Tubular Lumbar Decompressive Laminectomy and Foraminotomy

15 Tubular Lumbar Decompressive Laminectomy and Foraminotomy

Mengqiao Alan Xi and Mick Perez-Cruet

15.1 Introduction

Lumbar spinal stenosis is one of the leading causes of low back pain, leg pain, physical disability, and reduced quality of life in the elderly population.1 The aging intervertebral disk is prone to a series of biological changes that lead to its structural decline. As disk height is lost, the spinal canal and neural foramina can become constricted, resulting in spinal stenosis. This is further accentuated by the secondary hypertrophic changes in ligamentum flavum and facet joints.² Surgery represents a definitive treatment for the underlying pathology, directly addressing age-related deterioration in the structural integrity of the spine.³ As our active population ages, an increasing number of patients have shown interest in seeking surgical intervention for spinal stenosis to maintain their quality of life.⁴

Diagnosis of lumbar spinal stenosis depends on both clinical and radiographic evidence. The typical presenting symptoms of lumbar spinal stenosis include unilateral or bilateral low back pain, leg pain, weakness, paresthesia, and neurogenic claudication. While the other symptoms are relatively obvious, neurogenic claudication may not be readily differentiated from vascular claudication. It is characterized by symptomatic relief when the lumbar spine is placed in flexion. A useful diagnostic tool is the bicycle test, where the patient is instructed to ride a stationary bicycle while leaning forward on the handles.⁵ Alleviation of pain suggests neurogenic claudication, while aggravation of pain points to a vascular origin. Neurologic symptoms tend to remain benign until the very late stages of the disease, when foraminal dimensions become severely compromised. Impingement of the cauda equina can result from acute disk herniation at the level of preexisting stenosis, leading to autonomic disturbances, such as loss of bladder control.

If a constellation of these symptoms and signs are evident upon the initial visit, then plain films should be considered first to explore the existence of motion segment diseases. Once it is confirmed, the surgeon may proceed with MRI of the lumbar spine. The detailed soft tissue rendition on MRI is particularly useful in identifying disk abnormalities, facet and ligamentum flavum hypertrophy, and impinged neural structures (Fig. 15.1). Alternatively, myelography in conjunction with CT can be used in patients unsuitable for MRI or when the patient has had previous surgery and hardware placement. It is critical to understand, however, that a canal that appears stenotic on imaging may not be symptogenic. Surgery is indicated only in the presence of both radiographic and clinical evidence, to avoid complications associated with unnecessary decompression.

15.2 Surgical Options for Lumbar Decompression

Recently, minimally invasive spine surgery (MIS) has gained significant popularity among surgeons as an alternative to the traditional open approach. In open decompression, access to the lumbar spine is gained through a large incision, paraspinal muscles are stripped away, and the lamina is usually removed bilaterally, along with an en bloc resection of the spinous process and associated ligaments, including the ligamentum flavum. Although this method results in structurally complete decompression of the spinal canal, it imposes a large number of physical changes on the already degenerate spine, raising concern about too much decompression. Additionally, important structural elements of the spine are removed (i.e., spinous process and interspinous ligament) that are not part of the offending pathology. The surgical trauma and debris can lead to formation of extensive perineural scar, which may explain the suboptimal outcomes associated with open procedures (Fig. 15.2). Extensive paraspinal muscular retraction and injury often lead to scar and injury of these important structural support muscles.

Fig. 15.1 (a) Sagittal and (b) axial T2-weighted MRI demonstrates severe spinal stenosis at the L4–L5 level and hypertrophy of the ligamentum flavum (yellow arrows).

The minimally invasive laminectomy technique was designed as a more refined approach for the treatment of lumbar stenosis. In this method, microscopic or endoscopic visual access is achieved through a series of tubular muscle dilations, which preserve much of the musculature lining the spinal column.6,7 Initially, a bilateral approach was used that involved paired incisions on either side of the lumbar pathology. Later, a unilateral approach was developed to further reduce tissue damage and promote postoperative recovery.⁸ This is achieved through a single paraspinal incision followed by muscle dilation to approach the spine. The ipsilateral lamina and lateral recess are first decompressed. Then the working channel is readjusted to establish a trajectory to the contralateral side, whereupon the spinous process and contralateral lamina are undercut and the contralateral neural foramen is decompressed. After bony decompression, the ligamentum flavum is removed and facet fusion is performed. The technique has been refined to ensure adequate neural decompression while achieving arthrodesis that will help to prevent recurrence of the stenosis.

Fig. 15.2 (a) Sagittal and (b) axial T2-weighted MRIs showing open laminectomy (top images) versus (c) sagittal and (d) axial MRIs after minimally invasive laminectomy (bottom images). Note the extensive paraspinal scarring (yellow arrow) secondary to open decompression, while scarring is absent with the minimally invasive approach.

The contralateral decompression procedure, however, can present a challenge to surgeons, because the line of sight is confined by the circumference of the working channel. The endoscopic camera captures images beyond the boundaries of the working channel and projects them onto a monitor. Instruments can then reach to territories not directly visible and can be manipulated with camera guidance. One of the disadvantages of using an endoscopic system, however, is that it produces two-dimensional video images rather than the stereoscopic, three-dimensional images seen with surgical microscopy. In addition, it takes a certain amount of practice to acquire the hand-eye coordination for endoscopic maneuvers. It is therefore advisable to defer surgery on morbidly obese patients and same-level reoperation cases until considerable experience is attained, as these situations typically entail greater level of proficiency. Additionally, the camera tip of the endoscope tends to get dirty and frequently requires cleaning, which delays the procedure. For these reasons, we have moved away from the endoscope and developed a technique using the microscope. To facilitate contralateral decompression, the patient is tilted slightly away from the surgeon, the tubular retractor is wanded laterally, and the spinous process and contralateral lamina are undercut. In this manner, excellent microscopic visualization is used to achieve adequate decompression.

The METRx system (Medtronic, Memphis, TN) was one of the earliest instrument sets used for performing minimally invasive laminectomy. Our group has substantial experience with this system. The tubular retractor comes in different diameters, ranging from 14 mm to 26 mm in stainless material or 18 mm in disposable material. We typically use an 18-mm diameter tubular retractor for performing MIS laminectomy. Recently, newer systems have been developed that eliminate the K-wire and muscle dilators and allow for a safer approach to the spine (Fig. 15.3). Long, slender bayonetted instruments facilitate visualization through the working channel. The clinical safety and effectiveness of this system have been investigated and confirmed by several studies.^9,10,11 This chapter describes the MIS laminectomy technique.

Fig. 15.3 (a,b) Illustrations, (c) photo, and (d) intraoperative fluoroscopic images showing the application of the One-Step Dilator (Thompson MIS, Salem, NH) to approach the spine in a muscle-splitting fashion. The technique prevents muscle damage while approaching the spine bloodlessly.

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