Unilateral Lumbar Approach for Over-the-Top Bilateral Decompression

32 Unilateral Lumbar Approach for Over-the-Top Bilateral Decompression

Franziska C. Heider, Andreas Korge, and H. Michael Mayer

Summary

The main goal is a bilateral microsurgical decompression of the cauda equina using a unilateral over-the-top approach. The challenge is to achieve decompression with minimal iatrogenic trauma to anatomical structures in the approach region and in the target area.

Keywords: spinal canal disorders narrowing of the spinal canal surgical decompression microsurgery minimally invasive surgery over-the-top bilateral decompression crossover technique

32.1 Introduction

In the history of surgery, reducing iatrogenic tissue trauma has always been regarded as one of the basic principles. In the last two decades, minimally invasive surgery (MIS) techniques for spine surgery have been developed and increasingly used for degenerative conditions, as the usage of new surgical devices and techniques has envolved.1^,² However, MIS in spine surgery must achieve the same or better results than conventional treatment but with less morbidity.

After the adoption of microscope-assisted techniques in neurosurgery in 1977/1978, more and more procedures for lumbar spinal decompression using bilateral approaches with mono- to multisegmental laminotomy were used on an increasingly widespread scale.³^,⁴ In 1997, Spetzger et al²^,⁵ modified the microscope-assisted technique and first described the unilateral approach to only one side (laminotomy) for bilateral decompression of the lumbar spine in a study detailing clinical experiences, as well as providing anatomical considerations.²^,⁵ One year later, Young et al⁶ and McCulloch⁷ followed with studies that showed bilateral decompression of the lumbar spinal canal is practical via a unilateral laminotomy performing an ipsilateral and contralateral “over-the-top” bilateral decompression of both the spinal canal and nerve root canals.²^,⁶^,⁷

The minimally invasive unilateral lumbar approach for “over-the-top” bilateral decompression allows excellent decompression of bilateral lumbar spinal canal stenosis with clearance of the contralateral recess and neuroforamen.²^,⁴^,⁸ This is also refered to as unilateral laminotomy for bilateral decompression (ULBD). The main advantages of this technique are the diminished “access trauma” to the paravertebral muscles and to the facet joints. In particular, the inferior facet contralateral to the approach side as well as its outer capsular surroundings can be preserved completely.⁹ Especially in cases of central spinal or foraminal stenosis associated with degenerative lumbar scoliosis, decompression can be performed from the convex side, thus preserving the stability of the heavily loaded facet joint on the concave side.⁹^,¹⁰ The surgical goal of this minimally invasive, unilateral approach and technique is to decrease the amount of access damage as well as the trauma to the tissue on the way to the spinal canal (skin, muscles, facet joints, and lamina). In cases of bi- or multisegmental spinal canal narrowing/stenosis, the authors recommend to perform the so-called “Slalom” technique.⁹ This is an enlargement as well as improvement of the described MIS technique for selective multisegmental decompression through multiple microsurgical approaches with alternating approach sides. The spinal canal is reached through approaches with alternating the sides (e.g., left–right–left) to balance the tissue trauma on the way to the spine.⁹^,¹¹

32.2 Indications

The unilateral lumbar approach is the authors’ preferred approach for the treatment of a variety of degenerative spinal disorders including lumbar spinal stenosis, foraminal narrowing, and facet joint cysts. This technique is performed in patients presenting primarily with neurogenic claudication, leg or buttock symptoms, heaviness in the legs with or without radicular symptoms, with or without neurological deficits, and comparable magnetic resonance imaging (MRI) findings.²^,⁴^,⁹

As regards patient selection, in general there are no limitations regarding age, number of affected segments, or extent of narrowing.

Overall, the range of indications for the technique described here can be defined as follows:

a)Lumbar central stenosis.

b)Lumbar lateral recess spinal stenosis.

c)Lumbar foraminal stenosis.

d)Epidural lipomatosis.

e)Thecal sac compression due to facet joint cysts.

32.3 Contraindications

The unilateral lumbar approach is contraindicated in the following situations:

a)Major contraindications for general anesthesia and surgery.

b)Grade II spondylolisthesis and worse.

c)Significant lateral and/or vertical instability, and scoliosis.

d)Significant translational instability with dynamic canal narrowing.

e)Dominant/significant mechanical back pain.

The unilateral “over-the-top” approach for bilateral decompression is a key technique in spinal microsurgery for spinal stenosis. This decompression technique minimizes the potential instability associated with similar open procedures. For multisegmental lumbar decompression, the authors recommend the crossover “Slalom technique” with multiple skin incisions to minimize postoperative instability. As described elsewhere in this book, there are excellent surgical training opportunities using simulation and models that allow surgeons to gain experience.

32.4 Preoperative Planning

The preoperative evaluation and planning procedures are of particular importance in guaranteeing successful surgery, as well as excellent clinical outcome. Preoperative imaging provides vital information on the anatomical as well as the pathoanatomical structure and positioning of the spine, including malpositioning in all three dimensions—sagittal, frontal, and horizontal—and the topographical anatomy of the target area.

Preoperative imaging studies include mandatory standard X-rays in the anteroposterior (AP) and lateral views in a standing position, as well as functional X-rays with the patient in a lateral position (flexion–extension views). AP X-rays provide information on the curvature of the spine and on the configuration as well as size of the interlaminar window for entry toward the spinal canal. Flexion–extension views reveal the existence of possible vertical instability, as well as translational segmental slipping.

MRI is also obligatory for the preoperative planning stage. It is the diagnostic tool of choice for evaluating the neural structures including the situation within the central spinal and nerve root canals. It provides the most comprehensive information about soft-tissue structures, which may limit the size of the spinal canal such as discogenic pathologies, bulging yellow ligaments, and canal-narrowing synovial cysts. T1- and T2-weighted sagittal and T2-weighted axial images are most freuquently used in this regard (Fig. 32.1a–c). The additional contributation of contrast medium can be used to differentiate between remaining scar-tissue formation following prior surgery and primary pathologies.

Fig. 32.1 (a) T2-weighted sagittal magnetic resonance imaging (MRI) of a severe two-level spinal canal stenosis at the levels L2/L3 and L3/L4. (b, c) T2-weighted axial MRI of a severe spinal canal stenosis at the level L2/L3 (b) and L3/L4 (c).

With the widespread availability of MRI and due to the poor resolution of soft-tissue structures and its radiation emissions, computed tomography (CT) scan has lost much of its importance in the diagnosis of lumbar spinal stenosis. Only in cases of impossibility of MRI (e.g., patients with a pacemaker), CT scan is used.

In conclusion, a standard preoperative assessment is mandatory, including information on medical history and comorbidities, operative as well as anesthetic risks, current medication, and any blood laboratory abnormalities.

32.5 Patient Positioning

No specific patient preparation is required the day before surgery. If necesssary, shaving of the surgical area is performed.

General anesthesia and complete relaxation are reqired for the operation. Venous and arterial lines are placed to ensure continuous intraoperative anesthetic monitoring. The use of a urinary catheter is not necessary in mono- or bisegmental decompression cases. If the planned surgey time is estimated to be over 3 hours, a urinary catheter is mandatory. Cell-saving procedures, as well as blood transfusion, are not routinely required.

Usually, single dose of preoperative antibiotic prophylaxis is administrated approximately 20 minutes before skin incision with a second shot after 2 hours in longer operative procedure. Routinely, prolonged antibiotic therapy is not recommended.

In order to minimize preoperative complications, the authors refer to the World Health Organization Surgical Safety Checklist for all surgical interventions.

The patient is placed in a so-called knee-thorax position with hips and knees flexed at 90 degrees, and shoulders in 90 degrees abduction and 90 degrees external rotation (attention: avoid overextension of the shoulders) (Fig. 32.2). Hyperflexion of the hip and knee joint should be avoided to prevent restriction of venous blood flow from the legs with the accompanying major risk of deep venous thrombosis. Furthermore, the authors recommend to avoid overextension and hyperabduction of the shoulders to minimize the risk of brachial plexus irritations. Elbow (nervus ulnaris) and wrist joint (nervus medianus), as well as the shins are positioned on gel pads to avoid pressure sores. The abdomen should “hang” freely without any compression to maximally lower the pressure in the epidural veins. A support bracket is placed on the buttocks (Fig. 32.2). On the side opposite of the surgeon, a separate lateral support is placed at the trochanteric region to secure the patient while the operating table is tilted during the over-the-top decompression procedure (Fig. 32.3).