Human Cranial Bone Research Articles

Initial Upper Palaeolithic material culture by 45,000 years ago at Shiyu in northern China.

The geographic expansion of Homo sapiens populations into southeastern Europe occurred by ∼47,000 years ago (∼47 ka), marked by Initial Upper Palaeolithic (IUP) technology. H. sapiens was present in western Siberia by ∼45 ka, and IUP industries indicate early entries by ∼50 ka in the Russian Altai and 46-45 ka in northern Mongolia. H. sapiens was in northeastern Asia by ∼40 ka, with a single IUP site in China dating to 43-41 ka. Here we describe an IUP assemblage from Shiyu in northern China, dating to ∼45 ka. Shiyu contains a stone tool assemblage produced by Levallois and Volumetric Blade Reduction methods, the long-distance transfer of obsidian from sources in China and the Russian Far East (800-1,000 km away), increased hunting skills denoted by the selective culling of adult equids and the recovery of tanged and hafted projectile points with evidence of impact fractures, and the presence of a worked bone tool and a shaped graphite disc. Shiyu exhibits a set of advanced cultural behaviours, and together with the recovery of a now-lost human cranial bone, the record supports an expansion of H. sapiens into eastern Asia by about 45 ka.

Artificial intelligence analysis of the sterilization effects on the mechanical properties of human cranial bones

According to the literature, the patient’s own (autologous) bone remains the optimal graft material for cranioplasty. Autografts have an undoubted advantage over competing plastic materials of complete biological compatibility, as well as the absence of interstitial conflict and accessibility. Presently there is still not a single synthetic material that meets all the complex requirements for skull reconstruction in children due to the special complication of accommodating the skull structure that continues to grow. At the same time, the use of autograft is accompanied by the highest percentage of complications in the form of resorption and infection. The purpose of the present study was to evaluate the large volume of measurements (“big data”) obtained after nano-hardness testing of an autograft bone after various preliminary treatments. The latter included the currently optimal method of bone sterilization (boiling peroxide treatment). The measurements performed on different patient allografts were compared and the effects of bone treatment on the mechanical properties were evaluated and compared. Due to the complex hierarchical structural organisation of the bone, the correspondence between the composition, processing, structure, and properties of natural human bone materials were not obvious. Machine Learning, part of the Artificial Intelligence (AI) tool set, was applied to reveal the differences between scull bones of different types, treatment history and patients. It was found that after obtaining the principal mechanical properties of the chosen human skull bone sample it was possible to identify algorithmically the nature of prior bone sterilization and the patient’s sex.

Evaluation of ultrasound sensors for transcranial photoacoustic sensing and imaging

Photoacoustic imaging through skull bone causes strong attenuation and distortion of the acoustic wavefront, which diminishes image contrast and resolution. As a result, transcranial photoacoustic measurements in humans have been challenging to demonstrate. In this study, we investigated the acoustic transmission through the human skull to design an ultrasound sensor suitable for transcranial PA imaging and sensing. We measured the frequency dependent losses of human cranial bones ex vivo, compared the performance of a range of piezoelectric and optical ultrasound sensors, and imaged skull phantoms using a PA tomograph based on a planar Fabry–Perot sensor. All transcranial photoacoustic measurements show the typical effects of frequency and thickness dependent attenuation and aberration associated with acoustic propagation through bone. The performance of plano-concave optical resonator ultrasound sensors was found to be highly suitable for transcranial photoacoustic measurements.

Age-related changes in cationic compositions of human cranial base bone apatite measured by X-ray energy dispersive spectroscopy (EDS) coupled with scanning electron microscope (SEM).

One of the most common scientific methods to study the chemical composition of bone matter is energy-dispersive X-ray spectroscopy (EDS). However, interpretation of the data obtained can be quite complicated and require a thorough understanding of bone structure. This is especially important when evaluating subtle changes of chemical composition, including the age-related ones. The aim of current study is to create a method of processing the obtained data that can be utilized in clinical medicine and use it to evaluate the age evolution of bone chemical composition. To achieve this goal, an elemental composition of 62 samples of cadaver compact bone, taken from the skull base (age: Me = 57.5; 21/91(min/max); Q1 = 39.5, Q3 = 73.75), was studied with EDS. We used the original method to estimate the amount of Mg2+ cations. We detected and confirmed an increase of Mg2+ cation formula amount in the bone apatite, which characterizes age-related resorption rate. Analysis of cation estimated ratio in a normative bone hydroxylapatite showed an increase of Mg2+ amount (R = 0.43, p = 0.0005). Also, Ca weight fraction was shown to decrease with age (R=-0.43, p = 0.0005), which in turn confirmed the age-dependent bone decalcification. In addition, electron probe microanalysis (EPMA) and X-ray diffraction analysis (XRD) were performed. EDS data confirmed the EPMA results (R = 0.76, p = 0.001). In conclusion, the proposed method can be used in forensic medicine and provide additional data to the known trends of decalcification and change of density and crystallinity of mineral bone matter.

Phenotypic and Functional Characterizations of Mesenchymal Stem/Stromal Cells Isolated From Human Cranial Bone Marrow.

Mesenchymal stem/stromal cells (MSCs) are adult stem cells that were originally isolated from bone marrow. In contrast to long bone-derived MSCs that have been extensively characterized, our knowledge regarding to MSCs isolated from flat bones (e.g., cranial bones) remain less clear. In this study, MSCs were purified from human cranial bone marrow (CB-MSCs) and their transdifferentiation capacity and immunomodulatory functions were further characterized. Phenotypic analysis of CB-MSCs demonstrated high expression of CD73, CD90, and CD105 while negative for CD14, CD34, and HLA-DR. Further in vitro differentiation assay shown that CB-MSCs capable of differentiating into cell types of mesenchymal origin (i.e., adipocytes, osetoblasts, and chondrocytes) and collectively, these results indicated that cells isolated from cranial bone marrow in this study are bona fide MSCs according to the minimal criteria proposed by the International Society for Cellular Therapy. Following in vitro expansion, single colony-derived CB-MSCs (scCB-MSCs) were obtained and confocal microscopy analysis further revealed functional heterogeneity within primary CB-MSCs. Specifically, obtained scCB-MSCs exhibited GABA progenitor features, as determined by olig2 and nestin. As expect, scCB-MSCs were readily induced to differentiate into GABAergic neuron-like cells. Furthermore, immunomodulatory roles of scCB-MSCs were evaluated following co-culture with human peripheral blood lymphocytes and results shown that co-culturing with scCB-MSCs significantly suppressed lymphocyte proliferation and promoted differentiation of lymphocytes into regulatory T cells but not Th1/Th17 phenotype. Overall, our results indicated that CB-MSCs exhibited clonal heterogeneity with marked propensity to differentiate into neural-like cells and this might represent promising candidates for the treatment of neurodegenerative diseases.

Analysis of the corrosive effects of hydrochloric acid (HCl) on human bone: Preliminary microscopic study and observations for forensic purposes

The destruction of a corpse in caustic acid can cause complex forensic scenarios to deal with. Furthermore, the literature on the subject is poor, having been the few studies carried out only on animal bones. We carried out an experimental analysis on human cranial, ribs, vertebrae, and femur bone fragments. These samples were sent for dissolution by hydrochloric acid (HCl) at two different concentrations in the lab: 10% and 37%. We have performed macroscopic and microscopic histological and cytological observations at set time intervals: 3, 4, 19, 24, 48, and 72 h of immersion in acids. The purpose of the study was threefold: to investigate the temporal evolution of bone dissolution, evaluate the destructive effect of the two hydrochloric acids, and establish whether or not the human pattern of histological structure could be recognized. A more significant destructive action of HCl at 37% has been observed. In the 10% acid, the bone nature of the samples was demonstrable up to 24 h of immersion, but the human pattern of histological structure was already compromised at 19 h, being lost at 24 h. Instead, in the 37% acid, the bone nature of the sample was demonstrable only within 4 h of immersion, and the human pattern of histological structure was markedly compromised within 3 h. At 19 h of immersion, neither the recognition of the bone nor its human nature was feasible. These preliminary findings and observations may be of practical use in forensic investigations of bodies found in acidic substances, for which there is no scientific evidence to refer.

Ultra-structural morphology analysis of human cranial bone marrow mesenchymal stromal cells during neural differentiation

Neural differentiation of mesenchymal stromal cells has been widely studied. However, a comparative characterization of ultrastructural changes during neural differentiation has not been performed. In this study, we conducted scanning electron microscopy and transmission electron microscopy analysis to show the morphological changes in mesenchymal stromal cells upon induction of neural differentiation. In addition, transmission electron microscopy results demonstrated ultrastructural differences between human cranial bone marrow mesenchymal stromal cells and iliac crest bone marrow mesenchymal stromal cells. We propose that enriched microvesicles in cranial bone marrow mesenchymal stromal cells may be responsible for the increased efficiency of neural differentiation.

Respond of the different human cranial bones to pin-type head fixation device

BackgroundAt this juncture, there is no consensus in the literature for the use and the safety of pin-type head holders in cranial procedures.MethodsThe present analysis of the bone response to the fixation of the instrument provides data to understand its impact on the entire skull as well as associated complications. An experimental study was conducted on fresh-frozen human specimens to analyze the puncture hole due to the fixation of each single pin of the pin-type head holder. Cone-beam CT images were acquired to measure the diameter of the puncture hole caused by the instrument according to several parameters: the pin angle, the clamping force, and different neurosurgical approaches most clinically used.ResultsThe deepest hole, 2.67 ± 0.27 mm, was recorded for a 35° angle and a clamping force of 270 N at the middle fossa approach. The shallowest hole was 0.62 ± 0.22 mm for the 43° angle with a pinning force of 180 N in the pterional approach. The pterional approach had a significantly different effect on the depth of the puncture hole compared with the middle fossa craniotomy for 270 N pinning at 35° angle. The puncture hole measured with the 43° angle and 180 N force in prone position is significantly different from the other approaches with the same force.ConclusionsThese results could lead to recommendations about the use of the head holder depending on the patient’s history and cranial thickness to reduce complications associated with the pin-type head holder during clinical applications.

New lithostratigraphic and chronostratigraphic data for the fossil human skull-bearing eolianite of Rabat-Kebibat (Morocco)

The Kebibat quarry locates on the coastal area of Rabat. It is also known as ‘’The Rabat Human deposit’’ due to the presence of human cranial bones in the quarry deposit. These remains of Hominines are related to the archaic Homo sapiens.The revision of the geological and geochronological context of Kebibat and its surroundings allowed clarifying the morpho-litho-stratigraphic aspects of the different formations that constitute it, as well as their evolution during the Middle-Upper Pleistocene. The sedimentary unit that fossilized the human remains corresponds to a dune deposit (eolianite), which is part of a high-resolution sedimentary sequence (parasequence). Luminescence and U-Th dating indicate that this sequence was deposited between the end of the marine isotopic stage 7 (MIS 7) until the end of MIS 6.

Human bone and amniotic membrane banking in Bangladesh for grafting: the impact of the international atomic energy agency (IAEA) programme.

The idea of establishing a human tissue bank in Bangladesh was started in 1985. However, in 2003, with the active cooperation of international atomic energy agency (IAEA) and Bangladesh Atomic Energy Commission, a tissue bank laboratory was upgraded as a unit for tissue banking and research. Due to increasing demand of allograft, this unit was transformed as an independent institute "Institute of Tissue Banking and Biomaterial Research (ITBBR)" in 2016. This is the only human tissue bank in Bangladesh, which processes human bone and amniotic membrane to provide safe and cost-effective allografts for transplantation. Importantly, banking of human cranial bone as autograft has also started at ITBBR. These processed grafts are sterilized using gamma radiation according to the IAEA Code of Practice for the radiation sterilization of tissues allografts. The amount of grafts produced by the ITBBR from 2007 to 2018 were 120,800cc of bone chips, 45,420cm2 of amniotic membranes, 277 vials of de-mineralized bone granules (DMB), 95 pieces of massive bones, and 134 pieces of cranial bones. Overall, 112,748cc of bone chips, 40,339cm2 of amniotic membranes, 174 vials of DMB, 44 pieces of massive bones, and 64 pieces of cranial bones were transplanted successfully. Nevertheless, to cope up with the modern advanced concepts of cell and tissue banking for therapeutic purpose, ITBBR is working to set up facilities for skin banking, stem cells banking including amniotic and cord blood derived stem cells and scaffold designing. To ensure the quality, safety, ethical and regulatory issues are sustainable in cell and tissue banking practices, ITBBR always works with the Government of Bangladesh for enhancing the national tissue transplantation programme within the contemporary facilities.

Octacalcium phosphate bone substitute materials: Comparison between properties of biomaterials and other calcium phosphate materials.

Octacalcium phosphate (OCP) is a material that can be converted to hydroxyapatite (HA) under physiological environments and is considered a mineral precursor to bone apatite crystals. The structure of OCP consists of apatite layers stacked alternately with hydrated layers, and closely resembles the structure of HA. The performance of OCP as a bone substitute differs from that of HA materials in terms of their osteoconductivity and biodegradability. OCP manifests a cellular phagocytic response through osteoclast-like cells similar to that exhibited by the biodegradable material β-tricalcium phosphate (β-TCP). The use of OCP for human cranial bone defects involves using its granule or composite form with one of the natural polymers, viz., the reconstituted collagen. This review article discusses the differences and similarities in these calcium phosphate (Ca-P)-based materials from the viewpoint of the structure and their material chemistry, and attempts to elucidate why Ca-P materials, particularly OCP, display unique osteoconductive property.

Cranial flap fixation in sheep using a resorbable bone adhesive.

The authors' goal in this study was to investigate the use of a novel, bioresorbable, osteoconductive, wet-field mineral-organic bone adhesive composed of tetracalcium phosphate and phosphoserine (TTCP-PS) for cranial bone flap fixation and compare it with conventional low-profile titanium plates and self-drilling screws. An ovine craniotomy surgical model was used to evaluate the safety and efficacy of TTCP-PS over 2 years. Bilateral cranial defects were created in 41 sheep and were replaced in their original position. The gaps (kerfs) were completely filled with TTCP-PS (T1 group), half-filled with TTCP-PS (T2 group), or left empty and the flaps fixated by plates and screws as a control (C group). At 12 weeks, 1 year, and 2 years following surgery, the extent of bone healing, local tissue effects, and remodeling of the TTCP-PS were analyzed using macroscopic observations and histopathological and histomorphometric analyses. Flap fixation strength was evaluated by biomechanical testing at 12 weeks and 1 year postoperatively. No adverse local tissue effects were observed in any group. At 12 weeks, the bone flap fixation strengths in test group 1 (1689 ± 574 N) and test group 2 (1611 ± 501 N) were both statistically greater (p = 0.01) than that in the control group (663 ± 385 N). From 12 weeks to 1 year, the bone flap fixation strengths increased significantly (p < 0.05) for all groups. At 1 year, the flap fixation strength in test group 1 (3240 ± 423 N) and test group 2 (3212 ± 662 N) were both statistically greater (p = 0.04 and p = 0.02, respectively) than that in the control group (2418 ± 1463 N); however, there was no statistically significant difference in the strengths when comparing the test groups at both timepoints. Test group 1 had the best overall performance based on histomorphometric evaluation and biomechanical testing. At 2 years postoperatively, the kerfs filled with TTCP-PS had histological evidence of osteoconduction and replacement of TTCP-PS by bone with nearly complete osteointegration. TTCP-PS was demonstrated to be safe and effective for cranial flap fixation in an ovine model. In this study, the bioresorbable, osteoconductive bone adhesive appeared to have multiple advantages over standard plate-and-screw bone flap fixation, including biomechanical superiority, more complete and faster bony healing across the flap kerfs without fibrosis, and the minimization of bone flap and/or hardware migration and loosening. These properties of TTCP-PS may improve human cranial bone flap fixation and cranioplasty.

The effects of loading-direction and strain-rate on the mechanical behaviors of human frontal skull bone

Most fatal human skull injuries occur under impact loading conditions, such as car collisions, where the strain rates fall in the range of intermediate (1/s−102/s) and high (102/s−103/s) rates. Therefore, knowledge of the mechanical behaviors of human cranial bone at higher strain rates, i.e., intermediate and high strain rates, may provide insight into the prevention of skull injuries and help the design of efficient head protection systems. In the present study, the compressive mechanical behaviors of human frontal skull bone along and perpendicular to its through-the-thickness direction were experimentally characterized at quasi-static (0.01/s), intermediate (30/s) and high (625/s) strain rates in this study. A total number of 75 specimens prepared from three male donors with ages of 70–74 were separated into three groups: quasi-static (N = 23), intermediate (N = 23), and high (N = 29) strain rates. Experiments at quasi-static and intermediate strain rates were performed using a hydraulically driven materials testing system (MTS), while a Kolsky compression bar was used to load the skull bone specimen at high strain rates. X-ray computed tomography was performed to obtain the structural parameters and visualize the microstructures of the skull bone. The in-situ failure processes of the specimens under high-rate loading were documented by a high-speed camera. The human skull exhibited a loading-direction dependent mechanical behavior, as higher ultimate strength and elastic modulus were found in the direction perpendicular to the thickness when compared with those along the thickness direction, exhibiting an increasing ratio as high as 2 and 3 for strength and modulus, respectively. High-speed images revealed that the specimens loaded along the thickness direction generally failed due to the crushing in diploë (the trabecular bone tissue) whereas separation of the entire architecture was observed as the main failure mode when compressed in the perpendicular direction. The effect of loading rate was also evident: the skull specimens were increasingly brittle as strain rate increased from quasi-static to high rate for both the loading directions. The elastic modulus increased by a factor of 4 in radial direction and it increased by a factor of 2.5 in the tangential direction across the quasi-static, intermediate and high strain rates. Significant differences were also found in ultimate strength and work to failure as loading rate increased from quasi-static to high rates. The results also suggested that the strength in the radial direction was mainly depended on the diploë porosity while the diploë layer ratio played the predominant role in tangential direction.

Segmentation and visualization of the human cranial bone by T2* approximation using ultra-short echo time (UTE) magnetic resonance imaging

Segmentation of the human cranial bone from MRI data is challenging, because compact bone is characterized by very short transverse relaxation times and typically produces no signal when using conventional magnetic resonance imaging (MRI) sequences. In this work, we propose a fully automated segmentation algorithm, which uses dual-echo, ultra-short echo-time (UTE) MRI data. The segmentation was initialized by interval thresholding of approximated T2* relaxation time maps in the range of 1ms<T2*<3ms. This parameter range was derived from a manual region-of-interest analysis of high resolution data of the cranial layers, resulting in average T2* relaxation times of 1.7±0.3ms in the lamina externa, 2.5±0.3ms in the diploe and 1.7±0.2ms in the lamina interna. Segmentations were performed based on data of 8 healthy volunteers that were acquired with different acquisition parameters and spatial resolutions to test the stability of the algorithm. Comparison with computed tomography data demonstrated close agreement with the segmented UTE MRI data. Visualization of the segmented cranial bone was performed by volumetric rendering and by using the approximated T2* values for color coding, clearly visualizing the cranial sutures as well as their intersections.

The mechanical response of commercially available bone simulants for quasi-static and dynamic loading

Bone is a complex hierarchal structured material with varying porosity and mechanical properties. In particular, human cranial bone is essentially a natural composite consisting of low porosity outer and inner tables and a cancellous interior, or diploë. Experimental studies of biomechanically accurate cranial bone analogues are of high importance for biomechanical, forensics, and clinical researchers, which could improve the understanding and prevention of traumatic injury. Many reported studies use commercially available bone surrogates to draw biomechanical and forensics conclusions; however, their mechanical properties are not tabulated over a range of strain rates. This study elucidates the mechanical viability of three leading commercially available bone surrogates, i.e. Synbone, Sawbone, and Bonesim, over a large range of strain rates (10−3 to 103 s−1). Quasi-static compression testing was conducted using a universal testing machine and a Split-Hopkinson Pressure bar system equipped with high-speed video was used to determine the dynamic mechanical behavior of these materials. Micro-computed X-ray tomography (XRT) were performed on each material to investigate their pore structures and distributions. All materials exhibited strain rate dependent strength behavior, particularly at high loading rates (≥103 s−1). The Young's modulus was found to increase with strain rate from 10−3 to 10−1 s−1 for transversely and longitudinally loaded surrogate materials except for Synbone and the higher density Bonesim. The higher density Bonesim was determined to be the most suitable cranial bone simulant tested based on a combination of transverse Young's Modulus (1500 MPa), yield strength (19 MPa), ultimate strength (49 MPa), and ultimate strain (17%). These materials show limited promise for applications where the measured elastic properties and strengths are of interest.

U-series dating and classification of the Apidima 2 hominin from Mani Peninsula, Southern Greece

Laser ablation U-series dating results on a human cranial bone fragment from Apidima, on the western cost of the Mani Peninsula, Southern Greece, indicate a minimum age of 160,000 years. The dated cranial fragment belongs to Apidima 2, which preserves the facial skeleton and a large part of the braincase, lacking the occipital bone. The morphology of the preserved regions of the cranium, and especially that of the facial skeleton, indicates that the fossil belongs to the Neanderthal clade. The dating of the fossil at a minimum age of 160,000 years shows that most of the Neanderthal traits were already present in the MIS 6 and perhaps earlier. This makes Apidima 2 the earliest known fossil with a clear Neanderthal facial morphology. Together with the nearby younger Neanderthal specimens from Lakonis and Kalamakia, the Apidima crania are of crucial importance for the evolution of Neanderthals in the area during the Middle to Late Pleistocene. It can be expected that systematic direct dating of the other human fossils from this area will elucidate our understanding of Neanderthal evolution and demise.

A method for whole protein isolation from human cranial bone

The presence of the dense hydroxyapatite matrix within human bone limits the applicability of conventional protocols for protein extraction. This has hindered the complete and accurate characterization of the human bone proteome thus far, leaving many bone-related disorders poorly understood. We sought to refine an existing method of protein extraction from mouse bone to extract whole proteins of varying molecular weights from human cranial bone. Whole protein was extracted from human cranial suture by mechanically processing samples using a method that limits protein degradation by minimizing heat introduction to proteins. The presence of whole protein was confirmed by western blotting. Mass spectrometry was used to sequence peptides and identify isolated proteins. The data have been deposited to the ProteomeXchange with identifier PXD003215. Extracted proteins were characterized as both intra- and extracellular and had molecular weights ranging from 9.4 to 629 kDa. High correlation scores among suture protein spectral counts support the reproducibility of the method. Ontology analytics revealed proteins of myriad functions including mediators of metabolic processes and cell organelles. These results demonstrate a reproducible method for isolation of whole protein from human cranial bone, representing a large range of molecular weights, origins and functions.

Arthur Smith Woodward and his involvement in the study of human evolution

Abstract In 1884, Arthur Smith Woodward first met Charles Dawson, a solicitor and industrious amateur collector, antiquarian, geologist, archaeologist and palaeontologist. This began a long association and friendship centred on their mutual interest in palaeontology and human evolution. Dawson devised a complicated plot focused around the ancient river gravel deposits at Barkham Manor near the village of Piltdown, Sussex. In these gravels he planted stone tools and fossil mammal remains together with the lower jaw of an ape and numerous modern human cranial bones to deceive the scientific establishment into believing an early human ancestor had been found in his own back yard. Cleverly devised to provide anatomists and archaeologists with evidence for concepts that they wanted to believe were true, Dawson fuelled numerous contentious debates among scientists that quickly attracted international attention. Nothing could be more unfortunate than such a respectable scientist as Arthur Smith Woodward being taken in by the events of 1912, and then subsequently swept along by them well into his retirement right up to the time of his death in 1944.

Investigating histomorphological variations in human cranial bones through ontogeny

Through ontogeny, human cranial vault bones undergo differentiation in terms of their shape, size and tissue maturation. This differentiation is visible at both the macroscopic and microscopic levels. Preliminary data from a histological and compartmentalisation exploratory analysis of individuals with different ages suggest differences in the modelling and remodelling patterns through ontogeny. Child vault bones are primarily composed of avascular lamellar bone (largely vascularised), late juvenile or adolescent bones present the largest extension of mineralised areas (highly remodelled) and the lowest vascularisation (diploe is highly reduced), and the adult present highly vascularised bone in which the diploe is again largely extended. During childhood, the existence of an avascular lamellar bone promotes the sealing of the cranium bones surfaces whereas adult vault bones seem to become opened ectocranially due to the remodelling. We discuss the possibility that both effects could be related with the head thermoregulation.

Mechanical characterization of bone anchors used with a bone-attached, parallel robot for skull surgery

Bone-attached robots and microstereotactic frames, intended for deep brain stimulation and minimally invasive cochlear implantation, typically attach to a patient’s skull via bone anchors. A rigid and reliable link between such devices and the skull is mandatory in order to fulfill the high accuracy demands of minimally invasive procedures while maintaining patient safety. In this paper, a method is presented to experimentally characterize the mechanical properties of the anchor–bone linkage. A custom-built universal testing machine is used to measure the pullout strength as well as the spring constants of bone anchors seated in four different bone substitutes as well as in human cranial bone. Furthermore, the angles at which forces act on the bone anchors are varied to simulate realistic conditions. Based on the experimental results, a substitute material that has mechanical properties similar to those of cranial bone is identified. The results further reveal that the pullout strength of the investigated anchor design is sufficient with respect to the proposed application. However, both the measured load capacity as well as the spring constants vary depending on the load angles. Based on these findings, an alternative bone anchor design is presented and experimentally validated. Furthermore, the results serve as a basis for stiffness simulation and optimization of bone-attached microstereotactic frames.