Curtis Gaball

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.

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.

Technique to Reduce Time, Pain, and Risk in Costal Cartilage Harvest

Costal cartilage’s utility for reconstructing the nasal framework has been well documented and accepted since the turn of the 20th century, when Sir Harold Gillies began using this autograft in the reconstruction of wounds sustained on the battlefields of World War I.1 The complications associated with harvesting and using rib grafts are also well documented, and techniques have evolved with goals of reducing donor site morbidity and graft warping. The most common complaint after costal cartilage harvest is pain, regardless of purpose or extent of harvest.2 While pain may result in respiratory splinting, atelectasis, and possibly pneumonia, pneumothorax is the donor-site complication that the surgeon is most wary of intraoperatively and postoperatively. We describe a novel costal cartilage harvest technique that mitigates the risk of an inadvertent pleural tear, may be quicker, and, in conjunction with a long-acting local anesthetic, seems to reduce postoperative donor-site pain with its inherent risk for respiratory splinting and pneumonia.

Characteristics of maxillofacial injuries and safety of in-theater facial fracture repair in severe combat trauma.

The study objectives were to characterize maxillofacial injuries and assess the safety of in-theater facial fracture repair in U.S. military personnel with severe combat trauma from Iraq and Afghanistan. We performed a retrospective chart review of the Expeditionary Medical Encounter Database from 2004 to 2010. 1,345 military personnel with combat-related maxillofacial injuries were identified. Injury severity was quantified with the Abbreviated Injury Scale and Injury Severity Score. Service members with maxillofacial injury and severe combat trauma (Injury Severity Score ≥ 16) were included. The distribution of facial fractures, types, and outcomes of surgical repairs, incidence of traumatic brain injury, concomitant head and neck injuries, burn rate/severity, and rates of Acinetobacter baumannii colonization and surgical site infection were analyzed. The prevalence of maxillofacial injury in the Expeditionary Medical Encounter Database was 22.7%. The most common mechanism of injury was improvised explosive device (65.7%). Midface trauma and facial burns were common. Approximately 64% of the study sample sustained traumatic brain injury. Overall, 45.6% (109/239) had at least one facial bone fracture. Of those with facial fractures, 64.2% (n = 70) underwent surgical repair. None of the service members who underwent in-theater facial fracture repair developed A. baumannii facial wound infection or implant extrusion.

Biomechanics of the Rhombic Transposition Flap

Objective To develop a computational model of cutaneous wound closures comparing variations of the rhombic transposition flap. Study Design A nonlinear hyperelastic finite element model of human skin was developed and used to assess flap biomechanics in simulated rhombic flap wound closures as flap geometric parameters were varied. Setting In silico. Methods The simulation incorporated variables of transposition angle, flap width, and tissue undermining. A 2-dimensional second-order Yeoh hyperelastic model was fit to published experimental skin data. Resultant stress and strain fields as well as local surface changes were evaluated. Results For the rhombus defect, closure stress and strain were minimized for the transposition flap with a distal flap angle of 30° by recruiting skin from opposing sides of the defect. Alteration of defect dimensions showed that peak stress and principal strain were minimized with a square defect. Likelihood of a standing cutaneous deformity was driven by the magnitude of angle closure at the flap base. Manipulation of the transposition angle reoriented the primary skin strain vector. Asymmetric undermining decoupled wound closure tension from strain, with direct effects on boundary deformation. Conclusions The model demonstrates that flap width determines the degree of secondary tissue movement and impact on surrounding tissues. Transposition angle determines the orientation of maximal strain. Local flap design requires consideration of multiple factors apart from idealized biomechanics, including adjacent “immobile” structures, scar location, local skin thickness, and orientation of relaxed skin tension lines. Finite element models can be used to analyze local flap closures to optimize outcomes.

Biomechanics of the Monopedicle Skin Flap

Objective The design and implementation of skin flaps remains a puzzle for the reconstructive surgeon. The objective of the present study is to use finite element (FE) analysis to characterize and understand the biomechanics of the monopedicle skin flap design. Study Design The current study uses a nonlinear hyperelastic FE model of the human skin to understand the biomechanics of monopedicle-based flap designs as geometric flap parameters are varied. Setting In silico. Subjects and Methods The simulation included the displacement loading, stitching, and relaxation of various forms of the flap design. Stress and strain outcomes, previously correlated with scarring, necrosis, and blood perfusion, are reported for a basic monopedicle design as well as a number of modifications to this design. Results The results suggest that the length of the monopedicle flap should not exceed 3 times the size of the defect, as the benefit in reducing principal strain (deformation) is diminished beyond this point. Further, to minimize skin strain, the ideal Burrow’s triangle size can be described as proportional to flap length and inversely proportional to defect height, according to a linear function. Conclusion The ideal flap design should attempt to minimize not only the stress in the skin, but the size of the incisions and the degree of undermining. The results of our analyses provide guidance to increase the general understanding of monopedicle flap mechanics and provide context for the clinician and insight into designing a better monopedicle flap for individual situations.

Engineering Analysis of an Unreported Complication of Septoplasty

OBJECTIVES To describe a cause of recurrent nasal obstructive symptoms after septoplasties including the creation of a sizable submucous window and to suggest treatments for this complication. METHODS Case report of a woman presenting with side-changing nasal dyspnea approximately 1 year after undergoing septoplasty and engineering analysis of nasal cavity airflow. We created a computer model of the airway, analyzed varying sizes of surgical defects, and optimized the geometry of the submucous window. RESULTS An optimum area of resection to maximize the area of cartilage and/or bone resected and to minimize deflection of the septal area of iatrogenic litheness is a rectangular shape approximately 44 mm long by 12 mm high in our model. CONCLUSIONS A large submucous window can result in obstruction of nasal airflow after septoplasty owing to displacement of this compliant area with respiration under the forces described in the Bernoulli theorem. Treatment may include turbinate reduction and/or septal reconstruction.

Analysis and Optimization of the Rhombic Flap Wound Closure

Objective: 1) Develop a hyperelastic computational model of skin viscoelastic properties for analysis of wound closures, and 2) Apply the model to variations of the rhombic skin flap to quantify closure force vectors and optimize wound closure tension. Method: A computational model employing the finite element method was created to simulate skin defect closure employing rhombic transposition flaps. Variables of transposition angle, flap width, and tissue undermining were analyzed. Outcome measures of tissue stress, strain, and wound distortion were evaluated and optimized for a standard defect. Results: A second order Yeoh hyperelastic model was fit to previously published experimental skin data with good approximation of observed properties. In the analysis of transposition flap closures of the 60 to 120 degree rhomboid defect, the model suggests that a biomechanically ideal flap design is constructed with distal flap angle of 30 degrees, as is employed in the Webster flap, with the donor site near margin oriented parallel to the short axis of the defect, as in the traditional Limberg flap. This configuration minimizes tissue stress and strain and most evenly distributes wound tension across the closure line. Conclusion: The model quantitatively demonstrates several recognized principles of the rhombic flap. Square defects, as compared with rhomboid defects, close with lower tissue strain, but form a larger standing cutaneous deformity. The Webster flap best distributes wound tension across the incision line, and the Dufourmental modification alters the closure force vector.

Vioxx for adult post-tonsillectomy and UPPP pain: A randomized prospective controlled trial

Abstract Problem: In this randomized, double-blinded prospective randomized controlled trial, we studied whether adult patients benefit from Vioxx (rofecoxib), a selective cyclo-oxygenase (COX) 2 isoenzyme inhibitor in conjunction with Tylenol with a narcotic (codeine or hydrocodone) for post-tonsillectomy and uvulopalatopharyngoplasty (UPPP) pain. Methods: Forty patients undergoing tonsillectomy and/or UPPP (in separate arms) were given Tylenol with a narcotic and either rofecoxib or placebo. They were then asked to complete a questionnaire on a daily basis for 2 weeks, which was designed to track bleeding, throat and ear pain, fever, and the amount of narcotic pain medication taken. Results: There was no difference in the amount of narcotic taken or pain level between treatment and control groups. In addition, no difference in rates of bleeding or fever was detected. Conclusion: The treatment of adult post-tonsillectomy or UPPP pain postoperatively with Vioxx as an adjunct to Tylenol with a narcotic does not appear to be beneficial. Significance: Tonsillectomy and UPPP are very painful surgeries often requiring significant amounts of narcotic pain medication, which has undesirable side effects. Using rofecoxib, an anti-inflammatory, postoperatively as an adjunct would appear logical and is occasionally used because it does not have any increased bleeding risk like ibuprofen or aspirin and works via a different mechanism from that of Tylenol or narcotics. In addition, this pain is thought to be largely the result of local inflammation. Despite these facts, our data do not support its use beginning postoperatively. Support: none

Congenital pyriform aperture stenosis-management and novel approach

Abstract Objectives: We present a brief review of our preoperative preparation and surgical technique used in the correction of congenital pyriform aperture stenosis. We also discuss the postoperative care and potential complications of the procedure. Methods: Surgical correction of a congenital anomaly with the aid of 3-D modelling and microinstruments. Results: The outcome of our patient is reviewed as well as considerations for improvements in the treatment of future patients. Conclusion: Congenital pyriform aperture stenosis is a rare congenital deformity. When the stenosis is severe prompt intervention is required. The use of a CT-generated 3-D model greatly enhanced our surgical planning. The use of microinstruments allowed precise surgical correction complementing the preoperative surgical plan.