Biomedical subjects

Matthew J Silva

Publications and source records attributed to Matthew J Silva.

At least 19 recordsLinked to original sources

PubMed2007

Alendronate prevents bone loss and improves tendon-to-bone repair strength in a canine model.

Previously we showed a loss of bone and a concomitant decrease in mechanical properties in the first 21 days after flexor tendon insertion site injury and repair in a canine model. The goal of this short-term study was to suppress bone loss after insertion site repair using alendronate in an attempt to prevent the reduction in biomechanical properties. Flexor tendons of the second and fifth digits of the right forelimbs of canines were injured and repaired. Dogs received a daily oral dose of alendronate (2 mg/kg). One digit in each dog also received a local dose of alendronate in the bone tunnel at the time of surgery. The repair was evaluated for bone mineral density (BMD) and biomechanical properties and compared to data from a previous study in which no alendronate was used. Alendronate was effective in protecting the distal phalanx from resorption during tendon-to-bone healing (BMD was 94 and 104% of control for systemic alendronate and for systemic plus local alendronate, respectively). Alendronate treatment prevented much of the decrease in ultimate load that occurs in the first 21 days. Without treatment, ultimate load was 42% of control. With systemic alendronate treatment and systemic plus local alendronate treatment, ultimate load was 78 and 69% of control, respectively. Failure mode was significantly different when comparing alendronate treatment to repair alone. A lower incidence of suture pull through was found in alendronate treated dogs, suggesting less tendon degeneration. Ultimate load can be improved in association with preventing the bone loss that normally occurs during the early period following tendon-to-bone repair. These initial short-term data demonstrate the potential for a clinical treatment that could enhance tendon-to-bone healing.

Alendronate↗

PubMed2007

Bone formation after damaging in vivo fatigue loading results in recovery of whole-bone monotonic strength and increased fatigue life.

Bone has a remarkable capacity for self-repair. We previously reported a woven bone response after damaging in vivo fatigue loading of the rat ulna that led to a rapid recovery of whole-bone strength. In the current study we asked: does the bone response in the 12 days after damaging fatigue loading result in a bone that has normal fatigue properties? The right forelimbs of 52 adult rats were subjected to a single bout of in vivo fatigue loading. Nonloaded left forelimbs were used as controls. Ulnar geometric properties were assessed by peripheral quantitative computed tomography (pQCT) and ex vivo mechanical properties were assessed by three-point bending. On day 0, ulnae from loaded forelimbs had a 15-20% reduction in stiffness and ultimate force versus controls (p < 0.10), indicative of structural damage. On day 12, bone area at the midshaft was increased by 27% (p < 0.001) and microCT scans revealed periosteal woven bone at this site. This bone response led to a recovery of the monotonic properties of loaded ulnae at day 12 versus control (stiffness, p = 0.73; ultimate force, p = 0.96). Importantly, fatigue testing ex vivo at day 12 demonstrated significantly greater fatigue life in in vivo loaded ulnae versus controls (p < 0.001). Additionally, the slope of the fatigue-life curve was significantly less in loaded versus control ulnae (p < 0.002). We conclude that woven bone "repair" of a bone damaged by fatigue loading restores whole-bone strength and enhances resistance to further damage by repetitive loading.

Animals↗

PubMed2006

Biomechanical evaluation of 2 techniques for ulnar collateral ligament reconstruction of the elbow.

BACKGROUND: Elbow medial ulnar collateral ligament tears often result in pain and instability that may be career threatening in overhead-throwing athletes. Surgical reconstruction is frequently chosen to treat this injury. Ulnar collateral ligament reconstruction as described by Jobe is the most commonly used technique. Testing of this construct has not demonstrated that the biomechanical parameters of the native ligament are restored. A more recent construct, the docking technique, may more reliably reproduce these factors. HYPOTHESIS: Increasing the number of strands of palmaris longus tendon graft used in ulnar collateral ligament reconstruction and tensioning them using the docking technique result in a construct with improved biomechanical parameters as compared with the Jobe technique. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-three fresh-frozen human cadaveric elbows were randomized into 3 subgroups: Jobe (11), docking (12), and native (10). The Jobe and docking groups underwent reconstruction using their described palmaris tendon graft constructs. The ulnar collateral ligament was left intact in the native group. Elbows were potted and tested using a servohydraulic materials testing machine to apply a valgus moment at 30 degrees of elbow flexion. Maximal moments to failure, stiffness, and strain at maximal moment and with a 3 N.m force applied were determined using a 2-camera motion analysis system to track reflective markers spanning the site. RESULTS: The docking (14.3 N.m) and native (18.8 N.m) subgroups resulted in higher maximal moment to failure than did the Jobe (8.9 N.m) subgroup (P < .001). There was no significant difference between native and docking groups (P > .05). Native ligaments were stiffer (301.4 N.m) than were Jobe (74.3 N.m) or docking (80.8 N.m; P < .001). Native ligaments demonstrated lower strain at maximal force (0.087 mm/mm) and 3 N.m forces (0.030 mm/mm) than did the Jobe (0.198/0.057 mm/mm) or docking (0.287/0.042 mm/mm) subgroups. There was no difference in stiffness or strain between the Jobe and docking subgroups (P > .05). CONCLUSION: Neither technique reproduced the biomechanical profile of the native ulnar collateral ligament; the findings of this study suggest that the docking construct may offer initial biomechanical advantage over the Jobe construct.

Analysis of Variance↗

PubMed2006

The effect of varying magnitudes of whole-body vibration on several skeletal sites in mice.

It has been reported that whole-body vibration (WBV) is anabolic to trabecular bone in animal models and humans. It is likely that this anabolic response does not occur uniformly throughout the entire body. Two factors that may affect the observed anabolic response are vibration magnitude and skeletal site of interest. In this study, mice were loaded with WBV of varying magnitudes. After five weeks of loading, bone marrow was flushed from tibias in order to quantify osteoprogenitor cells. Staining with alizarin red (an indicator of mineralization) showed a significant decrease in percent stained area in the 0.3 g loaded group compared to the control group and the 1.0 g group. MicroCT analysis was performed at five skeletal sites: the proximal tibial metaphysis, femoral condyles, distal femoral metaphysis, proximal femur, and L5 vertebral body. Increasing magnitudes of WBV were associated with a non-dose-dependent increase in trabecular bone volume (BV/TV) at the proximal tibial metaphysis, although other sites were unresponsive. There were statistically significant increases in BV/TV in the 0.1 g group (32% increase) and 1.0 g group (43% increase) compared to control (p < 0.05). The 0.1 g and 1.0 g groups also had higher BV/TV than the 0.3 g loaded group. If this non-dose-dependent phenomenon is verified by future studies, it suggests that a range of magnitudes should be examined for each application of WBV.

Animals↗

PubMed2006

In vivo skeletal imaging of 18F-fluoride with positron emission tomography reveals damage- and time-dependent responses to fatigue loading in the rat ulna.

The skeletal response to damaging fatigue loading is not fully understood. We used (18)F-fluoride PET to describe the time course of the skeletal response following the creation of increasing levels of in vivo, fatigue-induced damage. The right forelimbs of 40 adult rats were loaded in vivo in cyclic compression to four levels of subfracture, fatigue displacement: 30, 45, 65, or 85% of fracture displacement. Rats were injected with a bone-seeking radionuclide ((18)F-fluoride) on days 0 (4 h), 2, 4, 7, 9, 11, 18, 24, and 30, and imaged using a small animal positron emission tomography (PET) scanner. We quantified fluoride uptake in the central 50% of the right (loaded) and left (control) forelimbs. There were significant increases in fluoride uptake in loaded forelimbs compared to control on day 0 for all displacement groups. Normalized uptake (loaded/control) reached peak levels 4 to 9 days after loading. Normalized uptake depended significantly on the level of fatigue displacement. Normalized uptake increased progressively from the 30 to the 45% displacement level (P < 0.001), and from the 45 to the 65% level (P < 0.001) but did not differ between 65 and 85% (P = 0.41). Histologically, we observed a rapid periosteal response with increased vascularity as early as day 1 and abundant woven bone formation between days 3 and 7. Periosteal and woven bone thicknesses were greater in bones subjected to more fatigue displacement. We conclude that a single bout of fatigue loading leads to a transient increase in the uptake of (18)F-fluoride, that the uptake is in proportion to the level of initial damage and is associated with increased vascularity and woven bone formation in the first week after loading.

Animals↗

PubMed2006

Use of the rat forelimb compression model to create discrete levels of bone damage in vivo.

Skeletal responses to damage are significant for understanding the etiology of stress fractures and possibly osteoporotic fractures. We refined the rat forelimb-loading model to produce a range of sub-fracture damage levels during in vivo cyclic loading. A total of 98 right forelimbs of anesthetized, male, 5-month old Fischer rats were loaded cyclically (2 Hz) in axial compression. Rats were killed immediately after loading. In the first experiment, forelimbs were loaded to fracture, which occurred after an increase in peak displacement of 2.0+/-0.2 mm, independent of peak force or cycle number. In the next experiment, we loaded forelimbs at a constant peak force until the peak displacement increased by 0.6-1.8 mm (30-90% of fracture displacement). Mechanical properties of the loaded (right) and contralateral control (left) ulnae were determined ex vivo using three-point bending, and cracks were analyzed using micro-computed tomography. Results demonstrated a dose-response between increased forelimb displacement and increased ulnar damage, with four discrete damage levels. "Low" damage was produced by cyclic loading to 30% of fracture displacement, with no visible cracks and a 10% strength loss. "Mild" damage was produced by loading to 45% of fracture displacement, with variable linear cracks and 20% strength loss. "Moderate" damage was produced by loading to 60-75% of fracture displacement, with consistent linear cracks and 40% strength loss. "High" damage was produced by loading to 85-90% of fracture displacement, with branching cracks and 60% strength loss. This loading model will be useful for examining biological responses to a range of sub-fracture damage levels in future experiments.

Animals↗

PubMed2006

Characteristics of the rat supraspinatus tendon during tendon-to-bone healing after acute injury.

Rotator cuff repair is known to have a high failure rate. Little is known about the natural healing process of the rotator cuff repair site, hence little can be done to improve the tendon's ability to heal. The purpose of this study was to investigate the collagen formation at the early repair site and to localize TGFbeta-1 and 3 during early healing and compare their levels to cell proliferation and histological changes. Bilateral supraspinatus tendons were transected and repaired in 60 rats. Specimens were harvested and evaluated at 0, 1, 3, 7, 10, 28, and 56 days. Histological sections were evaluated for cell morphology. Immunohistochemistry and in situ hybridization was performed to localize protein and mRNA for collagen types I and III and TGFbeta-1 and 3. Proliferating cell nuclear antigen (PCNA) assay was performed to measure cell proliferation, and cells were counted to determine cell density. Biomechanical properties were evaluated. Repair tissue demonstrated an initial inflammatory response with multinucleated cells present at 1 and 3 days, and lymphocytes and plasma cells presents at 7 and 10 days. Capillary proliferation began at 3 days and peaked at 10 days. Ultimate force increased significantly over the time period studied. Collagen I protein and mRNA significantly increased at 10 days, and reached a plateau by 28 and 56 days. Collagen III showed a similar trend, with an early increase, and remained high until 56 days. TGFbeta-1 was localized to the forming scar tissue and showed a distinct peak at 10 days. TGFbeta-3 was not seen at the healing insertion site. Cell proliferation and density followed the same trend as TGFbeta-1. A wound healing response does occur at the healing rotator cuff insertion site, however, the characteristics of the tendon after healing differ significantly from the uninjured tendon insertion site at the longest time-point studied. A distinctive collagen remodeling process occurred with an initial increase in the formation of collagen types I and III followed by a decrease toward baseline levels seen at time 0. Growth factor TGFbeta-1 was localized to repair tissue and coincided with a peak in cell proliferation and cellularity. Repair sites remained unorganized histologically and biomechanically inferior in comparison to previously described uninjured insertion sites.

Acute Disease↗

PubMed2006

Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model.

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p = 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendon-bone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel.

Animals↗

PubMed2006

Medial collateral ligament healing in macrophage metalloelastase (MMP-12)-deficient mice.

Medial collateral ligament (MCL) injuries heal by a wound repair scar response controlled by a complex cellular and cytokine environment. Many enzymes participate in wound repair, particularly the matrix metalloproteinases. We hypothesize macrophage metalloelastase (MME/MMP-12) deficiency results in impaired healing of MCL injury. One hundred fifty MME-deficient and 150 WT (MME+/+) mice underwent knee MCL transection with the opposite knee as a sham operated control. Mice were sacrificed at 3, 7, 28, 42, and 56 days. At each of the five time points, 15 mice were utilized for biological and 15 were utilized for biomechanical testing. Outcome measures were the presence of macrophages to represent the inflammatory phase of wound healing, collagen synthesis to assay for matrix repair, and biomechanical testing for repair strength. Immunohistochemistry demonstrated significantly fewer macrophages in cut MCLs from MME-deficient mice versus wild-type (WT) mice at 3, 7, 28, and 42 days (all p<or=0.04). In situ hybridization to Col1a1 mRNA in the MME-deficient cut MCLs at 7, 28, and 42 day time points showed a decreased level of type I pro-collagen mRNA compared to the WT cut MCLs (p<0.05). Biomechanical testing revealed cut ligaments from MME-deficient mice had significantly lower ultimate force and stiffness compared to cut ligaments from WT mice (p<0.001), with maximal differences of 40% at 7 days for ultimate force and 28 days for stiffness (p<0.05 by Tukey post hoc test). We conclude MME is important in the multifactorial cascade of knee MCL injury healing, showing significant differences in both the early inflammatory and in the matrix tissue synthesis phases.

Animals↗

PubMed2006

Role of connexin43 in osteoblast response to physical load.

Gap junctions are hexameric transmembrane channels formed by connexins, and are responsible for direct cell-to-cell communication. The most abundant gap junction protein in bone is connexin43 (Cx43), although connexin45 (Cx45) is also expressed. In the present study, we tested the hypothesis that bone cell responses to mechanical stimulation are dependent on the type of gap junction communication provided by Cx43 in vitro and in an in vivo model of physical load. Application of cyclic stretch to calvaria osteoblasts results in a modest but detectable increase in PGE2 levels, and the amount of PGE2 produced was lower in cells isolated from Cx43 null mice. Mice with an osteoblast-specific deletion of the Cx43 gene were subjected to an in vivo four-point bending protocol on the tibia. This resulted in fast and exuberant formation of woven bone at the region directly below the loading fulcrum in both osteoblast Cx43-deleted and wild-type mice. However, indirect measurement of endosteal bone apposition suggested a less pronounced effect of physical load in Cx43-deficient than in wild-type mice. Taken together, these results indicate that deficiency of Cx43 in osteoblasts attenuates but does not abolish anabolic responses to mechanical strain.

Animals↗

PubMed2005

Decreased collagen organization and content are associated with reduced strength of demineralized and intact bone in the SAMP6 mouse.

UNLABELLED: To examine the link between bone material properties and skeletal fragility, we analyzed the mechanical, histological, biochemical, and spectroscopic properties of bones from a murine model of skeletal fragility (SAMP6). Intact bones from SAMP6 mice are weak and brittle compared with SAMR1 controls, a defect attributed to reduced strength of the bone matrix. The matrix weakness is attributed primarily to poorer organization of collagen fibers and reduced collagen content. INTRODUCTION: The contribution of age-related changes in tissue material properties to skeletal fragility is poorly understood. We previously reported that bones from SAMP6 mice are weak and brittle versus age-matched controls. Our present objectives were to use the SAMP6 mouse to assess bone material properties in a model of skeletal fragility and to relate defects in the mechanical properties of bone to the properties of demineralized bone and to the structure and organization of collagen and mineral. MATERIALS AND METHODS: Femora from 4- and 12-month-old SAMR1 (control) and SAMP6 mice were analyzed using bending and torsional mechanical testing of intact bones, tensile testing of demineralized bone, quantitative histology (including collagen fiber orientation), collagen cross-links biochemistry, and Raman spectroscopic analysis of mineral and collagen. RESULTS: Intact bones from SAMP6 mice have normal elastic properties but inferior failure properties, with 60% lower fracture energy versus SAMR1 controls. The strength defect in SAMP6 bones was associated with a 23% reduction in demineralized bone strength, which in turn was associated with poorer collagen fiber organization, lower collagen content, and higher hydroxylysine levels. However, SAMP6 have normal levels of collagen cross-links and normal apatite mineral structure. CONCLUSIONS: Bones from SAMP6 osteoporotic mice are weak and brittle because of a defect in the strength of the bone matrix. This defect is attributed primarily to poorer organization of collagen fibers and reduced collagen content. These findings highlight the role of the collagen component of the bone matrix in influencing skeletal fragility.

Animals↗

PubMed2005

A new selective estrogen receptor modulator, CHF 4227.01, preserves bone mass and microarchitecture in ovariectomized rats.

UNLABELLED: A new SERM, CHF 4227.01, given to 6-month-old female rats immediately after ovariectomy, preserved bone mass and bone microarchitecture without affecting uterus weight. It also decreased serum cholesterol and fat mass in estrogen-deficient rats. INTRODUCTION: We tested the effect of a new benzopyran derivative, CHF 4227.01, with selective estrogen receptor modulator (SERM) activity on bone mass and biomechanics in ovariectomized (OVX) female rats in comparison with 17alpha-ethinylestradiol (EST), raloxifene (RLX), and lasofoxifene (LFX). MATERIALS AND METHODS: Four doses of CHF 4227.01 (0.001, 0.01, 0.1, and 1 mg/kg body weight [bw]/day) were administered in OVX animals daily by gavage 5 days/week for 4 months. EST was administered at a dose of 0.1 mg/kg bw/day, whereas RLX and LSX were administered at doses of 1 and 0.1 mg/kg bw/day, respectively, by gavage. In one group (Sham), rats were operated but the ovaries not removed; another OVX group was treated only with placebo. RESULTS AND CONCLUSIONS: Treatment with CHF 4227.01 (1.0 and 0.1 mg/kg bw), EST (0.1 mg/kg bw), LFX (0.1 mg/kg bw), or RLX (1.0 mg/kg bw) prevented bone loss on the lumbar spine and the proximal femur assessed in vivo by DXA. Volumetric BMD obtained by pQCT ex vivo confirmed protection from bone loss in the spine and proximal femur among rats treated with CHF 4227.01. This effect was associated with strong inhibition of bone resorption both histologically and biochemically. Furthermore, CHF 4227.01 preserved trabecular microarchitecture, analyzed by muCT, and maintained biomechanical indices of bone strength in the spine and proximal femur, effects also observed for RLX, whereas LSX was less protective of microarchitecture. CHF 4227.01 treatment did not affect uterine weight, prevented the increase in body weight and fat mass seen in OVX animals, and decreased serum cholesterol to below the average of intact animals. In conclusion, CHF 4227.01 exhibits a promising therapeutic and safety profile as a new SERM on both skeletal and extraskeletal outcomes.

Absorptiometry, Photon↗

PubMed2005

Finite element analysis of the mouse tibia: estimating endocortical strain during three-point bending in SAMP6 osteoporotic mice.

To support future studies of tibial bending in a murine model of senile osteoporosis (SAMP6), we sought to determine the relationship between applied external bending force and peak endocortical strain in the tibiae of SAMP6 and control SAMR1 mice. The lower hindlimbs of mice were loaded by three-point bending in the lateral-medial plane with a support length of 10 mm. Force-periosteal strain relations were first determined using standard strain gauge methods. Finite-element analysis (FEA) models of the tibia-fibula were generated based on microcomputed tomography images. After choosing appropriate boundary conditions, FEA predictions of periosteal strains were within 15% of measured values. FEA revealed a narrow (3-4 mm) region of the central tibia with well-developed bending strains (tension medially, compression laterally); outside this region, we observed high shear strains. Both the strain gauge data and the finite-element simulations indicated that the tibia of the SAMP6 mouse was 20-25% stiffer than the SAMR1 tibia, consistent with a larger moment of inertia and higher cortical bone modulus. Thus, higher levels of force are required to produce the same target values of strain in the SAMP6 tibia. The ratio of periosteal to endocortical strain in the region of interest was similar for the two mouse strains (1.5-1.6). Based on these ratios, we scaled the strain gauge data to estimate the force-endocortical strain relations for the two mouse strains. In conclusion, FEA, with supporting strain gauge measurements, has provided unique insight regarding the strain environment throughout the tibia during three-point bending in mice.

Animals↗

PubMed2005

Flexor digitorum profundus tendon to bone tunnel repair: a vascularization and histologic study in canines.

PURPOSE: Recent in vivo canine studies have shown incomplete restoration of the flexor digitorum profundus (FDP) insertion site after transection and repair to the cortical surface of the distal phalanx. Previous biomechanical analyses of tendon to bone surface repair have suggested that repair site gap formation of greater than 3 mm occurs frequently under physiologic loads. A recent ex vivo investigation into a novel repair of the FDP tendon into a bone tunnel in the distal phalanx showed improved tensile properties with a decrease in repair site gap formation. Time-zero data, however, do not always accurately reflect in vivo responses. The repair response of the FDP tendon when placed in an osseous compartment is not known. The purpose of this study was to analyze the histologic and vascular anatomic properties of the FDP insertion site after transection and repair in a bone tunnel within the distal phalanx. METHODS: Twenty-six FDP tendon to bone repairs were performed in 13 adult mongrel dogs after insertion site transection. The tendons were repaired in a bone tunnel in the distal phalanx. Vascular analysis of the tendon and repair site was performed by using a modified Spalteholtz technique and routine hematoxylin-eosin staining was used to assess histologic properties of the repair. RESULTS: In normal specimens the vascular analysis showed that there was a distal network of vessels extending 1- to 2-cm proximal to the FDP insertion site. At 10 days after repair the distal tendon segment tendon remained avascular. By 21 days after repair there was proximal migration of an unorganized reticular network of tendon surface vessels with sparse intratendinous communications. At 6 weeks after repair the structure of the distal tendon vascular network resembled that of normals. The vascular response of the tendon within the bone tunnel followed a similar time frame. Histologic analysis showed an inflammatory reaction in the bone tunnel leading to a progressive degradation of that portion of the FDP tendon that resided in the tunnel. Tendon necrosis was not seen. CONCLUSIONS: The FDP tendon, after insertion site transection and repair in a bone tunnel, undergoes a process of neovascularization and revascularization over a period of 6 weeks. There is a progressive loss of tendon parenchyma within the bone tunnel and the suture tracks appeared to serve as conduits for the ingrowth of inflammatory tissue. Restoration of the normal 4-zone tendon-bone interface was not seen. Although ex vivo biomechanical assessment of tendon repair in a bone tunnel appears promising, the repair response in vivo may not be favorable for tendon to bone healing. The progressive tendon degeneration that was observed here may have detrimental effects on repair site tensile properties, increasing the potential for early failure.

Animals↗

PubMed2005

Zone I flexor digitorum profundus repair: an ex vivo biomechanical analysis of tendon to bone repair in cadavera.

PURPOSE: Biomechanical studies of standard flexor digitorum profundus (FDP) tendon to bone repairs show ultimate strengths greater than the applied loads of early motion rehabilitation protocols. Strain data, however, indicate the potential for significant repair site gapping under these physiologic loads. Gaps in excess of 3 mm have been shown to prevent the time accrual of strength in midsubstance tendon repairs and may prevent the restoration of the normal architecture of the tendon-bone interface. Improving the time-zero tensile properties of FDP insertion site repairs may help obviate these issues and improve clinical outcomes. The purpose of this study was to evaluate the ex vivo biomechanical properties of 2 new repair techniques in comparison with the standard FDP tendon to distal phalanx cortical surface repair. METHODS: Thirty human cadaver FDP tendons were released from their insertion sites by sharp dissection and repaired to bone using 1 of 3 repair techniques. Load to failure testing was performed with a servohydraulic materials-testing system (model 8500R; Instron, Canton, MA) analyzing ultimate force, strain at 20 N, rigidity, force to 2-mm gap formation, and displacement at failure. RESULTS: The results of the failure tests indicate that repairs performed with the addition of a peripheral suture had a greater ultimate force, had increased resistance to gap formation, and had increased rigidity and decreased strain at 20 N compared with the tunnel-only and volar cortical surface to the distal phalanx repairs. Although there were no statistically significant differences in ultimate force or rigidity between the tunnel-only and volar cortical surface repairs, the tunnel-only repairs showed lower strain values and increased values for resistance to 2-mm gap formation when compared with the volar cortical surface repairs. There were no differences among any of the repair groups with regard to the magnitude of tendon displacement from the repair site at failure. CONCLUSIONS: The addition of a peripheral suture to the FDP tendon to bone tunnel repair construct improves the time-zero tensile properties as evidenced by statistically significant increases in ultimate force, rigidity, and resistance to gap formations of 2 mm. In comparison with a volar cortical surface repair, the bone tunnel-only repairs were effective at decreasing the amount of repair site strain during applied loads of 20 N. If these improved time-zero tensile properties persist during the early stages of healing, they may help decrease the incidence of repair-site gap formation associated with the forces of early motion rehabilitation protocols.

Aged↗

PubMed2005

Effect of several growth factors on canine flexor tendon fibroblast proliferation and collagen synthesis in vitro.

PURPOSE: Growth factor delivery may be useful to accelerate the rate of tendon healing. Before in vivo use, however, the effects of growth factors on tendon cells need to be well characterized. The purpose of this study was to evaluate the effects of 4 growth factors on intrasynovial tendon fibroblast proliferation and collagen production in vitro. Our first hypothesis was that platelet-derived growth factor BB (PDGF-BB) and basic fibroblast growth factor (bFGF) would promote cell proliferation and collagen production. Our second hypothesis was that there would be a positive effect from the combination of PDGF-BB and bFGF. METHODS: The growth factors PDGF-BB, bFGF, vascular endothelial growth factor (VEGF), and bone morphogenetic protein 2 (BMP-2) were evaluated in vitro with canine flexor tendon fibroblasts. The effects of single factors (PDGF-BB, bFGF, VEGF, or BMP-2) or a combination of factors (PDGF-BB and bFGF) on cell proliferation (ie, thymidine incorporation) and collagen production (ie, proline incorporation) were evaluated. RESULTS: The results supported our hypotheses. Cell proliferation increased significantly with PDGF-BB and bFGF. Collagen production also increased significantly with PDGF-BB and bFGF. Cell proliferation and collagen production were unchanged with VEGF and BMP-2. A dose-response effect was seen for PDGF-BB combined with bFGF. The combination of PDGF-BB and bFGF led to an increase in cell proliferation but no change in collagen production compared with each factor alone. CONCLUSIONS: The growth factors PDGF-BB and bFGF significantly increased flexor tendon fibroblast proliferation and matrix synthesis when applied singly. Administration of PDGF-BB and bFGF combined led to increased proliferation to single factors.

Animals↗

PubMed2004

Impaired marrow osteogenesis is associated with reduced endocortical bone formation but does not impair periosteal bone formation in long bones of SAMP6 mice.

UNLABELLED: We used the SAMP6 osteoporotic mouse to examine the link between marrow osteogenic potential and in vivo cortical bone formation. SAMP6 marrow supported less in vitro osteogenesis than marrow from SAMR1 controls; SAMP6 mice had a corresponding deficit in endocortical mineralizing surface. This marrow/endocortical defect did not affect the periosteum, where SAMP6 mice had normal to enhanced bone formation. INTRODUCTION: With aging, there may be a reduction in the number or proliferative capacity of bone marrow osteoprogenitors that may contribute to age-related decreases in bone formation. To examine the link between the ability of the marrow to support osteogenesis and age-related changes in bone formation, we measured in vitro and in vivo indices of osteogenesis in a model of osteoporosis, the senescence-accelerated mouse SAMP6. MATERIALS AND METHODS: Femora and tibias from SAMP6 and SAMR1 (control) mice were harvested at 2, 4, 6, and 12 months of age (168 bones total). Bone marrow cells were cultured under osteogenic conditions and stained for alkaline phosphatase (ALP) and alizarin red. Dynamic indices of bone formation were assessed histologically from calcein labels. RESULTS: ALP+ and alizarin red-positive areas were significantly less in cultures from SAMP6 bones versus SAMR1 (p < 0.05), indicating less osteogenic potential. For example, SAMP6 tibial cultures had 21% less ALP+ area and 36% less alizarin red-positive area than SAMR1. Marrow from tibias had 2-fold greater osteogenesis than femoral marrow (p < 0.001). SAMP6 mice had a deficit in endocortical mineralizing surface across all age groups (p < 0.05), but no deficit in mineral apposition rate. Last, despite the marrow and endocortical deficits, SAMP6 mice had normal or slightly increased periosteal bone formation, consistent with their larger bone size. CONCLUSION: SAMP6 bone marrow supports less in vitro osteogenesis than SAMR1, consistent with a lower concentration of marrow osteoprogenitors in SAMP6. SAMP6 mice have less endocortical mineralizing surface than SAMR1 at all ages but no detectable deficit in mineral apposition rate, which suggests a reduction in osteoblast number but normal function. Periosteal bone formation is unimpaired in SAMP6 mice, indicating that the marrow/endocortical defect does not affect the periosteal surface.

Animals↗

PubMed2004

Marrow stromal cells and osteoclast precursors differentially contribute to TNF-alpha-induced osteoclastogenesis in vivo.

The marrow stromal cell is the principal source of the key osteoclastogenic cytokine receptor activator of NF-kappaB (RANK) ligand (RANKL). To individualize the role of marrow stromal cells in varying states of TNF-alpha-driven osteoclast formation in vivo, we generated chimeric mice in which wild-type (WT) marrow, immunodepleted of T cells and stromal cells, is transplanted into lethally irradiated mice deleted of both the p55 and p75 TNFR. As control, similarly treated WT marrow was transplanted into WT mice. Each group was administered increasing doses of TNF-alpha. Exposure to high-dose cytokine ex vivo induces exuberant osteoclastogenesis irrespective of in vivo TNF-alpha treatment or whether the recipient animals possess TNF-alpha-responsive stromal cells. In contrast, the osteoclastogenic capacity of marrow treated with lower-dose TNF-alpha requires priming by TNFR-bearing stromal cells in vivo. Importantly, the osteoclastogenic contribution of cytokine responsive stromal cells in vivo diminishes as the dose of TNF-alpha increases. In keeping with this conclusion, mice with severe inflammatory arthritis develop profound osteoclastogenesis and bone erosion independent of stromal cell expression of TNFR. The direct induction of osteoclast recruitment by TNF-alpha is characterized by enhanced RANK expression and sensitization of precursor cells to RANKL. Thus, osteolysis attending relatively modest elevations in ambient TNF-alpha depends upon responsive stromal cells. Alternatively, in states of severe periarticular inflammation, TNF-alpha may fully exert its bone erosive effects by directly promoting the differentiation of osteoclast precursors independent of cytokine-responsive stromal cells and T lymphocytes.

Animals↗