EXERCISES
TO ENHANCE PROPRIOCEPTION
Darryl L. Millis, MS, DVM, Diplomate ACVS,
CCRP
Professor of Orthopedic Surgery
There
are many conditions that affect proprioception of small animals. The most obvious of these are neurologic
conditions. However, recent evidence
suggests that musculoskeletal conditions and injuries also affect
proprioception, especially of joints.
This paper will discuss current knowledge regarding proprioception and
exercises to enhance proprioceptive function.
The Science of Proprioception
The
proprioceptive system is responsible for detecting changes in the position of
the trunk, limbs, and head. The system
is distributed widely throughout all of the spinal nerves, and general
proprioception receptors are located in the muscles, tendons, and joints deep
to the surface of the body. The
receptors respond to changes in the length and position of the structures where
they are located. The postural control
system consists of three functional components, including biomechanical, motor
coordination, and sensory organization components.
Joint Proprioception
Ruffini
and Pacinian receptors have been identified in canine cruciate ligaments, and
are innervated by axons penetrating from the
peripheral synovium surrounding the ligament.
The proximal third of the ligament contains a greater number of
receptors. Because the cranial cruciate
ligament is capable of afferent input to the central nervous system, it is
important to the biomechanical and proprioceptive functions of the stifle
joint, including characteristics of movements and position-related stretches of
these ligaments. The effects of the
gamma-muscle-spindle system in the muscles around the knee are so potent that
stretches of the cruciate ligaments at relatively moderate loads may induce
major changes in responses of the muscle spindle afferents. These events may help regulate the muscular
stiffness around the knee joint. Thus,
the sensory system of the cruciate ligaments is able to significantly affect
functional stability of the knee joint.
Mechanoreceptors
have been studied in torn and reconstructed anterior cruciate ligaments in
animals and humans. In untreated anterior
cruciate ligament lesions in humans, normal mechanoreceptors remain in the
ligament 3 months after injury. Their
number then gradually decreases, and by the 9th month, few free nerve endings
are present.
The
correlation between the number of mechanoreceptors in ACL remnants and joint
position sense just before an ACL reconstruction in human patients has been
studied. A positive correlation between
the number of mechanoreceptors and accuracy of the joint position sense was
found, suggesting that proprioceptive function of the ACL is related to the
number of mechanoreceptors. Therefore, we should consider preserving ACL
remnants during ACL reconstruction.
Proprioception
declines with increasing age.
Proprioception is further impaired in elderly patients with knee
OA. Poor proprioception may contribute
to functional impairment in knee OA.
Arthritic
patients receiving physical therapy have improved joint position sense. It has been suggested that to improve
functional performance, patients with knee OA should undergo a carefully
constructed sensorimotor rehabilitation program in which pain, effusion and
fatigue are minimized.
Studies
have been performed in humans to test position sense of the knee joint before
and after fatigue. Muscle receptors
appear to be a primary determinant of joint position sense, and capsular
receptors may have a secondary role. The
data suggest that a change in the mechanism of appreciation of joint position
occurs after fatigue, possibly due to increased sensitivity of capsular
receptors from muscle-fatigue-induced laxity.
Appreciation of joint position was also found to be significantly more
sensitive after warm up. Therefore,
adequate warm-up prior to activity may be beneficial.
Conversely,
to test whether or not cryotherapy affects position sense of the knee, a cooling pad was
applied to knees of humans. Cooling for
15 minutes resulted in increased knee joint stiffness and decreased sensitivity
of the position sense. These findings should be considered in therapeutic programs
that involve exercise immediately after a period of cooling.
Although
infusion of saline to simulate acute joint effusion did not change the
subjects' proprioceptive ability, the effects of long-term effusions and the
nature of the inflammatory fluid may be responsible for the seeming loss of
proprioception observed in some clinical conditions with chronic joint
effusion. An elastic bandage placed on
the knee has a positive effect on joint proprioception, and may be recommended
in those patients with joint proprioception problems.
Neurological Conditions
There
are many approaches to physiotherapy following stroke injury in people. Supported treadmill training of people with a
stroke appears to have beneficial effects on proprioceptive function. A 4-week period of body weight support
treadmill training with up to 40% of their body weight supported resulted in
significantly improved clinical outcomes, including functional balance, motor
recovery, overground walking speed, and overground walking endurance. The supported group continued to have
significantly higher scores 3 months after training. The subjects with greater gait impairments
benefitted the most from training with body-weight support.
Another
study evaluated the delayed effects of a balance training program compared with
no training on hemiplegic stroke patients. Dynamic balance function of patients
in the visual feedback training group had significant improvements when
compared with the control group.
Activities of daily living also had significant improvements at 6 months
of follow up in the trained group.
Another study of elderly humans indicated that a short individualized
exercise program improved functional balance.
This improvement was maintained for at least one month, but wore off by
one year, suggesting that continued training may be necessary.
Strength
training should also be considered as part of the rehabilitation program for
patients. One study of chronic human
stroke patients underwent a progressive resistance strength training program to
evaluate changes in muscle strength, gait, and balance. Subjects participated in a 12 week resistance
training program. Lower limb strength
improved 68% on the affected side.
Repeated chair stand time decreased 21%.
Motor performance improved 9%, and static and dynamic balance improved
12%. These results support the concept
that strength training is an appropriate intervention.
Proprioceptive Training
When an animal is able to stand (independently or with assistance),
activities to improve balance may begin.
Dynamic balance is the animal’s ability to maintain balance while the
body is moving. The following exercises may be performed to challenge the
animal’s dynamic balance. These exercises should be conducted on a nonslip
surface to reduce the risk of falling.
Weight-Shifting
While
the animal is standing, a treat or ball may be used to encourage
weight-shifting. The dog will follow the treat up and down and side to side.
Start with small movements and progress to larger, more challenging movements.
The movement of the head causes the dog’s center of gravity (COG) to shift. As
the COG shifts, the dog must shift its weight to maintain its balance.
The
handler may also disturb the animal’s balance by gently pushing the animal at
the hips or shoulder. The goal is to disturb its balance just enough so the
animal can recover, being careful not to push too hard. Some dogs become conditioned to this activity
and shift their weight toward the therapist to prevent being pushed toward the
affected side. In this case, a rebound weight shift may be effective, with the
therapist gently pushing the animal toward the affected side. When the animal
shifts its weight to resist, the therapist suddenly releases pressure, and
simultaneously pushes gently toward the unaffected side. This results in a
sudden unbalancing; the animal initially shifts its weight toward the
unaffected side, but to keep from falling, it shifts its weight back to the
affected side. Additional challenges may
be added by slowly moving a supporting towel back and forth to force the dog to
shift its weight.
Weight
shifts may also be performed during walking. As the animal is walked, the
handler gently bumps or pushes the animal to one side. Caution should be used
to avoid falls and injury.
Balance Board
A
platform may be used to rock the dog forward and backward, and side to side. A
human Biomechanical Ankle Platform System (BAPS) board may be used to help the
animal practice proprioceptive positioning on just the forelimbs or the
hindlimbs. If the goal is to have the animal exercise using all four limbs,
then a specially made platform must be used that accommodates quadrupeds. It is
important to provide support to allow the animal to shift its weight and
exercise its proprioceptive mechanism.
Standing or Walking on Foam
Rubber, Mattresses, Air Mattresses
Altering
the texture of the ground challenges the animal’s functional walking
proprioceptive ability. Standing or walking on foam-rubber mattresses, air
mattresses, and trampolines allows the animal to negotiate various surfaces.
Exercise Balls and Rolls
Therapeutic
exercise balls and rolls designed for human use may be employed to improve
balance, coordination, and strength. The forelimbs are placed on the ball and supported
by the handler, requiring the dog to maintain static balance of the caudal
trunk and rear limbs. Dynamic balance may also be challenged as the ball or
roll is slowly moved forward, backward, and side to side, challenging the rear
legs to maintain balance while movement occurs. To address the cranial trunk
and forelimbs, the rear limbs are placed over the ball as the forelimbs are
asked to balance the body weight during both stance and gentle movements.
Assisted Ambulation/Gait
Training
If
a dog is unable to walk independently, a sling, towel, harness, or canine
cart may be used to support the animal as needed. Encourage the dog to move
slowly, allowing time for the dog to advance the limbs as independently as
possible. It may be necessary to manually assist the dog in the sequencing and
placement of the limbs. The emphasis is on weight-bearing with each and every
step, encouraging a slow gait.