AVN Knee

Can be Idiopathic or Secondary

SONK

Spontaneous Osteonecrosis Knee
Aetiology
Microtrauma
Primary vascular ischaemia

Pathogenesis/ Pathology

Necrosis
Inflammation/ Revascularisation
Repair
Remodelling
± secondary Osteoarthritis
Initially localized depression of condylar surface
Then articular sequestrum becomes partially separated as hinged flap
May separate completely
Result is crater with fibrocartilage base

Clinical Features

Usually healthy woman age 60+ years
Sudden onset of severe knee pain
Almost always medial femoral condyle
Exquisite local tenderness
May be effusion
Other side rarely involved
SONK of tibial plateau less common
Otherwise same as MFC
May resolve spontaneously » allow course of non-op Treatment

Radiology

X-ray

Initially normal
Later develop
Subchondral lucent line
Crescent Sign
Flattening of condyle
Patchy sclerosis
Can have rapid collapse into varus

Bone Scan

Investigation of choice
If have normal x-ray & painful knee in 60yr old think AVN & consider bone scan as may have degenerative meniscal tear at a/scope but don’t get better
Focal ↑ in uptake
One side of joint
If both sides involved then more likely Osteoarthritis

MRI

Discrete well defined low signal areas in subchondral region on T1

Classification

Modified Ficat & Arlet for Knee
Stage I
Normal plain X-ray
Stage II
Cystic or sclerotic lesion but normal bony contours
Stage III
Cresent sign or subchondral collapse
Stage IV
Narrowing of joint space with secondary changes
Insall
Stage1
Normal x-ray
Bone scan +ve
Stage2
Subtle flattening of weight-bearing portion of condyle
Stage3
Typical lesion with radiolucent area surrounded by sclerotic halo proximal & laterally
Stage4
Subchondral collapse
Stage 5
Degenerative change & varus or valgus angulation
Extent determined on AP film
Width of lesion > 50% of condyle » poor prognosis & tend to deteriorate rapidly

Management

Options are
Initially watch to see if resolves
A/S debridement & drilling
Retrograde or Antegrade
Bone graft or Osteochondral graft
Valgizing HTO
TKR if > 65yo
See treatment algorithm below

Secondary AVN

Much less common
Pathogenesis
Same sequence of events as SONK
Caused by
Steroid Therapy
Alcohol
Diver’s
Marrow Proliferative Disorder
Sickle Cell Disease
SLE

Clinical Features

Gradual onset of pain
Lateral condyle in 60%
Bilateral in 50%
Is the natural history less predictable than hip AVN?

Radiology

As for SONK

Management

No standard management as uncommon
Options as for SONK
SONK vs Atraumatic AVN
SONK Atraumatic AVN
> 55yrs Often mid 30’s
MFC Multiple areas
99% unilateral 80% bilateral
Knee only 60-90% other joint
Juxta-articular Epiphyseal/ diaphyseal/ metaphyseal
Treatment Results
AVN may spontaneously resolve » allow nonoperative treatment first
Arthroscope doesn’t appear to alter natural Hx
Core Decompression
Some success in stages 1 & 2
Site of lesion not predictive of outcome
Size of juxta-articular lesion
Large lesion fared worse than medium or small both for tibia & femur
But figures not recorded
Role not as defined as AVN of hip
Allograft experimental
HTO
Usually in younger high demand patient
Koshino
37pts with 5yr follow-up
Only 1pt with TKR
Best when initially varus & lesion pre-drilled or grafted
Arthroplasty
Unicompartmental reasonable in SONK as virtually always medial comp only
Marmor CORR 1993
89% good or excellent in 34 knees
TKR
Results not as good as for Osteoarthritis
85% success at 5yrs
Mont, Hungerford et al Sept 2000 TKR successful in 60%
71% = 34 of 48 TKR successful at 9 years
CONCLUSION
INITALLY WATCH AS MAY RESOLVE
CORE DECOMPRESSION WORTHWHILE WITH GOOD OUTCOME
TKR POOR RESULTS NOT UNLIKE AVN OF HIP
ALGORITHM
Stages I-III
- Non-Op 1st
Persistent symptoms + no progression
Core decompression
Persistent symptoms + X-ray progression » TKR
Initial presentation at Stage IV »TKR