Utility of the pedicle subtraction osteotomy for the correction of sagittal spine imbalance.

Introduction: Pedicle substraction osteotomy (PSO) in the lumbar spine is indicated in the treatment of large sagittal deformities of the lumbar spine. Substantial complications associated with PSOs include pseudarthrosis and mechanical failure. The purpose of the present study was to assess the complications of this procedure and the causes of mechanical complications.

Material And Methods: Fifteen patients aged between 38 and 79 years (mean age 63.8±12.82) were operated on between June 2011 and September 2014 for sagittal imbalance by means of one-level PSO. Pre-operative and post-operative values of radiological spino-pelvic sagittal parameters were measured. Clinical and radiological evaluations were conducted pre-operatively and post-operatively at six months and one year. Clinical evaluation included intra- and post-operative complications.

Results: Mean pelvic incidence was 54.86 ± 11.82°. Lumbar lordosis (LL) was measured to be 12.26 ± 18.48° pre-operatively and increased to 42.73 ± 14.05° post-operatively (p< 0.05). Mean gain of lordosis after PSO at index level was calculated to be 28 ± 11° (range, 14-41). SVA decreased post-operatively from 93.46 ± 36.69 mm to 61.73 ±38.68 mm (p< 0.05). Several complications (n = 8), including two minor (one dural tear with no clinical consequences and one transient radicular deficit) and six major with re-intervention, were observed in our series.

Discussions: Optimal post-operative correction in the sagittal plane: SVA <50 mm, LL= -(PI+10°) is an important parameter to reduce the risk of developing sagittal decompensation which is a common condition after PSO. Rate of complications after PSO is not negligible in the literature up to 45%.

Conclusions: The main cause of mechanical complications was insufficient sagittal correction. To limit the risk of mechanical complications and to achieve a good sagittal balance, PSO must be associated with additional SPOs or a second corrective surgery to obtain a solid anterior fusion.