Cervical spondylosis refers to age related degenerative changes in the upper region of the spinal column. Symptoms caused by this degeneration can be classified into axial neck pain, cervical radiculopathy and cervical myelopathy (syndrome of long tract findings from spinal cord involvement). Lifetime prevalence of axial neck pain is approximately 66%, with 5% of the population experiencing disabling pain at any given time. One of the most commonly prescribed treatments for cervical degenerative disorders is anterior cervical discectomy and fusion (ACDF). However, radiographic follow-up studies reveal that as many as 90% of treated patients develop progressive adjacent segment disease (ASD) with up to 25.6% requiring reoperation at an adjacent segment due to symptomatic ASD. Concern for ASD has been the rationale for developing total disc replacement (TDR) through preserving index level motion capability. However, recent mid to long term randomized trials reported similar clinical outcomes and post-operative re-operation rate at adjacent segments when comparing ACDF and TDR patient groups. Whether adjacent segment degeneration is an effect of surgery (ACDF or TDR) or merely represents the natural development of the disease remains unknown. Etiology of ASD is multifactorial and research has shown that altered adjacent level biomechanics following surgery could be a contributing factor. Although many imaging techniques have been used to research in-vivo cervical spine motion, few data have been reported on the changes in kinematics and arthrokinematics in spondylosis patients before and after ACDF or TDR surgery during dynamic, functional and weightbearing activities. Specifically, no other study has investigated patients before and after ACDF or TDR with age and sex matched asymptomatic controls to account for patient specific factors and to separate age-related degeneration. Understanding the biomechanical factors that can increase the risk for ASD is necessary to improve reoperation rate due to symptomatic ASD. This study is based on the hypothesis that the altered adjacent segment biomechanics after cervical surgery are strongly associated with the development of post-operative adjacent segment degeneration. Firstly, we will determine kinematics (i.e. 6DOF range of motion) and arthrokinematics (i.e. disc deformation and facet joint motion) in the adjacent segments in spondylosis patients before and after a C5-6 ACDF or TDR. Kinematics and arthrokinematics at adjacent segments (C2-C3, C3-C4, C4-C5 and C6-C7) in 10 ACDF and 10 TDR patients during functional activities (dynamic gait and full range of motion of the neck) before surgery and 18 months after surgery will be measured. Secondly, we will determine the relationship between the changes in biomechanics (kinematics, arthrokinematics) and biochemical composition (T1? and T2 relaxation values) in the spondylosis patients before and after an ACDF or TDR. This longitudinal, prospective study will provide pilot data for an in-depth understanding of the biomechanical component of cervical spine ASD after undergoing an ACDF or a TDR surgery. If our hypothesis is confirmed then this study will help clinicians predict symptomatic degeneration earlier and improve reoperation rate by showing whether ACDF or TDR is better at reducing symptomatic ASD. Alternatively, if no association between biomechanical and biochemical composition (T1? and T2 mapping sequences) is found, then this study will show that biological factors are the main drivers of ASD and increased attention should be placed on patient specific anatomy and pathology. This pilot data will be used to develop a R01 randomized clinical trial research proposal that can thoroughly isolate the biomechanical component of ASD by taking iatrogenic and patient specific anatomy in consideration and using a larger patient group with longer follow-up times. As a physician- scientist, it is my career goal to improve patient care through innovative translational basic science research and this research is at the heart of that goal.
Adjacent segment degeneration (ASD) was reported in up to 90% of patients with cervical spondylosis after fusion surgery, with an estimated 40% of patients requiring reoperation within 5-10 years. Mid to long-term randomized trials show that cervical total disc replacement (TDR) has similar reoperation rates at adjacent segment compared to ACDF. This study aims to evaluate adjacent segment biomechanics and arthrokinematics after ACDF or TDR surgery in order to improve early diagnosis and prognosis so reoperation rate can be lowered. This prospective longitudinal study will provide the initial biomechanical data on TDR and ACDF that can help build the next generation of motion preservation devices to better patient outcomes and lessen the burden of high healthcare costs.
