Written February 2023 by R.F. (Ric) Redden, DVM
Farrier/Veterinarian Podiatrist
*Due to the number of images, this displays best on our mobile app
How do we understand what we see? We simply must consider the tremendous benefits of detecting and processing the smallest details. The information that passes from eye to brain travels along a pathway. When the path is cluttered with other areas of interest it fogs the image, obscures the details, and we may miss a lot and never realize it. When we are just looking but not observant or inquisitive, we see but it does not transfer into our memory bank.
When we look with purpose, it changes the game plan. The purpose emphasizes what we are looking for. There are several ways to assess a foot: visual, photos, radiographs, venograms and MRI. We look for the unique characteristics that are within the range of norm, or better said, the range of health. Or we look for what is wrong. Either way there is a certain level of knowledge required for us to determine the healthy range as it relates to the external characteristics and internal soft tissue parameters, bone shape, genetic variations, and pathology.
I often get the question, "What is a normal palmar angle (PA)?" and it makes me realize the journey ahead of that student has just begun.
Let us practice programming what we see with purpose.
Visualize angles relative to plumb. Draw a few with a protractor then draw without it.
Fig 2. Sketch each prominent feature of this foot and think about the internal arrangement relative to external clues.
What we see and what we really understand is two totally different perspectives. Tuning one’s eye to see 3D is the key to unraveling the mechanical formula.
Fig 3. Practice sketching in a methodical fashion. Farriers this is a great way to learn the radiographic message.
Fig 4. Radiopaque ground marker, paste on the wall, and calibration aid are valuable. Which DP image is flipped?
Fig 5.
Learn the landmarks. A dot of radiopaque paste on the tip of the frog and another at the skin/frog junction is an identical plane as the palmar rim and a valuable landmark for farriers.
Fig 6.
Lens angle perpendicular to the subject, 24 to 30 inches away from subject and
direct light on your back makes great photos, void of bird’s eye distortion.
Use this space to sketch the model.
Fig 7.
Sketch the bones separately then put them inside the silhouette.
Practice, practice, practice. We learn by repetition.
Fig 8.
Note the PA of this untrimmed foot is very similar to the
growth ring pattern and for good reason.
Fig 9.
Study and sketch each mechanical component.
Note the stark differences in the profiles.
Fig 10.
As you sketch the suspension components visualize the forces
at play that interact as antagonists. When one component is
injured, structurally weak or displaying excessive strength, how
does that effect the balance and harmony of the big picture?
Fig 11.
Sketch the components and get your head wrapped around the
stark difference in DDFT function. Toe angles are only 8 degrees
different. Not bad for a mismatched pair.
Fig 12.
The negative PA has wider growth rings in the toe than the heel. Everyday since the last reset the toe outgrows the heel. This cycle increases with the passing of time. The heel tubules are already folded under the hoof and the papillae are functional, but growth planes are grossly distorted. Toward the end of the reset cycle the toe growth accelerates and the heel continues to crush. A vicious cycle. Think about the imbalance of forces. Why does this occur?
Fig 13.
Sketch the unique characteristics. Always think about the cause and effect.
Very small variances in distance make up the cumulative characteristics that make all feet strikingly different inside as well as out.
Fig 14.
This cadaver foot has a Note perpendicular pastern, congenital joint slope
distinct coronary band and medial rim listing. This is natural imbalance
typical of sinkers. for this foot.
Fig 15.
Note the linear alignment. The pastern is pushed forward due to the increased DDFT tension in this Grade 2 club foot. Note the dorsal face of P3 profile. That is consistent with even the low grades.
Fig 16.
The fetlock joint consistently slopes proximal to distal and medial to lateral. The pastern joint as a rule will slope in the opposite plane and the palmar rim may also be in an identical plane. The radiographic joint spaces are affected by stance therefore we should strive to obtain a natural stance when taking the DP or PD views. Images that reveal the pastern perpendicular to the ground offer a relative accurate assessment of static balance. However, conformation variables can prevent us from obtaining this preferred criterion. Emphases in the past has focused on the palmar rim as a balance indicator. However, asymmetry of the P2 and P3 frequently occurs which changes the perspective of which is most important, rim balance or joint spacing? My podiatry experience has been convincing that static joint balance trumps rim balance and mass trumps balance.
Fig 17.
The needle reveals the location of the opaque margin that can be visualized on the lateral image relative to the d (DEJ). The DEJ is a valuable landmark for monitoring the slightest laminae alterations that occurs with acute laminitis. The club foot bone profile results in a wider L zone along the distal 1/3 of the dorsal face that can be misinterpreted as capsular rotation. Looking closely at the parallel orientation between the horn and dorsal face of the proximal L zone confirms that distal widening due to bone remodeling should not be defined as capsular rotation as rotation due to laminitis occurs along the entire length of the L zone.
Fig 18.
Sound, high level horse with This foot is a Gr. 2 plus club
Gr. 2 club foot with typical with chronic laminitis. Note
remodeling of the distal, the L zone deviates along its
dorsal face. entire length.
The more information we seek the more we find and greater becomes our arsenal of options. Use the space below to sketch the unique differences in the margins of the two above L zones.
Fig 19.
As we think about mechanics let’s put a little life into our thoughts. Visualize the boat crank being the deep flexor group. The DDF tendon is a mere extension of the muscle that transfers the force of contraction as well as the laxity or dysfunction of the muscle fibers.
Listen to the crank click click as it suspends the wings of P3 raising the PA. Flip the lever and the handle spins counter clockwise lowering the PA.
Fig 20.
Note that the HL zone is questionable without paste to mark the wall margin and prevents a relatively accurate assessment of the CE zone and does not reveal the growth ring pattern.
Fig 21.
Examples of negative PA without crushed heels. The rockered Full Rocker Shoe is an easy way to reestablish digital alignment, remain in full training, and minimize heel crush.
Fig 22.
Growth rings are about 30 days apart. This horse blew an abscess in early April. The photo on the right was taken 7 months later.
Fig 23.
Note the bone side of the deep flexor and nutrient supply to the coffin bone.
Fig 24.
The above navicular bones are examples of three different perspective views of the same bones. Lesions on the tendon surface are difficult to put in relief as they often occur in the mid to distal tendon surface. The tunnel block is advocated as a reliable positioning aid. However, when the primary beam strikes the detector at an angle less than or greater than 90 degrees the result is image distortion that increases as the angle deviates further from 90 degrees.