DISEASES OF BONE AND DISEASES AFFECTING BONE

Diseases of bones and diseases affecting bone are frequently related to breed, age, and limb involvement. The following checklist of diseases which may result in lameness are presented as a summation of the disease conditions likely to result in lameness in dog.     

IMAGING: BONE*

Bone can be imaged by a variety of methods including survey radiography, stress radiography, contrast radiography, fluoroscopy, tomography, magnification radiography, xeroradiography, and nuclear imaging. Each of these imaging techniques and modalities is presented as it applies to diagnostic imaging of bone in veterinary medicine     

BONE INFECTION IN THE BOVINE APPENDICULAR SKELETON: A CLINICAL, RADIOGRAPHIC, AND EXPERIMENTAL STUDY

Four hundred and forty-five bovines with bone infection of the appendicular skeleton were selected for clinical and radiographic assessment. A distinction was made between hematogenous and post-traumatic origin (wound/fracture). Bone infection was classified into four types according to the site of infection: type 1 is metaphyseal and/or epiphyseal osteomyelitis close to the growth plate; type 2 is primary subchondral osteomyelitis mostly accompanied by septic arthritis; type 3 is infectious osteoarthritis with subchondral osteomyelitis implicating that infection in the subchondral bone originates from the infection. Type 4 summarizes bone infections which can not be categorized in the previous groups. Hematogenous osteomyelitis is 3.2 times more frequent than post-traumatic osteomyelitis. Within the different groups, the relation of hematogenous to post-traumatic infection changed significantly. In type 1 infection the ratio was 5/1, in type 2 the ratio was 8/1 and in type 3 it was 3/1. Epiphyseal or metaphyseal osteomyelitis exhibited early radiographic bone changes, whereas with infection eminating from the joint, the bone lesions were detected later, because the bone was infected as a consequence of a primary septic arthritis. In smaller bones, severe and complete bone destruction was often present. Hematogenous bone infection never involved the entire diaphysis. Actinomyces pyogenes was discovered to be the main etiologic agent, whether or not combined with anaerobes. Bone fragments from the metaphysis of young calves were subjected to the effect of pure cultures of different bacteria. Radiographic changes to the structure of the bone were not identified within 2 weeks. Rapid radiographic changes in osteomyelitis cannot be explained by the direct effect of the bacteria on bone tissue in vivo. General infections of the lungs, disorders of the intestines and other internal organs were rarely responsible for osteomyelitis or septic arthritis. Osteomyelitis and infectious osteoarthritis is probably often induced by external and internal traumatic events to joints and bones in cattle.     

RADIOGRAPHIC BONE LOSS CORRELATIONS AND TECHNETIUM-99m-MDP BONE UPTAKE IN LIGATURE-INDUCED PERIODONTAL DISEASE IN THE BEAGLE

The goal of this study was to develop an animal model for the study of acute periodontal disease using silk ligatures in combination with a soft diet in eleven purebred beagle dogs. The silk ligatures were placed subgingivally on the mandible second and fourth premolar on one side of the mouth; the opposite side served as a control. Dogs were monitored during the 16–20 weeks of ligature placement, and for 48 weeks after ligature removal. Development of periodontal disease was evaluated by radiopharmaceutical uptake into bone, radiographic evidence of alveolar bone loss, attachment loss, gingival index and prostaglandin level. Bone loss occurred on the ligatured side during the ligature phase of the study. Radiopharmaceutical uptake was correlated with radiographic evidence of bone loss during the ligature phase. No significant bone loss occurred during the post-ligature phase. Progressive periodontal disease was induced during ligature placement. However, a chronic less aggressive form was not sustained by soft diet alone after ligature removal.     

SALMONELLA CONTAMINATION OF MEAT AND BONE MEAL

The production of meat and bone meal from 8 rendering plants was examined for the presence of salmonellas. Of 164 samples of final product 114 (69.5%) were contaminated with salmonellas. Of 65 samples, collected at various points from the production line 35 (53.8%), and of 95 samples collected from the processing environment 79 (83.1%) were found to be contaminated with salmonellas. A total of 41 serotypes were found with S. havana, S. eimsbuettel, S. ohio and S. singapore being the most frequently isolated. Pre-enrichment of 25g samples in buffered peptone water, followed by enrichment in mannitol selenite cystine broth at 42 degrees C and Muller-Kauffmann Tetrathionate Broth at 37 degrees C and plating on Bismuth Sulphite Agar was found to yield 98.5% of the salmonella-positive samples.     

RADIUM-226-INDUCED BONE LESIONS IN BEAGLES

In a colony of Beagles that had received intravenous injections of ²²⁶Ra was a subgroup of 42 dogs that had limbs amputated because of the development of painful bone lesions. Information was gained from sequential radiographic studies plus examination of tissue harvested from the amputated limbs. Bone lesions that had their inception in bizarre, progressively expansile resorption cavities in which the process of normal bone tissue replacement was defective were identified. Some of these lesions were the site of development of bone sarcomas. This radiation-induced disturbance in bone repair was termed radiation osteodystrophy. The pathologic sequence in these Beagles in which a defect in the remodeling process of cortical bone leads to the development of lesions of radiation osteodystrophy and bone sarcoma was felt to be unique and thought to be a specific effect of chronic irradiation by ²²⁶Ra.     

COMPARISON OF GROSS AND HISTOPATHOLOGIC FINDINGS WITH QUANTITATIVE COMPUTED TOMOGRAPHIC BONE DENSITY IN THE DISTAL THIRD METACARPAL BONE OF RACEHORSES

Comparison of subchondral bone density determined by quantitative computed tomography (CT) with gross and histopathologic changes have not been made in horses. The goal of this study was to determine if mean quantitative CT density and mean voxel standard deviation are associated with the presence and severity of osteochondral lesions in the palmar aspect of the distal third metacarpal bone in racing horses. Metacarpophalangeal joints from nine racehorses were imaged using CT and scored for gross damage. Four-millimeter-thick sagittal and 30 degrees palmar dorsal plane sections were cut, decalcified and stained with hematoxylin and eosin from the distal third metacarpal bone. Microscopic osteochondral lesions and subchondral remodeling were scored on a scale of 0-3. Percent subchondral bone, expressed as the ratio of bone volume to tissue volume, was also measured. Mean quantitative CT density and mean voxel standard deviation were measured from three-dimensional models of CT images comparable with histologic sections. Mean quantitative CT density was not associated with lesion severity or number of lesions. A weak correlation between mean quantitative CT density and gross score was found, but mean quantitative CT density was not predictive for gross score. Mean voxel standard deviation was not correlated with gross or histopathologic measures, but was predictive of mild osteochondral lesions. Results support the association of subchondral remodeling with the development of palmar metacarpal lesions. However, there was not a strong correlation between mean quantitative CT density or mean voxel standard deviation and histopathologic lesions of the distal third metacarpal bone.     

BONE SARCOMA FOLLOWING ORTHOVOLTAGE RADIOTHERAPY IN TWO DOGS

In two dogs that received orthovoltage radiotherapy, osteosarcoma developed in irradiated bone 38 and 77 months after treatment. Irridiated bone in one dog was presumably normal prior to radiotherapy; irradiated bone in the other was infiltrated by an acanthomatous epulis. Both osteosarcomas were probably radiation induced. Radiation-induced bone sarcoma is an important, but uncommon, complication of radiaotherapy.     

BONE SCINTIGRAPHY FOR METASTASIS DETECTION IN CANINE OSTEOSARCOMA

The purpose of this study was to assess the usefulness of serial bone scintigraphy in the detection of skeletal and extraskeletal metastases in dogs with appendicular osteosarcoma. Twenty-six dogs with primary, appendicular osteosarcoma were entered into a limb-sparing protocol. Bone scintigraphy was performed upon presentation, after neoadjuvant therapy but prior to surgery and at selective intervals after limb-sparing surgery to evaluate for the presence of metastasis. Thoracic radiographs, and radiographs of other sites, were also made at the time of each bone scan. All dogs had a complete necropsy. No dog had bone or lung metastases detected prior to treatment. The bone scans, medical records, and radiographs of each dog were reviewed retrospectively. All but one dog developed metastatic disease. Bone metastatic sites were confirmed at necropsy in 12 of the 26 dogs. Seven of these 12 dogs had bone metastatic sites which were not producing clinical signs, i.e. an occult metastasis. In five of the seven dogs, the occult site was the first metastatic site detected. Extraskeletal metastases were identified scintigraphically in six of the 26 dogs, but these were clinically apparent prior to bone scintigraphy in each dog. Suspected malignant scintigraphic lesions were proven benign in six dogs. In five dogs with malignant bone lesions at necropsy the last bone scan prior to euthanasia was normal. The time interval between scintigraphy and necropsy was variable in these five dogs. All dogs without bone metastases at necropsy had normal bone scans. This study validates the usefulness of bone scintigraphy for detection of occult bone metastasis and improved ability for tumor staging in dogs with appendicular osteosarcoma.     

BONE LESIONS IN FOUR DOGS WITH VISCERAL LEISHMANIASIS

Skeletal radiographs of four dogs with confirmed visceral leishmaniasis were reviewed. The dogs had lived in the Mediterranean area for six to 36 months prior to returning to the United States, where they lived for an additional six to 41 months before clinical signs appeared. Clinical findings included lameness, fever, cutaneous lesions, muscle atrophy, lymphadenopathy, hepatosplenomegaly, and weight loss. The dogs exhibited two distinct radiographic patterns. Periosteal proliferation and increased intramedullary radiopacity of long and flat bones occurred in two dogs. Osteolysis of bones of the carpus, tarsus, and stifle was noted in two dogs. Differences in radiographic appearance were presumed to be due to different hematogenous routes of infection. Leishmaniasis should be considered in the differential diagnosis of dogs that have traveled in endemic areas and exhibit the described radiographic changes.     

RADIOGRAPHIC APPEARANCE OF THE NAVICULAR BONE IN SOUND HORSES

Radiographs of the navicular bone in 523 sound horses were reviewed. Detailed evaluation criteria were used. The incidence of radiographic changes and variations in normal horses were recorded. Results were tested for right-left limb difference and for age relationship. Variation in shape and bone structure was commonly seen in the navicular bone. Radiographic changes with an incidence of less than 2% included flexor cortex defects and calcification on the flexor surface. Fragments at the distal navicular bone border, calcification in the impar ligament and enthesiophytes at the proximal border were radiographic findings with an incidence of 2% to 10%. Abnormal canals at the distal border were found in 11% horses. Elongation of the lateral proximal extremity was commonly found. The mean width of the flexor cortex was 3.6 mm.     

DIAGNOSTIC SENSITIVITY OF BONE SCINTIGRAPHY FOR EQUINE STIFLE DISORDERS

Disorders of the stifle are a common cause of lameness in horses yet the accuracy of scintigraphy for diagnosis of stifle conditions is controversial. The aim of retrospective cross‐sectional study was to determine the diagnostic sensitivity (Se) of bone scintigraphy in detecting stifle disease and to determine if two orthogonal scintigraphic images improve diagnostic Se. Horses that underwent scintigraphic examination during a two‐year period were included. Horses were divided into two groups: group 1 (N = 23) had lameness that was localized to the stifle by intra‐articular analgesia and group 2 (N = 182) had lameness that was localized to a different location. Scintigraphic studies (one image or two images) were independently and retrospectively analyzed by two radiologists (R1 and R2). Sensitivity, specificity (Sp) and predictive values (PV), and were calculated for each type of study (one image or two images) and for each radiologist (R1 or R2). The Se to detect stifle disorders varied between radiologists (29.2% and 20.8%). The Sp was 84.5% and 88.3%. When two images were evaluated a decrease in the positive PV for both readers occurred. The Cohen kappa coefficient (κ) between readers was poor when one image (0.084) or two images (0.117) were evaluated. Findings from this study indicated that bone‐phase nuclear scintigraphy is reasonably specific but highly insensitive for detecting lameness originating from the stifle in a diverse population of both normal and affected horses. The addition of a caudal scintigraphic image acquisition did not improve diagnostic sensitivity.