External and Internal Fixation

what is external coaptation?

the use of external bandaging techniques to support and stabilise a limb. It involves applying rigid or semi-rigid materials as part of a dressing to provide mechanical support and restrict movement of bones or joins to allow healing

indications for use of splinting?

Protect a limb or joint prior to or after surgery

indications for use of casting?

stabilize selected fractures; support a limb or joint following surgery; immobilize the fracture site effectively

what is external coaptation not appropriate for? (contraindications)

proximal fracture (above the elbow or stifle)

toy breed dogs with antebrachial fractures

open fractures

cases with skin wounds

why would you not use external coaptation in toy breeds with antebrachial fractures?

coaptation carries a high risk of non-union due to poor vascular supply (there is limited soft tissue coverage for extraosseous blood supply) and a small medullary cavity

what materials might be used for a cast?

• Plaster of Paris gauze bandage 

• Resin-embedded fibreglass mesh bandage (e.g. Scotch Cast®, DynaCast®).

• Thermoplastics (e.g. Hexilite, Vetlite, Orthoplast)

what materials might be used for a splint?

• Custom-molded fibreglass or thermoplastic materials 

• Aluminium rods or strips

• Plastic "spoon" or commercial leg splints

• Improvised materials (e.g. wooden sticks, syringe cases) in emergencies 

what is the preferred option for a splint?

Custom-molded fiberglass or thermoplastic splints, as they conform to the limb and significantly reduce the risk of pressure sores or rubbing injuries

why would you avoid using a plastic “spoon” or commercial leg splint?

suitable only for short-term use (a few days at most); don’t match the animal’s anatomy, so they create areas of uneven pressure that can quickly lead to skin damage and necrosis

what are some complications associated with using external coaptation?

• Strike-through (wound fluid penetrating from the inside).

• Swollen or cold toes, indicating circulation issues.

• Moisture from licking, urine, or wet ground, leading to infection. 

• Failure to restrict activity, leading to displacement or pressure necrosis.  

what are some strategies for preventing complications associated with use of external coaptation?

• Good application technique.  

  • Use as little padding as possible to keep the splint/cast close to the skin (2-3 layers cast padding maximum)

  • Use a foam top (extra padding at the proximal end to prevent pressure sores and to absorb minor movement or swelling)

  • 2-toes-out rule (ensuring two toes are visible for monitoring). 

• Daily checks by owner - is the cast dry? Are the toes swollen? Are the toes cold? 

• Sudden changes in the dog's comfort warrant examination by a vet.

• Weekly veterinary checks for fit, function, and signs of skin damage. 

what is external skeletal fixation (ESF)?

A surgical method of fracture stabilization that involves placing pins through the skin and into the bone, which are then connected externally by clamps and bars; providing rigid support without placing implants directly at the fracture site, helping to preserve local blood supply and allowing easy access for wound care

what some indications for ESF use?

• Open fractures, where internal implants can increase the risk of infection

• Highly comminuted fractures, which cannot be reconstructed anatomically

• Poor soft tissue coverage, where internal fixation could further compromise blood supply

• Temporary stabilization (ex: prior to referral to an specialist surgeon)

• Diaphyseal fractures that can be aligned without precise anatomical reconstruction

what are the three main components of an ESF system?

pins, bars/rod, and clamps (to connect pins to bars)

what is a type 1A frame configuration?

unilateral, uniplanar — simple and commonly used, but is the weakest configuration

what is a type 1B frame configuration?

unilateral, biplanar — stronger (basically 2x Type 1As in different planes)

what is a type 2 frame configuration?

bilateral, uniplanar — bars on both sides, much more stable but more complicated to place

what is a modified type 2 frame configuration?

bilateral, uniplanar but with a mix of bilateral and unilateral pins (to simplify application)

what is a type 3 frame configuration?

bilateral, biplanar — most complex and stiff/strong

what pin site care is needed for ESF management?

keeping pin-skin areas clean and dry; gently clean with antiseptic solutions if discharge is noted; cover sharp ends to prevent trauma to patient or handlers

what regular monitoring is needed for an ESF?

daily checks by owner to look for swelling, discharge, bar loosening, toe termperature/color

veterinary rechecks every 1-2 weeks

what does de-staging the ESF frame entail?

once callus formation is sufficient, part of the frame may be removed to allow gradual loading of the limb

what are common complications associated with ESF?

pin tract infection, premature pin loosening, pressure necrosis, frame failure or misalignment, iatrogenic fracture

what are intramedullary (IM) pins?

long metal rods placed inside the medullary cavity of long bones.  They are often used in diaphyseal fractures to provide useful biomechanical support - but their limitations mean they are rarely used alone

How well do IM pins resist bending, rotation, and compression forces?

Great at resisting bending forces, which them them useful in diaphyseal fractures. On their own, they do not resist compression or rotation well

when is it justified to use an IM pin by itself?

a rotationally stable diaphyseal fracture in a very young animal when fragments interlock

what should IM pins be combined with in LONG OBLIQUE fractures?

cerclage wires or lag screws to provide rotational stability

what should IM pins be combined with in SHORT OBLIQUE or TRANSVERSE fractures?

external skeletal fixation (ESF) to form a "tied-in" frame that adds external stability.  A bone plate is often preferred

where are IM pins most commonly used?

the femur, tibia, and humerus

where should IM pins NOT be used and why?

the radius; required entry through the carpal joint, leading to joint damage

what are the two insertion techniques for IM pins?

normograde and retrograde

what is normograde insertion of an IM pin?

the pin is inserted from one end of the bone and advanced toward the fracture site

what is retrograde insertion of an IM pin?

the pin is inserted at the fracture site, then directed outward and reinserted across the fracture

what type of IM pin insertion is best for the femur?

normograde; retrograde insertion carries a higher risk of sciatic nerve injury

what type of IM pin insertion is best for the tibia?

normograde; retrograde pins may exit near the stifle joint and cause joint damage

what type of IM pin insertion is best for the humerus?

retrograde is commonly used and generally considered safe

what is cerclage wire?

metal wires wrapped around the circumference of a fractured bone

what is hemicerclage wire?

wires placed through predrilled holes in one of the fracture fragments and looped around the other

what indications for use of cerclage wire?

provide rotational stability in anatomically reconstructed LONG OBLIQUE or SPIRAL fractures; NEVER used alone (always in conjunction with other implants)

what can improper use of cerclage wire lead to?

• Loosening, allowing fragment movement

• Disruption of blood supply, compromising healing 

• Failure to stabilize the fracture

what is required to prevent cerclage wires to function effectively?

length of the fracture line to be at least twice as long as the diameter of the bone at the fracture site and the fracture to be anatomically reduced

what do bone plates resist?

bending, shear and rotation; locking plates also offer resistance to compressive forces

what advantage do locking plates have over traditional plates?

they do not rely on bone contact for stability (so don’t need to be pressed tightly against the bone), helping preserve periosteal blood flow

when is neutralization mode used for plate function?

fracture is oblique or wedge, lag screw is added to compress and reconstruct

what kind of healing does neutralization mode promote?

primary or secondary

what is the implant load when neutralization is used?

partially shared

when is compression mode used for plate function?

for simple, transverse or short oblique fractures

what kind of healing does compression mode promote?

primary healing, with minimal callus formation

what is the implant load when compression is used?

shared with bone

when is bridging mode used for plate function?

comminuted, non-reconstructable, unstable fractures

what kind of healing does bridging mode promote?

secondary healing

what is the implant load when bridging is used?

implant bears full load

what are some specialized and evolving techniques of internal fixation?

interlocking nails, locking compression plates, and SOP (string-of-pearls) plate