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Seeing the World Normal Again: an investigation into joint positional error.

What if everything that you saw with your eyes: every detail, every color every interpretation…was slightly wrong!?!  What if everything was the same shade of grey?  Or maybe just endless overlaps of grey? Everything seems perfectly normal from the outside, maybe through modification or adaptation, or even acceptance and avoidance. Well that might be exactly what is happening in the brain of some of your patients or clients!  And without the proper knowledge and resources, it may go unnoticed and untreated.

This blog is intended to help define and understand what joint position sense is (specifically at the cervical spine), how it might present in different conditions, and what the available resources are to help diagnose and treat it.

So let’s start with some definitions. 

What is proprioception and Joint Position Sense?

Proprioception can be defined as the unconscious perception of movement and spatial orientation arising from stimuli within the body itself in space.  An unconscious understanding of where body parts are, how they orient, and awareness of changes in location, whether large or small.  Several feedback mechanism act both together and independent of themselves to help give information to the central nervous system to enhance and maximize our body’s proprioception.  With regards to the head and neck area, there is a high density of muscle spindles in the small intrinsic musculature.  As a result, the neck musculature has an important role to play in postural control. An expansive number of experimental studies have demonstrated reduced postural control following neck muscle vibration or fatigue, and even ataxia following injection of local anaesthetic into the cervical tissues.  The dense network of mechanoreceptors in the soft tissues in this region not only controls multiple degrees of freedom of movements about each of its joints but, more importantly, gives the CNS information about the orientation of the head with respect to the rest of the body via direct neurophysiological connections to the vestibular and visual systems. Somatosensory information from the cervical region is the only region that has this direct access to the sense of balance and sense of sight.  There are extensive anatomical connections between neck proprioceptive inputs and vestibular inputs. If positional information from the vestibular system is inaccurate or fails to be appropriately integrated in the CNS, errors in head position may occur, resulting in an inaccurate reference for HNPS, and conversely if neck proprioceptive information is inaccurate, then control of head position may be affected.

To complement the muscle spindle feedback in position sense, the postural control system includes all the sensorimotor and musculoskeletal components involved in the control of two important behavioral goals: postural orientation and postural equilibrium. Postural orientation is the relative positioning of the body segments with respect to each other and to the environment, whereas postural equilibrium is the state in which all the forces acting on the body tend to keep the body in a desired position and orientation (static equilibrium) or to move in a controlled way (dynamic equilibrium). Postural control provides a stable body platform for the efficient execution of focal or goal-directed movements. The somatosensory, vestibular, and visual systems are the subsystems that provide sensory input to the postural control system.

Another subsystem, the Somatosensory Subsystem encompasses all of the mechanoreceptive information arising from the periphery which lead to the perception of pain, temperature, touch, and proprioception. The proprioceptive system of the cervical spine, in particular, is extremely well developed, as reflected by an abundance of mechanoreceptors, especially from the muscle spindles in the deep segmental upper cervical muscles. The muscle spindle system serves as the final common pathway for the regulation of the muscle stiffness required for various neuromuscular performances. Muscle spindle afferents appear particularly important, as they play the first violin in the proprioceptive ensemble, while other mechanoreceptors, such as the joint receptors and golgi tendon organs, fine tune the muscle spindle information, predominantly by reflex effects on the motoneurons.

The combined inputs from these systems give us our proprioception. And disturbances to the afferent input from the cervical region may be a possible cause of symptoms such as dizziness, unsteadiness, and visual disturbances, as well as signs of altered postural stability, cervical proprioception, and head and eye movement control.

How do we assess it?

Assessing sensorimotor impairment involves the assessment of proprioception – or joint position error (JPE) as it is termed in the neck – the assessment of oculomotor control and the assessment of postural stability. Research has demonstrated impaired control of the head and neck, altered eye movements and reduced postural control in both neck pain patients and whiplash injured patients. Proprioception is most easily assessed in the clinic using a laser attached to the head of the patient. The patient performs a physiological movement such as left cervical rotation with their eyes closed and attempts to return to the starting position – the neutral head position. This difference can be measured in centimeters to describe the joint position error. Postural stability in standing is very easily assessed in the clinic. A battery of balance tests from comfortable to narrow to tandem stances with eyes open and eyes closed should be included in the assessment of all neck pain patients. For the higher performing patient moving on to one leg stance and unstable surfaces would also be important. The cervical JPET tests one’s ability to relocate the head back to center after maximal or submaximal rotation in the transverse and sagittal planes. Per Treleaven’s research, clinical assessment cervical position sense can be assessed by using a laser pointer mounted onto a lightweight headband. Patients are asked to focus on the natural resting head position for a few seconds, sitting 90 cm away from a wall. With the eyes closed, they actively move the head and then try to come back to the resting position as accurately as possible. The difference between the starting and resting position of the laser beam on the wall can be measured in centimeters and then converted into degrees (angle = tan-1[error distance/90 cm]). Thus an approximately 7.1-cm error distance would translate to a meaningful error of 4.5° (as long as the subject is sitting 90 cm from the wall) and is called the joint position error (JPE). JPE can be assessed on return from all active cervical movements. Errors of greater than 4.5° are thought to suggest impairment in relocation accuracy of the head-neck. Patients might also demonstrate jerky or altered movement patterns, overshooting of the position in order to gain more proprioceptive feedback for the task, or “searching” for the position. Occasionally patients will also experience a reproduction of dizziness and/or unsteadiness with the task. 

Principles of motor control that address sensorimotor deficits in a more specific manner may be important for patients with complicated musculoskeletal problems. Coordination of movements is a core term in motor control and can be defined as the sensorimotor processes that organize and activate large and small muscles with the optimal amount of force in the most efficient sequence.

Cervical joint position sense can be retrained using a laser pointer mounted onto a headband with the light projected onto a wall, as described in the section on assessment. Patients practice relocating the head to a neutral position (guided by the laser beam) from their most difficult movement directions (for example, rotation to the right or following neck extension). This can then be performed with the eyes closed, using the laser for feedback with the eyes open on completion of the task. The task can be progressed by asking the patient to relocate the head position to different points throughout the range of motion (eg, left rotation 20°, 40°, and 60°) rather than the neutral head position. Performing these activities in more challenging standing positions can also be used as a progression for the exercises.

Cervical movement sense can be improved by moving the head, thus moving the laser, to trace patterns placed on a wall such as a figure-of-eight pattern. Patients can practice performing the task as accurately as possible, keeping the laser on the lines of the pattern. In both exercises accuracy should be encouraged at the outset; but once this has been established, the patient can attempt to perform the activities as quickly and as accurately as possible.

What’s the risk in not assessing cervical JPE?

The training of neck position sense is aimed at better perception of body posture, dissociation between body parts, and better awareness of the body's position in space, especially improvement of the patients' awareness of the head-neck and shoulder girdle posture, and is dependent on proprioceptive, visual, auditory, and vestibular cues.

Less accurate and less consistent repositioning performances were observed in fatigue relative to No fatigue condition, as indicated by increased absolute and variable errors, respectively. These results evidence that cervical joint position sense, is degraded by muscular fatigue. These observations are consistent with the existing literature reporting degraded proprioceptive acuity following muscle fatigue induced at the ankle,

As cervical joint position sense is considered to be predominantly signaled by muscle spindles, the effect of muscular fatigue on the muscle spindle system could provide a plausible neuro-physiological mechanism of the adverse effects of muscle fatigue on cervical joint position sense reported in the present study. This hypothesis is supported by evidences from previous animal studies of a modification of the discharge patterns of muscle spindles with muscle fatigue. Therefore, clinical implication stems from the concomitant observations of a reduced neck muscles strength and endurance capacity in patients with neck pain disorder would likely demonstrate impaired cervical proprioception and potential early global fatigue compared not normal. What we do know is the degraded cervical joint position sense observed with fatigue could contribute to the deleterious effects of cervical muscular fatigue on postural control during quiet standing as recently reported in the literature.

Another altered proprioceptive systems include gait. Martini (Archives of Phys Med 2011) described that concussed individuals displayed with significant differences in medial-lateral Centre of Mass displacement and displacement velocity were noted as well as the concussed group moved less and at slower speeds during testing and this conservative gait strategy appeared to remain in subsequent years.  This may present as impaired motor planning, a possible effect of impaired body awareness or normalization and is suggestive that post-concussive individuals may have alterations in body awareness and brain function that could persist for years and have the potential to influence work and health status and quality of life. This strikes the question of “Are we seeing the World after normal after certain injuries?”.  Or have we simply done what the human body is so good at?  Have we just adapted the way we see and feel to make a new normal? And what might be even more compounding is the trend of first line physicians in the U.S. to have the concussed patient simply rest until magnified symptoms resolve. Or worse yet, have standardized or computerized tests, without implementation by a trained rehab professional, dictate when an individual is ready to return to sport or work duties.  Recently in the AJSM, Brooks et al. in 2016 suggest that it is unclear if standard clinical tests have the sensitivity to detect subtle deficits in neurocognitive function.  And that changes in both neurocognitive and proprioceptive function may be a possible explanation for increased risk of injury after return to sports.  They found that concussed athletes have increased odds of sustaining an acute lower extremity musculoskeletal injury after return to play compared to non-concussed individuals.

And if the rested individual is able allowed to return to function without full examination, with mild symptoms of neck pain, this is what we know. Clinical Presentation Patients with neck pain seem to have a poor awareness of their head-neck posture, and some indeed complain about “a wobbling head,” which may be resultant of impaired cervical position sense.  Specific to the neck and head, several studies have documented the alterations in cervical Joint Position Sense after whiplash and with neck pain. De Vries et al in Manual Therapy in 2015 found that JPS error is generally higher in the neck pain population that in a control group of similar size.   And that JPS error was velocity dependent.  At higher motion speeds, more JPS error was noted as well as a correlation intensity of neck pain and presence of JPS error.  And we are potentially send these individuals back to sport or full function and work duties?  It is my strong opinion that we must properly assess JPE before we discharge and return to pre-morbid functional levels. Especially when Clinical Research Relocation tests that either relocate the natural head posture or the head to a set point in range have most commonly been used to verify poor awareness of the head-neck region in patients with neck pain to reflect impaired cervical position sense. These methods address a patient's ability to consciously indicate when a pre-specified position has been reproduced. Impairments have been demonstrated by these methods in subjects with neck pain of both idiopathic and traumatic origin (ie, whiplash injury).

Even if we do rehabilitate to the best of our ability and resources, we can’t ensure re-injury won’t occur.  For example, Nordstrom in 2014 found that footballers who sustained a concussion were more prone to injury that the rest of their teammates.  And this persisted for 1 year suggesting the presence of residual effects from the initial analysis.  The rehab protocols for testing JPE were not mentioned in this case however.

In other injury populations, the relationship between neurocognitive function and injury may be established.  Swanik, (AJSM 2007) found decreased reaction times, processing speeds, and visual-spacial disorientation may expose athletes to injury prone situations.  Perhaps testing normal, but still “seeing the World differently”, may lead to difficulty with interpreting and negotiating information when challenged with unanticipated events; momentarily leading to alterations of proper motor programming or typical muscle activity, effectively diminishing the dynamic restraint capabilities…commonly referred to as decreased/loss of situational awareness.  This might be taking some leaps to connect the dots…but if we aren’t properly testing for JPE then we cannot rule this connection out.

Nordstrom also found that a laser method for assessing JPSE had good test-retest reliability and a strong correlation with an ultrasound technique for measuring JSPE.  However, most outpatient clinic settings are not likely to have a reliable piece of laser equipment that can be used to properly and accurately test for JPS error. 

The Motion Guidance large strap and perpendicular mount can be used to assess "JPE"

The Motion Guidance large strap and perpendicular mount can be used to assess "JPE"

So if we can’t test for cervical JPS, then we aren’t directly treating it either.  And if we aren’t directly assessing or treating it, then we as rehabilitation specialists have to concede that it may go unnoticed and therefore be a potential and plausible outlier of increased risk of any future injury to that individual.  This is one reason why I prefer the Motion Guidance visual feedback system. This system allows any practitioner to turn their clinical setting into a immediate testing and training ground for multiple body parts including cervical JPS.  The system has a highly durable, two sided flag that has 2 targets standardized to Jull and Treleaven’s research.  One smaller target calibrated at 90 cm.  And a larger, multi-colored target calibrated at ~152 cm.  Another unique aspect of the MG device is found in that the mounting strap can be placed over the eyes of the patient to prevent the subject from attempting to use extra visual feedback to more accurately pass a JPS test.

Whatever you decide to your use your clinic, please….just decide….to actually use it!

Eric M. Dinkins, PT, MS, OCS, Cert MT. MCTA

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References

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