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PubMed1994

Flexor tendon growth in chickens.

We investigated the longitudinal growth of the flexor tendon in detail by marking tendons along their lengths in young chickens, using a microsurgical technique, and observing the separation of the marks at various times during tendon growth to establish normative standardized data on the longitudinal growth of flexor tendons. The interstitium throughout the entire tendon was found to increase in length, although the growth at the insertion zone was less marked than that in other areas. To determine the relationship between the growth of the tendon and the growth of the underlying bone, the lengths of the phalanges and metatarsus were measured. The distance from the insertion to the bifurcation of the tendon and the distance from the bifurcation to the most distal point of the musculotendinous junction also were measured. The findings suggest that the growth of tendon is proportionate to the growth of underlying bone. Tendon growth at the musculotendinous junction was studied in further detail, and no significant difference was found between growth at the most proximal zone of the tendon and growth at the zone within the musculotendinous junction.

Animals↗
PubMed1996

Nerve regeneration during patellar tendon autograft remodelling after anterior cruciate ligament reconstruction: an experimental and clinical study.

The innervation of the rat and human anterior cruciate ligament, patellar tendon, and patellar tendon autograft after reconstruction of the anterior cruciate ligament was investigated by immunohistochemical and histological methods. A rat model of reconstruction with patellar tendon autograft was evaluated during active graft remodelling (2-16 weeks) and compared with normal ligament and tendon. The knees of 10 patients who had undergone reconstruction with patellar tendon autograft were examined 5-37 months postoperatively (remodeling fully completed) with arthroscopy and biopsy. As a control, biopsies from normal ligament and tendon were obtained from four patients. Nerve fibers were identified using antisera for protein gene product 9.5, a general neural marker. Neuronal regeneration was assessed by the expression of growth-associated protein 43/B-50. The sensory type of innervation was characterized by assessing the distribution of nerves containing the sensory neuropeptides calcitonin gene-related peptide and substance P. Immunoreactivity for all neural markers was found in both rat and human anterior cruciate ligament and patellar tendon. Two weeks after reconstruction, the rat autograft was acellular and no innervation could be identified. After 4 weeks, the grafts were viable, and immunoreactivity for protein gene product 9.5, growth associated protein 43/B-50, and calcitonin gene-related peptide was found until the 16th week postoperatively. Immunoreactivity for substance P was found in rat autografts at 4 weeks postoperatively only. All biopsies of human patellar tendon autograft showed signs of the remodelling process being fully completed, with revascularization and a sinusoidal collagen pattern with fibroblast repopulation. Neuropeptide immunoreactivity, however, was not found. The presence of immunoreactivity to sensory neuropeptides in the anterior cruciate ligament and patellar tendon may indicate a nociceptive and neuromodulatory function of these structures. The expression of sensory neuropeptides in the rat patellar tendon autograft suggests a possible involvement of sensory innervation during healing of the graft.

Adult↗
PubMed2006

Achilles tendon characterization in GDF-7 deficient mice.

Growth/differentiation factors (GDFs) play a significant role in numerous skeletal tissues and processes. Previous work using the brachypod mouse has suggested that GDF-5 affects Achilles tendon composition, ultrastructure, and material behavior, as well as tendon repair. The aim of the present study was to examine the role of a related GDF family member, GDF-7 (BMP-12), in intact tendon by studying the Achilles tendon of genetically engineered knockout mice. Achilles tendons from 16-week-old GDF-7 -/- mice contained 14% less GAG/DNA than did wild type littermates (p = 0.0481), although collagen content was comparable to controls. Quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) results show that GDF-5 was upregulated two-threefold in response to the absence of GDF-7 protein. GDF-6 was also upregulated in knockouts, but to a lesser extent (twofold, p = 0.0013). On an ultrastructural level, GDF-7 deficient Achilles tendons exhibited a shift towards smaller diameter fibrils which resulted in a small but significant reduction in mean fibril diameter (-8%, p = 0.05). GDF-7 deficiency did not noticeably affect the expression of fibrillar collagens (I, III, V) or tendon proteoglycans (decorin, fibromodulin, lumican, biglycan, versican, aggrecan). Differences in tendon composition and ultrastructure were not biologically significant enough to have a noticeable effect on the structural or material behavior of the tendons. These results demonstrate that GDF-7 deficiency has a subtle effect on the composition and ultrastructure of murine Achilles tendon. The small magnitude of the observed differences may be due to overcompensation by related GDF family members.

Achilles Tendon↗
PubMed2002

Glycation-induced matrix stability in the rabbit achilles tendon.

Connective tissue susceptibility to nonenzymatic glycation was examined following 0, 2, 4, 6, 8, and 10 weeks of incubating the rabbit Achilles tendon in phosphate-buffered saline containing ribose (glycated). The biomechanical integrity of the glycated tendons was then compared to control tendons incubated in phosphate-buffered saline (non-glycated) at each time interval, while the biochemical stability of both groups of tendons was determined by examining collagen extractability and the formation of pentosidine at 8 weeks. Whereas there were no significant biomechanical differences between control and glycated tendons at 0- and 2-week intervals (P > 0.05), moderately significant increases in maximum load, energy to yield, and toughness of glycated tendons were observed at 4 weeks. Beyond 4 weeks of incubation, the differences between glycated and non-glycated tendons became highly significant, as glycated tendons withstood more load and tensile stress (P < 0.01 for each variable), attained significantly higher modulus of elasticity (P < 0.01), absorbed more energy (P < 0.01), and became tougher (P < 0.01) than controls. These differences in the biomechanical indices of the effects of glycation were stable between the 6th and 10th week of glycation. The maximum increases in the biomechanical measurements as a result of glycation were 29% for maximum load, 125% for stress, 19% for strain, 106% for Young's modulus of elasticity, 14% for energy to yield, and 57% for toughness. Biochemical analysis showed a 61% reduction in the extractability of neutral salt-soluble collagen, a 48% decrease in acid-soluble collagen, and a 29% decline in pepsin-soluble collagen in glycated tendons (P < 0.01). In contrast, there was a 28% increase in the amount of insoluble collagen and significantly higher amounts of pentosidine (P < 0.01) in glycated tendons. Collectively, these biomechanical and biochemical results suggest that nonenzymatic glycation may explain the altered stability of connective tissue matrix induced by the processes of diabetes and aging.

Achilles Tendon↗
PubMed1979

The incidence and variety of Golgi tendon organs in extraocular muscles of the rhesus monkey.

Golgi tendon organs of distal tendons of rectus muscles were traced in serial transverse sections using a light microscope and their identity confirmed with an electron microscope. One or two tendon organs were present in eight of ten muscles taken from four adult rhesus monkeys and none were present in the other two. Tendon organs were unusually small averaging 270 micrometers in length and 36 micrometers in maximum width; three of them were bifid at one or both ends and the remainder were fusiform. Some lay wholly within tendon without direct attachment of muscle fibres and in the others the tip of a single felderstruktur (slow, non-twitch) muscle fibre entered the tendon organ capsule proximally and occupied the full width. Nerve terminals of most tendon organs compared with those found in other muscles with similar organelles and variety of shape. In three tendon organs with inserted muscle fibres, however, terminals with regular profiles, larger aggregations of clear vesicles and fewer mitochondria were present. The latter type of terminal and the encapsulated filderstruktur muscle fibres are features shared by the large numbers of myotendinous cylinders present in extraocular muscles and it is argued that tendon organs and myotendinous cylinders might be of common origin. If this is the case, then the overwhelming majority of myotendinous cylinders suggests that tendon organs may be an aberrant development in extraocular muscles and of little significance in the total sensory output.

Animals↗
PubMed1990

Blood supply of the flexor digital tendon in the hand and its clinical significance.

An anatomical study on the blood sources and vascularity of the flexor digital tendon was conducted in the upper extremities of fresh cadavers by means of arterial injection and meticulous dissection of the transparent tendon under the microscope. According to whether or not synovial membrane surrounded the tendon, the flexor digital tendon can be divided into 2 regions: non-synovial and synovial. The major intrinsic blood supply of the digital tendon was in the form of longitudinal vascular bundles, while the transverse anastomotic branches were short and sparse. The non-synovial region of the tendon was covered by paratenon and the vascular distribution of this region was uniform. In the synovial sheath, the blood vessels distributed only on the dorsal side, while the volar side was devoid of vessels. The profundus and superficialis tendons had an avascular zone at the proximal interphalangeal and metacarpophalangeal joints respectively. It was considered that the difference of the vascular architecture might be related to the mechanical force to which the tendon was subjected. The nutrition of tendon was discussed and the selection of tendon graft at operation was suggested.

Hand↗
PubMed2001

The cell specific temporal expression of nitric oxide synthase isoforms during achilles tendon healing.

OBJECTIVE AND DESIGN: We have previously shown that nitric oxide synthase (NOS) activity is upregulated following tendon injury, and that this activity is important to Achilles tendon healing. The aim of this study was to identify the cellular distribution of nitric oxide synthase isoforms during tendon healing. MATERIAL OR SUBJECTS: Surgical division of the right Achilles tendon was performed in eighty-five male Sprague-Dawley rats. Healing Achilles tendons were harvested at 4, 7, 14 and 21 days following the surgery. The un-injured left Achilles tendons were used as controls. Using RNase protection assays, in situ hybridization and immunohistochemistry, mRNA and protein of NOS isoforms were evaluated. RESULTS: Minimal NOS expression was found in un-injured tendon. A cell specific temporal pattern for the mRNA and protein for all three NOS isoforms was found following injury to the Achilles tendon. iNOS was maximal on day 4 in macrophages and fibroblasts. eNOS was maximal on day 4 in endothelial cells and fibroblasts. bNOS expression gradually increased up to day 21 and was found only in fibroblasts. CONCLUSIONS: These results suggest that all three nitric oxide synthase isoforms are expressed by fibroblasts in a coordinated temporal sequence during tendon healing. The sequential pattern of NOS expression in healing fibroblasts suggests that each NOS isoform may play a different role in the healing process and provides opportunities to modify tendon healing in the clinical setting.

Achilles Tendon↗
PubMed2004

Tendon regeneration: an anatomical and histological study in sheep.

Utilization of the hamstring tendon in reconstruction of the anterior cruciate ligament (ACL) has become common in recent years. In MRI studies regeneration potential in harvested tendon has been observed. In the present study, 20 legs from ten sheep, which underwent 10 cm segment resection of tendon of musculus extensor digitalis lateralis (MEDL) were used. The sheep were killed 6 months after the operation and regenerated tendons were examined macroscopically and histologically. Dissection was performed in the tendon resection area and specimens were reharvested for histological examination. Regeneration of the tendon with normal anatomical topographies was found in all legs. Regeneration occurred on both sides of the resected tendon simultaneously. Regeneration was muscle-like in the proximal side but it was tendon-like in the distal side. The developed tendon was fused to the joint capsule and to the fascia at the joint line in all specimens. This study indicates that tendon has a potential for regeneration.

Animals↗
PubMed2006

Augmentation of tendon attachment to porous ceramics by bone marrow stromal cells in a rabbit model.

Tendon attachment to interconnected porous calcium hydroxyapatite ceramics (IP-CHA) with cultured bone marrow stromal cells (BMSC) was analysed. The purpose of this study was to evaluate whether BMSC in IP-CHA could augment the tendon attachment to IP-CHA histologically and biomechanically. Eighteen Japanese white rabbits were used. Cultured BMSCs were subcultured in IP-CHA. The grafted tendon and IP-CHA with BMSC complex were implanted in a bone defect of the knee [BMSC(+) group]. In the contralateral knee, a tendon and IP-CHA without BMSC complex were implanted [BMSC(-) group]. Histological findings of the interface between the tendon and IP-CHA were similar in the two groups 3 weeks after the operation. However, 6 weeks after the operation, more abundant bone formation around the tendon was observed in the BMSC(+) group. The direct apposition of the tendon to bone in pores and collagen fibre continuity between the tendon and fibrous tissue in pores were observed. In biomechanical evaluation, the maximum pull-out load of the tendon from the IP-CHA in the BMSC(+) group was significantly higher than that in the BMSC(-) group 6 weeks after the operation. BMSCs cultured in IP-CHA could augment tendon attachment to IP-CHA.

Animals↗
PubMed2001

Deleterious effects of local corticosteroid injections on the Achilles tendon of rats.

The purpose of this study was to examine the pathological changes in the Achilles tendon and its paratenon after intratendinous corticosteroid injections and to reveal the effects of this drug on healthy tendon. We also sought for the effects of these injections compared with compression with a clamp on the Achilles tendons of the rats. Fifty-two Achilles tendons in 26 male Wistar rats were included in the study. Betamethasone injections were applied to the left tendons at different intervals, while the right tendons served for compression with mosquito clamps for varied periods. At the end of 30 days, all of the tendons were excised and examined histopathologically according to a semiquantitative scoring system. Histopathologic evaluation demonstrated some degree of degeneration in both groups. Statistical analysis showed no significant difference among the two groups, but in macroscopic evaluation, the tendons in the betamethasone group demonstrated enlargement and strong adhesion to the subcutaneous tissue. We conclude that intratendinous betamethasone injections are as harmful as compression with a clamp and can be used as a degeneration-producing model in further studies. Enlargement of the tendon mass and strong adhesion to the subcutaneous tissue can be due to injection of the betamethasone partly outside the tendon.

Achilles Tendon↗
PubMed2001

Operative treatment in case of a closed rupture of the anterior tibial tendon.

Closed rupture of the tibial anterior tendon is a rare clinical entity. Case reports in the literature reveal a total of only 49 cases up to the year 2000. According to these reports, the age group affected is 50 to 70 years old, and there are more men than women affected. Although the functional limitation is quite considerable, late diagnosis is common. An appropriate clinical examination, including an exact history taking, should lead to the right diagnosis. Ultrasound examination and magnetic resonance imaging (MRI) may be helpful. 'Restitutio ad integrum' can only be achieved by operative treatment. If technically possible, reinsertion of the tendon directly into bone or direct tendon repair is preferred. After delayed diagnosis, a secondary reconstruction through tendon transfer or transplantation is often necessary. A 64-year-old woman presented with pain and swelling in the area of the ankle joint 5 months after falling. She showed insecurity in walking, and the heel-walk could not be demonstrated. The distal neurovascular function was intact. The area of the retinaculum showed a swelling, and the tendon was not palpable in comparison with the other forefoot. An intact tendon could not be seen by ultrasound, and MRI confirmed these findings. A complete rupture was noted during the operative revision. The proximal and the distal tendon stumps were found to be thickened and knotted, the proximal stump was also atrophic. An augmented tenoplasty was performed. Afterwards, the tendon was tense in the neutral position. The lower leg was put in a plaster cast for 6 weeks, followed by physiotherapy. Ten months after the operation, the tendon was palpable in the correct position, the dorsal extension was powerful, and the patient did not experience any difficulty. Rupture of the anterior tibial tendon is a rare clinical entity and should be considered in the differential diagnosis of pain in the area of the ankle joint. An early operative treatment is advantageous.

Ankle Injuries↗
PubMed2006

Biomechanical and immunohistochemical analysis of high hydrostatic pressure-treated Achilles tendons.

BACKGROUND: Reconstruction of bone defects caused by malignant tumors is carried out in different ways. At present, tumor-bearing bone segments are devitalized mainly by extracorporeal irradiation or autoclaving, but both methods have substantial disadvantages. In this regard, high hydrostatic pressure (HHP) treatment of the bone is a new, advancing technology that has been used in preclinical testing to inactivate normal cells and tumor cells without altering the biomechanical properties of the bone. The aim of this study was to examine the biomechanical and immunohistochemical properties of tendons after exposure to HHP and to evaluate whether preservation of the bony attachment of tendons and ligaments is possible. METHODS: For this, 19 paired Achilles tendons were harvested from both hindlimbs of 4-month-old pigs. After preparation, the cross-sectional area of each tendon was determined by magnetic resonance imaging (MRI). For each animal, one of the two tendons was taken at random and exposed to a pressure of 300 MPa (n = 9) or 600 MPa (n = 10). RESULTS: The contralateral tendon served as an untreated control. The biomechanical properties of the tendons remained unchanged with respect to the tested parameters: Young's modulus (MPa) and tensile strength (MPa). This finding is in line with immunohistochemical labeling results, as no difference in the labeling pattern of collagen I and versican was observed when comparing the HHP group (at 600 MPa) to the untreated control group. CONCLUSIONS: We anticipate that during orthopedic surgery HHP can serve as a novel, promising methodical approach to inactivate Achilles tendon and bone cells without altering the biomechanical properties of the tendons. This should allow one to preserve the attachment of tendon and ligaments to the devitalized bone and to facilitate functional reconstruction.

Achilles Tendon↗
PubMed2001

The effects of prolonged peritendinous administration of PGE1 to the rat Achilles tendon: a possible animal model of chronic Achilles tendinopathy.

We studied the effects of peritendinous Achilles tendon injections of prostaglandin E1 (PGE1) on the Achilles tendon of rats. Five groups of Sprague-Dawley rats (n = 24 each) were studied. Groups 1 to 4 received weekly peritendinous injections. In group 1, one side was injected with 800 ng of PGE1 in 0.5 ml of 0.9% NaCl and the contralateral side was injected with 0.5 ml of 0.9% NaCl. In group 2, one side was injected with 800 ng of PGE1. In group 3, one side was injected with 0.5 ml of 0.9% NaCl. In group 4, a syringe needle was inserted in the peritenon unilaterally, but no substances were administered. In groups 2, 3, and 4, the contralateral tendon was used as the control. In group 5, treatment was not administered. Eight rats in each group were killed at each time point, after 7, 21, and 35 days of treatment. On day 7, values for average water content and average wet weight of the tendons treated with PGE1 were significantly higher than those in the control tendons (analysis of variance [ANOVA]; P = 0.02), with a histological picture of acute inflammation. On day 21, approximately half of the PGE1-treated tendons showed fibrosis of the paratenon, with adhesions and intra-tendinous degeneration, with the other half still showing a picture of acute inflammation. On day 35, all of the PGE1-treated tendons showed fibrosis of the paratenon, with adhesions and intra-tendinous degeneration. At all time points, there was no evidence of pathology in the tendons that had not received PGE1. Sham peritendinous injections and injections of normal saline did not produce inflammation in the Achilles tendons. Initially, local administration of PGE1 produced acute inflammation of the tendon and its surrounding tissues. Prolonged PGE1 administration produced peri- and intra-tendinous degeneration, providing a cheap, reproducible model of Achilles tendinopathy, which would allow studies of the effects of conservative and surgical management of the condition.

Achilles Tendon↗
PubMed2004

TGF-beta1, TGF-beta3, and PGE(2) regulate contraction of human patellar tendon fibroblasts.

To understand the role of tendon fibroblast contraction in tendon healing, we investigated the contraction of human patellar tendon fibroblasts (HPTFs) and its regulation by transforming growth factor-beta1 (TGF-beta1), TGF-beta3, and prostaglandin E(2) (PGE(2)). HPTFs were found to wrinkle the underlying thin silicone membranes, demonstrating that these tendon fibroblasts are contractile. Using fibroblast populated collagen gels (FPCGs), exogenous addition of TGF-beta1 or TGF-beta3 was found to increase fibroblast contraction compared to non-treated fibroblasts in serum-free medium, whereas PGE(2) was found to decrease the tendon fibroblast contraction. Moreover, the tendon fibroblasts in collagen gels treated with TGF-beta1 contracted to a greater degree than those treated with TGF-beta3. Since the extent of fibroblast contraction is related to scar tissue formation, this differential effect of TGF-beta1 and TGF-beta3 on HPTF contraction supports the previous finding that TGF-beta1 induces scar tissue formation, whereas TGF-beta3 reduces its formation. Further, the reduced tendon fibroblast contraction by PGE(2) suggests that excessive presence of this inflammatory mediator in the wound site might retard tendon healing. Taken together, the results of this study suggest that regulation of human tendon fibroblast contraction may reduce scar tissue formation and therefore improve the mechanical properties of healing tendons.

Cell Size↗
PubMed2005

The interaction between osteoclast-like cells and osteoblasts mediated by nanophase calcium phosphate-hybridized tendons.

We developed a novel technique of hybridizing calcium phosphate (CaP) with bioorganic soft tissue using an alternating soaking process. By this technique, we hybridized CaP with a grafted tendon tissue to bond with a bone tunnel. Tendons were soaked in Ca and NaHPO(4) solutions alternately for 10 min. Needle-like CaP crystals 30-50 nm in length including low-crystalline apatite were deposited on and between collagen fibrils from the surface to 200 microm deep in the tendon. In light and transmission electron microscopic images, osteoclast-like cells and osteoblasts appeared on the implanted tendon and osteoid was observed on the tendon surface at 1 week postoperatively. At 2 weeks postoperatively, osteoclast-like cells resolved the tendon by forming Howship's lacuna-like spaces on the surfaces and osteoblasts formed osteoid in these spaces. Direct bonding between the implanted tendon and the newly formed bone was observed. At 3 weeks postoperatively, thick newly formed bone firmly bonded to tendon surface. From these results, we conclude that the tendons prepared by an accelerated CaP hybridization method efficiently enhance osteoclast-like cells and osteoblasts to bond the implanted tendons to newly formed bone.

Animals↗
PubMed2005

Tendon and nerve displacement at the wrist during finger movements.

BACKGROUND: Repetitive motion of the hand has been suggested as a major factor of pathogenesis of cumulative trauma disorders (e.g., carpal tunnel syndrome). The purpose of this study was to investigate the 3D displacement of the median nerve and extrinsic finger flexor tendons (flexor digitorum superficialis; flexor digitorum profundus) as a function of flexion/extension of metacarpophalangeal joints of the index and middle fingers. METHODS: Shim markers were placed on the median nerve, flexor digitorum superficialis, and flexor digitorum profundus tendons at the wrist region of seven cadaveric specimens for the purpose of digitization of tendon and nerve locations. The metacarpophalangeal joint of the index or middle finger was moved from 15 degrees extension to 75 degrees of flexion while the markers were digitized at increments of 15 degrees. Marker displacements were determined in the longitudinal, radial-ulnar, and dorsal-palmar directions. FINDINGS: Movement of metacarpophalangeal joint of the index or middle finger caused tendon and nerve displacements in the longitudinal, radial-ulnar, and dorsal-palmar directions. The longitudinal displacements of the median nerve and the flexor tendons were linearly correlated with angular movement of the metacarpophalangeal joint. The maximum longitudinal displacements of the flexor digitorum superficialis tendon, flexor digitorum profundus tendon, and median nerve were, on average, 14.7 mm, 11.9 mm, and 3.0 mm, respectively, for the index finger; and 18.4 mm, 14.5 mm, and 4.0 mm, respectively, for the middle finger. The radial-ulnar and dorsal-palmar displacements were irregular and relatively small. The maximum displacements in these transverse directions fell in the range of 1.4-5.1 mm for the median nerve and 1.9-7.3 mm for the flexor tendons. INTERPRETATIONS: Finger flexor tendons and median nerve move not only concurrently, but also differentially, in all anatomical directions. Tendon and nerve movement during prolonged repetitive hand movement may cause hand disorders such as carpal tunnel syndrome.

Aged↗
PubMed2005

Effects of cold and hot water immersion on the mechanical properties of human muscle and tendon in vivo.

BACKGROUND: Cooling and heating have been shown to affect the contractile properties of muscles. However, the reasons for these changes remain unclear. The present study aimed to quantify the mechanical properties of muscle and tendon during passive stretch and active contraction, and to investigate the effects of cooling and heating on the mechanical properties of muscle and tendon. METHODS: Before and after these conditions, the elongation of the muscle fascicle, tendon and aponeurosis of the medial gastrocnemius muscle was directly measured by ultrasonography, while the ankle joint was passively moved within the joint range of +15 to -30 deg (0 deg = neutral anatomic position; positive values for plantar flexion) and subjects performed ramp isometric plantar flexion up to the voluntary maximum. FINDINGS: While the muscle fascicle, tendon and aponeurosis stretched during passive dorsi-flexion, the elongation of the tendon was significantly greater than that of the aponeurosis. During isometric contraction, the maximal elongation of the tendon was significantly greater than that of the aponeurosis. After cooling and heating, no significant changes in the elongation of muscle fascicle, tendon and aponeurosis were found during passive stretch. Similarly, after both the immersions there were no changes in the relationship between the estimated muscle force and elongation of each structure (tendon-aponeurosis complex, tendon) during isometric contraction. INTERPRETATION: These results implied that the general application of icing and hot pack did not change the mechanical properties of muscle and tendon.

Adult↗
PubMed2005

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

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

Adolescent↗