Procedure Description: Direct Lateral Transpsoas Lumbar Interbody Fusion

Direct lateral transpsoas lumbar interbody fusion is performed with the patient in a right lateral decubitus position on a radiolucent table for a left sided approach. If necessary the spine may be approached from the right side particularly if L4-5 is tilted with convex right. The patient is secured with anterior and posterior cloth roll towels or taped to a closed Wilson frame. A large jell roll positioned transversely or flexing of the Wilson frame will wedge open the left flank (Figure 5).

Figure 5: Patient positioned in right lateral decuitus position on closed Wilson frame.

It is important to use support materials that will not impede fluoroscopic visualization. The right axilla and lower extremities are appropriately padded. The left upper extremity is supported with pillows or airplane splint. Biplanar fluoroscopy is used prior to skin preparation to visualize the spine and localize the skin incision (Figure 6).

Figure 6: Intraoperative fluoroscopy to assist in planning for skin incision.

A marker over the mid-lateral vertebral body at the appropriate disc space designates the preferred location for incision. In multi-level cases the skin incision is centered over the vertebra equidistant from the cephalic and caudal disc spaces to be instrumented. Standard preparation of the surgical field is then performed. Preparation of the operative field provides access to extend the approach, "Saber incision", should emergent situations dictate rapid control of vascular structures.

The skin is incised (usually 1 to 1-1/2 inches) through subcutaneous tissue down to the external abdominal oblique musculature. Each layer of muscle is bluntly split with large Kelley clamps in line with its fibers. The transversalis fascia is opened exposing the retroperitoneal fat. Digital palpation of the psoas muscle aids in localization of the lateral vertebral body contour. Large lateral osteophytes may make docking on the lateral disc space more difficult. In deformity cases, approaches within the concavity will bring the segmental vessels into close proximity of the target location. Upon entering the retroperitoneal space a blunt cannulated probe is directed towards the posterior wall of the abdominal cavity. Subsequently, it is maneuvered anteriorly positioned over the target disc space and confirmed with biplanar fluoroscopy (Figure 7).

Figure 7: Intraoperative fluoroscopy with blunt dilator over target disc space. Preferred entry location is just anterior to the midline of the vertebral body.

Neurophysiologic monitoring may improve the safety of probe placement. The probe is secured to the disc space via sharp guide wire followed by sequential tube dilation. A tabletop self-retaining system facilitates stabilization of the tube to the target disc. Inner tubes are removed and the disc space is prepared. Preparation requires trephining of the annulus to create the initial annulatomy, disc space dilation and fixation of the tube via fixation pin, to the lateral vertebral body (Figure 8).

Figure 8: Intraoperative fluoroscopy illustrating radiolucent tubular retractor fixated to vertebral body via single pin. Canulated dilator remains in place within L3-4 disc space.

Present instrumentation will allow utilization of self-distracting interbody devices up to 14 millimeters in height and 44 millimeters in length contoured for lumbar lordosis. The fusion bed is prepared by removal of the cartilaginous endplate. When necessary, the contralateral annulus is released (Figure 9).

Figure 9: Intraoperative fluoroscopy illustrating release of contraleral annulus.

Implants are positioned (Figures 10A, 10B, 10C); the working tubes are removed.

Figure 10A	Figure 10B

Figure 10C

Figures 10A, B,C: Intraoperative AP and lateral radiographs with clinical photograph showing placement of interbody device. Anterior or posterior instrumentation may be added for improved stabilization.

Muscle layers close anatomically upon removal of the tubes. Fascia over the external abdominal oblique is approximated followed by the subcutaneous layer and skin. Deep drains are not employed.