Showing papers by "Georg N. Duda published in 2005"

Angle stable locking reduces interfragmentary movements and promotes healing after unreamed nailing. Study of a displaced osteotomy model in sheep tibiae.

Abstract: BACKGROUND: Large interfragmentary movements may delay bone-healing. The hypothesis of the present study was that a reduction of interfragmentary movements, especially of torsional rotation and bending angles, would support the healing process and lead to improved healing following unreamed tibial nailing. The objective of this study was to investigate healing of an unstable tibial osteotomy site following stabilization with unreamed nailing with a modified tibial device that had angle stable holes for the locking bolts. We compared those findings with healing after stabilization of such sites with standard unreamed tibial nailing. The duration of the study period was nine weeks. METHODS: The site of a standardized displaced osteotomy (3-mm gap) in twelve ovine tibiae was stabilized with unreamed tibial nailing: six animals were treated with a modified nail that had angle stable holes for the locking bolts, and six were treated with standard unreamed tibial nailing. In vivo gait analysis with optical measurements of interfragmentary movements and simultaneous measurements of ground reaction parameters were performed three days after the operation and once weekly afterward. After the animals were killed at nine weeks, the treated and contralateral tibiae were explanted, the implants were removed, and radiographs were made and evaluated for bridged cortices. Each pair of tibiae was also mechanically tested until torsional failure, after which the whole callus region was subjected to histological and histomorphometric analysis. RESULTS: Throughout the examination period, the interfragmentary movements in all directions were significantly smaller in the group treated with the angle stable tibial nail than they were in the group treated with standard unreamed tibial nailing. The limbs treated with the angle stable tibial nails returned to almost full weight-bearing during the period of the investigation, whereas those treated with standard nailing did not. Histomorphometric analysis, radiographic data, and mechanical testing showed superior bone-healing following treatment with the angle stable tibial nail. CONCLUSIONS: Use of an angle stable tibial nail may help to reduce interfragmentary movements in vivo and thus lead to superior bone-healing compared with that following standard unreamed tibial nailing.

The morphology and biomechanical characteristics of subcutaneously implanted tissue-engineered human septal cartilage

Abstract: The purpose of the study was to examine the morphology and biomechanical characteristics of in vivo cultured tissue-engineered human septal cartilage as a prospective autogenous transplant material for subcutaneous implantation in reconstructive procedures. Chondrocytes were enzymatically isolated from human septal cartilage biopsies. The cell number was expanded in monolayer culture. Chondrocytes were then fixed on a non-woven poly-lactide-poly-glycolide (PGLA) polymer scaffold by means of fibrin glue. The PGLA-polymer construct was implanted subcutaneously on the back of athymic mice and allowed to mature for 6 or 12 weeks. After killing the mice, the formed cartilage was tested on a material testing machine with a highly standardized reproducible setting. Biomechanical testing consisted of an indentation test, which revealed the failure load and compressive modulus of the neocartilage. The failure load shows the upper limit of supported stress. The compressive modulus is a measure of the templates' stiffness. After testing, the templates were histologically stained. Native human septal cartilage served as a control group. Histological and macroscopic examination showed cartilage formation of a hyaline-like morphology. Histological staining revealed the synthesis of abundant mucopolysaccharid matrix. The biomechanical characteristics of neocartilage proved to be of no statistical difference compared to native human septal cartilage. The failure load and compressive modulus were initially somewhat lower and reached the control group's results after 12 weeks in-vivo. Summarizing, tissue engineered nasal cartilage matches typical mechanical characteristics of native hyaline cartilage. Its elasticity and failure load are of sufficient quality to meet the clinical requirements for reconstructive surgery.

Stress shielding in box and cylinder cervical interbody fusion cage designs.

Abstract: Study Design. A numerical analysis of stress shielding of the bone graft in box and cylinder interbody fusion cages was performed. Objectives. To evaluate the stress shielding characteristics of box and cylinder interbody fusion cages for the cervical spine with regard to their rigidity and contiguous pore size. Summary of Background Data. Cage design has been shown to influence loading of the augmented bone graft tissue. In addition, a large contiguous pore design is believed to be important to avoid stress shielding effects. Methods. A two-dimensional axisymmetric, biphasic finite-element model of the cage incorporating the bone graft and the adjacent vertebral bodies was developed. Analysis was performed in two parts. First, the vertebrae were loaded by an axial compressive force, and second, the effect of vertebral penetration by the interbody cage was simulated. Results. Straining of bone graft in the box cage was generally lower than that of the cylinder cage. The strains in the cylinder cage were seen to be more uniformly distributed, whereas in the box cage straining was concentrated in the graft under the endplates. Vertebral penetration by the cylinder cage resulted in significant straining of the bone graft (28% strain), whereas lower strains were determined in the box cage (a maximum of 17% strain). Conclusions. The central pore in the box design does not seem as effective as the fully open cylinder cage in transferring loads to the augmented graft tissue. Early penetration of the adjacent vertebrae by the cylinder cage may provide early postoperative stability and load the graft tissue, thereby imparting the necessary signals for fusion.

Surgical approach influences periprosthetic femoral bone density

Abstract: Our hypothesis was that the bone mineral density of the proximal femur is altered significantly by surgical approach. The change in long-term periprosthetic bone mineral density in relation to the alteration of the musculature after the anterolateral (Group A) and transgluteal approaches (Group B) has been compared. There were 35 hips (30 patients) in Group A and 47 hips (37 patients) in Group B. No significant differences were seen between groups with respect to age, gender, diaphyseal bone mineral density distribution, or average stem size in a Wilcoxon-Mann-Whitney test. Measurement of bone mineral density in femoral Gruen zones revealed a significant bone loss in Group B compared with Group A in the multivariate analysis, which was confirmed by univariate post hoc tests in Zones I, II, VI, and VII (multiple significance according to Bonferroni-Holm's procedure). The functional outcome, however, showed no significant differences between the two groups postoperatively. A potential reason for the bone mineral density shift might have been a redistribution of the musculoskeletal loading across the hip after a transgluteal, compared with an anterolateral, surgical approach. A difference in the muscular damage caused by the two surgical approaches seems to have a significant influence on the long-term bone loss.

Cementless stem fixation and primary stability under physiological-like loads in vitro.

Abstract: Primary stability and in consequence osteointegration are commonly related to the stem anchorage but also to the complex musculoskeletal loading of the hip region. This study investigated the influence of metaphyseal and meta-diaphyseal anchorage on the primary stability of cementless stems under physiological-like loading in vitro. Metaphyseal and meta-diaphyseal anchoring stems (n=6 each) were implanted into composite femora. Musculoskeletal loads, validated by in vivo data (peak joint force 2348 N), were applied using a mechanical set-up. Interface movements were recorded by seven displacement transducers and primary stability was compared. Both stems exhibited similar movement patterns and principally moved distally with a retroversional twist. Although elastic movements were comparable, the metaphyseal stem exhibited higher plastic deformations than the meta-diaphyseal stem, particularly for the metaphyseal, medio-lateral and antero-posterior components. Under physiological-like loading, the metaphyseal stem allowed higher interface movements and tended to initially migrate faster than the meta-diaphyseal stem and then stabilized. Elastic movements were comparable and seemed to be less influenced by the anchoring concept than by the mechanical properties of the bone. The analyses emphasize the importance of metaphyseal bone in proximal anchorage and the necessity of an accurate canal preparation to prevent excessive initial migration.

Component and method for assembling an implant arrangement

Abstract: The invention refers to a component for arrangement at an implant as well as a method for the assembling of an implant arrangement. The component comprises a basic component, at least one sensor arranged in the basic component for the detection of a measurement variable and for the generation of measuring data for the detected measurement variable, a telemetry device arranged in the basic component for transmitting and receiving data and a data transmission connection between the at least one sensor device and the telemetry device for the transmission of data between the at least one sensor device and the telemetry device, whereby the data comprise the measuring data. At the basic component, assembly means for mounting the basic component in an implant recess are formed.

Poly(D,L‐lactide) coating is capable of enhancing osseous integration of Schanz screws in the absence of infection

Abstract: Pin loosening is a major complication in external fixation. Biological and mechanical conditions play an important role in the maintenance and enhancement of the implant-bone interface in fracture fixation. It is thought that biodegradable coatings may be capable of preventing pin track infection and pin loosening. The goal of this study was therefore to analyze the influence of a biodegradeable coating on the osseous integration of Schanz' screws during fracture treatment. Standardized osteotomies (3-mm fracture gap) of the right tibiae were performed on 16 sheep and stabilized by an AO mono-lateral external fixator. Additional, mechanically less loaded Schanz' screws were also mounted. All screws were randomly coated with biodegradable poly(D,L-lactide). The sheep were sacrificed after 9 weeks. All screws were removed and rolled on blood agar plates for microbiological analysis. Histological sections of the pin tracks were histochemically and morphometrically analyzed. Clinically, no signs of severe infection were visible. Microbiological analysis revealed 14.8% colonization by Staphylococcus aureus in the coated and 29% in the uncoated screws. Histomorphometry of the bone surrounding the Schanz' screws revealed that significantly more osseous integration had occurred on poly(D,L-lactide)-coated screws in the absence of bacterial colonization. Significantly more bone remodeling and a higher osteoclastic activity was seen near the screw-bone interface in the uncoated screw group. Up to a threefold increase in new bone formation and more severe remodeling was observed around the screw entry compared to the pin exit in all groups. Loaded screws showed significantly more callus formation around the exit sites than their less loaded counterparts. In the present study, poly(D,L-lactide) coating of Schanz' screws was found to enhance osseous integration in the absence of bacterial colonization in sheep by causing less cortical remodeling and less osteoclastic activity in the cortices compared to uncoated screws. Additionally, the coating appeared to reduce the instances of pin track infections. Mechanical loading showed an adverse effect on bone formation and remodeling. It has been shown that both biological and mechanical factors play an important role in the maintenance of osseous integrity of the pin-bone interface. Poly(D,L-lactide) coating of Schanz' screws does not prevent osseous destruction and severe bacterial colonization along the pin tracts, but can improve osseous integration of Schanz' screws in the absence of infection.

Angle Stable Locking Reduces Interfragmentary Movements and Promotes Healing After Unreamed Nailing: A Study of a Displaced Osteotomy Model in Sheep Tibiae

Abstract: BACKGROUND: Large interfragmentary movements may delay bone-healing. The hypothesis of the present study was that a reduction of interfragmentary movements, especially of torsional rotation and bending angles, would support the healing process and lead to improved healing following unreamed tibial nailing. The objective of this study was to investigate healing of an unstable tibial osteotomy site following stabilization with unreamed nailing with a modified tibial device that had angle stable holes for the locking bolts. We compared those findings with healing after stabilization of such sites with standard unreamed tibial nailing. The duration of the study period was nine weeks. METHODS: The site of a standardized displaced osteotomy (3-mm gap) in twelve ovine tibiae was stabilized with unreamed tibial nailing: six animals were treated with a modified nail that had angle stable holes for the locking bolts, and six were treated with standard unreamed tibial nailing. In vivo gait analysis with optical measurements of interfragmentary movements and simultaneous measurements of ground reaction parameters were performed three days after the operation and once weekly afterward. After the animals were killed at nine weeks, the treated and contralateral tibiae were explanted, the implants were removed, and radiographs were made and evaluated for bridged cortices. Each pair of tibiae was also mechanically tested until torsional failure, after which the whole callus region was subjected to histological and histomorphometric analysis. RESULTS: Throughout the examination period, the interfragmentary movements in all directions were significantly smaller in the group treated with the angle stable tibial nail than they were in the group treated with standard unreamed tibial nailing. The limbs treated with the angle stable tibial nails returned to almost full weight-bearing during the period of the investigation, whereas those treated with standard nailing did not. Histomorphometric analysis, radiographic data, and mechanical testing showed superior bone-healing following treatment with the angle stable tibial nail. CONCLUSIONS: Use of an angle stable tibial nail may help to reduce interfragmentary movements in vivo and thus lead to superior bone-healing compared with that following standard unreamed tibial nailing.

Muskuloskeletale belastungen im schafshinterlauf: mechanische rahmenbedingungen der heilung

Abstract: Although the sheep is a standard model for the analysis of biological healing processes after surgical intervention at the knee and shank, the in vivo tibio-femoral joint contact forces and the resulting musculoskeletal loading conditions have yet to be studied in detail.The three-dimensional kinematics of three Merino-mix sheep right hind limbs were recorded using reflective markers that were attached to Schanz’ screws, firmly anchored in the bone. This motion data was used together with the simultaneously measured external loading (ground reaction forces) to calculate the muscle and joint contact forces, as well as the internal loads within the bones. Whilst the motion mainly occurred in the sagittal plane, significant out of plane motion was observed, especially at the hip and knee joint (ab/adduction hip: 13°, knee: 10°; internal/external rotation hip: 12°, knee: 14°). The axial component of the tibio-femoral contact force was 2.1 times body weight (BW). The medio-lateral and anterior-posterior shear forces amounted to only 0.7 times BW. The loading in the diaphysis of the tibia under physiological musculoskeletal conditions was mainly axial compression (0.89 BW) together with only small shear forces (0.15 BW). The results of the musculoskeletal analyses presented here add to the understanding of the mechanical loading conditions in sheep. This expanded knowledge aids in the interpretation

Musculoskeletal loading database: loading conditions of the proximal femur

Abstract: Knowledge of musculoskeletal loading conditions in humans is mandatory for the design of endoprosthestic and osteosynthetic devices. Also, new treatment options such as tissue generation and transplantation require knowledge of the mechanical loads under which tissue formation and regeneration takes place. In this manuscript, a database on musculo-skeletal loading of the proximal femur is presented. The data are based on individual patient gait and radiological data. By means of inverse dynamics and optimization techniques, the internal loads acting at the joint and within the muscles have been determined. The calculated hip contact force has been validated by means of in vivo measurements in four patients. The database is freely available and gives an estimate on internal loads acting at the proximal femur for activities like walking and stair climbing.

Bauteil und verfahren zum zusammenbau einer implantatanordnung

Abstract: Die Erfindung betrifft ein Bauteil (30) zum Anordnen an einem Implantat (2, 51) sowie ein Verfahren zum Zusammenbau einer Implantatanordnung. Das Bauteil umfasst ein Grundbauteil (33), mindestens eine in dem Grundbauteil angeordnete Sensoreinrichtung (35) zum Erfassen einer Messgrosse und zum Erzeugen von Messdaten fur die erfasste Messgrosse, eine in dem Grundbauteil angeordnete Telemetrieeinrichtung (34) zum Senden und Empfangen von Daten und eine Datenubertragungsverbindung (36) zwischen der mindestens einen Sensoreinrichtung und der Telemetrieeinrichtung zum Ubertragen von Daten zwischen der mindestens einen Sensoreinrichtung und der Telemetrieeinrichtung, wobei die Daten die Messdaten umfassen. An dem Grundbauteil sind Montagemittel (37) zum Montieren des Grundbauteils in einer Implantatausnehmung gebildet.