CERVICAL SPINE INJURIES (A) (A) Traction F F Torso (B)

Torso

N (B) Compression

N

Figure 4: The ‘escape direction’ for the cervical spine by movement of the head. A) Diagram showing head impact posterior to the head vertex and B) anterior to the head vertex showing that in impacts posterior to the vertex, part of the head velocity, the impact surface force, and the neck force all act to push the head into flexion and forward translation. In contrast, impacts that are more perpendicular to the spine (B) are less able to move out of the way because the head velocity, impact surface and neck force are less well aligned. Reproduced from Winklestein B and Myers B, 1997 (9)

Figure 3: Cervical spine and brachial plexus injuries (reproduced from Torg J and Ramsey-Emrhein 1997 (19))

injury to the brachial plexus. These trac- tion injuries occur as a result of shoulder depression and lateral flexion of the neck away from the injured side (Fig.3) (also see ‘Rehabilitation of brachial plexus injury’ on p13).

In rugby union this position is adopted as a player attempts to make a tackle. He grasps the opponent by closing both arms around his body. In this process he later- ally flexes his cervical spine to one side to prevent injury to the head.

Mechanisms of injury Certain sports have particular activities within the game which may lead to a high incidence of cervical spine injury. However for the purposes of this article we have concentrated on rugby. In rugby union the scrum and the tackle have been identified as activities which may lead to serious neck injury.

The scrum During engagement of the front row, play- ers may be injured during the initial con- tact phase, or if the scrum itself collaps- es. This may result in a hyperextension of the neck or a flexion-rotation injury with compression (2,3). Forces generated in the scrum can be quite considerable and consist of a combination of lateral, hori- zontal and vertical forces (4).

Milburn’s study (4) has shown that part of the force on individuals in the front row of the scrum is due to speed of engagement of the scrum rather than the number of players involved. Similarly the ‘hooker’ in the front row is more vulnerable to cervi- cal spine injury due to excessive loading of his spine during the scrum. Scher (2) found that on radiographic review players sustaining tetraplegia did so as a result of bilateral or unilateral locking of the zygo- apophyseal joints (synovial joints between the superior and inferior articular processes of adjacent vertebrae).

Biomechanists have explained that cervical spine injury is caused by the result of the ‘major injuring vector’ (Fig. 4) (5,6,7,8).

Similarly bending moments can arise from the resultant force acting in a perpendicu- lar distance from the spine. This is termed ‘eccentricity’ (9). The relationship and the effect of eccentricity on injury mechanism can be seen in figures 5 and 6.

Thus alteration in ‘eccentricity ‘ leads to a different injury sequence (9):

i) If compressive forces act behind the vertebral body, posterior element fracture occurs (Fig.6a)

Figure 5: Eccentricity in the cervical spine and its effect on injury (9)

ii) If the force acts through the middle of the vertebral body compression fractures occur (Fig.6c)

iii) If eccentricity is increased further anteriorally, burst fractures, wedge com- pression fractures and facet dislocations may occur (Figs.6d,e,f)

During engagement and ‘in-pushing’ in scrums, front row players often alter their neck position to either get more comfort- able or place pressure on their opponent.

This drastically alters the eccentricity of the cervical spine with the potential for serious consequences.

(a)

(b)

(c)

(d)

(e)

(f)

Figure 6: Relationship between the location of the resultant force, F, and the type of injury produced SportEX 11