Heterotopic Ossification

DefinitionHO Brooker 4

 

Extraskeletal bone formation in periarticular tissues 

- HA crystals within osteoid matrix

 

Different to calcification 

- osteoid matrix laid down

 

Types

 

1.  Myositis Ossificans

- post traumatic

 

2.  Heterotopic Ossification / associated with TJR

 

3.  Neoplastic Ossification

 

Epidemiology

 

Occurs 50-70% THR's

- significant in 20%

- clinically significant in 1%

 

More common in men x 2

 

Risk factors

 

High 

- previous hip / other hip HO

- incidence is 80%

 

Moderate

- hypertrophic OA

- active Ankylosing Spondylitis

- hyperostosis

- DISH 

- active Paget's 

- fracture (acetabular trauma, pre or intra operative)

 

Low

- THR

- posterior approach < Hardinge < transtrochanteric

 

Pathology

 

Similar cascade to fracture healing

- unknown trigger

- undifferentiated mesenchymal cells differentiate in osteoblasts

- occurs within first few days

- produce osteoid

- mineralised to bone (mature lamellar bone)

 

Two Precursor cells about the Hip / Friedenstein

 

1.  Determined Osteogenic Progenitor Cells

- from bone marrow

- develop into osteoblasts with inflammation

 

2.  Inducible Osteogenic Progenitor Cells

- need BMP to develop into osteoblasts

 

Brooker Classification

 

Only Type IV interferes with function

 

Type I:  Isolated islands of bone

 

Heterotropic Bone Brooker 1

 

Type II:  Bony spurs from pelves and proximal femur, gap > 1 cm

 

Heterotropic Bone Brooker 2

 

Type III:  Gap < 1 cm

 

Heterotropic Bone Brooker 3

 

Type IV:  Apparent ankylosis

 

Heterotropic Bone Brooker 4

 

Clinical Features

 

Usually none

- pain usually as it matures

- decreased ROM

- dislocation 2° impingement (rare due to loss of ROM)

- nerve irritation

- trochanteric bursitis

- hip can appear red, swollen and tender

 

X-ray

 

New bone in peri prosthetic soft tissues

- visible by 3-6/52

- extent determined by 3/12

 

Maturation continues for 12-18/12 

 

Bone Scan

 

Increased uptake = continued activity

- remain increased for 12/12

 

Bloods

 

Rise in serum alkaline phosphatase post surgery

- associated with HO

 

Management

 

1.  Prevention 

 

Identify at patients risk preoperatively

- Ankylosing Spondylitis / Pagets / Previous HO / DISH

 

A.  Surgical Technique

 

Gentle handling of tissues

- avoid muscle stripping

- lavage tissues

- drain wound

 

B.  NSAID

 

Indomethacin 50 mg bd for 1 week

- significant reduction in risk of HO

- 7 days as effective as 14 days

- as effective as postoperative radiation

 

Risk of GIT side-effects ~ 20%

- interaction with anticoagulants

- double risk of significant bleeding with DVT prophylaxis

 

Results

 

Knelles JBJS 1997

- 685 Primary THR

- 50mg bd Indocid for 1 week

- as effective as 1 x 7 Gy Post-op

 

C.  DXRT

 

For very high risk patients

- previous HO / indocid contraindicated because of PUD

- post surgical excision of HO

 

Dosing

- 700 Rad / 7 Gy < day 5

- 800 Rad 6h pre-op prevents HO

 

Side effects

1.  Delay incorporation of bone graft / union of trochanter

2.  May delay porous ingrowth with uncemented components

3.  Can make patient nauseous

4.  Nil evidence wound problems (shielded, low dose)

5.  Risk of malignancy - nil evidence at this low dose

 

D. Biphosphonates

 

Delay calcification and delay Xray appearance of bone 

- doesn't prevent osteoid formation

- calcification occurs once drug stopped

- no longer used

 

2.  Surgical Excision

 

Indications

 

Significant symptoms / reduced ROM & > Brooker III

- revision of prosthesis

 

Timing

 

Usually 12-18 / 12 post-operatively

- mature appearance on XR

- cold Bone Scan

- serum ALP normal

 

Prophylaxis

 

Radiotherapy post oeratively as high risk 

 

Results

 

Usually increased ROM

- unreliable effect on pain

- bone often reforms

 

Case

 

THR HO Brooker 4THR HO Brooker 4 Poster ExcisionTHR Post HO Excision Dislocation