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SA Orthopaedics > Fracture implants > Flashcards

Fracture implants Flashcards

1
Q

Apposition

A

the presence (or absence) and size of a fracture gap

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2
Q

Alignment

A

anatomical positioning of fragments relative to one another

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3
Q

Apparatus

A

the implants (type, size, number, positioning, function)

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4
Q

Fracture reduction

A

the process of aligning and approximating fracture fragments

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5
Q

Anatomic reconstruction

A

perfectly aligning and apposing the fracture fragments, typically with interfragmentary compression

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6
Q

Bridging fixation

A

aligning the proximal and distal fragments without eliminating the fracture gaps

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7
Q

Non-surgical methods of fracture fixation

A

Exercise restriction alone
External coaptation

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8
Q

Surgical methods of fracture fixation

A

External skeletal fixation with or without fracture reduction and repair

Internal fixation - using pins, bone plates, interlocking nails etc.

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9
Q

Exercise restriction alone as fracture fixation

A

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.

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10
Q

External coaptation as fracture fixation

A

involve the use of splints, casts or bandages to immobilise the fracture fragments.

Advantages are widespread availability and avoidance of surgery.

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11
Q

Limitations of coaptation for fracture fixation

A

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.

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12
Q

What injuries can casts be considered for?

A

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)

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13
Q

Implants available for internal fixation

A

Pins
- Intramedullary pins

Wires
- tension band wires
- cerclage or hemicerclage wire

Bone screws

Interlocking nails

Bone plates
- compression plate
- neutralisation plate
- bridging plate

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14
Q

Intramedullary pins

A

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

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15
Q

Which bones are intramedullary pins appropriate for?

A

Bones with a safe entry corridor
- Femur
- Tibia
- Humerus
- Ulna

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16
Q

Most commonly used intramedullary pins

A

Steinmann pins
K(kirschner) wires

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17
Q

How wide should intramedullary pins be?

A

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

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18
Q

Advantages of normograde insertion of pins

A

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

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19
Q

Normograde pin insertion

A

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.

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20
Q

Disadvantages of normograde pin insertion

A

Placement can be technically more difficult

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21
Q

Retrograde pin insertion

A

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.

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22
Q

Advantages of retrograde pin insertion

A

Easae of placement

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23
Q

Disadvantages of retrograde pin insertion

A

Less control over pin exit point
Higher liklihood of loosening
Pin follows path of least resistance so endosteal contact (frictional forces) may be less

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24
Q

What does pin loosening and migration proximally indicate?

A

Instability and movement at the fracture site

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25
Q

Pin migration distally into the joint suggests what?

A

Pin penetrated the cartilage at the time of insertion - retraction and redirection is ofter is often not successful at correcting this.

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26
Q

What length pin should be used?

A

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.

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27
Q

Tension band wire principle

A

active distracting forces are counteracted and converted into compressive forces.

28
Q

Tension band wire

A

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

29
Q

Principles for applying 2 K wires and a tension band wire

A

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

30
Q

Cercalge or hemicerclage wire

A

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.

31
Q

Sizes of cerclage wire used

A

Cats and small dogs: 22 gauge
Medium dogs: 20 gauge
Large dogs: 18 gauge

32
Q

Principles for use of cerclage wires

A

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

33
Q

Hemi cerclage wiring

A

Very infrequesntly used

Holes drilled through the bone on either side of the fracture and wire passed through

34
Q

Cortical screws

A

Narrower thread
Coarser pitch

Used primarily in diaphyseal or cortical bone

35
Q

Cancellous screws

A

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

36
Q

When can screws be used in primary fixation?

A

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.

37
Q

How to insert a screw as a lag screw

A

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.

38
Q

Use of screws as auxillary fixation

A

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.

39
Q

Screw sizes

A

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).

40
Q

Self tapping screws

A

Have a little tap attached to their tip

41
Q

Locking screws

A

Have a flatter pitch compared to cortical screws and a threaded head, which locks into the plate. They are also self tapping

42
Q

Interlocking nails

A

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.

43
Q

Bone plates

A

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.

44
Q

Compression plate

A

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.

45
Q

Static compression plates

A

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).

46
Q

Fractures suitable for axial compression

A

Transverse fractures, osteotomies, or arthrodeses

47
Q

Dynamic compression plates

A

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.

48
Q

Tension side of femur

A

Lateral

49
Q

Tension side of tbia

A

Cranial or medial

50
Q

Tension side of humerus

A

Cranial or lateral

51
Q

Tension side of radius

A

Craniomedial or cranial

52
Q

Neutralisation plate

A

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.

53
Q

Bridging plate

A

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.

54
Q

Fractures suitable for a bridging plate

A

Unreconsrtuctable plate

55
Q

Principles of plate fixation

A

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

56
Q

When is plate removal indicated

A

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

57
Q

Types of plates

A

Dynamic compression plate (DCP) - conventional plate

Locking compression plate (LCP)

Acetabular plate

Cuttable plates

Lengthening plate

T plates

Reconstruction plates

58
Q

Dynamic compression plate (DCP) - conventioal plate

A

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.

59
Q

Locking compression plate (LCP)

A

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.

60
Q

Cuttable plates

A

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

61
Q

Lengthening plate

A

Plate has a central portion without holes so useful in unreconstructable diaphyseal fractures as a buttress plate

62
Q

T plates

A

Useful in fractures with a small distal or proximal fragment as they allow placement of 2 to 3 screws in the fragment.

63
Q

Reconstruction plates

A

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.

64
Q

Arthrodesis

A

Salvage procedure

Plate over a joint

65
Q

Excision arthroplasty

A

Parts of the joint are removed e.g. head of the femur

66
Q

Joint replacement

A

Parts of the joint are replaced - can be surface or the whole end of a bone

SA Orthopaedics (13 decks)

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