Anterior spinal fusion (ALIF/OLIF/LLIF) with lumbosacral transitional vertebra: A systematic review and proposed treatment algorithm

Abstract

•Key anterior approaches differences in LSTV include vascular (aortic bifurcation/iliocaval confluence), muscular (psoas) and osseus anatomy (inter-crestal tangent/pubic symphysis), when compared to non-LSTV.•There are increased surgical deviations but not significantly greater complications for anterior approaches in LSTV.•Vascular awareness while accessing L45 will be in the presence of a more cephalad ABF and ICC with sacralized L5, and access to the deeper L56 level will be in the presence of a more caudal ABF and ICC in lumbarized S1.

Keywords: ABF; ALIF; ATP; Bertolotti; Castelvi; LLIF; Lumbarized; Lumbosacral transitional vertebrae; OLIF; Retroperitoneal; Sacralized.

Fig. 1

Flow diagram of systematic review. PRISMA (Page et al., 2021).

Fig. 2

A&2B: Adapted from Weiner et al. (Weiner et al., 2001). Access options on midline and lateral approaches for “Normal” and LSTV vascular anatomy. A: “Normal”: midline approach between ABF and ICC, lateral approach to L45. B: LSTV: midline approach is less likely whereas lateral approach may be considered, accepting anatomical variants including ABF, ICC and ALV.

Fig. 2

A&2B: Adapted from Weiner et al. (Weiner et al., 2001). Access options on midline and lateral approaches for “Normal” and LSTV vascular anatomy. A: “Normal”: midline approach between ABF and ICC, lateral approach to L45. B: LSTV: midline approach is less likely whereas lateral approach may be considered, accepting anatomical variants including ABF, ICC and ALV.

Fig. 3

Sacralized L5 case. a: disc degeneration at the functional (L45) lumbosacral level; b: axial MRI view of pathology, fluid in facets indicating significant segmental mobility, anterior vessels demonstrate right side artery and vein (R CIA and CIV) which are not in the surgical corridor, left side (L CIA and CIV) are in close proximity, traversing the surgical corridor from medial to lateral. Optimal disc access was unclear. Left side OLIF approach anterolateral to the disc revealed inadequate access but safely allowed access medial to the left CIA and CIV, thus caudal to the ABF/ICC; c: intervertebral cage and pedicle screws in situ.

Fig. 4

Sacralized L5 case. a: 10 years of mid-flexion instability, mild MRI evidence of disc degeneration at the functional lumbosacral level; b: high bifurcation revealed direct anterior access to the disc space, normally considered approachable from anterolateral access; c: intervertebral cage with facet joint wedges, note the high inter-crestal tangent (mid-L4).

Fig. 5

Sacralized L5 with coronal deformity. a: MRI T2 b: MRI Axial L4L5 (functional lumbosacral joint). The surgical approach to the bifurcation appeared accessible through a midline approach caudal to the bifurcation. The L45 transitional segment disc height approximates that of a L5S1 disc; c: an OLIF approach (semi-lateral position, flank incision) was taken as a utilitarian approach. The disc was difficult to access through the midline and a lateral trajectory was taken instead. This required a second IO window but ultimately was safely achievable with OLIF. d: final radiograph with partial coronal correction.

Fig. 6

Lumbarisation L56, a: pre-existing L1-L4 spinal instrumentation, non-contiguous stenosis and instability L56 requiring revision with extension to the pelvis, b: MRI T2, distal segment degeneration L4L5 L5L6, c: MRI T2, L56 facet erosion, achievable midline vascular access noted (not used), d: post-revision radiograph, instrumentation L1-Pelvis with L56 bullet cage, e: SPECT scan, pseudarthrosis L56 with cage subsidence and cyst formation. An anterior approach at L56 would have allowed a greater implant footprint and height, thus optimising segmental lordosis and fusion.

Fig. 7

Algorithm for LSTV abdominal approach. ABF: Aortic Bifurcation; ICC: Ilio-Caval Confluence. Dashed line indicates contra-indication.