Evaluation of collagen fiber maturation and ordering in regenerating tendons employing H-1 double quantum filtered NMR spectroscopy.

It is difficult to monitor the chronic stage of the healing process of ruptured tendons employing the present diagnostic modes. However, the results of this study have shown that 1H double quantum filtered (DQF) NMR spectroscopy is sensitive to the later stages of the healing process. Regenerated tendons of rabbits were dissected and measured at the end of the acute phase (three weeks), the subacute phase (nine weeks), and the chronic phase (13 and 18 weeks after tenotomy). Four parameters were determined by 1H DQF NMR spectroscopy: (a) the maximum signal intensity (h(max)) relative to the single quantum spectrum, (b) the creation time of the maximum signal intensity (tau(max)), (c) the decay time from the maximum signal intensity to a value half of that intensity (tau(1/2)) and (d) the residual dipolar splitting of water (delta), representing the order of the collagen fibers. The values of h(max), tau(max), tau(1/2), and delta of the intact Achilles tendons were 11.3+/-1.0%, 0.48+/-0.03 ms, 0.67+/-0.04 ms and 732+/-62 Hz (mean +/- SEM, n=6), respectively. In the regenerating tendon, h(max) increased from 0.41+/-0.12% at three weeks to 7.07+/-0.77% at 18 weeks, tau(max) decreased from 1.88+/-0.31 ms at three weeks to 0.72+/-0.04 ms at 18 weeks, tau(1/2) decreased from 11.6+/-1.8 ms at 3 weeks to 1.48+/-0.16 ms at 18 weeks, and delta increased from 129+/-8 Hz at three weeks to 414+/-29 Hz at 18 weeks. We have concluded that reordering of collagen fibers proceeds continuously even in the chronic stage of healing. Thus, the 1H DQF NMR spectroscopy is a useful non-invasive technique to evaluate the reconstruction and the order of collagen fibers in regenerating tendon. It is also suggested that tau(1/2) and h(max) are most useful for in vivo DQF NMR spectroscopy and imaging, respectively, in combination with tau(max).     

Sex matters in the establishment of murine tendon composition and material properties during growth

The existence of sex‐based differences in tendon and ligament injury rates has led investigators to test the hypothesis that sex plays a significant role in modulating tendon and ligament composition and material properties. To date, no studies have attempted to characterize how such differences develop during the course of normal tissue maturation and growth. Thus, the primary aim of the present study was to use a murine model to test the hypothesis that sex‐based differences in the normal age‐related development of tendon composition and material properties exist by assessing these parameters in the Achilles and tail tendons from 4‐, 6‐, 9‐, 12‐, and 15‐week‐old male and female C57Bl/6J mice. Despite significantly lower levels of total collagen content in females subsequent to sexual maturity (p < 0.0001), as well as a significant effect of sex on glycosaminoglycan content (p < 0.0001), Achilles tendon elastic modulus was not compromised in females. Female Achilles tendons did exhibit a significantly higher failure strain (p = 0.0201) and strain energy density (p = 0.0004) than did males, as well as a trend toward higher ultimate strength (p = 0.0556). In contrast to the high load‐bearing environment of the Achilles tendon site, sex did not have a statistically significant effect on any compositional or material property in the low load‐bearing tendon fascicles of the tail. These data support recent studies by others, which suggest that male and female tendons have a differential adaptational response to their local mechanical loading environment. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:631–638, 2010     

Effects of Interleukin-1 Receptor Antagonist on Collagen and Matrix Metalloproteinases in Stress-shielded Achilles Tendons of Rats

Based on previous studies showing that interleukin-1 (IL-1) significantly increased after stress shielding, this article reports further research into the possible therapeutic applications of IL-1 receptor antagonist (IL-1Ra).Forty rats whose left Achilles tendons were denervated and completely stress shielded were divided into 5 groups: 2-week phosphate-buffered saline (PBS); 4-week PBS; 2-week IL-1Ra; 4-week IL-1Ra; and normal control. The Achilles tendons were tested morphologically, and the changes in collagen I and III, matrix metalloproteinases (MMP)-1 and -3, and tissue inhibitors of metalloproteinase (TIMP)-1 were determined. The collagen fibrils in the IL-1Ra groups were morphologically more similar to those in the control group than to those in the PBS groups. The collagen I levels increased in the 2-week groups. Significant differences existed between the PBS and IL-1Ra groups at 4 weeks. The MMP-1 level increased dramatically after stress shielding and increased less in the 2-week IL-1Ra group than in the 2-week PBS group. The degree of decrease of MMP-3 in the IL-1Ra groups was significantly less than that in the PBS groups. The collagen III and TIMP-1 levels continued to increase, and no difference was found between the PBS and IL-1Ra groups. Interleukin-1 receptor antagonist prevented morphological deterioration and collagen metabolism of the denervated Achilles tendons after stress shielding, likely by inhibiting the decline of MMP-3 and increasing MMP-1 levels at an early stage.     

Complete stress shielding of the Achilles tendon: ultrastructure and level of interleukin-1 and TGF-β

Few studies emphasize the collagen metabolism-related cytokines and ultrastructure of the completely stress-shielded Achilles tendon. In this study, we used a rat model with complete stress shielding of the Achilles tendon to observe the changes in the ultrastructure of the Achilles tendon and concentration of IL-1 and TGF-β 3 weeks after stress shielding. The model group comprised 12 male Sprague-Dawley rats. The stress of the Achilles tendon of the left hind limb was shielded through tendon cerclage combined with sciatic nerve transection, and the right served as a normal control. Three weeks later, the ultrastructure of the Achilles tendon was observed under electron microscopy and IL-1 and TGF-β levels were determined by enzyme-linked immunosorbent assay. Compared with the control side, collagen fibrils of the shielded Achilles tendons were irregularly arranged and loose. The number of small-diameter collagen fibrils increased significantly with the decrease of the average diameter of collagen fibrils. At the same time, IL-1 concentrations increased significantly in the model group as compared to that in the control group, but no significant difference was found in TGF-β levels. These results suggest that IL-1 may play an important role in the change of ultrastructure after stress shielding.     

Murine tendon function is adversely affected by aggrecan accumulation due to the knockout of ADAMTS5

The present study examined the effect of ADAMTS5 (TS5) knockout on the properties of murine flexor digitorum longus (FDL) and Achilles tendons. FDL and Achilles tendons were analyzed using biomechanical testing, histology, and immunohistochemistry; further characterization of FDL tendons was conducted using transmission electron microscopy (collagen fibril ultrastructure), SDS-PAGE (collagen content and type), fluorescence-assisted carbohydrate electrophoresis for chondroitin sulfate and hyaluronan, and Western blotting for aggrecan, versican, and decorin abundance and distribution. FDL tendons of TS5(-/-) mice showed a 33% larger cross-sectional area, increased collagen fibril area fraction, and decreased material properties relative to those of wild type mice. In TS5(-/-) mice, aggrecan accumulated in the pericellular matrix of tendon fibroblasts. In Achilles tendons, cross-sectional area, stress relaxation, and structural properties were similar in TS5(-/-) and wild type mice; however, the TS5(-/-) tendons exhibited a higher tensile modulus and a weakened enthesis. These results demonstrate that TS5 deficiency disturbs normal tendon collagen organization and alters biomechanical properties. Hence, the role of ADAMTS5 in tendon is to remove pericellular and interfibrillar aggrecan to maintain the molecular architecture responsible for normal tissue function.     

Matrix remodeling in healing rabbit Achilles tendon

Biochemical, biomechanical and ultrastructural properties of the connective tissue matrix were investigated during the early remodeling phase of tissue repair in experimentally tenotomized and repaired rabbit Achilles tendons. Sterile surgical tenotomy was performed on the right Achilles tendons of 14 rabbits and allowed to heal for 15 days. The animals were euthanized and the Achilles tendons excised from both limbs. The left contralateral Achilles tendon of each rabbit was used as a control in the experiments. Prior to biochemical analysis, both intact and healing tendons were tested for their biomechanical integrity. The results revealed that the healing tendons had regained some of their physicochemical characteristics, but differed significantly from the intact left tendons. The healing tendons regained 48% tensile strength, 30% energy absorption, 20% tensile stress, and 14% Young's modulus of elasticity of intact tendons. In contrast, biochemical analysis showed that the healing tendons had 80% of the collagen and 60% of the collagen crosslinks (hydroxypyridinium) of normal tendons. Sequential extraction of collagen from the tissues yielded more soluble collagen in the healing tendons than intact tendons, suggesting either an increase in collagen synthesis and/or enhanced resorption of mature collagen in healing tendons compared to intact tendons. Electron microscopic studies revealed remarkable differences in the ultrastructure between intact and healing tendons. These observations could explain, in part, the connective tissue response to healing during the early phases of tissue remodeling.     

ADAMTS5 is required for biomechanically‐stimulated healing of murine tendinopathy

A recently developed murine model of tendinopathy, induced by TGF‐β1 injection, has been used to examine the reparative capacity of tendinopathic Achilles in Adamts5^?/? mice. After TGF‐β1 injection and 2 weeks of treadmill exercise, the Achilles from Adamts5^?/? mice exhibited a reduction in maximum tensile stress of approximately 60%. However, in contrast to wild type mice previously characterized by this model, Adamts5^?/? mice subjected to further treadmill exercise were unable to reverse this biomechanical deficit. This nonreparative phenotype was accompanied by a major deficiency, relative to wild‐type, in expression of Col1a1 and Col3a1 and an abnormally elevated expression of a wide range of integrins. In addition, the tendinopathic Adamts5^?/? mice showed a persistent accumulation of chondrogenic cells in the tendon body and an aggrecan‐rich fibrocartilaginous matrix within disorganized collagen fiber bundles. Moreover, consistent with the compromised biomechanical properties of the Achilles in the Adamts5^?/? mice, in vivo gait analysis revealed a strong trend (p = 0.07) towards increased swing time of the injected limb in Adamts5^?/? relative to wild‐type mice. These findings demonstrate that a deficiency in ADAMTS5 promotes a chondrogenic response to TGF‐β1 injection that is not reversed by treadmill exercise. Hence, repair of biomechanically compromised tendons exhibiting midsubstance chondroid accumulation requires ADAMTS5. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1540–1548, 2013

     

Unfavorable effect of knee immobilization on Achilles tendon healing in rabbits

This study was undertaken to assess the effect of knee immobilization on the treatment of Achilles tendon rupture. After their Achilles tendons were severed, rabbits were divided into 2 groups. In Group A, only the ankle joint was immobilized. In Group B, both the knee and ankle joints were immobilized. At 4 weeks after surgery, both the ultimate tensile force and stiffness of the severed tendons were significantly greater in Group A than in Group B. In Group A, dense collagen fibers were seen in the repaired tendons, and the bundles of collagen fibers were parallel to one another along the axis of the tendons. In contrast, in Group B, dilated veins and capillaries were seen in the repaired tendons, and the proliferation of connective tissue containing collagen fibers was severely reduced around these veins and capillaries and was in general irregular and uneven. These results suggest that knee immobilization retards the healing of a ruptured Achilles tendon without suture, due to congestion and tension deprivation produced by keeping the tendon static.     

Effect of stress deprivation and cyclic tensile loading on the material and morphologic properties of canine flexor digitorum profundus tendon: An in vitro study

The effect of stress deprivation and cyclic tensile loading on the mechanical and histologic properties of the canine flexor digitorum profundus tendon was examined using an in vitro system. Stress deprivation resulted in a progressive and statistically significant decrease in the tensile modulus over an 8-week period. Histologically, stress-deprived tendons demonstrated quantitative changes in the morphology and number of cells and in the alignment of collagen. The change in tensile properties was not associated with an alteration in the water content of the tissue, but the change appeared to be dependent on the presence of a viable cell population. Dead (acellular) tendons did not undergo any alteration in tensile modulus in this in vitro system. In vitro cyclic tensile loading of tendons over a 4-week time period resulted in a significant increase in the tensile modulus (93% of the control) compared with that of the stress-deprived tendons (68% of the control). This loading regimen also maintained the normal histologic pattern of the tendons. The results of this study are similar to those previously reported for in vivo studies and suggest that this in vitro model may represent a valid system with which to test the effects of various stress conditions on the tensile properties of tissues.     

Low‐level laser therapy in collagenase‐induced Achilles tendinitis in rats: Analyses of biochemical and biomechanical aspects

NSAIDs are widely prescribed and used over the years to treat tendon injuries despite its well‐known long‐term side effects. In the last years several animal and human trials have shown that low‐level laser therapy (LLLT) presents modulatory effects on inflammatory markers, however the mechanisms involved are not fully understood. The aim of this study was to evaluate the short‐term effects of LLLT or sodium diclofenac treatments on biochemical markers and biomechanical properties of inflamed Achilles tendons. Wistar rats Achilles tendons (n = 6/group) were injected with saline (control) or collagenase at peritendinous area of Achilles tendons. After 1 h animals were treated with two different doses of LLLT (810 nm, 1 and 3 J) at the sites of the injections, or with intramuscular sodium diclofenac. Regarding biochemical analyses, LLLT significantly decreased (p < 0.05) COX‐2, TNF‐α, MMP‐3, MMP‐9, and MMP‐13 gene expression, as well as prostaglandin E₂ (PGE₂) production when compared to collagenase group. Interestingly, diclofenac treatment only decreased PGE₂ levels. Biomechanical properties were preserved in the laser‐treated groups when compared to collagenase and diclofenac groups. We conclude that LLLT was able to reduce tendon inflammation and to preserve tendon resistance and elasticity. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1945–1951, 2012     

Unfavorable effect of knee immobilization on Achilles tendon healing in rabbits

This study was undertaken to assess the effect of knee immobilization on the treatment of Achilles tendon rupture. After their Achilles tendons were severed, rabbits were divided into 2 groups. In Group A, only the ankle joint was immobilized. In Group B, both the knee and ankle joints were immobilized. At 4 weeks after surgery, both the ultimate tensile force and stiffness of the severed tendons were significantly greater in Group A than in Group B. In Group A, dense collagen fibers were seen in the repaired tendons, and the bundles of collagen fibers were parallel to one another along the axis of the tendons. In contrast, in Group B, dilated veins and capillaries were seen in the repaired tendons, and the proliferation of connective tissue containing collagen fibers was severely reduced around these veins and capillaries and was in general irregular and uneven. These results suggest that knee immobilization retards the healing of a ruptured Achilles tendon without suture, due to congestion and tension deprivation produced by keeping the tendon static.     

Collagen V haploinsufficiency in a murine model of classic Ehlers–Danlos syndrome is associated with deficient structural and mechanical healing in tendons

Classic Ehlers–Danlos syndrome (EDS) patients suffer from connective tissue hyperelasticity, joint instability, skin hyperextensibility, tissue fragility, and poor wound healing due to heterozygous mutations in COL5a1 or COL5a2 genes. This study investigated the roles of collagen V in establishing structure and function in uninjured patellar tendons as well as in the injury response using a Col5a1^+/− mouse, a model for classic EDS. These analyses were done comparing tendons from a classic EDS model (Col5a1^+/− ) with wild‐type controls. Tendons were subjected to mechanical testing, histological, and fibril analysis before injury as well as 3 and 6 weeks after injury. We found that Col5a1^+/− tendons demonstrated diminished recovery of mechanical competency after injury as compared to normal wild‐type tendons, which recovered their pre‐injury values by 6 weeks post injury. Additionally, the Col5a1^+/− tendons demonstrated altered fibril morphology and diameter distributions compared to the wild‐type tendons. This study indicates that collagen V plays an important role in regulating collagen fibrillogenesis and the associated recovery of mechanical integrity in tendons after injury. In addition, the dysregulation with decreased collagen V expression in EDS is associated with a diminished injury response. The results presented herein have the potential to direct future targeted therapeutics for classic EDS patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2707–2715, 2017.

     

Unfavorable effect of knee immobilization on Achilles tendon healing in rabbits

This study was undertaken to assess the effect of knee immobilization on the treatment of Achilles tendon rupture. After their Achilles tendons were severed, rabbits were divided into 2 groups. In Group A, only the ankle joint was immobilized. In Group B, both the knee and ankle joints were immobilized. At 4 weeks after surgery, both the ultimate tensile force and stiffness of the severed tendons were significantly greater in Group A than in Group B. In Group A, dense collagen fibers were seen in the repaired tendons, and the bundles of collagen fibers were parallel to one another along the axis of the tendons. In contrast, in Group B, dilated veins and capillaries were seen in the repaired tendons, and the proliferation of connective tissue containing collagen fibers was severely reduced around these veins and capillaries and was in general irregular and uneven. These results suggest that knee immobilization retards the healing of a ruptured Achilles tendon without suture, due to congestion and tension deprivation produced by keeping the tendon static.     

The effects of extracorporeal shock waves on the rat Achilles tendon: is there a critical dose for tissue injury?

Introduction Extracorporeal shock waves (ESW) have been extensively studied in the field of orthopedics. Experimental and focused, well-designed clinical studies have suggested the clinical utilisation of ESW in several pathologies including delayed bone union, tennis elbow, and plantar fasciitis. However, the unwanted detrimental effects of ESW on various tissues have been questioned by some authors. In this experimental study, the effects of ESW were investigated at different intensity applications on the Achilles tendons of rat.Materials and methods A total of 32 adult Wistar albino rats was divided into four groups. The first three groups received 1000 impulses of 0.15 mJ/mm², 1500 impulses of 0.15 mJ/mm², and 2000 impulses of 0.20 mJ/mm², respectively. The last group was kept as the control group. Subsequently, Achilles tendons were harvested for histological studies from all rats at the 3rd week after a single application of ESW.Results There were no histological abnormalities observed in the Achilles tendons of the first two groups compared with the control group. No alteration in the histological configuration was observed, and consequently the pathologist who had been blinded could not differentiate these rats from the control group by light microscopy. However, in the high intensity group (2000 impulses of 0.20 mJ/mm²), grade II and III disorganisation of collagen fibers was noticed in 7 out of 8 rats, which was not detected in any of the rats from the first two groups (p<0.05). Consequently, the pathologist could distinguish the majority of the rats (7 out of 8) of this group from the remaining ones. Meanwhile, grade I lymphocyte infiltration was observed in some sections of the rats receiving the highest ESW dose.Conclusion This study confirms that ESW application at high intensity is associated with detrimental tissue effects. Additionally, it was suggested that the extent of tissue injury caused by ESW is dose-related.     

Nonsurgical treatment and early return to activity leads to improved Achilles tendon fatigue mechanics and functional outcomes during early healing in an animal model

Achilles tendon ruptures are common and devastating injuries; however, an optimized treatment and rehabilitation protocol has yet to be defined. Therefore, the objective of this study was to investigate the effects of surgical repair and return to activity on joint function and Achilles tendon properties after 3 weeks of healing. Sprague–Dawley rats (N = 100) received unilateral blunt transection of their Achilles tendon. Animals were then randomized into repaired or non‐repaired treatments, and further randomized into groups that returned to activity after 1 week (RTA1) or after 3 weeks (RTA3) of limb casting in plantarflexion. Limb function, passive joint mechanics, and tendon properties (mechanical, organizational using high frequency ultrasound, histological, and compositional) were evaluated. Results showed that both treatment and return to activity collectively affected limb function, passive joint mechanics, and tendon properties. Functionally, RTA1 animals had increased dorsiflexion ROM and weight bearing of the injured limb compared to RTA3 animals 3‐weeks post‐injury. Such functional improvements in RTA1 tendons were evidenced in their mechanical fatigue properties and increased cross sectional area compared to RTA3 tendons. When RTA1 was coupled with nonsurgical treatment, superior fatigue properties were achieved compared to repaired tendons. No differences in cell shape, cellularity, GAG, collagen type I, or TGF‐β staining were identified between groups, but collagen type III was elevated in RTA3 repaired tendons. The larger tissue area and increased fatigue resistance created in RTA1 tendons may prove critical for optimized outcomes in early Achilles tendon healing following complete rupture. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2172–2180, 2016.     

Macrophage depletion reduces cell proliferation and extracellular matrix accumulation but increases the ultimate tensile strength of injured Achilles tendons

Macrophages are present in large numbers and display specific and distinct phenotypes during the various phases of tissue repair. However, their role following tendon injury and during repair has never been investigated. We injected C57BL/6 mice daily for 4 days with liposome‐encapsulated clodronate to deplete circulating monocytes/macrophages. Placebo mice were injected with PBS. The left Achilles tendons of the mice were transversely sectioned and sutured using the 8‐strand technique. Macrophage accumulation and cell proliferation were significantly lower in the tendons of clodronate‐treated mice than in those of PBS‐treated mice on days 3 and 7 post‐injury. TGF‐β1 staining was significantly more intense in the tendons of PBS‐treated mice on day 7 post‐injury. Edema and the dry mass of the Achilles tendons were also higher in the PBS‐treated mice on days 7 and 14 post‐injury. No differences in absolute strength and stiffness were observed, but Young's modulus and maximal stress were significantly greater for tendons from the clodronate‐treated mice than those from PBS‐treated mice after 14 days of tendon repair. Overall, our findings showed that macrophages promote cell proliferation and extracellular matrix accumulation but their presence leads to inferior ultimate tensile strength of the Achilles tendons. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:279–285, 2014.     

Genome‐wide analysis identifies differential promoter methylation of Leprel2, Foxf1, Mmp25, Igfbp6, and Peg12 in murine tendinopathy

We have used a murine Achilles tendinopathy model to investigate whether tissue changes (such as collagen disorganization, chondroid metaplasia, and loss of tensile properties) which are broadly characteristic of human tendinopathies, are accompanied by changes in the expression of chromatin‐modifying enzymes and the methylation status of promoter regions of tendon cell DNA. Tendinopathy was induced by two intra‐tendinous TGF‐β1 injections followed by cage activity or treadmill running for up to 28 days. Activation of DNA methyltransferases occurred at 3 days after the TGF‐β1 injections and also at 14 days, but only with treadmill activity. Genome‐wide Methyl Mini‐Seq™ analysis identified 19 genes with differentially methylated promoters, five of which perform functions with an apparent direct relevance to tendinopathy (Leprel2 , Foxf1 , Mmp25, Igfbp6 , and Peg12) . The functions of the genes identified included collagen fiber assembly and pericellular interactions, therefore their perturbation could play a role in the characteristic disorganization of fibers in affected tendons. We postulate that a study of the functional genomics of these genes in animal and human tendon could further delineate the pathogenesis of this multi‐factorial complex disease. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:947–955, 2017.

     

Viscoelastic Properties of the Superficial Musculoaponeurotic System (SMAS): A Microscopic and Mechanical Study

A study was undertaken to determine the physical properties and microscopic structure of the superficial musculoaponeurotic system (SMAS) tissue. Forty virginal specimens and eight reoperated specimens were examined. The following findings were discovered. 1) Microscopic appearance shows the SMAS to consist of collagen fibers, a relatively high concentration of elastic fibers interspersed with fat cells. 2) On scanning electron microscopy, the virginal SMAS shows the collagen fibers to have a similar convoluted appearance as in the dermis. There is some evidence of parallelization of the collagen fibers in the reexcised SMAS specimens. 3) Mechanical testing (Instron) demonstrates that both the SMAS and preauricular skin were subjected to a series of loading/unloading tests at various rates, amplitudes, and stress relaxation tests. Both sets of specimens indicated definite viscoelastic properties. Although the mechanical behavior of both tissues was somewhat similar, the viscoelastic effect of the SMAS was less pronounced. A slackening effect of the SMAS indicated a gradual expansion of the SMAS postoperatively. These results could provide some indication of the long-term effects of SMAS surgery.     

Influence of biochemical composition on endplate cartilage tensile properties in the human lumbar spine

Endplate cartilage integrity is critical to spine health and is presumably impaired by deterioration in biochemical composition. Yet, quantitative relationships between endplate biochemical composition and biomechanical properties are unavailable. Using endplate cartilage harvested from human lumbar spines (six donors, ages 51–67 years) we showed that endplate biochemical composition has a significant influence on its equilibrium tensile properties and that the presence of endplate damage associates with a diminished composition–function relationship. We found that the equilibrium tensile modulus (5.9 ± 5.7 MPa) correlated significantly with collagen content (559 ± 147 µg/mg dry weight, r² = 0.35) and with the collagen/GAG ratio (6.0 ± 2.1, r² = 0.58). Accounting for the damage status of the adjacent cartilage improved the latter correlation (r² = 0.77) and indicated that samples with adjacent damage such as fissures and avulsions had a diminished modulus–collagen/GAG relationship (p = 0.02). Quasi‐linear viscoelastic relaxation properties (C, τ₁, and τ₂) did not correlate with biochemical composition. We conclude that reduced matrix quantity decreases the equilibrium tensile modulus of human endplate cartilage and that characteristics of biochemical composition that are independent of matrix quantity, that is, characteristics related to matrix quality, may also be important. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:245–252, 2014.