Biomedical subjects

Zong-Ping Luo

Publications and source records attributed to Zong-Ping Luo.

At least 19 recordsLinked to original sources

PubMed2006

Compressive loading at the end plate directly regulates flow and deformation of the basivertebral vein: an analytical study.

BACKGROUND: Metastatic diseases and infections frequently involve the spine. This is the result of seeding of the vertebral body by tumor cells or bacteria delivered by venous blood from Batson's plexus, which is hypothesized to enter the vertebral body via the epidural veins. Isolated spinal segments deform significantly at the bony end plate when under compression. This deformation could cause a volume change of the vertebral body and may be accompanied by retrograde flow of venous blood. To date, this process has not been investigated quantitatively. The purpose of this study was to determine the volume changes of the vertebral body and basivertebral vein for a vertebral body under compression. METHODS: A three-dimensional finite element mesh model of the L4 segment with both adjacent discs was modified from a 3-D computed tomography scan image. An octagon representing the basivertebral vein was introduced into the center of the vertebral body in the model. Four compressive orientations (1500 N) were applied on the top disc. The volume change of the vertebral body model and the basivertebral vein were then computed. RESULTS: The volume change of the vertebral body was about 0.1 cm3 (16.3% of the basivertebral vein) for the four loading conditions. The maximum cross-sectional area reductions of the basivertebral vein and volume reduction were 1.54% and 1.02%, for uniform compression. CONCLUSION: Our study quantified the small but significant volume change of a modeled vertebral body and cross-sectional areas and that of the basivertebral vein, due to the inward bulging of the end plate under compression. This volume change could initiate the reverse flow of blood from the epidural venous system and cause seeding of tumors or bacterial cells.

Journal Article↗

PubMed2006

Strength of damaged suture: an in vitro study.

PURPOSE: To determine the mechanical properties of damaged suture. METHODS: Undamaged and damaged sutures were tested by a single pull to failure. Sutures were damaged with a razor blade incorporated into a custom-designed jig. Sutures were tested to failure by straight pull and by pulling at 180 degrees through a suture anchor eyelet. The friction of sutures through anchors was also tested. RESULTS: For the straight line pull test, undamaged FiberWire (Arthrex, Naples, FL) had the highest load to failure (LTF) and ultimate tensile strength (UTS) of all sutures tested. Undamaged Orthocord (Mitek, Somerville, NJ) ranked second in both properties. Uncut polydioxanone (PDS) suture (Ethicon, Somerville, NJ) had a higher LTF and a comparable UTS with respect to Tevdek (Deknatel, Mansfield, MA) and Ethibond (Ethicon). For cut sutures, FiberWire and Orthocord had a significantly higher LTF and UTS than the other sutures tested. Suture stiffness was not significantly affected when the suture was cut. For the suture anchor test, FiberWire and Orthocord had the highest LTF, whether undamaged or damaged. When cut, PDS had the greatest loss of LTF and UTS during both tests. CONCLUSIONS: The newer polyethylene core sutures (FiberWire and Orthocord) have superior mechanical properties compared with other sutures. Their superior properties are maintained even when cut. Although uncut PDS had equivalent or superior strength compared with Ethibond and Tevdek, once cut, PDS suture was weakened significantly more compared with all other sutures tested. CLINICAL RELEVANCE: The mechanical properties of damaged suture are important to all surgeons who use suture arthroscopically.

Biomechanical Phenomena↗

PubMed2006

Gliding resistance of the posterior tibial tendon.

BACKGROUND: Abnormal gliding of the posterior tibial tendon may lead to mechanical trauma, degeneration, and eventually posterior tibial tendon dysfunction. Our study analyzed the gliding resistance of the posterior tibial tendon in intact feet and in feet with simulated flatfoot deformity. METHODS: An experimental system was developed that allowed direct measurement of gliding resistance at the tendon-sheath interface. Seven normal fresh-frozen cadaver foot specimens were studied, and gliding resistance between the posterior tibial tendon and sheath was measured. The effects of ankle and hindfoot position and the effect of flatfoot deformity on gliding resistance were analyzed. Gliding resistance was measured for 4.9 N applied load to the tendon. RESULTS: Mean gliding resistance for the neutral position was 77 +/- 13.1 (x10(-2) N). Compared to neutral position, dorsiflexion increased gliding resistance and averaged 130 +/- 38.9 (x10(-2) N), and plantarflexion decreased gliding resistance and averaged 35 +/- 12.6 (x10(-2) N). Flatfoot deformity increased gliding resistance compared to normal feet, averaging 104 +/- 17.0 (x10(-2) N) for neutral, 205 +/- 55.0 (x10(-2) N) for dorsiflexion, and 58 +/- 21.3 (x10(-2) N) for plantarflexion. CONCLUSIONS: The findings indicate that patients with a preexisting flatfoot deformity may be predisposed to develop posterior tibial tendon dysfunction because of increased gliding resistance and trauma to the tendon surface.

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PubMed2006

Ankle ligament tensile forces at the end points of passive circumferential rotating motion of the ankle and subtalar joint complex.

BACKGROUND: Ankle ligament injuries and instability are commonly observed. Knowledge of the relationship between the foot position and tensile forces of the ankle ligaments could be useful for treatment of ankle ligament disorders. The aim of this study was to measure the tensile forces of the ankle ligaments at the end points of passive circumferential rotating motion of the ankle and subtalar joint complex in various foot positions. METHODS: Ligament tensile forces of the anterior talofibular (ATF), calcaneofibular (CF), posterior talofibular (PTF), and tibiocalcaneal (TC) ligaments were measured simultaneously in eight cadaver specimens, with a force probe in each ligament in a custom-made ankle ligament testing device. Weights of 0.5 kg and 1 kg were applied to the foot through a loading arm to provide axial compression and a bending moment to the foot and ankle. The position of the loading arm was changed circumferentially in 10-degree increments. RESULTS: Maximal tensile force in the ATF ligament was observed in supination with plantarflexion (108 +/- 62.8 N at 0.5 kg and 130 +/- 39.1 N at 1 kg). The maximal tensile force in the CF ligament was observed in pronation with plantarflexion (68 +/- 48.6 N at 0.5 kg and 135 +/- 92.9 N at 1 kg). The maximal tensile force in the PTF ligament was observed in dorsiflexion (131 +/- 80.1 N at 0.5 kg and 109 +/- 36.3 N at 1 kg). The maximal tensile force of the TC ligament was observed in pronation with plantarflexion (49.0 +/- 80.1 N at 0.5 kg and 67.4 +/- 69.6 N at 1 kg). Relatively high magnitudes of tensile force were observed in the ankle ligaments, and the peak forces were related to the anatomic position of individual ligaments. CONCLUSIONS: The ATF ligament has an important role in the supination position in plantarflexion, CF and TC ligaments also are important for pronation in plantarflexion, and the PTF is an important stabilizer in dorsiflexion. This study provides baseline information for further research related to ligament instability and reconstruction operations.

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PubMed2006

Comparison of modified Broström and Evans procedures in simulated lateral ankle injury.

PURPOSE: The purpose of this study was to compare the modified Broström and Evans procedures for simulated lateral ankle instability in cadaveric lower extremities. METHODS: Six normal cadaveric ankles were loaded with inversion and internal rotation stress through the range of ankle flexion, and three-dimensional motion of the calcaneus and talus relative to the tibia were measured. An ankle stability testing device and a magnetic tracking system were used. Testing was performed in the intact condition, unstable condition after sectioning both the anterior talofibular (ATFL) and calcaneofibular ligaments (CFL), after the Gould modification of the Broström procedure, and after the Evans procedure. RESULTS: With inversion loading, both operations resulted in a significantly more stable ankle-hindfoot complex (calcaneal-tibial) than the unstable condition, but there was restricted motion after the Evans operation from neutral to plantarflexion. Tibiotalar inversion motion approximated normal after both operations, but subtalar motion was markedly restricted in the Evans procedure throughout the range of ankle flexion. With internal rotation loading, the Broström operation stabilized the ankle-hindfoot joint complex in plantarflexion. The Evans operation improved internal rotation stability, but restricted motion in all positions. Both operations improved tibiotalar internal rotation stability, but not to normal. The subtalar internal rotation was the same as the intact condition after the Broström operation, but markedly restricted after the Evans operation through the range of ankle flexion. CONCLUSIONS: Both operations improved ankle-hindfoot stability, but neither was successful in restoring it to normal as determined with the ankle stability testing device. The Evans procedure improved stability at the expense of creating abnormal subtalar function. The Broström operation improved stability without excessively restricting subtalar movement, but was not effective in addressing the internal rotation laxity.

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PubMed2005

Interactions between collagen IX and biglycan measured by atomic force microscopy.

The stability of the lattice-like type II collagen architecture of articular cartilage is paramount to its optimal function. Such stability not only depends on the rigidity of collagen fibrils themselves, but more importantly, on their interconnections. One known interconnection is through type IX and biglycan molecules. However, the mechanical properties of this interaction and its role in the overall stability remain unrevealed. Using atomic force microscopy, this study directly measured the mechanical strength (or the rupture force) of a single bond between collagen IX and biglycan. The results demonstrated that the rupture force of this single bond was 15pN, which was significantly smaller than those of other known molecule interactions to date. This result suggested that type IX collagen and biglycan interaction may be the weak link in the cartilage collagen architecture, vulnerable to abnormal joint force and associated with disorders such as osteoarthritis.

Biglycan↗

PubMed2005

Strain-related collagen gene expression in human osteoblast-like cells.

The gene expression of cells in the musculoskeletal system, such as in bone, cartilage, ligament and tendon, is profoundly affected by mechanical loading. Previous studies have demonstrated that the expression of many genes, including collagen types I and III, are affected by mechanical strain in diverse cell types, such as human osteoblast-like SaOs-2 cells. However, whether the effect of mechanical loading on collagen gene expression is strain-related remains unclear. The goal of this study was to determine the relationship between mechanical strain and the gene expression of collagen types I and III in SaOs-2 cells. A Flexercell cellular mechanical loading system was used to subject SaOs-2 cells to equibiaxial cyclic tensile stress at a rate of 0.5 Hz with various strains of 5%, 7.5%, 10%, and 12.5% for 24 h. The relative amount of mRNA of both collagen I and collagen III increased at 5% strain compared with that of the control. As the strain increased, the relative amount of mRNA of collagen I remained stable at strain levels up to 12.5%. However, the mRNA for collagen III began to drop when the strain was greater than 5%, until a 10% strain was reached. From the application of a 10% strain through the maximum loading of a 12.5% strain, the relative amount of collagen III mRNA remained stable at amounts lower than that of the control. Thus, the gene expression of collagen types I and III responds differentially to mechanical strain at various magnitudes.

Cell Line, Tumor↗

PubMed2005

Direct measurement of the rupture force of single pair of decorin interactions.

Decorin is one important member of the family of small leucine-rich proteoglycans, which are widely distributed in connective tissues in the body such as tendon and ligament. Decorin may be responsible for collagen fibril connection in those tissues. A recent hypothesis suggests that decorin may bind to collagen with its core protein while binding to another decorin through the interaction with their glycosaminoglycan (GAG) chains. However, there is no direct evidence supporting this hypothesis to date. In this study, the interaction of decorin GAG chains was directly determined for the first time. The rupture force of single bonds between decorins (GAG chains interaction) was determined directly as 16.5+/-5.1 pN using a laser tweezers/interferometer single molecular nanomechanical testing system. This information can improve our understanding of the mechanical properties of connective tissues at the molecular level.

Animals↗

PubMed2005

Combined effects of estrogen and mechanical loading on anterior cruciate ligament fibroblast biosynthesis.

For some time, estrogen has been suspected to play a negative role in anterior cruciate ligament (ACL) fibroblast biosynthesis; however, reports on this issue have been controversial. In a recent study, our group demonstrated a negative combined effect of estrogen and mechanical loading on the gene expression of major extracellular matrix component molecules in ACL fibroblasts.

Anterior Cruciate Ligament↗

PubMed2005

A modified cell culture method for autologous chondrocyte transplantation.

Autologous chondrocyte transplantation (ACT) is a promising method to treat chondral and osteochondral defects. This study introduced a modified method for cell culture in ACT. Porcine chondrocytes were cultured for 3 weeks under low hydrostatic pressure at 250 Pa. The results showed that the dry weight of the cartilage-like membrane in the loading group was 3.0 times more than the control group (no loading) (p < 0.01), and cell numbers were significantly increased by 3.1 times (p < 0.01) after a 3-week culture. Compared with the fresh tissue sample, the mRNA expression of collagen II was not statistically different and the mRNA of aggrecan was only slightly decreased by 19%. These data suggest that the hydrostatic pressure at this level significantly increased the cell numbers and biosynthesis of cultured chondrocytes.

Animals↗

PubMed2005

Stress distribution in the superior labrum during throwing motion.

BACKGROUND: Superior labrum anterior posterior lesions are common among athletes participating in overhead throwing sports. One described mechanism of injury is application of high local stress via repetitive loading of the long head of the biceps tendon attached to the superior labrum; however, the stress environment within the labrum has not been investigated to date. HYPOTHESIS: Biceps origin locations and throwing phases determine the stress distributions causing lesions of the superior labrum within the labrum itself. STUDY DESIGN: Descriptive laboratory study. METHODS: Three-dimensional finite element models of the labrum glenoid complex with anterior, central, and posterior biceps origins were developed at 4 orientations to simulate the phases of pitching: early cocking, late cocking, acceleration, and deceleration. RESULTS: The stress magnitudes at the labrum glenoid interface for the deceleration phase were highest for all biceps origins. Anatomical variations of the biceps insertion affected the stress only during the deceleration phase. Both the biceps origin and throwing phase influenced the location of high stress. CONCLUSION: Deceleration could be the throwing phase that causes tearing at the superior labrum. This finding provides further understanding for localizing the possible initiation of superior labrum anterior posterior lesions.

Arm↗

PubMed2005

Analysis of ankle-hindfoot stability in multiple planes: an in vitro study.

BACKGROUND: It is necessary to have an understanding of ankle and hindfoot motion and stability to accurately diagnosis and treat ankle-hindfoot disorders. METHODS: We devised an ankle ligament testing apparatus to more critically determine ankle stability in all planes with a constant rotational force applied (inversion, eversion, internal rotation, external rotation) throughout the range of sagittal plane motion in 13 cadaver specimens. Three-dimensional kinematics were determined with a magnetic tracking device. RESULTS: With inversion force applied, calcaneal-tibial inversion was greatest in maximal plantarflexion (mean 22.1 +/- 6.0 degrees) and gradually decreased with dorsiflexion, which indicated that the ankle had the most inversion instability in plantarflexion. With eversion force applied, calcaneal-tibial eversion gradually increased with increasing dorsiflexion to 12.7 +/- 7.4 degrees indicating that the most eversion instability was in dorsiflexion. With internal rotation force applied, calcaneal-tibial internal rotation from plantarflexion to neutral ankle position increased. With external rotation force application, external rotation from neutral to maximal dorsiflexion increased. CONCLUSIONS: Ankle laxity was not constant but varied depending on the plantarflexion-dorsiflexion position and the direction of the applied force. The degree of ankle laxity was greater with inversion and internal rotation torque. Variation in laxity between specimens was observed, consistent with previous reports. These data indicate that the ankle is less stable in plantarflexion when inversion and internal rotation forces are applied. This may explain why the lateral ankle ligaments are most prone to injury in this position. The ankle was less stable in dorsiflexion when eversion and external rotation forces were applied. This is consistent with the observation that deltoid ligament injuries occur in the neutral to dorsiflexion position. The study demonstrates the importance of examining patients with suspected ankle ligament injuries in several ankle positions. The ankle testing device has potential application for in vivo testing of patients with suspected ankle ligament instability.

Adult↗

PubMed2005

Pathomechanics of hallux valgus: biomechanical and immunohistochemical study.

BACKGROUND: One factor believed to contribute to the development of hallux valgus is an abnormality in collagen structure and makeup of the medial collateral ligament (MCL) of the first metatarsophalangeal joint (MTPJ). We hypothesized that the mechanical properties of the MCL in feet with hallux valgus are significantly different from those in normal feet and that these differences may be related to alterations in the type or distribution of collagen fibers at the interface between the MCL and the bone. MATERIALS AND METHODS: Seven normal fresh-frozen cadaver feet were compared to four cadaver feet that had hallux valgus deformities. The MCL mechanical properties, structure of collagen fibers, and content proportion of type I and type III collagen were determined. RESULTS: The load-deformation and stress-strain curves were curvilinear with three regions: laxity, toe, and linear regions. Laxity of the MCL in feet with hallux valgus was significantly larger than that of normal feet (p = 0.022). Stiffness and tensile modulus in the toe region in feet with hallux valgus were significantly smaller than those in normal feet (p = 0.004); however, stiffness and tensile modulus in the linear region were not significantly different. The MCL collagen fibrils in the feet with hallux valgus had a more wavy distribution than the fibrils in the normal feet. CONCLUSIONS: In general, strong staining for collagen III and to a lesser extent, collagen I was observed at the interface between the MCL and bone in the feet with hallux valgus but not in the normal feet. These results indicate that the abnormal mechanical properties of the MCL in feet with hallux valgus may be related to differences in the organization of collagen I and collagen III fibrils.

Adult↗

PubMed2005

In vitro regulation of single collagen fibril length by buffer compositions and temperature.

An understanding of collagen ultrastructure is very important for designing biopolymers mimicking collagen functions in tissue engineering, or for diagnosing abnormal collagen structure in clinical study. The present study examined formation of a large population of type I collagen single fibrils under different buffer compositions and temperatures. Fibril structures were investigated by dark-field microscopy and atomic force microscopy (AFM). In the phosphate buffered saline (PBS) buffer, the average lengths of single fibrils were 4.8+/-2.2, 5.0+/-1.9 and 9.2+/-5.0 microm for 37 degrees C, 33 degrees C and 29 degrees C, respectively. The differences were significant (P < 0.05) between 37 degrees C and 29 degrees C and between 33 degrees C and 29 degrees C. In the sodium phosphate (SP) buffer, the average lengths of single fibrils were 10.6+/-5.4, 11.1+/-4.5 and 19.6+/-11.7 microm for 37 degrees C, 33 degrees C and 29 degrees C, respectively. Similarly, the differences were significant (P < 0.05) between 37 degrees C and 29 degrees C and between 33 degrees C and 29 degrees C. While at the same temperature, the average lengths of single fibrils differed significantly (P < 0.05) between PBS and SP buffers. Single fibrils formed in SP buffer were found to have greater average length than those formed in PBS buffer.

Biocompatible Materials↗

PubMed2004

Tensile forces attenuate estrogen-stimulated collagen synthesis in the ACL.

The purpose of this study was to examine whether mechanical tensile forces affect estrogen regulation of collagen synthesis of anterior cruciate ligament fibroblasts at the mRNA level. Estrogen was studied at three physiologic levels, 10(-11), 10(-10), and 10(-9)M. The results revealed that estrogen alone stimulated Type I and III collagen synthesis at the mRNA level, and application of mechanical force decreased the expression of collagen Type I and III genes at all tested estrogen levels. These findings suggest that estrogen may directly regulate ligament structure and function by alteration of Type I and III collagen synthesis. This regulation is dependent on mechanical loading.

Animals↗

PubMed2004

Direct quantification of the rupture force of single hyaluronan/hyaluronan binding protein bonds.

The non-covalent bond between aggrecan and hyaluronan is critical for maintaining the normal structure and function of the extracellular matrix in articular cartilage. The failure of this bond can cause the loss of aggrecan and destruction of the extracellular matrix of articular cartilage. In this study, the rupture force of the single bond between hyaluronan and hyaluronan binding protein - the complex of the hyaluronan binding region of aggrecan and link protein - was directly measured with a nanomechanical testing system as 40+/-11 pN. The results were compared to a theoretical prediction based on a smart version of the Monte Carlo simulation.

Aggrecans↗

PubMed2004

Direct measurements of the compressive properties of single proteoglycan aggregates.

Proteoglycan aggregate is a major component of the extracellular matrix in articular cartilage and is considered to be responsible for the resistance to compression of this tissue. The reduced stiffness of articular cartilage due to the loss of proteoglycan aggregate has been reported in osteoarthritis. In order to understand the mechanical properties of extracellular matrix in articular cartilage at molecular level, the compressive properties of 36 single molecules of proteoglycan aggregate were directly measured using a laser tweezers/interferometer system. The proteoglycan aggregates showed resistance when compressed to approximately 30% of their contour length. The stiffness of proteoglycan aggregates increased non-linearly from 2.6+/-3.8 pN/microm (compressed to 30-35% of their contour length) to 115.5+/-30.9 pN/microm (compressed to 2.5-5% of their contour length).

Compressive Strength↗

PubMed2004

Glenoid suture anchor fixation strength: Effect of insertion angle.

PURPOSE: The purpose of this study was to determine the effect of varying insertion angles on the fixation strength of screw-in devices placed in the glenoid rim. Type of study Cadaveric biomechanical analysis. METHODS: Eighteen cadaveric glenoids had 3.0-mm cannulated screws inserted for a depth of 10 mm in all 4 quadrants: anterior superior (AS), anterior inferior (AI), posterior superior (PS), posterior inferior (PI). Screws were inserted along the orthogonal to the glenoid rim at the point of insertion or at angles that deviated from this vector by 20 degrees and 40 degrees. Load to failure was performed at 10 mm/s along the orthogonal to the point of insertion. RESULTS: For screws inserted orthogonal to the glenoid rim, the average load to failure was highest for the PS quadrant (733 +/- 369 N) and lowest for the AI quadrant (272 +/- 69 N). The AS and PI quadrants showed intermediate values (549 +/- 334 N and 484 +/- 141 N, respectively). Deviation from orthogonal correlated with decreased fixation strength. This decrease was statistically significant in the AS and PI quadrants, with deviation of 40 degrees, and in the AI quadrant, with deviation of 20 degrees, as well as 40 degrees. Conclusions Insertion angles for screw-in fixation devices should be orthogonal to the glenoid rim at the point of insertion to maximize strength. Deviation of 40 degrees from orthogonal compromises fixation in most quadrants and deviation as little as 20 degrees can compromise fixation in the AI quadrant. CLINICAL RELEVANCE: To maximize strength of labral reattachment to the bony glenoid, screw-in type fixation devices should be inserted as orthogonal to the glenoid rim as possible. This is especially true for Bankart repairs, because device pullout occurs at significantly lower loads in the anteroinferior quadrant compared with the other 3 quadrants. Deviating as little as 20 degrees further decreases fixation strength significantly.

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