Thomas M. Cervantes

Design and experimental evaluation of adjustable bone plates for mandibular fracture fixation

Conventional bone plates are commonly used for surgical mandibular fracture fixation. Improper alignment between bone segments, however, can result in malocclusion. Current methods of fixation require a surgeon to visually align segments of bone and affix a metal plate using bone screws, after which little can be done to adjust alignment. A method of adjusting fracture alignment after plate placement, without screw removal, presents an improvement over costly and risky revision surgery. A modified bone plate has been designed with a deformable section to give surgeons the ability to reduce misalignments at the fracture site. The mechanics of deformation for various adjustment mechanisms was explored analytically, numerically, and experimentally to ensure that the adjustable plate is comparable to conventional bone plates. A static force of 358.8 N is required to deform the adjustable bone plate, compared with predicted values of 351 N using numerical simulation and 362 N using a simple beam theory. Dynamic testing was performed to simulate in vivo loading conditions and evaluate load-capacity in both deformed and un-deformed bone plates. Results indicate that bending stiffness of a rectangular bone plate is 709 N/mm, compared with 174 N/mm for an octagonal plate and 176 N/mm for standard plates. Once deformed, the rectangular and octagonal plates had a stiffness of 323 N/mm and 228 N/mm, respectively. Un-deformed and deformed adjustable bone plates have efficacy in bone segment fixation and healing.

Evaluation of a minimally invasive renal cooling device using heat transfer analysis and an in vivo porcine model

Partial nephrectomy is the gold standard treatment for renal cell carcinoma. This procedure requires temporary occlusion of the renal artery, which can cause irreversible damage due to warm ischemia after 30 min. Open surgical procedures use crushed ice to induce a mild hypothermia of 20°C in the kidney, which can increase allowable ischemia time up to 2.5 h. The Kidney Cooler device was developed previously by the authors to achieve renal cooling using a minimally invasive approach. In the present study an analytical model of kidney cooling in situ was developed using heat transfer equations to determine the effect of kidney thickness on cooling time. In vivo porcine testing was conducted to evaluate the cooling performance of this device and to identify opportunities for improved surgical handling. Renal temperature was measured continuously at 6 points using probes placed orthogonally to each other within the kidney. Results showed that the device can cool the core of the kidney to 20°C in 10-20 min. Design enhancements were made based on surgeon feedback; it was determined that the addition of an insulating air layer below the device increased difficulty of positioning the device around the kidney and did not significantly enhance cooling performance. The Kidney Cooler has been shown to effectively induce mild renal hypothermia of 20°C in an in vivo porcine model.

Analysis and design of rolling-contact joints for evaluating bone plate performance.

An apparatus for testing maxillofacial bone plates has been designed using a rolling contact joint. First, a free-body representation of the fracture fixation techniques utilizing bone plates is used to illustrate how rolling contact joints accurately simulate in vivo biomechanics. Next, a deterministic description of machine functional requirements is given, and is then used to drive the subsequent selection and design of machine elements. Hertz contact stress and fatigue analysis for two elements are used to ensure that the machine will both withstand loads required to deform different plates, and maintain a high cycle lifetime for testing large numbers of plates. Additionally, clinically relevant deformations are presented to illustrate how stiffness is affected after a deformation is applied, and to highlight improvements made by the machine over current testing standards, which do not adequately re-create in vivo loading conditions. The machine performed as expected and allowed for analysis of bone plates in both deformed and un-deformed configurations to be conducted. Data for deformation experiments is presented to show that the rolling-contact testing machine leads to improved loading configurations, and thus a more accurate description of plate performance. A machine for evaluation of maxillofacial bone plates has been designed, manufactured, and used to accurately simulate in vivo loading conditions to more effectively evaluate the performance of both new and existing bone plates.

Renal Cooling Device for Use in Minimally Invasive Surgery

Over 58,000 patients suffer from renal cell carcinoma annually in the U.S. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however, there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ. It is deployed through a 15 mm trocar, wrapped around the kidney, and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 min. The ice slurry is then removed from the device and the device is retracted from the body. Modeling results and tests of the prototype in a simulated lab environment show that the device successfully cools porcine kidneys from 37°C to 20°C in 6–20 min.

Innovative Renal Cooling Device for Use in Minimally Invasive Surgery

Over 58,000 patients suffer from renal cell carcinoma annually in the US. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A novel device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ like a taco shell. It is deployed through a 12mm trocar, wrapped around the kidney and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 minutes. The ice slurry is then removed from the device and the device is retracted from the body. Tests of the prototype show that the device successfully cools porcine kidneys from 37 � C to 20 � C in under 5 minutes.