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PEEK Cages in Lumbar Fusion: Mid-term Clinical Outcome and Radiological Fusion.

STUDY DESIGN:: Historical cohort analysis. OBJECTIVE:: Evaluation of mid-term clinical outcome and radiological fusion in patients treated with a polyetheretherketone (PEEK) cage. SUMMARY OF BACKGROUND DATA:: Anterior Lumbar Interbody Fusion (ALIF) can be a good alternative in chronic low back pain when conservative treatment fails. Although titanium alloy cages give good fusion rates, disadvantages are the subsidence of the cage in the adjacent vertebrae and problematic radiological evaluation of fusion. PEEK cages, such as the Synfix-LR® cage (Synthes, Switzerland) should overcome this. METHODS:: From December 2004 until August 2007 a total of 95 patients (21 double-level, 74 single-level) with degenerative disc disease from L3-S1 were operated by a single surgeon. The number of reoperations was counted. Radiological fusion on CT-scan was scored with a new scoring system by an independent skeletal radiologist and orthopaedic surgeon. Intra-observer agreement and specificity were assessed. Clinical improvement was measured by the ODI score. The median duration of clinical follow-up was 47.7 months (range 29.9-61.6 months). RESULTS:: In total 26 patients were reoperated after a median of 17.6 months (range 6.7-46.9) of the initial surgery. In total 23 patients (18 single-level, 5 double-level) were reoperated for symptomatic pseudarthrosis. A moderate agreement (κ=0.36) and a specificity of 70% and 37% for the radiologist and orthopaedic surgeon, respectively, were found for scoring bony bridging. The ODI score improved after initial surgery, but reoperated patients reported a significantly lower improvement. CONCLUSIONS:: A high number of reoperations after an ALIF-procedure with the Synfix-LR® cage was found, mainly due to symptomatic pseudarthrosis. The absence of posterior fixation in combination with lower stiffness and the hydrophobic characteristics of PEEK probably leads to insufficient initial stability, creating suboptimal conditions for bony bridging, and thus solid fusion. The proposed ease of the evaluation of radiological fusion could not be supported. Clinicians should be alert on pseudarthrosis when patients treated with the Synfix-LR® cage presented with persisted or aggravated complaints.