Posterior spinal fusion in paralytic scoliosis and myelomeningocele.

The Shriners Hospital, Lexington, KY, experience with posterior spinal fusion for scoliosis in 50 patients with myelomeningocele was reviewed. Six patients were fused with Harrington rods and 47 of 50 patients were treated with some form of segmental fixation. The complication rate was 48% (24/50) resulting in 1.48 procedures per patient. The deep infection rate was 8% (4/50) and the pseudarthrosis rate was 16% (8/50). The use of modern segmental instrumentation systems has improved the pseudarthrosis rates for posterior spinal fusion in scoliosis associated with myelomeningocele but not to the point of displacing the current approach of an anterior and posterior spinal fusion.

Radiographic analysis of low contact stress meniscal bearing total knee replacements.

BACKGROUND: Meniscal bearing total knee replacements were developed to decrease the contact stresses on polyethylene and to reduce polyethylene wear. The kinematics of meniscal bearing knee replacements is poorly understood. The present study was designed to evaluate, with radiographic analyses, the motion of the meniscal bearings and the femoral rollback of the Low Contact Stress meniscal bearing knee replacement during knee flexion. METHODS: Eighty-one Low Contact Stress meniscal bearing total knee replacements in seventy-six male patients were assessed on fluoroscopically centered lateral radiographs made with the knee in full extension and in full flexion at an average of six years (range, twenty-four to 147 months) after the operation. The distance and direction of motion of the meniscal bearings and the center contact position of the femoral condyles were measured. Knee evaluations were performed with use of the Knee Society rating system. RESULTS: The average range of motion of the knees, measured on lateral radiographs, was 90 degrees (range, 45 degrees to 136 degrees). As they moved from terminal extension to terminal flexion, thirty-nine knees (48%) exhibited anterior motion of both bearings and sixteen (20%) demonstrated posterior motion of both bearings. Ten knees (12%) had reciprocal motion of the two bearings (one bearing moving anteriorly and one bearing moving posteriorly) with flexion, nine knees (11%) had motion of only one bearing, and seven knees (9%) had no motion of either bearing. When moving from full extension to full flexion, eighteen knees (22%) demonstrated femoral rollback, six knees (7%) showed no change in the position of femoral contact, and fifty-seven knees (70%) exhibited anterior sliding of the femoral condyles. Flexion of the knees demonstrating femoral rollback averaged 104 degrees (range, 76 degrees to 128 degrees), and flexion of the knees demonstrating anterior sliding averaged 94 degrees (range, 45 degrees to 125 degrees). The difference was significant (p = 0.03). According to the Knee Society rating system, the average clinical score for the entire group was 76 points (range, 27 to 100 points) and the average functional score for the entire group was 72 points (range, 30 to 100 points). The average clinical score was 79 points (range, 27 to 98 points) for the knees that exhibited anterior sliding of the femoral condyles and 87 points (range, 52 to 100 points) for those exhibiting femoral rollback (p = 0.09). The average functional scores were 64 points (range, 30 to 100 points) and 72 points (range, 45 to 100 points), respectively (p = 0.15). CONCLUSIONS: Radiographic analysis of meniscal bearing total knee replacements demonstrated an average anterior motion of both the medial and the lateral meniscal bearing of 4.7 mm (range, 1 to 14 mm) in thirty-nine knees (48%) as they moved from terminal extension to terminal flexion. Sixty-three knees (78%) demonstrated no femoral rollback as they were flexed. Knees with anterior sliding of the condyles had a significantly smaller average range of flexion (p = 0.03) and a lower average Knee Society score than did knees demonstrating femoral rollback. We believe that lack of rollback indicates a functional insufficiency of the posterior cruciate ligament.

Growth factor modulation of distraction osteogenesis in a segmental defect model.

A model was established in 39 dogs to investigate the growth factor modulation of regenerate bone in distraction osteogenesis. A segment of the diaphysis of the radius was resected unilaterally. An osteotomy was made proximal to the segmental defect to create a transport segment. A monolateral external fixator was applied. After a latency period, the segment was transported across the defect. One week after the transport assembly contacted the distal pin clamp, an ipsilateral osteotomy of the proximal ulna was performed. In 20 dogs, transforming growth factor-beta was injected into the regenerate bone halfway through the transport period. Four dogs were sacrificed before docking, when the regenerate bone was still immature. In specimens harvested halfway through the transport period, evidence was found of intramembranous ossification during distraction. In specimens harvested after the transport assembly contacted the distal pin clamp, evidence was found that the mature regenerate formed by endochondral ossification. Therefore, a combined mechanism of ossification is proposed for this segmental defect model that includes mechanical stimulus for bone differentiation. The one-time administration of transforming growth factor-beta retarded the formation of a stable, united regenerate. It is concluded that transforming growth factor-beta caused an effect opposite to that which was desired.

Evaluation of the acute cervical spine: a management algorithm.

BACKGROUND: Safe, efficient, and cost-effective evaluation of the spine is the goal in the trauma setting. At our Level I trauma facility, the trauma service, emergency medicine, radiology, anesthesia, and the spine service combined individual concerns into one agreed-upon clearance protocol. Here, we present the effectiveness of a new cervical spine clearance protocol. METHODS: A retrospective review was initiated of all trauma patients evaluated in a Level I trauma center the year before and after implementation of a new cervical spine protocol to determine the incidence of missed cervical injuries. An additional 6 months were reviewed to detect any missed injuries late in the study period. RESULTS: During the 2-year study period, 4,460 patients presented to the emergency room with some form of cervical spine precautions. Blunt trauma comprised 90% of the study population. According to the protocol, approximately 45% required further cervical radiographs after presentation. In the preprotocol year, 77 of 2,217 (3.4%) patients were diagnosed with cervical spine injuries, 16 of 77 (21%) with multiple level of injuries, and 25 of 77 (32%) with neurologic compromise. Three of 2,217 patients had missed cervical spine injuries on their initial evaluations. In the postprotocol year, 84 of 2,243 (3.4%) patients had cervical injuries, 25 of 84 (30%) with multiple levels of injuries and 28 of 84 (28%) with neurologic compromise. No patient evaluated during the protocol year was missed. All statistics between the two groups were not significant. CONCLUSION: The current protocol by risk stratifying patients on presentation is effective in assessing patients for cervical spine injuries.

Comparative biomechanics of hybrid external fixation.

OBJECTIVE: To compare the elastic stiffness, in several loading modes, of commercially available hybrid external fixation systems. DESIGN: Laboratory investigation using a polyvinylchloride pipe periarticular tibia fracture model. SETTING: Simulated periarticular fractures were created in an in vitro tibia fracture model. Instrumented specimens and intact controls were elastically tested in a biomaterials testing system. INTERVENTION: Groups of simulated periarticular tibia fractures were stabilized with one of six different hybrid external fixator designs. MAIN OUTCOME MEASUREMENTS: Elastic stiffness of each specimen was measured in compression, torsion, flexion bending, extension bending, and varus/valgus bending. RESULTS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. Specifically, the EBI Ring Connector fixator was stiffer than all others in all modes of testing. The Ace, Synthes, Smith & Nephew Richards, and How medica fixators were mechanically similar. The Zimmer Torus fixator was the least stiff fixator tested. CONCLUSIONS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. The choice of which hybrid external fixator to use should be made based not only on stiffness but also on ease of clinical application, patient comfort, customer support from the manufacturer, and cost. Clinical investigation of the efficacy of each of these devices is warranted.

Reamed intramedullary femoral nailing after induction of an "ARDS-like" state in sheep: effect on clinically applicable markers of pulmonary function.

OBJECTIVES/HYPOTHESIS: At present, the optimal treatment for appropriately resuscitated, multiply injured patients includes fixation of long bone fractures within twenty-four hours of injury. This management approach has been shown to decrease the incidence of pulmonary complications, multiple organ failure, and death. Some investigators have hypothesized that acute reamed intramedullary nailing of the femur (RIMNF) may result in pulmonary dysfunction as a result of the pulmonary fat embolization generated during this procedure. Patients with concomitant thoracic trauma may be at particular risk for this potentially severe complication. In an attempt to determine whether RIMNF can be safely carried out regardless of the severity of a pulmonary injury, we monitored the pulmonary effects of RIMNF in sheep in which an acute respiratory disorder (ARDS)-like state had been induced. Our hypothesis was that, if the pulmonary fat embolization that occurs as a result of RIMNF has a clinically significant effect, it would be detectable in an animal model in which a severe lung injury had been induced prior to the start of RIMNF. STUDY DESIGN: This was an acute experimental procedure performed on yearling sheep. METHODS: Reamed intramedullary nailing of the femur was performed in two groups of instrumented sheep. The first group had no pulmonary injuries. The second group had an ARDS-like state induced by intravenous infusion of perilla ketone prior to RIMNF. Perilla ketone increases pulmonary microvascular permeability without changing filling pressures and is used to induce a model of human ARDS. Hemodynamic and oximetric parameters were measured or calculated, as was pulmonary dynamic compliance during the experiment. RESULTS: Infusion of perilla ketone caused a significant pulmonary injury. RIMNF caused no additional significant effect on intrapulmonary shunt, mixed venous oxygen saturation, or dynamic compliance, which are clinically used to assess the severity of pulmonary dysfunction in injured patients. CONCLUSIONS: The fat embolization that occurs during RIMNF in an appropriately resuscitated sheep has no clinically significant effect on pulmonary function, even in the setting of a severe pulmonary dysfunction.

Myocardial tolerance to mechanical actuation is affected by biomaterial characteristics.

Direct mechanical ventricular actuation (DMVA) uses a pressure regulated heart cup, fabricated from silicone rubber (SR) for mechanical massage of the heart. Because DMVA has demonstrated potential for long-term circulatory support, investigations are currently exploring the use of more durable materials for fabricating DMVA heart cups. This study assessed the acute effects of heart cups fabricated from SR versus polyurethane (PU) on the myocardium. Dogs (n - 18) received DMVA for 4 hr of ventricular fibrillation (VF) using either SR (n = 10) or PU (n = 8) cups. Microspheres were used to determine perfusion during sinus rhythm (control) and at 2 and 4 hr of support. After support, myocardial biopsies were assayed for high energy phosphate content. Results demonstrated that PU cups required relatively frequent adjustments in drive line parameters that were likely due to material softening during PU cup support. Both PU and SR cups achieved similar hemodynamics during 4 hr of support. Myocardial perfusion, however, demonstrated a marked hyperemia at 4 hr of PU versus SR cup support. Regional high energy phosphate content was significantly decreased in hearts supported by PU versus SR cups. These results suggest that the relatively compliant characteristics of SR materials are important for achieving effective DMVA support without injuring the myocardium.