Full-Length Spine—Plain Radiographs

Introduction

The evaluation of spinal pathologies is dependent upon careful history, clinical examination, and appropriate full-length spine radiographs. Appropriate full-length spine radiographs should be obtained when evaluating a patient for suspected coronal, sagittal, or combined imbalance. Full-length spine should ideally include C7 and both femoral heads. This ensures that important landmarks used for parameter calculations are readily available. Plain radiographs can be obtained either through a standardized method using long-film acquisitions with a radiographic source located 72 inches away from the subject or, more recently, through the use of an EOS™ system. The EOS™ system is a slot-scanning device that allows simultaneous acquisition of full-length spine radiographs both in the PA (or AP) and in the lateral position with a significant dose reduction when compared with traditional digital radiography acquisitions.

The thoracic spine is typically composed of 12 thoracic vertebrae each bearing a pair of ribs. The lumbar spine is typically composed of 5 lumbar vertebrae. Normal variations include 11 or 13 thoracic vertebrae and 4 or 6 lumbar vertebrae, and can be seen in as much as 10% of the population. The spine is normally straight in the coronal plane with an accepted variation up to 10° before being considered a scoliosis. In the sagittal plane, the thoracic spine is normally in kyphosis (normal range 20–50°) and the lumbar spine is in lordosis. Lumbar lordosis is usually well correlated with pelvic incidence.

Radiographic imaging of the spine is a static representation of the patient’s everyday posture. It doesn’t take into consideration gait compensatory mechanisms or one’s functional limitations such as spasticity or limited range of motion. A careful evaluation of the patient’s gait is of critical importance to better understand the subtle variations in the patient’s sagittal and coronal profiles. Postural control is also highly dependent on integration at the central nervous system level of external stimuli, including proprioception, vestibular information, and visual information. This information is processed centrally, and posture derives from this complex and intricate process. Horizontal gaze (vision) is a central part of posture and plays an important role in the patient’s ability to stand with a normal posture. The other determinant of sagittal alignment is pelvic morphology, which dictates how the lumbar spine and, to some extent, how the thoracic spine will be aligned.

Image Acquisition

Radiographs should be acquired with the patient standing in a natural physiological load-bearing position. Hips and knees should be in their natural position for the patient but don’t need to be fully extended. These compensation mechanisms should, however, be noted during physical examination. If possible, head-to-toe image acquisition (as is possible with the EOS™ system) will give an insight into these compensation mechanisms. The arms should be positioned in a way allowing a good assessment of the thoracic spine. Classically, this is done either through a hands-on-clavicle (or hands-on-cheek) position or with the arms holding a support. More recently, a hands-on-wall in the EOS™ system has been advocated with the added benefit of being able to determine the bone age for adolescents. Jackson et al. evaluated the hands-on-clavicle vs. hands resting on a support with their arms at 30° and 45°, and found little difference between these positions. Ideally, to allow for comparison between images taken at different times, there should be some standardization in the position and the acquisition method. The images should span the whole spine from the base of the skull to the pelvis and include both femoral heads. This allows for specific spinal alignment parameters to be determined without repeat imaging.