General Session: Innovative Technologies I - Hall F

Presented by: A. Patwardhan

Author(s):

A. Patwardhan(1,2), J.-C. Le Huec(3), S. Khayatzadeh(2), R. Havey(2), G. Carandang(2), L. Voronov(2), A. Faundez(4)

(1) Loyola University Medical Center, Orthopaedic Surgery & Rehabilitation, Maywood, IL, United States
(2) Edward Hines Jr. VA Hospital, Musculoskeletal Biomechanics Laboratory, Hines, IL, United States
(3) Bordeaux University Hospital, Orthopaedic Surgery, Bordeaux, France
(4) Geneva University Hospitals, Department of Orthopaedic Surgery, Meyrin, Switzerland

Abstract

Introduction: We previously reported that transition from standing to erect-sitting in healthy adults involves flexion of L3-S1 segments, while transition from erect- to slumped-sitting causes further flexion in the L3-S1 segments and, in addition, induces flexion of L1-L3 segments. We hypothesized that multi-segment fusions in the L3-S1 region, duplicating standing lordotic alignment, would cause proximal segments to flex more in post-fusion sitting to make up for the loss of L3-S1 mobility. We tested this hypothesis by studying how patients with lower lumbar fusions adapt their lumbopelvic alignment as they transition from standing to sitting.

Methods: Postural adaptations of lumbar fusion patients were compared with those of 10 asymptomatic normal adults. Lumbosacral sagittal alignment parameters were measured by analyzing EOS radiographic images of the six patients with lower lumbar fusions: 4 patients with fusion to sacrum [L4-S1: 2, L3-S1: 1, and L3-L5 instrumented fusion with L5-S1 auto fused: 1]; 2 patients with L3-L5 fusion. Each patient was instructed to assume the following postures: (i) standing upright, (ii) erect-sitting, and (iii) slumped-sitting. Thoracolumbar mobility was also assessed using flexion-extension images.

Results: Fusion including the sacrum: In erect-sitting after fusion involving the sacrum, there was little change in the sacral slope compared to standing (Figure 1a,b). Consequently, the proximal segments experienced only small magnitudes of angular deformations when transitioning from standing to erect-sitting. Transition from standing to slumped-sitting was associated with posterior pelvic tilt that reduced the slope of the vertebral endplate of the most proximal fused vertebra. We observed large magnitudes of flexion deformations in proximal segments compared to standing or erect-sitting (Figure 1a-c). The angular changes at the immediate adjacent proximal segment approached the values observed in the maximum-flexed posture and were proportional to available flexion mobility. L3-L5 fusion: The response of proximal adjacent lumbar segments was variable depending on the available mobility in the L5-S1 segment. The patient in whom the L5-S1 segment was at its flexion limit when standing, behaved like patients with fusion to sacrum; slumped-sitting caused large flexion angulation at the immediate adjacent proximal segment. In another patient, the L5-S1 segment had flexion mobility reserve and underwent flexion deformation in both erect- and slumped-sitting postures, thereby attenuating the angular adaptations in proximal lumbar segments.

Conclusions: The available mobility in the lumbar spine dictates how the lumbopelvic sagittal alignment adapts to sitting postures in patients and healthy controls. Patients with lumbar fusions to sacrum appeared to approximate their "standing" lumbopelvic alignment when sitting erect, as has been previously noted by Lazennec. This also included patients with fusion to L5, in whom the L5-S1 segment had exhausted its flexion mobility. The proximal segments are burdened with increased compensatory flexion adaptation in slumped-sitting, much more than their counterparts in healthy normal adults. These preliminary observations suggest the natural sitting posture may be a risk factor for post-fusion adjacent segment breakdown.

Figure 1