Adjacent segment degeneration after single-segment PLIF: the risk factor for degeneration and its impact on clinical outcomes

Abstract

Purpose: To investigate: (1) the risk factors for radiologic cranial adjacent segment degeneration (ASD) after single-segment PLIF at the same level, and (2) the impact of the ASD on the clinical outcomes.

Methods: From October 2004 to May 2009, 109 patients who underwent PLIF for degenerative instability at L4/5 and have more than 2 years follow-up were studied retrospectively. We measured the preoperative bone mineral density (BMD), lumbar lordosis, the lumbosacral joint angle, the lumbar inclination, the height and the dynamic angulation of the intervertebral space at the fused segments and the upper adjacent segment, the sliding displacement between L3 and L4. Clinical outcomes were evaluated using the Japanese Orthopedic Association (JOA) score and the Oswestry Disability Index (ODI). Patients were divided into two groups according to the progression of L3-L4 degeneration: Group A without progression of L3-L4 degeneration, Group B with progression of L3-L4 degeneration. Clinical outcomes and radiologic measurement index between the two groups were compared, and the risk factors for progression of L3-L4 degeneration were analyzed. The correlation between clinical outcomes and progression of L3-L4 degeneration were also investigated.

Results: There were 11 patients (22%) classified into Group A. No significant difference was found between the two groups in terms of the lordosis angle at L1 and S1, the laminar inclination at L3, the pre-existing L3-L4 disk degeneration, the lordosis angle of L4-L5, the lumbosacral joint angle and preoperative BMD (P > 0.05). Significant differences were found between the two groups in age. No significant difference was found between the two groups in the ODI and the JOA score at the final follow-up (P > 0.05).

Conclusion: Radiologic degeneration of the cranial adjacent segment after single-segment PLIF did not significantly correlate with clinical outcomes. Age was a risk factor for radiologic degeneration, however, there was no significant correlation between degeneration and preoperative radiologic factors and bone mineral density (BMD).

Fig. 1

Image measurement indices: height of the intervertebral disc = (a + b)/2; angle α = angulation of the intervertebral space; angle γ = lordosis angle of the lumbar spine; angle β = lumbosacral joint angle

Fig. 2

Image measurement indices: The laminar inclination angle at L3 was defined as the angle formed by a straight line connecting the tip of the superior facet with the base of the inferior facet and a straight line connecting the midpoints of the anterior and posterior vertebral cortices on the lateral radiographs