Biomedical subjects

N Verdonschot

Publications and source records attributed to N Verdonschot.

At least 37 records · Page 2Linked to original sources

PubMed2004

Enhancement of initial stability of press-fit femoral stems using injectable calcium phosphate cement: an in vitro study in dog bones.

In this in vitro study we evaluated the initial stability of cementless femoral stems using an injectable calcium phosphate (Ca-P) cement. The cement was not used to form a cement mantle as is routinely done in PMMA cemented prostheses but functioned as an additive to fill the small gaps that exist between a press-fit placed titanium plasma sprayed implant and the bone bed. Six pair of Beagle femora were used in this study. In a random fashion, one femur of each pair was used for placement of a prosthesis without Ca-P cement, the contralateral was used for press-fit placement after injection of the calcium phosphate cement into the intramedullary canal. The reconstructions were placed in a MTS testing machine, tilted 15 degrees in varsus and 15 degrees of endorotation to obtain a physiological load on the femoral head. The load was applied stepwise from zero to a maximum of 100, 250 and 400 N, respectively. At each loading step the load was applied dynamically at a frequency of 1 Hz for 30 min. Between the loading steps, the load was removed for 10 min to allow elastic recovery. The stability of the stems was determined at each loading step with roentgen-stereophotogrammetric analysis. Results showed that with the prostheses without Ca-P cement the most important displacements were movement into varus (max. 818 microm under 400 N) and subsidence (max. 587 microm under 400 N). The displacements showed large variation. After unloading some elastic recovery occurred. In the specimens with Ca-P cement, displacements were negligible. As determined by an F-test the variations found were significantly smaller for the press-fit+Ca-P cement relative to the press-fit prosthesis at all loading steps (p<0.05). A paired t-test revealed significant differences in the mentioned displacements between the press-fit- and press-fit+Ca-P cement prosthesis at a loading with 400 N (P<0.05). On the basis of these results we conclude that the use of Ca-P cement increases the initial stability of press-fit inserted plasma-sprayed femoral prostheses and corrects for the high variability in displacements found with press-fit insertion of these femoral hip prostheses.

Adhesiveness↗

PubMed2004

Compensation for rotational malalignment after intramedullary nailing for femoral shaft fractures. An analysis by plantar pressure measurements during gait.

INTRODUCTION: Even though rotational malalignment due to a femoral shaft fracture leads to clinical complaints, a large number of patients may have none of significance. The ability to compensate may play a role. The purpose of this study is to give insight into aspects of compensatory gait of patients with a femoral malrotation and the relation with clinical complaints. METHODS: In a cross-sectional laboratory setting, foot-progression angles (FPA) during gait were measured using a foot scan device. Results were related to CT determined femoral torsion and clinical complaints. RESULTS: Patients with external (EMR) or internal malrotation (IMR) showed differences in foot-progression angles (DeltaFPA) in the same direction of their malrotation. Compared to IMR patients, EMR patients appeared to compensate less for their malrotation. No statistically significant differences were detected between these groups for absolute and relative compensation. EMR patients scored worse at the Oxford 12-item and WOMAC score and experienced more problems executing demanding activities than do patients without malrotation. Correlations were found between Oxford 12-item and WOMAC score and relative compensation. CONCLUSIONS: Femoral torsion and the FPA are strongly related. All patients compensate towards normal values of FPA at their fractured side. Patients who are less able to compensate have more physical complaints. EMR patients tend to have more complaints and difficulty compensating.

Adaptation, Physiological↗

PubMed2004

Twist and its effect on ACL graft forces.

Graft tension is a controversial topic in anterior cruciate ligament (ACL) surgery. Evidence suggests a narrow range of graft tensions, which allow the graft to remodel to a stable and mature neoligament. In previous cadaver experiments, we showed that twisting the graft could modulate the graft forces. In this study we hypothesized that the same phenomena would be found in patients, and that twisting the graft intraoperatively can reduce peak forces in the graft. The effects of twist on graft forces in bone-patellar tendon-bone grafts were measured during anterior cruciate ligament surgery on 15 consecutive patients using a custom-made tension-measurement device. Variations in surgical procedure that could potentially affect the graft force patterns were quantified. Graft force as a function of knee-flexion angle was measured with the graft in the neutral, untwisted position and repeated with the tibial bone block rotated externally or internally by 180 degrees. In eight of the 15 knees, external twisting of the graft reduced the maximal graft force to 50%. However, in five knees the forces in extension increased by twisting to a maximum of 300%. Of the surgical variables, only the femoral tunnel position appeared to have a consistent effect on the graft force pattern. Due to the unpredictable effect of graft twisting, a general recommendation on whether the graft should be twisted, and if so, in which direction, cannot be given. Intraoperatively, graft twisting may however be considered in every individual knee to modulate the graft force as a function of flexion angle.

Adolescent↗

PubMed2004

Modelling the fibrous tissue layer in cemented hip replacements: experimental and finite element methods.

The long-term fixation of cemented femoral components may be jeopardised by the presence of a fibrous tissue layer at the bone-cement interface. This study used both experimental and finite element (FE) methods to investigate the load transfer characteristics of two types of cemented hip replacements (Lubinus SPII and Müller-Curved) with a fibrous tissue layer. The experimental part investigated six stems of each type, where these were implanted in composite femurs with a specially selected silicone elastomer modelling the soft interfacial layer. Two fibrous tissue conditions were examined: a layer covering the full cement mantle, representing a revision condition; and a layer covering the proximal portion of the cement mantle, representing a non-revised implant with partial debonding and fibrous tissue formation. The FE method was used to model the full fibrous tissue layer condition, for both implants. The layer was modelled as a homogeneous, linearly isotropic material. A cross-comparison was performed of the experimental and FE findings. Agreement between experimental and FE models was verified to be within 15%. Varying the stiffness parameter of the FE soft tissue layer had little influence on the cortical bone strains, though had considerable effect on the cement strains. Stress shielding occurred for both stems under both fibrous tissue conditions, with the greatest reduction around the calcar. However, the cortical bone strains were generally larger than those for the equivalent well-fixed stems. The fibrous tissue layer was not found to increase the general strain pattern of the cement mantle, though localised regions of high stress were detected.

Arthroplasty, Replacement, Hip↗

PubMed2004

Rotational malalignment after intramedullary nailing of femoral fractures.

OBJECTIVES: Intramedullary nailing has been accepted as the treatment of choice for femoral shaft fractures. The aim of our study was to determine the incidence and implications of rotational malalignment after intramedullary nailing using computed tomography measurements. DESIGN: Cohort study. SETTING: Patients who postoperatively visited the orthopaedic outpatient and radiology clinics. PATIENTS: Seventy-six patients, 59 men and 17 women, with a mean age of 28.4 years (15-88). INTERVENTION: Patients treated on a fracture table with an antegrade reamed AO nail (n = 46) or Grosse Kempf nail (n = 30) for a unilateral femoral shaft fracture between 1988 and 1998 were included in the study. MAIN OUTCOME MEASUREMENTS: Patients filled out a questionnaire concerning pain, daily activities, and sport. Oxford, Western Ontario and McMaster University osteoarthritis index, and Harris Hip and Knee Society scores were obtained. Physical exams and computed tomography measurements were established. RESULTS: Twenty-one patients (28%) were found to have a rotational malalignment of 15degrees or more. There was no significant difference in rotational deformity with either the AO or Grosse Kempf nail. The incidence of malrotation was independent of the fracture level. Patients with a torsional deformity had difficulties with more demanding activities like running, sports, and climbing stairs. Patients with an external rotational malalignment (n = 12) have more functional problems than patients with an internal rotational malalignment (n = 9). Clinically determined rotation differences are not accurate (+/-20degrees) compared with the established computed tomography measurements. CONCLUSIONS: Rotational malalignment after intramedullary nailing for femoral fractures is found in 28% of the patients in this study. These patients have difficulties with more demanding activities, especially when they have an external torsional deformity.

Adolescent↗

PubMed2004

Effect of joint conformity on glenoid component fixation in total shoulder arthroplasty.

Results of shoulder replacements are inferior and must be improved. Two of the major problems of total shoulder replacements are loosening of cemented glenoid components and wear of polyethylene inlays of uncemented, metal-backed glenoid components. The aim of this study is to investigate the influence of joint conformity on glenoid-component fixation. Keeled glenoid components, with radii of curvature of 24, 25, or 29 mm, were cemented in bone substitutes, placed in a force-controlled test set-up, articulating against a 24 mm humeral head. They were loaded by a constant joint compression force (725 +/- 10 N) and a superior subluxation force (shear force), cyclically varying between 0 and 350 +/- 1 N. After 200,000 load cycles, the upper and lower glenoid component rim-displacements were measured by custom-made displacement sensors. Additionally, the shear-out strength has been measured to investigate the residual strength. The glenoid component structures with radii of curvature of 24, 25, and 29 mm showed maximum superior rim-displacements of 0.163 (SD = 0.01), 0.299 (SD = 0.0306), and 0.350 (SD = 0.0197) mm respectively, which is a significant difference (p < 0.05). The maximum shear-out strength of glenoid components with radii of curvature of 24, 25, and 29 mm was 2707 (SD = 452), 2648 (SD = 299), and 2631 (SD = 312) N respectively, which is not a significant difference (p < 0.05). However, the results indicate that a conform articulation shows smaller glenoid rim-displacements, which might be beneficial for long-term component fixation.

Arthroplasty↗

PubMed2004

Acetabular revision with impacted morsellised cancellous bone grafting and a cemented cup. A 15- to 20-year follow-up.

This study presents the clinical and radiological results of 62 consecutive acetabular revisions in 58 patients, at a mean of 16.5 years follow-up (15 to 20). The Kaplan-Meier survivorship for the cup with end-point revisions for any reason, was 79% at 15 years (95% confidence interval (CI); 67 to 91). Excluding two revisions for septic loosening at three and six years, and one revision of a well-fixed cup after 12 years in the course of a femoral revision, the survivorship was 84% at 15 years (95% CI; 73 to 95). At review there were no additional cases of loosening, although seven acetabular reconstructions showed radiolucent lines in one or two zones. Acetabular revision using impacted large morsellised bone chips (0.7 cm to 1.0 cm) and a cemented cup, is a reliable technique of reconstruction, when assessed at more than 15 years.

Acetabulum↗

PubMed2004

[Research methods in dentistry 5. The finite element method].

The finite element method is a commonly applied experimental research technique. The method comprises computer simulation of constructions under load and of internal mechanical processes, which enables the study of effects of geometrical and material variations. The analysis shows internal stresses and, consequently, predictions can be made of possible failure. In dentistry, the method is applied in disciplines, such as orthodontics, oral and maxillofacial surgery, implantology en restorative dentistry.

Computer Simulation↗

PubMed2003

Prevention of mesh-dependent damage growth in finite element simulations of crack formation in acrylic bone cement.

Peak stress levels predicted in finite element analysis (FEA) usually depend on mesh density, due to singular points in the model. In an earlier study, an FEA algorithm was developed to simulate the damage accumulation process in the cement mantle around total hip replacement (THR) implants. It allows cement crack formation to be predicted, as a function of the local cement stress levels. As the simulation is driven by mesh-dependent peak stresses, predicted crack formation rates are also likely to be mesh dependent. The aim of this study was to evaluate the mesh dependence of the predicted crack formation process, and to present a method to reduce the mesh dependence. Crack-propagation experiments were simulated. Experimental specimens, representing transverse slices of cemented THR reconstructions, were subjected to cyclic torsional loading. Crack development around the corners of the stem was monitored. The experiments were simulated using three meshes with increasing levels of mesh refinement. Crack locations and orientations were accurately predicted, and were virtually independent of the level of mesh refinement. However, the experimental crack propagation rates were overestimated considerably, increasing with mesh refinement. To eliminate the effect of stress singularities around the corners of the stem, a stress averaging algorithm was applied in the simulation. This algorithm redistributed the stresses by weighted spatial averaging. When damage accumulation was computed based on averaged stresses, the crack propagation rates predicted were independent of the level of mesh refinement. The critical distance, a parameter governing the effect of the averaging algorithm, was optimized such that the predicted crack propagation rates accurately corresponded to the experimental ones. These results are important for the validity and standardization of pre-clinical testing methods for orthopaedic implants.

Artifacts↗

PubMed2003

A three-dimensional finite element model of the polymerization process in dental restorations.

Restoration of dental restorations with resin composite is hampered by shrinkage of the material during the polymerization process. In this study, we simulated the polymerization process in a detailed three-dimensional finite element model of a human upper premolar with a cusp-replacing restoration. It was analyzed how the stress patterns changed during polymerization and it was assessed whether immediate failure of the restoration is likely to occur and if so, which locations within the restoration are at highest risk and what the clinical implications of these findings are for clinical practice. It was found that the stresses increased rapidly during polymerization and decreased again in the post-polymerization phase. At the interface, tensile stresses relaxed to a higher degree than the shear stresses. Stress values in the composite material and at the interface with the tooth tissue were lower than the reported strength values suggesting that immediate failure is unlikely. The safety factor against mechanical failure of the interface, however, was relatively low indicating that the interface between the composite material and the tooth tissue is at a higher risk for failure than the bulk of the restoration. Stress relaxation was less effective in areas where the interface surface was irregular. In common practice, irregular interface surfaces are used to increase the retention of the restoration. This study indicates that the increased retention may be compromised to some extent by higher shrinkage stresses. The fact that stresses considerably decreased during the post-polymerization period suggests that mechanical loading should be limited during the first few hours after restoration.

Bicuspid↗

PubMed2003

Experimental investigation of bone remodelling using composite femurs.

OBJECTIVE: To determine the load transfer patterns of femurs in the intact, immediate post-operative and long-term (remodelled) post-operative implanted conditions for Lubinus SPII and Müller-Curved cemented hip prostheses, and to examine to what extent remodelling may influence the long-term outcome. DESIGN: Experimental and finite element (FE) methods were applied to composite femurs under loads representing the heel-strike phase of gait, determining cortical bone and cement strains for the different femur conditions. BACKGROUND: The authors previously developed protocols to measure bone and cement strains, and to produce remodelled femur specimens, yet these have not been applied together to compare strain patterns of different femur conditions. The Lubinus SPII is clinically more successful than the Müller-Curved stem, with failure mainly due to aseptic loosening. METHODS: Cortical bone strains were determined in intact femurs. Six femurs each were implanted with the two stem types and cortical bone and cement strains were measured. Bone remodelling was recreated using a validated CAD-CAM procedure to remove a layer of proximal cortical bone, replicating a typical scenario found in stable clinical retrievals. Strains were remeasured. FE methods were used to compliment the experiments. RESULTS: Stress shielding was reduced with remodelling, though bone strains did not return to their intact values, particularly around the calcar. Cement strains increased with remodelling. Differences occurred between the two stems; the Müller-Curved produced a more severe strain transition. CONCLUSIONS: Procedures were successfully combined together to investigate in vitro the performance of two cemented stems, in immediate and long-term post-operative conditions. The increase of cement strains with remodelling is a potential indicator for in vivo cement failure. RELEVANCE: The consequences of femoral bone remodelling on the long-term success of joint replacements are not well understood, where remodelling may lead to increased bone and cement stresses.

Bone Remodeling↗

PubMed2003

The initial stability of cemented acetabular cups can be augmented by mixing morsellized bone grafts with tricalciumphosphate/hydroxyapatite particles in bone impaction grafting.

Tricalciumphosphate (TCP) and hydroxyapatite (HA) have been suggested as bone graft substitutes in a wide range of applications. In this study, the initial stability of cemented acetabular cups was determined after reconstructing a combined cavitary and segmental defect in a realistic acetabular revision surgery model. The defects were reconstructed with mixes of TCP/HA particles and human bone grafts using the bone impaction grafting technique. In comparison with defect reconstruction with human bone grafts only, cup translation and tilt decreased by 27% when mixes of bone grafts and porous TCP/HA particles were used and by 55% when mixing the bone grafts with solid TCP/HA particles. Increasing the TCP/HA ratio within the mix significantly decreased cup translation. From a biomechanical perspective, mixes of TCP/HA particles and bone grafts are an attractive alternative for morsellized bone grafts when using the bone impaction grafting technique in the reconstruction of large defects of the acetabulum.

Acetabulum↗

PubMed2003

The trochlea is bilinear and oriented medially.

Malfunctioning of total knee replacements often is related to patellofemoral problems. Because the trochlea guides the patella during flexion and extension, its geometry has a major influence in patellofemoral problems. There is controversy in the literature: relative to the mechanical axis, some authors have found a laterally oriented trochlea and others have found a medially oriented trochlea. The groove of implanted prosthetic femoral components always has lateral or neutral orientations. The objectives of the current study were to clarify the controversy found in the literature, to determine whether the trochlear orientation is truly linear, and to determine whether the orientation depends on the size of the femur. The trochleae of 100 human femurs were measured using a three-dimensional measurement system. Detailed analysis of the results indicated that the trochlea is best described as bilinear, with the distal half oriented 0.2 degrees +/- 2.8 degrees laterally and the proximal half oriented 4.2 degrees +/- 3.2 degrees medially. Trochlear orientation was not dependent on bone size.

Cadaver↗

PubMed2003

Does layering minimize shrinkage stresses in composite restorations?

Polymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young's modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp.

Chemical Phenomena↗

PubMed2003

A different fixation of the femoral component in total knee arthroplasty may lead to preservation of femoral bone stock.

Good femoral bone stock is important for the stability of the femoral component in revision knee arthroplasty. However, the primary total knee replacement (TKR) may cause significant loss of bone stock in the distal anterior femur. Earlier stress-induced bone remodelling simulations have suggested that a completely debonded component may save bone stock in the distal anterior region. However, these simulations did not consider the fixation of a debonded implant and possible secondary effects of micromotions and osteolysis at the interface. The current study tries to combine the preservation of bone stock with adequate component fixation. Different bone remodelling simulations were performed around femoral knee components with different sizes of bonding area and different friction characteristics of the debonded area. The fixation of the femoral component with different bonding characteristics is quantified with calculated implant-bone interface stresses. The results show that a bonded femoral component with a debonded inner side of the anterior flange may significantly reduce bone resorption in the endangered distal anterior femur, without jeopardizing the fixation of the femoral implant. This effect may be obtained in vivo by using a femoral component with a highly polished inner side of the anterior flange.

Arthroplasty, Replacement, Knee↗

PubMed2003

[A finite element model of a cusp-replacing adhesive restoration].

This article describes the development of a three-dimensional finite element model of a premolar, based on a micro-scale computed tomographic data-acquisition technique. Using the model shrinkage stresses were analysed during and after the polymerisation process of resin composite. The stress patterns generated were three-dimensional. The results of this study indicate that failure of the interface is more probable than failure of the composite material. The described procedure is a relatively easy method to produce a highly detailed 3-D finite element model of a premolar with an adhesive cups-replacing restoration.

Bicuspid↗

PubMed2002

Finite element and experimental models of cemented hip joint reconstructions can produce similar bone and cement strains in pre-clinical tests.

Finite element (FE) models could be used for pre-clinical testing of cemented hip replacement implants against the damage accumulation failure scenario. To accurately predict mechanical failure, the models should accurately predict stresses and strains. This should be the case for various implants. In the current study, two FE models of composite hip reconstructions with two different implants were validated relative to experimental bone and cement strains. The objective was an overall agreement within 10% between experimental and FE strains. Two stem types with different clinical results were analyzed: the Lubinus SPII and the Mueller Curved with loosening rates of 4% and 16% after 10 yr, respectively (Prognosis of total hip replacement. 63rd Annual Meeting of the American Academy of orthopaedic surgeons, Atlanta, USA). For both implant types, six stems were implanted in composite femurs. All specimens were subjected to bending. The Mueller Curved specimens were additionally subjected to torsion. Bone strains were recorded at 10 locations on the cortex and cement strains at three locations within the cement mantle. An FE model was built for both stem types and the experiments were simulated. Bone and cement strains were calculated at the experimental gauge locations. Most FE bone strains corresponded to the mean experimental strains within two standard deviations; most FE cement strains within one standard deviation. Linear regression between the FE and mean experimental strains produced slopes between 0.82 and 1.03, and R(2) values above 0.98. Particularly for the Mueller Curved, agreement improved considerably when FE strains were compared to the strains from the experimental specimen used to build the FE model. The objective of overall agreement within 10% was achieved, indicating that both FE models were successfully validated. This prerequisite for accurately predicting long-term failure has been satisfied.

Bone Cements↗

PubMed2002

Effect of load on the early incorporation of impacted morsellized allografts.

Impacted morsellized bone grafts are clinically successful to restore bony defects after failed total hip arthroplasties. The incorporation process seems to be dependent on the location where the reconstruction is performed, which suggests that load could play a role. In this study, we hypothesised that, as in fracture healing, physiological loading has a stimulatory effect on the process of early bone graft incorporation. To test this hypothesis we created a standardised defect in the distal femur of twelve goats. Allograft bone chips were impacted into the defect and a subcutaneous pressure implant was screwed in. With this implant the graft can be loaded under controlled circumstances. Six goats were subjected to a daily loading regime of 3 MPa, the other six were non-loaded. After five weeks the bone mineral density was measured with peripheral quantitative computer tomography. Thereafter, routine histology and histomorphometry were carried out. Bone mineral density was not affected by load. Histology revealed microscopic evidence of bone graft incorporation, which proceeded in a similar way in both loaded and non-loaded specimens. New bone was formed free in the stroma or on graft remnants after osteoclastic resorption of the graft. Only the area of active incorporating bone graft was higher under load. In conclusion, the formation of a new bony structure was not affected by load after five weeks. However, load resulted in a larger area of active graft incorporation at this early stage. Possibly biological and immunological factors govern the early incorporation process independent of the local loading regime.

Animals↗