Niels Hammer

Deformation behavior of the iliotibial tract under different states of fixation

BACKGROUND AND OBJECTIVE The iliotibial tract (tract) is an important structure for the biomechanics of both the hip and knee joint. While a detailed characterization of its mechanical properties might help to better understand its specific role in the load transfer from the pelvis to femur and tibia, determination of those properties is complicated by its particular structure of thin fibers in the fresh state. Moreover, although the tracts mechanical properties are often derived from cadaveric material chemically fixed with either ethanol or formaldehyde, the influence of such fixation methods remains to be elucidated. Aim of this study was to determine Youngs modulus (tensile modulus, YM) of the tract. We hypothesized that either ethanol or formaldehyde fixation would significantly increase the YM compared to the tracts condition in a fresh state. MATERIAL AND METHODS 13 specimens of tract were gained from donators. The ends of the probes were plastinated with resin creating a sharp interface between the clamp and the probe to prevent material slippage. The specimens were measured in their fresh state, under ethanol- and formaldehyde-fixed conditions and re-measured after rinsing with tap water. RESULTS The YM of the fresh probes averaged 397.3N/mm(2) with a standard deviation (SD) of 151.5N/mm(2). The YM of the ethanol-fixed specimens was significantly higher (673.2N/mm(2), SD 328.5N/mm(2), p<0.05). After rinsing with tap water, the YM decreased to 95% of the fresh condition value (377.4N/mm(2), SD 144.5N/mm(2), non-significant change from fresh). After formaldehyde fixation, the YM reached 490.3N/mm(2) (SD 143.0N/mm(2), p<0.05). When the formaldehyde-fixed specimens were rinsed, the YM was 114% of the value of the fresh condition (452.6N/mm(2), SD 115.1N/mm(2), non-significant change from fresh). CONCLUSIONS This study found a significant influence of the chemical fixation method on the YM of the IT tract. If such fixation is required, our results suggest using a treatment with ethanol and subsequent rinsing that results in minimal changes to the tracts YM. Furthermore, plastination of the ends of the specimens could be crucial to allow in vitro determination of valid YM of ligaments data that can then be integrated with confidence in further finite element analyses.

Ultimate stress and age-dependent deformation characteristics of the iliotibial tract.

BACKGROUND AND AIMS To understand biomechanics of ligaments and tendons data on their material properties are necessary. The iliotibial tract is a suitable model for virtual pelvic or lower extremity ligaments due to its parallel fibers, which facilitates biomechanical testing. Here, we determined Youngs modulus (YM) as secant stiffness between defined limits of the iliotibial tract and correlated the data to ultimate stress (US) of the specimens and to age, gender and body weight of the body donors. MATERIALS AND METHODS Thirty eight specimens from 12 iliotibial tracts of 10 young donors (mean age 31.2±9.1 years) were investigated biomechanically. After preconditioning, YM were determined in the ranges of 0-4 and 4-11 N/mm² of applied stress and from 4N/mm² of applied stress to US. RESULTS YM of the specimens were 84.7±30.2 (0-4 N/mm²), 335.4±101.9 (4-11 N/mm²), and 369.1±191.5 (4 N/mm² to US) N/mm², respectively. The mean US was 35.8±16.4 N/mm². YM and US correlated closely in the ranges of 4-11 N/mm² (r=0.95) and 4 N/mm² to US (r=0.91). YM did not correlate to age, body weight or gender within these young donors. Concerning tissue behavior a decrease of YM, i.e. weakening, is more common than an increase of YM, i.e. stiffening, before specimen failure. Overall, YM of specimens from young donors were significantly lower compared to those of old donors. DISCUSSION AND CONCLUSIONS This is the first study providing age-dependent nonlinear stiffness properties of the iliotibial tract. YM is significantly lower in young than in old donors and is thus a subject of alteration during life time.

Ethanol-glycerin fixation with thymol conservation: A potential alternative to formaldehyde and phenol embalming

Anatomical fixation and conservation are required to prevent specimens from undergoing autolysis and decomposition. While fixation is the primary arrest of the structures responsible for autolysis and decomposition, conservation preserves the state of fixation. Although commonly used, formaldehyde has been classified as carcinogenic to humans. For this reason, an adequate substitute was developed. Ethanol‐glycerin fixation and thymol conservation are described and compared with formaldehyde and phenol in this technical report. The setup, tissue qualities, financial aspects, and health concerns of this method are discussed. Ethanol‐glycerin fixation and thymol conservation provide outstanding haptic and optic tissue qualities. Typical formaldehyde and phenol effects, such as skin, airway, and eye irritation, as well as carcinogenic effects, can be circumvented by using ethanol‐glycerin and thymol instead. Ethanol‐glycerin fixation is more expensive than formaldehyde and requires an explosion‐proof facility. However, the absence of health effects and its convincing tissue qualities balance these higher costs. Therefore, ethanol‐glycerin fixation and thymol conservation provide a potential alternative and complement established fixation techniques. The use of carcinogenic formaldehyde and toxic phenol can be effectively restricted through the use of the described method. Anat Sci Educ.

Comparison of modified Thiel embalming and ethanol-glycerin fixation in an anatomy environment: Potentials and limitations of two complementary techniques.

Thiel‐fixed specimens have outstandingly lifelike visual and haptic properties. However, the original Thiel method is expensive and requires an elaborate setup. It is therefore of principal interest to modify the Thiel method in order to make it available to a broader user group. A modified Thiel embalming method will be described in detail and compared to ethanol‐glycerin fixation with the help of illustrative examples. The visual properties, haptic properties, the usability for performing histological investigations, costs and potential health aspects will be considered. Tissues fixed with the modified Thiel technique gave results similar to the original method, providing more realistic visual and haptic properties than ethanol‐glycerin embalming. However, Thiel fixation is significantly more expensive and requires more precautions to minimize potential health hazards than ethanol‐glycerin‐fixed tissues. In contrast to ethanol‐glycerin‐fixed specimens, the Thiel‐fixed specimens are not suitable for histological investigations. Both modes of fixation are inappropriate for biomechanical testing. Modified Thiel embalming simplifies the availability of body donors with lifelike properties and has cost‐saving advantages to the original technique. Thiel‐embalmed body donors are ideally suited for clinical workshops but have restrictions for student dissection courses in facilities with limited storage space, air circulation or technical staff. Vice versa, ethanol‐glycerin‐fixed body donors are well suited for student dissection courses in such an environment but are limited in their use for clinical workshops. Modified Thiel embalming therefore ideally complements ethanol‐glycerin fixation in order to provide customized solutions for clinical workshops and student dissection courses in a wide range of applications. Anat Sci Educ 8: 74–85.

Novel insights into the sacroiliac joint ligaments.

Study Design. The ligaments of the human sacroiliac joint (SIJ) were investigated morphometrically. Objective. A macroscopical study was performed to measure the anterior sacroiliac ligament (ASL), the interosseous sacroiliac ligament (ISL), and the posterior sacroiliac ligament (PSL), applying different methods of ligament visualization. Summary of Background Data. Little is known about the SIJ ligaments, especially about the ISL. Pelvic computer simulations neglect these ligaments due to the lack of information. Computer simulations of the SIJ ligaments may help to improve the clinical outcome of SIJ operations. Methods. Seven-Tesla MR images, CT images, and corresponding thin slice plastinates of the SIJ of 1 male and 1 female specimen were obtained. Serial sections of the SIJ of 32 frozen specimens (13 males, 19 females) were generated to gather measurements of the SIJ ligaments. Results. By means of the MR images and the plastinates, a virtual reconstruction of the SIJ ligaments was accomplished. Parallelepipeds were attributed to the cranial, middle, and caudal parts of all SIJ ligaments. This allowed precise measurements and statistical comparison including positional relationships. The ISL volumes and origin surfaces were the largest. Statistically, the ASL and PSL parameters were larger in males, while the ISL parameters were larger in females. The height of the cranial ASL part showed large negative correlations in spite of positive correlations of the other heights. Conclusion. The combined use of high-resolution MRI and thin slice plastination allows precise reconstructions of the SIJ ligaments. With these techniques, the ligaments can be visualized in situ and described morphometrically if based on substantive data. The SIJ ligaments are gender-dependent. This has to be taken into account for pelvic computer simulations.

The sacrotuberous and the sacrospinous ligament--a virtual reconstruction.

Little is known about the morphometric properties of the sacrotuberous ligament (ST) and the sacrospinous ligament (SS). The influence of ligaments on pelvic stability and the extent of reconstruction in case of instability are controversially discussed. The ST and the SS of 55 human subjects fixed in alcohol solution and of four fresh cadavers were measured. Both ligaments were defined as geometric figures. The ST was a contorted bifrustum, while the SS was a contorted frustum, both with elliptic planes. In all cases investigated, the ST and the SS fibres were twisted. For men, the ST and the SS had a mean length of 64 and 38 mm. For women, lengths of 70 and 46 mm were measured in the ST and the SS. The ST length, height and cross-sectional area showed gender-specific differences at statistically significant level. The ST and the SS volumes correlated closely, regardless of gender or side. Measurements of fresh ligaments of four unfixed cadavers showed similar results. The data obtained were then used to generate computer-based three-dimensional models of both ligaments, using the Catia software. Conclusively, the virtually generated ST and SS are suitable models to be included in pelvic fracture simulation, using the finite element method.

Substitution of Formaldehyde in Cross Anatomy Is Possible

The recent publication by Hauptmann et al. (1) in the Journal provided clear evidence for increased mortality from cancer induced by exposure to formalin, as outlined by The Final Report on Carcinogens Background Document for Formaldehyde of the National Toxicology Program (2). Hauptmanns data, along with a report by Figure 1. A–C) Examples of ethanol-and glycerin-fixed human tissue specimens are shown. A) The Erbs punctum nervo-sum (asterisk) is depicted in the lateral view of a dissected neck. Note the vivid color of the underlying sternocleidomas-toid muscle (M). C = clavicula, D = deltoid muscle, G = great auricular nerve, Pg = parotid gland, S = supraclavicular nerves, T = transverse cervical nerve. Specimen was fixed for 12 months before picture was taken. B) The opened left ventricle shows the aortic valve (V), the papillary muscles (P), and the ostia to the left coronary artery (Ol) and to the right coronary artery (Or). A = aorta, Ct = chordae ten-dineae, L = left ventricular myocardium, Tc = trabeculae carneae. Specimen was fixed for 15 months before picture was taken. C) The situs thoracis with peri-cardium (Pc), lungs (Ld = Lobus dexter, Ls = Lobus sinister), and phrenic nerve (Pn). Note the preservation of the neuro-vascular bundle of the ventral medias-tinum (Pv = pericardiacophrenic vessels). A = aorta, Iv = internal thoracic vessels, Vs = superior vena cava, Tp = truncus pulmonalis. The specimen was fixed for 12 months before picture was taken. Viegas et al. (3) demonstrating that medical students are exposed to formalin concentrations greater than 5 ppm during macro-scopic examinations, have caused medical institutions to reconsider the use of for-malin to fix and preserve cadavers and tissues. The emerging data indicating the toxicity of formalin have resulted in the closure of German dissecting rooms in medical schools and could potentially result in poor gross anatomy training and strongly affect the quality of medical staff education. A recent complaint by surgeons that a lack of knowledge in anatomy is already prevalent among young doctors (4) indicates that the development of new nontoxic fixatives are necessary to allow medical students to adequately study gross anatomy in a safe environment. To address this problem, the Institute of Anatomy at Universität Leipzig has developed an approach to conserve human cadavers for dissection courses with the use of a fixative consisting mainly of eth-anol and glycerin. This room temperature 1.5% glycerin solution is perfused …

Do Cells Contribute to Tendon and Ligament Biomechanics

Introduction Acellular scaffolds are increasingly used for the surgical repair of tendon injury and ligament tears. Despite this increased use, very little data exist directly comparing acellular scaffolds and their native counterparts. Such a comparison would help establish the effectiveness of the acellularization procedure of human tissues. Furthermore, such a comparison would help estimate the influence of cells in ligament and tendon stability and give insight into the effects of acellularization on collagen. Material and Methods Eighteen human iliotibial tract samples were obtained from nine body donors. Nine samples were acellularized with sodium dodecyl sulphate (SDS), while nine counterparts from the same donors remained in the native condition. The ends of all samples were plastinated to minimize material slippage. Their water content was adjusted to 69%, using the osmotic stress technique to exclude water content-related alterations of the mechanical properties. Uniaxial tensile testing was performed to obtain the elastic modulus, ultimate stress and maximum strain. The effectiveness of the acellularization procedure was histologically verified by means of a DNA assay. Results The histology samples showed a complete removal of the cells, an extensive, yet incomplete removal of the DNA content and alterations to the extracellular collagen. Tensile properties of the tract samples such as elastic modulus and ultimate stress were unaffected by acellularization with the exception of maximum strain. Discussion The data indicate that cells influence the mechanical properties of ligaments and tendons in vitro to a negligible extent. Moreover, acellularization with SDS alters material properties to a minor extent, indicating that this method provides a biomechanical match in ligament and tendon reconstruction. However, the given protocol insufficiently removes DNA. This may increase the potential for transplant rejection when acellular tract scaffolds are used in soft tissue repair. Further research will help optimize the SDS-protocol for clinical application.

Description of the iliolumbar ligament for computer-assisted reconstruction.

STUDY DESIGN The iliolumbar ligament (IL) was examined using morphometric and virtual methods. OBJECTIVES A macroscopic study was performed to measure the anterior (AIL) and the posterior part of the IL (PIL). SUMMARY OF BACKGROUND DATA Though being a widely accepted cause of low back pain and lumbosacral instability, the IL is neglected in computer-based biomechanical studies due to the lack of morphometric information. METHODS Frozen sections prepared from 29 human subjects were measured and 7-tesla MR images made to distinguish the AIL and PIL. Cuboids were designated as geometric figures to both parts of the ligament, allowing computer-based calculations of length, surface, volume and angle of positional relationships. RESULTS Based on 7-tesla MR imaging, virtual reconstruction was conducted for one male pelvis, including the IL. While left- and right-side parameters varied at a statistically significant level, no gender-dependencies could be determined. Lengths of 30 and 25 mm were measured for the AIL and PIL, as well as heights of 17-19 mm, respectively, and a thickness of 4mm. CONCLUSIONS Correlations between the side-dependent parameters and the AIL and the PIL of the same side indicate close functional relationships. Additional dependencies suggest that the IL is capable of compensating age-related as well as bone-attributed alterations in lumbosacral morphology. The IL data and the visualised ligament structures contribute to determination of the influence of the IL in spinal and sacroiliac stability by means of computer-assisted biomechanics.

Human Vagus Nerve Branching in the Cervical Region

Background Vagus nerve stimulation is increasingly applied to treat epilepsy, psychiatric conditions and potentially chronic heart failure. After implanting vagus nerve electrodes to the cervical vagus nerve, side effects such as voice alterations and dyspnea or missing therapeutic effects are observed at different frequencies. Cervical vagus nerve branching might partly be responsible for these effects. However, vagus nerve branching has not yet been described in the context of vagus nerve stimulation. Materials and Methods Branching of the cervical vagus nerve was investigated macroscopically in 35 body donors (66 cervical sides) in the carotid sheath. After X-ray imaging for determining the vertebral levels of cervical vagus nerve branching, samples were removed to confirm histologically the nerve and to calculate cervical vagus nerve diameters and cross-sections. Results Cervical vagus nerve branching was observed in 29% of all cases (26% unilaterally, 3% bilaterally) and proven histologically in all cases. Right-sided branching (22%) was more common than left-sided branching (12%) and occurred on the level of the fourth and fifth vertebra on the left and on the level of the second to fifth vertebra on the right side. Vagus nerves without branching were significantly larger than vagus nerves with branches, concerning their diameters (4.79 mm vs. 3.78 mm) and cross-sections (7.24 mm2 vs. 5.28 mm2). Discussion Cervical vagus nerve branching is considerably more frequent than described previously. The side-dependent differences of vagus nerve branching may be linked to the asymmetric effects of the vagus nerve. Cervical vagus nerve branching should be taken into account when identifying main trunk of the vagus nerve for implanting electrodes to minimize potential side effects or lacking therapeutic benefits of vagus nerve stimulation.