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of the deep digital flexor tendon using a thread-transecting technique. (A) Leg-stand with a fixed forelimb. A medial skin flap was created to access the medial palmar artery for distension of the vessels using saline. (B) An 18-gauge, 2-inch Tuohy

Open access
in American Journal of Veterinary Research

P almar navicular bone fibrocartilage (NBF) and deep digital flexor tendon (DDFT) degeneration/pathologies are largely responsible for the clinical signs associated with navicular disease, a prevalent source of performance-limiting forelimb

Open access
in American Journal of Veterinary Research

Deep digital flexor tendon injury in horses is a complex lameness problem because lesions can occur at 4 anatomic locations—distal to the distal sesamoid bone (navicular bone), at the level of the navicular bone, proximal to the navicular bone

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To demonstrate myofibroblasts in the accessory ligament of the deep digital flexor tendon (ie, distal check ligament) and deep digital flexor tendon of clinically normal foals.

Sample Population—Tissue specimens from 25 foals that were necropsied for reasons unrelated to this study and unrelated to musculoskeletal disease.

Procedure—The distal check ligament and deep digital flexor tendon of both forelimbs were examined histologically. Myofibroblasts were identified by immunohistochemical staining specific for alphasmooth muscle actin (α-SMA).

Results—Most of the cells in the distal check ligament and deep digital flexor tendon of all foals stained positive for α-SMA.

Conclusion and Clinical Relevance—Myofibroblasts made up most of the cells in the distal check ligament and deep digital flexor tendon of clinically normal foals. These cells have contractile ability and therefore, may play a role in flexure contracture of these tendons. The ability of tetracycline to chelate calcium or decrease the expression of the contractile protein α-smooth muscle actin could inhibit the myofibroblasts' ability to contract, thus providing a rationale for tetracycline administration as a treatment of distal interphalangeal joint flexor deformity in foals. (Am J Vet Res 2001;62:823–827)

Full access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate clinical and biomechanical consequences of desmotomy of the accessory ligament (AL) of the deep digital flexor tendon (DDFT) of equine forelimbs and determine whether this procedure is a viable treatment for chronic desmitis of the AL-DDFT.

Animals

6 adult Standardbred trotters.

Procedure

Biomechanical recordings obtained before and 6 months after desmotomy were compared. Walk and trot joint angles, ground reaction forces, peak joint moments, and tendon forces were assessed.

Results

Within 10 days after surgery, all horses were sound at a trot. Swelling, increased carpal flexion in the terminal stance phase, and incidental stumbling at the beginning of exercise were observed. Flexion angle in the carpal joints was significantly increased at the end of the stance phase. Peak moments around the distal interphalangeal joint and forces in the DDFT and AL-DDFT were decreased. Metacarpophalangeal joint angles, peak metacarpophalangeal joint moments, and peak loading of the suspensory ligament and the superficial digital flexor tendon were unchanged.

Conclusion

6 months after desmotomy, AL-DDFT strain was reduced without causing changes in joint angles or increasing tendon loads or joint moments that could be considered hazardous for the horses.

Clinical Relevance

Changes in locomotion that remained 6 months after AL-DDFT desmotomy would be acceptable for horses with chronic desmitis if conservative treatment failed. (Am J Vet Res 1998;59:347–351)

Free access
in American Journal of Veterinary Research

SUMMARY

Objective

To determine the effect of a specific galloping exercise regimen on collagen fibril mass-average diameters (MAD) in the deep digital flexor tendon (DDFT) and suspensory ligament (SL) of young Thoroughbreds.

Animals

12 Thoroughbred fillies, 21 ± 1 (mean ± SD) months old.

Procedure

6 horses underwent a specific 18-month treadmill training program involving galloping exercise. The remaining 6 horses served as controls, undertaking low-volume walking exercise over the same period. Sections were excised from the midpoint of the DDFT and SL, and small strips were dissected from central and peripheral locations for each structure. Fibril diameters were measured from micrographs of transverse ultrathin sections, using a computerized image analysis program. An MAD value was calculated for the central and peripheral regions of the DDFT and SL for each horse. Values for both regions were compared between exercised and control horses.

Results

The MAD did not change significantly with exercise for either the DDFT or the SL.

Conclusion

Loading of the DDFT as a result of this exercise regimen was not sufficient to stimulate collagen fibril hypertrophy, in keeping with current data that indicate this tendon, compared with the SL and superficial digital flexor tendon (SDFT), is subjected to low loads. Microtrauma, in terms of reduction in fibril MAD, may have occurred in the SL at a site different from that sampled. Another possibility is that, between the trot and the gallop, loading of the SL does not increase to the same extent as that of the SDFT. (Am J Vet Res 1998;59:64–68)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To describe microanatomic characteristics of the insertion of the distal sesamoidean impar ligament (DSIL) and deep digital flexor tendon (DDFT) on the distal phalanx in horses.

Sample Population—Healthy feet obtained from 62 horses of various breeds.

Procedure—Feet from 23 horses were used to histologically examine the insertion of the DSIL and DDFT (n = 7), its vasculature (10), and neural elements (6). In 39 other horses, the insertion zone was examined for proteoglycan.

Results—The insertion of the DSIL and dorsal half of the DDFT contained bundles of collagen fibers with intervening loose connective tissue septa with arteriovenous complexes (AVC) and nerve fibers. Microscopic examination revealed adaptive changes in the insertion with regard to proteoglycan content. In young adult horses, little or no staining for proteoglycans was evident, whereas in middle-aged horses, moderate proteoglycan staining was seen. Six older horses had slight proteoglycan staining at the insertion.

Conclusions and Clinical Relevance—The study revealed that this region contained a rich neurovascular complex between the collagen bundles. A gradual increase in production of proteoglycan, evident at the insertion of the DSIL and DDFT on the distal phalanx, indicates that adaptive responses to stress rather than age alone may be the primary determining factor. These observations indicate that this insertion site may be susceptible to stress during stance and impact loading, because this region appears to be strategically situated to regulate important neurovascular functions of the foot. (Am J Vet Res 2002;63:215–221)

Full access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate posttrauma biomechanical behavior of the scar attributable to desmotomy of the accessory ligament of the deep digital flexor tendon (AL-DDFT), compared with the histomorphologic and ultrasonographic appearance.

Animals

5 Standardbred trotters.

Procedure

Gross appearance, length, cross-sectional area (CSA), in vitro material properties, and ultrasonographic and histomorphologic features were studied 6 months after desmotomy. Tensile tests were conducted, with forces and elongation simultaneously recorded. Surgically treated limbs were compared with nontreated contralateral limbs.

Results

The CSA of the treated ligaments was increased threefold, and treated ligaments were 1 cm longer than control ligaments. In the healed AL-DDFT, stress and material stiffness were approximately a third of those values for controls. The functional characteristics, force and elongation at failure, reached 80% of control values. Ultrasonographic and the histomorphologic examination of the scar tissue revealed high amounts of randomly oriented collagen.

Conclusion

From the ultrasonographic and histomorphologic findings and the material properties, it was concluded that the scar tissue was of inferior quality. However, the functional properties had been restored for the most part by increase of the CSA. The length increase may lead to strain relief in the AL-DDFT after desmotomy.

Clinical Relevance

Desmotomy is recommended as treatment for chronic desmitis. (Am J Vet Res 1998;59:352–358)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine effects of tendon grip technique on in vitro surface strain measurements of equine deep digital flexor tendon (DDFT) when loaded in tension.

Sample Population

12 hind limb DDFT from 8 adult horses (mean age, 9.8 years [range, 4.5 to 17 years]; mean body weight, 472 kg [range, 450 to 509 kg]), with no clinical evidence of hind limb lameness.

Design and Procedure

After calibration, liquid mercury strain gauges were sutured to plantar surfaces of the tendons at distal (position 1), middle (position 2), and proximal (position 3) metatarsal regions. Each tendon was affixed to a materials testing machine (distally by the distal phalanx, and proximally by a metal clamp), and loaded once in tension, at a strain rate of 2.8 to 3.0%/s, to 3% clamp displacement. Liquid nitrogen was used to freeze the proximal ends of 6 tendons before placement in the clamp. Proximal ends of the remaining 6 tendons were left unfrozen. Surface strains were determined with the aid of low-resistance bridge circuits. Data were analyzed at time points corresponding to 1, 2, and 3% clamp displacement.

Results

Mean surface strains of tendons with frozen ends were significantly greater than those for tendons with unfrozen ends, and closer to strain measured by clamp displacement, at 1 and 2% clamp displacement. This difference was present but not significant at 3% clamp displacement. Mean local surface strain was not significantly different between the 3 gauge positions.

Conclusions

Freezing tendon ends is a useful technique to increase measured surface strains in equine DDFT, thereby making them closer to universal strain as measured by clamp displacement, and, thus, more likely to represent true surface strain. (Am J Vet Res 1996;57:111-115)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To localize substance P (SP) and neurokinin A (NKA) and their receptors in the insertion of the distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), and dorsal hoof wall of healthy feet of horses.

Sample Population—18 healthy feet from horses.

Procedure—Samples from the dorsal hoof wall and insertion of the DSIL and DDFT of 10 feet were processed for immunocytochemical analysis, using rabbit polyclonal antisera raised against SP and NKA. Tissue sections from 8 feet were incubated with I125-labeled SP to localize tachykinin receptors and their specificity and with control solutions of radioactive SP and excess nonradioactive SP to identify areas of nonspecific binding.

Results—Many nerves immunoreactive for SP and NKA were localized to the region of the insertion of the DSIL and DDFT and the accompanying microvasculature and arteriovenous complexes (AVC) as well as to the microvasculature of the dorsal hoof wall. Specific neurokinin 1 receptors were localized over the microvessels and AVC of the insertion zone and small microvessels of the hoof wall.

Conclusions and Clinical Relevance—These results document that the microvasculature of the equine foot is richly innervated and has specific receptors for tachykinins. Distributions of these tachykinin receptors on the microvasculature suggest that they form an important vasodilatory mechanism for controlling blood flow through the DSIL-DDFT insertion and dorsal hoof wall. (Am J Vet Res 2002;63:222–228)

Full access
in American Journal of Veterinary Research