Spondylolysis, spondylolisthesis and back pain

Spondylolysis (literally: "vertebral resorption") is a term adopted to denote a defect in the interarticular part of the vertebral arch. The term spondylolysis reflects a radiographic symptom rather than the anatomical essence of the pathology, since in most cases the presence of this bone defect is caused not by acquired "resorption" of a certain area of the vertebra, but by its vicious development - dysplasia. The frequency of spondylolysis in the population exceeds 5%. Spondylolysis is usually bilateral, in 85% of cases it is localized at the level of L5, about 10% - at the level of L4 vertebra. In case of unilateral damage, it is more often detected on the right. In almost 70% of cases, spondylolysis is asymptomatic and is accidentally detected during an X-ray examination. In the presence of clinical manifestations, the main symptom of the pathology is back pain, namely in the lower lumbar or lumbosacral spine, usually associated with pathological mobility of the vertebral arch.

In childhood and adolescence, spondylolysis is often combined with spondylolisthesis, which is an independent disease. The term spondylolisthesis was introduced by H. F. Kilian (1854) to denote the displacement of the overlying vertebral body relative to the underlying one in the horizontal plane. According to the direction of displacement, there are anterolisthesis (anterior displacement), retrolisthesis (posterior displacement), and lateral displacement. Spondylolisthesis is most often detected at the level of the lower lumbar (L4-L5) and lumbosacral (L5-S1) spinal motion segments, which account for more than 95% of cases of the disease. There are clear gender and racial differences in the frequency of spondylolisthesis: the frequency of the pathology is 5-6% in Caucasian men and 2-3% in women. At the same time, among the Eskimos, the pathology occurs in 50% of the population (!), while among African Americans it occurs in less than 3%.

Classification of spondylolysis

By pathogenesis:	A) congenital spondylolysis - a developmental defect (dysplasia) of the vertebral arch; B) acquired spondylolysis, including: - in case of functional overloads of dysplastic vertebrae (for example, in case of sacralization or tropism disorders of the lower lumbar vertebrae); - “overload” spondylolysis (like the “Loser zone”), with functional overloads of the initially normal spine.
Gap localization	A) typical - in the interarticular part of the arch; B) atypical, including: - retrosomatic - at the level of the arch leg; - retroisthmic - posterior to the articular processes
According to the clinical course	A) asymptomatic, B) with pain syndrome, including: - without spondylolisthesis, - with spondylolisthesis.

There are generally accepted classifications of spondylolisthesis based either on the determination of the pathogenetic mechanisms of the pathology or on a quantitative assessment of the degree of “slippage”.

Pathogenetic classifications of spondylolisthesis

Authors	Types of Spondylolisthesis
Wiltze L. J. L., Newman R. N., Macnab I. (1976)	Dysplastic spondylolisthesis. Isthmic or cervical (spondylolytic). Degenerative (senile) spondylolisthesis. Traumatic spondylolisthesis. Pathological (tumor, osteomyelitic) spondylolisthesis.
Wiltze LL, Rothmans, 1997	Congenital spondylolisthesis: A - with dysplasia of L5-S1 joints and their horizontal orientation; B - with sagittal orientation of intervertebral joints; C - with congenital anomalies of the lumbosacral vertebrae. Isthmic (cervical) spondylolisthesis: A - with spondylolysis; B - with elongation of the interarticular zone, with or without spondylolysis; C - with injury to the interarticular zone. Degenerative, including senile spondylolisthesis, associated with natural or pathological degeneration of joints. Traumatic spondylolisthesis with damage to the vertebrae outside the interarticular zone. Pathological spondylolisthesis, including in osteomyelitis or local oncological lesions. Post-surgical spondylolisthesis (after decompression of the spinal cord, nerve roots or after laminectomy).

Of the methods for quantitative assessment of spondylolisthesis, the simplest is the method of HW Meyerding (1932): the cranial endplate of the underlying vertebra is conventionally divided into 4 equal parts, and a perpendicular is lowered from the posteroinferior edge of the upper vertebra to the endplate of the lower one. The degree of listhesis is determined by the zone onto which the perpendicular is projected. More precisely, the magnitude of spondylolisthesis is characterized by determining the percentage of vertebral slippage, calculated by the Meyerding method using the formula

A/bx100%,

Where a is the distance from the posterior edge of the lower vertebra to the perpendicular drawn through the posteroinferior edge of the upper vertebra, b is the anteroposterior dimension of the upper endplate of the lower vertebra. Thus, the first degree of slippage corresponds to a displacement of up to 25%, the second - from 25 to 50%, the third - from 50 to 75%, the fourth - from 75 to 100%. The fifth degree of spondylolisthesis (or spondyloptosis) is characterized not only by the horizontal displacement of the upper vertebra anteriorly by the full anteroposterior dimension of the body, but also by its additional caudal displacement.

There are also other quantitative indicators characterizing the relationship of the lumbosacral vertebrae, such as the slip angle, the angle of sagittal rotation, and the angle of inclination (tilt) of the sacrum. These angles are calculated from a lateral X-ray of the spine.

The slip angle reflects the magnitude of the lumbosacral kyphosis. It is formed by the intersection of the line tangent to the lower endplate of the upper vertebra (L5) with the perpendicular, restored through the upper endplate of the lower vertebra (S1), to the line tangent to the posterior surface of its body. Normally, the slip angle is 0 or has a negative value.

The angle of sagittal rotation is determined by the intersection of lines drawn tangent to the anterior surface of the body of the upper (L5) and posterior surface of the body of the lower (S1) vertebrae. Normally, it is also equal to 0.

The angle of inclination (tilt) of the sacrum is determined by the intersection of the line tangent to the posterior surface of the body S1 of the vertical axis. The study is carried out on an X-ray taken in a vertical position. Normally, the indicator should exceed 30°.

I.M. Mitbreit (1978) proposed to evaluate the magnitude of spondylolisthesis by the values of the angles of displacement of the L4 and L5 vertebrae relative to the S1 vertebra. These angles are formed by the intersection of a vertical line drawn through the geometric center of the S vertebra with the lines connecting the geometric centers of each of the indicated vertebrae with the center of S1.

Determination of the degree of spondylolisthesis according to I. M. Mitbreit

Degree of displacement	Offset angle
	L5	L4
Norm I II III IV V	Up to 45° 46-60° 61-75° 76-90° 91-105° More than 105°	Up to 15° 16-30° 31-45°

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