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conservative treatment. Overall complication rate was 7%. The evidence presented in this systematic review was relatively low and the costs of the IPDs were high, which at that time were already widely used, therefore we needed more thorough (cost-) effectiveness data.
The design of the Felix Trial is presented in Chapter 4. The manufacturers of these new implants claimed that treatment with IPDs would give a faster recovery. Therefore, IPDs had to be superior at short-term (eight weeks) compared with (the gold standard) bony decompression. At least 160 patients had to be randomized. To enroll enough patients, fifteen hospitals participated in the study after approval of the protocol by the medical ethics committees.
The 1-year clinical results (presented in Chapter 5) did not show any benefit of treatment with IPD over bony decompression. This double-blinded study could not confirm the hypothesized short-term advantage of interspinous process device over conventional “simple” decompression. Furthermore, after 1-year significantly more patients were re-operated in the IPD group (29%) compared with the bony decompression group (8%). The subgroup analysis (Chapter 5) could neither assign any subgroup (such as elderly or obese people) which would benefit from treatment with IPDs.
The long-term (2-years) results were similar to the 1-year results (Chapter 6). The long-term follow-up did not show important differences in results (based on the ZCQ) comparing treatment with IPD and conventional bony decompression in patients with INC based on LSS. Furthermore, similar to the one-year analysis, the re-operation rate was significantly higher (overall and in the period between 52 and 104 weeks) in the IPD group compared with the bony decompression group. Back pain was hypothesized to be less in the group that underwent an operation with less tissue damage, namely the IPD without bony decompression group. However, to the contrary, the long-term back pain in IPD group was significantly – though not clinically relevant – higher compared with the conventional bony decompression group.
Chapter 7 describes the cost-benefit analysis of the Felix Trial. The economic evaluation showed less favourable QALY outcomes (not significant) after IPD. Healthcare costs were higher for IPD treatment compared with decompression. From a societal perspective the cost of IPD treatment were also higher, though not significant. Implantation of IPD is highly unlikely to be cost-effective compared with bony decompression for patients with INC caused by LSS. The use of these implants over the past three decades could therefore not be justified based on this study.
Summary
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