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Michelle A. Sandrey


To present the basic concepts of normal composition and structure of tendons and indicate how they are affected by acute and chronic tendon-injury pathomechanics.

Data Sources:

MEDLINE (1970-1999) and SPORTDiscus (1970-1999) were searched using the key words pathoanatomic, tendinitis, tendinosis, biomechanics, pathomechanics, histology, chronic, and mechanical behavior.

Data Synthesis:

Acute loading modes to tendons are based on the response of tendons to tensile and compressive stress. Chronic loading modes are based on frictional forces and repetitive movement.

Conclusions and Recommendations:

With an appreciation of the pathologic changes in acute tendon injuries, the clinician can better understand injury mechanics and the healing process. Until we know more about what is happening in and around the tendon, principally in the early and late phases of chronic injury we will not be able to adequately address injury classification of structures and, hence, the pathomechanics of chronic injury

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Sharon J. Dixon and David G. Kerwin

In this study, a modeling method was developed to estimate Achilles tendon forces in running. Owing to the common use of heel lift devices in the treatment of Achilles tendon injury, we investigated the influence of increased heel lift on Achilles tendon loading. The hypothesis was that heel lift manipulation can influence maximum Achilles tendon force. Responses to heel lift variation were found to differ among 3 elite runners demonstrating distinct running styles. A rearfoot and a midfoot striker demonstrated significant increases in maximum Achilles tendon force with increased heel lift, whereas a forefoot striker demonstrated no changes in maximum Achilles tendon force values with heel lift manipulation (p < .05). Analysis of the factors contributing to the observed changes in maximum Achilles tendon force highlighted the influence of the moment arm of ground reaction force and the moment arm of the Achilles tendon about the ankle joint center. The finding that increased heel lift may increase maximum Achilles tendon force suggests that caution is advised in the routine use of this intervention. The different responses to heel lift increase between subjects highlight the importance of classifying subjects based on running style.

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Kristinn I. Heinrichs and Catherine R. Haney

The efficacy of the nonoperative and operative approaches to Achilles tendon rapture has been debated in the literature. In addition, there is little consensus regarding postoperative immobilization with regard to immobilization type, casting position, cast time, and weight-bearing progression. The rehabilitation of the surgically repaired Achilles tendon has not been well described in the literature. The epidemiology and biomechanics of Achilles tendon rupture as well as splint fabrication and rehabilitation protocol for the surgically repaired Achilles tendon in two patients will be presented.

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Derek N. Pamukoff and J. Troy Blackburn

Greater lower extremity joint stiffness may be related to the development of tibial stress fractures in runners. Musculotendinous stiffness is the largest contributor to joint stiffness, but it is unclear what factors contribute to musculotendinous stiffness. The purpose of this study was to compare plantar flexor musculotendinous stiffness, architecture, geometry, and Achilles tendon stiffness between male runners with and without a history of tibial stress fracture. Nineteen healthy runners (age = 21 ± 2.7 years; mass = 68.2 ± 9.3 kg; height = 177.3 ± 6.0 cm) and 19 runners with a history of tibial stress fracture (age = 21 ± 2.9 years; mass = 65.3 ± 6.0 kg; height = 177.2 ± 5.2 cm) were recruited from community running groups and the university’s varsity and club cross-country teams. Plantar flexor musculotendinous stiffness was estimated from the damped frequency of oscillatory motion about the ankle follow perturbation. Ultrasound imaging was used to measure architecture and geometry of the medial gastrocnemius. Dependent variables were compared between groups via one-way ANOVAs. Previously injured runners had greater plantar flexor musculotendinous stiffness (P < .001), greater Achilles tendon stiffness (P = .004), and lesser Achilles tendon elongation (P = .003) during maximal isometric contraction compared with healthy runners. No differences were found in muscle thickness, pennation angle, or fascicle length.

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Federico Morelli, Andrea Ferretti, Fabio Conteduca, Francesca Nanni, Lucilla Monteleone and Marco Valente

The purpose of this study was to develop a new device, which represents a modification of the Cryo-Jaw described by Riemersa and Schamhardt and modified by Hamner et al., for in vitro biomechanical testing of tendons which allows the lower clamp to move in every direction and thus simulate a pathological dislocation of the knee. Tendons are fixed to the device by freezing the clamped part with dry ice. After fixation of their free ends, the lower clamp was rotated 45°, translated 1 cm, and angled 40° to simulate a knee sprain. Various configurations of bundles were tested: parallel, twisted, and braided. Tests were performed on 10 paired bovine bifurcated digital extensor tendons and 6 paired human hamstring tendons. Grafts were then tested to failure subjected to impulsive load, using a servohydraulic machine. The highest ultimate load recorded for parallel bundles was 4662 ± 565.71 N for bovine bifurcated digital extensor tendons, and 3057 ± 475.44 N for human hamstring tendons. In any case, the tendons ruptured midway, well clear of the frozen part; in no case was slippage of the tendons observed. Thus the device proposed allows one to test what happens to the graft of an ACL reconstructed knee during physiological and pathological movements because it can be easily displaced in every direction.

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Eric Winters, Steven Doty and Sean Newell


To explore changes in bovine Achilles-tendon elasticity relative to 3 thermal conditions.

Design and Setting:

Posttest-only design with assignment by convenience. Manufactured-apparatus-clamped excised tendon, delivered tensile stress, and provided strain measures. Stress was increased at 1-minute intervals. Strain was observed for each level of stress. Before testing, cold-group tendons were submerged in cold water for 20 minutes. Heat-group tendons were tested in the presence of an ultraviolet lamp. A third group of tendons was tested at room temperature.


Frozen bovine Achilles tendons provided by a meat-rendering factory and segmented into 3 longitudinal strips.


Stress and strain were sequentially measured. Elastic region was identified, elastic-region Young's modulus determined, and elastic limit calculated.


Young's modulus for cold was 0.956 gigapascal (GPa; ± 0.0621); room temperature, 0.753 GPa (± 0.0624); and heat group, 0.487 GPa (± 0.0407). Significant differences were identified between each of the 3 conditions.


A direct relationship was observed between imposed thermal energy and tendon elasticity. Thermal energy does not affect the elastic limit.

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Keitaro Kubo, Toshihiro Ikebukuro, Hideaki Yata, Minoru Tomita and Masaji Okada

The purpose of this study was to investigate muscle and tendon properties in highly trained sprinters and their relations to running performance. Fifteen sprinters and 15 untrained subjects participated in this study. Muscle thickness and tendon stiffness of knee extensors and plantar flexors were measured. Sprinter muscle thickness was significantly greater than that of the untrained subjects for plantar flexors, but not for knee extensors (except for the medial side). Sprinter tendon stiffness was significantly lower than that of the untrained subjects for knee extensors, but not for plantar flexors. The best official record of a 100-m race was significantly correlated to the muscle thickness of the medial side for knee extensors. In conclusion, the tendon structures of highly trained sprinters are more compliant than those of untrained subjects for knee extensors, but not for plantar flexors. Furthermore, a thicker medial side of knee extensors was associated with greater sprinting performance.

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Graham E. Caldwell

The effects of relative tendon/fiber proportion and tendon elasticity on the force output of the Hill muscle model (a contractile component [CC] in series with an elastic element [SEC]) were examined through computer simulation. Three versions of the Hill model were constructed. Model 1 examined the effect of relative tendon/fiber proportion on CC kinematics and kinetics during an isometric twitch, while Model 2 compared the effect of changes in tendon compliance. These models revealed force profile differences related to alterations in CC velocity, although the reasons underlying the variation in CC kinematics were different. The relative tendon/fiber proportion and tendon compliance differences were examined in combination in Model 3. Test simulations revealed response differences among the three model versions, and therefore verified Alexander and Ker's (1990) contention that the morphology of muscle is related to design criteria. It is suggested that the implementation of generalized muscle models to represent specific units of the musculoskeletal system should be done carefully and that the implementation process itself warrants further study.

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Tom A. Ranger, Wendy M. Braybon, Craig R. Purdam and Jill L. Cook


Lateral epicondylalgia, pain at the lateral elbow, is commonly associated with extensor carpi radialis brevis tendinopathy. The radial head, which abuts the extensor tendons and is elliptical in shape, may affect the extensor tendons during pronation of the forearm. Cadaverous studies have shown that the radial head may act as a cam in pronation, to offer a mechanical advantage to the common extensor tendon and to mitigate load on the origin of the extensor carpi radialis brevis tendon.


To determine the effect of radial-head position on the wrist-extensor tendons in vivo.


Repeated-measures design.




22 participants (12 male, 2 left-handed).

Main Outcome Measures:

Distance (mm) from subcutaneous fascia to radial head measured by ultrasound.


The radial head in supination was significantly deeper than either pronation or midprone, indicating a smaller cam effect in supination.


The authors recommend that the effect of radial-head position and its relationship to the area of tendon pathology be considered clinically in the rehabilitation of patients suffering from lateral epicondylalgia.

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Keitaro Kubo, Takanori Teshima, Norikazu Hirose and Naoya Tsunoda

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young’s modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass2/3) of the patellar tendon among the three groups. Stiffness and Young’s modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young’s modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.