Fracture implants Flashcards
Apposition
the presence (or absence) and size of a fracture gap
Alignment
anatomical positioning of fragments relative to one another
Apparatus
the implants (type, size, number, positioning, function)
Activity
Biological activity of the bone, status of healing progression
Fracture reduction
the process of aligning and approximating fracture fragments
Anatomic reconstruction
perfectly aligning and apposing the fracture fragments, typically with interfragmentary compression
Bridging fixation
aligning the proximal and distal fragments without eliminating the fracture gaps
Non-surgical methods of fracture fixation
Exercise restriction alone
External coaptation
Surgical methods of fracture fixation
External skeletal fixation with or without fracture reduction and repair
Internal fixation - using pins, bone plates, interlocking nails etc.
Exercise restriction alone as fracture fixation
restricted to undisplaced fractures, greenstick fractures or occasionally fractures of the pelvis, scapula or vertebrae where strong muscular forces act to immobilise the fracture fragments.
involves a period of restricted activity with confinement to a cage or room - usually 4 – 6 weeks for most fractures.
Prevention of weight bearing may be useful for scapula fractures by using a carpal flexion bandage or velpeau sling.
External coaptation as fracture fixation
involve the use of splints, casts or bandages to immobilise the fracture fragments.
Advantages are widespread availability and avoidance of surgery.
Limitations of coaptation for fracture fixation
Use is limited to the lower limbs (below elbow and stifle)
Joints above and below the affected bone must be immobilised increasing the likelihood of fracture disease.
Casts may be bulky and uncomfortable and be self traumatised leading to a necessity for replacement
Sores can develop under the cast
Some fracture types are poorly immobilised
All types need to be assessed and changed frequently
Prolonged use can lead to fracture disease (atrophy and contractures)
Can be labour intensive and expensive - if bandage needs to be changed frequently etc.
What injuries can casts be considered for?
Fractures in the lower limb
Simple fractures with some intrinsic stability
Transverse or interdigitating fractures
Fractures of the radius (or tibia) where the ulna (or fibula) are intact
On two orthogonal radiographs there should be at least 50% of the fracture ends in contact
Fractures in animals with good healing potential ensuring rapid bone union & thus avoiding overlong immobilisation (immature animals)
Implants available for internal fixation
Pins
- Intramedullary pins
Wires
- tension band wires
- cerclage or hemicerclage wire
Bone screws
Interlocking nails
Bone plates
- compression plate
- neutralisation plate
- bridging plate
Intramedullary pins
Placed in the middle or medullar of the bone
Used as auxillary fixation or combined
Enhance stiffness and strength of the overall fixation
Excesllent resistance to bending but minimal resistence to axial compression, torsion, shear, and tension
Which bones are intramedullary pins appropriate for?
Bones with a safe entry corridor
- Femur
- Tibia
- Humerus
- Ulna
Most commonly used intramedullary pins
Steinmann pins
K(kirschner) wires
How wide should intramedullary pins be?
Pin should approximate the internal diameter of the bone at the narrowest point (isthmus) but is often 70-80% or 30-40% with adjunctive implants
Advantages of normograde insertion of pins
More control over pin placement
The pin is more likely to engage the endosteum of the bone – increasing friction and stability
The pin is less likely to loosen as it is not pulled back and forth through the bone
Normograde pin insertion
implies insertion of the pin at one end of the bone, across the fracture and into the other side of the bone.
In the femur, particularly in cats, an IM pin should always be inserted normograde in order to minimise the risk of sciatic irritation.
Disadvantages of normograde pin insertion
Placement can be technically more difficult
Retrograde pin insertion
placement of the pin into the bone via the fracture.
The pin is then passed through one end of the bone, the fracture reduced and the pin passed back down the bone across the fracture.
Advantages of retrograde pin insertion
Easae of placement
Disadvantages of retrograde pin insertion
Less control over pin exit point
Higher liklihood of loosening
Pin follows path of least resistance so endosteal contact (frictional forces) may be less
What does pin loosening and migration proximally indicate?
Instability and movement at the fracture site
Pin migration distally into the joint suggests what?
Pin penetrated the cartilage at the time of insertion - retraction and redirection is ofter is often not successful at correcting this.
What length pin should be used?
The pin should be long enough to sit in the cancellous bone in the metaphysis and, if removal is planned, the other end needs to be long enough for retrieval once the fracture has healed.
Tension band wire principle
active distracting forces are counteracted and converted into compressive forces.
Tension band wire
The tensile forces exerted by contraction of muscles on fractures such as those involving the olecranon, greater trochanter, medial malleolus, acromion of the scapula, os calcaneus or tibial tuberosity can be overcome & converted into compressive forces by inserting two Kirschner wires and a tension band wire
Principles for applying 2 K wires and a tension band wire
Reduce the fracture
Place two parallel K wires perpendicular to the fracture
K wires should just penetrate the far bone cortex
A transverse hole is drilled through the diaphysis distal to the fracture site
Cerclage wire is inserted in a figure-8 pattern going around the protruding K wires and tightened
K wires bent over and ends cut
Cercalge or hemicerclage wire
This procedure refers to a circle of wire that completely (cerclage) or partially (hemicerclage) goes around the circumference of the bone.
This is NOT used as the sole method of fixation on any type of long bone fracture.
Sizes of cerclage wire used
Cats and small dogs: 22 gauge
Medium dogs: 20 gauge
Large dogs: 18 gauge
Principles for use of cerclage wires
Long oblique fracture
Use at least two wires to prevent pivoting
Must use additional primary fixation
Must NOT be used in comminuted fractures
Apply tightly
Restrict the use of the wires to areas where the bone can be reconstructed - not unreduced fractures
Should be placed 0.5cm from the fracture line and a gap of 1 to 1.5cm
WIres should be placed at narrowest part of bone or with a K wire to prevent slippage
Use pliers to twist wires- cut leaving 3 twists
Hemi cerclage wiring
Very infrequesntly used
Holes drilled through the bone on either side of the fracture and wire passed through
Cortical screws
Narrower thread
Coarser pitch
Used primarily in diaphyseal or cortical bone
Cancellous screws
Can be partially or fully thread
Wider thread due to less dense bone
Finer pitch (less threads)
weaker than cortical screws
Used to compress fragments of epiphyseal or metaphyseal bone
When can screws be used in primary fixation?
usually in the metaphyseal or epiphyseal area (cancellous bone which heals quickly).
If fractures are articular the fracture fragments should be compressed to ensure a stable repair and primary bone healing.
To accomplish interfragmentary compression screw threads should not engage in the near cortex (cis) only the far one (trans). Inserting a screw in this fashion makes it a lag screw.
How to insert a screw as a lag screw
The near fragment must be ‘overdrilled’ with a hole equal in size to the diameter of the screw threads – the glide hole so threads do not engage the near cortex.
A hole equal in diameter to the screw core is drilled in the far cortex – the thread hole.
An insert guide is placed in the glide hole prior to drilling the thread hole to ensure that the hole is drilled at the correct angle.
Use of screws as auxillary fixation
Oblique diaphyseal fractures or fractures with large bone fragments can be reduced and stabilised with lag screws.
(Lag screws are preferable to cerclage wires as they can be placed to give more compression)
Similarly to cerclage wires, screws are never used in isolation for repair of diaphyseal fractures but they are usually combined with plates.
Screw sizes
Commonly used are 1.5mm, 2mm, 2.4mm (more recently introduced), 2.7mm and 3.5mm.
To drill the hole, a drill bit one size smaller is used (eg a 2.7mm drill bit for a 3.5mm screw).
For conventional screws, the hole needs to be tapped with a tap of the same size as the screw (3.5mm tap for a 3.5mm screw).
Self tapping screws
Have a little tap attached to their tip
Locking screws
Have a flatter pitch compared to cortical screws and a threaded head, which locks into the plate. They are also self tapping
Interlocking nails
Specialised equipment is available for placing interlocking nails in dogs and cats.
Nails are available in 4.0,4.7, 6.0 and 8.0mm sizes.
They have 3 to 4 preplaced holes / nail and a temporary jig that attaches to the nail so once inside the bone a screw can be placed from the outside of the leg through the bone into the nail.
The advantage is that rotation, compression and nail migration are prevented and the nail is placed inside the bone – biomechanically a good position for resistance to bending.
Suitable fractures are mid diaphyseal, comminuted fractures in straight bones.
Bone plates
Many different types of bone plates
Can be inserted in different modes.
Plates may be inserted to function as a compression plate, neutralisation plate or bridging plate.
Compression plate
Compression of a fracture surface improves friction at the fracture site, minimises gap formation, encourages load sharing between implant and bone and is optimal for primary or direct bone union.
There are two types of compression.
When a plate is applied as a compression plate it implies that the static compression of fracture fragments is present.
Static compression plates
usually achieved by the application of a self compressing plate (DCP) (but can also be achieved by the use of a regular (round hole) plate and a compressing device).
Fractures suitable for axial compression
Transverse fractures, osteotomies, or arthrodeses
Dynamic compression plates
Results from the muscular tension across the bone during weight bearing.
The plate should be applied so it is under tension and the fracture fragments under compression (tension band principle).
The plate must be applied to the tension side of the bone.
The tension side of the bone is related to its anatomy and musculature.
Tension side of femur
Lateral
Tension side of tbia
Cranial or medial
Tension side of humerus
Cranial or lateral
Tension side of radius
Craniomedial or cranial
Neutralisation plate
This plate is also applied to the tension side of the bone to neutralise or overcome the forces (torsional, bending, compressive or distraction) to which the fractured bone may be subjected during healing.
Interfragmentary compression is supplied by lag screws or cerclage wires that are used to reconstruct the cylinder of bone.
The plate is applied across the reconstructed bone.
Fractures suitable for neutralisation plates include unstable fractures or osteotomies that can be anatomically reconstructed using lag screws or cerclage wires.
Most useful for simple oblique/spiral fractures.
Bridging plate
The plate is used to shore up fragments of bone thereby maintaining bone length.
A relatively larger plate should be selected when the plate is being used as a bridging plate.
There is some overlap in terminology with ‘biological plating’ where fragments are left unreconstructed to minimise disruption of blood supply.
Fractures suitable for a bridging plate
Unreconsrtuctable plate
Principles of plate fixation
Tension band principle
Minimum of two (or three) screws applied either side of a fracture
Minimum distance a screw is placed from fracture line is 5mm
Longer plate is better
Contouring the plate for conventional plates to maintain anatomical reduction
Prestressing the plate advisable for transverse fractures
Selection of proper plate size and screws is important
Try not to leave an empty screw hole over the fracture
When is plate removal indicated
Plates are loose, broken or bent
Plate acts as a thermal conductor - lameness in cold weather especially associated with tibial or radial fractures
Plate causes stress protection or interferes with the vascular supply to the bone resulting in osteoporosis.
Plate crosses a growth plate
Plate causes irritation – lick granuloma occasionally seen with superficial plates
Infection – if the fracture is stable then the plate should be left in place until healing has occurred prior to plate removal
Some surgeons will remove the plate routinely once the bone has healed – this generally should not be done sooner than 5 months after fracture repair in an adult animal
Types of plates
Dynamic compression plate (DCP) - conventional plate
Locking compression plate (LCP)
Acetabular plate
Cuttable plates
Lengthening plate
T plates
Reconstruction plates
Dynamic compression plate (DCP) - conventioal plate
The design of the screw holes in this plate is based on the spherical gliding principle.
As the screw is tightened the spherical screw head glides towards the centre of the plate until the deepest portion of the plate is reached.
The result is the bone fragment attached to the screw is displaced at the same time towards the fracture which results in compression of the fracture line.
When the load guide is used the fracture is compressed approximately 1mm for a 3.5mm plate.
A maximum of four screws (two each side of the fracture) can be inserted in the load position which results in a maximum of 4mm compression.
Locking compression plate (LCP)
This plate can be used with standard screws to create interfragmental or axial compression or with locking screws to create a stable plate-screw connection without loss of reduction, regardless of plate modelling.
Cuttable plates
Plate available in long lengths which are CUT to the desired length.
Particularly useful for cat long bone fractures or MT/MC fractures in large dogs.
Plates can be stacked (use two together – one on top of each other) to increase strength. Sizes available to take 1.5mm / 2.0mm & 2.7mm screws.P
Lengthening plate
Plate has a central portion without holes so useful in unreconstructable diaphyseal fractures as a buttress plate
T plates
Useful in fractures with a small distal or proximal fragment as they allow placement of 2 to 3 screws in the fragment.
Reconstruction plates
Plates can be contoured in 3 planes – bent, twisted and curved to allow accurate contouring and reconstruction of awkward shaped bones like the pelvis or mandible.
Arthrodesis
Salvage procedure
Plate over a joint
Excision arthroplasty
Parts of the joint are removed e.g. head of the femur
Joint replacement
Parts of the joint are replaced - can be surface or the whole end of a bone
