AVN Hip

Definition

• Nontraumatic or traumatic condition resulting in ishaemic, segmental, bone death of femoral head

Introduction

• Generally young-middle age males
• 20-50 years (average 38 years)
• M:F » 4:1
• Bilateral
• 50% without steroids
• 80% with steroids

Aetiology & Pathogenesis

• Unknown
• Controversial & multifactorial
• Multiple theories
  • Interruption arterial supply
  • Capillary occlusion
  • Intraosseous capillary tamponade (intraosseous HTN)
  • Injury to vessel wall
• Most Idiopathic are really is undiagnosed alcoholism
  • Need very little to be a risk (> 400ml/ weeks)

Vascular & Non Vascular Theories

Vascular

• Can be classified into the 4 categories above

Non Vascular

• Cytotoxics with transplantation
  • Osteocyte death
• Steroids
  • Some authors claim steroids cause direct cell necrosis
• DXRT

At Risk

Alcohol

• MOA uncertain
  • Altered fat metabolism with fat emboli & fat marrow cells
  • Capillary occlusion + Intraosseous HTN
• Bilateral 50-80%
• Often affects other sites

Steroids

• MOA probably from altered fat metabolism
• Steroids cause osteoblastic stem cells to become fat cells
  • Apidogenesis
• Existing marrow fat cells undergo hyperplasia & hypertrophy
  • Capillary occlusion + Intraosseous HTN
• Cumulative
• Dose x Time
• Overall risk 3-25%
• Onset ~ 6/12 » 3 years after steroid use
• Usually bilateral (80%) & multiple sites

Caisson Disease

• N² in blood vessels & extravascular
• Compressed air workers ~ 20%
• Army divers ~ 5%
• Location
  • Medullary > Juxtacortical
  • Humeral Head > Femoral

Pathology & Pathogenesis

• Wedge-shaped area of necrosis
• Nontraumatic typically starts in Anterolateral head
• Crescent Sign
• Separation of subchondral plate from necrotic cancellous bone
• Cysts
• Regions of bone reabsorption
• Failure is by accumulated stress fracture
• Natural History is to progress to collapse in > 90%
• Secondary Osteoarthritis results
• Poor healing response
  • Worst centrally
  • Partial peripherally
• Can use the following to discuss it
• 1. Necrosis
• 2. Inflammation/ Revascularisation
• 3. Repair
• 4. Remodelling
• 5. Secondary Osteoarthritis

Classification of Pathology

• Arlet & Durroux 1973
• All 4 can occur at one time
• Cartilage not necrotic
• Poor correlation with clinical stage

Type	Description
1	(Not Diagnostic) Haematopoietic marrow disappears Lipocytes separated by oedema Presence of foam cells
2	Necrotic marrow
3	Complete medullary & trabecular necrosis No evidence of vascular abnormality at this time
4	New bone laid on dead trabeculae – repair Complete necrosis with dense medullary fibrosis Four causes for Sclerosis in Dead Bone New bone apposition (on dead trabeculae) Micro-fracture/ Subchondral fracture Marrow saponification (calcified dead marrow) Relative osteopenia in surrounding bone (from inflammation)

Clinical Presentation

• Pain, worse with weight bearing
• Decreased ROM
• Sectoral Sign
• Tendency for ER on passive Flexion
• IR with hip Extended > IR in Flexion

Classification

Ficat 1985 + Modified by Hungerford

Stage	Description
0	MRI positive Double line positive on T2 Typically seen as the “silent contralateral hip” Preclinical Pre XR Cold scan
1	Clinically evident Pre XR Increased uptake on bone scan
2	Diffuse porosis Sclerosis either localized or linear arc Cystic areas of reabsorption
3	Collapse/ Flattening typically superior anterolateral head Crescent sign = subchondral fracture Preserved joint space
4	Osteoarthritis superimposed on a deficient head

Steinberg

• Divided Ficat III into
  • A = Collapse
  • B = No Collapse
• Divided Extent of Head Involved
  • Mild < 15%
  • Mod 15-30%
  • Severe > 30%

Japanese Investigation Committee

• Added XR location

	XR Location	Outcome
A	Medial	Good
B	Central	Intermediate
C	Lateral	Poor

ARCO

Stage	Description
0	Bone biopsy = AVN All other Ix normal
1	Normal X-ray MRI +ve
2	Typical X-ray changes no collapse
3	Collapse For stage 3 collapse on XR subdivided A = 2mm or < 15% B = 2-4mm or 15-30% C = > 4mm or > 30%
4	Osteoarthritis

Kerboul Combined Necrotic Angle (JBJS-B 1974)

• Guide to outcome
• Based on AP & Lateral XR
• AP + Lateral Necrotic Wedge Angle
• > 200° = Poor outcome expected

Investigations

XRay

• AP
  • Mottling
  • Sclerosis
  • Wedge
  • Collapse
• Frogleg Lateral
  • Early Anterior collapse

CT

• Limited place
• Can diagnose early collapse & flattening
  • ie distinguish grade II & III
  • 1/3 of Grade II upgraded to III by CT

Te Scan

• Sensitivity 80%
• Nonspecific
• Decreased uptake = infarction
• Increased uptake = alive bone repairing
• Pathognomonic “doughnut sign”
  • (cold ischaemic bone in hot revascularisation zone)
• “Cross-over” point may be false negative
• Most useful to investigate if head vascular after subcapital fracture
• Te99 antimony colloid
  • Taken up by bone marrow 4x more readily than sulfur colloid
  • Successfully predicting AVN following subcapital fracture within 24 hours

MRI

• Sensitivity – 100% in one series
• Very useful in Grade 0
• Signal
  • Normal marrow rich in fat = High signal intensity on T1
  • Dead marrow = Decrease in signal intensity on T1
• T1 Single Line Sign
  • Earliest
• Avascular/ Vascular bone interface
  • T2 Double Line Sign
• Two lines
  • 1. Avascular/ Vascular bone interface
    • Outer line of low signal Intensity
  • 2. Hypervascular Granulation Tissue
    • Inner line of high signal intensity

Functional Exploration of Bone

• Invasive 3 part investigation
  • 1. Bone Marrow Pressure (> 30mmHg abnormal)
  • 2. Intramedullary Venography
  • 3. Core Biopsy
• High sampling error
• Perform if doing Forage
• Now replaced by MRI

Diagnosis

• is established if any of the following are found
• Pathognomonic radiographic changes
  • Collapse of femoral head
  • Anterolateral sequestrum
  • Crescent sign
  • Double line on T2 MRI
  • “Cold in Hot” bone scan
  • Positive finding on biopsy

Natural History

• Asymptomatic Stage 0
  • 83% don’t progress after 5 years (Jergensen JBJSB 1995
    • Stage I – 88%
    • Stage II – 71%
    • Stage III – 27%
  • Stulberg Clinical Orthopaedics 1991
    • Controlled forage vs nonoperative
    • Success (no need for arthroplasty) 75% vs 29%
  • Metanalysis of 24 studies involving 1206 hips at 3 years
    • 37% did not progress radiologically
    • 33% required arthroplasty
  • Success related to stage
    • Stage I – 84%
    • Stage II – 65%
    • Stage III – 47%
  • Other Forage Series
    • Less success
      • ? Due to continued use steroids
      • ? Due to >30% head involvement
  • Gold standard in Stage I & II
  • Temporarily palliative in more severe lesions
• 2. Cortical Bone Grafts
  • Fibular, tibial, or iliac crest struts
  • Mechanical & biologic support
  • Tip of graft supports cartilage
  • NWB 3-6 months until radiographic evidence of healing
  • May be useful if forage fails in stage I & II ?
  • Contraindicated in Grade III
  • Early success 75%
  • Long term success 30%
• 3. Window Technique
  • Cartilage trapdoor or Cortical window
  • Evacuate necrotic bone
  • Pack with Cancellous Bone
  • Good-Excellent results in 60-80% Grade II & III
  • Meyer Trapdoor 1991
    • Grade III Good-Excellent 8/9 patients at 3 years
• 4. Vascularized Bone Grafts
  • Urbaniak 1987
  • To enhance revascularisation so that progression of necrosis altered
  • Vascularised grafts undergo more rapid & complete incorporation
  • Technically difficult & need the resources
  • Considerable variability
  • Donor site
    • Fibula
    • Ilium
    • GT
  • Muscle pedicle artery & vein used
    • Inferior gluteal
    • Profunda femoris
    • Circumflex
  • Must keep NWB for 6/12 to 1 year
  • Similar results as forage
  • Most studies have short term follow up in small numbers
  • Most comprehensive is Yoo – 81 hips at 5 years
    • Vascularised fibula to profunda femoris
    • 91% of Stage 2 & 3 had Good-Excellent results
    • 89% had no radiological progression
    • However the rate of conversion to THR is identical to forage at 20%
  • Indication
    • stage II & early stage III
    • Young patient
    • Large lesion
• 5. Osteotomy
  • Transfer load from necrotic area to undamaged part
  • Transection of bone may afford decompression
  • Procedure
    • Maybe flexion / extension / valgus / varus or rotational
    • If superolateral
      • Valgus + Flexion
    • If central
      • Varus + Flexion
  • Disadvantage
    • osteotomy makes subsequent THR difficult
  • Indications
    • Stage III disease
    • Small lesion (Kerboul combined necrotic angle < 200°)
    • No ongoing cause for AVN
  • Types
    • A. Varus/ Valgus Intertrochanteric Osteotomy
      • Best early
      • Rotate necrotic area out of WB if possible
      • Use CT/ MRI & Adduct + Abduction XR to decide osteotomy type
      • Aid union of subcapital fracture nonunion
      • Hungerford 1994 Varus Osteotomy
        • Grade III after 11years
        • 74% overall
        • 86% if CNA < 200°
      • Scher 1993 Valgus Osteotomy
        • 80% if steroids
        • Better results in grade III than forage
        • Poor if
          • CNA > 200°
          • Due to steroids
      • Contraindicated
        • Grade III with total head involvement
        • Grade IV
      • Indicataion
        • Typical patient will be young & active
        • Ficat III & < 30° involvement
    • B. Sugioka Osteotomy 1978
      • Transtrochanteric rotational osteotomy
      • Anterior rotate in axis of neck
      • Can rotate through 90°
      • Technically demanding
      • Variable reproduction
      • High complication rate
      • Poor results if not intertrochanteric with damage to blood supply of the head
      • Abandoned by some
      • Sugioka’s Indications
        • Early Disease with < 2/3 collapse on lateral
      • Sugioka osteotomy in 52 hips Stage III
        • 56-69% at average of 5 years successful
        • If > 50% involved then results poor
        • Deterioration with time – only 40% of hips surviving 7-10 years
        • Makes THR more difficult
• 6. Electrical Stimulation
  • Experimental
  • Improves forage results
  • ? Future adjuvant to surgery

Salvage After Collapse

1. Osteotomy

• Aim is to prevent collapse
• Move the avascular segment away WB area
• Also decompress intraosseous HT
• May be flexion / extension / varus / valgus / rotation
• Contraindicated with advanced collapse & grade IV

2. Osteochondral Allografts

• Experimental

3. Hemiarthroplasty

• Poor results
• 50% revision rate
• Loosening & Protrusio biggest problems
• Study showed almost universal acetabular cartilage disease at time of arthroplasty

4. THR

• If advanced
• Predictable
• Worse results than Osteoarthritis
• Younger age group
• High activity
• Poorer bone stock
• Ongoing systemic disease
• Defects in mineral metabolism
• Osteonecrosis in calcar & acetabulum as well
• 25 studies
  • high failure rate
• 30-50% revision rates at 10 years
• In < 50 yo with AVN cemented THR (metal on poly) has 50% failure rates at 10 years (Dorr)

5. Arthrodesis

• If young active patient with traumatic AVN
• Usually contraindicated if due to Alcohol or Steroids (80% bilateral)

Guiding Principles

• Try to stop aetiology
  • Stop alcohol
  • Stop steroids if can
• Observe silent contralateral hip until painful
• But discuss option of Forage
• Offer all painful hips some Treatment
• Nonoperative has higher rate of progression
• Forage is Gold Standard for Stage I & II
  • Stage I ~ 80% }
  • Stage II ~ 60% } halts progression
  • Stage III ~ 30% }
• Stage III management uncertain
  • If young
    • Still offer Forage as ~ 1/3 respond
    • Consider trapdoor graft if early stage III & small
    • Consider Osteotomy if CNA < 200°
      • Probably only if very young & wedge < 15° ?
      • Results not predictable especially with steroids
  • THR if > 65 years
• Stage IV
  • THR
    • Gold Standard
  • Poorer results
  • Arthrodesis
    • for young active patient with traumatic AVN (CI if caused by steroid or alcohol)