Improving the Outcome after Tendon & Ligament
Injuries
- Article based on how our equines recover after they
injure a Tendon or Ligament
Improving the Outcome after Tendon and Ligament Injuries
Tendon and ligament injury in horses causes both economic and
personal hardship for horse owners and industry professionals.
A prolonged period of layup and rehabilitation is necessary,
but whether the horse will be sound at the end of the
rehabilitation period is uncertain. Lameness due to tendon and
ligament injury is common in performance horses, affecting up
to 25% of racehorses over a career and accounting for up to 43%
of injuries in event horses, but it is also common to companion
horses. Chronic lameness often follows the initial injury, with
recurrence as high as 80% of racehorses with tendinitis.
Tendons connect muscle to bone, providing elasticity and
increasing both gait efficiency and support to the lower limb
alignment. Ligaments connect bone to bone, giving structural
support for joints and maintaining suspension of the fetlock
joint as part of the suspensory apparatus in the horse. Tendon
and ligament injury can be classified into three categories:
traumatic laceration or rupture; acute inflammation with
swelling and pain (tendinitis); and a more subtle degenerative
injury due to a failure to heal due to repetitive damage.
The connective tissues from which tendons and ligaments are
made are closely related. The highly organized structure of
tendon enables it to be both strong and elastic. The cells
within tendon produce the extracellular matrix that is
organized into the fibers responsible for tendon's unique
mechanical properties. The tendon fibers are made of the
protein collagen (predominately type I). The collagen forms
long interlaced fibers in the same alignment with the tendon
length, but the fibers also have a pleated pattern termed
"crimp" that, like a spring, gives elasticity to the
tendon.
When a tendon is injured, tendon fibers are ruptured or
degraded by the inflammation. Attempts at healing frequently
fall short of the exact structure of normal tendon. Abnormal
orientation, size and organization of the collagen fibers that
replace the original structure have less strength and
elasticity. This is thought to increase the risk of re-injury
once the healing process is over.
Because of the large amount of tissue matrix, tendons, and
ligaments have a relatively small number of blood vessels and
cells that can make new normal tendon. When the tendon is
damaged, the injured fibers and matrix need to be degraded and
removed during the inflammatory process. It is thought that
poor healing in tendons results from a prolonged and
inefficient inflammation needed to remodel the tendon and
prevent scarring. Therefore, tendon requires as long as nine to
12 month for complete healing. Even with a careful
rehabilitation program, re-injury is common.
Both acute and chronic degenerative lesions in ligament occur
in all equine endeavors, with suspensory ligament injury
(desmitis) being the most common. Suspensory ligament desmitis
can cause a chronic lameness and be resistant to currently
available treatment modalities. Also, because current therapies
have not been compared to each other or proven, it is often
difficult to know which one gives the best chance for complete
healing.
Our understanding of how some degenerative and acute injuries
are related to each other is incomplete. The current thinking
is that a low level of damage or degeneration occurs in the
tendon or ligament over time. This damage is not completely
repaired and can go unnoticed, because there may be no
lameness, pain or swelling.
The failure to completely heal may be due to the inability of
tendons to remodel or because of the repetitive forces these
structures experienced regularly during exercise. Then, at a
critical point during exercise or overexertion, the low-grade
injury can no longer hold up to normal use or perhaps to an
overload, creating an acute lesion with heat, swelling and
lameness. This injury typically starts in the center or core of
the tendon (called a core lesion), where blood and serum form a
clot that replaces the tendon fibers and creates more
inflammation that results in more damage over the following
days or weeks.
While diagnosis of tendon and ligament injuries has improved
dramatically in recent years and new treatment modalities are
being used, a long lay-up period and the risk of recurrence are
still factors for recovery. Newer treatments such as injection
with stem cells or platelet-rich plasma are promising, but
their benefit has not been fully characterized and they may not
decrease the time required for healing and remodeling.
Further research into the detection, causes and best treatments
for tendon and ligament injury are all needed. In a survey of
American Association of Equine Practitioners members by the
AAEP Foundation in 2009, musculoskeletal disease was ranked No.
1 as the equine body system that needs further research.
Additionally, 75% of respondents believed more research is
needed to specifically help treat tendon and ligament injury.
Though there has been much attention given to arthritis
research, relatively little research has been directed toward
tendon and ligament injury.
The importance of tendon and ligament injury cannot be
understated; it can be responsible for the development of joint
disease and is frequently associated with navicular disease.
Research on tendon and ligament injuries will to help prevent
and treat this cause of lameness.
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