QUANTITATIVE ASSESSMENT OF FUSION AFTER LUMBOSACRAL ARTHRODESIS

Abstract

Purpose of the study: The results of arthrodesis are often described in the literature by giving the rate of complications and the rate of fusion, but with little information on how the x-rays were assessed qualitatively. The purpose of this retrospective study was to ascertain how useful quantitative radiographic analysis is in evaluating the results of lumbosacral arthrodesis.

Material and methods:The study population included 53 patients who underwent lumbosacral arthrodesis after lumbar discectomy. Clinical data and scores were noted. Sagittal and flexion-extension x-rays of the lumbar spine were obtained at mean five years follow-up. Films were also collected from a group of asymptomatic patients. The quantitative biomechanical analysis was performed with a dedicated software after image digitalization. Spinal, pelvic and vertebral parameters were compared with standard values. The kinetic behavior of the lumbar spine was assessed by recording the intervertebral mobility (IM), and the localization of the rotation centers. Residual mobility of an instrumented segment was considered absent (solid fusion) for MI = 0–3, low (doubtful fusion) for MI = 3–5), and present (nonunion) for MI > 5. The values obtained were compared with statistical tests.

Results: Values recorded for lordosis and pelvis parameters were normal. At last follow-up, solid fusion was noted for 81% of cases, doubtful fusion for 15% and nonunion for 4%. Estimated fusion was correlated with clinical results (r=0.8) and was in agreement (87%) with the surgeon’s qualitative assessment. The adjacent levels presented decreased mobility in 40% of cases and long-term degradation in 17%. The position of the rotation center was normal in 50%.

Discussion: This preliminary study shows that analysis of the sagittal balance and lumbar kinetics provides quantitative information for outcome assessment. Calculating IM determines the residual mobility of the instrumented zone and enables a qualification of the fusion. AS a complement to IM, identifying the position of the rotation center enables a description of the kinematics of the adjacent levels.

Conclusion: Quantitative analysis enables an estimate of 4% for long-term nonunion, with fusion correlated with clinical outcome. Analysis of intervertebral mobility and the position of the rotation center is pertinent for assessment of fusion and the kinematics from lumbar stress x-rays.