South Shore Equine Clinic & Diagnostic Center
Equine Veterinary Services South Shore Boston Massachusetts

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"Cappy" 14-year-old Quarter Horse Gelding

Cappy was seen on the farm for a wound on his left hind leg.  The owner had first noticed a puncture wound on the lateral aspect of the distal metatarsus (outside of the cannon bone) when he came in from the pasture the previous week.  At that time there was minimal swelling and the wound appeared very small, so the owner opted to treat him at home on her own.

Left hind leg puncture wound
Cappy's puncture wound on his left hind leg.

When the wound was still open and draining after 3 days of treatment and the leg had developed some swelling that was not getting any better, the owner called SSEC for examination.  Upon initial examination at the farm, a moderate amount of swelling was observed throughout the mid-metatarsus (cannon bone) and the “puncture wound” was draining a small amount of purulent material (pus).  The wound was clipped, thoroughly cleaned, and then explored using a teat canula, which is a dull stainless steel probe that allows us to determine the depth and extent of a wound with minimal trauma to the tissues.  When inserted into the wound, the teat canula followed the draining tract proximally (toward the hock) to a depth of 5-6 centimeters and made contact with the bone.

Any time we are able to contact bone via a wound we are concerned about trauma to the bone, fractures, and the possible formation of a sequestrum.  A sequestrum is essentially a dead piece of bone.  If a bone is fractured and the edges of the bone remain well apposed in a normal position (non-displaced), the bone will most often heal well.  When a piece of bone breaks off and is moved away from its normal position (displaced) the blood supply cannot reach that piece and, therefore, it cannot heal.  That piece of bone dies and becomes a “foreign body” to the horse’s immune system, which mounts an attack on the piece of bone.  Additionally, skin will not heal over nonviable bone.  This accounts for the draining tract (a wound which constantly drains a small amount of pus) or non-healing wound seen with most sequestra.

Since we were concerned about possible damage to the bone, radiographs of the metatarsus were taken.

Radiograph: DLPMO view of the metatarsus
 
Radiograph: DP view of the metatarsus
DLPMO View
 
DP View

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As seen on the right side of each radiograph, there is a segment of thin bone that appears to be separated from the piece above.  The bone in question is the lateral (outside) splint bone, also called the fourth metatarsal bone (MTIV).  Splint bones are thin, non-weight bearing bones that run along the inside and outside of the cannon bone, both on front legs and back legs.  They are thought to be vestigial remnants of toes and in the hind leg extend from the level of the hock to a few inches above the fetlock.

Diagram of lower leg

The radiographs also show the fractured segment is displaced, meaning it is not able to heal on its own without removal of the dead piece.  Also, the radiograph on the left shows the displaced piece appears to be comminuted, meaning in 2 or more pieces (a radiolucent line is visible approximately in the middle of the displaced piece).  Surgical removal of fractures of the distal splint bone carries a good prognosis and generally a relatively quick recovery with minimal complications.  After discussion of the treatment options the owner elected for surgical removal of the fractured distal splint bone. 

Cappy was admitted to SSEC and prepped and induced for surgery the following morning.  Peri-operative antibiotics were administered and he was placed in right lateral recumbency (laying down on the right side) so the lateral aspect of the left hind limb was up for easier access.  An incision using the CO2 LASER was made over her left hind MT4 to expose the fractured fragments.  Using the LASER ensures less bleeding, less pain, and less post-operative swelling.  In addition, the LASER is also is bactericidal to the surrounding tissues as it dissects down to the fractured bone, killing any contaminants or bacteria from the associated wound. 

A total of 3 pieces of bone were recovered from the surgery site and the incision was closed in 3 layers.  A post-operative radiograph showed no further fragments remaining.  A bandage was placed over the site and he was transported back to the recovery room and recovered well.

Radiograph: post-operative view of metatarsus
Post-operative View

Cappy was discharged the following day on oral antibiotics and remained on stall rest with daily hand walking for 2 weeks.  The bandage was changed every 2-3 days to keep the surgical site clean and keep pressure over the site to minimize swelling.  The sutures were removed at 2 weeks post-operatively.  The surgical site looked great with minimal swelling, due in large part to the excellent after care provided by the owner.  We anticipate a full recovery for Cappy!

The left hind leg 2 weeks post-operatively
 
Surgical site barely visable from fractured splint bone
The left hind leg 2 weeks post-operatively.
 
You can barely see the surgical site.

Fractures of the splint bones can occur anywhere along the length of the bone on the front or back leg.  The scarce amount of soft tissue covering the splint bones makes them particularly vulnerable to injuries due to trauma such as a kick from another horse.  If left untreated fracture remnants can turn into a bone sequestrum leading to a non-healing wound.  Fracture remnants left untreated can also cause excessive callus formation which may result in secondary suspensory ligament desmitis, leading to chronic lameness.  The early diagnosis and removal of the fractured distal splint bone led to a great outcome for this case.

Take home message:  A puncture wound can often be very misleading.  If over a bone or near a synovial structure such as a joint or tendon sheath, puncture wounds can be very serious and have severe complications.  If left unchecked, these could potentially have catastrophic consequences.  It is always best to get any wound checked by your vet!

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