27 Minimally Invasive Deformity Correction Abstract Minimally invasive deformity correction techniques are evolving rapidly to aid in surgical treatment of adult spinal deformities. These techniques involve a combination of minimally invasive interbody fusion methods and percutaneous posterior pedicle screw and rod placement. Achieving a balanced spine in the coronal and sagittal planes is the ultimate goal of such surgery while aiming to reduce complications and readmissions. Minimally invasive techniques have the potential to reduce the risk of postoperative infections since muscle dissection is limited. Additionally, they may play a role in reducing the incidence of proximal junctional kyphosis as the posterior musculo-ligamentous tension band is preserved. This chapter provides a systematic approach for surgical correction of spinal deformities using minimally invasive techniques. Preoperative planning, intraoperative surgical techniques, and postoperative management including complication management are discussed. Keywords: minimally invasive surgery, percutaneous pedicle screws, transpsoas lateral interbody fusion, minimally invasive transforaminal lumbar interbody fusion Adult spinal deformity (ASD) is defined by the SRS-Schwab classification as being a deformity in the coronal plane or the sagittal plane or both.1 In the coronal plane, a Cobb angle of more than 30 degrees is considered significant, whereas in the sagittal plane significant deformity includes a pelvic tilt (PT) greater than 20 degrees, sagittal vertical axis (SVA) greater than 4 cm, or pelvic incidence–lumbar lordosis (PI-LL) mismatch greater than 10 degrees. Traditionally, these deformities were treated surgically with open approaches. However, with a better understanding of anatomy, minimally invasive surgical (MIS) techniques have been used to successfully treat patients with ASD.2,3,4,5,6 Commonly used MIS techniques for spine deformity correction currently include anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), lateral lumbar interbody fusion (LLIF), axial lumbar interbody fusion (AxiaLIF), and MIS posterior instrumentation and fusion (PSIF).3,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 Considering the high prevalence of ASD in the elderly population, it is important to assess these less invasive techniques that may offer a reduced risk of adverse events.2 The spectrum of ASD treated with MIS techniques includes adult idiopathic scoliosis, adult degenerative scoliosis, iatrogenic spinal deformity, and posttraumatic deformity. Surgical correction is indicated in these patients when they have exhausted nonoperative measures such as physical therapy, epidural injections, and facet blocks, and still continue to have mechanical back pain related to the spinal deformity. Surgery is also indicated in these patients if they suffer from lumbar radiculopathy or neurogenic claudication. Another relative indication is progressively worsening deformity with pain as the rib cage abuts the pelvis. At present, we do not recommend the use of MIS techniques for correction of ASD when the preoperative SVA is greater than 100 mm, or when the preoperative PI-LL mismatch is greater than 38 degrees.24 We also do not use the MIS techniques for curves with a Cobb angle greater than 90 degrees, rigid kyphotic deformities with fused segments, and osteoporosis with T-score at the femoral neck of less than –2.0. However, as the MIS techniques for correction of spinal deformity continue to evolve, the applicability of MIS techniques to treat greater deformities will also improve. Preoperative evaluation of the patient with ASD begins with a thorough history and physical examination. Patients are asked about the existence of back pain, leg pain, and symptoms of neurogenic claudication. The intensity of the pain and the disability caused by it is important to quantify. Additionally, patients should be questioned about the existence of scoliosis in adolescence to differentiate between idiopathic scoliosis and de novo scoliosis. Physical examination is of prime importance in these patients. The patients should be appropriately disrobed to allow for evaluation of the spinal deformity. Examination should begin with inspection of the patient in the standing position with their hips and knees extended. Their overall coronal and sagittal balance is observed, as is their ability to bend laterally. Patients should be assessed for leg-length discrepancy to rule that out as a confounding problem. A complete neurological examination should be performed. Special attention should be paid to any signs of myelopathy to ensure that cervical spine pathology is addressed appropriately if it exists. For patients with neurogenic claudication, the peripheral vessels should be palpated. Finally, the hips and knees are examined to rule them out as causative agents of the leg or back pain. All patients require 36-inch standing posteroanterior (PA) and lateral radiographs ( • Sacral slope (SS): The angle between the end plate of S1 and the horizontal axis. Fig. 27.1 (a,b) Preoperative 36-inch standing films of a patient with adult spinal deformity (ASD). • Pelvic tilt (PT): The angle between a line drawn from the center of the femoral head to the center of the S1 end plate, and a vertical line drawn from the center of the femoral head. • Pelvic incidence (PI): The angle between a line drawn from the center of the femoral head to the center of the S1 end plate, and another line drawn perpendicular to the S1 end plate at the center of the S1 end plate. PI is a morphological parameter that does not change with position and can also be calculated using the formula PI = SS + PT. • Lumbar lordosis (LL): The angle between the superior end plate of L1 and the end plate of S1. • Pelvic incidence–lumbar lordosis (PI-LL): The difference between PI and LL. • Thoracic kyphosis (TK): The angle between the superior end plate of T4 and the lower end plate of T12. • Sagittal vertical axis (SVA): Horizontal distance from the posterosuperior corner of S1 to the C7 plumb line. A negative value denotes that the C7 plumb line is posterior to the posterosuperior corner of S1. The PA radiographs are used to measure the Cobb angles of the thoracic, thoracolumbar, or lumbar curves in the coronal plane. When choosing the levels to instrument, we include all levels within the Cobb angle of a curve. Additionally, when the fusion crosses the thoracolumbar junction, we choose the upper instrumented vertebra (UIV) to be the vertebra below the first normal parallel disc irrespective of whether it is at L1, T12, T11, or T10. A CT scan is also obtained frequently to assess for preexisting fusion between spinal segments ( When using the AxiaLIF approach to fixate the L5–S1 level, it is imperative to obtain an MRI of the sacrum as well to evaluate the presacral space for any adhesions as well as to rule out any aberrant vasculature that may cross the midline on the anterior surface of the sacrum. The AxiaLIF procedure is not a part of our current algorithm for MIS treatment of adult spinal deformities. Finally, we carefully evaluate our patients for medical comorbidities and involve our medical team for preoperative optimization of their medical conditions. Fig. 27.2 (a,b) Coronal and sagittal cut of the CT scan of a patient with adult spinal deformity showing bridging osteophytes and fusion at the L2–L3 level. We use the Medtronic CD Horizon Longitude for percutaneous pedicle screw and rod placement. In our experience, this system is useful for multilevel placement of percutaneous pedicle screws and rods as it allows for gradual reduction of the spinal deformity via reduction screw extenders. Our current minimally invasive approach is composed of three main components for correction of spinal deformity: • Lateral transpsoas approach for discectomy, release, and fusion from T10 to L5. • ALIF versus TLIF at L5–S1 and sometimes at L4–L5. • Posterior multilevel percutaneous pedicle screw and rod placement. In carefully selected patients as mentioned in the “Indications and Contraindications” section, we have not found the need to perform posterior-based osteotomies to obtain sagittal or coronal balance. Our algorithm for MIS correction of spinal deformity is as follows: • Lateral transpsoas approach for discectomy, release, and fusion from T10 to L5 using 12-degree cages placed anteriorly. Sometimes the L4–L5 level cannot be addressed via the lateral approach. In those cases, it is then addressed in the second stage along with the L5–S1 level. • We usually wait 2 to 3 days to perform the second stage of the surgery and obtain 36-inch standing radiographs prior to second stage to reassess the sagittal and coronal alignment ( • If SVA is less than 5 cm and PI-LL is less than 10 degrees: MIS TLIF at L5–S1 and at L4–L5 if needed. • If SVA between 5 and 10 cm and PI-LL between 10 and –40 degrees: ALIF at L5–S1 and at L4–L5 if needed. • If SVA is greater than 10 cm or PI-LL is greater than 40 degrees: Posterior osteotomies may need to be performed. We have not encountered the need to perform osteotomies in patients selected according to the criteria mentioned in the “Indications and Contraindications” section. • This is followed by posterior multilevel percutaneous pedicle screw and rod placement. The patient is positioned on a radiolucent sliding table with a kidney rest in the right lateral decubitus position with the left side up. We almost exclusively perform the transpsoas approach through the left side as there is an increased risk of injury to the great vessels when approached from the right side, especially at L4–L5.25 The iliac crests of the patient are positioned just below the level of the kidney rest. The kidney rest is then elevated maximally to increase the distance between the rib cage and the iliac crest. An axillary pad is placed in the right axilla, while the left arm is secured on an elevated arm rest. The left hip is flexed to relax the psoas muscle and the femoral nerve. Extra padding is placed over the bony prominence of the fibular head to minimize risk of peroneal nerve palsy. Finally, the patient is secured to the table using bolsters and strapping tape (
27.1 Introduction
27.2 Indications and Contraindications
27.3 Preoperative Planning
27.3.1 Physical Examination
27.3.2 Radiographic Workup and Preoperative Imaging
Fig. 27.1). The lateral films must include adequate visualization of the auditory meatus proximally and the femoral heads distally. The lateral radiographs are used to measure the pelvic parameters and the sagittal profile of the spine as follows:
Fig. 27.2). This is especially important in patients who have had previous surgeries at the involved segments. We also obtain a bone density scan on all patients older than 50 years and reserve the use of MIS techniques for those patients whose T-score at the femoral neck is higher than –2.0. An MRI scan is obtained on all patients preoperatively to assess for stenosis of the spinal canal and neuroforamens. Furthermore, the MRI scan is used to assess the location of the vena cava, the descending aorta, and the lumbar plexus to ensure that these vital structures are not harmed during the lateral approach to the spine. Based on our experience, the lateral approach for interbody fusion is contraindicated in the presence of a high-grade spondylolisthesis, especially at the L4–L5 segment as the nerve root crosses more anteriorly and is thus in the direct path of the approach.
27.3.3 Instrumentation
27.4 Surgical Approach and Algorithm
27.4.1 Stage 1
Fig. 27.3). The crux of the reduction of the deformity takes place in the second stage during posterior instrumentation.
27.4.2 Stage 2
27.5 Surgical Technique
27.5.1 Transpsoas Discectomy and Fusion
Patient Positioning
Fig. 27.4).
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