Bret Baack

Trauma in the elderly.

One hundred geriatric patients who suffered injury severe enough to necessitate hospitalization were compared retrospectively to a random group of 100 younger patients. The elderly suffered different types of injury and died six times as often as their younger peers, even when controlled for injury severity. The PRE method was employed to examine outcome in both groups and was found to be strongly predictive of death in young patients. Age stratification aided significantly in predicting mortality in elderly patients. Regression analysis was employed to examine the data set to determine the relative importance of several variables in the prediction of ultimate mortality. By incorporating all the data from the entire data set, curves describing the contribution of age and shock to mortality corrected for all factors is possible. Increasing age after 65 increases mortality and this effect is dramatically increased by the presence of shock. This information may be useful in counselling the injured elderly and their families.

Biomechanical Optimization of Bone Plates Used in Rigid Fixation of Mandibular Fractures

PURPOSE To design and optimize a bone plate for fractures of the mandibular body that will provide maximum fracture stability with minimal implanted volume and patient intrusion. The design will be driven by the unique biomechanics specific to this fracture location. MATERIALS AND METHODS A finite element model of a fractured human mandible was created using tomography scans. Material properties were assigned to the cortical bone, cancellous bone, and dental region. Boundary conditions included simulating a unilateral molar clench and incisal loading. The bone plate design process included a shape optimization routine and design parameter analysis using the model. The optimized bone plate design was finally compared with standard bone plate configurations based on stress and strain measures. RESULTS For incisal loading, the newly designed InterFlex II plate has 69% of the fracture strain and only 34% of the plate stress of an 8-hole strut plate. For unilateral molar loading, those numbers improve even further to 59% and 27%, respectively. InterFlex II plate stresses are less than or equal to the paired plate configuration, and fracture strain is within 10% of the corresponding paired plate strain under both loading scenarios. In terms of mechanical performance, InterFlex II is in the same class as the commonly used paired plate configuration, despite having only 55% of the implanted volume. CONCLUSION A design process focused on shape and design variable optimization can produce bone plates that provide maximum fracture stability with minimum implanted volume.

Traumatic asphyxia in New Mexico: A five-year experience

Compression of the chest causing facial petechiae, violaceous facial hue, subconjunctival hemorrhages, and frequent mental status abnormalities has been termed traumatic asphyxia. We identified 35 such cases occurring in the State of New Mexico from 1980 to 1985 from records of the Office of the Medical Investigator (n = 30) and from cases presenting to the University of New Mexico Trauma Center (n = 5). Among those found at highest risk for traumatic asphyxia were people ejected from motor vehicles, men working under cars that were inadequately supported and fell onto the victims, children under the age of 5 years who were crushed under household furniture, and people involved in construction activities. Traumatic asphyxia following a moving motor vehicle accident was significantly associated with alcohol ingestion (p less than 0.001). Preventive and therapeutic strategies should focus on the groups and events identified.

Comparison of Plate-Screw Systems Used in Mandibular Fracture Reduction: Finite Element Analysis

A finite element model of the human dentate mandible has been developed to provide a comparison of fixation systems used currently for fracture reduction. Volume domains for cortical bone, cancellous bone, and teeth were created and meshed in ANSYS 8.0 based on IGES curves created from computerized tomography data. A unilateral molar clench was loaded on the model with a fracture gap simulated along the symphysis. Results based on Von Mises stress in cortical and cancellous bone surrounding the screws, and on fracture surface spatial fixation, show some relative differences between different screw-plate systems, yet all were judged to be appropriate in their reduction potential.

Biomechanical optimization of bone plates used in rigid fixation of mandibular symphysis fractures.

PURPOSE To design and optimize a bone plate for fractures of the mandibular symphysis that will provide maximum fracture stability with minimal implanted volume and patient intrusion. The design will be driven by the unique biomechanics specific to this fracture location. MATERIALS AND METHODS A finite element model of a fractured human mandible was created using computed tomography scans. The boundary conditions included simulating molar, canine, and incisal loading. The bone plate design process included a shape optimization routine and design parameter analysis using the model. The optimized bone plate design was finally compared with standard bone plate configurations according to stress and strain measures. RESULTS Compared with the miniplate combination, the InterFlex III plate, with the same thickness and just 14% more implanted volume, had only 55% of the plate stress and 25% less fracture strain under the strongest loads considered by the model. Compared with the band/fracture plate combination, the InterFlex plate had 88% of the fracture strain and 74% of the plate stress, despite having only 60% of the plate volume. CONCLUSIONS The results have demonstrated that the new optimized plate is a hybrid of fixation hardware with the small profile of the smallest miniplate configuration and the superior fixation strength and safety that exceeds that of the larger fracture plate configuration.

Biomechanical Analysis of Mandibular Angle Fractures

BACKGROUND Clinical evidence has suggested that minimal fixation can reduce complications of mandibular angle fractures, though no detailed biomechanical model has yet explored this unique and somewhat unexpected finding. METHODS The current study uses finite element analysis to biomechanically evaluate different fixation schemes used to fixate mandibular angle fractures. Three fixation scenarios were considered: a single tension band at the superior mandibular border, a single bicortical angle compression plate at the inferior border and the tension band and bicortical plate used together. RESULTS The dual plate model incurred the lowest von Mises stresses in the plates and the lowest principal strain in the callus. The tension band model observed the highest plate and screw von Mises stresses, but had fracture-site callus strain near to that of the dual plate model. The bicortical angle compression plate model observed the highest fracture-site callus strain. CONCLUSION The results from this study support the use of the single tension band configuration as a less invasive fixation approach to fractures of the mandibular angle. This is the first known study to explore and confirm clinical observations of angle fracture fixation outcomes with a detailed biomechanical modeling methodology.

Mechanical design optimization of bioabsorbable fixation devices for bone fractures.

Bioabsorbable bone plates can eliminate the necessity for a permanent implant when used to fixate fractures of the human mandible. They are currently not in widespread use because of the low strength of the materials and the requisite large volume of the resulting bone plate. The aim of the current study was to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a standard titanium bone plate. A finite element model of a mandible with a fracture in the body region is subjected to bite loads that are common to patients postsurgery. The model is used first to determine benchmark stress and strain values for a titanium plate. These values are then set as the limits within which the bioabsorbable bone plate must comply. The model is then modified to consider a bone plate made of the polymer poly-l/dl-lactide 70/30. An optimization routine is run to determine the smallest volume of bioabsorbable bone plate that can perform and a titanium bone plate when fixating fractures of this considered type. Two design parameters are varied for the bone plate design during the optimization analysis. The analysis determined that a strut style poly-l-lactide-co-dl-lactide plate of 690 mm2 can provide as much mechanical stability as a similar titanium design structure of 172 mm2. The model has determined a bioabsorbable bone plate design that is as strong as a titanium plate when fixating fractures of the load-bearing mandible. This is an intriguing outcome, considering that the polymer material has only 6% of the stiffness of titanium.

Steam press burns of the hand

Steam presses pose an occupational hazard to workers in the dry cleaning industry. Three patients with thermal burns to the hand from steam press accidents were recently treated at this institution. Each patient sustained deep second and third degree burns to the dorsum of the hand. Two patients required split-thickness skin grafts and have retained full range of motion and returned to full employment. One patient sustained destruction of extensor tendons and required a groin flap for coverage. Late tendon reconstruction will be necessary. Investigation revealed that older steam press models do not have an emergency release lever in case of accidental closure on a workers hand. Although newer models are equipped with a thigh-activated emergency release lever, a contact burn remains likely if the press closes on the operators hands. Some of the newest models have an attached safety bar that prevents the press from closing on the operators hands. It is recommended that older models either be modified with the attachment of a safety bar or replaced entirely.

Minimally invasive bioabsorbable bone plates for rigid internal fixation of mandible fractures.

OBJECTIVES To optimize design variables of a bioabsorbable bone plate using a finite element model of the mandible and to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a titanium plate. METHODS A finite element model of a mandible with a fracture in the body was subjected to bite loads. An analysis was run to determine the principal strain in the fracture callus and von Mises stress in a titanium plate. These values were then set as the limits within which the bioabsorbable bone plate must comply. The model then considered a bone plate made of the polymer poly(L-lactide-co-D,L-lactide) (P[L/DL]LA) 70/30. An optimization routine determined the smallest volume of bioabsorbable bone plate that can perform as well as a titanium bone plate when fixating mandibular fractures. RESULTS A P(L/DL)LA plate volume of 315 mm(2) with a thickness of 1.5 mm provided as much mechanical stability as a commonly used titanium strut structure of 172 mm(2). The peak plate stress was well below the yield strength of the material. CONCLUSIONS The P(L/DL)LA bioabsorbable bone plate design is as strong as a titanium plate when fixating fractures of the mandible body despite the polymer material having only 6% of the stiffness of the titanium. The P(L/DL)LA plate can be less than half the volume of its strut-style counterpart.

Effect of fracture healing on the fixation of a parasymphyseal mandibular fracture: a study using the finite element method

Trauma surgeries involving rigid internal fixation of mandibular fractures are often supplemented with a short postoperative period of Intermaxillary Fixation (IMF) or soft diet to delay patient functioning. A finite element model of the human mandible with a parasymphyseal fracture was created and anatomically loaded to determine the effect of fracture healing on measures associated with complications. Stress and strain measures were recorded while the stiffness of the fracture was increased to mimic fracture healing. According to the results of the model, delaying normal functioning for two weeks decreases stress and strain measures up to 50%.