Efficacy and biocompatibility of a photopolymerized, synthetic, absorbable hydrogel as a dural sealant in a canine craniotomy model.

OBJECT: A canine craniotomy model was used to evaluate the dural sealing efficacy and biocompatibility of a novel, synthetic, bioresorbable hydrogel. METHODS: Bilateral craniotomies were performed in 24 dogs assigned to six survival periods. In each animal a parasagittal durotomy was created and then repaired. At the treatment sites the hydrogel sealant was applied over the dural repair and photopolymerized. The repair was tested for leaks to 20 cm H2O by using a Valsalva maneuver. At the control sites the incisions were sutured and tested for leaks only. After uneventful survival periods, the leak test was repeated in three of the four animals in each group. Bone-dura adhesion was evaluated, after which the dura and underlying brain were removed, fixed, and examined histologically. En bloc histological investigation was performed on a specimen obtained from the fourth animal in each group. Over a 56-day period, 18 treated sites were tested for leaks. A leak was detected at a site remote from that of the repair in one animal; this was excluded from analysis. Thus 17 of 17 treated sites remained free of leaks. On the control side of one animal, there was a leak from a new dural tear at the cranial end of the durotomy, which occurred when the bone flap was removed. This site was also excluded from analysis. Eleven of 17 leak-tested control sites remained free of leaks over the study period. Bone-dura adhesions occurred in 15 of 19 control sites and had a mean adhesion score of 1.37 (range 0-4), whereas adhesions occurred in 10 of 19 treated sites with a mean adhesion score of 0.84 (range 0-3). No cortical reaction was noted. CONCLUSIONS: This novel hydrogel sealant is efficacious in sealing dural repair sites measuring up to 2 mm. Healing of the underlying dura is not compromised and exposed cortical tissue is not altered histologically.

In vivo forces during remodeling of a two-segment anterior cruciate ligament graft in a goat model.

An existing goat model was used to measure in vivo graft forces during walking, to determine if the forces set at surgery change over time under the same external load and if the forces in the graft during in vivo function can be dictated by the forces set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a composite graft consisting of a bone-patellar tendon-bone autograft and a synthetic augmentation segment. The forces in the graft segments were established intraoperatively by a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force, and in the seven other animals, the augmentation segment was set to carry 90% of the total force. The total graft force was the same in all animals. Graft forces due to anterior tibial loads of 67 N were measured before and after fixation and 6 weeks after surgery with the use of buckle transducers mounted extra-articularly over the anterior tibia. They were also measured during straight, level walking at 6 weeks. The forces changed significantly from just after surgery to 6 weeks later, such that the initially set load-sharing was eliminated by 6 weeks. At 6 weeks, a relatively smooth gait had been achieved, and the maximum total graft force in each animal during walking averaged 35 N and was of similar magnitude to forces generated by the anterior tibial loads of 67 N with the animal anesthetized. After fixation, forces in the tendon graft segments were significantly different between the group with high set forces and that with low set forces. At 6 weeks, when functional joint loads were approaching normal levels, the graft segment forces for the two groups were not significantly different. Load-sharing between tendon and augmentation segment and load in the tendon segment at 6 weeks could not be dictated at surgery.

Intraoperative force-setting did not improve the mechanical properties of an augmented bone-tendon-bone anterior cruciate ligament graft in a goat model.

It has been hypothesized that load affects the mechanical properties of an anterior cruciate ligament graft while it remodels. The goal of this study was to use an existing goat model to evaluate the effect of intraoperative set force on the postoperative mechanical properties of an autograft that had been augmented with a synthetic segment. The following questions were addressed. Do augmented autografts set with a high force intraoperatively have improved structural and material graft properties and lower anterior-posterior knee laxity at 3 months after surgery, compared with autografts set with a low intraoperative force? How do the structural and material properties of these implanted autografts compare with the mechanical properties of an intact anterior cruciate ligament or an unimplanted control autograft? The anterior cruciate ligament was reconstructed in seven goats with use of a composite graft consisting of a bone-patellar tendon-bone autograft and a synthetic augmentation device. A force-setting technique was used intraoperatively to establish the load-sharing between the autograft and augmentation segments such that the autograft carried either a high (16.5 N in four animals) or low (1.5 N in three animals) level of force, while the total force in the composite graft remained constant. Tensile testing was performed at 3 months after surgery to determine the material and structural properties of the autograft, the intact anterior cruciate ligament from the normal contralateral knee, and a control bone-patellar tendon-bone graft of similar size that was harvested from the contralateral knee at the time of necropsy and had never been implanted in the joint. The structural and material properties of the autografts initially set to high or low loads at surgery were not significantly different after 3 months of implantation. The strength and stiffness of the implanted tendons were an average of 24 and 20% of the strength and stiffness of the normal anterior cruciate ligament and 31 and 62% of the control tendons, respectively. Intraoperative set force in an augmented anterior cruciate ligament graft at the levels chosen in this study did not significantly affect weakening of the autograft at 3 months.

Method for establishing and measuring in vivo forces in an anterior cruciate ligament composite graft: response to differing levels of load sharing in a goat model.

In order to determine the appropriate load history for optimal remodeling of an anterior cruciate ligament graft, methods for establishing and measuring the graft force due to an external load could be set to a preselected value in in vivo are required. Our objectives with this study were to (a) develop a method in which the graft force due to an external load could be set to a preselected value in a living animal, (b) show that this force could be maintained after fixation, and (c) determine what happens to the forces after the animal has functioned for as long as 2 weeks postoperatively, when differing levels of load sharing between the segments had been set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a bone-patellar tendon-bone graft and a synthetic augmentation device. The forces in the graft segments were established, at the time of surgical fixation, with use of a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force; in the remaining seven animals, the augmentation segment was set to share 90% of the total graft force. Graft forces were measured, with the use of buckle transducers mounted extra-articularly over the anterior tibia, under a 67 N anterior tibial load at 60 degrees of knee flexion before and after fixation and at 2 weeks postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinicopathologic and histologic evaluation of Dirofilaria immitis-induced nephropathy in dogs.

Twelve beagles were infected with 200 Dirofilaria immitis infective larvae to study glomerular lesions associated with filariasis. All developed high serum levels of antibodies to dirofilarial antigens and became persistently microfilaremic. The dogs were killed at various times between 398 and 562 days post-infection and renal lesions were examined by light, electron, and immunofluorescent microscopy and antibody elution techniques. A membranoproliferative glomerulonephritis was observed in all dogs. Immunofluorescence was positive in all; predominantly in a fine granular pattern along the glomerular capillary wall. Ultrastructural examination showed intramembranous globular electron-dense deposits and a linear band of fine electron-dense particles in all dogs. Antibody elution studies demonstrated antibody reactive to dirofilarial antigens. In a subsequent experiment, an aqueous-soluble antigen prepared from adult female D. immitis was infused into the renal arteries of 5 heartworm-naive dogs. Immunofluorescent examination of the infused kidneys showed dirofilarial antigen present on the glomerular capillary wall in a fine granular pattern indicating there was adherence of the antigen to the capillary wall. These observations support the hypothesis of in situ immune complex formation as part of the pathogenesis of glomerulonephritis associated with dirofilariasis.

Ultrastructural immunocytochemical co-localization of serotonin and PNMT in adrenal medullary vesicles.

Previous immunocytochemical studies at the light microscopic level have demonstrated serotonin immunoreactivity in rat adrenal epinephrine-containing cells. In this study we have used electron microscopic immunocytochemical methods to study the subcellular distribution of serotonin and the enzyme responsible for epinephrine biosynthesis, phenylethanolamine-N-methyltransferase (PNMT). The distribution of the immunostaining was compared in adjacent serial thin sections using a post-embedding method in conjunction with peroxidase-antiperoxidase (PAP) immunocytochemistry. Serotonin immunoreactivity was associated with the limiting membrane as well as with the core of the chromaffin vesicles. In adjacent sections PNMT immunoreactivity was also seen in the serotonin-containing vesicles. However, its intravesicular distribution was different from that of serotonin; PNMT occupied the eccentric zone of the vesicles between the serotonin immunoreactive sites. These results are interpreted to be in support of biochemical studies claiming a serotonin uptake and storage capacity of adrenal chromaffin vesicle fractions as well as those which suggest serotonin is synthesized by chromaffin cells. The relative contribution of uptake and synthesis to the pool of serotonin that is stored in the vesicles is an open question. The co-localization of serotonin and PNMT in the same vesicle is suggestive of a capacity for co-release of serotonin and epinephrine by the adrenal medulla.