Chicken Model of Traumatic Femoral Head Osteonecrosis

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Chicken Model of Traumatic Femoral Head
Osteonecrosis

• Sarah Zawodny-Steward, MD (PGY-2)
• May 18, 2009
• OREF Virginia Resident Symposium

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Osteonecrosis

• Ischemic death of cellular elements in the
  epiphyses of bone
• Deterioration of subchondral bone and loss of
  mechanical integrity

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Etiology

• No discrete agent or pathologic mechanism
  identified, just theories
• Altered blood flow
• Direct cellular toxicity
• Impaired mesenchymal cellular differentiation
• Factors
• Corticosteroids
• Coagulation abnormalities
• Alcohol use
• Genetic polymorphisms
• Trauma (dislocation or fracture)

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Femoral Head Arterial Supply

• Proximal epiphyseal region is encased in
  avascular cartilage
• Increased risk of ischemia when periosteal and
  endosteal blood supply is interrupted

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Clinical Relevance

• Unrelenting course of pain and dysfunction
  leading to femoral head collapse
• Relatively young, active patients
• Mean age of presentation 38 years
• 20,000 new cases diagnosed annually
• Approximately 10 of all THAs
• Not optimal for young patients
• Conservative treatment options currently delay,
  but do not halt progression
• core decompression, osteotomy, nonvascularized
  bone matrix grafting, free vascularized fibular
  grafts, resurfacing procedures

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Animal Model of Osteonecrosis

• Experimental techniques must mimic clinical
  situations
• Regardless of where circulation is initially
  impeded (arteries, veins, capillaries,
  sinusoids), the endpoint is interruption of
  arterial flow
• The lack of effective treatments for ON is mainly
  due to the lack of an ideal animal model.

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Why Chickens?

• Existing models
• Rat
• Piglet
• Emu
• Sheep
• Quadruped animal models have failed to produce
  the human form of ON.
• Majority do not progress to collapse of the
  femoral head
• Biomechanical environment of the hip joint in
  bipedal animals is similar to humans.
• Chickens treated with glucocorticoid steroids
  have demonstrated the human form of ON in our
  research laboratory (Dr. Cui et al.)

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Traumatic Model of ON

• Surgical hip dislocation and disruption of the
  vascular supply to the femoral head
• Left hip is experimental side, Right serves as
  control.

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• Procedure

• 2 cm longitudinal incision over the greater
  trochanter
• Fascia of gluteus maximus incised to expose the
  greater trochanter
• Joint capsule detached and Ligamentum teres cut
• Femoral head dislocated from the acetabulum

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Procedure

• Periosteum of the femoral neck scored and
  surrounding periosteal vessels severed
• Femoral head relocated
• Surgical incision closed in layers

Microfil (orange) injected into arterial system
of chickens to map vessels supplying the femoral
head.
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Methods

• Total of 24 chickens
• 18wk female white leghorn
• 6 euthanized for tissue harvest at 4 time points
  4, 8, 12, and 20 weeks
• Femoral head and neck samples fixed in Formalin
• MicroCT
• Histological analysis
• Decalcification with 0.25M EDTA for 4-5 weeks
• Embedded in paraffin
• 7 µm coronal sections stained with HE

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Quantitative µCT imaging analysis
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Histology of Human Osteonecrosis

• Loss of thickness of trabecular bone
• Empty lacuna due to osteocyte death
• Appositional new bone formation on necrotic
  trabeculae
• Subchondral collapse, fracture, and/or cysts
• Marrow edema and/or necrosis
• Depletion of hematopoietic cells
• Fat cells are necrotic in the marrow
• Marrow space filled with eosinophilic fibrinoid
  material

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Control (10x)
8R (2x)
8L (2x)
Empty Lacunae
Normal Osteocytes
20 wk Experimental (10x)
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20 wk (8L) at 40x Necrotic Bone
New appositional bone formation
Dead Osteocytes
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Macroscopic Findings
Collapse
Subchondral Fracture
Necrotic Bone
Subchondral Cyst
Human specimen collected at time of Total Hip
Arthroplasty
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20 week (10L) Subchondral cyst formation
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20 week (9L) Collapse of subchondral bone, void
filled by fibrous tissue
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Conclusions

• Histologic changes consistent with Osteonecrosis
  seen as early as 4 weeks
• Trabecular bone loss, empty osteocyte lacunae,
  new bone formation on existing trabeculae
• Progression to human form of disease
• Cyst formation and collapse by 20 weeks
• MicroCT analysis shows decreased bone volume and
  increased porosity compared to controls.
• Successful traumatic model of osteonecrosis can
  be used to develop innovative treatments
• Tissue Engineering

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Core Decompression

• Most commonly used head preserving procedure for
  pre-collapse osteonecrosis
• Performed with or without bone graft or bone
  graft substitute

Core decompression performed on chicken femoral
head a 1.6 mm k-wire and a 2 mm drill bit were
used for testing under the fluoroscopic guidance,
the femurs were then dissected to examine the
position of the core tracts.
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Bone Graft Substitute

• Osteoconductive PLAGA sintered microsphere
  scaffold
• Osteoinductive and Angiogenic Stem cells
  expressing BMP and VEGF concurrently

SEM images of D1 cells on the PLAGA sintered
microsphere scaffolds at day 21(C 80)
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Special Thanks

• UVa Academic Orthopaedic Training Program
• Musculoskeletal Research Training Grant T32
  AR0509601 from the NIAMS, NIH
• Orthopaedic Research Education Foundation
• OREF Resident Clinician-Scientist Training Grant
• Orthopaedic Trauma Association
• OTA Resident Research Grant

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