Deranged jawneck motor control in whiplash

European Journal of Oral Sciences, February, 2004; 112: 2532.
Per-Olof Eriksson, Hamayun Zafar, Birgitta Hggman-Henrikson

FROM ABSTRACT:
Recent findings of simultaneous and well coordinated headneck movements during single as well as rhythmic jaw openingclosing tasks has led to the conclusion that ³functional jaw movements² are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. It can therefore be assumed that disease or injury to any of these joint systems would disturb natural jaw function. To test this hypothesis, amplitudes, temporal coordination, and spatiotemporal consistency of concomitant mandibular and head-neck movements during single maximal jaw opening-closing tasks were analysed in 25 individuals suffering from whiplash-associated disorders (WAD) using optoelectronic movement recording technique.

Compared with healthy individuals, the WAD group showed smaller amplitudes, and changed temporal coordination between mandibular and head-neck movements.

These findings in the WAD group reflect a basic importance of linked control of the jaw and neck sensory-motor systems.

In conclusion, the present results suggest that neck injury is associated with deranged control of mandibular and headneck movements during jaw openingclosing tasks, and therefore might compromise natural jaw function.

THESE AUTHORS ALSO NOTE:
³Anatomical, biomechanical, neuroanatomical, neurophysiological and clinical studies indicate that the mandibular and the craniocervical regions are functionally linked.²

³Functional jaw movements are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints.² [IMPORTANT] ³Natural jaw activities require a healthy state of both the mandibular and
the headneck motor systems.² There is an association between temporomandibular disorders (TMD) and neckshoulder symptoms. There is also evidence that occlusal treatment, (the improvement of bite stability) can give relief of both TMD and neckshoulder symptoms.

There is a functional relationship between the jaw and the headneck motor systems.

Studies indicate that head-neck trauma can be an etiological factor behind TMD.

³Natural jaw actions require a healthy state not only of the temporomandibular joint but also of the atlanto-occipital and the cervical spine joints.²

DISCUSSION:
³This study demonstrates a number of signs of deranged control of mandibular and headneck movements during single jaw openingclosing tasks in individuals suffering from WAD.²

There is disturbed jawneck behavior in WAD during rhythmic jaw movements. It has been shown that normally, concomitant mandibular and head neck movements are elicited and synchronized by preprogrammed neural commands, in common for the jaw and the neck motor systems.

However, this study shows that there is a change in the setting of neural programs for the control of mandibular and headneck movements during jaw openingclosing tasks in the WAD group.

³From an evolutionary point of view, our previous and present findings in healthy and WAD individuals may reflect a high survival value of precise jaw
opening in the basic and vital jaw behaviors of feeding, attack and defense.²

³Dysfunction is characterized by reduced amplitude and speed of movement, impaired force production and endurance, and disturbed coordination of movements of body segments.²

³Pain has a significant role in the onset of the jawneck dysfunction demonstrated in the WAD group.²

These authors proposed that the pathophysiological mechanisms behind the genesis and perpetuation of WAD jaw muscle tension and pain are from the firing of chemosensitive afferents of the fusimotor muscle spindle system. This altered information transmitted by muscle spindle afferents would cause disturbance in proprioception, muscle stiffness regulation and motor coordination. [IMPORTANT] Increased muscle tension reduces circulation, which would in turn generate increased amounts of algogenic substances, creating more main and dysfunction. There is recent evidence of strong reflex connections from masseter muscle afferents to fusimotor neurons in the cervical spine (i.e. intersegmental nociceptive connections between the jaw and the neck).

³This observation corroborates earlier support for intersegmental nociceptive connections between the trigeminal and the cervical spine regions.²

Injections of an inflammatory irritant in the deep paraspinal tissues was found to result in an increased and sustained myoelectric activity of jaw and neck muscles. [This indicates that deep neck irritation to the cervical spine produces contraction of the jaw muscles, potentially causing TMJ dysfunction]

³In view of the extraordinary large size and complexity of the human jaw muscle spindles it can be speculated that the jawneck sensorymotor system is especially vulnerable to onset, spread, and perpetuation of pain and dysfunction.² ³These data imply an important role of the fusimotormuscle spindle system in pathophysiological mechanisms behind pain-related jaw and neck dysfunction and a tight integration between the jaw and neck sensory-motor systems in the onset, spread and perpetuation of jaw-neck pain and dysfunction.

CONCLUSION:
³Neck injury, leading to whiplash associated disorders, is associated with deranged control of mandibular and head-neck movements during jaw opening-closing tasks, and therefore might compromise natural jaw function.

KEY POINTS FROM DAN MURPHY:
1) Jaw movements are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints.
2) Therefore, injury to the neck would disturb natural jaw function.
3) Anatomical, biomechanical, neuroanatomical, neurophysiological and clinical studies indicate that the mandibular and the craniocervical regions are functionally linked.
4) Natural jaw activities require a healthy state of both the mandibular and the headneck motor systems.
5) Temporomandibular disorders (TMD) and neckshoulder symptoms are linked.
6) The improvement of bite stability can give relief of both TMD and neckshoulder symptoms.
7) Head-neck trauma can be an etiological factor behind TMD.
8) Natural jaw actions require a healthy state not only of the temporomandibular joint but also of the atlanto-occipital and the cervical spine joints.
9) These authors propose the following mechanism of neck-jaw dysfunction:
   A)) Pain fires the muscle spindle system.
   B)) Altered information from the muscle spindle afferents causes disturbance in proprioception, muscle stiffness regulation and motor coordination.
   C)) Disturbances in proprioception increased muscle tension.
   D)) Increased muscle tension reduces circulation, generating more inflammation, pain and dysfunction.
10) Inflammatory in the deep cervical paraspinal tissues produces contraction of the jaw muscles, potentially causing TMJ dysfunction.
11) Neck injury from whiplash is associated with deranged control of mandibular movements which compromise jaw function.

COMMENT FROM DAN MURPHY:
These authors are indicating that the pain in the jaw following whiplash injury is not primarily from direct trauma to the jaw. Rather, they are presenting evidence that supports that whiplash injures the cervical spine. Injury to the upper cervical spine causes a reflex to the muscle spindles of the jaw muscles, which are extensive. The jaw muscles contract, resulting in more dysfunction and pain. In short, they are using a neurological model rather than an orthopedic model for TMD following whiplash trauma.