Alexander Synek

Primates display a wide range of locomotor behaviours, each resulting in distinct mechanical demands on the ankle joint. This study examines how variation in distal tibial shape and internal bone structure captures these locomotor adaptations. We examined the morphology of distal tibiae from eight extant catarrhine genera using canonical holistic morphometric analysis. Relative trabecular bone volume fraction was quantified across homologous three-dimensional volumes, and shape was assessed via a new geometric morphometric-based approach. Our analyses reveal taxonomic and locomotor differences in both distal tibial trabecular distribution and shape. Humans exhibit a squared tibial plafond with trabecular reinforcement at its center, reflecting vertical axial loading. African apes show a trapezoidal plafond with trabecular reinforcement linked to ankle flexion during climbing and quadrupedalism. Orangutans and hylobatids exhibit diverse trabecular distribution and morphology, consistent with multidirectional loading. Cercopithecoids display posterior trabecular reinforcement and narrower joint morphology, consistent with plantarflexed postures during quadrupedalism. Substantial covariation between tibial shape and trabecular distribution was identified across taxa, with functional gradients aligning with ankle loading regimes, showing that analyzing trabecular structure and external shape enhances our understanding of joint mechanics, offering critical insight for interpretation of primate locomotor diversity and evolution.

Removals of cephalomedullary nails (CMNs) after healed pertrochanteric femur fractures are sometimes requested by patients or medically indicated due to pain or screw cut-out. However, CMN removal carries a high risk of secondary femoral neck fracture, even in the absence of trauma. Consequently, decisions on nail removal and establishing a safe post-operative loading regimen can be challenging. This study investigated if finite element (FE) models can pre-operatively predict femoral strength after CMN removal to support these clinical decisions. Nine proximal femora of body donors who were treated with a CMN during their lifetime were included. Computed tomography (CT) scans were acquired with the CMN still in place, followed by virtual implant removal using image processing. Based on this scan, non-linear voxel-based FE models were created and femoral strength was predicted for a one-legged stance configuration. For validation, the CMNs were physically removed and femoral strength was assessed in a material testing machine. The FE models predicted the femoral strength accurately relative to the experiments (R ² = 0.94, CCC = 0.97). In conclusion, CT-based FE models demonstrate potential to predict femoral strength after CMN removal pre-operatively. This could help patients and clinicians to make an informed decision on implant removal and permissible post-operative weight-bearing.

Aims: Spontaneous neck fractures are feared complications of cephalomedullary nail removal after successful healing of per- and subtrochanteric fractures. To date, the initial postoperative stability as well as the correct weightbearing regimen remain unclear. The aim of this biomechanical ex vivo study was to evaluate the initial postoperative failure load after hardware removal of specimens, which received cephalomedullary nails during their lifetime.Methods: A total of 20 specimens of voluntary body donors were included in this study. Group 1 (n = 10) consisted of specimens that received cephalomedullary nails during their lifetime due to per- or subtrochanteric fractures. Each individual was matched for age, sex, femur size, and neck-shaft angle (Group 2 = control, n = 10). Biomechanical testing was performed in a single-leg stance setting, and volumetric bone mineral density (vBMD) was measured proximally at the femoral neck and distally at the epicondyles.Results: Groups 1 and 2 differed significantly in terms of failure loads (p = 0.002), fracture types, and ratios of proximal and distal vBMD (p = 0.035). Femora after nail removal were significantly weaker (1,835.0 N vs 4,523.0 N) and showed lower ratios of proximal to distal vBMD (0.74 vs 1.18), which indicated altered stress distributions at the femoral neck in presence of femoral neck screws. They were further characterized by predominantly subcapital buckle-type fractures, while the control Group 2 showed predominantly transcervical fractures.Conclusion: Altered stress distribution in presence of femoral neck screws leads to changes in biomechanical properties of the proximal femur, resulting in potentially unstable situations after nail removal in clinical settings. Elective removal of cephalomedullary nails should be undertaken with caution in view of the potentially increased fracture risk.Cite this article: Bone Joint Res 2025;14(5):365–372.

Purpose: Removal of volar locking plates after healing of a distal radius fracture is becoming increasingly common. However, it is unclear how the fracture healing proceeds and which defects remain. The aim of this study was to assess changes in bone microarchitecture and biomechanical properties in surgically treated radius fracture after volar locking plate removal. Methods: Twelve patients were recruited after undergoing plate removal. High Resolution Quantitative Computed Tomography (HR-pQCT) was used to perform scans of the fractured and contralateral distal radius on average one (M1) and 16 months (M2) after plate removal. Parameters measured were cortical- (Dcomp), trabecular- (Dtrab) and total bone density (D100), as well as cortical thickness (Ct.Th). Axial bone stiffness (FE.Kaxial) was determined through linear micro-finite element analysis (µFEA). Results: At M1, no significant differences between fractured and contralateral side were detected except for Dcomp. At the fractured side, all parameters except for Dtrab increased significantly between M1 and M2. At M2, Ct.Th and FE.Kaxial were significantly higher at the fractured side compared to the contralateral side, but Dcomp remained significantly lower. Qualitatively, closure of the screw holes was observed between M1 and M2, while large trabecular defects remained. Conclusion: Bone (re)modeling at the distal radius is an ongoing process even after plate removal and leads to a partial exaggeration of the bone properties relative to the intact contralateral side. It seems that the bone regains its biomechanical competence by closing screw holes and increasing cortical thickness, which compensates for trabecular defects that cannot be repaired. Level of evidence: III.

Fracture liaison services are essential to mitigate underdiagnosis and undertreatment of osteoporosis-related fractures. However, it often suffers from limited access to dual-energy X-ray absorptiometry (DXA) or high-resolution peripheral quantitative CT equipment. This in vivo study of 21 patients aims to evaluate the feasibility of dental cone beam CT (dCBCT) to analyse bone properties of human wrists, comparing with DXA and finite element (FE) analysis. dCBCT grey-scale values were transformed to HU using a phantom containing materials with known HU values. Strong correlations were found between bone mineral content (BMC) from dCBCT and DXA (r = 0.78 to 0.84, p < 0.001), as well as between BMC from dCBCT FE-predicted stiffness (r = 0.91) and maximum force (r = 0.93), p < 0.001. BMC values from dCBCT were higher than DXA measurements (2.34 g vs. 1.5 g, p < 0.001). Cortical thickness strongly correlated to bone mineral density (BMD) from dCBCT (r = 0.83, p < 0.001). No statistically significant correlations were found between trabecular bone microstructure and FE predictions. The results indicate the feasibility to analyse osteoporosis related bone properties of human wrists from corrected dCBCT data. The dCBCT values of BMD and BMC were strongly correlated with DXA.

Background: Osseointegration is essential for the long-term survival of cementless femoral stems and is dependent on periprosthetic bone quality and correct implantation technique. The aim of this study was to evaluate the 3-dimensional long-term fixation patterns of, and bone microarchitecture around, cementless hip stems. Methods: Four specimens with varying degrees of bone quality and fixation characteristics from body donors who had received Alloclassic Zweymüller hip stems during their lifetime (mean time in situ at the time of death: 12.73 years) were evaluated with use of radiographs, high-resolution computed tomography (CT) scans, and hard-tissue histology. The CT voxel size was 85 µm, and the following parameters were calculated: total bone volume, total bone volume fraction, trabecular bone volume, trabecular bone volume fraction, cortical bone volume, cortical bone volume fraction, and cortical thickness. Bone-implant contact and canal fill index values for each Gruen zone of the specimens were calculated with use of histological samples. Results: Femoral stems with apparently good cortical contact on clinical radiographs showed higher values for cortical bone volume, trabecular bone volume, and cortical thickness in the high-resolution CT analysis than femoral stems with apparently weak cortical contact on clinical radiographs. Based on the histological evaluation, the mean bone-implant contact ranged from 22.94% to 57.24% and the mean canal fill index ranged from 52.33% to 69.67% among the specimens. Conclusions: This study demonstrated different osseointegration patterns of cementless femoral stems on the basis of radiographs, high-resolution CT scans, and histological evaluation. Femora with high cortical bone volume and cortical thickness were associated with higher canal fill indices, whereas femora with low cortical bone volume and cortical thickness had lower canal fill indices and showed a characteristic corner-anchorage pattern. Clinical Relevance: Osseointegration patterns and thus the long-term survival of cementless femoral stems are dependent on cortical bone volume and cortical thickness.

Recently, promising results have been reported for detection of osteoporosis with use of an aluminum phantom. Therefore, the aim of this study was to evaluate the feasibility of radiography‐based bone mineral density (BMD) measurement using a graded aluminum phantom. This study included 27 postmenopausal women with a distal radius fracture. Aluminum phantom radiography of the healthy radius was conducted as well as high‐resolution peripheral quantitative computed tomography (HR‐pQCT) measurement of the ultradistal radius and dual energy X‐ray absorptiometry (DXA) of the radius, spine, and hip. A strong correlation was observed between aluminum phantom radiography‐based mean gray value (mGV) and DXA‐derived BMD, especially for the ultradistal radius (ρ = 0.75; p < 0.001). A moderate correlation for the femoral neck (ρ = 0.61 and p < 0.001) between modalities was found. Radius mGV and HR‐pQCT‐derived BMD only showed a moderate correlation (ρ = 0.48; p < 0.09). Aluminum phantom radiography might serve as a cost efficient, highly available, low‐radiation dose screening, and diagnostic method for osteoporosis additively to DXA measurements. Especially, an application in areas with constrained DXA availability and such as preoperative trauma settings would be beneficial. However, further investigation and assessment of specificity and sensitivity is needed.