Coordination and proprioception of the knee joint - validity and reliability of the Mr Cube measurement system

Research has shown that injuries and disorders of the knee - such as rupture of
the anterior cruciate ligament (ACL), patellar tendinopathy, and osteoarthritis
(OA) of the knee joint - result in serious impairments of physical functioning.
Next to the restoration and maintenance of biomechanical variables such as
joint motion and muscle strength, enhancement of neuromotor control is
considered an important component of the rehabilitation following injuries and
disorders of the knee. Neuromotor control is commonly referred to as the
ability to produce controlled movement through coordinated muscle activity,
i.e. coordination. Neuromotor control results from a complex interaction
between the somatosensory system and the musculoskeletal system. In a very
basic model, the neuromotor control system consists of 3 components: sensory
organs, neural pathways, and muscles.
Knee joint proprioception is essential to neuromotor control of the
knee joint. At present, proprioception can be defined as the cumulative neural
input to the central nervous system for specialised nerve endings called
mechanoreceptors. Proprioceptive afferent information from mechanoreceptors in
the muscles, ligaments, capsule, menisci, and skin contribute at the spinal
level to arthrokinetic and muscular reflexes which play a large part in dynamic
joint stability. It has been shown that a rupture of the ACL results in
decrease in afferent proprioceptive signals from mechanoreceptors in the ACL.
Impaired knee joint proprioception has also been established in patients with
knee osteoarthritis and, although altered knee joint proprioception has not
been established yet in patients with patellar tendinopathy, there are strong
indications that this is the case in these patients.
To date, there are a few measurement systems used to assess
proprioception and coordination of the knee joint. Proprioception of the knee
joint can, for instance, be measured by means of the Prosys system. However,
the measurements with this system are relatively time-consuming and can only be
made in a research setting. Moreover, proprioception is measured at the level
of the impairment, not on a functional level. Numerous functional tests are
available with which proprioception and coordination in a more functional
setting that resembles daily activities or sporting activities can be assessed,
for example a hop test or a jumping test. However, a combination of
proprioception and coordination has to be used to perform these tests.
Recently, a commercially available training and rehabilitation tool,
the Mr Cube, has gained popularity in the rehabilitation setting. With this
system, neuromotor control, especially proprioception and coordination, can be
functionally and dynamically trained. Moreover, the Mr Cube software contains
an application with which the proprioception and coordination can be assessed.
However, this assessment application has not been used yet as an outcome
measurement tool for neuromotor control of the knee. However, before this
system can be used as such, its validity, reliability and discriminant ability
needs to be established. Therefore, the aim of this study is to investigate the
validity, test-retest reliability and discriminant ability of the Mr Cube
system to assess knee function in healthy persons, and in three patient groups:
patients following ACL-reconstruction, patients with patellar tendinopathy, and
patients with knee osteoarthritis.

Objective of this study is to determine validity, test-retest reliability and
discriminant ability of the Mr Cube system to assess coordination and
proprioception of the knee joint in patients following ACL reconstruction,
patients with patellar tendinopathy, in patients with knee osteoarthritis, and
in healthy subjects.

Validity, test-retest reliability and discriminant ability of the Mr Cube
system will be determined in healthy subjects and in three patient populations.
In that sense, the study design is a cohort study with four cohorts.

To assess concurrent validity of the Mr Cube, participants of the study will
perform several tests, next to the Mr Cube tests:
- Assessment of the threshold to detect passive motion (TDPM). With these
measurements the proprioception of the knee joint will be assessed on the
level of the impairment (i.e. an artificial anterior cruciate ligament,
tendinopathy of the quadriceps tendon, osteoarthritis).

- Assessment of physical function skills by means of functional jump and hop
tests (patients following ACL reconstruction and patients with patellar
tendinopathy), or the timed-up-and-go test (patients with knee osteoarthritis).
With these functional tests a combination of proprioception, coordination and
muscle strength is measured.

- Subjective assessment of physical functioning by means of questionnaires. The
scores of the questionnaires will be used to determine whether there is a
relation between the score on the Mr Cube tests and the participant's opinion
of his/her physical functioning.

To determine test-retest reliability, the participants will perform the Mr Cube
tests for a second time, approximately one week following the first assessment.

Knowledge gained with this study can improve treatment and rehabilitation of
ACL reconstruction, patellar tendinopathy and knee osteoarthritis. The risks
involved with the measurements are negligible, since the measurements made in
this study are comparable to physical exercises that are performed during
physical therapy for rehabilitation of an ACL reconstruction, patellar
tendinopathy or knee osteoarthritis.