Thoracolumbar deformity arthrodesis to L5 in adult scoliotics

Abstract Purpose of study: For long deformity fusions to L5, the advantage of preserving the L5–S1 motion segment must be weighted against the potential for accelerated L5–S1 degenerative disc disease (DDD). Unfortunately, the incidence of subsequent L5–S1 DDD and the protective role of a deep-seated L5 have not been well defined. The purpose of this study is to define the incidence and sequelae of subsequent L5–S1 DDD and determine if a deep-seated L5 provides a protective role. Methods used: Thirty-four consecutive adult deformity patients fused from the thoracic spine to L5 at a single institution underwent radiographic, clinical and Scoliosis Research Society (SRS)-24 evaluation. Excluded were patients with previous lumbar spine procedures at levels distal to L4. For each patient, the L5–S1 disc was preoperatively assessed by X-ray magnetic resonance imaging and/or discography as being free of significant degeneration. Subsequent advanced L5–S1 DDD was defined by the L5–S1 disc height □ 50%, □ disk lordosis □ 50% or □ 3 mm new listhesis. L5 seating was characterized by the distance from the midpoint of the L5 pedicles to the intercrestal line (ICL). “Deep seated” L5 was defined by the L5 pedicles as greater than 10 mm below the ICL. Mean follow-up was 5.5 years (2.0 to 12.8 years). of findings: For the 34 patients (mean age, range, 47; 20 to 61 years), an average of 10.5 levels (range, 5 to 15) were fused. By latest follow-up, DDD developed in 23 of 34 patients (66%), □ disc height □ 50% (n=13, 38%), □ disc lordosis □ 50% at L5–S1 (n=17, 50%) or □ 3 mm new listhesis (n=4, 12%). Eight patients with L5–S1 subsequent DDD (35%) had □ 5 cm anterior shift of the C7 plumb from after surgery to latest follow-up compared with only one patient among those with preserved L5–S1 discs (10%; p=.15). Subsequent DDD resulted in arthrodesis extension to the sacrum for four patients at 3.5 years average. L5 was seated on average 6 mm below the ICL (15 to 35 mm). Patients with a deep-seated L5 had significantly less subsequent DDD at final follow-up (43% vs. 75%; p=.03). Smokers tended to □ incidence of DDD (87%) versus nonsmokers (47%; p=.18). The mean total SRS-24 and subset analyses tended to be superior for patients without subsequent DDD (p>.05): total SRS-24 (no DDD=90 vs. + DDD=81), pain (30 vs. 25), self-image (21 vs. 20), function (26 vs. 24) and satisfaction (13 vs. 12) at 4.5-year mean follow-up. Relationship between findings and existing knowledge: The incidence of subsequent L5–S1 disc degeneration after long fusions to L5 in adults has not been well defined by previous studies. In addition, few studies have examined the role of a deep-seated L5 in protecting against subsequent L5–S1 disc degeneration. Overall significance of findings: Subsequent L5–S1 DDD developed in 66% of patients after long adult fusions to L5. Relative but not absolute protection against progressive L5–S1 disc degeneration is provided by a deep-seated L5 (p=.03). SRS-24 total score showed a trend toward superior outcome when subsequent L5–S1 DDD did not develop. Disclosures: No disclosures. Conflict of interest: No conflicts.