Equine Deep Digital Flexor Research Articles

Ex vivo study shows novel, rapid, suture-free tenotomy technique for the equine deep digital flexor tendon.

To describe the feasibility of a novel thread-transecting technique for the tenotomy of the equine deep digital flexor tendon (DDFT). 39 equine distal limb specimens. Under ultrasonographic guidance, a surgical thread was percutaneously placed around the DDFT through 2 needle punctures (lateral and medial) using a Tuohy needle in equine limbs (22 forelimbs, 17 hindlimbs). The DDFT was transected by a back-and-forth motion of the thread until the loop emerged from the entry puncture site. Each specimen was dissected and assessed for completeness of transection and iatrogenic damage under direct visualization. Descriptive statistics were reported. Complete DDFT transection was achieved in all 39 limbs, taking an average of 8.6 minutes per procedure. Iatrogenic damage to surrounding structures occurred in 17 (44%) limbs, with 6 (15%) limbs having more than 1 structure damaged. Damage to the communicating branch of the palmar or plantar nerves was the most commonly seen. DDFT tenotomy in equine limb specimens was effectively performed using a novel thread-transecting technique. The procedure is quick, and no suturing is needed, but damage to surrounding structures is possible. Further assessment of the procedure and clinical significance of its potential iatrogenic damage in clinical cases is needed.

Macrophage phenotype impacts in vitro equine intrasynovial deep digital flexor tenocyte matrix metalloproteinase gene expression and secretion.

To investigate matrix metalloproteinase (MMP) and their inhibitors tissue inhibitor matrix metalloproteinase (TIMP) gene expression and secretion during equine deep digital flexor tendon (DDFT) tenocyte and macrophage (undifferentiated, proinflammatory, and regulatory) co-culture. Third passage DDF tenocytes and donor-matched macrophages differentiated from peripheral blood CD14+ monocytes from 5 healthy horses ages 9-11 years, euthanized for reasons unrelated to musculoskeletal conditions. Passage 3 DDT tenocyte aggregate cultures were co-cultured with undifferentiated (control), proinflammatory (granulocyte-macrophage colony-stimulating factor; GM-CSF pretreated and lipopolysaccharide + interferon gamma-primed; LPS+IFN-γ) or regulatory (interleukin-4 and interleukin-10-primed; IL-4 + IL-10) macrophages in direct and transwell co-cultures for 72 hours. MMP-1, -2, -3, -9, -13, and TIMP -1, -2 mRNA were measured via real-time Polymerase Chain Reaction (rtPCR). Co-culture media MMP -3, -9, and TIMP -1, -2 concentrations were quantified via ELISA. Direct co-culture of DDF tenocytes with proinflammatory macrophages for 72 hours increased MMP-1, -3, and -13 mRNA levels whereas, MMP-9 mRNA levels decreased. Direct and transwell co-culture with proinflammatory and regulatory macrophages resulted in increased MMP-3 and decreased MMP-9 media concentrations. While direct co-culture with regulatory macrophages significantly increased TIMP-1 mRNA, overall, TIMP mRNA and culture media concentrations were largely unchanged. Cell-to-cell contact between DDF tenocytes and macrophages is not essential to induce MMP gene expression and secretion. Co-culture systems offer a viable in vitro platform to screen and evaluate immunomodulatory properties of therapies aimed at improving equine intrasynovial tendon healing.

Interleukin-1β and methylprednisolone acetate demonstrate differential effects on equine deep digital flexor tendon and navicular bone fibrocartilage cells in vitro

To investigate the effects of interleukin-1β (IL-1β) and methylprednisolone acetate (MPA) on equine intrabursal deep digital flexor tendon (DDFT) and navicular bone fibrocartilage (NBF) cells in vitro. Third passage DDFT and NBF cells from 5 healthy donor horses ages 11-17 years euthanized for reasons unrelated to musculoskeletal conditions. Aggregate cultures were incubated with culture medium alone (control), 10 ng/mL IL-1β, 10 ng/mL IL-1β + 0.05 mg/mL MPA, or 10 ng/mL IL-1β + 0.5 mg/mL MPA for 24 hours. Extracellular matrix (ECM) gene expressions were assessed via real-time polymerase chain reaction (rtPCR). Culture media matrix metalloproteinase (MMP) -3 and -13 concentrations were quantified via ELISA. Total glycosaminoglycan (GAG) content in the cell pellets and culture media was also assessed. IL-1β and IL-1β combined with MPA significantly downregulated ECM gene expression to a greater extent in NBF cells compared with DDFT cells. IL-1β and IL-1β combined with MPA significantly upregulated MMP-3 culture media concentrations in DDFT cells only, and MMP-13 culture media concentrations to a greater extent in NBF cells compared with DDFT cells. NBF cells were more susceptible to IL-1β and MPA-mediated ECM gene expression downregulation in vitro. These results serve as a first step for future work to determine intrabursal corticosteroid regimens that limits or resolve the inflammation as well as take into consideration NBF cell biosynthesis in horses with navicular disease, for which currently no information exists.

Effect of single and double hemitenotomy on equine deep digital flexor tendon length and strength in experimental load challenges.

To evaluate a double hemitenotomy (DHT) technique as an alternative to complete deep digital flexor (DDFT) tenotomy. Experimental ex vivo study. Isolated DDFTs (n=30) and cadaveric forelimbs (n=16). In part 1, 15 isolated DDFT pairs were used. Two hemitenotomies were created in 1 DDFT while the other served as reference. Monotonic tensile load was applied. Tendon lengthening, load reduction, and load at failure were recorded. In part 2, 16 cadaveric forelimb pairs were subjected to DHT followed by complete tenotomy (CT) under monotonic compressive load. Differences between DHT and controls were assessed with Wilcoxon signed rank tests or Friedman tests. In isolated tendons and cadaveric forelimbs, DHT resulted in DDFT lengthening (median, +1.9 mm and + 3.05 mm) and load reduction (median, -16.7 and -11.2kg). Less lengthening was achieved with DHT compared to CT (P=.008). Load reduction did not occur between DHT and CT was observed during compressive testing (P=1). Load reduction following the first hemitenotomy incision was smaller when compared to the second (P=.022). Isolated DHT tendons failed at a tensile load of 195 kg, while no intact tendons failed (P=.0001). Double hemitenotomy was comparable to CT in load reduction. It reduced tensile strength, but load at failure was similar or exceeded the estimated DDFT load at stance. Hemitenotomy may be a useful alternative for surgical management of horses with laminitis, but in vivo studies are needed to confirm these findings.

Three-Dimensional Segmentation and in silico Comparison of Equine Deep Digital Flexor Tendon Pathology in Horses Undergoing Repeated MRI Examination.

The use of magnetic resonance imaging (MRI) has led to increased clinical and research applications using 3D segmentation and reconstructed volumetric data in musculoskeletal imaging. Lesions of the deep digital flexor tendon (DDFT) are a common pathology in horses undergoing MRI. Three-dimensional MRI reconstruction performed for volumetric tendon analysis in horses has not previously been documented. The aim of this proof-of-concept study was to evaluate the 3D segmentation of horses undergoing repeated MRI at several time points and to perform an analysis of the segmented DDFTs across time. MRI DICOM files were acquired from six horses undergoing repeated MRI examination of the foot for DDFT injury. Once segmented, volumetric tendon surface tessellation language (STL) files were created. Thickness and volumetric data were acquired for each tendon in addition to a tendon comparison across timepoints within each horse. Pearson correlation coefficients were calculated for comparison of MRI reports to computer analysis. There was a significant and positive correlation between MRI and medial record reports of clinical improvement or deterioration and computer analysis (r = 0.56, p = 0.01). The lower end range limit for tendon thickness varied between 0.16 and 1.74 mm. The upper end range limit for DDFT thickness varied between 4.6 and 23.6 mm. During tendon part comparison, changes in DDFT were reported between −3.0 and + 14.3 mm. Changes in DDFT size were non-uniform and demonstrated fluctuations throughout the tendon. The study was successful in establishing the volumetric appearance and thickness of the DDFT as it courses in the foot and tracking this over time. We encountered difficulties in accurate segmentation of the distal insertion of the DDFT as it blends with the distal phalanx. The data demonstrated that the DDFT can be segmented and volumetric studies based on size and shape can be performed using an in silico approach.

An equine tendon model for studying intra-tendinous shear in tendons that have more than one muscle contribution

Human Achilles tendon is composed of three smaller sub-tendons and exhibits non-uniform internal displacements, which decline with age and after injury, suggesting a potential role in the development of tendinopathies. Studying internal sliding behaviour is therefore important but difficult in human Achilles tendon. Here we propose the equine deep digital flexor tendon (DDFT) and its accessory ligament (AL) as a model to understand the sliding mechanism. The AL-DDFT has a comparable sub-bundle structure, is subjected to high and frequent asymmetric loads and is a natural site of injury similar to human Achilles tendons. Equine AL-DDFT were collected and underwent whole tendon level (n=7) and fascicle level (n=7) quasi-static mechanical testing. Whole tendon level testing was performed by sequentially loading through the proximal AL and subsequently through the proximal DDFT and recording regional strain in the free structures and joined DDFT and AL. Fascicle level testing was performed with focus on the inter-sub-bundle matrix between the two structures at the junction. Our results demonstrate a significant difference in the regional strain between the joined DDFT and AL and a greater transmission of force from the AL to the DDFT than vice versa. These results can be partially explained by the mechanical properties and geometry of the two structures and by differences in the properties of the interfascicular matrices. In conclusion, this tendon model successfully demonstrates that high displacement discrepancy occurs between the two structures and can be used as an easy-access model for studying intra-tendinous shear mechanics at the sub-tendon level. Statement of significanceOur study provides a naturally occurring and easily accessible equine model to study the complex behaviour of sub-tendons within the human Achilles tendon, which is likely to play a critical role in the pathogenesis of tendon disease. Our results demonstrate that the difference in material stiffness between the equine AL and DDFT stems largely from differences in the inter-fascicular matrix and furthermore that differences in strain are maintained in distal parts of the tightly joined structure. Furthermore, our results suggest that distribution of load between sub-structures is highly dependent on the morphological relationship between them; a finding that has important implications for understanding Achilles tendon mechanical behaviour, injury mechanisms and rehabilitation.

Ex vivo effects of corticosteroids on equine deep digital flexor and navicular fibrocartilage explant cell viability

To investigate the effects of triamcinolone acetonide (TA) and methylprednisolone acetate (MPA) on the viability of resident cells within the fibrocartilage on the dorsal surface of the deep digital flexor tendon (FC-DDFT) and fibrocartilage on the flexor surface of the navicular bone (FC-NB) of horses. 12 to 14 explants of FC-DDFT and of FC-NB from grossly normal forelimbs of 5 cadavers of horses aged 9 to 15 years without evidence of musculoskeletal disease. Explants were incubated with culture medium (control) or TA-supplemented (0.6 or 6 mg/mL) or MPA-supplemented (0.5 or 5 mg/mL) medium for 6 or 24 hours. Explant metabolic activity and percentage of dead cells were assessed with a resazurin-based assay and live-dead cell staining, respectively, at each time point. Drug effects were assessed relative to findings for the respective control group. Application of TA (at both concentrations) did not significantly change the cell viability of FC-DDFT explants. For FC-NB explants, TA at 6 mg/mL significantly reduced the metabolic activity and increased the percentage of dead cells at both time points. With either MPA concentration, FC-DDFT and FC-NB explants had reduced metabolic activity and an increased percentage of dead cells at 24 hours, whereas only MPA at 5 mg/mL was cytotoxic at the 6-hour time point. In ex vivo explants, TA was less cytotoxic to equine FC-DDFT and FC-NB cells, compared with MPA. Further work is warranted to characterize the drugs' transcriptional and translational effects as well as investigate their cytotoxicity at lower concentrations.

In vitro Effects of Methylprednisolone Acetate on Equine Deep Digital Flexor Tendon-Derived Cells.

Primary deep digital flexor tendon (DDFT) pathologies and those accompanying degenerative changes of navicular bone fibrocartilage are major causes of lameness associated with navicular disease. Intrasynovial corticosteroids are mainstay in the treatment due to the anti-inflammatory effects, but their effect on DDFT cell biosynthesis are unknown. The objective of this in-vitro study was to investigate the effects of methylprednisolone acetate (MPA) on cells isolated from the dorsal fibrocartilaginous region of forelimb DDFTs (DDFT-derived cells) of 5 horses (aged 11–17 years). Non-adherent aggregate cultures were established from third passage cells over a 72 to 96-h duration prior to treating with medium containing 0 (control), 0.05 and 0.5 mg/mL MPA for 24 h. Tendon and cartilage extracellular matrix (ECM) related gene expression, cell aggregate and culture medium GAG contents, culture medium collagen and MMP-3 and−13 concentrations were measured. After 24 h of treatment, only the higher MPA concentration (0.5 mg/mL) significantly down-regulated tendon ECM related genes; whereas, both MPA doses significantly down-regulated cartilage ECM related genes. MPA treatment did not affect the total GAG content of DDFT-derived cells or total GAG, soluble collagen and MMP-3 and−13 contents in culture medium compared to untreated controls. Future studies to determine the response of DDFT-derived cells with longer exposure times to corticosteroids and in the presence of inflammatory cytokines are necessary. These results are a first step in assessing the effects of intrasynovial medications on equine DDFT, for which currently no information exists.

Sympathetic Innervation and Adrenergic Receptors in Equine Deep Digital Flexor Tendinopathy: Preliminary Results

The aim of this study was to delineate the pattern of sympathetic innervation in the suprasesamoidean region of the deep digital flexor tendon (DDFT) in horses with tendinopathy by immunohistochemical labelling for tyrosine hydroxylase (TH) and α-1 adrenergic receptor (α1-AR). Twelve forelimbs were obtained from 10 horses with DDFT tendinopathy and six feet obtained from six horses were used as healthy controls. Post-mortem radiographic, ultrasonographic and gross examinations were performed on the suprasesamoidean area of the DDFT to assess the presence of tendinopathy. Longitudinal sections were collected and processed. Lesions were classified as core lesions, dorsal border lesions and parasagittal oblique splits. Immunohistochemistry was performed and the degree of immunoreaction was classified as absent, mild or marked. Seven core lesions, four dorsal border lesions and one parasagittal oblique split were identified. There was no increased expression of sympathetic innervation in samples with a dorsal border lesion of the DDFT compared with healthy samples. In contrast, core lesions showed increased expression of α1-AR and reduced expression of TH, which supports the hypothesis of a compensatory imbalance between the sympathetic mediator and the sympathetic receptors as a cause or effect of structural damage. In addition, adrenergic activation could stimulate cell proliferation and differentiation within these lesions.

Accuracy of open magnetic resonance imaging for guiding injection of the equine deep digital flexor tendon within the hoof.

Lesions of the distal deep digital flexor tendon (DDFT) are frequently diagnosed using MRI in horses with foot pain. Intralesional injection of biologic therapeutics shows promise in tendon healing; however, accurate injection of distal deep digital flexor tendon lesions within the hoof is difficult. The aim of this experimental study was to evaluate accuracy of a technique for injection of the deep digital flexor tendon within the hoof using MRI-guidance, which could be performed in standing patients. We hypothesized that injection of the distal deep digital flexor tendon within the hoof could be accurately guided using open low-field MRI to target either the lateral or medial lobe at a specific location. Ten cadaver limbs were positioned in an open, low-field MRI unit. Each distal deep digital flexor tendon lobe was assigned to have a proximal (adjacent to the proximal aspect of the navicular bursa) or distal (adjacent to the navicular bone) injection. A titanium needle was inserted into each tendon lobe, guided by T1-weighted transverse images acquired simultaneously during injection. Colored dye was injected as a marker and postinjection MRI and gross sections were assessed. The success of injection as evaluated on gross section was 85% (70% proximal, 100% distal). The success of injection as evaluated by MRI was 65% (60% proximal, 70% distal). There was no significant difference between the success of injecting the medial versus lateral lobe. The major limitation of this study was the use of cadaver limbs with normal tendons. The authors conclude that injection of the distal deep digital flexor tendon within the hoof is possible using MRI guidance.

Do low field magnetic resonance imaging abnormalities correlate with macroscopical and histological changes within the equine deep digital flexor tendon?

Correlating magnetic resonance (MR) imaging and histopathological findings is essential to validate low field MR imaging in lame horses. This study aimed to compare signal changes in the deep digital flexor tendon (DDFT) of the distal limb on low field MR imaging with macroscopical and histological findings. Cadaver limbs from lame horses with DDFT lesions were selected. The DDFT MR imaging findings and histopathological results were graded, and macroscopical abnormalities were recorded. There was a strong correlation between MR imaging and histopathology grades (rs = 0.76, p < 0.001) in the foot. There was moderate agreement (Kappa statistic 0.52) between the MR and histopathology grades; agreement was superior further proximal in the foot. The presence and severity of pathology in the DDFT are well represented by the presence and severity of MR imaging signal changes. The study supports the use of low field MR imaging for diagnosis of equine distal limb DDFT lesions.

Identification of surgically-induced longitudinal lesions of the equine deep digital flexor tendon in the digital flexor tendon sheath using contrast-enhanced ultrasonography: an ex-vivo pilot study.

BackgroundLongitudinal tears in the lateral aspect of the deep digital flexor tendon are the most common causes of pain localised to the equine digital flexor tendon sheath. However conventional ultrasonographic techniques provide limited information about acute lesions. Ultrasonographic contrast agents are newly developed materials that have contributed to advancement in human diagnostic imaging. They are currently approved for intravenous use in human and animal models. In this study we described intrathecal use in the horse. This study was undertaken to evaluate the reliability of standard and angle contrast-enhanced ultrasonography to detect and characterize surgically-induced longitudinal lesions in the deep digital flexor tendons.In this pilot study surgically-induced lesions were created in the lateral aspect of the deep digital flexor tendon within the digital flexor tendon sheath in 10 isolated equine limbs to generate a replicable model for naturally occurring lesions. Another 10 specimens were sham operated. All the limbs were examined ultrasonographically before and shortly after the intrasynovial injection of an ultrasound contrast agent containing stabilised microbubbles. The images were blindly evaluated to detect the ability to identify surgically-created lesions. The deep digital flexor tendons were dissected and a series of slices were obtained. The depth of longitudinal defects identified with contrast-enhanced ultrasound scans was compared to the real extent of the lesions measured in the corresponding gross tendon sections.ResultsContrast-enhanced ultrasonography with both angle and standard approach provided a significant higher proportion of correct diagnoses compared to standard and angle contrast ultrasonography (p < 0.01). Contrast-enhanced ultrasonography reliably estimated the depth of surgically-induced longitudinal lesions in the deep digital flexor tendons.ConclusionContrast-enhanced ultrasound of the digital flexor tendon sheath could be an effective tool to detect intrasynovial longitudinal tears of the deep digital flexor tendon, although an in vivo study is required to confirm these results for naturally occurring lesions.

Determination of equine deep digital flexor muscle volume based on distances between anatomical landmarks

In equine medicine the use of Botox® is experimental. Dosages are determined from human treatment-protocols and limited numbers of equine studies. Determination of target-muscle volume can be helpful to extrapolate human dosages. The aim of the study was to calculate a formula enabling the estimation of the deep digital flexor muscle (DDFM) volume based on distances between anatomical landmarks.Nineteen cadaveric limbs were collected and distance A (top of olecranon to Os carpi accessorium) and B (circumference of limb) were measured. Converting mathematical formulas, C was calculated: π × (((0.5B)/π)2) × A. DDFM volume was determined by water displacement. Linear Regression Analysis was used to analyse data.The line best fitting the observed points was: Ln(volume[ml]) = −1.89 + 0.98 × Ln(value C[cm3]). Correlation was highest when natural logarithm was applied to both variables and was 0.97.The calculated formula enables estimating DDFM volume of a living horse. This estimated volume can be useful to apply human Botox® treatment-protocols.

The use of magnetic resonance imaging in diagnosing equine deep digital flexor tendinopathies--own experience.

Deep digital flexor tendinopathy is a common problem in horses of different athletic disciplines. Nowadays, the use of magnetic resonance imaging is considered to be a noninvasive and superior choice for recognizing bone and soft tissue pathologies especially related to difficult to access structures within the hoof capsule.

Desmitis of the Accessory Ligament of the Equine Deep Digital Flexor Tendon: A Regenerative Approach

Background: Desmitis of the accessory ligament of the deep digital flexor tendon (ALDDFT) is a very common problem in different breeds of sport horses, with an inability to heal adequately after conservative therapy in many cases. However, the treatment of different kinds of tendon lesions with platelet-rich plasma (PRP), mesenchymal stem cells (MSCs), or even tenogenic induced MSCs have been reported with promising results. Methods: After MSC and PRP isolation of the peripheral blood (PB) of a donor horse, tenogenic induction of the MSCs (Tendo-Cell®) was confirmed, and samples were microbiologically tested and frozen. Adverse and clinical effects (macroscopic noticeable swelling, lameness and ultrasound imaging) of PRP (n=4), or Tendo-Cell® (n=4) were evaluated after a single intralesional injection in the ALDDFT in 8 horses. For each case, two independent veterinary practitioners were asked to give a score from 0-5, at approximately 6 weeks and 4 months after treatment (0=no ultrasonographic improvement and 5=90-100% improvement, or (nearly) no ultrasonographic abnormalities, the ligament has (almost) no hypo-echoic foci, and (nearly) the same fiber orientation as the contralateral ligament). Results: At approximately 6 weeks post injection, the ultrasound images of all 4 horses treated with PRP only slightly improved. Therefore, a score 2/5 was given by the two attending veterinarians to all 4 patients. In the Tendo- Cell® treated group, on the other hand, all 4 horses received a score 4/5 by the same veterinarians at 6 weeks after intralesional injection. This implicates that the lesions improved about 80% on the ultrasound images, which was much better than the 40% improvement in the PRP treated group. Conclusion: This study reports a positive clinical and ultrasonographical outcome after tenogenic induced MSC (Tendo-Cell®) treatment of desmitis of the equine ALDDFT, whereas no considerable improvements could be noticed after treatment with allogenic PRP.

Applicability, interests and limitations of the ultrasound examination in the equine deep digital flexor apparatus of the thoracic limb.

The deep digital flexor tendon apparatus is represented by the distal part of the deep digital flexor tendon, the distal digital annular ligament and podotrochlear bursa, being the part of the podotrochlear apparatus most prone to injuries. The purpose of this study was to develop a systematic ultrasonographic approach of this apparatus and to present the accuracy of the ultrasound exam in imaging this anatomical formation. The ultrasound exam was performed on 10 sound horses using the palmar and transcuneal approach. Detailed description of the transverse and longitudinal ultrasonographic images of this region is provided. The ultrasound of the foot has been done with a non-portable machine Aloka Prosound Alpha 10 (Aloka Co. Ltd., 6-22-1 Mure, Mitaka-shi, Tokyo, 181, Japan). Convex and microconvex multifrequence transducers, with a frequency varying between 5.0 to 10.0 MHz have been used. This technique allowed us to image all the components of the deep digital flexor apparatus with the specification that it presents some limitations in examining the collateral parts of the distal deep digital flexor tendon and distal digital annular ligament. The main advantages of this technique are: low cost, short examination time and applicability in the field.

Survey of the Occurrence of Equine Deep Digital Flexor Tendon Contraction (Clubfoot) in the Main Thoroughbred Breeding Area in Japan

At 114 ranches in the Hidaka District of Hokkaido, a total of 1,118 Thoroughbred foals that were born from January to June 2003 were examined at different times from May to September of the same year to ascertain the occurrence of clubfoot. Clubfoot was seen in a total of 179 foals (16%) at 89 ranches (78%). Also, 124 of the 179 foals (69.3%) had clubfoot of grade II or higher, and it was found that grade I was likely to be overlooked or rapidly advance. In the present study, the occurrence of clubfoot was higher than expected in the investigated region. Hence, it is necessary to establish accurate diagnostic techniques and clubfoot guidelines to minimize the impact.

Ex Vivo Strength Comparison of Bioabsorbable Tendon Plates and Bioabsorbable Suture in a 3‐Loop Pulley Pattern for Repair of Transected Flexor Tendons from Horse Cadavers

To test the failure strength and energy of 2 bioabsorbable implants applied to transected deep digital flexor tendons (DDFT) from adult horses. Ex vivo biomechanical experiment. Twelve pairs of deep digital flexor tendons harvested from the forelimbs of fresh equine cadavers. Poly-L-lactic acid tendon plates were custom manufactured for application to the cylindrical surface of an adult equine deep digital flexor tendon. Twelve pairs of DDFTs were transected 2 cm distal to the insertion of the distal check ligament of the deep digital flexor tendon. One tendon of each pair was randomly selected for repair with a biodegradable plate or a 3-loop pulley method. Size 2 polydioxanone suture was used in both repairs. Repairs were tested in tension to failure, with peak force (PF) and total energy (TE) at repair failure recorded in Newtons (N) and Joules (J), respectively. A paired t-test was used for statistical evaluation with a significant level set at P< or = .05. Mean+/-SD PF for failure of plated tendons (1507.08+/-184.34 N) was significantly greater than for sutured tendons (460.86+/-60.93 N). TE was also significantly greater for failure of plated tendons versus sutured tendons. Plate fixation of transected cadaver DDFTs appear to have superior immediate failure strength than 3-loop pulley repairs. Whereas in vivo testing is required, a bioabsorbable tendon plate may provide initial increased strength to support tendon healing and decrease external coaptation requirements.

Passive and active mechanical properties of the superficial and deep digital flexor muscles in the forelimbs of anesthetized Thoroughbred horses

The superficial (SDF) and deep digital flexor (DDF) muscles are critical for equine forelimb locomotion. Knowledge of their mechanical properties will enhance our understanding of limb biomechanics. Muscle contractile properties derived from architectural-based algorithms may overestimate real forces and underestimate shortening capacity because of simplistic assumptions regarding muscle architecture. Therefore, passive and active (=total – passive) force–length properties of the SDF and DDF muscles were measured directly in vivo. Muscles from the right forelimbs of four Thoroughbred horses were evaluated during general anesthesia. Limbs were fixed to an external frame with the muscle attached to a linear actuator and load cell. Each muscle was stretched from an unloaded state to a range of prefixed lengths, then stimulated while held at that length. The total force did not exceed 4000 N, the limit for the clamping device. The SDF and DDF muscles produced 716±192 and 1577±203 N maximum active isometric force ( F max), had ascending force–length ranges ( R asc) of 5.1±0.2 and 9.1±0.4 cm, and had passive stiffnesses of 1186±104 and 1132±51 N/cm, respectively. The values measured for F max were much smaller than predicted based on conservative estimates of muscle specific tension and muscle physiological cross-sectional area. R asc were much larger than predicted based on muscle fiber length estimates. These data suggest that accurate prediction of the active mechanical behavior of architecturally complex muscles such as the equine DDF and SDF requires more sophisticated algorithms.

Abstract of Current Literature

Effects of Tendon Grip Technique (Frozen Versus Unfrozen) on In Vitro Surface Strain Measurements of the Equine Deep Digital Flexor Tendon Am J Vet Res 57:111–115, 1996