Failure of Pelvic Fixation after Long Construct Fusions in Adult Deformity

Patients; Clinical and Radiographic Risk Factors

Woojin Cho, MD, PhD; Jonathan R. Mason, MD; Adam S. Wilson, MD; Christopher I. Shaffrey, MD; Francis H. Shen, MD; Adam L. Shimer, MD; Wendy M. Novicoff, PhD; Kai-Ming Fu, MD, PhD; Joshua Heller, MD; Vincent Arlet, MD

Rigid internal fixation → higher fusion rates Lumbosacral fusion: L5-S1 fixation alone: Pelvic fixation

Introduction

long constructs, high grade spondylolithesisunstable sacral fractures, sacral tumors

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Various Pelvic Fixation Methods : Galveston technique, S2 screws, four rod technique, S2 alar iliac screws, and S1-Iliac screws

S1-Iliac Screw Constructs : long term study with minimum 5 year follow up

5 nonunions out of 67 cases 23 removal of iliac screwsspondylolisthesis + long constructs No reports of the risk factors for failure(Tsuchiya K, Bridwell KH, Kuklo TR, et al. Spine 2006)

Introduction

To report the failure rate and risk factors for

failure of pelvic fixation with S1-Iliac screws

used at the base of long constructs in adult

deformity patients

Purpose

190 adult deformity patients: Retrospective review

Long construct instrumentation: > 6 levels with iliac screws

Clinical and Radiographic data

Methods 1

Failure (F) and Non-Failure (N-F) Major F: rod breakage between L4 and S1, failure of S1 screws (breakage, halo formation, or pullout), and prominent iliac screws requiring removal Minor F: rod breakage between S1 and iliac screws and failure of iliac screws (not require revision surgery)

Methods 2

Major Failure (Major F) Vs. Non-Failure (N-F) Clinical data: age, body mass index (BMI), number of comorbities, and previous revision surgery

Radiographic data (Preop, Postop, Change): pelvic incidence, pelvic tilt, sacral slope, sagittal balance, coronal balance, lordosis, and Fusion status (L4-S1)

Methods 3

Combined anterior and posterior fusion grading (L4-S1) (A modified Lenke’s fusion grading system)

Posterior Fusion (PF) : Grade A, B, C

Anterior Fusions (AF) : a sentinel sign at both L4-5 and L5-S1

Combined Fusions : PF or AF

Methods 4

Failure rate: Major F & minor F

Risk factors for failure of pelvic fixation: Major F Vs. N-F

Methods 5

190 patients → 67 patients

Overall Failure (F) rate: 34.3% Major F: 8 Pts (11.9%) rod breakage between L4 and S1, failure of

S1 screws (breakage, halo formation, or pullout), and prominent iliac screws requiring removal

Minor F: 15 Pts (22.4%) rod breakage between S1 and iliac screws and failure of iliac screws. (not require revision surgery)

Result 1

Results 2 (Major F Vs. N-F)Major (M) Failure Non Failure (N-F)

Avg ± SE Avg ± SEClinical Data

Age 66.98 ± 3.1 65.72 ± 1.5 0.723Body Mass Index (BMI) 30.11 ± 2.6 28.93 ± 1.1 0.684Comorbidity Number 4 ± 0.27 3.3 ± 0.22 0.061Smoker 0 2 *1.000Numbar of Levels Fused 9 ± 1.5 8.32 ± 0.50 0.668

Revision Surgeries 6 14 *0.043Radiographic Data

Pelvic Incidence (PI) 72.1 ± 3.4 62.7 ±1.3 0.015Preop Pelvic Tilt (PT) 34.9 ± 4.7 28.1 ±1.2 0.106Postop PT 34.5 ± 5.4 26.9 ± 1.1 0.106PT Change -0.4 ± 3.8 -1.22 ± 1.0 0.838Preop Sacral Slope (SS) 37.3 ± 3.8 34.59 ± 1.3 0.529Postop SS 37.63 ± 2.9 37.63 ± 2.9 0.588Preop Sagittal Balance 136 28.1 ± 50 101 28.1 ± 101 0.557

Postop Saggital Balance 70.3 ± 7.1 49.6 ± 6.8 0.05Preop CSVL (absolute value) 49.1 ± 10 24.8 ± 3.0 0.057Postop CSVL (absolute value) 26.6 ± 12 27.4 ± 3.3 0.951Change in CSVL (absolute value) 33.4 ± 7.7 18.4 ± 2.6 0.106Preop Lordosis -27.0 ± 8.3 -34.8 ± 3.2 0.404

Postop Lordosis -46 ± 2.5 -53.08 ± 1.6 0.033Change in Lordosis -19 ± 7.1 -18.3 ± 2.6 0.927

Major (M) Failure Non Failure (N-F)% Radiographic Fusion % Radiographic Fusion

Posterior Lateral Fusion 63% 73% *0.672Interbody Fusion 50% 51% *1.000Total Fusion 75% 89% *0.286

P value (T-test, *Fisher's exact test)

P Value (*Fisher's exact test)

Anterior Column Support (ALIF or TLIF)

Major F group - 87.5% of patients

Non Failure (N-F) - 84.1%

Result 3

Major F

Major F

Bilateral rods breakage at L5-S1 level which is considered Major failure because it needed a revision surgery due to psuedarthrosis.

Minor F

Minor F

Unilateral rod breakage below the S1 level which is a Minor failure because it doesn’t need a revision surgery as it can occur due to continuous motion at the SI joint after solid fusion at L5-S1.

The incidence of overall failure after pelvic fixation in adult deformity surgery : 34.3%

Major failure : 11.9%Minor failure : 22.4%

Risk factors for Major failures :

larger Pelvic Incidence, Revision Surgery, failure to restore Lumbar Lordosis failure to restore Sagittal Balance

Conclusion

Proper sagittal alignment

↑pelvic incidence → ↑ postoperative lumbar lordosis

↓lumbar lordosis → ↓ optimal sagittal alignment →

may predispose for more biomechanical stress on pelvic fixation → ↑ failure rate

Therefore, adult deformity surgeons who use pelvic fixation for long construct fusions should pay special attention to restoring optimal sagittal alignment to prevent pelvic fixation failure.

Discussion

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