Registry for Evaluation of Lumbar Arthrodesis Sagittal alignmEnt: Prospective Observational Study of the Relationship Between Pelvic Parameters, Lumbar Lordosis Mismatch-pelvic Incidence, and Lordosis Ratio vs. Post-surgical Clinical Outcome for Degenerative Disease

BACKGROUND AND STUDY RATIONAL

Degenerative pathology of the lumbar spine is very frequent affecting approximately 5.7% of the European population. Arthrodesis is a frequently adopted surgical treatment with different technical option, accounting for 30,000 procedures performed every year in Italy (trovare riferimento bibliografico) and over 450,000 procedures performed in the United States. However, lumbar vertebral arthrodesis for degenerative disease still remains burdened by clinical problems with significant occurrence of negative results consisting in lack of clinical improvement, late symptoms relapse or even clinical worsening. The evidence based medicine on this topics is still insufficient and generally does not exceed evidence class B.

The available guidelines are mainly based on level II studies and only offer recommendations that may support practitioners in clinical activity. Thus, surgical treatment of lumbar degenerative disease still remains extremely heterogeneous also considering the number of technical options available for the single pathology. Lack of standard of care leads to treatment stratetegies based on institutional, departmental, or personal experience, planned on inconsistent scientific evidences. The introduction in the clinical practice of the sagittal balance assessment, the evaluation of the meaning of pelvic parameters and of spino-pelvic mismatch has also offered a new evaluation criterion for lumbar degenerative pathology and for outcome of short lumbar arthrodesis surgery. Restoration of Sagittal alignment and Pelvic Index (PI)-Lumbar Lordosis (LL) mismatch is closely associated with a better outcome in spinal deformities, while there is still a lack of consistent evidence regarding short-segment arthrodesis for lumbar degenerative pathology.

Over the past 10 years, an increasing number of articles reported about associations between the presence of PI-LL mismatch, lumbar lordosis, pelvic tilt and outcome of lumbar arthrodesis for degenerative lumbar disease or occurrence of adjacent segment disease (ASD. A recent systematic meta-analysis highlighted a strong relationship between LBP and reduced lumbar lordotic curve especially when petients were analyzed with age-matched healthy controls. In 2000 Lazennec et al firstly analyzed the relationship between radiological parameters and postfusion pain focusing attention on the vertical position of the sacrum. Patients with pain persisting after arthrodesis showed both reduced SS and increased PT with PT reaching almost twice the normal value. Authors postulated that " achieving a strong fusion should not be the only goal. Appropriate position of the fused vertebrae is also of paramount importance to minimize muscle work during posture maintenance". An increased LL and SL was associated with better outcome (VAS, ODI) after unilateral instrumented TLIF single-level lumbar degenerative disease and after 1 level or 2-level PLIF for 2-level (L3-L4 and L4-L5) degenerative spondylolisthesis. Hioki et al described a positive linear correlation between increase in lordotic angle and improvement of JOA score at final outcome evaluation after two level PLIF.

Furthermore, reduction of pelvic tilt was associated with better outcome after PLIF surgery for spondylolisthesis as well as sacral slope increased to more than 30° after single level TLIF. The review by Le Huec et al. suggested that the increase in PT after surgery is associated with significant low back pain while the restoration of a normal PT results in a good clinical outcome. The study of Aoki et al was the first investigating influence of PI-LL mismatch on postoperative residual symtoms after 1 or 2 level TLIF. Larger PI-LL mismatch was significantly associated at 1 year follow-up with VAS for LBP, leg pain and leg numbness but not with postoperative disability (ODI). Detailed VAS analysis highlights association of mismatch with stending low back pain but not with LBP while sitting or in motion. Worse ODI scores were associate at 2 years follow-up with PI-LL mismatch after four-level lumbar fusion surgery (L2-S1); moreover, a significant correlations between PI-LL mismatch and improvement in both JOA score-VAS for LBP at 2 year follow up has been described for patients with lumbar degenerative scoliosis treated with short segment fusion (1, 2 or 3 level TLIF) at the affected levels. Radovanovic et al reported a better patient reported outcome in patients with SVA less than 50 mm. Patients with an SVA ≥ 50 mm presented reduced lumbar lordosis with increased mismatch and had a worse SF-36 PCS and Oswestry Disability Index (ODI; p = 0.043) as well as more back pain.