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Flat back after fusion


Introduction

Flat back syndrome is described as loss of lumbar lordosis, which alters the center of gravity, thereby shifting the head anterior to the sacrum causing sagittal imbalance. This is typically seen following multiple lumbar fusions with distraction of the lumbar spine that ultimately lead to loss of lumbar lordosis. It was first described in patients undergoing scoliosis repair with placement of Harrington distraction by Doherty. This resulted in forward inclination of the trunk and inability for upright posture. Patients were unable to stand erect without knee flexion and required cervical extension to maintain horizontal gaze. This ultimately leads to increased energy expenditure when standing upright, leading to back pain. In addition to back pain, patients may also report anterior thigh pain from constant flexion at the hips. While loss of lumbar lordosis can occur from degenerative changes leading to pelvic incidence to lumbar lordosis mismatch, another common cause is iatrogenic during fusion operations. Positioning such as kneeling or knee-chest position causes flexion of the hips and leads to loss of lumbar lordosis, while positioning that fully extends the hips accentuates lumbar lordosis. Other causes of loss of lumbar lordosis include posterior interbody fusion and segmental distraction, which can result in focal kyphosis. Return of normal posture requires the return of normal lumbar lordosis to restore the normal sagittal balance.

Example case

  • Chief complaint: back pain

  • History of present illness: A 65-year-old male with a history of multiple lumbar fusions in the past as well as cervical fusion beginning over 20 years ago, with his last surgery being approximately 10 years ago. He has had both decompressive and fusion surgery. He has not been able to lay down flat on his bed for many years. He has severe back and radicular pain and requires high doses of pain medication. He is unable to stand straight and complains of his back fatiguing. He denies weakness. He underwent imaging and was concerning for flat back syndrome ( Figs. 38.1–38.3 ).

    Fig. 38.1, Preoperative magnetic resonance images. (A) T2 sagittal and (B) T2 axial images demonstrating postoperative changes with loss of lumbar lordosis.

    Fig. 38.2, Preoperative computed tomography scans. (A) Sagittal, (B) coronal, and (C) axial images demonstrating postoperative changes of previous fusion with massive fusion mass.

    Fig. 38.3, Preoperative x-rays. (A) Anteroposterior (AP) and (B) lateral x-rays demonstrating positive sagittal balance with loss of lumbar lordosis.

  • Medications: AndroGel, armodafinil, omeprazole, valsartan, ranitidine

  • Allergies: nickel

  • Past medical and surgical history: hypertension, back pain, laminectomy, L1-S1 posterior spinal fusion, spinal cord stimulator placement and removal, anterior cervical discectomy and fusion

  • Family history: noncontributory

  • Social history: disabled, nonsmoker

  • Physical examination: awake, alert, and oriented to person, place, and time; cranial nerves II–XII intact; bilateral deltoids/triceps/biceps 5/5; interossei 5/5; iliopsoas/knee flexion/knee extension/dorsi, and plantar flexion 5/5

  • Reflexes: 2+ in bilateral biceps/triceps/brachioradialis with negative Hoffman; 2+ in bilateral patella/ankle; no clonus or Babinski; sensation intact to light touch

  • Belal Elnady, MD

  • Orthopaedic Surgery

  • Assiut University

  • Assiut, Egypt

  • Diego F Gómez MD MSc.

  • Neurosurgey

  • Fundación Santafe de Bogotá

  • Bogota, Colombia

  • John G. Heller, MD

  • Orthopaedic Surgery

  • Emory University

  • Atlanta, Georgia, United States

  • Daniel M. Sciubba, MD

  • Jeffrey Ehresman, BS

  • Neurosurgery

  • Johns Hopkins

  • Baltimore, Maryland, United States

Preoperative
Additional tests requested Conservative measures

  • SPECT/CT L-spine

  • EMG/NCS

  • DEXA

  • Anesthesiology evaluation

  • Vitamin D levels and titrate to normal levels if low

  • Pain management evaluation with narcotic titration

  • Medicine evaluation

  • Psychiatry evaluation

  • DEXA

  • Lumbar flexion-extension x-rays

Surgical approach selected L4-5 modified pedicle subtraction osteotomy and T10-ileum posterior fusion T10-S2 posterior fusion with L4 pedicle subtraction osteotomy

  • If agrees to pain and psychiatric evaluations,

  • Stage 1: posterior removal of L1-S1 instrumentation, T12-L1 laminectomy, redo L5-S1 decompression with facet osteotomies, L2-3 osteotomies, T10-pelvis with iliac bolts

  • Stage 2: L5-S1 ALIF

  • Stage 3: L2-3 XLIF and anterior column release if needed

  • Stage 4: T10-pelvis with posterior T10-L3 fusion and L5-S1 posterolateral fusion

  • Stage 1: removal of previous S1 screws and rods, placement of bilateral pelvic screws, posterior column osteotomy at L5-S1

  • Stage 2: ALIF

  • Stage 3: pedicle subtraction osteotomy at L4 (if lumbar lordosis not >40 degrees) followed by rod placement (L1-pelvis)

  • Surgical approach if 21

  • Surgical approach if 80

  • Same

  • Same

  • Same

  • Conservative management

  • Same

  • T10-pelvis fusion only

  • Closely match LL to PI

  • LL substantially less than PI

Goal of surgery Restore sagittal balance and LL Restore sagittal balance and LL, spinal cord decompression at L5-S1 Decompress stenosis at L5-S1 and L1-2, repair L5-S1 nonunion, correct sagittal balance (40–45 degrees of correction) Increase LL in order to decrease PI-LL mismatch, improve overall sagittal balance
Perioperative
Positioning Prone, no pins Prone on Jackson table, no pins

  • Stage 1: prone, no pins

  • Stage 2: supine, no pins

  • Stage 3: lateral, no pins

  • Stage 4: prone, no pins

  • Stage 1: prone, no pins on Jackson table

  • Stage 2: supine on Jackson table

  • Stage 3: prone, no pins

Surgical equipment

  • Fluoroscopy

  • IOM (MEP/SSEP/EMG)

  • Surgical microscope

  • Fluoroscopy

  • IOM (MEP/SSEP/EMG)

  • Plasma blade cautery

  • Aquamantys® bipolar

  • Fluoroscopy

  • BMP

  • Fluoroscopy

  • IOM (MEP/SSEP)

  • Ultrasonic bone scalpel

Medications None None None Tranexamic acid
Anatomical considerations Dura, nerve root Aorta, iliac arteries, dura sac, nerve roots Dura, nerve root, PLL Dura, spinal cord, iliac vessels, ureter
Complications feared with approach chosen Dural tear, CSF leak Excessive blood loss, nerve root injury, pedicle fracture, CSF leak Dural tear, CSF leak, nerve root injury, cage displacement Vascular injury, CSF leak
Intraoperative
Anesthesia General General General General
Exposure T10-sacrum T10-sacrum

  • Stage 1: T10-pelvis

  • Stage 2: L5-S1

  • Stage 3: L2-3

  • Stage 4: T10-pelvis

L1-pelvis
Levels decompressed L4-5 L5-S1

  • Stage 1: T12-L1, L5-S1

  • Stage 2: L5-S1

  • Stage 3: L2-3

  • Stage 4: none

Levels fused T10-sacrum T10-sacrum

  • Stage 1: none

  • Stage 2: L5-S1

  • Stage 3: L2-3

  • Stage 4: T10-pelvis

L1-pelvis
Surgical narrative Position prone, midline incision, subperiosteal dissection, expose from T10 to sacrum, extend previous fusion to T10 with pedicle screws and down to ilium with iliac screws, modified pedicle subtraction osteotomy at L4-5 level with posterior wedge closing osteotomy, rod insertion and compression to restore lumbar lordosis, wound closure in layers with drain Position prone with transverse rolls to increase LL, midline incision from T10-S2, subperiosteal dissection exposing posterior elements including facet joints and transverse processes, remove previous lumbar instrumentation, implant pedicle screws from T10 to S1 and S2 alar iliac screws, pedicle subtraction osteotomy at L4, closure of osteotomy with extension of hip joints and elevation of trunk, gentle compression between the pedicle screw head, position rod with lordotic contouring avoiding excessive stress on pedicle screws, careful attention to SSEP and MEP at this time, L5-S1 laminectomy with bilateral foraminotomy, apply autograft with bony substitutes along bony surfaces, layered closure with subfascial drain

  • Stage 1: position prone, posterior midline approach, expose T10-S3, remove all instrumentation from L1-S1, decompress T12-L1 stenosis, dissect out scar at L5-S1 nonunion, generously decompress L5 and S1 nerve roots with partial or complete facetectomies (closing wedge osteotomies), create closing wedge osteotomies at L2-3 bilaterally to facilitate XLIF during stage 2, place pedicles screws from T10-pelvis, layered closure

  • Stage 2 (3–5 days later after obtaining x-rays, CT, MRI): position supine with thick bolster at lumbosacral junction, standard left retroperitoneal approach to L5-S1 disc space, complete L5-S1 discectomy all the way back to posterior annulus but leaving it intact, release anterolateral annulus, insert appropriately sized cage with BMP-2, secure with screws into S1 end plate

  • Stage 3 (same day as stage 2): position lateral, target correction for XLIF depends on amount of correction achieved with L5-S1 ALIF, may be necessary to perform an anterior column release with release of ALL and lateral annular walls if greater correction needed, insert appropriate cage with BMP-2 and secure with either L2 or L3 screw fixation, standard closure

  • Stage 4 (same day as stage 3): position prone, x-ray to confirm anterior devices in place, complete posterior segmental instrumentation, compress across osteotomies to optimize final alignment, confirm adequate space for nerve roots prior to compressing, place bone grafts at L5-S1 and T10-L3, layered closure with drains

  • Stage 1 (day 1): position prone on Jackson table, skin incision from L1 to pelvis, subperiosteal dissection, previous hardware inspected and S1 screws and rods removed, place bilateral pelvic screws using external landmarks, confirm location with x-ray, stimulate all screws, posterior column osteotomy at L5-S1, wound irrigated and closed

  • Stage 2 (day 1): position supine, transverse incision between umbilicus and pubis down to anterior rectus sheath, retroperitoneal plane followed on left side to common iliac artery making sure to identify ureter/psoas/lower iliac vessels, dissect common iliac artery off of spine, place retractors, confirm L5-S1 disc space, remove L5-S1, curette edges and decorticate, cut large femoral strut graft using ultrasonic bone scalpel to optimal size, place demineralized bone matrix in disc space, confirm location with x-ray, one screw in L5 and one in S1 to hold graft in place, wound closed, imaging obtained

  • Stage 3 (day 2): position prone on Jackson table, incision and subperiosteal dissection from L1-pelvis exposing instrumentation, if LL was >40 degrees then place rods and compress, if LL <40 degrees then perform pedicle subtraction osteotomy at L4, remove bone above and below L4 pedicle, identify L3 and L4 nerve roots, separate L4 pedicles from L4 transverse processes, tin pedicles down until flush with spinal canal, complete with osteotomy with osteotome while protecting thecal sac and nerve roots, stimulate all screws, place lordotic rods, confirm LL >40 degrees with x-rays, decorticate exposed bone and place allograft and BMP, close in layers with drains

Complication avoidance Good debridement of disc space, gentle compression over pedicles to compress screws, attempt to achieve 360-degree fusion Position with transverse roll to increase LL, pedicle subtraction osteotomy to increase LL, careful attention to MEP and SSEP during closure of the osteotomy and compression on pedicle screw Multistage approach, remove scar at nonunion so that area can be properly decorticated, generous facetectomies posteriorly to avoid iatrogenic nerve root injury during anterior correction, imaging between stages, bolster for stage 2 to provide extension, leave posterior annulus at L5-S1 intact, anterior column release if more correction needed, confirm nerve roots decompress before compressing across osteotomies Three-stage approach, pelvic screws with anatomical landmarks, stimulate screws to confirm location, posterior column osteotomy to increase LL, femoral strut graft, pedicle subtraction osteotomy if needed to increase LL
Postoperative
Admission ICU ICU ICU ICU
Postoperative complications feared CSF leak, wound infection, instrument failure Neurological deficit, hematoma Epidural hematoma, wound infection, nerve root injury, medical complications, nonunion, loss of fixation CSF leak, vascular injury, new neurological deficit, hardware failure/spinal instability, nonunion
Anticipated length of stay 5–7 days 3 days 8–10 days 4–7 days
Follow-up testing T-L spine x-rays 2 weeks, 2 months, 6 months, 1 year after surgery CT T-L spine within 48 hours of surgery

  • Standing full length x-ray prior to discharge, 6 weeks, 3 months, 6 months, 12 months after surgery

  • CT T-L spine 6 or 12 months after surgery

CT T-L spine within 24 hours of surgery
Bracing None None TLSO when out of bed for 12 weeks None
Follow-up visits 2 weeks, 2 months, 6 months, 1 year after surgery 1 week after surgery 6 weeks, 3 months, 6 months, 12 months after surgery 3 weeks after surgery
ALL , Anterior longitudinal ligament; BMP , bone morphogenic protein; CSF , cerebrospinal fluid; CT , computed tomography; DEXA , dual-energy x-ray absorptiometry; XLIF , extreme lateral interbody fusion; EMG , electromyography; ICU , intensive care unit; IOM , intraoperative monitoring; LL; lumbar lordosis; MEP , motor evoked potential; NCS , nerve conduction study; PI , pelvic index; PLL , posterior longitudinal ligament; SPECT , single-photon emission computed tomography; SSEP , somatosensory evoked potential; TLSO , thoracic lumbar sacral orthosis.

Differential diagnosis

  • ▪

    Flat back syndrome

  • ▪

    Back pain

  • ▪

    Scoliosis

  • ▪

    Adjacent segment disease

  • ▪

    Proximal junctional kyphosis

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