Fractures of the Tibia and Fibula

Chapter 111 Fractures of the Tibia and Fibula

Erick L. Egger

Fractures of the tibia and fibula compose a significant proportion (15-20%) of all long bone fractures in small animals. In addition, the minimal soft tissue coverage of these bones increases the incidence of contamination of open fractures, which may result in infection and healing complications. Proper treatment of tibial and fibular fractures requires

• An understanding of the disruptive biomechanical forces that must be controlled to promote the healing process.
• Selection of a fixation technique that will control these forces.
• Application of fixation without damaging the fracture healing process or compromising the function of the limb.

ANATOMY, FUNCTION, AND BIOMECHANICS

OF THE TIBIA AND FIBULA

The anatomy of the tibia and fibula can be divided into regions based on their location, function, architecture, and the forces acting on them.

Epiphysis

• Proximally the epiphysis consists of
• The tibial plateau, which provides support for the articular cartilage of the distal stifle joint (for information concerning the stifle joint, see Chapter 110).
• The fibular head, which serves as the distal attachment for the lateral collateral ligament.
• The tibial tubercle, which is the insertion point of the patellar tendon of the quadriceps muscle.
• Distally, the epiphyseal region consists of
• The cochlea tibia, which supports the distal articular cartilage and articulates with the tibial tarsal bone.
• The medial malleolus, which is the proximal attachment of the medial collateral tarsal ligaments.
• The fibular epiphysis (lateral malleolus), which acts as the proximal attachment of the lateral collateral tarsal ligaments.
• The epiphyseal regions of the tibia and fibula are primarily composed of loosely woven, trabecular bone surrounded by a thin shell of dense cortex. This architecture limits the holding power of fixation implants, requiring extra care in their application.
• The epiphyseal regions that serve as ligament and tendon attachments are subjected to distractive forces. Consequently, repair of avulsion fractures of these areas must control these tensile forces.
• The epiphyseal regions that support articular cartilage are subjected to compressive loads that tend to separate the fragments, resulting in articular incongruity, instability, and eventually degenerative arthritis. Fixation of these fractures must provide anatomic reduction and rigid immobilization so that the fracture will heal with minimal callus formation, and so that early joint motion can be initiated to avoid joint stiffness.
• Because of ample blood supply and preponderance of cancellous bone in the epiphysis, fracture healing tends to be rapid. Consequently, fixation of these fractures usually is not prolonged or robust.

Physis

• The physeal regions of the tibia and fibula are located adjacent to the epiphysis and exist only in growing immature animals.
• The hypertrophied layer and calcifying layers of the physis are relatively fragile, and are commonly fractured with trauma.
• Because the cartilage layers are irregular and transverse, fractures tend to interdigitate well when reduced and require only control of bending forces.
• Because the physis is the origin of long bone growth, injuries to this region can cause premature cessation of growth resulting in shorter bone or angular deformity. Warn clients of this possibility, particularly in very young, actively growing patients.

Metaphysis

• The metaphysis is an indistinct region of bone located between the physis and the diaphysis (central shaft).
• The function of the metaphysis in the mature animal is the gradual alteration of the general construction of the bone from the wide-diameter thin cortex of the epiphysis to the narrow-diameter thick cortex of the diaphysis. The biomechanics and architecture of these regions change along their length.

Diaphysis

• The diaphysis is the central portion of the tibia and makes up the majority of its length.
• The tibial diaphysis is subjected to severe bending and torsional forces, in addition to axial compressive loads. Its hollow tubular construction of relatively thick cortical bone maximizes its effectiveness in resisting these forces.
• Relatively poor blood supply in cortical bone and longer moment arms associated with diaphyseal fractures generally mean these fractures heal slowly and require prolonged robust fixation.

PREOPERATIVE CONSIDERATIONS

General Considerations

• Examine the animal carefully for non-orthopedic injuries.
• Evaluate cardiovascular status. If cardiopulmonary problems are suspected, radiograph the thorax.
• Evaluate neurologic status. Determine deep pain perception in the fractured limb for local nerve damage, and proprioceptive and sensory perception in the other limbs for evidence of nerve or spinal cord trauma.
• Examine the animal carefully for concurrent musculoskeletal injuries.

Key Point

Nearly all small animals with tibial and/or fibular fractures are able to support themselves on the remaining three limbs. If not, suspect additional injuries.

• Determine the extent of soft tissue injury and fracture contamination.
• Cover all open fractures with sterile bandages to prevent further contamination, and debride as soon as possible.
• Broad-spectrum antibiotics are indicated if the fracture is open. Obtain samples for culture and sensitivity testing from the fracture site before beginning antibiotic therapy.
• Until definitive treatment is possible, support all tibial fractures with a compressive wrap (Robert Jones bandage) or splint to prevent additional soft tissue injury.

Specific Considerations in Selecting a Fracture Fixation Technique

• Determine the potential axial stability of the reduced fracture based on preoperative fracture radiographs.
• Stable fractures generally are simple transverse or short oblique. They tend to impact and become more stable upon weight bearing.
• Unstable fractures have patterns, such as long oblique or comminuted, which tend to override or collapse upon axial loading.
• Perform rigid fixation of extensively contaminated open fractures. However, avoid placing large implants in the fracture site.
• Fractures in immature animals heal quickly, but
• Premature physeal closure can occur with or without internal fixation.
• Immature animals rapidly develop joint stiffness with limb immobilization.
• Implants quickly loosen in the soft bone of immature animals.
• Fractures in very old animals heal slowly.
• Brittle bone in older animals often splinters when implants are applied.

SURGICAL PROCEDURES

Objectives

• Provide adequate stability for fracture healing to occur while causing minimal damage to the biologic healing process.
• Restore normal limb function by minimizing joint stiffness and muscle atrophy and avoiding subsequent degenerative joint disease.

Pin and Tension Band Wire Fixation

Indications

• Avulsion fractures of the fibular head
• Avulsion fractures of the lateral (fibular) malleolus and medial (tibial) malleolus (Fig. 111-1)
• Avulsion fractures of the tibial tubercle
image

Figure 111-1 Pin and tension wire fixation of a medial malleolar avulsion fracture. Do not violate the cochlear articular surface with the Kirschner wire (arrow).

Equipment

• General orthopedic pack
• Standard surgical pack
• Bone and fracture reduction forceps
• Periosteal elevator
• Jacob hand chuck
• Wire pliers and cutters
• Stainless steel monofilament orthopedic wire (18-22 gauge)
• Kirschner wires (0.035-0.062 inch)

Technique

1. Incise the skin directly over the affected bone.
2. Reduce and stabilize fracture with small fragment reduction forceps.
3. Create a transverse hole through the intact tibia approximately equidistant from the fracture line with the hand chuck and a Kirschner wire.
4. Insert two parallel Kirschner wires through the fragment, across the fracture, and into the parent bone.

Key Point

In the treatment of malleolar fractures, avoid penetrating the articular surface of the distal cochlea.

5. Pass orthopedic wire (18 gauge for most dogs, 20-22 gauge for small dogs and cats) through the transverse hole, cross the wire over the fracture site, and pass one end under the ligament or tendon attachment.
6. Twist both ends of wire together to form a figure eight. Tighten the wire just enough to compress the fracture (see Fig. 111-1).
7. Cut off excess orthopedic and Kirschner wires. Bend the Kirschner wires over and embed them in the soft tissues to trap the orthopedic wire loop and minimize soft tissue irritation.
a. In the treatment of tibial tubercle fractures, if the animal still has significant growth potential, do not use tension band wires because this procedure can induce premature physeal closure. If necessary, use additional Kirschner wires oriented perpendicular to the physis for fixation stability.
8. Close soft tissues routinely.

Interfragmentary Lag Screw Fixation

Indications

• Intra-articular fractures of the proximal epiphysis (tibial plateau) and distal epiphysis (tibial cochlea)
• Reconstruction of comminuted shaft fractures prior to neutralization plating (see Fig. 111-7)
image

Figure 111-7 Use of a plate to protect a reconstructed comminuted tibial fracture from excessive bending forces. The screw and wires maintain reduction, and the plate “neutralizes” the weight-bearing forces.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Fractures of the Tibia and Fibula

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