Non-Projective Two-Weight Codes.

It has been known since the 1970's that the difference of the non-zero weights of a projective Fq-linear two-weight code has to be a power of the characteristic of the underlying field. Here, we study non-projective two-weight codes and, e.g., show the same result under mild extra conditions. For small dimensions we give exhaustive enumerations of the feasible parameters in the binary case.

Bone regeneration in critical-size defects of the mandible using biomechanically adapted CAD/CAM hybrid scaffolds: An in vivo study in miniature pigs.

The study aimed to analyze bone regeneration in critical-size defects using hybrid scaffolds biomechanically adapted to the specific defect and adding the growth factor rhBMP-2. For this animal study, ten minipigs underwent bilateral defects in the corpus mandibulae and were subsequently treated with novel cylindrical hybrid scaffolds. These scaffolds were designed digitally to suit the biomechanical requirements of the mandibular defect, utilizing finite element analysis. The scaffolds comprised zirconium dioxide-tricalcium phosphate (ZrO2-TCP) support struts and TCP foam ceramics. One scaffold in each animal was loaded with rhBMP-2 (100 µg/cm³), while the other served as an unloaded negative control. Fluorescent dyes were administered every 2 weeks, and computed tomography (CT) scans were conducted every 4 weeks. Euthanasia was performed after 3 months, and samples were collected for examination using micro-CT and histological evaluation of both hard and soft tissue. Intravital CT examinations revealed minor changes in radiographic density from 4 to 12 weeks postoperatively. In the group treated with rhBMP-2, radiographic density shifted from 2513 ± 128 (mean ± SD) to 2606 ± 115 Hounsfield units (HU), while the group without rhBMP-2 showed a change from 2430 ± 131 to 2601 ± 67 HU. Prior to implantation, the radiological density of samples measured 1508 ± 30 mg HA/cm³, whereas post-mortem densities were 1346 ± 71 mg HA/cm³ in the rhBMP-2 group and 1282 ± 91 mg HA/cm³ in the control group (p = 0.045), as indicated by micro-CT measurements. The histological assessment demonstrated successful ossification in all specimens. The newly formed bone area proportion was significantly greater in the rhBMP-2 group (48 ± 10%) compared with the control group without rhBMP-2 (42 ± 9%, p = 0.03). The mean area proportion of remaining TCP foam was 23 ± 8% with rhBMP-2 and 24 ± 10% without rhBMP-2. Successful bone regeneration was accomplished by implanting hybrid scaffolds into critical-size mandibular defects. Loading these scaffolds with rhBMP-2 led to enhanced bone regeneration and a uniform distribution of new bone formation within the hybrid scaffolds. Further studies are required to determine the adaptability of hybrid scaffolds for larger and potentially segmental defects in the maxillofacial region.

Approach to standardized material characterization of the human lumbopelvic system-Specification, preparation and storage.

The complexity of the osseo-ligamentous lumbopelvic system has made it difficult to perform both, the overall preparation as well as specimen harvesting and material testing with a reasonable amount of time and personnel. The logistics of such studies present a hurdle for reproducibility. A structured procedure was developed and proved, which allows all necessary steps to be carried out reproducibly and in a reasonable time. This enables the extraction of 26 soft tissue, 33 trabecular and 32 cortical bone specimens from this anatomical region per cadaver. The integrity of the specimens remains maintained while keeping requirements within manageable limits. The practicability of the intended five-day specimen harvesting and testing procedure could be demonstrated on five test and two pre-test sequences. The intended minimization of physical, biological, and chemical external influences on specimens could be achieved. All protocols, instructions and models of preparation and storage devices are included in the supporting information. The high grade of applicability and reproducibility will lead to better comparability between different biomechanical investigations. This procedure proven on the human pelvis is transferable to other anatomical regions.

The sacrotuberous ligament is preloaded in situ.

The objective of this study was to evaluate the intrinsic preload of the sacrotuberous ligament. Preload measurements and anatomical experiments were performed on 20 specimens from 10 human cadavers and assessed to consider the thesis of the ligamentous tension band system as a possible load distribution. The result was an unexpectedly high preload force with an overall average of 118 N ± 74 N. Age has been significantly different between females and males in the cohort (median 94 vs. 77 years). Nevertheless, there is preliminary evidence of the sex-dependent sacrotuberous ligament preload force with an average value of approximately 65 N for the 10 female cadaver specimens and 172 N for the 10 male cadaver specimens. The assessment of further influencing factors and their statistical evaluation also showed a dependence of the sacrotuberous ligament preload force on body height, age and elastin content. Thus, the sacrotuberous ligament is more preloaded in the cadaver than previously assumed in the literature. Therefore, and contrary to most assumptions, it could possibly also be more preloaded in a living person in an upright position under a muscular load. This leads to the hypothesis that pelvic stability is more dependent on ligamentous preload than previously thought. These considerations should be taken more into account in numerical simulations of sacroiliac joint function.

Atraumatic femoral head necrosis: a biomechanical, histological and radiological examination compared to primary hip osteoarthritis.

INTRODUCTION: Atraumatic necrosis of the femoral head (AFHN) is a common disease with an incidence of 5000-7000 middle-aged adults in Germany. There is no uniform consensus in the literature regarding the configuration of the bone in AFHN. The clinical picture of our patients varies from very hard bone, especially in idiopathic findings, and rather soft bone in cortisone-induced necrosis. A better understanding of the underlying process could be decisive for establishing a morphology-dependent approach. The aim of this study is the closer examination of the condition of the bone in the AFHN compared to the primary hip osteo arthritis (PHOA). MATERIALS AND METHODS: The preparations were obtained as part of elective endoprosthetic treatment of the hip joint. Immediately after sample collection, thin-slice CT of the preserved femoral heads was performed to determine the exact density of the bone in the necrosis zone. Reconstruction was done in 0.8-1 mm layers in two directions, coronary and axial, starting from the femoral neck axis. Density of the femoral heads was determined by grey value analysis. The value in Hounsfield units per sample head was averaged from three individual measurements to minimize fluctuations. For biomechanical and histomorphological evaluation, the samples were extracted in the load bearing zone perpendicular to the surface of the femoral head. Group-dependent statistical evaluation was performed using single factor variance analysis (ANOVA). RESULTS: A total of 41 patients with a mean age of 64.44 years were included. The mean bone density of the AFHN samples, at 1.432 g/cm3, was about 7% higher than in the PHOA group with a mean value of 1.350 g/cm3 (p = 0.040). The biomechanical testing in the AFHN group showed a 22% higher-but not significant-mean compressive strength (20.397 MPa) than in the PHOA group (16.733 MPa). On the basis of histological analysis, no differentiation between AFHN and PHOA samples was possible. CONCLUSIONS: The present study (NCT, evidence level II) shows that AFHN has a very well detectable higher bone density compared to PHOA. However, neither biomechanical stress tests nor histomorphological evaluation did show any significant difference between the groups. The results allow the conclusion that there is no "soft" necrosis at all in the AFHN group.

Influence of the fixation technique on the mechanical properties of human cancellous bone of the femoral head.

BACKGROUND: The femoral head is of central importance for the force transmission from the suprapelvic body mass to the lower extremity. However, the condition of the subcortical bone and its mechanical properties in case of pathological changes due to coxarthrosis or femoral head necrosis differ from the healthy condition. METHODS: Fresh femoral heads were gathered during hip total endoprosthesis surgeries and cylindrical cancellous bone samples were extracted with a hollow drill. By means of a uniaxial tensile-compression test system, the compressive strength was determined for two different specimen types (fresh and 24 h storage in acetone). Exemplary tests on an exceptionally large femoral head were performed to compare properties of fresh, fresh-deep-frozen and acetone-stored samples. FINDINGS: The deformation behaviour and the material parameters determined were very heterogeneous. For most of the specimens, a destructive material test was successfully carried out, i.e. the compressive strength was determined. The average strength of fresh specimens was slightly higher than that of acetone specimens. On the other hand, the average Young's modulus of the acetone specimens was higher than that of the fresh specimens. INTERPRETATION: The lower Young's moodulus of the fresh samples compared to the acetone samples could indicate a causal effect of the degreasing influence of the acetone. The partly considerable individual differences in compressive strength and failure compression can have patient-specific influencing factors such as constitution and physical fitness as well as causes in the initial pathological condition.

The influence of different sample preparation on mechanical properties of human iliotibial tract.

In the run-up to biomechanical testing, fresh human tissue samples are often frozen in order to inhibit initial decomposition processes and to achieve a temporal independence of tissue acquisition from biomechanical testing. The aim of this study was to compare the mechanical properties of fresh tissue samples of the human iliotibial tract (IT) to fresh-frozen samples taken from the same IT and those modified with different concentrations of Dimethylsulfoxide (DMSO) prior to freezing. All samples were partial plastinated and destructive tensile tests were conducted with a uniaxial tensile test setup. A plastination technique already established in the laboratory was modified to improve the clamping behaviour of the samples. Material failure was caused by a gradual rupture of the load-bearing collagen fibre bundles. Contrary to our expectations, no significant difference was found between the tensile strength of fresh and fresh frozen specimens. The addition of 1 wt% DMSO did not increase the tensile strength compared to fresh-frozen samples; an addition of 10 wt% DMSO even resulted in a decrease. Based on our findings, the use of simple fresh-frozen specimens to determine the tensile strength is viable; however fresh specimens should be used to generate a complete property profile.

Three-dimensional reduction and finite element analysis improves the treatment of pelvic malunion reconstructive surgery: A case report.

RATIONALE: Pelvic malunion is a rare complication and is technically challenging to correct owing to the complex three-dimensional (3D) geometry of the pelvic girdle. Hence, precise preoperative planning is required to ensure appropriate correction. Reconstructive surgery is generally a 2- or 3-stage procedure, with transiliac osteotomy serving as an alternative to address limb length discrepancy. PATIENT CONCERNS: A 38-year-old female patient with a Mears type IV pelvic malunion with previous failed reconstructive surgery was admitted to our department due to progressive immobilization, increasing pain especially at the posterior pelvic arch and a leg length discrepancy. The leg discrepancy was approximately 4 cm and rotation of the right hip joint was associated with pain. DIAGNOSIS: Radiography and computer tomography (CT) revealed a hypertrophic malunion at the site of the previous posterior osteotomy (Mears type IV) involving the anterior and middle column, according to the 3-column concept, as well as malunion of the left anterior arch (Mears type IV). INTERVENTIONS: The surgery was planned virtually via 3D reconstruction, using the patient's CT, and subsequently performed via transiliac osteotomy and symphysiotomy. Finite element method (FEM) was used to plan the osteotomy and osteosynthesis as to include an estimation of the risk of implant failure. OUTCOMES: There was not incidence of neurological injury or infection, and the remaining leg length discrepancy was ≤ 2 cm. The patient recovered independent, pain free, mobility. Virtual 3D planning provided a more precise measurement of correction parameters than radiographic-based measurements. FEM analysis identified the highest risk for implant failure at the symphyseal plate osteosynthesis and the parasymphyseal screws. No implant failure was observed. LESSONS: Transiliac osteotomy, with additional osteotomy or symphysiotomy, was a suitable surgical procedure for the correction of pelvic malunion and provided adequate correction of leg length discrepancy. Virtual 3D planning enabled precise determination of correction parameters, with FEM analysis providing an appropriate method to predict areas of implant failure.