Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

172. Posterolateral Arthrodesis for Spondylolisthesis

James T. Guille and Reginald S. Fayssoux

DEFINITION

images Spondylolisthesis refers to translation of one vertebra in relation to another in the sagittal plane.

images In the child and adolescent, this most commonly occurs at the L5–S1 junction.

images Most patients are asymptomatic.

images Most patients commonly present for low-grade back pain and not for radicular symptoms.

ANATOMY

images Pars interarticularis includes portions of the lamina, transverse processes, and pedicle.

images There is anterior forward slippage of the fifth lumbar vertebral body on the sacrum.

images In longstanding cases, the superior endplate of the sacrum becomes dome-shaped, and accordingly the inferior endplate of L5 becomes concave and beaks at the anteroinferior corner (FIG 1).

images The transverse processes are often hypoplastic.

images The posterior elements of L5 are detached (Gill fragment).

images The nerve roots of L5 are draped over the dome of the sacrum.

PATHOGENESIS

images In spondylolisthesis the pars interarticularis is either elongated or discontinuous.

images An isthmic defect is the result of chronic loading of a pars interarticularis that is genetically predisposed to fatigue failure.

images A dysplastic slip is secondary to congenital anomalies of the lumbosacral articulation, including maloriented or hypoplastic facets and sacral deficiency. The pars is poorly developed, allowing for elongation or eventual separation and forward slippage.

NATURAL HISTORY

images Isthmic

images Most patients have mild or no symptoms.

images Most present with some degree of slip.

images Less than 4% demonstrate slip progression.

images

FIG 1  CT image showing rounding of S1 vertebral body and beaking of L5 vertebral body.

images Risk factors for progression include diagnosis before the adolescent growth spurt, girls, and greater than 50% slip.

images Dysplastic

images Higher frequency of progression

images More likely to have neurologic problems

images More likely to require operative treatment

PATIENT HISTORY AND PHYSICAL FINDINGS

images Patients typically present with low back pain of insidious onset, occasionally with radiation to the buttock or posterior thigh.

images Radicular symptoms and disturbance of bowel and bladder function are rare with spondylolysis or low-grade spondylolisthesis but may be reported with high-grade slips.

images Specific physical activities and sports participation (sports with repetitive hyperextension of the lumbar spine—for instance, football linemen, gymnasts, divers)

images Tight hamstrings are common, resulting in a mild crouched gait.

images Inspection, palpation, and range of motion

images Flattened lumbar lordosis

images Heart-shaped buttocks

images Sacrum appears vertically oriented

images Visible or palpable step-off at the spinous processes of the involved levels (FIG 2)

images Limited lumbar flexion and extension

images Lumbar hyperextension frequently will elicit pain

images Neurologic examination

images Lumbar sensory and motor root testing

images Evaluation of deep tendon reflexes and abdominal reflexes

images Rectal examination indicated in patients with bowel or bladder dysfunction

images Straight leg-raise testing to assess nerve root irritation and popliteal angle measurements to assess hamstring spasm and contracture

images

FIG 2  Clinical photograph of child with high-grade spondylolisthesis. Note step-off of spinous processes.

images Popliteal angles greater than 40 degrees indicate significant hamstring tightness; this is the most common neurologic finding in patients with spondylolisthesis.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images Standing posteroanterior (PA) and lateral radiographs of the entire spine

images Standing PA radiographic view allows for evaluation of coexisting scoliosis secondary to paraspinal spasm, whether idiopathic or olisthetic.

images Standing lateral view is useful for assessing global sagittal balance.

images Spot lateral view of the lumbosacral junction is useful for identifying spondylolytic defects and documenting the degree of spondylolisthesis (FIG 3A).

images Supine lateral hyperextension view of lumbosacral junction to assess passive reduction of L5 on S1.

images Meyerding classification

images Quantifies amount of forward translation

images Based on percentage subluxation of L5 on S1 (FIG 3B)

images Grade I: less than 25%

images Grade II: 25% to 50%

images Grade III: 50% to 75%

images Grade IV: 75% to 100%

images Grade V (spondyloptosis): more than 100%

images Slip angle

images Quantifies degree of lumbosacral kyphosis.

images Line drawn parallel to superior border of S1 unreliable because of the rounding of the superior sacrum occurring secondary to the slip.

images Angle subtended by intersection of a line drawn along the superior endplate of L5 and the perpendicular of a line drawn along the posterior cortex of the sacrum (FIG 3C).

images Slip angle greater than 50% is associated with a greater risk of slip progression, instability, and development of postoperative pseudarthrosis.

images Single-photon emission computed tomography (SPECT) of the lumbosacral spine

images Limited utility in spondylolisthesis.

images Most effective method for detecting spondylolysis when plain radiographs are normal and patient history and physical examination are suggestive.

images Increased radionuclide uptake in an intact pars, lamina, or pedicle is consistent with stress reaction (can treat).

images Relative decrease in tracer uptake on serial SPECT scans has been correlated with improvement of clinical symptoms and signs in patients treated for symptomatic spondylolysis.

images Computed tomography (CT) with sagittal and coronal reconstructions is the best modality for defining the bony anatomy (FIG 3D).

images CT can evaluate for degree of cortical disruption, lysis, and sclerosis at the pars, lamina, or pedicle.

images 2D and 3D CT reconstruction of the spine is useful to clarify the pathoanatomy of the region for preoperative planning.

images Magnetic resonance imaging (MRI)

images For evaluation of the health of the L4–L5 disc (if viable, try to preserve level; if desiccated, include in fusion).

images

FIG 3  A. Spot lateral radiograph of L5–S1 junction. B. Meyerding classification. Percentage slip defined as A/B × 100%. C. Slip angle. Angle subtended by line drawn along superior endplate of L5 and perpendicular of line tangential to posterior cortex of sacrum. D. CT image of the lumbosacral junction. The pathoanatomy is clearly visualized. E. MRI of the spine shows well-hydrated intervertebral discs cephalad to the slip.

images For evaluation of posterior protrusion of the L5–S1 disc. Reduction at this level can cause herniation of the disc, resulting in cauda equina syndrome (FIG 3E).

NONOPERATIVE MANAGEMENT

images Most children and adolescents with low-grade spondylolisthesis respond to nonoperative measures, including activity restriction, physiotherapy, and brace treatment.

images Low-grade isthmic spondylolisthesis rarely progresses and can be followed with serial radiographs at 6-month intervals until the patient is skeletally mature. After this, radiographs can be done on a yearly basis.

images Patients with low-grade dysplastic spondylolisthesis are at greater risk for progression, development of neurologic deficit, and need for operative intervention.

images High-grade spondylolisthesis (over 50% slippage) responds less reliably to nonoperative measures.

images There is no evidence to support prophylactic fusion for asymptomatic high-grade isthmic spondylolisthesis.

images Physical therapy is the mainstay of treatment, with emphasis on hamstring stretching. It is our observation that patients who can overcome their hamstring tightness and spasm tend to have less pain and fare better. Persistent tightness of the hamstrings is associated with continued pain and, perhaps, an ultimate need for operative treatment.

SURGICAL MANAGEMENT

images Indicated for the child with persistent low back or leg pain.

images Rarely indicated in patients with less than 50% slippage. In these patients, all efforts at nonoperative treatment should be exhausted before an operation is considered, as it is known by natural history that the chance of progressive slippage is low.

images Indicated for the symptomatic, skeletally immature or mature individual with greater than 50% slippage.

images Based on the patient's degree of slippage and symptoms, several operative options are available.

images Posterolateral in situ fusion

images Gold standard, with longest follow-up.

images Reserved for patients with no neurologic symptoms.

images Does not correct deformity unless patient is postoperatively placed in a hyperextension bilateral pantaloon spica cast.

images With or without instrumentation. Use of instrumentation can obviate the need for postoperative immobilization and may increase fusion rates.

images Postoperative immobilization ranges from nothing to a brace with thigh extension to a bilateral pantaloon spica cast.

images Gill procedure (removal of posterior elements of L5) is done if preoperative neurologic symptoms are present or reduction is planned.

images Bohlman posterior transsacral arthrodesis

images Can be used with or without instrumentation

images Can reduce slip angle

images Can provide anterior interbody support through a posterior-only approach

images Provides opportunity for decompression of L5 and S1 nerve roots

images Instrumented posterolateral fusion with reduction of L5–S1, posterior lumbar interbody fusion, and sacral dome osteotomy

images Extensive, time-consuming procedure

images Sacral dome osteotomy effectively shortens the spine and allows for posterior translation of L5 on S1

images Gill procedure at L5 to allow for displacement after reduction

images Requires exploration and decompression of L5 and S1 nerve roots

images Anterior interbody support is achieved by L5–S1 discectomy and posterior lumbar interbody fusion procedure

Preoperative Planning

images Type of incision (midline versus transverse curvilinear)

images Will decompression be needed?

images Should fusion extend to L4?

images What type of bone graft will be used?

images Will instrumentation be used?

images Will postoperative immobilization be used?

images Consultation with neuromonitoring for preoperative baseline somatosensory evoked potentials (SSEPs) and electromyographic (EMG) studies

images Consultation with urology for urodynamic studies

Positioning

images Neurologic monitoring leads are placed for SSEPs and EMGs.

images Multiple large-bore intravenous lines, an arterial line, and a Foley catheter are placed.

images The patient is then transferred to the prone position on a standard operating table, with care taken to ensure that the hips are at the level of the table joint so that flexion and extension of the lumbar spine can be controlled by movement of the table.

images Extension of the hips may direct the superior endplate of the sacrum toward the inferior endplate of L5.

images Flexion of the hips may allow for more of a passive postural reduction (FIG 4).

images Bolsters underneath the chest and anterior superior iliac spines prevent abdominal compression and allow epidural venous return, thus decreasing epidural bleeding during spinal surgery.

images All bony prominences are well padded, including medial elbows, knees, shins, and ankles.

images A lateral fluoroscopic image is taken at the lumbosacral junction to see if passive postural reduction has occurred.

images After the patient is properly positioned on the table, baseline neurologic monitoring is obtained before the start of the procedure.

Approach

images We prefer a standard midline incision from L4 to the sacrum.

images This allows for bilateral posterolateral exposure of the spine out to the tips of the transverse processes.

images If desired, bone graft can be harvested from both ilia.

images

FIG 4  Patient positioning. Note flexion of hips.

TECHNIQUES

EXPOSURE

images  The patient is prepared and draped in the standard fashion.

images  A PA fluoroscopic image is taken to verify levels.

images  The incision is marked and Marcaine with epinephrine is injected along the course of the incision for local anesthesia and hemostasis.

images  The skin is sharply incised with a no. 15 blade scalpel and retractors are placed.

images  Electrocautery is used to dissect through the subcutaneous fat until the fascia is reached.

images  The spinous processes are identified via palpation. Care needs be taken at the L5–S1 level because of the displacement of L5 on S1 (TECH FIG 1).

images  Bovie cautery is used to subperiosteally expose the posterior elements out to the tips of the transverse processes.

images  At L5 the transverse processes are very deep within the wound.

images  Care needs be taken while exposing the transverse processes as the nerve roots lie anterior to them.

images  The sacrum is exposed posterolaterally out to the level of the ala.

images

TECH FIG 1  Exposure of lumbosacral spine.

INSTRUMENTATION

images  We prefer to place the pedicle screws before performing the decompression and reduction.

images  Fluoroscopic imaging is often necessary when placing screws at the L5 level because of the distorted anatomy.

images  We use fluoroscopic imaging for the placement of S1 screws to ensure tricortical purchase anteriorly on the sacrum.

images  We have found it useful to use polyaxial screws at all levels, with reduction screws at L4 and L5.

images  If difficulty is encountered while placing screws at L5, the surgeon can wait until the decompression is done and then use a Woodson elevator to palpate the pedicle within the canal.

images  Placement of pedicle screws at L5 can be difficult because the surgeon must direct the screws in an awkward trajectory.

images  When placing pedicle screws we prefer an exaggerated lateral trajectory to provide for better pullout strength.

images  Consideration can be given to bicortical purchase (anterior penetration) with the L5 screws to increase pullout strength during reduction.

DECOMPRESSION

images  Decompression is done if preoperative neurologic symptoms exist or if a reduction is planned.

images  Both lamina and the spinous process of L5 are removed en bloc (Gill fragment; TECH FIG 2A).

images  The L5 nerve roots are identified and are traced from their exit from the dura out the neural foramina. It is crucial that the nerve roots be decompressed if a reduction is to be considered (TECH FIG 2B).

images  The S1 nerve roots are often found draped over the sacrum, and again care should be taken that adequate space exists for their displacement after reduction.

images

TECH FIG 2  A. Posterior elements of L5 vertebra (Gill fragment). The ruler shows size in centimeters. B. Intraoperative photograph after removal of Gill fragment. The L5 nerve roots can be identified.

ROD PLACEMENT

images  Rod length should be measured and an exaggerated lordosis will be needed to be bent into the rod. If this is not done, the surgeon risks pullout of the L5 screws during rod placement (TECH FIG 3).

images  The amount of lordosis will depend on the amount of reduction desired: if no reduction is planned, the rod will have more lordosis to allow for in situ placement.

images  Conversely, reduction of L5 can also be achieved by distraction at L4–S1.

images  Reduction screws greatly facilitate rod placement at both L4 and L5.

images

TECH FIG 3  Intraoperative fluoroscopic image of lumbosacral junction. Note the lordosis of the rod to minimize risk of pedicle screw pullout.

BONE GRAFT

images  During the initial exposure of the spine, all soft tissue attachments should have been removed from the posterior elements.

images  The facet joints are best removed with a large rongeur.

images  The posterior elements are decorticated with a burr.

images  Large amounts of bone graft are placed in the posterolateral gutters. An attempt should be made to place bone anterior to the tips of the transverse processes.

images  When a Gill procedure is done, this unfortunately removes surface area for fusion at the lumbosacral junction.

images  Care should be taken that no bone graft fragments impinge on the exiting nerve roots.

CLOSURE

images  At our institution, before closure the wound is assessed for any frank bleeding vessels and bone graft is placed. Drains are placed for wounds considered at risk for hematoma formation.

images  Fascia is closed with figure 8 braided absorbable suture (no. 1 Vicryl). The goal is a watertight closure.

images  Subcutaneous layers are closed with interrupted braided absorbable suture (no. 0 and 2-0 Vicryl). The goal is to decrease wound tension.

images  Skin is closed with a running single filament absorbable (3-0 Monocryl). The goal is cosmetic closure.

images  Skin closure is reinforced with 1-inch 3M Steri-Strip Adhesive Tape Closures and surgical adhesive (Mastisol Liquid Adhesive).

images  Sterile compression dressings are applied to decrease the risk of postoperative hematoma.

images  Extreme care needs to be taken when transferring the patient to the stretcher.

images  An assistant is needed to hold the hips and knees flexed at 90 degrees during transfer.

images  Pillows need to be placed under the thighs to hold the hips and knees flexed.

images

POSTOPERATIVE CARE

images Careful neurologic examinations need to be performed postoperatively, especially if a reduction has been done. All lumbar nerve roots need to be tested.

images The Foley catheter is removed on postoperative day 2 and urinary function is closely monitored.

images If the plan is for the patient to be placed in a spica cast, he or she is returned to the cast room 1 week after surgery and placed on a Risser table in hyperextension. A pantaloon hip spica cast is applied.

images If instrumentation is used, no postoperative immobilization is required.

images

FIG 5  Postoperative radiograph.

images The hips and knees are progressively extended (pillows removed) as tolerated. This may take several days.

images Patient may be out of bed to a chair the morning after surgery with the hips and knees flexed.

images Ambulation is progressed as the patient is able to tolerate increased flexion at the hips and knees.

images The patient is followed clinically and radiographically at monthly intervals to assess progress (FIG 5). Consideration should be given to performing a CT scan at 6 months to assess the quality of the spinal fusion mass.

OUTCOMES

images If reduction is performed, there may be an improvement in clinical appearance.

images Hamstring spasm is often relieved after operative intervention.

COMPLICATIONS

images Wound hematoma

images Infection

images Pseudarthrosis

images Urinary retention may require prolonged use of a Foley catheter or intermittent straight catheterization.

images Neurologic injury

images The risk of neurologic complication increases with the amount of reduction performed.

images Motor deficits that are detected at the conclusion of the procedure are probably best treated with exploration and release of correction.

images Fortunately, most motor deficits will improve with time, although improvement and recovery may take several months.

images Postoperative radicular-like symptoms are managed with close observation and liberal use of gabapentin.

REFERENCES

1. Frennered AK, Danielson BI, Nachemson AL. Natural history of symptomatic isthmic low-grade spondylolisthesis in children and adolescents: a seven-year follow-up study. J Pediatr Orthop 1991;11:209–213.

2. Lenke LG, Bridwell KH, Bullis D, et al. Results of in situ fusion for isthmic spondylolisthesis. J Spinal Disord 1992;5:433–442.

3. Muschik M, Zippel H, Perka C. Surgical management of severe spondylolisthesis in children and adolescents: anterior fusion in situ versus anterior spondylodesis with posterior transpedicular instrumentation and reduction. Spine 1997;22:2036–2043.

4. Pizzutillo PD, Hummer CD III. Nonoperative treatment for painful adolescent spondylolysis or spondylolisthesis. J Pediatr Orthop 1989;9:538–540.

5. Pizzutillo PD, Mirenda W, MacEwen GD. Posterolateral fusion for spondylolisthesis in adolescence. J Pediatr Orthop 1986;6:311–316.

6. Smith MD, Bohlman HH. Spondylolisthesis treated by a single-stage operation combining decompression with in situ posterolateral and anterior fusion: an analysis of eleven patients who had long-term follow-up. J Bone Joint Surg Am 1990;72A:415–421.



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