Jon Wagner

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.

Dog Bites of the Scalp, Face, and Neck in Children

Objective To update the surgical management of injuries from dog bites of the scalp, face, and neck in children.

Infection Rates Following Perioperative Prophylactic Antibiotics Versus Postoperative Extended Regimen Prophylactic Antibiotics in Surgical Management of Mandibular Fractures

PURPOSE To determine whether or not an extended regimen of prophylactic antibiotics following either open or closed reduction of mandibular fractures is beneficial in lowering the rate of infection in postoperative patients. PATIENTS AND METHODS This study is a retrospective chart review of 150 patients treated operatively for both complicated and uncomplicated mandibular fractures at University of New Mexico Health Sciences Center in Albuquerque, NM, between January 1, 2000 and June 12, 2007. Treatment modalities used were closed reduction with maxillomandibular fixation or open reduction and internal fixation with either wire osteosynthesis or rigid internal fixation. Patients fell into 1 of 2 groups: the first group received antibiotics perioperatively, which consisted of no more than 24 hours of antibiotics in the postoperative period; the second group received extended regimen antibiotics, which consisted of anywhere from 24 hours to 10 days of antibiotics in the postoperative period. Seventy-five patients were included in each group. The type of antibiotic prescribed was at the discretion of the operating surgeon. This study was conducted using an intention-to-treat analysis. Postoperative infection was diagnosed either subjectively or objectively by the clinician evaluating the patient at follow-up appointments. RESULTS In the extended antibiotic group, 8 out of 75 subjects (10.67%) developed infection. In the perioperative antibiotic group, 10 out of 75 subjects (13.33%) developed infection. Statistical analysis using chi(2) distribution showed that this difference in proportions was not significant (chi(2) = 0.06, P = 0.8). CONCLUSION This study found that the use of postoperative prophylactic antibiotics does not have a statistically significant effect on postoperative infection rates in surgical management of complicated or uncomplicated mandibular fractures.

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.

Salvage of partial facial soft tissue avulsions with medicinal leeches

BACKGROUND: Medicinal leeches have been demonstrated to be extremely useful and safe in the salvage of venous outflow compromised tissue, particularly in digit replants and various forms of flaps. OBJECTIVE: To demonstrate the utility of medicinal leeches in the salvage of venous outflow-compromised traumatic soft tissue avulsions in key facial structures. METHODS: A retrospective review of 4 cases involving the external ear, nose, lip, and scalp in which apparent venous outflow compromise was present. Medicinal leeches were applied acutely in each of these 4 cases, salvaging each of the partially avulsed soft tissue segments. RESULTS: Complete or near complete salvage of each soft tissue segment after using medicinal leeches. CONCLUSIONS: Although it is unusual for a partial soft tissue avulsion of the face to require medicinal leech therapy, situations may occur in which there is adequate arterial inflow but inadequate venous outflow. In such cases, medicinal leeches may play a very important role in salvaging the soft tissue segment. This is particularly important in vital structures such as the ear, nose, lip, and eyelid in which acute or secondary reconstruction is complex. EBM rating: C.

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.

Preoperative laboratory testing for the oral and maxillofacial surgery patient

Studies estimate that approximately 60% of preoperative testing could be eliminated without adversely affecting patient care. Unnecessary testing tends to cause extra risk to the patient, inefficient operating room schedules, and unnecessary costs. These extra tests may be hazardous to patients because of the pursuit and treatment of borderline positive or false-positive results. Furthermore, extra testing may also increase medicolegal risk, because the abnormalities that are discovered are usually not noted on the chart. A reliable and effective method for ordering laboratory tests to assess patients preoperatively and reduce morbidity and cost is presented.

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%.

Keeping abreast of the medical/dental literature: A simplified approach

Surveys report journal reading to be the most important continuing education activity in terms of practitioner preference. Clinical reading can be increased by perfecting the skills and habits that will permit selection of the most useful articles. In this article, an algorithm and basic methods are presented to enhance the practitioners skill in reviewing the literature.

Silicone gel breast implant rupture presenting as a fluctuant back mass after latissimus dorsi breast reconstruction.

The authors describe a patient who presented with acute onset of a lower back fluctuant mass 12 years after breast reconstruction with a latissimus dorsi musculocutaneous flap and silicone gel implant. Aspiration and subsequent surgical exploration revealed this mass to be free-flowing silicone gel within a cavity that was confluent with the breast implant capsule through an axillary tunnel. Excision of the back cavity, explantation with subtotal capsulectomy, and implant replacement resolved the problem. Although distant migration of extracapsular silicone gel from the breast to the axilla, arm, abdomen, and groin has been described, the authors think this represents the first reported case of distant migration of silicone gel to the lower back.