Atlas of Human Skeleton Hardness Obtained Using the Micro-indentation Technique.

OBJECTIVES: Measure and systematically evaluate the distribution of microhardness in the human skeleton. METHODS: Three fresh corpses were obtained, aged 62 (male), 45 (female), and 58 years (male). Soft tissues were removed, and all axial and unilateral appendicular bones were freshly harvested. All three skeletons were examined by X-ray and computed tomography (CT) to exclude skeletal pathology. Only bones from donors with no known skeletal pathology were included in the study. Axial and unilateral appendicular skeleton bones from each of the three donors were obtained, except for ear ossicles, hyoid bone, tailbone, and 14 phalanges of the foot, for which samples were difficult to obtain. Precision bone specimens with a thickness of 3 mm, which were cut with a Buehler IsoMet 11-1280-250 low-speed diamond saw (Buehler, USA), were obtained from all important anatomic sites in a direction perpendicular to the mechanical axis of each bone. Micro-indentation (the Vickers hardness test) was performed on the surface of each specimen using a microhardness tester with a diamond indenter. Hardness value (HV) was computed for each indentation. Each bone specimen was divided into several regions of interest. Indentations were carefully made and computed. Then we analyzed the data to identify hardness distribution rules at different anatomic sites. RESULTS: In total, 5360 indentations were made in 1072 regions of interest in each donor. Hardness of the axial and appendicular bones were all inhomogeneous depending on the anatomic sites, but the distribution of microhardness followed certain rules. The mean hardness value ranged from 24.46 HV (HV = hardness value, kgf/mm2 ) for the sacrum to 53.20 HV for the shaft of the tibia. The diaphysis was harder than the metaphysis, and the proximal and distal epiphysis had lower values (8.85%- 40.39%) than the diaphysis. Among the long bone diaphyses, the tibia cortical bone (51.20 HV) was the hardest, harder than the humerus (47.25 HV), the ulna (43.26 HV), the radius (42.54 HV), and the femur (47.53 HV). However, in some anatomic sites such as the lumbar vertebra (cortical bone 32.86 HV, cancellous bone 31.25 HV), the cortical shells were sometimes not harder than the internal cancellous bones. The lumbar vertebra (32.86 HV) was harder than the cervical vertebra (28.51 HV) and the thoracic vertebra (29.01 HV). CONCLUSIONS: The distribution of microhardness in the human skeleton follows certain rules. These distribution rules could be used to predict the mechanical properties of bone and progress in this field could provide data for the basis of a new three-dimensional printing technique, which may lead to new perspectives for custom-made implants.

Finite element analysis of spiral plate and Herbert screw fixation for treatment of midshaft clavicle fractures.

Both spiral plate and Herbert screw fixations have been clinically adopted for treating midshaft displaced clavicle fractures. However, the biomechanical properties of the 2 implant fixations have not yet been thoroughly evaluated. Here we report the results of a finite element analysis of the biomechanical properties of midshaft clavicle fractures treated with Herbert screw and spiral plate fixation. Hebert screw fixation showed stress distribution similar to intact clavicle under all loading conditions, but provided less stability than did spiral plate fixation. Postoperatively, excessive shoulder activities and weight-bearing should be avoided. Spiral plate fixation provides greater stability, but is associated with stress shielding. These results demonstrate that Herbert screw fixation is suitable for the treatment of simple displaced clavicluar fractures, but excessive shoulder activity and weight-bearing should be avoided after the operation. Therefore, spiral plate fixation may be preferred for patients requiring an early return to activity.

Microhardness distribution of the tibial diaphysis and test site selection for reference point indentation technique.

Indentation hardness test is a good in vitro method of bone quality assessment. The purpose of this study is to explore the distribution characteristics of bone tissue microhardness in tibial diaphysis and provide theoretical support for the test site selection of the reference point indentation technique.Three fresh right tibias were obtained from 3 cadaver donors. The tibial diaphysis was evenly divided into 6 sections. Bone specimens with a thickness of 3 mm were cut from each part. After appropriate management, micro-indentation tests were performed in various regions of the specimens to acquire the microhardness values of the tibial diaphysis. Statistical analysis was performed by randomized block design variance analysis to study the distribution characteristics of bone microhardness.72 regions were selected for 360 effective indentations. We found that the bone microhardness is inhomogeneous in tibia diaphysis. Mean hardness value of the anterior, medial, posterior, lateral region of tibia diaphysis was 45.58 ±â€Š4.39 Vickers hardness (HV), 52.33 ±â€Š3.93 HV, 54.00 ±â€Š4.21 HV, 52.89 ±â€Š4.44 HV, respectively. The anterior cortex exhibits lower microhardness value than the other regions (P < .001). Within the same region, microhardness varies significantly with positions in the tibial diaphysis. The variations in indentation hardness are bound to have a significant impact on the comparability of different reference point indentation (RPI) studies.The results of this study indicated the regional microhardness difference in the human tibia diaphysis. The microhardness of different planes in the same region is also inconsistent. Inhomogeneous distribution of indentation microhardness would have considerable influence in the test site selection of RPI technique. The data collected in our study would contribute to the design of highly precise 3D printing implants and bionic bones with gradient elastic modulus.

Bone Hardness of Different Anatomical Regions of Human Radius and its Impact on the Pullout Strength of Screws.

OBJECTIVE: To investigate the bone hardness of different anatomical regions of the human radius and its impact on the pullout strength of screws. METHODS: Fresh radius bones were obtained from three donated cadavers. They were divided into three parts: proximal metaphysis, shaft, and distal metaphysis. The proximal metaphysis contains the head, neck, and radial tuberosity. The distal metaphysis includes the palmaris radius and the styloid process. The shaft of the radius was divided into nine segments of equal length. The bone hardness of three radiuses, one from each cadaver, was measured by Vickers microindentation hardness tests, and the screw pullout strength was examined in the other three radiuses using a materials testing machine. The trend between radius hardness and pullout strength was analyzed by using an analysis of variance randomized block design. Pearson correlation analysis was performed to evaluate the linear correlation between the bone hardness and the pullout strength of the human radius. RESULTS: The mean hardness ranged from 33.30 HV (the head) to 43.82 HV (the diaphysis). The hardest part of the radius was the shaft, with a value of 42.54 ± 5.59 HV. The proximal metaphysis had a hardness value of 34.15 ± 6.48 HV, and the distal metaphysis hardness value was 35.24 ± 5.17 HV. The shaft was 23.5% harder than the proximal metaphysis and 20% harder than the distal metaphysis. The microhardness test demonstrated that the bone hardness value of the diaphysis was significantly higher than those of both the proximal and distal metaphysis of the radius (both P < 0.05). The mean pullout strength values ranged from 552 N (the distal metaphysis) to 2296 N (the diaphysis). The greatest pullout strength of the radius was observed for the shaft, with a pullout strength of 1727.96 ± 111.44 N. The pullout strength of the proximal metaphysis was 726.33 ± 236.39 N, and the pullout strength of the distal metaphysis was 590.67 ± 36.30 N. The pullout strength of the shaft was 138% greater than that of the proximal metaphysis and 190% greater than that of the distal metaphysis. The pullout strength was also higher in the diaphysis than at both ends of the radius (both P < 0.05). A positive correlation was found between bone hardness and pullout strength (R = 0.927, P < 0.001). CONCLUSIONS: Bone hardness and screw pullout strength are higher in the diaphysis of the radius than at either end. The pullout strength is positively related to bone hardness in the human radius.

Comparison of Proximal Femoral Geometry and Risk Factors between Femoral Neck Fractures and Femoral Intertrochanteric Fractures in an Elderly Chinese Population.

BACKGROUND: Few studies have investigated the differences in proximal femoral geometry and risk factors between patients with different types of hip fracture, especially in elderly Chinese. This study aimed to assess the differences in proximal femoral geometry parameters between patients with femoral neck fractures and patients with intertrochanteric fractures to provide guidance for individualized customized prosthesis and accurate reconstruction of proximal femurs in elderly Chinese patients. METHODS: We retrospectively studied the electronic medical records of 198 elderly patients over 65 years of age who were admitted to the orthopedic department with hip fractures between January 2017 and December 2017 in The Third Hospital, Hebei Medical University. Age, fracture site, gender, and proximal femoral geometry parameters (neck shaft angle [NSA], center edge angle [CEA], femoral head diameter [FHD], femoral neck diameter [FND], femoral neck axial length [FNAL], hip axial length [HAL], and femoral shaft diameter [FSD]) were recorded. Student's t-test was used to compare the continuous variables, Chi-square test was used to analyze categorical variables, and multiple logistic stepwise regression analysis was used to evaluate the influencing factors of hip fracture type. RESULTS: Statistically significant differences in NSA (137.63 ± 4.56° vs. 132.07 ± 4.17°, t = 1.598, P < 0.001), CEA (37.62 ± 6.77° vs. 43.11 ± 7.09°, t = 5.597, P < 0.001), FND (35.21 ± 3.25 mm vs. 34.09 ± 3.82 mm, t = 2.233, P = 0.027), and FNAL (99.30 ± 7.91 mm vs. 103.58 ± 8.39 mm, t = 3.715, P < 0.001) were found between the femoral neck fracture group and femoral intertrochanteric fracture group. FHD, FND, FSD, HAL, and FNAL were different between sexes (all P < 0.001). The greater NSA was the risk factor for femoral neck fractures (odds ratio [OR]: 0.70, P < 0.001), greater CEA and longer FNAL were risk factors for femoral intertrochanteric fractures (OR: 1.15, 1.17, all P < 0.001), and greater FND was a protective factor for femoral intertrochanteric fractures (OR: 0.74, P < 0.001). CONCLUSIONS: We demonstrate differences in geometric morphological parameters of the proximal femur in different hip fracture types, as well as an effect of sex. These differences should be considered in the selection of prostheses for fracture internal fixation and hip replacements. These data could help guide the design of individualized customized prostheses and improve the accurate reconstruction of the proximal femur for elderly Chinese hip fracture patients.