|The anterior cruciate ligament (AGL) is an intra-articular element
structure of paramount importance for normal knee movement since
it secures simultaneously static and dynamic stability .
|Dynamic stability is supported by the presence of specific
ligament mechanoreceptors which are proved to be an essential
element for proprioception as it has been revealed by a few anatomical
and histological studies [2-10].
|The existence of mechanoreceptors and their potential role in
knee function has been discussed for over a century. However only
recently in 1984 their existence was proved on the human ACL after
the identification in the ligament of type III (according to Freeman
and Wyke) and free endings receptors .
|Afterwards more detailed studies identified three types of
mechanoreceptors by different morphologic characteristics: two types
of Ruffini end organs, Paccinian corpuscles and a smaller number of
free nerve endings. In this study was reported that neural elements
comprise about 1% of the area of the ligament .
|Even though the definition of proprioception has been attempted
many years ago, there still is no widely accepted definition. Sherrington
introduced this term in the literature who thus described the result
of afferent nerve impulses from muscles, tendons, joints and relevant
tissues. The processing of the input results in controlling reflexes and
muscle control .
|This description defines proprioceptive sensation primarily as a
sensory process. Recently the meaning of the term proprioception
has been extended and also includes the interaction of afferent and
efferent pathways of the somatosensory system .
|Most authors refer to two types of proprioceptive sensation for
clinical reasons. Static proprioception is defined as joint position
sense that is the direction of limbs in space and the perception of
their interrelationship. Dynamic proprioception or else kinesthesia
includes the sense of limb movement and speed changes, acceleration
or deceleration .
|Those two elements of proprioception should be accompanied by
the last but not least important element of proprioceptive sensation of
force/tension, occurring during muscle contraction [12,14].
|Injury to joint structures such as ACL the menisci and following
osteoarthritic changes are combined with mechanoreceptor damage.
The following damage of afferent pathways and CNS transmission of
information results in disturbing joint position sense and kinesthesia
. Reduced proprioceptive sensivity is recorded apart from ACL
damage, with aging [16-20] while impaired joint position sense is
recorded as a result of osteoarthritic changes in the knee [19,21,22].
|Sensory proprioception following ACL tear has been studied in
detail. The reproduction of the predetermined angle (JPS) and the
threshold to detection of passive motion (TTDPM) are the most
commonly used sensorimotor system measurement techniques 
|Two other methods of assessment of neuromuscular control is the
reflex hamstring contraction latency (RHCL) , and the assessment
of postural control .
|Most studies report a reduction in proprioceptive sensation
following injury and ACL insufficiency [26-32] while the opposite
opinion has gained limited support [33-35]. During the acute phase
of ligament injury, it is not clear if joint inflammation and oedema
contribute in proprioceptive deficit . Still, those parameters are
considered not to be related to static and dynamic proprioception
reduction which is evident in chronic ACL insufficiency .
|As sensory receptors are presented not only in the anterior
cruciate ligament but also in the skin, muscles, tendons and the other
tissues surrounding the knee [14,38-42], the damage ensued in the
sensimotor system by the injured ligament may also represent an
afferent pathway damage that results in a decrease of neuromuscular
control and dynamic joint stability.
|In that case afferent pathway damage or reflex action on muscle
spindles results in a decrease in neuromuscular control and dynamic
|Thus the proprioceptive deficit of a knee with ruptured or non
functional ACL is probably not only the result of the loss of ligamentous
mechanoreceptors and the subsequent loss of proprioceptive feedback
 but also the consequence of the abnormal neurologic output from
the capsule and the remaining ligaments .
|The Anterior Cruciate Ligament is not only a primary restraint to
anterior tibial translation but is also an important dynamic stabilizer
of the knee joint as well.
|However ACL contribution to the knee proprioception has not
yet been totally clarified. Further laboratory and clinical research is
required, so that a better understanding of this complex mechanism
can be reached.
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