Biomechanical evaluation of fixation techniques for bridging segmental mandibular defects.

OBJECTIVE: To compare biomechanical properties of currently available plating systems used to reconstruct segmental mandibular defects. DESIGN: Controlled in vitro investigation. SETTING: Academic medical center laboratory. INTERVENTIONS: Thirty-two polyurethane mandibles were equally divided among 4 groups: mandibles with a 4-cm lateral segmental defect that was bridged with a (1) 3.0-mm locking-screw reconstruction plate, (2) 2.4-mm low-profile reconstruction plate, or (3) 2.4-mm reconstruction plate and (4) uncut (control) mandibles. All plates were contoured and secured to the synthetic mandibles with 4 bicortical screws on either side of the defect. Three constructs from each group were subjected to contralateral-molar single-load-to-failure testing. Mean yield displacement, yield load, and bending stiffness were quantified and compared among the 4 groups. The single-load-to-failure data were used to establish conditions for fatigue testing; such testing was then performed on the remaining 5 samples in each group. Mean cycles to failure were measured and compared among the 4 groups. RESULTS: Mean yield displacement, yield load, and bending stiffness were comparable among the plated groups. Both the 3.0-mm locking-screw and 2.4-mm low-profile reconstruction plate designs withstood 1580 and 1124 times more cycles to failure, respectively (P = .005), than did the control group. The other reconstruction plate was also superior to the unplated controls, offering an 865-fold improvement. CONCLUSIONS: All 3 mandibular fixation device systems tested produce comparable levels of single load to failure biomechanical integrity; however, the higher-profile plating system design offered slightly superior fatigue performance. No differences in performance were observed between the locking and nonlocking designs; neither failed at the screw-substrate interface.

Comparison of 3 methods of detecting acute respiratory distress syndrome: clinical screening, chart review, and diagnostic coding.

BACKGROUND: Although the incidence of acute respiratory distress syndrome has been studied, few researchers have prospectively assessed the search tool used to identify cases. METHODS: For 5 months, all patients admitted to a medical intensive care unit in a teaching hospital were evaluated daily to determine whether criteria for acute respiratory distress syndrome were met, and physicians' progress notes and discharge summaries for these prospectively identified patients were reviewed for mention of the syndrome. Discharge forms were reviewed for the codes (International Classification of Diseases, Ninth Revision) specific to acute respiratory distress syndrome (518.82 or 518.85). RESULTS: Of 314 patients admitted, 65 prospectively met the criteria for acute respiratory distress syndrome. Of these 65 patients, 31 had acute respiratory distress syndrome mentioned in their progress notes, and 4 of the 31 were subsequently assigned a code of 518.82 or 518.85. Patients with a physician's notation for acute respiratory distress syndrome in their charts had a higher mortality (22/31 [71%]) than did the patients with no such notation (10/34 [29%]). This difference could not be accounted for by differences in length of stay, mean age, score on Acute Physiology and Chronic Health Evaluation III, or number of days in the unit before meeting the criteria. CONCLUSIONS: The incidence of acute respiratory distress syndrome is underestimated when based on either diagnostic coding or physicians' notes without testing of the accuracy of coding. Both physicians and medical record coding specialists may require training in use of terms related to acute respiratory distress syndrome.

Does plate adaptation affect stability? A biomechanical comparison of locking and nonlocking plates.

PURPOSE: The purpose of this investigation was to determine whether the degree of plate adaptation and effects of locking influenced the mechanical behavior of the plate/screw/substrate system for 2.0-mm monocortical superior border plates and 2.4-mm reconstruction plates secured at the inferior border intended to stabilize simulated mandibular angle fractures. MATERIALS AND METHODS: A total of 130 polyurethane synthetic mandible replicas (Synbone, Landquart, Switzerland) were used in this investigation. Five controls each, for incisal edge and molar loading, as well as 5 samples each for 2.4-mm locking and nonlocking reconstruction plates and 2.0-mm locking and nonlocking monocortical superior border plates, intimately adapted (0.0-mm offset), 1.0-mm offset and 2.0-mm offset were subjected to loading at the incisal edge and molar region with an Instron 1331 (Instron Corp, Canton, MA) servohydraulic mechanical testing unit. Load/displacement data were recorded, and yield load, yield displacement, and stiffness were determined. Mean and standard deviation values were calculated. Statistically significant differences were determined for the effects of locking and degree of plate adaptation using a 1-way analysis of variance (P <.05). For differences within categories and among groups, a Sheffé multiple-comparison test was performed. First-order polynomial best-fit curves were created for each group to further evaluate and compare the mechanical behavior. RESULTS: There were no statistically significant differences (P <.05) for yield load, yield displacement, and stiffness within the 2.4 and the 2.0 locking categories for both molar and incisal edge loading. For the 2.4 nonlocking category, there were statistically significant differences for yield load, yield displacement, and stiffness between the 0.0-mm offset group and both the 1.0-mm and 2.0-mm offset groups for both molar and incisal edge loading but not between the 1.0-mm and 2.0-mm groups. For the 2.0 nonlocking category, there were statistically significant differences for yield load, yield displacement, and stiffness between both the 0.0-mm and 1.0-mm offset groups and the 2.0-mm offset group for both molar and incisal edge loading but not between the 0.0-mm and 1.0-mm groups. CONCLUSIONS: The degree of adaptation (amount of offset) affected the mechanical behavior of the nonlocking systems evaluated. It did not affect the locking systems. Failure occurred as an "all-or-nothing" pattern.

A biomechanical evaluation of mandibular condyle fracture plating techniques.

OBJECTIVES: The purpose of this investigation was to evaluate the biomechanical behavior of various rigid internal fixation techniques for mandibular condylar process fractures. MATERIALS AND METHODS: Synthetic mandible replicas (Synbone, Landquart, Switzerland) were used to evaluate a control, and four monocortical mandibular condyle plating techniques. Each group was subjected to linear loading in lateral to medial, medial to lateral and posterior to anterior directions by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. Yield load, yield displacement, and stiffness were measured. In addition, each group was subjected to torsional loading using an Instron 8521 (Instron). Yield torque, yield rotation, and stiffness were measured. Five samples were tested for each group and method of loading (n = 100). Means and standard deviations were derived and compared for statistical significance using a 1-way analysis variance (P <.05). Third-order polynomial best-fit curves were also created for each group to further evaluate and compare the mechanical behavior. RESULTS: Statistically significant differences were noted between fixation groups for the different mechanical measures evaluated under the different conditions of linear loading. Statistically significant differences were noted between groups for yield rotation during torsional loading. Although different in magnitude, similar patterns of mechanical behavior were observed in the third-order polynomial best-fit curves for lateral to medial loading, medial to lateral loading and torsional loading. For posterior to anterior loading, different patterns of mechanical behavior were noted between the experimental groups, but similar behavior was noted between the control and mini dynamic compression plate CONCLUSIONS: While differences were noted between each of the fixation systems in their abilities to resist loads under the conditions tested, the mini dynamic compression plate provided the most favorable mechanical behavior. Based on the presumed clinical parameters, we can suggest that none of the systems evaluated were ideal for the treatment of mandibular condyle fractures, but that the mini dynamic compression plate is the closest to an effective means for reconstruction.