John Street

Vascular endothelial growth factor stimulates bone repair by promoting angiogenesis and bone turnover

Several growth factors are expressed in distinct temporal and spatial patterns during fracture repair. Of these, vascular endothelial growth factor, VEGF, is of particular interest because of its ability to induce neovascularization (angiogenesis). To determine whether VEGF is required for bone repair, we inhibited VEGF activity during secondary bone healing via a cartilage intermediate (endochondral ossification) and during direct bone repair (intramembranous ossification) in a novel mouse model. Treatment of mice with a soluble, neutralizing VEGF receptor decreased angiogenesis, bone formation, and callus mineralization in femoral fractures. Inhibition of VEGF also dramatically inhibited healing of a tibial cortical bone defect, consistent with our discovery of a direct autocrine role for VEGF in osteoblast differentiation. In separate experiments, exogenous VEGF enhanced blood vessel formation, ossification, and new bone (callus) maturation in mouse femur fractures, and promoted bony bridging of a rabbit radius segmental gap defect. Our results at specific time points during the course of healing underscore the role of VEGF in endochondral vs. intramembranous ossification, as well as skeletal development vs. bone repair. The responses to exogenous VEGF observed in two distinct model systems and species indicate that a slow-release formulation of VEGF, applied locally at the site of bone damage, may prove to be an effective therapy to promote human bone repair.

Is human fracture hematoma inherently angiogenic

This study attempts to explain the cellular events characterizing the changes seen in the medullary callus adjacent to the interfragmentary hematoma during the early stages of fracture healing. It also shows that human fracture hematoma contains the angiogenic cytokine vascular endothelial growth factor and has the inherent capability to induce angiogenesis and thus promote revascularization during bone repair. Patients undergoing emergency surgery for isolated bony injury were studied. Raised circulating levels of vascular endothelial growth factor were seen in all injured patients, whereas the fracture hematoma contained significantly higher levels of vascular endothelial growth factor than did plasma from these injured patients. However, incubation of endothelial cells in fracture hematoma supernatant significantly inhibited the in vitro angiogenic parameters of endothelial cell proliferation and microtubule formation. These phenomena are dependent on a local biochemical milieu that does not support cytokinesis. The hematoma potassium concentration is cytotoxic to endothelial cells and osteoblasts. Subcutaneous transplantation of the fracture hematoma into a murine wound model resulted in new blood vessel formation after hematoma resorption. This angiogenic effect is mediated by the significant concentrations of vascular endothelial growth factor found in the hematoma. This study identifies an angiogenic cytokine involved in human fracture healing and shows that fracture hematoma is inherently angiogenic. The differences between the in vitro and in vivo findings may explain the phenomenon of interfragmentary hematoma organization and resorption that precedes fracture revascularization.

Pneumatic Tourniquets in Extremity Surgery

Pneumatic tourniquets maintain a relatively bloodless field during extremity surgery, minimize blood loss, aid identification of vital structures, and expedite the procedure. However, they may induce an ischemia‐reperfusion injury with potentially harmful local and systemic consequences. Modern pneumatic tourniquets are designed with mechanisms to regulate and maintain pressure. Routine maintenance helps ensure that these systems are working properly. The complications of tourniquet use include postoperative swelling, delay of recovery of muscle power, compression neurapraxia, wound hematoma with the potential for infection, vascular injury, tissue necrosis, and compartment syndrome. Systemic complications can also occur. The incidence of complications can be minimized by use of wider tourniquets, careful preoperative patient evaluation, and adherence to accepted principles of tourniquet use.

Tourniquet-induced systemic inflammatory response in extremity surgery.

BACKGROUND Tourniquet-induced reperfusion injury in animals produces significant systemic inflammatory effects. This study investigated whether a biologic response occurs in a clinically relevant model of tourniquet-induced reperfusion injury. METHODS Patients undergoing elective knee arthroscopy were prospectively randomized into controls (no tourniquet) and subjects (tourniquet-controlled). The effects of tourniquet-induced reperfusion on monocyte activation state, neutrophil activation state, and transendothelial migration (TEM) were studied. Changes in the cytokines implicated in reperfusion injury, tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-10 were also determined. RESULTS After 15 minutes of reperfusion, neutrophil and monocyte activation were significantly increased. Pretreatment of neutrophils with pooled subject (ischemia-primed) plasma significantly increased TEM. In contrast, TEM was not significantly altered by ischemia-primed plasma pretreatment of the endothelial monolayer. Significant elevation of tumor necrosis factor-alpha and IL-1beta were observed in subjects compared with controls after 15 minutes of reperfusion. There was no significant difference in serum IL-10 levels between the groups at all the time points studied. CONCLUSION These results indicate a transient neutrophil and monocyte activation after tourniquet-ischemia that translates into enhanced neutrophil transendothelial migration with potential for tissue injury.

The angiogenic response to skeletal injury is preserved in the elderly

Angiogenesis is essential for normal bone formation and repair. Avascularity characterizes aberrant fracture union in the elderly, while angiogenic mechanisms during cutaneous wound repair are attenuated in aged humans. We hypothesized that skeletal injury results in local (circulating) and systemic (fracture site) ‘angiogenic’ responses and that these reparative mechanisms are attenuated with advanced patient age. This prospective study examined peripheral blood and fracture hematoma from 32 patients, 16 under 40 years and 16 over the age of 75, undergoing emergent surgery for isolated fracture. The angiogenic cytokines vascular endothelial growth factor (VEGF) and platelet‐derived growth factor (PDGF) were assayed. Endothelial cell cultures were supplemented with patient plasma and fracture hematoma and angiogenesis determined in vitro by measuring cell proliferation and blood vessel tube formation. Angiogenesis was determined in vivo using a murine dorsal wound pocket model and quantification of new blood vessel formation after 7 days. We found that all injured patients, irrespective of age, have elevated plasma and fracture hematoma levels of VEGF and PDGF. These elevated cytokine concentrations translate into biologically significant angiogenic effects, in vitro and in vivo. These effects are primarily VEGF mediated and are not dependent on patient age. The biological activity of these growth factors does not diminish with advanced age. Thus skeletal injury does result in local and systemic angiogenic responses whereby angiogenic cytokine availability and activity is preserved in the aged suggesting alternative mechanisms for the development of avascularity in delayed and fracture non‐union in the elderly.

Thromboprophylaxis using a low molecular weight heparin delays fracture repair.

Low molecular weight heparins are significantly superior to unfractionated heparin or warfarin in the prevention of thromboembolic episodes associated with orthopaedic surgery. Therapeutic doses of heparin and warfarin have been shown to delay bone repair in a rabbit model. The current study investigated the effect of prophylactic administration of a low molecular weight heparin, enoxaparin, on the healing of a closed rabbit rib fracture. Fracture healing was assessed using histomorphometric, histologic, and immunohistochemical methods at 3, 7, and 14 days, and biomechanical testing with torsional loading was assessed after 21 days. Bone repair was significantly attenuated at all times in animals receiving subcutaneous enoxaparin compared with that of the control animals. Numerous putative mechanisms for this phenomenon are discussed, and additional studies are proposed to elucidate the effects of this pharmacologically diverse group of compounds on all aspects of bone physiology and repair.

Intraobserver and interobserver reliabilty of measures of kyphosis in thoracolumbar fractures.

BACKGROUND CONTEXT Consensus documents have recently been developed enumerating the radiographic parameters thought to be most valid in the clinical evaluation of patients with thoracolumbar fractures. PURPOSE The objective of this study was to assess the measurement reliability of plain X-rays, computed tomography (CT), and magnetic resonance imaging (MRI) and their inter-modality agreement, as the three imaging modalities are often clinically interchangeable. This process is an essential reliability evaluation of the measurement parameters being proposed. STUDY DESIGN This study evaluated the interobserver and intraobserver reliability of plain radiographs, CT, and MRI measurements of sagittal kyphosis in thoracolumbar fractures. PATIENT SAMPLE Suitable plain X-ray, CT, and MRI radiographic imaging of ten cases of thoracolumbar fracture were examined. METHODS Suitable plain X-ray, CT, and MRI radiographic imaging of ten cases of thoracolumbar fracture were examined by ten independent spine surgery fellowship-trained observers. OUTCOME MEASURES Cobb angle measurement, Gardner segmental deformity angle, and anterior body compression percentage were measured. RESULTS Regardless of the imaging modality or the parameter being measured, the intraobserver reliability is always better than the interobserver. Plain radiography has better overall, interobserver and intraobserver reliability, followed by CT and then MRI. Reliability is very high in general, with the highest reliability for intraobserver reliability of the linear measures on plain radiographs. The inter-modality agreement is highest for plain X-ray and CT. CONCLUSIONS This study demonstrates that Cobb angle measurement, Gardner segmental deformity angle, and anterior body compression percentage are reliable measures of thoracolumbar fracture kyphosis with very high interobserver and intraobserver reliability and very high inter-modality agreement of plain X-ray with CT.

N-acetylcysteine attenuates lung injury in a rodent model of fracture

BACKGROUND Neutrophil-mediated lung injury is a cause of significant morbidity and mortality in patients with multiple injuries. We have shown previously that fracture hematoma can activate neutrophils and is thus a putative mediator of the systemic inflammatory response syndrome (SIRS), acute respiratory distress syndrome (ARDS) and multiple organ failure (MOF) in those patients with severe skeletal trauma. Our aim was to establish a rodent model of fracture which caused lung injury and subsequently to administer a drug following fracture to attenuate the lung injury. The drug we chose was N-acetylcysteine, a potent antioxidant. ANIMALS AND METHODS Adult Sprague-Dawley rats were assigned to 4 groups: (1) general anesthetic only, (2) general anesthetic with bilateral femur fractures and nailing, (3) general anesthetic and N-acetylcysteine, (4) general anesthetic with bilateral femur fractures and nailing and N-acetylcysteine after the injury (n = 6 in each group). The dose of N-acetylcysteine was 0.5 mg/kg which was given intraperitoneally after injury to the treated groups. The rats were killed 24 hours after injury and some parameters of lung injury were evaluated--i.e., bronchoalveolar lavage (BAL), lung tissue myeloperoxidase levels (MPO) and wet/dry ratios of lung tissue. The results were analyzed, using one-way analysis of variance. RESULTS Bilateral femur fracture produced a significant lung injury, measured by increases in MPO (25-43 microg/g tissue) and BAL protein (460-605 microg/mL). This effect was attenuated by treatment with N-acetylcysteine (MPO 43-9 microg/mL, BAL protein 605-198 microg/mL). INTERPRETATION N-acetyl cysteine, if given after skeletal trauma, is of potential therapeutic benefit, in preventing SIRS, ARDS and MOF.

Adverse events in surgically treated cervical spondylopathic myelopathy: a prospective validated observational study.

Study Design. Prospective observational study. Objective. Using validated tools to accurately identify and quantify incidence of and risks for inpatient adverse events (AEs) associated with surgical management of cervical spondylopathic myelopathy (CSM) with the goal of assisting physicians and patients in decision making. To identify patient-/disease-/technique-specific, independent risk factors for developing AEs perioperatively and affecting length of stay for patients treated surgically for CSM. Summary of Background Data. Previous studies have reported an overall perioperative complication rate between 15.6% and 18.52%. Methods. A total of 104 patients underwent surgery for CSM in our academic quaternary referral center. The average age was 60.3 years (range, 34–86 yr) with a male preponderance (n = 77, 74%). The severity of myelopathy and significant comorbidities was measured and was in keeping with previously assessed populations. Surgical approach was anterior-alone (39.4%), posterior-alone (55.8%), or combined (4.8%) surgery. Inpatient AE data were collected in a rigorous, contemporaneous fashion using the previously validated Spine Adverse Events Severity System (SAVES) tool. Results. A total AE rate of 42.3% was documented in surgically managed patients with CSM (intraoperative = 13.5%, postoperative = 37.5%). Statistically significant risk factors for postoperative AEs were identified, including number of comorbidities (P = 0.012), anterior surgical approach (P = 0.003), and number of levels operated on (P = 0.031). Multiple risk factors for length of stay were also identified, including number of AEs (P < 0.0001), Nurick Score (P < 0.0001), number of levels operated on (P = 0.006), and occurrence of deep wound infection (P < 0.0001). Conclusion. We report higher perioperative AE rates than previously recognized, due to the use of a validated, rigorous data collection tool. Multiple novel patient/disease severity/surgical factors with high statistical significance on perioperative AEs have been identified. Level of Evidence: 3

Factors predictive of topographical accuracy in spine level localization

BACKGROUND Pre-operative spine level localization by palpation of anatomical landmarks (ribs, spinous processes) in posterior approaches for surgeries from T4 to L2 is often inaccurate. This can lead to ineffective utilization of procedural time, increased radiation dose, potentially longer skin incision and wrong level surgery. Factors affecting topographical accuracy includes body mass index (BMI) of the patient, congenital or acquired deformity and knowledge of topographical anatomy. METHODS All patients had the presumed location of their pathology marked on the skin using anatomical landmarks prior to application of the Target Tape® (Vancouver, BC, Canada) and verification using an anterior-posterior radiograph. Potential factors predictive of accurate pre-operative spine level localization such as age, gender, BMI, palpable deformity, pathology related interspinous distance (ISPD) and pathology related skin to spinous process distance were evaluated. RESULTS A prospective study was performed with 30 consecutive patients undergoing posterior spine surgery (T4 to L2). Accuracy of pathology related spine level localization using anatomical landmarks was only 40%. Pathology related ISPDs of more than 10 mm and palpable deformity was significantly correlated with successful determination of spine levels using anatomical landmarks. CONCLUSIONS This study showed that poor spine level localization using anatomical landmarks was associated with pathology related ISPDs of less than 10 mm. Conversely, patients with palpable spinal deformity have their levels easily localized.