Chapter 64

Posterolateral Arthrodesis for Spondylolisthesis

James T. Guille and Reginald S. Fayssoux

DEFINITION

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

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

• Most patients are asymptomatic.

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

  ANATOMY

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

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

• 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).

• The transverse processes are often hypoplastic.

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

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

  PATHOGENESIS

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

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

• 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

• Isthmic

  • Most patients have mild or no symptoms.

  • Most present with some degree of slip.

  • Less than 4% demonstrate slip progression.

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

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

• Dysplastic

  • Higher frequency of progression

  • More likely to have neurologic problems

  • More likely to require operative treatment

     

    PATIENT HISTORY AND PHYSICAL FINDINGS

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

• 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.

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

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

• Inspection, palpation, and range of motion

  • Flattened lumbar lordosis

  • Heart-shaped buttocks

  • Sacrum appears vertically oriented

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

  • Limited lumbar flexion and extension

  • Lumbar hyperextension frequently will elicit pain

• Neurologic examination

  • Lumbar sensory and motor root testing

  • Evaluation of deep tendon reflexes and abdominal reflexes

  • Rectal examination indicated in patients with bowel or bladder dysfunction

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

     

     

     

     

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

     

     

     

    • 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

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

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

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

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

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

      • Meyerding classification

        • Quantifies amount of forward translation

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

          • Grade I: less than 25%

          • Grade II: 25% to 50%

          • Grade III: 50% to 75%

          • Grade IV: 75% to 100%

          • Grade V (spondyloptosis): more than 100%

      • Slip angle

        • Quantifies degree of lumbosacral kyphosis.

        • Line drawn parallel to superior border of S1 unreliable

      because of the rounding of the superior sacrum occurring secondary to the slip.

  • 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).

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

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

  • Limited utility in spondylolisthesis.

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

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

  • 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.

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

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

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

• Magnetic resonance imaging (MRI)

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

     

     

     

     

     

     

     

    A B C

     

     

     

     

     

    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

    D E discs cephalad to the slip.

     

    • 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

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

      • 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.

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

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

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

      • 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

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

      • 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.

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

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

      • Posterolateral in situ fusion

        • Gold standard, with longest follow-up.

        • Reserved for patients with no neurologic symptoms.

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

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

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

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

      • Bohlman posterior transsacral arthrodesis

        • Can be used with or without instrumentation

        • Can reduce slip angle

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

        • Provides opportunity for decompression of L5 and S1 nerve roots

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

        • Extensive, time-consuming procedure

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

  • Gill procedure at L5 to allow for displacement after reduction

  • Requires exploration and decompression of L5 and S1 nerve roots

  • Anterior interbody support is achieved by L5–S1 discec-tomy and posterior lumbar interbody fusion procedure

    Preoperative Planning

• Type of incision (midline versus transverse curvilinear)

  • Will decompression be needed?

  • Should fusion extend to L4?

  • What type of bone graft will be used?

  • Will instrumentation be used?

  • Will postoperative immobilization be used?

• Consultation with neuromonitoring for preoperative baseline somatosensory evoked potentials (SSEPs) and electromyo-graphic (EMG) studies

• Consultation with urology for urodynamic studies

  Positioning

• Neurologic monitoring leads are placed for SSEPs and EMGs.

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

• 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.

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

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

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

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

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

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

  Approach

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

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

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

     

     

     

     

     

    FIG 4 • Patient positioning. Note flexion of hips.

     

    EXPOSURE	TECHNIQUES
    fashion.
    injected along the course of the incision for local anes-
    thesia and hemostasis.
    retractors are placed.
    neous fat until the fascia is reached.
    needs be taken at the L5–S1 level because of the dis-
    placement of L5 on S1 (TECH FIG 1).
    rior elements out to the tips of the transverse processes.
    wound.
    processes as the nerve roots lie anterior to them.
    the ala. TECH FIG 1 • Exposure of lumbosacral spine.
    INSTRUMENTATION
    the decompression and reduction. within the canal.
    screws at the L5 level because of the distorted anatomy. cause the surgeon must direct the screws in an awkward
    screws to ensure tricortical purchase anteriorly on the ■ When placing pedicle screws we prefer an exagger-
    sacrum. ated lateral trajectory to provide for better pullout
    els, with reduction screws at L4 and L5. ■ Consideration can be given to bicortical purchase (ante-
    surgeon can wait until the decompression is done and strength during reduction.
    DECOMPRESSION cial that the nerve roots be decompressed if a reduction A is to be considered (TECH FIG 2B).   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. B

    • The patient is prepared and draped in the standard

    • A PA fluoroscopic image is taken to verify levels.

    • The incision is marked and Marcaine with epinephrine is

    • The skin is sharply incised with a no. 15 blade scalpel and

    • Electrocautery is used to dissect through the subcuta-

    • The spinous processes are identified via palpation. Care

    • Bovie cautery is used to subperiosteally expose the poste-

    • At L5 the transverse processes are very deep within the

    • Care needs be taken while exposing the transverse

    • The sacrum is exposed posterolaterally out to the level of

    • We prefer to place the pedicle screws before performing then use a Woodson elevator to palpate the pedicle

    • Fluoroscopic imaging is often necessary when placing ■ Placement of pedicle screws at L5 can be difficult be-

    • We use fluoroscopic imaging for the placement of S1 trajectory.

    • We have found it useful to use polyaxial screws at all lev- strength.

    • If difficulty is encountered while placing screws at L5, the rior penetration) with the L5 screws to increase pullout

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

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

    • The L5 nerve roots are identified and are traced from their exit from the dura out the neural foramina. It is cru-

    • 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.

     

     

     

     

     

     

     

    TECHNIQUES	ROD PLACEMENT traction at L4–S1. TECH FIG 3 • Intraoperative flu- oroscopic image of lumbosacral L4 and L5. the rod to minimize risk of pedi- cle screw pullout.
    	BONE GRAFT elements. ■ When a Gill procedure is done, this unfortunately removes
    	CLOSURE hematoma formation. ■ Sterile compression dressings are applied to decrease the (no. 1 Vicryl). The goal is a watertight closure. ■ Extreme care needs to be taken when transferring the absorbable suture (no. 0 and 2-0 Vicryl). The goal is to de- ■ An assistant is needed to hold the hips and knees flexed crease wound tension. at 90 degrees during transfer.

    • 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).

    • 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.

    • Conversely, reduction of L5 can also be achieved by dis-

    • Reduction screws greatly facilitate rod placement at both junction. Note the lordosis of

    • During the initial exposure of the spine, all soft tissue at- place bone anterior to the tips of the transverse tachments should have been removed from the posterior processes.

    • The facet joints are best removed with a large rongeur. surface area for fusion at the lumbosacral junction.

    • The posterior elements are decorticated with a burr. ■ Care should be taken that no bone graft fragments im-

    • Large amounts of bone graft are placed in the pos- pinge on the exiting nerve roots. terolateral gutters. An attempt should be made to

    • At our institution, before closure the wound is assessed ■ Skin closure is reinforced with 1-inch 3M Steri-Strip for any frank bleeding vessels and bone graft is placed. Adhesive Tape Closures and surgical adhesive (Mastisol Drains are placed for wounds considered at risk for Liquid Adhesive).

    • Fascia is closed with figure 8 braided absorbable suture risk of postoperative hematoma.

    • Subcutaneous layers are closed with interrupted braided patient to the stretcher.

    • Skin is closed with a running single filament absorbable ■ Pillows need to be placed under the thighs to hold the (3-0 Monocryl). The goal is cosmetic closure. hips and knees flexed.

     

    PEARLS AND PITFALLS

    Bovie electrocautery

    Neurologic monitoring with preoperative baseline studies

    Postoperative neurovascular checks

    • Decreased bleeding

    • Helps minimize risk of neural injury

    • Neurovascular checks must be done frequently postoperatively and all lumbar nerve roots must be tested.

     

     

     

     

    POSTOPERATIVE CARE

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

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

       

• 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.

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

   

   

   

   

   

  FIG 5 • Postoperative radiograph.

   

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

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

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

  • 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

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

  • Hamstring spasm is often relieved after operative intervention.

    COMPLICATIONS

  • Wound hematoma

  • Infection

• Pseudarthrosis

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

• Neurologic injury

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

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

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

  • 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.