Arthroscopic landmarks of the equine carpus

The radiocarpal and middle carpal joints of 4 clinically normal horses and 24 necropsy specimens were examined with an arthroscope to describe the topographic anatomy of these joints. The carpal bones of the radiocarpal joint had congruent articular surfaces in extension, but carpal flexion resulted in a stairstep between the radial and intermediate carpal bones. The variable surface anatomy, as well as the restricted synovial space and the technical limitations of the arthroscope, contributed to the need for more than one arthroscopic approach to the radiocarpal joint to ensure a thorough examination. The middle carpal joint's hinge-like biomechanics resulted in a spacious synovial cavity that was more amenable to arthroscopic examination. Careful planning was necessary to ensure that areas of interest were distant from the arthroscope-insertion site to allow the best perspective possible. The lateral approach to the middle carpal joint provided the best viewing of both facets of the intermediate and third carpal bones as well as the dorsal rim of the radial carpal bone. The medial approach did not allow complete inspection of these areas.     

The incidence and severity of intercarpal ligament damage in the equine carpus

SUMMARY The arthroscopic findings in 104 intercarpal joints in 76 horses were reviewed to determine the incidence and severity of changes in the medial intercarpal ligament. Damage to the intercarpal ligament was observed in 43 joints in 35 horses, ranging from mild fraying of the edges of the ligament to complete disruption of all fibres. This represented an incidence of 41% of joints being affected. In 9 joints examined arthroscopically primarily as a further diagnostic procedure, ligament damage was evident in all cases. In horses undergoing arthroscopic surgery primarily for the treatment of osteochondral chip or slab fractures, there was some correlation between the severity of articular cartilage damage and the presence of ligament damage.     

Correlation between radiographie and arthroscopic findings in the equine carpus

The radiographic and arthroscopic findings in 150 carpal joints in 114 lame horses were compared. Chip, slab, or sagittal fractures were identified in 130 (87%) joints. In 101 (78%) of these there was good agreement between radiographic and arthroscopic findings on the number and position of fractures. In 23 (18%) joints, chip fractures additional to those seen radiographically were found arthroscopically. In one joint a large chip fracture from the craniolateral aspect of the distal radius was identified only by arthroscopy, while in 6 joints fractures were identified only by radiography. Observed causes of lameness, other than intra-articular fractures, included degenerative joint disease, synovitis, ruptured intra-carpal ligaments, and haemarthrosis. Correlation between the radiographic and arthroscopic assessment of degenerative joint disease was poor. It was concluded that both radiography and arthroscopy should be used to obtain the most accurate assessment of the equine carpus.     

Arthroscopic approaches to the palmar aspect of the equine carpus

OBJECTIVE: To identify sites for arthroscopic access to the palmar aspects of the antebrachiocarpal (AC) and middle carpal (MC) joints, and describe visible carpal bone surfaces for each approach. STUDY DESIGN: Prospective experimental study. ANIMALS: Equine carpi: 16 cadavers, 8 live horses. METHODS: A latex model was used to identify possible sites for arthroscopic access to the palmar aspects of the AC and MC joints. Carpi (n = 24) were examined arthroscopically and arthroscopic access sites and visible carpal bone surfaces were described. RESULTS: Arthroscopic approaches and instrument portals were developed for the medial and lateral aspects of the palmar pouches of the AC and MC joints. The palmar surface of the radial carpal bone and radius, and the dorsal articular surfaces of the accessory carpal bone, could be viewed using palmar approaches to the AC joint. The palmar aspect of the radial, third and second carpal bones (medially) and ulnar and fourth carpal bones (laterally) could be observed using a palmar approach to the MC joint. CONCLUSIONS: Arthroscopic access, using separate medial and lateral portals to the AC and MC joints, allowed assessment of portions of the caudodistal radius, the palmar surfaces of the radial, ulnar, second, third and fourth carpal bones, and the dorsal aspect of the accessory carpal bone. CLINICAL RELEVANCE: Arthroscopic approaches to the palmar aspect of the carpus could be used to remove fracture fragments, and to assess the medial palmar intercarpal ligaments.     

Synovial regeneration in the equine carpus after arthroscopic mechanical or carbon dioxide laser synovectomy

OBJECTIVE: To compare synovial regeneration in the equine carpus after mechanical or CO(2) laser synovectomy. STUDY DESIGN: Arthroscopic partial synovectomy was performed in the radiocarpal and intercarpal joints. SAMPLE POPULATION: Twelve horses, 3 to 6 years of age, were randomly divided into 3 groups. METHODS: The antebrachiocarpal and intercarpal joints in each horse were randomly assigned a treatment such that each horse had one joint treated as a control (arthroscopic lavage), one in which a mechanical or CO(2) laser partial dorsal carpal synovectomy was performed, and one in which a combination of the mechanical and laser techniques was performed. The groups were euthanized for collection of specimens, respectively, at 1, 3, and 6 months postoperatively. The synovial membrane was evaluated grossly, histologically, and by transmission and scanning electron microscopes (TEM and SEM). RESULTS: The synovial villi failed to regenerate in all groups. At 1 month, the intimal cell layer was incomplete and the surface was still granulating. At 3 months, intimal regeneration was complete but more mature in the CO(2) laser synovectomy groups than in the mechanical synovectomy groups. Intimal regeneration was complete in all groups at 6 months. The subintima was replaced with fibrous tissue that separated the original subintimal vascular bed from the regenerated synovial surface. The CO(2) laser required preliminary training to operate effectively, and the air environment altered the intraoperative evaluation of the synovectomy site. CONCLUSIONS: Villous regeneration does not occur in horses after surgical synovectomy. All synovial membranes healed with a fibrous subintima and less populated intima. The CO(2) laser is capable of performing a more superficial synovectomy than that achieved with mechanical synovectomy using a motorized arthroscopic synovial resector. CLINICAL RELEVANCE: Mechanical or CO(2) laser synovectomy may be performed in the horse; however, additional evaluation is needed to determine the physiological significance of the lack of villus regeneration in this species. A combination of the resection techniques is not advised because of the increased risk of full-thickness capsular defects.     

The effect of a treatment protocol on the prognosis of equine laminitis

All horses and ponies with laminitis treated at the Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, between 1995 and 1998 were analysed retrospectively (n = 152). Based on the results of this study and on the world-wide knowledge on laminitis a standardised treatment protocol was adopted in 1999. Fifty-eight patients have been treated for laminitis between 1999 and 2001 following the treatment protocol. Compared to our hospital-population (orthopaedic patients), mares and ponies are at higher risk developing laminitis, but the prognosis does not differ between sexes as between breeds. Radiological evidence of rotation of the third phalanx seems to be of minor importance for the prognosis. Distal displacement of the third phalanx, however, seems to worsen the prognosis. The outcome of the acute cases is significantly better in the group treated following the protocol, than in the group without protocol. The outcome of the chronic cases is not influenced by the treatment protocol. Although the cases in both groups differ, as they are all clinical cases, our data suggest that the standardised treatment protocol results in a better outcome for cases of acute laminitis.     

The effect of age and parity on the development of equine chronic endometrial disease

The results of a retrospective analysis of 3,804 endometrial biopsy specimens collected from non-pregnant mares during the course of routine equine stud farm practice demonstrates a significant and practically useful correlation between the severity of chronic degenerative endometrial disease (CDE) diagnosed and age of mare at the time of examination. There were significant correlations between the number of foals born and the mares' barren years prior to biopsy and the severity of CDE, but the differences were not sufficiently large to be useful. Correlations between the severity of chronic infiltrative endometritis (CIE) and age or pre-biopsy parity were minimal. The results suggest that using similar histopathological criteria to those used by Kenney and Doig (1986), mares up to nine years of age should have no signs of CDE, mares up to 13 years of age should have no more than mild signs, mares up to 15 years of age should have no more than moderate signs and mares aged 17 years or older are likely to have severe signs. We believe that these guidelines are a useful, objective aid for formulating a breeding prognosis.     

The effect of sodium heparin on equine articular cartilage.

This study compared the effect of sodium heparin and gentamicin sulphate on equine articular cartilage (AC) explants in order to investigate the possible use of sodium heparin in the treatment of infectious arthritis. Six concentrations of sodium heparin and gentamicin sulphate were tested. The supernatant and explant digest were assayed for glycosaminoglycan (GAG) content with the dimethyl-methylene blue assay and the per cent loss of GAG was calculated. A significant (P< 0.001) increase in percentage GAG loss was noted for the sodium heparin groups when compared to the control, whilst no significant increase was found among the treatment groups (P =0.782). For gentamicin, no significant difference in percentage GAG loss was found between the control and three of the five treatment groups (P =0.667). The percentage GAG loss in the sodium heparin treated AC explants was greater than for any of the gentamicin-treated AC explants. It can be concluded that sodium heparin sulphate stimulates an increase in GAG release from equine articular cartilage explants, though no firm conclusions can be drawn on its use in treating equine infectious arthritis. Copyright Harcourt Publishers Ltd.     

The effect of training on equine metacarpal bone breaking strength

Right third metacarpal bones (n=24) from Thoroughbreds, 24 to 48 months old and in race training, were tested to failure in 3 point bending. The neutral load axis was estimated and the distance from the axis to the outer dorsal cortical surface measured. Mid-diaphyseal dorsopalmar and lateromedial outer cortical and medullary diameters were measured. Breaking strength, cortical area and area moment of inertia were also calculated. Significant correlations were demonstrated between months in training and dorsopalmar bone diameter, cortical area and area moment of inertia. Significant linear models were illustrated between the same 3 variables and number of months in training. It was concluded that increased duration of training significantly enlarges dorsopalmar bone diameter, cortical area and area moment of inertia. Training did not affect metacarpal bone breaking strength as determined by 3 point bending.     

The effect of exercise and conditioning on equine red blood cell characteristics

The effect of exercise and conditioning on 2,3-diphosphoglycerate levels was studied in nine mature horses. During a 12 minute exercise bout producing heart rates of 165 bpm, 2,3-DPG was significantly increased (p<.05). In addition, exercising levels of 2,3-DPG were increased (p<.05) approximately 8% after a six-week submaximal conditioning program. These increases could not be entirely attributed to changes in erythrocyte number. Mean corpuscular volume was also increased during exercise (p<.05) but was not altered by conditioning.     

The effect of drugs commonly used in the treatment of equine articular disorders on the activity of equine matrix metalloproteinase-2 and 9

Loss of articular cartilage, which is the most important pathological lesion occurring in osteoarthritis, has been shown to be enzymatically mediated. The matrix metalloproteinases (MMPs) are a group of enzymes which have been implicated in this degradation of articular cartilage matrix. The use of pharmacological agents to inhibit this catabolic process in the joint is a potential route for therapeutic intervention.
  The gelatinase MMPs, MMPs-2 and 9, were purified by affinity chromatography from equine cell cultures. The ability of phenylbutazone, flunixin, betamethasone, dexamethasone, methylprednisolone acetate (MPA), hyaluronan, pentosan polysulphate and polysulphated glycosaminoglycan (PSGAG) to inhibit equine MMPs-2 and 9 were assessed by two degradation assays. Whilst some agents did have direct effects on MMP activity, these effects were only obtained at concentrations which were unlikely to be achieved for any length of time in vivo . It is improbable that any pharmacological agent, currently used in the horse, has a significant effect on gelatinase MMP activity.     

The effect of shape,age and extension on the compliance of equine tracheal segments

The influence of the age and weight of the animal as well as that of the extension and the shape of the trachea on the mechanical properties of the cervical trachea was studied in 33 isolated tracheal segments obtained from freshly slaughtered horses. The relationship between intraluminal pressure and volume was determined in the cervical tracheal segments positioned firstly under normal longitudinal tension and secondly in hyperextension. At the same time, changes in the area of the cross-section of the lumen (X-SA) at the midpoint of the segment were measured using photographs obtained by slit-lamp transillumination and endoscopy. The sagittal (DS) and transverse (DT) diameters were determined for each segment and the DT/DS ratio was calculated to give an estimate of the shape of the X-SA. The results showed that (i) neither the age nor the weight of the horses had any influence on the mechanical properties of the trachea; (ii) extension decreases the compressibility of the tracheal segment in vitro; (iii) there is a wide variation in the extrathoracic tracheal X-SA shape in horses; and (iv) the shape of the X-SA has a major influence on the mechanical properties of the trachea. It was concluded that (i) hyperextension of the neck will partly facilitate respiration at high levels of ventilation by elongating the trachea and by decreasing its collapsibility; and (ii) the tracheal collapse which may occur during high levels of ventilation will be more or less important depending on the individual X-SA shape.     

Effect of feed rate and drill speed on temperatures in equine cortical bone.

OBJECTIVE: To examine the amount of heat generated in equine cortical bone by a 6.2-mm drill, using low- and high-speed and controlled feed rate drilling. SAMPLE POPULATION: 10 metacarpal bones harvested from five 2-year-old draft-type horses. PROCEDURE: Drilling on metacarpal bones was done using a machine shop mill with which the feed rate and drill speed could be precisely controlled. Bones were drilled, using 6 combinations of feed rate (1, 2, and 3 mm advance/s) and drill speed (317 and 1,242 revolutions/min [rpm], with maximal temperatures recorded by thermocouples placed 1, 1.5, and 2 mm from the drill. Maximal temperatures were evaluated for the effect of feed rate, drill speed, cortical thickness, and distance from the drill, using linear regression analysis. RESULTS: Increasing feed rate from 1 to 2 and from 2 to 3 mm/s significantly decreased mean maximal temperature. Increasing drill speed from 317 to 1242 rpm significantly increased mean maximal temperature. Increasing cortical thickness significantly increased mean maximal temperature, and increasing the distance from the drill hole significantly decreased mean maximal temperatures. CONCLUSIONS: On the basis of our results, we recommend using low drill speeds while applying sufficient axial force to advance the drill as rapidly as possible through the bone. CLINICAL RELEVANCE: Results of using this in vitro model suggest that temperatures at the drill-bone interface may be sufficiently high to result in significant thermal necrosis when drilling equine cortical bone.