O&T: Basic Science Flashcards
Osteoporosis
- Amount of bone is decreased + Structural integrity of ***trabecular bone is impaired
- Cortical bone becomes more porous + thinner bone weaker —> more likely to fracture
Osteoporotic fracture:
- 2/3 people never present for medical attention (∵ not notice at all)
- Many rapidly respond to simple non-operative treatment
Diagnosis:
Bone density
- WHO standardized bone density measurements of total hip / lumbar spine
—> Normal >833 mg/cm2
—> Osteopenia 648-833 mg/cm2
—> Osteoporosis <648 mg/cm2
—> Severe (established) osteoporosis: already have fragility fracture
Normal bone structure:
- Density ↑
- Porosity ↓
- Strong
Osteoporotic bone:
- Density ↓
- Porosity ↑
- Fragile
- Prone to fracture
Investigations:
- DEXA (dual energy X-ray absorptiometry: calibrate absorption level of X-ray against soft tissue thickness)
—> Bone mineral density (BMD) (NOT bone marrow density)
—> T-score + Z-score
(NB: Vertebral BMD may be overestimated due to subchondral sclerosis in end plates in spondylosis)
T-score:
- Comparison of patient’s BMD to that of healthy ***thirty years old of same sex and ethnicity
- Indications: Post-menopausal women + Men over 50 yo
Z-score:
- Comparison of patient’s BMD to that of BMD value of their ***corresponding age group of same sex and ethnicity
- Indications: Premenopausal women, Men under the age of 50, Children (∵ skeleton not fully developed, cannot compare with 30 yo)
(From JC036: WHO definition of Osteoporosis - Normal: T score >= -1 - ***Osteopenia: -2.5 < T < -1 - ***Osteoporosis: T <= -2.5 - Established osteoporosis: T <= -2.5 + Fracture)
Osteoporotic spinal fracture
- Common
- Aging population
Clinical features:
- Back pain
- Acute fracture
- Non-union - Deformity
- Multiple fractures (multiple level) - Neurological deficits
- Acute / Delayed
Types:
1. Flexion compression fracture (**Wedge fracture)
- during flexion compression force exerted on **Anterior vertebral column
—> wedge shaped fracture
—> usually benign: Mechanically stable + Neurologically safe (∵ not involve posterior column / middle column)
- Anterior column: Compression force
- Middle column: No compression force
- Posterior column: None / Distraction force (severe)
- Axial compression fracture (**Burst fracture)
- centre of gravity acting vertically on **Anterior + ***Middle column —> Mechanically unstable
- Progressive collapse
—> Collapse of vertebral body / column
—> Retropulsion of bony fragment compressing on spinal cord
—> Neurological deficit (may have delayed neurology)
—> Onset 2 months after fracture (∵ fragments may slowly migrate to spinal canal)
—> Non-union (i.e. cannot heal by itself) —> Require surgery
- Anterior column: Compression force
- Middle column: Compression force
- Posterior column: No force
Other classification:
- Type A (0-4): Compression injuries
- Type B (1-3): Distraction injuries
- Type C: Translation injuries (Displacement / Dislocation)
3 Column theory of Denis
- Anterior column
- Anterior longitudinal ligament
- Anterior annulus fibrosus
- 2/3 Vertebral body - Middle column
- Posterior longitudinal ligament
- Posterior annulus fibrosus
- 1/3 Vertebral body - Posterior column
- Posterior ligamentous complex (Supraspinous ligament, Interspinous ligament, capsule + Ligamentum flavum)
- Pedicles
- Facets
- Lamina
- Spinous process
- Transverse process etc.
Surgical problems in osteoporosis
- High risk surgical candidates
- Poor bone quality causing difficulty in:
- Bone graft
- Seating of bone graft
- Internal fixation - Multiple fracture levels
- Fractures adjacent to fixation after surgery
- reasons:
—> stress redistribution on lower spine due to instrumentation, resulting stress concentration at lower vertebra adjacent to implant
- may be solved by Vertebroplasty
Surgery treatment in Osteoporotic spinal fracture
Process:
- ***Anterior decompression (for Neurological deficit)
- ***Anterior column reconstruction with bone graft (for Poor bone quality)
- ***Long posterior fixation (for Mechanical stability)
1st stage: Posterior instrumentation + Correction of kyphosis
- with Titanium bar (cell friendly, tissue compatible)
- Cement augmentation of pedicle screws
2nd stage: Anterior decompression + Fusion
- Excise all bony fragments out
- Fusion with Bone graft (Auto / Allograft)
Minimally invasive surgery: Vertebroplasty
- Puncture into vertebral body via pedicle —> Inject bone cement into vertebral body —> Augmentation of vertebral body to stabilise fractured vertebrae
- NOT correct kyphosis, only solve fracture
- Out-patient
- LA
Indications:
- Painful osteoporotic fracture of the spine between T10 to L5 (cannot do upper spine ∵ pedicle size too small for cannula)
- Persistent pain despite conservative treatment
- Progressive collapse of vertebral body
- Osteoporotic fracture non-union
Complications:
- Cement leakage
- in front of vertebral body: exothermic material can damage blood vessels in front of vertebral body —> ***Thrombosis
- into spinal canal due to breaching of medial pedicle wall (if puncture site not correct) - Thromboembolism (DVT / PE)
- due to cement leakage
- require Anticoagulation - Spinal cord puncture
- due to incorrect pedicle probe placement
Minimally invasive surgery: Kyphoplasty
- Correction of kyphosis
- Cement augmentation
- Minimally invasive technique
Same as Vertebroplasty except:
- Kyphoplasty uses balloon dilatation to dilate vertebral body before injection of cement
Incidence of cement leakage is lower with kyphoplasty, due to
- Creating a cavity by the balloon
- Cement is not injected under pressure
- Compacted cancellous bone by balloon dilatation act as a barrier
Disadvantage:
- Expensive ~€2,600 per injection
Other new technologies: Vesselplasty
Balloon (made of biomaterial) leave inside vertebral body
—> Bone cement leak out of balloon in a controlled manner
—> Enhance integration of bone cement with surrounding bone + Even lower risk of cement leakage
Bone cement biomaterials: PMMA
PMMA:
- Plastic biomaterial
- Exothermic properties can cause effective pain relief but also induce tissue necrosis
- Not ideal cement: chemical, thermal, mechanical properties and non-bioactive
- Adverse clinical results
—> Cement leakage into spinal canal
—> Cement fracture of vertebral end-plate
—> Cause Adjacent level fractures?
—> Long term result of having a foreign material which does not osseointegrate?
Ideal bone cement for Vertebroplasty:
- Radioopaque (allow monitoring during surgery)
- Easily injectable (without a large delivery system)
- Has a low setting temp (less exothermic —> less risk of tissue necrosis)
- Adequate stiffness (not too hard causing adjacent level fracture)
- Bioactive (enhance integration into bone)
Strontium-containing hydroxyapatite
(Sr-HA) bioactive bone cement has shown promise over PMMA
