Intimate relationship between instability and degenerative signs at L4/5 segment examined by flexion-extension radiography

Abstract

Relationship between lumbar disc degeneration and segmental instability has remained controversial. Using instability factors that found close relations with symptoms in flexion-extension radiographic study, their relationship with degenerative findings was examined. More than (≥) 3 mm slip in neutral position (SN), ≥3 mm translation (ST), and ≥10° angulation (SA) at L4/5 segment were defined as instability factors and were applied on 447 patients who had low back and/or leg pain and satisfied inclusion criteria for accurate measurements. Radiologic findings for degeneration were disc height including three groups with different disc heights divided by mean ± 1 standard deviation, length of the anterior spur formation, presence of vacuum phenomenon, and endplate sclerosis. As results, group with SN factor was the oldest in age and the lowest in disc height; in contrast, group with SA was the youngest in age and the highest in disc height. The group with ST showed a mid-standing position in both age and disc height. These findings indicate that instability factors are intimately related to age and disc height. The three different disc height groups showed more anterior slip according to the progression of the disc height diminution. Presence of the apparent spur formation and/or vacuum phenomenon had an intimate relationship with the ST factor. Disc height was the most important in the examined parameters and showed an intimate relationship with age and instability factors. Although the etiology is still unknown, clinical common knowledge, that a diminution of disc height with progressive degeneration had a close relation with anterior vertebral slippage, was firstly confirmed. This study allows comprehensive understanding of segmental instability and is useful for considering surgical indications.

Fig. 1

Disc height ratio of the groups with various instability factors. Group A had all 3 instability factors (SN+ST+SA; SN: ≥3 mm slip, ST: ≥3 mm translation, and SA: ≥10° angulation), Group B: SN+SA, Group D: SN alone, Group E: ST+SA, Group F: ST alone, Group G: SA alone, Group H: none of the 3 factors. The numbers in each bar indicates the mean age of the group. Closed bars showed the groups which had the SN factor

Fig. 2

Disc height ratio of the groups with/without a typical instability factor. Groups D, F, G, and H represent the same groups as in Fig. 1. Age and disc height differences were more distinctive. The closed bar indicates the disc height ratio of the group which had SN factor alone

Fig. 3

Amount and direction of the slip in three different disc height groups. Amount of slip was measured using the lateral radiograph in neutral standing position. Positive and negative signs indicate the relative position of the L4 landmark to the L5 landmark in the sagittal plane, therefore a positive value means anterior slip of the L4, and a negative means posterior slip. According to the decreased disc height, more anterior slip was observed. HDH high disc height, MDH medium disc height, LDH low disc height

Fig. 4

Relationship between disc height and segmental angulation. According to the decrease in disc height, less angulation was observed. HDH high disc height, MDH medium disc height, LDH low disc height

Fig. 5

Incidence of vacuum phenomenon. Vacuum phenomenon was observed the most frequently in group F with ST factor alone, and was significantly higher than in groups G, E, A, and H. Closed bars shows the group which had SN factor

Fig. 6

Disc height and classified grades of disc degeneration. Disc height of grade 2 degeneration group was the highest and gradually decreased heights were observed in the order grade 1, 3, 4, and 5 degeneration groups. The height of grade 5 was the lowest and the difference was statistically significant compared to the others (p < 0.05). The numbers in the bar indicate the number of patients in each group

Fig. 7

Scheme showing considerable mechanism of the anterior slip with progressive disc degeneration. According to the diminishing disc height with progressive degeneration, increased anterior slip was observed. Factors such as spinal alignment, trunk muscle, ligament and soft tissues, and facet orientation and tropism, are thought to be promoting factors in addition to the degeneration of discs and facet joints