Concerns about reduced strength, fatigue resistance, and oxidative stability of highly crosslinked UHMWPE have limited the acceptance of these materials for TKR. It was hypothesized that a new crosslinked UHMWPE stabilized with vitamin E would substantially improve wear performance and resistance to oxidative degradation without compromising mechanical properties. The purpose of this study was to comprehensively test this hypothesis in vitro.

GUR1020 was machined from isostatic molded bar-stock, crosslinked with 100 kGy, and then doped with vitamin E. This material was compared to direct molded GUR1050 UHMWPE. Both materials were gamma irradiation sterilized as for clinical use. Small punch testing, crack growth rate fatigue testing and oxidation index measurements were performed on each material before and after accelerated aging. Knee simulator testing evaluated wear of each material for 5-million walking cycles. CR knees were tested on a 6-station AMTI knee simulator; PS knees were tested on two 4-station Instron-Stan-more knee simulators. Statistical differences in all metrics were evaluated for significance with ANOVA (p < 0.05).

After 4-week accelerated aging, the control material showed elevated oxidation, loss of small punch mechanical properties and decreased fatigue crack growth resistance. In contrast, the vitamin E stabilized material had minimal changes in these properties. Further, the vitamin E stabilized material exhibited 85% reduction in wear for both the CR and PS designs.

Highly crosslinked UHMWPE stabilized with vitamin E appears to be promising for use as a bearing surface in TKA.

To investigate differences between the Reamer Irrigator Aspirator and the AO reamer on fat embolism outcome using a porcine model.

All animal procedures were approved and performed in accordance with the Animal Care Committee at St. Michael’s hospital. Following anesthetic administration, the animals were stabilised for thirty minutes. One third of the pig’s blood volume was withdrawn to simulate hemorrhagic shock. Each animal was kept in a state of hypovolemia for an hour before transfusion and resuscitation. Once the animal was stabilised surgical exposure of the distal femur was completed. A 12 mm Reamer Irrigator Aspirator or AO reamer was used depending on which group the animal was assigned to. Blood work was obtained at: baseline, immediately after induction of hypovolemia, one hour post hypovolemia, post stabilization, one minute, five minutes, 1.5 hours and three hours after reaming. The results were analyzed for activation of the coagulation system, platelet and neutrophil activation, and cytokine elevation. ANOVA was the primary tool used to assess statistical significance.

There was no statistical difference between the two reamers with respect to PT, APTT, and fibrinogen. There was a statistical difference in D-dimer at 1.5 and three hours post-reaming, with the RIA showing a lower value. Neither reamer demonstrated any systemic platelet nor neutrophil activation. TNF-alpha spiked immediately post-reaming with the RIA group returning to baseline values and the AO group remaining elevated. There is a spike in IL-1B post reaming in the AO group, however this was not seen in the RIA group. No statistical difference was detected between the two reamers.

All markers for platelet and neutrophil activation and the coagulation cascade were measured at the systemic level. Although there is no statistical difference between the RIA and AO reamer, it is possible that activated cells were removed from the systemic circulation and sequestered as thrombi in the pulmonary microvasculature. This hypothesis may be supported by a drop in platelet count and an increase in D-dimer, with the AO reamer suggesting greater thrombi formation. The trends in IL-1B and TNF-alpha seem to suggest that the RIA abrogates the post-reaming proinflammatory state.

This study was undertaken to assess the contribution of pulmonary fat embolism to systemic platelet activation in a rabbit model of fat embolism. Fifteen NZW rabbits were randomly assigned into one of two groups: fat embolism and control. Fat embolism was induced via intramedullary canal pressurization with a 1–1.5 ml bone cement injection. Only the animals that underwent fat embolism displayed consistent platelet activation, as demonstrated by platelet degranulation and procoagulatory surface expression. These findings suggest that fat embolism plays a role in platelet activation and in the overall activation of hemostasis following trauma.

The objective of this study was to use a recently developed rabbit model of fat embolism to assess the systemic hemostatic response to pulmonary fat embolism.

Our findings demonstrate platelet activation following forced liberation of bone marrow contents into the circulation only in the FE group, as demonstrated by CD62P elevation (a marker of platelet degranulation) and annexin V elevation (a marker of procoagulatory surface expression). Platelet activation also coincided with significantly lower platelet counts in the FE group at two and four hours post embolism, suggesting platelet aggregation.

These findings suggest that fat embolism plays a role in platelet activation and in the overall activation of hemostasis following trauma.

Platelet count decreased significantly at two and four hours post knee manipulation only in the FE group. Annexin V expression increased significantly in the FE group at two and four hours post knee manipulation. Lastly, CD62P expression only increased significantly in the FE group at two hours post knee manipulation

Fifteen New Zealand White male rabbits were randomly assigned into one of two groups: control and fat embolism (FE). In FE group (n=8), the intramedullary cavity was drilled, reamed and pressurized with a 1–1.5 ml bone cement injection. In the control group (n=7), a sham knee incision was made, exposing both femoral condyles, but was immediately closed without further manipulations. All animals were mechanically ventilated for an additional monitoring period of four hours post-surgical closure. For flow cytometric evaluation of platelet activation, blood samples were stained with fluorescence-conjugated antibodies against CD41 (FITC), CD62P (P-selectin) and annexin V (FITC). Platelet events were identified by their characteristic CD41 staining and size and were analyzed using a flow cytometer. All animals were mechanically ventilated for four hours post surgical closure.

The implications of platelet activation following fat embolism are numerous, ranging from adherence and aggregation, to secretion of key components of both the coagulation and inflammatory cascades.

The purpose of this study was to determine the effect of positioning (lateral vs. supine) on pulmonary patho-physiology following pulmonary contusion and fat embolism in a canine model of polytrauma. Platelet and neutrophil activation were assessed using flow-cytometry. There were no significant differences between groups in CD62P and CD11/18 MCF (markers of platelet and neutrophil activation, respectively) following fat embolism. However, only animals in the lateral position displayed significant increases in both measures as compared to baseline values. Lateral positioning may exert an early effect on proinflammatory and coagulation activation, and may play a role in the development of acute lung injury.

It has previously been suggested that acute lung injury can be influenced by patient positioning, be it lateral or supine. The purpose of this study was to determine the effect of positioning on pulmonary pathophysiology associated with concomitant pulmonary contusion and fat embolism in a canine model of polytrauma.

Twelve dogs were randomly assigned to one of two surgical positioning groups, lateral and supine. The dogs were subjected to pulmonary contusion by application of force between 200–250 N/m² for thirty seconds in three areas of one lung. Two hours later, fat embolism was induced via reaming of the ipsilateral femur and tibia and cemented nailing. Two hours later, the dogs were sacrificed. For flow-cytometric evaluation of platelet and neutrophil activation, venous blood samples were stained with fluorescence-conjugated antibodies against CD62P and CD11/18, respectively. There were no significant differences between the groups in CD62P and CD11/18 mean channel fluorescence (MCF) following pulmonary contusion and fat embolism. However, only animals in the lateral positioning group displayed significant increases in CD62P and CD11/18 MCF at two hours following fat embolism as compared to baseline values.

Our findings suggest that lateral positioning, autoregulation and preferential blood flow to the contused non-dependent lung may render lung tissue more susceptible to congestion and lead to activation of both platelets and neutrophils. Lateral positioning may have an early effect on activation of the inflammatory and coagulation cascades and may be significant in the development of posttraumatic acute lung injury.

This study was undertaken to assess the contribution of pulmonary fat embolism caused by intramedullary femoral canal pressurization to the development of acute lung injury in the presence of resuscitated hemorrhagic shock. Twenty-seven NZW rabbits were randomly assigned into one of four groups: resuscitated hemorrhagic shock and fat embolism, resuscitated hemorrhagic shock, fat embolism, and control. Fat embolism was induced via intramedullary cavity with a 1–1.5 ml bone cement injection. Only the animals that underwent resuscitated shock and fat embolism displayed amplified neutrophil activation and alveolar infiltration. These findings suggest that the combination of resuscitated shock with fat embolism initiates an inflammatory response, which may play a role in the development of fat embolism syndrome.

The objective of this study was to assess the contribution of pulmonary fat embolism caused by intramedullary femoral canal pressurization to the development of acute lung injury in the presence of resuscitated hemorrhagic shock.

Only the animals that underwent resuscitated shock and fat embolism displayed amplified neutrophil activation and alveolar infiltration.

These findings suggest that the combination of resuscitated shock with fat embolism initiates an inflammatory response, which may play a role in the development of fat embolism syndrome.

CD11b mean channel florescence was only significantly elevated in the HR/FE group at two and four hours post knee manipulation. Moreover, greater infiltration of alveoli by leukocytes was only significantly higher in the HR/FE group as compared to controls.

Twenty-seven NZW rabbits were randomly assigned into one of four groups: resuscitated hemorrhagic shock + fat embolism (HR/FE), resuscitated hemorrhagic shock (HR), fat embolism (FE), and control. Hypovolemic shock was induced via carotid bleeding for one-hour prior to resuscitation. For fat embolism induction, the intramedullary cavity was drilled, reamed and pressurized with a 1–1.5 ml bone cement injection. For evaluation of neutrophil activation, blood was stained with antibodies against CD45 and CD11b and analyzed with a flow cytometer. Animals were mechanically ventilated for four hours post surgical closure. Postmortem thoracotomy was performed, and three stratified random blocks of each lung were processed for histological examination.

Our findings suggest that FE by itself does not cause lung injury, as there were no apparent differences between the control and FE animals. Only the HR/FE animals revealed a higher number of infiltrating neutrophils into alveolar spaces and greater neutrophil activation.

The purpose of this study was to determine the effect of positioning (lateral vs. supine) on pulmonary pathophysiology following pulmonary contusion and fat embolism in a canine model of polytrauma. Platelet and neutrophil activation were assessed using flow-cytometry. There were no significant differences between groups in CD62P and CD11/18 MCF (markers of platelet and neutrophil activation, respectively) following fat embolism. However, only animals in the lateral position displayed significant increases in both measures as compared to baseline values. Lateral positioning may exert an early effect on proinflammatory and coagulation activation, and may play a role in the development of acute lung injury.

It has previously been suggested that acute lung injury can be influenced by patient positioning, be it lateral or supine. The purpose of this study was to determine the effect of positioning on pulmonary pathophysiology associated with concomitant pulmonary contusion and fat embolism in a canine model of polytrauma.

Twelve dogs were randomly assigned to one of two surgical positioning groups, lateral and supine. The dogs were subjected to pulmonary contusion by application of force between 200–250 N/m² for thirty seconds in three areas of one lung. Two hours later, fat embolism was induced via reaming of the ipsilateral femur and tibia and cemented nailing. Two hours later, the dogs were sacrificed. For flow-cytometric evaluation of platelet and neutrophil activation, venous blood samples were stained with fluorescence-conjugated antibodies against CD62P and CD11/18, respectively.

There were no significant differences between the groups in CD62P and CD11/18 mean channel fluorescence (MCF) following pulmonary contusion and fat embolism. However, only animals in the lateral positioning group displayed significant increases in CD62P and CD11/18 MCF at two hours following fat embolism as compared to baseline values.

Our findings suggest that lateral positioning, autoregulation and preferential blood flow to the contused non-dependent lung may render lung tissue more susceptible to congestion and lead to activation of both platelets and neutrophils. Lateral positioning may have an early effect on activation of the inflammatory and coagulation cascades and may be significant in the development of posttraumatic acute lung injury.

The purpose of this study was to determine the effect of positioning (lateral vs. supine) on pulmonary pathophysiology following pulmonary contusion and fat embolism in a canine model of polytrauma. Platelet and neutrophil activation were assessed using flow-cytometry. There were no significant differences between groups in CD62P and CD11/18 MCF (markers of platelet and neutrophil activation, respectively) following fat embolism. However, only animals in the lateral position displayed significant increases in both measures as compared to baseline values. Lateral positioning may exert an early effect on proinflammatory and coagulation activation, and may play a role in the development of acute lung injury.

It has previously been suggested that acute lung injury can be influenced by patient positioning, be it lateral or supine. The purpose of this study was to determine the effect of positioning on pulmonary pathophysiology associated with concomitant pulmonary contusion and fat embolism in a canine model of polytrauma.

Twelve dogs were randomly assigned to one of two surgical positioning groups, lateral and supine. The dogs were subjected to pulmonary contusion by application of force between 200–250 N/m² for thirty seconds in three areas of one lung. Two hours later, fat embolism was induced via reaming of the ipsilateral femur and tibia and cemented nailing. Two hours later, the dogs were sacrificed. For flow-cytometric evaluation of platelet and neutrophil activation, venous blood samples were stained with fluorescence-conjugated antibodies against CD62P and CD11/18, respectively.

There were no significant differences between the groups in CD62P and CD11/18 mean channel fluorescence (MCF) following pulmonary contusion and fat embolism. However, only animals in the lateral positioning group displayed significant increases in CD62P and CD11/18 MCF at two hours following fat embolism as compared to baseline values.

Our findings suggest that lateral positioning, autoregulation and preferential blood flow to the contused non-dependent lung may render lung tissue more susceptible to congestion and lead to activation of both platelets and neutrophils. Lateral positioning may have an early effect on activation of the inflammatory and coagulation cascades and may be significant in the development of posttraumatic acute lung injury.