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Biomedical subjects

Kjeld Søballe

Publications and source records attributed to Kjeld Søballe.

At least 19 recordsLinked to original sources
PubMed2007

Local alendronate increases fixation of implants inserted with bone compaction: 12-week canine study.

Bone compaction has been shown to increase initial implant fixation. Furthermore, bone compaction creates a peri-implant zone of autograft that exerts osteoconductive properties. We have previously shown that locally applied bisphosphonate (alendronate) at 4-week observation can preserve the autograft generated by bone compaction. We now investigate whether the increased amount of autograft, seen at 4 weeks, can increase implant osseointegration and biomechanical fixation. Porous-coated titanium implants were bilaterally inserted with bone compaction into the proximal part of tibia of 10 dogs. On the right side, local bisphosphonate was injected into the bone cavity prior to bone compaction immediately prior to implant insertion. On the left side, saline was used as control. Observation period was 12 weeks. Locally applied bisphosphonate significantly increased biomechanical implant fixation (approximately twofold), bone-to-implant contact (1.2-fold), and peri-implant bone volume fraction (2.3-fold). This study indicates that local alendronate treatment can increase early implant osseointegration and biomechanical fixation of implants inserted by use of bone compaction. Long term effects remain unknown.

Alendronate↗
PubMed2006

Use of high-resolution MRI for investigation of fluid flow and global permeability in a material with interconnected porosity.

We present a multi-scale experimental approach designed to improve the investigation of both localized and global fluid flow in biomaterials with randomly interconnected porosity. Coralline hydroxyapatite (ProOsteon 500 from Interpore-Cross), having a relatively well-defined porosity, was used as an in vitro model of typical bone architecture. Axial fluid velocity profiles within the pores of a cylindrical hydroxyapatite sample were characterized using high-resolution MRI in conjunction with the measurement of global flow and associated permeability based on the Darcy-type relationship. Assuming Newtonian fluid behaviour, image analysis permitted computation of local porosity, intra-pore fluid shear, and visualization of flow heterogeneity within the sample. These results may benefit applications in biomaterials for the evaluation of factors influencing bony incorporation in porous scaffolds and on porous implant and bone surfaces. Normal and diseased biological tissues are also clinical relevant applications.

Bone Substitutes↗
PubMed2006

[Postoperative analgesia following total knee arthroplasty].

Total knee arthroplasty (TKA) is associated with considerable postoperative pain which may be difficult to manage. This article describes advantages and disadvantages of the different analgesic techniques used for pain treatment after TKA, for example i.v. patient-controlled analgesia, epidural pain treatment, and peripheral nerve blocks (especially femoral and sciatic blocks). Randomised studies suggest that peripheral nerve blocks have the best effect and have fewest side effects. Intra-articular administration of analgesics is the most recently introduced technique.

Analgesia↗
PubMed2006

High-resolution magnetic resonance flow imaging in a model of porous bone-implant interface.

PURPOSE: To evaluate the application of high-resolution MRI methodology for characterizing the fluid velocity field and evaluate fluid shear field within a simplified in vitro model of a bone-implant interface. MATERIALS AND METHODS: The study used a specific micromotion canine bone implant that has been used for over a decade in the experimental evaluation of anatomical, biomaterial, mechanical and surgical factors influencing the quality of the implant interface. To allow its implementation in an MR coil, a nonmagnetic model of the micromotion implant was fabricated. The model consisted of a cylinder of polymethylmethacrylate (PMMA) representing the implant, located within an annular controlled gap into a block of coralline-derived bulk porous hydroxyapatite (HA; Interpore Cross International, Irvine, CA, USA). The assembly was potted in a polycarbonate shell and connected to a gravity-feed flow system consisting of a water fluid reservoir and peristaltic pump. Cross-sectional fluid velocity images through the principal axis of the implant were generated using a phase-encoding MR imaging technique; axial fluid flow was derived, and fluid shear was evaluated using a Newtonian fluid model. RESULTS: Due to the nonuniform gap of the actual experimental construct, a highly nonuniform flow through the annular gap and a secondary flow through the porous HA block were observed. Axial velocity magnitudes in the range 0.04 to 14 mm/s were measured, and the flow velocities within the annular gap and the surrounding bone differed by nearly two orders of magnitude. Image analysis showed that 95% of total flow passed through the annular gap and 5% was transported through the porous HA block. Fluid shear was computed within the porous structure and the annular gap, and they differed by one order of magnitude. CONCLUSION: We demonstrated that high-resolution MR flow imaging has the resolution to measure fluid transport processes noninvasively through a nonmagnetic model bone implant. Gap fluid flow and fluid flow into the permeable skeleton (HA block) were quantified, and these data allowed the noninvasive determination of fluid shear. These promising results are encouraging for applications in biological tissue, artificial bone substitutes, tissue engineering and clinically relevant studies concerning implant fixation.

Animals↗
PubMed2006

Bone compaction enhances fixation of weight-bearing hydroxyapatite-coated implants.

The effect of bone compaction vs conventional drilling on the fixation of hydroxyapatite-coated implants was examined in a weight-bearing canine model. In each dog, one knee joint had the implant cavity prepared with drilling, the other with compaction. Eight dogs were euthanized after 2 weeks and 8 dogs after 4 weeks. Femoral condyles from additional 7 dogs represented time 0. Compacted specimens had significantly higher bone implant contact and energy absorption at time 0. Compaction significantly increased ultimate shear strength at 0 and 2 weeks. There was no significant difference in implant fixation after 4 weeks. The results of this study suggest that compaction may be beneficial in optimizing the crucial initial implant stability, even when hydroxyapatite-coated implants with osteoconductive properties are inserted in vivo.

Animals↗
PubMed2006

The bovine bone protein lyophilisate Colloss improves fixation of allografted implants--an experimental study in dogs.

BACKGROUND: Impacted morselized bone allograft is a well-established way of giving joint arthroplasties additional support in situations where there is insufficient bone stock. For long-term survival of the implant, early implant fixation is important. We hypothesized that Col-loss, a bone protein lyophilisate, might improve early implant fixation of allografted implants. METHOD: We inserted 4 porous-coated Ti implants in the distal femurs of 16 dogs. All implants were surrounded by a 2.5-mm gap, which was impacted with morselized allograft with or without Colloss. In each dog, the implants were treated with no Collos or low-, middle- or high-dose (0, 10, 20 and 40 mg) Colloss per cm3 allograft. The observation time was 4 weeks. RESULTS: Mechanical implant fixation was improved for all 3 groups with Colloss-treated implants (p < 0.05). The best anchorage was seen in the middle-dose group, where fixation was improved by 100%. We saw a dramatic reduction in fibrous tissue on the surface of the Colloss-treated implants (p < 0.001). The Colloss groups showed increased ongrowth of new bone (p < 0.01) and accelerated gap remodeling (p < 0.05). INTERPRETATION: Colloss can improve early osseointegration and fixation of allografted implants.

Animals↗
PubMed2006

Locally delivered TGF-beta1 and IGF-1 enhance the fixation of titanium implants: a study in dogs.

BACKGROUND: Osteogenic growth factors have been suggested to enhance the fixation of implants used in joint replacement. We examined the effect of locally delivered transforming growth factor-beta1 and insulin-like growth factor-1 in a biodegradable poly (D, L-lactide) coating. MATERIAL AND METHODS: In a paired study using 9 dogs, unloaded titanium implants surrounded by a 1-mm gap were inserted into the proximal humerus. The growth factors were incorporated in a poly (D, L-lactide) coating at a 1% (w/w) ratio of TGF-beta1 and a 5% (w/w) ratio of IGF-1. Control implants were uncoated. After 4 weeks, the implants were evaluated by mechanical push-out test and by histomorphometry. RESULTS: A twofold increase was seen in mechanical fixation (strength, stiffness, energy absorption) for the growth factor-treated implants (p = 0.04). Similar results were seen in histomorphometry, as bone ongrowth was 2.5 times higher (p = 0.02), and gap healing was 30-110% higher (p = 0.04) for the growth factor-treated implants than for the control implants. Ongrowth of fibrous tissue was eliminated by the treatment. INTERPRETATION: TGF-beta-1 and IGF-1, locally delivered in a biodegradable poly(D,L-lactide) coating, enhance the mechanical fixation and osseointegration of titanium implants in cancellous bone, and no fibrous tissue is produced in the growth factor treated implants.

Animals↗
PubMed2006

Walking pattern in 9 women with hip dysplasia 18 months after periacetabular osteotomy.

BACKGROUND: Periacetabular osteotomy improves radiographic predictors of osteoarthrosis and diminishes pain and functional impairment. No changes in function quantified by gait analysis have yet been documented. We evaluated the functional outcome of periacetabular osteotomy in relation to gait. METHODS: The gait pattern of 9 women (median age 39 years) with hip dysplasia who were treated with unilateral periacetabular osteotomy was analyzed before periacetabular osteotomy and an average of 1.5 years afterwards. Data were collected using 5 video cameras and 2 force plates. An inverse dynamics approach was used to calculate sagittal joint angles and moments in the stance phase. RESULTS: Postoperatively, all subjects walked with an increased extension of the knee joint during the entire stance phase compared to the preoperative movement pattern. INTERPRETATION: The subjects achieved a more upright walking pattern but continued to relieve the hip joint by maintaining a reduced flexor moment.

Acetabulum↗
PubMed2006

Detection of bony defects around cementless acetabular components in total hip arthroplasty: a DEXA study on 10 human cadavers.

BACKGROUND: We studied the ability of DEXA to detect bony defects around cementless acetabular components in total hip arthroplasty. The aim of our study was to provide a tool for detection and quantification of osteolytic lesions for the planning of revision cases. METHODS: We measured BMC in 10 human pelvis specimens retrieved from post mortem. We created standardized defects behind inserted acetabular components and compared the ash weights of the removed bone to the corresponding BMC measurements. RESULTS: We found a good correlation between the BMC differences measured and the corresponding ash weights. INTERPRETATION: We conclude that DEXA can detect even small defects in the bone adjacent to the cup.

Absorptiometry, Photon↗
PubMed2006

No difference in early cellular response of the pseudo-synovial membrane after total hip arthroplasty: comparison of 3 combinations of bearing materials.

BACKGROUND: Wear-resistant bearing materials may hypothetically reduce chronic inflammation in the pseudosynovial membrane as compared to less wear-resistant bearing materials such as polyethylene. We assessed the foreign body response in the pseudosynovial membrane in vivo after total hip replacement. METHODS: 37 patients from a larger prospective randomized trial of 225 patients had biopsies taken arthroscopically from the artificial hip joint (i.e. the pseudosynovial membrane) 1 year after insertion of the implant. All patients had an identical hip prosthesis (Bimetric-RingLoc) except for the bearing materials, which consisted of polyethylene on zirconia, CoCr on CoCr, or alumina on alumina. Histological quantification was performed on 2-mum-thick semi-thin plastic sections or paraffin sections by point counting technique to compare the volume fraction of macrophages, granulomas and endothelial cells in biopsies of the pseudosynovial membrane. RESULTS: The median macrophage volume fractions for polyethylene-on-zirconia bearing material (n = 15), CoCr-on-CoCr (n = 9), and alumina-on-alumina (n = 11) were 0.02, 0.04, and 0.004, respectively. The median granuloma volume fractions for polyethylene-on-zirconia (n = 13), CoCr-on-CoCr (n = 9), and alumina-on-alumina (n = 13) were 0.02, 0.04, and 0.02, respectively. The median endothelial cell volume fractions for polyethylene-on-zirconia (n = 15), CoCr-on-CoCr (n = 9), and alumina-on-alumina (n = 11) were 0.03, 0.02, and 0.05, respectively. Statistical analysis showed no significant differences between the three groups with the different bearings with respect to volume fraction of macrophages, granulomas and endothelial cells. INTERPRETATION: Our study demonstrated that a granulomatous inflammation is a common finding in non-loose implants as early as 1 year after the operation not demonstrating a difference in macrophages and granuloma formation with the various bearing materials. Thus a high volume fraction of macrophages was found in the osteoarthritis control group compared to the operated group.

Adult↗
PubMed2006

Effect of topical alendronate treatment on fixation of implants inserted with bone compaction.

Bone compaction has been shown to enhance the critical initial implant stability that is important for secure long-term fixation. We investigated whether topical bisphosphonate treatment improves fixation of implants inserted with bone compaction. Porous-coated titanium implants were inserted with bone compaction into the knees of eight dogs. In the right knee, topical bisphosphonate treatment was applied before bone compaction. Saline was used as a control in the left knee. The knees were observed for 4 weeks. We found an increase in total bone-to-implant contact and total bone density around the implants in the bisphosphonate-treated group. These were results of increased nonvital bone-to-implant contact and increased nonvital periimplant bone density. No change in biomechanical fixation was found. Studies with a longer followup are needed to investigate whether the preservative effect of alendronate on nonvital bone might enhance implant fixation by osteoconduction.

Administration, Topical↗
PubMed2006

The other hip in unilateral hip dysplasia.

UNLABELLED: We reviewed transverse pelvic computed tomography scans of 197 consecutively referred adult patients with hip pain thought to be secondary to developmental dysplasia. A center-edge angle of 20 degrees or less was considered the upper normal value. Four groups were identified: 69 patients with apparently unilateral right developmental dysplasia (left hip center-edge angles greater than 20 degrees), 26 patients with apparently unilateral left developmental dysplasia (right hip center-edge angles greater than 20 degrees), 68 patients with bilateral developmental dysplasia, and 34 patients with bilateral borderline developmental dysplasia (bilateral center-edge angles less than or equal to 25 degrees). The pelvic computed tomography scans were compared with computed tomography scans of 41 control subjects with healthy hips. The joint anatomy of patients with developmental dysplasia differed from that of control subjects in almost all aspects. Acetabular anteversion was larger in control subjects compared with patients with developmental dysplasia. We found inverse relationships between femoral anteversion and the anterior acetabular sector angle and coronal and sagittal center-edge angles in dysplastic hips, and also between femoral neck-shaft angles and the anterior acetabular sector angle. There was an inverse relationship between reduced anterior support developmental dysplasia in which plain radiographs suggested unilateral dysplastic abnormality only, computed tomography scans revealed both hips to be abnormal. The data suggest that patients referred with seemingly unilateral developmental dysplasia also are at risk of having contralateral dysplastic malformation. LEVEL OF EVIDENCE: Diagnostic study, Level II (development of diagnostic criteria on consecutive patients [with universally applied reference "gold" standard]). See the Guidelines for Authors for a complete description of levels of evidence.

Acetabulum↗
PubMed2006

Comparison of performance of conventional and minimally invasive surgery acetabular reamers.

UNLABELLED: Acetabular reaming in minimally invasive surgery can be done using a newly designed minimally invasive reamer. The new minimally invasive reamer is narrower and chamfered, which results in two sharp edges. This design may result in acetabular cavities with less ideal spheres than those achieved with conventional reaming. We compared the acetabular shapes in nine pairs of cadaver acetabula. Minimally invasive reaming was performed in one acetabulum of each pair, and conventional reaming was performed on the contralateral side. A new digitizing technique, optical three-dimensional scanning, was applied to the reamed acetabula to determine the reamers' performance. Best-fit spheres were calculated for the reamed cavities, and all reamers were measured for exact dimensions. There were small deviations between the diameters of the reamer and the reamed cavity for the minimally invasive (mean, 0.1 mm; standard deviation, 0.5 mm) and conventional (mean, 0.3 mm; standard deviation, 0.4 mm) reamers. There were no significant differences between minimally invasive and conventional reaming. The mean differences between the reamer domes and the measured values showed a discrepancy of 2.2 mm (standard deviation, 0.08 mm) in the minimally invasive surgery group and 2.8 mm (standard deviation, 0.09 mm) in the conventional group. Although the acetabular reamer design has been modified, there were no significant differences in the acetabular shapes after minimally invasive or conventional reaming. LEVEL OF EVIDENCE: Therapeutic Study, Level II (prospective comparative study with no statistically significant difference). See the Guidelines for Authors for a complete description of levels of evidence.

Acetabulum↗
PubMed2005

In vivo effects of RGD-coated titanium implants inserted in two bone-gap models.

RGD (Arg-Gly-Asp) coating has been suggested to enhance implant fixation by facilitating the adhesion of osteogenic cells to implant surfaces. Orthopedic implants are unavoidably surrounded partly by gaps, and these regions represent a challenging environment for osseointegration. We examined the effects of cyclic RGD-coated implants on tissue integration and implant fixation in two cancellous bone-gap models. In canines, we inserted loaded RGD-coated implants with 0.75-mm gap (n = 8) and unloaded RGD-coated implants with 1.5-mm gap (n = 8) into the distal femur and proximal tibia, respectively. Control gap implants without RGD were inserted contralaterally. The titanium alloy (Ti-6Al-4V) implants were plasma sprayed and cylindrical. The observation period was 4 weeks and the fixation was evaluated by push-out test and histomorphometry. Mechanical implant fixation was improved for RGD-coated implants. Unloaded RGD-coated implants showed a significant increase in bone whereas both loaded and unloaded implants showed a significant reduction in fibrous tissue anchorage. The results are encouraging, because RGD had an overall positive effect on the fixation of titanium implants in regions where gaps exist with the surrounding bone. RGD peptide coatings can potentially be used to enhance tissue integration in these challenging environments.

Animals↗
PubMed2005

Degeneration in dysplastic hips. A computer tomography study.

BACKGROUND: Hip dysplasia is considered pre-osteoarthritic, causing degeneration in young individuals. OBJECTIVE: To determine the pattern of degenerative change in moderate to severely dysplastic hips in young patients. DESIGN AND PATIENTS: One hundred and ninety-three consecutively-referred younger patients with hip pain believed to be caused by hip dysplasia constituted the study cohort. The average age was 35.5 years (range, 15-61 years). They were examined by close-cut transverse pelvic and knee computed tomography and antero-posterior radiographs (CT). We identified 197 hips with moderate to severe dysplasia, and 78 hips with normal morphology in the study cohort, whilst 111 hip joints were borderline dysplastic according to preset definitions. Comparative analyses of anatomy and distribution of degeneration between dysplastic and normal hips in the study cohort were performed. RESULTS: In dysplastic hips the anterior acetabular sector angle was significantly and inversely associated to femoral anteversion (p < 0.001). The center-edge (CE) angle, the acetabular angle (AA), and the acetabular depth ratio (ADR) were significantly interrelated (p < 0.001; correlation coefficients ranging from -0.8 to 0.7). Fifty-one hips were subluxated (24R/27L). There were no cases of complete dislocation. The formation of subchondral cysts or osteophytes in dysplastic hips was significantly associated with reduced minimum joint space width (p ranging from 0.005 to 0.02). However, in 67 hips with acetabular cysts, only 6 hips had minimum joint space widths = 2.0 mm (8.9%) in the coronal plane. In 96 cases with acetabular cysts found in the sagittal plane, 43 cases had minimum joint space widths = 2.0 mm (44.7%). Bony rim detachment at the site of labral insertion was recorded in 30 hips. Twenty-three of these were dysplastic (p = 0.01). CONCLUSIONS: Degeneration was most often found in the anterolateral part of the dysplastic hip joints. Most cysts were located above the transition zone between the bony and the fibrocartilaginous acetabulum, and we found a significantly- increased number of cases with avulsed bony fragments at the antero-lateral labral insertion in dysplastic hips compared to normal hips. It seems likely that the early degenerative process in dysplastic hips originates at the watershed zone between the acetabular labrum and the acetabular cartilage in response to subluxation and femoroacetabular impingement.

Adolescent↗
PubMed2005

Gene therapy with human osteoprotegerin decreases callus remodeling with limited effects on biomechanical properties.

Osteoprotegerin (OPG) is a naturally occurring protein, which prevents bone resorption by inhibition of osteoclastogenesis, function, and survival. Therefore, recombinant OPG may be an attractive drug in the treatment of chronic bone resorptive diseases such as osteoporosis. Gene therapy has the potential to achieve long-term treatment by delivering genes of anti-resorptive proteins to the recipient. The effects of OPG gene therapy on fracture healing have not been described previously. The influence of OPG gene therapy on callus formation, callus tissue structural strength, apparent material properties, and histology of tibia fractures in rats was investigated after 3 weeks and 8 weeks of healing. Intramuscular administration of adeno-associated virus (AAV) vector-mediated OPG resulted in increased levels of OPG in serum of approximately 100 ng/ml throughout the study period. Control animals with fractures received transduction with an AAV reporter gene construct (AAV-enhanced green fluorescent protein (eGFP)), and in this group serum OPG levels remained at baseline (<10 ng/ml). After 3 weeks of healing, AAV-OPG treatment reduced the number of osteoclasts in the callus tissue (33%, P < 0.001). However, AAV-OPG treatment did not influence callus dimensions, callus bone mineral content (BMC), fracture structural strength, or apparent callus tissue material properties. After 8 weeks of healing, AAV-OPG treatment reduced the number of osteoclasts in the callus tissue (31%, P < 0.001) compared with AAV-eGFP fractures. Furthermore, deposition of new woven bone at the fracture line of the original cortical bone was hampered (new woven bone present: in all AAV-eGFP animals, in 41% of AAV-OPG-treated animals, P < 0.001). AAV-OPG treatment also increased callus BMC (18%, P = 0.023) compared with AAV-eGFP fractures. AAV-OPG did not influence callus dimensions, structural strength of the fractures, or ultimate stress, whereas elastic modulus was reduced in the AAV-OPG groups (37%, P = 0.039). The experiment demonstrates that AAV-OPG gene therapy decreases the fracture remodeling, but this does not influence the structural strength of healing fractures.

Animals↗
PubMed2005

Biomechanical analysis of the shear behaviour adjacent to an axially loaded implant.

Good mechanical fixation of an implant to the surrounding bone is important for its longevity, and is influenced by both biological and mechanical factors. This study parametrically evaluates the mechanics of the interface with a computationally efficient analytic structural model of the shear stress field and global shear stiffness of an axially loaded implant. The utility of the analytic model was first established by validating its assumptions with a case-specific finite element model. We then used the analytic model for a sensitivity analysis of the relationship between the pattern of tissue growth and shear properties of the interface for our previously reported loaded in vivo experimental micromotion device. The bone located directly at the implant surface was found to be the most effective site for increasing interface stiffness. This suggests that the implant surface is the most desirable site for bone growth, yet is also the most mechanically challenging environment due to its maximal shear stresses. Thus, these findings support the further investigation of osteo-conductive coatings and other biological stimuli to overcome the challenging mechanics, and to promote bone growth directly at the implant surface. The model also demonstrated that the mechanical contribution to the global implant shear stiffness of a commonly observed isolated sclerotic bone rim is very limited. The results of this sensitivity analysis agree with experimental studies with the micromotion device, and with clinical studies reporting good results with osteo-conductive coatings.

Animals↗