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PubMed2001

Effects of tension direction on strength of tendon repair.

We investigated changes of tensile strength in tendon repair according to tension direction. Thirty-six fresh-frozen digital flexor tendons were divided into 4 groups with 9 tendons each. The tendons were repaired by the modified Kessler method. Sutured tendons were pulled against pulleys at angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees to the direction of the pull of the testing machine in the 4 groups, respectively. The repaired tendons were tested in a tensile machine to determine 2-mm gap formation force and ultimate strength of the tendons. The 2-mm gap formation force and ultimate strength in the tendons pulled at 0 degrees were statistically higher than those in the tendons pulled at 30 degrees, 60 degrees, and 90 degrees. The 2-mm gap formation force of the tendons pulled at 30 degrees, 60 degrees, and 90 degrees was 86% +/- 10%, 73% +/- 9%, and 64% +/- 8% of that at 0 degrees, respectively. Ultimate strength of tendons pulled at 30 degrees, 60 degrees, and 90 degrees was 89% +/- 9%, 82% +/- 11%, and 76% +/- 8% of that at 0 degrees, respectively. Values of the 2-mm gap formation force and ultimate strength were statistically the lowest in the group with a pulling angle of 90 degrees. There was no statistically significant difference in repair strength between tendons tested at 0 degrees and those in the model without pulleys. The strength of tendon repair changed considerably according to direction of tension added to the tendons. The gap formation force and ultimate strength decreased as angles of tension increased. The results imply that a repaired tendon will be weakened as the finger is increasingly flexed. The decrease in repair strength should therefore be considered in planning a tendon suture to tolerate active finger flexion and a tendon motion protocol after primary tendon repair.

Analysis of Variance↗
PubMed1999

Patellar tendon augmentation after removal of its central third limits joints tissue changes.

The central third of the patellar tendon is commonly used to reconstruct the injured anterior cruciate ligament. Some studies have noted changes in joint tissues following this procedure. It has been postulated that these changes may be associated with increased stress on the remaining tendon following harvest of the graft. In our study, the central third of the patellar tendon was excised in three groups of rabbits. The central tendon defects in two of the three groups were fitted with different augmentation devices to augment the host tendon during the healing process. All rabbits followed a daily treadmill exercise regimen for 12 weeks following the operation. Biomechanical testing of the tendon revealed that in nonaugmented tendons the cross-sectional area and the length of the patellar tendon significantly increased 112 and 16%, respectively. There was histological evidence of host-tendon remodeling throughout the cross section and extensive fibrosis in the infrapatellar fat pad. Augmentation of the tendon significantly reduced these changes, with the least change noted in the group with the greatest augmentation. The rabbits with augmentation devices retained tendon dimensions similar to those of the contralateral intact tendon, and tendon remodeling occurred only in the defect area. The rabbits with augmentation devices exhibited little to no fibrosis of the fat pad. Structural properties of augmented and nonaugmented tendons were similar despite the size differences, indicating higher tissue quality in the augmented tendons. This study suggested that complications of the knee joint (i.e., tendon proliferation and fat pad fibrosis) noted after anterior cruciate-ligament reconstruction with the autogenous patellar tendon may be limited by the implantation of an augmentation device.

Animals↗
PubMed1998

[Experimental study of homograft of repeated freezing-thawing treated and ultra-low-temperature treated tendon].

In order to compare the immunogenecity and biological properties of homologous tendon grafts after treatment from different methods of freezing, tendons from chickens received repeated freezing-thawing treatment or ultra-low-temperature treatment, and then, the post-treatment tendons were preserved in liquid nitrogen for 3 months before transplantation. The autogenous tendon transplantation was served as the control. It was found that in the group of repeated freezing-thawing treated tendons, the tendon cells all died and while in the ultra-low temperature treated tendons the active rate of tendon cells was 92.5% +/- 3.4%, and the histological observation showed that transplantation of frozen tendons would result in extensive infiltration of inflammatory cells in the grafted tendons and the peritendinous adhesion was serious than that of the autografts. The active flexion function, hydroxyproline levels and the biomechanical analysis showed no significant differences between the repeated freezing-thawing treated homografts and the ultra-low-temperature treated homografts, and that the autografts was definitely superior to the homografts. The conclusions were: (1) Transplantation of the homologous tendons from the two different methods of freezing could receive considerable success and there was no significant difference between them; (2) Transplantation of frozen homologous tendon graft might give successful result which was probably due to the preservation of the cellular activity of the tendon cells following freezing treatment and elimination of the antigen presenting cells in the tendon as well, and (3) Although the cellular components of the tendon were damaged and the antigenicity of the tendon was lowered, it did not necessarily mean that homologous tendon graft would always be successful in transplantation.

Animals↗
PubMed1995

Fibrocartilage associated with human tendons and their pulleys.

The presence of fibrocartilage in tendons that wrap around bony or fibrous pulleys is well known. It is an adaptation to resisting compression or shear, but the extent to which the structure of most human tendons is modified where they contact pulleys is less clear, for there has been no single comprehensive survey of a large number of sites. Less is known of the structure of the corresponding pulleys. In the present study, 38 regions of tendons that wrap around bony pulleys or pass beneath fibrous retinacula have been studied in routine histology sections taken from each of 2 or 3 elderly dissecting room cadavers. Most of the corresponding pulleys have also been examined. Fibrocartilage was present in 22 of the 38 tendon sites and it was most conspicuous where the tendons pressed predominantly against bone rather than retinacula and where they showed a large change in direction. Fibrocartilage was more characteristic of tendons at the ankle than the wrist, probably because the long axis of the foot is at right angles to that of the leg. There was considerable variation in the structure of tendon fibrocartilage. The most fibrocartilaginous tendons had oval or round cells embedded in a highly metachromatic matrix with interwoven or spiralling collagen fibres. At other sites, fibrocartilage cells were arranged in rows between parallel collagen fibres. The differences probably relate to differences in development. A single tendon could be modified at successive points along its length and fibrocartilage could be present in the endotenon and epitenon as well as in the tendon itself. Pathological changes seen in 'wrap around' tendons were fragmentation and partial delamination of the compressed surface, chondrocyte clustering, fatty infiltration and bone formation. Three types of pulleys were described for tendons--bony prominences and grooves, fibrous retinacula and synovial joints. The extent of cartilaginous differentiation on the periosteum of bony pulleys frequently mirrored that in the corresponding tendon. The cartilage or fibrocartilage prevents the tendon from 'sawing' through the bone. Some of the best known retinacula were largely fibrous, though the inferior peroneal retinaculum and the trochlea for the superior oblique were cartilaginous. The results underline the considerable regional heterogeneity in different tendons and their pulleys. They show that one tendon is not like another and that tendons may need to be carefully selected for particular surgical transfers or joint reconstructions.

Aged↗
PubMed2006

Effect of TGF-beta inducible early gene deficiency on flexor tendon healing.

The role of transforming growth factor beta (TGF-beta) in tendon healing is still not clearly established. TGF-beta affects gene expression primarily through the activation of the Smad signaling pathway. The first step in the Smad pathway is the expression of TGF-beta inducible early gene (TIEG). Recently, a TIEG knockout mouse has been developed. The purpose of this study was to examine the healing potential of flexor tendons in mice lacking the TIEG gene, and to further examine what role the TIEG pathway plays in flexor tendon repair. Twenty-two mice, consisting of 11 normal wild-type mice and 11 TIEG knockout mice, were euthanized at 8 to 12 weeks of age. The second through fifth FDL tendons of both hind feet were transected and repaired in zone 2. The repaired tendons were removed from the mice and placed into tissue culture. Tendons were then examined at days 3, 7, 14, 21, and 42 after surgery. Hematoxylin and eosin (HE) staining and immunohistochemical staining for TGF-beta, collagen type I, and collagen type III were performed. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to examine expression of TGF-beta1, beta2, beta3, and collagen type I and III. At 42 days after surgery, HE staining showed coaptation of lacerated tendon ends in both groups. Both groups showed healing of the lacerated tendon, but the chronologic expression pattern of TGF-beta was different between the knockout and normal tendons. TIEG deficient tendons had delayed expression of TGF-beta when compared with control tendons. The collagen mRNA expression pattern was similar with both groups, but the expression level was different, with TIEG knockout tendons having a lower expression of collagen type I mRNA (p < 0.001). TGF-beta is thought to play a major role in tendon healing. Healing of tendons in the TIEG knockout mouse suggests the possibility of tendon healing in the absence of the Smad pathway. The knockout mouse model described in the present study provides a novel means for further understanding of the tendon healing process through isolated deletion of specific growth factors.

Animals↗
PubMed2004

Collagen fibres of the spontaneously ruptured human tendons display decreased thickness and crimp angle.

PURPOSE: To study collagen fibre thickness and crimp formation in healthy and ruptured human tendons. METHODS: The thickness, crimp angle and wavelength of the collagen fibres were analyzed by interference and polarization microscopy and the samples were studied by transmission and scanning electron microscopy in four different healthy human tendons (Achilles, Quadriceps, Biceps brachii and Extensor pollicis longus) and in 66 spontaneously ruptured tendons. RESULTS: In the normal (healthy) tendons, the diameter and crimp angle of the collagen fibres varied greatly between the four different tendons, the thickest fibres with the largest crimp angle being in the Achilles and Quadriceps tendons, whereas the Biceps brachii and Extensor pollicis longus, tendons that bear lighter strains but carry functions of high specificity, were found to have substantially smaller collagen fibres with lower crimp angle. Ruptured tendons had significantly smaller collagen fibre diameter than the normal tendons, the fibre diameter being -36% in comparison to their healthy counterparts in the Achilles tendons (P < 0.0001), -24% in the Quadriceps tendons (P < 0.0001), -37% in the Biceps brachii (P < 0.0001) and -14% in the Extensor pollicis longus (P = 0.10), respectively. Similarly, the crimp angle of the collagen fibres was also found to be lower in the ruptured tendons than in healthy, normal tendons. Further, the collagen fibres in the ruptured human tendons showed great variation in the crimp angle between the adjacent fibres and in the successive crimps of the same fibre. CONCLUSION: Our results show that spontaneously ruptured tendons display focal regions with decreased collagen fibre thickness, decreased crimp angle and disrupted crimp continuity, microscopic alterations that possibly result in reduced strength of the tendons being less resistant to tensile forces, and thus, place them at increased risk of ruptures.

Achilles Tendon↗
PubMed2002

Achilles tendon healing: long-term biomechanical effects of postoperative mobilization and immobilization in a new mouse model.

The aim of the study was to investigate the long-term effects of postoperative immobilization as opposed to mobilization on the biomechanical attributes of healing Achilles tendons in a new experimental mouse model. In 114 Balb-C-mice the left Achilles tendon was transected and sutured by the Kirchmayr-Kessler technique. The tendons healed either under postoperative immobilization effected by fixing the upper ankle joint in equinus position or under mobilization through a limited range of movement. The contralateral Achilles tendons served as internal control. All tendons were tested biomechanically at short intervals up to the 112th postoperative day in terms of load to failure [N], tendon deflection [mm] and tendon stiffness [N/mm], and were evaluated histologically after 8 and 112 days. Postoperative mobilization resulted in a continuous and significantly more rapid restoration of load to failure in comparison to the immobilization group. Tendon deflection was decreased by postoperative mobilization, whereas under immobilization it paradoxically increased still further in the later course. After 112 days the tendons of the mobilization group had regained their original tendon stiffness, whereas the tendons after immobilization reached only about half the values seen in the control tendons. Histologically, postoperative mobilization led to increased immigration of inflammatory cells in the early phase. In the late phase, as compared to immobilization, tendon structure was more mature, with fibre bundles arranged in parallel and interposed tendocytes. Tensile loading of the healing tendon by postoperative mobilization leads to fundamental changes in the biological process of tendon healing resulting in accelerated restoration of load to failure and reduced tendon deflection.

Achilles Tendon↗
PubMed2002

Treatment of tendon disorders. Is there a role for corticosteroid injection?

Tendon injuries and other tendon disorders are a source of major concern in competitive and recreational athletes and in many working conditions requiring repetitive movements. The exact etiology, pathophysiology, and healing mechanisms of the various tendon complaints are, however, only partly known and even origin of pain in the chronic tendon disorders is unknown. Thus, the treatment strategies recommended for tendon complaints vary considerably and the given treatment is frequently based on empirical evidence only. Corticosteroid injections are one of the most commonly used treatments for chronic tendon disorders. Despite their popularity, the biologic basis of their effect and the systematic evidence for their benefits are largely lacking. In addition to suppressing inflammation, the effects of local corticosteroid injections could be mediated through their effect on the connective tissue and adhesions between the tendon and the surrounding peritendinous tissues by inhibiting the production of collagen, other extracellular matrix molecules, and granulation tissue in these sites. Also, if the pain in tendinopathy is a result of stimulation of nociceptors by chemicals released by the damaged, degenerated tendon, corticosteroids might mediate their effect thorough alterations in the release of these noxious chemicals, the behavior of these receptors, or both. Achilles tendinopathy, rotator-cuff tendinopathy, tennis elbow, and trigger finger are among the most frequent tendon problems. There is good evidence, however, strongly supporting the use of local corticosteroid injections in the trigger finger only. This can be to the result of either a true lack of the effect or just a lack of good trials in the other complaints. Intimidation with adverse effects of peritendinous corticosteroid injections is based on case reports only rather than convincing data from controlled clinical studies. In light of the animal studies, corticosteroid injection into tendon substance should be avoided, although the true incidence of side effects after local corticosteroid injection(s) for tendon disorders is unknown. Also, the relevance of the steroid used, the tissue affected, the extent of the tendon problem, the duration of the symptoms, the phase of healing at the time of injections, and the postinjection events remain undetermined. Although a complete tendon rupture with loading after steroid injection has been reported, no reliable proof exists of the deleterious effects of peritendinous injections; conclusions in literature are based mainly on uncontrolled case reports that fail under scientific scrutiny, whereas scientifically rigorous studies have not been performed. An acute tendon disorder often responds favorably to early intervention with conservative treatment modalities. Local corticosteroid injections gives good short-term results in prolonged or subacute cases that do not respond to the conventional conservative treatments. Although corticosteroid injections are one of the most commonly used treatment modalities for chronic tendon disorders, there is an obvious lack of good trials defining the indications for and efficacy of such injections, and subsequently, many of the recommendations for the use of local corticosteroid injections do not rely on sound scientific basis. Thus, there is an obvious need for high-quality basic science studies and controlled clinical trials in examining the effects corticosteroids on various tendon disorders.

Adrenal Cortex Hormones↗
PubMed2006

The effect of achilles tendon lengthening on ankle dorsiflexion: a cadaver study.

BACKGROUND: Tendon lengthening is an important cause of morbidity after Achilles tendon rupture. However, direct measurement of the tendon length is difficult. Ankle dorsiflexion has, therefore, been used as a surrogate measure on the assumption that it is the Achilles tendon that limits this movement. The aim of this investigation was to assess the relationship between Achilles tendon length and ankle dorsiflexion. The primary question was whether or not the Achilles tendon is the structure that limits ankle dorsiflexion. The secondary purpose was to quantify the relationship between Achilles tendon lengthening and dorsiflexion at the ankle joint. METHODS: Five cadaver specimens were dissected to expose the tendons and capsular tissue of the leg and hindfoot. Fixed bony reference points were used as markers for the measurements. In the first specimen, the Achilles tendon was intact and the other structures that may limit ankle dorsiflexion were sequentially divided. In the other specimens the Achilles tendon was lengthened by 1 cm intervals and the effect upon ankle dorsiflexion movement was recorded. RESULTS: Division of the other tendons and the capsular tissue around the ankle joint did not affect the range of ankle dorsiflexion. When the Achilles was divided the foot could be dorsiflexed until the talar neck impinged upon the anterior aspect of the distal tibia. There was a mean increase of 12 degrees of dorsiflexion for each centimeter increase in tendon length. CONCLUSION: The Achilles tendon is the anatomical structure that limits ankle dorsiflexion, even when the tendon is lengthened. There was a linear relationship between the length of the Achilles tendon and the range of ankle dorsiflexion in this cadaver model. Ankle dorsiflexion would appear to be a clinically useful indicator of tendon length.

Achilles Tendon↗
PubMed2004

Biomechanics and pathophysiology of overuse tendon injuries: ideas on insertional tendinopathy.

Tendons behave viscoelastically and exhibit adaptive responses to conditions of increased loading and disuse. High-resolution, real-time ultrasound scanning confirms the applicability of these findings in human tendons in vivo. In addition, recent biomechanical studies indicate that strain patterns in tendons may not be uniform, as tendons show stress-shielded areas and areas subjected to compressive loading at the enthesis. These areas correspond to the sites where tendinopathic characteristics are typically seen. This indicates that some tendinopathies may, paradoxically, be considered as 'underuse' lesions despite the common beliefs that they are overuse injuries. Classic inflammatory changes are not frequently seen in chronic athletic tendon conditions and histopathology features in tendinopathic tendons are clearly different from normal tendons, showing an exaggerated dysfunctional repair response. Tendinopathies are traditionally considered overuse injuries, involving excessive tensile loading and subsequent breakdown of the loaded tendon. Biomechanical studies show that the strains within the tendons near their insertion site are not uniform. If the material properties are similar throughout the tendon, forces transferred through the insertion site preferentially load the side of the tendon that is usually not affected initially in tendinopathy. In that case, the side affected by tendinopathy is generally 'stress shielded'. Thus, the presence of differential strains opens the possibility of alternative biomechanical explanations for the pathology found in these regions of the tendon. The traditional concept of tensile failure may not be the essential feature of the pathomechanics of insertional tendinopathy. Certain joint positions are more likely to stress the area of the tendon commonly affected by tendinopathy. Incorporating different joint position exercises may exert more controlled stresses on these affected areas of the tendon, possibly allowing better maintenance of the mechanical strength of that tendon region and, therefore, prevent injury. Such exercises could stress a healing area of the tendon in a controlled manner and thus stimulate healing once an injury has occurred. Additional work is needed to prove whether such principles should be incorporated in current rehabilitation techniques.

Aging↗
PubMed2003

Quantitative assessment of blood vessels of the human Achilles tendon: an immunohistochemical cadaver study.

BACKGROUND: The pathogenesis of Achilles tendon rupture remains unclear, but vascular patterns may play an important role. Hypoxia is considered to be an important factor in the aetiology of tendon degeneration. METHODS: Statements from the literature regarding the vascularization of the Achilles tendon are controversial. We determined the vascular density of the Achilles tendon using a new method involving antibodies against laminin, a component of the basement membrane. RESULTS: The blood supply of the Achilles tendon mainly arose from the anterior paratenon of the tendon from which vessels run into the tendon. The proximal part of the tendon was supplied by a recurrent branch of the posterior tibial artery, while the distal part of the tendon was vascularized by the rete arteriosum calcaneare, supplied by the fibular and posterior tibial arteries. An avascular area could be seen close to the insertion of the tendon to the calcaneus. Three regions with different vascular density could be determined in the Achilles tendon. The distal part of the Achilles tendon had a vascular density of 56.6 vessels/cm(2). In the middle part of the tendon, the vascular density was much lower: 28.2 vessels/cm(2). The proximal part of the tendon had a vascular density of 73.4 vessels/cm(2). CONCLUSION: The reduced vascularization in the tendon waist may be a predisposing factor for degeneration and spontaneous rupture of the human Achilles tendon.

Achilles Tendon↗
PubMed2003

Differential strain patterns of the human gastrocnemius aponeurosis and free tendon, in vivo.

AIM: The mechanical characteristics of the human free tendon and aponeurosis, in vivo, remains largely unknown. The present study evaluated the longitudinal displacement of the separate free Achilles tendon and distal (deep) aponeurosis of the medial gastrocnemius muscle during voluntary isometric contraction. METHODS: Ultrasonography-obtained displacement of the free tendon and tendon-aponeurosis complex, electromyography of the gastrocnemius, soleus, and dorsiflexor muscles, and joint angular rotation were recorded during isometric plantarflexion (n = 5). Tendon cross-sectional area, moment arm and segment lengths (L(o)) were measured using magnetic resonance imaging. Tendon force was calculated from joint moments and tendon moment arm, and stress was obtained by dividing force by cross-sectional area. The difference between the free tendon and tendon-aponeurosis complex deformation yielded separate distal aponeurosis deformation. Longitudinal aponeurosis and tendon strain were obtained from the deformations normalized to segment lengths. RESULTS: At a common tendon force of 2641 +/- 306 N, the respective deformation and Lo were 5.85 +/- 0.85 and 74 +/- 0.8 mm for the free tendon and 2.12 +/- 0.64 and 145 +/- 1.3 mm for the distal aponeurosis, P < 0.05. Longitudinal strain was 8.0 +/- 1.2% for the tendon and 1.4 +/- 0.4% for the aponeurosis, P < 0.01. Stiffness and stored energy was 759 +/- 132 N mm(-1) and 6.14 +/- 1.89 J, respectively, for the free tendon. Cross-sectional area of the Achilles tendon was 73 +/- 4 mm2, yielding a stress of 36.5 +/- 4.6 MPa and Young's modulus of 788 +/- 181 MPa. CONCLUSION: The free Achilles tendon demonstrates greater strain compared with that of the distal (deep) aponeurosis during voluntary isometric contraction, which suggests that separate functional roles may exist during in vivo force transmission.

Achilles Tendon↗
PubMedDate not supplied

Matrix remodeling in healing rabbit Achilles tendon.

Biochemical, biomechanical and ultrastructural properties of the connective tissue matrix were investigated during the early remodeling phase of tissue repair in experimentally tenotomized and repaired rabbit Achilles tendons. Sterile surgical tenotomy was performed on the right Achilles tendons of 14 rabbits and allowed to heal for 15 days. The animals were euthanized and the Achilles tendons excised from both limbs. The left contralateral Achilles tendon of each rabbit was used as a control in the experiments. Prior to biochemical analysis, both intact and healing tendons were tested for their biomechanical integrity. The results revealed that the healing tendons had regained some of their physicochemical characteristics, but differed significantly from the intact left tendons. The healing tendons regained 48% tensile strength, 30% energy absorption, 20% tensile stress, and 14% Young's modulus of elasticity of intact tendons. In contrast, biochemical analysis showed that the healing tendons had 80% of the collagen and 60% of the collagen crosslinks (hydroxypyridinium) of normal tendons. Sequential extraction of collagen from the tissues yielded more soluble collagen in the healing tendons than intact tendons, suggesting either an increase in collagen synthesis and/or enhanced resorption of mature collagen in healing tendons compared to intact tendons. Electron microscopic studies revealed remarkable differences in the ultrastructure between intact and healing tendons. These observations could explain, in part, the connective tissue response to healing during the early phases of tissue remodeling.

Achilles Tendon↗
PubMed2004

Semitendinosus regrowth: biochemical, ultrastructural, and physiological characterization of the regenerate tendon.

BACKGROUND: Previous studies have suggested that hamstring tendons can regenerate following harvesting for anterior cruciate ligament reconstruction. HYPOTHESIS: This "neo-tendon" is a true, functional tendon, not scar tissue. STUDY DESIGN: Controlled laboratory study. METHODS: Semitendinosus tendons were harvested from 35 New Zealand white rabbits using a standard tendon stripper. The rabbits were sacrificed 9 to 12 months following the index procedure and thoroughly evaluated. RESULTS: Thirty-one rabbits were available at the time of sacrifice. The neo-tendon was present in 26 rabbits but was highly variable in size and location of its tibial insertion. Histologic and immunohistochemical staining confirmed that the regenerate tissue was indeed tendon with normal cellularity, organization, and immunolocalization of type I collagen. Electron microscopy showed regeneration of organized collagen tissue that simulated native tendon but with a smaller cross-sectional diameter. Functionally, the neo-tendon was able to transmit force across the musculotendinous junction but at a significantly slower rate than the opposite, control leg. Biomechanical properties of the neo-tendon were significantly less than the control side. Biochemical analysis revealed that the neo-tendons contained glycosaminoglycans and collagen, but levels were significantly lower than normal tendons. CONCLUSIONS: Semitendinosus tendons regenerate with biologically reactive tendinous tissues in an animal model. This tissue has many of the characteristics of a normal tendon but appears to be inferior to the original musculotendinous unit at 9- to 12-month evaluation. Further characterization of the "lizard tail phenomenon" is still needed. CLINICAL RELEVANCE: Hamstring tendon regrowth may have a dramatic impact on postoperative function of patients who undergo anterior cruciate ligament reconstruction with these tendons. Further modulation of this regeneration may further reduce graft harvesting morbidity.

Animals↗
PubMed2005

In vivo mechanical properties of the human Achilles tendon during one-legged hopping.

Compliant tendons act as energy stores, which benefit the energetics and power output of a muscle-tendon unit. However the compliance of tendon and the material properties may vary between individuals and hence alter the energy storing capacity of the tendon. We aimed to determine the in vivo Achilles tendon (AT) stress and strain during one-legged hopping and hence the contribution of elastic recoil to mechanical energy changes. We simultaneously measured the length of the Achilles tendon from the muscle-tendon junction to the insertion on the calcaneous and the approximate AT force in ten male participants. The position of the muscle-tendon junction was determined using ultrasound images that were projected into three-dimensional space. Achilles tendon force was measured using inverse dynamics. The results demonstrated that one-legged hopping elicited high tendon strains and that the force-length relationship of the whole tendon is relatively linear, particularly at high strains. The stiffness, elastic modulus and hysteresis varied across the population (inter-quartile range of 145-231 N mm-1, 0.67-1.07 GPa and 17-35%, respectively). These values are within the reported biological range. An average of 38 J of energy was recovered from the elastic recoil of the tendon, which contributes 16% of the total average mechanical work of the hop (254 J). The high strains measured here (average peak strain was 8.3%) and in other studies may be possible due to the complex architecture of the Achilles tendon; however, prolonged hopping may well cause tendon damage. In conclusion, the properties of the elastic Achilles tendon can contribute significantly to the total mechanical work of the body during one-legged hopping; however, individual variation in the properties of the tendon vary the energy storing capacity of this structure.

Achilles Tendon↗
PubMed2002

Treatment of partial lacerations in flexor tendons by trimming. A biomechanical in vitro study.

BACKGROUND: Treatment of a partial laceration in zone 2 of a flexor tendon is controversial. The intact part of the tendon can usually sustain forces of normal unresisted motion, and repaired partially lacerated tendons can actually be weaker than unrepaired ones. However, complications such as triggering or entrapment have been reported in association with unrepaired tendons. The purpose of this study was to measure the biomechanical behavior following trimming of the tendon as an alternative to repair. METHODS: Thirty-six flexor digitorum profundus tendons were harvested from sixteen unpaired fresh-frozen cadaveric human hands and were randomly assigned to be subjected to either 50% or 75% partial laceration, which was either lateral or volar, and were then assigned to no repair, repair with a running suture, or trimming. Mean and maximum gliding resistances were measured as the flexor digitorum profundus glided through the bone-A2 pulley complex and the flexor digitorum superficialis. Values were normalized to those measured in the intact tendon. The tendons were then distracted to failure, and maximum load and stiffness were recorded. RESULTS: There was triggering or entrapment of eight unrepaired tendons; two cases were severe, and six were minor. When no severe trigger was obvious, the unrepaired tendons had the lowest tendency for gliding resistance, followed by the tendons treated with trimming and then by those treated with the running suture. Overall, the tendons with a volar laceration had higher mean and maximum gliding resistance than those with a lateral laceration (p < 0.05), those with a 75% partial laceration had higher mean gliding resistance than those with a 50% laceration (p < 0.05), and the tendons that were repaired with running suture had higher mean gliding resistance than those treated with trimming (p < 0.05). Tendon strength was not significantly different among the three types of treatment. CONCLUSIONS: From the perspective of gliding resistance after partial tendon laceration, no repair appears necessary unless triggering is a problem. If triggering occurs, then trimming of a partially lacerated tendon may be a reliable alternative to repair, at least in terms of gliding resistance and strength.

Adult↗
PubMed1994

Achilles tendon injuries in athletes.

Two-thirds of Achilles tendon injuries in competitive athletes are paratenonitis and one-fifth are insertional complaints (bursitis and insertion tendinitis). The remaining afflictions consist of pain syndromes of the myotendineal junction and tendinopathies. The majority of Achilles tendon injuries from sport occur in males, mainly because of their higher rates of participation in sport, but also with tendinopathies a gender difference is probably indicated. Athletes in running sports have a high incidence of Achilles tendon overuse injuries. About 75% of total and the majority of partial tendon ruptures are related to sports activities usually involving abrupt repetitive jumping and sprinting movements. Mechanical factors and a sedentary lifestyle play a role in the pathology of these injuries. Achilles tendon overuse injuries occur at a higher rate in older athletes than most other typical overuse injuries. Recreational athletes with a complete Achilles tendon rupture are about 15 years younger than those with other spontaneous tendon ruptures. Following surgery, about 70 to 90% of athletes have a successful comeback after Achilles tendon injury. Surgery is required in about 25% of athletes with Achilles tendon overuse injuries and the frequency of surgery increases with patient age and duration of symptoms as well as occurrence of tendinopathic changes. However, about 20% of injured athletes require a re-operation for Achilles tendon overuse injuries, and about 3 to 5% are compelled to abandon their sports career because of these injuries. Myotendineal junction pain should be treated conservatively. Partial Achilles tendon ruptures are primarily treated conservatively, although the best treatment method of chronic partial rupture seems to be surgery. Complete Achilles tendon ruptures of athletes are treated surgically, because this increases the likelihood of athletes reaching preinjury activity levels and minimises the risk of re-ruptures. Marked forefoot varus is found in athletes with Achilles tendon overuse injuries, reflecting the predisposing role of ankle joint overpronation. Athletes with the major stress in lower extremities have often a limited range of motion in the passive dorsiflexion of the ankle joint and total subtalar joint mobility, which seems to be predisposing factor for these injuries. Various predisposing transient factors are found in about one-third of athletes with Achilles tendon overuse injuries; of these, traumatic factors (mostly minor injuries) predominate. The typical histological features of chronically inflamed paratendineal tissue of the Achilles tendon are profound proliferation of loose, immature connective tissue and marked obliterative and degenerative alterations in the blood vessels. These changes cause continuing leakage of plasma proteins, which may have an important role in the pathophysiology of these injuries. The chronically inflamed paratendineal tissues of the Achilles tendon do not seem to have enough capacity to form mature connective tissue.

Achilles Tendon↗
PubMed1999

Double-stranded hamstring tendons for anterior cruciate ligament reconstruction.

Bone-patellar tendon-bone autograft is the most commonly used tissue for ACL reconstruction; however, the harvesting of patellar tendon as a free graft can lead to significant morbidity. Alternate grafts may lower morbidity, yet the most commonly used alternate grafts including the double-stranded semi-tendinosus or gracilis have not been studied biomechanically. This study investigated the morphometric and biomechanical properties of double-stranded semi-tendinosus and gracilis tendons separately along with the patellar and quadriceps tendons obtained bilaterally from six fresh, 77-year-old cadaveric specimens. The quadriceps tendon was the thickest and therefore had the largest cross-sectional area, whereas double-stranded semitendinosus had the highest mean peak load to failure (1029+/-158.4 N), 11.5% and 10.3% stronger than patellar tendon and quadriceps tendons, respectively. Midsubstance rupture occurred in the hamstring tendons, whereas the patellar and quadriceps tendons failed at the bone-tendon junctions. Semitendinosus tendons with higher cross-sectional area had higher peak loads to failure. This linear relationship between cross-sectional area and the peak load to rupture also was observed in the other tendon groups (except gracilis). These results indicate that despite a lower cross-sectional area of the double-stranded semitendinosus, this tendon demonstrated a comparable mean peak load to rupture and stress compared with patellar and quadriceps tendons. It also was demonstrated that combined double-stranded semitendinosus and gracilis tendons produce a stronger graft with initial strength twice that of the patellar tendon, but requires further testing.

Aged↗