Effects of exercise on the diameter of collagen fibrils in the central core and periphery of the superficial digital flexor tendon in foals.

OBJECTIVE: To determine the effects of exercise on collagen fibril diameter distribution in the superficial digital flexor tendon (SDFT) of foals. ANIMALS: 43 Dutch Warmblood foals. PROCEDURE: From 1 week until 5 months of age, group-1 foals (n = 14) were housed in stalls and not exercised, group-2 foals (14) were housed in stalls but were exercised, and group-3 foals (15) were maintained at pasture. Biopsy specimens were collected from the SDFT at 2 months, and 8 foals in each group were euthanatized at 5 months. Remaining foals were housed together in a loose stall and paddock until euthanatized at 11 months. After euthanasia, specimens were collected from the SDFT; all specimens were analyzed by use of electron microscopy. Collagen fibrillar index (CFI), mass average diameter (MAvD), and area dependent diameter (ADD) were compared among groups. RESULTS: Exercise-related differences in fibril distribution were not detected among groups at 2 months. At 5 months, ADD in peripheral specimens was significantly greater in group 1 than group 3. At 11 months, MAvD in core specimens was significantly less in group 3, compared with the other groups. However, in peripheral specimens, MAvD was significantly less in groups 2 and 3. CONCLUSIONS AND CLINICAL RELEVANCE: Collagen fibril restructuring in the SDFT of foals is in part an exercise-driven process. Withholding exercise may cause a delay in fibril development that can be partially overcome by increasing exercise at a later age. Exercise type may also affect remodeling of the SDFT in foals.

Long-term consequences of experimental desmotomy of the accessory ligament of the deep digital flexor tendon in adult horses.

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.

Effects of experimental desmotomy on material properties and histomorphologic and ultrasonographic features of the accessory ligament of the deep digital flexor tendon in clinically normal horses.

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.

Recovery of equine forelimb function after desmotomy of the accessory ligament of the deep digital flexor tendon.

The recovery process of the equine locomotor system after desmotomy of the accessory ligament of the deep digital flexor tendon (AL-DDFT) was investigated by studying the movement patterns and joint moments in 6 horses before and 10 days and 6 months following surgery. Using a modified CODA-3 system the joint angles and angular velocities of the lower limb were assessed in the operated forelimb as before the operation. Simultaneously ground reaction forces were measured and joint moments calculated. At 10 days and 6 months after the operation the carpal joint started to bend earlier in the stance phase. At that instant, the fetlock joint was more extended and displayed a higher angular velocity. The moment of the coffin joint was significantly decreased 10 days after desmotomy. After 6 months it had recovered considerably, but still the shape of the curve was significantly different compared to that before the operation. The fetlock joint moment was not affected, but turned out to be generated for a greater part by the suspensory ligament and the superficial digital flexor 10 days after the operation. Further analysis of these results showed that 6 months after the desmotomy the locomotor system was able to cope with almost similar external moments. To accomplish this, it had adopted a new co-ordination pattern during the recovery process.

Load redistribution after desmotomy of the accessory ligament of the deep digital flexor tendon in adult horses.

An analysis of joint moments was used to study the biomechanical implications, load redistribution and kinematic pattern following desmotomy of the accessory ligament of the deep digital flexor tendon (AL) in adult horses. Recordings of 6 sound horses were made before and 10 days after desmotomy of the AL of the right forelimb at the walk and the trot. Kinematic recordings of the right forelimb and the left distal forelimb were made using the CODA-3 system. Kinetic recordings of the ground reaction forces in both forelimbs were made using a Kistler force plate simultaneously with the kinematic recordings. Radiographic localisation of the CODA-3 markers in both distal limbs allowed an analysis of coffin and fetlock joint moments, moment arms and forces in the digital flexor tendons. No transfer of load from the operated to the contralateral limb was found. In the operated limb the total joint moment of the coffin joint decreased substantially due to a reduced moment arm of the vertical ground reaction force component during the entire stance phase, while the fetlock joint moment decreased only slightly. To compensate for the loss of AL function, the superficial digital flexor tendon (SDFT) took a higher load during midstance, while at the end of the stance phase, the deep digital flexor tendon (DDFT) carried a higher load with a marked load peak just before heel off. While the compensation was adequate during midstance (no changes in maximal hyperextension of the fetlock joint), a prolonged hyperextension of the fetlock joint together with a rapid flexion at the start of the swing phase indicated that the DDFT was unable to compensate completely for the loss of AL function. It was concluded that the changes in total joint moments and increases in loading of the SDFT and DDFT allow locomotion without serious overloading of the compensating tendons following AL desmotomy.

Allograft rejection in cattle with bovine leukocyte adhesion deficiency.

In the present investigation cell-mediated immunity in animals with bovine leukocyte adhesion deficiency (BLAD) was studied by means of skin transplantation experiments. Autograft and allograft behaviour in animals with BLAD was compared with the behaviour of simultaneously transplanted autografts and allografts in healthy controls. Allograft survival time was prolonged in three BLAD cattle (28, 30, and 72 days) compared to six healthy controls (12-14 days). When transplantations were repeated on one animal with BLAD using skin grafts from the same donor, accelerated rejection was observed (allograft survival time decreased from 72 days at primary to 35 days at secondary and to 21 days at tertiary transplantation), suggesting the development of immunological memory. Graft-infiltrating lymphocytes that were obtained from allograft biopsies during the period of rejection, were shown to be from recipient origin (beta 2-integrin negative). Our findings demonstrate that, although prolonged allograft survival is observed in cattle with BLAD, skin allografts are ultimately rejected.

In vitro mechanical properties of the accessory ligament of the deep digital flexor tendon in horses in relation to age.

The material properties of the accessory ligament of the deep digital flexor tendon (AL) of 21 forelimbs from horses between ages one day and 15 years were determined. The force (634-11416 N), failure stress (45-138 N/mm2), failure strain (7-24%) and tangent modulus (33-1639 MPa) are presented in relation to age. Tangent modulus did not indicate changes in elasticity due to age. The results demonstrate that complete ligament failures (CLF) of ALs of older horses (mean 7835 N) occur at lower forces than ALs of young adult horses (mean 8894 N). Sudden decreases, 'dips', in the force-time curves were noticed in ligaments from foals and yearlings and in ligaments from horses > 10 years. They were interpreted as the failure of a number of fibres which either fail at lower forces or are subject to higher forces than the rest. These differences in mechanical properties could be the result of age related differences in the material properties of ALs of older horses similar to alterations in collagenous tissue in other species. When analysing the data of the proximal, middle and distal regions of the ligaments separately, higher strain and elasticity were found in the distal compared to the proximal parts. It is suggested that the clinical occurrence of desmitis of the AL of older horses could be due to fibrillar failure caused by differences in the material properties of the ligaments.

Desmitis of the accessory ligament of the deep digital flexor tendon in the horse: clinical and ultrasonographic features. A report of 24 cases.

The clinical and ultrasonographic features of desmitis of the accessory ligament of the deep digital flexor tendon (carpal check ligament) are reported in a series of 24 horses. Lameness associated with the carpal check ligament especially was found in Warmblood riding horses ranging in age from 6 to 18 years with a mean age of 11.3 years. The most striking clinical feature was a firm, painful swelling medially and laterally in the proximal and/or mid metacarpal region, corresponding with the dorsoproximal-palmarodistal oblique direction of the carpal check ligament. Sonographically swelling of the carpal check ligament was common, the enlarged ligament mostly showing a type 1-2 texture. Occasionally a more localized lesion with a type 3-4 texture was present. About 40% of the horses also showed additional lesions in (one of three other flexor tendons or ligaments in the metacarpal region. Most horses were treated conservatively, i.e. boxstallrest and/or a controlled exercise regime were applied. From the 19 horses available for follow up (1-36 months), only 3 horses resumed full work. Obviously the prognosis of this injury is guarded.