Protein Levels and Microstructural Changes in Localized Regions of Early Cartilage Degeneration Compared with Adjacent Intact Cartilage.

OBJECTIVE: It was hypothesized that the respective protein profiles of bovine cartilage from sites of localized mild to moderate (GI to GII) degeneration versus adjacent sites of intact tissue would vary in accordance with the tissue microstructural changes associated with a pre-osteoarthritic state. METHODS: A total of 15 bovine patellae were obtained for this study. Paired samples of tissue were collected from the lateral region of each patella. If the patella contained a site of degeneration, a paired tissue set involved taking one sample each from the degenerated site and the intact tissue adjacent to it. Sufficient tissue was collected to facilitate 2 arms of investigation: microstructural imaging and proteome analysis. The microstructural analysis used a bespoke tissue preparation technique imaged with differential interference contrast optical microscopy to assess fibrillar scale destructuring and underlying bone spicule formation. An iTRAQ-based proteome analysis was performed using liquid chromatography-tandem mass spectrometry to identify the differential levels of proteins across the intact and degenerated cartilage and further, the results were validated with multiple reaction monitoring assay. RESULTS: In the healthy cartilage pairs, there was no significant variation in protein profiles between 2 adjacent sample sites. In pairs of tissue that contained a sample of GI/GII tissue, there were both significant microstructural changes as well as the difference in abundance levels of 24 proteins. CONCLUSIONS: From the known functions of the 24 proteins, found to be strongly aligned with the specific microstructural changes observed, a unique "proteins ensemble" involved in the initiation and progression of early cartilage degeneration is proposed.

Ontogenetic variation in the sensory structures on the pedipalps of cosmetid harvestmen (Arachnida, Opiliones, Laniatores).

In arachnids, pedipalps are highly variable appendages that may be used in feeding, courtship, defense, and agonistic encounters. In cosmetid harvestmen, adults have pedipalps that feature flattened femora, spoon-shaped tibiae, and robust tarsal claws. In contrast, the pedipalps of nymphs are elongate with cylindrical podomeres and are adorned with delicate pretarsi. In this study, we used scanning electron microscopy to examine the distribution of cuticular structures (e.g., sensilla chaetica, pores) on the elements of the pedipalps of adults and nymphs of three species of cosmetid harvestmen. Our results indicate that there is considerable ontogenetic variation in the morphology of the trochanter, femur, patella, tibia, and tarsus. The pretarsus of the nymph has a ventral patch of setae that is absent from the adult tarsal claw. We observed this structure on all three cosmetid species as well as on the pedipalps of an additional seven morphospecies of nymphs collected in Belize and Costa Rica. This structure may represent a previously unrecognized autapomorphy for Cosmetidae. Examinations of the pedipalps of antepenultimate nymphs of additional gonyleptoidean harvestmen representing the families Ampycidae, Cranaidae, Manaosbiidae, and Stygnidae revealed the occurrence of unusual, plumose tarsal setae, but no setal patches on the tarsal claw.

The effect of hip adduction angle on patellar position measured using real time ultrasound scanning.

INTRODUCTION: There are limited in vivo studies investigating the influence of the Iliotibial Band (ITB) on patellar position, despite numerous references in the literature to this relationship. The purpose of this study was to investigate how the ITB influences patellar position, in vivo, indirectly through alteration of frontal plane hip position. METHOD: Twelve healthy, asymptomatic, male subjects (age 23 ± 2.6 years) had their patellar position examined using real time ultrasound scanning. The knee was passively placed into 20° flexion and combined with hip neutral, 20° hip adduction and 20° hip abduction. Mean patellar position (distance from the lateral border of the patella to the edge of the intersection of the trochlear groove and lateral femoral condyle) was measured, with the smaller values representing a position whereby the patella is drawn more laterally and closer to the lateral femoral condyle. RESULTS: Mean patellar position for neutral was 8.1mm (± 1.72 mm). Following 20° hip abduction the mean patellar position was 8.9 mm (± 1.7 9 mm), this was a statistically significant change in patellar position (p=0.003). Following 20° hip adduction the mean patellar displacement was 7.3mm (± 1.4mm) which, again, was a statistically significant change in patellar position (p=0.009). The results indicate that with the hip adduction the patella was positioned significantly more laterally (smaller value for distance). DISCUSSION: The results of this study support the hypothesis that hip adduction which is likely to create loading and lengthening of the ITB causes significantly greater lateral displacement of the patella, than when the hip is abducted and the ITB unloaded.

Comparative and morphological analysis of commonly used autografts for anterior cruciate ligament reconstruction with the native ACL: an electron, microscopic and morphologic study.

Ligaments and tendons are similar in composition but differ in proportion and arrangement. Tendons are being used as grafts for the ACL reconstruction. Their microscopic structure has not been sufficiently studied and compared to the native ACL. A null hypothesis was declared stating that the anterior cruciate ligament should be histological, morphologically and functionally different from the tendon grafts used for ACL reconstruction. We investigated similarities and differences of the structure of ACL and tendons used as a graft tissue for ACL reconstruction. In this study, standardized samples of quadriceps, hamstrings (semitendinosus and gracilis) and patellar tendons, and the ACL were harvested from 26 autopsies (average age 36.4) and were investigated using light and electron microscopy, immunohistochemistry and morphometry. The thickness of the collagen fibrils, collagen organization and diameter, the fibril/interstitium ratio, density of fibroblasts and blood vessels, and distribution of the collagen type I, III and V fibrils were analyzed. The semitendinosus showed the highest density of fibroblasts and blood vessels, while the gracilis the highest fibril/interstitium ratio. No differences regarding the thickness of collagen fibrils and distribution of fibrils were found. The ACL had the highest concentration of type III and V collagen fibrils as well as elastic fibers. The histological and ultrastructural appearance of the ACL differs from those of the tendons used as graft, for ACL reconstruction. Its ultrastructure is varied and complex, with its collagen fibers bundles lying in many directions.

Platelet-rich plasma enhances the initial mobilization of circulation-derived cells for tendon healing.

Circulation-derived cells play a crucial role in the healing processes of tissue. In early phases of tendon healing processes, circulation-derived cells temporarily exist in the wounded area to initiate the healing process and decrease in number with time. We assumed that a delay of time-dependent decrease in circulation-derived cells could improve the healing of tendons. In this study, we injected platelet-rich plasma (PRP) containing various kinds of growth factors into the wounded area of the patellar tendon, and compared the effects on activation of circulation-derived cells and enhancement of tendon healing with a control group (no PRP injection). To follow the circulation-derived cells, we used a green fluorescent protein (GFP) chimeric rat expressing GFP in the circulating cells and bone marrow cells. In the PRP group, the numbers of GFP-positive cells and heat-shock protein (HSP47; collagen-specific molecular chaperone)-positive cells were significantly higher than in the control group at 3 and 7 days after injury. At the same time, the immunoreactivity for types I and III collagen was higher in the PRP group than in the control group at early phase of tendon healing. These findings suggest that locally injected PRP is useful as an activator of circulation-derived cells for enhancement of the initial tendon healing process.

High-resolution diffusion tensor imaging of human patellar cartilage: feasibility and preliminary findings.

MR diffusion tensor imaging (DTI) was used to analyze the microstructural properties of articular cartilage. Human patellar cartilage-on-bone samples were imaged at 9.4T using a diffusion-weighted SE sequence (12 gradient directions, resolution = 39 x 78 x 1500 microm(3)). Voxel-based maps of the mean diffusivity, fractional anisotropy (FA), and eigenvectors were calculated. The mean diffusivity decreased from the surface (1.45 x 10(-3) mm(2)/s) to the tide mark (0.68 x 10(-3) mm(2)/s). The FA was low (0.04-0.28) and had local maxima near the surface and in the portion of the cartilage corresponding to the radial layer. The eigenvector corresponding to the largest eigenvalue showed a distinct zonal pattern, being oriented tangentially and radially in the upper and lower portions of the cartilage, respectively. The findings correspond to current scanning electron microscopy (SEM) data on the zonal architecture of cartilage. The eigenvector maps appear to reflect the alignment of the collagenous fibers in cartilage. In view of current efforts to develop and evaluate structure-modifying therapeutic approaches in osteoarthritis (OA), DTI may offer a tool to assess the structural properties of cartilage.

Are unilateral and bilateral patellar tendinopathy distinguished by differences in anthropometry, body composition, or muscle strength in elite female basketball players?

BACKGROUND: Overuse injury to the patellar tendon (patellar tendinopathy) is a major reason for interrupted training and competition for elite athletes. In both sexes, the prevalence of unilateral and bilateral tendinopathy has been shown to differ. It has been proposed that bilateral pathology may have a different aetiology from unilateral pathology. Investigation of risk factors that may be unique to unilateral and bilateral patellar tendinopathy in female athletes may reveal insights into the aetiology of this condition. OBJECTIVES: To examine whether anthropometry, body composition, or muscle strength distinguished elite female basketball players with unilateral or bilateral patellar tendinopathy. METHODS: Body composition, anthropometry, and muscle strength were compared in elite female basketball players with unilateral (n = 8), bilateral (n = 7), or no (n = 24) patellar tendinopathy. Body composition was analysed using a dual energy x ray absorptiometer. Anthropometric measures were assessed using standard techniques. Knee extensor strength was measured at 180 degrees /s using an isokinetic dynamometer. z scores were calculated for the unilateral and bilateral groups (using the no tendinopathy group as controls). z scores were tested against zero. RESULTS: The tibia length to stature ratio was approximately 1.3 (1.3) SDs above zero in both the affected and non-affected legs in the unilateral group (p<0.05). The waist to hip ratio was 0.66 (0.78) SD above zero in the unilateral group (p<0.05). In the unilateral group, leg lean to total lean ratio was 0.42 (0.55) SD above zero (p<0.07), the trunk lean to total lean ratio was 0.63 (0.68) SD below zero (p<0.05), and leg fat relative to total fat was 0.47 (0.65) SD below zero (p<0.09). In the unilateral group, the leg with pathology was 0.78 (1.03) SD weaker during eccentric contractions (p<0.07). CONCLUSIONS: Unilateral patellar tendinopathy has identifiable risk factors whereas bilateral patellar tendinopathy may not. This suggests that the aetiology of these conditions may be different. However, interpretation must respect the limitation of small subject numbers.

The effect of normal saline irrigation at different temperatures on the surface of articular cartilage: an experimental study in the rat.

PURPOSE: To determine, with an electron microscope, the effects of irrigation fluid at different temperatures on the surface of articular cartilage. TYPE OD STUDY: Experimental in vivo study. METHODS: With a scanning electron microscope, we investigated the effect of 2 hours of irrigation with normal saline at 3 different temperatures (4 degrees C, 25 degrees C, and 37 degrees C) on articular hyaline cartilage in an in vivo rat knee model study. The contralateral knees were used as controls. We then compared the results. RESULTS: Specimens irrigated with cold (4 degrees C) fluid seemed to show the most uneven surface and apparent fibril exposure. Those irrigated with fluid close to body temperature (37 degrees C) showed the most even surface without fibril exposure. CONCLUSIONS: Although further work is needed to evaluate the long-term effects, using warm irrigation fluid to maintain the intra-articular environment at a more physiologically normal temperature may help reduce damage to cartilage during irrigation.

Patellar component stability improves with pulsatile lavage in total knee arthroplasty.

In a cadaver study, we prepared 37 fresh frozen human patella pairs to determine the efficacy of jet lavage in comparison to syringe lavage with respect to cement penetration and stability of the polyethylene patellar component after patellar resurfacing. For 12 patella pairs, sagittal sections were obtained at predefined levels using a diamond saw. Cement penetration was significantly greater (P<0.0001) in the jet lavage specimens compared to the syringe lavage specimens. For the remaining 25 patella pairs, pullout tests were performed on patellar components using a traction-compression device. The maximum force required to cause mechanical failure was significantly greater (P<0,0001) in jet lavage specimens compared to syringe lavage specimens. Our results support the routine use of jet lavage for cleansing the patellar bed prior to cement application in cemented patellar resurfacing.

An immunohistochemical study of the rabbit suprapatella, a sesamoid fibrocartilage in the quadriceps tendon containing aggrecan.

The rabbit suprapatella is a sesamoid fibrocartilage in the deep surface of the tendon of vastus intermedius and an integral part of the knee joint. We report the presence of a variety of proteoglycans (aggrecan and versican), glycosaminoglycans (chondroitin 4 and 6 sulfate, dermatan sulfate, keratan sulfate) and glycoproteins (tenascin) in its extracellular matrix and the intermediate filament vimentin in the fibrocartilage cells. The most significant finding is the presence of aggrecan in the extracellular matrix, along with its associated link protein and several of its integral glycosaminoglycans. Aggrecan probably enables the suprapatella to withstand compression. Although it can be assumed that aggrecan metabolites detected in synovial fluid from some human joints are predominantly associated with articular hyaline cartilage, the presence of aggrecan in the rabbit suprapatella means that this cannot be assumed for all animal knee joints. We conclude that it is important for orthopedic researchers who use animal models for arthritis research to check for the presence of a suprapatella when joint fluid analyses are interpreted.

Role of uppermost superficial surface layer of articular cartilage in the lubrication mechanism of joints.

The uppermost superficial surface layer of articular cartilage, the 'lamina splendens' which provides a very low friction lubrication surface in articular joints, was investigated using atomic force microscopy (AFM). Complementary specimens were also observed under SEM at -10 degrees C without dehydration or sputter ion coating. Fresh adult pig osteochondral specimens were prepared from the patellas of pig knee joints and digested with the enzymes, hyaluronidase, chondroitinase ABC and alkaline protease. Friction coefficients between a pyrex glass plate and the osteochondral specimens digested by enzymes as well as natural (undigested) specimens were measured, using a thrust collar apparatus. Normal saline, hyaluronic acid (HA) and a mixture of albumin, globulin, HA (AGH) were used as lubrication media. The surface irregularities usually observed in SEM studies were not apparent under AFM. The articular cartilage surface was resistant to hyaluronidase and also to chondroitinase ABC, but a fibrous structure was exhibited in alkaline protease enzymes-digested specimens. AFM analysis revealed that the thickness of the uppermost superficial surface layer of articular cartilage was between 800 nm and 2 microm in adult pig articular cartilage. The coefficient of friction (c.f.) was significantly higher in chondroitinase ABC and alkaline protease enzymes digested specimens. Generally, in normal saline lubrication medium, c.f. was higher in comparison to HA and AGH lubrication media. The role of the uppermost, superficial surface layer of articular cartilage in the lubrication mechanism of joints is discussed.

Histomorphometric analysis of the normal adult patella.

The patellae of 6 male and 2 female, 40 to 70 year-old individuals, who were healthy at the time of their violent death, were assessed by computer-assisted image analysis. The means of the bone density (percentage of bone in the respective field of interest) ranged from approximately 20% to approximately 30% in the central spongiotic zones, from approximately 40% to approximately 80% in the superior and inferior peripheral zones, and approximately 40% to approximately 60% in the subchondral zone. Bone densities were greatest in the lateral parts of the subchondral and spongiotic territories. The bony trabeculae were haphazardly distributed in the central spongiotic zones. They were commonly oriented vertically or parallel to the surface of the patella in the peripheral and subchondral zones. In conclusion, the histomorphometric data presented validate the rationale of reaming the articular aspect of the patella into a dome-shaped configuration with preservation of a circumferential bony bulwark in the preparation for the implantation of a thick polyethylene-based component with a concave undersurface.

Ultrastructural findings after intraarticular application of hyaluronan in a canine model of arthropathy.

We investigated the effect of intraarticularly applied hyaluronic acid (hyaluronan) on the cartilaginous structure of experimentally induced chondromalacia patellae in dogs. For the induction of chondromalacia, we used the Pond-Nuki technique, which involved severance and resection of the anterior cruciate ligament, as a canine model of arthropathy in 27 foxhounds (three groups of nine animals each). In a pilot study, we evaluated the effect of resection of the anterior cruciate ligament with no therapy. Patellar specimens were retrieved at 3, 6, and 12 weeks postoperatively. Subsequently, we compared a treatment group that received intraarticular injections of hyaluronan with a placebo group that received saline solution. The groups were compared at 3, 6, and 12 weeks postoperatively. Three animals from the treatment and placebo groups received five injections of hyaluronan during one of the 4-week intervals (weeks 3-6, 6-9, or 12-15). Specimens were retrieved 5 weeks after the last injection. In both groups, the uninvolved contralateral knee served as a control. The specimens were taken from the medial and lateral patellar poles. Histological analysis included light microscopy and transmission electron microscopy. The structural and ultrastructural changes were assessed qualitatively and were quantified with use of a modified Mankin score. Our results indicate that chondromalacia patellae may be induced with the Pond-Nuki technique. We found a significant reduction (p < 0.01) of cartilaginous lesions in the hyaluronan group compared with the placebo group. Our results suggest that intraarticularly applied hyaluronan is effective in delaying the degenerative process of cartilage degradation. Therefore, we conclude that the use of hyaluronan may be indicated during the early stages of chondromalacia.

The mechanism of joint capsule thermal modification in an in-vitro sheep model.

The purpose of this study was to understand the mechanism responsible for joint capsule shrinkage after nonablative laser application in an in-vitro sheep model. Femoropatellar joint capsular tissue specimens harvested from 20 adult sheep were treated with one of three power settings of a holmium:yttrium-aluminum-garnet laser or served as a control. Laser treatment significantly shortened the tissue and decreased tissue stiffness in all three laser groups, whereas failure strength was not altered significantly by laser treatment. Transmission electron microscopic examination showed swollen collagen fibrils and loss of membrane integrity of fibroblasts. A thermometric study revealed nonablative laser energy caused tissue temperature to rise in the range of 64 degrees C to 100 degrees C. Electrophoresis after trypsin digestion of the tissue revealed significant loss of distinct alpha bands of Type I collagen in laser treated samples, whereas alpha bands were present in laser treated tissue without trypsin digestion. The results of this study support the concept that the primary mechanism responsible for the effect of nonablative laser energy is thermal denaturation of collagen in joint capsular tissue associated with unwinding of the triple helical structure of the collagen molecule.

The interface between bone and tendon at an insertion site: a study of the quadriceps tendon insertion.

Traumatic avulsions of ligament or tendon insertions rarely occur at the actual interface with bone, which suggests that this attachment is strong or otherwise protected from injury by the structure of the insertion complex. In this study we describe the terminal extent of quadriceps tendon fibres where they insert into the patellae of adult rabbits, humans, dogs and sheep. Specimens were examined by scanning electron microscopy (SEM) and light microscopy (LM). To facilitate tracing of tendon fibres the specimens were decalcified for SEM, and polarised light microscopy (PLM) was used in the LM segment of the study. By SEM it was possible to identify mature bone by the presence of osteocytes and a lamellar organisation. PLM and SEM showed that, unlike tendon fibres elsewhere, those in the calcified fibrocartilage were not crimped. No specific cement line was identified by SEM. Tendon fibres interdigitated among separate bone lamellar systems, (osteons or marrow spaces), but did not merge with the collagen systems of individual lamellae. The interdigitation was more extensive and the margin between tendon and bone was less distinct in the anterior third of the insertion. The segment of calcified tendon which interdigitated with bone stained less intensely blue and was less cellular than the more proximal calcified fibrocartilage zone adjacent to the tidemark. Lamellar collagen fibres of the bony trabeculae in the anterior patella were unusually parallel and longitudinal in orientation, making distinction of interposed tendon fibres difficult on LM and PLM sections. LM, SEM and transmission electron microscopy of rabbit patellae at birth revealed that anterior quadriceps tendon fibres extended over the patella in a fibrous cellular layer. By 2 wk of age, this layer had acquired chondroid features (i.e. cell lacunae and metachromasia) and contained vessels extending from patellar marrow. At 6 wk of age, part of this fibrocartilaginous layer was replaced by mature bone and osteoid. In the young adult animal, the quadriceps tension interdigitates extensively with the patellar bone. This segment of the insertion is perhaps the remnant of calcified fibrocartilage which has been remodelled by bone formation.

The effect of radiofrequency energy on the ultrastructure of joint capsular collagen.

This study evaluated the effect of radiofrequency energy on the histological and ultrastructural appearance of joint capsular collagen. Femoropatellar joint capsular specimens from adult sheep were treated with one of three treatment temperatures (45 degrees C, 65 degrees C, and 85 degrees C) with a radiofrequency generator or served as control in a randomized block design. Twenty-four specimens (n = 6) were processed for histological examination as well as ultrastructural analysis using transmission electron microscopy. A computer-based area determination program was used to calculate the area affected in histological samples. Histological changes consisted of thermal tissue damage characterized by collagen fiber fusion and fibroblastic nuclear pyknosis at all application temperatures with clear demarcations between treated and untreated tissue. Mean tissue affected ranged from 50.4% for 85 degrees C to 22.5% for 45 degrees C. There was a strong correlation between treatment temperature and percent area affected (P < .001, R2 = .65). Ultrastructural alterations included a general increase in cross-sectional fibril diameter and loss of fibril size variation with increasing treatment temperature. Longitudinal sections of collagen fibrils showed increased fibril diameter and the loss of cross-striations in the treated groups. Thermally induced ultrastructural collagen fibril alteration is likely the predominant mechanism of tissue shrinkage caused by application of radiofrequency energy.

Effects of in situ freezing and stress-shielding on the ultrastructure of rabbit patellar tendons.

The effects of in situ freezing and the combination of in situ freezing and stress-shielding on the microstructure and ultrastructure of the patellar tendon were studied with use of 20 mature rabbits. The patellar tendon was frozen in situ with liquid nitrogen to kill fibroblasts and then was completely released from stress by chronically pulling a stainless-steel wire installed between the patella and the tibial tubercle. Microstructurally, the freezing treatment induced separation of collagen fiber bundles and fibroblast necrosis at 3 weeks, although the separation disappeared at 6 weeks. Ultrastructurally, small collagen fibrils with a diameter of less than 90 nm were predominant; at 6 weeks, the area occupied by collagen fibrils had decreased. In the frozen-shielded tendon, numerous large spaces were observed in the matrix at 3 weeks. This treatment increased the number of fibrils with a diameter greater than 360 nm and decreased the number of collagen fibrils per unit of area and the area occupied by collagen fibrils at 3 weeks. This study demonstrated that in situ freezing and the combination of in situ freezing and stress-shielding leads to a smaller volume of collagen fibrils per unit of cross section of the patellar tendon by mechanisms that remain to be defined.

Patellar tendon and anterior cruciate ligament have different mitogenic responses to platelet-derived growth factor and transforming growth factor beta.

The healing responses of the anterior cruciate ligament and the patellar tendon differ markedly. The anterior cruciate ligament fails to heal, whereas the patellar tendon heals slowly. The basis of these differences is unknown. Since cellular proliferation is a critical element of healing, we investigated the response to explants of anterior cruciate ligament and patellar tendon from sheep knees to platelet-derived growth factor-AB and transforming growth factor beta 1 as a function of time and dose. Explants cultured for 48, 72, and 96 hours with transforming growth factor beta 1 (0-100 ng/ml) or platelet-derived growth factor-AB (0-200 ng/ml) were radiolabeled for the final 24 hours with [3H]thymidine, and DNA synthesis was quantified as trichloroacetic acid-precipitable radioactivity normalized to dry tissue weight. Statistical analyses (analysis of variance) showed that transforming growth factor beta 1 induced a significant proliferative response in the anterior cruciate ligament at 96 hours with equivalent responses at 10, 50, and 100 ng/ml, whereas the patellar tendon only responded to one condition, 10 ng/ml at 96 hours. Conversely, the patellar tendon had a significant dose-dependent response to platelet-derived growth factor-AB at 72 and 96 hours, whereas the anterior cruciate ligament showed no proliferative response to platelet-derived growth factor-AB. The minimal response of anterior cruciate ligament to platelet-derived growth factor-AB could explain, at least in part, the poor repair capacity of this tissue. The response of the anterior cruciate ligament to transforming growth factor beta suggests that exogenous transforming growth factor beta may promote initial healing. Although growth factors have the potential to modulate soft-tissue repair, tissue responses in tendons and ligaments may vary at different anatomic sites.

Biomechanical effects of stress shielding of the rabbit patellar tendon depend on the degree of stress reduction.

A rabbit model was used to discover whether the effects of stress shielding on the mechanical properties of the patellar tendon depend on the degree of stress reduction. Ninety mature female Japanese White rabbits were divided into three groups: completely stress-shielded partially stress-shielded and sham-operation and contralateral controls. In the experimental groups, tension applied to the patellar tendon was 0%, approximately 30%, and 100% of the normal tension, respectively, with a polyester artificial ligament. Tensile tests were carried out on patella-patellar tendon-tibia complexes harvested 1, 2, 3, 6, or 12 weeks after surgery. The tensile strength decreased in comparison with the sham-operation group to 50.2, 13.5, 9.7, and 20.7% in the completely stress-shielded group and to 75.2, 57.6, 59.6, 57.3, and 72.9% in the partially stress-shielded group. The tensile strength in the completely stress-shielded group was significantly less than that in the partially stress-shielded group at 1, 2, 3, and 6 weeks. The cross-sectional area of the patellar tendon significantly increased to 132, 206, 237, and 136% in the completely stress-shielded group and to 136, 170, 175, 155, and 127% in the partially stress-shielded group compared with the sham-operation group. The cross-sectional area of the completely stress-shielded tendon was significantly larger than that of the partially stress-shielded tendon at 1, 2, and 3 weeks. This study demonstrated that effects of stress shielding on the mechanical properties of the patellar tendon were dependent on the degree of stress shielding.

Histochemical and ultrastructural study of the extracellular matrix fibers in patellar tendon donor site scars and normal controls.

Lesions of the anterior cruciate ligament are extremely common and frequently demand surgical treatment in order to avoid disabling sequels. The use of a central one-third of the patellar tendon as an autograft for surgical reconstruction of a damaged cruciate ligament is common. Although several investigations in human and animal models have demonstrated long-term graft viability, there have been cases of loosening and rupture of the graft. In these occasions, a new substitute for the torn structure must be found. Owing to its inherent accessibility, the patellar tendon has been elected one of the choices of donor tissue. In order to evaluate the characteristics of the remaining scar, we performed a histochemical and ultrastructural study using biopsy material obtained from the central one-third of the donor tendon of 8 patients. This material was analyzed by comparing the ultrastructural picture with the results obtained using the specific method for collagen-containing fibers (Picrosirius-polarization) by light microscopy; four normal patellar tendons were used as controls. Despite the resemblance with the normal tissue, our results show that the healed tissue does not restore the tendon ad integrum, neither at the light microscopic nor at the electron microscopic levels. Structural differences can be responsible for biomechanical alterations. Impaired biomechanical properties can, at least partly, explain some of the clinical complications observed in patients submitted to this surgical technique. However, without performing biomechanical studies in this kind of tendons, we are neither allowed to encourage nor to reject the use of scars as donor tissue for a second surgery.