Much of the research on scoliosis surgery in adolescents seeks to outline any risk factors that may result in failure. With Adult Scoliosis the goals of surgery become different: decompression of stenosis, restoring spinal balance, and improving deformity, pain and disability. Adult Scoliosis surgery is accompanied by high rates of major complications (28-54%), readmission (11-20%), need for revision surgery (11-42%).
A recent study from Europe sought to determine the risk factors associated with deformity correction, complications, revision surgery, and outcomes. They also looked at predictors for postoperative changes and symptomatic adjacent segment disease (ASD).
Adjacent segment degeneration refers to changes or symptoms observed at levels of the spine next to a previously fused segment or segments. Adjacent segment disease (ASD) refers to the development of new radiculopathy (a disease of the root of a nerve, such as from a pinched nerve) or myelopathy (a nervous system disorder that affects the spinal cord) next to the site of a previous fusion. Because the cause of the degeneration is yet unknown (i.e. whether it is due to the spinal fusion itself or due to the natural history of the degenerative disease) much of the research conducted on adult spinal fusion has a focus on adjacent segment disease.
The authors first wanted to determine factors for complications and revision surgery as well as to access surgery outcomes. They state that for many adult scoliosis patients, fusion to the sacrum is not required.
“Compared to Adolescent patients, adult scoliosis with intended fusion stopping in the lumbar spine is characterized by increased rigidity and lower rates of spontaneous correction of the unfused fractional curves. Residual wedging of the lowest instrumented vertebra (LIV) can increase the risk of and accelerate adjacent segment degeneration, adding-on and revision surgery due to mechanical degeneration decompensation of the mobile lumbar segments.”
Because of this, the authors looked back on previously conducted scoliosis surgeries and analyzed 448 adult patients–145 of which had degenerative-type Adult Scoliosis. The patients were an average of 51 years in age and received their follow-up 40 months after surgery. Of the patients included in the study, 51% had major lumbar curves, 24% had single thoracic or double major curves, 54% had stable vertebra at L5 and 34% had fusion to S1. The average number of posteriorfusion levels was eight and implant density 73%.
They found that 20% of patients had a “non-union” of the the fusion–18 % at L5-S1. They also found that the risk for non-union at L5-S1 increased with age, low screw density, and postoperative sagittal imbalance. 32 % of patients in the study had revision surgery. Risk for revision was increased in fusions to S1, increased BMI, sagittal imbalance, age and disc wedging distal to the LIV. To a varying degree, they also found clinical outcomes negatively correlated with revision, ASD, perioperative complications, age, low postoperative curve correction, and sagittal and coronal imbalance at follow-up. Also, 59 patients had ASD, which related to preoperative and postoperative sagittal and coronal factors of deformity.
Overall they found that the amount of correction achieved in the sagittal (a vertical plane which divides the body into right and left halves) and coronal planes (a vertical plane which divides the body into front and back halves) had a significant impact on the outcome of surgery as well as revision rates. Based on these findings, the authors suggest that risk for complications associated with adult scoliosis surgery might be reduced by:
“restoration of sagittal balance, appropriate deformity correction and advanced lumbosacral fixation”. The use of preoperative LIV-TO and LIV-TO on bending/traction-films were shown to be useful for surgical planning, selection of the LIV and prediction of follow-up-TO, respectively. Parameters of sagittal balance rather than coronal deformity predicted (symptomatic adjacent segment disease) ASD.”