Superficial Flexor Tendon Research Articles

Bony palmar ridges of the phalanges of the human fingers

On imaging studies, bony ridges can be seen at the palmar aspect of the phalanges of the fingers. Our purpose was to address the following: (1) which structures insert on to the ridges and what is the histological appearance? (2) Is there a difference between the different fingers? (3) Is there a correlation between the ridges and age? Two observers retrospectively evaluated 270 radiographs (135 men; 135 women; mean age 44 years), and 33 CT scans (22 men; 11 women; mean age 46 years). Three cadaveric hands were also studied. The ridges were graded using a 4-point scale. A Chi-square test was used to compare the different fingers (p < 0.05) and to study the prominence of the ridges in relation to age (p < 0.05). On histology with routine stains the A2 pulley was inserted on the ridges of the proximal phalanx, and the flexor superficialis and A4 pulley on the ridges of the middle phalanx. On histology, the insertion showed a transition zone consisting of fibrocartilage. The prominence of the ridges was significantly different between fingers with III and IV categorized higher than II and III. There was a significant correlation with age for all fingers except for the middle phalanx of II and III. The bony palmar ridges have characteristics of enthesophytes. They correspond to the insertion site of the A2 pulley, and the flexor superficialis tendon and A4 pulley, at the proximal and middle phalanx, respectively. The ridges become more prominent with age, and their prominence is different between the fingers with III and IV categorized higher than II and V.

Wiederherstellung der Daumenendgelenkbeugung durch Transposition der oberflächlichen Beugesehne des Ringfingers

Restoration of active thumb flexion at the distal joint. Loss of active flexion of the interphalangeal (IP) joint of the thumb if there is a transection of the flexor pollicis longus (FPL) tendon at the tendon channel of the thumb or thenar and direct suture is not possible but the tendon channel is intact, as alternative procedure to a free tendon graft if the transection is proximal to the tendon channel and the muscle of the FPL is contracted/injured or the FPL tendon is unharmed but the FPL muscle is partially or complete paralyzed. Insufficiency of the FPL tendon channel, impairment of the superficial or deep flexor tendon of the ring finger, limited passive motion of the proximal and distal thumb joints, acute local general infection and non-compliance or incapacity of the patient. The surgical technique depends on the necessity of transosseous refixation of the FDS IV at the base of the distal phalanx of the thumb or the possibility of woven sutures through the FPL proximal to the tendon channel. If the tendon channel is intact the distal part of the FPL tendon is shortened to 1cm, the FDS IV tendon is cut distal to the chiasma of Camper, pulled through the carpal tunnel and moved into the channel of the FPL tendon and fixed transosseously through the base of the distal phalanx of the thumb. If the transection of the FPL tendon is located proximal to the tendon channel and muscle of the FPL is injured, FDS IV tendon will be woven using the Pulvertaft technique through the FPL tendon at the distal forearm. Postoperative 6weeks motion of thumb flexion without resistance in relieved position of the thumb through a thermoplast splint and 6weeks of functional use of the hand with increasing weight bearing. In this study 10patients with FDS IV transposition to reconstruct an isolated rupture of the FPL tendon could be followed for an average of 4.1years postoperatively. The active range of motion of the IP joint of the thumb averaged 65° (10-100°), 8/10patients achieved an equal active and passive range of motion of the IP joint of the thumb, in 2patients some flexion insufficiency remained, 9 patients could reach the fingertip of the small finger with the thumb and 1patient lacked 3mm. Contracture of the proximal thumb joint developed in two patients. After removal of the FDSIV tendon two patients developed contracture of the PIP joint of the ring finger. The grip force was reduced to 81 %, lateral grip to 83 % and pinch grip to 77 %. The DASH score averaged 18 (0-31) and 8/10patients would choose to undergo this surgery again.

Operative Behandlung der Krallenhand mittels Lassoplastik

The aim is correction of claw deformity of the fingers by intrinsic paralysis. Indications are claw deformity of fingers caused by palsy or functional loss of the interosseus or lumbrical muscles as far as the function of the superficial and deep flexors of the finger is intact. Contraindications are loss or paralysis of finger flexors supplied by the median nerve, fixed extension or flexion contracture of the finger joints, osteoarthritis and other malfunctions of the finger joints, no active flexion and extension of the interphalangeal joints due to compromised tendon gliding. Relative: Upper ulnar nerve palsy with functional loss of the deep flexor of the small and ring finger and possibly of the middle finger. The operation technique involves detachment of the flexor digitorum superficialis IV tendon (FDSIV) distal to Camper's chiasm, division of the tendon into separate strips, interweaving of each tendon strip into the proximal part of the A2 pulley of the affected fingers. In cases of claw deformity of all fingers it may be advantageous to apply the superficial flexor tendon of the long finger in addition to the FDSIV tendon as otherwise the FDSIV tendon has to be divided into four strips resulting in relatively thin tendon strips. If the FDSIII and IV tendons are applied, the two strips of the FDSIV tendon are used for lassoplasty of the small and ring fingers and the FDSIII tendon for lassoplasty of the middle and index fingers. Postoperative management includes immobilization of the operated fingers by a dorsoulnar forearm plaster cast including the metacarpophalangeal joints which are flexed to 70°. After 2weeks replacement of the cast by a thermoplastic splint for another 4weeks. During the whole period exercises for the finger and thumb should be carried out. From April 2003 to June 2012 a total of 17patients, 8female and 9male were surgically treated for claw deformity. The dominant hand was affected in seven patients. The average age was 46 ± 15 (22-80) years, the average interval from onset of ulnar palsy to lassoplasty was 61 ± 91 (3-288) months. The final follow-up was performed after an average of 42 ± 32 (2-112) months. Claw deformity was resolved in 14 out of the 17patients. The grip strength was on average 58 ± 28 % (11-96%) of the unaffected hand, the mean disabilities of the arm, shoulder and hand (DASH) score was 32 ± 18 (5-68) points and the degree of patient satisfaction 7 ± 2 (0-10). According to own results and those in the literature lassoplasty can be recommended for the treatment of claw deformity.

Transposition der oberflächlichen Beugesehnen von Mittel- und Ringfinger zur Wiederherstellung der Daumen- und Fingerstreckung (Boyes-Transfer)

Restoration of extension in the metacarpophalangeal joints of the fingers as well as in the interphalangeal joint of the thumb by transfer of the superficial flexor tendons of the long and ring fingers (flexor digitorum superficialis III and IV). The indications for surgery are substantial loss and palsy of muscles innervated by the radial nerve and its roots. The procedure is contraindicated by reversible radial palsy, palsy or substantial loss of flexors, limited passive mobility due to contracture, ankylosis or instability of the affected joints, instability of the wrist joint, palsy of the wrist flexors, ankylosis of the wrist joint in an unfavorable position, adhesions of flexor or extensor tendons, insufficient soft tissue coverage or soft tissue defects and passage of transposed tendons through scarred tissue. The surgical technique involves division of the superficialis tendons of the long and ring fingers proximal to Camper's chiasm and routing of the tendons to the dorsum of the hand through separate fenestrations of the interosseus membrane. The flexor digitorum superficialis tendon III is interwoven into the tendons of the extensor pollicis longus und extensor indicis and the flexor digitorum superficialis IV is interwoven into the extensor digitorum tendons. Forearm splinting in 20° wrist extension including the metacarpophalangeal joints of the fingers in extension and the thumb in the automatic stop position for 4weeks leaving the proximal and distal interphalangeal joints free. From March 1999 to January 2010 a Boyes' transfer was performed in 13patients (8female and 5male) and the right side was affected in 8, the left side in 5 and the dominant hand in 7cases. The patient age at the time of surgery was an average of 47 ± 17 (13-73) years. The interval between radial palsy and tendon transfer was an average of 79 ± 144 (4-543) months. The final follow-up was performed at an average of 82 ± 35 (32-165) months. According to the Haas scoring system finger extension was excellent in 5, good in 5, fair in 3 and unfavorable in 4cases and thumb extension was excellent in 5, good in 3, fair in 1 and unfavorable in 5patients. The mean disabilities of the arm, shoulder and hand (DASH) score was 36 ± 24 (11-85) points. Although disability of varying degrees persisted in all patients, Boyes' transfer is considered to be a safe procedure to restore finger and thumb extension with excellent and good functional results, a high degree of patient satisfaction and few complications.

Percutaneous flexor tenotomy for preventing and treating toe ulcers in people with diabetes mellitus

IntroductionThe purpose was to examine the effectiveness of flexor tenotomy in a modified technique to prevent and heal neuropathic and neuroischaemic pressure ulcers on the tip of the toe in claw- or hammer-toe deformities in people with diabetes. Patients and methodsA consequetive 4 years series of 38 patients was retrospectively studied. Percutaneous tenotomy on the superficial and deep flexor tendons was performed in 65 toes through a small transverse plantar stab incision just proximal to the web level. There were 16 (42%) patients with 27 ulcerated toes and 22 (58%) patients with 38 toes with impending ulceration. Ten patients had neuropathic ulcers and six patients had neuro-ischaemic ulcers. Sixteen patients (42%) had macrovascular disease. Ten (26%) had proliferative rethinopathy, 7 (18%) macroalbuminuria and 18 (47%) microalbuminuria. ResultsAll surgical incisions healed uneventfully. Twenty-five (93%) of the toe ulcers healed in median 21 days (range 7–224 days). Three patients had recurrence of the ulcer. There were no infections in the incisions or toe amputations. No patients treated with preventive tenotomy experienced toe ulceration. No complications were recorded in neuro-ischaemic ulcers. During the follow up period of median 31 months (range 2–48 months) 33 other ulcers were recorded in 18 patients (47%). One of these developed a transfer ulceration under the adjacent metatarso-phalangeal joint and another had a late pressure ulcer on a neighbouring toe. The other 31 ulcers were not related to ulcers treated with tenotomy. ConclusionTenotomy is a simple, safe and effective procedure for preventing and treating distal plantar neuropathic toe ulcers in claw toe or hammer toe deformities in people with diabetes with or without serious co-morbidity. The results suggest that tenotomy should be considered also in neuroischaemic ulcers.

Sonographic Measurements of Subsynovial Connective Tissue Thickness in Patients With Carpal Tunnel Syndrome

A major pathologic finding in patients with idiopathic carpal tunnel syndrome is noninflammatory fibrosis and thickening of the subsynovial connective tissue. The objective of this study was to determine the ability of sonography to depict this thickening by comparing subsynovial connective tissue thickness in patients with carpal tunnel syndrome and healthy control participants. Longitudinal sonograms of the middle finger superficial flexor tendon and subsynovial connective tissue were obtained at 3 levels: at the wrist crease (proximal tunnel), at the hook of the hamate (mid tunnel), and at the distal edge of the transverse carpal ligament (distal tunnel). The thickness of the subsynovial connective tissue perpendicular to the direction of the tendon and the diameter of the flexor digitorum superficialis tendon at the same level were measured. Then, a thickness ratio was created. At all 3 levels, the subsynovial connective tissue was thicker in patients than in controls (P < .0001) with a thickness ranging from 0.60 to 0.63 mm in patients and 0.46 to 0.50 mm in controls. The thickness ratio was significantly greater in patients at the hamate and distal levels (P = .018 and .013, respectively). With this study, we have shown that it is possible to measure subsynovial connective tissue thickness with sonography, and the tissue is thicker in patients with carpal tunnel syndrome than in healthy controls.

Biomechanical responses of different rat tendons to nandrolone decanoate and load exercise

Androgenic-anabolic steroids (AAS) have been associated with an increased incidence of tendon rupture. The aim of this study was to compare the biomechanical properties of the rat calcaneal tendon (CT), superficial flexor tendon (SFT), and deep flexor tendon (DFT), and to determine the effect of jump training in association with AAS. Animals were separated into four groups: sedentary, trained, AAS-treated sedentary rats (AAS), and AAS-treated and trained animals. Mechanical testing showed that the CT differed from the DFT and SFT, which showed similar mechanical properties. Jump caused the CT to exhibit an extended toe region, an increased resistance to tensional load, and a decreased elastic modulus, characteristics of an elastic tendon capable of storing energy. AAS caused the tendons to be less compliant, and the effects were reinforced by simultaneous training. The DFT was the most affected by training, AAS, and the interaction of both, likely because of its involvement in the toe-off step of jumping, which we suggest is related to the rapid transmission of force as opposed to energy storage. In conclusion, tendons are differently adapted to exercise, but responded equally to AAS, showing reduced flexibility, which is suggested to increase the risk of tendon rupture in AAS consumers.

Minimally Invasive Management of Dorsiflexion Contracture at the Metatarsophalangeal Joint and Plantarflexion Contracture at the Proximal Interphalangeal Joint of the Fifth Toe

Several surgical options have been described to manage persistent dorsiflexion contracture at the metatarsophalangeal joint and plantarflexion contracture at the proximal interphalangeal joint of the fifth toe. We describe a minimally invasive technique for the management of this deformity. We perform a plantar closing wedge osteotomy of the 5th toe at the base of its proximal phalanx associated with a lateral condylectomy of the head of the proximal phalanx and at the base of the middle phalanx. Lastly, a complete tenotomy of the deep and superficial flexor tendons and of the tendon of the extensor digitorum longus is undertaken. Correction of cock-up fifth toe deformity is achieved using a minimally invasive approach.

Gene expression in distinct regions of rat tendons in response to jump training combined with anabolic androgenic steroid administration

The aim of this study was to evaluate the expression of key genes responsible for tendon remodeling of the proximal and distal regions of calcaneal tendon (CT), intermediate and distal region of superficial flexor tendon (SFT) and proximal, intermediate and distal region of deep flexor tendon (DFT) submitted to 7weeks of jumping water load exercise in combination with AAS administration. Wistar male rats were grouped as follows: sedentary (S), trained (jumping water load exercise) (T), sedentary animals treated with AAS (5mg/kg, twice a week) and animals treated with AAS and trained (AAST). mRNA levels of COL1A1, COL3A1, TIMP-1, TIMP-2, MMP-2, IGF-IEa, GAPDH, CTGF and TGF-β-1 were evaluated by quantitative PCR. Our main results indicated that mRNA levels alter in different regions in each tendon of sedentary animals. The training did not alter the expression of COL1A1, COL3A, IGF-IEa and MMP-2 genes, while AAS administration or its combination with training reduced their expression. This study indicated that exercise did not alter the expression of collagen and related growth factors in different regions of rat tendon. Moreover, the pattern of gene expression was distinct in the different tendon regions of sedentary animals. Although, the RNA yield levels of CT, SFT and DFT were not distinct in each region, these regions possess not only the structural and biochemical difference, but also divergence in the expression of key genes involved in tendon adaptation.

Kinetics of Crimp and Slope Grip in Rock Climbing

The aim was to investigate differences of the kinetics of the crimp and the slope grip used in rock climbing. Nine cadaver fingers were prepared and fixated with the proximal phalanx in a frame. The superficial (FDS) and deep (FDP) flexor tendons were loaded selectively and together with 40 N in the crimp grip (PIP joint flexed 90°/DIP joint hyperextended) and the slope grip position (<25° flexed/50° flexed respectively). Five different grip sizes were tested and the flexion force which was generated to the grip was measured. In the crimp grip the FDP generated more flexion force in small sized holds whereas the FDS generated more force in the larger holds. During the slope grip the FDP was more effective than the FDS. While both tendons were loaded, the flexion force was always greater during crimp grip compared with the slope grip. The FDP seems to be most important for very small holds using the crimp grip but also during slope grip holds whereas the FDS is more important for larger flat holds.

Spontaneous rupture of the flexor superficialis tendon of ring finger: a case report and review of literature

Compared with flexor digitorum profundus (FDP) tendon injury, the isolated rupture of flexor digitorum superficialis (FDS) tendon in a finger is a rare report in the literature. The pathogenesis is still unclear if we consider only tendon rupture without congenital anomalies or other diseases. The diagnosis is clinical, but it can be confirmed by ecography or magnetic resonance imaging (MRI). We report the case of a flexor superficialis (FS) tendon closed rupture of the ring finger of right hand in a 57-year-old patient. The diagnosis was confirmed by MRI. No surgical repair was used, given the limited clinical repercussions.

Gene expression in different regions of rat tendons submitted to load exercise associated with nandrolone decanoate administration

The use of anabolic androgenic steroids (AAS) increases risk for tendon injury, however, little is known about the effect of AAS in tendon gene expression. This study evaluated the expression of genes involved on tendon remodeling of the proximal and distal regions of calcaneal tendon, intermediate and distal region of superficial flexor tendon and proximal, intermediate and distal region of deep flexor tendon submitted to jumping water load exercise associated with AAS administration. Wistar male rats were grouped as follows: sedentary (S), trained (T), AAS-treated (10 mg/kg/week) sedentary rats (AAS) and AAS-treated and trained rats (AAST). mRNA levels of COL1A1, COL3A1, TIMP-1, TIMP-2, MMP-2, IGF-Ia, GAPDH, CTGF and TGF-β were evaluated by real-time PCR. Training did not alter the expression of COL1A1, COL3A1 and MMP-2 genes, while AAS administration or its association with training reduced theses gene expression. IGF-Ia enhanced with exercise, while AAS and AAST decreased their expression. In conclusion, the training did not alter the collagen expression and main growth factors in different regions of rat tendon. However, AAS or AAST showed harmful effects in the tendon ECM remodeling. The gene expression was distinct in each tendon region of sedentary animals, indicating that these regions possess a variance in expression of key genes responsible for the tendon adaptation. Grant from FAPESP-06/50986-6.

Gedeckte Ruptur der tiefen Beugesehne des Kleinfingers

Closed ruptures of the deep flexor tendons are rare, even though they occur more often than those of the superficial flexor tendons. We report about a closed distal rupture of the deep flexor tendon of the little finger as experienced by a 50-year-old man who suffered an injury at work. The proximal stump allocated to the torn flexor tendon of zone I had noticeably pulled back to the middle of the palm of hand, and had come to rest around the tendon of the ring finger. We illustrate the problems linked with diagnosis, care and follow-up treatment of such a case.

Apparent transverse compressive material properties of the digital flexor tendons and the median nerve in the carpal tunnel

Carpal tunnel syndrome is a frequently encountered peripheral nerve disorder caused by mechanical insult to the median nerve, which may in part be a result of impingement by the adjacent digital flexor tendons. Realistic finite element (FE) analysis to determine contact stresses between the flexor tendons and median nerve depends upon the use of physiologically accurate material properties. To assess the transverse compressive properties of the digital flexor tendons and median nerve, these tissues from ten cadaveric forearm specimens were compressed transversely while under axial load. The experimental compression data were used in conjunction with an FE-based optimization routine to determine apparent hyperelastic coefficients (μ and α) for a first-order Ogden material property definition. The mean coefficient pairs were μ=35.3kPa, α=8.5 for the superficial tendons, μ=39.4kPa, α=9.2 for the deep tendons, μ=24.9kPa, α=10.9 for the flexor pollicis longus (FPL) tendon, and μ=12.9kPa, α=6.5 for the median nerve. These mean Ogden coefficients indicate that the FPL tendon was more compliant at low strains than either the deep or superficial flexor tendons, and that there was no significant difference between superficial and deep flexor tendon compressive behavior. The median nerve was significantly more compliant than any of the flexor tendons. The material properties determined in this study can be used to better understand the functional mechanics of the carpal tunnel soft tissues and possible mechanisms of median nerve compressive insult, which may lead to the onset of carpal tunnel syndrome.

Petrus Camper's Work on the Anatomy and Pathology of the Arm and Hand in the 18th Century

Petrus Camper (1722-1789) was a professor of anatomy and surgery at the Universities of Franeker, Amsterdam and Groningen. During the mid-18th century, he performed dissections to study the anatomy and pathology of the arm. Based on his findings, he published one of the most detailed anatomical atlases of the arm and hand in history, entitled Demonstrationum anatomico-pathologicarum liber primus brachii humani fabricam et morbos. In his atlas, he describes the "chiasma" indicating the intersections of the superficial and deep flexor tendons, which are essential for the gripping function of the hand. Camper's anatomical studies and elaborate illustrations contributed to a better understanding of the anatomy and pathology of the arm.

L’atteinte des tendons fléchisseurs dans la maladie goutteuse. À propos d’un cas et revue de la littérature

We present a case of synovial and flexor tendons gouty involvement associated to the flexion contracture of a single digit. The case was treated surgically by tenosynovectomy and resection of the flexor superficialis tendon followed by arthrolysis of the proximal interphalangeal joint. This rare etiology of flexion contracture must be taken into account in every patient with a history of gout and tendon pathology.

Fresh autogenous and allogenous tendon graft in rabbit model

Tendons are soft connective tissues consisting of parallel collagen fibers embedded within an extracellular matrix. Blood supply to the tendon is reported to be poor and, as a result, healing often progresses slowly. Autogenic, allogeneic, and xenogeneic tendon transplantations have been performed in reconstructive tendon surgery; however, there is little information on fresh allogeneic tendon transplantation experimentally. The aim of this study is to evaluate fresh autogenous and allogenous tendon graft in the rabbit to determine which gives the better result, clinically and histopathologically. Ten 1-year-old male New Zealand Albino rabbits weighing 3.5 ± 0.5 kg were used in this study. In five rabbits (group I), about 3 cm of the superficial flexor tendon was resected and a created defect was filled with the same 3-cm harvested tendon and sutured with 2/0 polypropylene in a single modified Kessler suture pattern and the tendon sheath was sutured over the transplanted tendon completely. In the remaining five rabbits (group II), the harvested segment was changed between rabbits and created defects were filled with changed segment allogenous tendon, all other procedures were identical to group I. The main histopathological and gross evaluation showed graft acceptance by recipients in both groups. Our results showed that no significant tissue reaction or graft rejection was observed when fresh allogeneic tendon was transplanted in a rabbit model.

A Cadaver Model That Investigates Irreducible Metacarpophalangeal Joint Dislocation

Controversy exists over the pathologic anatomy of irreducible dorsal metacarpophalangeal (MCP) dislocation. The aim of this work is to develop a cadaveric model of MCP joint dislocation that closely simulates the clinical situation and to study the structures around the MCP joint and their contribution to irreducibility of the dislocation. Nine fresh-frozen cadaveric specimens were amputated at the radiocarpal joint and stabilized in a specially formulated fixture. The dislocation was created by an impact load delivered by a servohydraulic testing machine, at a displacement rate of 1000 mm/s and with a maximum displacement of 60 mm. An irreducible dislocation was successfully created in 6 index fingers. An attempt at closed reduction was followed by a dissection of the dislocated joint. In the 6 examined specimens, the flexor tendons were ulnar to the joint in all cases, the radial digital nerve was superficial (5 cases) or radial (5 cases) to the metacarpal head, and the lumbrical was usually radial (5 of 6 cases) to the joint. Division of the superficial transverse metacarpal ligaments, natatory ligaments, flexor tendons, or lumbricals does not aid reduction of the dislocation. Division of the volar plate was necessary for reduction of the dislocation in all 6 cases, whereas division of the deep transverse metacarpal ligaments does not allow reduction of the dislocation. We present a model for creating an irreducible MCP joint dislocation using an impact load that simulates the clinical situation. The volar plate is the primary structure preventing reduction of the dislocation. Division of the deep transverse metacarpal ligament is not effective in reducing the dislocation. The flexor tendons, lumbricals, superficial transverse metacarpal ligament and natatory ligaments do not contribute to irreducibility. The anatomy of the structures surrounding the MCP joint is variable, and careful dissection to prevent iatrogenic injuries is mandatory.

Ostrich tendon (new xenogenic) transplantation in rabbit model

Since tendons are subjected to repeated motion and degeneration over time, they are prone to both acute and chronic injuries. In addition, the blood supply to the tendon is generally poor; as a result, healing often progresses slowly. Autogenic, allogenic and xenogenic tendon transplantations have been performed in reconstructive tendon surgery. There is no report on ostrich (xenograft) tendon transplantation to other species. The aim of this study was to evaluate ostrich flexor tendon transplantation in a rabbit model. Seven male New Zealand white rabbits 1 year old and weighing 4.0 ± 0.5 kg were used in this study. Approximately 3 cm of the superficial flexor tendon was resected, and created defects were filled in all rabbits with 3-cm harvested ostrich chick tendon and sutured with 2/0 polypropylene in a single Modified Kessler suture pattern. The main histopathological and gross evaluation showed graft necrosis and sequestration. Our results showed that ostrich tendon displays severe antigenicity and elicits a vigorous inflammatory reaction and is, therefore, not recommended for use as a xenogenic tendon graft for the replacement of tendons or ligaments.

Morphological and biomechanical studies on the common calcaneal tendon in dogs

Spontaneous rupture at the distal part of the gastrocnemius tendon (GT) is the second most common non-traumatic tendon injury in dogs, whereas the other strands of the common calcaneal tendon do not seem to have a predisposition to rupture. In order to discover why we investigated the common calcaneal tendons of 63 dogs microscopically and biomechanically. Both the gastrocnemius and superficial digital flexor tendon (SFT) had multiple low vascularized fibrocartilaginous areas within their distal course as opposed to regular parallel fibered areas in the proximal tendon areas. Biomechanical testing revealed that the distal sections in both tendons show a 50% and 70% lower tensile strength (F(max)/kg BW) than the proximal sections (p<0.01), respectively. On the contrary, tensile load (F(max)/mm(2)) only differed minimally between proximal and distal sections in both tendons (8% and 9%, respectively), whereas the tensile load of the distal gastrocnemius tendon is 35% lower than of the distal superficial flexor tendon (p<0.01). To the authors' knowledge, this is the first study to experimentally show that there are different biomechanical properties within the same tendon. The maximum load to failure is lower in the GT compared to the SFT within the same dog which explains its higher incidence of rupture in the field. The avascular fibrocartilaginous structure in the distal gastrocnemius tendon seems to play a further role in the pathogenesis of spontaneous rupture.