Richard D. Park

Response of aorta and branch arteries to experimental intraoperative irradiation

Injury to the aorta was evaluated in dogs 2 and 5 years after fractionated irradiation (EBRT), intraoperative irradiation (IORT) or a combination. Doses greater than 20 Gy IORT combined with 50 Gy EBRT given in 2 Gy fractions or 30 Gy IORT alone were accompanied by a significant risk of aneurysms or large thrombi as determined at necropsy 4 to 5 years following irradiation. Narrowing of the aorta as detected by aortography occurred at 5 years but was not detected earlier. The ED50 for aortic narrowing was 38.8 Gy IORT and 31 Gy IORT plus 50 Gy EBRT. The ED50 for branch artery injury was 24.8 Gy IORT alone and 19.4 Gy IORT plus 50 Gy EBRT. The difference in ED50s for IORT alone and IORT plus EBRT indicates that the contribution of the EBRT dose in terms of an IORT dose for aortic narrowing was 7.8 Gy and for branch artery injury was 5.4 Gy. The ED50 for incidence of small thrombi in the aorta was about 29 Gy for IORT alone and 23.5 Gy for IORT combined with EBRT. Fibrous thickening of the adventitia was measured and the effect of the 50 Gy EBRT component of a combination of EBRT and IORT was determined to be equivalent to 10 to 12 Gy IORT. Based on the various estimates, IORT doses of 10-15 Gy have an effect of 5 times or greater the amount given in 2 Gy fractions. At all EBRT doses and at lower IORT doses the intima was greatly thickened. At IORT doses of 20 Gy or above there was a dose related decrease in intimal thickness to near normal values. This was probably due to cell killing or inhibition of intimal proliferation that predominated at higher doses. Although the risk of serious vascular complications appears low following IORT of humans, this may be due to short observation times and the fact that IORT doses currently used are usually 20 Gy or less; this may be near the tolerance for late response of larger arteries. Only one dog in this study had complete rupture of the aorta causing death. Five other dogs at high IORT doses had near ruptures of the aorta but were clinically normal.

Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales.

REASONS FOR PERFORMING STUDY Radiography in presale examinations of TB yearlings has become standard practice in recent years. OBJECTIVES To describe the prevalence and distribution of radiographic changes in the fetlocks, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings in central Kentucky when these joints were examined as part of routine pre- and post sale evaluations. METHODS Horses subjected to radiographs included the fore (n = 1127) and hind (n = 1102) fetlocks, carpi (n = 1130), tarsi (n = 1101), stifles (n = 660) and fore feet (n = 300). Radiographic changes were categorised by location and type of change present (e.g. lucency, fragment) for each series. RESULTS In the fore fetlocks 1.6% had fragmentation of the proximal dorsal first phalanx and 0.5% fragmentation of the proximal palmar aspect. In the hind fetlocks 5.9% had fragmentation at the plantar aspect and 3.3% fragmentation dorsally. Lucencies, fragments or loose bodies were detected at the dorsal aspect of the distal third metacarpus in 2.8% and, at the same location on the third metatarsus, 3.2%. Most yearlings (98%) had vascular channels in the proximal sesamoid bones and irregular vascular channels (> 2 mm wide or with nonparallel sides) were more common (79%) than regular vascular channels (56%). The intermediate ridge of the distal tibia was the most common location for fragmentation in the tarsus (4.4%). CONCLUSIONS While some radiographic changes, e.g. vascular channels in proximal sesamoid bones, are very common in Thoroughbred yearlings, others, e.g. fragmentation or subchondral lucency within joints are quite rare usually affecting less than 5% of the population. POTENTIAL RELEVANCE Veterinarians should expect to find radiographic changes in Thoroughbreds presented for examination prior to the yearling sales. The rarity of some changes thought to affect soundness or racing performance will make further invesigation of these conditions in horses without clinical signs more difficult.

Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance

REASONS FOR PERFORMING STUDY Although the radiographic examination of yearlings has become commonplace at some large Thoroughbred sales, there are few data to support the decisions facing veterinarians who are asked to evaluate future racing potential. OBJECTIVES To identify radiographic changes in the fetlocks, proximal sesamoid bones, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings associated with future racing performance during ages 2 and 3 years. METHODS Radiographs from routine pre- and post sale examinations of 1162 yearlings were used to identify individual radiographic changes in sale yearlings. Starting a race, the percent of starts placed, money earned and earnings per start were used to assess racing performanceand examined for associations with the radiographic changes observed. RESULTS Overall 946 (81%) yearlings started at least one race during ages 2 or 3 years. Fourteen of 24 (58%) yearlings with moderate or extreme palmar supracondylar lysis of the third metacarpus, 8 of 14 (57%) of those with enthesophyte formation on the proximal sesamoid bones and 19 of 30 (63%) of those with dorsal medial intercarpal joint disease started a race. The odds of starting a race when age 2 or 3 years were 3 times lower for yearlings with these changes (P < 0.01) compared with yearlings that did not have these changes. Twenty-five of 36 (69%) yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock started a race and these yearlings were also less likely (OR = 0.51, P = 0.07) to start a race. Yearlings with enthesophyte formation on hind proximal sesamoid bones placed in a smaller percentage of starts (16%, P = 0.01) earned less money (987 US dollars, P = 0.02) and had lower earnings per start (252 US dollars, P = 0.03) compared to starters without this change. CONCLUSIONS Although many of the changes observed on radiographs of sale yearlings do not appear to influence future racing performance, some are associated with reduced performance. POTENTIAL RELEVANCE The results of this study are best applied in parallel with the clinical impressions of veterinarians experienced in examining radiographs of sale yearlings. Some findings support those established in the literature as incidental findings and others suggest new areas for concern not previously reported as a problem in Thoroughbred sale yearlings.

Development of subchondral cystic lesions after articular cartilage and subchondral bone damage in young horses

The objective of this study was to determine if damage to the articular cartilage alone or articular cartilage plus subchondral bone of the distal medial femoral condyle of young, exercised horses resulted in the formation of subchondral cystic lesions. Twelve Quarter Horses (age 1-2 years), free of clinical and radiographic signs of osteochondrosis and lameness were used. In 6 horses (Group 1), a 15 times 1 mm linear full thickness defect in the articular cartilage was made arthroscopically on the weightbearing surface of the distal aspect of the medial femoral condyle. In the other 6 horses (Group 2), a 15 times 3 mm full thickness elliptical cartilage defect was made, followed by burring a 5 mm diameter, 4 mm deep hole into the subchondral bone. Three weeks after surgery, all horses were hand walked and trotted for 2 weeks and then exercised for 6 min daily, 5 days a week for the next 14 weeks on a treadmill. They were then turned onto a small paddock for 6 weeks (6 months total). The development of subchondral cystic lesions was determined using radiography. Bone activity in the femoral condyle was monitored with nuclear scintigraphy. All horses that developed subchondral cystic lesions radiographically were subjected to euthanasia for gross and histological examination of the lesions. No subchondral cystic lesions and no clinical abnormalities were detected in the horses in Group 1. Subchondral cystic lesions developed radiographically in 5 of 6 horses in (Group 2). Scintigraphic findings of horses with subchondral cystic lesions were inconsistent. Histological examination of lesions revealed variable quantities of fibrous connective tissue, fibrocartilage and bone, with evidence of bone remodelling adjacent to the subchondral cystic lesion. The results suggest that damage to articular cartilage plus subchondral bone, but not articular cartilage alone, of the distal medial femoral condyle may lead to the development of subchondral cystic lesions. These findings indicate that all subchondral cystic lesions in horses may not be osteochondrosis-type lesions and that trauma to weightbearing articular surfaces of young horses may be a predisposing factor.

Comparison of Surgical Treatment Options for Cranial Cruciate Ligament Disease in Large‐Breed Dogs with Excessive Tibial Plateau Angle

OBJECTIVE To identify surgical techniques performed by veterinary surgeons for the treatment of cranial cruciate ligament disease in large-breed dogs with excessive tibial plateau angle (eTPA), compare their outcomes, identify risk factors for postoperative complications, and compare outcome and complication rate with tibial plateau leveling osteotomy (TPLO) in dogs without eTPA. STUDY DESIGN Multicenter, case-control study. ANIMALS eTPA group (TPA>or=35 degrees)=58 dogs (78 stifles); control group (TPA<or=30 degrees)=58 dogs (72 stifles). METHODS Control and eTPA group dogs were identified. Medical records, radiographic reviews, and pet-owner interviews were used to identify surgical treatments performed, their complications, and outcome. Odds ratios with 95% confidence intervals, chi(2) tests, and t-tests were calculated to discern differences between eTPA and control-group dogs. RESULTS TPLO was the most common treatment for eTPA. Owner-perceived outcome was superior for eTPA group dogs when TPLO resulted in TPA<or=14 degrees compared with those with postoperative TPA>14 degrees. Loss of tibial plateau leveling during convalescence was the most commonly observed major complication; addition of ancillary implants to TPLO significantly reduced its incidence. Postoperative complications were more common in dogs with eTPA than in dogs without eTPA; however, no difference in owner-perceived outcome was identified. CONCLUSIONS Surgical treatment of dogs with eTPA has a higher complication rate, but comparable outcome to that of dogs without eTPA. CLINICAL RELEVANCE Postoperative TPA<or=14 degrees and addition of ancillary implants are recommended when using TPLO to treat dogs with eTPA.Objective— To identify surgical techniques performed by veterinary surgeons for the treatment of cranial cruciate ligament disease in large-breed dogs with excessive tibial plateau angle (eTPA), compare their outcomes, identify risk factors for postoperative complications, and compare outcome and complication rate with tibial plateau leveling osteotomy (TPLO) in dogs without eTPA. Study Design— Multicenter, case–control study. Animals— eTPA group (TPA≥35°)=58 dogs (78 stifles); control group (TPA≤30°)=58 dogs (72 stifles). Methods— Control and eTPA group dogs were identified. Medical records, radiographic reviews, and pet-owner interviews were used to identify surgical treatments performed, their complications, and outcome. Odds ratios with 95% confidence intervals, χ2 tests, and t-tests were calculated to discern differences between eTPA and control-group dogs. Results— TPLO was the most common treatment for eTPA. Owner-perceived outcome was superior for eTPA group dogs when TPLO resulted in TPA≤14° compared with those with postoperative TPA>14°. Loss of tibial plateau leveling during convalescence was the most commonly observed major complication; addition of ancillary implants to TPLO significantly reduced its incidence. Postoperative complications were more common in dogs with eTPA than in dogs without eTPA; however, no difference in owner-perceived outcome was identified. Conclusions— Surgical treatment of dogs with eTPA has a higher complication rate, but comparable outcome to that of dogs without eTPA. Clinical Relevance— Postoperative TPA≤14° and addition of ancillary implants are recommended when using TPLO to treat dogs with eTPA.

Effects of exercise vs experimental osteoarthritis on imaging outcomes

OBJECTIVE To identify changes in imaging outcomes in a controlled model of osteoarthritis (OA) vs exercise. METHOD Sixteen 2-year-old horses were randomly assigned to an exercise control (n=8) or an exercise OA (n=8) group. All horses had middle carpal joints arthroscopically explored and an osteochondral fragment was induced in one middle carpal joint of the OA group. All horses were treadmill exercised for the duration of the study (91 days). Clinical, radiographic, nuclear scintigraphic, computed tomographic and magnetic resonance imaging (MRI) examinations were performed and outcomes of these were compared between groups. Imaging results were correlated to clinical, biomarker and gross pathologic results. RESULTS The OA group had significant increases in clinical outcomes and most imaging parameters. Specifically, the OA group showed significant increases in radiographic lysis and nuclear scintigraphic uptake. There was very little change in subchondral bone density, but a significant change in subchondral bone edema. Radiographic lysis, radial carpal bone edema and nuclear scintigraphy were strongly correlated with clinical changes and radial carpal bone edema was strongly correlated with changes in Type I and Type II collagen found in the synovial fluid. CONCLUSIONS OA induced significant changes in imaging parameters beyond the adaptation seen with exercise. Bone edema detected with MRI was closely correlated with collagen biomarkers detected in the synovial fluid.

Ureteral injury following experimental intraoperative radiation.

Beagle dogs were randomized to receive a range of total dose delivered in three different protocols. Sixteen dogs received external beam radiation therapy (EBRT), 32 dogs received intraoperative irradiation (IORT), and 32 dogs received combinations of external beam radiation therapy and intraoperative irradiation. A sublumbar field was irradiated which always included the left ureter. Dogs were observed for 5 years; sequential excretory urograms were done at 6 months, and 1 and 5 years. Morphometric analysis of tissues were also done. The canine ureter tolerated 17.5 Gy intraoperative irradiation with no evidence of injury and 25 Gy intraoperative irradiation with a low probability of injury. The ED50 for radiographic abnormalities was 32.9 Gy. When 50 Gy external beam radiation therapy was given prior to intraoperative irradiation, the ureter tolerated 10 Gy intraoperative irradiation with no evidence of injury and 17.5 Gy with a low probability of injury. The ED50 was 29 Gy intraoperative irradiation after EBRT. The external beam radiation therapy had little effect on the ureter when given alone or prior to intraoperative irradiation. Clinical signs of renal disease occurred only in dogs who had received bilateral ureteral irradiation intraoperatively at doses of 32.5 Gy intraoperative irradiation and 25 Gy intraoperative irradiation after external beam radiation therapy. Histologic evidence suggests that the chronic injury of the ureter expressed at 5 years is of vascular etiology. The early injury may be due to ulceration of the epithelium.

Comparison of Radiographic and Anatomic Femoral Varus Angle Measurements in Normal Dogs

OBJECTIVE To determine if the clinically practiced method of radiographic femoral varus angle (R-FVA) measurement is repeatable, reproducible, and accurate. STUDY DESIGN Radiographic and anatomic study. ANIMALS/SAMPLE POPULATION: Normal Walker hound cadavers (n=5) and femora (n=10). METHODS Cadavers were held in dorsally-recumbent and torso-elevated positions as 3 craniocaudal radiographs were made of each femur, by each of 2 different technicians. Femora were then harvested for direct measurement of anatomic femoral varus angle (A-FVA). R-FVA was measured on each radiograph by each of 3 examiners on 3 separate occasions. Intra-observer (repeatability) and inter-observer (reproducibility) variance in R-FVA measurement and the strength of relationship between R-FVA and A-FVA (accuracy) were determined. RESULTS Mean (+/-SD) A-FVA was 5.2+/-2.1 degrees (range, 2.4-8.2 degrees). Mean (+/-SD) R-FVA was 5.8+/-1.0 degrees (range, 2.7-9.6 degrees). Intra-observer variance (range: 11-16%) and inter-observer variance (16%) were acceptable. The strength of relationship between measured R-FVA and A-FVA (maximum adjusted R(2)<0) was unacceptably low regardless of observer, patient position, or radiographic technician. CONCLUSION R-FVA measurement was repeatable and reproducible, but not statistically accurate in predicting A-FVA in these 5 normal Walker hounds. The detected inaccuracy may be real or the result of a selection bias for normal dogs obscuring the true relationship. CLINICAL RELEVANCE R-FVA may not be an accurate method of femoral varus measurement in dogs with A-FVA<10 degrees. Using Slocums criteria for distal femoral osteotomy (R-FVA>10 degrees), the procedure would not have been erroneously performed in any of the normal dogs of this study.

COMPUTED TOMOGRAPHIC APPEARANCE OF PRIMARY LUNG TUMORS IN DOGS

Canine primary lung tumors typically appear radiographically as a well-circumscribed solitary mass in the periphery of a caudal lung lobe. Consolidated and diffuse forms of primary lung tumors have also been described. Nineteen dogs with computed tomographic (CT) images of the thorax and a histological diagnosis of primary lung tumor (17 primary carcinomas and two primary sarcomas) were evaluated retrospectively to characterize the CT findings. All primary lung tumors were bronchocentric in origin with internal air bronchograms. The bronchi were typically narrowed, displaced, and often obstructed by the tumor. Eighteen of 19 (95%) of the tumors were solitary and there was one pneumonic/alveolar form. Most solitary tumors were well circumscribed (17/18), located in the central to periphery of the lung (14/18), and in a cranial or caudal lobe (16/19). Most primary lung tumors (11/17) had mild to moderate heterogeneous contrast enhancement. Five of 19 dogs (26%) had evidence of pulmonary metastasis. Internal mineralization (3/19) and tracheobronchial lymphadenopathy (4/19) were also identified. On CT examination, solitary, well circumscribed, bronchocentric masses with internal air bronchograms are consistent with a primary pulmonary tumor in dogs.

Primary osteosarcoma distal to the antebrachiocarpal and tarsocrural joints in nine dogs (1980-1992)

The medical records of nine dogs with primary osteosarcoma distal to the antebrachiocarpal or tarsocrural joint were reviewed. Eight of the nine dogs were treated with surgical removal of the primary tumor; seven received adjuvant chemotherapy; and one dog was treated with chemotherapy alone. Median survival of dogs in this series was 466 days. Six of the nine dogs died of causes attributable to osteosarcoma, and both skeletal and pulmonary metastases occurred. Survival of dogs with osteosarcoma distal to the antebrachiocarpal or tarsocrural joint was somewhat longer than survival of dogs with osteosarcoma of more common appendicular sites. However, these are aggressive tumors with a high potential for metastasis.