AVN SONK

 

SONK              vs                          Atraumatic AVN

 

>55                                              Often mid 30's

MFC                                              Multiple areas

99% unilateral                               80% bilateral

Knee only                                      60-90% other joint

Juxta-articular                                Epiphysis / diaphysis / metaphysis

 

Primary Spontaneous Osteonecrosis Knee (SONK)

 

Clinical

 

Usually healthy woman age 60+ years

- sudden onset of severe knee pain with normal Xray

 

Site

 

Almost always MFC (SONK is a MONK)

- there are case reports of LFC SONK

 

99% unilateral

 

Exquisite local tenderness

- may be effusion

 

SONK of tibial plateau less common 

 

Aetiology

 

Yamamoto et al JBJS Am 200

- histological study

- evidence of microtrauma / insufficiency fracture

- initial event

- postulated that osteonecrosis is then secondary event around lesion

 

Primary vascular osteonecrosis may be much more rare

 

X-ray

 

Initially normal

 

Later develop

- subchondral lucent line / crescent Sign

- flattening of condyle

- patchy sclerosis

- can have rapid collapse into varus with development degenerative changes

 

Spontaneous Osteonecrosis of the Knee

 

Bone Scan

 

Normal x-ray & painful knee in 60 year old think AVN

- consider bone scan

- probably superceded by MRI

 

Findings

- focal increase in uptake on one side of joint 

- if tibia and femur more likely OA

 

MRI

 

May be normal in early stages

 

TI

-  low signal areas in subchondral region 

 

SONK MRI Sagittal

 

T2

- low signal

- surrounding high intensity signal secondary to oedema

 

MRI SONK T1

 

Staging Insall

 

Stage 1 

- normal x-ray with positive bone scan / MRI

 

Stage 2 

- subtle flattening of weight bearing portion of condyle

 

Stage 3 

- typical lesion

- radiolucent area with sclerotic halo

 

Stage 4 

- halo thickened with subchondral collapse

 

SONK Xray Stage 4

 

Stage 5 

- degenerative change

- varus or valgus angulation

 

 

Arthroscopic findings

 

Localised area of flattened cartilage

- discoloured

- eventually demarcates

- develop flap of cartilage over necrotic bone

 

The articular sequestrum becomes partially separated as hinged flap

- may separate completely

- cartilage defect becomes filled with necrotic debris and fibrocartilage

- develop OA

 

Management

 

Non Operative Management

 

NHx

 

Many will resolve spontaneously

- especially small lesions

- best prognosis if chondral surface intact

 

Yates et al Knee 2007

- followed up 20 patients diagnosed on MRI

- average resolution of symptoms and lesion over 6 months

 

Program

 

Decrease impact exercises

Consider unloading brace

Analgesia / NSAID's

Consider bisphosphonates

Follow for 6 - 12 months with repeated MRI looking for resolution / progression

 

Operative Management

 

Intact chondral surface / Stage 1 lesion

 

Decompression / Percutaneous Drilling

 

Indication

- failure non operative treatment > 6/12

 

Forst et al Arch Orthop Trauma Surg 1998

- 16 patients with average age 60

- percutaneous drilling with 3 mm drill

- instant resolution of pain

- cannot prevent progression of disease if chondral flattening present

 

Chondral Defect

 

Microfracture

 

Akgun et al Arthroscopy 2005

- debridement of chondral defect and microfracture

- 26 patients average age 48

- 71% could participate in strenous exercise with minimal exertion

- in the remainder the ON progressed on MRI

 

HTO

 

Technique

- unload MFC

- younger high demand patient

- combine with microfracture / osteochondral grafting

 

Osteochondral grafting

 

Tanaka et al Knee 2009

- 6 patients average age 50

- stage III and IV

- good results in knee scores at 2 years

 

UKA

 

Good option as disease is unicompartmental

 

Langdown et al Acta Orthop 2005

- 29 knees treated with Oxford UKA

- good outcomes and no implant failures at average 5 years

 

TKR

 

Secondary osteonecrosis

 

Knee AVN 1Knee AVN 2

 

Causes

- Steroid Therapy (90%)

- Alcohol

- SLE

- Sickle Cell Disease

- Diver's / Caisson's

- marrow proliferative disorder

- chemotherapy

 

Clinical

 

Gradual onset of pain

- lateral condyle in 60%

- younger patients, mid 30's

 

Site

 

Bilateral in 50%

- 70% have other joints involved

 

MRI

 

More extensive involvement through knee

 

Operative Options

 

Indications

- failure non operative treatment

- continued pain

 

Percutaneous Drilling / Decompression

 

Marulanda et al JBJS Br 2006

- percutaneous drilling in 61 knees with secondary ON

- successfull in all 24 knees with small lesions

- successful in 32/37 (86%) knees with large lesions