Faculty Bibliography

The bone-implant interface formed in a canine distal femur was examined by means of a Raman microprobe using an implant model designed to test calcium phosphate surface coatings. By using the 960 cm-1 band of calcium phosphate to characterize the interface and adjacent mineral, we obtained spatial and compositional information about the attachment of bone to the synthetic calcium phosphate coating on a titanium support. The interface between bone and the synthetic calcium phosphate is approximately 30-40 microns in width

The use of natural coral as a bone graft substitute is common in Europe. However, the bone-coral bonding mechanism remains elusive. A rat subcutaneous model was used to demonstrate changes at the surface of resorbable calcium carbonate in the form of natural coral. Histological results indicated in vivo formation of a calcium phosphate (CaP)-rich layer on the surface of the coral confirmed by backscattered electron imaging and X-ray microanalysis. There appears to be a combination solution-mediated dissolution/cell-mediated degradation of the natural coral with subsequent surface conversion or precipitation. The end result is a CaP-rich layer on the coral. Though this layer has been observed previously, it was originally thought to be a histological artifact. This result is similar, however, to what is seen with Bioglass and glass ceramics and may also explain the good bonding of bone to hydroxyapatite. The fact that this layer is also present on natural coral after implantation in soft tissue sites may explain the intimate bone apposition observed when natural coral is placed in bony sites

STUDY DESIGN. The ability of hydroxyapatite (HA) materials to enhance the fixation strength of posterior spinal instrumentation was examined in 19 adult mongrel dogs. METHODS. Sixteen dogs underwent bilateral placement of lumbar transpedicular screws from L1 to L6, sacral alar screws, and posterior iliac rods. The six transpedicular screw test groups included standard and plasma-sprayed HA-coated screws with the recommended insertion technique, standard and HA-coated screws with a poor initial fit insertion technique using an oversized pilot hole, and HA-grout augmentation of standard and HA-coated screws with a poor initial fit. The sacral alar screws and posterior iliac rods were either uncoated or HA-coated. Six dogs were killed immediately; ten dogs were killed at 6 weeks, and the fixation elements were mechanically tested or histologically examined. Three additional dogs and synthetic bone material were used for additional baseline mechanical testing. RESULTS. The strength of standard screws with recommended insertion did not change after 6 weeks in vivo. HA-coated screws were initially 13% less resistant to pull out than standard screws, but this difference was not significant at 6 weeks. Screws inserted with a poor initial fit technique were significantly weaker initially; at 6 weeks, pull-out strength was similar to the standard screws properly inserted. The HA-grout material significantly enhanced pull-out strength for both screw types at 6 weeks. Sacral alar screw pull-out strength was not significantly different between standard and HA-coated screws initially or at 6 weeks. HA-coated rods were initially twice as resistant to pull out than standard rods and became stronger after 6 weeks in vivo, whereas standard rods became significantly weaker. Histologically, the quantity and morphology of bone around all implants was similar, with HA-coated rods and screws demonstrating regions of direct attachment to bone. An osteoconductive response and new bone formation was observed within the HA-grout material. Scanning electron microscopic observation of mechanically tested implants revealed a shear failure of surrounding bone (and HA if present) at the screw outer thread margin or at the bone-metal or HA-metal interfaces for the posterior iliac rods. CONCLUSIONS. The strength of poorly inserted transpedicular screws was significantly enhanced in vivo by the resorbable HA-grout material. The lower strength of HA-coated screws was attributed to screw geometry changes resulting from the coating process, and modifications of screw coating are recommended

To evaluate the influence of type I collagen and hydroxyapatite coatings on the ability of Dacron fiber to achieve biologic fixation to bone, tows with the following coatings were evaluated in vivo: avian collagen (A); an avian collagen/hydroxyapatite composite (AH); bovine tendon collagen (B); a bovine tendon collagen/hydroxyapatite composite (BH); and plain (uncoated) Dacron tow (C). The Dacron tows were placed unstressed in the cancellous bone of both lateral femoral condyles of rabbits. Tissue reaction to each kind of Dacron tow was evaluated histopathologically, histomorphometrically and biomechanically. Inflammatory reaction was apparent around the AH and BH Dacron fibers at 2 weeks. There was no such reaction in the A, B, and C specimens, thus implicating the hydroxyapatite particles as the cause. At later time periods specimens A, B, and C all induced new bone formation. Direct contact between the Dacron fibers and trabecular bone was apparent in A and B. The pull-out strength of the B fibers was higher than the controls at a statistically significant level, but there was no significant difference between any of the other specimens and C (controls). There was no significant difference between any coating and controls at 8 or 16 weeks. Dacron fibers coated with bovine tendon collagen exhibited the best biocompatibility to bone and improved the anchoring to bone in the early time intervals by maintaining direct contact between Dacron fibers and trabecular bone.(ABSTRACT TRUNCATED AT 250 WORDS)

BACKGROUND: Carcinoid of the ampulla of Vater is a rare lesion that may produce obstructive jaundice. Analysis of nodal involvement as a function of primary tumor sizes indicated that metastases occur with tumors smaller than 2.0 cm. The case of a 36-year-old woman is presented and the literature reviewed in an attempt to define the treatment of choice. METHODS: The English literature was reviewed, and 27 cases including the current one were identified. All cases were traced to the original case report. Clinical outcome data were tabulated. RESULTS: The mean age of the sample group was 48.5 years, with 52% men and 48% women. Jaundice occurred in 60% of patients. Ampullary carcinoid developed in nine patients in association with von Recklinghausen disease. Treatment included pancreaticoduodenectomy, local excision, and biliary-enteric and endoscopic stenting. Seven patients had positive nodes. Four had metastatic disease at the time of surgical treatment. Long-term survivals of 5.5 years and 5 years were achieved after local excision and pancreaticoduodenectomy, respectively. CONCLUSIONS: Long-term survival is possible after local excision or pancreaticoduodenectomy.

A study was conducted to evaluate the osteoconductive ability of a particulate, low-temperature hydroxylapatite (HA(LT)) material (OsteoGen; Impladent, Holliswood, NY). An implantable chamber model was used to determine the ability of this material to encourage bone ingrowth into channels lined with either rough-surfaced titanium or rough-surfaced plasma-sprayed hydroxylapatite. The HA(LT) material increased bone ingrowth into the titanium-lined channels comparable with that in plasma-sprayed hydroxylapatite-coated channels. It was incorporated into ingrowing bone without intervening soft tissue, with the bone bonding directly to the material surface in much the same fashion as it bonds at the plasma-sprayed hydroxylapatite surface. Mechanical testing of the ingrown bone showed no weakness because particles were incorporated. At 12 weeks, the particles began to show signs of dissolution. It was concluded that the HA(LT) material is a biocompatible, osteoconductive material that conducts bone ingrowth in much the same way as high-temperature particulate hydroxylapatite ceramics. This material has the additional desirable property of being slowly resorbable, a beneficial characteristic for many bone-filling applications

Test implant plates surgically retrieved from distal femurs of dogs were studied by Raman spectroscopy in order to characterize the bone-implant interface. The implant surface consisted of phosphate mineral, plasma sprayed on a titanium substrate. On the basis of its spectroscopic signature, the phosphate mineral of bone and the implant surface formed a mixed phase in the interface

Growth rates of rat tendon fibroblasts cultured in a three-dimensional carbon fiber matrix were compared with those of cells cultured on standard flat culture plates. The carbon fiber has been used as a tissue scaffold for tendon and ligament repair in animal and clinical studies. While cell growth on the culture plates appears to follow a growth curve containing a lag phase, a log phase, and plateau phase of growth, cell growth in the fiber matrix was characterized by a suppressed log phase of growth. SEM and cytotoxicity studies indicated that this effect was not caused by growth-inhibiting or cytotoxic substances from the carbon fiber. While we cannot rule out the possibility that cell growth was influenced by the surface chemistry of the carbon substrate, evidence from this and other studies suggests that the observed effect was caused by a lack of readily available surface area for cell attachment and growth on the small fibers. Because cell colonies growing on individual fibers are limited (at least in theory) to growing in two directions only, they enjoy limited opportunities for cell migration and growth--in contrast with cell colonies on flat culture plates. These results suggest fundamental differences in the mechanisms controlling cell growth on planar vs. three-dimensional fiber substrates

The use of bovine tendon as a xenograft material in humans is attractive because of its ready availability and favorable mechanical characteristics. Previous research has shown that the fibroblasts and some extracellular proteoglycans and glycoproteins, not the collagen matrix itself, in bovine tendon are primarily responsible for its antigenicity. Various attempts have been made to decrease the antigenicity of these grafts. A chloroform/methanol (CM) extraction procedure has been developed that selectively removes the fibroblasts from bovine tendon without destroying the collagen matrix. The mechanical, immunologic, and local host tissue responses to these grafts were compared to autografts and to untreated and glutaraldehyde-treated bovine tendon xenografts. The humoral immune response to a purified bovine Type I collagen product was also studied. The central two-thirds of a rabbit Achilles tendon were replaced with a reversed autograft or an experimental graft. Histologic examination of one- and two- week specimens showed an acute inflammatory response to all grafts. Untreated grafts stimulated a severe inflammatory response and were almost completely resorbed by two weeks. Glutaraldehyde-treated grafts were encapsulated. Cellular repopulation was minimal and inflammatory response was more persistent than in the autograft and CM groups. Inflammatory response to CM-treated grafts was similar to that of autografts. The CM grafts repopulated rapidly with host cells. The mechanical strength of CM grafts was equal to autograft controls at 12 weeks. The mechanical strength of untreated and glutaraldehyde-treated grafts was significantly lower. Measurement of the humoral immune response to these grafts was conducted in an independent group of animals using an enzyme-linked immunosorbent assay. A significant antibody response to untreated, glutaraldehyde-fixed, and CM-treated grafts was detected at 30 days. Antibody titers to glutaraldehyde-fixed and untreated grafts remained elevated at 60 and 90 days. In the CM group, antibody titers decreased to the level of autograft controls by 90 days. No significant antibody response was detected toward purified bovine Type I collagen.

A technique for the insertion of a central venous access device in the patient with thrombocytopenia is described. Using the Seldinger technique, a wire is placed into the internal jugular vein. A catheter tunneled from the anterior part of the chest is inserted through a peel-away sheath into the central venous system. The incision is then closed.