Chapter 10 The spine

General principles and anatomical features 238

1 The main concern in any spinal injury is less with the spine itself than with the closely related neurological elements (the spinal cord, issuing nerve roots and cauda equina).

2 If there is no neurological complication the chances of later neurological involvement must be assessed; if there is some risk of this, precautions must be taken to see that this is avoided at all stages.

3 If there is an incomplete paraplegia or other major neurological problem complicating the injury great care must be taken to see that no deterioration is allowed to occur.

4 If paraplegia is present and complete, the prognosis regarding potential recovery must be firmly established as early as possible. Only if this is pronounced total and permanent can vigilance in the handling of the spinal injury be relaxed.

In summary, the key to the management of spinal injuries is a thorough understanding of the nature of any damage to the bony elements, the supportive ligamentous structures, and the related neurological structures.

2 Anatomical features (after Kapandji¹) (a): The components of a typical vertebra have a complex relationship, and can be illustrated with an exploded diagram. The elements comprise the vertebral body (1) composed of cancellous bone covered with an outer shell of cortical bone, the horseshoe-shaped neural arch (2), two articular masses or processes which take part in the facet (interarticular) joints (3) and the transverse (4) and spinous (5) processes.

3 Anatomical features (b): When these components are brought together they form a protective bony covering for the cord (6) and the issuing nerve roots (7). The neural arch (2) is divided by the articular processes (3) into pedicles (8) and laminate (9).

4 Anatomical features (c): The vertebrae are bound together by the following structures: The supraspinous (1), interspinous (2), intertransverse (3) and capsular ligaments (4), and the ligamentum flavum (5): together these form the so-called posterior ligament complex. Playing a less powerful but nevertheless important role are the posterior (6) and anterior (7) longitudinal ligaments and the annular ligaments (8). Trauma may result in damage to any of the bony or ligamentous structures of the spine, in isolation or in combination.

5. Assessment of spinal injuries (a): In managing any case of spinal injury it is important to determine which structures have been involved and the extent of the damage they have suffered; with this information an assessment may be made of the risks of complication. Note: 1. The history may direct you to the type of injury to suspect; 2. The clinical examination may be a valuable guide to the extent of bony and ligamentous injury (and any neurological complication); 3. Investigation by X-ray and CT scan is likely to provide the most information; and MRI scans if available may help clarify the extent of any associated soft tissue damage, especially the intervertebral discs and the posterior ligament complex.

It is important to make an early assessment of the stability of the spine, i.e. to assess whether it is able to withstand stress without progressive deformity or further neurological damage. Instability may be purely mechanical (e.g. in some compression fractures where further kyphotic deformity may occur). Instability may be neurological (e.g. where shifting or further extrusion of bone fragments within the spinal canal may lead to neurological deterioration). Combined mechanical and neurological instability may be present. In assessing instability it may be helpful to regard the spine as having three main elements or columns.

6 Assessment of spinal injuries (b): The middle column (M) consists of the posterior longitudinal ligament (1), the posterior part of the annular ligament (2), and the posterior wall of the vertebral column (3). Unstable injuries occur when damage to the middle column is combined with damage to either the anterior column or damage to the posterior column.

7 Assessment of spinal injuries (c): The posterior column (P), vital for stability, comprises the neural arch, the pedicles, the spinous process, and the post. ligt. complex. The anterior column (A) is formed by the anterior longitudinal ligament, and the anterior parts of the annular ligament and vertebral body. Note that failure of these columns in their role as supports can be due to bony or ligament involvement. Four categories are recognised in the Denis Classification of spinal injury:

8 Compression fractures (a): Simple compression fractures are common stable injuries involving the anterior column only. Hyperflexion of the spine round an axis passing through the disc space leads to mechanical failure of bone with either anterior (Illus.) or lateral wedging. The height of the posterior part of the vertebral body is maintained. (Note that severe wedging – e.g. more than 15–20° – often indicates damage to the other columns and a burst fracture or fracture dislocation.)

9 Burst fractures (b): Axial loading of the spine may cause failure of the anterior and middle columns. One or both end plates may be involved, and bone fragments may be extruded into the spinal canal, compromising the neurological structures and more controversially causing neurological instability. Radiographs may show the vertebral body fracture, loss of vertebral height, and in the AP, laminar fractures and separation of the pedicles. (Illus: CT scan showing displacement of bony fragments both anteriorly and posteriorly.)

10 Seat belt type injuries (c): Rapid deceleration causes the spine to jack-knife round an axis brought forward by the lap strap part of a seatbelt, and tension forces lead to failure of the posterior and middle columns. The spine is unstable in flexion. Failure may occur entirely through bone (Chance fracture) (1), or ligaments (2), or a combination (3), involving either one (1 & 2) or two (3) levels of the spine. Injuries of this pattern may be seen in situations outside road traffic accidents, but the essential element is tension failure.

11 Fracture–dislocations (d): All 3 columns fail in these unstable injuries. Suspect if: 1. There are multiple rib or transverse process fractures (as from D1 to D8 the ribs and sternum give additional support to the spine); 2. There is a slight increase in the height of a disc or a fracture of an articular process. Types:

(a) Flexion–rotation fracture–dislocation. There is often a fracture of an articular process on one side (F), or a slicing fracture through a vertebral body, leading to rotation and subluxation of the spine.

12 Fracture–dislocations (d) ctd: Shear types of fracture–dislocation: In the posteroanterior type (1) the upper segment shears forwards, often with fracture of the posterior arch at 1 or 2 levels. In the anteroposterior type (2) there is complete ligamentous disruption, but often no fracture. In the flexion–distraction type (3) there is an anterior annular tear with stripping of the anterior long. ligt. allowing anterior subluxation: this is a tension type of injury as in the seatbelt lesion.

13. Neurological examination: basic principles: Where there is evidence of a deficit, a thorough neurological examination is required on admission; this must include as a minimum:

1 Testing for evidence of muscle activity and power in all muscle groups below the level of injury.

2 Testing sensation of pin prick and light touch over the entire area affected.

3 Testing proprioception.

4 Testing the reflexes – the tendon reflexes, the plantar responses; the anal reflex (stimulation of the perineum leading to contraction of the external anal sphincter) and the glansbulbar reflex (compression of the glans leading to perineal muscle contraction).

Note also the following points:

1 Where the spinal cord is involved, the neurological level should be determined.

2 The neurological level and the level of any bony injury should be correlated. Absence of any obvious bony injury at the neurological level should lead to further local investigation (e.g. by MRI scan).

3 The severity of any deficit should be assessed.

4 If the findings indicate a complete spinal lesion, the examination should be repeated after 6 hours, 12 hours and 24 hours.

14 Anatomical features (a):Note: 1. The spinal cord ends at L1; any injury distal to this can involve the cauda but not the cord. 2. All the lumbar and sacral segments of the cord lie between T10 and L1 only. 3. Injuries at the thoracolumbar junction produce a great variety of neurological disturbances as:

(a) the cord may or may not be transected,

(b) the nerve roots may be undamaged, partly divided or completely divided.

15 Anatomical features (b): Cervical cord:

Note: 1. The phrenic nerve arises from C4, with minor contributions from C3 and C5. Cord section proximal to the phrenic nerve will lead to rapid death from respiratory paralysis. Those with lesions at C4-5, and more distal, are capable of respiration without external support.

2. C2 and C3 supply the vertex and occiput (accounting for pain here in upper cervical lesions).

C5–T1 contribute to the brachial plexus. (The illustration is diagrammatic.)

16 Assessing the neurological level of cord or nerve root injury: Cord or root damage is reflected in disturbance of myotomes or dermatomes.

Myotomes (a): As a rule, motion in each joint is logically controlled by four myotomes in sequence: viz. Hip flexion, L2, 3, extension L4, 5. Knee extension, L3, 4 (including knee jerk), flexion L5, S1. Ankle dorsiflexion L4, 5, plantar flexion S1, S2 (including ankle jerk). (In addition, inversion is controlled by L4 and eversion by L5, S1.)

17 Myotomes (b): In the upper limb, the arrangement is less regular: Shoulder abduction C5, adduction C6, 7. Elbow flexion C5, 6 (including biceps jerk), extension C7, 8 (including triceps jerk). Wrist flexion and extension; both C6, 7. Finger flexion and extension, C7, 8. Pronation and supination C6 (including supinator jerk). Hand intrinsic muscles T1.

18. MRC grading: Muscle activity should be assessed using the MRC scale:

M0 – No active contraction

M1 – a flicker of movement can be seen or palpated, but this is not enough to produce movement

M2 – weak contraction which can produce movement if gravity is eliminated

M3 – contraction weak, but can produce movement against gravity

M4 – strength not full, but can produce movement against gravity and some resistance

M5 – full strength

Motor index score: This is useful for assessing the extent of motor loss, and for gauging any improvement or deterioration. In the upper limb, biceps, the wrist extensors, triceps, flexor digitorum profundus and the hand, intrinsics are each assessed using the MRC Grading system and added together. The totals for the right upper extremity and left upper extremity (RUE and LUE) are noted (25 in each normal limb). The procedure is repeated in the lower limb, using the hip flexors, quadriceps, tibialis anterior, extensor hallucis longus, and gastrocnemius.

19 Dermatomes (a): In the upper limb, the anterior axial line follows the line of the second rib from the angle of Louis, and continues down the anterior aspect of the arm, splitting near the middle finger which is supplied by C7. The other dermatomes are arranged in a regular fashion on either side of the axial line. If indicated, a sensory index score may be made for each limb (0 = absent sensation; 1 = impaired; 2 = normal).

20 Dermatomes (b): The lumbar and sacral dermatomes have a complex arrangement which is difficult to commit to memory. Remember by the facts that: 1. The outer border of the foot is supplied by S1; 2. The medial part of the foot and the lateral part of the leg by L5; 3. The ‘stocking top’ area is supplied by L2 and 4. the saddle area by S3. ‘We kneel on L3, stand on S1, and sit on S3.’

21 DETERMINING THE SEVERITY OF NEUROLOGICAL INVOLVEMENT

It is helpful to record the extent of any neurological impairment, and the Frankel Scale is a simple and direct method of doing so:

Frankel A: complete paralysis

Frankel B: only sensory function below the injury level

Frankel C: incomplete motor function below the injury level

Frankel D: fair to good motor function below the injury level

Frankel E: normal function

TYPES OF INCOMPLETE CORD INJURY:

A number of cord syndromes are recognised. These include the following.

Anterior column syndrome

The damage is to the anterior two thirds of the cord and commonly occurs in burst fractures of the spine where there is compression of the cord and interruption of its blood supply by fragments of bone which have been forced into the spinal canal. There is complete motor paralysis and loss of sensation to pin prick and light touch, but proprioception and perception of deep pressure are retained. There is greater muscle loss in the legs than in the arms. This has the worst prognosis of all cord syndromes, with only 10–15% having any functional recovery. No return of sensation to pin prick or temperature in the sacral area after 24 hours is a very poor prognostic indicator.

This is the commonest incomplete cord syndrome, and generally follows a hyperextension injury. It is particularly common in the older patient who has a degree of cervical spondylosis (see also Frame 71). The cord may be affected over several segments, with involvement of both grey and white matter. The effects are curiously greater in the arms than in the legs. In the upper limbs, lower motor neurone lesions predominate, with a partial flaccid paralysis of the fingers and arms, and loss of pain and temperature sensation. In the lower limbs the lesion is an upper motor one, resulting in a spastic paralysis, usually with sparing of sensation, but sometimes with bladder and bowel involvement. This lesion pattern is sometimes referred to as ‘man in a barrel’ syndrome (MIB), a typical example being an elderly man who is able to walk but whose shoulders are immobile and his hands anaesthetic.