Minimally Invasive Transforaminal Lumbar Interbody Fusion with Expandable Cages.

Background: Minimally invasive surgical transforaminal lumbar interbody fusion (MIS-TLIF) is an increasingly common procedure for the treatment of lumbar degenerative pathologies. The MIS-TLIF technique often results in less soft-tissue injury compared with the open TLIF technique, reducing postoperative pain and recovery time^1-3. However, the narrow surgical aperture of this minimally invasive technique has increased the difficulty of interbody cage placement. Expandable cages were designed to improve ease of insertion, improve visualization around the cage on insertion, reduce neurological retraction and injury by passing the nerve root with the implant in a collapsed state, and enable better disc-height and lordosis restoration on expansion⁴.

Description: This procedure is performed with the patient under general anesthesia and in a prone position. The appropriate spinal level is identified with use of fluoroscopy, and bilateral paramidline approaches are made utilizing the Wiltse intermuscular approach. Pedicle screws are placed bilaterally. A pedicle-based retractor or tubular retractor is passed along the Wiltse plane, and bilateral inferior facetectomies are performed. A foraminotomy is performed, including a superior facetectomy on the side with compression of the exiting nerve root. A thorough discectomy with end-plate preparation is performed. The disc space is sized with use of trial components. The cage is then implanted with a pre-expansion height less than the trialed height and is expanded under fluoroscopy. After expansion, the cage is backfilled with allograft and local autograft. Finally, the rods are contoured and reduced bilaterally, followed by closure in a multilayered approach.

Alternatives: Nonoperative alternatives to the minimally invasive TLIF technique include physical therapy or epidural corticosteroid injections. When surgical intervention is indicated, there are several approaches that can be utilized during lumbar interbody fusion, including the posterior, direct lateral, anterior, or oblique approaches⁵.

Rationale: Expandable cages are designed to be inserted in a collapsed configuration and expanded once placed into the interbody space. This design offers numerous potential advantages over static alternatives. The low-profile, expandable cages require less impaction during placement, minimizing iatrogenic end-plate damage. Additionally, expandable cages require less thecal and nerve-root retraction and provide a larger surface footprint once expanded.

Expected outcomes: The MIS-TLIF technique has been shown to significantly reduce back pain, leg pain, and disability, and to significantly increase function, with most improvements observed after 12 months postoperatively. Patients may experience a 51% and 39% reduction in visual analogue pain scores and Oswestry Disability Index scores, respectively⁶. The results for expandable cages compared with traditional static cages in TLIF surgery require further study.

Important tips: The technique utilized during insertion and placement of interbody cages plays an important role in cage subsidence. To reduce the risk of cage subsidence, cages should be placed level with the end plate and in contact with the apophyseal ring anteriorly. Additionally, caution should be taken when expanding the cage to ensure that the cage is not overexpanded, which may also increase the risk of mechanical failure and intraoperative subsidence.It is critical to understand the flexibility of the disc space and the osseous quality of the patient in order to know how much expansion may be applied through the cage without subsidence.If bullet-type cages are utilized, the tip of the cage should cross midline of the vertebral body to avoid generating iatrogenic scoliosis.Spine bone density should be investigated preoperatively in at-risk patients in order to identify osteoporotic patients, who are at greater risk for subsidence and instrumentation failure.Although advances in device technology are welcomed, surgeons should maintain a strong focus on technique to reduce complications and improve clinical outcomes when utilizing expandable cages.

Acronyms & abbreviations: TLIF = transforaminal lumbar interbody fusionMIS = minimally invasive surgeryALIF = anterior lumbar interbody fusionMRI = magnetic resonance imagingCT = computed tomographyPEEK = polyetheretherketoneAP = anterioposteriorEMG = electromyographyDVT = deep vein thrombosisPE = pulmonary embolusODI = Oswestry Disability IndexEXP = expandable.