Introduction
- Indications
- Principles of Internal Fixation
- Types of Internal Fixation
- Complications
Indications
- Failure to obtain or maintain fracture reduction
- 1. Irreducible fractures
- Fractures that cannot be reduced except by operation
- 2. Unstable fractures
- Fractures that are inherently unstable & prone to redisplacement after reduction
- 3. Fractures that unite poorly
- Principally fractures of the femoral neck
- 4. Pathological fractures
- Fractures in which bone disease may prevent healing
- 5. Multiple fractures
- Where fixation of one fracture facilitates treatment of the others
- 6. Fractures in patients who present nursing difficulties
- Eg. paraplegics, multiply injured patients, elderly
- 1. Irreducible fractures
Principles of Internal Fixation
- The aim of treatment is to produce stable fracture fixation, with a minimum of devascularisation, & early motion & partial loading
Principles (AO)
- 1. Anatomical reduction of the fracture fragments, particularly articular
- 2. Stable internal fixation
- 3. Preservation of the blood supply
- dependent on surgical technique
- 4. Early active pain-free mobilisatio of muscle & joints
- (reduces joint contracture & loss of motion & dystrophy)
- Stable fixation
- Fixation that prevents motion of the fragments
- Stable fixation is best represented by a simple fracture with a rigid plate applied across the fracture in compression
- Introduction of compression introduced stability
- Compression allows the transfer of force from fragment to fragment rather than via the implant
- Stable fixation restores the load bearing capacity
- Compression 2 effects
- Produces preloading, maintaining close contact of the fragment surfaces
- Produces friction which resists transverse displacement & torque about the long axis
- Strain
- Relative deformation of a tissue ยป Displacement of fragments divided by the width of the fracture gap
- Represents the degree of instability
- At very low levels of strain the bone heals by primary healing
- At intermediate levels healing is by callus
- At high levels nonunion occurs
- Instability is best tolerated by multifragmentary fractures because the displacement is distributed over several interfaces & the individual strain is low
- Strain is very high for bone fragments separated by a single narrow gap & these fractures are very intolerant of even minute displacement
- This explains why in some situations where mobility has not been abolished (intramedullary nailing) the fracture heals while in other instances where only a very small gap is left even macroscopically invisible movement is not tolerated
- natural healing of bone tends to follow these principles in that concentric callus is formed about the fracture site producing a mechanical advantage & as the tissue differentiates a more rigid approximation of the fracture occurs
- At the same time resorption of the fracture ends occurs widening the interfragment gap & decreasing the strain value
Types of Internal Fixation
1. Lag screws
2. Plates
3. Intramedullary Nails
4. Tension Band Wiring
Lag Screws
- Stability is achieved by compression & bone contact
- Load transfer occurs directly from fragment to fragment & not via the implant
- Should be placed perpendicular to the fracture line
- Screw can apply 2000-4000N
- Drilling & insertion of a lag screw stimulates bone formation around the threads & maximum strength is reached at 6-8 weeks & at all times remsins higher than when inserted
- One screw is never strong enough to achieve stable fixation & 2-3 screws are required
Plates
Seven types
- 1. Neutralisation plate
- 2. Compression plate
- 3. Buttress plate
- 4. Bridging plate/ wave plate
- 5. Antiglide plate
- 6. Tension-band plate
- 7. Spring plate
Neutralisation Plate
- Protect lag screws from bending, shear, & rotation
- Eg. lateral malleolus fracture
Compression plate
- Applied to tension side of eccentrically loaded bone
- Can produce 600N compression (cf. 2000-4000N compression with lag screw)
- Plate should be overbent to produce compression on far side as well as near cortex
- Inner screws applied first
- Function of grooves on LCDCP
- Improve blood circulation by minimising plate-bone contact
- More even distribution of stiffness through the plate
- Allows small bone bridge beneath the plate
- Eg. transverse or short oblique radial fracture
Buttress plate
- Physically protects underlying thin cortex
- Often for metaphyseal fractures
- Eg. tibial plateau & distal radius fractures
Bridging plate
- Treatment of multifragmented fractures
- Bridge segment of comminution with indirect reduction & minimal disruption to blood supply
- Compression occasionally possible
- Eg. comminuted ulnar fracture
Antiglide plate
- Secured at apex of fragment of oblique fracture to physically block shortening or displacement
- Eg. Weber B ankle fracture with posterior plate
Tension-band plate
- Same principle as TBW with application on tensile surface of eccentrically loaded bone & conversion of tension forces to compression forces
- Eg. olecranon plate
Number of cortices
- Humerus 6
- Radius & ulna 5
- Femur 7
- Tibia 6
Intramedullary Nail
Fixation of diaphyseal fractures of long bones
Types
- Reamed vs Unreamed
- Cylindrical vs Slotted
- Locked vs Unlocked
- Anterograde vs Retrograde
Examples
- Humeral nails
- Forsythe nails
- Femoral & tibial nails
- Long Gamma nails
- Expandable nails
Hollow nails associated with higher incidence of infection?
Tension-band Wiring
- Relies upon compression by the dynamic component of the functional load
- Conversion of tension forces to compression forces
- Allows some load-induced movement
- Patella & olecranon fractures
Bioabsorbable Materials
- Poly-lactic acid (PLA)
- Not induce bone reaction
- ~ 2 years to resorb
- Screws & wires available
- Poly-glycolic acid (PGA)
- Associated with cyst formation
- ? not used anymore
Complications
- Infection
- Nonunion
- Patient factors
- Injury factors
- Bone factors
- Surgical factors
- Implant failure
- Refracture