Key differentials

Stifle key differentials

Cranial cruciate ligament disease

Medial patella luxation

Osteochondrosis

Tibial tuberosity avulsion

Cranial cruciate ligament disease

Effusion ± OA

Medial patella luxation

OA ± malalignment

Diagnosed by palpation

Osteochondrosis of the femur

Defect/ flattening femoral condyle ± fragment

Tibial tuberosity avulsion

Tibial tuberosity pulled cranially/ proximally

Young dogs, 4–8 months

Elbow key differentials

Elbow dysplasia until proven otherwise (ununited anconeal process, fragmented coronoid process, osteochondrosis)

IOHC

Panosteitis

Elbow dysplasia

OA in young large-breed dog

Ununited anconeal process, fragmented coronoid process, osteochondrosis

Ununited anconeal process

Lucent line at anconeal process

Young large-breed dog; anconeal process should close by 20–22 weeks

Fragmented coronoid process

Often just OA; fragment hard to see

Humeral osteochondrosis

Humeral condyle defect ± fragment, OA

Incomplete ossification humeral condyle

Lucent line through humeral condyle

Springer Spaniel > Cocker Spaniel > French Bulldog

Elbow panosteitis

Medullary sclerosis in radius/ ulna

Young large-breed dog, especially GSD, ~6–18 months

Hip key differentials

Hip dysplasia

Hip osteoarthritis

Avascular necrosis of the femoral head

Metaphyseal osteopathy

Capital physeal fracture/ slip

Hip dysplasia

Subluxation/laxity ± OA

Hip osteoarthritis

Morgans line

Ring of osteophytes

Remodelling of the femoral head and neck

Acetabulum remodelling

Avascular necrosis of the femoral head

Femoral head/neck lysis + collapse

Young small-breed dogs, usually 5–12 months, often unilateral

Metaphyseal osteopathy

Femoral neck “apple-coring” lysis

Capital physeal fracture/ slip

Widened/ slipped capital physis

Shoulder key differentials

Osteochondrosis

Panosteitis

Shoulder panosteitis

Medullary sclerosis in humerus

Young large-breed dog, especially GSD, ~6–18 months

Osteosarcoma locations

Away from the elbow - distal radius, proximal humerus

Close to the stifle - distal (and proximal) femur, proximal (and distal) tibia

Does not cross the joint

Spine key differentials

IVDD

Discospondylitis

Vertebral neoplasia

Ventral spondylosis

Atlantoaxial subluxation

IVDD

Narrowed disc space ± mineralised disc / vacuum phenomenon

Discospondylitis

Endplate lysis both sides + sclerosis ± later spondylosis

Vertebral neoplasia

Aggressive lesion centred on vertebral body

Ventral spondylosis

New bone from endplates; hooks/bridges

Atlantoaxial subluxation

C1–C2 instability; dens compresses cord

Joint neoplasia differentials

Cross the joint

Synovial cell sarcoma, histiocytic sarcoma, haemangiosarcoma

Primary bone neoplasia differentials

Osteosarcoma most common; others uncommon

Older large-breed dogs; smaller peak around 2 yrs, bigger peak around 8 yrs

Primary bone neoplasia appearance

Aggressive bone lesion, usually metaphyseal, does not cross joint

Secondary/ metastatic neoplasia differentials

Carcinoma, melanoma, haemangiosarcoma

Secondary/ metastatic neoplasia appearance

Often diaphyseal, mono/polyostotic aggressive lesion

Multicentric neoplasia differentials

Lymphoma, multiple myeloma, histiocytic sarcoma, myeloproliferative/ leukaemia

Multicentric neoplasia appearance

Mono/polyostotic aggressive lesions

Hypertrophic osteodystrophy bones

Inflammatory metaphyseal bone disease - metaphyses of long bones

Young large-breed dogs, 2–7 months

Hypertrophic osteodystrophy radiographs

Metaphyseal changes, especially distal radius, ulna, tibia

Hypertrophic osteopathy

Secondary periosteal new bone due to disease elsewhere

All 4 limbs, especially distal limbs

Older dogs

Hypertrophic osteopathy radiographs

Periosteal new bone along diaphyses; worse near carpus/tarsus

Atraumatic capital physeal fracture

Widened/ slipped capital physis, usually bilateral

Male, overweight cats, possibly early desexed

Digit lesion ddx

Neoplasia - primary soft tissue neoplasia (squamous cell carcinoma)

Cats - lung digit syndrome (primary lung carcinoma)

Osteomyelitis from a nail bed infection