J Korean Soc Spine Surg.  1998 Nov;5(2):205-214.

Changes of the Adjacent-Unfused Mobile Segment After Instrumental Lumbar Fusion: More Than 5-Years Follow-up

• Ha KY
• Kim KW
• Park SJ
• Lee YH

Abstract

STUDY DESIGN: This retrospective study was designed to find the causes of adjacent-segment changes and to investigate the correlation between these changes and clinical results in long-term follow-up patients after instrumental lumbar fixation and posterolateral fusion.
OBJECTIVE
To quantify how immobilization of a rigid spinal segment fixation effect the pre-existing degenerated adjacent-segment and to observe the adjacent-segment changes, contributing factors of adjacent-segment changes and to investigate the the correlation between clinical results and adjacent-segment changes. SUMMARY OF LITERATURE REVIEW: The reduction in the number of mobile lumbar segments with posterior instrumentation and fusion causes an increased stress in the unfused segment, predisposing them to early degeneration. In addition, the adjacent-segment above the rigid fixation is a particular problem in the previously degenerative spine, which accelerated degeneration at adjacent-segment Many clinical studies reported that stress of the adjacent-segment could develop the significant incidence of spondylolisthesis, spondylolysis and spinal stenosis.
MATERIALS AND METHODS
Forty patients were retrospectively reviewed who underwent wide laminectomy and intertransverse fusion with posterior instrumentation. Inclusion in the study required minimum of 5 years of clinical and radiographic follow-up. Nineteen patients were diagnosed as degenerative spondylolisthesis, degenerative scoliosis in 8, pure spinal stenosis in 6 and lytic spondylolisthesis in 7. The most common fused segments were L4-5 in 16. Initial radiographs including plain radiogram, CT and MRI were classified with respect to presence of degeneration adjacent to fused segments. A preoperative spinal instability was diagnosed when any of the following conditions were noted at adjacent above the fusion: 1) >15degrees angulatory instability, 2) >3mm translation, 3) >5degrees lateral angulation, 4) >grade 1 rotational deformity, and postoperative adjacent changes were diagnosed 1) same as preoperative instability criteria, 2) fracture, 3) spinal stenosis, 4) spondylolysis. Clinical results were categorized as poor, fair, good and excellent.
RESULTS
Of 40 patients, 16(40%) patients had significant adjacent-segment changes such as instability in six, fracture in aye, spinal stenosis in four and lysis in one. Incidence of adjacent- segment changes was significantly higher in more than 54-years old. Degenerative scoliosis had a higher adjacent-segment chanties and showed statistically significant between preoperative disease and adjacent-segment changes. Nine patients who had a preoperative instability showed significant adjacent-segment changes. Of remained 31 patients, only 7 patients had adjacent-segment changes. There was a statistically significant difference according to preexisting adjacent-segment degeneration. All five patients with grade 3 degeneration developed significant adjacent-segment changes. In overall clinical results, all 7 poor cases had significant adjacent-segment changes. Of them,5 patients should undergo reoperation.
CONCLUSION
Inevitable compensatory mechanism occurs at adjacent segment, resulting from stress concentration and alteration in motion kinematics after fusion. The most important factors associated with adjacent-segment changes were age, pre-existing degeneration and preoperative instability. The adjacent-segment changes had a significant correlation with poor clinical results.

MeSH Terms

Biomechanical Phenomena
Congenital Abnormalities
Follow-Up Studies*
Humans
Immobilization
Incidence
Laminectomy
Magnetic Resonance Imaging
Middle Aged
Reoperation
Retrospective Studies
Scoliosis
Spinal Stenosis
Spine
Spondylolisthesis
Spondylolysis