Deep Flexor Tendon Research Articles

Case report

A total of 17 dairy cows with sole ulcers were treated, and the healing process observed [USA; date not given]. Nine cows had mature, uncomplicated ulcers where the exposed corium appeared only slightly damaged in 6 cases, and more seriously damaged in 3 cases. The remaining 8 animals had complicated ulcers, all of which had a discharging tract at the ulcer site with swelling of the heel, coronary band, and flexor aspect of the digit extending to and above the metatarsus. Ulcers were regarded as typical lesions (Rusterholz ulcers) in 16 cows, and one cow had a heel ulcer. 16 of the 17 cows had ulcers that occurred on the lateral claw of the rear foot. Three cases had mature sole ulcers on one of the lateral hind claws, and early ulcers as evidenced by sole haemorrhage on the lateral claw of the opposite foot. Eight of nine uncomplicated ulcers showed progressive reduction in size following treatment. Using finger pressure, no pain response was present at the ulcer site after one week in 8 of 9 cases (89%). Ulcers with granulating corium healed more slowly (range 41-60 days; mean 48) compared with those where the corium appeared normal (range 12-28 days; mean 20). Sole ulcers recurred in 2 of the 9 cases (22%) within one month after the cow began bearing weight on the affected claw. In one of these cows, ulcers developed on 3 of the 4 hind claws. Histopathological examination of the left rear medial and lateral claws from this cow showed marked changes in the ventral surface of the third phalanx and the dermal papillae, as well as abnormal keratogenesis. Partial tenovaginotomy with resection of the deep flexor tendon was performed in 6 of the complicated sole ulcer cases. In the other 2 cases, tenovaginotomy was followed by claw amputation due to the intraoperative diagnosis of concurrent septic arthritis of the distal interphalangeal joint. In cases of partial tenovaginotomy, healing occurred over a period of 49-81 days (mean 68 days). Complications included excessive granulation tissue, abscess formation of the proximal outer compartment of the digital flexor tendon sheath, and overextension of the toe. For optimal healing to occur, weekly evaluation for the first 4 weeks following treatment may be beneficial with the following objectives: ascertain presence and position of the claw block; determine if progressive healing is occurring; determine if complications may be developing, such as a discharging tract at the ulcer site or swelling of the heel, coronary band or flexor surface of the digit; and finally, recheck for the presence of loose horn overgrowing the ulcer site which may result in further injury to the exposed corium and delay healing.

Molecular support for a sister group relationship between Pici and Galbulae (Piciformes sensu Wetmore 1960)

Woodpeckers, honeyguides, barbets, and toucans form a well‐supported clade with approximately 355 species. This clade, commonly referred to as Pici, share with the South American clade Galbulae (puffbirds and jacamars) a zygodactyls foot with a unique arrangement of the deep flexor tendons (Gadow's Type VI). Based on these characters, Pici and Galbulae are often considered sister taxa, and have in traditional classification been placed in the order Piciformes. There are, however, a wealth of other morphological characters that contradicts this association, and indicates that Pici is closer related to the Passeriformes (passerines) than to Galbulae. Galbulae, in turn, is considered more closely related to the rollers and ground‐rollers (Coracii). In this study, we evaluate these two hypotheses by using DNA sequence data from exons of the nuclear RAG‐1 and c‐myc genes, and an intron of the nuclear myoglobin gene, totally including 3400 basepairs of aligned sequences. The results indicate a sister group relationship between Pici and Galbulae, i.e. monophyly of the Piciformes, and this association has high statistical support in terms of bootstrap values and posterior probabilities. This study also supports several associations within the traditional order Coraciiformes, including a sister group relationship between the kingfishers (Alcedinidae) and a clade with todies (Todidae) and motmots (Momotidae), and with the bee‐eaters (Meropidae) placed basal relative to these three groups.

Computed tomography and morphometry of the carpal canal in the dog

This study has been carried out to determine the normal size and shape of the carpal canal in the dog and to describe the salient anatomic structures with the aid of computed tomography. Computed tomographic examination of the carpal region was performed in the left and right forelimbs of 5 male and 5 female healthy German shepherd dogs, respectively. Areas, depths and widths of the carpal canal and identification of the anatomical structures were determined at two levels of the carpal region. The frozen forelimbs of two cadavers were sectioned with a saw to correlate the CT images with these sections. All scans were studied using both bony and soft tissue windows. The measurements of the right and left carpal canals did not differ significantly in male or female dogs, respectively although they were larger in the male than female dogs. In addition to this, the measurements of the carpal canal were larger in the distal than the proximal slice. The lateral tip of the deep digital flexor tendon was located more cranially in the distal part than in the proximal part of the carpal canal. Thus, the distance between the bones and the deep digital flexor tendon decreased and the distance between the deep and superficial digital flexor tendons increased. This localization is important in regard to neuropathy because the median nerve was located between the deep and superficial flexor tendons and this region was wider at the distal than the proximal part of the carpal canal. As a result of this study, it was found that the carpal canal of the dog much resembled that of humans and this similarity can easily generate a predisposition to focal neuropathy namely, carpal tunnel syndrome in dogs.

LUMBRICAL TEARS IN ROCK CLIMBERS

Performance rock climbing places high demands on the hand and may lead to specific injuries. In a “one-finger-pocket” hold, the interphalangeal joints remain in 20–40° flexion. To increase the maximum force of the holding finger by the quadriga effect, the interphalangeal joints of the adjacent fingers become almost maximally flexed. Holding a “one-finger-pocket” with the ring or small finger leads to a shift of the deep flexor tendons which increases the distance between the two adjacent origins of either the third or the fourth lumbrical. This may cause disruption and tear of that muscle. An organized haematoma in the third lumbrical was visible by ultrasonography in one of the three cases described.

The early surface cell response to flexor tendon injury

Purpose: The migratory response of surface fibroblasts to flexor tendon injury was studied by their selective labeling with a vital dye. Method: The surfaces of 30 rat deep flexor tendons were bathed in 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine percholate (DiI), a vital dye for 5 minutes. The residual dye was removed by thorough irrigation. A partial tenotomy was made in the stained section by cutting out a central window. Semiquantitative cell counts and position of stained fibroblasts were noted by examination under fluorescent light at 0, 1, 3, 5, and 7 days. Results: The surface fibroblasts readily took up the vital dye at day 0. By day 1 dyed cells had moved into the cut. By day 3 they had migrated laterally into the core substance of the tendon. Core dyed cell counts at days 1, 3, 5, and 7 were significantly different compared with day 0 core dyed cell counts. Conclusions: This cell migration from the surface of the cut to the tendon core is likely to be vital in the early stages of tendon healing. (J Hand Surg 2003;28A:221-230. Copyright © 2003 by the American Society for Surgery of the Hand.)

Isolated flexor muscles of the little toe in the feet of an individual with atrophied or lacking 4 th head of the M. extensor digitorum brevis and lacking the 4 th tendon of the M. extensor digitorum longus

While dissecting the body of a 75-year-old male we observed variations in the Mm. flexor digitorum brevis and longus of both feet. In the left foot, the 4th tendon of the M. flexor digitorum brevis was atrophied and the respective tendon of the M. flexor digitorum longus to the little toe was absent. In the right foot, the 4th tendons of both the Mm. flexor digitorum brevis and longus to the little toe were absent. The lacking deep flexor tendon to the little toe in the left foot was replaced by an isolated flexor muscle originating from the medial and lateral processes of the calcaneal tuberosity, which additionally had connections to the tendinous plate of the M. flexor digitorum longus and the M. quadratus plantae. The absent superficial and deep flexor tendons to the little toe in the right foot were replaced by an isolated flexor muscle arising from the M. quadratus plantae distal from the medial process of the calcaneal tuberosity. The tendon of both isolated flexor muscles inserted in the distal phalanx of the little toe. The left isolated flexor muscle for the little toe had connections to the M. flexor digitorum longus and the M. quadratus plantae. From these results it seems likely that the M. quadratus plantae could be regarded as additional flexor head (caput breve or plantare) of the M. flexor digitorum longus as is described in classic textbooks. In the individual's lifetime the described variation perhaps led to the possibility of an isolated flexion of the little toe.

THE ROLE OF HUMAN-DERIVED FIBRIN SEALANT IN THE REDUCTION OF POSTOPERATIVE FLEXOR TENDON ADHESION FORMATION IN RABBITS

This study assessed the role of a novel fibrin sealant (Vivostat®) in adhesion reduction after flexor tendon surgery. The deep flexor tendons of the 2nd and 4th digits of the left paw of 20 rabbits were exposed and a standard partial injury was performed on each. The rabbits were randomized to either immediate post-injury treatment with Vivostat® or no treatment. In each case active movement of the 2nd digit was prevented while the 4th digit was allowed to move normally. The two groups were assessed at 14 days for adhesion formation with a tensiometer. The right paw acted as the unoperated control. Results showed that there was no significant difference in the force needed to remove the tendon from its sheath when comparing the two Vivostat®-treated groups to the unoperated controls. There was, however, a highly significant difference in this force between the non-Vivostat®-treated groups and the unoperated controls. This suggests a beneficial effect of Vivostat® in reducing post surgical tendon adhesion formation.

Effect of Growth Factors on Type I Collagen Synthesis in Cultured Rabbit's Deep Flexor Tendon Cell

Purpose : This study focuses on the change of the expression of type-I collagen mRNA and extent of collagen synthesis caused by four kinds of growth factos (TGF-, IGF-I, EGF, PDGF) and their combinations to elucidate the effects of growth factors on rabbit's flexor tendon. Materials and Methods : Cells were isolated from rabbit’s flexor tendons and cultured with DMEM containing 0.5% fetal bovine serum. Growth factors were then given either independently or in combination. On the 5th, 10th, and 15th day, the cells were collected and the cell proliferation rate was analyzed. The expression of type-I collagen mRNA was analyzed by Northern blot. Results : The expression of type-I collagen mRNA increased significantly in the IGF, PDGF, PDGF/EGF, and PDGF/IGF groups (p

Regional adaptations in three rat tendons

Although detailed histological and immunocytochemical studies have been published for the rat calcanear tendon (CT), little is known of the structure, composition and biomechanics of the deep (DFT) and superficial (SFT) flexor tendons. In this study, we examined the structural specialization of these three tendons in 90-day-old rats by applying histochemical and biochemical assays to different tendon regions (proximal, intermediate and distal regions of the DFT and SFT, and proximal and distal regions of the CT). There were regional differences in tissue structure, glycosaminoglycan type and content, swelling properties and in the amount and distribution of elastic fibers. Dermatan sulfate occurred in all regions, but chondroitin sulfate predominated in the intermediate region of the DFT and in the distal region of the CT. These two chondroitin sulfate-bearing regions showed swelling in water, while all other regions lost fluid in water. Fibrocartilaginous sites were observed on the CT, one at the insertion to the bone and another distally at the innermost area of the tendon. The intermediate region of the DFT showed round cells disposed in lacunae, while the proximal and distal regions were typically fibrous. The intermediate region of the SFT showed a wavy array of collagen bundles but neither toluidine blue staining in the matrix nor round cells. Elastic fibers were present in each region of the three tendons, but were more prominent in the intermediate zone of the SFT. These results demonstrate regional variation in the three tendons. Tendon differentiation may occur by an increase in the number of elastic fibers and by variations in the arrangement of collagen fibers, without fibrocartilage formation.

DEVELOPMENT OF POLYVINYL ALCOHOL-HYDROGEL (PVA-H) SHIELDS WITH A HIGH WATER CONTENT FOR TENDON INJURY REPAIR

The main problem in tendon repair is adhesion formation between the tendon and surrounding tissue. To prevent this, we have developed adhesion preventive shields using polyvinyl alcohol hydrogel (PVA-H) with 90% water content. This implant experiment used the deep flexor tendon of the 3rd toe of the domestic fowl. Injured tendons shielded with PVA-H healed within about 3 weeks without adhesion to the surrounding tissues. Neither breakage of the PVA-H shield itself nor infection or degeneration in the surrounding tissue was observed. These results show that tendon is capable of intrinsic repair, and was able to regenerate using synovial nutrition through the PVA-H. The high water content of PVA-H may be clinically useful and applicable to adhesion preventive shields for tendon repair.

EARLY BREAKING STRENGTH OF REPAIRED FLEXOR TENDON TREATED WITH 5-FLUOROURACIL

This study investigated the effect of a single intraoperative application of 5-fluorouracil, which may diminish peritendinous adhesion formation, on the tensile strength of repaired digital flexor tendons after 7, 14 and 21 days of healing. Twenty-seven deep flexor tendons from 14 rabbits were exposed to 5-fluorouracil (50 mg/ml) for 5 minutes immediately after repair whereas matched control tendons were exposed to normal saline. Tensile testing at 7, 14 and 21 days revealed no significant differences in the gap or ultimate strengths of the 5-fluorouracil treated and control tendons.

Development of the shields for tendon injury repair using polyvinyl alcohol — hydrogel ( PVA‐H)

In recent years, marked advances have been made in repair techniques for tendon injury, but the treatment of finger flexor tendon injury is still one of the most difficult and important problems in the orthopedic field. The main problem in tendon repair is adhesion between the tendon and surrounding tissue. To prevent this adhesion and achieve tendon union, we developed adhesion preventive shields for tendon repair using polyvinyl alcohol hydrogel ( PVA-H) with 90% water content, and carried out an implant experiment using the deep flexor tendon of the third toe of domestic fowl. Injured tendons shielded with PVA-H showed union at about 3 weeks after the operation without adhesion to the surrounding tissue and good function such as gliding and range of motion. Neither breakage of the PVA-H shield itself nor infection, nor degeneration in the surrounding tissue were observed. These results confirmed that the tendon itself has repair ability, and the tendon is regenerated by synovial nutrition through PVA-H. High water content PVA-H may have clinically potential and be applicable to adhesion-preventive shields for tendon repair. However, re-rupture was observed, probably due to accidental tendon injury at an early period after the operation. In some cases, tendon immobilization methods to prevent re-rupture might be necessary. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 344–351, 2001

Isolation of proteoglycans from tendon.

Proteoglycans make up less than 1% of the dry weight of a dense connective tissue such as tendon (1). Most of this proteoglycan is a small molecule called decorin. Because decorin has only one glycosaminoglycan chain, it cannot be separated from other proteins by the CsCl density-gradient centrifugation method that was originally used to purify aggrecan from cartilage. The basic approach described in this chapter is to extract proteoglycans from the tissue with 4 M guanidine, a solution that will denature collagen and disrupt most kinds of noncovalent molecular interactions. The cross-linked collagen of adult tendon remains insoluble during this extraction, allowing the proteoglycans and other soluble proteins to be separated from the bulk of the tissue by centrifugation. Proteoglycans are then separated from other extracted proteins by ion-exchange chromatography, taking advantage of the anionic nature of the glycosaminoglycan chain. This method has been used to quantitate and isolate proteoglycans from the tensile (proximal) and compressed (distal) regions of bovine deep flexor tendon. These mechanically distinct regions of flexor tendon are characterized by differences in proteoglycan amount and type (2). The method is equally applicable to isolation of proteoglycans from human tendon or from other dense connective tissues (3). Once isolated, the large proteoglycans can be separated from smaller ones by sieve chromatography. These isolated proteoglycans and their unique core proteins and glycosaminoglycan chains are of sufficient purity to then be examined by specific analytical techniques or used in functional assays.

Development of the shields for tendon injury repair using polyvinyl alcohol--hydrogel ( PVA-H).

In recent years, marked advances have been made in repair techniques for tendon injury, but the treatment of finger flexor tendon injury is still one of the most difficult and important problems in the orthopedic field. The main problem in tendon repair is adhesion between the tendon and surrounding tissue. To prevent this adhesion and achieve tendon union, we developed adhesion preventive shields for tendon repair using polyvinyl alcohol hydrogel ( PVA-H) with 90% water content, and carried out an implant experiment using the deep flexor tendon of the third toe of domestic fowl. Injured tendons shielded with PVA-H showed union at about 3 weeks after the operation without adhesion to the surrounding tissue and good function such as gliding and range of motion. Neither breakage of the PVA-H shield itself nor infection, nor degeneration in the surrounding tissue were observed. These results confirmed that the tendon itself has repair ability, and the tendon is regenerated by synovial nutrition through PVA-H. High water content PVA-H may have clinically potential and be applicable to adhesion-preventive shields for tendon repair. However, re-rupture was observed, probably due to accidental tendon injury at an early period after the operation. In some cases, tendon immobilization methods to prevent re-rupture might be necessary.

HYALURONIC ACID MODULATES CELL PROLIFERATION UNEQUALLY IN INTRASYNOVIAL AND EXTRASYNOVIAL RABBIT TENDONS IN VITRO

As tendons differ in biochemical composition and cellular capacities, we have compared dose response effects of hyaluronic acid on cell proliferation and synthesis of matrix components in intermediate and proximal segments of intrasynovial deep flexor tendons and extrasynovial peroneus rabbit tendons in vitro. Compared with matched control tendons, hyaluronic acid inhibited cell proliferation in intermediate and proximal intrasynovial flexor tendon segments at the concentrations of 0.1–2.0 mg/ml and 0.5–2.0 mg/ml respectively, but in extrasynovial tendon segments only at the concentration of 0.5 mg/ml. Hyaluronic acid did not affect synthesis of proteoglycan, collagen and non-collagen protein in either type of tendon. These results show that hyaluronic acid modulates cell proliferation unequally in intra- and extrasynovial tendons without affecting the synthesis of matrix components in the two types of tendons, indicating differential hyaluronic acid sensitivity and a possible mechanism of action.

Proteins in the tensile region of adult bovine deep flexor tendon.

Tendon proteoglycans and proteins (other than Type I collagen) were solubilized by sequential extraction of powdered adult bovine deep flexor tendon. Only the proximal (tensile) region of this tendon was used. The experiments involved 24-hour extraction with phosphate buffered saline (to remove components that are readily soluble), followed by repeated extraction with 4 mol/L guanidine (to break noncovalent bonds holding components into the tissue), and then extraction with 4 mol/L guanidine containing dithiothreitol (to dissociate components held by disulfide bonds). Proteins accounting for approximately 5% of the tissue dry weight could by removed by the extraction protocol. Proteins were identified by Western blotting and correlation with stained gels. The major extracted components were identified as decorin, Type VI collagen, fibromodulin and a member of the leucine rich repeat protein family (PRELP). In addition an oligomeric matrix protein initially identified in cartilage (COMP), aggrecan, and biglycan were present. Most of these proteins were entirely extracted in cold 4 mol/L guanidine. However, some Type VI collagen and cartilage oligomeric matrix protein could not be removed unless the tissue was reduced with dithiothreitol. Many of these proteins have been considered as molecules that are primarily or exclusively components of cartilage. Cartilage and tendon are tissues with different histologic appearance and different function. However, the fact that the same biochemical components are found in cartilage and tendon shows the relatedness of these connective tissues and the cells that produce them. Tissue engineering attempts to reconstruct tendon using only its major or unique components may omit significant aspects of the tissue's structure.

Giant Lipoma of the Hand.

A 70-year-old man was referred by his GP to the hand surgery clinic with an enlarging swelling in the thenar eminence of his left hand. He first noticed this swelling 18 months previously. There was no preceding trauma. He noticed that the size of the swelling was increasing gradually and felt a constant cramp-like pain in his hand with intermittent parasthesia on the ulnar side of the thumb. Examination revealed a soft, nonfluctuant, nontender swelling in the bulk of the thenar eminence with indistinct margins. There was no objective neurological deficit. Plain X-rays showed a radiolucency in the first web space (Figs. 1 and 2). MRI scan showed a mass which gave a signal similar to fat and was well encapsulated, passing behind the flexor tendons in the palm. The high-signal T1 and T2 images were interpreted as typical of lipoma (Figs. 3 and 4). In view of the increase in size of the swelling and the discomfort, marginal excision was done. The mass extended deep into the carpal tunnel and was intimately attached to the lumbrical of the long flexor tendon to the index finger. The common digital nerve to the first web space was stretched over the lump and was dissected free. The lipoma extended underneath the flexor tendons and seemed to have a pedicle arising from the synovium around the deep flexor tendons. The lipoma was 8 cm 5 cm in size. The patient made an uneventful recovery and his symptoms of pain and parasthesia settled within 2 weeks. Histological examination demonstrated a large benign lipoma.

Proteoglycan Composition and Biosynthesis in Superficial and Deep Digital Flexor Tendons of Standardbred Horses

SummaryProteoglycan (PG) levels and their respective biosynthesis were determined in explant cultures taken from the mid-metacarpal (MMC) and metacarpophalangeal (MCP) regions of normal equine superficial and deep digital flexor tendons. Five standard-bred horses (2-5 years old) were used and explants dissected from the MMC and MCP regions of the superficial and deep digital flexor tendons. The explants (3 mm2) were cultured in Ham’s F12 media supplemented with 1% FBS. After 24 h, Na2S35SO4 was added and the culture continued for a further 48 h. The media was removed and the explants were lyophilized and weighed. The explants and media were then subject to papain digestion and the DNA and sulphated glycosaminoglycans (S-GAG) concentrations and incorporation of [35S] sulphate into PGs determined by established methods.The MMC regions of the superficial and deep digital flexor tendons contained less PGs than the MCP regions and these were predominantly small. The MCP regions, not only contained higher concentrations of PGs, but these were of larger hydrodynamic size. The incorporation of [35S] sulphate into PGs was also higher in explants from the MCP region. These data indicate that in those regions of equine flexor tendon, subjected to both, compression and tension, PG content and biosynthesis is higher than in regions which only transmit tensional loads. These findings are consistent with the adaptive role of tenocytes to the nature and level of the mechanical stresses imposed upon them.The proteoglycans (PGs) and DNA content and their biosynthesis were determined in cultures of expiants obtained from the mid-metacarpal (MMC) and metacarpophalangeal (MCP) regions of normal superficial and deep digital flexor tendons of five standard bred horses (2– years old). It was shown that the MMC region of the superficial and deep flexor tendon contained less PGs than the MCP regions. Moreover, the biosynthesis of PGs was enhanced in the MCP explants and the size of these molecules was larger than made by cells of the MMC region.

経皮けん鞘切開術を行った弾発指３５４指の検討

Three handred and fifty-four trigger fingers in 292 patients treated initially by percutaneus A-1 pulley release technique from July 1996 to May 1998 were reviewed retrospectively.There were 255 (87.3%) females, 37 (12.7%) males, with a mean age of 52.4 (range 36-84 years). The Thumb was most frequently involved (159 digits), followed by middle finger (96), index finger (66), ring finger (30), and little finger (3).They consisted of 242 (262 digits) idiopathic patients, 36 (74) hemodialysis, and 14 (18) rheumatoid arthritis.Of the 354 trigger fingers, 339 (95.8%) had complete resolusion of triggering with the disappearance of snapping after percutaneus release. Reoperations (percutaneus or open surgery) were required in 12 (3.4%) fingers 9 for residual snapping after release, 2 for uneven movement with pain by the tendon nobule and incompletely released A-1 pulley, 1 for the narrow between the thick tendontheath and tendon nodule.At reoperation, residual snapping and uneven movement were considered to be caused by incompletely release in 6 fingers, hypertrophy of the tenosynovium in 3, snapping in A-2 pulley in 2, and adhesion between the deep and superficial flexor tendons in 1.Pain over 4 weeks after surgery was found in 19 fingers, and Metacarpo-phalangeal joint flexion iontracture like “Dupuy treins contrcture” occured in 3, but no infection and no neuro-vascular injury were seen.We reccommend this technique for outpatients with trigger fingers, because of its safety, simplicity, few complication, and patient's satisfaction with high successful rate.

In situ expression of collagen and proteoglycan genes during development of fibrocartilage in bovine deep flexor tendon.

A region of fibrocartilage develops in bovine deep flexor tendon where the tissue wraps around bone and is subjected to compressive and shear forces in addition to tension. There is no fibrocartilage at this location in fetal tendon or in adjacent adult tendon that is subjected to tensional load only. We investigated the development of fibrocartilage in tendon using in situ hybridization to localize cells that express collagen and proteoglycan genes typical of either tendon or cartilage. The signal for type I collagen and decorin was high in cells throughout fetal and newborn tendon, as is expected in a growing tissue composed predominantly of type I collagen. No signal for aggrecan was seen in either fetal or newborn tendon. No hybridization with any of the probes for collagen or proteoglycan was detected in cells in the tensional region of adult tendon, indicating that the cells in this tissue are normally quiescent. However, the cells in the fibrocartilage of adult tendon displayed a high level of expression for types I and II collagen, decorin, biglycan, and aggrecan. This suggests that the fibrocartilage in adult tendon is a dynamic tissue. Expression of type IIA collagen is considered a marker of prechondrocytes. Type IIA collagen gene expression was present throughout both the tensional and compressed regions of fetal and newborn tendon but was absent in cartilage and adult tendon. This suggests that cells located throughout fetal tendon may have the capacity to develop as chondrocytes. Fibrocartilage signal was detected for type I collagen in 75% of the cells and for type II collagen in 50% of the cells at one location in adult tendon, suggesting that some cells in this tissue could have expressed mRNA for both type I and type II collagen.