Caracterización por Ultrasound Tissue Characterization de los tendones rotulianos de jugadores de baloncesto; comparación entre profesionales versus formativos y asintomáticos versus sintomáticos / Patellar tendon analysis by ultrasound tissue characterization; comparison between professional and amateur basketball players. Asymptomatic versus symptomatic

Introducción: La ecografía convencional permite identificar los cambios macroscópicos que se producen en el tendón patológico, sin embargo, estos cambios no se correlacionan bien con los síntomas o la respuesta al tratamiento. La Ultrasound Tissue Characterization (UTC) evalúa la estructura del tendón en 3 dimensiones y la clasifica en 4 eco-tipos. El objetivo de este estudio fue investigar la estructura del tendón rotuliano de jugadores de baloncesto utilizando la técnica de la UTC y estudiar las diferencias entre jugadores profesionales y formativos, comparando la pierna dominante con la pierna no dominante, y sintomáticos con asintomáticos. Material y métodos: Un total de 40 tendones rotulianos (20 jugadores de baloncesto) se incluyeron en el estudio. La estructura del tendón rotuliano (proximal, medial y distal) se cuantificó mediante UTC en el inicio de la pretemporada. La fiabilidad inter e intraobservador se estudió mediante el coeficiente de correlación intraclase (CCI). Resultados: La edad media de los 10 jugadores profesionales y la de los 10 jugadores formativos fue de 28,1 años (DE 4,5) y 17,6 (DE 1,13), respectivamente. El espesor del tendón rotuliano fue mayor en los jugadores profesionales (p < 0,05), en la pierna dominante (p < 0,05) y en los tendones sintomáticos (p < 0,05). No se encontraron diferencias significativas para los eco-tipos, excepto en el caso del eco-tipo II del tendón rotuliano derecho en la porción proximal entre los jugadores profesionales y los académicos (p = 0,05), y en los eco-tipo III y IV del tendón derecho en su porción proximal entre los jugadores sintomáticos y los asintomáticos (p < 0,05). Se encontró una buena-alta fiabilidad con estas técnicas (CCI = 0,80-0,99). Conclusiones: Se ha caracterizado el patrón ecográfico de los tendones rotulianos de jugadores de baloncesto utilizando UTC. El espesor del tendón rotuliano es mayor en los jugadores profesionales que en los jugadores académicos. También se ha observado mayor grosor de los tendones sintomáticos que de los asintomáticos. No hubo diferencias importantes en el patrón de UTC entre los jugadores profesionales y los académicos ni entre los sintomáticos y los asintomáticos (AU)

Introduction: Conventional ultrasound helps to identify the macroscopic changes produced in the injured tendon. However, these changes do not correlate well with the symptoms or the response to treatment. The ‘characterization of tissues by ultrasound’ (UTC) evaluates the structure of the tendon in 3 dimensions and classifies it into 4 echo-types. The aim of this study was to investigate the structure of the patellar tendon in basketball players using the UTC technique, and to study the differences between professional and amateur players by comparing the dominant leg with the non-dominant one, and the asymptomatic with the asymptomatic ones. Material and methods: The study included 40 patellar tendons (20 basketball players). The structure of the patellar tendon (proximal, medial, and distal) was quantified by means of UTC at the beginning of the pre-season. The within and between observer reliability was measured using the intraclass correlation coefficient (ICC). Results: The mean ages of the 10 professional players and 10 amateur players were 28.1 years (SD 4.5) and 17.6 years (SD 1.3), respectively. The thickness of the patellar tendon was greater in the professional players (P < .05), in the dominant leg (P < .05), and in symptomatic tendons (P < .05). There were no significant differences in the echo-types, except in the case of echotype II in the proximal portion of the right patellar tendon, between professional and amateur players (P = .05). Similarly, there was a difference in echo-type III and IV of the proximal portion of the right tendon between symptomatic and asymptomatic players (P < .05). A good, high reliability was found with these techniques (ICC = .80-.99). Conclusions: The ultrasound pattern of the patellar tendons of basketball players has been characterised using UTC. The thickness of the tendon is greater in professional players than in amateur players. It has also been observed that the symptomatic tendons are thicker than in asymptomatic ones. There were no significant differences in the UTC patterns between professional and amateur players, or between symptomatic and asymptomatic ones (AU)

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 mass2/3 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 mass2/3 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.

Double-Blind Randomized Controlled Trial: Injection of Autologous Blood in the Treatment of Chronic Patella Tendinopathy-A Pilot Study.

OBJECTIVE: To assess the efficacy of autologous blood injections (ABIs) against saline in patients with chronic recalcitrant patella tendinopathy (PT). DESIGN: Double-blind randomized controlled study. SETTING: Homerton Hospital Sports Medicine department. PATIENTS: Those with a diagnosis of refractory patellar tendinopathy were recruited between March 2010 and March 2012. INTERVENTIONS: Using 2 practitioners, patients were randomized to either receive ABIs or saline injections. MAIN OUTCOME MEASURES: All patients completed the Short-Form McGill Pain Questionnaire (MPQ), a visual analog scale (VAS), and a Victoria Institute of Sport Assessment for Patella Tendinopathy scale over a 12-month period. RESULTS: Twenty-two patients completed the final review at 12 months and were included in the study. Subjects ranged in age from 22 and 61 years and were randomized to 11 in each ABI and saline groups. Autologous blood injection group had a mean duration of symptoms of 16.7 months, whereas that of the saline group was 19.2 months. The saline group mean VAS score was reduced from 7.9 to 4.5 at 1 month (P = 0.003) and 3.3 (P = 0.005) at 1 year. With ABI, the score was reduced from 7.5 to 4.5 (P = 0.005) at 1 month and 3.1 (P = 0.003) at 1 year. Victoria Institute of Sport Assessment for Patella Tendinopathy, MPQ, and VAS scores improved significantly in both groups. CONCLUSIONS: This study demonstrated that both the ABI and saline groups experienced a significant improvement in symptoms. However, when the results were compared, there was no statistical difference between the 2 groups. CLINICAL RELEVANCE: This research showed that tendon fenestration is an alternative cost-effective treatment for recalcitrant PT.

Moderate Exercise Mitigates the Detrimental Effects of Aging on Tendon Stem Cells.

Aging is known to cause tendon degeneration whereas moderate exercise imparts beneficial effects on tendons. Since stem cells play a vital role in maintaining tissue integrity, in this study we aimed to define the effects of aging and moderate exercise on tendon stem/progenitor cells (TSCs) using in vitro and in vivo models. TSCs derived from aging mice (9 and 24 months) proliferated significantly slower than TSCs obtained from young mice (2.5 and 5 months). In addition, expression of the stem cell markers Oct-4, nucleostemin (NS), Sca-1 and SSEA-1 in TSCs decreased in an age-dependent manner. Interestingly, moderate mechanical stretching (4%) of aging TSCs in vitro significantly increased the expression of the stem cell marker, NS, but 8% stretching decreased NS expression. Similarly, 4% mechanical stretching increased the expression of Nanog, another stem cell marker, and the tenocyte-related genes, collagen I and tenomodulin. However, 8% stretching increased expression of the non-tenocyte-related genes, LPL, Sox-9 and Runx-2, while 4% stretching had minimal effects on the expression of these genes. In the in vivo study, moderate treadmill running (MTR) of aging mice (9 months) resulted in the increased proliferation rate of aging TSCs in culture, decreased lipid deposition, proteoglycan accumulation and calcification, and increased the expression of NS in the patellar tendons. These findings indicate that while aging impairs the proliferative ability of TSCs and reduces their stemness, moderate exercise can mitigate the deleterious effects of aging on TSCs and therefore may be responsible for decreased aging-induced tendon degeneration.

The time course of in vivo recovery of transverse strain in high-stress tendons following exercise.

OBJECTIVE: To evaluate the time course of the recovery of transverse strain in the Achilles and patellar tendon following a bout of resistance exercise. METHODS: Seventeen healthy adults underwent sonographic examination of the right patellar (n=9) and Achilles (n=8) tendons immediately prior to and following 90 repetitions of weight-bearing quadriceps and gastrocnemius-resistance exercise performed against an effective resistance of 175% and 250% body weight, respectively. Sagittal tendon thickness was determined 20 mm from the enthesis and transverse strain, as defined by the stretch ratio, was repeatedly monitored over a 24 h recovery period. RESULTS: Resistance exercise resulted in an immediate decrease in Achilles (t7=10.6, p<0.01) and patellar (t8=8.9, p<0.01) tendon thickness, resulting in an average transverse stretch ratio of 0.86±0.04 and 0.82±0.05, which was not significantly different between tendons. The magnitude of the immediate transverse strain response, however, was reduced with advancing age (r=0.63, p<0.01). Recovery in transverse strain was prolonged compared with the duration of loading and exponential in nature. The average primary recovery time was not significantly different between the Achilles (6.5±3.2 h) and patellar (7.1±3.2 h) tendons. Body weight accounted for 62% and 64% of the variation in recovery time, respectively. CONCLUSIONS: Despite structural and biochemical differences between the Achilles and patellar tendon, the mechanisms underlying transverse creep recovery in vivo appear similar and are highly time dependent. These novel findings have important implications concerning the time required for the mechanical recovery of high-stress tendons following an acute bout of exercise.

Basic mechanisms of tendon fatigue damage.

Pathologic processes intrinsic and extrinsic to the tendons have been proposed as the underlying cause of rotator cuff disease, but the precise etiology is not known. Tear formation is, in part, attributable to the accumulation of subrupture tendon fatigue damage. We review the molecular, mechanical, and structural changes induced in tendons subjected to controlled amounts of fatigue loading in an animal model of early tendinopathy. The distinct tendon responses to low and moderate levels of loading, as opposed to high levels, provide insight into the potential mechanisms for the therapeutic benefits of exercise in the treatment of rotator cuff tendinopathy. The progression of damage accumulation leading to fiber rupture and eventual tendon tearing seen with higher loading illustrates the progression from tendinopathy to full-thickness tearing. We hope that this more realistic animal model of tendon fatigue damage will allow better assessment of biologic, mechanical, tissue-engineering, and rehabilitation strategies to improve repair success.

Tensile properties of human collagen fibrils and fascicles are insensitive to environmental salts.

To carry out realistic in vitro mechanical testing on anatomical tissue, a choice has to be made regarding the buffering environment. Therefore, it is important to understand how the environment may influence the measurement to ensure the highest level of accuracy. The most physiologically relevant loading direction of tendon is along its longitudinal axis. Thus, in this study, we focus on the tensile mechanical properties of two hierarchical levels from human patellar tendon, namely: individual collagen fibrils and fascicles. Investigations on collagen fibrils and fascicles were made at pH 7.4 in solutions of phosphate-buffered saline at three different concentrations as well as two HEPES buffered solutions containing NaCl or NaCl + CaCl2. An atomic force microscope technique was used for tensile testing of individual collagen fibrils. Only a slight increase in relative energy dissipation was observed at the highest phosphate-buffered saline concentration for both the fibrils and fascicles, indicating a stabilizing effect of ionic screening, but changes were much less than reported for radial compression. Due to the small magnitude of the effects, the tensile mechanical properties of collagen fibrils and fascicles from the patellar tendon of mature humans are essentially insensitive to environmental salt concentration and composition at physiological pH.

A mechanistic study for strain rate sensitivity of rabbit patellar tendon.

The ultrastructural mechanism for strain rate sensitivity of collagenous tissue has not been well studied at the collagen fibril level. Our objective is to reveal the mechanistic contribution of tendon's key structural component to strain rate sensitivity. We have investigated the structure of the collagen fibril undergoing tension at different strain rates. Tendon fascicles were pulled and fixed within the linear region (12% local tissue strain) at multiple strain rates. Although samples were pulled to the same percent elongation, the fibrils were noticed to elongate differently, increasing with strain rate. For the 0.1, 10, and 70%/s strain rates, there were 1.84±3.6%, 5.5±1.9%, and 7.03±2.2% elongations (mean±S.D.), respectively. We concluded that the collagen fibrils underwent significantly greater recruitment (fibril strain relative to global tissue strain) at higher strain rates. A better understanding of tendon mechanisms at lower hierarchical levels would help establish a basis for future development of constitutive models and assist in tissue replacement design.

Lower strength of the human posterior patellar tendon seems unrelated to mature collagen cross-linking and fibril morphology.

The human patellar tendon is frequently affected by tendinopathy, but the etiology of the condition is not established, although differential loading of the anterior and posterior tendon may be associated with the condition. We hypothesized that changes in fibril morphology and collagen cross-linking would parallel differences in material strength between the anterior and posterior tendon. Tendon fascicles were obtained from elective ACL surgery patients and tested micromechanically. Transmission electron microscopy was used to assess fibril morphology, and collagen cross-linking was determined by HPLC and calorimetry. Anterior fascicles were markedly stronger (peak stress: 54.3 +/- 21.2 vs. 39.7 +/- 21.3 MPa; P < 0.05) and stiffer (624 +/- 232 vs. 362 +/- 170 MPa; P < 0.01) than posterior fascicles. Notably, mature pyridinium type cross-links were less abundant in anterior fascicles (hydroxylysylpyridinoline: 0.859 +/- 0.197 vs. 1.416 +/- 0.250 mol/mol, P = 0.001; lysylpyridinoline: 0.023 +/- 0.006 vs. 0.035 +/- 0.006 mol/mol, P < 0.01), whereas pentosidine and pyrrole concentrations showed no regional differences. Fibril diameters tended to be larger in anterior fascicles (7.819 +/- 2.168 vs. 4.897 +/- 1.434 nm(2); P = 0.10). Material properties did not appear closely related to cross-linking or fibril morphology. These findings suggest region-specific differences in mechanical, structural, and biochemical properties of the human patellar tendon.

The effect of cryopreservation or heating on the mechanical properties and histomorphology of rat bone-patellar tendon-bone.

The effects of cryopreservation on tendon allograft have been reported, but remain unclear, particularly the potential effects on mechanical properties and histological changes by ice crystal formation. There are also few studies about effects of heating for sterilization of tendon. We evaluated the effect of cryopreservation or heating on the mechanical properties and histomorphology of rat bone-patellar tendon-bones (BTBs). BTBs were processed by cryopreservation at -80 degrees C for 3 weeks, or heating at 80 degrees C for 10 min. Tensile testing and histomorphological examination were performed. The cryopreservation of tendons showed less influences on their mechanical properties. When cryopreserved BTBs in frozen state were fixed by freeze-substitution method, many spaces were observed in interfibrillar substances. These results suggest that the collagen fibers of cryopreserved tendons were histomorphologically affected by ice crystals. The heating of tendons completely destroyed the collagen fibers of the tendons and is therefore thought to be inappropriate for the sterilization of BTBs.

Structure relates to elastic recoil and functional role in quadriceps tendon and patellar ligament.

Tendons and ligaments have similar but slightly different structure and composition. Crimps of tendons and ligaments are morphological structures related to the elastic functional properties of these connective tissues. Aim of this study was to investigate the morphological arrangement of collagen fibres, fibrils and crimping pattern of suprapatellar (rectus femoris tendon-RFT and vastus intermedius tendon-VIT) and infrapatellar connective tissues (patellar ligament-PL) to relate their structural aspects to their common function role of leg extension. RFT, VIT and PL were removed from knees of Sprague-Dawley rats and light and electron microscopy (TEM and SEM) performed. Sagittal sections showed that collagen array and crimping pattern were similar in RFT and PL but differed from VIT. Morphometric analysis confirmed that crimp number was about the same in RFT and PL (5.4+/-1.4 and 6.1+/-2.8 respectively), but it was almost three times higher in VIT (14.5+/-4.7). Similarly crimp top angle in RFT and PL (141.5+/-15.0 degrees and 146.2+/-12.2 degrees respectively) was significantly higher than in VIT (122.3+/-14.8 degrees ) and the crimp base length was more than twice as wide in RFT (75.5+/-22.6microm) and PL (72.3+/-28.9microm) than in VIT (36+/-14.1microm). The smaller, fewer and most crimped crimps in VIT show that this tendon has a greater elastic recoil and responds to higher forces as among quadriceps muscles the vastus intermedius belly contributes the most during knee extension. By contrast, RFT acting as a "stopper" tendon also plays a ligament role by limiting an excessive flexion of the joint during postural rest position of the knee.

Variation of diameter distribution, number density, and area fraction of fibrils within five areas of the rabbit patellar tendon.

The purpose of this investigation is to show microstructural information at various regions within the rabbit patellar tendon. The properties of the rabbit patellar tendon are well documented mechanically, but detailed information at the microscopic level is not available. Increasing attention has been directed to soft tissue microscopy as the demand for development of biologically inspired materials increases. Microstructural examination of the tendon fibrils is performed to provide further insight into understanding of the structure to function relations within the rabbit patellar tendon. Limited studies on rabbit patellar tendon collagen fibrils at the microscopic level have been computed. Furthermore, evaluation of structure-function relations in multiple regions of any given specimen of a particular tissue type has not been conducted. In this study the number density, area fraction, and diameter distribution of collagen fibrils have been determined. Overall, this examination showed considerable variation within each section of the tendon. Correlating these structural results with mechanical tests of the tendon portions in the various regions could provide additional information on the mechanics of the rabbit tendon as well as insight into development of artificial tissue constructs.

A histological and ultrastructural evaluation of the patellar tendon 10 years after reharvesting its central third.

PURPOSE: This study was undertaken to evaluate the histologic and ultrastructural characteristics of the patellar tendon 10 years after reharvesting its central third. HYPOTHESIS: In the long term, after its central third is reharvested, the patellar tendon does not regain a normal histological and ultrastructural appearance. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Twelve consecutive patients (4 women, 8 men) who underwent anterior cruciate ligament revision surgery using reharvested ipsilateral patellar tendon autografts were included in the study. Percutaneous biopsy samples were obtained from the central and lateral parts of the patellar tendon under ultrasonographic guidance at a median of 116 months (range, 102-127 months) after the revision procedure. Eleven biopsy specimens from asymptomatic patellar tendons obtained from open anterior cruciate ligament reconstructions served as controls. The histologic characteristics and the presence of glycosaminoglycans were assessed using a light microscope, and the ultrastructure was assessed using a transmission electron microscope. RESULTS: The histological evaluation revealed deterioration in fiber structure, increased cellularity, and increased vascularity in both the central and peripheral parts of the reharvested patellar tendon specimens compared with normal tendon specimens. No difference in the amount of glycosaminoglycans was seen in specimens from either part of the reharvested patellar tendons and the control specimens. The ultrastructural evaluation revealed that all the control specimens had a normal morphologic appearance and a compact extracellular matrix with regularly oriented collagen fibrils. Furthermore, in the control specimens, the fibril diameter was heterogeneous, with all fibril size classes present. Specimens from the central and the lateral part of the reharvested tendon displayed pathological cell appearance and a more heterogeneous extracellular matrix. The lateral specimens from the reharvested tendons also displayed all fibril size classes but with a more homogeneous distribution. In the central specimens, the largest fibril size class was absent. CONCLUSION: Ten years after its central third was reharvested for anterior cruciate ligament revision surgery, the patellar tendon had not normalized in terms of its histological and ultrastructural appearance.

Lateral force transmission between human tendon fascicles.

Whether adjacent collagen fascicles transmit force in parallel is unknown. The purpose of the present study was to examine the magnitude of lateral force transmission between adjacent collagen fascicles from the human patellar and Achilles tendon. From each sample two adjacent strands of fascicles (phi 300-530 mum) enclosed in a fascicular membrane were dissected. The specimen was deformed to approximately 3% strain in three independent load-displacement cycles in a small-scale tensile testing device. Cycle 1: the fascicles and the fascicular membrane were intact. Cycle 2: one fascicle was transversally cut while the other fascicle and the fascicular membrane were kept intact. Cycle 3: both fascicles were cut in opposite ends while the fascicular membrane was left intact. A decline in peak force of 45% and 55% from cycle 1 to cycle 2, and 93% and 92% from cycle 2 to cycle 3 was observed in the patellar and Achilles tendon fascicles, respectively. A decline in stiffness of 39% and 60% from cycle 1 to cycle 2, and of 93% and 100% from cycle 2 to cycle 3 was observed in the patellar and Achilles tendon fascicles, respectively. The present data demonstrate that lateral force transmission between adjacent collagen fascicles in human tendons is small or negligible, suggesting that tendon fascicles largely act as independent structures and that force transmission principally takes place within the individual fascicles.

Calcific tendonitis : a model.

Calcific tendonitis is a common clinical condition associated with high rates of tendon rupture, prolonged symptoms, and poor response to therapy. Little is known about the pathogenesis of calcifications in tendons and consequently few effective therapies are available. We hypothesized that tendon calcification, like pathologic calcification in other sites, was generated by extracellular organelles known as matrix vesicles and that isolated matrix vesicles would constitute the basis for a useful model of this process. Tendon matrix vesicles were isolated from adult porcine patellar tendons using enzymatic digestion and differential centrifugation. Vesicle morphology was examined with electron microscopy. Levels of calcium, phosphate, pyrophosphate, ATP, and mineralization-associated enzymes were measured and compared with articular cartilage vesicles from porcine articular cartilage. Vesicles were embedded in agarose gels with or without type I collagen or dermatan sulfate and incubated in calcifying salt solution trace labeled with (45)calcium. (45)Calcium in the vesicle fraction was measured after 5-7 days. The type of mineral formed was determined by micro-x-ray diffraction. Matrix vesicles isolated from adult porcine tendon were similar morphologically to those obtained from articular cartilage. They contained mineralization-related enzymes and formed hydroxyapatite mineral in vitro. Mineralization was suppressed by levamisole and modulated by extracellular matrix components. Matrix vesicles isolated from tendons mineralize in vitro. This model may aid in the study of the pathogenesis of calcific tendonitis as well as serve as a means to identify effective therapies for this common disorder.

Tendons and ligaments are anatomically distinct but overlap in molecular and morphological features--a comparative study in an ovine model.

Tendons and ligaments are similar in composition but differ in function. Simple anatomical definitions do not reflect the fact individual tendons and ligaments have unique properties due to their adaptation to a specific role. The patellar tendon is a structure of particular clinical interest. A null hypothesis was declared stating that the patellar tendon is not significantly different in terms of matrix composition and collagen fibril diameter to other tendons. The lateral and medial collateral ligaments (LCL, MCL), anterior and posterior cruciate ligaments (ACL, PCL), together with the long digital extensor, superficial digital extensor, and patellar tendons (LDET, SDFT, PT) were harvested from three cadaveric ovine hindlimbs. The extracellular matrix was assessed in terms of water, collagen, and total sulphated glycosaminoglycan (GAG) content. The organization of the collagen component was determined by an ultrastructural analysis of collagen fibril diameter distributions, together with values for the collagen fibril index (CFI) and mass-average diameter (MAD). There were significant differences between ligaments and tendons. The PT had a bimodal collagen fibril diameter distribution with CFI 72.9%, MAD 202 nm, water content 53.1%, GAG content 2.3 microg/mg, and collagen content 73.7%, which was not significantly different from the other tendons. The results of this study support the null hypothesis suggesting that the patellar tendon is similar to other tendons and demonstrate that tendons have different characteristics to ligaments.

Ultrastructural collagen fibril alterations in the patellar tendon 6 years after harvesting its central third.

BACKGROUND: Clinically, donor site problems are common, even in the long term after anterior cruciate ligament reconstruction using patellar tendon autograft. However, there is a lack of knowledge in terms of the mid- and long-term ultrastructural appearance of the previously harvested tendon in humans. HYPOTHESIS: The patellar tendon does not regain normal ultrastructure 6 years after harvesting its central third and leaving the defect open. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Thirteen patients were included in the study. Biopsy specimens were obtained from the central and lateral thirds of the patellar tendon under ultrasound guidance 71 months (range, 68-73 months) after the reconstruction. Ten biopsy specimens from other subjects with asymptomatic patellar tendons served as controls. The sections were evaluated using transmission electron microscopy. Longitudinal sections were used for morphological evaluation, and the fibril diameter was measured on the transverse sections and grouped into 5 diameter classes. RESULTS: All control specimens were found to have a compact extracellular matrix with regularly oriented collagen fibrils. Specimens from the lateral part of the harvested tendons displayed a more heterogeneous extracellular matrix. In 3 specimens, the extracellular matrix was different from that of the control specimens. Specimens from the central part of the harvested tendons displayed an even more heterogeneous extracellular matrix, with 8 specimens judged as heterogeneous. The fibril diameter in control specimens displayed the most heterogeneous pattern, and all 5 fibril classes were present. All fibril classes were found in the lateral biopsy specimens from the previously harvested tendons, but the 2 smallest fibril classes (0-30 and 31-60 nm) were significantly more dominant compared with control specimens (P < .0001). In the central specimens from the previously harvested tendons, only the 3 smallest size classes were found (P < .0001 vs controls). CONCLUSION: Six years after harvesting its central third and leaving the defect open, the patellar tendon revealed a "more heterogeneous matrix" with changes in ultrastructural morphology and relative fibril diameter distribution compared with normal control tendon.

Neoligamentization process of BTPB used for ACL graft: histological evaluation from 6 months to 10 years.

Following anterior cruciate ligament (ACL) reconstruction with the middle third part patellar tendon, the graft undergoes histological rearrangement due to biomechanical action, which transforms it into a structure similar to the normal ACL. The purpose of our study was to make a qualitative and quantitative histological evaluation, by transmission electron microscopy (TEM), of the neoligamentization process of a bone-patellar tendon-bone (BTPB) graft used as pro-ACL at different follow-up times. We analysed the ultrastructure of collagen fibrils by focusing on their size and distribution with respect to a normal patellar tendon and a normal ACL used as controls. Our results showed that up to 24 months follow-up, progressive ultrastructural changes towards the normal ACL were observed. At longer times after surgery (48 and 120 months) no further changes were evident and the ultrastructure showed a marked reduction in large fibrils, which was typical of the control patellar tendon, and a significant increase in small fibrils. The ultrastructure seemed to combine fibrils from two different morphological units. The BPTB graft used as ACL underwent a transformation process for up to two years. After that period the transformation ceased and for ten years failed to reach the ultrastructural aspect of a normal ACL. However, from an architectural point of view the graft was slowly transformed into a structure similar to ACL with respect to the different mechanical stresses the ligament has to sustain.

The effect of hyaluronan on tendon healing in rabbits.

PURPOSE: Enhancement of the healing of the tendon-bone junction is important for anterior cruciate ligament reconstruction using the hamstring tendon. We examined the effect of hyaluronan injection into the bone tunnel on the healing of the tendon-bone junction. TYPE OF STUDY: Experimental study. METHODS: The medial half of the patella tendon of Japanese white rabbits was detached from the tibial insertion and transplanted into a drill hole in the tibial tuberosity with a pullout fixation. The bone tunnel was filled with 0.5 mL of hyaluronan (MW, 0.8 million) or without hyaluronan in the contralateral knee as the control. Biomechanical testing was performed at 3 (n = 6) and 6 weeks (n = 4) with histologic analysis (n = 3). RESULTS: Maximum failure load of the patella-patellar tendon-tibia complex in the knee treated with hyaluronan was higher than that in the control side in each rabbit at 3 weeks: 98 +/- 6 N in the hyaluronan group and 76 +/- 12 N in the control group (P < .01). Histologic analysis showed that hyaluronan improved tendon healing. Although maximum failure load increased in both groups, the failure load was not significant at 6 weeks. CONCLUSIONS: Our study found improved tendon healing to bone in the first 3 weeks for Japanese white rabbits treated with hyaluronan. CLINICAL RELEVANCE: Because hyaluronan treatment produces a clinical effect, even in only the early phase after ligament surgery, it could improve rehabilitation and produce a better outcome for ligament reconstruction.

Viability of allogeneic bone marrow stromal cells following local delivery into patella tendon in rabbit model.

Bone marrow stromal cells are potentially useful for tendon repair and regeneration. To provide lasting benefits, the seeded cells must survive implantation at local tendon sites. Our objective was to determine the in vivo fate of allogeneic bone marrow stromal cells (bMSCs) at different time points after implantation into patella tendon defects (i.e., at 2, 3, 5, and 8 weeks). The protocol involved the labeling of bMSCs with green fluorescent protein (GFP) or carboxyfluorescein diacetate (CFDA) before implantation. A window defect (5 x 5 mm) was created at the central portion of rabbit patella tendon and subsequently treated with GFP- or CFDA-marked bMSCs. The marked bMSCs were loaded into the window defect with fibrin glue. Upon sacrifice of the rabbits at the different time points, the implant site of the patellar tendon was immediately retrieved and the viability of the labeled cells was assessed under confocal microscopy. The results showed that the seeded bMSCs remained viable within the tendon wound site for at least 8 weeks after implantation. The cell morphology was changed from a round shape at 2 weeks to a spindle shape at 5 weeks after implantation. This study demonstrated that the bMSCs remained viable for prolonged periods after implantation and therefore have the potential to influence the formation and remodeling of neotendon tissue after tendon repair.