Navigated 2-level posterior lumbar fusion: a 5-cm-incision procedure

The indications for navigated PLF were symptomatic 2-level degenerative disc disease. Navigated PLF takes one incision, the length of which is about 5 cm. Through the 5-cm incision, pedicle screw placement, decompression, discectomy, cage insertion, and bone grafting can be performed. Accordingly, because of the incision’s being small, blood loss can be decreased. Another advantage of navigated PLF is that the pedicle screws are inserted under the guidance of the infra-red navigators, which not only make the procedure safer but also completely avoid the operation personnel’s exposure to radiation.

The indications for conventional PLF were the same as those of navigated PLF. Navigated PLF is performed with the patient under general anesthesia and in prone position on a carbon-fiber operating table. A 5-cm longitudinal median incision is made. Detachment of paravertebral muscles and exposure of laminas are performed bilaterally.

Firstly, a patient tracker is fixed to the spinal process (Fig. 1) followed by a 3D scanning using a C-arm (Fig. 2). After the scanning, the image data are transferred within 30 s from the 3D C-arm to the navigation workstation. As a result, the lumbar spine of the patient can be tracked by the navigation system in real time. Meanwhile, the navigated instruments are also being tracked.

Secondly, under the guidance of the navigator, six pedicle screws (multi-axial, 6.5-mm diameter) are inserted one by one. When a screw is being inserted, the muscles are pulled laterally and the operator always has the visual of the entry point (Fig. 3). Once all the six pedicle screws have been inserted, another 3D scanning is usually performed to check the position of each screw. If all the screws have shown to be well placed, the patient tracker is removed from the spinal process.

Lastly, a retractor is inserted to give the operator the visual of the laminas, by which decompression, discectomy, cage insertion, bone grafting, rod instrumentation, and screw nuts locking are performed (Fig. 4). Circumferential decompression of the dural sac and nerve roots was completed by removal of the lateral part of the lamina of the two vertebrae, and was considered satisfactory until only the middle pedicle remained visible. Posterolateral fusion using both autograft and allograft was performed in every case.

A comparative study was performed between navigated PLF and conventional PLF. Forty patients who were indicated for 2-level lumbar fusion were included and randomized to either navigated PLF group or open-PLF group. Blood loss, operation time, incision length, complications, bed rest period, and length of hospitalization were recorded. Oswestry Disability Index (ODI) scoring was also performed for each patient before surgery, 3 months after surgery, and 2 years after surgery.

As shown by the results, the navigated PLF showed several advantages compared to the conventional PLF. The navigated PLF group showed significantly less intraoperative blood loss. This finding is in accordance with the previous studies. As shown in Table 5, the average intraoperative blood loss of 2-level conventional PLIF were reported to be 612 ml (by Sakaura [10]) and 1277.6 ml (by Hioki [11]), while the average intraoperative blood loss of 2-level minimally invasive TLIF was much less, which was reported to be 206 ml (by Scarone [12]). This could be due to the navigated PLF’s having smaller incision and less soft-tissue destruction. Furthermore, the current study showed that the navigated PLF procedure had less postoperative blood loss in comparison with the conventional PLF (662.3l vs. 437.5 ml, p = 0.007). Regarding operation time, both of the previous and current studies showed similar results, the time consumption of minimally invasive and conventional lumbar fusion were comparable (Table 5).

As for clinical outcomes, the both groups showed significant ODI-score improvements, which also compared well with the previous studies [3‐9].

Several minimally invasive procedures have been developed in order to lessen the approach related morbidity. Schwender et al. [1] presented the first clinical series reporting on minimally invasive transforaminal lumbar interbody fusion (MiTLIF). A paramedian, muscle-sparing approach was performed through a tubular retractor. Facetectomy, discectomy, and interbody cage insertion through the tube were performed. Bilateral percutaneous pedicle screw-rod placement was then accomplished with the Sextant system. Scheufler et al. [3] reported their clinical study on percutaneous transforaminal lumbar interbody fusion (pTLIF). Decompression, discectomy, and interbody cage insertion were performed through tubular retractors followed by percutaneous pedicle screw-rod fixation. Isaacs et al. [2] developed microendoscopic transforaminal lumbar interbody fusion (METLIF). Hemilaminectomy, unilateral facetectomy, and microdiscectomy were performed using microendoscopy-assisted lumbar fusion through a working channel. Bilateral percutaneous pedicle screws were then inserted.

All the minimally invasive techniques mentioned above require totally four to seven incisions, and one of these incisions has to be around 4 cm (ranging from 3.5 to 4.5 cm) so that an expandable retractor can be accommodated. The present technique requires only a single 5-cm incision, and hence greatly decreases the number of incisions, which is one of the superiorities of navigated PLF over the other minimally invasive techniques. However, small skin incision does not necessarily mean small muscle injury. Navigated PLF in the current study still involves muscle detachment and ligamentous disruption, which should be improved in the future. Small skin incision could be a problem for navigation, because the patient tracker could be moving when the wound is being retracted laterally. As such, patient tracker must be fixed firmly and care must be taken when retracting the wound.

The length of incision could be further decreased if the pedicle-screw direction was well designed [13].

Another important advantage of navigated PLF is that the pedicle screws are inserted under the guidance of the infra-red navigators, which not only make the procedure safer but also completely avoid the operation personnel’s exposure to radiation.