Fabellae and popliteal sesamoid bones in cats

Radiographs of the stifle joints of cats revealed a lack of mineralisation in the medial os fabella in a high percentage of domestic cats and also some exotic species of cat. In all the post mortem examinations undertaken the medial sesamoid bones were smaller. In the non-radiopaque sesamoid bones there was a solid mass which on histological examination consisted of fibrocartilage, whereas the radiodense sesamoid bones consisted of lamellar osseous tissue. The lack of mineralisation of the medial fabellae seems to be more prevalent in domestic than in pedigree cats. None of the exotic cats had mineralised tissue in the medial fabellae. Lack of mineralisation of the sesamoid bones is not significant clinically.     

Multiloculated solitary (unicameral) bone cyst in a young dog

A 20‐month‐old female spayed Staffordshire Terrier (22.3 kg) presented to the Orthopedic Surgery Service at North Carolina State University Veterinary Teaching Hospital for evaluation of a 6‐week history of toe‐touching to nonweight‐bearing lameness in the right hind limb. Radiographs of the right stifle revealed a multiloculated lytic lesion of the distal femur, with a large open lytic zone centrally, numerous osseous septations peripherally, and focal areas of cortical thinning and loss. An aspirate of the right distal femoral lesion yielded mildly cloudy serosanguineous fluid. Cytologic examination of the fluid revealed a pleomorphic population of discrete cells that exhibited marked anisocytosis and anisokaryosis and a variable nuclear‐to‐cytoplasmic (N:C) ratio, which were interpreted as probable neoplastic cells, with few macrophages, and evidence of hemorrhage. Given the clinical signs of pain, lesion size, and concern for malignant neoplasia, amputation of the right hind limb was performed. Histologically, the lesion had undulating walls 1‐3 mm thick with a continuous outer layer of dense fibrous tissue and an inner layer composed of reactive cancellous bone with no cortical compacta remaining. Remnants of thin fibrous or fibro‐osseous septa projected from the bony wall into the cyst lumen. The final histologic diagnosis was a benign multiloculated solitary (unicameral) bone cyst of the distal right femur. Based on the histopathologic findings, it was speculated that the cells identified on cytology were a mixture of developing osteoclasts, osteoblasts, endothelial, and stromal cells. This is the first report describing the cytologic examination of a solitary bone cyst in veterinary medicine.     

Multilobular tumour of bone at an unusual location in the axilla of a dog

Multilobular tumour of bone is a rare neoplasm of cartilage, bone and connective tissue that is seen almost exclusively in association with the skull of veterinary patients. A four-year-old, spayed Jack Russell terrier was presented to the University of Georgia Veterinary Teaching Hospital because of a progressive swelling in the right axilla. Radiographs of the region showed the mass to be caudal to the scapula, unattached to bone and to have numerous punctate calcific opacities throughout its substance. Excisional biopsy of the mass was carried out under general anaesthesia and histopathological examination showed it to be multilobular tumour of bone. This case report documents the occurrence of multilobular tumour of bone at a site other than the head. This tumour should be considered in the differential diagnosis of soft tissue masses with calcific opacities.     

Popliteal sesamoid displacement associated with cruciate rupture in the dog

Distal displacement of the popliteal sesamoid is a useful parameter in the interpretation of tibial compression radiographs in cases of cranial cruciate ligament rupture in the dog. An accuracy of 99 per cent and a specificity of 100 per cent were achieved by assessing the localisation of the sesamoid bone in the diagnosis of cruciate disease.     

Management of proximal sesamoid bone fractures in the horse

The case records of 49 horses with proximal sesamoid bone fracture were studied. The population consisted of 20 Thoroughbreds, 20 Standardbreds, 5 Quarter Horses, 2 Arabians, and 2 grade horses. The fractured bones were classified into 5 categories: apical fractures, basilar fractures, abaxial fractures, middle one-third fractures, and bilateral comminuted-distracted fractures. Apical fractures occurred most frequently in the Standardbred, with the prevalence of medial fracture being equal to that of lateral fracture. Basilar fractures occurred predominantly in the Thoroughbred, with the highest prevalence in the lateral sesamoid bone of the right front fetlock. Bilateral comminuted-distracted fractures also occurred primarily in the right front fetlock. The prognosis following surgical removal of apical fractures appeared to be superior to that for stall rest alone. The prognosis for basilar fractures was poor.     

Lacrimal bone agenesis in a dog

A 20-month-old neutered male dachshund dog was referred because of a 10-week history of swelling close to the medial canthus of the left eye. Recurrence of the lesion and cytological appearance of the fluid content were suggestive of inflammation. Computed tomography revealed a triangular-shaped bone defect in the skull deep to the lesion. Computed tomography dacryocystography demonstrated contrast medium pooling within the maxillary recess and nasal cavity rather than filling the lacrimal duct. Lacrimal bone agenesis was diagnosed.Key clinical message:Congenital skull including lacrimal bone agenesis may be responsible for swelling of the medial canthus of the eye and computed tomography dacryocystography is helpful in making a diagnosis.     

Use of magnetic resonance imaging to diagnose distal sesamoid bone injury in a horse

CASE DESCRIPTION: A 5-year-old Appaloosa mare was examined for severe left forelimb lameness of 4 months' duration. CLINICAL FINDINGS: Lameness was evident at the walk and trot and was exacerbated when the horse circled to the left. Signs of pain were elicited in response to hoof testers placed over the frog of the left front hoof, and a palmar digital nerve block eliminated the lameness. Radiographs revealed no abnormalities, but magnetic resonance imaging (MRI) revealed increased bone density in the medullary cavity of the distal sesamoid (navicular) bone in the proton density and T2-weighted images and a defect in the fibrocartilage and subchondral bone of the flexor cortex. TREATMENT AND OUTCOME: Because of the absence of improvement after 4 months and the poor prognosis for return to soundness, the mare was euthanatized. An adhesion between the deep digital flexor tendon and the flexor cortex defect on the navicular bone was grossly evident, and histologic evaluation revealed diffuse replacement of marrow trabecular bone with compact lamellar bone. Changes were consistent with blunt traumatic injury to the navicular bone that resulted in bone proliferation in the medullary cavity. CLINICAL RELEVANCE: Use of MRI enabled detection of changes that were not radiographically evident and enabled accurate diagnosis of the cause of lameness. Navicular bone injury may occur without fracture and should be considered as a differential diagnosis in horses with an acute onset of severe unilateral forelimb lameness originating from the heel portion of the foot.     

Asceptic necrosis of bone in a dog

Necrosis of intramedullary bone and bone marrow elements is reported in the long bones of a dog. Radiographically lesions were evident as an irregular increase in intramedullary density. On gross postmortem examination necrotic tissue appeared as yellow-white deposits on the endosteal surface and in the medullary cavity. Microscopically, necrotic bone had empty lacunae and was often covered by basophilic, woven bone. The cause and pathogenesisof aseptic necrosis of bone are discussed.     

Unusual presentation of avulsion of the lateral head of the gastrocnemius muscle in a dog

A five-and-a-half-year-old, male neutered golden retriever was presented with sudden onset, plantigrade stance of the left pelvic limb one month after a traumatic incident. A diagnosis of avulsion of the lateral head of the gastrocnemius muscle was made based on clinical signs and radiographic assessment. Initial wire reduction and fixation were unsuccessful. However, reduction and fixation with monofilament leader line augmented with a trans-hock external fixator resulted in a successful outcome. The dog had a normal gait 18 months after revision surgery.     

Diagnosis and management of proximal sesamoid bone fractures in the horse

Fractures of the proximal sesamoid bones (PSBs) range in severity from simple to complex and comminuted and can be articular or nonarticular. The majority of PSB fractures are diagnosed in racehorses, but PSB fractures, especially simple ones, do occur in sport horses undertaking various disciplines. For simple apical, basilar and abaxial articular PSB fractures, surgical removal via arthroscopy carries the best prognosis for return to athletic performance. Removal of apical and abaxial PSB fractures generally result in a favourable prognosis for return to racing but are dependent on the amount of suspensory ligament injury. Removal of basilar PSB fracture fragments results in a less favourable or fair prognosis for return to racing. Mid‐body PSB fractures typically require (lag screw) surgical fixation preferably with arthroscopic guidance and carry a fair to guarded prognosis for return to racing.     

Maxillary bone epithelial cyst in a dog

A swelling ventromedial to the left eye of a one-year-old, neutered male Labrador failed to respond to antibiotic and anti-inflammatory therapy. Plain and contrast radiography revealed a spherical, radiolucent area, 1.5 cm in diameter, dorsomedial to the fourth maxillary premolar and rostral to the ethmoid region. The lesion was thin-walled, with a smooth radiopaque margin, and was clearly demarcated from the surrounding structures. Dacryocystography demonstrated no apparent physical association between the lesion and the nasolacrimal duct, the latter appearing normal. Ultrasonography of the lesion showed a round, anechoic structure consistent with the appearance of a cyst. Prior to surgical excision of the lesion, intralesional fluid was aspirated. Bacteriology of the fluid was negative for both aerobic and anaerobic organisms. Cytological examination of the fluid showed a few macrophages and small lymphocytes; neither significant inflammatory component nor neoplastic cells were found. Histology showed the lesion to be a benign epithelial cyst. The dog recovered uneventfully and there was no clinical evidence of recurrence within a two-year follow-up period.     

Polyostotic cystic bone lesions in a dog

The clinical, radiological, and pathological features of a polyostotic cystic bone lesion in a 9-month-old Doberman Pinscher are described. The patient was diagnosed as having nutritional secondary hyperparathyroidism at 6 weeks of age and after dietary correction it remained clinically normal until 9 months when there was sudden left hind-limb lameness due to a pathological fracture through a cystic lesion in the distal femur. Radiography revealed additional cystic structures in the metaphyses of the left radius, and left and right tibia. Pseudofractures were associated with two of the cystic lesions.
In some areas the cysts were crossed by trabeculae and in others there were bony ridges on the inner cystic wall. The cavities were lined with flesh-coloured fibrillar material which formed a lacy network extending into cavities. Histologically, multiple small cysts were present adjacent to the larger cavities noted radiographically. The secondary spongiosa and the metaphyseal periosteum were the major abnormal tissue sites. The small cysts appeared to arise in an oedematous and congested metaphyseal spongiosa. The cysts were accompanied by small foci of intense osteoclasis but unattended by compensatory bone production, and the consequent possibility of pseudofractures is an important clinical consideration. Earlier reports demonstrated that resolution of the lesions will follow surgical drainage and curettage of the cystic cavity. Of six cases of polyostotic cystic bone lesions observed in the dog, five were in the Doberman Pinscher breed.     

Fibrous dysplasia of mandibular bone in a dog

A nine-year-old, male German shepherd dog was presented with a firm, discrete mass lingual to the interdental space of the mandibular left third and fourth premolars. The lesion was excised and diagnosed as fibrous dysplasia of bone based on histopathologic examination. Fibrous dysplasia of bone is a rare, non-aggressive, radiolucent, non-neoplastic lesion considered developmental in origin. Usually observed as a solitary lesion, it has been reported in animals and man in the polyostotic form. The disease process causes deformity of bone which may lead to loss of bone strength. Clinical signs are secondary to site specific problems associated with expansile bone lesions. Oral examination performed 18-months postoperatively indicated no signs of recurrence.