Biomedical subjects

Brian K Bay

Publications and source records attributed to Brian K Bay.

7 recordsLinked to original sources

PubMed2005

The behavior of thoracic trabecular bone during flexion.

Thoracic compression fractures are often described as anterior wedge fractures. Although the radiographic signs of these fractures are easily identified, the mechanism of the trabecular failure is not well understood. The current study addressed this mechanism in the lower thoracic spine by measuring the trabecular strain. Trabecular strain was measured in six human thoracic cadaver spines during 1) compressive and 2) flexural loading. The strains were measured at incremental loads using a texture correlation. They were analyzed by global contour plots and regional analysis of the T11 vertebrae. Specimens loaded under only compression exhibited uniform strains in the vertebral body. During flexion, however, the strains were concentrated in the anterosuperior margin of the vertebral body and the compressive and shear strain magnitudes in this region were significantly increased. These results demonstrate that the flexural position places the lower thoracic spine at greater risk of anterior compression fracture as seen clinically.

Aged↗

PubMed2004

Development of an animal model of acetabular fractures.

A closed intraarticular fracture is a complex injury that consists of a physical disruption of the subchondral bone and articular surface, and an impaction injury to the articular surface that occurs at the time of the fracture. Few experimental models have been able to incorporate the elements of displaced articular fractures and blunt impaction injury to the articular surface. This work details the initial stages of an attempt to develop such model. Using a model of a dorsal wall fracture of the acetabulum in a goat, we have developed a bench-top method for assessing articular contact stress. Additionally, preliminary in vivo survival data are presented.

Acetabulum↗

PubMed2003

Trabecular bone strain changes associated with subchondral stiffening of the proximal tibia.

Subchondral stiffening is a hallmark pathologic feature of osteoarthritis but its mechanical and temporal relationship to the initiation or the progression of osteoarthritis is not established. The mechanical effect of subchondral stiffening on the surrounding trabecular bone is poorly understood. This study employs a relatively new application of digital image correlation to measure strain in the trabecular region of the proximal medial tibia in normal specimens and in specimens with simulated subchondral bone stiffening. Coronal sections from eight normal human cadaveric proximal tibiae were loaded in static compression and high resolution contact radiographs were made. Repeat contact radiographs were collected after the subchondral bone near the jointline was stiffened using polymethylmethacrylate. Digital images, made from loaded and unloaded contact radiographs, were compared using in-house software to measure trabecular displacement and calculate trabecular bone strain. Overall strain was higher in the stiffened specimens suggesting experimental artifiact significantly affected our results. Consistent increases in median maximum shear strain, median maximum principal strain, median minimum principal strain, and peak shear strain were measured near the inner and outer edges of the stiffened segment. Our experiment provides direct experimental measurement of increases in trabecular bone strain caused by subchondral stiffening, however, the clinical and biologic importance of strain increases is unknown.

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PubMed2003

Trabecular bone strain changes resulting from partial and complete meniscectomy.

Previous studies have documented how partial and complete meniscectomy affect articular contact pressure, but changes in load transfer through the complete osteochondral structure of the proximal tibia after partial and complete meniscectomy are not well known. The current study measured trabecular bone strain changes in the medial tibial plateau resulting from partial and complete medial meniscectomy. Midcoronal sections were prepared from knees from cadavers. High quality digital images, made from contact radiographs of loaded samples, were compared with digital images of unloaded samples using in-house software to measure trabecular bone strain. Measurements were made on specimens with an intact medial meniscus, after removal of the inner (2/3) of the meniscus, and after complete meniscectomy. Partial meniscectomy caused minimal increases in trabecular bone strain throughout the proximal tibia. However specimens with complete meniscectomy had significant trabecular bone strain increases. Many patients sustaining meniscus tears are young, therefore, it is important to understand mechanical changes associated with partial meniscectomy. The data suggest partial meniscectomy causes little change in load transfer through the proximal tibia, supporting partial meniscectomy as a good surgical option for patients with meniscus tears.

Aged↗

PubMed2003

Biomechanical comparison of posterior pelvic ring fixation.

OBJECTIVE: To determine relative stiffness of various methods of posterior pelvic ring internal fixation. DESIGN: Simulated single leg stance loading of OTA 61-Cl.2, a2 fracture model (unilateral sacroiliac joint disruption and pubic symphysis diastasis). SETTING: Orthopaedic biomechanic laboratory. OUTCOME VARIABLES: Pubic symphysis gapping, sacroiliac joint gapping, hemipelvis coronal plane rotation. METHODS: Nine different posterior pelvic ring fixation methods were tested on each of six hard plastic pelvic models. Pubic symphysis was plated. The pelvic ring was loaded to 1000N. RESULTS: All data were normalized to values obtained with posterior fixation with a single iliosacral screw. The types of fixation could be grouped into three categories based on relative stiffness of fixation: For sacroiliac joint gapping, group 1-fixation stiffness 0.8 and above (least stiff) includes a single iliosacral screw (conditions A and J), an isolated tension band plate (condition F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate stiffness) includes a tension band plate and an iliosacral screw (condition E), one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (greatest stiffness) includes two anterior sacroiliac plates (condition D), two iliosacral screws (condition B), and two anterior sacroiliac plates and an iliosacral screw (condition C). For sacroiliac joint rotation, group 1-fixation stiffness 0.8 and above includes a single iliosacral screw (conditions A and J), two anterior sacroiliac plates (condition D), a tension band plate in isolation or in combination with an iliosacral screw (conditions E and F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate level of instability) includes either one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (stiffest fixation) consists of two iliosacral screws (condition B) and two anterior sacroiliac plates and an iliosacral screw (condition C). DISCUSSION: Under conditions of maximal instability with similar material properties between specimens, differences in stiffness of posterior pelvic ring fixation can be demonstrated. The choice of which method to use is multifactorial.

Fracture Fixation↗

PubMed2002

Trabecular bone strain changes associated with subchondral bone defects of the tibial plateau.

OBJECTIVE: To measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the medial tibial plateau. DESIGN: Cadaveric biomechanical model. SETTING: Contact radiographs were made from coronal sections of human cadaveric proximal tibia under no load and loaded to 400 newtons (N). Digital images made from contact radiographs of unloaded specimens were compared to corresponding digital images of loaded specimens using in-house software that detects trabecular deformation and measure trabecular bone strain. INTERVENTION: Ten specimens were loaded intact and with three increasing circular subchondral bone defects and centered under the subchondral plates in the medial tibial plateau that were 10%, 20%, and 30% of the coronal width of the medial plateau. MAIN OUTCOME MEASURE: Maximum shear strain and minimum principal strain were measured at approximately 2,600 discrete points in the trabecular bone in the medial tibial plateau. RESULTS: Trabecular strain increased most dramatically as defects increased from the medium (20%) to the large (30%) defect. The regions of greatest strain elevation were between the physeal scar and joint line near the medial cortex. Small (10%) and medium (20%) defects resulted in modest strain elevations. CONCLUSIONS: Subchondral defects cause size-dependent elevations in trabecular bone strain in the medial tibial plateau. A size threshold may exist, above which the trabecular bone is subjected to rapidly increasing deformation under load.

Aged↗

PubMedDate not supplied

Trabecular bone strain changes associated with subchondral comminution of the distal tibia.

OBJECTIVE: To measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the distal tibia. DESIGN: Cadaveric biomechanical model. SETTING: Contact radiographs were made from sagittal sections of human cadaveric distal tibia under no load and loaded to 400 N. Digital images, made from contact radiographs of unloaded specimens, were compared to corresponding digital images of loaded specimens using custom software that measures trabecular deformation and calculates trabecular bone strain. INTERVENTION: Twelve specimens were initially loaded intact in compression. Testing was repeated after creating three increasing circular subchondral bone defects in the center of a sagittal cross-section of the distal tibia. Defects were 10%, 20%, and 30% of the sagittal diameter of the distal tibia. MAIN OUTCOME MEASURES: Maximum shear strain, maximum principal strain, and minimum principal strain were measured in six discrete regions in the trabecular bone in the distal tibia. RESULTS: Small defects (10%) caused minimal strain elevations. Significant increases in trabecular bone strain were measured with medium (20%) and large (30%) defects. Compressive strain increases as high as 1400 microstrain (10 strain) were measured adjacent to and proximal to the defects with medium and large defects. CONCLUSIONS: Subchondral defects cause size-dependent elevations in trabecular bone strain in the distal tibia. Medium and large defects caused rapidly increasing trabecular bone deformation under load.

Adult↗