Introduction to Small Animal Musculoskeletal Imaging

1. Introduction to Small AnimalMusculoskeletal Imaging Dr. LeeAnn Pack Diplomate ACVR

2. Musculoskeletal Radiography • Permit localization and characterization of a lesion • Size, shape, margination, number, position, opacity • Normal radiographic anatomy • Diseases are often bilateral in the appendicular skeleton • Radiographic terms – use appropriately

3. Fractures:Principles of Radiographic Examination • 2 orthogonal views • Sedation/ anesthesia • Include joint above and below • Immediate post-operative repair radiographs should always be obtained • When needed, radiograph opposite limb for comparison (esp. in young animals)

4. Classification of Fractures • External communication • Open (compound) vs closed • Extent of damage • Complete vs incomplete • Direction and location of fracture line(s) • Simple, comminuted, multiple, etc….. • Stability • Location • Diaphysis, metaphysis, epiphysis • Special types => Salter-Harris, pathologic

5. Open (Compound) vs. Closed • Communicating wound to external surface open fracture • May see gas within soft tissues or large soft tissue defects • May see causal object (gunshot)

6. Extent of Damage • Complete => both cortices fractured • Incomplete => fracture through one cortex • Greenstick Complete 

7. Direction and Location of Fracture Line • Simple => one fracture line • Transverse • Oblique • Spiral Transverse

8. Direction and Location of Fracture Line • Comminuted • Multiple fracture lines usually meet at a common point • One or more small fragments

9. Pathologic Fractures • Bone is weakened by pre-existing lesion • Fracture happens spontaneously • No history of trauma • Tumors, infection, hyperparathyroidism • Lysis may not be obvious • BIOPSY at the fracture site and do CHEST RADS if a fracture seems to have occurred for no reason!!!

10. Pathologic Fractures Secondary to Osteosarcoma

11. Salter-Harris Classification of Physeal Fractures • Classification system developed by human physicians and adopted for animals • Correlated with prognosis • Higher number = higher chance of premature physeal closure (worse prognosis) • Premature closure • Bone foreshortening • Angular limb deformities

12. Salter-Harris Classification

13. Salter-Harris Type I • Separation of metaphysis from epiphysis • Occurs through layer of hypertrophied cells

14. Salter Harris Type I Always do two views!!

15. Salter-Harris Type II • Most common • Fracture line travels through growth plate for variable distance then extends into metaphysis

16. Salter-Harris Type II

17. Salter-Harris Type III • Fracture line travels through growth plate for variable distance then extends through epiphysis into articular surface

18. Salter-Harris Type IV • Metaphyseal fracture line extending through the physis and epiphysis to exit through the articular cartilage • Distal humeral condylar fractures

19. Salter-Harris Type V and VI • Type V – Compression of growth plate resulting from crushing force transmitted through physis • Type VI – eccentric physeal impaction resulting in transphyseal bridging

20. Radiographic Evaluation of Fracture Healing • ABCDs of fracture healing • Alignment of fracture segments • Bone healing and callus formation • Cartilage– implants away from joint, articular fxs • Device– appearance of implants (adjacent lysis, positional change) • Soft tissues– swelling, emphysema, atrophy

21. Radiographic Evaluation of Fracture Healing • The A’s • Apparatus • Alignment • Apposition • Activity

22. Fracture Healing Complications • Absence of callus formation • Instability/ large fracture gap • Zone of radiolucency around fixation devices • Bending or breaking of fixation devices • Fracture-associated sarcomas • Esp. femur (mean 5.8 yrs post-fracture) • Implant induced??

23. Implant Failure • Can see catastrophic failure with bending or breakage of implants • Lucency around implants • Loosening • Osteomyelitis

24. Nonunion Atrophic • When all signs of repair have ceased and further healing will not occur without surgical intervention • Types • Hypertrophic-”elephant’s foot” • Atrophic-sharp edges Hypertrophic

25. Malunion • A fracture that has healed in a position that is not anatomic

26. Soft Tissue Abnormalities • Intra-capsular soft tissues • Enlargement of soft tissue within the joint • Stifle, tarsus and carpus easiest to evaluate • Swelling usually conforms to joint margins • Can be caused by: • Effusion • Soft tissue proliferation • Tumor

27. Intra-capsular ST Swelling Normal IC Swelling

28. Bone Abnormalities • Bones response • Bone production - osteoblast • Periosteal reaction and sclerosis • Takes 12-14 days after insult • Bone loss – osteoclast • Lysis • 30-50% bone loss required to be seen on radiographs

29. Bone Loss • Determining Aggressiveness • Zone of transition • The less distinct the margin  the more aggressive the lesion

30. Focal Bone Loss • Geographic Lysis • Large area of lysis • Usually less aggressive • If destroys the cortex  aggressive

31. Focal Bone Loss • Geographic lysis • Expansile appearance • Expansion of the cortex around an enlarging mass  less aggressive • Note the intact cortex in the picture

32. Bone Cyst

33. Focal Bone Loss • Moth Eaten lysis • Multiple smaller areas of lysis • Areas may become confluent • More aggressive than geographic lysis

34. Permeative Lysis

35. Primary Bone Tumors • Radiographic Signs: • Lesion may be primarily productive, lytic or both • Lytic or productive lesions usually have an aggressive appearance • Away from the elbow and toward the knee

36. Primary Bone Tumors • Radiographic Signs: • Typically mono-ostotic • Typically located in the metaphysis • Lesions typically do not cross joints

37. Primary Bone Tumor

38. Fungal Osteomyelitis • Radiographic Signs: • Typically lesions are seen in the metaphysis • Appear similar to primary bone tumor • Often extensive destruction when a joint is infected (septic arthritis) • Often is poly-ostotic

39. Fungal Osteomyelitis • Etiological Agents: • Blastomyces dermatitidis • Southern states, mid-west and south-west • Coccidioides immitis • Westernstates • Histoplasma capsulatum • Mid-western states • Cryptococcus neoformans & Aspergillosis • Throughout the US

40. Bacterial Osteomyelitis • Usually secondary to: • Gunshot wound • Penetrating wound ( dog or cat bite) • Previous surgery (implants) • Open fracture • May be seen secondary to septicemia in young animals or animals which are immuno-compromised

41. Bacterial Osteomyelitis • Radiographic Findings • Early = ST swelling • May take 10-14 days before periosteal reaction is seen • Periosteal reaction is typically solid and extends along the shaft of the diaphysis

42. Synovial Cell Sarcoma • Early in the disease there is intra-capsular and/or peri articular swelling • Swelling then turns to a mass effect • Later there is bone lysis of multiple bones of the joint

43. Synovial Cell Sarcoma

44. Synovial Cell Sarcoma

45. Cruciate Ligament Rupture • Cranial displacement of the infra-patellar fat pad • Caudal displacement of the fascial stripe

46. Cruciate Ligament Rupture • DJD • Base and apex of the patella • Proximal aspect of the trochlear ridge • Medial and lateral aspects of the distal femur and proximal tibia • Fabellae

47. Cruciate Rupture

48. OCD Shoulder Elbow Stifle Tarsus Retained Cartilage Core Fragmented Medial Coronoid Process Ununited Anconeal Process Panosteitis Hypertrophic Osteodystrophy Hip Dysplasia Legg-Calve-Perthes Developmental MS Diseases

49. Osteochondrosis • Subchondral defect – flattening • Surrounding sclerosis as time progresses • Joint mice • Secondary DJD • Locations: shoulder, elbow, stifle, tarsus

50. Shoulder OCD • Subchondral defect on the caudal aspect of the humeral head • May see a joint mouse • May just be flattened • Secondary DJD • May need arthrogram or explore