Intrasynovial Flexor Tendon Research Articles

Growth factors and canine flexor tendon healing: Initial studies in uninjured and repair models

The role of growth factors in a variety of bone and soft tissue healing processes has been studied extensively in numerous recent models, yet little is known about the specific growth factors that may be playing a role in flexor tendon healing. We used a number of established protein purification techniques and bioassays to isolate and partially characterize a heparin-binding growth factor from unoperated canine tendons. Our data provide evidence that basic fibroblast growth factor, a potent angiogenic growth factor, is present in normal canine intrasynovial flexor tendons. We then studied repaired canine flexor tendons to further elucidate the role of growth factors in the tendon healing process. Heparin-sepharose elution profiles from three repair intervals (3, 10, and 17 days) were graphed and compared to known profiles of isolated growth factors. The three repair intervals demonstrated two elution profile peaks, consistent with varying amounts of platelet-derived growth factor and epidermal growth factor. Although additional experimentation is required to identify definitively the various protein isolates, these data provide compelling evidence that a variety of growth factors are present in uninjured and healing digital flexor tendons.

Variations in cellular proliferation and matrix synthesis in intrasynovial and extrasynovial tendons: An in vitro study in dogs

Intrasynovial and extrasynovial flexor tendon grafts recently have been shown to have dissimilar patterns of cellular survival and host integration within the digital sheath. In an effort to determine if fundamental differences exist between these two types of tendons, we investigated the biochemical composition and cellular activity of intrasynovial and extrasynovial tendon segments of 12 adult mongrel dogs in short-term explant culture in MCDB 105 and in DMEM media. Proteoglycan, collagen and noncollagen protein synthesis and content and DNA synthesis were determined following culture in both media. Intrasynovial tendon segments cultured in MCDB 105 medium synthesized significantly less collagen, noncollagen protein, and DNA and had similar amounts of proteoglycans compared to extrasynovial tendons. Comparison of intrasynovial and extrasynovial tendon segment responses in DMEM medium showed that intrasynovial tendons synthesized more proteoglycan, protein, and DNA than they did in MCDB 105. Extrasynovial tendons had similar rates of matrix component and DNA synthesis in both media. Findings that the synthesis of matrix components and DNA between intrasynovial flexor and extrasynovial peroneal tendon segments differ significantly indicate that intrasynovial flexor tendons may be specially adapted to the nutritional milieu provided by an intrasynovial environment. These data are supported by the selective successful stimulation of fibrocartilaginous segments within intrasynovial flexor tendons in media favored for the culture of cartilaginous tissue.

Maintenance of the gliding surface of tendon autografts in dogs.

To determine whether there are differences in the extent to which the superficial cellular layers remain viable and contribute to the healing process, extra- and intrasynovial hindlimb donor tendons of 12 dogs (24 tendons) were labeled with 3H-thymidine in vitro and transferred to the medial and lateral toes of the forepaw. After transplantation, the distribution and amounts of remaining labeled cells within the healing tendon grafts were determined at 1 and 3 weeks after surgery by scintillation countings and autoradiographic examinations. The two types of tendon grafts showed different turnover rates for the elimination of labeled DNA. At 1 week, 25 percent of labeled DNA remained in the extrasynovial grafts and 65 percent in the intrasynovial grafts. The two types of tendon grafts also showed different healing responses histologically. Autradiographic examinations showed that the majority of labeled cells were located in the periphery of the control tendons and that the numbers of labeled cells within the newly proliferated superficial areas of both types of tendon grafts decreased over time. These findings indicate that intrasynovial flexor tendons may possess improved prerequisites for superficial cellular survival and tendon gliding following autogenous tendon grafting.

Genetic expression for type I procollagen in the early stages of flexor tendon healing

To determine the precise mechanism by which contact tendon healing occurs at the cellular level, the production of pro α(I) collagen messenger RNA (mRNA) produced by fibroblasts of healing intrasynovial flexor tendons was determined by an in situ hybridization technique. The repair site and the proximal and distal tendon stumps of repaired tendons treated with early controlled passive mobilization were fixed and buffered in formalin, 3, 7, 10, and 17 days after repair. A complimentary DNA (cDNA) probe corresponding to α(I) procollagen mRNA was labeled with [ 32P]d-CTP. After hybridization, autoradiography, and staining of the sections, the level of procollagen mRNA was assessed by microscopic examination. Rising levels of procollagen mRNA, indicating progressively increasing levels of synthetic collagen activity, were detected in the healing tendons through 10 days. A moderate decrease in procollagen mRNA was seen at 17 days. Genetic expression for procollagen mRNA was localized specifically to the epitenon cells on the tendon surface overlying the repair site and to cells in the gap between the tendon stumps. No detectable expression was noted in endotenon fibroblasts. The finding of high levels of expression for procollagen type I mRNA in the surface layer of healing tendons demonstrates that cells intrinsic to tendon epitenon contribute the greatest quantity of native tendon collagen to the repair site during these important early intervals after tendon suture.

The revascularization of healing flexor tendons in the digital sheath. A vascular injection study in dogs.

The role of revascularization in the nutritional support of repair of the flexor tendons is not completely understood. To explore the extent to which intrasynovial flexor tendons revascularize after transection and suture, a vascular injection study was carried out in a canine model. The tendons to the second and fifth digits of the forepaw in twelve adult mongrel dogs were transected and repaired. There were twenty-four experimental tendons and twenty-four normal tendons. The limb was placed in a polyurethane shoulder-spica cast, and the paw was treated with immediate protected passive mobilization. At three, seven, ten, seventeen, and twenty-eight days, the animals were killed and the major arteries supplying both the paw that had been operated on (left) and the contralateral normal paw (right) were injected with 200 milliliters of India ink. Segments of repaired and normal tendons were then clarified by a modified Spalteholz technique. The normal tendons demonstrated a well developed mesotenon that provided vascularization of the proximal portion of the flexor digitorum profundus tendon. A consistent three-cubic-millimeter avascular intrasynovial portion of tendon was noted. Distally, vessels arose from the vinculum breve, supplying the terminal twenty millimeters of tendon substance. In the experimental tendons, longitudinal and transverse clarified sections showed consistent revascularization of the site of repair by proximal vessels in the absence of ingrowth of peripheral adhesions. Vessels in the epitenon progressively extended for a distance of ten millimeters, through normally avascular regions, to reach the site of repair by the seventeenth postoperative day. Intratendinous vessels about the site of repair consistently originated from surface vessels, rather than from extensions of pre-existing intratendinous vessels. New vessels penetrated all areas, including the normally avascular volar segments of tendon, irrespective of previous topical zones of avascularity. Proximal vascular plexi were characterized by large tortuous vessels with frequent circuitous branches. More distal vessels had a longitudinally oriented, feathery appearance.

Healing of digital flexor tendons

The effect of an elapsed interval of time between injury and operative repair of the flexor tendons was investigated in a canine model. Transected intrasynovial flexor tendons were repaired either immediately or after a delay of seven or twenty-one days. The biomechanical, biochemical, and morphological characteristics were compared at three and six weeks. The values for angular rotation, linear excursion, ultimate load, and linear slope were determined; concentrations of collagen and reducible collagen cross-links, an index of newly synthesized collagen, were measured; and the ultrastructural morphology of the tendons was examined by high-voltage electron microscopy. For the tendons that were repaired immediately, the values for angular rotation were 9.4 +/- 3.2 and 13.0 +/- 3.7 degrees at three and six weeks; for those that were repaired at seven days, 4.1 +/- 1.3 and 2.5 +/- 1.4 degrees; and for those that were repaired at twenty-one days, 2.7 +/- 0.8 and 4.7 +/- 0.7 degrees. There was a significant effect of the delay until repair on the angular rotation and linear excursion in all three groups (p less than 0.005 for both). Tensile testing of the bone-tendon complex revealed no significant effect of the delay on the values for ultimate load (p greater than 0.05). There were no significant differences in total concentration of collagen at the sites of repair or in the levels of reducible Schiff-base cross-links (indicators of newly synthesized cross-links) in tendons from the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the mechanism of diet-induced hepatic inactivation of vitamin D

The biochemical means by which accelerated rehabilitation alters intrasynovial flexor tendon repair site collagen synthesis and extracellular matrix maturation are not fully understood. We hypothesized that an increased level of applied rehabilitative force in a clinically relevant animal model would hasten the maturation of the repair site extracellular matrix as demonstrated by total collagen and collagen cross-link assessment. Twenty-eight flexor digitorum profundus tendons from 14 adult dogs were transected and repaired. The animals received either low- or high-force rehabilitation and were killed 10, 21, and 42 days after surgery. A 10-mm segment of tendon surrounding the repair site was obtained. Biochemical analysis showed that total collagen concentration was significantly reduced at each time point, that the reducible cross-link ratio of dihydroxylysinonorleucine to hydroxylysinonorleucine was significantly increased at each time point, and that the nonreducible pyridinoline cross-link content was significantly decreased at 10 days in both rehabilitative groups. Total collagen content did not vary to a statistically significant degree with either time or as a function of rehabilitation type. Based on these findings several clinically relevant observations can be made. Increasing collagen concentration and repair site maturation do not explain the previously demonstrated increased tensile properties of tendon that occur between 3 and 6 weeks after repair. Higher force rehabilitation does not alter the biochemical composition of the healing tendon through 6 weeks. Coupled with other recent data these findings suggest that high-force rehabilitation does not stimulate accelerated healing after intrasynovial flexor tendon repair. (J Hand Surg 2001;26A:841–846. Copyright © 2001 by the American Society for Surgery of the Hand.)

Oxidative enzyme metabolism in rabbit intrasynovial flexor tendons. I. Changes in enzyme activity of the tenocytes with age

Clinically, the results of surgical repair to tendons within the digital canal are generally unsatisfactory. It is not known whether the tendon cells themselves have the capacity to effect repair, or whether dependence on surrounding tissues is necessary. Our lack of understanding of these problems is partly due to an inadequate knowledge of tendon metabolism. The activities of three oxidative enzymes, succinate dehydrogenase (citric acid cycle), glucose-6-phosphate dehydrogenase (pentose phosphate pathway), and lactate dehydrogenase (glycolysis), were measured in flexor tendons of young and adult rabbits. The same enzymes were also measured in rat liver for comparison. The results showed that adult tenocytes were entirely dependent on anaerobic metabolism for their energy supply, and that their biosynthetic capability for nucleic acid and fat production was extremely limited. In contrast, the synovium was more active metabolically, and might be expected to have a greater capability for repair following injury. Young rabbit tenocytes were somewhat more active metabolically, and showed some capacity for aerobic metabolism and production of cofactors for biosynthesis. Generally, however, rabbit tendon as a whole would appear to have only a limited ability for repair, based on its metabolic activity. There are areas of fibrous cartilage within the tendon which always occur at regions subject to particular stress. These regions were metabolically more active than the tendon itself.

Oxidative enzyme metabolism in rabbit intrasynovial flexor tendons. II. Studies of nutritional pathways

The nutritional pathways of intrasynovial tendons have been investigated by transplantation of a free tendon graft to the knee joint. These grafts developed adhesions to host tissues as early as 2 days after operation. Central necrosis was apparent after 1 week. By 3 weeks postoperation, metabolically active infiltrating cells from the synovial layer of the tendon removed necrotic material, and began the process of partial regeneration of the tendon. This was clearly apparent at 9 weeks. At this stage, the new tenocytes had assumed the metabolic pattern of normal adult tendon cells. It is concluded that the vascularised synovial layer of the tendon is of paramount importance in the remodeling process.

Oxidative enzyme activity in rabbit intrasynovial flexor tendons. III. Changes in enzyme activity of hypovascular tendons after physical activity

The nutritional pathway of intrasynovial tendons has been investigated under conditions of hypovascularity, while allowing normal functioning of the tendons. By 1 week, central necrosis of the tendon had developed. The repair process was seen to begin from the synovium, which by this time had recovered its normal blood supply. The synovial cells were metabolically more active than the tenocytes, and took part in the remodeling process.