Degenerative Scoliosis: Is There an Advantage to Using Minimally Invasive Techniques to Treat Degenerative Scoliosis?

9 Degenerative Scoliosis: Is There an Advantage to Using Minimally Invasive Techniques to Treat Degenerative Scoliosis?

MIS: Chun-Po Yen and Juan S. Uribe
Open: Christopher I. Shaffrey

9.1 Introduction

Adult scoliosis is a spinal deformity in skeletally mature patients with a Cobb angle of greater than 10° in the coronal plane. Based on the pathogenesis, adult scoliosis can be classified into the following: type 1, primary (de novo) degenerative scoliosis (DS); type 2, progressive idiopathic scoliosis in adult life; and type 3, secondary DS consequent to idiopathic scoliosis, pelvic obliquity, or metabolic bone diseases (such as osteoporosis).1 DS begins with asymmetric degeneration of the intervertebral discs. Subsequently, the lack of competency in the facets and asymmetric compression fracture of osteoporotic vertebrae cause progression of the curve. Spondylolisthesis and translational or rotational dislocations are often associated with DS and further complicate the deformity.

9.2 Indications of Surgery for Adult Degenerative Scoliosis

Conservative treatment might be adequate and should be tried in the majority of patients with DS. With a gradual shift to an aging society and a longer life expectancy, there is a rise in the prevalence of adult DS and increasing demand from the patients for a better quality of life (QOL). To this end, surgical intervention has been increasingly utilized to treat DS, although the risks of surgeries have traditionally been considered higher compared to those for adolescent idiopathic scoliosis (AIS) given the old age, medical comorbidities, and deficient bone stock in adults. Studies have shown that surgically treated patients with adult DS had a significantly greater improvement in back or leg pain and QOL when compared with nonoperatively managed patients.2,3,4 In general, patients with the following conditions are candidates for surgery: claudication or radicular symptoms due to canal, lateral recess, or foraminal stenosis; back pain related to degenerated discs/facets or muscular fatigue that failed conservative management; neurological deficits; instability; and progression of curve. Surgeries usually consist of decompression, instrumentation, fusion, realignment, or a combination of all of these based on patient’s symptoms, degree of instability, severity and flexibility of curve, and presence of sagittal imbalance.

Unlike AIS, adult DS are usually rigid and may require a combined anteroposterior approach, especially in those with advanced disease. Silva and Lenke provided a graded treatment recommendation for selection of surgical procedures based on the clinical and radiological findings of DS patients.⁵ Level I treatment consists of limited decompression for those with only claudication or radiculopathy caused by stenosis. Radiographically, suitable patients are those with anterior osteophytes, scoliosis less than 30°, and subluxation less than 2 mm without sagittal imbalance. This is with a caveat that progression of scoliosis might occur. Level II treatment involves addition of limited posterior lumbar instrumented fusion and is indicated in patients with stenosis requiring a wide decompression but without anterior osteophytes. Level III treatment involves instrumented fusion of lumbar curve and is indicated in patients with primary symptom of back pain and radiographically with significant curve and subluxation without sagittal imbalance. Level IV treatment involves addition of anterior spinal fusion and is indicated in patients with loss of lumbar lordosis. Level V treatment involves extension of instrumented fusion to thoracic region and is indicated in patients with flexible sagittal imbalance. Level VI treatment involves osteotomy and is indicated in patients with stiff or fixed sagittal imbalance.

9.3 Advantages of Minimally Invasive Surgery

Minimally invasive surgery (MIS) is intended to achieve the same goals of open surgery while minimizing the collateral damage from the access. Decompression is usually accomplished in an indirect manner through placement of large footprint interbody cages and is usually selected for patients with mild to moderate stenosis. This technique has the benefits of avoiding prior surgical scar and obviating nerve root injury and unintentional durotomy.

MIS technique for DS relies heavily on anterior column manipulation and support. Direct manipulation of the anterior and middle columns permits a potentially greater degree of deformity correction compared with posterior approach alone. This is advantageous for osteoporotic patients given the large footprint cages placed across the hard apophyseal ring reduce the risk of subsidence and loss of indirect decompression. The anterior column support can be achieved through a mini-open anterior or lateral approach. MIS lateral approach has been gaining significant interests, as the approach does not require an access surgeon. In patients with significant sagittal imbalance, an anterior longitudinal ligament (ALL) release and placement of a hyperlordotic cage can achieve a 15° or more lordosis and can be performed at multiple levels without significant blood loss or nerve manipulation.6

Posterior instrumentation is usually required to augment the stability and maintain the correction. Placement of percutaneous screws for long segment has been proved feasible with the aims of minimizing paraspinal muscular injury and preserving posterior tension band.

Fig. 9.1 Preoperative and postoperative 36-inch long-cassette radiographs of a 48-year-old woman with lumbar degenerative scoliosis. She underwent a hybrid minimally invasive correction of adult degenerative scoliosis and kyphosis. The coronal Cobb angle improved from 59° to 30°, the lumbar lordosis increased from 31° to 72°, and the pelvic tilt decreased from 31° to 22°.

9.4 Advantages of Open Surgery

The open posterior approach remains the workhorse for correcting adult DS. All surgical procedures can be performed in a single position, and the posterior anatomy is certainly more familiar to the spine surgeons.

DS patients with severe stenosis usually require a wide decompression, which can be adequately addressed under direct visualization in an open setting. Interbody fusion is usually performed through a transforaminal lumbar interbody fusion (TLIF). Compared to posterior lumbar interbody fusion, a unilateral approach with less dural/nerve retraction allows for an anterior placement of a large lordotic cage. In cases undergoing anterior-placed TLIF cages, posterior column osteotomy, and compression, an increase in segmental lordosis can range from 6° at L1/L2 level to 22° at L5/S1 level.7 For patients with rigid or fixed DS and those with sagittal imbalance, posterior column osteotomy and three-column osteotomy such as pedicle subtraction osteotomy (PSO) or vertebral column resection (VCR) are powerful tools to realign the spine in both coronal and sagittal planes.

Placement of pedicle screws under direct visualization reduces the use of imaging guidance and lowers radiation exposure of the surgeons and patients. Manipulation of posterior rods to correct the three-dimensional deformity is more feasible in an open fashion. In addition, a wide exposure of posterior spinal structure allows robust posterolateral fusion.

9.5 Case Illustration

A 48-year-old woman presented with back pain and progression of kyphoscoliosis. She had a history of AIS, and underwent a placement of the Harrington rod at the age of 15 years. The rod “popped out” 2 years later and was subsequently removed. She stated that she has been “relatively straight” until 3 years ago when she started to lean to the right and forward. Clinically, she presented with mid- and low back pain and anterior thigh pain without other neurological deficits.

On 36-inch long-cassette X-rays, she had a coronal Cobb angle of 59°, lumbar lordosis of 31°, pelvic incidence of 73°, and pelvic tilt of 31° ( Fig. 9.1). Computed tomography (CT) demonstrated posterolateral fusion mass from T4 to L3 with pseudoarthrosis between T12 and L3 ( Fig. 9.2). Magnetic resonance imaging (MRI) demonstrated multilevel moderate foraminal stenosis on the concave side of the curve.

Based on the history and imaging findings, the patient is likely to have partially corrected AIS with secondary DS in the lumbar region. Given her symptoms and progression of kyphoscoliosis, she was considered a candidate for correction surgery.

9.6 Surgical Technique in Minimally Invasive Surgery

The patient underwent a two-stage surgery. The first stage was performed in a posterior open fashion. She was placed in a prone position on a Jackson table, with exposure of posterior elements from T11 to iliac crest. Bilateral T11 to S1 pedicle screws and iliac bolts were placed under the assistance of fluoroscope, followed by L1/L2, L2/L3, and L3/L4 posterior column osteotomy to remove the prior fusion mass, and L4/L5 and L5/S1 medial facetectomy. Two temporary rods were placed across L1 to L4 pedicle screws. Three days later, the patient was brought back to the operating room and underwent the second stage surgery, which included a mini-open L5/S1 anterior lumbar interbody fusion (ALIF) with placement of a 30° hyperlordotic cage in supine position; right L1/L2, L2/L3, L3/L4, and L4/L5 lateral lumbar interbody fusion (LLIF) with 10° lordotic cages in lateral position; and placement of posterior rods from T11 to ilium in posterior position. At 6-month follow-up, long-cassette X-rays demonstrated improved radiographic parameters. The Cobb angle reduced to 30°, lumbar lordosis increased to 72°, and pelvic tilt reduced to 22°. Her pain improved significantly ( Fig. 9.1; Fig. 9.3).

Fig. 9.2 (a,b) Preoperative thoracic and lumbar and (c,d) spine computed tomography images demonstrated fusion mass from T4 to L3 with pseudoarthrosis between T12 and L3.

Fig. 9.3 (a) Pre- and (b) postoperative photographs of the patient.

9.7 Surgical Technique in Open Surgery

The patient was placed in a prone position on a Jackson table. The abdomen was left hanging free to increase the venous blood return and reduce intraoperative bleeding. A longitudinal skin incision was followed by a subperiosteal dissection of the paravertebral muscles to complete exposure of the bony structures. Pedicle screws are inserted from T10 to S1 and iliac screws were placed bilaterally using a combination of anatomic landmarks and fluoroscopic guidance. Multilevel posterior column osteotomy was performed from T12 to S1. A temporary rod was placed on the convex side from L4 to S1 under distraction. A distractor attached to the pedicle screws on the concave side where the TLIF was planned further opens the disc space between L4/L5 and L5/S1. The inferior facets of L4 and L5 and cranial part of superior facets of L5 and S1 were removed to expose the Kambin triangles. After adequate discectomy and preparation of the end plates, the hyperlordotic cages filled with recombinant human bone morphogenetic protein 2 (rhBMP-2) (Infuse; Medtronic Sofamor Danek, Inc., Memphis, TN) and autografts were placed to the ventral part of intervertebral space at L4/L5 and L5/S1. The use of rhBMP-2 was an off-label indication in the TLIF procedure. Autologous bone graft was packed in the residual disc space. Permanent rods contoured as desired were then placed and secured with compression across the levels of TLIF. Further rod rotation, intersegmental compression/distraction, and in-situ rod bending were performed to correct kyphoscoliosis. Decortication of posterior elements was performed followed by placement of rhBMP-2 along with autografts and allografts to reinforce fusion.

9.8 Discussion of Minimally Invasive Surgery

MIS techniques use specialized instruments to minimize approach-related soft-tissue damage. The techniques reduce blood loss, minimize postsurgical pain, and expedite patient’s recovery. In addition, wound infections are reduced because of limited surgical exposure. Given the adults with DS are more likely to have medical comorbidities, less blood loss and fluid requirement reduces cardiopulmonary and renal burden; early mobilization decreases risk of venous thromboembolism; and less narcotics consumption reduces occurrence of ileus.

For patients with mild to moderate stenosis associated with DS, indirect decompression can be accomplished by restoration of disc height following the placement of a large footprint inter-body cage through a mini-open anterior, lateral, or posterolateral approaches. For those with severe stenosis, a direct decompression might be needed and can be accomplished through a tubular retractor or a small incision.

Unlike adolescent spinal curves, adult scoliotic deformities are usually rigid and often require a combined anteroposterior approach. Anterior column surgeries provide access to the load-bearing elements of the spine and allows for greater corrective forces to be applied. Combining the use of interbody cages, the anterior approach provides structural stability, decreases stress on pedicle screws, improves fusion rates, offers better lumbar lordosis, and thereby potentially necessitates fewer surgical levels to treat the deformities.8 The anterior column surgeries can be performed through mini-open ALIF and LLIF.

ALIF has long been considered the gold standard technique for interbody fusion. It affords a direct access for discectomy, release of ALL to restore lordosis, and placement of a large cage for arthrodesis. For patients with DS, augmentation of the lumbosacral segment in long constructs with interbody fusion at L5–S1 improves biomechanical stability and reduces the risk of lumbosacral pseudoarthrosis.^9,10 The procedure can be performed through a mini-open or laparoscopic approach with minimal access-related complications.

LLIF uses a retroperitoneal transpsoas corridor to perform a lumbar interbody fusion without violating ALL, posterior longitudinal ligament, and the posterior tension band.^11,12

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