The effect of anabolic steroids on the biomechanical and histological properties of rat tendon.

Twenty-four male rats were divided into four groups, with anabolic steroids and exercise as variables. Biomechanical tests and histological evaluations were performed. The results of the biomechanical tests suggested that anabolic steroids produce a stiffer tendon, which fails with less elongation. The energy at the time when the tendon failed, the toe-limit elongation, and the elongation at the time of the first failure were all affected significantly. Changes in the force at failure were not statistically significant. No alterations of structure were noted when the specimens were viewed with light microscopy. Alterations of the sizes of the collagen fibrils were noted on electron microscopy.     

Low-level laser therapy combined with platelet-rich plasma on the healing calcaneal tendon: a histological study in a rat model

The objective of this study was to investigate the effects of low-level laser therapy (LLLT) treatment alone (λ?=?660 nm and λ?=?830 nm) or associated with platelet-rich plasma (PRP). We used 54 male rats divided into six groups, with nine animals each: group 1, partial tenotomy; group 2 (GII), PRP; group 3 (GIII): λ660?nm; group 4 (GIV), λ830?nm; group 5 (GV), PRP + λ660?nm; and group 6 (GVI), PRP + λ830?nm. The protocol used was power density 0.35 W/cm², energy 0.2 J, energy density 7.0 J/cm², time 20 s per irradiated point, and number of points 3. Animals in groups GII, GV, and GVI received treatment with PRP, consisting of a single dose of 0.2 mL directly into the surgical site, on top of the tenotomy. Animals were killed on the 13th day post-tenotomy and their tendons were surgically removed for a quantitative analysis using polarization microscopy. The percentages of collagen fibers of types I and III were expressed as mean ± SD. Higher values of collagen fibers type I were obtained for groups GV and GVI when compared with all other groups (p?<?0.05), whereas groups GIII and GIV showed no significant difference between them (p?>?0.05). For collagen type III, a significant difference was observed between GII and all other groups (p?<?0.5), but no significant difference was found between GIII and GIV and between GV and GVI. Results showed that the deposition of collagen type I was higher when treatment with PRP and LLLT was combined, suggesting a faster regeneration of the tendon.     

The effect of rhPTH on the healing of tendon to bone in a rat model

Successful rotator cuff tendon repair depends on secure tendon‐to‐bone healing. Recombinant human parathyroid hormone (rhPTH) has been shown in multiple studies to accelerate bone healing. Recent studies have also shown that rhPTH is chondrogenic by increasing chondrocyte recruitment and differentiation. We hypothesized that rhPTH would improve tendon‐to‐bone healing in a rat rotator cuff repair model. One hundred and fourteen Sprague Dawley rats underwent division and repair of the supraspinatus tendon. Fifty seven rats received daily subcutaneous injections of 10 µg/kg of rhPTH. Rats were sacrificed at 3, 7, 14, 28, and 56 days for histologic and immunohistochemical analysis. In addition, rats in each group were sacrificed at 14, 28, and 56 days for biomechanical testing and micro CT analysis. At 2 weeks the controls had a significantly higher load to failure than the rhPTH group. At 28 and 56 days there were no differences in load to failure. rhPTH specimens had significantly higher stiffness at 56 days. MicroCT analysis showed that the rhPTH group had significantly greater total mineral content at all time points, as well as significantly higher bone volume (BV) at 14 and 28 days. Histologically, the rhPTH specimens had more fibrocartilage, osteoblasts, and blood vessels at all timepoints, with significantly better collagen fiber orientation at 28 and 56 days. Although treatment with rhPTH resulted in an increase in bone and mineralized fibrocartilage formation, as well as better collagen fiber organization, this did not translate into improved biomechanical properties. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:769–774, 2012     

The effect of extracorporeal shock waves on a rat model of injury to tendo Achillis. A histological and biomechanical study

The effects of extracorporeal shock waves (ESWT) on tendon healing were assessed by observing histological and biomechanical parameters in a rat model of injury to the tendo Achillis. The injury was created by inserting an 18-G needle through tendo Achillis in 48 adult Wistar albino rats. The animals were divided into three groups. The first group received radiation only after the operation. The second received no shock waves and the third had 500 15 KV shocks on the second post-operative day. All the rats were killed on the 21st day after surgery. Histopathological analysis showed an increase in the number of capillaries and less formation of adhesions in the study group compared with the control group (p = 0.03). A significantly greater force was required to rupture the tendon in the study group (p = 0.028). Our findings suggest a basis for clinical trials using ESWT.     

The influence of indomethacin on tendon healing. A biomechanical and biochemical study

The influence of indomethacin on the biomechanical and biochemical properties of tendons during their healing was investigated. In 68 New Zealand White rabbits a transverse tenotomy followed by repair with a criss-cross suture was performed in the plantaris longus tendon of the left hind limb. The leg was immobilized for 4 weeks postoperatively in a long-leg plastic splint. Half of the animals were treated with indomethacin, 10 mg/kg/day orally, and the other half with placebo. After 4, 8, and 16 weeks of treatment the animals were killed and biomechanical and biochemical parameters were measured. After 16 weeks there was a significant increase in tensile strength in the indomethacin group. There were only small biochemical differences between the groups. However, there was a slight but significant decrease in the amount of soluble collagen in the indomethacin group. This may indicate a higher degree of cross-linkage following indomethacin treatment, which might explain the increased tensile strength.     

Effects of immobilization on achilles tendon healing in a rat model

The aim of this study was to evaluate the effects of immobilization and mobilization on the functional and biomechanical recovery of injured Achilles tendons. Male Sprague-Dawley rats were allocated randomly into four groups: (a) sham operation, (b) division only (surgical transection of the Achilles tendon without immobilization), (c) “dummy” external fixation (division of the Achilles tendon and application of Kirschner wires), and (d) rigid external fixation (division of the Achilles tendon and immobilization with Kirschner wires connected by two triangular frames). All procedures were performed on the right lower limb; the left, uninjured, lower limb served as an internal control. Kirschner wires and external fixators were removed on day 12. Functional performance was determined from measurements of hind pawprints of rats walking preoperatively and on postoperative days 1, 3, 5, 7, 9, 11, 13, and 15. On day 15, the animals were killed and biomechanical evaluations were performed on both the injured and the uninjured Achilles tendon constructs. No functional or mechanical deficits were observed in the sham-operation group. Animals subjected to division of the Achilles tendon had an initial functional deficit that returned to near normal by day 15. The application of Kirschner wires was associated with an impairment of the functional performance of the rat as well as of the mechanical properties of the tendon-bone constructs. Immobilization by connection of the Kirschner wires to an external frame had an additional, highly significant (p < 0.001) detrimental effect on the functional and mechanical recovery of Achilles tendon-calcaneal complexes.     

Eccentric training improves tendon biomechanical properties: A rat model

The treatment of choice for tendinopathies is eccentric reeducation. Although the clinical results appear favorable, the biomechanical changes to the tissue are not yet clear. Even if the mechanotransduction theory is commonly accepted, the physiology of tendons is not clearly understood. We aimed to better define the biomechanical and histological changes that affect healthy tendon after eccentric and concentric training. This study compared the effects of two methods of training (eccentric [E] training and concentric [C] training) with untrained (U) rats. The animals were trained over a period of 5 weeks. The tricipital, patellar, and Achilles tendons were removed, measured and a tensile test until failure was performed. A histological analysis (hematoxylin and eosin and Masson's trichrome stains) was also realized. There was a significant increase in the rupture force of the patellar and tricipital tendons between the U and E groups. The tricipital tendons in the control group presented a significantly smaller cross‐sectional area than the E‐ and C‐trained groups, but none was constated between E and C groups. No significant difference was observed for the mechanical stress between the three groups for all three tendons. Histological studies demonstrated the development of a greater number of blood vessels and a larger quantity of collagen in the E group. The mechanical properties of tendons in rats improve after specific training, especially following eccentric training. Our results partly explained how mechanical loading, especially in eccentric mode, could improve the healing of tendon. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:119–124, 2012     

The effect of fibrin clot on healing rat supraspinatus tendon defects

The possibility that fibrin clot, with its chemotactic and mitogenic factors, might improve the healing of a defect in the rat supraspinatus tendon was evaluated. Bilateral defects were surgically created in the rat supraspinatus tendon near the humeral insertion. One defect in each rat was filled with fibrin clot from a donor animal while the other side acted as a control. The tendons were evaluated at 3, 6, and 12 weeks. On histologic evaluation persistent defects were seen at all time points, whereas the healing tissue became less cellular with better collagen organization over time. Fibrin clot remained in the healing defects of treated shoulders at early time points. Biomechanically, there was improvement of properties over time, but they did not approach those of normal tendon by 12 weeks. There was no effect from addition of the fibrin clot except at 3 weeks, where it led to a decrease in material properties.     

Achilles tendon healing: long-term biomechanical effects of postoperative mobilization and immobilization in a new mouse model.

The aim of the study was to investigate the long-term effects of postoperative immobilization as opposed to mobilization on the biomechanical attributes of healing Achilles tendons in a new experimental mouse model. In 114 Balb-C-mice the left Achilles tendon was transected and sutured by the Kirchmayr-Kessler technique. The tendons healed either under postoperative immobilization effected by fixing the upper ankle joint in equinus position or under mobilization through a limited range of movement. The contralateral Achilles tendons served as internal control. All tendons were tested biomechanically at short intervals up to the 112th postoperative day in terms of load to failure [N], tendon deflection [mm] and tendon stiffness [N/mm], and were evaluated histologically after 8 and 112 days. Postoperative mobilization resulted in a continuous and significantly more rapid restoration of load to failure in comparison to the immobilization group. Tendon deflection was decreased by postoperative mobilization, whereas under immobilization it paradoxically increased still further in the later course. After 112 days the tendons of the mobilization group had regained their original tendon stiffness, whereas the tendons after immobilization reached only about half the values seen in the control tendons. Histologically, postoperative mobilization led to increased immigration of inflammatory cells in the early phase. In the late phase, as compared to immobilization, tendon structure was more mature, with fibre bundles arranged in parallel and interposed tendocytes. Tensile loading of the healing tendon by postoperative mobilization leads to fundamental changes in the biological process of tendon healing resulting in accelerated restoration of load to failure and reduced tendon deflection.     

2-Octylcynanoacrylate-assisted microvascular anastomosis in a rat model: long-term biomechanical properties and histological changes

The aim of this study was to establish the long-term biomechanical and histological properties of 2-octylcyanoacrylate-assisted microvascular anastomosis over conventional suture-only anastomosis in the laboratory rat model. The biomechanical and histological properties of three groups of vessels were compared: 1) vessels with 2-octylcyanoacrylate-assisted anastomoses (study group); 2) vessels with suture-only anastomoses (control group); and 3) normal unoperated vessels (sham group). In total, 144 adult rats were used, and these were studied at 1 week, 1 month, 3 months, and 6 months postanastomosis. At 6 months, the tensile strength of study vessels was significantly higher than control vessels. The stiffness of study and control vessels was similar at all time intervals. Histologically, there was no evidence that 2- octylcyanoacrylate caused toxicity to vessel walls, and there was less perivasacular foreign-body giant-cell reaction in the study group compared to the control group. Long-term follow-up showed that microvascular anastomosis with 2-octylcyanoacrylate in rat femoral arteries had superior tensile strength and similar stiffness to vessels anastomosed with sutures only, without adverse effects to surrounding tissues.     

Flexor tendon healing in the rat: a histologic and gene expression study

PURPOSE: To establish a rat flexor tendon laceration and repair model to investigate the molecular mechanisms of flexor tendon healing. METHODS: Surgery was performed on rat flexor digitorum longus tendons from both hind feet. Repaired tendons were harvested at 0, 3, 7, 14, 21, 28, 42, 56, and 84 days after surgery. Histologic study (first 84 days) and gene expression study (first 28 days) of several collagens and matrix metalloproteinases (MMPs) were performed. RESULTS: In the histologic study pre-existing collagen bundles were degraded between days 7 to 21. Newly formed collagen fibers crossed the repair site by day 28. Remodeling of the collagen fibers continued until day 84. Gene expression of type I collagen decreased initially and then returned gradually to the initial level by day 28, whereas expression levels of types III, V, and XII collagen were increased after surgery. The expression levels of MMP-9 and MMP-13 peaked between days 7 to 14, whereas MMP-2, MMP-3, and MMP-14 levels increased after surgery and maintained high levels until day 28. CONCLUSIONS: The rat tendon laceration model represented the entire tendon healing process. The results of this study suggest that MMP-9 and MMP-13 participate only in collagen degradation, whereas MMP-2, MMP-3, and MMP-14 participate not only in collagen degradation but also in collagen remodeling.     

Effects of supplemental oxygen and hyperbaric oxygen on tendon healing in a rat model

Systemic supplemental oxygen therapy (SOT) and hyperbaric oxygen therapy (HBOT) have been shown to positively impact wound healing. The purpose of this study was to evaluate the effects of SOT and HBOT on tendon healing in a rat tendon model. The right patellar tendon of 90 male Sprague-Dawley rats was completely sectioned. Animals were randomized to receive HBOT, SOT, or room air therapy. Animals were sacrificed at 3- and 6-weeks postoperatively. The ultimate tensile strength in axial extension was compared between groups. Statistical significance was calculated using the Student's t-test. The SOT group exhibited the highest tensile strength at both time-points, although HBOT was the only treatment that exhibited a statistically significant increase in tensile strength between time-periods (p = 0.006). There was no statistical difference in ultimate tensile strength when the three groups were compared at the 3- or 6-week time-points. Results presented here cannot support the premise that intermittent HBOT or SOT significantly increases the healing of tendon repairs.     

Is cultured tendon fibroblast a good model to study tendon healing?

Cultured tendon fibroblasts (CTFs) from intact explants are widely used to study tendon healing in vitro. The significance of these findings may rely on similarities between CTFs and healing tendon fibroblasts in situ. Our purpose was to compare CTFs with fibroblasts cultured from healing tendons. We cultured CTFs from intact and healing tendons at day 7 and day 14 postinjury in a rat model of patellar donor site injury. The mRNA expression of COL1A1, COL3A1, decorin, and biglycan, with or without supplementation of 1 ng/mL TGF‐β1, was compared by quantitative real‐time RT‐PCR. The expression of proliferation cell nuclear antigen (PCNA) and α‐smooth muscle actin (α‐SMA) was determined by immunostain. COL3A1 and decorin mRNA in CTFs was lower as compared to day 7 healing fibroblasts, but its biglycan mRNA level was higher than day 14 healing fibroblasts. TGF‐β1 increased COL1A1 and decorin mRNA in CTFs, but decreased the mRNA of all four genes in day 7 healing tendon fibroblasts. CTFs exhibited lower PCNA immunopositivity as compared to day 7 and day 14 healing fibroblasts, but a higher α‐SMA immunopositivity than cultured day 14 healing fibroblasts. These findings showed that CTFs did not resemble healing tendon cells with respect to major cellular activities related to tendon healing. Thus, fibroblasts from healing tendon may be a more appropriate model for studying cellular activities in tendon healing. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:374–383, 2008     

The effect of fibrin glue on tendon healing and adhesion formation in a rabbit model of flexor tendon injury and repair

Abstract

Fibrin glue has been widely used in a variety of surgical procedures to promote haemostasis and tissue bonding. It can also be used as a cell carrier for stem cells on tendons. However, the data about the effect of fibrin glue on flexor tendon healing is very limited. The present study examined the role of fibrin glue TISSEEL® in a rabbit model of flexor tendon injury. The rabbits were killed 3 or 8 weeks after the operation. The range-of-motion of the fingers and biomechanical properties of tendons were measured and compared between the control group and TISSEEL-treated group. The findings have shown that the range-of-motion in the TISSEEL-treated group was significantly different from that of the control group at 3 weeks after the operation. However, there is no significant difference in range-of-motion at 8 weeks after the operation. Moreover, there is no significant difference in biomechanical properties between the control group and TISSEEL-treated group. The results indicate that TISSEEL may attenuate adhesion formation at the early stage of flexor tendon repair. However, there is no significant effect on biomechanical features during tendon repair. In conclusion, this study has shown that it may be safe to use TISSEEL in tissue engineering applications for tendon regeneration and healing.     

Biochemical, histological, and biomechanical analyses of canine tendon

To define the matrix composition and architecture of canine flexor tendon, and to correlate tissue structure with applied mechanical loading, five anatomical regions of flexor tendon were studied. Histologically, two prominent fibrocartilaginous areas were observed on concave aspects of the tendon. The location of the major fibrocartilaginous area at the metacarpophalangeal joint correlated well with the region predicted by biomechanical modeling to be under greatest compressive loads during standing and claw movement. Comparative biochemical analysis showed an elevated water content, a five-fold higher hexuronic acid content, and a larger hydroxylysine/hydroxyproline ratio in this region relative to that for more tendinous areas. The major glycosaminoglycan component of fibrocartilaginous areas was chondroitin sulfate, whereas in other areas dermatan sulfate and hyaluronic acid dominated. Cell density and DNA analyses indicated a slightly higher cellularity for fibrocartilaginous areas and the region of vinculum insertion. These data document the existence of discrete areas of specialization within the flexor tendon that appear to be an adaptation to nutritional and mechanical factors.     

The effects of initial end contact on medial collateral ligament healing: a morphological and biomechanical study in a rabbit model

In this investigation, the effect of initial end contact on medial collateral ligament (MCL) healing was studied in the rabbit model. Sixty-eight 1-year-old New Zealand white rabbits were separated into two groups. In one group, a 4 mm saggital Z-plasty was performed in the right MCL midsubstance (contact group), and in the other group, an analogous 4 mm midsubstance segment was removed (gap group). Left knees were unoperated to serve as internal contralateral MCL controls. Animals had unrestricted cage activity until sacrifice in groups of eight at 3, 6, 14, and 40 weeks postoperatively. Early results demonstrated that contact and gap injuries healed with what appeared to be scar tissue both morphologically and biomechanically. In both groups, laxities recovered to their contralateral values within 6 weeks and biomechanical viscoelastic behaviors recovered to 68-92% of contralaterals by 14-40 weeks. Despite these similarities, contacts showed morphological and biomechanical evidence of improved healing over gaps. Contact scars remodeled more quickly, recovered laxity more quickly, and were generally closer to contralaterals than gaps in terms of their structural strength, stiffness, and material behaviors, after 40 weeks of healing. With the exception of appearances and failure stress, all measured properties of contact healing MCLs were statistically indistinguishable from contralateral MCLs at 40 weeks of healing. These advantages of contact healing in this model support speculations that there are differences in the early rate and possibly in the later quality of ligament healing when cut rabbit MCL ends are in proximity. Longer-term studies to define end points and mechanisms of healing are required.