Biomedical subjects

John A Szivek

Publications and source records attributed to John A Szivek.

7 recordsLinked to original sources

PubMed2006

Functionally improved bone in calbindin-D28k knockout mice.

In vitro studies indicate that Calbindin-D28k, a calcium binding protein, is important in regulating the life span of osteoblasts as well as the mineralization of bone extracellular matrix. The recent creation of a Calbindin-D28k knockout mouse has provided the opportunity to study the physiological effects of the Calbindin-D28k protein on bone remodeling in vivo. In this experiment, histomorphometry, microCT, and bend testing were used to characterize bones in Calbindin-D28k KO (knockout) mice. The femora of Calbindin-D28k KO mice had significantly increased cortical bone volume (60.4% +/- 3.1) compared to wild-type (WT) mice (45.4% +/- 4.6). The increased bone volume was due to a decrease in marrow cavity area, and significantly decreased endosteal perimeters (3.397 mm +/- 0.278 in Calbindin-D28k KO mice, and 4.046 mm +/- 0.450 in WT mice). Similar changes were noted in the analysis of the tibias in both mice. The bone formation rates were similar in the femoral and tibial cortical bones of both mice. microCT analysis of the trabecular bone in the tibial plateau indicated that Calbindin-D28k KO mice had an increased bone volume (35.2% +/- 3.1) compared to WT mice (24.7% +/- 4.9) which was primarily due to increased trabecular number (8.99 mm(-1) +/- 0.94 in Calbindin-D28k KO mice compared to 6.75 mm(-1) +/- 0.85 in WT mice). Bone mineral content analysis of the tibias indicated that there is no difference in the calcium or phosphorus content between the Calbindin-D28k KO and WT mice. Cantilever bend testing of the femora demonstrated significantly lower strains in the bones of Calbindin-D28k KO mice (4135 micro strain/kg +/- 1266) compared to WT mice (6973 micro strain/kg +/- 998) indicating that the KO mice had stiffer bones. Three-point bending demonstrated increased failure loads in bones of Calbindin-D28k KO mice (31.6 N +/- 2.1) compared to WT mice (15.0 N +/- 1.7). In conclusion, Calbindin-D28k KO mice had increased bone volume and stiffness indicating that Calbindin-D28k plays an important role in bone remodeling.

Animals↗

PubMed2006

A comparison of the effects of radiofrequency treatment and mechanical shaving for meniscectomy.

PURPOSE: The goal of this ex vivo pilot study was to compare radiofrequency treatment with cutting and shaving treatment of meniscal tears by use of a mechanical testing procedure and electron microscopy to establish the mechanical characteristics and qualitative appearance of meniscal tissue after the use of each of these procedures. METHODS: In this study 136 menisci were explanted and divided into 4 groups: a damaged, untreated control group; a group damaged in the same way as the control group and treated by mechanical shaving of the meniscal tear; a group damaged in a similar way and then treated by radiofrequency by use of a radiofrequency wand; and a fourth group in which plunge-cutting by use of the radiofrequency wand was used to resect the tissue, beginning at the superior surface of the meniscus in a place that corresponded to the location of the meniscal tears. The menisci were then tested for strength by applying radial tension to the tear. Electron microscopy at low and high magnification was used to evaluate the appearance of the surface of the menisci after shaving or radiofrequency treatment. RESULTS: Static mechanical testing to failure showed no significant difference between the control group and the 3 test groups. However, there was a statistically significant difference between the radiofrequency-treated groups and the mechanically shaved group at the .033 level. On fatigue testing, there was no statistically significant difference in the failure cycles, but the coefficient of variation was 8 times greater for the mechanically shaved menisci versus the radiofrequency-treated menisci. Scanning electron microscopy showed that the mechanically treated menisci had flat surfaces with clefts or fissures. The radiofrequency-treated menisci had a homogeneous appearance without clefts. CONCLUSIONS: This study showed that radiofrequency-treated damaged tissue leaves a qualitatively different surface from the mechanically treated menisci, which failed at a significantly higher load on static testing. On fatigue testing, there was greater variation in the number of cycles to failure of mechanically treated specimens versus the radiofrequency-treated menisci. CLINICAL RELEVANCE: Although recurrent meniscal tears are uncommon, they may be of value in evaluating different methods of meniscectomy. This study points out mechanical and qualitative differences between shaved and radiofrequency-treated meniscectomy.

Animals↗

PubMed2005

In vivo strain measurements from hardware and lamina during spine fusion.

Currently, spine fusion is determined using radiography and clinical evaluation. There are discrepancies between radiographic evidence and direct measurements of fusion, such as operative exploration and biomechanical or histological measurements. In order to facilitate the rapid return of patients to normal activities, a monitoring technique to accurately detect fusion in vivo and to prevent overload during the postoperative period would be useful. The objectives of this study were to develop an implantable monitoring system consisting of CPC-coated strain gauges and a radio transmitter to detect the onset of fusion and measure strain during postsurgical activities. A patient underwent anterior release and fusion, followed by posterior instrumentation and fusion with segmental spinal instrumentation. Four strain gauges were placed during surgery. One was attached to the left-side rod and one to each of the lamina at T9, T10, and T11. An externally powered implanted radio transmitter attached to the gauges was placed in a subcutaneous pouch. Strains were monitored weekly and tabulated during various activities for 7 months. Peak strains during twisting and bending were tabulated to detect the onset of fusion. Strains were also recorded during activities such as climbing off an examination table, rising from a chair, and climbing stairs. Strains collected from the left rod indicated that, immediately postoperatively, it was loaded at acceptable levels. The largest and most consistent strain changes measured from the lamina were recorded during twisting.

Adolescent↗

PubMed2004

Transforming growth factor-beta1 accelerates bone bonding to a blended calcium phosphate ceramic coating: a dose-response study.

In vivo strain measurements can facilitate the study of the bone remodeling response to loading and load changes. Calcium phosphate ceramic (CPC) coatings have been used to attach strain gauges to bone for extended periods of time, but require up to 12 weeks for adequate CPC-to-bone bonding. Transforming growth factor beta 1 (TGF-beta1), an osteoinductive growth factor, was used as a surface enhancement to accelerate bone growth and bonding to CPC particles. The aim of this study was to find an optimal dosage of TGF-beta1 to accelerate the attachment process. CPC-coated strain gauges were enhanced with doses of 0.5, 1.0, or 2.0 microg of TGF-beta1 per gauge. Gauges were placed on the femora of dogs, which were exercised daily and fed ad libitum. After 3, 6, and 12 weeks, gauge attachment was quantitatively assessed using mechanical testing and histomorphometry. Gauge attachment was also qualitatively assessed using back scatter electron microscopy. Agreement of the mechanical test results with both the back scatter electron microscopy images and histomorphometry results showed that the 1.0 microg per gauge dose of TGF-beta1 is an optimal dose to accelerate bone formation and attachment to CPC-coated strain gauges.

Animals↗

PubMed2004

Bilateral symmetry of biomechanical properties in mouse femora.

Bone healing and remodeling are commonly examined in animal models by comparing one femur (experimental) to the contralateral femur (control) with the assumption that they are identical with respect to their biomechanical properties. While past studies have characterized the symmetry in geometrical properties in many types of animal bones, few studies have compared the symmetry in the biomechanical properties. The purpose of this study was to determine whether there is symmetry in the mechanical properties of mouse femora. Strain gauges were attached to the posterior surface of the femora of C57BL/6 mice, parallel to the long axis of the bone. The femora were mechanically tested in cantilever bending while strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Mouse femora demonstrated an average strain difference of 0.4% in tension and 1.4% in compression. Elastic moduli differed by 6.6% and 0.9% in tension and compression, respectively, and failure strength differed by an average of 2.0%. Statistical analysis showed there were no significant differences in strain, modulus, or failure load values for the mice, indicating mechanical and geometrical symmetry of mouse femora in cantilever bending.

Anatomy, Cross-Sectional↗

PubMed2003

Evaluation of a new CPC-to-gauge bonding technique with the use of in vitro fluid flow.

Strain gauging enables the measurement of bone deformation during physical activity, leading to a better understanding of the physiological effects of loading on bone growth and remodeling. Development of a technology that will withstand long-term in vivo exposure and bond securely to bone is imperative for accurate, consistent measurement collection. Polysulfone is currently used to attach calcium-phosphate ceramic (CPC) particles, which promote bone-to-gauge bonding, to polyimide-backed strain gauges. This study evaluated the use of an implant-grade epoxy as an alternative CPC-polyimide adhesive. Polyimide-epoxy-CPC interfaces were loaded to failure and shear strengths calculated. In vitro studies providing a constant flow of medium over test specimens were designed, and long-term in vitro fluid exposure studies of the epoxy's shear strength were conducted. Average shear strength of polysulfone-polyimide interfaces were reported to be 7 MPa. The average shear strength of the epoxy-polyimide interface before long-term in vitro exposure was 17 MPa, which is stronger than the shear strength of the bone-CPC interface. The strength of the epoxy-polyimide interface decreased to 6.8 MPa after 24 weeks in vitro and 3 MPa after 24 weeks in vivo.

Animals↗

PubMed2002

An implantable strain measurement system designed to detect spine fusion: preliminary results from a biomechanical in vivo study.

STUDY DESIGN: The strain distribution on the thoracic vertebrae during anteroposterior bending and torsion was examined for use with an implantable strain gauge system and miniature radio transmitter, which also were evaluated. OBJECTIVES: To identify strain gauge placement sites by testing cadaver spines in vivo, and to evaluate an implantable gauge bonding technique and subminiature radio transmitter for accurate strain monitoring. SUMMARY OF BACKGROUND DATA: Fusion is determined currently through the use of radiographic techniques. Discrepancies exist between radiographic evidence and more direct measurements of fusion such as operative exploration4,5,12 and biomechanical or histologic measurements.12,15 To facilitate the return of patients to full unrestricted activity, it would be useful to develop a technique for accurate in vivo determination of fusion. METHODS: Three cadaver spines were tested during anteroposterior bending and torsional loading in the control, instrumented, and instrumented plus polymethylmethacrylate states. The spines were instrumented with an ISOLA(R) (Acromed Corporation, Cleveland, Ohio) construct, and a simulated fusion was achieved through the application of polymethylmethacrylate. Strain gauges were attached in uniaxial, biaxial, and rosette configurations. The principal strains were calculated. Calcium phosphate ceramic-coated gauges were implanted in patients and recovered after up to 15 months in vivo. A radio transmitter was developed and tested for use in patients. RESULTS: The largest and most consistent strain changes after simulated fusion were recorded during torsional loading on the laminae of a vertebra directly underneath a hook. Calcium phosphate ceramic-coated strain gauges showed excellent bone bonding to the lamina when fusion occurred. Radio telemetry accurately tracked strain magnitudes and strain rates expected in patients. CONCLUSIONS: The consistency obtained in torsional loading indicates that this type of loading will provide the most useful data from patients in vivo. Excellent bonebonding and accurate strain transmission using a long-term strain measurement system and miniature radio transmitter indicate that strains collected from patients with this system will be accurate.

Adult↗