number of problems can arise in the horse’s foot as a result
of having too much tension on the deep digital flexor (DDF) tendon.
These include differences
in front feet appearance, clubbed feet, delamination of the hoof
wall (white line disease), navicular inflammation, and laminitis
many cases the cause of excessive DDF tension is unknown. Several
have been implicated, such as developmental orthopedic disease
(DOD), a difference in length between thoracic limbs, eating
(i.e. standing with one limb forward and the other back), pain
higher up in the affected limb(s), the horse being “right-”
versus “left-handed” (or vice-versa), genetics, and
rate of growth. Despite the actual cause(s), the consequences
of increased DDF tension are fairly consistent.
one thoracic limb demonstrates more DDF tension than the other.
This is usually evidenced by the horse having two
front feet (one more contracted than the other). In our experience,
the RF limb appears to be more affected 70% of the time.
In order to
understand the effects excessive DDF tendon tension has in the
foot, it is important to first understand the anatomy. The thoracic deep digital flexor tendon arises from the deep digital
flexor muscle. The DDF muscle has two portions, one attaching
on the ulna and the other (larger) attaching to the humerus. The
muscle courses along the backside of the radius, eventually giving
rise to the DDF tendon just above the carpus (knee).
DDF tendon courses behind the carpus, down along the back
(palmar aspect) of the cannon bone, around the back of
around the navicular bone in the back of the foot, and inserts
on the underside of the third phalanx (P3).
location, routing, and attachments of the DDF result in
two primary forces that affect structures within the foot.
across the navicular bone and
downward or rotational pull on P3.
consequences of increased deep digital flexor tendon in the
foot are a direct result of one or both of these forces.
Clubbed foot: A foot is “clubbed” if the heel has grown to
the point of breaking the distal limb axis forward, where the
angle of the foot is steeper than the angle of the pastern. Because
the tendon inserts on the underside of P3, increased tension will
pull or "rotate" the bone downward, eventually creating
a steep hoof angle, high/contracted heels, and potentially a broken-forward
axis. A broken-forward axis can in turn result in malarticulation
of the coffin joint and arthritis. This can occur in one or both
It is important
to realize that although one foot may be smaller, higher, and
con- tracted than the other it may not necessarily be “clubbed”.
A difference in foot angle, however, does suggest that the “steeper”
limb has more DDF tension than its contra- lateral counterpart.
A foot is not considered “clubbed” until the distal
limb axis is broken forward (A).
line" disease of the foot: Rotation of P3 downward can result
in separation of the sensitive and insensitive tissue along the
laminar interface of the hoof. This is called delamination. This
separation occurs slowly and is usually not associated with inflammation
and pain (laminitis). Dishing of the hoof wall generally confirms
that separation/ delamination has occurred.
Many owners treat this problem by infusing a combination of astringents,
antibiotics, and fungicides into the separated tissue in hopes
that they will eliminate the various infectious agents that frequently
invade this area. We should realize, however, that the primary
problem is not infection. Bacteria and fungi are everpresent!
The problem is the fact that they have an open space into which
to invade. Eliminating the delaminated (open) space effectively
eliminates the infection.
Navicular inflammation: The DDF tendon uses the navicular bone as a fulcrum as it courses
around the back of the foot. The anatomy is similar to the way
a pulley functions as a fulcrum for a rope. Increased tension
on the DDF tendon results in increased pressure across the navicular
bone and a greater chance of developing inflammation in this area.
Simply put, this is why horses develop “navicular disease”.
Laminitis: Since laminitis can result from both biomechanical and metabolic
processes within the laminae of the foot, increased tension/ distraction
along the laminar interface (via the tension on the DDF tendon)
increases the horse’s predisposition for developing laminitis
as well as his/ her chances of experiencing digital collapse (P3
rotation) once tissue weakening has occurred.
aforementioned problems can be directly linked to excessive tension
of the DDF tendon, it stands to reason that treatment strategies
should include techniques designed to reduce DDF tension. Less
DDF tension means less pressure across the navicular bone and
less rotational pull on P3.
the DDF tendon can be reduced by a) lengthening the tendon or
b) shortening the distance between the origin and insertion of
horses, treatment strategies
directed at "stretching" or lengthening
the DDF tendon and/or limiting the growth rate of
the associated bones may prove beneficial. These
Trimming as much heel as possible. This will INCREASE DDF
tension, but may also help to stretch t. This should not
be done if the horse develops lameness or if there is evidence
of hoof delamination (dishing). It should also not be attempted
in older horses, as it will usually worsen the problem(s).
of the DDF tendon muscle. "Loosening" the DDF
muscle will reduce DDF tendon tension. We recommend consulting
a massage therapist on effective ways to relax the DDF
energy intake. Some people associate increased DDF tension
with growth rate. If the bones grow faster than the tendons,
tendon tension may increase to an excessive level.
Proper diet. Flexural contracture of the DDF tendon,
one manifestation of developmental orthopedic disease
(DOD), has been associated with mineral imbalance (e.g.
Distal accessory (check) desmotomy. The
distal accessory or “check” ligament
is an extension of the palmar carpal ligament (on
the back of the carpus) that joins the DDF tendon
at the level of the mid cannon bone. By restricting
excessive movement of the DDF tendon through it
attachments, the distal accessory ligament functions
to keep the DDF tendon in “check”.
If excessive DDF tendon tension persists by the
time the horse reaches 8-10 months of age, then
surgical intervention in the form of distal accessory
(check) desmotomy is often elected. Cutting the
check ligament physically releases tension on the
DDF tendon, allowing it to “lengthen”.
18-24 months or age, the DDF tendon has lost most of
its pliability, and is generally not willing to “stretch” easily.
In older horses, therefore, treatment strategies are
usually directed at shortening the distance between
the origin and insertion of the tendon. This is typically
accomplished through corrective shoeing.
The two basic
ways that DDF tension is reduced through corrective shoeing is
Increasing heel length relative to toe length. This can be accomplished
by trimming more toe (from the solar or bottom surface) than heel.
However, since only so much toe is available for trimming, the
use of a wedged pad is often required. Elevating the heels results
in “dropping” of the fetlock. Consequently, tension
is transferred from the flexor tendons to the suspensory apparatus.
be noted, however, that there is a limit to the degree one
can elevate the heels. Excessive heel elevation can result
in malarticulation of the coffin joint, crushing of the heels,
and/ or excessive stress to the suspensory apparatus.
breakover of the foot. By moving the breakover point of the foot
backward (palmarad), the stride length of the limb is shortened.
Consequently, there is less degree of limb/ foot extension and
therefore less tension on the DDF tendon during movement. The
breakover point is moved backward by trimming toe and/or rolling
or rockering the shoe.
the shoe, the farrier rasps or grinds the corner of the shoe
where it meets the ground surface at the toe area.
The 90° angle at this corner is eliminated and is therefore
removed from the breakover process. When rockering the shoe, the
farrier elevates the front of the shoe off of the ground, usually
at about a 30° angle. The front corner of the shoe is completely
lifted off of the ground and is therefore not incorporated in
the breakover process. Rockering the shoe influences where along
the toe the foot will break over, so it is important to know the
foot’s normal breakover pattern.
used to facilitate breakover is generally determined by farrier
In cases of
a severe and/or life-threatening foot problem occurring as a result
of excessive DDF tension (i.e. laminitis), transection of the
tendon may be considered. Of course, cutting the tendon eliminates
its tension and therefore dramatically decreases the pressure
across the navicular bone as well as the downward pull on the
third phalanx. Consequently, this technique can quickly and effectively
alleviate clinical problems associated with excessive DDF tension.
However, since an intact DDF tendon is required for sound movement,
this approach is considered only for salvage purposes; return
to performance is not expected.
As previously stated, the original cause of excessive DDF tendon
may not be known or treatable. Therefore, DDF tension may continue
to increase over time, constantly challenging our efforts to alleviate
it. No treatment strategy can therefore be considered a permanent
If you have
any further questions or concerns regarding problems related to
excessive tension of the deep digital flexor tendon, don’t
hesitate to call the office and let us know.