A Biomechanical Evaluation of Casting Technique and Cast Core Size Effect

BACKGROUNDS

The goals of this study were to (1) compare the effect of casting technique on biomechanical function with different casting materials and different cast core diameters, and (2) compare the strength of a cast based on the number of layers in relation to the core diameter.

METHODS

Two standardized cylindrical cast model sizes were used to simulate forearm and short leg casts (core diameter: 60 mm, 100 mm) with 2 different casting techniques (non-smoothing vs. smoothing with lamination), utilizing 2 casting materials [fiberglass and Plaster of Paris (POP)]. Each cast was created using 3 different layers (Fiberglass: 2 to 4 layers; POP: 3 to 5 layers). Ultimate load-to-failure and flexural rigidity were analyzed through cyclic 4-point bend testing.

RESULTS

The biomechanical comparison between forearm and short leg casts were significantly different regardless of the same number of layers for both casting materials and between 2 casting techniques. Increased cast thickness significantly increased the ultimate load-to-failure and bending strength. An increased core diameter size significantly decreased the cast's ultimate load-to-failure (fiberglass: 50% to 108%; POP: 10% to 93%) and bending strength (fiberglass: 17% to 35%; POP: 37% to 49%). Casting technique with smoothing with lamination technique had a negative biomechanical effect on POP and a minimal effect on fiberglass.

CONCLUSION

The number of layers to apply for a cast should be based on the size of the extremity. Smoothing and lamination technique did not significantly improve the cast mechanical behavior.

CLINICAL RELEVANCE

The findings of this study provide valuable evidence, analysis, and supplementary knowledge that helps guide physicians in proper casting technique.

The Effect of Bone Quality on Treatment of Intertrochanteric Fractures with Helical Blade Versus Lag Screw Fixation in Cephalomedulary Nails

Introduction

The specific aim of this retrospective study was to determine whether bone quality has any effect on the complication rates or overall survivorship between helical blades and lag screws in cephalomedullary nails used for intertrochanteric hip fractures.

Methods

The authors reviewed clinical charts and radiographic studies of patients between January 2012 and August 2019. We reviewed radiographic images (pre-, intra-, and post-operative) to evaluate fracture fixation type, fracture reduction grade, and post-operative complications. We collected dual energy x-ray absorptiometry scan results (T-score) and serum alkaline phosphatase (ALP) isoenzyme activity values to evaluate patient bone quality.

Results

We included 303 cases (helical: 197, screw: 106) in the study. Complications were found in 31 (16%) helical blade cases and 23 (22%) lag screw cases. No statistically significant difference was detected when comparing complication rates with patient bone quality between the two groups. These two groups had similar one-year implant survivorship with respect to T-score, the low ALP level group, and normal ALP level group. The helical blade had higher implant survivorship compared to lag screw in five-year survival rate with respect to osteoporotic group, high ALP level group, and normal ALP level group (osteoporotic: 77% vs 69%, high ALP: 73% vs 67%, normal ALP: 70% vs 64%).

Conclusions

Similar complication rates were observed between helical blade and lag screw constructs in cephalomedullary femoral nails when accounting for patient bone quality. However, the helical blade design had a higher five-year survival rate.

Intestinal graft versus native liver cytokine expression in a rat model of intestinal transplantation: effect of donor-specific cell augmentation

INTRODUCTION

Immunomodulation by portal vein delivery of donor antigen reduces intestinal graft rejection. We investigated the impact of portal venous donor-specific cell augmentation (blood versus bone marrow) on cytokine expression in intestinal grafts versus native livers.

METHODS

Ten groups of intestinal transplants (brown Norway male to Lewis female rats) varied by (1). the type of donor-specific cell augmentation and (2). the use and dose of tacrolimus-based immunosuppression. Tissue samples for histologic analysis and cytokine mRNA analysis were obtained at designated time points.

RESULTS

Without immunosuppression, no type of cell augmentation reduced the rate of rejection. With immunosuppression, outcome was significantly better after portal donor-specific blood transfusion (versus bone marrow infusion). Irrespective of the type of cell augmentation, severe rejection caused strong intragraft expression of IL-1alpha, IL-1beta, IFN-gamma, and TNF-alpha; liver expression mainly involved TNF-alpha. Of note, nonimmunosuppressed, cell-augmented rats showed hardly any differences in cytokine expression in their grafts versus significant increases in their native livers. With immunosuppression, bone marrow infusion (versus blood transfusion) increased intragraft cytokine expression of IL-1alpha, IL-1beta, IFN-gamma, as well as TNF-alpha, and liver expression of IL-1beta.

CONCLUSIONS

(1). Rejection and donor-specific cell augmentation independently caused differences in intragraft versus native liver cytokine expression after intestinal transplants. (2). Portal donor-specific blood transfusion (versus bone marrow infusion) lowered the incidence of rejection and diminished intragraft cytokine up-regulation. (3). In our study, TNF-alpha appeared to be the cytokine most strongly associated with rejection.

Continuity between wound macrophage and fibroblast phenotype: analysis of wound fibroblast phagocytosis

Analysis of phagocytic activity in wound fibroblasts was chosen as a means to assess the possible continuity between macrophage and fibroblast phenotypes. Fibroblast phagocytosis of uncoated, IgG-coated, or collagen-coated fluorescent beads was analyzed by flow cytometry in vivo and in vitro. Phagocytosis of fluorescent beads by procollagen I-positive cells (fibroblasts) was evaluated in vivo by injecting beads into subcutaneously implanted sponge wounds in anesthetized Fisher rats. Phagocytic activity of a purified population of wound fibroblasts was measured in vitro and correlated with oxidation state using hydroethidium. In the wound environment, 50-60% of the cells that engulfed uncoated, IgG-coated, or collagen-coated beads were procollagen I-positive cells (i.e., fibroblasts). Procollagen I-positive cells engulfed uncoated and IgG-coated beads in preference to collagen-coated beads in vivo. Cultured wound fibroblasts engulfed uncoated, IgG-coated, and collagen-coated particles. The majority of fibroblasts that engulfed beads were in an elevated oxidation state. We conclude that substantial fibroblast phagocytosis occurs in the wound, but scavenger receptor-mediated fibroblast phagocytosis is different from that of macrophages. Additional markers will be helpful in defining the macrophage fibroblast continuum.

Insulin is degraded extracellularly in wounds by insulin-degrading enzyme (EC 3.4.24.56)

The exact mechanism by which insulin reverses impaired wound healing is unknown. Previous investigators have shown that insulin is degraded in experimental wounds, suggesting that the action of insulin may be locally modified. The following study corroborates these findings and identifies the major proteinase responsible for insulin degradation in wound fluid (WF). Adult male Fisher rats were wounded by subcutaneous implantation of polyvinyl alcohol sponges while under pentobarbital sodium anesthesia. WF and serum were collected on 1, 5, 10, and 14 days postinjury. Decreased insulin concentration in late WF correlated with an increased insulin-degrading activity. Multiple proteinases appear to participate in the overall degradation of insulin in WF. However, the primary enzyme responsible for insulin degradation in WF was characterized by immunoprecipitation and immunoblotting and identified as the neutral thiol-dependent metalloproteinase, insulin-degrading enzyme (EC 3.4.24.56). Exogenous steroid administration caused a decrease in WF insulin-degrading activity. Glucagon and adrenocorticotrophin degradation was also observed, whereas minimal degradation of insulin-like growth factors I and II and epidermal growth factor was detected in WF. The ability to extracellularly degrade insulin may represent a unique mechanism for the regulation of this hormone's role in healing wounds.

Altered wound arginine metabolism by corticosterone and retinoic acid

Arginine metabolism plays an important role in many aspects of inflammation and wound healing. In this study, we tested the hypothesis that steroids and vitamin A have differential effects on arginine metabolism and thereby may provide a mechanism by which steroids impair wound healing, and vitamin A improves this impairment. Rats were treated with subcutaneous corticosterone pellets 2 days prior to wounding. Intraperitoneal injections of all-trans retinoic acid in peanut oil were administered at the same time and repeated 2 and 4 days later. Polyvinyl alcohol sponges were implanted subcutaneously through a dorsal incision. On Postwounding Days 1, 5, 10, and 15, wound fluid was recovered from the sponges and assayed for nitrite/nitrate (NOx), citrulline, arginine, and ornithine concentrations as well as arginase activity. Steroid treatment decreased the metabolism of arginine to nitric oxide in the early phase of wound healing, and retinoic acid did not change this relationship. Corticosterone also decreased metabolism of arginine to ornithine in the later wound. This depression was inhibited by concomitant administration of retinoic acid. Considering the importance of nitric oxide in host defense and ornithine as a precursor for polyamine and proline synthesis, these data provide a mechanism by which vitamin A improves wound strength, but does not improve wound infection rates in steroid-treated animals.

Differential regulation of macrophage arginine metabolism: a proposed role in wound healing

Nitric oxide (NO) and ornithine, products of NO synthase or arginase, respectively, have opposing biological activities. The effect of mediators of leukocyte activation and inhibition on arginine metabolism of resident mouse peritoneal exudate cells (MPEC) was determined. Factors that increased basal NO synthase activity, interferon (IFN)-gamma and lipopolysaccharide (LPS), decreased arginase activity in intact cells. Transforming growth factor (TGF)-beta1 decreased IFN-gamma-stimulated NO synthase activity and produced a reciprocal increase in urea and ornithine release. TGF-beta1 had no effect on the activity of these enzymes in LPS-stimulated MPEC. Corticosterone (Cort, 100 ng/ml) decreased the basal activity of both enzymes. However, Cort inhibited NO synthase activity and increased ornithine release in MPEC exposed to IFN-gamma or LPS. The difference between arginase activity in intact cells vs. that of cell lysates suggested intracellular inhibition of arginase activity. Products of NO synthase, NO and citrulline, were shown to inhibit MPEC arginase activity under maximal assay conditions. Intracellular pH was not altered by exposure of MPEC to LPS, IFN-gamma, TGF-beta, and Cort. This reciprocal change in arginine metabolism is proposed to be an important component of wound healing. Expression of NO synthase creates a cytotoxic environment that may be important to the early phase of wound healing. As wound healing progresses, increased arginase activity produces an environment favorable for fibroblast replication and collagen production.

Wound fluid amino acid concentrations regulate the effect of epidermal growth factor on fibroblast replication

Growth factors and amino acids (AA) are required for cell proliferation. A comparison of the AA composition of wound fluid (WF) to that of Eagle's medium reveals that AA in WF may be limiting to cell replication. Yet WF supports fibroblast replication and stimulates AA uptake. Epidermal growth factor (EGF) stimulates fibroblast replication and stimulates human wound healing when applied topically. We evaluated the interactions between EGF and AA concentrations found in WF. Wound fibroblasts were cultured in media prepared to mimic the AA concentrations found in WF on days 1, 5, and 10 and in the presence of varying concentrations of EGF. Fibroblasts cultured in all three experimental media showed a dose response to EGF for both tritiated-thymidine uptake (proliferation) and AA uptake. The fibroblast proliferation in response to EGF was augmented by the AA composition of day-5 WF. These data show a dose-dependent effect of EGF on fibroblast replication and AA uptake in the absence of serum that is augmented by the particular AA combination found in day-5 WF and suggests that an optimal physiologic AA profile may aid in EGF stimulation of wound fibroblast replication.

Glucose metabolism in injured tissue: a longitudinal study

Injured tissue is characterized by increased glucose uptake and increased lactate production as compared to normal tissue. These metabolic changes have been attributed to the presence of inflammatory cells in injured tissues. To correlate these metabolic changes with changes in the inflammatory cell population at various times after injury, we studied the lambda-carrageenan hindlimb wound model in anesthetized rats. Perfusion studies demonstrated that at 3 and 5 days after injury glucose uptake was increased in injured hindlimbs, compared with hindlimbs from pair-fed control animals. At 3, 5, and 10 days after injury, lactate production from glucose was increased in injured hindlimbs, compared with hindlimbs from pair-fed control animals. These metabolic changes were not related to differences in body weight or food intake. There was no difference in glucose oxidation or in oxygen consumption in injured hindlimbs, compared with hindlimbs from pair-fed control animals. The increased glucose uptake and increased lactate production from glucose was coincident with the presence of inflammatory cells--predominantly macrophages--at the site of injury. It is suggested that the glucose metabolism in injured tissue reflects the metabolism of the inflammatory cells at the site of injury.

The effect of endotoxin on glucose metabolism in skeletal muscle requires the presence of plasma

The administration of endotoxin in vivo results in an increase in glucose utilization through an as yet undetermined mechanism. This study evaluated (1) the contribution of blood to the increased glucose utilization noted following endotoxemia, (2) the direct action of endotoxin on skeletal muscle glucose uptake in an isolated hindlimb perfusion system and in incubated muscle, and (3) the possibility that the increased glucose uptake in skeletal muscle mediated by endotoxin requires the presence of plasma. Incubation of blood with 50 and 100 mg/L of endotoxin increased glucose uptake and lactate production in a dose-dependent manner. Muscle incubations and perfusions in the absence of plasma and white blood cells showed that glucose uptake and lactate production were not affected by the presence of 50 to 250 mg/L of endotoxin, while 500 mg/L of endotoxin produced a 26.2% decrease in glucose uptake. In contrast, incubation of muscle in the presence of plasma and endotoxin increased glucose uptake by 37%. These findings suggest that (1) the increased glucose utilization of endotoxemia is only partially explained by increased glucose metabolism by blood, (2) endotoxin does not have a direct effect on the glucose uptake of skeletal muscle, and (3) an interaction of endotoxin with a component of plasma is required for an endotoxin-mediated increase in glucose utilization by skeletal muscle.

Somatomedin-A inhibits glucagon-stimulated hepatic gluconeogenesis

Somatomedin/insulin-like growth factors have been noted to produce insulin-like actions on the liver that include the ability to inhibit the formation of glucagon-stimulated but not basal c-AMP production. This raises the possibility that these compounds may also be able to inhibit glucagon-stimulated hepatic gluconeogenesis. The purpose of this study was to determine the effects of varying concentrations of somatomedin-A on glucagon-stimulated gluconeogenesis in isolated perfused rat liver. The infusion of glucagon increased the rate of gluconeogenesis from 0.0038 +/- 0.001 to 0.042 +/- 0.007 microM 14C-glucose made from 14C-alanine per min. This action of glucagon was reduced to 22% of its maximum by the coinfusion of 1 microU/ml of SM-A and completely eliminated by the coinfusion of 100 microU/ml of SM-A. Somatomedin alone did not alter the basal rate of gluconeogenesis. The decrease in the release of 14C glucose from livers that had been stimulated by glucagon could not be attributed to increased glycogenolysis. Thus, it appears that the reduction in 14C release represents SM-A mediated reduction in glucagon-stimulated gluconeogenesis.

Glucose uptake and flux through phosphofructokinase in wounded rat skeletal muscle

Skeletal muscle injured with lambda-carrageenan has increased aerobic glycolysis. To assess the regulation of this process, the tissue concentrations of glycolytic intermediates, the flux through phosphofructokinase (PFK), and the intracellular concentrations of PFK effectors were examined in wounded rat skeletal muscle and in macrophages, the predominant inflammatory cell in the early stages of this wound model. Autoradiography demonstrated increased 2-deoxy-D-glucose uptake in wounded tissue compared with nonwounded muscle. 2-Deoxy-D-glucose was localized to the cellular infiltrate. The glycolytic intermediate concentrations demonstrated a facilitation of PFK in macrophages and wounded tissue as compared with nonwounded muscle. Wounded tissue had twice the flux through PFK compared with nonwounded muscle (10.0 +/- 0.6 wounded vs. 4.9 +/- 0.4 mumol.h-1.g-1 nonwounded). Macrophages had the highest flux through PFK (63.7 +/- 5.7 mumol.h-1.g-1) and when coincubated with muscle, the combined flux through PFK was equal to that of wounded muscle. The increase in glycolysis associated with wounded tissue may be explained by increased glucose uptake and increased flux through PFK by the inflammatory cells present in wounded tissue.

The temporal characteristics of the metabolic and endocrine response to injury

The neuroendocrine and substrate responses immediately after injury have been extensively investigated in man and animals. The purpose of the present study was to examine simultaneously, the temporal, metabolic and endocrine consequences of a single uniform injury induced by the injection of lambda-carrageenan into the hindlimbs of male Sprague-Dawley rats and to compare this response to that observed in semistarved pair-fed control animals. Immediately after injury there was a decrease in the plasma hematocrit, increase in tissue water and peripheral vasoconstriction that suggested hypovolemia. This was followed by a restoration of the blood volume by 1 day as reflected in hemodilution. Alterations in insulin, glucagon, ACTH, corticosterone, epinephrine, norepinephrine, and dopamine in wounded animals occurred during the first 5 days. However, similar changes were observed in pair-fed control animals from days 1 to 5. These findings implied that the early endocrine response observed from 0 to 24 hours after injury arises, primarily as a result of hypovolemia, whereas the response observed from 1 to 5 days appeared to be the result of semistarvation. In contrast to the endocrine alterations observed, alterations in the plasma concentrations of lactate, acetoacetate and beta-hydroxybutyrate persisted for up to 15 days. The presence of these substrate alterations in the absence of hormonal stimuli suggest that nonendocrine mechanisms exist to induce these alterations. The possibility is raised that these substrate alterations may be, at least in part, the result of the inflammatory infiltrate.

The relationship of purine metabolism to the macrophage-mediated increase of high energy phosphates in skeletal muscle

Previous investigations have demonstrated that the high energy phosphate and adenine nucleotide content of wounded tissue are decreased. Purine metabolism was investigated in incubated lambda-carrageenan wounded skeletal muscle and in muscle exposed to peritoneal macrophages or macrophage-conditioned media. Wounded muscle released predominately uric acid into the incubation medium; whereas, nonwounded muscle released inosine, hypoxanthine, and xanthine as well as uric acid. Macrophages incubated with nonwounded muscle changed the purine release pattern toward one of wounded muscle. The conversion of inosine to allantoin and uric acid by macrophages increased linearly with the addition of up to 1 X 10(7) macrophages per incubation. Muscles incubated in macrophage-conditioned media had a decreased release of inosine and hypoxanthine and higher tissue levels of creatine phosphate, ATP, ADP, AMP, and adenosine compared to muscles incubated in standard media. These data suggest that the macrophage determines the pattern of purine release from wounded skeletal muscle in the incubated system and that in conditioned media a high energy phosphate promoting factor may exert its effect by mechanisms that augment the adenine purine pool.

Can lactate be used as a fuel by wounded tissue?

The role of lactate in the metabolism of the healing wound is poorly understood. The purpose of the present studies was to determine if despite a net lactate production, wounded (Wx) tissue could metabolize lactate and use it as an oxidative fuel. The extensor digitorum longus muscles (EDL) of weanling, male, Fischer rats were injured with lambda-carrageenan or injured thermally, and 5 and 3 days later, respectively, were incubated in a standard incubate that contained varying amounts of lactate (0 to 6 mmol/L added). Lactate uptake and oxidation, occurred in lambda-carrageenan Wx EDL, thermally injured EDL and non-Wx EDL in a dose-dependent manner. At lactate concentrations of less than 3 mmol/L in the incubate, there was net lactate production, but at lactate concentrations of 6 mmol/L there was no net lactate production by both Wx and non-Wx EDL. The increase in lactate oxidation was not associated with an alteration in the tissue content of adenosine triphosphate or creatine phosphate. It was associated with a reduction in glucose oxidation in Wx and non-Wx EDL and by a decrease in glucose uptake by Wx EDL. These data suggest that lactate may be used as an oxidative fuel by wounded tissue and in this regard may substitute for glucose.

Alteration in pyruvate metabolism in the liver of tumor-bearing rats

Weight loss associated with tumor burden has been postulated to be due to an energy imbalance resulting from increased hepatic gluconeogenesis secondary to Cori cycle activity. The mechanisms which control pyruvate metabolism are inherent to the control of gluconeogenesis in the liver. Therefore, the metabolism of pyruvate was evaluated in a transplanted tumor model in rodents which has previously shown an increased rate of hepatic gluconeogenesis. Female Lewis-Wistar rats received a s.c. injection of a suspension of mammary tumor cells in the left flank. Tumor-bearing rats were allowed ad libitum food consumption, and non-tumor-bearing controls were pair-fed to the consumption of their tumor-bearing cohorts. At Days 12, 13, and 14 following inoculation, tumor-bearing and non-tumor-bearing controls were used for in vivo body composition analysis or subjected to isolated liver perfusion. Animals were not fasted prior to sacrifice. Pyruvate use by the livers of tumor-bearing and pair-fed non-tumor-bearing rats was evaluated in the presence of 8 mM glucose and 5 mM lactate. Pyruvate clearance was increased by 270%, and pyruvate intake was increased by 212% compared to pair-fed non-tumor-bearing rats. Oxidation of pyruvate to CO2 was increased 130%, and pyruvate conversion to lactate was increased by 197% above that seen in pair-fed non-tumor-bearing rats. Gluconeogenesis from pyruvate was increased by 184% in tumor-bearing rats. The increased gluconeogenesis in tumor-bearing rats above that of control animals at a 5 mM lactate concentration suggests that some factor, other than substrate supply, may stimulate gluconeogenesis in tumor-bearing rats. Although the use of pyruvate was greater in tumor-bearing rats, the disposal of pyruvate carbon into CO2, lactate, and glucose was proportionally the same in both groups. Therefore, these data suggest that the increased metabolism of pyruvate in tumor-bearing rats is controlled by a mechanism affecting cellular pyruvate transport.