A new study suggests that patients with adult spinal deformity should be assessed for pelvic incidence minus lumbar lordosis (PI-LL) mismatch (PI-LL >10 degrees) as it may be a primary indication for surgery in the setting of pain and disability.
Presenting the results of the study at IMAST (International Meeting on Advanced Spine Techniques; 10–13 July, Vancouver, Canada), Justin S Smith (Department of Neurosurgery, University of Virginia, Charlottesville, USA) told delegates that although increased sagittal imbalance (sagittal vertical axis >5cm) can be a primary indicator for surgical correction, sagittal vertical axis alone does not fully account for global alignment. He explained that the pelvis is also a key regulator of spinal alignment and a source of compensation, commenting that the mismatch between PI and LL, sagittal vertical axis, and pelvic tilt were recently found to be strongly correlated with health related quality of life (HRQOL).
Smith added that a subset of patients with sagittal spino-pelvic malalignment have “compensated flatback deformity” (sagittal vertical axis <5cm; PI-LL mismatch >10 degrees) and that few data existed for these patients. The aim of the new study (which was conducted through the International Spine Study Group), was therefore, to compare disability and treatment outcomes following surgery of patients with compensated flatback deformity (sagittal vertical axis 10 degrees) with those of patients with decompensated flatback deformity (sagittal vertical axis >5cm).
In the prospective, multicentre study, the investigators reviewed consecutive surgical patients. The inclusion criteria were: adult spinal deformity, ≥5 levels posterior instrumentation, minimum of one-year follow-up, and decompensated or compensated flatback deformity. Smith noted that at baseline, decompensated patients (98) were older than the compensated patients (27). They also had lower mean magnitude of maximum Cobb angle, greater thoracic kyphosis, higher sagittal vertical axis, similar pelvic tilt, and more PI-LL mismatch.
At the one-year follow-up point, the compensated and decompensated patient groups each had significant improvements in all of the radiographic measures assessed. However, decompensated patients continued to have greater mean thoracic kyphosis and greater mean sagittal vertical axis.
Both decompensated and compensated groups had significant improvements (p≤0.001 and p≤0.007, respectively) for each of the HRQOL scores measured in the study, and most of these improvements were found to exceed the respective thresholds of minimum clinically important difference (MCID). The magnitude of improvement in each of the HRQOL measures did not differ significantly between the decompensated and compensated patient groups. Furthermore, the percentage of patients in each group reaching MCID for improvement in each HRQOL measure also did not differ significantly between the groups, suggesting that both compensated and decompensated patients achieved a similar degree of improvement in HRQOL with surgical treatment.
Concluding, Smith stated: “PI-LL mismatch should be evaluated for adult deformity patients and can be considered a primary surgical indication in the setting of concordant pain and disability.” This abstract was awarded the Whitecloud Award for the Best Clinical Paper through the Scoliosis Research Society at the 2013 IMAST meeting, and the corresponding manuscript has been submitted for publication.