Chapter 13 Lumbar spine

Conditions affecting the region

Trauma

Wedge fractures can occur when the anterior border of a vertebral body is crushed due to flexion or vertical pressure, i.e. a high fall landing on the feet or head. More serious bony injury can occur, including fracture and dislocation of vertebrae, which can cause misalignment of the vertebral column. Below the first lumbar vertebra (L1) the cauda equina is more resistant to injury than the spinal cord. Plain radiography is most likely to be undertaken in the acute setting when injury has been sustained.

Pars interarticularis fractures are shown on oblique lumbar spine projections; this type of injury can result in a spondylolisthesis (forward slippage of one vertebra in relation to the vertebra below), although plain radiography may not be the most appropriate investigative method. L5 slippage on the first sacral segment (S1) is most frequently found. These are often incidental findings on images and are not usually directly related to specific traumatic incidents.

Back pain

Studies have shown that only a very small percentage of requests for plain radiography change patient management ³ and so they are not cost-effective.⁴ The high radiation dose associated with lumbar spine radiography should not be used to provide patient reassurance, or indeed reassurance for the referrer.⁵

Metastatic disease

Metastatic disease is characterised by secondary deposits seen as lytic, and in some cases sclerotic, lesions; pathological fractures may be present. Nuclear medicine imaging or MRI are generally the most appropriate examinations for early detection.²

Congenital processes

Spina bifida

This is a congenital defect that usually occurs in the lumbosacral region. The laminae do not fuse, causing the vertebral arch to be incomplete posteriorly. Spina bifida has varying degrees of severity, as it may or may not be associated with protrusion of the meninges and spinal cord. Today, plain radiography is unlikely to be required as an initial investigation, as awareness of the existence of the abnormality is usually raised after routine prenatal ultrasound scanning. In spina bifida occulta the defect does not involve the meninges or spinal cord and is usually an incidental finding on an anteroposterior (AP) radiograph of the area.

Challenges of the lumbar spine examination

There are a number of challenges the radiographer will encounter when positioning a patient, not only due to the patient’s physical shape and size but in judging the radiographic planes of the body in relation to the patient and X-ray table. The following tips may be helpful in overcoming difficulties that may be encountered.

Positioning tips

When initially studying a patient’s X-ray request form, prior knowledge of their clinical history assists in the problem-solving and decision-making processes crucial for the optimum choice of positioning technique required, in order to achieve a high-quality diagnostic image. Initial clinical evaluation of the shape of the spine will assist in any positioning adjustment requirements when the patient is placed on the X-ray couch. This is particularly important for patients with abnormal configurations of the spine.

The patient should be made to feel comfortable and relaxed; tension can cause difficulty when attempting to move a patient into position. The examination gown should be adjusted if necessary to ensure that no folds will interfere with their movement into the required position and that the anatomical landmarks can be easily palpated. If the gown design includes a split, this must be at the back of the patient, to allow for visualisation of the spinal column while palpating its surface markings.

Palpation of the prime anatomical landmarks is important when adjusting the patient into the correct position for each projection. Clinical palpation is a skill which, if practised with reservations, can lead to mistakes. Physical contact involving the lower trunk, as required for lumbar spine examination, requires a degree of tact and diplomacy while using precision and gentleness but firmness.

A key requisite for accurate positioning of the lateral lumbar projections is to assess the position of the long axis of the vertebral column in relation to the image receptor (IR). The column should be palpated and visually assessed along the lumbar section, with the eyes level with the vertebrae. Radiographers often assess visually from a point that is higher than the spine; this does not give a true impression of the vertebral position. Palpation of the spinous processes is also essential and must be implemented in addition to visual assessment, as the muscles on the posterior aspect of the patient can sag (especially in the middle-aged and elderly), giving an inaccurate impression if visual assessment only is used.

For lumbar spine X-ray examinations the anatomical landmarks chosen during positioning set-up techniques are considered reasonably standard, although their position relative to the surrounding anatomical structures can vary due to osteological changes. Excessive fatty tissue can also cause difficulty in palpation techniques and there is a large variation in total body fat in individuals of varying age and between populations. Therefore, standardisation of the anatomical sites used for positioning and palpation is important.

AP lumbar spine (Fig. 13.1A,B)

IR is horizontal; an antiscatter grid is employed

Figure 13.1 AP lumbar spine.

Positioning

• The patient is supine with their arms placed on the pillow and legs extended

• The knees may be supported with a pad for patient comfort; to reduce the lumbar lordosis and enable better visualisation of the intervertebral joint spaces, the legs should be supported with the femora at 45° or more to the table-top

• The median sagittal plane (MSP) is 90° to the table-top and the coronal plane is parallel to the table-top

• Gonad protection should be applied to all patients; if it is correctly positioned it will not obscure any relevant detail, and is essential to reduce the dose to the gonads

Beam direction and focus receptor distance (FRD)

Vertical central ray, 90° to the IR

100 cm FRD

Centring

In the midline, at the level of the lower costal margin (level of L3)

Collimation

Psoas muscles, transverse processes of LV1–LV5, T12/L1 joint space, sacroiliac joints

Note that this technique may be performed erect, either standing or seated; the positioning is the same but a vertical IR and antiscatter device are used.⁶ The central ray direction is adjusted accordingly.

Criteria for assessing image quality

• Psoas muscles, transverse processes of LV1–LV5, T12/L1 joint space, sacroiliac joints are demonstrated

• Spinous processes are in the centre of vertebral bodies, demonstrating no rotation

• L2/L3 and L3/L4 joint spaces are demonstrated; other intervertebral spaces will be projected obliquely due to lumbar curvature

• Sharp image demonstrating soft tissue of abdominal viscera in contrast to bone and air in the gastrointestinal tract; detail of bony cortex and trabeculae; spinous processes visualised through vertebral bodies

Common errors	Possible reasons
Spinous processes not in the midline of vertebral bodies	1. Rotation of the spine – MSP not perpendicular to the IR. Adjust the patient position so that the pelvis and shoulders are not rotated
Spinous processes not in the midline of vertebral bodies	2. Scoliosis may cause this appearance and may not be improved upon. This is distinguishable from rotation due to position error by the distinct lateral curve of the column and potential variation of rotation down its length⁷
No intervertebral discs clearly demonstrated	Excessive lordosis – the direction of the primary beam can be adjusted so that the beam is directed through the required joint spaces (see comments below)

Expose on arrested respiration

Exposure is made on arrested respiration, to prevent blurring of abdominal contents. The respiratory phase is unimportant as the diaphragm will not move over the body of L1 in either phase. It is likely, though, that selection of exposure factors will be affected by opposite phases of respiration, as extreme inspiration will increase the volume and density of abdominal tissue overlying the lumbar area. This will be likely to necessitate an increase in exposure factors, which will result in an increase in radiation dose to the patient and a decrease in image contrast due to increased scatter from the greater tissue volume and density.

An alternative to demonstrate the transverse processes free from overlying gas shadows is to use a long exposure with the patient gently panting, using the effect of autotomography to prevent the gas obscuring bony detail.

It has commonly been believed that the curvature of the lumbar spine can be reduced by an angled pad being placed under the knees, enabling better visualisation of the intervertebral joint spaces by associated flattening of the lumbar lordotic curve.⁸ The effectiveness of knee flexion is traditionally claimed to be felt by a simple experiment: if one lies supine with the legs extended a flat hand will slide easily under the arch made by the lumbar curve. When the knees and hips are flexed, the hand feels the lumbar area press down onto its dorsal aspect, suggesting a reduction in lumbar curve. The more the hips and knees are flexed, the more the curve appears to reduce. But is the movement felt by the hand merely muscular movement rather than reduction of lordosis? Would an increase in knee/hip flexion actually show a more significant lumbar curve reduction?

The effect has been disputed by Murrie et al.,⁹ but this research was undertaken on a very small sample of seven examinations and this raises questions on the validity of the research. It is also noted that Murrie et al. flexed the knees over a pad, which may not offer adequate hip flexion to reduce the lumbar curve.

Further research on this topic was performed on a larger sample of 60 volunteers by Downing,¹⁰ who found that the lumbar curve was effectively reduced by up to 64%, but that in order to be effective the femora should be at 45° to the table-top, as described in the technique description. Note that the key is the angle between the femora and the table-top, not the angle of flexion of the knees.

However, the question must be asked ‘Do we require all joint spaces to be visualised on an AP?’: information regarding intervertebral disc spaces is more readily available on the lateral view, and on MRI, which after all is the investigation of choice for most lumbar pathologies.

Posteroanterior (PA) or AP?

Owing to the anterior curvature of the lumbar spine it would seem reasonable that the PA projection could be preferable to AP, as in this position the diverging X-ray beam coincides more closely with the intervertebral joint spaces, enabling better demonstration.

This is not, however, a commonly adopted practice, reasons being the magnification and consequent unsharpness due to increased object–receptor distance (ORD). This could be compensated for by an increase in FRD and exposure factors.

Colleran ¹¹ showed that the magnification produced does not cause a significant reduction in image quality and indeed recommends its adoption because of the superior demonstration of the sacrum, sacroiliac joints and intervertebral joint spaces. Her work has resulted in the adoption of the PA projection in a small number of imaging departments.