Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Rasoulinejad, Parham

2nd Supervisor

Bailey, Chris


3rd Supervisor

Zdero, Radovan



Long spinal fusions are the mainstay of treatment in adult spinal deformity; however, proximal junctional kyphosis (PJK) is a common and potentially catastrophic complication that can occur following this procedure. It has been hypothesized that using semi-rigid constructs at the superior aspect of the instrumentation may decrease this complication. The objective of this thesis was to determine if there is a biomechanical advantage between various semi-rigid constructs utilized in long spinal fusions to help decrease the risk of PJK. Nine human cadaveric spines (T1 – T12) instrumented with the standard all-pedicle-screw construct (APS) were compared to various semi-rigid constructs including sublaminar bands (SB), supralaminar hooks (SLH), transverse process hooks (TPH), and short pedicle screws (SS). Results demonstrated that TPH reduced motion at the junction between the instrumented and non-instrumented spine segments and had the most linear change in motion. In comparison, SLH and SS were found to have a high degree of stiffness. No differences were seen between APS and SB. Overall, semi-rigid constructs alter the biomechanics at adjacent levels. TPH provides the most gradual change in motion, which may reduce mechanical stress and decrease the risk of PJK.

Summary for Lay Audience

Adult spinal deformity (ASD) is a disorder where the spine is abnormally curved which can cause symptoms such as back pain, leg pain, and weakness or numbness in the legs. It is a common condition, affecting approximately 8-13% of the adult population. Treatment for ASD includes physiotherapy, medications, and injections; however, if these treatments fail, surgery can be performed. This involves straightening the spine and fusing the vertebrae (the bony building blocks of the spine) together. In order to do this, screws are placed into the vertebrae and a long rod is attached on either side of the spine. This surgery has been shown to help alleviate symptoms associated with ASD and has become the mainstay of treatment for this condition. However, complications can occur after surgery. One such complication is called proximal junctional kyphosis (PJK). This occurs when the spine above the part that is fused collapses forward. Unfortunately, this can cause people to experience significant pain, they can have damage to the spinal cord and nerves, the screws and rods can break, and a second surgery may be needed to correct this.

One of the reasons PJK occurs is due to the very sudden change in the amount of movement between the fused part of the spine and the not fused part, which creates a lot of stress at the junction where they meet. To help decrease the risk of PJK occurring, semi-rigid instruments were created to be placed at this junction to allow a more gradual change in movement. This project looked into different types of these semi-rigid instruments to help determine if one is better than the other.

To do this, we completed a biomechanical study to assess how four different semi-rigid instrumentations effect movement of the spine. We used spines from people that had donated their bodies to research, which were then tested by moving them through many directions of motion and recording their movement for comparison. Overall, we found that several of the semi-rigid instruments did lead to a more gradual change in motion at the junction between the fused and not-fused spine. This information will help surgeons decide which semi-rigid instruments to use during surgery for ASD to help reduce the risk of developing PJK.

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