Search Results (92)

Background: Implantation of modularly built-up stems with a tapered and fluted design is currently state of the art in revision total hip arthroplasty (RTHA). Nevertheless, implant-specific major complications like breakage of taper junctions as well as periprosthetic fractures (PPFs) may lead to failure of reconstruction during follow-up. Methods: A cohort of 117 cases receiving femoral RTHA by a modular stem was investigated retrospectively with a mean follow-up of 5.7 (0.5–13.7) years. Cumulative risk and potential factors affecting the occurrence of PPFs were calculated with the Kaplan–Meier method. In addition, cases were presented to discuss operative treatment options. Results: A cumulative risk of PPF of 12.1% (95% CI: 0–24.6%) was calculated at 13.7 years. Female patients had significantly higher risk compared to male patients (0% after 13.5 years for male patients vs. 20.8% (95% CI: 0.5–41.2%) after 13.7 years for female patients; log-rank p = 0.0438) as all five patients sustaining a PPF during follow-up were women. Four fractures were treated by open reduction and internal fixation. Non-union and collapse of the fracture occurred in one patient after closed reduction and internal fixation. Conclusions: Postoperative PPF after femoral revision with a modular stem has shown to be a frequent complication within this mid-term follow-up. Female patients were at a significantly higher risk in this aged cohort, indicating osteoporosis as a risk factor. The surgical treatment of PPF with an integrated long-stemmed prosthesis is challenging and thorough considerations of adequate operative treatment of PPFs are strongly advised in order to limit complication rates. Full article

Accurate estimation of individual tree stem volume is essential for forest resource assessment and the implementation of sustainable forest management. In South Korea, traditional regression models based on non-destructive and easily measurable field variables such as diameter at breast height (DBH) and total height (TH) have been widely used to construct stem volume tables. However, these models often fail to adequately capture the nonlinear taper of tree stems. In this study, we evaluated and compared the predictive performance of traditional regression models and two machine learning algorithms—Random Forest (RF) and Extreme Gradient Boosting (XGBoost)—using stem profile data from 1000 destructively sampled Chamaecyparis obtusa trees collected across 318 sites nationwide. To ensure compatibility with existing national stem volume tables, all models used only DBH and TH as input variables. The results showed that all three models achieved high predictive accuracy (R² > 0.997), with XGBoost yielding the lowest RMSE (0.0164 m³) and MAE (0.0126 m³). Although differences in performance among the models were marginal, the machine learning approaches demonstrated flexible and generalizable alternatives to conventional models, providing a practical foundation for large-scale forest inventory and the advancement of digital forest management systems. Full article

Accurate estimation of stem profiles is critical for forest management, timber yield prediction, and ecological modeling. However, traditional taper equations often fail to capture species-specific growth variability and exhibit significant biases, particularly in the upper stem regions. Machine learning regression models were applied to estimate Quercus mongolica stem profiles across South Korea, and performance was compared with that of a traditional taper equation. A total of 2503 sample trees were used to train and validate Random Forest (RF), XGBoost (XGB), Artificial Neural Network (ANN), and Support Vector Regression (SVR) models. Predictive performance was evaluated using root mean square error, mean absolute error, and coefficient of determination metrics, and performance differences were validated statistically. The ANN model exhibited the highest predictive accuracy and stability across all diameter classes, maintaining smooth and consistent stem profiles even in the upper stem regions where the traditional taper model exhibited significant errors. RF and XGB models had moderate performance but exhibited localized fluctuations, whereas the Kozak taper equation tended to overestimate basal diameters and underestimate crown-top diameters. Machine learning models, particularly ANN, offer a robust alternative to fixed-form taper equations, contributing substantially to forest resource inventory, carbon stock assessment, and climate-adaptive forest management planning. Full article

Bamboo forests are among China’s key strategic forest resources, characterized by rapid growth and high carbon sequestration efficiency. Traditional management practices primarily aim to maximize economic benefits by regulating stand density to enhance yields of bamboo culms and shoots. However, the influence of density regulation on the growth and carbon accumulation of spring bamboo shoots remains insufficiently understood. Therefore, this study focuses on moso bamboo (Phyllostachys edulis (Carrière) J. Houzeau) stands and investigates shoot emergence during the shooting period across four stand density levels: D1 (1400 stems/ha), D2 (2000 stems/ha), D3 (2600 stems/ha), and D4 (3200 stems/ha). The study analyzes the dynamics of shoot emergence, height development, and morphological traits under varying stand densities, and explores patterns of carbon accumulation during the shooting period, thereby clarifying the effects of stand density on shoot quantity, growth quality, and carbon sequestration. The main findings are as follows: the number of emerging shoots decreased with increasing stand density, ranging from 2592 to 4634 shoots per hectare. The peak shoot emergence period in the D1 stand was extended by 3 days compared to D2 and D3, while the D4 stand entered the peak emergence period 6 days later than D2 and D3. The rapid height growth phase in D1 occurred 3 days earlier than in D2 and D3, and 6 days earlier than in D4. Results from the variable exponent taper equation indicated that spring shoots in the D2 and D4 stands had larger basal diameters, following the order D4 > D2 > D3 > D1. Shoots in the D2 stand exhibited the smallest taper, with the order being D2 < D3 < D1 < D4. During the late stage of shoot emergence (3 May to 9 May), all stands entered a period of rapid carbon accumulation per individual shoot. In the early stage, carbon accumulation followed the order D1 > D2 > D4 > D3; in the middle stage, the order shifted to D4 > D3 > D2 > D1; and in the final stage, the trend was D1 > D4 > D3 > D2. Within the 30-day investigation period, the carbon storage in spring shoots reached up to one-quarter or even one-third of the total accumulation during the growth period. The D1 stand exhibited the highest rate of increase in the proportion of individual shoot carbon storage. Full article

Background and objectives: The objective was to validate the Beyond the Vancouver classification. Based on this algorithm, it was hypothesized that cemented polished tapered stems with an intact cement mantle and cementless stable stems with defined criteria could be classified as stable and therefore treated with open reduction and internal fixation (ORIF). Materials and Methods: This retrospective, single-center cohort study re-analyzed patients initially diagnosed with Vancouver type B2 fractures treated with ORIF between 2007 and 2020. Clinical and radiological outcomes were extracted from medical reports. A combined radiological and clinical score was used as the main outcome measure. Patients categorized according to the Beyond the Vancouver classification were compared for functional outcome. Results: 42 patients (25 male, 17 female) with a median (range) age of 83 years (75–88 years) and follow-up time of 25 weeks (12–35 weeks) were reviewed. It was found that ORIF achieved excellent or good results in 81% of cases for stems classified as stable (n = 16) and in 30% of cases for stems classified as loose (n = 23). Successful cases (30%), although classified as loose, all had the same fracture pattern: an intact greater trochanter and a fracture fragment attached laterally to the stem with distal fixation of the stem. Conclusions: This case series suggests that certain Vancouver B2 fractures can be treated with ORIF. The Beyond the Vancouver classification may support the categorization of ‘stable’ and ‘loose’ stems. The validity of the algorithm was supported by the observation that ORIF provided excellent and good results for the majority of stems classified as ‘stable’, but poor results for stems classified as ‘loose’. Furthermore, the fracture pattern has been shown to be a crucial factor that should be considered when treating distally fixed cementless stems. The classification was therefore expanded to include the specific fracture patterns in cementless distally fixed stems that can be successfully treated with ORIF. The Beyond the Vancouver classification can provide further guidance in the identification of ‘loose’ or ‘stable’ stems. Full article

The stem taper function is essential in predicting diameter outside bark (DOB) variations along the tree height, contributing to volume estimation, harvest planning, and precision forestry. Traditional taper models, such as the Kozak function, offer interpretability but often fail to capture nonlinear growth dynamics and regional variability, particularly in the upper stem segments. This study aimed to evaluate and compare the prediction accuracy of conventional and machine learning-based taper models using Pinus densiflora, a representative conifer species in Korea. Field data from two ecologically distinct regions (Gangwon and Central Korea) were used to build and test four models: the Kozak taper function, random forest, extreme gradient boosting, and an artificial neural network (ANN). Model performance was assessed using the RMSE, R², and MAE, along with stem profile visualizations for representative trees. The results showed that the ANN consistently achieved the highest prediction accuracy across both regions, particularly at an upper crown zone relative height (RH) > 0.8, while maintaining smooth and stable taper curves. In contrast, the Kozak model tended to underestimate the diameter of the upper stem. This study demonstrates that machine learning models, particularly ANNs, can effectively enhance the taper prediction precision and serve as practical tools for data-driven forest management and the implementation of precision forestry in Korea. Full article

Pure red cell aplasia (PRCA) following major ABO-mismatched allogeneic hematopoietic stem cell transplantation (HSCT) is a challenging complication, affecting 7–10% of patients and significantly impacts quality of life. Despite half of patients showing a resolution within three–six months after HSCT, PRCA might require treatment. Various therapeutic approaches have been investigated, including erythropoietin, plasmapheresis or immunomodulatory therapies (rituximab, bortezomib, corticosteroids, donor lymphocyte infusion (DLI), or the early tapering of immunosuppressive drugs), and TPO-mimetic agents, though responses have generally remained suboptimal. Recently, daratumumab has emerged as a promising, safe, and effective treatment for PRCA, documented by numerous case reports and series. We present a case of PRCA arising in a patient with mixed chimerism following a sibling HSCT for aplastic anemia (AA). In line with the literature, our findings highlight the effectiveness of daratumumab in PRCA from the first dose, although daratumumab administrations were delayed by the onset of infectious complications. Our case supports the earlier introduction of daratumumab in the treatment strategy of PRCA to avoid patient exposure to ineffective therapies that carry risks of increased immunosuppression and infections. Indeed, in our specific case, the early introduction of daratumumab may interrupt the immune hematologic mechanism underlying PRCA, which, in the context of mixed chimerism, could increase the risk of graft failure. Full article

Background: The use of tapered monobloc stems in revision total hip arthroplasty (RTHA) has shown excellent results, with low implant-dependent failures due to aseptic loosening. Infection is one of the main failure reasons, but further problems, like periprosthetic fractures (PPFs), may endanger the function and duration of the implant in the long run. Methods: A consecutive series of 121 cases after femoral RTHA with a monobloc device was retrospectively investigated, and a Kaplan–Meier analysis was performed. The mean follow-up was 13.0 (range: 0.8–23.8) years. Results: PPF occurred in six patients during follow-up. The cumulative risk for PPF was 5.2% (95% CI: 1.1–9.4%) after 23.8 years. Female gender was associated with a significantly higher risk compared to male gender (9.1% (95% CI: 2.1–16.1%) after 23.1 years vs. 0% after 23.8 years; log-rank p = 0.0034). Patients operated with stems with a length equal to or longer than the calculated median length were also at a significantly higher risk of PPF during follow-up (10.2% (95% CI: 2.4–17.9%) after 23.8 years vs. 0% after 23.1 years; log-rank p = 0.0158). Diabetes at the time of index operation also significantly influenced the occurrence of a PPF during follow-up (n = 4 patients with PPF out of 107 without (4.0% (95% CI: 0.2–7.8%) after 23.8 years vs. n = 2 out of 14 with diabetes (15.4% (95% CI: 0–35.0%) after 21.1 years; log-rank p = 0.0368). The failure rate with implant removal as an endpoint due to aseptic loosening was 0%, and with infection it was 3.4% (95% CI: 0.1–6.7%), after 23.8 years. Conclusions: Although no removal of the implant due to a PPF was necessary, the cumulative risk for PPF after femoral revision with a tapered and fluted monobloc stem was higher in this long-term follow-up series compared to implant failure due to infection or aseptic loosening. Female gender and diabetes was associated with a significantly higher risk of PPF during follow-up. The use of longer stems than necessary is not preventive of PPF, and should be avoided. Full article

Stem volume is a critical factor in managing and evaluating forest resources. At present, stem volume is commonly estimated indirectly by constructing a taper model that utilizes sampling, diameter at breast height (DBH), and tree height. However, these estimates are constrained by errors arising from spatial and stand environment variations as well as uncertainties in height measurements. To address these issues, this study aimed to accurately estimate stem volume using light detection and ranging (LiDAR) technology, a key tool in modern precision forestry. LiDAR data were used to build comprehensive three-dimensional models of forests with multi-platform LiDAR systems. This approach allowed for precise measurements of tree heights and stem diameters at various heights, effectively mitigating the limitations of earlier measurement methods. Based on these data, a Kozak taper curve was developed at the individual tree level using LiDAR-derived tree height and diameter estimates. Integrating this curve with LiDAR data enabled a hybrid approach to estimating stem volume, facilitating the calculation of diameters at points not directly identifiable from LiDAR data alone. The proposed method was implemented and evaluated for two economically significant tree species in Korea: Pinus koraiensis and Larix kaempferi. The RMSE comparison between the taper curve-based approach and the hybrid volume estimation method showed that, for Pinus koraiensis, the RMSE was 0.11 m³ using the taper curve-based approach and 0.07 m³ for the hybrid method, while for Larix kaempferi, the RMSE was 0.13 m³ and 0.05 m³, respectively. The estimation error of the hybrid method was approximately half that of the taper curve-based approach. Consequently, the hybrid volume estimation method, which integrates LiDAR and the taper model, overcomes the limitations of conventional taper curve-based approaches and contributes to improving the accuracy of forest resource monitoring. Full article

Background: Although tapered and fluted stems are frequently used in revision total hip arthroplasty (RTHA), major complications following the implantation of these implants, like periprosthetic fractures, are less investigated. As epidemiological data do not exist yet, the incidence of PPF in a mid- to long-term follow-up is unknown and potential risk factors have not been detected. Methods: Propensity score matching (PSA) of two retrospectively investigated cohorts after femoral RTHA with either modular (n = 130) or monobloc prosthesis (n = 129) was executed. A total of 186 cases, including 93 of each device, were finally analyzed during a mean follow-up period of 9.1 (0.5–23.1) years. The time-dependent risk of PPF was calculated using a Kaplan–Meier analysis. Results: The cumulative risk for PPF of the whole cohort was 5.7% (95% CI: 1.7–9.8%) at 23.1 years, for the modular device, 13.0% (95% CI: 0–26.0%) after 13.7 years and the monobloc stem, 3.4% (95% CI: 0–7.1%) after 23.1 years, without a significant difference between the two designs (log-rank p = 0.1922). All eight fractures occurred in women and there was one collapse of the fracture after open reduction and internal fixation. The cumulative risk was 10.1% (95% CI: 3.1–17.1%) at 23.1 years compared to 0% after 21.4 years in men (log-rank p = 0.0117). Diabetes was significantly associated with the presence of PPF during follow-up (non-diabetic, 4.4% (95% CI: 0–8.2%) after 21.3 years vs. diabetic, 16.6% (96% CI: 0–34.5%) after 13.3 years; log-rank p = 0.0066). Longer reconstructions showed also a significantly higher fracture risk (equal or longer than median implant length vs. shorter; 10.5% (95% CI: 3.1–17.1%) after 21.4 years vs. 1.0% (95% CI: 0–3.1%) after 23.1 years; log-rank p = 0.0276) but did not correlate with a preoperative defect situation. Conclusions: The cumulative risk for PPF after femoral revision with tapered and fluted devices is a relevant failure reason in this mid- to long-term investigation. There was no difference between the monobloc stem or modular implant. Women and diabetics are at risk, and the choice of a longer implant than necessary is neither prophylactical for PPF nor useful in the case of the operative treatment of a PPF after femoral RTHA with these revision devices. Full article

This study addressed multi-product optimization in Cedrelinga cateniformis plantations in the Peruvian Amazon, aiming to maximize volumetric yields of logs and sawn lumber. Data from seven plantations of different ages and types, established on degraded land, were analyzed by using ten stem profile models to predict taper and optimize wood use. In addition, the structure of each plantation was evaluated using diameter distributions and height–diameter ratios; log and sawn timber production was optimized using SigmaE 2.0 software. The Garay model proved most effective, providing high predictive accuracy (adjusted R² values up to 0.963) and biological realism. Marked differences in volumetric yield were observed between plantations: older and more widely spaced plantations produced higher timber volumes. Logs of optimal length (1.83–3.05 m) and larger dimension wood (e.g., 25.40 × 5.08 cm) were identified as key contributors to maximizing volumetric yields. The highest yields were observed in mature plantations, in which the total log volume reached 508.1 m³ha⁻¹ and the sawn lumber volume 333.6 m³ha⁻¹. The findings demonstrate the power of data-driven decision-making in the timber industry. By combining precise modeling and optimization techniques, we developed a framework that enables sawmill operators to maximize log and lumber yields. The insights gained from this research can be used to improve operational efficiency and reduce waste, ultimately leading to increased profitability. These practices promote support for smallholders and the forestry industry while contributing to the long-term development of the Peruvian Amazon. Full article

Technological developments have allowed helicopter airborne laser scanning (HALS) to produce high-density point clouds below the forest canopy. We present a tree stem classification method that combines linear shape detection and model-based clustering, using four discrete methods to estimate stem diameter. Stem horizontal size was estimated every 25 cm below the living crown, and a cubic spline was used to estimate where there were gaps. Individual stem diameter at breast height (DBH) was estimated for 77% of field-measured trees. The root mean square error (RMSE) of DBH estimates was 7–12 cm using stem circle fitting. Adapting the approach to use an existing stem taper model reduced the RMSE of estimates (<1 cm). In contrast, estimates that were produced from a previously existing DBH estimation method (PREV) could be achieved for 100% of stems (DBH RMSE 6 cm), but only after location-specific error was corrected. The stem classification method required comparatively little development of statistical models to provide estimates, which ultimately had a similar level of accuracy (RMSE < 1 cm) to PREV. HALS datasets can measure broad-scale forest plantations and reduce field efforts and should be considered an important tool for aiding in inventory creation and decision-making within forest management. Full article

Teak [Tectona grandis L.f.] has a wide distribution range in tropical countries and is Nepal’s second most planted commercial tree species. This study aimed to develop a robust and reliable taper equation for Teak species in Nepal. To achieve this, 15 parametric taper equations were fitted and evaluated using the diameter and height data of 100 trees sampled from two stands of the Sagarnath Plantation projects, Nepal. The data set was split into training (90%) and testing (10%) sets based on the trees’ ID, and model fitting was conducted in two phases. In the first phase, nonlinear models were fitted to the training data using 10-fold cross-validation, and the performance was evaluated based on fit and validation statistics. The top five models were further analyzed in the second phase using a mixed effects framework to account for variance and correlation structures. The modified Bi model performed best under a fixed effects modeling framework (R² = 0.96, RMSE = 1.83 cm). However, the Sharma and Zhang model performed the best under a mixed-effects modeling framework (R² = 0.97, RMSE = 1.54 cm). Therefore, we suggest using the modified Bi under fixed effects and variable exponent equation of Sharma and Zhang under mixed-effects modeling as a taper equation for Teak. The Sharma and Zhang’s equation is recommended for its high accuracy and better performance over previously recommended variable exponents equations. Full article

The concept of tree or stem form has been central to forest research for over a century, playing a vital role in accurately assessing tree growth, volume, and biomass. The form factor is an essential component for expressing the shape of a tree, enabling more accurate volume estimation, which is vital for sustainable forest management and planning. Despite its simplicity, flexibility, and advantages in volume estimation, the form factor has received less attention compared to other measures like taper equations and form quotient. This review summarizes the concept, theories, and measures of stem form, and describes the factors influencing its variation. It focuses on the form factor, exploring its types, parameterization, and models in the context of various tropical species and geographic conditions. The review also discusses the use of the form factor in volume estimation and the issues with using default or generic values. The reviewed studies show that tree stem form and form factor variations are influenced by multiple site, tree, and stand characteristics, including site quality, soil type, climate conditions, tree species, age, crown metrics, genetic factors, stand density, and silviculture. The breast height form factor is the most adopted among the three common types of form factors due to its comparative benefits. Of the five most tested form factor functions for predicting tree form factors, Pollanschütz’s function is generally considered the best. However, its performance is often not significantly different from other models. This review identifies the “Hohenadl” method and mixed-effects modelling as overlooked yet potentially valuable approaches for form factor modelling. Using the form factor, especially by diameter or age classes, can enhance tree volume estimation, surpassing volume equations. However, relying on default or generic form factors can lead to volume and biomass estimation errors of up to 17–35%, underscoring the need to limit variation sources in form factor modelling and application. Further recommendations are provided for improving the statistical techniques involved in developing form factor functions. Full article

Background: Complications such as periprosthetic fractures necessitate challenging revision surgeries. In particular, femoral stem revisions can be complicated by poor bone quality, making primary stability and leg length restoration difficult to achieve. Modular fluted tapered stems (MFTSs) have emerged as a viable option for these complex cases. This study aims to describe a reproducible three-step technique for femoral stem revision using MFTSs. The technique focuses on (1) obtaining distal primary stability, (2) restoring leg length, and (3) ensuring overall implant stability. Materials and methods: We conducted a retrospective analysis of ten patients who underwent revision THA using this three-step technique, with a minimum follow-up of 12 months. The mean patient age was 70.7 years, and the average follow-up was 24.2 months. Limits were the small sample size, the lack of clinical outcomes and the short-term follow-up. Results: There was no subsidence, a mean leg length discrepancy of 4 mm (p: 0.604), and no dislocations. However, heterotopic ossifications (HOs) were observed in 25% of patients, although no trochanteric migrations occurred. One patient experienced an intraoperative femoral fracture, which was successfully treated. Conclusions: This three-step approach can break down the revision procedure, making it more accessible to surgeons. The findings suggest that this technique is effective in achieving reliable outcomes in femoral stem revisions, potentially improving the standard of care for patients requiring complex THA revisions. Full article