Jörg Böhme

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.

Clinical implementation of finite element models in pelvic ring surgery for prediction of implant behavior: A case report

BACKGROUND Osteosyntheses to stabilize pelvic-ring fractures were developed for younger patients, and are not universally indicated for elderly people. We present the results of parallel-arranged numerical simulations of fixation treatment that an elderly patient with a bagatelle-injured pelvic ring fracture received using a patient-specific finite element model. METHODS The clinical course of an osteosynthetic stabilized pelvic ring fracture, based on an actual case, was numerically simulated using a patient-specific finite element model. FINDINGS A previously validated finite element model of a human pelvis was customized with computed tomography data from a patient with a stabilized pelvic-ring fracture. Numerical simulation was used to analyze primary stability. The clinical process, represented by radiologic examinations, was compared with the results from the finite element simulation. Implant loosening as well as newly-occurring fractures were shown to coincide with regions with the highest stress levels. INTERPRETATION The results from the patient-specific finite element model closely resembled the actual clinical course especially in terms of the location of high strain concentration and subsequent implant loosening. This indicates that patient-specific finite element models have a potential to play an important role in planning osteosynthesis according to biomechanical stability.

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.

Finite element analysis of acetabular fractures—development and validation with a synthetic pelvis

Acetabular fracture presents a challenging situation to trauma surgeons today due to its complexity. Finite element (FE) models can be of great help as they can improve the surgical planning and post surgery patient management for those with acetabular fractures. We have developed a non-linear finite element model of the pelvis and validated its fracture prediction capability with synthetic polyurethane pelves. A mechanical experiment was performed with the synthetic bones and fracture loads and patterns were observed for two different loading cases. Fracture loads predicted by our FE model were within one standard deviation of the experimental fracture loads for both loading cases. The incipient fracture pattern predicted by the model also resembled the actual pattern from the experiment. Although it is not a complete validation with human cadaver bones, the good agreement between model predictions and experimental results indicate the validity of our approach in using non-linear FE formulation along with contact conditions in predicting bone fractures.

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.

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.

Einfluss der Standard-Computertomografie hinsichtlich Frakturklassifikation und Therapie von Beckenringfrakturen bei Patienten über dem 65. Lebensjahr

BACKGROUND The incidence of pelvic ring fractures in elderly patients increases continuously. Several studies showed that the complexity of injury is often underestimated and a fracture of the posterior pelvic ring not visible with conventional X-rays. The aim of this study was to determine the influence of routine CT on incidence, classification of and therapy for pelvic ring fractures in patients aged over 65 years. PATIENTS AND METHODS Between 2004 and 2010, 310 elderly patients with a pelvic ring fracture were admitted to a German university level 1 trauma centre. Patients of group 1 (2004-2006) were examined with CT only if a pelvic ring fracture was diagnosed by X-ray and pain in the posterior pelvic ring persisted so that mobilisation was impossible. In group 2 (2007-2010) CT was used for routine examination. Demographic data, injury mechanism and severity (ISS) were documented as well as time and type of diagnostic procedure. Also fracture classification (AO), time and type of treatment were investigated in correlation with total hospital stay. RESULTS 252 (82 %) patients were female, the median age was 81 years (65-100 years). 228 (74 %) had a low energy trauma, 41 (13 %) a traffic accident and 12 (4 %) had fallen from heights over 3 m. Only in 29 (9 %) cases was no trauma evident. 35 (11 %) patients were injured with an ISS over 16 and classified as polytrauma. The mean ISS was 26.8 ± 11.7. In group 2 the incidence of type A fractures decreased from 64 % to 36 %, whereas the incidence of type B fractures increased from 25 % to 49 % as did isolated sacrum fractures from 1 % to 6 %. Also the indication for operative stabilisation changed in type B fractures from 33 % to 40 % and in isolated sacrum fractures to 71 %. Total hospital stay was between eight and ten days in non-operative and between 20 and 22 days in operative treatment. CONCLUSION A low energy trauma is the major cause of injury for patients of an age over 65 years with a pelvic ring fracture. With the routine CT examination type B fractures and isolated sacrum fractures are seen more often than expected and resulting in a change of treatment procedures.

Emergency Treatment of Multiply Injured Patients with Unstable Disruption of the Posterior Pelvic Ring by Using the "C-Clamp"

AbstractPurpose:Evaluation of the therapeutic usefulness of the “pelvic C–clamp” (PCC) during emergency treatment of multiply injured patients with unstable disruption of the posterior pelvic ring.Patients and Methods:The data of 28 patients with polytrauma in combination with an unstable fracture of the posterior pelvic ring (average Injury Severity Score [ISS]: 49 points; average Polytrauma Score [PTS]: 41 points) were retrospectively analyzed from the moment they were admitted to the emergency room until 48 h after admittance. The PCC was used immediately for primary stabilization of the pelvis after clinical diagnosis of the unstable pelvic fracture. Main outcome measurements: development of mean blood pressure, development of oxygenation level, period of time until the PCC was placed, number of blood units needed, period of time until circulatory stabilization occurred.Results:The PCC was applied in all cases within an average of 64.7 min after trauma. Seven patients (25%) died within the first 45 min after admission. The surviving patients showed:• an increase in mean blood pressure of 25% 20 min after application of the PCC,• a hemodynamic stabilization 6 h after application of the PCC,• a stabilization of the oxygenation level 6 h after application of the PCC,• a decrease in the number of required blood units 6 h after application of the PCC.Conclusion:The present study shows, that the application of the PCC to critically injured patients with unstable pelvic fractures leads to stabilization of the vital parameters within a short period of time.

Outcome and 2-Year Survival Rate in Elderly Patients With Lateral Compression Fractures of the Pelvis:

Introduction: Osteoporotic pelvic ring fractures are a rising problem for surgeons in industrialized countries. There is no evidence-based treatment strategy especially for lateral compression (LC) fractures involving the sacrum. The aim of this study was to evaluate and compare outcome and survival rate of nonoperative and operative treatment strategies for lateral compression fractures. Patients and Methods: In a retrospective study, 128 patients (aged ≥65 years) with an Orthopedic Trauma Association (OTA) types B2.1 and B3.3 fracture were included and analyzed regarding demographic and treatment data and adverse events. After a follow-up period of at least 2-year survival rate, quality of life and pain were evaluated using the EuroQol-5D and Short Form–12 questionnaires and the visual analog scale. Results: Fifty patients (78.3 ± 7.6 years) obtained operative treatment and 77 patients (82.7 ± 7.9 years) obtained nonoperative treatment. One died within 24 hours after admission. High rates of complications occurred in both groups (operative group: 18% and nonoperative group: 8%). Eighteen percent (14 of the 77) of conservatively treated patients needed operative treatment after discharge due to worsening pain and mobilization. The 2-year follow-up showed a high overall mortality (30%), with a significant higher survival rate for operatively treated patients (2-year survival: operatively treated 82% vs conservative 61%). No difference was found in pain and quality of life. Discussion: Elderly patients display a high rate and variety of complications and mortality in the aftermath of lateral compression fractures of the pelvis. Although a significantly higher 2-year survival rate for operatively treated patients was found, this study cannot give proof of superior position for operative treatment. Due to lacking data for alternative treatment algorithms especially for fracture-related immobilized patients, we recommended operative treatment with the aim to reduce complications related to prolonged bed rest and ensure early mobilization.

Biomechanical analysis of stiffness and fracture displacement after using PMMA-augmented sacroiliac screw fixation for sacrum fractures

Abstract Cement augmentation of pedicle screws is the gold standard for the stabilization of osteoporotic fractures of the spine. In-screw cement augmentation, in which cement is injected through the cannula, is another option for fracture stabilization of fragility fractures of the sacrum. However, biomechanical superiority of this technique compared to conventional sacroiliac screw fixation has not been tested. The present study compares the stability of cement-augmented and non-cement-augmented sacroiliac screw fixation in osteoporotic sacrum fractures under cyclic loading. Eight human donor pelvises with intact ligaments and 5th lumbar vertebra were dissected. A vertical shear fracture was created as a combination of a sacrum fracture and cutting of the symphysis. Both sides were tested in a single-limb-stance setup with 10,000 loading cycles applied. Stiffness of the pelvis and displacement of the fracture were measured using a hydraulic testing machine and a 3D image correlation system. The augmented screw fixation failed in two of eight pelvises, and the non-augmented screws failed in three of eight pelvises. CT scans showed no leakage of cement. In-screw polymethylmethacrylate (PMMA) augmentation showed no advantage based on measured displacement of the sacrum fractures or stiffness for sacroiliac screw fixation of fragility fractures of the sacrum.