Mechanical properties of collagen fascicles from stress-shielded patellar tendons in the rabbit.

OBJECTIVE: To know the effects of stress shielding applied to the patellar tendon on the collagen fascicles.DESIGN: The mechanical properties of collagen fascicles obtained from stress-shielded patellar tendons were compared to those of collagen fascicles from non-treated patellar tendons and those of stress-shielded bulk patellar tendons in the rabbit.BACKGROUND: Effects of stress deprivation and stress enhancement on the mechanical properties of knee joint tendons and ligaments have been extensively studied in various animal models. However, the roles of such substructural components as collagen fascicles in the remodeling of tendons and ligaments have not been studied well.METHOD: Tensile and viscoelastic properties of collagen fascicles obtained from the rabbit patellar tendons which were completely stress-shielded for 1 to 3 weeks by a special method developed by the authors were determined using a micro tensile tester.RESULTS: Stress shielding significantly decreased the tangent modulus, tensile strength, and strain at failure of collagen fascicles. However, these changes were much smaller than those observed in bulk tendons. The relaxation of stress-shielded collagen fascicles was greater than that of non-treated ones.CONCLUSIONS: Ground substance and mechanical interaction between collagen fascicles have important roles in the remodeling of tendons and ligaments.RELEVANCE: Knowledge of the role of such substructural components as collagen fascicles in the remodeling of tendons and ligaments is essential not only to the basic biomechanics of knee joint tendons and ligaments but also to the development of their reconstruction methods using autografts.     

Mechanical properties of collagen fascicles from in situ frozen and stress-shielded rabbit patellar tendons

OBJECTIVE: To know the effects of stress shielding on the biomechanical properties of collagen fascicles obtained from in situ frozen patellar tendons (an autograft model). DESIGN: Collagen fascicles of approximately 300 microm in diameter were obtained from in situ frozen rabbit patellar tendons and also from in situ frozen and stress-shielded ones, and their mechanical properties and fibroblast density were determined. BACKGROUND: Stress shielding changes the mechanical properties of in situ frozen patellar tendons in which there exist no fibroblasts. The mechanisms of this phenomenon have not been studied well. METHOD: Patellar tendons of both in situ frozen group and in situ frozen and stress-shielded group were frozen in situ by liquid nitrogen to kill fibroblasts. Then, in the in situ frozen and stress-shielded group, no tension was applied to the tendons for 2, 3, and 6 weeks, while normal tension was applied to the tendons of the in situ frozen group. Tensile properties of the collagen fascicles obtained from these tendons were determined using a microtensile tester, and were compared to the collagen fascicles from non-frozen, stress-shielded patellar tendons. RESULTS: Tangent modulus and tensile strength of collagen fascicles from the in situ frozen and stress-shielded group progressively decreased with the time of stress shielding; however, these decreases were much smaller than those of the fascicles obtained from non-frozen, stress-shielded tendons. Although there were few fibroblasts in the patellar tendon of the in situ frozen and stress-shielded group at 2 weeks, the modulus and strength of the fascicles from the posterior portion were significantly lower than those in the in situ frozen group. In addition, the reduction of strength caused by stress shielding was much smaller in collagen fascicles than in bulk patellar tendons. CONCLUSION: The mechanical properties of collagen fascicles in in situ frozen tendons (an autograft model) are affected by stress shielding even under acellular condition.RelevanceThe in situ frozen, stress-shielded patellar tendon is a model of augmented autografts which are clinically used for the reconstruction of injured anterior cruciate ligaments. The sub-macroscopic studies of the tendon are useful to understand the mechanisms of the reduction of graft strength and its gradual recovery observed after reconstruction.     

Effect of cyclic stretching on the tensile properties of patellar tendon and medial collateral ligament in rat

BACKGROUND: Although dynamic stretching is often prescribed before exercise is undertaken, research has rarely been conducted to determine what effects dynamic stretching has on tendon and ligament injury prevention. The hypothesis is that the mechanical properties of tendon and ligament will increase in an ultimate tensile loading test after sinusoid cyclic stretching. METHODS: Ten paired rat medial collateral ligaments and patellar tendons were used with and without 150 sinusoid cyclic stretching in either side to determine the influence of cyclic stretching on the mechanical behavior of the tendons and ligaments. FINDINGS: The increase in ultimate stress and elastic modulus was significant after sinusoid cycling in both the medial collateral ligaments and the patellar tendons. An adequate sinusoid cyclic stretching could increase the mechanical properties of tendon and ligament under optimization of cyclic strain. INTERPRETATION: A better understanding of the mechanical behavior of tendon and ligament after a series of dynamic stretching prior to exercise may lead to the development of training strategies that could reduce the incidence of injury during sports activities.     

Effects of stress deprivation on mechanical properties of the in situ frozen-thawed semitendinosus tendon in rabbits

OBJECTIVE: To clarify the effect of complete stress deprivation on the mechanical properties of the in situ frozen-thawed semitendinosus tendon, an idealized autograft model. DESIGN: Ninety-six rabbits were divided into three groups. In the frozen group (n=36), we applied the freeze-thaw treatment to the semitendinosus tendon to necrotize fibroblasts in the tendon. In the frozen and stress-shielded group (n=30), after we applied the same freeze-thaw treatment to the tendon, we completely released the tendon from stress. In the sham group (n=30), a sham operation was applied. In each group, 6 rabbits were sacrificed at 0 (only in the frozen group), 1, 2, 3, 6 and 12 weeks after surgery. BACKGROUND: Previous studies have not clarified remodeling of the semitendinosus autograft in ligament reconstruction or its idealized model. METHODS: The tendon was frozen with liquid nitrogen. The tendon was released from stress with the originally developed technique using a polyester tape. In each period, 5 out of the 6 rabbits were evaluated with tensile testing, and the remaining rabbit was histologically observed. RESULTS: Complete stress shielding significantly increased the cross-sectional area of the frozen-thawed tendon at 1 and 2 weeks, while it significantly inhibited the increase of the area due to the freeze-thaw treatment at 3 and 6 weeks. Complete stress shielding significantly reduced material properties of the frozen-thawed tendon after 2 weeks. CONCLUSIONS: The frozen-thawed semitendinosus tendon has unique remodeling characteristics under a stress-shielded condition, which were not the same as those of the frozen-thawed patellar tendon. RELEVANCE: Remodeling of the semitendinosus tendon autograft under stress-shielded conditions may be different from that of the patellar tendon autograft.     

Effects of maturation on the mechanical properties of regenerated and residual tissues in the rabbit patellar tendon after resection of its central one-third

Background

The central one-third portion of the patellar tendon is commonly used as a graft for the reconstruction of the anterior cruciate ligament. Although several studies have been carried out on mechanical properties of healing tendons in mature animals, there have been no studies on regenerated and residual tissues in the immature patellar tendon after the removal of its central portion.

Methods

An entire one-third defect was made in the patellar tendon of 2-, 3- and 6-month-old rabbits. After 3 weeks, the tissue regenerated in the defect and the residual tissue were biomechanically and histologically evaluated.

Findings

The length of patellar tendons in 6-month-old animals after the resection of its central one-third was significantly longer than that in age-matched controls. The cross-sectional area of all operated tendons was significantly larger compared to age-matched controls. There were no significant effects of maturation on the mechanical properties of regenerated and residual tissues in operated tendons, although tensile strength and tangent modulus of normal tendons were significantly greater in 6-month rabbits than in immature ones. The histology of each of regenerated and residual tissues was similar in the three groups.

Interpretation

There were no remarkable effects of maturation on regenerated and residual tissues after the removal of the central one-third tendon. However, the strength and the modulus of normal tendons are significantly lower in immature patients than in mature ones. Therefore, surgeons should take account of the inferior mechanical properties of the tendon in skeletally immature patients at the time of surgeries for the reconstruction of the anterior cruciate ligament.     

The changes in mechanical properties of regenerated and residual tissues in the patellar tendon after removal of its central portion

OBJECTIVE: To know the temporal changes of the mechanical properties of the regenerated and the residual tissues in the patellar tendon after removal of the central portion.Design. The regenerated and the residual tissues were compared to sham-operated tendons. BACKGROUND: Although the structural properties of the whole patellar tendon after removal of the central portion have been investigated, no studies have distinguished between the regenerated and the residual tissues.Methods. For 52 skeletally mature rabbits, a full-thick, segmental defect was made at the central portion of the right patellar tendon, while a sham operation performed in the left tendon. At 3, 6, 12, and 24 weeks, we evaluated the mechanical properties and fibroblast density of the regenerated and the residual tissues as well as the blood flow and tissue dimensions of the patellar tendon. In addition, non-treated patellar tendons from six rabbits were served as the control for mechanical testing. RESULTS: The tangent modulus and the tensile strength of the regenerated tissue progressively increased with time. On the other hand, these parameters of the residual tendinous portion decreased until 6 weeks, although they gradually increased thereafter. The tensile strength of the regenerated and the residual tissues at 24 weeks were approximately 80% and 75%, respectively, of the non-treated, control tendon. Abundant blood flow and cell proliferation were observed in the regenerative tissue until 6 weeks. CONCLUSION: The mechanical properties of the regenerated and the residual tissues after removal of the central portion in the patellar tendon are much different from those of the original tendon. RELEVANCE: The present study showed inferior mechanical properties of the residual and the regenerated tissues for up to 24 weeks after removal of the central portion in the patellar tendon. Therefore, the aggressive rehabilitation that applies excessive load to the patellar tendon should be avoided at an early stage after harvesting the tendon for ligament reconstruction.     

The mechanical properties of the human patellar tendon are correlated to its mass density and are independent of sex

BACKGROUND: A diverse range of values for the mechanical properties of the human patellar tendon has been reported in the literature. Donor age has been excluded as a factor that causes this disparity. However, the effects of donor sex and tissue mass density on the mechanical properties of the patellar tendon have not been established. More importantly, predictors of the mechanical properties of the patellar tendon, used as grafts in anterior cruciate ligament reconstruction surgeries, are not available. METHODS: Uniaxial tension tests were performed to determine the effects of donor sex and mass density of the tissue on the mechanical properties of twenty unpaired human patellar tendons (10 male and 10 female; age, 17-50). Mass density of the patellar tendon was determined by measuring its volume and mass. FINDINGS: No evidence of sex-based differences in any of the mechanical properties of the patellar tendon was found. The results revealed a diverse range of mass densities extending from a low of 0.76 g/cm(3) to a high of 2.68 g/cm(3) (250% difference). Furthermore, it was determined that the ultimate tensile strength (mean=58.71 MPa), elastic modulus (mean=507.38 MPa) and strain energy density (mean=4.59 MPa) of the patellar tendon were significantly correlated to its mass density. The tensile strength and elastic modulus were significantly higher for those patellar tendons having a mass density greater than 1.67 g/cm(3). INTERPRETATION: The mass density of the patellar tendon may be considered as an indicator of mechanical properties of the patellar tendon or graft quality.     

The effect of transforming growth factor-beta on mechanical properties of the fibrous tissue regenerated in the patellar tendon after resecting the central portion

BACKGROUND: No investigators have studied the effects of an application of growth factors on the in vivo tissue regeneration in the tendon after resecting the central portion. The purpose of this study is to clarify whether an application of transforming growth factor (TGF)-beta1 increases the mechanical properties of the regenerated tissue in the patellar tendon after resecting the central portion. METHODS: Thirty female rabbits were divided into three groups, after a 3 mm wide and 10 mm long tendon substance was resected from the central portion in the patellar tendon. In Group I, 5-ng TGF-beta1 dissolved in 0.1-ml saline was injected into the resected portion in the patellar tendon. In Group II, only 0.1-ml saline was injected into the resected portion. In Group III, nothing was injected. All animals were sacrificed at 6 weeks after surgery. Mechanical and histological evaluations were made concerning the regenerated tissue and the unresected tendon tissue in the patellar tendon. FINDINGS: Concerning the regenerated tissue, the tangent modulus and the tensile strength of Group I were significantly greater than those of Groups II and III, while there were no significant differences in these parameters between Groups II and III. INTERPRETATION: The application of TGF-beta1 significantly increases the tangent modulus and the tensile strength of the fibrous tissue regenerated in the patellar tendon after resecting the central portion. This study has provided basic important information on the utility of TGF-beta1 in the in vivo tendon regeneration.     

Stress-strain characteristics of in situ frozen and stress-shielded rabbit patellar tendon

To assess the effects of stress shielding on the stress-strain behaviour of the in situ frozen tendon, which simulates an ideally oriented autogenous graft, patellar tendons (PT) of 26 Japanese white rabbits underwent in situ freezing with and without the stress shielding treatment. The patella-PT-tibia complexes excised at 3 and 6 weeks postoperatively were loaded between 0% and 3% strain. The material constants were computed by fitting the data to a constitutive equation. The material constants showed that the initial slope of the stress-strain curve of the group without stress shielding was significantly steeper than that of the group with stress shielding at 3 weeks, but not at 6 weeks. The increase in the slope of the stress-strain curve of the group without stress shielding was significantly more than that of the group with stress shielding at both 3 and 6 weeks.     

Mechanical properties of intrasynovial and extrasynovial tendon fascicles

BACKGROUND: Tendon grafting in tendon reconstruction often involves the interchange of intrasynovial and extrasynovial tendons. Although many studies have examined the cellular and biological differences between tendons of various sources, few have studied the mechanical properties of these two different types of tendons. The purpose of this study was to investigate the mechanical properties of intrasynovial and extrasynovial tendons. METHODS: Canine peroneus longus (extrasynovial) and flexor digitorum profundus (intrasynovial) tendons, further subdivided into intrasynovial tendinous and intrasynovial fibrocartilaginous segments, were used in the study. An indentation test was used to measure the compressive modulus. Tensile testing was performed on 400mum longitudinal sections. FINDINGS: The compressive modulus of the intrasynovial fibrocartilaginous segment was significantly higher than that of the intrasynovial tendinous segment, which was in turn significantly higher than that of the extrasynovial tendon (P<0.0001). The tensile modulus of extrasynovial tendon was significantly higher than that of intrasynovial fibrocartilaginous and intrasynovial tendinous segments (P<0.005). The tensile modulus of the intrasynovial fibrocartilaginous and tendinous segments was not significantly different (P=0.14). INTERPRETATION: The results suggest that extrasynovial tendons exhibit superior tensile properties but inferior compressive properties when compared to intrasynovial tendons, which is consistent with their biological role in situ, but which could lead to complications when these tendons are repositioned during tendon graft surgery.     

The effects of immobilization on the mechanical properties of the patellar tendon in younger and older men

Background

It remains unknown if inactivity changes the mechanical properties of the human patellar tendon in younger and older healthy persons. The purpose was to examine the effects of short-term unilateral immobilization on the structural and mechanical properties of the patellar tendon in older men and younger men, in vivo.

Methods

Eight older men and eight younger men underwent 14 days of unilateral immobilization. All individuals were assessed on both sides before and after the intervention. MRI was used to assess whole patellar tendon dimensions. The mechanical properties of the patellar tendon were assessed using simultaneous force and ultrasonographic measurements during isometric ramp contractions.

Findings

In older men, tendon stiffness [Pre: mean 2949 (SD 799) vs. Post: mean 2366 (SD 774) N mm^− 1, P < 0.01] and Young's Modulus [Pre: mean 1.2 (SD 0.3) vs. Post: mean 1.0 (SD 0.3) GPa, P < 0.05] declined with immobilization on the immobilized side. On the control side, tendon stiffness [Pre: mean 3340 (SD 1209) vs. Post: mean 2230 (SD 503), P < 0.01] and Young's Modulus [Pre: mean 1.5 (SD 0.4) vs. Post: mean 0.9 (SD 0.3) GPa, P < 0.05] also decreased with immobilization. In younger men, tendon stiffness [Pre: 3622 (SD 1760) vs. Post: mean 2910 (SD 1528) N mm^− 1, P < 0.01] and Young's Modulus [Pre: mean 1.7 (SD 1.1) vs. Post: mean 1.4 (SD 0.8) GPa, P < 0.05] decreased only on the immobilized side.

Interpretation

Short-term immobilization led to impaired mechanical properties of the patellar tendon on the immobilized side in both younger men and older men, which can influence the function of the muscle–tendon complex.     

Structural and material properties of human foot tendons

BackgroundsThe aim of this study was to assess the mechanical properties of the main balance tendons of the human foot in vitro reporting mechanical structural properties and mechanical material properties separately. Tendon structural properties are relevant for clinical applications, for example in orthopedic surgery to elect suitable replacements. Tendon material properties are important for engineering applications such as the development of refined constitutive models for computational simulation or in the design of synthetic materials.MethodsOne hundred uniaxial tensile tests were performed to obtain the mechanical response of the main intrinsic and extrinsic human foot tendons. The specimens were harvested from five frozen cadaver feet including: Extensor and Flexor tendons of all toes, Tibialis Anterior and Posterior tendons and Peroneus Brevis and Longus tendons.FindingsCross-sectional area, load and strain failure, Young's modulus and ultimate tensile stress are reported as a reference of foot tendon mechanical properties. Two different behaviors could be differentiated. Tibialis and Peroneus tendons exhibited higher values of strain failure compared to Flexor and Extensor tendons which had higher Young's modulus and ultimate tensile stress. Stress–strain tendon curves exhibited proportionality between regions. The initial strain, the toe region and the yield point corresponded to the 15, 30 and 70% of the strain failure respectively.InterpretationMechanical properties of the lesser-studied human foot tendons are presented under the same test protocol for different engineering and clinical applications. The tendons that work at the inversion/eversion plane are more deformable at the same stress and strain rate than those that work at the flexion/extension plane.     

Functional loading augments the initial tensile strength and energy absorption capacity of regenerating rabbit Achilles tendons.

The biomechanical effect of functional loading was studied in surgically tenotomized, repaired and immobilized right Achilles tendons of 34 rabbits. Beginning from the 5th day after surgery, loading was initiated by removing the immobilization casts of the animals to permit unrestricted weight-bearing to tolerance. At each of 12, 18 and 21 days after surgery, functionally loaded tendons and their corresponding nonloaded controls were excised and compared for differences in tensile strength, tensile stress and energy absorption capacity. Functional loading induced a twofold increase in the tensile strength (P less than 0.05) and energy absorption capacity (P less than 0.05) of the tendons, at both 12 and 18 days after surgery. No statistically significant differences were observed in the tensile strength and energy absorption capacity of the tendons at 21 days after surgery. Statistically significant differences in tensile stress were not observed at any time period throughout the study. These findings demonstrate that functional loading augments the tensile strength and energy absorption capacity of experimentally tenotomized tendons without promoting re-rupture, but only during the very early stages of healing. Even though the healing process of rabbit tendons may differ from healing of human tendons, these results suggest that similar beneficial effects may be attained if repaired human Achilles tendon ruptures are carefully loaded during the very early rather than later stages of healing.     

局部注射肝素钠免跟腱系统生物力学性质的变化

背景: 跟腱腱围炎会导致跟腱生物力学特件的改变,日前以局部注射肝素钠治疗较为普遍,但其对跟腱生物力学特性影响的报道甚少.目的: 观察跟腱劳损后生物力学性质及黏弹性的变化,同时验证肝素钠对跟腱生物力学特性及黏弹性的影响.设计、时间及地点: 于2005-03/12存四川省骨科医院生物力学实验室完成随机对照动物实验.材料: 50只成年日本大耳白兔,体质量(4.10±0.23)kg,用于制备跟腱劳损动物模型.方法: 50只动物随机分为对照组(n=20)、训练组(n=12)和肝素钠组(n=18).动物3周运动训练后继续训练,同时开始跟腱腱围及跟腱止点的肝素局部注射,2次/周.6周后进行跟腱的循环蠕变和应力松弛测定,最后进行跟腱的断裂实验.主要观察指标: 测定不同运动后跟腱的生物力学特性及黏弹性的变化,包括跟腱的横截面积、循环蠕变、滞后环、应力松弛、强度特性和应力-应变.结果: 训练组和肝素钠组动物的滞后环明显减小,应力松弛加快.训练后跟腱的屈服载荷及能量、断裂能量、屈服应力、应变能力明显高于对照组.肝素钠组所有生物力学指标都得到改善.结论: 大强度运动可使跟腱的黏弹性下降,局部注射肝素钠可改善跟腱的强度特性和黏弹性.劳损后跟腱腱围和跟腱止点局部注射肝素钠对改善跟腱系统的强度特性和黏弹性有益.     

The biomechanical effects of low-intensity ultrasound on healing tendons

The effect of low-intensity ultrasound on the healing strength of tendons was studied in experimentally tenotomized, repaired and immobilized right tendo calcaneus (Achilles tendon) of 24 rabbits. Ten tendons were sonicated in continuous waves at a space-averaged intensity of 0.5 W cm-2 for 5 min every day. The remaining 14 tendons were mock-sonicated as controls. After nine consecutive treatments, the tendons were excised under anesthesia and compared for differences in tensile strength, tensile stress and energy absorption capacity. Sonication at 0.5 W cm-2 induced a significant increase in the tensile strength (p less than .02), tensile stress (p less than .005) and energy absorption capacity (p less than .001) of the tendons. These findings suggest that high-intensity sonication may not be necessary to augment the healing strength of tendons and that sonication at similarly low intensities may enhance the healing process of surgically repaired human tendo calcaneus.     

Low-load behaviour of the patellar tendon graft and its relevance to the biomechanics of the reconstructed knee

BACKGROUND: Although the linear elastic (high-load) properties of patellar tendon graft used for anterior cruciate ligament (ACL) reconstruction are studied extensively, the low-load properties of the graft, associated with the toe region of its load-deformation curve, are largely neglected. The objectives of this study were to (i) determine the properties of the patellar tendon in the low-load region and compare to that of the intact ACL, (ii) assess the extent of variability in these properties and relate them to donor factors, and (iii) establish the theoretical importance of low-load properties to the function of the reconstructed knee. METHODS: The patellar tendons of 20 unpaired fresh frozen human knees (10 males and 10 females) were harvested. The central portions were trimmed, measured, and tested in tension to failure. The stress-strain curves were fitted with a bi-linear model and the graft properties were measured. FINDINGS: The low-load region modulus of elasticity, E 0, of the patellar tendon, ranged from 49 MPa to 276 MPa in males and 63 MPa to 279 MPa in females. The strain at which the graft transitions from its low-load region to its linear elastic region (epsilon* approximately 4.6%) is on average above the strain levels experienced by the ACL during daily activities (epsilon approximately 4%). Donor sex, height and body mass were found to significantly affect some of the mechanical properties of the low-load region. INTERPRETATION: The results suggest that the low-load region properties of the patellar tendon, not the linear elastic properties, govern the biomechanics of the tibiofemoral joint during the early healing period. Also, a wide variability of graft properties in the low-load region exists partly due to certain donor factors. Clinicians should be aware of the low-load region behaviour of the graft and its influence on time=0 behaviour of the reconstructed knee.     

膝关节固定后髌骨腱的生物力学改变

背景：骨关节固定常作为防止受伤组织被再次损伤的方法。目的：膝关节固定对兔髌骨腱力学特性及超微形态的影响。方法：将20只成年兔等分为固定组和对照组。固定组兔左后肢通过石膏和2个可调铝夹板,保持膝伸直,踝关节屈曲90°,固定6周后,取髌骨腱-骨复合物,观察两组髌骨腱的生物力学性能和超微结构变化。结果与结论：膝关节固定6周拉伸强度和切线模量分别下降至对照组的64.44%和53.08%（P〈0.01）,但两组伸长率和最大负荷差异没有显著性意义。两组材料常数及应力应变关系曲线完全不同。固定组髌骨腱的横截面积明显大于对照组（P〈0.01）,小胶原纤维占有优势。说明固定不仅会导致髌骨腱生物力学的变化,而且对髌骨腱自身也产生影响。     

Creep and the in vivo assessment of human patellar tendon mechanical properties

BACKGROUND: Owing to the viscoelastic nature of tendons it may be that the total excursion and hence strain experienced by the tendon under load may be affected by the duration of contraction. Here we examine the effect of contraction duration on the measured in vivo mechanical properties of the patellar tendon. METHODS: Nine healthy young men aged 21 (SEM 0.5 years) performed three short (3-4s) and three long (10-12s) maximal ramped isometric contractions on an isokinetic dynamometer, with real-time recordings of patellar excursions using B-mode ultrasonography synchronised with forces to determine tendon mechanical properties. FINDINGS: Maximal patellar excursion was approximately 42% (P<0.001, effect size (r)=0.9) lower for the short 3.6 (SEM 0.4mm) vs. the long 6.2 (SEM 0.4mm) contractions. Similarly, across the range of forces tested, strain was approximately 42% (P<0.001, r=0.9) lower for the short vs. the long contractions 4.5 (SEM 0.5) vs. 8.0 (SEM 0.9%), respectively. Tendon stiffness however, was approximately 77% greater (4648 SEM 434 vs. 2633 SEM 257 N mm(-1), P<0.001, r=0.9) for short vs. long contractions. INTERPRETATION: Contraction duration significantly affects tendon strain and associated measures of stiffness at all levels of force. The implications of this finding are twofold in that the results: (a) indicate that in order to compare tendon mechanical properties within or across studies, duration of contraction must be standardised and (b) have possible implications on training protocols and associated injury risks.     

冻干韧带脱细胞支架材料的生物相容性及优势

背景:韧带脱细胞基质是通过各种脱细胞方法将韧带组织内的细胞成分清除,降低免疫原性,同时对纤维支架结构破坏轻微,保留了细胞外基质的机械性能.目的:评价冻干兔髌韧带脱细胞支架的生物相容性及优势.方法:取兔髌韧带,利用1%脱氧胆酸钠行脱细胞处理,制备冻干和未冻干脱细胞韧带支架.结果与结论:冻干韧带脱细胞支架保持了冻干前的胶原结构与力学特征,无细胞残留,其浸提液对细胞生长无抑制作用,无全身急性毒性反应,无热原存在,且原发刺激指数为0分,皮内刺激实验阴性.体内埋植实验显示冻干韧带脱细胞支架表现为免疫原性小,炎症反应轻的特点.说明冻干韧带脱细胞支架具有较好的生物相容性,且制作简单,便于消毒、包装、保存.     

A comparison of the quasi-static mechanical and non-linear viscoelastic properties of the human semitendinosus and gracilis tendons

Background

Over 50-% of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and non-linear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length.

Methods

Specimens were subjected to a series of uniaxial tensile tests: 1-h static stress-relaxation test, 30 cycle cyclic stress-relaxation test and load to failure test. To describe the non-linear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress-relaxation experiment.

Findings

The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon.

Interpretation

The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and non-linear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection.