WHAT’S NEW in the veterinary world?
Research is all about furthering understanding and updating information. Peter Green MRCVS reports on recent findings that have shed new light on old knowledge
WINDGALL – OR CYST?
SOME terms for equine problems go back centuries: terms such as “splints”, “spavin” and “thoroughpin”. Another is “windgall”, which is a fluid distension of the digital flexor tendon sheath of the fetlock. This fluid-filled tendon sheath lubricates the flexor tendons as they pass around the back of the fetlock. A strong strap of fibrous tissue, the annular ligament, sits like a belt around the sheath and tendons. True, old fashioned windgalls rarely cause lameness; they are simply an enlargement of the sheath, with increased synovial fluid bulging out above the annular ligament.
These well recognised and common features may be frowned upon in showing circles, but they are usually harmless. True windgalls occur on both the inside and outside of the limb. The test of whether a fluid swelling above the fetlock is a true windgall is to lift the limb, flex the fetlock and see if the swelling can be reduced and dissipated by gently pressing with the fingers and thumb.
If the fluid moves away under gentle pressure, it is a windgall.
Recently, a rather different fluid swelling just above the fetlock has been recognised. These are firm, tight bulges of fluid that occur where you would find a windgall, and look the same. But they are different. They are “synoviocoeles” or “synovial cysts” and they arise because of a tear in the wall of the tendon sheath. This allows synovial fluid to escape from the sheath and form a cyst under the skin. The natural repair process attempts to heal this aperture, but the healing tissue creates a form of one-way valve that allows fluid out, but not back into the tendon sheath. As the horse moves and works, the pressure in the cyst increases. Synoviocoeles cannot be deflated by digital pressure when the limb is lifted and flexed and, unlike windgalls, synoviocoeles can cause lameness.
In a recent report, surgeons describe 10 horses in whom synoviocoeles were causing lameness, confirmed by local anaesthetic of the synoviocoele, which resolved the lameness. In all cases the synoviocoele cyst was deflated by keyhole surgery, in which a permanent two-way connection was made between the cyst and the tendon sheath, allowing fluid to pass back into the sheath. All 10 cases made a good recovery and returned to work, although one horse suffered subsequent tendon injury and was retired. The lesson is that sometimes an oldfashioned windgall may actually be something else.
NUMBING THE PAIN
ANOTHER recent report also contrasts old and new, this time with the local anaesthetic used to perform nerve blocks in horses during lameness examinations. One of the oldest local anaesthetic injections is lignocaine, known in the USA as lidocaine. It was first marketed in the 1940s, has been around for years and is relatively cheap to produce and to buy.
Most equine nerve blocks are undertaken with another, more modern local anaesthetic, mepivacaine, which horse vets use because it is believed to give fewer side effects, such as local swelling of soft tissues in the leg. Mepivacaine is considerably more expensive than lignocaine.
In a recent study, vets in the USA performed median and ulnar nerves blocks on lame horses using first one drug, then the other. Lignocaine and mepivacaine were equally effective and there was no evidence that lignocaine caused more side effects. There was no more localised swelling, even though the median and ulnar nerve blocks were high in the leg where there is lots of sensitive soft tissue. The old fashioned, cheap drug was just as good as the expensive modern one.
However, one word of caution. Lignocaine is sold in 50 and 100 ml bottles. Nerve blocks need meticulous sterile and hygienic conditions. Once a bottle is opened, it can’t be used for multiple patients and nerve blocks need only a few millilitres of injection. Mepivacaine is available in small, single-use (10ml) vials. Maybe it is the packaging, not the performance, that determines whether the new drug or the old drug is used.
FURTHER READING
● SYNOVIOCOELES:
Veterinary Surgery. 2022;51(2):311-319. doi:10.1111/vsu.13751
● LOCAL ANAESTHETICS:
Veterinary Surgery. 2022;51(2):279-285. doi:10.1111/vsu.13754