PubMed Health⌕ Search

Biomedical subjects

W R Walsh

Publications and source records attributed to W R Walsh.

At least 37 records · Page 2Linked to original sources
PubMed2003

Response of a calcium sulfate bone graft substitute in a confined cancellous defect.

Calcium sulfate, plaster of Paris, has a long clinical history for use as a bone graft substitute in various skeletal sites. The current authors examined the in vivo response of calcium sulfate pellets alone or in combination with autogenous bone graft in a bilateral critical-size distal femoral cancellous defect in an adult sheep model. New thick bone formation was seen in defects filled with calcium sulfate pellets alone. Increased immunostaining for bone morphogenetic protein-2, bone morphogenetic protein-7, transforming growth factor-beta, and platelet derived growth factor was seen in defects filled with calcium sulfate pellets alone and in combination with autograft. The local acidity during calcium sulfate resorption is proposed as a possible in vivo mechanism for this type of material.

Animals↗
PubMed2002

The influence of design parameters on cortical strain distribution of a cementless titanium femoral stem.

The strain distribution imposed on a femur following a total joint replacement is an important factor, in proximal bone loss due to stress shielding, and long term clinical success. This study investigated how five different design parameters of a cementless titanium femoral prosthesis influenced cortical strains. Test loads were applied and strains were measured with and without an abductor force simulation, using six human cadaveric femora. The cementless design used demonstrated significant calcar loading proximally and a similar strain distribution to the intact femur distally. Implant gross geometry was the major factor in determining the cortical strain distributions under abductor simulation in both axial and torsional loading.

Aged↗
PubMed2002

The effect of substrate roughness and hydroxyapatite coating thickness on implant shear strength.

This study examined the role of substrate preparation and hydroxyapatite (HA) coating thickness on bone ongrowth and shear strength in a bilateral bicortical sheep model. Plasma-sprayed and grit-blasted titanium implants with different thickness HA coatings were examined at 4, 8, 12, and 26 weeks after implantation. Shear strength increased with time for all implants. Plasma-sprayed implants were superior to grit-blasted implants at all time points. The 100-microm-thick HA layer used in the present study provided greater fixation and ongrowth and less resorption compared with the 50-microm-thick layer. We did not observe any advantage in using a thicker HA coating for the titanium substrates examined.

Analysis of Variance↗
PubMed2002

The function of the posterior cruciate ligament in an anteroposterior-gliding rotating platform total knee arthroplasty.

Knee kinematics after total knee arthroplasty is dictated primarily by implant geometry and native soft tissue constraints. This study highlights the importance of a functioning posterior cruciate ligament in limiting excessive anteroposterior translation in a mobile bearing knee design that relies on native posterior cruciate ligament integrity and postarthroplasty tensioning for stability rather than any inherent mechanical design stability, such as anterior rails or stops.

Adult↗
PubMed2002

Surface roughness of the proximal and distal bearing surface of mobile bearing total knee prostheses.

Proximal and distal articulations surface roughness measurements were done on 8 mobile bearing knee designs immediately after removal from sterile packaging. Roughness parameters Ra and Rp based on ISO 97, representing mean deviation from the smooth surface line and mean peak to smooth surface line, were recorded using a contact surface profilometer at 10 random sites in the anteroposterior and mediolateral direction on the femoral and tibial metal components and the proximal and distal surface of the ultra-high molecular weight polyethylene (PE) inserts. No differences were found for surface roughness values for the metal components. Surface roughness values were greater for the distal PE bearing surfaces compared with the proximal PE bearing surfaces for each design tested. The roughness values for the PE inserts showed a directional dependence. Complex kinematics of mobile bearing knees coupled with this rougher distal interface could influence the rate of generation of wear particles and total volume of particles produced especially in the early postoperative period.

Humans↗
PubMed2001

A curved edge moderates high pressure generated by a laparoscopic grasper.

BACKGROUND: Very high pressures are generated at the interface between the tip of laparoscopic graspers and tissue. The pressure profile suggests that the high pressure is due to stress concentration at the edge of the jaw. Stress concentration at an edge can be modified by curving the edge. This study sought to determine the effect of a curved edge on pressures generated by the jaw of a laparoscopic grasper. METHODS: Pressure generated at the instrument tissue interface was measured by a thin film pressure transducer. The two instruments that we compared were identical in every respect except the profile of the jaw edge. One was unmodified; the other had a rounded grasping edge. Load and handle pressure were constant throughout. Tissue pressures generated by the grasper were recorded as the angle of load was increased from vertical (0 degrees ) to 135 degrees. RESULTS: Localized pressures at the tip of the unmodified instrument reached a maximum of 1500 kPa. Pressures at the tip of the curved instrument reached a maximum of 920 kPa under identical conditions. CONCLUSION: High pressures generated at the tip of laparoscopic graspers can be reduced by rounding the edge of the jaw.

Laparoscopy↗
PubMed2001

Resistance forces acting on suture needles.

Understanding the resistance forces encountered by a suture needle during tissue penetration is important for the development of robotic surgical devices and virtual reality surgical simulators. Tensile forces applied to skin and tendon during suturing were measured. Fresh sheep achilles tendons were tensioned with a static load 4.9 N, 9.8 N or 19.6 N and sheepskin with 0.98 N, 2.9 N or 4.9 N static load. A straight 2/0 cutting suture needle in series with a load cell on a materials testing machine penetrated the tissue at 90 degrees with a velocity of 1, 5 or 10mm/s for each tissue tension (n=5). Continuous load versus displacement data was obtained and penetration load and stiffness were noted. The load versus displacement curve for skin during needle penetration demonstrated two characteristic peaks, corresponding to initial penetration and emergence of needle from the undersurface of the tissue. Increasing the tension within the tissue (skin and tendon) increased the amount of force required to penetrate the tissue with a suture needle (p<0.05). Needle displacement rate did not affect the resistance to needle penetration (p<0.05). This study provides a simple model for measuring force-feedback during needle penetration of soft tissues and is a good starting point for future studies of the penetration resistance properties of human tissues.

Achilles Tendon↗
PubMed2001

Stabilization of the posterior limb of the medial canthal tendon using biodegradable tag anchors: a cadaveric model.

PURPOSE: This study describes and tests in a cadaveric model a new method of fixation designed for potential stabilization of the posterior limb of the medial canthal tendon, using biodegradable Tag anchors. METHODS: Study of the possibility of performing surgery to repair medial ectropion using biodegradable polyglyconate Tag anchors was commenced in the sheep cadaveric head model, and in the whole dry human skull model. This was then performed using five preserved human cadaveric whole heads, and pullout tensions were estimated in four of these. Computed tomography and magnetic resonance imaging were obtained for this model in the fifth head, and computed tomography was performed on the whole dry human skull. Dissections were carried out to establish the site of the bony defect in each of the heads. RESULTS: It was possible to obtain good Tag anchor fixation in bone overlying the maxillary and ethmoidal sinuses of the sheep, and in a young human skull. It was also possible to place adequately the anchor in the medial wall of the orbit close to the posterior lacrimal crest in all cases in the human cadaveric model. Pullout strengths were evaluated and found to range from 3.5 N to 12.4 N (mean, 7.5 N). Computed tomography and magnetic resonance imaging failed to demonstrate the biodegradable anchors in both the dry human whole skull and in the fifth cadaveric head, but did demonstrate the bony defects in the medial orbital walls through which the anchor passed. CONCLUSIONS: We have shown, for the first time, the stability of biodegradable Tag anchor fixation in a human cadaveric head model using pullout tensions and dissection studies. This method would allow adequate strength and stability to provide for control of fixation of the medial end of the lower eyelid in patients with medial ectropion and medial canthal tendon laxity.

Absorbable Implants↗
PubMed2000

Morphometric and mechanical evaluation of titanium implant integration: comparison of five surface structures.

Achieving a stable bone-implant interface is an important factor in the long-term outcome of joint arthroplasty. In this study, we employed an ovine bicortical model to compare the bone-healing response to five different surfaces on titanium alloy implants: grit blasted (GB), grit blasted plus hydroxyapatite (50 microm thick) coating (GBHA), Porocoat(R) (PC), Porocoat(R) with HA (PCHA) and smooth (S). Push-out testing, histology, and backscatter scanning electron microscope (SEM) imaging were employed to assess the healing response at 4, 8, and 12 weeks. Push-out testing revealed PC and PCHA surfaces resulted in significantly greater mechanical fixation over all other implant types at all time points (p <.05). HA coating on the grit-blasted surface significantly improved fixation at 8 and 12 weeks (p <.05). The addition of HA onto the porous coating did not significantly improve fixation in this model. Quantification of ingrowth/ongrowth from SEM images revealed that HA coating of the grit-blasted surfaces resulted in significantly more ongrowth at 4 weeks (p <.05).

Alloys↗
PubMed2000

Patterns of failure at the instrument-tissue interface.

BACKGROUND: The effect of jaw design on grip security and tissue trauma is poorly understood. This project establishes an in vitro model of the instrument-tissue interface. MATERIALS AND METHODS: Aluminum jaws with teeth of differing size and shape gripped fresh sheep stomach with variable apposing (squeeze) pressure. The tissue was extracted at a rate of 50 mm/min until either the grip or the tissue failed. The load at which the grip failed, the maximum (peak) load generated, and the mode of failure were noted. The data were analyzed using ANOVA and a post hoc Duncan's multiple range test when appropriate. RESULTS: Increasing the apposing pressure increased grip security. Grip security of 1- and 2-mm pitch teeth were significantly greater than for plane jaws and smaller-pitch teeth (P < 0.001). Of the wave pattern jaws, 2-mm pitch waves also had significantly greater grip security than plane jaws and smaller pitch waves (P < 0.01). Wave pattern jaws produced significantly less tissue trauma than teeth (P < 0.0001). CONCLUSIONS: Increasing the size of instrument teeth increases grip security but at the expense of tissue trauma. Wave pattern jaws result in significantly less tissue trauma than teeth. This model measures grip security precisely and allows for comparison between jaws of different patterns.

Animals↗
PubMed2000

A new technique of subtrochanteric shortening in total hip arthroplasty: surgical technique and results of 9 cases.

Total hip arthroplasty for severe chronic proximal femoral migration, most commonly seen in congenital dislocation of the hip, has been associated with high rates of complications. A new technique of femoral subtrochanteric shortening osteotomy with the prosthesis in situ is described. This technique minimizes the potential complications, allows for correction of severe femoral neck anteversion, and gives excellent rotational stability, while preserving the proximal femur for better press-fit cementless fixation. In this series, there were 9 cases: 6 women and 2 men with a mean age of 53 years (range, 26-77 years). The average follow-up period was 56 months (range, 6-86 months). The mean preoperative Harris Hip Score was 31 (range, 20-35), and the mean postoperative score was 81 (range, 60-98). At follow-up, all patients reported significant pain relief and functional improvement. All osteotomies appeared to be healed on radiographs by 12 weeks. There were 3 complications. The first complication was a recurrent dislocation resulting from muscle incompetence, which was revised using a constrained liner and a 32-mm head with no further dislocations. The second complication was a breach of the femoral shaft, which was treated operatively using a longer stem. The third complication was a proximal femoral shaft split, which was treated by leaving the cerclage wire in situ. This technique should be considered in cases of congenital dislocation of the hip and when femoral shortening is needed.

Adult↗
PubMed2000

Does the sheep mandible relapse following lengthening by distraction osteogenesis?

AIM: Distraction osteogenesis is a technique used to lengthen the shortened mandible. However, the long term stability of the distracted mandibular bone is not known. The aim of this study was to assess if the sheep mandible relapses following lengthening, and to assess the quality of distracted bone up to 1 year post lengthening. METHODS: Twenty-four sheep had bilateral external mandibular distractors applied, with three sheep as controls. Titanium marker screws were positioned both proximal and distal to the distraction zone in all sheep. Following a 5 day latency period, the interdental gap was distracted 1 mm/day for 20 days, with a subsequent 20 day consolidation period. Ante-mortem serial X-rays were used to assess for relapse by measuring the distance between the screws. The animals were sacrificed at either 3, 6, 9 or 12 months post-distraction. At post mortem, the distance between the screws was re-measured. The distracted bone was assessed mechanically and histologically. RESULTS: The mean mandibular lengthening obtained was 13.2 mm. There was no relapse of the mandible over 12 months. The distracted bone had attained the strength and stiffness of undistracted bone by 6 months post-distraction (p < 0.05). Histological evaluation revealed significant amounts of lamellar bone by 6 months post-distraction. CONCLUSIONS: No relapse occurred for 12 months post distraction lengthening. The bone formed following distraction was stable and of good quality. These findings lend support to the use of distraction osteogenesis in clinical practice.

Analysis of Variance↗
PubMed2000

Increased formation and decreased resorption of bone in mice with elevated vitamin D receptor in mature cells of the osteoblastic lineage.

The microarchitecture of bone is regulated by complex interactions between the bone-forming and resorbing cells, and several compounds regulate both actions. For example, vitamin D, which is required for bone mineralization, also stimulates bone resorption. Transgenic mice overexpressing the vitamin D receptor solely in mature cells of the osteoblastic bone-forming lineage were generated to test the potential therapeutic value of shifting the balance of vitamin D activity in favor of bone formation. Cortical bone was 5% wider and 15% stronger in these mice due to a doubling of periosteal mineral apposition rate without altered body weight or calcium homeostatic hormone levels. A 20% increase in trabecular bone volume in transgenic vertebrae was also observed, unexpectedly associated with a 30% reduction in resorption surface rather than greater bone formation. These findings indicate anabolic vitamin D activity in bone and identify a previously unknown pathway from mature osteoblastic cells to inhibit osteoclastic bone resorption, counterbalancing the known stimulatory action through immature osteoblastic cells. A therapeutic approach that both stimulates cortical anabolic and inhibits trabecular resorptive pathways would be ideal for treatment of osteoporosis and other osteopenic disorders.

Animals↗
PubMed2000

Mechanical and histologic evaluation of Collagraft in an ovine lumbar fusion model.

The purpose of this study was to determine the effectiveness of a composite material composed of Type I bovine dermal collagen, 65% hydroxyapatite, and 35% tricalcium phosphate ceramic (Collagraft Bone Graft Matrix Strip NeuColl Incorporated, Palo Alto, CA) as a bone graft substitute for spinal fusion with and without the use of autologous bone marrow in an ovine lumbar spine model with pedicle screw fixation. Twenty-four adult sheep underwent a single level posterolateral (intertransverse process) L3-L4 lumbar fusion with one of three graft materials combined with rigid pedicle screw fixation. The three graft materials were Collagraft, Collagraft with marrow, and autogenous corticocancellous bone graft. Animals were euthanized 6 months after surgery and evaluated using dual energy x-ray absorptiometry, radiographs, histologic analysis, and mechanical testing. Dual energy xray absorptiometry between the transverse processes revealed that the mineral densities for the two Collagraft groups were significantly higher than the autogenous bone graft group. Histologic analysis confirmed that Collagraft was highly compatible and was well incorporated into the fusion mass. Both Collagraft groups had thick trabeculae and a mixture of lamellar and plexiform bone. The autogenous bone graft group had a smaller fusion complex, composed primarily of lamellar bone with thinner and fewer trabeculae. All three groups had similar mechanical properties. These results support the use of Collagraft in spinal fusion with pedicle screw fixation.

Absorptiometry, Photon↗
PubMed2000

Effect of distraction rate on biomechanical, mineralization, and histologic properties of an ovine mandible model.

Craniofacial microsomia is a common congenital malformation. Ilizarov's method of distraction osteogenesis applied to the mandible has yielded promising results both experimentally and clinically. Because the technique is used predominantly in a pediatric population, length of treatment and compliance may be problematic. To date, the limits of distraction rate in the craniofacial skeleton have not been defined. This study was designed to investigate the effects of distraction rate, in a large animal model, on the mineralization, biomechanical, and histologic properties of lengthened mandibles. Clinically faster distraction rates would decrease the overall treatment time. Twenty-four animals were divided into four groups, with varying rates of distraction (1, 2, 3, and 4 mm/day). A uniaxial distractor at the angle of the mandible was used. The mandibles were lengthened to 24 mm and fixed for a period of 5 weeks, when the animals were killed. The specimens were analyzed with respect to mineralization using dual energy x-ray absorptiometry, biomechanical strength, through a modified three-point bending test, and histologic properties with hematoxylin and eosin stains. Biomechanical, mineralization, and histologic analyses of the samples indicated that group 1 (1 mm/day) samples were significantly superior (p<0.05) to those of group 4 (4 mm/day). Although bone formation was achieved in all groups, group 1 (1 mm/day) demonstrated the strongest biomechanical and histologic properties. Bone mineral density obtained using dual energy x-ray absorptiometry may be clinically useful as a reliable, noninvasive, and relatively cheap predictor for removal time of the fixator.

Animals↗
PubMed2000

A biomechanical comparison of the Z step-cut and basilar crescentic osteotomies of the first metatarsal.

The basilar crescentic osteotomy is a popular procedure for the correction of moderate to severe hallux valgus deformity. Dorsiflexion due to malposition of the osteotomy, fixation failure, or late contracture of the soft tissues can lead to lateral metatarsalgia. This study compares the mechanical properties of the Z step cut osteotomy Scarff to those of the crescentic osteotomy in cantilever-bending. The ultimate load, maximum bending moment and energy absorbed were significantly greater for the Scarff osteotomy compared to those in the crescentic osteotomy (p < 0.001). Values for stiffness did not differ between the two osteotomies. Failure of the cortical bone-bridge between the screw-hole and the osteotomy was observed in all crescentic osteotomies, while fracture of the proximal dorsal bridge was seen in all Scarff osteotomies.

Biomechanical Phenomena↗
PubMed2000

Exposure in difficult total knee arthroplasty using coronal tibial tubercle osteotomy.

Exposure in a total knee arthroplasty can be challenging regardless of whether it is a difficult primary or a revision. Various techniques both proximal and distal to the patella have been described and implemented to gain exposure and improve knee flexion. When patella eversion is not possible due to previous surgery or severe preoperative knee flexion contracture, a coronal tibial tubercle osteotomy may be utilized. We present successful results utilizing the coronal tibial tubercle osteotomy procedure. The technique involved in this series is based on that described by Whiteside. It involves the development of a long lateral musculoperiosteal flap incorporating the tibial tubercle and anterior tibia, and leaving the proximal tibial cortex intact. This is extended along the tibia distally for 10 cm. It finishes by gradually osteotomising the anterior surface of the tibial crest. The tubercle is reattached with wires at the end of the procedure. This technique minimizes complications that have been associated with the tibial tubercle osteotomy. The 10 knees in 9 patients, who had total knee arthroplasty with a coronal tibial tubercle osteotomy, were reviewed pre and postoperatively. All knees were assessed using the Hospital for Special Surgery knee score (HSS). The scores averaged 43.6 preoperatively (range, 29 57) and 79.2 postoperatively (range, 67 90), and the mean range of motion was 59.5 degrees preoperatively and 78.0 degrees postoperatively. There were no cases of extension lag. Fixed flexion deformity was present in 3 cases postoperatively. Average time to union at the proximal and distal ends of the osteotomy was 8 and 24 weeks respectively. There was no evidence of nonunion and no other significant complications occurred.

Journal Article↗