Publication Date



Open access

Degree Type


Degree Name

Doctor of Philosophy (PHD)


Biomedical Engineering (Engineering)

Date of Defense


First Committee Member

Loren Latta

Second Committee Member

Seth Williams

Third Committee Member

Peter Tarjan

Fourth Committee Member

Chun Yuh Huang

Fifth Committee Member

Weiyong Gu


Lumbar spine fusion (LSF) is a common surgical procedure used in the treatment of lower back pain. Numerous studies have been conducted investigating the effects of LSF. Biomechanical studies have found that mechanical changes at adjacent joints create cumulative stress and pain, while clinical studies suggest that many patients develop symptomatic adjacent segmental disease (ASD) following LSF, which may necessitate additional surgery. Recently, ASD pain following LSF has been attributed to accelerated sacroiliac (SI) joint degeneration. Normal SI joints are mobile segments adjacent to the lumbosacral spine articulation and it has been hypothesized that altered biomechanics at the SI joints due to LSF could accelerate degeneration of the joints. The purpose of this study was to obtain a better understanding of the biomechanics at the SI joints and to determine whether LSF causes biomechanical changes at the SI joints. Six cadaver pelves were tested in flexion/extension, torsion, double leg compression and single leg compression, under four conditions: 1) intact, 2) after a 360 degree instrumented fusion at L4-5, 3) after a 360 degree instrumented lumbosacral fusion at L4-S1 and 4) after a unilateral SI joint fusion. Anterior and posterior SI joint movements were recorded during the study, along with load/displacement data. This study proved that motion does exist at the SI joints, although it is quite variable between specimens and between right and left SI joints within an individual specimen. It was also determined that changes in biomechanics do occur at the SI joints following fusion (L4-5, L4-S1 and unilateral SI joint fusion). Anteriorly, an overall increase in motion was detected at the SI joints during axial compression as fusions were performed. The posterior SI joints also demonstrated increased motion, however, this increase was detected in all of the parameters tested (flexion/extension, torsion and axial compression). However, due to the small number and variability of specimens tested, significance could not be established. The results of this study may help surgeons make more informed decisions, by being made aware of SI joint degeneration as a possible side effect of fusion surgeries, and taking that into consideration when determining a treatment plan.


Lumbar Spine; Motion; Arthrodesis