7 Ischemic Diseases
Osteonecrosis
Definition
Osteonecrosis describes the death of osseous structures (trabecular bone, bone marrow, cortical bone) in the epiphyses of convex articular surfaces.
Pathology
pathophysiologically primary critical disruption of blood supply to subchondral region
additional vascularization disorders (impairment of blood inflow/outflow) cause diminished oxygen supply and result in irreversible cell death
Primary (Spontaneous) Osteonecrosis of the Knee joint (SONK)
occurring in older patients (> 55 years)
no known risk factors
localization: weight-bearing zones of femoral condyle (medial > lateral), tibial condyles less frequently involved
stages in disease course differ from secondary osteonecrosis
stages:
– early stage (reversible): bone marrow edema at typical site, weight-bearing region of the joint
– late stage: flattening of condyles, collapse of articular surface, secondary arthritis
Secondary Osteonecrosis
occurring among younger patients (20–55 years)
localization: not necessarily restricted to weight-bearing zones
disease course in stages
stages/ARCO (Association Research Circulation Osseous) classification:
– stage 0: plasmostasis
– stage I: reversible initial stage, sufficient reparative processes, fibrovascular tissue formation
– stage II: irreversible early stage, insufficient repair mechanism, lesion with sclerotic rim
– stage III: subchondral fracture, osteochondral fracture, condylar flattening
– stage IV: arthritic changes, articular destruction
Etiology
SONK:
– unclear
– traumatic origin?
– preexisting joint damage (meniscal lesion)
– osteoporosis
secondary osteonecrosis:
– risk factors: alcohol abuse, hypercholesterinemia, hyperuricemia
– diseases: hypercortisolism (cortisone therapy), hemoglobinopathies (sickle-cell anemia), Gaucher disease, caisson disease
Clinical Signs
SONK:
– sudden onset of pain
– patient can usually recall onset almost exactly
– pain depending on weight bearing
secondary osteonecrosis:
– uncharacteristic pain
– insidious onset
– night pain
Diagnostic Evaluation
Recommended Radiography Projections
anteroposterior (AP)
lateral
tunnel view
Findings
SONK:
– stage I: normal
– stage II: flattening of the condyles in weight-bearing zones
– stage III: radiolucent area with poorly defined sclerotic rim
– stage IV: lesion has dense appearance, osteochondral fracture, separation with sclerosis at the lesion site
– stage V: signs of osteoarthritis, deformity
secondary osteonecrosis:
– stage 0/I: negative
– stage II: sclerotic rim
– stage III: flattened contour, crescent sign
– stage IV: collapse, articular destruction
(→ complementary method)
Findings
exclusion of associated changes
effusion
cysts
Role of Imaging
differentiation between SONK and secondary osteonecrosis
evaluation of extent of necrosis
exclusion of subchondral fractures, associated edema, additional changes of articular structure
(→ complementary method)
Recommended Imaging Modes
axial slices
no contrast material (plain)
bone windows
multislice CT: thin slices, sagittal/coronal reconstructions
Findings
stage 0/I: negative
stage II: lesion with sclerotic rim, irregular bone structure
stage III: subchondral fracture
stage IV: deformity
Basic Treatment Strategies
SONK
early stage: conservative (reduce mechanical stresses)
later stages: high tibial osteotomy
advanced late stage: unicondylar prosthesis
Secondary osteonecrosis
early stage: reduce weight bearing
late stages: knee endoprosthesis
Indications
confirmation of diagnosis
differential diagnosis
localization, extent
staging
prognosis
Recommended Imaging Planes
sagittal
coronal
possibly axial
Recommended Sequences
T1-weighted spin-echo (T1 SE)
turbo inversion recovery magnitude (TIRM) (or fat-saturated T2-weighted [FS T2])
fast PD SE (osteochondral fracture)
possibly i.v. administration of contrast material
Findings
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