An in vitro
biomechanical study using porcine lumbar
segments as specimens.
To evaluate the effects of interbody cage
support and endplate strength on the stability of instrumented segments.
Summary of Background Data.
The anterior lumbar
interbody fusion (ALIF
is widely used to restore disc height and support the anterior column. Transpedicle or posterior spinal fusion or facet screw
fixation (FSF) can improve the stability of the vertebra-instrumented segments. The cage
position can affect the anterior support and initial stability
of the ALIF
region, but there is no consistent data on its biomechanical effects on ALIF
Nine variations of 3 instrumentation modes (intact, ALIF
/FSF) and 3 cage
positions (type I, anterolateral; type II, mediolateral; and type III, posteromedial) are tested under 5 lumbar
motions. The range of motion and axial displacement are used as comparison indices for the different variations.
placement serves as support for the intervertebral loads while the posterior fixation behaves as lever to further enhance the anterior support. At the endplate-cage
interfaces, the endplate strength directly affects the cage
subsidence. Type III exhibits higher stability for standing due to the greater strength of the endplate in the posterior region. Otherwise, type I consistently has higher stability for all other types of motion.
The initial stability
of the ALIF
region is affected by the moment arm and the mechanical strength of the engaged endplates. Type I has greater moment arm and provides more efficient support to the instrumented segments. Endplate strength provides an ability to withstand lumbar
loads and suppress the cage
subsidence. Bone quality at the endplate-cage
interfaces must therefore be cautiously evaluated preoperatively.
Level of Evidence: N/A