1.  Field of the Invention
The present invention relates to the field of protective boots for horses.  More particularly, the present invention the relates to an equine protective boot which allows for proper support, flexibility and proper blood flow in the condylar area of the horse leg. 
2.  Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Tendon injury is one of the most common forms of musculoskeletal injuries that occur to horses competing in all disciplines.  Injuries to the musculoskeletal system have been found to account for 82% of all injuries to racehorses competing National Hunt and flat races, and of these 46% involved tendons ligaments (Williams et al.  2001; Ely et al.  2004).  Another study reported that tendon or ligament strain accounts for 53% musculoskeletal injuries that occur during hurdle and steeplechase races (Pinchbeck et al.  2004).  A 12-year epidemiological study found that tendon injury was the most common reason for retirement in racing Thoroughbreds in Hong Kong (Lam et al.  2007).  Furthermore, it has been found that, over the period of one season, 15% of both National Hunt horses (Ely et al.  2004) and Thoroughbred flat racehorses (Kasashima et al.  2004) in training suffered from a tendon at ligament injury as diagnosed by ultrasound.  Some tendons are much more prone to injury than others; the majority of tendon injuries (97-99%) occur to the forelimb tendons (Kasashima et al.  2004; Lam et al.  2007), with the superficial digital flexor tendon (SDFT) being injured 75-93% of cases and the remaining injuries occurring to the suspensory ligament (SL) (Ely et al.  2004; Kasashima et al.  2004). 
Tendon injury is one of the most common causes of wastage in the performance horse; the majority of tendon injuries occur to the superficial digital flexor tendon whereas few occur to the common digital extensor tendon.  These days, a myriad of products are available to protect a horse's legs from injury, including many different types of ankle boots, skid boots, splint boots, knee boots, support boots, and leg wraps.  These products often offer new designs and incorporate new materials.  With all the innovations there still isn't a support boot that is used to track horses in the race industry or used in races.  They are bulky and the outer layer is made mainly from loop fabric material, which tends to gather dirt and sand.  Support boots as we know them actually inhibit the motion of the ankle, as the main panels are one piece covering the third metacarpal and a portion of the proximal phalanx, then strapping them together.  Support boots serve mainly as protection from strikes and offer ligament support at the cost of a loss of motion.  Another pitfall in support boots is the retention of heal. 
For example, U.S. Pat.  Nos.  5,910,126, 5,115,627 and 5,579,627 describe various types of equine leg wraps and supports.  Generally speaking, these prior devices include flexible panels configured to wrap about the lower portions of horse's legs and have attachment means for securing the panels in place.  Typically, the flexible panels are formed of resilient neoprene or similar foam materials having conventional loop facings promoting heat buildup and accumulating debris. 
Furthermore, the one-piece equine leg wraps of the prior art cover and strap the bones inhibiting the motion.  For example, U.S. Pat.  No.  5,579,627 describes a wrap including an integral lower fastener to provide additional support for the fetlock joint.  Another conventional method for support is the use of elastic wraps applied straight on to the limbs.  This practice has its pitfalls as well.  If applied wrongly or left too long, it can cause tendon damage and constrict the flow of blood. 
FIG.  1 shows an anatomical view of the ankle 10 of a horse.  The ankle 10 has a hoof 12.  A common digital extensor tendon (digital extensor tendon) 14 runs along the front of the horse's leg over the cannon bone 15.  The fetlock joint 16 is shown generally behind the digital extensor tendon 14.  A superficial digital flexor tendon 20 (digital flexor tendon) extends along the back, of the ankle 10 of the horse.  Proximal sesamoid bones 18 are shown at the bottom of the digital flexor tendon 20.  Adjacent the sesamoid bones 18, there is shown a palmar digital vein 22.  Another palmar digital vein is present on the opposite side of the ankle. 
As discussed above, prior art equine leg wraps typically inhibit movement of the digital extensor tendon 14.  Further, many of these prior art equine leg wraps and boots also inhibit blood flow through the palmar digital vein 22. 
It is an object of the present invention to provide an equine protective boot that allows for proper support, flexibility and proper blood flow in the condylar area of a horse's leg. 
It is another object of the present invention to provide an equine protective boot that bridges the horse's digital extensor tendon. 
It is another object of the present invention to provide an equine protective boot which prevents heat buildup at the horse's ankle. 
It is yet another object of the present invention to provide an equine protective boot which prevents bowed tendons, particular bowed digital flexor tendons. 
It is a farther object of the present invention to provide an equine protective boot that absorbs shocks and strikes. 
It is yet another object of the present invention to provide an equine protective boot which repels sand, dirt and water. 
It is yet another object of the present invention to provide an equine protective boot which prevents hyper-extension in the horse's ankle. 
Finally, it is another object of the present invention to provide an equine protective boot which aids in the turnover of the foot in motion, preventing stumbling, increasing speed and relieving biomechanical stress. 
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.