Wound healing of tendon--I. Physical, mechanical and metabolic changes

Biplanar High-Speed Fluoroscopy of Pony Superficial Digital Flexor Tendon (SDFT)-An In Vivo Pilot Study

The superficial digital flexor tendon (SDFT) is the most frequently injured structure of the musculoskeletal system in sport horses and a common cause for early retirement. This project's aim was to visualize and measure the strain of the sound, injured, and healing SDFTs in a pony during walk and trot. For this purpose, biplanar high-speed fluoroscopic kinematography (FluoKin), as a high precision X-ray movement analysis tool, was used for the first time in vivo with equine tendons. The strain in the metacarpal region of the sound SDFT was 2.86% during walk and 6.78% during trot. When injured, the strain increased to 3.38% during walk and decreased to 5.96% during trot. The baseline strain in the mid-metacarpal region was 3.13% during walk and 6.06% during trot and, when injured, decreased to 2.98% and increased to 7.61%, respectively. Following tendon injury, the mid-metacarpal region contributed less to the overall strain during walk but showed increased contribution during trot. Using this marker-based FluoKin technique, direct, high-precision, and long-term strain measurements in the same individual are possible. We conclude that FluoKin is a powerful tool for gaining deeper insight into equine tendon biomechanics.

Evaluation of Stem Cell Therapies in a Bilateral Patellar Tendon Injury Model in Rats

Regenerative medicine provides novel alternatives to conditions that challenge traditional treatments. The prevalence and morbidity of tendinopathy across species, combined with the limited healing properties of this tissue, have prompted the search for cellular therapies and propelled the development of experimental models to study their efficacy. Umbilical cord matrix-derived mesenchymal stem cells (UCM-MSC) are appealing candidates because they are abundant, easy to collect, circumvent the ethical concerns and risk of teratoma formation, yet resemble primitive embryonic stem cells more closely than adult tissue-derived MSCs. Significant interest has focused on chitosan as a strategy to enhance the properties of MSCs through spheroid formation. This paper details techniques to isolate UCM-MSCs, prepare spheroids on chitosan film, and analyze the effect of spheroid formation on surface marker expression. Consequently, creation of a bilateral patellar tendon injury model in rats is described for in vivo implantation of UCM-MSC spheroids formed on chitosan film. No complication was observed in the study with respect to morbidity, stress rising effects, or tissue infection. The total functional score of the operated rats at 7 days was lower than that of normal rats, but returned to normal within 28 days after surgery. Histological scores of tissue-healing confirmed the presence of a clot in treated defects evaluated at 7 days, absence of foreign body reaction, and progressing healing at 28 days. This bilateral patella tendon defect model controls inter-individual variation via creation of an internal control in each rat, was associated with acceptable morbidity, and allowed detection of differences between untreated tendons and treatments.

Experimental measurement and quantification of frictional contact between biological surfaces experiencing large deformation and slip

Interactions between contacting biological surfaces may play significant roles in physiological and pathological processes. Theoretical models have described some special cases of contact, using one or more simplifying assumptions. Experimental quantification of contact could help to validate theoretical analyses. The objective of this study was to develop a general mathematical approach describing the dynamics of deformation and relative surface motion between contacting bodies and to implement this approach to describe the contact between two experimentally tracked tissue surfaces. A theoretical formulation (in 2-D and 3-D) of contact using the movement of discrete tissue markers is described. The method was validated using theoretically generated 3-D datasets, with <1% error for a wide range of parameters. The method was applied to the contact loading of opposing articular cartilage tissues, where displacements of cell nuclei were tracked optically and used to quantify the movements and deformations of the surfaces. Compared to tissues with matched material properties, tissues with mismatched material properties exhibited increased disparities in lateral expansion and relative motion (sliding) between the contacting surfaces.

Effect of beta-aminopropionitrile and hyaluronic acid on repair of collagenase-induced injury of the rabbit Achilles tendon

Collagenase was injected into the Achilles tendon of both hind legs of 10 clinically normal adult male New Zealand white rabbits. One month after induction of the injury, beta-aminoproprionitrile (BAPN) or hyaluronic acid (HA) was injected into the tendon core of the right hind leg of each rabbit, the left hind leg being left untreated. The treatment effects were evaluated by electron microscopy and analysis of the glycosaminoglycan (GAG) content of samples at 2 and 6 months post-treatment. At 2 months, collagen fibrils in tendons from both hind legs were relatively small in diameter, irregularly arranged, and interspersed with abundant active tenocytes as compared with those in normal tendon uninjured by collagenase. In the matrix, the amount of HA increased, but chondroitin-6-sulphate was eliminated. At 6 months, BAPN-treated tendons had small-diameter, regularly arranged collagen fibrils. HA-treated tendons, on the other hand, had large diameters, as well as regularly arranged collagen fibrils by comparison with non-treated tendon. The results suggest that HA, unlike BAPN, promoted healing.

Ultrasonographic and histopathological findings in equine superficial digital flexor tendon injury

The ultrasonographic and histopathological findings in 12 normal and 28 injured superficial digital flexor tendons, with lesions ranging in duration from 2 days to 15 months, were compared. A consistent relationship between the ultrasonographic and histological findings was demonstrated. The echogenicity of lesions, the distinctness of their delineation from the surrounding tissue, and the presence and arrangement of the linear echoes were useful features by which to assess the ultrasonograms. Acute lesions were anechoic, a complex mixture of anechoic and hypoechoic areas, or diffusely hypoechoic. These appearances represented haemorrhage, fibrolysis and early granulation tissue. Fibroplasia and granulation tissue produced well to moderately well defined hypoechoic lesions. Chronic fibrosis was characterised by heterogeneously echogenic areas which were poorly defined from the surrounding tissue and had irregularly-arranged linear echoes on longitudinal images. Intratendinous scar formation resulted in multiple hyperechoic foci. Extensive peritendinous lesions were readily apparent on ultrasonograms, but intertendinous adhesions were more difficult to assess, and produced ill-definition of the borders between the superficial and deep digital flexor tendons.

Some effects of gamma irradiation on patellar tendon allografts

The purpose of this study was to investigate possible causes for altered mechanical properties of patellar tendon allografts, used for reconstructive surgery, after sterilization with 2.0 Mrads gamma irradiation. The tissues were analyzed using a Hydrothermal Isometric Tension (HIT) device in conjunction with biochemical assays of soluble collagen and electron microscopy to understand the action of this processing. Gamma irradiation was found to significantly lower the shrinkage temperature and tended to increase the rate of isometric tension development. While no significant alteration in the acetic acid solubility was noted, the processing doubled the solubility of collagen to pepsin. This could mean that the predominant effect of the gamma irradiation at this dose level is polypeptide chain scission. The stiffening of the HIT curve may suggest some minor cross linking also occurred. The damaging effect of gamma irradiation, however, was not significant enough to cause any major disruption of the normal banding pattern in collagen. These data support earlier biomechanical data showing that using current processing methods, 2.0 Mrads of gamma irradiation sterilization significantly decreases the tensile strength and modulus of human patellar tendon graft tissues.

Tensile strength comparison of dowel plug technique to standard techniques of tendon-bone attachment

Since tendon transplantation relies on successful fixation of the tendon transplant, a quantitative comparison of various methods of tendon attachment to bone was investigated in mongrel dogs. The methods included attaching tendon to periosteum, suturing a tendon to itself after passing through bone, stapling, and wedging a dowel plug into a hole with the tendon. Tests to failure were conducted at 0, 10, 28, and 63 days of healing. The dowel plug technique provided strong immediate fixation. After 63 days the staple, the tendon passed through bone, and the dowel plug techniques showed significant increases in strength. On tendons of similar size, the dowel plug method showed the greatest tensile strength when compared to the staple fixation. This method was a simple, reproducible technique.

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 development of mechanical strength of surgically anastomosed arteries sutured with Dexon

The strength of surgically anastomosed arteries of the rat sutured with Dexon thread is studied. The abdominal aortas and the carotid arteries were severed, sutured and then the wounds were closed and the animal healed. After a specific period of time up to 13 months, the vessels were taken out and tested in uniaxial loading condition. The stress-strain relationship of the vessels was measured, and then the vessels were pulled to failure. It was found that the strength of the anastomosis was the lowest in about 4 months. In the first day, the force at failure was about the same as that of the control. Then the strength decreased with time, until a minimum was reached in 4-6 months. The tensile force to failure was about 25% of the control for the carotid artery and 49% of the control for the abdominal aorta. The corresponding values of the tensile stress at failure were 17 and 11%, respectively. The different percentages of forces and stresses were caused by the thickening of the vessel wall in the neighborhood of the suture line in the healing process. After 4-6 months, the strength gained again. At 13 months, the strength of the anastomosis was about the same as that of the control. The stretch ratio at failure was approximately constant through all periods.

Influence of ionic environment of the stress relaxation behavior of an invertebrate connective tissue

The rheological properties of an invertebrate connective tissue were measured in three different ionic environments. Short-term stress relaxation tests were conducted on sections of holothurian (Echinodermata) body wall immersed in isotonic monovalent and divalent salt solutions and deionized water. Using a reduced modulus format, the viscoelastic behavior over the experimental time scale was described by a two term Maxwell equation with empirically determined spring constants and relaxation times. In addition, equilibrium relaxation moduli (Ge) were estimated from the empirical relationship of Chasset and Thirion (1965, in Physics of Non Crystalline Solids, ed. Prins, North Holland). The experiments indicated that both relaxation times and equilibrium moduli decreased in the presence of monovalent and divalent inorganic ions whereby the effect of the Na+ was greater than that of the Ca++. The present findings are compared with those reported for vertebrate connective tissue.

Medial collateral ligament healing. A multidisciplinary assessment in rabbits

Medial collateral ligament healing without treatment has been studied in a rabbit model. Complete midsubstance gaps were found to heal by distinct scar formation over time. This healing process was fast since the gap was bridged quickly; however, more subtle changes in appearance of the healing tissue continued for many months. The ligament "scar" was found to be structurally abnormal chemically and mechanically even at long-term followup. A plateau in its improvement suggests that the scar may never approach normal ligament characteristics (without treatment). A baseline of ligament healing by scar formation has been established.

Cyriax's Friction Massage: A Review

This article reviews the existing literature on connective tissue in an attempt to provide additional substantiation for the use of Dr. James Cyriax's friction massage. J Orthop Sports Phys Ther 1982;4(1):16-22.

Mechanical properties of traumatized rat tendo-achilles and the effect of an anti-inflammatory drug on the repair properties

This paper reports on the effect of orally administered flurbiprofen, a potent inhibitor of prostaglandin synthesis (cyclo oxygenase inhibitor), on the mechanical properties of traumatized rat tendo-achilles to see if the F2 alpha prostaglandin was affected and hence the repair process. The drug (1 mg) was administered daily for 7 days to 18 rats whose tendo-achilles were traumatized by crimping using a predetermined force (50 N) applied for 10s. Eighteen sham control rats were identically traumatized and given daily the same volume of liquid (water) not containing the drug. Forty non-traumatized, untreated rats were examined as controls. In vitro studies showed that there was no significant difference in the stress--strain and relaxation characteristics between the three groups and no histological differences were observed.

Biomechanics of tendon healing

The biomechanics of tendon healing was investigated with unsutured rat achilles tendons. After two, three, and four weeks of healing tensile parameters were assayed with a bone-muscle-tendon-bone preparation elongated to failure at a controlled physiological strain rate. In the third week of healing, stiffness, strength, and energy absorbing capacity all increased approximately 50%. These changes correlated with early fibroplasia. In the fourth week of healing, strength, energy absorbing capacity and elongation to failure all increased relatively more than stiffness. Histologically, larger fibers with better longitudinal alignment developed during this period. At the end of four weeks the tendon's strength was approximately 25% of normal. To summarize, the return of stiffness in a healing tendon preparation correlated with the presence of fibroplasia and the return of other tensile parameters was a function of the amount and organization of the fibroplasia.