Rascal is an indoor cat...so it was a surprise when Rascal's owner came home to find a very deformed looking paw. AND very sore to-boot! AND we have no idea how he did it.
Some thoughts might be that he got it caught in something (I have seen a broken leg in a pup who's leg slipped between the slats in the seat of a cane chair, and the pup fell forward off the chair...), or something fell on the paw, or a door swung shut on it. It was very painful and Rascal was unable to even place any weight on that paw.
The X-rays showed all four of the long bones of the paw (the Metacarpal bones, the same bones we have between our wrist and our knuckles) were fractured, and that they were very laterally deviated.
The large solid arrows point to the fractures. Note that the breaks are downwards as well as outwards.
- Carpal bones, or Carpus: this is the wrist.
- The Dew Claw, also known as the 1st digit (phalanges) the equivalent of our thumb.
- This joint is equivalent to our knuckle joint.
Being quite young at 6 months of age, Rascal's healing ability is very good - and quick. So quick that the bones have already, even after only a few days, begun to set at this awkward angle. If left, the bones would all fully heal in this position leaving Rascal to hobble and limp around and the abnormal pressures on the wrist would result in arthritis and ongoing pain. Rascal would also have great difficulty climbing the curtains...or his dad's trouser legs...or jumping and landing without hurting himself further!
The initial incision (left) exposes criss-crossing tendons, nerves and blood vessels all covering the broken bones.
To repair the fractures required delicate surgery. Very fine pins (called Kirschner Wires) needed to be placed within the medulla (the central hollow of the bones) and the bones re-aligned before the "K" wires were advanced into the medulla of the other part of the broken bone. The "K" wires are ONLY 0.35mm thick! They bend very easily, and so must be advanced slowly, mm by mm, to avoid kinking them.
In this photo, the toe (at left side of picture) is bent downwards as the pin (actually called a K Wire) is drilled through the medulla (the hollow centre of the bone filled with bone marrow) and out at the knuckle (you can SEE the K wire coming out on the left side of the photo).
The broken bones are situated UNDER tendons, nerves and various blood vessels, and we aim to minimise any trauma to these tissues to avoid permanent nerve damage, to avoid adversely affecting the normal function of the paw, AND to ensure as rapid a recovery/healing as possible. I wore 2.5X Magnifying glasses to assist in the accuracy of the surgery. In larger patients, the wires or pins are inserted from the knuckle end, angled downwards from just outside/above the knuckle joint, and as they enter the medulla cavity they bend and pass along inside the medulla cavity. In small patients, the K wires are so fine they drill staight through without following the medulla cavity, so we have introduced the K wire from the fractured end of the bone.
With the fractured bones aligned and the drill now on the other end of the K wire (at the knuckle where you saw it coming out in the photo above) end the wire is advanced back up the medulla and into the hole of the medulla of the other fragment of the fractured bone! The post-Operation X-Ray shows the final position of the two K wires and that all four fractured metacarpal bones are well aligned.
Here are the pins removed from a small tenterfield terrier (needed four K wires - see below), just to show you how small and delicate these pins are. They are VERY easy to bend, and need to be placed into bones very very carefully!!!
In MOST cases where all four metacarpal bones are broken, re-aligning and pinning the central two bones automatically re-aligns the other two AND provides an internal splint to keep them in position. This is because there is connective tissue between the metacarpals, attaching the bones together but still allowing some movement. HOWEVER a splint must still be applied to the outside as well because if the patient places any weight on the paw, it will bend the thin K wires and prevent healing.
Because Rascal is only young and still growing, his pins will only have to be in place for 4 weeks before removal.
A few days after Rascal's surgery, I had to remove the pins from ANOTHER patient's paw that broke all four metacarpals eight weeks previously. In this case it was a small dog, a four year old tenterfield terrier, and all four bones required pinning because the outer two did not re-align correctly with just the central two K wires.
After many weeks, the ends of some of the pins started to rub under the skin, making locating them for removal very easy (Black Arrows). One pin (under white arrow) was very difficult to find as the end had tuned inward and was buried under scar tissue from the healing process and could not be felt.
Note that the we bend the ends of the pins that protrude from the bones:this is for two reasons. One, it helps prevent the pin from loosening and then migrating or moving in or out of its original position. This is VERY important because with the patient's activity and the very sharp cutting end of the pin in the medulla, the pin can edge itself along and burrow right up into the wrist joint causing immense pain and severe arthritis!
Secondly, by bending the end of the K wire up, it helps keep it out of the knuckle joint, allowing the toe to be in its normal position and minimising damage to the knuckle joint. Before the K wires are bent upwards, the toe is actually forced down at the knuckle joint and cannot be moved upwards. This would be painful for the patient!
Recognising that the bones have actually healed enough for pin removal can be difficult. On first glance, you might think that all the fractures are still present and not healed! But, in fact, they have. Bones form a callus when healing: a swelling of less dense bone that bridges between broken bones and with time "remodels" back to the more normal shape and density. When a fracture is particularly well stabilised, these calusses are smaller as is noted here.
In the X-ray, the long fine arrows show the callus bridging the fracture of the left metacarpal. The long solid arrows show an increased density in the space of the fracture sites of the middle two metacarpals demonstrating that there has been healing across this space. The black dashed line outlines a larger callus indicating slightly more movement at this fracture site. This may have been due to this toe pushing a little against the middle inside of the splint when the patient 'clunked' around when he walked. Interestingly, this was the most difficult to locate and remove K wire!
The short thick white arrow is pointing at the dew claw.
Out of interest: The naming of the digits is started from the dew claw or our thumb as the first digit, then digits 2, 3, 4 & 5. It is the same for the metacapals (MCs), so in the X-ray above the fine arrows point to Metacarpal 5, MC 5. The dashed black line is bulging out of MC 2, and MC 1 is the dew claw at the right.
When the K wires are first removed, an external support bandage is reapplied and the patient confined in a cage because the FIST jump off of any height could re-fracture all the bones because full strength hasn't been attained yet. Bones strengthen with use. The internal K wires PLUS the external splint has allowed healing but has reduced the amount of active work-load on the bones. Hence the bone in the fractures is still only moderately strong. The support bandage is removed after 5 days, and after a further 10 days in a cage, the bones should be strong enough for most activities.
AFTER THIS, IF the patient is extremely active in the jumping department, leaping around excitedly, then it is wise to only walk on a lead if a dog, and keep confined in a cage at other times, or if a cat , then keep in a cage for an additional couple of weeks if possible. Rascal will heal quickly and won't need as long in a cage!