No abstract

We investigated the hypothesis that hindlimb unloading inhibits healing in fibrous connective tissue such as ligament. Male rats were assigned to 3- and 7-wk treatment groups with three subgroups each: sham control, ambulatory healing, and hindlimb-suspended healing. Ambulatory and suspended animals underwent surgical rupture of their medial collateral ligaments, whereas sham surgeries were performed on control animals. After 3 or 7 wk, mechanical and/or morphological properties were measured in ligament, muscle, and bone. During mechanical testing, most suspended ligaments failed in the scar region, indicating the greatest impairment was to ligament and not to bone-ligament insertion. Ligament testing revealed significant reductions in maximum force, ultimate stress, elastic modulus, and low-load properties in suspended animals. In addition, femoral mineral density, femoral strength, gastrocnemius mass, and tibialis anterior mass were significantly reduced. Microscopy revealed abnormal scar formation and cell distribution in suspended ligaments with extracellular matrix discontinuities and voids between misaligned, but well-formed, collagen fiber bundles. Hence, stress levels from ambulation appear unnecessary for formation of fiber bundles yet required for collagen to form structurally competent continuous fibers. Results support our hypothesis that hindlimb unloading impairs healing of fibrous connective tissue. In addition, this study provides compelling morphological evidence explaining the altered structure-function relationship in load-deprived healing connective tissue.

Recent scientific studies evaluating laser energy for tissue welding and thermokeratoplasty have demonstrated that the application of laser energy at non-ablative levels can alter collagen's structural and biochemical properties. A recent pilot study has demonstrated that the non-ablative application of holmium: yttrium-aluminum-garnet (Ho:YAG) laser energy to the joint capsule of patients with glenohumeral instability shrank the joint capsule, stabilizing the shoulder in the majority of the patients treated. Based on the collective findings of these studies, we hypothesized that thermal modification of dense collagenous tissues such as joint capsule, ligament, and tendon can be achieved by applying non-ablative laser energy. The purpose of this study was to evaluate the effect of laser energy at non-ablative levels on joint capsular mechanical, biochemical, histological, and ultrastructural properties in an in vitro rabbit model. Joint capsular tissues harvested from rabbit femoropatellar joints were treated by one of three power settings (5 watts (SW), 10 watts (lOW), 15 watts (15W)) or served as control in a randomized block design. Laser energy was applied using a Ho:YAG laser in 4 transverse passes across the tissue at a velocity of 2 mm/sec with the handpiece set at 1 .5 mm from the synovial surface in a 3TC tissue bath. Forty-eight specimens (n=12) were mechanically tested to determine tissue shrinkage, stiffness and viscoelastic properties. Twenty-four specimens (n=6) were processed for biochemical analysis to evaluate type I collagen content and non-reducible crosslinks. Twenty-four specimens (n=6) were processed for histological examination and transmission electron microscopy for ultrastructural analysis.Laser treatment significantly shortened the tissue by 9% (SW), 26% (lOW), and 38% (15W). Joint capsular stiffness decreased significantly in the lOW (77% decrease) and 15W (90% decrease) groups. Laser energy application did not significantly alter the viscoelastic properties of the tissue and the biochemical parameters evaluated, including type I collagen content and non-reducible crosslinks. Histological analysis revealed thermal alteration of collagen (fusion) and fibroblasts (pyknosis), with each subsequently higher laser energy causing significantly greater morphologic change over a larger area. Transmission electron microscopy revealed alteration of collagen ultrastructure, with significantly increased fibril crosssections for each of the treated groups compared to control. The fibrils began to lose their distinct edges and their periodical cross-striations at subsequently higher energy densities. This study demonstrated that laser energy at non-ablative levels can significantly alter joint capsular length and its structural properties. Ultrastructurally, laser energy caused disruption of the regular collagen organization. The results of this study suggested that the effects of laser energy were secondary to thermal denaturation of collagen with heat stable crosslinks maintained. To further clarif...

We established quantitative histochemical assays for the enzymatic activity of succinate dehydrogenase and alpha-glycerol phosphate dehydrogenase for cat skeletal muscle. A computer-enhanced image analysis system was used to quantitate the histochemical enzyme-activity reaction products. We describe a series of experiments that verify the reliability and validity of the assays. Histochemically determined enzyme activities were linear with respect to tissue thickness and reaction time. Biochemically determined enzyme activities were also linear with respect to tissue thickness and incubation time. Consecutive tissue sections, assayed either histochemically or biochemically, were used to establish a linear regression equation that allowed quantitative histochemically determined reaction rates, measured in optical density per minute, to be calibrated as nanomoles per minute.

Objective. To determine the effects of low intensify weight-bearing exercise on osteoarthntis [OA)

White Leghorn roosters (3 wk old) were randomly assigned to runner or control groups. Runners were subjected to a progressive treadmill running program for 8 wk, 5 days/wk at 70-80% maximal O2 consumption (VO2 max). After 8 wk, runners showed a significant elevation in gastrocnemius fumarase activity (51%) and a 21% increase in VO2max compared with controls. The exercise program induced a significant increase in tendon collagen deposition (46%) without any changes in DNA, proteoglycan, and collagen concentrations or tendon dry weight. Also, tendon collagen from runners contained fewer (50%) pyridinoline cross-links. These results suggest that high-intensity exercise causes greater matrix-collagen turnover in growing chickens, resulting in reduced maturation of tendon collagen.

No abstract

Traditionally, ligaments and tendons (L and T) have been regarded as metabolically inert structures. However, sufficient biochemical evidence on the metabolism of collagen has indicated that such a concept is no longer tenable. To determine whether L and T respond to increased or decreased levels of chronic exercise, studies were undertaken to measure their aerobic capacities. For comparative purposes, similar measurements were obtained from liver and skeletal muscles secured from normal and hypophysectomized male rats. Oxygen consumption and cytochrome oxidase (CO) activity was recorded from cell suspensions that had been prepared with the inclusion of collagenase and with elastase added to the medium. The O2 results showed that L and T had values that were approximately 10 times lower than liver tissue and 7.5 times less than the means from skeletal muscles. Hypophysectomy caused marked reductions in O2 uptake of liver and muscle tissues; but had no impact on L and T. When CO activity of these connective tissues were evaluated, immobilization and hypophysectomy caused significant reductions that ranged from -36% to -59% respectively. Training, on the other hand, resulted in increases of less than 10% in the activity of this enzyme within L and T while being elevated in muscle tissue by 58%. It was concluded that the metabolic activity of L and T was lowered with decreased levels of physical activity but it was unclear why chronic exercise did not produce the opposite effect.