Indepth Equine Podiatry Symposium Notes Written and presented January 2010 by R.F. (Ric) Redden, DVM
PIII fractures have been described in the literature and classified according to location, which can be helpful for those familiar with the classification. However, even though PIII fractures as a rule do not occur as commonly as other acute foot problems, they should be considered in your tentative diagnosis when acute lameness is presented. Foot abscesses are far more common than fractures and should also be considered high on the suspect list. The clinical signs and history of spontaneous foot pain is classic for both syndromes.
Distinguishing PIII fractures from the abscessed foot is often not as straightforward as one would think, as quite frequently radiographs do not clearly reveal fracture lines for a few days, even weeks, following injury. Also, fractures occur in several different planes and other locations that are not described in the literature, which further complicates the diagnosis. Fractures can occur along with septic conditions that appear to be the primary problem and often overshadow the initial problem. Pathological fractures can occur due to cumulative damage from other disease syndromes such as laminitis, full thickness toe cracks, abscess, white line disease, high grade club feet, etc.
Palmar Rim Fractures
This type of fracture can occur due to direct trauma sustained when horses gallop over hard ground (dry or frozen), with extremely thin soles. This condition clearly mimics bilateral laminitis as the clinical signs are quite similar. Radiographs can be conclusive; however a very soft exposure is required to visualize small fragments of bone that have broken away from the very thin palmar rim. The 65 ° DP view and 45 ° 65 ° medial and lateral oblique views reveal the fracture best. It can also be seen on the lateral and occasionally the DP view. Shoes should be pulled for these views to prevent superimposition of the shoe over the area of concern and unwarranted scatter radiation that reduces resolution and detail.
Very low KV, high MA and very low MAS are used to clearly reveal the fracture. This is not a problem with traditional film as you simply cut the KV 5-10 units and significantly reduce time, which drops MAS. MA is always at its highest peak at low KV settings. If you must use a hot light to reveal the fracture, you most likely will miss a few. When using a digital unit you may not have the option or means to create a very soft exposure simply due to pre-set algorithms. I prefer my traditional system for all foot images over most CR and DR units as it offers far more flexibility and higher detail and resolution.
Unless the fracture becomes septic it does not need to be removed. A protective hospital plate shoe and limited exercise for a few weeks works well for my cases. When septic, this fracture can be confused with acute laminitis as there may be drainage from the sole and the clinical signs are very similar. However, the horn-lamellar (HL) zone does not confirm laminitis and even though the sole may be quite thin, it is not due to PIII displacement.
Septic bone fragments should be removed and the sole protected by a hospital plate shoe until it has healed and cornified. I apply the shoe, apply a surgical scrub to the sole and remove the fragments using a local block and light sedation. A hospital plate works great when applied prior to surgery as it makes a nice pressure pack, preventing unwarranted granulation tissue. When used properly, this shoe does not increase the risk of post op sepsis.
Type 1 Wing Fractures
Wing fractures normally occur on the right front medial wing in horses working at high speed going counterclockwise medial wing left front when working clockwise. The coffin bone at the time of birth is quite small relative to the hoof and has a totally different shape as the wings of the bone have not developed. The wings grow from the body of the bone, with the majority of growth occurring over the first year of life. However, with most breeds the wings may continue to calcify and grow in length for 10 years or more and in rare cases can extend to the limits of the heel bulbs. Saddlebreds and most Arabian horses have a very short palmar surface relative to their size in comparison to other horses. Bone shape is as unique to the breed as hoof shape is, which is why there are many capsule stereotypes that we can recognize from breed to breed.
Acute wing fractures appear radiographically as a distinct fracture line that is normally quite small and can be difficult to diagnose at the time of injury. Very soft 65 ° DP and 45 ° 65 ° lateral and medial oblique views as a rule reveal the fracture best. However, the skyline view shot through the heel as well as DP oblique view can also reveal the fracture. Areas of isolated ossification on PIII that occur quite frequently due to the normal wing maturation process can often be confused with a fracture when there is a history of heel pain. Note that the areas of separate ossification as a rule are not painful, and have distinguishing characteristics from fractures.
Wing fractures as a rule are quite easy to treat, as stall rest for a few weeks and a bar shoe with good frog support allow most horses to continue training after 3-4 months of very limited exercise. Many of these fractures do not heal bone to bone, but form a gelatinous union that may appear to have callous formation. Palmar digital neurectomy has been used quite successfully as an alternative to taking the horse out of training for 3-4 months. The dark side of this treatment option is the occasional neuroma and inherent risk of hot nails, puncture wounds or excessive trauma to the desensitized heel.
Articular Wing Fractures
Articular wing fractures pose a slightly different problem than Type 1 wing fractures as they are normally very painful, causing grade 4-5 lameness, and most can be demonstrated radiographically at the time of injury. Only a few cases will require a few days to displace before being revealed radiographically.
Several views are needed to fully assess the fracture.
65 ° DP view with moderate penetration. This view reveals the joint margin. The thinner areas of the coffin bone will be overexposed when using traditional film.65 ° 45 ° oblique view. Adaptable oblique angles can often clearly define the path of the fracture.DP view with hard penetration and beam centered just below the coronary band. This is one of my favorite views as it reveals the distal displacement of the main body of PIII.
The 65 ° DP view may also reveal a step fracture, but fails to clarify the plane of displacement. Looking closely at the DP view from a mechanical point of view and considering the broad attachment of the DDF and its function, one can better understand how displacement occurs. As load goes on the foot, the action of the DDF pulls the larger body of bone distally as it is no longer anchored to the wing. The displacement and constant movement of the two separate pieces of bone is most likely the seat of pain.
Articular wing fractures as a rule do not pose a serious problem even though they are often very painful for several days. Some heal bone to bone with four months rest and a simple bar shoe. Others never heal but have a distinct fissure line for the remainder of the horses life. Those that heal with a step at the joint invariably have some ° of arthritis that can cause future soundness issues. For some unknown reason, grade 2 or higher club feet are more prone to articular fractures than the lower PA profile feet. Traditionally bar shoes, cap shoes and foot cast have been used to treat the acute pain as well as the fracture. Dealing with the pain is our first priority, as it potentially causes very serious and often life threatening contralimb laminitis. Considering the cause for pain can lead us to a meaningful solution. Greatly decreasing DDF action minimizes or prevents fracture displacement, and consequently diminishes the pain associated with the grating together of raw ends of bone. However, it is prudent to prevent DDF tension from displacing the large body of PIII shortly after injury as the natural healing mode quickly fills the fracture gap and can jeopardize successfully re-establishing good joint alignment.
A large majority of articular fractures never heal bone to bone, but form a callous that bridges the surface of the bone. A cartilaginous matrix forms along the center of the fissure line. Radiographically this may appear to have a bony union but it is often the superimposed bone on the surface that offers this illusion. I have taken several coffin bone fractures from retired horses that apparently had articular fractures as two and three year olds. They have either died of old age or were euthanized due to the infirmities of old age, and close scrutiny of the boiled out bones have provided conclusive evidence of this type of bony bridging.
How to Adequately Reduce Displacement
Before determining a shoeing protocol, know the existing PA. Use a shoe or device that will raise the PA to a minimum of 20 °s. A self-adjusting rocker action device with wedge is preferable over a straight wedge setup as the horse can pick and choose the precise PA that not only provides stability but also more pain relief. The large majority of cases show a favorable response to pain within minutes after application despite increased heel loading from the high PA. The fragments apparently do not grate against each other. More conservative shoes can produce good results, however the pain response is extended over that of quickly reducing inward folding of the large body of bone, and most therapeutic shoes do not address DDF tension. Therefore the majority of fractures heal with a step malalignment.
Most articular fractures require 4-5 months for recovery. When the step persists, arthritic conditions are a threat to soundness. Nerving is an option for articular fractures and is often used as a last resort when the goal is to return to athletic training. However, complications can arise from neurectomies. Hot nails from routine shoeing are a higher risk than normal, and puncture wounds from wires, nails, loose shoes, and sharp objects often go undetected for several days as lameness is obscured by the neurectomy. Sequestrum can form along the fracture line when a horse continues training and cannot feel the pain. The sequestrum often becomes septic and can potentially be life threatening.
Extensor Process Fractures
Fractures through the extensor process are relatively rare, but are quite painful and may be difficult to assess clinically. Cases with acute fractures and cysts within the extensor body are normally sounder when moving over hard ground rather than soft, which is just the opposite of most load induce