. Bacteria can produce an extracellular polymeric substance (EPS), thereby rendering infections difficult to treat. Recently, a novel antimicrobial wound gel system has been developed to address EPS-associated infections. This new technology is comprised of various components that act to break bonds and cross-linking within EPS, induce lysis, and provide a moist environment to promote healing. In this paper, we provide a background of: (1) wound infections; (2) biofilms; and (3) current dressing options. We will then describe a novel antimicrobial gel therapy with a summary of a randomized control trial (RCT). MATERIALS AND METHODS: We describe an RCT protocol for patients undergoing primary TKA at two large tertiary care centers. Patients will be randomized 1:1 using permutated block methodology to either standard of care (SOC) or a novel antimicrobial wound gel system, yielding 750 patients in each treatment arm. Inclusion criteria include patients scheduled to undergo primary TKA. The primary outcome is the appearance of a surgical-site complication. CONCLUSION: We briefly describe the background of wound healing and biofilm, as well as current treatment modalities including antimicrobial dressings and a novel technology developed to address the EPS component of bacteria. In addition, we describe a protocol for a randomized controlled trial examining the effects of this novel therapy on surgical-site complications in patients undergoing primary TKA.

Comparison of a Smartphone App to Manual Knee Range of Motion Measurements.

Background: Digital technology has emerged as a useful tool for preoperative and postoperative patient engagement and for remote patient monitoring. Smartphones are equipped with motion-sensing technology, and apps can be designed which use these features to create a simple method for measuring range of motion. The purpose of this study was to determine the accuracy of digital technology in assessing knee range of motion using a smartphone app, compared to traditional goniometric measurements in an office setting. Methods: Fifty-three (53) patients in a clinical practice were enrolled between October 2019 and March 2020. Three separate measurements were taken during the patient encounter: (1) the surgeon, (2) the app, and (3) the physical therapist. Intraclass correlations were computed to assess the agreement between (1) the surgeon and app and (2) that between the physical therapist and surgeon. Results: When measuring flexion, the correlation between either the surgeon or therapist with the app was good, whereas the comparison between the surgeon and therapist was moderate. All extension measurement comparisons, between the app, surgeon, and therapist, showed moderate correlation. Limits of agreements showed that 80% of the difference between surgeon and app is within 10 degrees for extension and 11 degrees for flexion. Body mass index did not affect the accuracy of the measurements. Conclusion: Digital app measurements were comparable to measurements made by either a surgeon or physical therapist with a manual goniometer in the clinical setting and may be beneficial for measuring and monitoring patients' range of motion remotely.

Can We Approach a Zero Percent Infection Rate In Total Knee Arthroplasty? A Program To Achieve This Goal With Antimicrobial Agents.

Periprosthetic joint infections (PJIs) are one of the most feared complications in the realm of adult reconstruction due to the substantial morbidity and mortality associated with these cases. Advancements in arthroplasty have been made across a variety of areas of interest including implant surfaces, implant design, material science, etc., but a focus on infection prevention and treatment is of utmost importance. A new technology has been created that targets biofilm and aims to prevent infection in total joint arthroplasty. In this manuscript we aim to describe the benefits of this technology and describe the ideal use in a case scenario format. We believe that with this technology that we can approach the goal of a zero periprosthetic infection rate.

Optimizing Total Knee Arthroplasty With ROSA® Robotic Technology.

A new robotic platform (ROSA® Knee system, Zimmer Biomet, Warsaw, Indiana) for total knee arthroplasty (TKA) has been created to increase precision of bony resections and knee balancing while maintaining surgeon autonomy. Our aim is to discuss: (1) the background of robotic technology in orthopedics, (2) current literature and potential benefits of the ROSA® Knee system, and the (3) optimal surgical technique for this specific robotic TKA platform. Early literature regarding this robotic system is promising as studies have shown precision of its bony resections, accuracy of overall limb alignment, and low early revision rates. There is a need for continued research on clinical outcomes using this platform, and the intention is to provide a review with insight into the potential advantages of robotics and the ideal surgical technique for successful use of this system.

Protocols for the Use of a Novel Biofilm-Disrupting Wound Irrigation Solution for Prevention of Surgical-Site Infections After Total Joint Arthroplasty.

Surgical-site infections are potential complications of total joint arthroplasties. Many strategies, ranging from preoperative to postoperative, have been developed in an attempt to mitigate this morbidity. Biofilms have been implicated in difficulties of treatment. Therefore, antimicrobials have been increasingly used to combat these problems. In this report, we will summarize different protocols which utilize a new antimicrobial solution. Providing surgeons with an effective prevention option for these infections is crucial for positive outcomes and the continued advancement in the practice of total joint arthroplasty.

Recent increases in tropical cyclone precipitation extremes over the US east coast.

The impacts of inland flooding caused by tropical cyclones (TCs), including loss of life, infrastructure disruption, and alteration of natural landscapes, have increased over recent decades. While these impacts are well documented, changes in TC precipitation extremes-the proximate cause of such inland flooding-have been more difficult to detect. Here, we present a latewood tree-ring-based record of seasonal (June 1 through October 15) TC precipitation sums (ΣTCP) from the region in North America that receives the most ΣTCP: coastal North and South Carolina. Our 319-y-long ΣTCP reconstruction reveals that ΣTCP extremes (≥0.95 quantile) have increased by 2 to 4 mm/decade since 1700 CE, with most of the increase occurring in the last 60 y. Consistent with the hypothesis that TCs are moving slower under anthropogenic climate change, we show that seasonal ΣTCP along the US East Coast are positively related to seasonal average TC duration and TC translation speed.

The Effects of Depression and Anxiety on 90-day Readmission Rates After Total Hip and Knee Arthroplasty.

BACKGROUND: Patients undergoing total joint arthroplasty have higher rates of anxiety, depression or anxiety and depression than the general population and higher costs of care, which lead to higher levels of postoperative dissatisfaction and readmission rates. We evaluated the readmission rates of patients undergoing total hip or knee arthroplasty with diagnoses of anxiety, depression, or both. METHODS: Our hospital's prospectively collected data from Michigan's statewide total joint database were reviewed from 2013 to 2018. Rates of anxiety, depression or anxiety and depression were determined based on preoperative anxiolytic or antidepressant medications using National Drug Codes. RESULTS: A total of 4107 cases were included. Of which 4.28% had a readmission within the 90-day global period, and 12% had a history of depression or anxiety or both. For the entire cohort, those on anxiolytic medication were 153% more likely to be readmitted than those not on medication (P = .017). When comparing total hip arthroplasty (THA) or total knee arthroplasty (TKA), patients taking anxiolytic medication and undergoing TKA were 120% more likely to undergo readmission within 90 days (P = .021). Patients on depression medication alone were not at increased risk of readmission in the TKA cohort (P = .991). For THA, neither diagnosis appeared a risk factor for readmission (P = .852). CONCLUSIONS: Patients with depression, anxiety, or both undergoing TKA were at a statistically significant risk of readmission within 90 days compared with patients without these diagnoses. Anxiety and depression were both risk factors for readmission, but anxiety appeared to have a more significant impact. Patients undergoing THA on the other hand did not appear to share this risk profile.

Quantifying Patient Engagement in Total Joint Arthroplasty Using Digital Application-Based Technology.

BACKGROUND: Digital patient engagement has been suggested as a mean to increase patient activation and patient satisfaction after total joint arthroplasty. The purpose of this study was to assess patient engagement with application-based educational tools and to explore what content was most useful to patients in the perioperative period surrounding total hip arthroplasty (THA) and total knee arthroplasty (TKA), respectively. METHODS: Patients undergoing THA and TKA between October 2017 and January 2020 were enrolled to use an application-based digital technology. The App provides comprehensive patient education using a series of modules delivered at set intervals preoperatively and postoperatively. Patient engagement was defined as patients viewing at least one time the modules that were sent, or marking them as completed. Patient satisfaction was assessed using an in-application survey. RESULTS: Complete data were available on 207 patients of which 95 (46%) underwent THA and 112 (54%) underwent TKA. The average age was 60 years. 54% with patients invited to the program completed registration. An average compliance rate of 48% (41 modules engaged out of 83) was observed. Of all modules completed, the top three most popular categories included physical therapy/exercise videos, health literacy, and anxiety/stress/pain management. The least viewed category was nutrition planning and education. CONCLUSION: When presented educational material related to THA and TKA, patients had a high rate of compliance. Digital technology platforms provide a scalable, meaningful approach to engaging patients throughout the continuum of joint replacement care and may serve as a cost-effective adjunct to traditional methods.

High-Energy Blast Injury Requiring Transradial Amputation with Associated Essex Lopresti and Terrible Triad Injuries of the Elbow: A Rare Presentation.

CASE: Blast injuries to the upper extremity can be devastating and emotionally stressful injuries. We describe a case of a high-energy blast injury to an upper extremity from an explosive. The transfer of energy caused severe soft tissue/bony damage to the hand, but also led to associated Essex Lopresti and terrible triad injuries. The patient required emergent transradial amputation by hand surgery as well as definitive fixation by our orthopaedic team. CONCLUSION: We describe a unique salvage operation that established forearm pronosupination, elbow flexion, and proper prosthetic fitting. We feel that describing our technique could help others in treating this injury if encountered.

Production of [89 Zr]Oxinate4 and cell radiolabeling for human use.

[89 Zr]Oxinate4 is a Positron Emission Tomography (PET) tracer for cell radiolabeling that can enable imaging techniques to help better understand cell trafficking in various diseases. Although several groups have synthetized this compound for use in preclinical studies, there is no available data regarding the production of [89 Zr]Oxinate4 for human use. In this report, we describe the detailed production of [89 Zr]Oxinate4 under USP <823> and autologous leukocyte radiolabeling under USP <797>. The final product presented high radiochemical purity and stability at 24 h post synthesis (>99%) and passed in all quality control assays required for clinical use. [89 Zr]Oxinate4 did not compromise the white blood cells viability and did not show considerable cellular efflux up to 3 h post labeling. The translation of this technique into human use can provide insight into several disease mechanisms since [89 Zr]Oxinate4 has the potential to label any cell subset of interest.

Risk factors for manipulation under anaesthesia after total knee arthroplasty.

AIMS: Postoperative range of movement (ROM) is an important measure of successful and satisfying total knee arthroplasty (TKA). Reduced postoperative ROM may be evident in up to 20% of all TKAs and negatively affects satisfaction. To improve ROM, manipulation under anaesthesia (MUA) may be performed. Historically, a limited ROM preoperatively was used as the key harbinger of the postoperative ROM. However, comorbidities may also be useful in predicting postoperative stiffness. The goal was to assess preoperative comorbidities in patients undergoing TKA relative to incidence of postoperative MUA. The hope is to forecast those who may be at increased risk and determine if MUA is an effective form of treatment. METHODS: Prospectively collected data of TKAs performed at our institution's two hospitals from August 2014 to August 2018 were evaluated for incidence of MUA. Comorbid conditions, risk factors, implant component design and fixation method (cemented vs cementless), and discharge disposition were analyzed. Overall, 3,556 TKAs met the inclusion criteria. Of those, 164 underwent MUA. RESULTS: Patients with increased age and body mass index (BMI) had decreased likelihood of MUA. For every one-year increase in age, the likelihood of MUA decreased by 4%. Similarly, for every one-unit increase in BMI the likelihood of MUA decreased by 6%. There were no differences in incidence of MUA between component type/design or fixation method. Current or former smokers were more likely to have no MUA. Surprisingly, patients discharged to home health service or skilled nursing facility were approximately 40% and 70% less likely than those discharged home with outpatient therapy to be in the MUA group. MUA was effective, with a mean increased ROM of 32.81° (SD 19.85°; -15° to 90°). CONCLUSION: Younger, thinner patients had highest incidence of MUA. Effect of discharge disposition on rate of MUA was an important finding and may influence surgeons' decisions. Interestingly, use of cement and component design (constraint) did not impact incidence of MUA. Level of Evidence II: Prospective cohort study. Cite this article: Bone Joint J 2020;102-B(6 Supple A):66-72.

Incidence of Heterotopic Ossification in Direct Anterior Approach to Total Hip Arthroplasty with use of Aspirin as Thromboembolic Prophylaxis.

CONTEXT: Heterotopic ossification (H.O.) is a common occurrence after total hip arthroplasty (THA) with significant potential clinical ramifications. Controversy still exists regarding the exact etiology of the disorder, including possible risk factors. Surgical technique, surgical approach, postoperative medication protocols and even thromboembolic prophylaxis have been implicated in the formation of H.O. Our study looked at one institution with a single surgeon performing direct anterior THA (DAA THA) in patients who received aspirin (ASA) as monotherapy for thromboembolic prophylaxis. METHODS: Patients at a single institution who underwent DAA THA between 2015 and 2019 were identified by CPT code. 45 patients ultimately met inclusion criteria. Postoperative radiographs were analyzed retrospectively for H.O. according to the Brooker classification. Several patient characteristics and comorbidities were statistically analyzed using Chi-square tests, Fisher Exact tests, Wilcox rank sum tests, and Pearson correlation. RESULTS: 12 patients (26.7%) were found to have heterotopic ossification (67% Class 1, 8% Class 2, 25% Class 3, and 0% Class 4); with a median follow up of 35 weeks (range: 12-96). 25% of these patients received ASA 325mg BID while 75% received ASA 81 BID. No statistical differences in development of H.O. were detected among age, gender, BMI, sex, race, diabetes, or NSAID use in the post-operative interval. There were significantly more smokers in the H.O. group (50% vs. 9%, p<0.006). CONCLUSIONS: Our analysis aimed to quantify the incidence of H.O. with consistency in surgical approach and post-operative protocol. There have been few studies on this topic, and we believe it is very relevant with the increasing use of aspirin in the post-operative protocol for thromboembolic prophylaxis. Our retrospective analysis identified H.O. at rates similar to previous studies in DAA.

Low-Grade Chondrosarcoma of the Proximal Phalanx: A Rare Presentation.

CASE: Chondrosarcomas are the second most common primary malignant sarcoma of the bone, though it is overall a rare tumor. Our case presents a 36-year-old Caucasian male who complained of an enlarging mass at his third finger MCP joint. After assessing the full clinical scenario, it was determined that wide excision with ray resection would provide the best result for this patient. CONCLUSION: This study explains a rare malignancy presenting in the proximal phalanx of the hand. The following report will review chondrosarcomas involving the hands, help differentiate between low-grade chondrosarcomas and enchondromas, and briefly cover treatment modalities.

Mountain pine beetle selectivity in old-growth ponderosa pine forests, Montana, USA.

A historically unprecedented mountain pine beetle (MPB) outbreak affected western Montana during the past decade. We examined radial growth rates (AD 1860-2007/8) of co-occurring mature healthy and MPB-infected ponderosa pine trees collected at two sites (Cabin Gulch and Kitchen Gulch) in western Montana and: (1) compared basal area increment (BAI) values within populations and between sites; (2) used carbon isotope analysis to calculate intrinsic water-use efficiency (iWUE) at Cabin Gulch; and (3) compared climate-growth responses using a suite of monthly climatic variables. BAI values within populations and between sites were similar until the last 20-30 years, at which point the visually healthy populations had consistently higher BAI values (22-34%) than the MPB-infected trees. These results suggest that growth rates two-three decades prior to the current outbreak diverged between our selected populations, with the slower-growing trees being more vulnerable to beetle infestation. Both samples from Cabin Gulch experienced upward trends in iWUE, with significant regime shifts toward higher iWUE beginning in 1955-59 for the visually healthy trees and 1960-64 for the MPB-infected trees. Drought tolerance also varied between the two populations with the visually healthy trees having higher growth rates than MPB-infected trees prior to infection during a multi-decadal period of drying summertime conditions. Intrinsic water-use efficiency significantly increased for both populations during the past 150 years, but there were no significant differences between the visually healthy and MPB-infected chronologies.

Radial growth rate increases in naturally occurring ponderosa pine trees: a late-20th century CO2 fertilization effect?

The primary objective of this study was to determine if gradually increasing levels of atmospheric CO2, as opposed to 'step' increases commonly employed in controlled studies, have a positive impact on radial growth rates of ponderosa pine (Pinus ponderosa) in natural environments, and to determine the spatial extent and variability of this growth enhancement. We developed a series of tree-ring chronologies from minimally disturbed sites across a spectrum of environmental conditions. A series of difference of means tests were used to compare radial growth post-1950, when the impacts of rising atmospheric CO2 are best expressed, with that pre-1950. Spearman's correlation was used to relate site stress to growth-rate changes. Significant increases in radial growth rates occurred post-1950, especially during drought years, with the greatest increases generally found at the most water-limited sites. Site harshness is positively related to enhanced radial growth rates. Atmospheric CO2 fertilization is probably operative, having a positive effect on radial growth rates of ponderosa pine through increasing water-use efficiency. A CO2-driven growth enhancement may affect ponderosa pine growing under both natural and controlled conditions.