What are the forces that act on non-diaphyseal (epiphyseal) bone vs. diaphyseal bone that can lead to fractures?
Compression is the only force that acts on sites of fracture in non-diaphyseal. Compression comes from the impact of weight-bearing, not twising or bending as in the case of diaphyseal-bone fractures.
In diaphyseal bone, compression, shear, torsion and tension occur at the site of fracture.
Since compression is the only force acting upon non-diaphyseal-bone fracture sites, what implications does this have for the type of fixation to use for healing?
The compression forces are typically lower on the non-diaphyseal-bone fracture sites, so the fixation methods can be "lighter".
What are all the different types of non-diaphyseal-bone fractures that occur?
(Think here especially of joints and other points where bones articulate with each other)
Intra-articular or Peri-articular
Extra-capsular non-articular (aka metaphyseal)
What is avulsion and give some examples of a fracture caused by avulsion.
These are fractures of major muscular insertions close to joints due to force of muscle.
- Gluteal muscles & abductors of the hindlimb insert into the major trochanter of the femur and can pull off the trochanter.
- Triceps pull off a fragment of the olecranon.
What type of fixation method(s) are best for fractures due to avulsion?
Tension bands - secured with a couple of pins & cerclage wire, resist avulsion force. Together with muscles, the wire generates downward force of compression.
What causes an intra-capsular or peri-capsular fracture? Give some examples.
Major & Minor types - a fracture at the epiphysis occurs at the articular surface/joint.
- Carpal fracture or fragment (Salter I-VI)
-fractures can start from metaphyseal region and extend through physis down to articular surface (Salter IV)
Most concerning are Salter V& VI (not shown), which occur along the line of physis & can lead to physeal growth problems/uneven growth of distal limbs, ie., limb deformity
- slow-growing ulna physis restricts growth of radius caudally & laterally → abnormally bowed radius
- shortened & bent tibia
What are the main fixation methods you would use for an intra-articular or peri-articular fracture?
Normally open reduction with internal fixation (ORIF) + compression (ie no callus at joint)
- occasionally removal of small chips
- occasionally conservative for non-weight-bearing
- if joint can’t be properly fixated, then consider
- need to stop synovial-fluid ingress into joint
- can fix fragments with lag screw
What are basic rules of application when fixing intra-articular or peri-articular fractures with open reduction and internal fixation with compression, or lag screws?
- monitor continually
- keep joints aligned
- might give it time & ideally self-healing with normal
- if equine, confine to stall, ensure good nutrition - can wait until growth ends before surgery & fix definitively in adulthood
In cases of fracture along the line of the physis, which causes slow growth and limb deformity: cut slow-growing limb to relieve apposing limb & bridge overgrown-side of physis to allow slow side to catch up
- plates, screws, K-wires
- shortened tibia can be straightened & extended by
dynamic ESF (very extreme & costly)
What happens in an intra-capsular non-articular fracture? What are some examples?
This is also called a metaphyseal fracture - it occurs below the physis, away from the epiphysis, and not where the bones articulate but still within the capsule. See illustration.
- ingress of synovial fluid to fracture can cause complications
- lack of vasculature can be another complication
Examples (see illustration):
- Hip fracture ie., head of femur breaks off within acetabulum
- Ilial fracture - femoral neck fracture
What are the types of fixations used to fix an intra-capsular, non-articular fracture?
- Some can be fixated simply due to helpful force distributions
- two or three parallel orthopaedic wires or pins engage fragment; act of load-bearing causes compression (see illustration)
- plates & screws & k-wires
How does an extra-capsular non articular fracture occur, and what are some examples?
Extra-capsular non-articular fractures are fragments or fractures above or below the articular surface, and they can be metaphyseal.
Examples (see radiograph):
Neck of femur breaks but hip joint still intact
Malleolus fracture at ankle - fracture occurs proximal to joint capsule
How are extra-capsular non-articular fractures fixed for healing?
Crossed K-wires or crossed springy rush pins through fragments (see radiograph of malleolus-fracture fixation on the left).