Introduction: Flat Back is a syndrome of sagittal imbalance often associated with back pain commencing in the lumbar region and progressively ascending. It is noted after posterior instrumentation to the lumbosacral junction, with various arthropathies and following compression fractures of the dorsolumbar and lumbar spines. In an attempt to maintain vertical posture, muscle fatigue causes back pain which persists until the condition is rectified. A compensatory pelvic tilt produces hip/hamstring pain and is relieved once lumbar correction is established. The cause of pain is unknown. The aim of this radiological study is to identify abnormal parameters which may contribute to sagittal imbalance and back pain.

Methods: Seven fully mobile subjects without fractures served as normal cohorts. Thirty-four consecutive patients aged 18 to 83 years with vertebral compression fractures were studied. There were 28 males. CT scout views of the full length spine in prone and supine positions provided functional scanograms for the Cobb measurement of thoraco-lumbar kyphosis and lumbar lordosis. Degrees of sagittal imbalance were graded as I, II and III, in accordance with the presence of dorsolumbar kyphosis, loss of lumbar lordosis and rigidity in functional views. Previous CT, MRI, Bone Scans were used to exclude other sources of pain such as protruding discs, annular tears, listhesis or un-united fractures. No patients with neurological signs were included. Three sets of measurements were taken:

Dorsolumbar angulation: On prone films, Cobb angle was measured at upper T12 and lower L1 end plates (normal 0°; with standard deviation +3/−3).

Lumbosacral angular motion: On functional films, lines were drawn on the upper end plates of L5 and S1. The resulting differences [(+)-(−)] between functional angles were compared with the normal values obtained from the literature (i.e. in excess of 26° of combined motion). The difference between standing lateral functional radiography and the prone/supine scanography was accepted.

Sacral inclination: On supine films, the angle between a vertical line (a perpendicular to horizontal baseline) and the upper S1 endplate.

Results: There wasÊsignificant reduction in the radiation dose for CT scanograms when compared to conventional radiography: with sparing of bone marrow by 74–80%. The frequency of the abnormal radiological parameters was as follows:

Dorsolumbar angulation: 26 showed (positive) kyphotic angles up to 30°−40°.

Lumbosacral angular motion: In view of the spinal rigidity found in most cases, a compensatory excess mobility was expected at 5/1 level, but the opposite was confirmed. Indeed, 27 patiens showed exaggerated (negative) extension shift (of −5°−10°); amongst these 10 were with complete loss of flexion; 12 were with partial flexion (a forward shift of up to 15°), but 5 with full flexion, permitted by a lumbar kyphosis.

Sacral inclination: twenty-eight patients showed a shift to a diminished angle of 25°–35° as compared to 35°–55° in 15 control spines.

The patients were grouped according to the number of selected abnormal radiological parameters present. The cases were graded: Grade I (1 abnormality) – 2 cases, Grade II -13 cases and Grade III – 19 cases. The threshold for imbalance was (1) at least one severe thoracolumbar compression (or an equivalent combination of multiple minor thoraco-lumbar compression fractures) for D/L kyphosis and (2) a single lumbar fracture with at least 50% compression.

Discussion: The cause of pain in post-traumatic sagittal imbalance remains unclear. This study suggests three possible sources of pain, individually or in combination, namely altered angulation at the dorsolumbar junction, reduced motion at L/S level and sacral verticalisation. A more extensive study will be required for verification and interpretation of these preliminary data. It is important to expand the study to variants other than loss of lumbar lordosis.

Introduction: Flat Back Syndrome resulting from decreased lumbar lordosis or increased thoracolumbar kyphosis was initially described by Doherty¹ in post scoliotic surgery patients. This decompensation was later coined as fixed sagittal imbalance and was also detected in patients operated for ankylosing spondylitis or with fractured vertebrae. Various clinical symptoms were included in the syndrome such as stooped posture, knee/ hip flexion compensation, fatigue of para-spinal muscles, neck pain and upper spinal deformities, imbalanced gait. Surgical corrections were described by Kostuik², Lagrone³, Farcy⁴ and others. The “normal” assessments were varying, but accepted according to Propst-Proctor⁵ and Bernhardt & Bidwell Segmental measurements⁶. The clinical diagnosis was supported by radiological evaluation using the Cobb technique and a plumbline alignment from odontoid to promontorium. This evaluation required multiple sets of x-ray films.

Methods: Our preliminary study is aiming at describing in detail the clinical syndrome in patients with lower dorsal and upper lumbar vertebral compressions. Scanogram CT- imaging of the spine is suggested for diagnosis, a rapid technique reported to be with at least 40% reduced radiation^7,8. The scanogram is suggested to be functional as it is repeated in prone and in supine positions. The two films were superimposed and rigidity assessed, angles were measured (Cobb) at the T/L junction (two above and two levels below the fracture) and of the lumbar lordosis (from Inferior L1 to superior L5).

Results: This technique was applied to eight patients: the clinical syndrome is detailed with one additional, as yet unreported feature, namely the sleeping position. These were patients with two, three or four vertebral compressions, resulting in imbalance of the dorsolumbar junction and deformity of the lumbar lordosis. All patients had increased T/L kyphosis of varying degrees, all but one had parallel loss of lordotic curvature.

Discussion: A different imaging technique, functional and less irradiating is suggested for the diagnosis of fixed sagittal imbalance of the dorsolumbar spine and is applied to deformities resulting from fractured vertebrae. The clinical syndrome is enlarged with one feature, namely sleeping in prone position. These early impressions need a larger prospective study for confirmation.