Analysis of baseline sagittal balance indicators and compensatory mechanisms at adult degenerative scoliosis in elderly patients operated on minimally invasive lateral lumbar interbody fusion

Study Design: 

Retrospective single-center study.

Background: 

Spinal alignment is crucial for maintaining upright posture, neural protection, and skeletal stability. Surgical treatment of adult degenerative scoliosis (ADS) is complex due to variability in clinical presentations and radiological parameters. Restoration of sagittal and coronal balance through minimally invasive techniques, including minimally invasive lateral lumbar interbody fusion (MI-LLIF), especially in elderly patients has demonstrated efficacy in reducing pain and enhancing quality of life.

Purpose: 

To evaluate the baseline sagittal alignment and compensatory mechanisms in elderly ADS patients operated on MI-LLIF, emphasizing the predictive value of key radiological parameters.

Materials and Methods: 

This was a retrospective review of 51 elderly patients with lumbar degenerative scoliosis treated using MI-LLIF. Radiological parameters evaluated were the coronal Cobb angle (CCA), pelvic incidence (PI), sacral slope, pelvic tilt (PT), lumbar lordosis (LL), PI-LL mismatch, L4-S1 lordosis, thoracic kyphosis, sagittal vertical axis, spino-sacral angle (SSA), and the Index Barrey (IB). Radiological assessment with X-ray was used before operation and mean 2.7 years follow-up.

Results: 

Preoperative CCA was 15° (11;20). The average PT was 21.9°, what confirmed the presence of sagittal imbalance in 98% of elderly patients with ADS. In accordance with IB, 18 (35%) patients were identified as balanced due to compensation mechanisms (IB <0.5). Global sagittal imbalance (IB >0.5) was revealed in 33 (65%) patients. The main reason of sagittal imbalance was L4-S1 lordosis insufficiency (80%). The main compensation mechanisms were retroversion of the pelvis (98%), hypokyphosis (67%), and hyperextension at the L4-S1 level (14%).

Conclusions: 

All patients have spinopelvic malalignment according to IB, and the main reason for its development was deficiency of L4-S1 and LL. The most sensitive markers of sagittal imbalance were PT with the calculation of target individual values, IB and SSA. The main compensatory mechanisms of sagittal imbalance are retroversion of the pelvis, thoracic hypokyphosis, and hyperextension in the overlying segments.