Lumbar facet joint and intervertebral disc loading during simulated pelvic obliquity.

Background Context: Intervertebral disc and facet joints are the two primary load-bearing structures of the lumbar spine, and altered loading to these structures may be associated with frontal plane spinal deviations.

Purpose: To determine the load on the lumbar facet joint and intervertebral disc under simulated frontal plane pelvic obliquity combined loading, an in vitro biomechanical study was conducted.

Study Design/setting: An in vitro biomechanical study using a repeated-measures design was used to compare L4-L5 facet joint and intervertebral disc loading across pure moment and combined loading conditions.

Methods: Eight fresh-frozen lumbosacral specimens were tested under five loading conditions: flexion/extension, lateral bending, axial rotation using pure moment bending (±10 Nm), and two additional tests investigating frontal plane pelvic obliquity and axial rotation (sacrum tilted left 5° and at 10° followed by a ±10-Nm rotation moment). Three-dimensional kinematics, facet load, and intradiscal pressures were recorded from the L4-L5 functional spinal unit.

Results: Sagittal and frontal plane loading resulted in significantly smaller facet joint forces compared with conditions implementing a rotation moment (p<.05). The facet joint had the highest peak load during the 10° combined loading condition (124.0±30.2 N) and the lowest peak load in flexion (26.8±16.1 N). Intradiscal pressure was high in lateral flexion (495.6±280.9 kPa) and flexion (429.0±212.9 kPa), whereas intradiscal pressures measured in rotation (253.2±135.0 kPa) and 5° and 10° combined loading conditions were low (255.5±132.7 and 267.1±127.1 kPa, respectively).

Conclusions: Facet loading increased during simulated pelvic obliquity in frontal and transverse planes, whereas intradiscal pressures were decreased compared with sagittal and frontal plane motions alone. Altered spinopelvic alignment may increase the loads experienced by spinal tissue, especially the facet joints.