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
Arlet & Durroux Classification of Pathology
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

Ficat & Hungerford Classification of AVN
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
Japanese Investigation Committee
  XR Location Outcome
A Medial Good
B Central Intermediate
C Lateral Poor

ARCO

ARCO Classification of AVN Hip
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)
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