December 14, 2018
3 min read

New guided approach to instrumented lumbar fusion evolved from earlier methods

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The recent introduction of 3-D-printed and patient-matched pedicle screw guides has modernized spine surgery planning and procedures. The process for this patient-matched approach provides for an efficient and effective technique that reduces radiation exposure and can save hospitals and health systems on expenditures for capital purchases, such as navigation systems or CT-scanning technology. In addition, surgeons are less reliant today on free-hand techniques than they once were.

This year, 3-D-printed, patient-matched pedicle screw guides were introduced for instrumented lumbar fusion in the form of MySpine MC (Medacta International), which guides pedicle screws in a trajectory that evolves from the well-established cortical bone trajectory (CBT).

The patient-matched, CT-based preoperative planning process involved, which is a key aspect of this instrumented technique, allows for selection of optimal screw length, diameter and trajectory to maximize cortical bone contact. The system accommodates larger screw diameters and lengths, as well as four points of cortical bone contact for enhanced fixation. Using the placement guide helps ensure pedicle screw placement is accurate, reproducible and reliable.

Nima Salari
Nima Salari

Build the preoperative plan

Once a surgical candidate is identified, preoperative CT scans are obtained according to a specialized low-dose radiation protocol. A detailed preoperative plan is built with an engineer via a web-based planning tool. In this phase of planning, surgeons can determine screw size, diameter, length and, ultimately, the optimal trajectory to achieve strong cortical bone fixation (Figure 1).

In addition to providing enhanced fixation, this guided technique, which evolved from CBT, eliminates the need for intraoperative navigational systems and reduces radiation exposure, muscular dissection and operative time.

After the preoperative plan is approved and finalized, it is converted into a 3-D-printed bone model with a matching drill guide which are shipped terminally sterile and can therefore be immediately used intraoperatively. Using the model and drill guide, the bone model that was created can be compared to a patient’s unique anatomy and the surgeon can practice the exact fit of the drill guide before performing dissection (Figure 2).

instrumented lumbar fusion
Figure 1. The patient-specific preoperative planning process using the web-based tool is shown.
Figure 2. A 3-D-printed model of the patient’s vertebral segment is created and can be compared to the patient’s anatomy prior to surgery.
Figure 3. The minimally invasive surgery midline approach through which the procedure is done is shown (a). It is performed through an incision that is less than 2-inches long (b).
Figure 4. Preplanning and postoperative images show the screw trajectory used.
Figure 5. The drill guide is shown in place from the surgeon’s perspective (a) and close-up (b).

Source: Nima Salari, MD


Small incision minimizes blood loss

The MySpine MC guide is adapted for a minimally invasive midline approach that can be performed through an incision that is smaller than 2 inches. The approach helps minimize tissue damage and blood loss and is associated with a faster recovery and less rehabilitation time for patients (Figure 3).

Screw placement that I have performed via the drill guide has proven to be more reliable than placement done with traditional free-hand approaches. This approach also required fewer operative steps, as well as less equipment and time to complete the surgery (Figure 4).

Once the midline approach is completed, the appropriate surfaces, such as areas of the pars interarticularis and lamina, and portions of the lamina that fall over the inferior articular process, should be exposed to accommodate the drill guide. The drill guides are applied in the same way that was practiced using the 3-D-printed bone model, and drilling can begin to create the screw holes (Figure 5).

Screws placed for interbody fusion

At this point, the surgeon can proceed with a standard fusion approach. The screws are placed at any time during the case that is appropriate to provide fixation for posterior lumbar interbody fusion or transforaminal lumbar interbody fusion or to back up an anterior lumbar fusion.

After surgery, patients can typically return home within 24 hours. They can be evaluated and monitored using radiographs and follow-up imaging to ensure healing is proceeding properly and according to the standard protocol used following any spinal surgery. Postoperative care associated with this technique is in line with other minimally invasive spine fusion cases and may include a shorter hospital stay and less need for postoperative narcotics.

Disclosure: Salari reports he has a consulting agreement with Medacta.