ALL YOU NEED ABOUT INTERNAL FIXATION OF FRACTURED BONE

ALL YOU NEED ABOUT INTERNAL FIXATION OF FRACTURED BONE
Types of fixation

Fixation can be divided into external and internal fixations
 Internal fix­ation

Are implants that are fitted directly on to or put down the inside of the bone and are then covered with soft tissues and skin
  
,Internal fixation can allow accurate reduction of fractures, and allows strong and stable fixation, so that the patient can rapidly return to everyday activities, with the minimum of inconvenience
  
Internal fixation is best performed under a tourniquet, if possible in order to obtain a blood-free view


Internal fixation requires careful preplanning and the best surgery is performed if the fractures are drawn out on stencils first, and the problems of reduction and obtaining mechanical stability planned in advance

Soft-tissue dissection should be kept to a minimum but must be adequate to obtain a clear view and access
External fixation
 Are those where the mechanical strength of the construct is outside the skin or fixation of fracture outside the skin

There are two main ways in which a fracture can be held which make a profound difference to the way in which the fracture heals
  
Rigid fixation blocks the normal callus formation of bone healing.The bone appears to be unaware that there is a frac­ture if there is no movement at the fracture site

As the bone undergoes normal physiological remodelling. the fracture cleft is gradually obliterated by new bone
This takes about a year During that time the fixation must share the loads normally taken by the bone

Most implants fatigue under the repetitive load imposed by the human body and will soon fail if the bone does not heal and take over its original function

Fracture healing is therefore a race against time: the bone must unite before the implant fails or the construct will col­lapse

Non-rigid means of fixing (such as plaster of Paris) allow limited movement and loading of the fracture site

 The aim is to allow movement and load to stimulate callus formation without allowing the fracture to redisplace

This delicate bal­ancing act depends on the quality of the fixation the type of fracture and the compliance of the patient

Rigid versus non-rigid fixation

• Rigid fixation allows immediate loading but does not stimulate callous formation
• Non rigid fixation risks loss of reduction but stimulates rapid callus formation

Semi-rigid fixation

If the fixation of the fracture is not completely rigid then some callus will form rapidly. but the patient may be able to resume near-normal function because the fracture is held stable if not immobile by the fixation

 This partial rigidity therefore offers the best of both worlds with rapid biological healing combined with the benefits of early mobilisation of the patient

Types of Internal fixation

Screws
  
 Can be used to hold plates on to bone or can he used in their own right to hold bone fragments together
In orthopaedics, screws have been standardised to an agreed set of diameters
The threads of the screws also come in two standard forms. one for cortical and the other for cancellous bone

The size of these thread, and their pitch (the distance between each thread) are specifically designed to give the best possible grip in healthy human bone
The drills which create the holes for these screws are also standerdised allow as snug a fit of the screws as possi­ble without putting under load on the bone Taps are also sup­plied which cut the grooves in the bone to take the threads of the screws tables are available in every orthopaedic theatre to show which drill should be used for which screw

Plates and screws


• Sizes of screw and plates are now standardised

• Maximum grip is obtained without risking crocking the bone

• Nevertheless, plates must be plated on the tension side of the bone

Lagging
 
If a screw is to be used to compress two bone fragments together it is important that the thread of the screw should grip only the distal fragment in which the tip of the screw is embedded. as the screw is tightened the shoulder of the screw (the part that tapers in under the head) presses down on the proximal fragment and compresses the two fragments together. If the thread of the screw engages with the proximal fragment the screw can actually hold the fragment apart


There are techniques used to ensure that the fragments are drawn together as the screw is tightened

First a screw can be used which has no proximal thread. just a smooth shaft this known as lag screw

An alternative strategy is to use a fully threaded screw but to drill the hole in the proximal fragment to a slightly larger size so that the screw threads cannot engage with the wall of the hole

This is called lagging the drill hole and serves the same purpose as using a lag screw

Lagging

• Ensures that bone fragments are drown together as the screw is tightened

Plates

Plate, come in several sizes. each designed to be used with a stan­dard set of screws

 They are designed to fit on to the curved sur­face of bone and to be held there by screws

 The plates can be used in several ways and there are specific plate designed for each function

Use of plates
 
• They can butress,compress or neutralise plates

• In all cases their strength is in tension

• They are not good at resisting bending

Buttress plates: Buttress plates prevent one fragment of bone slip­ ping on another
They are especially useful in oblique fractures in load bearing bones, when they will stabilise what is a very unstable­ fracture configuration

Dynamic compression plates :(DCP) Dynamic compression plates have oval screw holes in them with tapered walls

If the screw holes are drilled into the bone at one end of these holes (there are drill guides to assist in doing this) then the plate slides along the bone as the screw is tightened home

If the plate has already been firmly fixed to the other fragment then the slip can be used to compress the fragments of bone tightly together

This has the ben­efit of stabilising the construct by increasing the area of contact. it also appears to stimulate healing by putting the bone edges in close apposition

Neutralisation plates :Neutralisation plates are used to prevent bone ends from being distracted

They can be used to resist angular forces by being placed on the side of a bone that goes into tension when load is applied the side that opens when the fracture bends
Plates with screws are excellent at resisting tension
 and this is how they are used in neutralisation

Plates have very little resistance to bending and so should never be put on the side of the bone that is in compression and which will go into concave angulation when load is applied

Wires

Wires are much less traumatic than plates and screws
 They can be used temporarily to hold fragments reduced while plates and screws are applied
They can also be used to resist shear where loads are not great. They are especially useful m children's frac­tures, when plates and screws could damage the epiphyseal plate

Wires can cross the growth plate without causing long-term effects and if left protruding from the skin can be removed when the fracture is secure without the need for a further surgery

The value of wires

• Can be introduced and removed percutaneously

• Safe to cross an epiphyseal plate

• Can be used as a guide for cannulated screws

Kapanji wires These are a technique which can be used in fractures in which Impaction may have left a defect that leaves the fracture unstable when reduced


After the fracture has been dis­impacted and reduced, wires are introduced into the fracture cleft on the side of the defect

 As soon as the tip of the wire is in the medulla the wire is tilted so that its tip travels proximally and embeds on the Inside of the far cortex

 One or more wires placed in this way substitute for the missing cortex and work with the intact periosteum on the other side to create a stable reduction

Figure-of-eight wiring This allows a strong wire suture to be woven over the cortex of bone which is held in tension

The device is not prominent and so fits well subcutaneously and is commonly used on the olecranon and on the patella 

Intramedullary nails

Implants driven down the medulla of a long bone sutter from a significant mechanical disadvantage because they must be narrower than the bone into which they are introduced, The resistance of an implant to bending and twisting proportional to the square of its diameter, Nevertheless, the medulla can provide a natural guide for the implant, and introducing the nail into one end of the bone (under image intensifier control) minimizes the risk of infection from opening the fracture, .and preserves the periosteal blood supply


 Nails are now available for the humerus and tibia as well as the femur

 In recent years the scope of intramedullary nails has been increased by the introduction of the locking nail
 
This system has hole through the nail at each end. using jigs or an image intensifier screw can be passed through the bone, the hole in the nail and out through the opposite cortex of the bone. This produces a construction that holds the bone rigidly,and is especially resistant to twisting it follow an intramedullary nail to be used for a far greater range of long bone fractures including those in the metaphysis some of the newer nails can now be passed down the medulla without requiring any reaming in advance the unreamed nails this makes the operation quicker and reduces the trauma to the patient

Advantages of intramedullary nails

• Now available for all major long bones

• Can be put in closed and unreamed

• Locking screws gives great stability

• Periosteal blood supply is preserved

• Patient can be mobilised early

Disadvantages and complications of internal fixation

The disadvantages of internal fixation are those of damage to soft tissues, especially blood supply


The rigidity of fixation slows the natural healing process, even though it allows earlier mobilisation of the patient

Internal fixation is technically demanding, requires a large range of implants and instruments, and is best performed in ultra clean theatres as infection is a disaster
 
This includes size and type of plates and position of screws. Only in this way can the operation be performed quickly and cleanly (minimising the risk of tissue damage and infection) so that the strongest fixation is obtained.
 There are complications inherent in using a tourniquet such as cuff damage to nerves as a result of inflation to an excessive pressure and problems of reper­fusion injury if the cuff is left inflated for too long.

Exposure of the fracture may damage the soft-tissue attachments to the bone and produce avascular fragments, which will delay or even prevent fracture union


The risk of infection can be minimised by cleaning out open
fractures and leaving them open with the fractures stabilised until it is certain that all dead and contaminated tissue has been removed


Only when they are clean should they be closed delayed primary closure

When internal fixation is used, infection is min­imised by performing quick, tidy and well-planned surgery, and by adhering to strict theatre discipline on theatre sterility
. Surgery should be covered by three doses of a broad-spectrum antibiotic which has good activity against Staphylococcus (the most common infective organism) and Streptococcus (the second most common

Internal fixation can also leave unsightly scars, and should be planned to minimise cosmetic deformity without compromising­ access

Drills and screws can damage nerves and vessels


 Drill guards should always be used to prevent soft tissues being inadvertently dragged into a spinning drill

When the drill is cutting into the far cortex, the hand that the surgeon is using to hold the drill should have a straight finger resting on the limb through which the drill is passing

Only light pressure should be applied to the drill so that when the drill then comes out through the far cortex it will not suddenly penetrate deep in the soft tissues on the far side of the bone where it might perforate a nerve or vessel .

Complications of Internal fixation

• Damage to soft tissues and blood supply

• Risk of introducing infection

•Callus formation is inhibited


Indications for removal of internal fixation

Implants for internal fixation are made of surgical-grade stainless steel and should not corrode


Nevertheless, the alloys con­tain transitional metal such as chromium and vanadium, whose salts are allergenic toxic and may even be carcinogenic

Despite this, there is little evidence that metalware left in patients for long periods causes any chemical or even allergic problems

Children should have metalware removed if it is likely to compromise growth

It should be removed as early as possible because periosteal bone grows rapidly over the plates and makes their removal difficult

 Internal fixation also shields the bone around it from load and so may cause local osteoporosis

The load passing down the bone may then peak at the end of a plate (a stress raiser) and cause a fracture

 Internal fix­ation of a fracture next to an old plate already embedded in the bone is very difficult to manage

Despite this, it is now normal practice to leave plates and even intramedullary nails in the patient unless they are causing pain or there is another specific reason for the patient to receive another general anaesthetic for another procedure
in which case plates can be removed at the same time

Reasons for removing metalwork

• Plates may load shield, producing osteoporosis

• Salts of stainless steel may be toxic in long term 


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