Interlaminar Lumbar Instrumented Fusions (ILIF)

Introduction

As the population ages, the incidence of lumbar spinal stenosis and the number of available surgical options for its treatment continue to increase. To date, posterolateral spinal fusion via pedicle screw and rod fixation has been regarded as the mainstay surgical treatment option for stabilization of a degenerative spinal segment. The intended benefits of this treatment include reduced back pain and prevention of continued degeneration of the segment through stabilization and development of bony fusion. However, pedicle screw and rod constructs carry significant morbidity, such as cerebrospinal fluid leaks, neural injury from misplacement of pedicle screws, adjacent segment degeneration and disease, and instrumentation-related complications. In addition, this procedure often injures the unfused rostral facet joints and its musculotendinous attachments. Furthermore, pedicle screw and rod fusion constructs require greater operative times, which may be difficult for elderly patients to tolerate.

In many patients, pedicle screw and rod fixation may be an overtreatment. In the degenerative spine in which there is mechanical back pain and the presence of neurologic symptoms with or without grade I spondylolisthesis, the unfavorable adverse outcomes and increased morbidity of instrumented fusion may not be worth the risks. In contrast, decompression without fusion may fail to address all of the patients’ symptoms and may fail to slow the progression of degenerative changes. The interlaminar lumbar instrumented fusion (ILIF) technique was developed to overcome the potential shortcomings of these current treatment standards by avoiding pedicle screw fixation while creating stabilization in a minimally disruptive surgical technique.

Indications

The ILIF procedure is indicated in cases where decompression and spinal stabilization is required. The most common indication is grade I degenerative spondylolisthesis and spinal stenosis. The authors typically choose this procedure in a patient with advanced age where a more aggressive pedicle screw construct is less desirable.

Limitations

There are a number of limitations of ILIF. The patient’s site of spinal compression must be located at the interspinous space. If the compression is significant in the craniocaudal direction and the spinous process and significant portions of the laminae will have to be resected to perform an adequate decompression, the ILIF procedure will not be possible. The procedure is not possible in revision cases in which the spinous processes have previously been resected. Care must be taken in patients with severe osteoporosis. In these patients it may be easy to fracture the spinous process during plate placement. This procedure is not ideal for those patients with high-grade instability. Lastly, there is limited bony surface area for bony fusion during this procedure. The facets may be packed with auto or allogenic bone; many of the implants also permit the placement of fusion material within the device.