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PubMed1996

Relationship between joint motion and flexor tendon force in the canine forelimb.

To increase in vivo tendon force and gliding after flexor tendon repair, a variety of modifications to the methods by which protective passive motion is administered have been advocated. To determine the relationship between the prime variables, wrist and digital position, muscle activation, and in vivo tendon force, a clinically relevant canine model was developed. Force was measured in the flexor tendon during several joint manipulation paradigms: single-finger flexion-extension with the wrist flexed (group 1F), single-finger flexion-extension with the wrist extended (group 1E), four-finger flexion-extension with the wrist flexed (group 4F), four-finger flexion-extension with the wrist extended (group 4E), and synergistic wrist and finger motion where wrist extension and finger flexion were performed simultaneously, followed by wrist flexion and finger extension (group SYN). In addition, tendon force was measured during electric stimulation of the proximal flexor muscle mass. Passive tendon force with the wrist extended (groups 1E and 4E) was two to three times greater than that measured with the wrist flexed, independent of the number of digits moved. With the wrist extended, peak tendon force reached 1,997 g +/- 194 g during single-digit manipulation (group 1E), compared to only 853 g +/- 104 g with the wrist flexed during the same maneuver (group 1F). Statistical comparison between means revealed that groups 1E and 4E were significantly different from groups 1F, 4F, and SYN (p < .005). There were no significant differences between groups 1E and 4E or between groups 1F, 4F, and SYN (p > .200). Active muscle force elicited by electrical stimulation and passive force varied dramatically as the wrist was flexed from full extension 3460 g +/- 766 g to full flexion 427 g +/- 239 g (p < .001). Simultaneously, passive tension decreased from 940 g +/- 143 g with wrist extended to 76 g +/- 37 g with the wrist flexed. These data indicate that wrist position has the greatest effect on flexor tendon force during motions that are commonly used to rehabilitate flexor tendon repairs. Thus, if force is to be controlled during passive motion, wrist-joint angle will have the dominant effect, while the number of digits manipulated will have much less of an effect. If the clinical goal is to minimize tendon force, rehabilitation could be carried out with the wrist flexed, whereas if the goal is to increase tendon force, rehabilitation could include exercise programs that use a greater degree of wrist extension.

Animals↗
PubMed2001

Healing of full-thickness tears of avian supracoracoid tendons: in situ hybridization of alpha1(I) and alpha1(III) procollagen mRNA.

Although clinically significant, much remains unknown about the healing of the torn rotator cuff tendon, because of unavailability of appropriate animal model. The human supraspinatus tendon faces the subacromial bursa superiorly, and the joint capsule inferiorly, while the digital flexor tendon is surrounded by the synovium. We hypothesized that the supraspinatus tendon heals by the process which is different from that observed with digital flexor tendons, in which epitenon cells migrate into the torn portion circumferentially. The avian supracoracoid tendon was adopted for this experiment because of its similarity to the human supraspinatus tendon. We developed a full-thickness tendon laceration followed by primary suture. The objective of this study was to detect localization of the responsible cells for repair of the tendon. We examined the process using histology and in situ hybridization. Starting at week 1 the peritendon cells of the bursal side proliferated and migrated into the laceration site. At week 6, the tendon stumps were continuous with new connective tissue. High-level expression of procollagen mRNA in the proliferating peritendon cells on the bursal side demonstrates to contribute to the reparative process, which progressed to the joint side. This mode of repair is different from that of the digital flexor tendon.

Animals↗
PubMed1994

The structure and vascularization of the biceps brachii long head tendon.

In the present study we examined the structure and the blood supply of the long biceps tendon as well as the surface of the intertubercular sulcus, using tissue samples from children and adults. The applied methods were light and electron microscopy, immunohistochemistry, and arterial injection techniques. The tendon represents a sliding tendon with the intertubercular sulcus and humeral head as hypomochlion. The parts facing the humerus show some ultrastructural features of fibrous cartilage, the ovoid chondrocyte-like cells of the tendon lying within felt-like matrix. In the opposite part adjacent to the capsule, the tendon resembles a traction tendon. The intertubercular sulcus is covered by fibrous cartilage. The tendon is supplied with arteries from three different sources. The density of intratendinous vessels in the traction zone is comparable to that of other tendons, while in the sliding zone it is markably decreased. The immediate vicinity of the sliding surface is avascular. Our findings show that the long biceps tendon is structurally adapted to both its functions as sliding and traction tendon. The blood supply seems to be related to the metabolic requirements of the different parts of the tendon.

Adolescent↗
PubMed2002

The integrated function of muscles and tendons during locomotion.

The mechanical roles of tendon and muscle contractile elements during locomotion are often considered independently, but functionally they are tightly integrated. Tendons can enhance muscle performance for a wide range of locomotor activities because muscle-tendon units shorten and lengthen at velocities that would be mechanically unfavorable for muscle fibers functioning alone. During activities that require little net mechanical power output, such as steady-speed running, tendons reduce muscular work by storing and recovering cyclic changes in the mechanical energy of the body. Tendon stretch and recoil not only reduces muscular work, but also allows muscle fibers to operate nearly isometrically, where, due to the force-velocity relation, skeletal muscle fibers develop high forces. Elastic energy storage and recovery in tendons may also provide a key mechanism to enable individual muscles to alter their mechanical function, from isometric force-producers during steady speed running to actively shortening power-producers during high-power activities like acceleration or uphill running. Evidence from studies of muscle contraction and limb dynamics in turkeys suggests that during running accelerations work is transferred directly from muscle to tendon as tendon stretch early in the step is powered by muscle shortening. The energy stored in the tendon is later released to help power the increase in energy of the body. These tendon length changes redistribute muscle power, enabling contractile elements to shorten at relatively constant velocities and power outputs, independent of the pattern of flexion/extension at a joint. Tendon elastic energy storage and recovery extends the functional range of muscles by uncoupling the pattern of muscle fiber shortening from the pattern of movement of the body.

Animals↗
PubMed2000

Structure of the tendon connective tissue.

Tendons consist of collagen (mostly type I collagen) and elastin embedded in a proteoglycan-water matrix with collagen accounting for 65-80% and elastin approximately 1-2% of the dry mass of the tendon. These elements are produced by tenoblasts and tenocytes, which are the elongated fibroblasts and fibrocytes that lie between the collagen fibers, and are organized in a complex hierarchical scheme to form the tendon proper. Soluble tropocollagen molecules form cross-links to create insoluble collagen molecules which then aggregate progressively into microfibrils and then into electronmicroscopically clearly visible units, the collagen fibrils. A bunch of collagen fibrils forms a collagen fiber, which is the basic unit of a tendon. A fine sheath of connective tissue called endotenon invests each collagen fiber and binds fibers together. A bunch of collagen fibers forms a primary fiber bundle, and a group of primary fiber bundles forms a secondary fiber bundle. A group of secondary fiber bundles, in turn, forms a tertiary bundle, and the tertiary bundles make up the tendon. The entire tendon is surrounded by a fine connective tissue sheath called epitenon. The three-dimensional ultrastructure of tendon fibers and fiber bundles is complex. Within one collagen fiber, the fibrils are oriented not only longitudinally but also transversely and horizontally. The longitudinal fibers do not run only parallel but also cross each other, forming spirals. Some of the individual fibrils and fibril groups form spiral-type plaits. The basic function of the tendon is to transmit the force created by the muscle to the bone, and, in this way, make joint movement possible. The complex macro- and microstructure of tendons and tendon fibers make this possible. During various phases of movements, the tendons are exposed not only to longitudinal but also to transversal and rotational forces. In addition, they must be prepared to withstand direct contusions and pressures. The above-described three-dimensional internal structure of the fibers forms a buffer medium against forces of various directions, thus preventing damage and disconnection of the fibers.

Collagen↗
PubMed2003

Tendon properties in relation to muscular activity and physical training.

Movement is caused by force transmission from contracting muscles to bone via tendon. The collagen structure of tendon is organized in a very hierarchical manner. The collagen fibril is considered the basic force-transmitting unit of tendon, and it is embedded in a hydrophilic extracellular matrix of proteoglycans, glycoproteins and glycosaminoglycans. It has recently been shown in human peritendinous tissue is more metabolically active in response to activity than previously thought, although it remains to be established, if the level of activity influences affects fibril diameter and/or total tendon cross-sectional area. Moreover, it cannot be unequivocally concluded that tendon adaptation to physical activity is one of a quantitative and/or qualitative nature. The currently available information is almost exclusively obtained from animal data, however, techniques such as microdialysis for tendon metabolism and ultrasound combined with MRI for tendon mechanical properties has already provided information on human tendon behavior, and is likely to further add to our understanding of how tendon adapt to physical activity. This review will address the structure and function of tendon, and the current knowledge of how tendons respond to activity with respect to biomechanical properties.

Animals↗
PubMed2001

Arthroscopic visualization of the subscapularis tendon.

PURPOSE: This study was conducted to define what portion of the subscapularis tendon is visualized during standard diagnostic glenohumeral arthroscopy and to determine the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve. TYPE OF STUDY: Anatomic (cadaveric) analysis. METHODS: Six fresh-frozen human cadaveric shoulders were placed in a simulated lateral decubitus position with longitudinal traction and 45 degrees of shoulder abduction. Glenohumeral arthroscopy was performed on each specimen using a standard posterior portal for visualization. The 4 corners of the visible portion of the subscapularis were tagged with arthroscopic sutures. The shoulders were subsequently dissected. The surface area defined by the 4 suture tags and the surface area of the entire subscapularis tendon were calculated for each specimen. The dimensions of these areas and the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve were measured with calipers. RESULTS: The arthroscopically tagged portion of the subscapularis tendon represented only a small percentage (26% +/- 11%) of the entire tendon. The majority of the subscapularis tendon is veiled by the middle and inferior glenohumeral ligaments. There was a significant distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve (32.8 +/- 6.0 mm). The mean height of the visible portion of the tendon represented 44% of the mean overall height of the subscapularis. CONCLUSIONS: These data suggest that arthroscopic visualization of the subscapularis is incomplete. Lesions involving the concealed portion of the subscapularis tendon may not be detected arthroscopically. The wide margin of safety between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve is relevant to the placement of anteroinferior (trans-subscapularis) arthroscopy portals as well as to performing arthroscopic anterior capsular releases.

Arthroscopy↗
PubMed2000

Cyclical testing of zone II flexor tendon repairs.

Kessler, Strickland, or modified Becker repairs, all augmented with a running circumferential epitenon suture, were performed for simulated zone II flexor tendon lacerations in the index, long, and ring fingers of 12 fresh-frozen cadaveric specimens. Each hand was tested with a tensiometer built for curvilinear testing of human flexor tendons in an intact hand. Each tendon was cycled 100 times, then examined for gapping before testing to failure. Maximum load to failure, including tendon load and pinch force, was recorded for each tendon. We propose that combining the advantages of cyclical testing and a curvilinear model is the most effective way of testing flexor tendon repairs capable of undergoing an early active motion protocol. None of the repaired tendons failed during the cyclic portion of testing. The average gapping after cycling for the 3 suture techniques was 0.12 +/- 0.35 mm for the Kessler technique, 0. 00 +/- 0.00 mm for the Strickland technique, and 0.19 +/- 0.26 mm for the modified Becker technique. The maximum tendon loads to failure were 33.8 +/- 6.8 N for the Kessler technique, 30.4 +/- 5.64 N for the Strickland technique, and 76.3 +/- 9.02 N for the modified Becker technique. There was a statistically significant difference between the modified Becker repair and the other 2 repairs for maximum tendon load and pinch force to failure. The results of this study show that all 3 tendon repair techniques can withstand forces reported with passive motion, but only the modified Becker repair allows sufficient strength above those forces that are estimated for active motion during tendon healing.

Biomechanical Phenomena↗
PubMed2003

Biomechanical evaluation of flexor tendon function after hamate hook excision.

PURPOSE: Hamate hook fractures are uncommon injuries for which treatment is controversial. Excision of the hamate hook is considered to be the preferred method of treatment but the effects of hamate excision are not clearly delineated. The purpose of this study was to determine what effect, if any, excision of the hamate has on flexor tendon function. METHOD: The biomechanical effects of hamate hook excision on flexor tendon function were studied in fresh cadaveric forearm specimens with wrists fixed in 3 positions (neutral, 30 degrees extension, 30 degrees extension with 30 degrees ulnar deviation). Flexor tendon force, flexor tendon excursion, and flexor tendon shift were evaluated. RESULTS: Flexor tendon force decreased after hamate hook excision (11% in neutral, 14% in 30 degrees extension, and 15% in 30 degrees extension with 30 degrees ulnar deviation). The flexor profundus tendons had a 7- to 11-mm increase in proximal tendon excursion after hamate hook excision depending on the position of the wrist, and the flexor profundus tendons of the small finger shifted 4 to 5 mm in ulnar direction. CONCLUSIONS: The hamate hook provides some biomechanical advantage for flexor tendon function and cadaveric changes in tendon force after its excision suggest that power grip may be decreased after hamate hook excision.

Biomechanical Phenomena↗
PubMed2002

Dorsal-enhanced sutures improve tension resistance of tendon repair.

Thirty-six fresh pig flexor tendons were repaired using either the modified Kessler method or the Tang method. Nine tendons from each group were tested in an Instron tensile testing machine with the tendons passing 90 degrees around a pulley. The other nine tendons from each group were pulled linearly by the testing machine. The 2 mm gap formation force of the tendons repaired with the modified Kessler and Tang methods and pulled at 90 degrees were 64%+/-5% and 79%+/-9% respectively of those forces recorded during linear testing. The ultimate strengths of tendons repaired by the modified Kessler and Tang methods and pulled at 90 degrees were 76%+/-6% and 81%+/-8% respectively of the forces measured during linear testing. The percentage gap formation and ultimate strength of the Tang method was significantly higher than that of the modified Kessler suture when the tendons were pulled around a pulley. This demonstrates that the Tang suture, with its main components in the dorsal part of the repaired tendon, has greater tension resistance capacity than conventional tendon sutures which are placed in the middle of the tendon. This study suggests that dorsally-enhanced multiple tendon sutures are better placed to sustain the tension generated during active finger flexion.

Animals↗
PubMed2003

[The Mantero technique for flexor tendon repair - an alternative?].

PURPOSE: Regaining free tendon gliding after reconstruction of flexor tendons is essential to restore full function to the affected finger. Mantero et al. described a pull-out suture technique for the repair of flexor digitorum profundus (FDP) lesions in zone 1, allowing early postoperative active mobilisation and thus minimizing the risk of tendon adhesions. In a retrospective study we examined the results after Mantero tendon repair and compared these with the results after different reconstructive procedures in the literature. METHODS AND MATERIAL: Between 1995 and 2001, the FDP tendon in zone 1 and distal half of zone 2 distal to the chiasma respectively the flexor pollicis longus (FPL) tendon were reconstructed in 96 patients using the Mantero technique. 87 (90 %) patients, with a male to female ratio of 2 : 1, were re-examined an average of 43 (4 to 84) months postoperatively. We evaluated the isolated function of the finger joints, the total range of motion of the affected finger and grip strength and compared all values to the contralateral healthy side and assessed the functional results according to the Buck-Gramcko score and the patients' satisfaction according to the DASH score. Special attention was directed to the influence of the patients' age, gender, art of trauma, accompanying injuries or level of the lesion on the postoperative results. Furthermore, we evaluated whether clinical results depended on which finger was injured. RESULTS: 71 % (n = 62) of all injuries were found in the distal zone 2 or distal zone Th 2 in the thumb. While 81 % (n = 70) were caused by a clean cut, 10 % (n = 9) were due to a circular saw injury and 9 % (n = 8) due to a crush injury. The average DASH score value was 5.4 (0 to 37.5) with excellent and good results according to the Buck-Gramcko score in 90.8 % (n = 79) of all patients. Only the patients' age (> 50 years vs. < 20 years) and the digit involved (little finger vs. index, middle and ring fingers) had a significant influence on the postoperative results. Aside from superficial skin necrosis in 10 % of all cases, in which no further operative therapy was necessary, no other complications occurred. Interestingly, no ruptures of the sutured tendons were found, although active mobilisation was initiated immediately. Compared to the literature, the 90,8 % excellent and good results are equivalent to those of other studies concerning reconstruction after flexor tendon injuries using the Mantero technique and tend to be better than other reconstructive procedures. CONCLUSION: Based on our results, we consider the Mantero technique to be a good alternative to other forms of flexor tendon reconstruction in zone 1 and distal zone 2. Advantages include the possibility of immediate postoperative mobilisation and placing a secure tendon suture, even if the distal tendon stump is very short.

Adolescent↗
PubMed2004

[In vitro fabrication of tendon substitutes using human mesenchymal stem cells and a collagen type I gel].

BACKGROUND AND PURPOSE: Reconstruction of tendon tissue is problematic in many cases. Since direct tendon suture is often impossible, major reconstruction with the use of free tendon transplants or tendon transposition is necessary. Important motor units often have to be sacrificed for reconstructive purposes. In this study we investigated whether long tendon-like substitutes can be fabricated in vitro from human mesenchymal stem cells (MSCs) and a collagen type I gel when cultured under cyclic stretching conditions. MATERIAL AND METHODS: MSCs were obtained from bone marrow aspirates of the iliac crest. Cells were suspended in a collagen type I gel and polymerized in a glass-cylinder with defined size. The fabricated tendon substitutes underwent static stretching for 14 days followed by cyclic stretching for 21 days in a special manufactured bioreactor. Non-stretched substitutes served as a control. RESULTS: Macroscopically the stretched tendon substitutes showed an increased opacity and a smoother surface structure compared to the non-stretched control. The stretched substitutes displayed more spindle-shaped, longitudinal orientated cells, a tendon-like organization of the collagen matrix, and a parallel organization of the collagen fibers when stained with Hematoxylin/Eosin and Elastica. CONCLUSION: Long tendon substitutes could be fabricated from MSCs and a collagen type I gel by cyclic stretching and showed tendon-like parallel collagen fibers and spindle-shaped cells. The use of MSCs in combination with adequate scaffold materials has great therapeutic potential for the development of autologous transplantable tendon substitutes.

Bioreactors↗
PubMedDate not supplied

Cross-linking in collagen by nonenzymatic glycation increases the matrix stiffness in rabbit achilles tendon.

Nonenzymatic glycation of connective tissue matrix proteins is a major contributor to the pathology of diabetes and aging. Previously the author and colleagues have shown that nonenzymatic glycation significantly enhances the matrix stability in the Achilles tendon (Reddy et al., 2002, Arch. Biochem. Biophys., 399, 174-180). The present study was designed to gain further insight into glycation-induced collagen cross-linking and its relationship to matrix stiffness in the rabbit Achilles tendon. The glycation process was initiated by incubating the Achilles tendons (n = 6) in phosphate-buffered saline containing ribose, whereas control tendons (n = 6) were incubated in phosphate-buffered saline without ribose. Eight weeks following glycation, the biomechanical attributes as well as the degree of collagen cross-linking were determined to examine the potential associations between matrix stiffness and molecular properties of collagen. Compared to nonglycated tendons, the glycated tendons showed increased maximum load, stress, strain, Young's modulus of elasticity, and toughness indicating that glycation increases the matrix stiffness in the tendons. Glycation of tendons resulted in a considerable decrease in soluble collagen content and a significant increase in insoluble collagen and pentosidine. Analysis of potential associations between the matrix stiffness and degree of collagen cross-linking showed that both insoluble collagen and pentosidine exhibited a significant positive correlation with the maximum load, stress, and strain, Young's modulus of elasticity, and toughness (r values ranging from.61 to.94) in the Achilles tendons. However, the soluble collagen content present in neutral salt buffer, acetate buffer, and acetate buffer containing pepsin showed an inverse relation with the various biomechanical attributes tested (r values ranging from.22 to.84) in the Achilles tendons. The results of the study demonstrate that glycation-induced collagen cross-linking is directly associated with the increased matrix stiffness and other mechanical attributes of the tendon.

Achilles Tendon↗
PubMed2004

Expression of VEGFR-1 and VEGFR-2 in degenerative Achilles tendons.

Evidence suggests neovascularization is involved in the etiology of spontaneous Achilles tendon rupture. Therefore we investigated expression of the receptors of one of the most important angiogenic factors, the vascular endothelial growth factor in normal and pathologic human Achilles tendons by immunohistochemical and molecular biology methods. Light microscopy showed degenerative changes in all spontaneously ruptured tendons with a higher vascular density compared with controls of healthy tendons from a cadaver. The vascular endothelial growth factor receptors-1 and 2 could be immunostained in endothelial cells of ruptured and fetal tendons, but not in normal tendons. Reverse transcription-polymerase chain reaction showed messenger ribonucleic acid of both receptors are expressed in ruptured and fetal tendons but not in normal tendons. These results prove the reexpression of the major receptors for the angiogenic peptide vascular endothelial growth factor, the vascular endothelial growth factor receptor-1, and the vascular endothelial growth factor receptor-2 in ruptured and fetal tendons and support our theory that high vascular density is associated with the pathogenesis of tendon degenerations. Inhibiting angiogenesis could be a new approach in the therapy of degenerative Achilles tendon disease.

Achilles Tendon↗
PubMed2001

Differential expression of transforming growth factor-beta receptors in a rabbit zone II flexor tendon wound healing model.

Flexor tendon repair in zone II is complicated by adhesions that impair normal postoperative gliding. Transforming growth factor-beta (TGF-beta) is a family of growth factors that has been implicated in scar formation. The TGF-beta family of proteins binds to three distinct classes of membrane receptors, termed RI, RII, and RIII. In this study, we analyzed the temporal and spatial distribution of TGF-beta receptor isoforms (RI, RII, and RIII) in a rabbit zone II flexor tendon wound healing model.Twenty-eight adult New Zealand White rabbit forepaws underwent isolation of the middle digit flexor digitorum profundus tendon in zone II. The tendons underwent transection in zone II and immediate repair. The tendons were harvested at increasing time points: 1, 3, 7, 14, 28, and 56 days postoperatively (n = 4 at each time point). The control flexor tendons were harvested without transection and repair (n = 4). Immunohistochemical analysis was used to detect the expression patterns for TGF-beta receptors RI, RII, and RIII. Immunohistochemical staining of the transected and repaired tendons demonstrated up-regulation of TGF-beta RI, RII, and RIII protein levels. TGF-beta receptor production in the experimental group (transection and repair) was concentrated in the epitenon and along the repair site. Furthermore, the TGF-beta receptor expression levels peaked at day 14 and decreased by day 56 postoperatively. In contrast, minimal receptor expression was observed in the untransected and unrepaired control tendons. These data provide evidence that (1) TGF-beta receptors are up-regulated after injury and repair; (2) peak levels of TGF-beta receptor expression occurred at day 14 and decreased by day 56 after wounding and repair; and (3) both the tendon sheath and epitenon have the highest receptor expression, and both may play critical roles in flexor tendon wound healing. Understanding the up-regulation of TGF-beta isoforms and the up-regulation of their corresponding receptors during flexor tendon wound healing provides new targets for biomolecular modulation of postoperative scar formation.

Animals↗
PubMed2005

Microarray analysis of mechanical shear effects on flexor tendon cells.

BACKGROUND: Adhesion formation after flexor tendon repair remains a clinical problem. Early postoperative motion after tendon repair has been demonstrated to reduce adhesion formation while increasing tendon strength. The authors hypothesized that during mobilization, tendon cells experience mechanical shear forces that alter their biology in a fashion that reduces scar formation but also activates key genes involved in tendon healing. METHODS: To test this hypothesis, primary intrinsic tenocyte cultures were established from flexor tendons of 20 Sprague-Dawley rats and sheared at 50 rpm (0.41 Pa) using a cone viscometer for 6 and 12 hours. Total RNA was harvested and compared with time-matched unsheared controls using cDNA microarrays and Northern blot analysis. RESULTS: Microarray analysis demonstrated that mechanical shear stress induced an overall "antifibrotic" expression pattern with decreased transcription of collagen type I and collagen type III. Shear stress down-regulated profibrotic molecules in the platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor signaling pathways. In addition, shear stress induced an overall decrease in transforming growth factor (TGF)-beta signaling pathway molecules with down-regulation of TGF-beta2, TGF-beta3, TGF-RI, and TGF-RII expression. Moreover, sheared tendon cells increased expression of matrix metalloproteinases and decreased expression of tissue inhibitors of metalloproteinase, an expression pattern consistent with an antifibrotic increase in extracellular matrix degradation. However, the authors also found up-regulation of genes implicated in tendon healing, specifically, vascular endothelial growth factor-A and several bone morphogenetic proteins. Interestingly, the known mechanoresponsive gene, TGF-beta1, also implicated in tendon healing, was differentially up-regulated by shear stress. Northern blot validation of our results for TGF-beta1, TGF-beta2, TGF-beta3, and collagen type I demonstrated direct correlation with the authors' microarray data. CONCLUSIONS: The authors demonstrate an overall antifibrotic expression pattern in response to shear stress in tendon cells that may provide insight into the mechanisms by which early mobilization decreases adhesion formation without impaired tendon healing.

Animals↗
PubMed1976

Frequency of tendon organ discharges elicited by the contraction of motor units in cat leg muscles.

1. The responses elicited in individual tendon organs by the contraction of single motor units were studied in peroneus longus, peroneus brevis, tibialis anterior and soleus muscles. 2. No simple relation was found between the discharge frequency of a tendon organ and the tension produced in the muscle tendon by the contraction of individual motor units. 3. The sensitivity of a given tendon organ to contractile tension was not the same for each of the motor units which elicited its discharge. There was no correlation between the sensitivity of the receptor and the strength of the motor units. 4. Upon repetitive stimulation of a tendon-organ-activating motor unit at increasing rates, the frequency of the receptor sustained discharge reached a maximal value for rates of stimulation eliciting submaximal tetanic tension. Higher rates only produced an increase in the dynamic component of the tendon organ response. 5. These observations show that the contractile tension sensed by a tendon organ is not a simple fraction of the tension which appears at the muscle tendon. They might be accounted for as consequences of the fine structure of tendon organs and of variations in the number of muscle fibres contributed by different motor units to the bundle inserted on each receptor. The location of most tendon organs at musculo-aponeurotic junctions rather than in the tendon proper, could also be responsible for some of the observed discrepancies.

Action Potentials↗
PubMed2000

Extrinsic cell infiltration and revascularization accelerate mechanical deterioration of the patellar tendon after fibroblast necrosis.

This study was performed to determine the contribution of extrinsic cell infiltration and revascularization into the patellar tendon in alteration of the mechanical properties of the patellar tendon after intrinsic fibroblast necrosis using 77 rabbits. In Group I, after the patellar tendon underwent the in situ freeze-thaw treatment, a wrapping treatment was performed to inhibit any extrinsic cell infiltration into the tendon. In Group II, the patellar tendon underwent the freeze-thaw treatment without any of the wrapping treatment. In Group III, the patellar tendon underwent the same wrapping treatment but without any freeze-thaw treatment. The cell culture study demonstrated that the in situ freeze-thaw treatment killed from 97 to 100 percent of the cells in the patellar tendon. Histologically, no cells were found in the midsubstance of the patellar tendon in Group I at 1, 3, and 6 weeks. In Group II, a number of cells and some vessels were found scattered in the tendon at 3 and 6 weeks. Mechanically, the elastic modulus and the tensile strength of the patellar tendon of Group II were significantly lower than those of Groups I and III at 3 and 6 weeks. These facts suggest that extrinsic cell infiltration and revascularization from the surrounding tissues accelerate the deterioration of the mechanical properties of the patellar tendon matrix after intrinsic fibroblast necrosis.

Animals↗