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PubMed2005

Effect of Achilles tendon loading on plantar fascia tension in the standing foot.

BACKGROUND: The plantar fascia, which is one of the major arch-supporting structures of the human foot, sustains high tensions during weight-bearing. A positive correlation between Achilles tendon loading and plantar fascia tension has been reported. Excessive stretching and tightness of the Achilles tendon are thought to be the risk factors of plantar fasciitis but their biomechanical effects on the plantar fascia have not been fully addressed. METHODS: A three-dimensional finite element model of the human foot and ankle, incorporating geometrical and material nonlinearity, was employed to investigate the loading response of the plantar fascia in the standing foot with different magnitudes of Achilles tendon loading. FINDINGS: With the total ground reaction forces of one foot maintained at 350 N to represent half body weight, an increase in Achilles tendon load from (0-700 N) resulted in a general increase in total force and peak plantar pressure at the forefoot of up to about 250%. There was a lateral and anterior shift of the centre of pressure and a reduction in the arch height with an increasing Achilles tendon load as a result of the plantar flexion moment on the calcaneus. From the finite element predictions of simulated balanced standing, Achilles tendon forces of 75% of the total weight on the foot (350 N) were found to provide the closest match of the measured centre of pressure of the subject during balanced standing. Both the weight on the foot and Achilles tendon loading resulted in an increase in tension of the plantar fascia with the latter showing a two-times larger straining effect. INTERPRETATION: Increasing tension on the Achilles tendon is coupled with an increasing strain on the plantar fascia. Overstretching of the Achilles tendon resulting from intense muscle contraction and passive stretching of tight Achilles tendon are plausible mechanical factors for overstraining of the plantar fascia.

Achilles Tendon↗
PubMed2006

Mechanical properties of the triceps surae tendon and aponeurosis in relation to intensity of sport activity.

The purpose of the present study was to investigate whether the mechanical properties (i.e. force strain relationship) of the triceps surae tendon and aponeurosis relate to the performed sport activity in an intensity-dependent manner. This was done by comparing sprinters with endurance runners and subjects not active in sports. Sixty-six young male subjects (26+/-5 yr; 183+/-6 cm; 77.6+/-6.7 kg) participated in the study. Ten of these subjects were adults not active in sports, 28 were endurance runners and 28 sprinters. All subjects performed isometric maximal voluntary plantar flexion contractions (MVC) on a dynamometer. The distal aponeuroses of the gastrocnemius medialis (GM) was visualised by ultrasound during the MVC. The results showed that only the sprinters had higher normalised stiffness (relationship between tendon force and tendon strain) of the triceps surae tendon and aponeurosis and maximal calculated tendon forces than the endurance runners and the subjects not active in sports. Furthermore, including the data of all 66 examined participants tendon stiffness correlated significantly (r=0.817, P<0.001) with the maximal tendon force achieved during the MVC. It has been concluded that the mechanical properties of the triceps surae tendon and aponeurosis do not show a graded response to the intensity of the performed sport activity but rather remain at control level in a wide range of applied strains and that strain amplitude and/or frequency should exceed a given threshold in order to trigger additional adaptation effects. The results further indicate that subjects with higher muscle strength possibly increase the margin of tolerated mechanical loading of the tendon due to the greater stiffness of their triceps surae tendon and aponeurosis.

Adaptation, Physiological↗
PubMed2005

In vivo motion transmission in the inactive gastrocnemius medialis muscle-tendon unit during ankle and knee joint rotation.

The purposes of this study were: (a) to quantify the influence of passive ankle and knee joint angular displacement on the estimated mechanical and architectural properties of the gastrocnemius medialis (GM) muscle-tendon unit, and (b) to determine the strain distribution of separate structures (tendon, aponeurosis and fascicle) during passive lengthening of the GM muscle-tendon unit at rest. Ten male subjects participated in the study. The passive ankle and knee joint movements were performed on an isokinetic dynamometer. The kinematics of the left leg were recorded using the Vicon 624 system with 8 cameras. Two ultrasound probes were used to examine the elongation of the tendon, the aponeurosis, the fascicles and the angle of pennation of the GM. To calculate the elongation of the GM muscle-tendon unit the Achilles tendon path was reconstructed using a series of small reflective markers. The results show that the passive ankle joint angular displacement has a considerable influence on the elongation of the tendinous and architectural structures of the GM muscle-tendon unit. In contrast, the influence of knee joint angular displacement on the GM fascicle length and pennation angle becomes relevant only at knee angles greater than 144 degrees . The contribution of the tendon to the elongation of the GM muscle-tendon unit at rest is relevant because of its greater resting length in comparison to the resting length of the GM fascicles. The results indicate the existence of slackness in the inactive GM muscle-tendon unit between 121 degrees and 107 degrees ankle angle and between 65 degrees and 144 degrees knee angle.

Adult↗
PubMed2004

Assessment of mRNA levels for matrix molecules and TGF- beta1 in rabbit flexor and peroneus tendons reveals regional differences in steady-state expression.

This study analysed the differences on a molecular level between two segments of the deep flexor tendon, and compared the intrasynovial flexor tendon with the tendon sheath and the extrasynovial peroneus tendon in a rabbit model. The TRIspin method of RNA extraction was combined with the reverse transcription polymerase chain reaction to assess mRNA levels in the tissue segments. Significant differences were detected for all genes studied. mRNA levels for aggrecan, biglycan and collagen III were significantly higher in the fibrocartilaginous proximal segment of the flexor tendon. Collagen I was higher in the flexor tendon than the sheath and the peroneus tendon, and TGF-beta1 was significantly lower in the peroneus tendon. This study demonstrates differences at the mRNA level between different segments of tendon, indicating that the tendon tissue may be adapted to its environment.

Aggrecans↗
PubMed2004

Application of porous-media theory to the investigation of water ADC changes in rabbit Achilles tendon caused by tensile loading.

The water apparent diffusion coefficient (ADC) in rabbit Achilles tendon is anisotropic, diffusion-time dependent, and changes as a function of tensile load. Water ADC changes of tendon under mechanical load are thought to be due to the extrusion of water from the more restricted tendon core to a relatively unrestricted bulk phase at the periphery (rim) of the tendon. Tensile loading may influence water ADC values by changing the spatial separation of restricting barriers (e.g., increasing the tendon fibril packing density). To explore this issue, we have applied porous-media theory to the investigation of water ADC changes in rabbit Achilles tendon under two different mechanical loading conditions (a baseline condition with a minimal tensile stress and a second in which the tensile stress was approximately 1 MPa). Diffusion sensitivity was applied in directions parallel and perpendicular to the long axis of the tendon. The short diffusion-time behavior of the resulting time-dependent ADC curves was used to indirectly infer information regarding the average surface area to volume ratio of the space available for molecular diffusion. From these values, we estimated a 40% reduction in volume available for diffusion in the perpendicular direction after tensile loading, but only a 10% reduction in the parallel direction. These differences are consistent with the known geometry of the tendon microstructure and suggest an increase in fibril packing density upon loading. The long diffusion-time behavior of the time-dependent ADC curves was used to indirectly infer the tortuosity of the diffusion pathways through the interstitial space. The tortuosity in the direction perpendicular to the tendon long axis was approximately 2.5 times greater than that in the parallel direction. Stimulated-echo measurement of the ADC values at longer diffusion times resulted in T1 spin editing of water with shorter T1 values (and correspondingly lower ADC values). The resulting increase in water ADC with increasing diffusion time was attributed to multiple components arising from the (overlapping) distribution of T1 values in the core and rim regions of the tendon.

Achilles Tendon↗
PubMed2003

Magic angle imaging of the achilles tendon in patients with chronic tendonopathy.

AIMS: To assess the Achilles tendon in patients with chronic tendonopathy using magnetic resonance (MR) magic angle imaging, and to compare the appearances and uptake of contrast medium in abnormal tendons with those in normal tendons. MATERIAL AND METHODS: Eight patients with chronic Achilles tendonopathy and five normal controls were examined with the long axis of the tendon placed at 55 degrees and at 0 degrees to the main magnetic field. Conventional two-dimensional (2D) multi-slice images were obtained and T1 values were calculated before, and for up to 1h after the administration of intravenous gadodiamide. Both the unenhanced appearance and the pattern of enhancement in the tendon were compared. RESULTS: In the patients with tendonopathy, high signal intensity areas were evident on the short T1 inversion recovery (STIR) images obtained at 55 degrees in all tendons. Contrast medium enhancement was seen in six tendons and was most obvious on the images obtained at the magic angle. This was initially focal and then spread more diffusely within the tendon. After contrast medium administration, T1 values were significantly reduced in the tendonopathy group compared with normal controls (p<0.01). On the late post-contrast medium images obtained at 55 degrees, enhancement was evident in most of the tendon and correlated well with high signal intensity seen on STIR images. CONCLUSION: The use of magic angle MR imaging improved the demonstration of signal changes in the Achilles tendon in chronic tendonopathy. The STIR images obtained at the magic angle showed more obvious signal change than those obtained at 0 degrees. The changes due to enhancement were much more evident on images obtained at 55 degrees than at 0 degrees. The uptake of contrast medium was greater in the patients than in normal controls.

Achilles Tendon↗
PubMed2003

Systemic vanadate ingestion modulates rat tendon repair.

The chronic ingestion of vanadate prevents the appearance of myofibroblasts within granulation tissue of full excision wounds in rats, yet these wounds close at an optimal rate. Myofibroblasts are reported in the repair of transected tendons. Here we investigate tendon repair in the absence of myofibroblasts. Vanadate in saline drinking water was given to rats in the experimental group, while rats in the control group received saline alone. The Achilles tendon of the left leg of each rat was transected and suture repaired. On day 10, both repaired tendons and uninjured tendons from the right leg were harvested and processed for histology. By immunohistology the repaired tendons of control rats had myofibroblasts (fibroblasts with alpha smooth muscle actin positive stress fibers), while myofibroblasts were absent in healing tendons from vanadate-treated rats. By transmission electron microscopy and polarized light optics, repaired tendons of control rats demonstrated thin, loosely packed, immature collagen fiber bundles. Collagen fiber bundles from healing tendons of the vanadate-treated group were thicker, uniformly packed, and more mature. The chronic ingestion of vanadate promotes the more rapid organization of collagen fiber bundles of healing transected tendons in the absence of myofibroblasts.

Achilles Tendon↗
PubMed2004

In vivo tendon force measurement of 2-week duration in sheep.

Tendon tension in vivo may be determined indirectly by measuring intratendinous pressure, by using a buckle transducer or by measuring the tendon strain. All of these methods require appropriate calibration, which is highly dependent on various variables. To measure the tendon load in vivo during a period of 2 weeks in sheep, a measurement technique has been developed using a force sensor interposed serially between the humeral head and the tendon end. Within a supporting frame, a flexion-sensitive force transducer is subjected to three-point bending stress. The load is transmitted by sutures from the tendon end through a hole in the sensor frame, orthogonal to the force transducer. In this configuration, the sensor measures the tensile force acting on the tendon, largely independent of the loading direction. The sensor was screwed to the humeral head and connected to the tendon end which was previously released from its insertion site along with a bone chip, using sutures. Connecting wires passed subcutaneously to a skin outlet about 30 cm away from the transducer. The sensor output was linear to the measured load up to 300 N, with maximum hysteresis of 18% full scale. All sensors worked in vivo without drift over a period of up to 14 days with no change in the calibration data. Forces up to 310 N have been recorded in vivo with daily tension measurements. This study shows that serial tendon tension measurement is feasible and allows for reliable, repeatable recording of the absolute tendon tension at the expense of tendon integrity.

Animals↗
PubMed2003

Synovial sheath cell migratory response to flexor tendon injury: an experimental study in rats.

PURPOSE: We aimed to investigate the degree of participation of synovial sheath cells in the process of tendon healing by selective cell labeling and direct observation of migrational pathways. METHODS: We designed a novel rat animal model that employed vital dye staining of synovial sheath cells. The flexor digitorum profundus (FDP) tendon was removed from its sheath and vital dye was applied directly to the synovial sheath cells. A window was cut in the removed tendon before being returned to the sheath, thus placing a tendon injury adjacent to the labeled synovial sheath cells. The synovium remained intact at all times, and labeling was confirmed to be localized to the synovium. The migrational response of the synovial sheath cells to the tendon injury was observed by harvesting the tendons at 1, 3, 5, and 7 days (n = 6 for each time period) after injury and assessing tendon response with frozen sections under ultraviolet microscopy. RESULTS: Labeled synovial sheath cells were observed within the substance of the healing tendon 24 hours after injury, with numbers increasing with time for up to 5 days, but decreasing by day 7. CONCLUSIONS: This study confirms that in the rat model synovial sheath cells move into the healing tendon area and then migrate into the tendon core.

Animals↗
PubMed1995

Anatomy of the extensor tendons of the fingers: variations and multiplicity.

The extensor tendons to the fingers were dissected in 43 adult hands. The most common distribution pattern of the extensor tendons of the fingers was: (1) a single extensor indicis proprius (EIP) tendon that inserted ulnar to the extensor digitorum communis (EDC) of the index; (2) a single EDC-index; (3) a single EDC-long; (4) a double EDC-ring; (5) an absent EDC-small; and (5) a double extensor digiti quinti (EDQ) with a double insertion. Frequent variations included, a double EIP tendon; a double or triple EDC-long tendon; a single or triple EDC-ring tendon; and a single or double EDC-small tendon. The extensor medii proprius was noted in 5 specimens. Increased multiplicity of any tendon was not associated with multiplicity of any other tendon, but was associated with a thinner (type 1) junctura tendinum between EDC-index and EDC-long. An absent EDC-small was related to an increased incidence of a double EDC-ring and the presence of a thick type 3 junctura tendinum between the EDC-ring and the EDQ or dorsal aponeurosis of the small finger. Knowledge of potential tendon multiplicity and variations may help in the identification and repair of these structures.

Adult↗
PubMed1981

Intrinsic tendon cell proliferation in tissue culture.

This study examines the potential of tendon cells to participate in tendon repair. Explants were prepared from chicken sublimis tendons and studied in tissue culture. Under defined culture conditions, in the absence of tendon sheath, tendon cells were observed to migrate in a limited concentric fashion around the margin of a 2 mm window in the explant. When a plasma clot was present in the window, tendon cell migration and proliferation were accelerated and continued until the window was confluent with cells. Electron micrographs demonstrated that these tendon cells were fibroblasts associated with extracellular collagen fibrils. Specific biochemical analyses confirmed that these tendon fibroblasts were synthesizing collagen. This in vitro study demonstrates that tendons contain active fibroblasts capable of proliferation, migration, and collagen synthesis. These findings support the hypothesis that tendons can heal by intrinsic processes.

Animals↗
PubMed1998

Molecular studies in flexor tendon wound healing: the role of basic fibroblast growth factor gene expression.

Basic fibroblast growth factor (bFGF) is a cytokine that plays a fundamental role in angiogenesis. This study examines bFGF messenger RNA (mRNA) expression in a rabbit flexor tendon wound healing model. Thirty-four New Zealand white rabbit forepaws underwent transection and repair of the middle digit flexor digitorum profundus tendon in zone II. Tendons were harvested at increasing time intervals and analyzed by in situ hybridization and immunohistochemistry. Few tenocytes and tendon sheath cells expressed bFGF mRNA in unwounded tendons. In contrast, tendons subjected to transection and repair exhibited an increased signal for bFGF mRNA in both resident tenocytes concentrated along the epitenon and infiltrating fibroblasts and inflammatory cells from the tendon sheath. These data demonstrate that (1) normal tenocytes and tendon sheath cells are capable of bFGF production, (2) bFGF mRNA is upregulated in the tendon wound environment, and (3) the upregulation of this angiogenic cytokine occurs in tenocytes as well as in tendon sheath fibroblasts and inflammatory cells.

Animals↗
PubMed1998

Flexor tendon-pulley interaction after pulley reconstruction: a biomechanical study in a human model in vitro.

Ten cadaver digits were used to evaluate excursion resistance between a tendon and pulley after completing 4 methods of pulley reconstruction (Bunnell's, Kleinert's, Lister's, and Karev's techniques). Five tissues (palmaris longus tendon, extensor digitorum tendon, flexor digitorum superficialis tendon, extensor retinaculum, and volar plate) were used to reconstruct the A2 pulley. Intrasynovial tissue sources (extensor retinaculum, volar plate, and flexor digitorum superficialis tendon) produced less excursion resistance than extrasynovial tissue sources (extensor digitorum tendon and palmaris longus tendon). The models using the extensor retinaculum and volar plate as reconstructive materials produced less excursion resistance than the normal A2 pulley, whereas the models using the palmaris longus tendon produced the highest excursion resistance. Bunnell's technique of pulley reconstruction produced less excursion resistance than Kleinert's technique with all 3 tissues tested. The results of the in vitro study of excursion resistance between the tendon and reconstructed pulley demonstrated that Lister's technique of pulley reconstruction using the extensor retinaculum produced the least resistance to tendon gliding.

Biomechanical Phenomena↗
PubMed2001

In vivo microdialysis and immunohistochemical analyses of tendon tissue demonstrated high amounts of free glutamate and glutamate NMDAR1 receptors, but no signs of inflammation, in Jumper's knee.

This investigation describes, to our knowledge, the first experiment where the microdialysis technique was used to study certain metabolic events in human patellar tendons in combination with immunohistochemical analyses of tendon biopsies. In five patients (four men and one woman) with a long duration (range 12-36 months) of pain symptoms from Jumper's knee (localized tenderness in the patellar tendon verified as tendon changes with ultrasonography or MRI), and in five controls (four men and one woman) with normal patellar tendons, a standard microdialysis catheter was inserted into the patellar tendon under local anestesia. The local concentrations of glutamate (excitatory neurotransmitter) and prostaglandin E2 (PGE2) were registered under resting conditions. Samplings were done every 15 min during a 2 h period. In all individuals (patients and controls) biopsies were taken for immunohistochemical analyses. The results showed that it was possible to detect and measure the concentrations of glutamate and PGE2 in the patellar tendon with the use of microdialysis technique. There were significantly higher concentrations of free glutamate, but not PGE2, in tendons with tendinosis compared to normal tendons. In the biopsies, there were no inflammatory cell infiltrates, but, for the first time, it was shown that there was immunoreaction for the glutamate receptor NMDAR1 in association with nerve structures in human patellar tendons. These findings altogether indicate that glutamate might be involved in painful Jumper's knee, and further emphasizes that there is no chemical inflammation (normal PGE2 levels) in this chronic condition.

Adult↗
PubMed1991

[Incomplete section of a superficial flexor tendon in zone II: successive complications and quadriga syndrome].

Partial section of the flexor tendon may be asymptomatic and heal without sequelae. However, in the absence of primary treatment, they may lead to subsequent complications such as: tendon locking due to incarceration of a partially detached slip of tendon, jump phenomena due to irregularity of the surface or the volume of the tendon, which induces a sudden jerk as the tendon passe through the retinaculum, and lastly, secondary tendon rupture. These complications all occurred in the case reported here, who also presented with syndrome of the quadriga. Locking of the intact deep flexor tendon by the ruptured superficial tendon interfered with the movements of the other fingers. Resection of the ruptured tendon was able to restore complete function. Opinions diverge concerning the need to suture partial sections of the flexor tendons, but the authors agree on the great importance of meticulous surgical exploration and immediate controlled mobilisation, which ensures the best functional results.

Adult↗
PubMed1995

The distal tendon of the biceps brachii. Structure and clinical correlations.

The structure and blood supply of 42 distal biceps tendons were investigated by means of light and electron microscopy as well as by immunohistochemistry. Possible structural causes for the rupture of the tendon are discussed. The distal biceps tendon wraps around the radius during pronation of the forearm. In this area the tendon is exposed to pressure and shearing forces in addition to those caused by tension. Two fibrocartilaginous areas were regularly observed. Large chondrocyte-like cells were found inside the fibrocartilage. As an expression of strain, the extracellular matrix is rich in acidic glycosaminoglycans and stains intensely with toluidine blue at pH 1. Electron microscopy showed a granular pericellular matrix that increases in size towards the gliding surface. Type I collagen is the main component of the distal biceps tendon. Type II collagen is found in tendon fibrocartilage but not in traction tendons. The gliding surface of the tendon is made up of reticular fibres that are equivalent to type III collagen. Monoclonal antibodies revealed the presence of dermatan-sulfate, keratansulfate and chondroitin-4- as well as chondroitin-6-sulfate. Blood vessels are usually absent in fibrocartilage, as was shown with a polyclonal antibody against the basement membrane component laminine. There are significant differences between the extracellular matrix of traction and gliding tendons, which may be responsible for the location of tendon rupture.

Adolescent↗
PubMed2002

Spatial arrangement of white muscle fibers and myoseptal tendons in fishes.

We describe the arrangement of white muscle fibers and tendinous myoseptal structures and the relation of these structures to each other in order to provide an anatomical framework for discussions and experimental research on fish swimming mechanics. For the three major craniate groups, the petromyzontids, myxinids and gnathostomes, we identify three conditions that differ remarkably. Myxinids are characterized by asymmetrical myosepta with long cones. Within a single myoseptum these are connected by collagenous fibers that are almost oriented longitudinally. Distinct tendons are absent in myxinid myosepta. Petromyzontid myosepta lack cones and distinct myoseptal tendons, whereas gnathostomes bear cones and distinct tendinous structures: the lateral band, epineural (epipleural) tendon and myhabdoid tendon. Myoseptal fibers of petromyzontids and myoseptal tendons of gnathostome myosepta are firmly anchored in the skin. Myxinids lack firm myoseptal-skin-connections. Their muscular arrangement is neither comparable to that of petromyzontids nor to that of gnathostomes. The latter two bear archlike arrangements of muscle fibers spanning several segments that are hypothesized to play a role during bending. In gnathostomes, archlike helical muscle fiber arrangements (HMFAs) are present that span the length of several body segments and are multiply intersected by myosepta. Hence, a series of tendinous lateral bands of myosepta is embedded in HMFAs. The posterodorsally oriented HMFAs are underlain by posteroventrally oriented crossing muscle fibers (CMFs). Bending may be generated by contraction of the muscle fibers belonging to an HMFA and the simultaneous counteraction of CMFs. Moving caudally, this anterior muscle fiber arrangement gradually changes, eventually becoming the posterior muscle fiber arrangement. This pattern suggests that the function of the myomeres will also change. Three additional putative roles of myoseptal tendons can be deduced from their relations to white muscle fibers in gnathostomes (and in part in petromyzontids): (1) Posterior transmission of anteriorly generated muscular forces via lateral bands and/or myorhabdoid tendons. These tendons are more robust posteriorly. Anterior and posterior cones appear to play an important role in force transmission. (2) Pulling on collagen fibers of the skin via lateral bands and myorhabdoid tendons, suggesting a transmission of muscular forces that puts the skin into tension. (3) Resisting radial expansion of contracting muscle fibers by epineural (epipleural) tendons. By the latter two mechanisms modulation of body stiffness is likely to be achieved.

Animals↗
PubMed2002

Force transmission via axial tendons in undulating fish: a dynamic analysis.

Sonomicrometrics of in vivo axial strain of muscle has shown that the swimming fish body bends like a homogenous, continuous beam in all species except tuna. This simple beam-like behavior is surprising because the underlying tendon structure, muscle structure and behavior are complex. Given this incongruence, our goal was to understand the mechanical role of various myoseptal tendons. We modeled a pumpkinseed sunfish, Lepomis gibbosus, using experimentally-derived physical and mechanical attributes, swimming from rest with steady muscle activity. Axially oriented muscle-tendons, transverse and axial myoseptal tendons, as suggested by current morphological knowledge, interacted to replicate the force and moment distribution. Dynamic stiffness and damping associated with muscle activation, realistic muscle force generation, and force distribution following tendon geometry were incorporated. The vertebral column consisted of 11 rigid vertebrae connected by joints that restricted bending to the lateral plane and endowed the body with its passive viscoelasticity. In reaction to the acceleration of the body in an inviscid fluid and its internal transmission of moment via the vertebral column, the model predicted the kinematic response. Varying only tendon geometry and stiffness, four different simulations were run. Simulations with only intrasegmental tendons produced unstable axial and lateral tail forces and body motions. Only the simulation that included both intra- and intersegmental tendons, muscle-enhanced segment stiffness, and a stiffened caudal joint produced stable and large lateral and axial forces at the tail. Thus this model predicts that axial tendons function within a myomere to (1) convert axial force to moment (moment transduction), (2) transmit axial forces between adjacent myosepta (segment coupling), and, intersegmentally, to (3) distribute axial forces (force entrainment), and (4) stiffen joints in bending (flexural stiffening). The fact that all four functions are needed to produce the most realistic swimming motions suggests that axial tendons are essential to the simple beam-like behavior of fish.

Animals↗