Paraspinal muscle damage is inevitable during conventional posterior lumbar fusion surgery. Minimal invasive surgery is postulated to result in less muscle damage and better outcome. The aim of this study is to monitor metabolic changes of the paraspinal muscle and to evaluate paraspinal muscle damage during surgery using microdialysis (MD).

Posterior approach is a common and important surgical procedure for various lumbar diseases. Owing to the anatomy, the damage of paraspinal muscle is inevitable during conventional posterior lumbar fusion surgery. Degeneration and malfunction of the paraspinal muscle might associate with pain and inferior postoperative clinical outcome.

Inclusion criteria:

• patients who undergo conventional instrumented posterolateral lumbar fusion.

Exclusion criteria:

• previous fusion
• chronic metabolic disease
• tumor or metastasis
• postoperative surgical complications and complications during surgery