Orthopaedic Surgery (Bones and Joints)

1) Fractures
Defined as a break in a bone. Unfortunately, fractures are classified into different types, which simply have to be learned.
Firstly, how do fractures occur?

-Acquired fractures are the result of trauma to the bones which exceeds the normal strength of that particular bone.

-Pathological fractures are the result of a disease process in the bone causing weakening of the structure. The commonest causes of this by far are poor diet (lack of Calcium causing rickets), and tumours invading otherwise normal bone.

Secondly, the fractures themselves are classified, more or less by severity. Different categories can be combined to provide a precise description of the fracture.

-Simple. Fractures with a single break
-Compound. Fractures with more than one break.
-Closed. No wound allowing access to the fracture.
-Open. Wound accompanying the fracture giving access to the damaged bone.
-Greenstick. Fractures in immature growing bones, in which the bone bends, a fracture line forms but it does not physically break the bone into separate pieces.
-Avulsion. The tension on a ligament or tendon causes a piece of bone to break away at the attachment site.

2) Signs of a fracture
Check out your First Aid notes on Fractures as an aid to revision. Signs of a fracture are acute onset Pain, Swelling and Bruising, and Loss of Use of the affected part if it is a limb. Fractured legs often have a characteristic “swinging” motion and are held completely off the floor. There may be obvious malformation. In non-greenstick fractures, if the animal allows palpation of the site, there is usually crepitus, as the broken bone ends move across each other.

First Aid Refresher
Remember First Aid prevents further injury. In the case of a fracture this means preventing further soft tissue damage, and preventing any further contamination of an open fracture.
This means where possible (i.e. usually limbs) cover the site and immobilise it. A dressing firm enough to immobilise a limb has the added advantage of stopping haemorrhage and haematoma formation around the fracture. REMEMBER FRACTURES ARE PAINFUL. ENSURE THE SAFETY OF ALL PERSONNEL INVOLVED IN HANDLING THE ANIMAL, INCLUDING THE OWNER.
The Robert Jones dressing is rightly regarded as one of the best all purpose immobilising dressings. Key points are:
-Use enough padding. A Labrador sized forearm may well take 2 or 3 full rolls of cotton wool.
-remember to put the stirrups on first
-It is difficult to overtighten an R-J dressing if there is adequate padding. The classic description is that it should sound like a watermelon when tapped.
-Remember to leave access to the toe tips to monitor circulation.
A good Robert Jones dressing can be left on for several days quite comfortably.

Immobilisation also has the advantage of reducing pain.

3) Common Fractures
Most fractures in animals affect the limbs, as the commonest cause of a fracture is the RTA.
In mature animals, the bones tend to fracture along lines of weakness, so for instance fractures of the humerus are often spiral, following the shape of the bone. Most of these are therefore DIAPHYSEAL, involving the shaft. This also applies to smaller bones such as metacarpals and metatarsals.
In immature bones, there are different areas of weakness, usually where the growth plates lie. Fractures at or near the growth plates are physeal (through the plate) or epiphyseal (through the epiphysis).
Other fractures commonly seen in RTA’s are pelvic and rib breaks.

4) Fixing fractures: a) External Fixation.

Bones heal by forming a scar using cells from the endosteum (Inside the bone) and the periosteum (Outside the bone). The scar is called a callus, and the more movement experienced by the bone ends, the bigger a callus they build in an attempt to heal, and the longer it takes. The point of fixation, therefore is to reduce the bone end movement to a minimum.

As the name external implies, this means applying external support to immobilise the fracture. In practice this means splints and casts.

i) Splints. Usually there are two splint types on a practice shelf- Aluminium and foam “finger” or Zimmer splints, and green plastic gutter splints. Zimmer splints are comfortable but not very firm, so only useful for small bones or small creatures. Gutter splints are usefully firm, but only applicable to immobilising fairly straight bones (e.g. Metatarsals, radius/ulna).

ii) Casts. This method of external immobilisation allows more unusual bone shapes to be catered for, so producing better alignment than simple gutters. The ideal is to immobilise one joint on either side of the fracture. There are many different casting materials, and decision as to use is often made on the basis of cost. The oldest and cheapest is Plaster of Paris. This can provide satisfactory casts but is heavy and does not withstand external wetting or wear and tear very well. See Jones’ for a good resume of Plaster of Paris use. More modern external fixating materials are either Resin type impregnated materials or thermoplastics.
Resins are effectively bandages soaked in a plastic which starts to set on contact with air or water, forming a hard material a bit like Araldite. Thermoplastics are plastic meshes which soften when heated then harden again as they cool to form a cast.

General principles of casting
Know the materials in your particular practice. Casts must be adequately padded underneath, particularly over pressure points such as the hock, but not over-padded so that they do not provide adequate immobilisation. Padding should have 50% overlap on each turn, and should protrude from the end of the cast. A lot of casting will be done in smaller pets which can be successfully immobilised with reasonable amounts of material.
If the casting material “goes off” in use, like a Resin, then only prepare a working amount at any time. Thermoplastics can be re-heated.
Casts can be applied as a wound-round bandage or by preparing strips and using slabs of material lengthwise on the limb.

Advantages of a cast: Relatively easy to apply, P-O-P is cheap, no surgery.
Disadvantages: The limb is lost to view, pressure sores are a real problem with many casts, the cast may be heavy, not waterproof, subject to external damage, only suitable for straightforward breaks.

Alternative casts
Split casts and gutter casts are often useful in smaller animals or as additional support to other forms of immobilisation.
Split casts are casts applied then cut longitudinally to form two halves which can be re-assembled to enclose the limb. These have the advantage of allowing inspection, but are not quite as immobilising.
Gutter casts are casts which support one side of a limb, which is then strapped down into the cast, These can be useful to avoid pressure points, but again are not as immobilising.

iii) The external fixator. In this technique, pins are driven through bone fragments from side to side across the affected limb, so that lengths of pin protrude on either side. The pieces of bone are then re-aligned, and the pins locked in place using external pins and wires to join them together. This provides a Meccano-like frame around the fracture. This technique is extremely useful in very complicated fractures or twisted areas of bone. It also provides good access to the limb to monitor progress. Often used in birds, as the entire apparatus can be removed after healing. It may also be used in addition to internal methods where aligning bones externally cannot be achieved.

iv) Extension splints. Still in the syllabus but not often used, these are splints constructed so that limbs are pulled into extension using bandages on a frame, so the fracture ends fall into line as the limb extends. They have largely been superseded by external fixators.

Fixing Fractures b) Internal Fixation
As the name implies, internal fixation means inserting materials inside the animal / bone to stabilise the fracture and allow healing. The advantages of internal fixation are that stabilisation and alignment can be very good indeed, allowing fast healing and minimal callus formation. The disadvantages are that it requires surgery, and leaves foreign material inside the body, at least temporarily but often permanently. Some implants are very expensive.

Materials used in internal fixation:
-Intramedullary Pins. There is a wide variety of pins in use for insertion into the medullary cavity. Steinmann pins are the most common, sometimes used with a threaded end and with a trochar point.
Rush Pins are short pins with a bevelled point at one end and a hook at the other, used to re-attach fractured epiphyseal pieces. Kuntschner Nails are pins with a groove down the centre so that they have flattened sides at a right angle to each other, providing extra resistance against bending.
-Wires. Kirschner Wires (K-Wires) are very thin pins with a bevelled point at one end. They are often used “stacked” across a fracture instead of a single Steinmann pin. Cerclage wire is stainless steel wire on a roll used to encircle fractured bone ends and draw them together, in conjunction with other fixation.
-Plates. Steel plates with holes for screwing to the bone. There are many different plate types, some adapted specifically for use in one fracture type.
-Screws. Can be used alone to stabilise one bone fragment on another (e.g. Condyle fractures) or in conjunction with plates.
- The ASIF / AO system. A system of internal fixation using specialised plates, screws and other equipment which is designed to give better alignment and stabilisation of fractures. Compression plates are used in which the screw holes are designed to bring the edges of a plated fracture together as the screw is tightened.

5) After care
In the clinic, care involves ensuring pain is kept to a minimum, so use of analgesics. Also, if patients are immobile, pressure or bed sores and soiling of dressings can be a problem.
When the animal returns home, then the owners have to be counselled carefully on potential problems. Fractures generally take at least 6-8 weeks to heal. Animals with casts are visibly compromised so owners tend to be fairly careful. Animals with external fixation may appear to be doing better, but they are still healing, and owners should be in no doubt that severe damage can result from over-exercise. In the case of casts, unusual smells or suddenly dull or uncomfortable animals need investigating. With all fractures, sudden lameness and deterioration is a cause for concern. Monitoring the healing of a fracture can often only be done by further X-rays, although a palpable callus at the fracture site is a sign of healing.

6) Complications
-Malunion- the bone heals incorrectly aligned.
-Delayed union- healing is much slower than expected (?excessive movement).
-Non-union- the fracture fails to heal. Can be a problem in Toy and Chondrodystrophic breeds.
-Osteomyelitis - infection of the bone, either introduced at the time of injury or at surgery. Will persist if there are implants although healing will take place, so usually antibiotics are prescribed until the fracture has healed then implants are removed.
-Pressure sores in casts.

7) Luxations and Subluxations
A luxation is a complete separation or displacement of the bones forming a joint so that the joint becomes non-functional. A subluxation is a partial separation, so that the joint may retain function.

Some joint abnormalities which cause luxation or subluxation are congenital (at birth e.g. shoulder dysplasia leading to luxation) or inherited (may be congenital or develop later, e.g. hip dysplasia).

Most luxations are, however, due to trauma, usually RTA’s. Luxations are usually obvious as the limb is held in an abnormal position, although owners will usually report luxations far more often than they occur, e.g. after cat bites to the fore-arm.

Common luxations: Hip, elbow, carpus, hock, phalanges.
Common sub-luxations: Hip, stifle, shoulder, hock.
Luxations and sub-luxations may also occur at the same time as a fracture.

Treatment:
- X-rays are always necessary because of the possibility of a fracture pretending to be a luxation or occurring at the same time.
-CLOSED reduction is preferable where possible. The joint is restored to normal anatomy by manipulating the limb. This usually requires anaesthesia or deep sedation to relax the muscles, and often brute force is necessary, especially in large breeds.
-OPEN reduction may be necessary, in which surgery is used to replace the joint and repair any ligamentar damage if possible. Major surgery may be necessary in joints which are not automatically stable, e.g. the tarso-metatarsal joint.

Post - operative
The joint will be unstable for up to 4 weeks and prone to re-luxation. Some joints are not stable without surgery. Support dressings are therefore necessary (practice those Ehmer slings for hip luxation!), and the owners must have strict instructions as to rest and appropriate exercise (i.e. none). Cage rest may be the best option if possible. The commonest complication is re-luxation.

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