Natural Balance Guidelines

Research has shown that the third phalanx and the distal sesamoid bone can be in different positions in relationship to the hoof capsule. Understanding the position of these bones in relationship to the hoof capsule in three dimensions is helpful in diagnosing lameness in the equine foot. Various positions, movements, alignment of the bones to each other and changes in these measurements after trimming, shoeing, or surgeries can be assessed through radiographs using radio-opaque markers. DORSAL/PALMER(PLANTAR) POSITION OF PIII Radio-opaque markers used on the foot when taking lateral radiographs will show the dorsal/palmer position of PIII relative to the hoof capsule. Measurements from the radiographs can then be applied to the hoof capsule to assist in placing the shoe under the bony column. FOOT PREPARATION The foot is prepared by removing dirt in the sulchi and sole. A thumb tack is placed into the true apex of the frog. The true apex is defined as the location where the frog blends with the sole. This area has a color and texture difference and is an easily identifiable standard for farriers and veterinarians. Color and Texture Difference at Frog/Sole Junction Often the superficial layers of the frog grow over the true apex necessitating the use of a sharp hoof knife to remove any overgrowth of the apex of the frog and thus allow identification of the true apex. Identification of True Apex Under False Apex PROXIMAL/DISTAL POSITION OF PIII The proximal/distal position of PIII relative to the hoof capsule can be discerned by placing a radio-opaque marker on the dorsal hoof wall with the most proximal aspect of the wire at the coronet where the last hair leaves the skin. Last Hairs Leaving Coronet: Location of Prox. Aspect of Wire MEDIAL/LATERAL POSITION OF PIII Medial/lateral position of PIII is measured radiographically by placing two radio-opaque markers on the dorsal hoof wall. The ungual cartilage is palpated where it turns and progresses distally to the coronary band. A wire is placed at this location with the most proximal aspect of the wire at the coronet where the last hairs leave the skin parallel to the horn tubules. Wires Located where Ungual Cartilage Meets Coronary Band RADIOGRAPHIC TECHNIQUE, LATERAL VIEW To appreciate bone position when weight bearing, horses are stood on blocks simultaneously with limbs equally weighted, either both front limbs or hind limbs. The blocks are of a height so the x-ray beam intersects 3/8 - 5/8 inch distal to coronary band when the x-ray machine is sitting on the ground, two and one-half inches for our machine. Blocks measuring seven inches long and six inches wide give good surface area for support of the foot yet are not too bulky. A metal wire is imbedded into the block along the long side of the block through the center of the block. The foot to be radiographed is placed at the edge of the block, so to assure that the cassette touches the hoof capsule. The limb is placed so MC III or MT III is perpendicular to the ground as evaluated with a level placed at mid-MCIII or MTIII. The focal field distance is important and needs to be consistent because measurements from the radiograph are transferred directly to the solar aspect of the foot. Knowing the focal/field distance for the machine used that will not get magnification for is also critical. To learn the focal/field distance that will not have any magnification for your machine the following simple procedure can be used. Imbed two penny nails, 2 inches apart into the block the foot is placed upon for radiography. Assure the cassette touchs the hoof. Radiograph the foot and measure the distance between the penny nails on the radiograph. If the distance measured on the radiograph equals the distance measured between the nails on the block, that focal/field distance does not have any magnification. We use a Min-Ray machine, 100 KvP, with a focal/field distance of 28 inches from the tape measure to the cassette. In taking the radiograph, angle the x-ray machine so the x-ray beam is parallel to both heel bulbs so that the wings of PIII are superimposed. To facilitate this, we use an extendable/retractable pointer held along the side of the x-ray machine that extends to the heel bulbs. The center of the x-ray beam is positioned about ½ inch below the coronary band, 2 ½ to 3 inches dorsal to the heel bulbs. This position will center the beam over the navicular bone and intersection. The film/cassette combination we have found to have the most detail and practicality is the 3- M ultra-detail plus film in 3-M Veterinary EQ 2/6 rare earth screens or Kodak Lanex Regular screens. This film/screen combination gives us the contrast to visualize the thumbtack through the clip of a shoe. Our distance is 28 inches, KVP is 64, time is .06 seconds. SUMMARY OF RADIOGRAPHIC TECHNIQUE 1. Thumb tack in true apex 2. Both limbs on blocks 3. Set limbs perpendicular to ground 4. Cassette touching medial hoof wall 5. Dorsal wire placed 6. Focal/field distance measured 7. Pointer to bisset heel bulbs 8. Center of beam at 2.5 inches dorsal to heel bulbs RADIOGRAPHIC TECHNIQUE, DORSAL/PALMER VIEW The radiograph is taken from a dorsal/palmer direction with the x-ray beam perpendicular to the fetlock. Exposures KVP increases by 4-6 and time by .02 seconds. ASSESSMENT OF POSITION OF PIII AND NB FROM RADIOGRAPH Once the radiograph has been taken with the above technique, the radiograph can be used to locate where to place the shoe so the shoe, a supporting structure, is under the bony column, the supporting tissue of the body. To make this application, place the radiograph on a viewing screen and draw a line on the radiograph perpendicular to the ground touching the tip of the coffin bone. Measure ¼ inch, (.6 cm) dorsal to this line and draw a second line parallel to the first. The location where the second line, the most dorsal line, meets the sole is the location of breakover. Distance from Thumbtack to Most Dorsal Line at Toe is Transfered to Sole Breakover is defined as the last part of the foot to leave the ground. This is not the location where the shoe ends. The shoe ends dorsal to this line. Tip of Coffin Bone Breakover in Shoe End of Shoe For horses weighing over 1150 pounds, the breakover distance used is ½ inch dorsal from the tip of PIII. For ponies under 700 pounds, a shorter distance is used. In the hind feet, these distances are decreased by 1/8 inch. Using the radiograph, the dorsal/palmer(plantar) position of PIII relative to the hoof capsule can be measured. To do this, draw a third line, perpendicular to the ground where the breakover of the hoof capsule meets the ground. The distance from this third line to the second line gives a measurement of the dorsal position of the hoof capsule relative to PIII. A) Distance from Thumbtack to Most Dorsal Aspect of Hoof Capsule is Dorsal/Palmer Position of PIII Variations in the dorsal position of the hoof capsule have varied from at the tip of PIII to 2.5 inches dorsal to the tip of PIII. To use the radiograph for therapeutic shoeing purposes, measure the distance from the second line to the thumb tack. On the solar surface of the foot, use this same measurement starting from where the thumb tack was placed, at the true apex of the frog, and measuring dorsally toward the toe the same distance as measured on the radiograph. This location on the solar surface is where the breakover or roll in the shoe is located. A) Breakover Distance Measured on Radiograph is Transfered to Sole A) Location of Breakover B) Location of End of Shoe It has been scientifically shown that this method will help align the phalangeal bones to each other and move the navicular bone proximally. (Page, Eq Vet Sc, accepted, 2000, AAEP 1999) Change in angle between PI and PIII 5 minutes after trimming with breakover ¼ inch dorsal to tip of PIII. PROXIMAL/DISTAL MEASUREMENTS FROM THE RADIOGRAPHS On the radiograph, draw a horizontal line at the level of the wire. Draw a second horizontal line, at the most proximal aspect of the extensor process. The distance between these two lines is measured and termed: distal descent of PIII. Dorsal Aspect of Wire vs. Dorsal Aspect of Extensor Process Values on horses negative to palmer digital block and clinically sound varies between 1/8 inch to ½ inch. Measurements on horses which are lame in tight circles similar to laminitic horses have measurements between 5/8 and as much as 7/8 inch. Some trends which are noticed are often less distal descent in the club foot as opposed to the non-club on the same horse, and greater descent on more massive horses. The amount of distal descent gives us an evaluation of strain to the laminae as well as need for support under the bony column. MEDIAL/LATERAL APPLICATION FROM RADIOGRAPHS Evaluation of the radiograph is done by drawing a horizontal line at the proximal border of each wire. Comparing the lines to the second phalanx will demonstrate medial/lateral imbalance. We find no detectable lameness if there is 1/8 inch disparity or less between the two lines. Dorsal Aspect of Medial and Lateral Wires Compared If you have questions or would like more information on these techniques, you may contact Dr. Page via e-mail: cecpc@aol.com

End Notes   1  Page BT, Bowker RM, Ovnicek G, Hagen T. How to mark the hoof for radiography. Proceedings, 45th Ann. Convention AAEP, 1999