Describe the forces acting on a fractured diaphyseal bone (the middle of the bone, the shaft of a long bone, for example).
Since bones are curved generally & not straight, they bend to resist normal weight-bearing and pulling-action from muscles. Bending thus generates the greatest force on curved bones, causing them to break more easily at the diaphyseal site than pulling.
Compression & Tension - caused by bending loads from weight-bearing
Shear - ie., displacement of fracture perpendicular to long axis of bone; caused by bending loads from weight bearing and asymmetrical twisting loads from muscles pulling on bone
Torsion - Twisting forces from muscular contraction
Say you have a diaphyseal fracture ie., a fracture in the middle of a long bone. What is an example of:
External Coaptation / Coaption
What are the basic rules of application?
Bandages & casts
Basic rules of application:
- only works if there is still some partial stability in bone
- should be minimally displaced fractures in thick periosteum
- minimal malalignment
- for fractures of radius where ulna still intact
- for fractures of tibia where fibula still intact
- for fractures of metacarpals or metatarsals
where some still intact
- animal is skeletally immature so fast-healing
What are the advantages and disadvantes of using external coaption ie., bandages and casts?
- no open surgery - cheap
- easy to apply
- gives little control/stability to fracture
- can result in further severe malalignment
- cannot apply to fractures proximal to elbow or stifle
- cast-associated injuries in 60% of cases; expensive to fix these
What are the two main techniques used in internal fixation of a diaphyseal fracture?
1. Plates & Screws
2. Interlocking Nail
How do plates and screws work? What are the basic rules of application?
How it works:
Plate held flush against bone, held in place by screws driven in perpendicularly through width of bone
Basic rules of application:
Can be used to achieve primary or secondary union:
- compression (primary/direct)
- neutralisation (secondary/indirect) - fracture is re-constructed so plates & screws protect the reconstruction, allowing for callus formation
- buttress (secondary) - transfers all the weight to the buttress (plate) to allow for callus formation
What are the advantages and disadvantages of using the plates and screws method of internal fixation of a diaphyseal fracture?
- can achieve perfect reduction
- no bulky external element (“hidden inside animal”)
- big range of implants avail.
- minimally invasive
- large equipment range required
- large skill base required
- normally needs open surgery
How is the Interlocking Nail technique of internal fixation used in diaphyseal fracture healing?
Medullary nail is driven through centre of bone along axis and held in place (“interlocked”) by perpendicularly inserted screws that span width of bone.
What are the advantages of the Interlocking Nail and what are the disadvantages of the procedure?
- can be used semi-closed
- very strong when used in simple & comminuted fractures, esp. resisting bending
- limited skill base (not used in UK)
- implants must match bone
- only tibia & femur
- requires specialist equipment
What type of equipment can augment plates and screws and other fixations?
Orthopaedic wire aka cerclage wire - Strong piece of wire only used in completely reconstructable fractures; paired wires twisted outside of bone to stabilise long oblique fractures. Must be very tight.
K-wire aka Kirschner wire - Stainless steel pins driven into bone percutaneously for pin fixation. Not “screws” so do not pull distal bone toward proximal for compression.
What is an Intramedullary Pin?
Same as the medullary pin of the Interlocking Nail technique but isn’t locked into position; smooth pin driven through medullary cavity & exits cortex at one end
** should always be combined with another fixation method eg., ESF, cerclage wire, plate.
- can place in humerus, ulna, femur & tibia
- partial resistance to major loading forces such as bending (shear)
- cannot place in radius
- does not resist compression or rotation
What is a type of External Fixation?
External Skeletal Fixation (ESF)
What is the External Skeleton Fixation? How does it work?
1) Pins drive into skin to penetrate bone
2) Clamps connect pins & connecting bar
3) Connecting bar (ext. frame)
- semi-rigid, allowing small movement that’s stimulatory for callus formation
- usually used for secondary union, callus formation
- can be used in neutralisation mode, taking on some torsional & shearing force from fracture eg, in comminuted, reconstructable tibial fracture where tibia is shattered into large fragments
What are the advantages and disadvantages of using the External Skeletal Fixator for fixing a diaphyseal fracture?
- quick & easy to apply
- relatively cheap - don’t need a lot of equipment
- can do it closed, without surgery
- similar technique can be used with a wide variety of patients
- pins can loosen (pin-tract infection)
- difficult to apply compression
- cannot achieve perfect reduction
What is a lag screw and when is it used?
Squeezes two bone fragments together for direct union, placed at right-angle to fracture line. Does create compression as it screws distal end to proximal (unlike a pin).
Can augment plates & screws & other fixations but it will not resist loading forces.
Shouldn't be used alone.