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Prevention of adjacent level degeneration above a fused vertebral segment :

Long term effect, after a mean follow-up of 8.27 years, of the semi-rigid intervertebral fixation as a protective technique for pathological adjacent disc

G. PERRIN, A. CRISTINI

Neurological hospital ­ Lyon, France

Presented at the IMAST 2003 (International Meeting for Advanced Spine Technologies)

L

UMBAR fusion may lead to accelerated degeneration of the disc adjacent to the instrumentation, due to different factors that have been well defined in the literature (2,4,5,7,8,11). One of these factors is the hyper rigidity of the fused segments due to the instrumentation which leads to concentration of the mechanical stress on the adjacent discs

(1,3,6,9,10). This problem is increased in case of preoperative pathological adjacent disc (collapsed, prolapsed or black disc). In case of such association of severe instable lumbar lesion and adjacent mild degenerative disc, it is more advisable to protect this adjacent disc with bisegmental fixation and semirigid element (Figure 1) (11, 12).

Figure 1 : Examples of degenerative indications for complementary adjacent semi-rigid fixation above a circumferential arthrodesis

(a) Spondylolisthesis L5/S1 with adjacent pathological disc on discography

(b) Spondylolisthesis L5/S1 with adjacent L4/L5 black disc on pre-op MRI

(c) Spondylolisthesis L5/S1 with adjacent prolapsed L4/L5 disc

Method

operated on between 1993 and 1997 for L5/S1 or L4/L5 spondylolisthesis. These patients had PEEK or titanium impacted cages implanted for stabilization of a very unstable isthmic spondylolysis, and two level posterior fixations with a

A

RETROSPECTIVE study has been carried out on 34 patients,

semi-rigid element on the level above the intervertebral arthrodesis (Figure 2). The goal of the study was to evaluate the effects of the controlled micro-movements on the "free" hyper stimulated segment adjacent to the instrumentation which plays the role of a "neo-hinge" intervertebral level.

(a)

(b)

Figure 2 : Semi-rigid posterior fixation with titanium cage (a) or PEEK cage (b), showing the semi-rigid "transitional zone" between the fixed segment and the "free" adjacent level

Twenty-two patients were examined with clinical evaluation and radiological assessment after long-term follow-up. Mean follow-up : 8.27 years

Years of follow-up Number of cases

6 2

7 3

8 8

9 5

10 4

The authors have measured the height of the intervertebral disc, the vertebral slippery and the angular mobility at the semi-rigid instrumented level and at the above level. Clinical outcomes have been evaluated according to Visual Analogic Scale (VAS) and Patient Satisfaction Scale (PSS) .

Results

Fused segments :

after implantation of cages and posterior fixation, 22 cases (100%) of documented fusion appeared by formation of new bone bridges and absence of intervertebral motion (Figure 3). No dismantling of the fixation system or screw breakage was experienced.

Figure 3 : Evaluation of fusion on PLIF level 6 months post op 8 years post op

The level adjacent to the fused disc was protected by the semi-rigid fixation. Posterior interarticular facets spontaneous fusion occurred in only 4 cases (18.5%). Conservation of the disc height was documented in 18 cases (82%) (Figure 4). Dynamic X-rays showed intervertebral motion of this protected level in 15 cases (68.2%). Among these 15 patients, 12 showed mobility inferior to 4° and 3 superior to 4°.

Figure 4 : Conservation of the disc height at the semi-rigid level

Pre op

Immediate post op

7 years post op

as neo-hinge disc. At the "free" adjacent intervertebral level, above the instrumented spinal segment, severe new degeneration was documented in only one case (4.6%) with discal collapsus and new arthrotic conditions. No slipping or degenerative spondylolisthesis was observed. Harmonious and physiological lordosis was restored for 16 patients. Hyperlordotic deformity occured in 4 cases. Intervertebral motion of this "free" disc was assessed as inferior to 4° in 11 cases (52.4%) and superior to 4° in 10 cases (47.6%) (Figure 5). No spontaneous fusion of this disc was observed.

Adjacent " free " disc

Figure 5 : Intervertebral motion of the upper adjacent level

8 years post op

Clinical outcomes

The long-term clinical outcomes were excellent, with persistent mild low back pain inferior to 50% for 16 patients and absence of radicular symptoms in 16 cases according to VAS (Visual Analogue Scale). After clinical assessment by using SF36 scale, 21 patients (91%) remained very satisfied from the surgical protocol. No patient experienced failure of the fixation system and no revision surgery was required.

Low back pain (LBP):

16 cases (72%) : pain < 5/10 Preoperatively LBP 8.36 1-year FU 5.12 8.27-year FU 3.4

Radicular leg pain (RLP):

15 cases (68.2%) : pain < 1/10 Preoperatively RLP 6.23 1-year FU 3.2 8.27-year FU 2.1

Patient's satisfaction scale:

Grade 1 : 21 patients (91%) were very satisfied and would have resumed the same surgery, if necessary.

Conclusion

P

REVENTIVE protection of the intervertebral level adjacent to the fused segment is indicated in case of adjacent degenerative disc. Semi-rigid fixation for this adjacent level seems to create the mechanical conditions for a temporary transitional intervertebral zone between the rigid fused segment and the "free" adjacent hypersollicitated level above the spinal instrumentation. This biomechanical intermediate zone seems to be very important before the restoration of the physiological lordosis and the balance of the lumbar spine. Such temporary semi-rigid fixation seems to be an efficient measure to prevent adjacent level degeneration.

Bibliography

1. Axelsson P: The spondylolytic vertebra and its adjacent segment. Mobility measured before and after posterolateral fusion. Spine 1997; 22 (4):414-417 2. Brunet JA: Acquired spondylolysis after spinal fusion. The Journal of Bone and Joint Surgery 1984: 720-724 3. Dekutoski MB : Comparison of in vivo and in vitro adjacent segment motion after lumbar fusion. Spine1994; 19 (15): 17454. Eck JC: Adjacent-segment degeneration after lumbar fusion: a review of clinical, biomechanical, and radiologic studies. The American Journal of Orthopedics 1999: 336-340 5. Etebar S: Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability. J Neurosurg 1999; 90: 163-169 6. Ha KY: Effect of immobilization and configuration on lumbar adjacent-segment biomechanics. The Journal of Spinal Disorders 1993; 6 (2): 99-105 7. Harris RI: Acquired spondylolysis as a sequel to spine fusion. The Journal of Bone and Joint Surgery 1963; 45 A (6): 1159-1170 8. Lee KC: Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 1988; 13 (3): 375-377 9. Lee KC: Lumbosacral spinal fusion: a biomechanical study. Spine 1984; 9 (6): 574-581 10. Nagata H: The effects of immobilization of long segments of the spine on the adjacent and distal facet force and lumbosacral motion. Spine 1993; 18 (16): 2471-2479 11. Perrin G.: Surgical treatment of severe lateral and foraminal spine degenerative stenosis in lumbar spine stenosis. Robert Gurzbung & Marek Szpaski. Lippincott - Williams & Wilkins. Philadelphia, USA 2000 ; 313-320 12. Perrin G.: Usefulness of intervertebral titanium CH cages for PLIF and posterior fixation with semi-rigid Isolock plates. Robert Gurzbung & Marek Szpaski. Lippincott - Raven. Philadelphia, USA 1996 13. Wimmer C. : AP-Translation in the proximal disc adjacent to lumbar spine fusion. Acta Orthop Scand 1997; 68 (3): 269-272

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