Nerve Injury to the Posterior Rami Medial Branch During the Insertion of Pedicle Screws Comparison of Mini-Open Versus Percutaneous Pedicle Screw Insertion Techniques

Study Design. The risk for transection of the medial branch nerve (MBN) after minimally invasive insertion of pedicle screws was evaluated in a human cadaver model. Objective. The purpose of this study is to compare the risk of MBN transection after pedicle screw insertion using mini-open versus percutaneous minimally invasive techniques. Summary of Background Data. The multifidus muscle is innervated by the MBN that originates from the posterior rami. Since the anatomic course of the MBN passes near the mamillary process it is vulnerable to injury during pedicle screw insertion, even if minimally invasive spine techniques are implemented. Methods. Five cadaveric specimens were used for the study. Pedicle screws were inserted into the lumbar spine using either percutaneous or mini-open techniques. The integrity of the MBN was examined directly through anatomic dissection of the posterior spine. Results. The soft tissue damage area around the screw insertion site was significantly greater in the mini-open compared with the percutaneous technique. MBN transection was observed in 84% (21/25) of the pedicles when using the mini-open technique and in 20% (5/25) when the percutaneous insertion technique was used (P < 0.01%). Conclusion. Using a percutaneous technique for pedicle screw insertion significantly reduces the risk of injury to the MBN. We therefore recommend using this technique especially at the most cephalic levels to minimize the risk of denervating the multifidus muscle fascicles that originate from the adjacent mobile level.