Examination of knee extensor and valgus moment arms of the patellar tendon in older individuals with and without knee osteoarthritis

BACKGROUND

Joint moment arm is a major element that determines joint torque. This study aimed to investigate factors associated with knee extensor and valgus moment arms of the patellar tendon in older individuals with and without knee osteoarthritis.

METHODS

Thirty-six participants with knee osteoarthritis (mean age, 78.1 ± 6.0 years) and 43 healthy controls (mean age, 73.0 ± 6.3 years) were analyzed. Magnetic resonance images (MRI) from the knee joint and thigh were acquired using a 3.0 T MRI scanner. The three-dimensional moment arm was defined as the distance between the contact point of the tibiofemoral joint and the patellar tendon line. The three-dimensional moment arm was decomposed into sagittal and coronal components, which were calculated as knee extensor and valgus moment arms, respectively. Quadriceps muscle volume, epicondylar width, bisect offset, Insall-Salvati ratio, and Kellgren-Lawrence grade were assessed. Multiple regression analyses were performed in the healthy control and knee osteoarthritis groups, with knee extensor and valgus moment arms as dependent variables.

FINDINGS

Knee extensor moment arm was significantly associated with epicondylar width and the Insall-Salvati ratio in the healthy control group and with Kellgren-Lawrence grade, epicondylar width, and quadriceps muscle volume in the knee osteoarthritis group. Valgus knee moment arm was significantly associated with bisect offset in both the groups.

INTERPRETATION

Knee size, osteoarthritis severity, and quadriceps muscle volume affect the knee extensor moment arm in knee osteoarthritis, whereas lateral patellar displacement affects the valgus knee moment arms in older individuals with and without knee osteoarthritis.

Quantitative evaluation of the biomechanical and viscoelastic properties of the dog patellar tendon in response to neuromuscular blockade at different stifle angles

The patellar tendon (PT) is crucial for maintaining stability and facilitating movement in the stifle joint. Elastography has been recognized as a prominent method for evaluating PT properties in humans and dogs. The utilization of oscillation methods in canine studies remains limited despite their extensive documentation in human studies. Our study represents the first effort to quantitatively assess and compare the effects of muscle relaxant on the biomechanical and viscoelastic characteristics of the PT at varying stifle angles in living dogs. Five healthy female beagles were used in this study. Biomechanical (tone, stiffness, and decrement) and viscoelastic (relaxation time and creep) properties of the PT were measured using MyotonPRO (Myoton Ltd, Estonia) prior to and following administration of rocuronium (0.5 mg/kg/body weight) at normal, extended, and flexed positions. Rocuronium was selected for its safety, controllability, and widespread clinical use in veterinary anesthesia. Two-way analysis of variance showed that tone, stiffness, and decrement were significantly higher (P < 0.001) in the control group than in the muscle relaxation group. At the same time, relaxation time and creep were significantly lower (P < 0.001) in the control group than in the muscle relaxation group. The findings indicate that stifle angle position and muscle rexalant administration fundamentally alter the biomechanical loading conditions of the PT, leading to changes in its viscoelastic properties. Therefore, this novel quantitative data could benefit clinical settings that necessitate accurate and objective methods for risk identification and monitoring PT biomechanics in dogs.

Patellar Tendon Adaptations to Downhill Running Training and Their Relationships With Changes in Mechanical Stress and Loading History

ABSTRACT

Bontemps, B, Gruet, M, Louis, J, Owens, DJ, Miríc, S, Vercruyssen, F, and Erskine, RM. Patellar tendon adaptations to downhill running training and their relationships with changes in mechanical stress and loading history. J Strength Cond Res 38(1): 21-29, 2024-It is unclear whether human tendon adapts to moderate-intensity, high-volume long-term eccentric exercise, e.g., downhill running (DR) training. This study aimed to investigate the time course of patellar tendon (PT) adaptation to short-term DR training and to determine whether changes in PT properties were related to changes in mechanical stress or loading history. Twelve untrained, young, healthy adults (5 women and 7 men) took part in 4 weeks' DR training, comprising 10 sessions. Running speed was equivalent to 60-65% V̇O2max, and session duration increased gradually (15-30 minutes) throughout training. Isometric knee extensor maximal voluntary torque (MVT), vastus lateralis (VL) muscle physiological cross-sectional area (PCSA) and volume, and PT CSA, stiffness, and Young's modulus were assessed at weeks 0, 2, and 4 using ultrasound and isokinetic dynamometry. Patellar tendon stiffness (+6.4 ± 7.4%), Young's modulus (+6.9 ± 8.8%), isometric MVT (+7.5 ± 12.3%), VL volume (+6.6 ± 3.2%), and PCSA (+3.8 ± 3.3%) increased after 4 weeks' DR (p < 0.05), with no change in PT CSA. Changes in VL PCSA correlated with changes in PT stiffness (r = 0.70; p = 0.02) and Young's modulus (r = 0.63; p = 0.04) from 0 to 4 weeks, whereas changes in MVT did not correlate with changes in PT stiffness and Young's modulus at any time point (p > 0.05). To conclude, 4 weeks' DR training promoted substantial changes in PT stiffness and Young's modulus that are typically observed after high-intensity, low-volume resistance training. These tendon adaptations seemed to be driven primarily by loading history (represented by VL muscle hypertrophy), whereas increased mechanical stress throughout the training period did not seem to contribute to changes in PT stiffness or Young's modulus.

Specific collagen peptides increase adaptions of patellar tendon morphology following 14-weeks of high-load resistance training: A randomized-controlled trial

ABSTRACTThe purpose of this study was to investigate the effect of a supplementation with specific collagen peptides (SCP) combined with resistance training (RT) on changes in structural properties of the patellar tendon. Furthermore, tendon stiffness as well as maximal voluntary knee extension strength and cross-sectional area (CSA) of the rectus femoris muscle were assessed. In a randomized, placebo-controlled study, 50 healthy, moderately active male participants completed a 14-week resistance training program with three weekly sessions (70-85% of 1 repetition maximum [1RM]) for the knee extensors. While the SCP group received 5g of specific collagen peptides daily, the other group received the same amount of a placebo (PLA) supplement. The SCP supplementation led to a significant greater (p < 0.05) increase in patellar tendon CSA compared with the PLA group at 60% and 70% of the patellar tendon length starting from the proximal insertion. Both groups increased tendon stiffness (p < 0.01), muscle CSA (p < 0.05) and muscular strength (p < 0.001) throughout the intervention without significant differences between the groups. The current study shows that in healthy, moderately active men, supplementation of SCP in combination with RT leads to greater increase in patellar tendon CSA than RT alone. Since underlying mechanisms of tendon hypertrophy are currently unknown, further studies should investigate potential mechanisms causing the increased morphology adaptions following SCP supplementation.Trial registration: German Clinical Trials Register identifier: DRKS00029244..

PIEZO1 gain-of-function gene variant is associated with elevated tendon stiffness in humans

Prolonged periods of increased physical demands can elicit anabolic tendon adaptations that increase stiffness and mechanical resilience or conversely can lead to pathological processes that deteriorate tendon structural quality with ensuing pain and potential rupture. Although the mechanisms by which tendon mechanical loads regulate tissue adaptation are largely unknown, the ion channel PIEZO1 has been implicated in tendon mechanotransduction, with human carriers of the PIEZO1 gain-of-function variant E756del displaying improved dynamic vertical jump performance compared with noncarriers. Here, we sought to examine whether increased tendon stiffness in humans could explain this increased performance. We assessed tendon morphological and mechanical properties with ultrasound-based techniques in 77 participants of Middle- and West-African descent, and we measured their vertical jumping performance to assess potential functional consequences in the context of high tendon strain-rate loading. Carrying the E756del gene variant (n = 30) was associated with 46.3 ± 68.3% (P = 0.002) and 45.6 ± 69.2% (P < 0.001) higher patellar tendon stiffness and Young's modulus compared with noncarrying controls, respectively. Although these tissue level measures strongly corroborate the initial postulate that PIEZO1 plays an integral part in regulating tendon material properties and stiffness in humans, we found no detectable correlation between tendon stiffness and jumping performance in the tested population that comprised individuals of highly diverse physical fitness level, dexterity, and jumping ability.NEW & NOTEWORTHY The E756del gene variant causes overactivity of the mechanosensitive membrane channel PIEZO1 and is suspected to upregulate tendon collagen cross linking. In human carriers of E756del, we found increased patellar tendon stiffness but similar tendon lengths and cross-sectional areas, directly supporting the premise that PIEZO1 regulates human tendon stiffness at the level of tissue material properties.

Persons with Patellar Tendinopathy Exhibit Greater Patellar Tendon Stress during a Single-Leg Landing Task

PURPOSE

This study aimed to compare peak maximum principal stress in the patellar tendon between persons with and without patellar tendinopathy during a simulated single-leg landing task. A secondary purpose was to determine the biomechanical predictor(s) of peak maximum principal stress in the patellar tendon.

METHODS

Using finite element (FE) modeling, patellar tendon stress profiles of 28 individuals (14 with patellar tendinopathy and 14 pain-free controls) were created at the time of the peak knee extensor moment during single-leg landing. Input parameters to the FE model included subject-specific knee joint geometry and kinematics, and quadriceps muscle forces. Independent t -tests were used to compare the peak maximum principal stress in the patellar tendon and biomechanical variables used as input variables to the FE model (knee flexion, knee rotation in the frontal and transverse planes and the peak knee extensor moment) between groups. A stepwise regression model was used to determine the biomechanical predictor(s) of peak maximum principal stress in the patellar tendon for both groups combined.

RESULTS

Compared with the control group, persons with patellar tendinopathy exhibited greater peak maximum principal stress in the patellar tendon (77.4 ± 25.0 vs 60.6 ± 13.6 MPa, P = 0.04) and greater tibiofemoral joint internal rotation (4.6° ± 4.6° vs 1.1° ± 4.2°, P = 0.04). Transverse plane rotation of the tibiofemoral joint was the best predictor of peak maximum principal stress in the patellar tendon ( r = 0.51, P = 0.01).

CONCLUSIONS

Persons with patellar tendinopathy exhibit greater peak patellar tendon stress compared with pain-free individuals during single-leg landing. The magnitude of peak patellar tendon stress seems to be influenced by the amount of tibiofemoral rotation in the transverse plane.

Relationships between tendon structure and clinical impairments in patients with patellar tendinopathy

The clinical relevance of altered tendon structure in patellar tendinopathy is contested since structural change persists after symptom resolution. The purpose of this study was to explore the relationships between tendon structure and clinical impairments in patellar tendinopathy. In this retrospective, secondary analysis of individuals with patellar tendinopathy (n = 41), tendon structure (thickness, cross-sectional area [CSA], shear modulus, and viscosity), symptom severity, lower extremity function (counter-movement jump [CMJ] height), and quadriceps muscle performance (knee extension force and central activation ratio [CAR]) were recorded for the symptomatic limb. Relationships among structure, symptom severity, lower extremity function, and quadriceps muscle performance were examined using sequential regression models. Adjusting for age, sex, body mass index, and pain levels, there were significant positive relationships for thickness (p < 0.001, β = 0.718) and viscosity (p = 0.006, β = 0.496) with CMJ height. There were significant negative relationships between CSA with both CMJ height (p = 0.001, β = -0.538) and CAR (p = 0.04, β = -0.517). This is the first study to demonstrate relationships between tendon structure and lower extremity function or quadriceps muscle performance in patients with patellar tendinopathy. Clinical significance: Since structural changes persist after symptom resolution, addressing these changes may assist in restoring lower extremity function and quadriceps muscle performance.

Metabolic and molecular responses of human patellar tendon to concentric- and eccentric-type exercise in youth and older age

Exercise training can induce adaptive changes to tendon tissue both structurally and mechanically; however, the underlying compositional changes that contribute to these alterations remain uncertain in humans, particularly in the context of the ageing tendon. The aims of the present study were to determine the molecular changes with ageing in patellar tendons in humans, as well as the responses to exercise and exercise type (eccentric (ECC) and concentric (CON)) in young and old patellar tendon. Healthy younger males (age 23.5 ± 6.1 years; n = 27) and older males (age 68.5 ± 1.9 years; n = 27) undertook 8 weeks of CON or ECC training (3 times per week; at 60% of 1 repetition maximum (1RM)) or no training. Subjects consumed D₂O throughout the protocol and tendon biopsies were collected after 4 and 8 weeks for measurement of fractional synthetic rates (FSR) of tendon protein synthesis and gene expression. There were increases in tendon protein synthesis following 4 weeks of CON and ECC training (P < 0.01; main effect by ANOVA), with no differences observed between young and old males, or training type. At the transcriptional level however, ECC in young adults generally induced greater responses of collagen and extracellular matrix-related genes than CON, while older individuals had reduced gene expression responses to training. Different training types did not appear to induce differential tendon responses in terms of protein synthesis, and while tendons from older adults exhibited different transcriptional responses to younger individuals, protein turnover changes with training were similar for both age groups.

Effect of Knee Angle and Quadriceps Muscle Force on Shear-Wave Elastography Measurements at the Patellar Tendon

Shear-wave elastography (SWE) is a non-invasive imaging technique that provides estimates of tissue stiffness via shear-wave speed measurements. No standardized protocol currently exists for SWE of the patellar tendon, which may be influenced by knee angle and quadriceps muscle force. In this study, the reliability of SWE in cadaveric patellar tendons was examined at three knee angles (0°, 30° and 60°) and three quadriceps muscle forces (0, 50 and 100 N). Shear-wave speed was significantly higher at a knee angle of 60° than at 0° or 30° (increases of 7% and 9%, respectively), and when the quadriceps muscle force was greater than or equal to 50 N (increase of 15%). SWE of the patellar tendon displayed excellent repeatability regardless of knee angle as long as no quadriceps force was generated (intra-class correlation coefficient ≥0.91). This research illustrates the importance of controlling knee angle and quadriceps force for consistency and comparison of SWE results.

Association between patellar tendon moment arm and running performance in endurance runners

A shorter joint moment arm (MA) may help maintain the necessary muscle force when muscle contractions are repeated. This beneficial effect may contribute to reducing the energy cost during running. In this study, we examined the correlation between patellar tendon MA and running performance in endurance runners. The patellar tendon MA and quadriceps femoris muscle volume (MV) in 42 male endurance runners and 14 body size-matched male untrained participants were measured using a 1.5-T magnetic resonance system. The patellar tendon MA was significantly shorter in endurance runners than in untrained participants (p = 0.034, d = 0.65). In endurance runners, shorter patellar tendon MA correlated significantly with better personal best 5000-m race rime (r = 0.322, p = 0.034). A trend toward such a significant correlation was obtained between quadriceps femoris MV and personal best 5000-m race time (r = 0.303, p = 0.051). Although the correlation between patellar tendon MA and personal best 5000-m race time did not remain significant after adjusting for the quadriceps femoris MV (partial r = 0.247, p = 0.120), a stepwise multiple regression analysis (conducted with body height, body mass, patellar tendon MA, and quadriceps femoris MV) selected the patellar tendon MA (β = 0.322) as only a predictive variable for the personal best 5000-m race time (adjusted R2  = 0.081, p = 0.038). These findings suggest that the shorter patellar tendon MA, partially accorded with the smaller quadriceps femoris size, may be a favorable morphological variable for better running performance in endurance runners.

Examination of the proximodistal patellar position in small dogs in relation to anatomical features of the distal femur and medial patellar luxation

Objective

To determine the influence of anatomical features of the distal femur on the proximodistal patellar position and compare the proximodistal patellar position between dogs with and without medial patellar luxation (MPL).

Study design

Retrospective case series (n = 71).

Methods

Mediolateral-view radiographs of clinical cases of dogs weighing less than 15 kg were obtained. The stifle joint angle, patellar ligament length, patellar length, size of the femoral condyle, trochlear length, and trochlear angle were measured and included in multiple linear regression analyses to ascertain their effects on the proximodistal patellar position. Radiographs were divided into MPL and control groups. The effects of MPL on the proximodistal patellar position and morphological factors were also examined.

Results

The final model for the proximodistal patellar position revealed that the patella became distal as the ratio of the patellar ligament length to patellar length decreased, the trochlear angle relative to the femur increased, the trochlear length relative to the patellar length increased, or the trochlear length relative to the femoral condyle width decreased. The proximodistal patellar position in the MPL group was not significantly different from that in the control group despite the trend towards a distally positioned patella (p = 0.073). The MPL group showed a significantly shorter trochlea (p<0.001) and greater trochlear angle relative to the femur (p = 0.029) than the control group.

Conclusion

The proximodistal patellar position depends on multiple factors, and its determination based on PLL/PL alone may not be appropriate. Dogs with MPL did not have a proximally positioned patella compared with dogs without MPL. Although hindlimbs with MPL had a shorter trochlea than those without patellar luxation, this difference did not appear to be sufficient to displace the patellar position proximally in small dogs, possibly compensated by increased trochlear angle relative to the femur.

Tendon Biomechanics and Crimp Properties Following Fatigue Loading Are Influenced by Tendon Type and Age in Mice

In tendon, type-I collagen assembles together into fibrils, fibers, and fascicles that exhibit a wavy or crimped pattern that uncrimps with applied tensile loading. This structural property has been observed across multiple tendons throughout aging and may play an important role in tendon viscoelasticity, response to fatigue loading, healing, and development. Previous work has shown that crimp is permanently altered with the application of fatigue loading. This opens the possibility of evaluating tendon crimp as a clinical surrogate of tissue damage. The purpose of this study was to determine how fatigue loading in tendon affects crimp and mechanical properties throughout aging and between tendon types. Mouse patellar tendons (PT) and flexor digitorum longus (FDL) tendons were fatigue loaded while an integrated plane polariscope simultaneously assessed crimp properties at P150 and P570 days of age to model mature and aged tendon phenotypes (N = 10-11/group). Tendon type, fatigue loading, and aging were found to differentially affect tendon mechanical and crimp properties. FDL tendons had higher modulus and hysteresis, whereas the PT showed more laxity and toe region strain throughout aging. Crimp frequency was consistently higher in FDL compared with PT throughout fatigue loading, whereas the crimp amplitude was cycle dependent. This differential response based on tendon type and age further suggests that the FDL and the PT respond differently to fatigue loading and that this response is age-dependent. Together, our findings suggest that the mechanical and structural effects of fatigue loading are specific to tendon type and age in mice. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:36-42, 2020.

Strain Ratio Measurements of Patellar and Achilles Tendons With Different Reference Regions in Healthy Volunteers

Strain ratio measurements of tendons vary because of the reference tissue selection. The main purpose of this study is to highlight, in detail, the numeric variability attributable to the use of various reference materials on strain ratio measurements of patellar and Achilles tendons. Measurements were performed at the proximal, middle and distal thirds of the patellar and Achilles tendons on the dominant site of healthy volunteers. A total of 3 references were used: the Hoffa's fat pad for the patellar tendon, the Kager's fat pad for the Achilles tendon, subcutaneous tissue and Aquaflex gel pads (Parker Laboratories, Fairfield, NJ, USA) for both tendons. Although the same methods were used by the same physician for each tendon site on repeated measurements, strain ratio values had numeric variability with various reference materials in each measurement. Therefore, comparison of numeric strain ratio results of various studies with various reference materials could confuse the clinical interpretations of these numeric data, and, using a reference material with standard stiffness like Aquaflex ultrasound gel pads, should be considered by verifying these results with further studies.

Comparison of interobserver agreement between the evaluation of bicipital and the patellar tendon reflex in healthy dogs

The reliability of reflex-assessment is currently debatable, with current literature regarding the patellar tendon reflex (PTR) as highly reliable, while the biceps tendon reflex (BTR) is regarded to be of low reliability in the dog. Such statements are, however, based on subjective observations rather than on an empirical study. The goals of this study were three-fold: (1) the quantification of the interobserver agreement (IA) on the evaluation of the canine bicipital (BTR) and patellar tendon (PTR) reflex in healthy dogs, (2) to compare the IA of the BTR and PTR evaluation and (3) the identification of intrinsic (sex, age, fur length, weight) and extrinsic (observer´s expertise, body side) risk factors on the IA of both reflexes. The observers were subdivided into three groups based on their expected level of expertise (neurologists = highest -, practitioners = middle–and veterinary students = lowest level of expertise). For the BTR, 54 thoracic limbs were analyzed and compared to the evaluation of the PTR on 64 pelvic limbs. Each observer had to evaluate the reflex presence (RP) (present or absent) and the reflex activity (RA) using a 5-point ordinal scale. Multiple reliability coefficients were calculated. The influence of the risk factors has been calculated using a mixed regression-model. The Odds Ratio for each factor was presented. The higher the level of expertise the higher was the IA of the BTR. For RP(BTR), IA was highest for neurologists and for RA(BTR) the IA was lowest for students. The level of expertise had a significant impact on the degree of the IA in the evaluation of the bicipital tendon reflex: for the RA(BTR), practitioners had a 3.4-times (p = 0.003) and students a 7.0-times (p < 0.001) higher chance of discordance. In longhaired dogs the chance of disagreement was 2.6-times higher compared to shorthaired dogs in the evaluation of RA(BTR) (p = 0.003). Likewise, the IA of the RP(PTR) was the higher the higher the observers´ expertise was with neurologists having significantly highest values (p < 0.001). The RA(PTR) has been evaluated more consistent by practitioners and students than the RA(BTR). For practitioners this difference was significant (< 0.01). Our data suggests that neurologists assess the bicipital and patellar tendon reflex in dogs most reliably. None of the examined risk factors had a significant impact on the degree of IA in the evaluation of RP(PTR), while students had a 4.4-times higher chance of discordance when evaluating the RA(PTR) compared to the other groups. This effect was significant (p < 0.001). Neurologists can reliably assess the bicipital and patellar tendon reflex in healthy dogs. Observer´s level of expertise and the fur length of the dog affect the degree of IA of RA(BTR). The influence of the observer´s expertise is higher on the evaluation of the BTR than on the PTR.

An 8-week resistance training protocol is effective in adapting quadriceps but not patellar tendon shear modulus measured by Shear Wave Elastography

Habitual loading and resistance training (RT) can lead to changes in muscle and tendon morphology as well as in its mechanical properties which can be measured by Shear Wave Elastography (SWE) technique. The objective of this study was to analyze the Vastus Lateralis (VL) and patellar tendon (PT) mechanical properties adaptations to an 8-week RT protocol using SWE. We submitted 15 untrained health young men to an 8-week RT directed for knee extensor mechanism. VL and PT shear modulus (μ) were assessed pre and post intervention with SWE. PT thickness (PTT), VL muscle thickness (VL MT) and knee extension torque (KT) were also measure pre and post intervention to ensure the RT efficiency. Significant increases were observed in VL MT and KT (pre = 2.40 ± 0.40 cm and post = 2.63 ± 0.35 cm, p = 0.0111, and pre = 294.66 ± 73.98 Nm and post = 338.93 ± 76.39 Nm, p = 0.005, respectively). The 8-week RT was also effective in promoting VL μ adaptations (pre = 4.87 ± 1.38 kPa and post = 9.08.12 ± 1.86 kPa, p = 0.0105), but not in significantly affecting PT μ (pre = 78.85 ± 7.37 kPa and post = 66.41 ± 7.25 kPa, p = 0.1287) nor PTT (baseline = 0.364 ± 0.053 cm and post = 0.368 ± 0.046 cm, p = 0.71). The present study showed that an 8-week resistance training protocol was effective in adapting VL μ but not PT μ. Further investigation should be conducted with special attention to longer interventions, to possible PT differential individual responsiveness and to the muscle-tendon resting state tension environment.

Computational model for the patella onset

The patella is a sesamoid bone embedded within the quadriceps tendon and the patellar tendon that articulates with the femur. However, how is it formed is still unknown. Therefore, here we have evaluated, computationally, how three theories explain, independently, the patella onset. The first theory was proposed recently, in 2015. This theory suggested that the patella is initially formed as a bone eminence, attached to the anterodistal surface of the femur, while the quadriceps tendon is forming. Thereafter, a joint develops between the eminence and the femur, regulated by mechanical load. We evaluated this theory by simulating the biochemical environment that surrounds the tendon development. As a result, we obtained a patella-like structure embedded within the tendon, especially for larger flexion angles. The second and third theories are the most accepted until now. They state that the patella develops within tendons in response to the mechanical environment provided by the attaching muscles. The second theory analyzed the mechanical conditions (high hydrostatic stress) that (according to previous Carter theories) lead to the differentiation from tendon to fibrocartilage, and then, to bone. The last theory was evaluated using the self-optimizing capability of biological tissue. It was considered that the development of the patella, due to tissue topological optimization of the developing quadriceps tendon, is a feasible explanation of the patella appearance. For both theories, a patella onset was obtained as a structure embedded within the tendon. This model provided information about the relationship between the flexion angle and the patella size and shape. In conclusion, the computational models used to evaluate and analyze the selected theories allow determining that the patella onset may be the result of a combination of biochemical and mechanical factors that surround the patellar tendon development.

Patellar tendon properties distinguish elite from non-elite soccer players and are related to peak horizontal but not vertical power

PURPOSE

To investigate potential differences in patellar tendon properties between elite and non-elite soccer players, and to establish whether tendon properties were related to power assessed during unilateral jumps performed in different directions.

METHODS

Elite (n = 16; age 18.1 ± 1.0 years) and non-elite (n = 13; age 22.3 ± 2.7 years) soccer players performed vertical, horizontal-forward and medial unilateral countermovement jumps (CMJs) on a force plate. Patellar tendon (PT) cross-sectional area, elongation, strain, stiffness, and Young's modulus (measured at the highest common force interval) were assessed with ultrasonography and isokinetic dynamometry.

RESULTS

Elite demonstrated greater PT elongation (6.83 ± 1.87 vs. 4.92 ± 1.88 mm, P = 0.011) and strain (11.73 ± 3.25 vs. 8.38 ± 3.06%, P = 0.009) than non-elite soccer players. Projectile range and peak horizontal power during horizontal-forward CMJ correlated positively with tendon elongation (r = 0.657 and 0.693, P < 0.001) but inversely with Young's modulus (r = - 0.376 and - 0.402; P = 0.044 and 0.031). Peak medial power during medial CMJ correlated positively with tendon elongation (r = 0.658, P < 0.001) but inversely with tendon stiffness (r = - 0.368, P = 0.050).

CONCLUSIONS

Not only does a more compliant patellar tendon appear to be an indicator of elite soccer playing status but it may also facilitate unilateral horizontal-forward and medial, but not vertical CMJ performance. These findings should be considered when prescribing talent selection and development protocols related to direction-specific power in elite soccer players.

Normal Range of Patellar Tendon Elasticity Using the Sharewave Elastography Technique: An In Vivo Study in Normal Volunteers

In-vivo investigation of tendon mechanical properties in healthy subjects using Shear Wave Elastography (SWE) techniques is a relatively new field of study. This work aims to evaluate the elastic properties of the patellar tendon in various knee range of flexion. Twenty healthy adult subjects were enrolled in the study. Shear wave speed (SWS) in the patellar tendon was measured in three different positions: Knee extended, knee semi-flexed (30°), and knee flexed (90°). Mean shear modulus was 50.9 +- 33.1 kPa in knee extension position, 137.5 +- 50.7 kPa in 30° flexion position, and 226.5 +- 60.3 kPa in 90° flexion position. The lowest shear modulus was obtained at rest with the knee in a fully extended position. These results are in agreement with those previously reported on Achilles tendon and triceps muscles. Shear modulus values obtained in our study could be considered as baseline values for further investigations in adults.

Mechanical Analysis of Extra-Articular Knee Ligaments. Part two: Tendon grafts used for knee ligament reconstruction

OBJECTIVES

The aim of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions and to compare those results with the mechanical properties of native knee ligaments.

METHODS

Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar tendon. Uniaxial testing to failure was performed using a standardized method and mechanical properties (elastic modulus, ultimate stress, ultimate strain, strain energy density) were determined.

RESULTS

The elastic modulus of the gracilis tendon (1458±476MPa) (P<0.001) and the semitendinosus tendon (1036±312MPa) (P<0.05) was significantly higher than the ITB (610±171MPa), quadriceps tendon (568±194MPa), and patellar tendon (417±107MPa). In addition, the ultimate stress of the hamstring tendons (gracilis 155.0±30.7MPa and semitendinosus 120.1±30.0MPa) was significantly higher (P<0.001, respectively P<0.05), relative to the ITB (75.0±11.8MPa), quadriceps tendon (81.0±27.6MPa), and patellar tendon (76.2±25.1MPa). A significant difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon (24.6±5.9%) and the hamstrings (gracilis 14.5±3.1% and semitendinosus 17.0±4.0%). No significant difference in strain energy density between the grafts was observed.

CONCLUSIONS

Material properties of common grafts used for knee ligament reconstructions often differ significantly from the original knee ligament which the graft is supposed to emulate.

Shear Wave Elastography Is a Reliable and Repeatable Method for Measuring the Elastic Modulus of the Rectus Femoris Muscle and Patellar Tendon

OBJECTIVES

The purpose of this study was to determine intraobserver, interobserver, and inter-day reliability levels for stiffness measurements of the patellar tendon and rectus femoris muscle using shear wave elastography (SWE).

METHODS

This study was conducted on 12 healthy male individuals. Two examiners measured mean shear wave velocity values of the patellar tendons and rectus femoris muscles of both extremities using a 9L4 (4-9 MHz) transducer and an Acuson S3000 ultrasound system (Siemens Medical Solutions, Mountain View, CA). The elasticity images were acquired by the Virtual Touch tissue imaging quantification technique (Siemens Medical Solutions). Measurements were repeated 20 minutes and 1 week after the first measurements. The reliability of SWE measurements was assessed by means of the intraclass correlation coefficient (ICC).

RESULTS

The 12 participants ranged in age from 19 to 33 years (mean age ± SD, 25.33 ± 4.56 years). For the patellar tendon stiffness measurements with SWE, it was found that intraobserver reliability (ICC, 0.91-0.92) and interday reliability (ICC, 0.81-0.83) were excellent, and interobserver reliability (ICC, 0.71) was good. For the rectus femoris muscle stiffness measurements with SWE, it was found that the intraobserver reliability (ICC, 0.93-0.94), interday reliability (ICC, 0.81-0.91), and interobserver reliability (ICC, 0.95) were perfect.

CONCLUSIONS

Shear wave elastography using the Virtual Touch tissue imaging quantification technique is a reliable and repeatable technique for patellar tendon and rectus femoris stiffness measurements according to intraobserver, interday, and interobserver ICC values.

Sagittal patellar tilt and concomitant quadriceps hypotrophy after tibial nailing

PURPOSE

The aim of the study was to analyse the patellofemoral alignment in the sagittal plane following tibial fracture surgery with intramedullary nailing and its relationship to parapatellar muscle status.

METHODS

The patellofemoral MRI results of 27 patients (15 males and 12 females) treated with locked intramedullary nailing following tibia shaft fracture were reviewed. The mean age of the patients was 41.8 (±15) years. The patella-patellar tendon angle (P-PT) and the distance between the inferior patellar pole and the tibial tubercle (DP-TT) were evaluated for both the operated extremity and the contralateral normal side. MRI assessment of the infrapatellar fat pad, quadriceps, sartorius, gracilis, semi-membranosus muscles and biceps muscles was also carried out. The correlation between the changes in skeletal muscle mass, the volume of the infrapatellar fat pad and the alterations in the DP-TT distances and P-PT angles were analysed.

RESULTS

The quadriceps muscle cross-sectional diameter had a mean of 157.2 mm(2) (115.6/319.5) in the operated extremity, and it was 193 mm(2) (77.6/282.2) in the non-operated normal side (p = 0.001). For the Gracilis muscle, the mean was 84.4 mm(2) (19.7/171) at the operated extremity and 75.7 mm(2) (26.9/238.2) on the normal side (p = 0.05). The cross-sectional areas of the semi-membranosus, sartorius and biceps muscles in the operated and non-operated extremity were not noticeably different (n.s). The P-PT angle was 153° (129.7/156.4) in the operated extremity and 145.7° (137.6/163.4) in the non-operated normal extremity (p < 0.05). While DP-TT distance was 11.4 mm (9.4/20.4) in the operated extremity, it was 14.1 mm (7.3/17.1) in the non-operated extremity (p = 0.001). The correlation analyses revealed that the quadriceps hypotrophy negatively correlated (r = -0.4, p = 0.02) with the P-PT angle but positively correlated with the increase in gracilis muscle volume (r = 0.4, p = 0.03).

CONCLUSION

This study revealed that patellofemoral joint kinematics in the operated extremity was diminished in the sagittal plane correlating with the quadriceps muscle volume loss and gracilis muscle hypertrophy. The modalities focused on both preventing and treating the hypotrophy of the quadriceps muscle following the surgical treatment of tibial fracture, which may help to overcome this quite common pathology.

Are Sport-Specific Profiles of Tendon Stiffness and Cross-Sectional Area Determined by Structural or Functional Integrity?

The present study aimed to determine whether distinct sets of tendon properties are seen in athletes engaged in sports with contrasting requirements for tendon function and structural integrity. Patellar and Achilles tendon morphology and force-deformation relation were measured by combining ultrasonography, electromyography and dynamometry in elite ski jumpers, distance runners, water polo players and sedentary individuals. Tendon cross-sectional area normalized to body mass^2/3 was smaller in water polo players than in other athletes (patellar and Achilles tendon; -28 to -24%) or controls (patellar tendon only; -9%). In contrast, the normalized cross-sectional area was larger in runners (patellar tendon only; +26%) and ski jumpers (patellar and Achilles tendon; +21% and +13%, respectively) than in controls. Tendon stiffness normalized to body mass^2/3 only differed in ski jumpers, compared to controls (patellar and Achilles tendon; +11% and +27%, respectively) and to water polo players (Achilles tendon only; +23%). Tendon size appears as an adjusting variable to changes in loading volume and/or intensity, possibly to preserve ultimate strength or fatigue resistance. However, uncoupled morphological and mechanical properties indicate that functional requirements may also influence tendon adaptations.

Effects of Heavy Strength Training on Running Performance and Determinants of Running Performance in Female Endurance Athletes

Purpose

The purpose of the current study was to investigate the effects of adding strength training to normal endurance training on running performance and running economy in well-trained female athletes. We hypothesized that the added strength training would improve performance and running economy through altered stiffness of the muscle-tendon complex of leg extensors.

Methods

Nineteen female endurance athletes [maximal oxygen consumption (VO_2max): 53±3 ml∙kg^-1∙min^-1, 5.8 h weekly endurance training] were randomly assigned to either normal endurance training (E, n = 8) or normal endurance training combined with strength training (E+S, n = 11). The strength training consisted of four leg exercises [3 x 4–10 repetition maximum (RM)], twice a week for 11 weeks. Muscle strength, 40 min all-out running distance, running performance determinants and patellar tendon stiffness were measured before and after the intervention.

Results

E+S increased 1RM in leg exercises (40 ± 15%) and maximal jumping height in counter movement jump (6 ± 6%) and squat jump (9 ± 7%, p < 0.05). This was accompanied by increased muscle fiber cross sectional area of both fiber type I (13 ± 7%) and fiber type II (31 ± 20%) in m. vastus lateralis (p < 0.05), with no change in capillary density in m. vastus lateralis or the stiffness of the patellar tendon. Neither E+S nor E changed running economy, fractional utilization of VO_2max or VO_2max. There were also no change in running distance during a 40 min all-out running test in neither of the groups.

Conclusion

Adding heavy strength training to endurance training did not affect 40 min all-out running performance or running economy compared to endurance training only.

Acute Effects of Kinesio Taping on Knee Extensor Peak Torque and Stretch Reflex in Healthy Adults

Kinesio Tex tape (KT) is used to prevent and treat sports-related injuries and to enhance muscle performance. It has been proposed that the direction of taping may either facilitate or inhibit the muscle by having different effects on cutaneous receptors that modulate excitability of the motor neurons. This study had 2 goals. First, we wished to determine if KT application affects muscle performance and if the method of application facilitates or inhibits muscle performance. This was assessed by measuring isokinetic knee extension peak torque in the knee extensor. Second, we assessed neurological effects of taping on the excitability of the motor neurons by measuring the reflex latency and action potential by electromyography (EMG) in the patellar reflex. The study was a single-blind, placebo-controlled crossover trial with 28 healthy volunteers with no history of knee injuries. Participants received facilitative KT treatment, inhibitory KT treatment, or Hypafix taping of the knee extensor. There were significant differences in the peak torque between 3 treatments (F(2,54) = 4.873, P < 0.01). Post hoc analysis revealed that facilitative KT treatment resulted in higher knee extensor peak torque performance than inhibitory KT treatment (P = 0.036, effect size 0.26). There were, however, no significant differences in the reflex latency (F(2,54) = 2.84, P = 0.067) nor in the EMG values (F(2,54) = 0.18, P = 0.837) in the patellar reflex between the 3 taping applications. The findings suggest that the direction of KT application over the muscle has specific effects on muscle performance. Given the magnitude of effect is small, interpretation of clinical significance should be considered with caution. The underlying mechanism warrants further investigation.

Improved biomechanical and biological outcomes in the MRL/MpJ murine strain following a full-length patellar tendon injury

Musculoskeletal injuries greatly affect the U.S. population and current clinical approaches fail to restore long-term native tissue structure and function. Tissue engineering is a strategy advocated to improve tendon healing; however, the field still needs to establish biological benchmarks for assessing the effectiveness of tissue-engineered structures. Investigating superior healing models, such as the MRL/MpJ, offers the opportunity to first characterize successful healing and then apply experimental findings to tissue-engineered therapies. This study seeks to evaluate the MRL/MpJ's healing response following a central patellar tendon injury compared to wildtype. Gene expression and histology were assessed at 3, 7, and 14 days following injury and mechanical properties were measured at 2, 5, and 8 weeks. Native patellar tendon biological and mechanical properties were not different between strains. Following injury, the MRL/MpJ displayed increased mechanical properties between 5 and 8 weeks; however, early tenogenic expression patterns were not different between the strains. Furthermore, expression of the cyclin-dependent kinase inhibitor, p21, was not different between strains, suggesting an alternative mechanism may be driving the healing response. Future studies will investigate collagen structure and alignment of the repair tissue and characterize the complete healing transcriptome to identify mechanisms driving the MRL/MpJ response.

Quadrupled Hamstring Graft Strength as a Function of Clinical Sizing

PURPOSE

This study sought to compare the strength of quadrupled hamstring tendon (QHT) grafts of 6 to 9.5 mm in clinical diameter with that of 10-mm bone-patellar tendon-bone (BPTB) grafts.

METHODS

Twenty cadaveric semitendinosus and gracilis tendons were combined into QHT grafts. These were sized using a standard graft-sizing device and an area micrometer, yielding grafts ranging from 6 to 9.5 mm in diameter. The grafts were tested to failure. Five 10-mm BPTB grafts were also sized and tested.

RESULTS

Clinical sizing did predict the strength of the graft but not profoundly. As a material alone, without consideration of fixation in bone tunnels, QHT grafts were stronger than BPTB grafts. Graft strength decreased with size, but a linear relation between strength and diameter (r(2) = 0.715, P < .001) was found to be as good as the expected quadratic fit (r(2) = 0.709). Compared with BPTB grafts, even the smallest QHT grafts (diameter <6.5 mm) were still significantly stronger than 10-mm BPTB grafts (P = .004). The elastic moduli of the QHT and BPTB grafts were 761 ± 187 MPa and 615 ± 403 MPa, respectively; elongations at failure were 12.0% ± 2.0% and 7.5% ± 1.6%, respectively; and failure stresses were 105 ± 18 MPa and 50 ± 14 MPa, respectively.

CONCLUSIONS

This work shows that a clinical size of QHT grafts of 6 mm in diameter is not a concern regarding the strength itself. For a possible lower-end prediction of acceptable size, assuming that a gracilis-semitendinosus graft would have only the stress of the weakest measured QHT graft of 88 MPa, a graft of 5.5 mm in diameter would suffice, having more strength in newtons than the average patellar tendon.

CLINICAL RELEVANCE

Clinically sized QHT grafts have a higher failure strength than 10-mm patellar tendon grafts. Therefore the strength of the graft cannot account for the higher clinical failure rates of smaller hamstring grafts in active patients in clinical studies.

Region-specific tendon properties and patellar tendinopathy: a wider understanding

Patellar tendinopathy is a common painful musculoskeletal disorder with a very high prevalence in the athletic population that can severely limit or even end an athletic career. To date, the underlying pathophysiology leading to the condition remains poorly understood, although reports suggesting that patellar tendinopathy most frequently concerns the proximal posterior region of the tendon has prompted some researchers to examine region-specific tendon properties for a better understanding of the etiology and potential risk factors associated with the condition. However, to date, research concerning the in vivo region-specific tendon properties in relation to patellar tendinopathy is very scarce, perhaps due to the lack of validated techniques that can determine such properties in vivo. In recent years, a technique has been developed involving an automated tendon-tracking program that appears to be very useful in the determination of region-specific tendon properties in vivo. In terms of regional variations in tendon properties, previous research has demonstrated differences in structural, mechanical, and biochemical properties between the discrete regions of the patellar tendon, but the extent to which these regional variations contribute to patellar tendinopathy remains elusive. In addition, with respect to treatment strategies for patellar tendinopathy, previous research has utilized a wide range of interventions, but the use of eccentric exercise (EE) and/or heavy-slow resistance (HSR) training appear to be most promising. However, the optimal program design variables of EE and HSR training that induce the most favorable effects are yet to be determined. This review article provides a detailed discussion of all of the above to allow a better understanding of the etiology and potential risk factors associated with the condition as well as the most effective treatment strategies. First, a comprehensive literature review is provided with respect to region-specific structural, mechanical, and biochemical properties, in association with patellar tendinopathy. Second, the automated tendon-tracking methodology is outlined to assist future researchers in the determination of region-specific tendon properties. Finally, potential treatment strategies are discussed, particularly with regards to the use of EE and HSR training for the management of patellar tendinopathy.

Influence of loading rate on patellar tendon mechanical properties in vivo

BACKGROUND

Rate-dependent properties of tendons have consistently been observed in vitro but in vivo studies comparing the effects of loading duration on this feature remain conflicting. The main purpose of the present study was to evaluate whether tendon loading rate per se would affect in vivo tendon mechanical properties.

METHODS

Twenty-two physically active male subjects were recruited. Patellar tendon deformation was recorded with ultrasonography under voluntary isometric contractions at rates of 50, 80 and 110Nm/s, controlled via visual feedback.

FINDINGS

Subjects were able to accurately generate all three loading rates (Accuracy=2% to 15%), with a greater steadiness at 50 (CV=12.4%) and 110Nm/s (CV=13.1%) than at 80Nm/s (CV=22.9%). Loading rate did not appreciably affect strain or stress. However, stiffness (ɳp(2)=0.555) and Youngs's Modulus (ɳp(2)=0.670) were significantly higher at 80Nm/s (21.4% and 21.6%, respectively) and at 110Nm/s (32.5% and 32.0%, respectively) than at 50Nm/s. Similarly, stiffness and Young's modulus were 9.9% and 8.8% higher, respectively, at 110Nm/s than at 80Nm/s.

INTERPRETATION

These results indicate that in vivo measurements of patellar tendon mechanics are influenced by loading rate. Moreover, they bear important methodological implications for in vivo assessment of mechanical properties of this tendon and possibly other human tendons.

Murine patellar tendon biomechanical properties and regional strain patterns during natural tendon-to-bone healing after acute injury

Tendon-to-bone healing following acute injury is generally poor and often fails to restore normal tendon biomechanical properties. In recent years, the murine patellar tendon (PT) has become an important model system for studying tendon healing and repair due to its genetic tractability and accessible location within the knee. However, the mechanical properties of native murine PT, specifically the regional differences in tissue strains during loading, and the biomechanical outcomes of natural PT-to-bone healing have not been well characterized. Thus, in this study, we analyzed the global biomechanical properties and regional strain patterns of both normal and naturally healing murine PT at three time points (2, 5, and 8 weeks) following acute surgical rupture of the tibial enthesis. Normal murine PT exhibited distinct regional variations in tissue strain, with the insertion region experiencing approximately 2.5 times greater strain than the midsubstance at failure (10.80±2.52% vs. 4.11±1.40%; mean±SEM). Injured tendons showed reduced structural (ultimate load and linear stiffness) and material (ultimate stress and linear modulus) properties compared to both normal and contralateral sham-operated tendons at all healing time points. Injured tendons also displayed increased local strain in the insertion region compared to contralateral shams at both physiologic and failure load levels. 93.3% of injured tendons failed at the tibial insertion, compared to only 60% and 66.7% of normal and sham tendons, respectively. These results indicate that 8 weeks of natural tendon-to-bone healing does not restore normal biomechanical function to the murine PT following injury.

Varying whole body vibration amplitude differentially affects tendon and ligament structural and material properties

Whole Body Vibration (WBV) is becoming increasingly popular for helping to maintain bone mass and strengthening muscle. Vibration regimens optimized for bone maintenance often operate at hypogravity levels (<1G) and regimens for muscle strengthening often employ hypergravity (>1G) vibrations. The effect of vibratory loads on tendon and ligament properties is unclear though excessive vibrations may be injurious. Our objective was to evaluate how tendon gene expression and the mechanical/histological properties of tendon and ligament were affected in response to WBV in the following groups: no vibration, low vibration (0.3G peak-to-peak), and high vibration (2G peak-to-peak). Rats were vibrated for 20 min a day, 5 days a week, for 5 weeks. Upon sacrifice, the medial collateral ligament (MCL), patellar tendon (PT), and the Achilles Tendon (AT) were isolated with insertion sites intact. All tissues were tensile tested to determine structural and material properties or used for histology. Patellar tendon was also subjected to quantitative RT-PCR to evaluate expression of anabolic and catabolic genes. No differences in biomechanical data between the control and the low vibration groups were found. There was evidence of significant weakness in the MCL with high vibration, but no significant effect on the PT or AT. Histology of the MCL and PT showed a hypercellular tissue response and some fiber disorganization with high vibration. High vibration caused an increase in collagen expression and a trend for an increase in IGF-1 expression suggesting a potential anabolic response to prevent tendon overuse injury.

Validation of an empirical damage model for aging and in vivo injury of the murine patellar tendon

While useful models have been proposed to predict the mechanical impact of damage in tendon and other soft tissues, the applicability of these models for describing in vivo injury and age-related degeneration has not been investigated. Therefore, the objective of this study was to develop and validate a simple damage model to predict mechanical alterations in mouse patellar tendons after aging, injury, or healing. To characterize baseline properties, uninjured controls at age 150 days were cyclically loaded across three strain levels and five frequencies. For comparison, damage was induced in mature (120 day-old) mice through either injury or aging. Injured mice were sacrificed at three or six weeks after surgery, while aged mice were sacrificed at either 300 or 570 days old. Changes in mechanical properties (relative to baseline) in the three week post-injury group were assessed and used to develop an empirical damage model based on a simple damage parameter related to the equilibrium stress at a prescribed strain (6%). From the derived model, the viscoelastic properties of the 300 day-old, 570 day-old, and six week post-injury groups were accurately predicted. Across testing conditions, nearly all correlations between predicted and measured parameters were statistically significant and coefficients of determination ranged from R² = 0.25 to 0.97. Results suggest that the proposed damage model could exploit simple in vivo mechanical measurements to predict how an injured or aged tendon will respond to complex physiological loading regimens.

Implementation of an iPhone wireless accelerometer application for the quantification of reflex response

The patellar tendon reflex represents an inherent aspect of the standard neurological evaluation. The features of the reflex response provide initial perspective regarding the status of the nervous system. An iPhone wireless accelerometer application integrated with a potential energy impact pendulum attached to a reflex hammer has been successfully developed, tested, and evaluated for quantifying the patellar tendon reflex. The iPhone functions as a wireless accelerometer platform. The wide coverage range of the iPhone enables the quantification of reflex response samples in rural and remote settings. The iPhone has the capacity to transmit the reflex response acceleration waveform by wireless transmission through email. Automated post-processing of the acceleration waveform provides feature extraction of the maximum acceleration of the reflex response ascertained after evoking the patellar tendon reflex. The iPhone wireless accelerometer application demonstrated the utility of the smartphone as a biomedical device, while providing accurate and consistent quantification of the reflex response.

Biomechanical evaluation of medial patellofemoral ligament reconstruction

BACKGROUND

The medial patellofemoral ligament (MPFL) is the most frequently injured soft tissue structure following acute lateral patellar dislocation. MPFL reconstruction has become a popular option to restore patellar stability following lateral patellar dislocation due to the high incidence of recurrent instability following conservative management. Anatomic reconstruction of the MPFL minimizes graft length changes during full knee range of motion and restores patellar stability.

MATERIALS & METHODS

Four fresh frozen cadaver specimens underwent biomechanical testing in a materials testing machine. With the knee fixed in 30° of flexion, the patella was translated laterally a distance of 10 mm and continuous force-displace- ment data was collected with the intact MPFL and again following a newly described MPFL reconstruction technique. Lateral force-displacement and stiffness data were calculated, allowing comparison between the intact and reconstructed MPFL.

RESULTS

The average lateral restraining force provided by the intact MPFL was 10.6 ± 5.7, 36.6 ± 2.7, and 69.0 ± 5.9 N while the lateral restraining force following MPFL reconstruction was 0.4 ± 4.3, 50.3 ± 16.3, and 110.2 ± 17.5 N at 1, 5, and 10 mm of lateral displacement, respectively.

CONCLUSION

Anatomic MPFL reconstruction displays similar lateral restraining force compared to the intact MPFL at low levels of lateral displacement. At higher levels of displacement, the reconstructed MPFL provides increased lateral restraining force compared to the intact MPFL, improving patellar stability in pathologic knees.

The effects of immobilization on the mechanical properties of the patellar tendon in younger and older men

BACKGROUND

It remains unknown if inactivity changes the mechanical properties of the human patellar tendon in younger and older healthy persons. The purpose was to examine the effects of short-term unilateral immobilization on the structural and mechanical properties of the patellar tendon in older men and younger men, in vivo.

METHODS

Eight older men and eight younger men underwent 14 days of unilateral immobilization. All individuals were assessed on both sides before and after the intervention. MRI was used to assess whole patellar tendon dimensions. The mechanical properties of the patellar tendon were assessed using simultaneous force and ultrasonographic measurements during isometric ramp contractions.

FINDINGS

In older men, tendon stiffness [Pre: mean 2949 (SD 799) vs. Post: mean 2366 (SD 774) N mm(-1), P<0.01] and Young's Modulus [Pre: mean 1.2 (SD 0.3) vs. Post: mean 1.0 (SD 0.3) GPa, P<0.05] declined with immobilization on the immobilized side. On the control side, tendon stiffness [Pre: mean 3340 (SD 1209) vs. Post: mean 2230 (SD 503), P<0.01] and Young's Modulus [Pre: mean 1.5 (SD 0.4) vs. Post: mean 0.9 (SD 0.3) GPa, P<0.05] also decreased with immobilization. In younger men, tendon stiffness [Pre: 3622 (SD 1760) vs. Post: mean 2910 (SD 1528) N mm(-1), P<0.01] and Young's Modulus [Pre: mean 1.7 (SD 1.1) vs. Post: mean 1.4 (SD 0.8) GPa, P<0.05] decreased only on the immobilized side.

INTERPRETATION

Short-term immobilization led to impaired mechanical properties of the patellar tendon on the immobilized side in both younger men and older men, which can influence the function of the muscle-tendon complex.

The magnitude and character of resistance-training-induced increase in tendon stiffness at old age is gender specific

Human tendon mechanical properties are modified with loading. Moreover, there are indications that the training response in the tendon is gender specific. The aim of the current study was to examine whether in vivo patella tendon stiffness (K) differentially alters with training in older males compared with females. We also aimed to identify which endocrine pathway underlies the responses. Maximal knee extensor forces were also monitored to determine the training effect on muscle function. Fourteen healthy, habitually active older persons (seven males aged 74.0 ± 1.2 years (mean±SEM) and seven females aged 76.7 ± 1.2 years) were tested at baseline and after 12 weeks of weekly, progressive resistance training. With training, percentage increase in quadriceps maximum voluntary isometric force (MVC) was similar in males (2,469.6 ± 168.0 to 3,097.3 ± 261.9 N; +25.3 ± 6.1% (p < 0.01)) and females (1,728.8 ± 136.3 to 2,166.5 ± 135.8 N; +30.4 ± 15.1% (p < 0.05)), respectively. K increased more in males (338.0 ± 26.6 to 616.9 ± 58.7 N/mm; 79.8 ± 4.2% (p < 0.001)) compared to females (338.9 ± 31.0 to 373.2 ± 25.8 N/mm; +13.0 ± 3.7% (p < 0.001)). Interestingly, a pattern was found whereby below ~40% MVC, the females showed their greatest degree of K changes, whereas the males showed their greatest degree of K change above this relative force level. This gender contrast was also true at a standardised force level (1,200 N), with 5.8 ± 0.4% vs. 82.5 ± 1.8% increments in the females (i.e. value change from 380.3 ± 14.1 to 402.4 ± 13.3 N/mm) and the males (i.e. value change from 317.8 ± 13.8 to 580.2 ± 30.9 N/mm), respectively (p < 0.001). While circulating levels of both IGF-I and IL-6 did not alter with training, IGFBP-3 showed a significant training effect (19.1 ± 4.8%, p < 0.001) and only in the male sub-group (p = 0.038). We show here that with training, in vivo older females' tendon is less dramatically modulated than that of males'. We also show that the relative forces, at which the greatest adaptations are exhibited, differ by gender, with a suggestion of endocrine adaptations in males only. We thus propose that both training and rehabilitation regimens should consider gender-specific tendon responsiveness, at least in older persons.

Effect of prolotherapy on cellular proliferation and collagen deposition in MC3T3-E1 and patellar tendon fibroblast populations

Proliferative therapy, or prolotherapy, is a treatment for damaged connective tissues involving the injection of a solution (proliferant) which causes local cell death and triggers the body's wound healing cascade. Physicians vary in their use of this technique; it is employed for ligaments but has also been investigated for tissues such as cartilage. Physicians also vary in treatment regiments using different dosses of the proliferant. This study evaluates several proliferant dosages develop an optimal dosage that maximizes cell and collagen regeneration. This study also looks at cell and collagen regeneration in response to proliferant exposure outside of the healing cascade. MC3T3-E1 cells and patellar tendon fibroblasts were exposed to various amounts of the proliferant P2G and monitored over several weeks. The results showed an inverse relationship between proliferant concentration and cell viability and collagen production in MC3T3-E1 cells. Following exposure, cell populations experienced an initial decrease in cell number followed by increased proliferation. Trichrome staining over 4 weeks showed an increase in collagen production after proliferant exposure. However the cell numbers and amounts of collagen from the treated groups never surpassed those of the untreated groups, although collagen production was comparable in fibroblasts. The results of this basic study show that there is an effective proliferant dosage and point to a local response to the proliferant that increases cell proliferation and collagen production separate from the wound healing cascade. This local response may not be adequate for complete healing and assistance from the body's healing cascade may be required.

Site dependence of thickness and speed of sound in articular cartilage of bovine patella

Researchers have made efforts to quantify thickness of articular cartilage as well as its acoustic and mechanical properties using various ultrasound (US) techniques during the last decades, because they are important indicators of articular cartilage degeneration. However, the variation of the thickness and speed of sound of articular cartilage at different anatomical sites would result in the uncertainty of US assessment of degeneration. In this paper, the site dependences of speed of sound and thickness of bovine patellar articular cartilage (n = 10) were investigated using a custom-made US measurement system. The thickness and speed of sound of articular cartilage at different locations of the bovine patella were measured on excised specimens ex situ using a noncontact US approach. A total of 10 patellae were tested. The results showed the overall mean value of the speed of sound in the articular cartilage at the 25 measured sites was 1626 +/- 86 m/s (range, 1507 to 1834 m/s). No statistically significant difference in the speed of sound was observed among the 25 locations or among the four quadrants of the patella. The highest speed of sound (1834 +/- 74 m/s) was obtained at the medial-upper quadrant and the lowest value (1507 +/- 74 m/s) at the medial-lower quadrant. Further grouping of the data revealed that the speed of sound in the central region (1633 +/- 21 m/s) was significantly (p < 0.01) larger than that for the surrounding region (1621 +/- 22 m/s). The overall mean thickness of the patellar articular cartilage was 1.34 +/- 0.34 mm. No significant difference was obtained in the thickness among the 25 locations and also among the four quadrants. However, when the thickness values were divided diagonally, a significant difference (p < 0.01) was observed between the upper region (1.27 +/- 0.11 mm) and the lower region (1.31 +/- 0.41 mm) of the patellae. Although no significant differences in the thickness and speed of sound among the tested sites were observed, it was demonstrated in this study that they did show some degree of site dependence.

Eliminating impingement optimizes patellar biomechanics in high knee flexion

BACKGROUND

We investigated the impact of eliminating the impingement between extensor mechanism and tibial insert on patellar tracking and patellar ligament tension in high knee flexion.

METHODS

Six cadaveric specimens were tested on an Oxford-type testing rig. The Genesis II knee system was implanted into each specimen knee with the traditional tibial insert and high-flex insert successively. Compared to traditional insert, the high-flex insert was characterized with a chambered anterior post and a chambered anterior lip which eliminates patella-post and patellar ligament-anterior lip impingements. The patella was tracked with an NDI Optotrak Certus system. The patellar ligament tension was measured using a NKB S-type tension transducer.

RESULTS

There was a decrease of resultant patellar translation relative to the femur with statistically significant (P<0.05) at 90 degrees to 150 degrees of knee flexion and a decrease of patellar ligament tension with statistical significance (P<0.05) at 100 degrees, 120 degrees, 130 degrees, and 140 degrees of flexion using high-flex insert compared to traditional insert.

CONCLUSIONS

Eliminating the impingement between extensor mechanism and implant in high knee flexion altered patellar tracking and reduced patellar ligament tension, which would facilitate high knee flexion.

Can Patellar Tendon Angle reveal sagittal kinematics in total knee arthroplasty?

The Patellar Tendon Angle is strongly correlated with both patello-femoral and tibio-femoral joint kinematics. Thus, the Patellar Tendon Angle might be regarded as a concise indicator of the antero-posterior translation of the femur with respect to the tibia. Twelve subjects, who had undergone total knee arthroplasty, were investigated by video-fluoroscopy during step-up/down. The kinematics at the replaced knee was reconstructed by means of 3D fluoroscopy. The Patellar Tendon Angle and the knee-flexion angle were measured on sagittal fluoroscopic images with software designed for the purpose. The slope of the linear trend of the Patellar Tendon Angle versus knee-flexion angle relationship correlated significantly with the mean (p = 0.001), most anterior (p = 0.001), and most posterior (p = 0.016) position reached by the femur over the tibia. The Patellar Tendon Angle versus knee-flexion angle relationship provides relevant information about the anterior or posterior positioning of the femur over the tibia, but it cannot be interpreted as quantification of the actual antero-posterior translation of the femur over the tibia.

Rehabilitation following microfracture for chondral injury in the knee

Full-thickness chondral defects in the knee are common, and these articular cartilage lesions may present in various clinical settings and at different ages. Articular cartilage defects that extend full thickness to subchondral bone rarely - by providing a suitable environment for new tissue formation and takes advantage of the body's own healing potential. Proper surgical technique and rehabilitation improve the success rate of the microfracture procedure. The goals are to alleviate the pain and disability that can result from chondral lesions and restore joint conformity, thereby preventing late degenerative changes in the joint.

Effect of lateral heel wedges on sagittal and transverse plane kinematics of trotting Shetland ponies and the influence of feeding and training regimes

REASONS FOR PERFORMING STUDY

Lateral heel wedges are used to treat horses and ponies with patella fixation or bone spavin. However, these therapies are purely empirically based and lack scientific evidence.

OBJECTIVES

Lateral heel wedges would change joint motion in the sagittal, but mainly in the transversal planes, in healthy horses. This effect would be increased by restricted feeding and decreased by extra training.

METHODS

A group of 24 Shetland ponies age 3 years was used, as foals had been assigned to restricted and ad libitum (ad lib) feeding, and low and high level training groups of 6 animals each. An experienced judge evaluated passive patella luxation in the square standing pony, using a score of 0 (normal) to 4 (stationary patella luxation). The motion of the markers, glued to the skin covering skeletal landmarks on the left fore- and hindlimbs, was recorded 3 dimensionally at a frequency of 300 Hz using a modified CODA-3 apparatus while trotting on a treadmill at a speed of 3.0 m/sec, before and directly after 5 degrees lateral heel wedges had been applied to the hindlimbs. After data analysis, the kinematic variables in the sagittal and transversal plane, under these 3 conditions (wedge, feeding, training), were compared statistically using a multivariate repeated measures analysis, general linear model (P < 0.05).

RESULTS

In the sagittal plane, an acute change in hind hoof conformation resulted in a less animated trot with a less protracted forelimb and less hindlimb flexion. This is similar, although less pronounced, to the decrease in limb flexion reported previously as a result of restricted feeding. More specifically, lateral heel wedges resulted in significant changes in the transversal plane angles of all joints in the hindlimb. The stifle joint became maximally 1.8 degrees more adducted just before the end of the stance phase, while the tarsal joint was 2.9 degrees and fetlock joint 4.7 degrees more abducted (P < 0.05). In the restricted feeding group, stifle joint adduction was 85 degrees and tarsal joint abduction 5.6 degrees larger than in the ad libitum feeding group (P < 0.05). The patella luxation score was also significantly higher in this group (1.8) compared to ponies fed ad libitum (0.9).

CONCLUSIONS

The acute effects of lateral heel wedges on the equine locomotor system in the transversal plane movement relieve tension from the medial patellar ligament and decrease pressure on the medial side of the tarsal joint. However, the fetlock joint experiences considerably more out of plane stress. Poor body condition resulted in a 2x worse patella luxation score, while the effect on stifle and tarsal joint movement in the transversal plane was almost 5x and 2x larger, respectively, than a lateral wedge.

POTENTIAL RELEVANCE

The clinical importance of general body condition for maintaining lateral stability in the equine hindlimbs is established, but future research may prove that wedges are beneficial to treat patella fixation and bone spavin in the long term.

Evaluation of bone-tendon junction healing using water jet ultrasound indentation method

The re-establishment of bone-tendon junction (BTJ) tissues with the junction, characterized as a unique transitional fibrocartilage zone, is involved in many trauma and reconstructive surgeries. Experimental and clinical findings have shown that a direct BTJ repair requires a long period of immobilization, which may be associated with a postoperative weak knee. Therefore, it is necessary to evaluate the morphologic and mechanical properties of BTJ tissues in situ to better understand the healing process for the purpose of reducing the adverse effects of immobilization. We previously reported a noncontact ultrasound water jet indentation system for measuring and mapping tissue mechanical properties. The key idea was to utilize a water jet as an indenter as well as the coupling medium for high-frequency ultrasound. In this article, we used ultrasound water jet indentation to evaluate the BTJ healing process. The system's capability of measuring the material elastic modulus was first validated using tissue-mimicking phantoms. Then it was employed to assess the healing of the BTJ tissues after partial patellectomy over time on twelve 18-week-old female New Zealand White rabbits. It was found that in comparison with the normal control samples, the elastic modulus of the fibrocartilage of the postoperative samples was significantly smaller, while its thickness increased significantly. Among the postoperative sample groups, the elastic modulus of the fibrocartilage of the samples harvested at week 18 was significantly higher than those harvested at week 6 and week 12, which was even comparable with the value of the control samples at the same sacrifice time. The results suggested that the noncontact ultrasound water jet indentation system provided a nondestructive way to evaluate the material properties of small animal tissues in situ and thus had the ability to evaluate the healing process of BTJ.

Efficacy and tolerability of eperisone in patients with spastic palsy: a cross-over, placebo-controlled dose-ranging trial

BACKGROUND AND OBJECTIVES

Central muscle relaxants are a clinical option in patients with spastic palsy. Eperisone is a central muscle relaxant used in several conditions, but its therapeutic potential in spastic palsy needs to be verified. This dose-ranging trial compares two doses of eperisone in patients with spastic palsy associated to cerebral or spinal diseases.

PATIENTS AND METHODS

In this randomized, placebo-controlled, double-blind, three-way cross-over study, patients (18-75 years) with spastic palsy received eperisone 150 mg/day, eperisone 300 mg/day, or placebo for 8 weeks. Treatment periods lasted for 14 days. Objective clinical parameters (intensity of spasticity and physiological reflexes) and functional parameters (walking capability, capability to climb stairs, rigidity) were measured. Tolerability was also evaluated.

RESULTS

Eighteen patients were enrolled. The reduction in the intensity of spasticity versus the beginning of each treatment cycle was significant with eperisone 300 mg/day (p = 0.004). Similar findings were observed in the evaluation of patellar reflex (p = 0.01), while the other reflexes were not significantly different. Walking capability was significantly improved with eperisone 300 mg/day (p < 0.05). No significant differences were observed in the capability to climb stairs and in rigidity. A trend towards a reduction in pain was noted with eperisone 300 mg/day versus placebo. The incidence of adverse events was similar in all groups.

DISCUSSION

Eperisone 300 mg/day might be an effective and well-tolerated treatment for spastic palsy. Larger studies are required to further characterize the efficacy of eperisone in this therapeutic area.

The structural properties of the lateral retinaculum and capsular complex of the knee

Although lateral retinacular releases are not uncommon, there is very little scientific knowledge about the properties of these tissues, on which to base a rationale for the surgery. We hypothesised that we could identify specific tissue bands and measure their structural properties. Eight fresh-frozen knees were dissected, and the lateral soft tissues prepared into three distinct structures: a broad tissue band linking the iliotibial band (ITB) to the patella, and two capsular ligaments: patellofemoral and patellomeniscal. These were individually tensile tested to failure by gripping the patella in a vice jaw and the soft tissues in a freezing clamp. Results: the ITB–patellar band was strongest, at a mean of 582 N, and stiffest, at 97 N/mm. The patellofemoral ligament failed at 172 N with 16 N/mm stiffness; the patellomeniscal ligament failed at 85 N, with 13 N/mm stiffness. These structural properties suggest that most of the load in-vivo is transmitted to the patella by the transverse fibres that originate from the ITB.

Treating patellar tendinopathy with Fascial Manipulation

According to Fascial Manipulation theory, patellar tendon pain is often due to uncoordinated quadriceps contraction caused by anomalous fascial tension in the thigh. Therefore, the focus of treatment is not the patellar tendon itself, but involves localizing the cause of this incoordination, considered to be within the muscular fascia of the thigh region. Eighteen patients suffering from patellar tendon pain were treated with the Fascial Manipulation technique. Pain was assessed (in VAS) before (VAS 67.8/100) and after (VAS 26.5/100) treatment, plus a follow-up evaluation at 1 month (VAS 17.2/100). Results showed a substantial decrease in pain immediately after treatment (p<0.0001) and remained unchanged or improved in the short term. The results show that the patellar tendon may be only the zone of perceived pain and that interesting results can be obtained by treating the muscular fascia of the quadriceps muscle, whose alteration may cause motor incoordination and subsequent pathology.

Synovial mesenchymal stem cells accelerate early remodeling of tendon-bone healing

Tendon-bone healing is important for the successful reconstruction of the anterior cruciate ligament by using the hamstring tendon. Mesenchymal stem cells (MSCs) have attracted much interest because of their self-renewing potential and multipotentiality for possible clinical use. We previously reported that MSCs derived from synovium had a higher proliferation and differentiation potential than the other MSCs that we examined. The purpose of this study was to investigate the effect and mechanism of the implantation of the synovial MSCs on tendon-bone healing in rats. Half of the Achilles' tendon grafts of rats were inserted into a bone tunnel from the tibial plateau to the tibial tuberosity with a suture-post fixation. The bone tunnel was filled with MSCs labeled with fluorescent marker DiI or without MSCs as the control. The tendon-bone interface was analyzed histologically, and collagen fibers were quantified. At 1 week, the tendon-bone interface was filled with abundant DiI-positive cells, and the proportion of collagen fiber area was significantly higher in the MSC group than in the control group. By 2 weeks, the proportion of oblique collagen fibers, which appeared to be Sharpey's fibers, was significantly higher in the MSC group than in the control group. At 4 weeks, the interface tissue disappeared, and the implanted tendon appeared to attach to the bone directly in both groups. DiI-labeled cells could no longer be observed. Implantation of synovial MSCs into bone tunnel thus accelerated early remodeling of tendon-bone healing, as shown histologically.

The responses of extrinsic fibroblasts infiltrating the devitalised patellar tendon to IL-1beta are different from those of normal tendon fibroblasts

In order to clarify the role of cytokines in the remodelling of the grafted tendon for ligament reconstruction we compared the responses to interleukin (IL)-1beta, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-beta1 of extrinsic fibroblasts infiltrating the frozen-thawed patellar tendon in rats with that of the normal tendon fibroblasts, in regard to the gene expression of matrix metalloproteinase (MMP)-13, using Northern blot analysis. We also examined, immunohistologically, the local expression of IL-1beta, PDGF-BB, and TGF-beta1 in fibroblasts infiltrating the frozen-thawed patellar tendon. Northern blot analysis showed that fibroblasts derived from the patellar tendon six weeks after the freeze-thaw procedure in situ showed less response to IL-1beta than normal tendon fibroblasts with respect to MMP-13 mRNA gene expression. The immunohistological findings revealed that IL-1beta was over-expressed in extrinsic fibroblasts which infiltrated the patellar tendon two and six weeks after the freeze-thaw procedure in situ, but neither PDGF-BB nor TGF-beta1 was over-expressed in these extrinsic fibroblasts. Our findings indicated that IL-1beta had a close relationship to matrix remodelling of the grafted tendon for ligament reconstruction, in addition to the commencement of inflammation during the tissue-healing process.

The anisotropic compressive mechanical properties of the rabbit patellar tendon

In this study, we examine the transverse and longitudinal compressive mechanical behavior of the rabbit patellar tendon. The anisotropic compressive properties are of interest, because compression occurs where the tendon attaches to bone and where the tendon wraps around bone leading to the development of fibro-cartilaginous matrices. We quantified the time dependent viscoelastic and anisotropic behavior of the tendon under compression. For both orientations, sections of patellar tendon were drawn from mature male white New Zealand rabbits in preparation for testing. The tendons were sequentially compressed to 40% strain at strain rates of 0.1, 1 and 10% strain(s) using a computer-controlled stepper motor driven device under physiological conditions. Following monotonic loading, the tendons were subjected to stress relaxation. The tendon equilibrium compressive modulus was quantified to be 19.49+/-11.46 kPa for the transverse direction and 1.11+/-0.57 kPa for the longitudinal direction. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain(s) in the transverse orientation were 13.48+/-2.31, 18.24+/-4.58 and 20.90+/-8.60 kPa, respectively. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain/s in the longitudinal orientation were 0.19+/-0.11, 1.27+/-1.38 and 3.26+/-3.49 kPa, respectively. The modulus values were almost significantly different for the examination of the effect of orientation on the equilibrium modulus (p=0.054). Monotonic loading of the tendon showed visual differences of the strain rate dependency; however, no significant difference was shown in the statistical analysis of the effect of strain rate on compressive modulus. The statistical analysis of the effect of orientation on compressive modulus showed a significant difference. The difference shown in the orientation analysis validated the anisotropic nature of the tendon.

Gender-specific in vivo measurement of the structural and mechanical properties of the human patellar tendon

Human patellar tendon stress (sigma), strain (epsilon), stiffness (K), and tensile or Young's modulus (E), are determined in vivo through voluntary isometric contractions monitored with B-mode ultrasonography. The limitations in previous studies are: (1) they have generally not accounted for the fact that the distal attachment of the patellar tendon (the tibial tuberosity) also displaces; thus, they have underestimated epsilon (and, hence, injury risk) while overestimating K; (2) no gender effect has been studied despite the fact that females are seen to have higher incidences of tendon-related injuries. The current investigation therefore aimed to determine the gender specific values of sigma, epsilon, K, and E of the patellar tendon while also accounting for distal displacement of the patellar tendon. Healthy young males (aged 23.1 +/- 1.3 years, n = 10) and females (aged 21.3 +/-0.9 years, n = 10) were tested. The maximal epsilon of the young males was approximately 5-10% higher than that reported in earlier literature. Average female versus male values for epsilon, sigma, K, and E, taken at the same force level as the males for comparison purposes, were respectively 10.6 +/- 1.0 versus 9.0 +/- 1.0%, 36.9 +/- 1.4 versus 28.9 +/- 0.9 MPa, 1053 +/- 108 versus 1652 +/- 216 N x mm(-1), and 0.61 +/- 0.08 versus 0.68 +/- 0.10 GPa (p < 0.05). There are gender differences in tendon structural and mechanical properties. The current methodology may be useful in a clinical context where early prediction of injury risk and/or monitoring of reconstructed tendon needs to be an accurate, objective, and reliable method if optimal functionality is to be achieved.

Region specific patellar tendon hypertrophy in humans following resistance training

AIM

To examine if cross-sectional area (CSA) differs along the length of the human patellar tendon (PT), and if there is PT hypertrophy in response to resistance training.

METHODS

Twelve healthy young men underwent baseline and post-training assessments. Maximal isometric knee extension strength (MVC) was determined unilaterally in both legs. PT CSA was measured at the proximal-, mid- and distal PT level and quadriceps muscle CSA was measured at mid-thigh level using magnetic resonance imaging. Mechanical properties of the patellar tendons were determined using ultrasonography. Subsequently, subjects performed 12 weeks of heavy resistance knee extension training with one leg (Heavy-leg), and light resistance knee extension training with the other leg (Light-leg).

RESULTS

The MVC increased for heavy-leg (15 +/- 4%, P < 0.05), but not for light-leg (6 +/- 4%). Quadriceps CSA increased in heavy-legs (6 +/- 1%, P < 0.05) while unchanged in light-legs. Proximal PT CSA (104 +/- 4 mm(2)) was smaller than the mid-tendon CSA (118 +/- 3 mm(2)), which again was smaller than distal tendon CSA (127 +/- 2 mm(2), P < 0.05). Light-leg PT CSA increased by 7 +/- 3% (P < 0.05) at the proximal tendon level, but was otherwise unchanged. Heavy-leg PT CSA increased at the proximal and distal tendon levels by 6 +/- 3% and 4 +/- 2% respectively (P < 0.05), but was unchanged at the mid tendon level. PT stiffness increased in heavy-legs (P < 0.05) but was unchanged in light-legs. Modulus remained unchanged in both legs.

CONCLUSIONS

To our knowledge, this study is the first to report tendon hypertrophy following resistance training. Further, the data show that the human PT CSA varies along the length of the tendon.