Fracture Fixation Systems

Fracture Fixation Systems are External Coaptation and Internal Coaptation methods.

External Coaptation

External coaptation Fracture Fixation Systems may be used to provide patient comfort before surgery and decrease soft tissue damage. It may also used as the primary repair in some conditions.

Casts

Full leg casts encircle the limb to stabilize a fracture. They can be used as primary means of stabilization or as supplement to internal fixation devices. The functional period of cast is short, usually no longer than 6 weeks before cast complications dictate removal. The classical cast material is plaster of Paris. Synthetic cast made up of fiber glass or polypropylene substrate impregnated with water activated polyurethane resin are used recently.

External skeletal fixators are a versatile and affordable treatment for long bone fracture, corrective osteotomies, joint arthrodesis and temporary joint immobilization. They are not indicated for articular fractures and are rarely used for pelvic and spinal fractures. External fixators are well suited for stabilization after closed reduction of comminuted fractures. External fixators can be adjusted during and aftersurgery to improve fracture alignment. The functional period for external fixators varies depending on the frame constructed, but it is related to the onset of pin loosening.

Classification of External Skeletal Fixators

Classified by the number of planes occupied by the frame and the number of sides of the limb from which the fixators protrudes-

1. Unilateral-Uniplanar Type Ia
2. Unilateral-Biplanar Type Ib
3. Bilateral-Uniplanar Type II
   • Maximal type II – frames filled with full pins
   • Minimal type II – constructed with minimum of 2 full pins
4. Bilateral-Biplanar Type III
5. Circular External Fixators

Internal Fixation

Intramedullary pins and Kirschner wires

Intramedullary (IM) pins are used for diaphyseal fractures of the humerus, femur, tibia, ulna and metacarpal and metatarsal bones. IM pins are contraindicated for the radius because the insertion point of the pin generally interferes with carpus. The biochemical advantage of IM pins is resistant to applied bending loads but disadavantage include poor resistance to axial (compressive) or rotational loads and lack of fixation with bone.

Steinmann pins or Kirschner wires may be used as crossed pins (wires) or placed in a triangulated pattern to stabilize metaphyseal and physeal fracture in young animals. Kirschner wires also used as IM pins in very small animals.

IM Pins

IM pins are smooth, round, 316L stainless steel rods. The most common pin used in veterinary are Steinmann pins, which are available in sizes ranging from 1/16 to ¼ inch and comes with variety of point designs. They can be single armed (One end with a point and one end blunt) or double armed (a point at each end). The most popular point designs are trocar points and chisel points. Trocar points have a triple cutting edge and cut through Cancellous bone easily. Chisel points have a two sided cutting edge that is slightly more effective in cutting through dense cortical bone.

IM pins may be smooth or may have threads at one end to increase the pin holding power in Cancellous bones. Steinmann pin used as IM pins are generally driven with a Jacob chuck.

Kirschner wires are small in diameter ranging from 0.035 inch to 0.062 inch smooth pin, which generally have trocar points at each end.

Application

Select an IM pin that equals 60% to 70% of the diameter of the marrow cavity at the isthmus of the bone when pairing the IM pin with cerclage wire. Select two pins of the same length before starting the procedure. The second pin serves as guiding pin when laid over the external surface of the limb. An IM pin may be normograde or retrograde for placement in femur or humerus. IM pins must be normograde in the tibia to prevent damage to the stifle.

Normograde Pining

• Start the pin at the appropriate location at one end of the long bone 
• Drive it down the medullary canal to the fracture
• Reduce the fracture
• Continue to drive the pin until it seats in metaphyseal bone

Retrograde Pining

• First expose the fracture
• Insert the pin into the medullary canal of the appropriate bone segment
• Drive the pin to exit the bone segment
• Replace the pin chuck on the exited portion of the pin and withdraw it until the pin point is within the medullary canal.
• Reduce the fracture
• Drive the pin to seat in metaphyseal bone.
• Check the pin insertion length using guiding pin as a reference
• Check for pin interference in the distal joint by flexing and extending the joint.
• Crepitation or decreased range of motion may indicate pin interference.
• Radiography will confirm the position of the pin and presence of pin in the joint
• If necessary, retract the pin so it no longer interferes with the joint.
• Apply cerclage wire in case of long oblique fractures or a bridging plate.
• When satisfied with the pin position, cut the excess pin with a pin cutter.
• Suture the soft tissue over the pin.

Cross pining

• To apply Steinmann pins or K wires as crossed pins to secure a physeal or metaphyseal fracture
• Reduce the fracture
• Insert the pin on lateral and medial surfaces on the epiphyseal segment.
• Drive the lateral pin across the fracture to exit on the medial surface.
• Drive the medial pin across the fracture to exit on lateral surface of the metaphyseal segment.
• Check the fracture stability and pin position,
• Bend the pin tip and cut off the excess.

Interlocking Nails

Interlocking nails are inserted in the medullary canal and locked in place with screws or cross-locking bolts placed through the proximal and distal fracture segments and the nail. Interlocking nail resists all forces acting on fractures. The nail provide bending support, whereas the locking bone screws or bolts provide axial and rotational support. The interlocking nail is used primarily for middiaphyseal humeral, femoral or tibial fracture, it is contraindicated for radius. The nails come in various length and sizes with holes at each end for screw insertion. Screw should be placed atleaced 2cm from the fractured line. Interlocking nail available for veterinary use are 4, 4.7, 6, 8 and 10mm in diameter, with five or six length available in each size. Each nail has three or four screw holes. And they are 11 or 22 mm apart.

Orthopaedic wire

Cerclage and Hemicerclage wire

Orthopaedic wire is often used as cerclage wire or hemicerclage wire. It is used in combination with other orthopaedic implants to supplement asial, rotational and bending support of fractures. The term cerclage used to denote the use of orthopedic wire placed around the circumference of the bone.

Hemicerclage wire or interfragmentary wire is termed to denote wire that is placed through the predrilled hole in the bone.

Indication

Cerclage wire is either used to provide stability to anatomically reconstructed long oblique or spiral fractures or to hold multiple fragments in position. To function as a stabilizer, wire must generate sufficient compression force to prevent the fragment from moving or collapsing under weight-bearing loads. To accomplish this three criteria must be met,

1. The length of the fracture line should be two or three times the diameter of marrow cavity
2. There should be maximum of two fracture lines
3. The fracture must be anatomically reduced

Tension bands

Tension is the predominant force when avulsion fractures occur at appoint where group of muscles originate or insert in bone. Contraction of muscle group in these sites generates tension that pulls the bony insertion or origin from its anatomical location. The most effective way to resist tension is through the application of a tension band. The purpose of tension band is to convert distractive tensile force into compressive force.

Equipment needed for placement of tension band includes mall Steinmann pin or K wire and orthopedic wire.

Plate and screw fixation

Stabilization of fracture with bone plates and screws is a popular method of fracture fixation. Bone plates and screws offer a versatile method of fracture stabilization and can stabilize any long bone fracture.

Screws used as lag screws causes compression at the fracture, increasing the friction between the fragments and resisting the force acting on the fracture. Two or more screws must be used to counteract bending forces in diaphysis, but they are not sufficient to withstand large loads generated by weight bearing without plate support.

Bone plates achieve fixation by friction generated by the application of a well-contoured plate to the bone surface using screws. When applied properly, bone plates effectively resist the axial, bending and torsional forces acting on the fractured bone. Increasing the plate size, using a broad lengthening plate, or using a plate pin combination may strengthen the implant or reduce the strain sufficiently to reduce the risk of fatigue failure. Minimally Invasive Plate Osteosynthesis (MIPO), where a plate is inserted percutaneously and secure to the bone above and below the fracture, minimize the biological damage.

Equipment and supplies

• Drill guide and sleeves
• Depth guage
• Screw driver
• Bending and torquing irons
• Bone plate (DCP, LCDCP, LCP)
• Cortical and cancellous screw
• Lag screw