Minimally Invasive Lumber decompression

MILD technique

Lumbar canal stenosis is generally described as compression of the neural elements related to a variety of degenerative changes including: facet hypertrophy, hypertrophic ligamentum flavum, and bulging of the intervertebral disc. In LSS, the space within the spinal canal narrows, which leads to asymptomatic compression of nerves and ultimately symptomatic neurogenic claudication. The goal of any surgical treatment of LSS is relief of symptoms by adequate neural decompression while preserving as much of the anatomy, stability, and biomechanics of the lumbar spine as possible. Endoscopic and traditional open surgical treatment of LSS may not only require the 1.5-6 cm incisions mentioned above, but also involve a wide laminectomy and undercutting of the medial facet with foraminotomy; leading to local tissue trauma, scarring, and potential postoperative spinal instability.

The minimally invasive lumbar decompression (MILD) procedure offers a minimally invasive alternative to a standard laminotomy-laminectomy. Typically, mild is performed using local anesthesia and IV sedation to keep the patient comfortable. This procedure treats LSS by removing small, but adequate, portions of laminar bone and debulking the ligamentum flavum.

This improves the space in the spinal canal while minimizing trauma to the surrounding tissue and bony structures. The restoration of space is confirmed during the procedure utilizing the continuous contralateral oblique epidurogram. Purposeful design elements of the surgical instruments used in the mild procedure include built-in safety features such as blunt tips to protect structures at the posterior approach and special top cutting surfaces for precision cutting at the desired angle. The disposable mild kit also includes a portal stabilizer to minimize medial and lateral movement during the procedure, and an instrument depth guide. The typical mild patient is elderly, often 65 years of age or older, and presents with lumbar spine neurogenic claudication symptoms thought to be concordant with findings of lumbar stenosis verified through imaging (MRI or CT) studies. Conservative measures have or vascular claudication, is relieved by flexion and not by mere cessation of walking as in vascular claudications.

Use of a simple standing test or, historically the Van Gelderen bicycle test, can assist when distinguishing between vascular and neurogenic claudication. The clinical symptoms from LSS result from a constrained cross sectional area of the canal either due to direct compression of the nerve roots that comprise the cauda equina, or due to reduction of venous outflow resulting in nerve root ischemia (or some combination of the two). The presence of a hypertrophied ligamentum flavum, compromising the anterior-posterior and lateral dimensions of the spinal canal identifies optimal candidates for the procedure.

At the beginning of the procedure the patient is placed in the prone position on a radiolucent operating table, draped, and sterilely prepped. Appropriate bolstering is used as needed. An epidurogram is then performed for the purpose of identifying the hypertrophic ligament flavum. Utilization of the contralateral oblique view presents the thickest cross-section of the lamina, providing optimal ligamentum infolding imaging.

Next, the interlaminar space is identified through fluoroscopic visualization. After the trajectory has been planned and the patient’s skin marked, the mild 6G portal and 7G trocar are inserted percutaneously. These  devices are advanced along the desired trajectory under fluoroscopic guidance. Once positioned, the trocar is removed, leaving the access portal in the interlaminar space. The mild Bone Sculptor Rongeur isalleviated symptoms satisfactorily. Neurogenic claudication is triggered by axial loading activities and unlike intermittent placed through the access portal to the lamina. The physician carefully rotates this device, which precisely cuts and then removes small pieces of bone. Once sufficient access is obtained, the Rongeur is removed and the mild Tissue Sculptor is advanced through the portal under the lamina into the dorsal aspect of the hypertrophic ligamentum flavum. Debulking of the ligamentum flavum is accomplished by removing the collagen laden posterior portion of the ligament, while leaving the ventral fibers of the ligament intact. An improved/easier contrast flow (reduction of infolding), along with limited availability of tissue to be removed, are clear indicators of the decompression endpoint on epidurogram. The procedure can be performed bilaterally and on multiple vertebral levels at one or more settings. It should be noted that the angle of the cutting tip on the instrumentation requires a new incision and instrument insertion when the procedure is being performed bilaterally or at another level. Once adequate decompression has been achieved at the final operative level, the portal is removed and the wound typically closed with a sterile adhesive bandage. Since there is minimal soft tissue trauma, patients are usually observed for two hours after the procedure (or per facility standard protocol used for light sedation and local anesthetic) and subsequently discharged as clinically indicated. Patients are allowed to ambulate as tolerated and instructed to increase activities slowly. No implants are left behind and future treatment is not impeded by the mild procedure.

Exaple videos of th MILD technique